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FRESH-WATER
BIOLOGY

BY

HENRY BALDWIN WARD, Ph.D.

Professor of Zoology in the University of Illinois, Special Investigator
FOR THE United States Bureau of Fisheries, Etc.

AND

GEORGE CHANDLER WHIPPLE

Professor of Sanitary Engineering in Harvard University and the
Massachusetts Institute of Technology

WITH THE COLLABORATION OF A STAFF
OF SPECIALISTS

FIRST EDITION

NEW YORK

JOHN WILEY & SONS, Inc.

London: CHAPMAN & HALL, Limited

1918

Copyright, 1918

BY

HENRY BALDWIN WARD

AND

GEORGE CHANDLER WHIPPLE

Stanbopc iprcss

F. H.GILSON COMPANY
BOSTON, USA.

COLLABORATORS

Edward Asahel Birge, Dean of the College of Letters and Science in the University

of Wisconsin
Nathan Augustus Cobb, United States Department of Agriculture
Wesley Roswell Coe, Professor of Biology in the SheflSeld Scientific School of Yale

University
Herbert William Conn, Late Professor of Biology, Wesleyan Uhiversity
Charles Benedict Davenport, Director of the Station for Experimental Evolution,

Cold Spring Harbor, Long Island, N. Y.
Charles Howard Edmondson, Assistant Professor of Zoology in the University of

Oregon
Carl H. Eigenmann, Professor of Zoology in Indiana University
Herbert Spencer Jennings, Professor of Zoology in Johns Hopkins University
Edwin Oakes Jordan, Professor of Bacteriology in the University of Chicago
Charles Dwight Marsh, United States Department of Agriculture
John Percy Moore, Professor of Zoology in the University of Pennsylvania
James George Needham, Professor of Limnology in Cornell University
Edgar William Olive, Curator of the Brooklyn Botanic Garden
Arnold Edward Ortmann, Curator of Invertebrate Zoology in the Carnegie Museum,

Pittsburgh
Arthur Sperry Pearse, Associate Professor of Zoology in the University of Wiscon-
sin
Raymond Haines Pond, Late Professor of Botany in the Texas Agricultural College
Edward Potts, Late of Meadville, Pa.

Jacob Ellsworth Reighard, Professor of Zoology- in the University of Michigan
[Richard Worthy Sharpe, Instructor in Biology in the Dewitt Clinton High School,

New York City

[Victor Ernest Shelford, Assistant Professor of Zoology in the University of Illinois
Frank Smith, Professor of Zoology in the University of Illinois
Julia Warner Snow, Associate Professor of Botany in Smith College
Caroline Effie Stringer, Head of the Department of Biology in the Omaha High

School
Bryant Walker, Detroit, Mich.
Robert Henry Wolcott, Professor of Zoology in the University of Nebraska.

PREFACE

For the ordinary student and teacher on this continent fresh-
water life has a significance heretofore greatly underestimated.
In most parts of the country it lies at one's very door, readily ac-
cessible, and is indeed the only type of aquatic existence which can
be studied Uving and at work. This fact gives to fresh-water life,
once the student has been introduced into its domain, an appeal-
ing interest that fetters his attention and stimulates his desire
to know something more of it. Among the most remarkable of
early works that followed hard upon the first use of the micro-
scope are some great classics which represent work in this very
field.

Various European countries possess elaborate monographs on
fresh-water organisms as a whole and on single groups, but no
attempt has been made heretofore to deal with North American
fresh-water hfe in its entirety, and few treatises have essayed to
cover completely any group of fresh-water organisms. American
workers in general have accordingly avoided this field and the few
who have attempted to engage in its study have found their prob-
lems very difficult to solve.

The preparation of the present work was undertaken many years
ago with the purpose of stimulating the study of the material so
easily obtainable and of aiding workers of all grades to acquire
some definite and precise knowledge of the organisms met in such
study. Each chapter has been handled by a specialist on the group
and the results achieved by this method have a significance that
could not have been attained in any other way. Conditions en-
tirely unavoidable led to the completion of the different parts of
the work at somewhat different dates. It is believed that this
will not, in fact, impair the value of the work as a whole and
will find an excuse in the magnitude of the task. Individual
chapters represent a survey of the group treated that is complete

vi PREFACE

for this continent up to the time at which the chapter was
closed.

The first few chapters are devoted to a discussion of general bio-
logical factors. Evident space limits prevented extended discus-
sion of many most interesting biological topics, which are at best
only outHned here. The exact citation of sources at the close
of these chapters will aid the reader to pursue such topics further
if desired. Not all discussions on general questions have been
confined to the introductory chapters. The chapter on Rotifera,
by Jennings, presents an admirable description of Ufe processes,
which, altho written specifically for that group, appHes with ap-
propriate modifications to all groups of many-celled organisms.
In the chapter on Copepoda, Marsh has treated with some detail
the general question of distribution as illustrated by this group;
yet the very factors which he shows to be operative in it are
those that lie at the basis of the distribution of most if not all
other groups. The discussion of the aquatic vertebrates by Eigen-
mann is purely biological and the systematic outhne is omitted
entirely, since that of itself would demand an entire book for its
adequate presentation. The same is true of the chapter on Bac-
teria, by Jordan, and of that on the higher aquatic plants which are
treated by Pond in the physiological (chemico-physical) aspect
primarily.

Apart from those just mentioned all chapters conform to the
same general plan. Each is devoted to a single group of organ-
isms and opens with a general account of the occurrence and his-
tory of the group. The description of the anatomy of the forms
treated is very brief and deals chiefly with such features as are of
special value in the key. Similarly the life history is given in
condensed form. More attention is devoted to the biological
relations which at this point are discussed with reference to the
entire group, whereas individual features are left for later record
under individual species except as they are needed for illustrations
of general questions. Care has been exercised to include descrip-
tions of special methods for collecting, preserving, and studying
the organisms of each particular group.

Special details both biological and morphological regarding genera

PREFACE vii

and species are included under a synoptic key which comes at the
close of each chapter except as noted above; in some cases it is
carried to species but in others only to genera. The form utilized
for the keys has been in constant use for many years at the Uni-
versity of Illinois, having been applied to many aquatic types by
Professor S. A. Forbes and his associates. The introductory num-
ber of each key line is followed by an alternative number printed
in parentheses and on reaching a decision that this line is not ac-
ceptable, the student proceeds at once to the line introduced by
the alternative number; in case a given alternative is accepted the
further course of the inquiry is indicated by a number at the close
of the line.

In order to achieve maximum ease in use and perspicacity in
grasping the facts presented, all the information on a given form,
viz., the illustration, the description, and the biological features with
the frequence, range, and other special data, are included between
the key line which introduces the name and the key line next fol-
lowing. The total information on a single type forms thus a solid
panel and appeals promptly and as a whole to the eye and mind of
the student. Each chapter closes with a brief list of the most
essential references to the topic. No textbooks are cited and only
such works are noted as may be considered indispensable for pres-
ent-day study of North American forms. The student is cautioned
not to regard any such list as in any sense a bibliography of the
subject.

To encompass such a mass of material within the limits of a
single volume, even tho it be generous in size, has necessitated
brevity of treatment at every point. Technical terms are defined
or discussed only once and no glossary is introduced. The index
includes important terms and all of the scientific names used in
the keys so that the reader can find every item promptly.

A serious effort was made to attain uniformity in the use of
names thruout the entire work but the worker will find that this
end was not fully achieved. The most conspicuous failure in this
particular obtains in the citation of host names for various para-
sitic species. In all such cases that name is employed which was
used by the authority from which the record is cited. It was felt

viii PREFACE

that in the absence of monographic revisions of the species of
parasites noted any other method would have been indefensible
in a brief treatise.

Abundant use has been made of figures to illustrate the forms
described. Most of the illustrations are new and many of them
drawn by the author of the chapter especially for this work.

In chapter II certain figures and tables are taken with modi-
fications from Shelford's American Communities in Temperate
America by courtesy of the Geographic Society of Chicago and the
University of Chicago Press.

It would be impossible to acknowledge all of the aid which has
been extended during the progress of the work. Valuable sugges-
tions from many sources have been freely extended us and as freely
utilized.

To all of our colleagues who, in spite of multitudinous difficulties
and seemingly interminable delays, have worked so generously to
perfect their individual chapters the sincerest thanks of the editors
are due. Especial mention should be made of the numerous help-
ful suggestions and criticisms given outside their own chapters
during the preparation of the work by Professors E. A. Birge and
Frank Smith. Grateful acknowledgement is also due E. C. Faust
and H. G. May for aid in reading and checking proof.

Finally, it is a pleasure as well as a duty to express our apprecia-
tion of the work of the publishers. Their forbearance and continued
kindly assistance during the long and difficult period of preparation
has made possible the completion of the work and its presentation
to the scientific worker in attractive form.

CONTENTS

Chap. Page

I. Introduction, Henry B. Ward i

II. Conditions of Existence, Victor E. Shelford 21

III. Methods of Collecting and Photographing, Jacob Reighard 61

IV. Bacteria, Edwin O. Jordan go

V. Blue-Green Algae (Cyanophyceae) , Edgar W. Olive 100

VI. The Fresh- Water Algae (Excluding the Blue-Green Algae), Julia W.

Snow 115

VII. The Larger Aquatic Vegetation, Raymond H. Pond 178

VIII. Amoeboid Protozoa (Sarcodina), C. H. Edmondson 210

IX. Flagellate and Ciliate Protozoa (Mastigophora et Infusoria), H. W.

Conn and C. H. Edmondson 238

X. The Sponges (Porifera), Edward Potts 301

XI. Hydra and Other Fresh- Water Hydrozoa, Frank Smith 316

XII. The Free-Living Flatworms (Turbellaria) , Caroline E. Stringer :i2^

XIII. Parasitic Flatworms, Henry B. Ward 365

XIV. The Nemerteans, Wesley R. Coe 454

XV. Free-Living Nematodes, N. A. Cobb 459

XVI. Parasitic Roundworms, Henry B. Ward " 506

XVII. The Wheel Animalcules (Rotatoria), H. S. Jennings 553

XVIII. Gastrotricha, Henry B. Ward 621

XIX. Aquatic Earthworms and other Bristle-Bearing Worms (Chaetopoda),

Frank Smith 632

XX. The Leeches (Hirudinea), J. Percy Moore 646

XXI. The Fairy Shrimps (Phyllopoda) , A. S. Pearse 661

XXII. The Water Fleas (Cladocera), Edward A. Birge 676

XXIII. Copepoda, C. Dwight Marsh 741

XXIV. The Ostracoda, R. W. Sharpe 790

XXV. Higher Crustaceans (Malacostraca) , A. E. Ortmann 828

XXVI. The Water-Mites (Hydracarina) , Robert H. Wolcott 851

XXVII. Aquatic Insects, James G. Needham 876

XXVIII. Moss Animalcules (Bryozoa), Charles B. Davenport 947

XXIX. The Mollusca, Bryant Walker 957

XXX. The Aquatic Vertebrates, C. H. Eigenmann 102 1

XXXI. Technical and Sanitary Problems, George C. Whipple 1067

ix

i

I

CHAPTER I
INTRODUCTION

By henry B. ward

Professor of Zoology in the University of Illinois

On the surface of the globe, water and life are intimately asso-
ciated. As water grows scantier life becomes more restricted until
with the total failure of water life also disappears. In regions where
water is very scarce the few organisms that exist have learned to
store water or to discharge vital functions with a minimum supply
and thus to meet the natural defects of the situation.

The hydrosphere, or the total water mass on the globe, forms the
subject of study for hydrography which is readily subdivided into
(i) oceanography, that deals with the vast continuous mass of
salt water in the ocean, and (2) limnology, which treats of the vari-
ous fresh-water units. The term limnology is sometimes re-
stricted in its application to the more stable bodies such as lakes
and ponds, in which case rheology is used to cover various types of
flowing waters. All fresh water is distributed over the surface of
the land and variably grouped into separate series of systems
connected with each other only through the ocean to which each
system is joined. The rare desert systems, such as terminate in
the Carson Sink or the Dead Sea, are exceptional in having no
present connection with the ocean.

Fresh water is deposited on the land in the form chiefly of rain
or snow, and tends ultimately to reach the sea, though first and
last a considerable part is taken up by evaporation and goes back
directly into the atmosphere. Much of the precipitation soaks
into the ground to reappear elsewhere in springs or by seepage
to feed ponds and streams. Activity or rate of movement dis-
tinguishes two classes of water bodies: the flowing water of streams
and the temporarily quiet water of lakes. The latter almost
always form parts of stream systems and have thereby an inti-
mate connection with the ocean that is of fundamental importance
in determining the origin of fresh-water organisms.

2 FRESH-WATER BIOLOGY

The more or less actively flowing waters appear in the form of
springs or rivulets, then increase and unite to make brooks, creeks,
and rivers. The transition is ordinarily gradual and size has only
a secondary influence on the biological character of the stream.
The rate of flow, and the physical and chemical character of the
soil over and through which water drains into a stream and by
which its banks and beds are formed are the chief factors in de-
termining its life.

From the tiniest rivulet to the mightiest river one may find
every possible intermediate stage, and between the swiftest moun-
tain torrent and the most sluggish lowland stream there exists
every intermediate gradation. Biologically considered, the torrent
imposes on the development of life within its waters evident me-
chanical Hmitations which are not present in the slow-flowing
streams. Ordinarily the biological wealth of a stream varies in-
versely with its rate of flow, and anything which stops or checks
the flow makes conditions more favorable for the development of
life. Flowing waters are thinly inhabited and also present con-
siderable difficulties to the student; hence they are relatively un-
explored territory.

Waters of the static type, characterized by lack of flow, form an
equally continuous series from the great lakes or inland seas pro-
gressing by insensible gradations through lake, pond, and pool to
the morass or swamp. In the first group size permits more wind
action; it also pro\ides greater stability in level as well as in
thermal and chemical conditions. Possessing only limited com-
munication with the ocean these bodies of water constitute biolog-
ical units of great definiteness. The lake is a microcosm; a minute
repHca of the ocean, it responds more quickly to changes in its en-
vironment, is simpler to grasp and easier to study. Yet it is
withal the most complicated of inland environments (Shelf ord).

The distinction between water bodies of different size is often
indefinite. Puddle, pond, and lake form in fact a continuous
series. Yet in a strict sense lakes are characterized by a central
region deep enough to exceed the Kmits of growth of the flora in
the shore zone. Ponds are shallow lakes, usually insignificant in
area, yet still of relative permanence. They constitute distinct

INTRODUCTION 3

units of environment. These more nearly stable units, the lakes
and ponds, are often rich in life. They are exceptionally favorable
for study and have been extensively investigated both in Europe
and in this country.

The temporary water body, a puddle or pool, whatever its area,
affords only conditions for transient existence that are sometimes
irregular in their recurrence and sometimes present themselves
with considerable regularity. They are fitted for organisms that
reproduce very rapidly during the favorable season and also have
special means of tiding the species over the unfavorable period.
Purely temporary water bodies, such as pools that form in hol-
lows after a heavy rain or in a wet season, develop little if any
life. Such places on poor soil are most barren of all; the aquatic
life increases with the fertility of the soil, the age of the water body,
and the consequent accumulation of organic debris. Residual
ponds, water bodies in which the drying out is more gradual and
often incomplete and in which a central area may be protected from
complete desiccation by vegetation or proximity to the general water
level, afford conditions at the opposite extreme. The wide stretches
of lowland subject to periodic overflow from great inland rivers like
the Illinois, Missouri, and Danube in certain regions, develop a rich
flora and fauna which equals or exceeds- in abundance that found
under other circumstances (Antipa, Forbes). Similarly among
ponds adjacent to a lake basin the permanent are poorer than
those which dry out for a time (Shelf ord).

The smaller water body presents nearly uniform conditions
throughout and therewith also a single series of inhabiting organ-
isms. The entire area falls within the shore or shallow water
zone which is hmited to such parts as support fixed plants. In
this general region are readily distinguished two zones, (a) that
of the emergent vegetation where the larger plants reach conspicu-
ously above the water level and constitute the dominant feature
to the eye, and (2) that of submerged vegetation in which the
plants rarely project at all above the surface and in consequence
the water itself dominates the view. Both of these regions may be
subdivided on the basis of the particular form of vegetation which
is common in a given portion. In a swamp these regions are often

4 FRESH-WATER BIOLOGY

the only ones that are present. But in a pond one can usually
determine the existence of a third zone in which the fixed vegeta-
tion is lacking.

With increase of the water body in size or more especially in
depth, new conditions are presented. The littoral region passes
over insensibly into a deeper bottom region with its own biological
series and to a free open- water area known as the limnetic region.
The corresponding region in the ocean is designated the pelagic
and this term is also used by some for the fresh- water area. The
plants and animals in this region are characteristic; they constitute
what is called the plankton, the floating life of the water. Such
organisms remain suspended in water during their entire existence;
they Kve and die ''on the wing." In the larger lakes the shore
zone loses in prominence whereas the pelagic and bottom regions
gain in distinctness and relative importance.

Lakes vary widely in character and abundance in different
regions. They are infrequent in areas that are physiographically
old and most abundant in glaciated territory, where they occur
in eroded rock basins, in partially filled rock valleys, in hollows
over the moraine, and more rarely at the margin of the ice sheet.
Sometimes lakes are found in old volcanic craters, in the depres-
sions of a lava-covered area, or behind a lava flow dam. They
occur regularly in streams as mere expansions in the course or are
formed by the inflowing delta of a lateral tributary or when the
stream breaks through a narrow neck and leaves an ox bow or cut-
off lake at the side. One finds them often on low coastal plains
some distance from the shore, more commonly close to the sea
and even on the same level with it. Old lakes without an outlet
become strongly alkaline or saline and develop aquatic Hfe of a type
pecuHar to each. Most lakes, however, are fresh and shelter organ-
isms of the same general type.

Taken together lakes compose one-half the fresh water on the
surface of the globe. They present an infinite variety of physical
features in rocky, sandy, swampy margins, in steep and shallow
shores, in regular and broken contours with no islands or many,
with shallow water or depths that carry the bottom far below the
level of the sea.

INTRODUCTION 5

They vary in the chemical character of the soil in the lake basin
as well as in their banks and bed, in the degree of exposure to
wind and sunshine, in the relative inflow and outflow in ratio to
their volume, in their altitude as well as in geographic location.
All of these and many other factors modify and control the types of
living things and their abundance in the waters. Lake, pond,
and swamp are successive stages in change from the water-filled
hollow to the terrestrial plain that ultimately occupies the same
location. Along the margin of the lake, especially at the points
where tributary streams empty into it, the inflowing water brings
detritus of all sorts that builds out the shore and forms a shelf on
which the littoral vegetation gains a foothold. As the lake grows
old this region increases at the expense of the pelagic and bottom
areas, until the latter disappears and the former persists only in
reduced amount. Finally the entire area is conquered by deposits
of silt and growth of vegetation. The swamp comes and is made
over into dry land traversed in winding channels by the stream
system that is responsible for these changes. In other cases the
outflowing stream cuts down the level and ultimately drains the
lake.

Lakes are thus in a geologic sense only temporary features of
the river system to which they belong. Similar influences direct
the evolution of the stream from the violent instability of its
youth to the sluggish stability of its age. During this process of
evolution the life in the waters undergoes parallel changes. At
first the fauna is scanty but increases in numbers and variety as
new habitats are created. Unstable and intermittent conditions
indicate paucity of life; but when the aquatic environment be-
comes more permanent organisms more easily invade the territory
successfully and its life grows increasingly complex as time goes on.

Lakes influence noticeably the life of a stream system in that they
act as filters or settling basins for inflowing waters and also regulate
the volume of the discharge; thus the outflowing stream is free
from sediment and approaches constancy in level. This greater
permanence militates against the development of certain types of
life but favors others. The continued dilution of the stream by
the addition of water free from life and the removal of such organ-

6 FRESH-WATER BIOLOGY

isms as are produced at a given point by the constant flow of the
water make the river plankton scanty in amount, but many fresh-
water lakes produce an immense number of plankton organisms.
These have been much studied in recent years and about them
alike in ocean and fresh water has grown up a new study, Plank-
tology, the Planktonkunde of the Germans.

Among the forms of the open water are some, primarily the fishes,
which manifest indi\idual power of movement adequate to make
them independent of water movements, storms, and distances.
They can thus determine their own distribution in an active fashion
and stand in marked contrast with the plankton, for the latter is
unable to regulate effectively its location, and is dependent upon
the winds and waves for its dispersal. Typical plankton organ-
isms, in fresh water known together as the limnoplankton, are
found only in water bodies of some size, whereas in small lakes or
ponds the circumscribed open-water area contains life which con-
sists of migrants from shore and shallow water regions. Whereas
on the land higher forms, especially domestic animals, depend on
the higher fixed plants for food, in the water the higher types de-
pend upon the smaller floating plant and animal organisms which
transform inorganic materials and organic debris into available
food substances.

The floating organisms which taken together constitute the plank-
ton are grouped into two purely artificial classes according to
methods used in collecting. The constant use of fine nets (cf. p. 74)
for collecting plankton organisms led to a conception of this type
of life that unconsciously assigned a minimum limit in size. Thus
the organisms taken in the plankton net are all that the older
authors included under the term plankton, an assemblage which
should be termed more correctly the net plankton. It is well known
through the work of many investigators during recent years and
includes a great variety of Crustacea and Rotifera with many Pro-
tozoa and Protophyta, and less regularly some other types.

Within very recent times there has been obtained by more
precise methods of collecting what has been termed by Lohmann
the nannoplankton (dwarf plankton) with a size limit he set arbi-
trarily at 25/x. It consists of the most minute organisms only,

INTRODUCTION

those that (Fig. i) pass through the meshes of the finest silk gauze,
Swiss bolting cloth No. 25,* having meshes that measure 0.04 to
0.05 mm. square. The nannoplankton is composed chiefly of
flagellates and algae; although bacteria are constantly present they
apparently form but a minor con-
stituent in bulk and weight. The
number and variety of these or-
ganisms is truly astonishing even
in the clear waters of Alpine
lakes where according to Ruttner
they stand to the organisms of
the net plankton numerically in
the ratio of 160 : 3 and at least
two-thirds of them are still un-
described and difficult to include
in known genera. The maximum
number of nannoplanktonts thus
far recorded is from Lake Men-
do ta, Wis., where Cyclotella has
been found to the number of over
30,000,000 per liter of water.

Ruttner also calculates the vol-
ume of the nannoplankton in the
Lunzer lakes as three times that
of net plankton. According to
Birge and Juday the weight of its
dry organic matter varies in three
Wisconsin lakes from slightly
less (rarely) to 15 or 20 times
more than that of the net plankton and is ordinarily 5 to 6 times
as great. This amount is unquestionably of marked importance
both scientifically and practically, and the character of the or-
ganisms indicates even more clearly their fundamental impor-
tance in the problems of aquatic biology.

Plankton organisms are characterized by transparency, delicate
colors, and above all by their power of floating due to buoyancy and

* New No. 25 is identical with No. 20 of older authors (Lohmann).

Fig. I. A piece of bolting cloth No. 20 with
plankton organisms drawn between the meshes
to show relative size. Above, Rhizosolenia alata.
Upper row, left mesh: Gymnodinium. beneath
Amphidiniiun rotundatum and Exuviaella hallica,
right Pouclictia parva; middle mesh: Proroccn-
triim micans and Khynchomonas marina; right
mesh: Nitschia sigmalella. Acliradina pulcltra,
Halteria rubra. Nitschia clostcrium. Middle row,
left mesh: Tintinnopsis nana, Tintinnus steen-
strupi, Oxyrrhis phaeocysticola; middle rnesh:
chain of small Chaetoceras species, above it on
the left Tlialassiosira nana and saturni, on the
right Carteria; right mesh: chain of large
Chaetoceras species (Chaet. didymum), Tintinnop-
sis beroidea. Lower row, left mesh: Rhodomonas
baltica, Distephanus speculum; middle mesh:
Strombidium caudatum (?), Meringosphaera maii-
terranea. Amoeba; right mesh: Coccotithophora
wallichi. beneath on the left Pontosphaera huxltyi,
on the right Coccotithophora leptopora. above on
the right Chr>somonadine without shell, at the
very bottom Rhabdosphaera claviger. X no.
(After Lohmann.)

8 FRESH-WATER BIOLOGY

form resistance in contrast with related organisms. The buoyancy
is achieved by oil droplets and gas bubbles formed in the cells
whereas heavy cell walls and skeletal structures are wanting. Flo-
tation-apparatus in the shape of lateral wings, bristles, spines,
or a body form like a parachute, a spiral thread, or a gelatinous
cover — pro\'ides against rapid sinking. Ostwald has determined
that the rate of sinking is equal to the excess weight of the organism
above that of an equal water volume divided by the product of the
form resistance and the viscosity of the fluid.

Generally speaking great depth in a water body and large inflow
in proportion to volume are unfavorable to the abundant develop-
ment of the plankton organisms whereas minimal depth and scanty
inflow favor the production of plankton.

When water is first deposited on the earth it is almost absolutely
pure, containing only the minute amount of materials which it
has leached out of the atmosphere. From the ground over which
it flows or the soil through which it percolates come substances
organic or inorganic, in solution and suspension, here of one type
and there of another, that serve to enrich it and make of it an
environment capable of supporting life. "The aquatic popula-
tion of a lake or stream is thus sustained by the wastes of the land,
materials which would otherwise be carried down practically un-
altered to the sea; and rivers and lakes may be looked upon as a
huge apparatus for the arrest, appropriation, digestion, and assimi-
lation of certain raw materials about to pass from our control"
(Forbes).

For the determination of physical data on the character of bodies
of water, methods and apparatus of considerable complexity have
been devised, largely by students of oceanography, and adapted
later to fresh-water conditions. By such means the investigator
is enabled to measure in a comparative way, and sometimes in
absolute fashion, and to record environmental conditions such as
the depth, temperature, turbidity, and other physical features of
the water body. Some of these determinations are simple and
require only limited apparatus; others are complex and beyond
the powers of the ordinary student of aquatic biology. The appli-
cation of such data to biologic problems is discussed in part in the

INTRODUCTION 9

following chapter. An adequate consideration of methods and
apparatus demands more space than is available here and for
further information the student is referred to manuals deahng with
that phase of aquatic investigation. General methods of collect-
ing and photographing aquatic organisms form the subject of a
separate chapter while such methods as are applicable to the study
of each special group are discussed in the chapter on that group.

The environment of water organisms as of all others is a com-
plex of many elements. The physical factors are determined by
the materials held in suspension or in solution in the water, by its
temperature, depth, movement, illumination, shore and bottom.
Chemical factors are found in the acidity or alkalinity of the water
and in the gases, salts, and other materials in it. The organisms
themselves make the biological environment. Living or dead, as
food or feeder, parasite or host, friend, enemy, or neutral, each
living thing contributes to the sum total of the biological complex
by which each living unit is surrounded. It is the problem of
science to unravel this tangle and to determine the relation of each
constituent, living or non-living, to the others. The conditions of
existence to which organisms are subject in different aquatic en-
vironments and the influence which these environments exert on
organisms in general are discussed in the following chapter. In
subsequent chapters an attempt has been made to present these
relations as illustrated by each group of organisms. To become
thoroughly acquainted with a single group involves a knowledge
of the relations its members bear to every other organism in the
community.

No climate is too rigorous for fresh-water life. It exists in
fresh-water lakes at 77° N. L., hardly if ever free from ice, often
only slightly melted and with a maximum temperature of less than
2° C. at the bottom. The Shackleton expedition described an
extensive microfauna at 77° 30' S. L. from Antarctic lakes that
are frozen solid for many months, often for several years. At the
other extreme of temperature evidence is less complete but C}'pris
is recorded from hot springs at 50° C, ciliates and rotifers from
waters at 65° C, Oscillaria and nostocs from places that are
recorded at 70° to 93° C

lO FRESH-WATER BIOLOGY

The aquatic life of a permanent fresh-water body is variable
within certain limits of time and space. Each season witnesses
the coming and going of certain types which are active only in
definite periods and by resting spores, gemmules, or eggs bridge
over the intervening time. This known seasonal succession is so
definite that it gives the life of fresh water a changing character
as clear if not as conspicuous to the eye as that on land. One
may readily confuse with seasonal succession (i) the numerical
variation of a species or group due to favorable or unfavorable
conditions, and (2) the migrations which alter vertically or hori-
zontally through various water levels the distribution of a given
organism.

One can demonstrate also a stratification of aquatic organisms
of at least two types: vertical, as when different species are found
to occur within definite limits of depth, and horizontal, as when
species are confined to particular regions of streams or lakes. Such
relations are discussed fully elsewhere.

PecuHar types of aquatic environment, such as elevated lakes,
saline lakes, and underground waters, have each special types of
living organisms. Some of these special environments have been
made the objects of extended study which has shown the clear rela-
tion of their Hfe to that of other fresh-water bodies of the region
while demonstrating at the same time that they present a distinct
character of their own (cf. Zschokke, Banta).

The life of fresh water is probably not original but derived. It
came from the sea, by migration through brackish waters or swamps
or up into stream systems, by the gradual freshening of marine
basins cut off from the sea and converted into fresh-water bodies,
by direct transport from one body of water into another through
the agency of the wind, on the feet of birds or other wandering
animals, and finally by invasion from the land direct. Perhaps
the bottom forms came first, as conditions there were first estabhshed.
Certainly the plankton forms found no opportunity for existence
in the violent instabihty of a young stream. At present the shore
forms are the most abundant and the most varied.

In some deep lakes has been found a peculiar bottom fauna,
designated as the fauna relicta, which is composed of types unlike

INTRODUCTION II

other fresh-water forms and closely related to marine animals.
This fauna is often regarded as the survival from a period when
connections with the ocean were more immediate, or when climatic
conditions were different as during a glacial epoch.

The poverty of fresh-water life in variety and number of types
in comparison with that of the sea has often been emphasized.
Experimental data show it can hardly be due to lack of opportu-
nity for marine organisms to adapt themselves to fresh water for
in some geologic periods conditions have been very favorable
though in others distinctly the opposite. The severity of the
fresh-water climate, the obstacle of an ever outflowing current
and the relative newness of fresh-water bodies are evident difficul-
ties. Furthermore marine animals have generally free-swimming
embryos, distributed by water movements and sure therefore to be
eliminated gradually from the fresh-water environment even if
the adults were introduced successfully. Fresh-water animals
rarely have free-swimming larval stages and manifest what is
known as an accelerated or abbreviated development in which the
young on emerging from the egg is at a well-advanced stage.

Man has been a powerful agent in modifying fresh-water life.
By hunting and fishing he has exterminated many forms directly.
Through modifications of streams or shore for commercial pur-
poses he has indirectly eliminated many more and finally by pol-
luting the waters with sewage and waste he has rendered extensive
water areas almost devoid of aquatic life except bacteria and even
incapable of supporting any other forms. Streams below great
cities and in mining and manufacturing districts are aquatic
deserts.

Fresh-water biology is relatively a new field of study. Its
earliest records on this continent are hardly more than half a cen-
tury old. Among individual investigators in this field mention
should first be made of S. A. Forbes, whose pioneer work on the
Great Lakes has been followed by important work on the Illinois
river system. The work of Birge on Wisconsin lakes, of Reighard
on Lakes Erie and St. Clair, and of Kofoid on the Illinois river,
warrant also especial notice. Many others whose names and work
are recorded in the following chapters have made valuable con-

12 FRESH-WATER BIOLOGY

tributions to the general and special problems of fresh-water
biology.

Fresh-water biological stations have aided by organized effort
the conquest of the field. The activities of the Illinois State
Laboratory of Natural History on the Illinois river, of the Wis-
consin Geological and Natural History Survey on the lakes in that
state, of the U. S. Bureau of Fisheries on the Mississippi, of Ohio
State University on Lake Erie, of the University of Montana
Biological Station on Flathead Lake in the Rocky Mountains,
show the variety and scope of these interests. Unfortunately
only the first three are active all the year through. Other uni-
versities, notably ^Michigan, Indiana, Iowa, Colorado, North
Dakota, and Cornell, have participated in the study of fresh-water
life during part of the year or for a short series of years, and much
emphasis has been laid upon the lake biological station as a factor
in teaching biology. Few of these enterprises have had contin-
uous existence or permanent support. Such institutions are slowly
but surely gaining ground; their future development will aid both
the investigations of pure science and the application of such dis-
coveries to the solution of practical problems. The significance
for man of the problems outlined in this chapter and their bearing
upon the progress of social development have been discussed in
the final chapter of the book.

Save insects which moreover are primarily terrestrial forms, no
t>pe of fresh-water life has developed to the diversity and com-
plexity attained by the same type in the ocean. Yet each type
has achieved a variety well illustrated in the subsequent chapters.
Only a few of those that occur in the ocean are unrepresented in
fresh water and even strictly terrestrial groups like the mammals
and flowering plants or aerial forms Like birds have their aquatic
representatives. In subsequent chapters each of these groups is
discussed from the biological standpoint and in its especial rela-
tions to fresh-water life as well as with regard to its relative impor-
tance as a factor in the fresh-water flora and fauna.

The records of science contain only scanty references to the
t>^es of fresh-water life and their distribution on the North Amer-
ican continent, and regarding all other continents save one the
records are even more fragmentary. Of Europe alone is the in-

INTRODUCTION 13

formation adequate to outline a picture of the life in fresh water.
A comparison of the records shows conspicuously the uniformity
of fresh-water life on the surface of the globe, especially among
plankton organisms. Many of the forms discussed on later pages
are identical with those that occur in Europe and many more are
closely related species. The uniformity noted is not confined to
Europe and North America, but extends, within the limits of records
already made, to other continents also and even to the islands of
the sea. It is most striking perhaps among the lowest groups
as was emphasized by Schewiakoff for Protozoa.

This uniformity is due in part at least to the ease of dispersal
that the lower forms in the fresh-water fauna and flora enjoy.
They uniformly have hard-shelled resting spores, gemmules, or
eggs which are very resistant to adverse conditions, and are pro-
duced in enormous numbers. These structures are carried from
point to point on the feet of birds and other migrating animals
and are blown about in the dust until suitable conditions, e.g.j
temperature and moisture, incite development and the beginning of
a new life cycle.

Fresh-water life includes both plant and animal organisms of
various types. The number of groups represented among the plants
is not so great as the animals furnish. For details on individual
groups the student is referred to the appropriate chapter. The
following plant groups are found in fresh water:
Schizomycetes Lowest type of plant life in the water; either

or Bacteria saprophytic or parasitic in habit; found in great

variety in different sorts of aquatic environment.
For a general discussion of their relations to
fresh water consult Chapter IV, page 90.
Algae Characteristic and abundant aquatic plants,

nearly all free-living, found in all kinds of water
bodies; represented by a great variety of genera
and species.

For Cyanophyceae or Blue-Green Algae, see
Chapter V, page 100.

For other classes of Algae see Chapter VI, page
11^.

14 FRESH-WATER BIOLOGY

Higher Plants Among these plants which are more typically

land organisms, a few species of various sorts have
become a part of the fresh-water flora. In this
change they have undergone important modifica-
tions adapting them to an aquatic existence. No
synoptic treatment of these forms has been at-
tempted.
For general biological relations involved see
Chapter VII, page 178.
Animals are represented in fresh water by many more types and
varieties than are plants. A brief outline of the various animal
groups indicates in general the part played by each in aquatic life
and will serve to correlate the various chapters dealing with in-
dividual groups. Zoologists are not agreed as to the number and
rank of the subdivisions of the animal kingdom which should be
recognized; and other texts will show some variations from the
system used here. The student should bear in mind that the order
in the printed text does not express the relationship between higher
and lower groups and no arrangement in a hnear series can show
that relationship. The phyla are indicated by full-faced type.
Protozoa Characteristic water-hving forms with numerous

or Single- parasitic t\T)es; represented in fresh water by

celled Animals . ^ ^, . , . 4- u j

many species frequently found m great abundance;

in all regions and in all types of water bodies. The

following four sub-phyla are usually recognized.
Sakcodina The amoeboid Protozoa furnish both free-Uving

and parasitic species.

For the former see Chapter VIII, page 210.
Mastigophora Flagellate Protozoa include both free-living and

parasitic species; forms of the first type are

treated in Chapter IX, page 238.
Infusoria Ciliate Protozoa include both free and parasitic

species.

For the former see Chapter IX, page 271.
Sporozoa Exclusively parasitic forms; certain types are

abundant in fresh-water animals everywhere.

North American forms almost unknown. Group

not treated in this book.

INTRODUCTION

15

Porifera
or Sponges

Coelenterata

Echinodermata

Platyhelminthes
or Flatworms

TURBELLAEIA

OR Feee-living
Flatworms

Trematoda
OR Flukes

Cestoda
OR Tapeworms

Nemertina

Nemathelminthes
or Round-
worms

Preeminently marine; fresh-water bodies shelter
a considerable number of characteristic siliceous
forms all embraced in a single family, SpongilUdae.

These are described in Chapter X, page 301.
A group manifesting great variety and abundance
in the sea, represented in fresh water by a very few
widely scattered types, both polyps and medusae,
all belonging to one class, the Hydrozoa; other
classes confined to the sea.

For Hydrozoa see Chapter XI, page 316.
Includes crinoids, brittle-stars, starfish, sea-ur-
chins, and sea-cucumbers; not represented in fresh
water by a single known species.
Four classes are recognized, all of which furnish
important representatives to the fresh-water
fauna.

Common in salt and fresh waters; species found
in the latter generally insignificant in size. A few
are terrestrial in moist environments.

See Chapter XII, page 323.
All species parasitic; many in or on fresh-water
animals; with developmental stages, embryos
(miracidia) and larvae (cercariae) that occur free-
swimming in fresh water.

See Chapter XIII, page 369.
Exclusively parasitic forms. Adults common in
fresh-water vertebrates; developmental stages in
various aquatic animals, mostly invertebrates;
rarely with a free-swimming embryonic stage.

See Chapter XIII, page 424.
Mostly marine; a very few species of small size
and simple organization widely distributed in
fresh water.

See Chapter XIV, page 454.
A confused group of three classes showing little
similarity in structure and associated in a single
phylum largely as a matter of convenience. All
are well represented in the fresh-water fauna.

i6

FRESH-WATER BIOLOGY

Nematoda
OR True Round-
worms

GORDIACEA

OR Hair Snakes

ACANTHOCEPHALA

OR Thorny-
headed Worms

Trochelminthes
or Trochal
Worms

Rotatoria
OR Wheel

Animalcules

Gastrotricha

Coelhelminthes
(Annelida)
or Segmented
Worms

Chaetopoda or
Bristle Worms

HiRUDINEA

OR Leeches

Both free and parasitic forms common in all sorts
of environments; free-living species most abun-
dant in fresh waters and in moist soils; parasitic
species common in fresh-water hosts.

For free-living Nematoda, see Chapter XV,

page 459-

For parasitic Nematoda, see Chapter XVI,

page 510.
Parasitic in young life in insects; adult stage free-
living in fresh water.

See Chapter XVI, page 535.
Exclusively parasitic, without trace of alimentary
system. In many fresh-water hosts. Adults in
vertebrates; larval forms imperfectly known,
parasitize invertebrates.

See Chapter XVI, page 542.
Among the most characteristic of aquatic or-
ganisms. Favorite objects of study with the
early microscopists.

Microscopic free-Uving forms, very rarely para-
sitic. Abundant in fresh- water bodies of all sorts;
rare in the sea.

See Chapter XVII, page 553.
Minute free-living forms. Abundant in fresh water
to which the group is limited. Imperfectly known.

See Chapter XVIII, page 621.
Two classes in fresh water both well represented;
other classes exclusively marine.

One sub-class (Polychaeta) confined to the sea
save for rare types in fresh-water bodies near the
ocean; the other sub-class (OHgochaeta) found
mostly in fresh water and on land.

See Chapter XIX, page 632.
Both free-living and parasitic species, the former
mostly in fresh water with a few species also on
land in moist regions; rarely marine, as ectopara-
sites of fishes.

See Chapter XX, page 646.

INTRODUCTION

17

Arthropoda

Crustacea

ARACHNroA

Insecta

Tentaculata

Bryozoa
OR Moss
Animalcules

Three of the five classes usually recognized are
found in fresh water.

Only one sub-class, Cirripedia or Barnacles fur-
nishes no fresh-water representatives. The others
are well represented in the fresh-water fauna.
With few exceptions free-living forms.
For Phyllopoda see Chapter XXI, page 661.
For Cladocera see Chapter XXII, page 676.
For Copepoda see Chapter XXIII, page 741.
For Ostracoda see Chapter XXIV, page 790.
For Malacostraca see Chapter XXV, page 828.
Chiefly terrestrial with some parasitic forms.
One or two spiders have secondarily invaded fresh
water. ^ Among the mites one sub-order, the Hy-
dracarina, is exclusively aquatic. Nearly all
species inhabit fresh water.

For Hydracarina, or Water Mites, see Chapter
XXVI, page 851.
Two aberrant groups often attached to this
class are the following:

Linguatulida, exclusively parasitic, occur rarely
in fresh-water hosts.

Tardigrada, minute free-living forms known as
water bears; a few species not uncommon in
fresh water.
Typically land animals which in some cases
(especially for developmental stages) have gone
into fresh water and manifest secondary adapta-
tions to aquatic life.

See Chapter XXVII, page 876.
Of two classes, one, the Brachiopoda, is exclusively
marine. The other follows:
Sessile animals, nearly always colonial; exclu-
sively free-living; chiefly marine but with some
fresh-water forms widely distributed.
See Chapter XXVIII, page 947.

l8 FRESH-WATER BIOLOGY

MoUusca Of the five classes commonly recognized, three

which are relatively small are not represented in
fresh water. Two main classes Lamellibranchia
(bivalves) and Gastropoda (univalves) common in
fresh waters, widely distributed.

See Chapter XXIX, page 957.
Chordata Three of the four sub-phyla are exclusively

marine in distribution; but the fourth, the Verte-
brata, which is also the largest and best known,
plays an important part in the fresh-water fauna.
No attempt has been made to give a synopsis of
fresh-water vertebrates.

For a discussion of biological relations of the

Vertebrata to aquatic existence see Chapter

XXX, page 102 1.

IMPORTANT GENERAL REFERENCES

The literature on the subject is so extensive that only the most important
and essential items are listed below. Many general papers of marked value
had to be omitted for lack of space. All contributions bearing on a special
phase of the subject have been listed at the end of the chapter on that topic.
Longer bibliographies appear in Steuer, Wesenberg-Lund, Needham, and others.
In general only the latest or most general paper of a given author is listed here.

Antipa, Gr. 191 2. Das Ueberschwemmungsgebiet der unteren Donau.

Bukarest. 496 pp., 3 charts, 23 pi.
Apstein, C. 1896. Das Siisswasserplankton. Methode und Resultate der

quantitativen Untersuchungen. Kiel und Leipzig. 200 pp., 5 pi.
Banta, a. M. 1907. The Fauna of Mayfield's Cave. Carnegie Inst.,

Washn., Pub. 67; 114 pp.
BiRGE, E. A. 1895-6. Plankton Studies on Lake Mendota. I, II.

Trans. Wis. Acad., 10: 421-484, 4 pL; 11: 274-448, 28 pi.
BiRGE, E. A. and Juday, C. 1911-14. The Inland Lakes of Wisconsin.

Bull. Wis. Geol. Nat. Hist. Surv., 22, 27.
1914. A Limnological Study of the Finger Lakes of New York. Bull. U. S.

Bur. Fish., 23: 525-609.
Blochmann, F. 1895. Die mikroskopische Tierwelt des Siisswassers. Ham-
burg. 2 Aufl.
Brauer, a. 1909. Die Siisswasserfauna Deutschlands. Jena. (19 parts

by 32 authors.)
Ekman, S. 1915. Die Bodenfauna des Vattern quaHtativ und quantitativ

untersucht. Int. Rev. ges. Hydrobiol., 7: 146-204, 275-425, 8 pi.

INTRODUCTION

19

Eyferth, B. 1900. Einfachste Lebensformen des Tier- und Pflanzenreiches.

Braunschweig. 3 Aufl., 584 pp., 16 pi.
Forbes, S. A. 19 14. Fresh Water Fishes and their Ecology. Urbana, III.

19 pp., 31 pi.
FoREL, F. A. 1892-1904. Le Leman, monographie limnologique. 3 vol.

Lausanne.
1 90 1. Handbuch der Seenkunde. Allgemeine Limnologie. Stuttgart.
^249 pp., I pi., 16 figs.
Fric, a. und Vavra, V. 1894 -1902. Untersuchungen liber die Fauna der

Gewasser Bohmens, Prag.
FuRNEAUx, W. 1896. Life in Ponds and Streams. London and New York.

406 pp. 8 pi. 311 text figs.
Hensen, V. 1887. Ueber die Bestimmung des Planktons oder des im Meere

treibenden Materials an Pflangen und Tieren. Komn. wiss. Untersuch.

d. Deutschen Meere zu Kiel. V. Bericht, 107 pp., 6 pi.
Knauthe, K. 1907. Das Siisswasser. Neudamm. 663 pp., 194 figs.
KoEOiD, C. A. 1903. Plankton of the Illinois River, 1894-1899. I, II.

Bull. 111. State Lab. Nat. Hist., 6: 95-629, 50 pi; 8: 1-360, 5 pi.
Lampert, Kurt. 1910. Das Leben der Binnengewasser. Leipzig. II Ed.

856 pp., 17 pL, 279 figs.
LoHMANN, H. 191 1. Ueber das Nannoplankton und die Zentrifugierung

kleinster Wasserproben zur Gewinnung desselben in lebendera Zustande.

Int. Rev. ges. HydrobioL, 4: 1-38, 5 pi.
MuRR.\Y, Sir John and Pullar, L. 19 10. Bathymetrical Survey of the

Scottish Freshwater Lochs. Edinburgh. 6 vols.
Needham, J. G. and Lloyd, J. T. 191 5. The Life of Inland Waters.

Ithaca. 438 pp., 244 figs.
OsTWALD, W. 1903. Theoretische Planktonstudien. Zool. Jahrb., Syst.,

18: 1-62.
1903. Zur Theorie der Schwebevorgange sowie der specifischen Gewichts-

bestimmungen schwebender Organismen. Arch. ges. Physiol., 94: 251-

272.
Pascher, a. 1913. Die Susswasserflora Deutschlands, Osterreichs und der

Schweiz. Jena. (16 parts by various authors.)
Putter, A. 1909. Die Erniihrung der Wassertiere und der StofThaushalt

der Gewasser. Jena. 168 pp.
Regnard, p. 1891. La vie dans les eaux. Paris.
Reighard, J. E. 1894. A Biological Examination of Lake St. Clair. Bull.

Mich. Fish Com., No. 4; 60 pp., i chart.
Russell, I. C. 1895. Lakes of North America. Boston. 125 pp., 23 pi.

1898. Rivers of North America. New York. 327 pp., 17 pi.
ScHEWLAKOFF, W. 1 893. Ueber die geographische Verbreitung der Siiss-

wasser-Protozoen. Mem. Acad. Sci. St. Petersbourg, 41, No. 8; 201 pp.,

4 pi.

20 FRESH-WATER BIOLOGY

Shelford, V. E. 1913. Animal Communities in Temperate America.

Chicago. 362 pp., 306 figs.
Steuer, H. 1910. Planktonkunde. Leipzig and Berlin, 723 pp., 365 figs., i pi.

1910a. Leitfaden der Planktonkunde. 382 pp., 279 figs., i pi.
Stokes, A. C. 1896. Aquatic ^Microscopy for Beginners. 3d Ed. Trenton.

326 pp.
Ward, H. B. 1896. A Biological Examination of Lake ^lichigan in the

Traverse Bay Region. Bull. Mich. Fish Com., No. 6; 100 pp., 5 pi.
1898. The Freshwater Biological Stations of the World. Rept. Smith.

Inst., 1898: 499-513, 3 pl-
Wesenberg-Lund, C. 1908. Plankton Investigations of the Danish Lakes.

Copenhagen. Dan. Freshwater Biol. Lab. Op. 5; 389 pp., 46 pl.

19 10. Grundziige der Biologic und Geographic des Siisswasserplanktons,
nebst Bemerkungen liber Hauptprobleme zu kiinftiger limnologischer
Forschung. Int. Rev. ges. Hydrobiol., 3: 1-44. (Biol. Suppl., Heft i.)

Whipple, G. C. 1914. Microscopy of Drinking Water. 3d Ed. New
York. 409 pp., 19 pl.

Zacharias, O. 1 89 1. Die Tier- und Pflanzenwelt des Siisswassers. Leip-
zig. 2 vols.
1909. Das Plankton. Leipzig. 213 pp.

ZscHOKKE, F. 1900. Die Tierwelt der Hochgebirgsseen. Denkschr. Schweiz.
naturf. Ges., 37; 400 pp., 4 charts, 8 pl.

191 1. Die Tiefseefauna der Seen Mitteleuropas. Eine geographisch-
faunistische Studie. Leipzig. 246 pp., 2 pl.

Contributions to Canadian Biology. Fasc. II. Freshwater Fish and Lake
Biology. (Various authors.) Sessional Paper No. 396. 191 5. Ottawa.
222 pp., 21 pl.

JOURNALS

American Naturalist. Especially Synopses of North American Invertebrates
(older volumes), edited by W. M. Woodworth.

Annales de biologic lacustre. E. Rousseau. Brussels since 1906.

Archiv fiir Hydrobiologie und Planktonkunde. Stuttgart since 1905. (Con-
tinuation of Forschungsberichte aus der Biologischen Station zu Plon; 10
parts, 1 893-1 903.)

Internationale Revue der gesammten Hydrobiologie und Hydrographie.
R. Woltereck. Leipzig since 1908.

Transactions of the American Microscopical Society. T. W. Galloway, Ripen,
Wis. Since 18S0.

CHAPTER II
CONDITIONS OF EXISTENCE

By victor E. SHELFORD

Assistant Professor of Zoology, University of Illinois. Biologist Illinois State Laboratory
of Natural History

Conditions of existence are of importance only in so far as they
affect the life and death processes of organisms. The present
knowledge of such effects is far from complete and there is justifi-
cation for noting in detail only those conditions which observation
and experiment have shown to be important. Nevertheless if no
scientific observations or experiments had ever been made upon
organisms, water and its properties would occupy an important
place in a discussion of conditions of existence of aquatic life.

Water possesses certain thermal properties and certain charac-
teristic relations to other substances which put it in a class quite
apart from the vast majority of chemical substances (Henderson).
The thermal properties of water are such as to make it a very fit
condition of existence for organisms. In raising the temperature
of water one degree centigrade, several times as much heat is ab-
sorbed as in the case of various other common substances, except
living matter itself. This property moderates both winter and
summer temperatures to which aquatic organisms are subjected
(Birge). Ice melts at fully a hundred degrees lower than the fus-
ing point of other common environmental substances and the latent
heat of melting ice is proportionately high. Thus in melting, ice
absorbs large quantities of heat and in freezing water gives off this
heat again. This further modifies the aquatic cHmate as compared
with one that might be afforded by some other substance. The
latent heat of evaporation of water is also relatively high and this
tends to prevent the evaporation of all the water from the surface
of the land.

The expansion of water on freezing is one of its most important

2 2 FRESH-WATER BIOLOGY

properties. If water contracted on freezing ice formed at the sur-
face would sink to the bottom, more would be formed and accu-
mulate at the bottom in winter. Here it would thaw very slowly
or not at all in summer and the entire surface of the earth would
thus quickly become refrigerated. The expansion of water on heat-
ing is also very important as it is responsible for the setting up of
currents which ventilate the aquatic environment.

Water is by far the most general solvent for other substances.
No other Uquid will dissolve so many common substances. Though
it is one of the most stable and inert compounds, like salts in solu-
tion, it dissociates into parts or ions and a very small proportion
of pure water is in the form of H"*" (the cation bearing a positive
electric charge) and 0H~ (the anion bearing a negative electric
charge). These ions are known respectively as hydrogen and
hydroxyl ions. At 25° C. 1000 grams of pure water contain
0.000,000,1 gram of ionized hydrogen and 0.000,001,7 gram of ionized
hydroxyl. Salts in solution in water are ionized. For example
common salt, NaCl, exists chiefly as Na"^ and Cl~. Henderson
states that solutions in water are the best source of ions. The
variety and complexity of the environment of aquatic organisms
and the number and variety of chemical reactions are increased by
the presence of ions.

As compared with air, water is much denser, being 773 times as
heavy. Gases and other solutes are presented to organisms in
solution and gases need not be taken into solution by surfaces
moistened by body fluids as in the case of land organisms. The
diffusion of gases is less rapid in water than in air. Some food
substances are in solution in water; many food organisms float in
it on account of its great density. This enables some aquatic
animals to rest in one position and secure food without effort.

Physical and Chemical Conditions

Physical conditions can be separated from chemical conditions
only arbitrarily. Combinations of the various physical conditions
in water may be included under the term physiography. Physi-
ography in the broad sense includes topography of the land asso-

CONDITIONS OF EXISTENCE 23

dated with aquatic environments, size and texture of surface ma-
terials, direction of prevailing winds, etc.

In streams the strength of the current is a function of volume of
water and slope of stream bed. The amount of sediment carried
and the size of the sediment particles is determined by the strength
of the current and by the character of the materials eroded. The
character of the stream floor, the ventilation of the environment,
and hence its gaseous content as well as turbidity, are determined
by the same factors. All these factors combined comprise impor-
tant conditions of existence which while they influence organisms are
often so difflcult to analyze into constituent controlUng factors that
for ordinary purposes it is better to lump them together under the
head of physiographic conditions in streams. Fishes and mollusks
migrate upstream during floods and downstream during drought
periods. Thus different species of fishes in a number of streams
about equally accessible to Lake Michigan but differing in size and
age as shown in Fig. 2 are very definitely related to the longitudinal
conditions in the various streams, each fish species penetrating up
stream to a point characterized by certain physiographic conditions,
regardless of the size of the stream as a whole (compare Table I
with Fig. 2). An analysis of the physical factors to which the
fishes respond and which thus determine the locahty they occupy
would be a very intricate task but by a simple method of physio-
graphic analysis the differences in their ecological constitution is
clearly brought out. Thus important features of conditions of exist-
ence may be determined by physiographic analysis and the classifi-
cation of streams should be determined by physiographic age and
physiographic conditions.

Conditions of existence in lakes and ponds are markedly influ-
enced by physiographic conditions. High surrounding country
broken into hills and valleys influences the action of winds on the
surface. Wind is important in determining circulation. The sur-
rounding topography determines the carrying power of streams and
thus the amount of sediment carried into lakes. The amount of
sediment determines the depth of light penetration.

The depth of lakes and ponds is definitely related to physio-
graphic conditions. Coastal lakes are usually shallow with sandy

24

FRESH-WATER BIOLOGY

or muddy bottom. Morainic lakes are usually relatively deep
with clay bottoms and sides. Solution lakes and ponds of limestone
regions usually have abrupt rocky sides.

TABLE I

Showing the Distribution of Fish (Nomenclature after Forbes and
Richardson) in Three Illinois Streams at the Times Indicated

(The observations on Pettibone Creek were repeated in four succeeding years
with the same results. Stars indicate presence; numbers refer to Fig. 2)

Name of stream and common
name of fish

Date and scientific name

I

*
*

?
*

2

*

*
*

*
*

3

*
*
*

*
*
*
*

*
*
*

4

*

*
*
*
*
*

*
*
*
*

*
*
*
*

5

*

*
*

6

*
*
*

7

Glencoe Brook

August, 1907

Semotiliis atromaculatus . .
1007—8 . ...

Horned dace

County Line Creek

Horned dace . ...

Semotiliis atromaculatus..

Rhinichthys atronasus. . . .

Boleosoma nigrum

Pimephales promelas

Pimephales notatus

Catostomus commersonii. .
September, 1909, and April,
1910

Semotiliis atromaculatus . .

Chrosomtis erythrogaster. .

Rhinichthys atronasus. . . .

Boleosoma nigrum

Catostomus commersonii. .
September, 1909

Semotiliis atromaculatus. .

Chrosomus erythrogaster. .

Rhinichthys atronasus. . . .

Catostomxis commersonii. .

Pimephales notatus

Esox vermiculatus

Lepomis pallidus

Micropterus salmoides —
Esox lucius

Black-nosed dace

Johnny darter

Blackhead minnow

Blunt-nosed minnow. .

Common sucker

Pettibone Creek ^

Red-bellied dace

Black-nosed dace

Johnny darter

Common sucker

Bull Creek-Dead River.
Horned dace . . .

Red-bellied dace

Black-nosed dace

Common sucker

Blunt-nosed minnow. .

Little pickerel

Bluegill

Large-mouthed black
bass ....

Pike

Crappie

Pomoxis annularis

Moxostoma aureolum

Erimyzon sucetta

Abramis crysoleucas

Notropis cornutus

Red-horse

Chub-sucker

Golden shiner

Common shiner

Cayuga minnow

Tadpole cat

Schilbeodes gyrinus

The lower part of Pettibone Creek has been destroyed by the United States Naval School,
otherwise the table would include the records for a point 5 and perhaps a point 6. but probably not 7.

Physical factors include bottom, currents, light, temperature,
density, pressure, viscosity, etc.

The size of bottom materials is an important condition of exist-
ence. In streams the current sorts the materials, leaving the coars-

ffiMir

CONDITIONS OF EXISTENCE

25

est in the swiftest current and the finest in the most sluggish cur-
rent. In the curves of streams the current is usually swiftest on
the outside and most sluggish on the inside. Dift'erent animals

JjAKE MICHIGAN

Fig. 2.
Diagrammatic arrangement of four streams flowing into Lake Michigan. The streams are mapped to
a scale of one mile to the inch, and the maps are placed as closely together as possible in the diagram.
The intermediate shore lines are shown in broken lines which bear no relation to the shore lines which
exist in nature. Toward the top of the diagram is west. Each number on the diagram refers to the pool
nearest the source of the stream which contains fish, as follows: i, homed dace (Semotilus alromaculatiis) ;
2, red-bellied dace {Chrosomus erythrogaster) \ 3, black-nosed dace {Rhinichthys atronasus); 4, the suckers
and minnows; 5, the pickerel and blunt-nosed minnow; 6, sunfish and bass; 7, pike, chub sucker, etc.
The bluff referred to is about 60 feet high. The stippled area is a plain just above the level of the lake.
(After Shelford.)

tend to occupy the different kinds of bottom materials (Fig. 3).
Thus the differentiation of bottom constitutes an important differ-
entiation of conditions of existence.

The bottom of a swift stream eroding sandy soil is very unstable
and the fauna very sparse. Such streams are essentially aquatic
deserts and only a few burrowers are able to live in them. Sandy
bottomed streams with sluggish current have a luxuriant fauna
of burrowers and flora of rooted vegetation. Rocky and stony
streams have rich faunas of clinging and hiding animals.

In lakes and ponds the importance of bottom is determined by
the strength of wave action and the amount of current. The
fine bottom materials around the margin of a large lake are con-
stantly moved about; the particles grind upon one another mak-
ing the presence of bottom organisms impossible. Thus the sandy

26

FRESH-WATER BIOLOGY

shores of the Great Lakes down to a depth of eight feet or more are
usually almost entirely without bottom organisms.

The character of terrigenous bottom is an important condition of
existence chiefly where current or wave action is strong and becomes
of httle or no importance where there is no movement, as in the

■'.'.' •■.■'•.■'-■•*■"*

Fig. 3.
The form of bottom and size of bottom materials in a cross section of the North Branch of the Chicago
River with distribution of animals, a to d natural size, a, burrowing may-fly nymph (Ilexagenia sp.);
b, small bivalve {Spharium slamineum), two individuals, two views; c, viviparous snail {Campeloma in-
tegrum), seen from two sides; d, the long river snail, young and full grown (Pleurocera elevatum) ', e, cross
section of the stream with reference to a curve (/). (Original.)

bottom of one of the Great Lakes. However, bottoms of soft muck
containing putrescible organic matter occur in the absence of current
and constitute a condition of existence sharply differentiated from
terrigenous bottoms because they can support only certain types of
organisms, mainly anaerobes, and but few of these. Many aquatic
animals use the bottom materials in the construction of their cases,
nests, etc. Thus the caddis worms (certain species of Mollana
and Geora) build cases of sand grains weighted at the sides by small
pebbles. The horned dace and several other fishes associated with
it use pebbles to build their nests. The pebbles must be of a cer-
tain average size. Many animals form associations (memory) with

CONDITIONS OF EXISTENCE

27

reference to certain stones or pebbles under or near which they live
(e.g., mayfly nymphs) and thus work out simple homing paths.

As has been stated, in streams the rate of flow is determined by
volume of water and slope of stream bed. In a comparatively
straight stream the current is swiftest in the center at the top and
least swift at the sides near the bottom; the center of the stream
bed has a current intermediate between the two. Thus sluggish
portions of streams like the Fox River (lUinois) may be swift
enough at the bottom of the center to support some swift stream
animals such as Hydro psyche and Heptageninas. There are back
eddies about stones and other obstructions so that currents in
streams are somewhat irregular.

In lakes circulation is determined by wind and differences in
temperature. A lake which is equal in temperature throughout
has a complete circulation (Fig. 4 A). The wind indicated by the
arrow (W) tends to pile the water up on one side. To compensate

..<m

Fig. 4.

The circulation of the water (A) in a lake of equal temperature; (B) in a lake of unequal tempera-
ture. W represents the direction of the wind; E, epilimnion; T, thermocline; H, hypolimnion.
(After Birge.)

for this currents are started downward along the shore and a cir-
culation across the bottom and upward on the other side is initiated.
Very shallow lakes and deeper lakes in the cold months of the year
have a complete circulation. Lakes of unequal temperature are
very different. For example a deep lake has a uniform tempera-
ture for a time in the spring just after the ice melts, complete cir-
culation takes place and the bottom waters are aerated. As the

28 FRESH-WATER BIOLOGY

sun warms the surface waters they become so much lighter than
the deeper colder waters that the currents set up to compensate
for the piling up of the water by the wind can no longer flow to
the bottom and a superficial circulation is accordingly set up
(Fig. 4 B). A distinct thermocUne (T) is thus established. The
epilimnion (E) is warm and constantly aerated by circulation and
the hypolimnion ill) is stagnant. In the autumn as the water
gradually cools the thermocline gradually migrates to the bottom
and the earlier, complete circulation (Fig. 4 A) is again established.

In addition to the general circulation, waves and their action
must be considered. As was noted in connection with bottom, the
shifting of fine bottom materials eliminates most animals from
sandy shores. On rocky shores in large lakes are representatives
of some of the same animal species found in swift streams. The
alternating current does not appear to exclude many such species.
In small lakes and ponds the small wave action removes decaying
organic matter and thus renders portions of the shores suitable
for animals requiring or preferring a terrigenous bottom. The
location of such shores which are usually sandy is determined
largely by the form of the lake or pond and the direction of pre-
vailing winds and inflow of water.

Currents influence animals directly by bringing pressure against
parts. Sessile animals respond to currents by changes in growth
•form. But few fresh water sessile animals have been studied in this
respect, and the exact character of such responses cannot be stated,
though sponges and polyzoa are known to vary greatly. Motile
animals as a rule turn with their heads upstream and either move
against the current, making progress upstream, or remain in one
position by swimming enough to maintain themselves. Fishes
under experimental conditions will often swim against a current
which is stronger than their optimum until they are exhausted.
Many fishes orient themselves by visual impressions of the bottom
as they float downstream. Others appear to orient by differences
in pressure on the two sides of the body or by rubbing against the
bottom as they float down. Sight is probably ineffective during
floods on account of sediment. Current is essential to the spinning
of the characteristic cocoons and cases of some insects Hving in

CONDITIONS OF EXISTENCE 29

rapids. They make a shapeless mass without it. A few animals
require very complete aeration or they die very quickly. Suckers
appear to die from lack of oxygen while the rainbow darter adds
something to the water in which it lives which is not removed by
artificial aeration and which kills the fish unless the number of fishes
is small or the water changed often.

Light penetrates clear water to great depths. During the cruise
of the Michel Sars the penetration of sufficient light to markedly
affect the most sensitive photographic plates in 80 min. was found
at a depth of 1000 meters (latitude 31° 20', June 5-6. Sun nearly
over head; for methods see Murray and Hjort). No effect was
obtained at 1700 meters with an exposure of two hours. Light
sufficient to affect the plates in 2 hours lies somewhere between
1000 and 1700 meters. There were many rays of all kinds at 100
meters but least of the red. Though penetration is rarely as great
in fresh water as in the sea, light may possibly penetrate to the
bottom of Lake Baikal which is the deepest fresh water lake known
(1300 to 1700 meters are reported).

In temperate latitudes light does not penetrate so far vertically
because it enters the water obliquely. The depth of penetration
can easily be calculated for any latitude or season from the angle
of declination of the sun, when the penetration in similar water is
known for other latitudes and seasons.

The most important factor limiting the penetration of light into
fresh water is turbidity. Forel found the light penetration in
Lake Geneva (Switzerland) greatest when the lake contained least
sediment. Table II gives the depth of light penetration in Lake
Geneva in March when it is clearest. Forel used much less sen-
sitive plates than were used on the Michel Sars, the sun was much
lower in the horizon and the locality 15 degrees farther north.
Thus Forel's records show that light did not diminish notably in
the first 25 meters, fell off gradually in the second 25 meters and
then dropped off rapidly to zero for his plates at no meters. Fol
and Sarasin with more sensitive silver salts than were used by Forel
found that light reached 200 meters in winter. It is altogether
probable that the plates and apparatus of the Michel Sars would
show much light at three or four times the depth given by Forel.

30

FRESH-WATER BIOLOGY

TABLE II

Showing Depth of Light Penetration in Lake Geneva (Switzerland) and

Conditions Affecting the Same in Both Lake Geneva (after

Forel) and Lake Michigan

In the eighth column the relative results are given in seconds, in terms
of the effect on the photographic plate, of exposures to the sun.

Lake Michigan

Rainfall

Inches

2.0
2-3
2-5
2.7
35
3-7

Centi-
meters

Velocity of wind
at noon

Miles
per
hour

Meters

per
second

5-1
5-2
6.4
6.9

8.9
9-4 I
9.2!

7.2 I

7-7 I
6.6 I
6.6 1
5-3 !

17

8

8.

20

0

9-

20

4

9-

IQ

4

8.

18

3

8.

14

4

6.

14

6 i

6.

13

4 ;

6.

16

7

7

17

6

7

19

0

8

19

■9

8

Month

Lake Geneva, Switzerland

Rainfall and
light

Prec.
in cm.

January. .
, February.
.March. . . .

, April

. May

.June

•July

.August. . .
. September
.October. .
. November
. December

Light
limit at
depth in
meters

87
65

72

no

.68

.91

75

•.S9

.08

45

.04

.42

50

. 10

■ 4

'5

. II

1 .

Light and depth

Intensity
of light
(March)
at depth
in next
column

Depth

500 sec.
500 sec.
500 sec.
400 sec.
360 sec.
120 sec.

60 sec.

25 sec.

10 sec.
2 sec.
o sec.

0.0
19.6
25.2
45-5
55-5
65.6
75-6
857
95-8
105.4
115.6

Little work on the depth of light penetration has been under-
taken in the North American waters. In Table II the rainfall
and wind velocity over Lake Michigan are shown and the rainfall
for Lake Geneva (Switzerland). The greatest light penetration
in Lake Geneva comes when the rainfall is low and when the
mountains are still frozen. The Lake Michigan water commission
found in a brief period of study that the greatest turbidity fell in
January, February, March, and April. The table indicates that
this is in months with high wind velocity. The great rainfall of
the spring and early summer months tends to keep Lake Michigan
turbid, so the greatest light penetration may be predicted for Aug-
ust which has least rain and least wind.

Various streams are normally so muddy that light cannot be ex-
pected to penetrate more than a few feet and the fauna accordingly
lives in very faint light. Others, as for example streams and lakes

CONDITIONS OF EXISTENCE 31

in some of the western mountains, arc very clear and one can see
to depths of 5 to 15 meters. Depth at wliich objects may be seen
is measured by lowering a white disc 20 cm. in diameter known as
the disc of Secchi.

When light penetrates water the red rays are most rapidly ab-
sorbed, then orange, yellow, etc. In the Michel Sars measure-
ments there were scarcely any red rays at 500 meters, one-half the
depth at which hght was measured. Fol found off Nice that when
down in 30 meters of water he could see a stone 7-8 meters away and
a bright object at a distance of 25 meters. Red animals looked
black, while green and blue green algae looked quite bright.

In water there is no dawn or twihght. The surface of the water
reflects practically all the light when the rays come to it very
obliquely. Fol found that in 10 meters of water solar Hght dis-
appeared quite suddenly long before sunset. In Funchal Harbor
(Madeira) the Prince of Monaco used Regnard's apparatus in which
a film is moved before an opening by clockwork, and found that at
20 meters in March the day lasted 9 hours whereas at 40 meters
the film showed the effects of light for only about 15 minutes at

2 P.M.

Light profoundly influences the migrations and distribution of
animals probably largely because it has a marked effect on Kfe
processes. Unfortunately, however, with the exception of ultra-
violet Ught which penetrates the atmosphere into low altitudes in
minimal amount, very little is known of the actual physiological
effects of light. Under experimental conditions animals usually
avoid or select the blue end of the spectrum. Red usually acts as
darkness or very faint Hght. Thus animals hving in very strong
light usually accumulate in blue or violet when exposed to spectrum
colors. Animals hving in darkness collect in the red. Animals
living in moderate hght usually wander about throughout the spec-
trum but a majority congregate in the blue. Probably animals
are affected through photo-chemical reactions which are brought
about most often by the blue end of the spectrum. Daphnias
select the brightest part of the spectrum which is the green or the
yellow for most organisms, brightness being determined by some
specific effect of particular wave lengths upon the light recipient

32

FRESH-WATER BIOLOGY

organs. Yellow is brightest to the human retina. In addition to
color animals react to direction and to intensity of light. Prob-
ably the majority of fresh-water animals react more strongly to
direction than to intensity. Hydro psyche and Argia do not react
to intensity at all but react to direction very sharply. Experi-
mental conditions in which direction away from source accompanies
a sharp decrease in intensity gives sharpest reactions with most
aquatic animals.

Animals react to intensity with reference to an optimum. The
optimum usually corresponds to the usual light in their natural
environments. The organism may often be modified by changes
in the chemical character of the water, or even by rough handling
{Daphnia, Ranatra), so that it selects a different optimum, or re-
verses its reaction to direction of rays.

Many animals react to shadows or small areas of illumination.
Thus frogs will hop to a shadow in the middle of a sunny field and
Amblystoma will follow a person along a sunny road. This type
of behavior is doubtless an important thing under water but has
been but little investigated.

One of the topics which has absorbed much of the attention of
limnologists is the daily depth migrations of certain Crustacea.
They usually accumulate near the surface at night and in deeper
water during the day. The causes of these migrations are very
complex and Hght is an important factor. Dice has recently dis-
cussed the matter in full. Light is probably important in confin-
ing certain animals in deep water, in turbid streams, under stones
and logs and in caves, ground water, etc.

The early invention of the thermometer has led to quite com-
plete investigation of temperature and an over-estimation of its
importance in the direct control of the distribution of life in water.
The tendency of modern investigation is to weaken the belief in
its direct importance.

Stream temperatures are probably about the same at the various
points in any cross-section, except the shallow sluggish margin on
warm summer days. The extent to which daily, seasonal, and
weather fluctuations in atmospheric temperature afifect a lake is
determined by the depth and size. Small lakes with incomplete

CONDITIONS OF EXISTENCE

33

circulation in summer are cold at the bottom, being heated at the
surface only (Fig. 4 B). Lake Michigan is a large deep lake and
none of the seasonal temperature changes extend to the deepest
parts (Table III). In summer the water of the surface is warmed,
but if the vertical circulation is complete all the heat in the waters
flowing downward at the leeward side (Fig. 4 B) must be absorbed
above no meters (Table III) when the temperature of maximum
density is recorded. These are chiefly bottom records and do not
therefore represent the temperatures at the same level in the open
water, especially in the shallower situations where the sun's energy
is distributed through a thinner layer of water.^

TABLE III

Temperature

OF Lake

Michigan (After Ward)

Temperature
at depth in
next column

Depth

Date

Hour P.M.
unless stated

Sky

Tem-
perature
of air

Tem-
perature
at sur-
face

"C.

18.3

16.7

7.2

7-5

7-2
5-2

5-1

4-2
4-2

°p

64
62

44
45
44
41
41
39
39

9
0

9

5
9
3

I

5
5

Meters

5-66

11.32

22.63

32.06

43 38

55-93

108. 22

1 1 2 . 00

132.66

Feet
18.6
37.1
74-1
105.2

142.3
183-5
355-0
367-5
436.0

A\ig. 16
Aug. 18
Aug. 18
Aug. 16
Aug. 25
Aug. 16
Aug. II
Aug. 16
Aug. 18

4:05

9:00 A.M.
12:25
5:10

3:25
12:05
10:30 A.M.

1:50

4:30

Clear
Cloudy
Clearing
Clear

°C.
16.7
18.9
16.7
16.7
20.0
15-6

16^7
18.9

18
17
17
18

19
18
18
18
18

3

2

5
3
4
3
9
3
3

Clear
Hazy
Clear
Scattered
clouds

Most fresh-water animals are poikilothermic or cold-blooded and
their temperature varies with the surrounding temperature. IMam-
mals and birds with the exception of the manatee and rare fresh-
water dolphins and seals are not truly aquatic. Truly aquatic
warm-blooded animals usually have a thick covering of fat which
is a poor conductor of heat. A few fishes maintain 10° C. or more
above the surrounding medium, but for most fresh-water animals
0.1° to 5.0° C. are reported. Rogers recently reported only very
minute difference for goldfish. This heat is due to metabolism.

^ Temperatures below the surface may be taken with a thermometer in a two-gallon
bottle filled at the desired lev^el or better with a Negretti-Zambra reversing ther-
mometer. For devices making continuous records of temperature, the thermophone
i of Whipple or Friez's soil and water thermograph may be used.

34

FRESH-WATER BIOLOGY

Cold increases the metabolism of warm-blooded animals and
decreases that of cold-blooded animals. In the cold-blooded
animals a rise of io° C. within limits reasonably compatible with
life increases the rate of metaboUsm, or rate of development of
young, by two or three times. This is taken as evidence that
life is a chemical process because similar changes in temperature
have corresponding changes in rate of chemical reaction.

Thus animals aquatic in their developmental stages and which
happen to be in very shallow temporary water are automatically
accelerated in development as the sun warms the water, evaporates
it and decreases its volume at the same time increasing its tempera-
ture.

Animals react to temperature with considerable precision. Both
marine and fresh-water animals can recognize differences of 0.2° C.
and will turn back when such slight differences are encountered
under experimental conditions.

Pressure in water increases with depth. The results given by
Forel are shown in Table IV.

TABLE IV

Pressure in atmospheres

I

2

3

5

8

10

20

Depth in meters

10.328

20.6

30 -9

51-5

82.4

103.27

206 . 49

There is a little less than one atmosphere increase in pressure
for each 10 meters of depth. According to this, animals in the
deepest parts of a lake like Lake Michigan are living under a
pressure of about 375 pounds to the square inch.

The effect of pressure on organisms was studied by Regnard.
Contrary to the popular idea he found that gelatine, agar, and
various plants and animals and excised parts of animals take up
water, swell and increase in weight under high pressure. This is
true even of terrestrial insects. At 400 to 600 atmospheres Para-
mecia become swollen and immobile, including the cilia. They
recover from ten minutes' exposure. Carp become Hstless at 200
atmospheres, die at 300 and become swollen and rigid at 400
atmospheres. Salmon ova are destroyed at 400 atmospheres but

CONDITIONS OF EXISTENCE

35

chlorophyll bodies of green algae continue to work at 600 atmos-
pheres and cress seeds have germinated after an exposure to 1000
atmospheres.

Table V shows the conditions and distribution of Ufe in Lake
Michigan. The greatest pressure is 27 atmospheres which on
the basis of the work of Regnard would seem trivial. Animals
may react to pressure differences but this is not known as no pres-
sure gradient can be estabhshed without involving gravity also.
Pressure would appear to play a relatively insignificant role.

TABLE V
Conditions in Lake Michigan

Approximate physical conditions

Depth

Vegetation and animals

Meters

Feet

Strong wave action

0-1.5

o-S

Bottom organisms wanting
on sandy shores, abundant
on rocky shores

Limit of sand-moving waves

8

26

Organisms abundant

Limit of daily temperature fluc-
tuations; limit of wave action;
beginning of light decrease;
pressure about 2^ atmospheres

25

82

Lowest record of Chara and
Cladophora. Lower limit of
MoUusks except Sphasridae

Pressure 4 atmospheres, light re-
duced to f

39

128

Scanty filamentous algce

Seasonal temperature fluctua-
tions less than i° C; light re-
duced to 1; pressure 5^ atmos-
pheres

54

177

Lower limit of most shallow

water animals
Nostoc and diatoms

Light i; pressure 7 atmospheres

70

230

No bottom plants recorded

Probably dark as night; pressure
II atmospheres; little change
in temperature; nearly uniform
conditions

115

377

No plants recorded

Greatest depth in lake; pressure
27 atmospheres

274

900

No plants recorded

With a rise of temperature both the density and viscosity of
water decrease. This tends to cause such organisms as behave
like small inanimate particles to sink. Ostwald suggested that
these differences are responsible for the depth migrations of
plankton organisms. He considered that a decrease in viscosity

36 FRESH-WATER BIOLOGY

causes them to sink. The diffusion currents bring them up again
(Johnstone). This is no doubt a matter deserving investigation.
Turbidity is important largely through its relation to Ught. Most
aquatic animals will tolerate much sediment, at least under
experimental conditions.

Chemical factors are not directly or clearly separable from
factors that may be regarded as physical or biological. Under
this heading are considered dissolved gases, inorganic salts,
acidity, alkaUnity, and neutrality.

In order to support animals and plants continuously water must
contain certain minerals and gases in solution. Salts (carbonates,
sulphates, and chlorides) of magnesium, calcium, potassium, and
sodium, and salts of iron and siUcon are practically always in solu-
tion in water and their presence in definite proportions is beheved to
be essential to the Hfe of organisms. Pure distilled water has been
shown to be harmless to certain animals for comparatively short
periods but it is doubtful if it will sustain life indefinitely. Dis-
solved gases in definite proportions are essential.

The occurrence of gases and their solubility under experimental
conditions are shown in Table VI. A standard method of express-
ing quantity of gas in solution is in cubic centimeters per liter at
0° C. and 760 mm. of mercury. Values are commonly given in
these terms.

Nitrogen is the most inert and least important of the dissolved
gases. It rarely has any direct effect on animals and plants and
this apparently only when present in considerable excess of satu-
ration. Under such conditions it accumulates in the blood vessels
and tissues of fishes, crayfishes, insects, etc. In the organs of
circulation it may thus stop the blood flow and the animals die of
asphyxia. Birge and Juday state that in lakes in the region of
the thermocline and below an excess of 1 2 to 38 per cent of satura-
tion occurs, but under the conditions of pressure there this would
have no effect. It is probable that in nature this condition of
excess is not commonly great enough and does not often occur for
a time long enough to cause any fatal results. Several hours or
days, depending upon the excess, are required. Excess nitrogen is
a great source of difficulty in aquaria.

CONDITIONS OF EXISTENCE

TABLE VI
Showing the Solubility and Distribution of Atmospheric Gases

37

Composi-
tion of air
in percent-
ages

Gas values in cubic centi-
meters per liter at 0° C. and
760 mm. mercury

Gas

At. temp. 20° C.
760 mm.

Maximum
amounts
found in
natural fish
waters,
springs
excepted

Kind of water having gas

content given in preceding

column

Water
absorbs
from air

Water
absorbs
pure gas

Nitrogen, argon,

etc

Oxygen

Carbon dioxide ....
Ammonia

Methane

Hydrogen sulphide.

79.02
20.95

0.03

Small
traces
locally

12.32
6.28

0.27

15.00
28.38

901 .00
Very
large
quanti-
ties
34.00
2900 . 00

19.00
24.00

30.00
14.00

10.00
0-55

Lakes

Streams, lakes in
winter, or with
green algae

Ponds

Sewage contami-
nated

Bottom of lake
Lakes, and sewage
contaminated

The oxygen content of water varies from o cc. per liter to 25 cc.
in the presence of green algas on sunny days. The bottoms of lakes
and ponds where much putrescible matter occurs are usually
without oxygen. The hypolimnion of lakes with a thermocline
is in part without oxygen in summer. Probably free oxygen is
usually necessary to most organisms except anaerobic bacteria.
Most animals that have been studied in behavior experiments
select water with some oxygen. While some species of fishes such
as suckers, small mouthed black bass, and some cyprinids appear
to be affected by a considerable decrease from saturation at
ordinary temperatures, this appears to be the exception rather
than the rule. Increase to 25 cc. per liter under experimental
conditions does not appear to have any marked effect upon fishes
so far as life and death are concerned. Allee working on isopods
found that an increase in oxygen increases size, vigor, and amount
of positive response to current as well as efficiency of response to
current. His results have been confirmed by several students
who have repeated the experiments using different forms.

Juday has shown that a long list of common protozoa, worms,

^8 FRESH-WATER BIOLOGY

insects, etc., can live for a long time without free oxygen, and in
fact occur in the putrescible organic muds of the bottoms of lakes
and ponds and the hypolimnion of thermocline lakes in summer.
They evidently obtain oxygen from some chemical compounds.
Carbohydrates are present in the sea in solution in minute
quantity and there is every reason to believe them present in fresh
water. Packard found that marine Fundulus embryos live in lack
of oxygen from 73 to 141 per cent longer in the presence of glucose,
maltose, levulose, and cane sugar, the amount of increase in resist-
ance differing with the different sugars. Lactose has no such effect,
probably because it cannot be absorbed or digested.

According to Mathews' depolarization theory oxygen is obtained
from the water in a manner analogous to the oxidation of alcohol
to acetic acid. In the presence of O2 the reaction is as follows:

C2H5OH + 02 = CH3COOH + H2O.

In the absence of oxygen and the presence of levulose
C2H5OH + H2O = CH3COOH + 2 H2
2 H2 + 2 C6H12O6 = 2 CeHuOe.

The levulose unites with the hydrogen and thus permits the
protoplasm to use the oxygen. The protoplasm is thus a strong
reducing agent.

High respiratory quotients of various animals are further evi-
dence of anaerobic respiration. The respiratory quotient is

Vol. CO2 given off _ j^ aerobic animals this value is less than i
Vol. O2 absorbed

because oxides other than CO2 are given off and CO2 does not rep-
resent all the oxygen used. Thus when the quotient is more than
I it indicates that oxygen is obtained from some source other than
free oxygen. The respiratory quotient of the medical leech is
usually near or a little more than i while that of a sea cucumber
{Cucumaria) and a sea sponge (Suberites) is over 2.5 (Putter). A
large number of aquatic animals are probably able to secure oxygen
from compounds containing it and they are therefore facultative
anaerobes to a considerable degree.

Distribution of organisms in water is not clearly correlated with
oxygen content. The minimum for most animals is comparatively

CONDITIONS OF EXISTENCE 39

low as, for example, in fishes insufficient oxygen acts on the respira-
tory center through the development of organic acid in the blood
due to incomplete oxidation, and causes the respiratory movements
to be increased. There is some evidence that respiratory activity is
increased through direct reflex action through the gills and opercles.
This increased respiratory activity supplies plenty of oxygen.

Ammonia occurs in minimal quantities in natural waters but
may be present in some quantity in sewage or gas works wastes.
Ammonia like the other gases (CO, SO2, and C2H4) introduced into
streams by gas works is not only extremely poisonous, but fishes
do not turn back from it when they encounter it and are often
overcome without giving the avoiding reactions which protect fishes
from excesses of other substances normal to fish environments.

Methane is a saturated hydrocarbon and has minor effects upon
organisms though it may be present in the hypolimnion of lakes in
considerable quantity. Traces of carbon monoxide occur also.

Hydrogen sulphide is usually present in very small quantities in
the bottoms of lakes and sewage contaminated streams. It is
very abundant in salt lakes and arms of the sea. It results from
putrefactions and from the reduction of sulphates through the
action of the bacteria which prey upon organic sulphur (Lederer).
Though very poisonous it is not ordinarily present in sufficient
quantity, to injure fishes (Shelf ord and Powers) though its absorp-
tion of oxygen ^ reduces the amount of this gas very materially.

Carbon dioxide is the most important gas in fresh water. In
small quantities it is essential rather than detrimental to aquatic

^ Samples of water without oxygen must be handled with utmost caution as an ap-
preciable amount of oxygen will be absorbed through the surface exposed by the nar-
row neck of a 250 cc. bottle in a few seconds. Biologists are very likely to attempt
great accuracy in putting up solutions and to exercise insufficient care in taking and ti-
trating samples. For ordinary work, in making up solutions it is sufficient to weigh to
one decimal place; chemicals must be carefully selected; especially, KI. The normal
solutions used will not be correct if made by an unskilled person; a correcting factor
must be used which may as well be 0.876 as 0.989. Skill in titrating and standardiz-
ing with solutions made by a chemist should be acquired. For methods see Birge and
Juday, and Sutton. Routine sanitary analyses include several items of unknown or
doubtful value to Hving organisms and do not include some of the most important
determinations such as acidity, alkalinity, hydrogen sulphide, and carbonaceous
materials that might be absorbed as food. Determinations are often not made at
once, and samples are commonly not collected from important animal habitats within
the body of water.

40 FRESH-WATER BIOLOGY

animals. In large quantities it is rapidly fatal acting as a narcotic.
It is particularly injurious in the absence of oxygen which absence
is usually associated with it. Abundant oxygen decreases its
toxicity because blood has greater affinity for oxygen than for
carbon dioxide and the latter is crowded out of combination. On
account of the fact that it is usually accompanied by lack of
oxygen, putrescible muck bottom, etc., its presence in quantities
greater than 6 to 7 cc. per liter if accompanied by a bottom en-
tirely of such muck would indicate that the water was unsuitable
for trout, basses, sunlishes, and crappies.

One of the most important characteristics of a water is its
acidity or alkalinity. Protoplasm must maintain essential neu-
trahty or it will die. It possesses a very effective physico-chemical
mechanism based upon the presence in excess of very weak acids
(carbonic and phosphoric) and alkalies in the form of carbonates
and phosphates. Since protoplasm must remain nearly neutral
the acidity or alkalinity of the surrounding medium cannot be
great. Thus Wells found that fishes do not live well in alkaUne
water but become sluggish and inactive. Neutrality is likewise
toxic to some fresh-water fishes. They require a certain amount of
acid. The optimum acidity for the difi'erent species dift'ers. The
optimum for the bluegill {Lepomis pallidus Mit.) is i to 3 cc. of
carbon dioxide per liter and for crappies {Pomoxis annularis Raf.)
4 to 6 cc. per liter. Wells showed by using various other acids
that the hydrogen ions are the important factor. In other words
fishes require a certain concentration of hydrogen ion. Neutrality
is avoided by fishes. In the absence of acidity they select alka-
line in preference to neutral water. Fishes and various crusta-
ceans will live in distilled water if it is slightly acid, while it is
rapidly fatal if neutral and more rapidly fatal if alkaline. The
toxicity of much ordinary distilled water is due to colloidal copper
or other metal from coolers, in suspension in it.

Wells made a rearrangement of some of the data of Birge and
Juday which showed that various plankton organisms are distrib-
uted with reference to alkalinity, neutrality, and acidity,^ a few

1 In the determination of alkalinity and acidity great care should be exercised in
the making of collections so as to prevent the escape of CO2. The choice of indi-

CONDITIONS OF EXISTENCE

41

species showing a distinct avoidance of neutrality. In a number
of species the number of individuals on either side of neutrality
was greater than at the neutral region (Table VII).

TABLE VII

Showing Correlation between Distribution and Alkalinity and Acidity

TO Phenolphthalein (after Wells)

(Figures show numbers of individuals in a cubic meter of water)

Name of animal

Alkalinity in cc. per liter
of CO2 to make neutral

Pleosoma R

Asplanchna R.

Diaphanosoma C.

Diaptomus Co

Anuraea P.

Cyclops Co.

Notholca R.

Daphnia C.

Ceratium P.

Polyarthra R.

Triarthra R.

3.925
11,320

2,885
7,850
4,000

13,775

625

1,260

52,330

12,350

o

o

400

2,750

6,660

1,250

7,620

685

650

104,500

1,620

n. c.

o

o

n. c.

17,350

200

7,620

65

400

85,160

2,350

o

Neu-
trality

O

O

260

2,220

30

25

o

130
2,025

160
n. c.

Acidity in cc. of CO2
per liter

0.25-0.5 0.75-1

o
o
o

1,440
20

30

65

1,145

11,760

1,190

1,050

o
o
o

390

20
o
o

25
750

,240
,110

o

o

o

100

20

5
o
o

1,670
40

2,425

R = Rotifer, C = Cladoceran, P = Protozoan, Co = Copepod, n. c. = no collection.

The amount of salt in parts per million which ranges from 50-
500 in water occupied by numerous fresh-water species is of com-
paratively little significance to animals but of much importance to
plants. The effect of most salts upon organisms is due to the
character of the ions, valence, electrical charges, etc. The effect
of any combination of salts is due to their combined action. For
example, marine animals will not live in NaCl alone even when
the osmotic pressure is the same as in sea water; it is very toxic.
They will not live in NaCl and KCl or NaCl and CaCl2; all three

cators is also very important. Methyl orange is unafifected by CO2 and other organic

acids because of their small ionization. Thus Marsh's conclusion, based upon methyl

orange, that if water becomes acid it kills fishes is incorrect for this reason and because

H+ 10^ N H+ 10-* N

it turns red at ,=r^ -—-^ and remains yellow at prz^ r-rr . Phenolphthalein is color-

OH-io-i^N -^ OH-io-»N

less at ^^z^ ^:^^^ and turns red at pr^- — — - . Rosalie acid is rose at ^r^j —i-^r

OH- 10-6 N OH- 10-6 N OH- 10^ N

which is true neutrality. In the table above true neutrality probably falls in the first

column to the right of the center. CO2 production may be sufl'icient to neutralize

this slight alkalinity in the layer of water next to the animal. The terms alkalinity

and acidity are used in this chapter in the sense of concentration of H+ and OH" ions.

42 FRESH-WATER BIOLOGY

are necessary. This is believed to be due to the neutralization of
the toxicity of the NaCl by the other salts; this is known as antag-
onism. The effects are due to the cations, one anion being suffi-
cient though some are more favorable than others.

Salts present in excess, or without the proper antagonistic salts
or ions, and salts not commonly present in quantity in fresh water
are toxic to fresh-water animals. The toxicity varies for different
salts and according to the concentration of hydrogen or hydroxyl
ions which accompany it. Ammonia salts are poisonous to fishes
if present in company with carbonates. Carbonates are not essen-
tial to the hfe of fishes as sulphates may be substituted entirely,
at least for short periods. Carbonates alone are fatal to fishes
because of their alkalinity. In the presence of CO2, however,
carbonates are converted into bicarbonates which are normally
present in all natural fish waters. Bicarbonates accompanied by
a small excess of CO2 are not harmful. Of the salts of potassium,
the sulphate is most poisonous ; sodium salts are less injurious than
those of potassium. The presence of an excess of calcium causes
the tail fins of the rock bass to degenerate and this fact was prob-
ably responsible for the tailless trout found in certain waters of
the British Isles where the water was contaminated with waste
from paper mills. There is much evidence that calcium tends
to lower the metabolic activity of organisms.

As shown by Wells fishes react to salts in solution. They are
usually negative to nitrates, more or less positive to chlorides
(markedly so to NaCl) but are decidedly negative to CaCL and
MgCl2. They are positive to ammonium chloride and are usually
very negative to sulphates. The reaction of the fishes to the salts
was shown to have a distinct relation to the acidity of the water, as
fishes that were decidedly negative to Na2S04 for instance in slightly
acid water were made positive to this salt by running the experiment
in strongly acid water {i.e., 20 cc. COo per liter). A part of the
effect of ions lies in their effect on permeability. Alkalies increase
permeability of protoplasm. Acids first decrease and later increase it.

In animals and plants there are various rhythms of activity con-
stituting parts of their physiological life histories or recurring
functions lying within them. These often coincide with rhythms

CONDITIONS OF EXISTENCE 43

of conditions. The principal environmental rhythms are daily,
seasonal, weather, and lunar, and, in the sea, tidal.

Rhythms of fresh-water organisms have been but little studied.
From the seasonal standpoint it has been observed that some organ-
isms tend to do certain things even though the external conditions
which usually accompany them are delayed, thus showing that the
environmental rhythms have been impressed upon the organism.
The best examples of this have to do with the tide and thus do not
belong to fresh water. Bohn found that there are rhythms of
activity related to tide. The green fiatworm (Convoluta roscojfensis)
comes to the surface of the sand at low tide and descends as the
tide comes in. The worm continues to ascend and descend at
tide time for several days after having been removed from the sea
and kept in an aquarium.

One of the best known rhythmic movements in fresh water is
the daily depth migration of Crustacea. Whether they show any
tendency to make such movements when placed under uniform
conditions is not known. Lunar rhythms likewise appear to have
been Httle investigated among fresh-water organisms though Kofoid
noted rhythmic monthly increases of Illinois River plankton. The
best examples of these are found among the marine worms. The
Atlantic palolo swarms within three days of the last day of the last
quarter of the June 29 to July 28 moon (Mayer), the swarming
taking place under the influence of the light of the moon.

Various single factors have been regarded as of prime importance
in the control of organisms. Thus many writers emphasize food,
others temperature, etc. Merriam has maintained for years that
the total of temperature above an arbitrary minimum during the
growing season controls the distribution of life in North America.
Sanderson has shown that for some insects and some horticultural
plants winter temperatures are more important, just as may be
the case with organisms like fresh-water sponges and bryozoans
having winter bodies, and aquatic plants with seeds and spores.
Marine workers emphasize salinity and density. Birge and Juday
emphasize oxygen. All these ideas have important bearings on
questions of aquatic biology but no one of them is adequate.

Dormancy sometimes makes otherwise insignificant conditions

44 FRESH-WATER BIOLOGY

important. It is a common characteristic of the eggs of rotiiiers,
of Crustacea, insects, and other arthropods, and also of the spores
and seeds of plants. Many crustaceans deposit eggs in the autumn
which require freezing before they will hatch. Some, as for exam-
ple those of the fairy shrimp (Eubranchipus) , require both summer
drying and winter freezing. The statoblasts of the fresh-water
Bryozoa germinate better after freezing or drying. Thus some
simple condition such as the rupture of the egg shell or covering
may be a requirement for growth as it is in some seeds.

Any scheme that fails to consider the complete physiological
hfe history in relation to complete annual cycles is inadequate.
Still, because of the complexity of the problems involved simple
indices must be sought which will indicate the condition of waters
with reference to as many important factors as possible. These
indices must be selected with two facts in mind: First, that there
is in each annual cycle of the life of an individual or a species a
period of maximum sensitiveness; this falls at or near the breeding
period or at the time of appearance of young. Second, adequate
measure of hydrographic conditions are to be found in the peculiar
character of the annual rhythm rather than in the totals of this
or that factor for the year or a particular period.

Many organisms, especially food fishes, deposit their eggs on the
bottom. It is to the bottom that the dead bodies of organisms
sink and at the bottom that they decompose and produce poi-
sonous substances in greatest quantity. Decomposition of the
bodies of plants and animals results finally in gases such as
ammonia, carbon dioxide, hydrogen sulphide, methane, etc.
The presence or absence of fishes and their animal food is con-
trolled by (a) their ability to recognize the presence of strange
or detrimental substances and to turn back when such are en-
countered, and (b) by their survival or death in situations where
they cannot escape the deleterious conditions. Their ability to
recognize common injurious substances has been shown to be
very marked and precise. The difference between different
species is one of degree and special habits. The effects of the
various decomposition products are the same in a wide range of
species with only slight differences in degree. The less sensitive

CONDITIONS OF EXISTENCE 45

fishes are usually of less food value. Food fishes usually live asso-
ciated with organisms which, like themselves, are very sensitive
to decomposition products, and usually disappear with the
fishes.

Indices are of three types, (i) results of the inspection of the
bottom, (2) results of chemical tests of the water for decomposi-
tion products, and (3) for fishes the presence or absence of index
organisms of a semi-stationary character, such as snails, etc.,
see p. 52. Here the first two types only will be considered.

If a body of water is to support desirable game fishes it should
have an area of terrigenous bottom covered with from 6 inches to
2 feet of water for breeding grounds and an area of submerged
(Chara, etc.) and of emerging vegetation to supply food. It is
probable that for the best results these three should be about
equal. The terrigenous bottom should be comparatively free from
putrescible material. Humus which does not contain putrescible
material or even the roots of plants may be used by a few game
fishes for breeding. The amount of terrigenous (non-putrescible)
bottom up to one third that occupied by vegetation and muck is a
rough index of the suitabifity of an ordinary pond or lake (see
Fig. 7, p. 58) for game fishes and associated organisms. In river
bottom lakes and bayous floods may remove putrescible material
and leave bottoms composed chiefly of silt upon which luxuriant
vegetation springs up. Forbes has shown that productivity of
carp, and fishes generally, bears some direct relation to the area
fairly wefl supplied with submerged vegetation. The second index
must be appHed to such waters.

The second index is essential but must accord with the first.
The chemical character of the water must be such that the fishes
will not suffer from it or leave on account of it. Carbon dioxide
results from the decomposition of organic matter. In the process
oxygen is consumed so that the presence of any large quantity of
carbon dioxide nearly always indicates lack of oxygen. While
exact figures cannot be given it is probable that the carbon dioxide
content of water over breeding grounds (terrigenous bottom) should
not average more than three cubic centimeters per liter, nor ex-
ceed six cubic centimeters during the summer months. Such

46 FRESH-WATER BIOLOGY

amounts are not usually accompanied by lack of oxygen. Thus
the amount of carbon dioxide may be taken as an index oj the
suitability of the water. Excessive acidity due to carbon dioxide
probably favors the germination of the Saprolegnias fungi which
are very destructive of fish eggs and fishes.

Food and Biological Conditions

Nitrates are necessary for the growth of aquatic plants and an
insuflicient quantity is secured from mineral soil. Nitrogen can
be fixed only by nitrogen fixing bacteria, such as Clostridium, an
anaerobe, and Azotobacter, an aerobe. These bacteria occur on
plants and animals in the mud of the bottom of bodies of water.
Plants and animals provide carbon compounds for the bacteria;
bacteria provide nitrates or nitrites.

Ammonia results from the decomposition of the dead bodies of
plants and animals. The bacteria {Nitrosomonas, Nitrobacter, Ni-
trococcus) oxidize it to nitrous acid; nitrous acid, to nitric acid.
These acids unite with bases to form nitrates and nitrites. Work-
ing against these two sources of nitrate and nitrite are various
denitrifying bacteria {e.g., Bacterium actinopelte), which reduce
nitrogen compounds to free nitrogen. Their work is greatly influ-
enced by temperature. Baur placed nitrate inoculated with Bacte-
rium actinopelte at several temperatures with results as follows:

a. Temperature, 25° C: Denitrification initiated 24 hours after
inoculation; in 7 to 11 days later without nitrate.

b. Temperature, 15° C: Denitrification initiated 4 days after
inoculation; in 27 days the solution was without nitrate.

c. Temperature, 4 to 5° C: Denitrification began 20 days after
inoculation; denitrification incomplete 112 days after.

d. Temperature, 0° C: Denitrification not initiated.

The quantity of life in water is believed to be in proportion to
the available nitrogen compounds. The greatest quantity of plank-
ton in the sea is in the polar regions in the summer. It has been
suggested that the greater retarding effect of low temperature on
the denitrifying organisms as compared with the nitrate producers
is a cause of the greater quantity of life in the colder waters. Loeb
holds the theory that the greater quantity is due to the longer fife

CONDITIONS OF EXISTENCE 47

of the organism in cold water. Dissolved nitrogen is important
for the work of nitrogen fixing bacteria. Oxygen is necessary for
the production of CO2. Carbon dioxide is necessary for the starch
building of chlorophyll-containing plants and animals. These green
organisms form the chief food basis of all other organisms. Pro-
teids or other complex foodstuffs are necessary for all animals. It is
only animals which contain chlorophyll in the form of algae Uving
symbiotically in their bodies, that can survive without taking in
complex foodstuffs. Proteids are made only when starch, nitrates,
and several other inorganic foods are present. Because of their
proteid and starch demands light is indirectly necessary to animals
which can live in darkness.

According to Putter and Raben, who confirmed his determina-
tions using better methods, sea water, and probably fresh water as
well, contains amino-acids, oils, and carbohydrates. Putter has
shown that many aquatic animals absorb nutrition from solution
which renders them only in part dependent upon plankton.

Plants are commonly covered with a coating of small organisms,
so that animals such as snails may rasp the surface and secure food
without eating the plant tissues themselves. One could probably
remove all the larger plants and substitute glass structures of the
same form and surface texture without greatly affecting the immedi-
ate food relations. Aquatic plants are of particular use to animals
as cHnging, hiding, and nesting-places.

The quantity of plankton has been much studied. Quantity
is usually expressed as number of organisms per Hter or cubic
meter of water, determined by counting a part of a collection; or
in cubic centimeters per cubic meter of water. Ward found an
average of 11.5 cc. per cubic meter in water from the surface 2 m.;
from 2 to 25 m., 3.9 cc; 25 m. to bottom, 0.4 to 1.5 cc, in Lake
Michigan (August). Pine Lake, a small lake adjoining, contained
relatively less plankton than Lake Michigan, the surface stratum
containing more and the deeper strata much less. Lake Michigan
contains twice as much plankton as Lake St. Clair. A small
European lake (Dobersdorfer See) contains about ten times as
much plankton as Lake Michigan. Kofoid found the average for
the year to be 2.71 cc. per cubic meter for the Illinois River and

48 FRESH-WATER BIOLOGY

71.36 cc. per cubic meter the maximum; 684 cc. per cubic meter
(Turkey Lake, Ind.) is the largest amount recorded by Juday.

Small streams and lakes with large inllow and outflow have little
plankton. Large amount of plankton is usually associated with
much CO2, little oxygen, and a large amount of dissolved carbonate.

The amount of plankton fluctuates from season to season. The
maximum for the Illinois River is from April to June. It gradually
decreases until December and January, when the minimum is
reached. The light of the moon may increase photosynthesis and
thus the amount of phyto-plankton (Kofoid). The maximum of
Entomostraca was found by Marsh to fall in July, August, and
September, difi'ering in different years. In smaU bodies of water an
abundance of plankton is usually, though not invariably, associated
with a large quantity of larger animals and rooted plants. Large
lakes like the Great Lakes are exceptions to this because of the
absence of shallow water vegetation.

Liebig's Law of Minimum has been appHed to plankton by
Johnstone who states it as follows: ''A plant requires a certain
number of foodstuffs if it is to continue and grow, and each of
these food substances must be present in a certain proportion.
If one of them is absent the plant will die; if one is present in a
minimal proportion, the growth will also be minimal. This will be
the case no matter how abundant the other foodstuft's may be.
Thus the growth of a plant is dependent upon the amount of that
foodstuff which is presented to it in minimal quantity." The
amount of plankton probably follows the same law. All food
substances must be present in correct proportions. The amount
of plankton may be determined by a deficiency in the amount of
one substance.

The quantity of plant and animal life probably increases with
the age of bodies of water with small outlet (see Fig. 7, p. 58).
This is because foodstuffs are washed in with inflowing water, and
because rooted plants absorb food from soil in which they grow, and
when they die and decay these foodstuffs are added to the water
and made available to plankton and to animals in general. Accord-
ingly, the older the pond and the longer rooted vegetation has
grown, the greater the quantity of Hfe up to the time the pond

CONDITIONS OF EXISTENCE

49

becomes intermittent. This principle is illustrated by an age
series of ponds at the south end of Lake Michigan. These are
similar in size and age increases in order back from the lake.

TABLE VIII

Showing the Number of Entomostraca in Approximately go Liters of

Water (After Shelford)

Body of water

September 3.4.
1909

April 30, 1910

Average number
of collections
in parentheses

Relative
age of
ponds

Wolf Lake

213

232

4,115

556

539

2,773

1.039

351

2,870

2, goo

9,333
19,866
Aug. 28, 1912
104

1,556 (3)

4,781 (3)

11,991 (3)

874 (6)

927 (6)

2,680 (6)

Prairie Pond I

6

Prairie Pond II

28

Pond I

Pond VII... .

14

28

Pond XIV.. .

133

Pond XXIX ....

60*

PondLII

2,600

1 1 ,400

2,480

104*
178*
I go*

PondLXXXIX

Pond CXV

Here the number of Entomostraca is greater in the older ponds though some irregularities occur,
related to the amount of rainfall. In rainy seasons the increase with age appears almost throughout
the series.

* Intermittent ponds which show irregularities.

TABLE IX

Showing Ratio of Number or Quantity of Different Organisms when

the Maximum is 100 (After Shelford)

Rooted vegetation
Entomostraca ....

Midge larvae

vSphaeridae

Gilled snails

Lunged snails

Amphipoda

Crayfishes

Insects

Fish

Relative age of ponds

20
32
80
o
20
10

50

10

40

100

60

35
80

50
50
50
go
50
go
87

100

100
100
100
100
100
100
100
100
87

The Entomostraca are rated on the basis of actual count of six collections. The other figures are

estimates.

In passing from younger to older ponds an increase is noted in
the number of animals, excepting fish. These appear to decrease,
probably because of the increasing unsuitability of the ponds as fish

50

FRESH-WATER BIOLOGY

breeding places. The oxygen content decreases, particularly on
the bottom. The distribution of the hsh present in these ponds,
in so far as breeding habits were known, was found to be corre-
lated with the distribution of the bottom upon which they breed.
This becomes less and less in amount as the ponds grow older.

TABLE X

Showing Quantit.\tive Results of Examination of Factors Related to

Quantity of Plankton (Original)

No. of
collections

Total carbonates in parts per million

CO2, cc. per liter at bottom

Oxygen, cc. per liter at bottom

Bacteria per cc

Pond numbers — age-series

2

14

28

138.800
0.0
6.28

779

160. 200
3-4
3-47
2450

160.300
2.7
2.78
3550

On the whole the carbonates, CO2, and bacteria are greater in
quantity according to age. Oxygen on the whole is less.

The increase in quantity of animals with increase of soil fer-
tility supports Knauthe's contention that with fishes productivity
of water is directly correlated with the richness of the soil. The
weak place in Knauthe's ideas Hes in the fact that as quantity in-
creases quahty decreases. The game basses and sunfishes give way
to the more inferior types and these are gradually succeeded by
bullheads, mud-minnows and dogfish. This is due to the destruc-
tion of breeding bottom for the desirable fishes by putrescible
organic matter which results in much carbon dioxide, hydrogen
sulphide, ammonia, and lack of oxygen. The German carp comes
into such a series rather late and thus productivity in carp is no
doubt correlated with a fertile substratum.

The amount and kind of rooted vegetation are very important to
animals. Of all the aquatic situations which present themselves
the largest lakes have fewest attached plants, and these are all
algae. Cladophora, Chara and filamentous algae are the most com-
mon. These do not appear to have been recorded below about
25 meters; some of them require solid bodies for attachment and
are probably most abundant on the rock outcrops of shallow water.

The vegetation of young streams consists largely of holdfast

CONDITIONS OF EXISTENCE

51

algae similar to those among the rocky shores of a lake. These are
of importance to animals. Sluggish streams have rooted aquatic
vegetation.

The vegetation is used as breeding places. Eggs are stuck into
plant tissues by the predaceous diving beetles (Dytiscidae) and by
the water scorpions (Ranatra). Eggs are attached to plants by
the electric light bug (Belostomidae), back swimmers, may-flies,
caddis-flies, water scavengers (Hydrophihdae) , long horned leaf
beetles {Donacia), snails, and many fishes (Umbra, and probably
Abramis). Young animals are often dependent upon plants for
shelter, to escape from enemies, etc. Many insects must come
to the surface for oxygen. The most important of these are the
Dytiscidae (adults and larvae), the Hydrophihdae (adults and larvae),
the back swimmers, Zaitha, Belostoma, Donacia, snails, Ranatra,
and Haliplidae. Some, for example Zaitha and dragon-fly nymphs,
lie in the vegetation and wait for their prey.

Different kinds of vegetation have different values for animals.
The bulrush is barren for the following reasons: (i) hardness
makes it a bad place for eggs; (2) there are no cHnging places;
(3) there is little shade; (4) it gives a high temperature in summer;
(5) there is no great addition of oxygen by vegetation; (6) it
does not afford a suitable place for securing food. Equisetum is
unfavorable for similar reasons. Elodea is excellent; Myriophyl-
lum, good; water-Hlies and Chara, only fair.

Animal Communities

Plants and animals select their habitats through physiological
characters. Sessile plants and animals have disseminules which
usually come to rest in a great variety of conditions and grow to
maturity only in those conditions that are suitable to stimulate
development. The physiological character of the reproductive
bodies and external conditions are responsible for the distribution.

Animals select their environments by one of three methods:
(i) by wide dissemination of reproductive bodies and selective
survival, (2) by turning back when the environment in which they
move about is found to change, and (3) by selection after trial in
connection with migration.

52

FRESH-WATER BIOLOGY

Numbers of animals select the same environment because of
physiological similarity. All the animals occupying a relatively
uniform habitat constitute an animal community. A physiological
agreement exists among the animals of a community. The rapids
community of a large creek is in a general agreement in reactions
to certain factors, and disagreement in respect to factors differ-
ing in intensity vertically. In Fig. 5 is shown a noteworthy agree-
ment in reaction to bottom and current under experimental condi-

^oSTRATA

OPEJy WATER
AMONG
STONES

Son stones

V UNDER
^STONES

SPECIES

ETHEOSTOMA

POSITIVE REACTIONS HYDROPSYCHE OR RAPIDS COMMUNITY

2

iJi

0 6

=

^

m

L-U

■

1-^

—

--.

4(i0

CAMBARUS

z

■ 1 1 -j^

=

=

3p

t

Ki

:::

--4

—

-

"^^^^^^

:!7=

=^

=

^

...

—

..J

60NI0BASIS

'I;;

\{'\\

'^p

=^

--=

£r:-T-

Mz:

^

\

1 1 1 '1

HYDROPSYCHE

1

i

<!

.---'

1 1 L'-'

—

—

ARGIA

-V

'r~.

=----

-:|^^^^H^H

-=^^--

-^

- -^

-j

~~i

--,.

PERLA

'rll

Jz?--

-i-yz

IrZZ

-^-rflHH^HI^^^H

i

i

^

,--

•'

HEPT/IGENINA

zzTi

:-:-}

V:-~:

,=^7

— -

1

1

--

—

""}

PSEPHENUS

-Jf?

■:-!-:

33:

-34lHHlllill -

^^

by

1

{

^

{STRONG current!
HARD BOTTOM |
MEDIUM LIGHT

UNDER STONES R^
ON STONES ESISI
STRONG LIGHT ^^

AMONG STONESf?^
WEAK LIGHT ^^
KINAESTHESIA tHJ

Fig. 5-
To show the agreement and disagreement of the reactions of the animals of the rapids community.
Note agreement of reaction to bottom and current and disagreement in two other reactions related to the
level at which the animals live. These results were obtained by placing the animals under experimental
conditions in which they had a choice between different kinds of bottom, different strengths of light, and
in which their behavior in a water current was noted. In the case of water current the percentage of ani-
mals headed upstream is given. When headed upstream animals are said to be positive to current. In
the case of the other stimuli the percentage of animals in the kind of conditions available was noted and the
animals are said to be ixjsitive to the conditions in which tlie greatest number are found. Thus note
that the darter (ElheoUoma) was 80 per cent among the stones and is said to be positive to this kind of
situation. It will be noted that if the animals had been 100 per cent positive to the various stimuli the
entire 400 units would be occupied in the diagram. This could be true only if there were no other factors
entering into the reactions ol the animals. The common names of the animals are as follows: Etheo-
iiotna, darter, Cambarus, crayfish; Goniobasis, snail; Ilydropsyche, caddice worm; Argia, damsel tly;
Perla, stone lly; neptagemna, may-lly sub-family; Pscphenus, water penny.

tions. The preference for hard bottom in these experiments means
the avoidance of sand as only sand and hard bottom were present
in the experiments. Animals living under stones were under stones
m darkness in the experiments. The snail (Goniobasis) which lives
on stones was found on stones in the experiments. The darter
(Etheostoma) and the crayfish (Cambarus) which live among stones
were found among stones in the experiments. Thus the different

CONDITIONS OF EXISTENCE

53

animals differ in their relations to bottom and are in disagreement
with reference to their vertical distribution in nature. Turning
to reactions to hght one finds a comparable difference. Animals
living beneath stones show a preference for weak light; those living
on stones, medium Hght; those among stones, strong Hght. If one
were to study the community in full one would find that reactions
to many other factors are of importance. Associative memory no
doubt plays a role. Thus there is agreement in reaction to factors
of prime importance in the community habitat as a whole and
disagreement in respect to factors differing strikingly in the levels
in which the animals live within the community habitat. These

Black bass adults
Black bass young

Fig. 6.
Food relations of aquatic animals. Arrows point to animal doing the eating. For explanation see text.
(Original.)

levels are called strata. The pool community shows a striking
difference from the rapids community in the presence of a strong
preference for sand bottom and in the presence of the burrowing
habit, both of which are wanting among the animals of the rapids
community. The non-burrowing pool species are positive to cur-
rent but the burrowing species do not respond within ordinary
lengths of time.

Forbes has devised a method by which the frequency ot associa-
tion may be determined for any two or more species. Data re-
garding such frequency may be obtained from collections made so

54

FRESH-WATER BIOLOGY

as to cover several animal communities. The association which
would result from an indiscriminate distribution is first eliminated.
Then from the total number of collections, the number of collec-
tions containing each species, and the number of collections con-
taining both species, he derives a coefficient of association by very
simple calculations.

Each animal prefers certain food. The food relations of pond
animals are shown in Fig. 6. For purposes of illustration one may
suppose the existence of a community composed of the species
named only.

Any marked change of conditions will disturb the balance in an
animal community. Assuming that because of some unfavorable
conditions in a pond during their breeding period the black bass
decrease markedly, the pickerel, which devours young bass, must
feed more exclusively on insects. The decreased number of black
bass would reheve the drain upon the crayfishes, which are eaten
by the bass; crayfishes would accordingly increase and prey more
heavily upon the aquatic insects. This combined attack of pick-
erel and cra>'fishes would cause insects to decrease and the number
of pickerel would fall away on account of the decreased food supply.
Meanwhile the bullheads, which are general feeders and which eat
aquatic insects, might feed more extensively upon mollusks because
of the decrease of the former, but would probably decrease also
because of the falling off of their main article of diet. It may
reasonably be assumed that the black bass would recover its num-
bers because of the decrease of pickerel and bullheads, the enemies
of its young. A further study of the diagram shows that a balance
between the numbers of the various groups of the community
might soon result. Under certain circumstances, such as the ex-
tinction of the black bass, the resulting condition would be entirely
different from the original one, but a balance between supply and
demand would nevertheless finally be established. The commu-
nity is said to have equilibrated when such a condition is reached;
that is, a new equilibrium is established, which fnay or may not be
like the old.

The causes of fluctuations of numbers of organisms are numer-
ous. Cold winters often destroy aquatic vertebrates. Large rain-

CONDITIONS OF EXISTENCE 55

fall dilutes the plankton and in streams carries it away. Too
little sunshine causes a poor production of the chlorophyll bearing
organisms which are a food basis of others. Open winters favor
denitrihcation and may be unfavorable to certain lower invertebrates.

Animals fed upon certain kinds of food supply enzymes digest-
ing that kind of food in the proper quantity. The proportion of
the different kinds of enzymes changes with changes in diet. Under
proper experimental conditions anti-pepsin, anti-trypsin, etc., are
developed by organisms. Organisms may develop immunity to
toxins introduced into the alimentary canal with food, but the
process is a slow one. The introduction of toxins, or bacteria re-
producing them, directly into the blood is doubtless a common
thing among aquatic animals which are probably as subject to
injury and disease as are land animals (see Hill or Rosenau).
Various aquatic organisms must possess natural immunity for the
various decomposition products of fresh water (see under bacteria,
p. 94). Acclimatization must often involve the development of
immunity. As knowledge along these lines is increased the con-
viction that enzymes, toxins, immunity and related phenomena
play a very important role in the life of fresh-water animals grows
proportionately. Lillie has recently found that comparable phe-
nomena are of great significance in connection with the fertiliza-
tion of the eggs of marine animals and future investigation along
these lines will doubtless be of much importance.

Ecological classification must be based upon community or phy-
siological make up, behavior, and mode of life and similarity of
habitat. Those natural groups of animals which possess likenesses
are the communities which must be recognized. One community
ends and another begins where a general more or less striking
difference in the larger physiological characters of the organisms
concerned occurs. These communities generally occupy relatively
uniform environments. For any given organisms the other organ-
isms of the community are a part of the conditions of existence.
There is general agreement in the recognition of strata, of associa-
tions as communities based upon minor differences in habitats,
and formations based upon larger major differences in habitats
and considerable agreement in the use of consocies and mores.

56 FRESH-WATER BIOLOGY

Communities of different orders are given below with taxonomic
divisions of corresponding magnitude opposite for comparison.
With the exception of the tirst, these taxonomic groupings do not
bear the slightest relation to the ecological groupings, but are added
to indicate magnitude.

Ecological Groups Taxonomic Groups

(Mos) Mores Form (forms) (species)

Consocies Genus

Stratum or story Family

Association or society Orde;

Formation Class

Extensive formation Phylum

(Aquatic and terrestrial) (Vertebrates and invertebrates)

Mores ^ are groups of organisms in full agreement as to physio-
logical life histories as shown by the details of habitat preference,
time of reproduction, reaction to physical factors of the environ-
ment, etc. The organisms constituting a mores usually belong to
a single species but may include more than one species or one
species may occupy two or more habitats and be made of several
mores (Shelford; AUee).

Consocies are groups of mores usually dominated by one or two
of the mores concerned and in agreement as to the main features
of habitat preference, reaction to physical factors, time of repro-
duction, etc.

Strata are groups of consocies and organisms not so grouped,
occupying the recognizable vertical divisions of a uniform area.
Strata are in agreement as to material for abode and general physi-
cal conditions but in less detail than the consocies which constitute
them; for example, the understone stratum of a rapid brook (see
Fig. 5, p. 52).

1 Mores (latin singular mos), "behavnor," "habits," "customs"; admissible
here because behavior is a good index of physiological conditions and constitutes the
dominant phenomenon of a physiological life history and of community relations.
This term is used just as form and forms are used in biology, in one sense to apply
to the general ecological attributes of motile organisms, in another sense to animals
or groups of animals possessing peculiar attributes. When applied in this latter
sense to single animals or a single group of animals the plural is used in a singular con-
struction. This seems preferable to using the singular form mos which has a different
meaning and introduces a second word. The organism is viewed as a complex of
activities and processes and mores is therefore a plural conception.

CONDITIONS OF EXISTENCE 57

A given animal is classified primarily with the stratum in which
it breeds, as being most important to it, and secondarily with the
stratum in which it feeds and lives, as in many cases most im-
portant to other animals. The migration of animals from one
stratum to another makes the division Une difficult to draw in
some cases. Still, the recognition of strata is essential even though
a rigid classification is undesirable.

Associations are groups of strata uniform over a considerable
area. The majority of 7nores, consocies, and strata are different in
different associations. A minority of strata may be similar. The
term is applied in particular to stages of formation development
of this ranking. The unity of association is dependent upon the
migration of the same individual and the same mores from one
stratum to another at different times of day or at different periods
of their life histories. Such migration is far more frequent than
from one association to another.

Formations are groups of associations. Formations differ from
one another in all strata, no two being closely similar. The num-
ber of species common to two formations is usually small (e.g.,
5 per cent). Migrations of individuals from one formation to
another are relatively rare.

The following is a list of the commoner fresh-water commu-
nities:

I. Communities of ice, snow, and glacier pools (Moore).

They live at 0° C. or below throughout the year (worms, insects, and
crustaceans) .

II. Stream Communities (Shelf ord).

1. Communities of snow and ice fed streams. They live at a little above
the freezing point most of the year. Insects are the chief inhabitants.

2. Intermittent Stream Communities

a. Intermittent rapids — variable conditions and fauna

b. Intermittent pool — variable conditions and fauna

c. Permanent pool — variable aquatic conditions and hardy animals

3. Permanent Stream Communities

a. Spring dominated stages

(i) Spring consocies — often few or no animals on account of

water conditions
(2) Spring brook associations

58

FRESH-WATER BIOLOGY

Creek and River Communities

a. Pelagic sub-formations, independent of bottom and shores

b. Riffle formation (turbulent water formation)

c. Sand or gravel bottom formations

d. Sandy bottomed stream sub-formation, shifting bottom sub-

formation, aquatic desert

e. Silt or sluggish stream communities

(i) Sluggish-stream sub-formations

(2) Pelagic formations

(3) Bare bottom formations

(4) Vegetation formations

■' QlftciALTUl

Fig. 7-
Three stages in the history of a glacial lake. A, An early stage showing bare bottom, and submerged
and emerging vegetation; B and C, successive stages in the deposition of i>eat and marl and the migration
of the submerged vegetation toward the center; Erosion and bare bottom are indicated near the shore at
the right in A and B but are absent in C. The area inside the emerging vegetation is the plankton
region, (.^fter Trauseau.)

III. Large Lake Communities (Shelf ord; Whipple).
Pelagic formations

Eroding rocky shore sub-formations (turbulent water formations)
Depositing, shifting-bottom sub-formations
Lower shore formations
Deep water formations

CONDITIONS OF EXISTENCE

59

IV. Lake-Pond Communities (see Figs. 7 and 8) (Shelf ord).

1. Pelagic sub-formations

2. Terrigenous bottom formations

3. Vegetation formations

a. Submerged vegetation associations

b. Emerging vegetation associations

4. Temporary pond formations (Shelford)

Conditions of existence in fresh water at any given point are
changing in a definite direction. This change involves every item
of the environment which has been enu-
merated on the preceding pages. Streams
wear down their beds, wear their valleys
wider, reduce the speed of their current,
grind their coarse bottom materials into
the finest silt. The waves of lakes cut
away the shores, grind up the rocks they
break off in this process, and deposit the
silt thus produced in the bottom. Streams
lower the outlets of lakes and carry detri-
tus into them.

Ponds and small lakes support vegeta-
tion which decays, filKng their bottoms
with putrescible material which is gradu-
ally transformed to humus with a lowering
of oxygen and the development of poison-
ous decomposition products. The ponds sar^p^-j^^i^^
and lakes are thus filled as well as drained the ?5iqn ofTmeJgirJ v^egTtation^

J ,, , 1 /- n 1 -I , Crosses indicate the region of sub-

and all become swamp and finally dry land, merged vegetation. stippUng indi-

11. cates the region of deep water or the

Streams gradually erode their wav down hypoiimnion. The region of piank-

•^ "^ ton occupies the entire lake except

to sea level and become meandering base Z^Sr:li^^t:l:.7t^:Zt:l
level streams with fine silt bottom, sluggish ^^"^^^^^-^
current and an abundance of vegetation. The base level streams
and dry land are the ultimate fates of all bodies of fresh water.
With the changes enumerated, there is always almost complete
change of animal and plant Kfe. The physiological requirements
of the Kfe of the first stages of the process are entirely different
from those of the last.

Fig. 8.
Diagrammatic representation of a

6o FRESH-WATER BIOLOGY

IMPORTANT REFERENCES

.\dams, Chas. C. 1913. Guide to the Study of Animal Ecology. New York.

BiRGE, E. A. and Juday, C. 1914- (See list in Chapter I.)

Forbes, S. A. 1877. The Lake as a Microcosm. Peoria Science Assoc.

FoREL, F. A. 1892-1904. (See list in Chapter I.)

Henderson, L. J. 1913. The Fitness of the Environment. New York.

Hill, L., Moore, B., Macleod, J. J. R., Pembrey, M. S., and Beddard,

A. P. 1908. Recent Advances in Physiology and Biochemistry. London.
Johnstone, James. 1908. Conditions of Life in the Sea. Cambridge.
Mayer, A. G. 1908. The Swarming of the Atlantic Palolo. Carnegie

Inst. Pub. 102.
Moore, J. P. 1899. A Snow Inhabiting Enchytraeid. Proc. Acad. Nat.

Sci., Phila., 1899 : 125-149.
Bibliography and general remarks on snow-inhabiting animals.
Murray, Sir John and Hjort, J. 191 2. The Depths of the Ocean. Lon-
don.
NEEDHAii, J. G. and Lloyd, J. T. 191 5. (See list in Chapter I.)
Packard, W. H. 1907. The Effect of Carbohydrates on Resistance to Lack

of Oxygen. Am. Jour. Physiol., 18 : 164-180.
Regnard, p. 1891. (See Hst in Chapter I.)
RosENAU, M. L. 1914. Preventative Medicine and Hygiene. Sec. II,

Ch. I. Boston.
Shelford, V. E. 1913. (See list in Chapter I.)
Shelford, V. E. and Powers, E. B. 191 5. An Experimental Study of the

Migrations of Herring and other Salt Water Fishes. Biol. Bull., 28 :

315-334-

Ward, H. B. 1896. (See list in Chapter I.)

Wells, M. M. 191 5. The Reaction and Resistance of Fishes in their Natural
Environment to Acidity, Alkalinity and Neutrality. Biol. Bull., 29 :
221-257.
1915a. The Resistance and Reactions of Fishes in their Natural Environ-
ments to Salts. Jour. Exp. Zool., 19 : 243-283.

Whipple, G. C. 1898. Classification of Lakes According to Temperature.
Am. Nat., 32 : 25-53.

CHAPTER III

METHODS OF COLLECTING AND
PHOTOGRAPHING

By JACOB REIGHARD

Professor of Zoology in the University of Michigan; Formerly Director of the Lake Laboratory of the
U. S. Bureau of Fisheries, at Pul-in-Bay, Ohio

Methods of Collecting

I. Vertebrates

I. Fish must be collected under the state laws which usually
forbid the use in inland waters of any apparatus except hook and
Hne or dip or lift nets held in the hand. In most states licenses to
use nets for scientific purposes may be obtained either from the
state fish commission or from the game and fish warden.

(a) Seines are long nets with a weighted lead line attached to
the lower edge and a cork Hne attached to the upper edge so that
the nets remain upright in the water. When the net is so stretched
that it forms rectangular meshes "square mesh" is the length in
inches of one side of a single square. For use in brooks or for col-
lecting small shore fishes, seines twelve or twenty-four feet long
and four or five feet in depth are suitable. The former should
be of one-quarter inch square mesh, while the latter may be of
one-half inch square mesh.

For larger fish, seines of fifty and one hundred feet in length, five
to nine feet deep and of inch mesh should be used, but larger
seines are not easily handled by two persons. The longer seines
should be of the twine ordinarily used for such purposes and
knotted at every crossing. For the shorter lengths the excellent
and cheaper ''common-sense" minnow seines which are woven to
resemble coarse burlap may be used. Very serviceable seines
may be made of a good quality of heavy bobbinet which may
be had of dealers in dry goods. All seines are much more
efficient if provided with a bag at the center, as is the Baird col-

6i

62 FRESH-WATER BIOLOGY

lecting seine, but seines of this form are expensive and not abso-
lutely necessary.

Seines can be used only where the bottom is free from large
stones or deadwood and the water not much obstructed by vegeta-
tion. A brail, or stout pole, is fastened by a double half-hitch to
both cork and lead lines at each end of the seine so as to extend
from the cork Hne to the lead Hne and keep the seine stretched
between the two lines. The seine is then operated by two persons
each of whom holds a brail in such a way that the lead line is kept
close to the bottom which it sweeps, while the seine forms an arc
of a circle between the two brails. At the end of the haul the
seine is best landed on a gently sloping bank by seizing the lead
line and drawing it in first to the bank. Where the bank does
not afford a suitable landing place a short seine may be ^'tripped "
in any depth of water by quickly pulling up the lead line until it
Hes in the same horizontal plane as the cork line. The seine sag-
ging between the two lines retains the fish. A short seine may be
throwTi or cast from a boat in deep water and immediately drawn
in and tripped. Small surface-swimming fishes are caught in this
way. Where a long seine is to be used in water too deep to wade,
a heavy weight is attached to the lower end of one brail so as
to keep it upright in the water. To the same brail a short rope
is so fastened that it extends loosely from one end of the brail
to the other. To the middle of this short rope, or bridle, is
attached a long hauHng rope. The end of the seine is then
carried out into deep water by means of a boat and the free
end of the hauling rope brought back to shore, from which the
seine is hauled in by means of the rope. If a hauling rope and
weight are attached to each brail the seine may be set in the water
at any convenient distance from shore and parallel to it and may
then be hauled to shore by means of the ropes.

(b) Trammel nets consist of one web of fme twine of about one
inch mesh between two webs of coarse twine of about six inches
mesh. A length of one hundred feet and a depth of six or eight
feet is convenient. The finc-meshed web is much deeper than
the coarser ones and all three are attached between a single
cork line and a single lead line. The net is ''laid" in a boat

METHODS OF COLLECTING AND PHOTOGRAPHING 63

(see below under gill nets) and is set by stretching it along the
seaward edge of vegetation or other shelter in which fish lurk and
from which they cannot be taken with other nets. The net may
be fastened to stakes or allowed to float in water of about its
own depth, where it stands upright like a fence. The fish are
then driven from their shelter toward the net, which they strike
with such force as to carry the nearly invisible, fine web through
the meshes of the coarser webs, so as to form pockets in which
the fish are held. The trammel net is easily transported and
very effective, especially in slightly turbid water or at night.

(c) Fyke Nets. A fyke net is made like a seine, but at its middle
is left a circular opening bordered by a hoop of wood or iron. To
the hoop is attached the pot, a series of truncated cones of netting
open at both ends. The smaller end of the first cone leads into
the larger end of the second cone and this often into a third.
The last cone of the pot is closed at its smaller end by a draw
string. Both ends of the lead and cork lines should be tied into
loops and the net should be ''laid" in a boat (see below under
gill nets) and taken to the place of setting together with two stout
poles of suitable length, a rope and a heavy stone or other anchor.
The loops at one end are shd over a pole which is then thrust or
driven into the bottom. The net is then paid out from the boat
rowed in the direction in which it is desired to set it. When the
pot is reached it is thrown overboard. When the other end of the
net is reached it is fastened to a pole set in the bottom in the
manner already described, but the net is left quite slack between
the two poles. The pot is then picked up, the rope attached to
the terminal funnel and the whole pulled usually toward the shore. ^
The pull causes the net to bend into a V the wings of which
stretch from the pot to the poles. The anchor is now attached to
the end of the rope and thrown overboard. If the water is deep
a small cord with a float at one end is attached by its opposite
end to the anchor line and serves to pull up the anchor line when
the pot is to be lifted. The anchor line may be tied back to a

^ The larger fish usually taken in a fyke are caught as they go from the vegeta-
tion zone or beyond it into shoal water. They might be caught as they leave the
shoal water by setting the net the other way about.

64

FRESH- WATER BIOLOGY

Stake and the anchor dispensed with. Fykes are usually set across
the mouth of a small bay or inlet but may be placed anywhere.
In running water the net may face either up or down stream. It
may be necessary to set a row of stakes across the stream above
the net to catch drift wood. When lish attempt to enter the bay
or inlet across which the net is set, they follow the wings of the
fyke and enter the pot from which they are unable to escape.
The net may be left set for a long time and the fish taken from it
at intervals by lifting the pot and loosening the draw string. The
wings of a fyke may be from fifteen to fifty feet long according to
its location, but for brook use fykes are made without wings.

Fig 9 Showing one end of a gill net as set when used in the cod fishery on the Massachusetts Coast.
I, end of the net. 2, anchor line. 3, anchor. 4, buoy line. 5. buoy. (After Ooode.)

The fyke is an excellent net for catching turtles, but should then
be modified as indicated in the section on turtles (p. 66).

(d) Gill nets are made of very fine cotton or linen twine and of
various meshes. Inch or two-inch square mesh and a length of
one hundred or one hundred and fifty feet are useful for collecting.
The nets are intended to be left out for days, at least, on the
bottom in deep water. They stand upright in the water (Fig. 9)
and the fish strike them usually at night and become entangled in
the meshes, so that they are commonly dead when the nets are
Hfted.

A small rope of at least the length of the net is attached to one
end of the cork line and a stone or other heavy weight to serve as
an anchor is made fast to the other end of the rope. The anchor

METHODS OF COLLECTING AND PHOTOGRAPHING 65

is placed in the boat and the rope carefully coiled near it. The
net is then carefully "laid" by folding it back and forth after
the manner of a folding fan. It is not necessary to keep the net
stretched to its full width between the cork and lead lines. When
the opposite end of the net is reached a second and equal anchor
Hne with anchor attached is made fast to the cork line. A number
of gill nets may be fastened together end to end and used as a
single net, with a single pair of anchor lines and anchors. It is
convenient to lay the net on a '' setting board " four or five feet
long and as wide. The board may be made like a batten door of
smooth boards and placed across the stern of the boat, where the
net is to be set. The net should be set where it is thought fish
will run, as across a narrow neck connecting two parts of a lake or
across the mouth of a bay. If the net is set down the wind it may
be handled by a single person. The upper anchor is thrown out
and, as the boat drifts with the wind, first the anchor line and
then the net are paid out, and care is taken that the net is not
fouled in going over the side of the boat. When the second anchor
line has been paid out to near its middle a small rope, long enough
to reach to the surface of the water is made fast to it and to the
free end of this is fastened a piece of wood to serve as a float.
When the end of the second anchor line is reached, the net is
pulled taut, and the second anchor thrown over. The fish may
be removed from the net by pulling up the float line until the
anchor line is recovered and by then running along this and the
cork line of the net, hand over hand, allowing the part of the net
that has been examined to fall back into the water.

{e) Traps. A cylinder is formed of wire netting of one-fourth
or one-half inch mesh. Into one end of this is fitted a cone of the
same material with its apex directed inward. The apex is trun-
cated so as to leave an opening two or more inches in diameter.
A similar cone may be fitted over the other end of the cylinder or
this may be closed by a flat cover of netting. One end of the
.cylinder must be removable to permit baiting and removal of the
fish. The cylinder may be two or three feet long and a foot in
diameter and the cone eight inches deep — but larger sizes may be
used to advantage. The trap is baited with fish or meat hung

66 FRESH-WATER BIOLOGY

near its middle by a wire and is lowered to the bottom at any
depth by a cord supported by a float. It is used chiefly for smaller
fish, crayfish, or Necturus. It may be set anywhere but is espe-
cially useful where water is obstructed by vegetation, rocks, or
fallen trees so that nets cannot be drawn.

(/) Care of nets. Both fyke nets and gill nets should be taken
from the water at intervals, washed, dried, and mended before they
are agidn used. For mending it is necessary to have a supply of
twine of which the nets are made and several wooden shuttles or
needles such as fishermen use; it is also necessary to learn the
knot used in maJdng nets by hand. All nets when taken from
the water should be washed and carefully dried before being put
away. If left with the twine clogged with accumulated organic
matter they rapidly decay and this decay is the more rapid if the
nets are damp. They may be stored by hanging them loosely in
some dry loft or they may be packed in bags and hung from the
ceihng by cords. If left accessible to rats or mice they may be
ruined by being utilized as nest material.

In laying a net for storage or transportation the lead and cork
lines should each be folded back and forth on itself. The lead
Line should be so folded that the leads are brought together and
they should then be securely tied together. If this precaution is
not taken the loose leads, carrying the lead line with them, become
woven back and forth through the net and the whole is almost
inextricably tangled together.

2. Turtles. Turtles are best taken in a turtle net which is a form
of fyke net. It should be of heavy twine and coarse mesh and, if it
is desired to keep the turtles alive, should be modified as follows:
The terminal section of the pot is made cyhndrical or the whole
pot may be made with square hoops. A circular opening is cut in
the upper side of the terminal section of the pot and to this is
attached the lower end of a cylinder of netting which extends to
the water's surface. The upper end of this cylinder is attached to
an opening cut in one side of a wooden box provided on the oppo- ,
site side with a hinged lid fastened with a hasp. The box is sup-
ported at the surface of the water on poles set in the bottom.
When turtles reach the terminal section of the pot they are able

METHODS OF COLLECTING AND PHOTOGRAPHING 67

to enter the box through the cylinder of netting and are thereby
saved from drowning which would ensue if they could not reach
the air. They may be removed through the lid at the convenience
of the collector.

II. Invertebrates

Invertebrates are to be collected in three situations: in the
aquatic vegetation bordering the shore, in the open water, beyond
this vegetation-zone, and on the bottom, so that the apparatus
suitable to each of these situations may be separately considered.

It is convenient to consider first those methods designed for
quahtative work, for finding out what organisms are present, and
second those methods by which the number or quantity of organ-
isms present in a unit volume of water or under a unit area of sur-
face may be determined.

A. Collecting in Littoral Vegetation

1. By dip nets. The dip net (Fig. 10) is here of greatest use. It
consists of a conical netted bag about one foot in diameter and
eighteen inches deep attached to a

stout ring of brass or iron, firmly

fixed to a stiff, wooden handle seven

or eight feet long. The lower third of

the net may often be advantageously

lined with thin, cotton cloth to retain

smaller organisms. A form of this net

adapted to scraping flat surfaces, such ^^^

as logs, flat stones, banks, etc., is also ^

, /_,. . ^ - . . , Fig. 10. Two forms of dip net. For de-

ShOWn (Fig. 10). It has a Semi-CirCUlar scription see text. (From photographs

rim and a shallow bag of canvas with

a bottom of No. 6 or 8 bolting cloth. The handles used on dip
nets are rake handles. The iron rings may be made by any
blacksmith. The bags are sold as minnow dip nets by dealers
in fishing tackle or by mail-order houses.

2. By collecting larger aquatic plants. With such nets many
forms visible to the naked eye may be collected directly, or the

68

FRESH-WATER BIOLOGY

Fig. II. Pieters' plant
grapple. (. After
Pieters.)

aquatic vegetation may be obtained and searched for smaller

organisms. Many forms that are detected with difficulty in the
field appear in abundance in the water of small
dishes containing aquatic plants, when allowed to
stand undisturbed for some days (annehds, flat
worms, rotifers, hydras, protozoa, etc.). Sub-
merged vegetation which grows in deeper water
and cannot be reached by other means may be
obtained by dragging behind a boat the grapple
(Fig. ii) described as follows by Pieters (1901):
"This is made by passing four or five bent steel
wires through a piece of i^-inch pipe and bending
back the free ends to make hooks. The pipe was
filled with lead to make it heavier and a rope

fastened through the loops of the wires."

3. TJie cone dredge. Many organisms are too small to be readily

collected with dip nets and many escape when aquatic vegetation

is gathered. These may be readily obtained

by this ingenious device of Professor E. A.

Birge, which may be run among aquatic plants

where the townet cannot be used.

The cone dredge (Fig. 12) now used by

Professor Birge consists of four parts.

A. The body is a cy Under of sheet copper
three inches in diameter and one inch deep,
wired at its lower edge to form a lip on the
outside. A brass wire bent into a V with an
eye at its apex is soldered by its free ends
inside the body while its apex extends upward
like the bail of a pail.

B. A cone of brass wire netting of about
twenty meshes to the inch fits over the bail.
Its base is soldered to the body and its apex
to the eye of the bail which projects through
it. Two flat loops of wire soldered to the

outside of the body serve for the attachment of cords.

C. The net is a conical bag of cheesecloth eighteen to twenty-

FlG. 1

Cone dredge. At
bottom hinnel-filtc-rforuse
with the drcflpc. (Original
photograph from appara-
tus loaned by Professor
Birge.)

METHODS OF COLLECTING AND PHOTOGRAPHING 69

two inches long and may, by altering the dimensions, be cut out
according to the directions given for the townet. It should be
faced with strong muslin for two or three inches at each end. It
is tied by its upper end over the flange on the body.

D. The screw lip consists of the screw top of a kerosene oil can,
extended by soldering to the male screw a copper cylinder an inch
and a quarter long. The cylinder is wired at its top to form a
projecting flange over which the tip of the net is tied. The cap
is weighted by soldering to it a lead ring of about two ounces.
Two loops of wire soldered to the outside of the screw tip serve for
the attachment of cords from the loops on the body and these
support the weight of the screw tip and take the strain off the
net.

This net may be readily dragged behind a boat among dense
water plants by means of a cord attached to the eye. The cone
fends off the water plants and lessens the amount of debris entering
the net and clogging it. The net may also be thrown from shore
to a distance of thirty or forty feet and safely hauled back through
thick vegetation. It may also be run at some depth or along the
bottom by attaching a suitable weight to the hne, two or three feet
in front of the cone.

When a haul has been made the screw cap is removed so that
the contents of the net fall into a cup or jar of water. Several
successive hauls may be united. WJien the foreign matter which
always enters the net has settled to the bottom of the jar, the clear
water containing the entomostraca is poured into a metal funnel
with a long neck made of brass wire gauze of about forty meshes to
the inch (Fig. 12). The neck, which serves as a filter, terminates
in a tin ring which is corked. When the entomostraca have been
filtered from the water, the cork is removed and the catch washed
into an eight-dram homeopathic vial, short form, in which it is
preserved.

When many catches from different localities are to be kept sep-
arate. Professor Birge uses flat bags, one by three inches, made by
stitching together on the sewing machine pieces of India linen.
Before going into the field the bags are numbered and strung on
a thread so that they may be pulled off in order. The catch is

70

FRESH-WATER BIOLOGY

poured through an ordinary tin funnel into the bags, which are
then tied and placed in the preservative.

An "improved" form of cone dredge has been described by Wol-
cott (1901), who has worked out a standard type of holder for cone
dredge, dip net, sieve, and scoop. A folding-cone dredge is sold
under the name simplex plankton net. Its cone is made of cloth.

The plankton pump may also be used for collecting free swim-
ming forms among aquatic vegetation.

In making collections along the margin of a pond or stream, or
in the puddles of a bog or half-dried ditch, it is advantageous to
use a dipper with a cane or short bamboo handle. One may
fasten to such a handle a wide-mouth bottle, a dipper with fine
metal gauze bottom, a pruning hook or other apparatus for
securing samples of the plant or animal Hfe in such places as are
somewhat inaccessible. A shallow glass dish or white soup plate
is very useful in examining immediately refuse obtained from the
margin or bottom of such pools. By some such means the heavier
particles of sand and silt may be separated from the collection
before it is preserved.

B. Bottofn Collecting

The dredge that is commonly used in deep-sea work is of little
value in fresh water owing to the relative barrenness of lake bottoms.
The larger bottom vegetation may be obtained at any depth by the
use of Pieters' grapple already described. For the smaller organ-
isms that Hve in the superficial ooze of the bottom, the cone dredge
or the townet may be used. A weight heavy enough to bring the
line to the bottom is attached to the towline two or three feet in
front of the net. The cone dredge when attached to a weighted
line may be made to run along the bottom by weighting the screw
tip, but in that case it is well to fasten a band of cloth about the
base of the wire cone so as to leave only the upper part free.
The net, while admitting water through the tip of the wire cone,
then gHdes over the bottom without scraping up mud. A townet
mounted on runners, as shown here (Fig. 13), has been found
very useful by the writer for taking organisms just above soft
bottom. From the iron ring which supports the mouth of the

METHODS OF COLLECTING AND PHOTOGRAPHING

71

in. 14. Triangle dredge
ds used by the writer.
For description see
text. (From an orig-
inal photograph.)

net four pieces of half-inch band iron extend radially for about
three inches and then turn and run parallel to one another for some
distance beyond the tip of the net.
Here they are bent inward and
riveted at the center.

To collect organisms that live
in the bottom it is necessary to
use some form of dredge that will
bring up the bottom material.
To bring up the superficial ooze
the weight attached to the townet
line or cone dredge line may have
the form of a rake, or be other- '

. , 1 . . Tig. i^. Townet on

wise irregular, so that it stirs up runners, designed

, ^ by the writer. For

the ooze and drives animals from description see

text. (Fromanong-

it to be caught in the net. For inai photograph.)
animals that cannot be thus dislodged the writer has used a
triangle dredge (Fig. 14). This consists of a bag of one-fourth-
inch square mesh netting, or burlap, or other coarse material,
lined at the bottom with muslin and hung from a wrought-iron
frame which may be made by any blacksmith. The frame
consists of an equilateral triangle, twelve to fifteen inches on
each side, of heavy band iron, and of three stout iron rods,
one extending from each angle of the triangle at right angles
to its surface, to a distance of about three feet. The edge of
the triangle is formed into large saw-teeth bent slightly out-
ward so that they tend to dig into the bottom. An eye at each
corner serves to attach a rope which extends to the hauling line.
The rods serve to keep the triangle upright when the net is drawn
along the bottom, so that the mouth of the bag is open and the
teeth plow into the bottom.

Another useful type of dredge has the form of a triangular or
quadrangular pyramid, whose side and slant height are each about
six inches. A number of stout steel wires, about six on each side,
are soldered together so as to form the apex of the pyramid, while
their opposite ends are bent slightly outward beyond its base, so
that they project like the teeth of a comb. The framework thus

y2 FRESH-WATER BIOLOGY

formed is covered ^vith wire cloth and the apex of the pyramid is
filled with lead to the depth of an inch and a half. An eye at each
angle serves to attach a cord. This dredge is very effective in
collecting bottom mollusca.

C. Open Water Collecting — Qualitative Methods
I. The toii'uet is the simplest device for collecting the plankton

organisms which abound in the open water. The following direc-
tions for making a townet are modified from
Kofoid (1898). The completed net (Fig. 15)
consists of a conical bag of India linen or better
of silk bolting cloth hung from a ring which is sup-
ported by three cords. The bolting cloth may
be number 12, 16 or 20 and is to be had from
dealers in mill supplies, but discarded cloth may
often be obtained from flour mills. Before cut-
ting the cloth should be shrunk by boiling in
soapsuds and then pressed. A pattern for cutting
two nets twelve inches in diameter from a yard

^wkhoutbuK. /Hvlre of forty-inch wide bolting cloth is given (Fig. 16).
dr"aw ?hies. hp, head j^g cloth has bccn doublcd lengthwise (with the

piece sewn to top of net. ^11 .1 1

linT^ '(Modified'^fmm warp) and is shown with the fold at the right and
^°fo'd) the two free edges at the left. With a radius equal

to the length of the cloth two arcs are struck from the points a
and b as centers. These arcs, which form the tops of the completed
nets, must be equal in length to one-half the circumference of the
net hoop and these lengths may be most readily determined by
rolling the net ring along the arcs. An additional width must be
allowed on the piece d, since this is in two parts and has two
seams. This is accomplished by cutting the two pieces apart
along the line ab a quarter of an inch to the right of the diagonal.
The pieces are then formed into cones and closed by a French
seam along the side and by the seam across the apex. The top
of the net is finished by sewing on a band made of a doubled
strip of butcher's linen, cut bias and provided with a heavy cord
sewed into its upper margin. The net is attached to the ring
by over-cast stitches of heavy thread. The ring r (Fig. 15) of

METHODS OF COLLECTING AND PHOTOGRAPHING

73

No. 5 spring brass wire, standard American gage, has three pairs
of wire rings h soldered on it at equal distances to hold the
drawlines dl in place. To the drawlines at
their junction a short cord wl may be attached
for the support of a weight.

If the net is used in this form the catch
must be removed from it by turning it inside
out and sousing the tip in a bottle of water.
It is more convenient to cut off the tip of
the net along the line ij and tie into it a
screw tip like that described below for the
cone dredge, but without the weight. A short
glass tube closed by a rubber stopper or a
bucket like that of the plankton net may be
used in place of the screw tip. Provided with
a bucket the net is identical with the plankton
net except that it lacks the canvas cone.

The townet may be dragged behind a boat
either at the surface or submerged to any depth
by means of a weight attached to the weight
line. When the haul is completed the net is
soused in the water or water is thrown on its outer surface, until
the contents are washed to the tip of the net, which is then turned
inside out and the contents obtained by rinsing the tip in a bottle
of water, or allowing them to fall into preserving fluid. The pro-
cedure for a net provided with a bucket is described under the
plankton net and cone dredge.

2. Plankton Cylinders. Various forms of apparatus have been
designed for collecting plankton from a rapidly moving boat. These
are made with a very small opening for the entrance of water and
with a large filtering surface. They are designed to reduce the
pressure of the water on the filtering surface. They are described
by Steuer and others. They are chiefly of use in the sea or in
other situations accessible only to large vessels and are little em-
ployed in fresh water. The plankton cylinder is one form of such
apparatus in which a torpedo-shaped metal jacket admits water
through a small opening on its conical end and carries the filtering
gauze in the interior or on its other end.

Fig. i6. Showing method of
laying out a pattern for cut-
ting two townets from a
yard of cloth forty inches
wide, a-b, line along which
cloth is to be cut. c-d, the
two net patterns, e-f, seam
by which the bottom of the
net is closed if no bucket is
attached (see Fig. 15). g-h,
line of attachment of bucket.
i-j, line along which net is
cut ofif when bucket is used.
(.'\fter Kofoid.)

FRESH- WATER BIOLOGY

D. Quantilalivc Methods in Open Water

I. The Quantitative Plankton Net. The plankton net and pump
are intended for the collection of plankton for quantitative inves-
tigations. The plankton net differs from the townet described
in that its rim extends upward into a truncated cone of canvas
(Fig. 17), and that it is provided with a removable bucket.

The canvas cone hinders bottom ooze from entering the net and
also hinders the slopping out of the contents as the net is drawn
above the surface. It serves further to lessen the diameter of the
net opening, so that a larger fraction of the column of water above
the net opening is filtered and less of it is pushed aside by the
resistance of the filtering gauze.

The plankton net (Fig. 17) in use at the University of Wisconsin
is here first described with the permission of Professor Birge. The

ring which supports the net is about
seven inches in diameter and from this
measurement the other dimensions of
the apparatus may be roughly measured
on the figure. The canvas cone stretches
from the net ring to an upper ring and
both rings are of one-eighth-inch spring
brass wire. Three eight-shaped pieces
of lighter wire are strung on each ring
through one opening, while the other
opening receives the eyes on the ends
of three connecting rods which hold the
two rings together. The upper support-
ing ring has three brass rings soldered to
it for the attachment of the draw lines.
The canvas cone and the band, which
is ordinarily sewn to the top of the net,
are in this case cut from one piece of
shrunken canvas. This is sewn around
the upper supporting ring and is attached
to the inside of the lower ring by means of a tape sewn to its out-
side. The bolting cloth net (No. 16 or No. 20 cloth) is sewn to

Fig. 17. Wisconsin plankton net.
(Original photograph from appa-
ratus loaned by Professor Birge.)

METHODS OF COLLECTING AND PHOTOGRAPHING

75

8. Bucket of Wisconsin plankton net. From
apparatus loaned by Professor Birge. At right is one
of the writer's tubes for filtering plankton. For de-
scriptions see text. (From original photographs.)

the inside of the band, with its margin turned back over its outer

surface for the fraction of an inch. By this construction the canvas

cone folds conveniently for transportation, while the inner surfaces

of cone and net are continuous and smooth, so that plankton

organisms do not readily lodge

on them. If convenience in

transportation is not important

the cone may be better made

of sheet brass.

The original feature of this ^^J^^^,

net is the bucket (Figs. i8 and

19), which is made of telescope

tubing of two sizes. The smaller size (two inches in internal

diameter) is used to make the headpiece shown attached to the net

in Fig. 17. This (Fig. 19, a) is one
and three eighths inches long and is
fastened to the net by means of a
brass band clamp (Fig. 19, h) made of
two pieces, with wings at the ends
through which pass clamp screws.
A pin soldered into the headpiece
fits a hole in each half of the clamp
and prevents its turning when the
bucket is twisted to remove it (seen
near the upper margin of Fig. 19, a).
Three brass rings soldered to the out-
side of the band clamp serve to attach
cords which extend to the lower sup-

"'SJJn pialtT ^"."TXalpi'ift porting ring of the canvas cone and

headpiece clamp; c, bucket; d, e, lower and j.-\ • T_ ^ r 4-1, ^ U ^1 *.

upper band clamps; /, one of the side Carry thC WClght Ot the bUCkct.

clamps with screws; g, side clamp in posi- —,, , t./t-'* n\' j rj_i

tion; h, semi-cylindrical rod soldered to 1 hC OUCket (-Tig. lo) IS made 01 tClC-

strip between windows; /, stem of the plug . i • i r

which closes the spout seen below at left of SCODC tubmCf of a SlZC whlCh IltS OVCr

c; J, millimeter scale. For description see ^

'^£^A!:Zhyi';ltT£^'''''''^'- that used for the headpiece.^ Pieces

are cut from the sides of this so as
to form four windows separated by strips about one-half inch wide.
These strips are strengthened by soldering to the inside of each a
semi-cyHndrical rod about one-quarter inch in diameter (Fig. ig,h).

76 FRESH-WATER BIOLOGY

The bottom of the bucket which is conical and ends in a tapering
spout is shrunk into place flush with the lower edge of the windows,
after heating the bucket in a jet of steam. A taper plug of brass,
with a long stem (Fig. 19, i) which ends in a milled head, is
inserted from within and closes the spout. The edge of the
bucket has an L-shaped incision which receives a pin soldered
to the outside of the headpiece so as to form a bayonet catch
which holds the bucket in place on the headpiece. The four
windows in the bucket are closed by a single piece of bolting
cloth, held in place by a band clamp at top and bottom (Fig. 19
d, e) and by four side clamps gg screwed between the windows.
The holes for the screws are conveniently burned through the
bolting cloth with a hot wire.

A cheaper bucket described by Kofoid (1898) is shown in section

in Fig. 20. It is a cylinder of sheet copper around the top of which

are soldered two light-wire rings, which serve to

/ hold in place the string 5, which ties the tip of the

I
I

h'

W.

net to the bucket. In the sides of the cyHnder are
cut three equidistant windows, each one and one-
half by one and three-quarters inches, which are
closed by brass wire gauze wg, soldered to the
edges. Gauze containing two hundred meshes

Fig. 20. Simple townet ,. . , n r it-

bucket as seen in sec- per hnear mch answers very well for these wm-

tion. b, conical bottom. r i t i • r

rf/>, drip point, rr', wire doWS. Thc bottOm of thC bUCkct IS a cone 01
rings soldered to top of ^ • i • i

bucket. 5, string by coppcr With a Central openmg which continues

which tip of net is tied ^^ ^ °

Ihe^two^wi^frfngr^J! i^^^ ^ short, obliqucly-pointed tube /. The open-
fot%mp?ying°^%"T iHg is closcd by a rubber stopper with a wire
o/'the''th^rJ^lindoTs handle which extends above the top of the bucket

cut in sides of bucket. i • i . • ^ ^

The rubber stopper with and IS bent into a loop.

wire handle is seen at . i ti i

center of bucket. (After The fiet IS constructcd likc thc townct, except

Kofoid.) . .

that the tip is cut off at the point ij (Fig. 16)
and the silk slit along the dotted lines between gh and ij to
allow for the fitting and fastening of the bucket in place.

The plankton net is drawn from the bottom to the surface,
and the organisms that have been caught in it are washed into
the bucket by throwing water onto the outside of the net, or by
sousing it in the water. The net is then lifted above the water,

METHODS OF COLLECTING AND PHOTOGRAPHING 77

the bucket removed, and the water allowed to drain from it.
When only so much water remains as tills the conical bottom
of the bucket, the stopper is drawn and the contents allowed to
fall into a suitable container. Organisms adhering to the inside
of the bucket are then rinsed into the container with a httle filtered
or distilled water from a wash bottle. If the contents are to be
preserved they may be allowed to fall directly into a bottle
which contains the preservative or fixing fluid, so concentrated
that the addition of the plankton brings it to its normal consti-
tution. Ninety-five per cent alcohol may be used and in that
case the plankton may be allowed to fall from the bucket into
about three times its own volume of alcohol, so that it is preserved
in alcohol of about 70 per cent strength.

If it is desired to use a fixing fluid before preservation in alcohol,
the stronger picrosulphuric acid may be diluted with two volumes
of water and three volumes of this may be used to one of plankton,
so that the latter is fixed in Kleinenberg's solution. Other fluids
may be used in like manner, adapted either to the plankton as a
whole, or to special groups of plankton organisms. The plankton
is then best caught in a strainer made by removing the bottom of
a short eight-dram homeopathic vial and tying bolting cloth over
the neck (Fig. 18). The plankton may be kept in this strainer
by tying bolting cloth over the bottom, and the strainer may
then be passed through fixing fluids and grades of alcohol. The
fluids may be made to enter the strainer by withdrawing the air
by means of a pipette held against the bolting cloth (Reighard,
1894).

Plankton nets may be made closable and various devices have
been used for this purpose (e.g., by Marsh, 1897). Such a net may
be lowered, drawn upward any desired distance, then closed and
drawn to the surface. It thus filters only that part of the column
of water through which it is drawn while open, and aids the inves-
tigator to determine what forms occur at various depths.

Although the plankton net may seem to filter a vertical column
of water, the base of which is equal in area to the net opening,
it does not in practice do this. The resistance of the net gauze
causes a certain part of this column to be pushed aside. The part

78 FRESH-WATER BIOLOGY

pushed aside not only is greater as the net moves faster but is
increased as the net becomes clogged and is therefore greater
toward the end of the haul than at its beginning. The filtering
capacity of the net gauze is further liable to change with age, as
its pores clog and its threads loosen and tend to obstruct the
openings. Although elaborate methods have been devised for
determining the errors of the plankton net, no one of them is satis-
factory.

2. The Plankton Pump. The difficulties encountered in the use
of the plankton net for accurate quantitative work have led to the
development of the plankton pump, which is now largely used in
conjunction with the ordinary plankton net and which, used in that
connection, has nearly displaced the closable plankton net (Birge,
1895; Marsh, 1897) in fresh water. This may be any pump which
delivers at each stroke a known and constant volume of water.
The water is drawn through a hose which extends from the pump
to any desired depth and may terminate in a metal cone, closed
by very coarse wire netting, which serves to exclude foreign bodies
from the hose. From the pump the water may be conveniently
dehvered through a shorter hose to some device for filtering the
plankton from it. For this purpose a plankton net is used. The
net may be suspended in air and the water pumped into it, but
some small organisms are thus forced through the net gauze and
lost, and others are doubtless injured by the impact of the stream
of water and the weight of the water in the net. This is avoided
if the net be held under water with only the canvas cone above
the surface. The whole operation may be readily carried out by
one person if the net be supported in the water by a wooden
float surrounding the cone (Fig. 23) and the delivery hose be
attached to the net (Kofoid, 1897). When sufficient water has
been pumped, the net is taken up and the catch removed and
treated in the usual way.

The end of the suction hose may be allowed to remain at any
desired depth during the pumping. The pump is calibrated so
that the volume of water delivered at each stroke is known. The
number of strokes made during any haul is counted, so that a
simple calculation gives the total volume of water pumped.

METHODS OF COLLECTING AND PHOTOGRAPHING

79

The end of the hose may also be lowered to near the bottom and
may then, while pumping is in progress, be slowly drawn upward at
a uniform rate. In this way is pumped a vertical column of water
which extends from the bottom to the surface, and the volume of
such a column may be calculated.

The following forms of plankton pump may be referred to
briefly.

(a) Fordyce pump (Fordyce, 1898). This invention of Professors
Ward and Fordyce is shown in perspective (Fig. 21) and in sec-
tion (Fig. 22). It "is practically a force pump. . . . The cylinder

qf^"^

Fig. 21. Fordyce's pump and strainer. For description see
text. (After Fordyce.)

Fig. 22. Fordyce's pump in sec-
tions. For description see text.
(After Fordyce.)

of the pump is eleven by three and one-half inches and has a capacity
347J cubic inches per stroke. The stroke of the piston is definite
in length and is regulated by a lock nut as shown in the plate. The
valves used are finely-ground check valves, to which it is believed
the accuracy of the working of the apparatus is largely due. The
pump is connected with the water by a hose one and one-half
inches in diameter, whose lower end is adjusted to the various ver-
tical zones of water by means of attachment to a floating block."
For filtering the water Fordyce uses the device shown in Fig. 21,
at the left of the pump. This Is similar to the device already de-
scribed in connection with the Wisconsin plankton net, and is used
in the same way. It is provided with a rim to which a cover of
wire netting may be attached to exclude foreign matter. A net

8o

FRESH-WATER BIOLOGY

of bolting cloth may be attached outside the wire gauze filter, and
the whole instrument is then adapted for the various work of the
ordinary net.

On account of its cheapness and portabiHty a pump of this form
is probably best adapted for work not carried on from a station
especially equipped for aquatic biology.

{b) The clock pump has been used for some years at the Uni-
versity of Wisconsin (Juday, 1904). At Wisconsin the pump is
fixed to the bottom of the boat and the water, drawn through
a half-inch garden hose, is pumped into a submerged plankton
net of No. 20 bolting cloth.

Fig 2\ Thresher tant-pump m use. Ihe water reaches the pump through the hose at the left and is
delivered to the net through the hose at the right. The net cone is seen supported by a rectangular
wooden float. (After Kofoid.)

(c) The thresher tank-pump, a double-acting force pump with
two cylinders each six by nine inches, has been used by Kofoid
(1897). The mode of using the pump is shown (Fig. 23). This
pump is fastened to the boat and is too heavy to be carried or
to be used apart from a permanent mounting.

3. The Water Bottle. To obtain small samples of water for the
study of the nannoplankton a water bottle may be used. Many
complicated and expensive forms of these bottles have been devised
(see Helland-Hansen) for use at all depths in the sea. The bottle
described by Theiler appears to be the simplest and least expensive
of them. For use in fresh water a Meyer's bottle (Fig. 24) serves
fairly well and is easily made. A stout glass bottle of one or

METHODS OF COLLECTING AND PHOTOGRAPHING 8i

two liters capacity, and with a good-sized neck is provided with a
tight rubber stopper to which is attached the draw-cord by which
the bottle is to be lowered and the stopper drawn. Beneath the
bottle is attached a weight a little heavier than needed to sub-
merge the empty stoppered bottle. The bottle may be lowered
to a depth of a hundred feet or less and the stopper removed
by jerking on the draw-cord.

E. Quantitative Study of the Net Plankton

If the plankton net were a perfect instrument it should catch
all the organisms contained in the vertical column of water through
which it is drawn, that is, in a column of the diameter of the net
opening and equal in height to the distance through which the
net is drawn. But the net filters only a part of the column of
water through which it is drawn, a part which 'depends on the age
of the net, the rate at which it is drawn and upon
the rapidity with which it becomes clogged while
being drawn. If the net is of the form described
above, is cleansed by throwing a stream of water on
it after each haul and is drawn at about the rate
of one meter per second, it filters about 40 per cent
of the column of water which it traverses. Hence,
^o know the total amount of plankton in the column
of water traversed by the net, we must multiply the
amount actually taken by two and one-half. This
number is called the coefficient of the net. The
coefficient depends on the construction of the net,
on the fineness of the gauze used, and on the rate
at which the net is drawn, and must therefore be
determined by calculation for each net for the
different rates. Not only does the net filter but a
part of the water and a different part at different
times, but it removes from the water filtered only b^otUe. Sfter

. r .-, . . , . . -r-, Wiley and Jones.)

a part 01 the organisms contamed m it. Even the
finest gauze permits a leakage through it of very many small
organisms. Owing to the sources of error indicated the net
method is useful chiefly with the larger organisms, such as crus-

82

FRESH-WATER BIOLOGY

tacea. Smaller organisms escape in variable quantity and the
smallest are not caught at all. When the pump is used a known
volume of water is drawn from a known source and all of this is
filtered, so that the source of error arising from a varying and
uncertain net coefficient is eliminated. The leakage error remains
uncorrected so long as a net is used to separate the
plankton from the water. The plankton obtained
by nets whether directly or by aid of the pump
may be treated quantitatively by the following
methods:

(a) The volume may be obtained by allowing the
alcohoHc material to stand for 24 hours in gradu-
ated tubes (carbon tubes of the chemist) until it has
settled, when the volume may be read off. There

is thus obtained in cubic centimeters the volume of

^'°'iesig^ed°b?'Hen' OHC catch and from this may be calculated the vol-
ume per cubic meter or under one square meter of
the original water.

{h) The approximate weight may be obtained by
, drying the sample on filter paper and weighing it.

by screws; m, spool- ^ o r- ir t. o c.

tSedS^'the^'TstoJ' ^^^ ^^^ weight is obtained by deducting the weight
giass?Ecc£tdy^ o^ the filter paper, and from this the number of
Snff "nd^Se glS grams of plankton per cubic meter of water or under

tube is of known vol- ^ . f , i i i. j

ume; /.piston-rod onc squarc mctcr of surface may be calculated.

sen. A. glass vessel
which contains di-
luted plankton. B,
strong glass tube. In-
side the tube is a pis-
ton made of alternate
layers of metal : and
cork h. held together

with handle; A', cover
of vessel. (From Ap-
stein, after Hansen.)

(c) Chemical analyses may be made of the dried
material and from these the quantities of the
various constituents: ash, organic material, siHca, etc., may be
calculated per cubic meter of water or per square meter of
surface.

(d) The organisms may be counted in the Sedgwick-Rafter cell.
The ordinary plankton catch is so concentrated that it is impos-
sible to count the organisms in it until it has been diluted. A
measured quantity of water added to the plankton for this pur-
pose replaces the alcohol or fixing fluid. This water is then agitated
to distribute the organisms uniformly through it and a carefully
measured sample is taken from it with a specially constructed pipette
provided with a piston (Fig. 25). The organisms in the sample are

METHODS OF COLLECTING AND PHOTOGRAPHING 83

then counted by transferring the sample to a glass cell under the
microscope. If the bottom of the cell is ruled in squares the
contents of a certain number of these may be counted without
the use of the eyepiece micrometer and the whole number present
in the cell estimated. In the case of the larger and rarer organisms
it is best to count all that the cell contains.

Since the total volume of water from which the catch was made
is known, the number of each sort of organism per cubic meter of
water or under each square meter of surface may be easily calcu-
lated, or the numbers in the entire lake may be approximately
determined.

F. Quantitative Study of the N anno plankton*
The nannoplankton may be studied in two ways, namely, by
enumerating the various organisms, or by obtaining a sufhcient
quantity to determine its dry weight. In the former method the
organisms may be counted directly, which is very desirable for
the more abundant forms, or they may be concentrated either by
filtering or by centrifuging. The filters that are most generally
used for concentration are hard surface filter paper and sand.
When filter paper is used the filtered organisms are carefully
washed from the paper, the volume of the wash water containing
the organisms is taken, and samples of it are then used for enumera-
tion. It is necessary to use hard surface filter paper in order to
prevent undue loss of organisms in the meshes of the paper. Even
with the best quality of hard surface paper, many individuals become
embedded in the meshes so firmly that they cannot be washed out.
For all counting the Sedgwick-Rafter counting cell is to be used.

The Sedgwick-Rafter sand filter as described by Whipple has
been used extensively in sanitary work. In this method also there
is a considerable loss of organisms since some of them are so small
that they pass between the grains of sand and since it is practically
impossible to separate all of the organisms from the sand after
filtration. In all filtering methods the filters soon become clogged,
which decreases the rapidity of the filtering very markedly.

* This section has been prepared by Chancey Juday of the Wisconsin Geological
and Natural History Survey.

84 FRESH-WATER BIOLOGY

The centrifuge is the most convenient as well as the most ef-
ficient instrument for obtaining the nannoplankton. A rather
high speed machine is best, one which makes 2500 or more revo-
lutions per minute, and the electrically driven type is most satis-
factory. For most fresh-water organisms the sedimentation is
complete in five to eight minutes at this speed, but occasionally
for some forms a second centrifuging is necessary. In bodies of
fresh water the nannoplankton is usually so abundant that only a
small quanrity of water, not more than 15 cc, is required for a
sample. Thus the standard makes of centrifuges will serve for
such investigations. The glass tube which holds the sample of water
should be well tapered at the bottom. This form concentrates the
material on a small area from which it can be removed more con-
veniently as well as more completely. The material is taken up
together w^th one cubic cendmeter of water in a long pipette and
is then transferred to a Sedgwick-Rafter counting cell. This cell
and its use are fully described by Whipple. Sometimes it is de-
sirable to centrifuge 50 or even 100 cc. in order to study the rarer
forms. For enumeration studies a combination of the direct count-
ing and the centrifuge methods gives the most satisfactory results.

Whenever possible, Hving material should be used for the count-
ing. The samples may be preserved in formaldehyde neutralized
with sodium carbonate and then centrifuged at a later time, but
some of the monads are recognized with difficulty after preserva-
tion. Most of the flagellates do not move rapidly enough to
oft"er any serious difficulty in counting them alive but the ciHates
do. When the latter are present, it is best to make a special count
for them. They are readily killed by placing a drop of iodine
solution in the corner of the counting cell before the sample is in-
troduced.

Material for a study of the dry weight as well as the organic
matter of the nannoplankton may be obtained either by filtering
a relatively small sample of water through a coarse-grained alundum
cone or by passing a large sample of water through a power centri-
fuge that acts continuously. In the former process the sample of
water, from one to five liters, is filtered through the cone and the
material and cone are then thoroughly dried in an oven. The

METHODS OF COLLECTING AND PHOTOGRAPHING 85

weight is taken and the cone is weighed again after having Ijeen
ignited. The loss in weight represents the organic matter.

Larger samples of material are needed for more accurate quan-
titative work, and especially for the study of the chemical com-
position of the nannoplankton. For the latter purpose at least
two or three grams of organic matter are required. In order to
secure this amount, even from a lake which is rich in plankton, it
is necessary to centrifuge one to two thousand liters of water.
This process requires an apparatus that will act continuously.
For this work the Wisconsin Geological and Natural History
Survey is using a De Laval clarifier and filter, belt style, A size,
in which the water is first centrifuged and then filtered. This
machine has a maximum speed of 6000 revolutions per minute and
will both centrifuge and filter from ten to twelve liters per minute.
In general about ninety per cent of the material is deposited in the
bowl of the centrifuge and ten per cent on the filter papers. This
method requires a special laboratory and equipment {cj. Juday,
1916).

Very little is known of the bacterial portion of the nannoplank-
ton. The culture methods used for the other bacteria do not seem
to be well adapted to the strictly aquatic forms and only a small
part of them can be obtained with a centrifuge. Recently, how-
ever, it has been found that the direct count method of Brew can
be used for determining the number and distribution of aquatic
bacteria, but no results have thus far been published.

G. Special Methods for Invertebrates

Special methods for collecting and preserving various sorts of
fresh-water organisms are described in the chapters devoted to
invertebrate groups. To secure the best results it is necessary
to become familiar with the habits of the animals. The collection
of the larv^ of aquatic insects is facilitated by the use of the
ingenious apparatus made by the Simplex Net Company. The
imagos of many such insects are readily collected at night by
some one of the forms of traps used by entomologists in which
a light serves as a lure.

86 FRESH-WATER BIOLOGY

Under-water Photography

If the water is clear and the surface unruffled, near objects may
be seen almost as clearly in natural waters as in air. If the
camera be pointed at them, the resulting picture rarely shows more
than the surface of the water, as opaque as that of milk and with as
little visible beneath it. It is as though the camera has been pointed
at the blue sky. This result is due to the light of the sky and other
distant objects retlected from the surface of the water into the
camera. This strong light, which the eye neglects, obscures in the
negative the effects of the weaker light from objects beneath the

Fig. 26. The sirr: -, v. u>e Inr photM-r.ipliiii^ wl.jcii. un i. , .1 ,..r description see text

(From an original photograph.)

surface of the water; if it be cut off by a screen these objects ma^
be photographed.

This is shown (Fig. 26) in a photograph of the nest of a black bas:
in about eight inches of water. Little can be seen beneath th(
water, except within the reflected image of the screen. Withii
this image the reflected sky light is cut off, although the sun shine:
from the left full upon the nest of clean stones. What is clear ii
the photograph lies not within the shadow of the screen but withii
its image. A longer exposure would have given a clear picture o
what Hes within the narrow shadow at the bottom of the screen
In field practice a serviceable and portable screen may be made b;
tying a square of black, opaque cloth to two poles stuck slantinj

METHODS OF COLLECTING AND PHOTOGRAPHING

«7

■

in the bottom. Occasionally dense foliage, a bridge or building is
so placed as to form a natural screen, within the image of which
photography is possible.

If the surface of the water is rough the photograph may be
made through the bottom of a water glass (Fig. 27). The glass
(Fig. 28) is a frame of galvanized
iron with a bottom of plate glass.
The bail of band iron serves to
hold the screen (Fig. 27). The
glass shown here is two feet square
and is supported on legs run
through thimbles at the corners
and held in place by set screws.
That shown in Figure 28 is a
foot square and is intended to
float. At the left is shown a
cover for the bottom of the water
glass. This protects the glass
during transit.

The difflculties arising from the
rough or reflecting surface of the
water may be overcome by placing
the camera beneath that surface.
For this purpose a reflecting camera
is to be preferred, since it permits focusing with the sensitive plate
uncovered. Any dealer in photographicgoodscan supply catalogues
of such cameras showing their mechanism. Here it need only be said
that the ground glass is placed in the top of the camera and the oper-
ator looks at it through a hood extending from the top of the camera.
He focuses the full-sized image on the ground glass and while
looking exposes the plate by pressing a button at the side of
the camera. For use under water such a camera is placed in a
water-tight box (Fig. 29), with a plate glass front through which
the lens looks. The hood of the camera extends into the pyrami-
dal Hd of the box and the operator looks into it through a second
plate of glass. A milled head, shown on the right of the box, is
connected through a water-tight stuffing box with the focusing

Fig. 27. Water glass supported on legs as used
in rough water of a brook. For description see
text. (From an original photograph.)

88

FRESH-WATER BIOLOGY

head of the camera, while a similar arrangement on the opposite
side of the box operates the mechanism which controls the expo-
sure. The operator wades and holds the box beneath the surface
of the water with only the upper part of the hood exposed. With
the right hand he focuses, with the left he makes the exposure.

/y

Fig. 28. Floating water glass. For description Fig. 29. Water-tight metal box with plate-glass
see text. (From an original photograph.) front for enclosing a reflecting camera when used

under water. For description see text. (From
an original photograph.)

After each exposure the box must be opened to change the plate.
For details the reader should consult the literature cited.

Means of Securing Collecting Apparatus

The various types of commercial nets described may be had of dealers in
fishing nets. The Simplex Net Company of Ithaca, N.Y., supplies ingenious
folding townets, plankton nets, and dip nets. The special apparatus mentioned
can be constructed by any skilled mechanic under direction.

IMPORTANT REFERENCES ON APPARATUS AND METHODS

1896.

Apstein, C.
BiRGE, E. A. 1895

FORDYCE, ChAS. ]

State Hist. Soc
IIelland-Haxsen,

(See list in Chapter I.)
(See list in Chapter I.)
898. A New Plankton Pump.
, 2: 293-296.
B. 191 2. The Ocean Waters, an Introduction to Physi-

Proc. and Coll. Neb.

cal Oceanography. I. General Part (Methods^
u. Hydrog., Hydro gr. SuppL, i. ser., Heft 2.
Hensen, V. (See list in Chapter I.)

Int. Rev. ges. Hydrob.

METHODS OF COLLECTING AND PHOTOGRAPHING 89

JUDAY, Chancey. 1896. The Plankton of Turkey Lake. Proc. Ind. Acad.
Sci., 1896. (Description of plankton net and its use.)
1904. The Diurnal Movement of Plankton Crustacea. Trans. Wis. Acad.

Sci. Arts, and Letters, 14: 534-568, 2 figs. (Clock pump and its use.)
1916. Limnological Apparatus. Trans. Wis. Acad., 18; 566-592, 5 pi.
Received too late for adequate consideration in the text.

KoFom, C. A. 1897. Plankton Studies. I. Methods and Apparatus in

Use in Plankton Investigations at the Biological Experiment Station of

the University of Illinois. Bull. 111. State Lab. Nat. Hist., 5: 1-25, 7 pi.

1898. Hints on the Construction of a Tow Net. Jour. Appl. Micros., i:

111-113, 5 figs.
1903. (See list in Chapter I.)
KoLKWiTZ, R. 1907. Entnahme und Beobachtungs-instrumente fiir biol-
ogische Wasseruntersuchungen. Mitth. Kgl. Prufungsamt f. Wasserver-
sorg. u. Abwasserbeseit. zu Berlin, Heft 9: 111-144, 22 figs.
Marsh, C. D. 1897. On the Limnetic Crustacea of Green Lake. Trans.

Wis. Acad., 11: 179-224, 10 pi. (Description of closable net.)
Needham, James G. 1903. An Outdoor Equipment for College Work in
Biology. Am. Nat., 37: 867-874, 2 figs. (Description of plankton ap-
paratus.)
Reighard, Jacob. 1894. (See list in Chapter 1.)

1898. Methods of Plankton Investigation in Their Relation to Practical
Problems. Bull. U. S. Fish Comm., 17: 169-175.

1908. The Photography of Aquatic Animals in their Natural Environment.
Bull. U. S. Bureau Fish., 27: 41-68, 4 pi.

1909. An Experimental Field Study of Warning Coloration in Coral Reef
Fishes. Carnegie Inst., Washington, Publication 103: 257-325, 5 pi.
(Contains reproductions of photographs made with camera under water.)

1910. Methods of Studying the Habits of Fishes, with an Account of the
Breeding Habits of the Horned Dace. Bull. U. S. Bureau Fish., 28:
1111-1136, 7 pi.

RuTTNER, Franz. 1914. Ueber einige bei der Untersuchung der Lunzer Seen
verwendeten Apparate und Geratschaften. Int. Rev. ges. Hydrob. u.
Hydrog., 6: 53-62, i pi.

Steuer. 1910. (See list in Chapter I.)

Theiler, a. 1914. Ein neuer Wasser- und Planktonschopfer nach Fried-
inger. Int. Rev. ges. Hydrob. u. Hydrog. Biol. Suppl. Band 6, Heft 4.

Ward, H. B. 1896. (See list in Chapter I.)

Ward, R. H. 1895. Improved Methods of Collecting Aquatic Micro-organ-
isms. Amer. Mo. Micr. Jour., 16: 33-4 1> i P^-

Whipple, G. C. (See list in Chapter I.)

WoLCOTT, R. H. 1901. A Modification of the Birge CoUecting Net. Jour.
Appl. Micros., 4: i407-i409» 4 figs.

CHAPTER IV
BACTERIA

By EDWIN O. JORDAN

Professor of Bacteriology in the University of Chicago

Bacteria are unicellular organisms, for the most part very
small. Considerable differences in size, however, are observed.
A certain large, rod-shaped species studied by Schaudinn measures
from 50M to 60/X in length and from 4/i to 5)u in width. On the
other hand the bacillus of influenza averages about 0.5^ in
length and 0.2/x in width. The average rod-shaped bacterium,
such as is found in water and soil, measures about 2^ in length
and about 0.5^ in diameter. Some microorganisms are known
to exist which are so small that they will pass through the pores of
the finest Berkefeld filter and remain invisible under the most
powerful lenses, but it is not surely established that all these so-
called ultramicroscopic organisms belong to the group of bacteria.

For the methods of studying bacteria, special laboratory man-
uals or guides should be consulted. A number of such guides are
in existence, among which may be mentioned Heinemann (191 1)
and Frost (1905). In any case a proper familiarity with laboratory
methods can be gained only with the assistance of a skilled labora-
tory instructor possessed of individuality and resource.

Bacteria are generally classed as plants rather than animals,
but, as is well known, the dividing line between animals and plants
is an entirely arbitrary one, and there is no general agreement
among naturalists respecting what shall constitute a determina-
tive plant or animal characteristic. It is largely considerations of
convention and convenience that place them among the plants.
From their lack of chlorophyl and the fact that they multiply by
division or fission the bacteria are classed as Schizomycetes or fission
fungi.

Within the group of bacteria themselves classification is, for
practical purposes, especially important, but because they are so

90

BACTERIA 91

minute in size and the observable differences in structure are so
slight, any classification grounded on morphological characters,
such as that of Migula (1897), meets with many difficulties, and
would seem at present to be premature. Because of the great prac-
tical importance of physiological quaUties, bacteriologists have
come to lay great stress upon bacterial functions, and considera-
tions of convenience have often led to groups being established on
physiological characteristics. The practice of dealing with bacteria
in related groups is growing. For the identification of specific and
group characters the Report of the Committee of the Society of
American Bacteriologists on Method of Identification of Bacterial
Species should be consulted.

The forms of bacteria are very simple. The complex and elabo-
rate structures found among certain other groups of unicellular
organisms (diatoms, desmids, radiolaria) do not occur among bac-
teria. Three principal type forms are recognized: the sphere
(coccus or micrococcus), the rod (bacillus), and the spiral (spirillum

Fig. 30. Forms of Bacteria.

and spirochsete) (Fig. 30). Closely resembling these are certain
filamentous organisms known as Trichomycetes, which connect the
bacteria with the higher fungi or moulds.

The minute size of bacteria renders the study of their liner
structure somewhat difficult, but a few features have been clearly
determined. Most species, perhaps all, are provided with a cap-
sule or outer layer of gelatinous substance originating from the
cell-membrane and seen in stained preparations surrounding the
cell like a halo. The capsule is much more prominently developed
in some species than in others. The cell-memhrane is chiefly re-
markable for its chemical composition, differing as it does from the
cell-membrane of the higher plants in not being composed of cel-
lulose. The nature of the cell-substance of bacteria has been the
object of much discussion from the standpoint of its relation to the

92

FRESH-WATER BIOLOGY

nuclear substance of higher cells. It has been held by different
observers that a bacterial cell is to be compared either to a free
nucleus or to an unnucleated mass of cytoplasm, but these views
have now been practically abandoned. It seems to be clear from
the researches of recent investigators that the chromatin substance
instead of being gathered together in a definite nucleus, as in the
cells of most higher forms of life, is fragmented and distributed
irregularly through the body of the cell. The bacterial chromatin
is usually present in great abundance, varies in amount and in
position in different kinds of bacteria and occurs most frequently
in a finely-divided condition. Not only are particles of chromatin
scattered through the cell, but other granules that react to stains
in special ways are present in the cell substance, particularly in
certain species. The physiological significance of these so-called
metachromatic granules, as they occur for example in the diphtheria
bacillus, is unknown, but it seems probable that they are to be
looked upon as reserve food substances.

Many forms of bacteria show independent movement, distinct
from the oscillating or trembling movement exhibited by all minute
particles suspended in water and known as the Brownian movement.
The power of motility depends upon the possession of long, fragile,
filamentous appendages termed flagella. In the case of certain
large spirilla, flagella can be seen on the living, unstained cell, but
ordinarily special methods of staining must be applied to demon-
strate their presence. The position of the flagella on the cell body
differs in different species. Some species possess a single flagellum
at one pole, as is the case with the cholera spirillum ; others have a
flagellum at either pole; others have polar tufts of flagella; and
still others possess flagella attached to the sides as well as the
ends of the cell (typhoid bacillus) (Fig. 30). In certain nonmotile
bacteria, such as the anthrax bacillus, no flagella have been observed.

Under certain conditions some bacteria pass from the ordinary
or vegetative stage into a highly resistant state, known as a spore
or endospore. The spores of bacteria are approximately spherical or
oval, are stained with great difficulty with the ordinary aniline
dyes and resist destructive agencies, such as heat and chemical
disinfectants, much better than the vegetative forms from which

BACTERIA 93

they spring. A single cell, as a rule, gives rise to but one spore, so
that spore formation can not be looked upon as a process of multi-
plication. It is generally considered that the bacterial spore is a
resting stage, physiologically similar to an encysted amoeba and
serving to tide the species over a period of hard times. Not all
bacteria are spore producing; in fact the number known to form
spores is rather limited.

Great adaptabiUty is shown by bacteria to extremes of tempera-
ture. Some species have been found multiplying in the water of
polar seas at or near the freezing point, while others have been
found living in the water of hot springs at a temperature of 79° C.
Most of the ordinary bacteria found in pond or river water multiply
abundantly at a temperature of about 20° C. When water is
frozen, most of the bacteria that it contains are killed at once. A
small proportion survive, but in gradually diminishing numbers,
so that at the end of a few weeks clear ice is practically sterile.
Bacteria contained in masses of organic matter, however, may
have their life in ice considerably prolonged.

Bacteria not only adapt themselves to great extremes of tem-
perature, but to varied sources of food supply. Many species can
content themselves with relatively simple chemical compounds,
such as the ammonium salts of the organic acids. Others require
for their development complex nitrogenous substances. The nitri-
fying bacteria, so abundant in most soils and waters, obtain the
energy necessary for their development altogether from inorganic
compounds. On the other hand, certain bacteria are entirely
dependent upon particular organic compounds present in the bodies
of the higher animals, and can thrive only in the presence of blood
serum or similar fluids.

Fundamental differences exist among bacteria in respect to their
relative need for oxygen. Some, the obligatory aerobes, require free
oxygen for the maintenance of their life activities, while others, the
obligatory anaerobes, do not grow except in the almost complete
absence of free oxygen. There are also some, the facultative anaer-
obes, that can multiply either in the presence or absence of free
oxygen. The anaerobic bacteria, as a class, thrive best in the pres-
ence of substances capable of undergoing reduction or fermentation.

94 FRESH-WATER BIOLOGY

The addition of glucose or nitrate, for example, to ordinary nutrient
broth will enable certain species of bacteria to grow under condi-
tions otherwise unfavorable. The relation between anaerobic Hfe
and food supply is an intimate one. The anaerobes, in a word, are
those organisms able to obtain their needed energy from the simple
splitting of organic compounds without oxidation. If a microorgan-
ism is so specialized to an anaerobic mode of life that the presence
of oxygen, except in minute quantities, interferes with its habitual
method of attacking food substances, it is an obligatory anaerobe.
In a modified form, therefore, Pasteur's conception of fermentation
as "hfe without air" is not very far from the modern view.

Those decompositions of organic substances that are usually
termed putrefactions and are characterized by the evolution of
malodorous gases such as hydrogen sulphide and the production of
substances like skatol, indol, mercaptan, etc., are due to the agency
of anaerobic bacteria. In fact, researches indicate that the putre-
factive decomposition of native proteins is wholly the work of the
obligatory anaerobes. As is well known, the ooze at the bottom oi
ponds and streams is peculiarly the home of such anaerobic decom-
positions.

Bacteria are everywhere present in natural bodies of water.
They are more abundant as a rule in surface waters than in ground
waters. Deep well waters and spring waters in certain regions
often contain very few bacteria, perhaps only five to ten per cubic
centimeter, while the water of lakes and ponds usually contains
several hundred, and ordinary river water contains numbers that at
times rise into the thousands and tens of thousands. As a general
rule, sewage-polluted waters contain more bacteria than pure waters.
An excessively polluted stream, such as the Chicago River once
was, may hold as many as several milHon bacteria per cubic centi-
meter.

The number of bacteria in a river water varies greatly at differ-
ent seasons of the year, being generally larger in the colder months
than in summer. Probably this is due in part to the winter in-
crease in current caused by rains and melting snows which prevents
sedimentation; in part to the heavy rains of winter which wash into
a stream numberless germs from cultivated lands, and partly also

BACTERIA 95

to the lower temperature of the water in winter which favors
the continuance of bacterial vitality. In highly-polluted rivers the
processes of decomposition are retarded by cold weather; in con-
sequence, bacteria together with their food substances travel for a
greater distance down stream in winter than in summer. This
condition has been shown to exist, for example, in the Illinois
River which is heavily polluted with Chicago sewage.

Besides these important seasonal fluctuations, daily and hourly
changes may be noticed, depending upon the amount of rainfall,
the velocity of the current, the direction and force of the wind and
perhaps the germicidal action of sunlight. For these reasons, it is
necessary, in order to interpret correctly the sanitary significance
of the bacterial content of any body of surface water, to make re-
peated examinations under a variety of circumstances and with
particular attention to the effect of modifying conditions. In the
case of ground waters (wells, springs, etc.), the number of bacteria is
less affected by changes in external conditions, but here also great
caution is necessary in drawing conclusions from a limited number
of observations.

The following table gives some conception of the number of
bacteria that may be found by the gelatin plate method in various
bodies of water. Great variations occur and any such tabulation
can have only an approximate value.

Per cubic centimeter

Sewages or sewage-polluted waters 100,000 to 1,500,000

Rivers not highly polluted 1,000 to 10,000

Lakes and ponds not highly polluted 100 to 1,000

Pure spring waters 5 to 50

The enormous number of bacteria which such figures show to be
present in all natural bodies of water comprises many different
kinds. There is no special and characteristic class of " water
bacteria," but germs from the air, from the soil, from decomposing
animal and plant substances and from the healthy and diseased
tissues of animals and plants may at times hnd their way into
water. The bacterial flora of a given stream or pond is therefore

g6 FRESH-WATER BIOLOGY

constantly changing, and varies from time to time not only in the
number, but in the nature of the individuals composing it (Fig. 31).
Little work has yet been done upon the changes in the kinds of
bacteria in river or lake water due to the shifting seasons and other

factors, but there is no doubt
that important differences do
exist. Many varieties of bac-
teria have been isolated from
water. During the course of
a study of the bacteria in the
water of the IlHnois River
the writer found that out of
543 cultures, 17 well-defined
groups and 41 subgroups were
represented. These groups
include a number of pigment-
, . . producing or chromogenic

Fig. 31. — Photograph of "plate culture," showing ^ ° r i • i

different kinds of bacterial colonies. (Original.) formS, SOmC of whlCh arC

among the most common inhabitants of water, and also a number
of bacterid closely related to organisms associated with the
production of disease in the higher animals. Among the bacteria
commonly found in natural waters may be mentioned B. fluo-
rescens vars. liqiiejaciens and non-liqiiefaciens (the green water
bacillus), B. suUilis (the hay bacillus), B. mesentericus (the potato
bacillus), B. proteus and B. cloacae (commonly associated with the
decomposition of vegetable and animal matter), B. liquefaciens,
B. hyalinus, B. violaceiis, and many chromogenic and non-chromo-
genic micrococci; in polluted waters, B. coli is usually found in
large numbers and organisms of the B. proteus t^^De and strepto-
cocci are more abundant than in normal waters.

It is well known that the germs of several of the principal infec-
tious diseases of man are commonly conveyed in drinking water.
Typhoid fever and Asiatic cholera are familiar examples. Both
the typhoid bacillus and the cholera spirillum have been found in
water, although, partly because the technical difficulties of investi-
gation are considerable, partly because the longevity of these
organisms in water is Umited, positive findings have not been very

BACTERIA 97

frequent. Under ordinary conditions there is no reason to suppose
that pathogenic bacteria multiply in water or that they retain
their vitahty for more than a few weeks. In polluted soil, however,
they may Uve much longer than in water, and a river may be con-
tinuously polluted during a long period by bacteria that are washed
into it from accumulations of fecal material. Other pathogenic
bacteria occasionally water-borne are the dysentery bacillus and
the anthrax bacillus.

Since the search for specific pathogenic bacteria in a water is
hardly ever likely to be crowned with success, various indirect
means for determining the purity of a water have been proposed.
The most useful of these analytical methods is the test based on
the determination of the relative number of Bacillus coll. This,
the colon bacillus, is a normal inhabitant of the healthy human
intestine and is found in large numbers in fresh sewage where, by
appropriate methods, it is usually detected in each -j o o o o ^■^- ^^~
amined. Since it is also present in the droppings of many of the
larger domestic animals and hence occurs in garden soil and in
pastures, its occasional presence in water does not necessarily in-
dicate possible or even probable pollution with fecal matter of
human origin. The researches of many investigators, however,
have shown that the relative abundance of Bacillus coli in water
is a very satisfactory criterion of the sanitary quahty of such a
water. If, for example, it is found uniformly present in a water in
each I c.c. sample, the water is looked upon as distinctly suspicious.
In cases, however, where it is rarely found in i c.c. samples and
only occasionally when quantities as large as lo c.c. or even 50 c.c.
are examined, the water is usually considered potable.

The bacteria in water stand in important relations to the life of
other aquatic plants and animals. It is a familiar fact that but for
bacterial activity the nitrogen and carbon in complex organic com-
pounds once bound would remain forever locked up and unavail-
able for the nutrition of other forms of Hfe. As is well known also,
the first steps in decomposition or the breaking down of organic
substances are due to bacterial agency. Ammonia and ammoni-
acal compounds are among the chief nitrogenous products of tliis
decomposition. The processes of disintegration and oxidation do

q8 fresh-water biology

not end with the production of such a relatively simple compound as
ammonia. Further oxidation of the ammonia to nitrites takes
place and the nitrites in turn are oxidized to nitrates. The for-
mation of nitrites and nitrates, Hke the formation of ammonia, is
due to bacterial activity; this process is known as nitrification.
Special and peculiar varieties of bacteria are concerned in the proc-
ess of nitrihcation. One species is able to oxidize ammonia to
nitrite, but is unable to carry the process of oxidation any further.
At this stage of decomposition a second species takes up the work
and completes the process by oxidizing the nitrites to nitrates.

If we follow the fate of the nitrogen introduced into a sewage-
polluted river, we find that there occurs first a breaking down of
the albuminous compounds and a consequent increase in the
amount of "free ammonia" in the water; further down, nitrites
begin to appear and eventually nitrates are found. A river water
in which the process of nitrification has occurred and which is
therefore rich in nitrates affords a peculiarly favorable medium
for the growth of plant Hfe and often ''blooms" with a myriad of
microscopic algae. The presence of a multitude of algae in-
fluences in its turn the Hfe conditions of aquatic protozoa and of
higher animal organisms. At times when through the advent of
low temperature or other unfavorable conditions the algae die off,
the albuminous compounds constituting their dead bodies undergo
decomposition; ammonia, nitrites, and then nitrates are again
formed, and the nitrogen cycle begins anew. The food supply of
the whole plankton of fresh-water streams and ponds is therefore
dependent upon the activity of bacteria, and the share of these
organisms in producing or modifying the conditions under which
all aquatic life is possible can never be ignored.

BACTERIA 99

IMPORTANT REFERENCES ON BACTERIA

Clemesha, W. W. 191 2. The Bacteriology of Surface Waters in the Tropics.
London.

HoRROCKS, W. H. 1901. Introduction to the Bacteriological Examination
of Water. London.

Houston, A. C. 1913. Studies in Water Supply. London.

Jordan, E. 0. 1903. The Kinds of Bacteria Found in River Water. Jour-
nal of Hygiene, 3:1.

MiGULA, W. 1900. System der Bacterien. Jena.

OHLMtJLLER and Spitta. 1910. Wasser u. Abwasser. 3d ed., Berlin.

Prescott and Winslow. 1913. Elements of Water Bacteriology. 3d ed.,
New York.

Report of the Committee on Standard Methods of Water Analysis to the
Laboratory Section of the American Public Health Association.

Savage, W. G. 1906. Bacteriological Examination of Water Supplies.
London.

CHAPTER V
BLUE-GREEN ALGAE (CYANOPHYCEAE)

By EDGAR W. OLIVE

Curator of the Brooklyn Botanic Garden

The blue-green algae are found principally in fresh waters,
although numerous forms occur also in the sea, and are almost
universally distributed over the whole earth. In moist climates
they are particularly abundant, growing in almost every conceiv-
able situation as gelatinous masses or strata on rocks, stones, the
trunks of trees, damp ground, etc. Many of them occur abun-
dantly in both marine and fresh-water plankton. The peculiar
phenomenon of 'Svater-bloom" (or 'forking" or ''blooming" of
the lakes, "breaking of the meres," "Flos aquae," " Wasserblute ")
is due to the sudden appearance in lakes and ponds of a surface
scum formed of vast quantities of certain plankton species of these
organisms. This frothy scum, forming the so-called "water-
bloom," is of common occurrence in midsummer in quiet waters,
especially after a protracted period of heat. Disagreeable "pig-
pen" odors and bad tastes are caused by such masses when decay
sets in, due, according to Jackson and Ellms, to the decay of highly
nitrogenous organic matter in which partially decomposed sulphur
and phosphorous compounds play a large part. The occurrence of
blue-green algae in pubHc water supplies often thus becomes of
great economic importance; and Moore has found in this connec-
tion that such algal growths in reservoirs may be readily eradicated
or their growth prevented by the use of a dilute solution of copper
sulphate.

In addition to their importance as polluting organisms in water
reservoirs, some recent observations appear to indicate that cer-
tain plankton forms of blue-green algae are sometimes used as food
by fish fry. Their indirect importance in this respect may be
regarded as well established, since Birge has shown that the com-

BLUE-GREEN ALGAE lOi

mon plankton Crustacea, which themselves form the basis of the
food of many small fishes, depend to a great extent upon Aphani-
zomenon, Anabaena, and other blue-green algae for their own sus-
tenance.

Some species of Cyanophyceae have become adapted to living in
hot springs; these organisms, in fact, together with certain sulphur
bacteria, constituting the sole organic hfe of thermal springs.
According to the careful observations of Setchell, the blue-green
algae grow in some abundance in thermal waters up to 68° C,
and scantily in springs showing a temperature as high as 75°-
77° C.

The varied colors — shades of yellow, orange red, pink, blue,
and blue green — shown by the siliceous deposits around certain
hot springs of the Yellowstone Park, are due in great part to the
presence of brilliantly colored blue-green algae within the deposit.
Weed has discussed the part played by these algae in the formation
of carbonaceous and siliceous rocks about hot springs.

Some of the Cyanophyceae, principally of the genera Scytonema,
Stigonema, and Nostoc, are found associated with certain fungi to
form lichens; while still others, notably Nostoc and Anabaena, occur
regularly endophytically in the roots of Cycads and in the leaves
of Azolla and other water plants.

Like the bacteria, with which these algae are supposed to show
close relationship, most of the Cyanophyceae possess cell walls
which become much swollen and mucilaginous in their outer layers.
Thus most of the filamentous forms become invested in either a
thin mucous sheath or a tough, lamellose sheathing tube. Many
of the colonial forms consist of masses of cells embedded in a thick,
jelly-like matrix, the external surface of which is often covered
with a thin cuticle.

Much dispute has arisen in recent years as to the nature of the
contents of the cells of these algae. On examination with the
compound microscope, one usually notes a number of granular
bodies, apparently of two kinds — numerous small granules and a
few larger, clear ones. In the shorter-celled species, the smaller
and more numerous granules frequently He in regular double rows,
on either side of the cross walls which separate the cells. In the

I02 FRESH-WATER BIOLOGY

longer-celled forms, such as Nostoc and Tolypothrix, the small
granules generally occur abundantly in all parts of the peripheral
protoplasm. These minute granules are generally regarded as the
"cyanophycin granules" (Borzi), and they are probably albumi-
nous in their nature and serve as reserve food. The few larger
granules mentioned above are more hyaline and transparent than
the cyanophycin granules, and they appear to lie in or near the
center of the cell. These larger granules have been called by
Palla ''slime globules"; by Zacharias "Centralkorner." Their
function is in dispute.

The cells of favorable forms of the blue-green algae, e.g., Oscil-
lator ia, show two more or less evident portions of the protoplasm —
a peripheral layer, to which the pigment is confined and in which
the cyanophycin granules lie, and a central colorless part, the
so-called ''central body." The majority of recent studies on the
subject maintain that the central body is a nucleus, although this
conclusion has been several times disputed. Carefully stained,
thin sections show, however, that it is made up of both chromatic
and achromatic substances. Moreover, Macallum and others find
in the central body complex proteid substances containing phos-
phorus and "masked" iron to a marked degree, which they regard
as characteristic constituents of chromatin. Fischer claims, how-
ever, to have demonstrated by means of a tannin-safranin stain
that the central body is filled with certain carbohydrates, of the
nature of glycogen.

The central body divides according to some, by simple amitotic
di\dsion; while others beHeve that the division is mitotic. At any
rate, the division of this nucleus, or central body, precedes the
division of the cell, and, as in other lower plants, the two processes
appear to take place independently of each other. Cell division is
accomplished in these forms in the same manner as has been
described for many other filamentous Thallophytes, by constric-
tion: a ring-formed wall grows in from the outer wall, similarly to
the closing of an iris diaphragm, and finally cuts the cell in two.

The varying shades of color shown by these organisms are caused
by varying mixtures of the green chlorophyll and the reddish or
bluish phycocyanin, the pigments being apparently confined to

BLUE-GREEN ALGAE 103

the peripheral cytoplasm. The phycocyanin may readily be ex-
tracted by killing the plant, when the plasma membrane at once
allows the dissolved pigment to pass out through the cell wall.
When plants are dried and pulverized, then soaked in water, a
solution of the bluish coloring matter is thus readily obtained. A
quicker method is to place the blue-green algae in chloroform water
(made by shaking up a small quantity of chloroform in water,
allowing it to settle, then decanting the water, which is then used
in the experiment), or in water containing a few drops of carbon
bisulphide, for a short time. Death of the plants at once ensues
and the dichroic phycocyanin passes out into the surrounding
water, leaving the filaments bright green from the remaining chlo-
rophyll pigment.

Sap vacuoles occur sometimes in the cells of the Cyanophyceae,
particularly in the older elongated cells of such forms as Tolypo-
thrix and Calothrix. Another kind of vacuole, filled with gas, is
said by Klebahn and others to occur in certain free-floating blue-
green algae, such as Coelosphaerium, Anabaena, and Oscillatoria,
when they rise to the surface to form water-bloom. These authors
regard the so-called gas vacuoles as directly concerned with the
floating capacity of the algae which possess them; their contentions
have been disputed a number of times, however, and the gas
vacuole theory is regarded by many as untenable.

Sexual reproduction is unknown among the blue-green algae.
Asexual multiplication takes place in the simpler forms by cell
division and subsequent separation of the daughter cells. In the
higher, filamentous Hormogoneae, short one- to few-celled fila-
ments, knoJWTi as hormogonia, are regularly set free and these frag-
ments form new plants. Spherical or cylindrical resting spores are
formed in some species by the growth in size of the vegetative cells
and by the thickening of the walls.

Heterocysts are special cells developed in some forms from ordi-
nary vegetative cells, whose significance is not well understood.
Their protoplasmic contents apparently soon die and one or two
polar thickenings appear in the cell. Undoubtedly they are at
times connected with the breaking up of the filaments, but in some
cases they normally occur at the basal ends only of the filaments.

I04

FRESH-WATER BIOLOGY

A few of the Cyanophyceae show remarkable oscillating, gliding,
or rotating movements, the cause of which has never been satisfac-
torily explained. In Oscillatoria and Spirulina, these movements
are particularly conspicuous.

CYANOPHYCEAE

(myxophyceae, phycochromophyceae, schizophyceae)

Algae possessing more or less of a blue-green color; free-floating or living in
gelatinous masses or strata; sexual reproduction unknown, reproducing asexu-
ally by means of cell division, the daughter cells either soon separating into
more or less independent cells, or remaining adherent to form tilaments or
plates or solid colonies. The vegetative cells each made up of two more or
less easily distinguishable parts: a colored peripheral cytoplasm, which contains
the bluish or reddish phycocyanin, in addition to the chlorophyll pigment, and
also generally a number of minute granular bodies — the "cyanophycin gran-
ules"; and the colorless ''central body," which is the nucleus of the cell.
Embedded in the central body, in addition to the chromatic and achromatic
substances, there usually occur a few large, globular, transparent bodies —
the so-called "slime globules." Sap vacuoles sometimes occur in the cyto-
plasm. Thick-walled resting spores are formed in some species; heterocysts
are also found in certain forms, which are peculiar cells, whose protoplasmic
contents apparently soon die and whose significance is but Uttle understood.

1 (25) One-celled plants, hving either free or united into colonies by

being embedded in a common gelatinous matrix.

Order Coccogoneae Thuret . . 2

2 (24) Cells generally free-floating or forming a gelatinous stratum; not

differentiated into base and apex.

Family Chroococcaceae . . 3
3(8,11) Cell division in one plane only 4

4 (7) With wide mucous covering 5

5 (6) Cells elongate, each with a special mucous coat. Gloeothece Nageli.

Cells oblong or cylindrical, with thick, sometimes lamel-
lose, gelatinous membrane; single or united into micro-
scopically small colonies, which are enclosed after the
manner of Gloeocapsa within the gelatinous membrane of
the mother cell. On wet rocks, rarely floating.

Fig. 32. Gloeothece confltuns Nageli. X 4So. (After West.)

6 (5) Cells httle longer than broad, many adhering together to form
large, irregular colonies, enclosed by a common mucous
matrix Aphanothece Nageli.

Cells oblong, dividing only at right angles to the long
axis; forming irregular, gelatinous colonies which some-
times grow to be an inch or more in diameter. At
margins of lakes and on wet rocks.

Fig. 33. Aphanothecemicroscopica'Na.gtU. X 1000. (Original.)

BLUE-GREEN ALGAE 105

7 (4) Cells with thin cell walls Synechococcus Nageli.

Cells comparatively large, cylindrical or ellipsoidal, living
usually singly or sometimes forming small families of two
to four united in a row or chain. Cell-contents blue-green,
sometimes yellowish, pinkish, or pale orange. Free-floating
in ponds and pools, or on rocks.

Fig. 34-

Synechococcus aeruginosus
Kirchner.)

Nageli. X 575- (After

8(3,11) Cell-division in two planes 9

9 (10) Cells spherical or oblong, forming flat, plate-like colonies.

Merismopedia Mey en .

Cells usually adhering in groups of four, and arranged in reg-
ular rows to form a flat, rectangular, plate-like colony. In
plankton, in ponds, and lakes.

Fig. 35. Merismopedia elegans ^..'QtdiXin. X 450. (After West.)

10 (9)

11(3,8)

12 (23)

13 (16)

14 (15)

Cells flat, quadrangular in outline, sohtary, or forming small

colonies Tetrapcdia Reinsch.

Cells with thin membrane; solitary or united into flat colonies of 2 to 16
cells.

Cell-division in three planes 12

Cells united into definite, often comparatively large colonies. 13

Colonies more or less regularly spherical 14

Colonies hollow; cells closely and regularly arranged at the surface.

Coclosphaeriiim Xageli.

Cells globose or oblong, forming on the surface of lakes and
ponds microscopically smaU, hollow, spherical colonies em-
bedded in a mass of mucus; reproduction by means of single
cells escaping from the colony as well as through the con-
striction of old colonies to form new ones. Common in fresh-
water plankton.

Fig. 36. Coelosphaeriutn kutzingianum Nageli. X 465- (Original.)

Colonies solid; cells sparsely scattered through the jelly, pyriform
in shape Gomphosphacria Kiitzing.

Cells enclosed by a colorless gelatinous matrix to form micro-
scopically smaU, solid, globular, or ellipsoid colonies; the peripheral
cells grouped in pairs and egg-shaped or pyriform, or (during
division) heart-shaped. In ponds,^ stagnant water, etc.

Fig. 37. Gomphosphaeria aponina Kiitzing. X 465- (Original.)

16(13) Colonies, when old, generally not spherical i?

17 (18, 19) Colonies microscopically small, solid, globular, or clustered.
' ^ "^ Microcystis Kutzing.

(Probably should be united with Clathrocystis .) Cells spherical, or through
pressure somewhat angular; uniting in great numbers to form microscopic-
ally small solid colonies. Common in ponds and ditches.

15 (14)

io6

FRESH-WATER BIOLOGY

1 8 (17, 19) Colonies at first globular, later irregular in shape, and perforated
or netted Clathrocystis Henfrey.

Cells spherical, united in great numbers to
form at first globular, later irregular colonies,
which often become clathrate, forming an open
meshwork. Common in lakes and ponds; C.
aeruginosa Henfr. is often thrown upon rocks
along shores to form, mixed with Coelosphacrium
kiitzingianum Niig., the so-called "green paint."

Fig. 38.

Clathrocystis aeruginosa Henfrey. X 465.
(Original.)

19 (17, 1 8) Colonies irregular in shape, frequently forming films 20

20 (21, 22) Individual mucous coats clearly evident for each daughter cell of

the colony Gloeocapsa Ktitzing.

Cells spherical, with thick, often
lamellose, gelatinous membrane;
solitary or generally united into
microscopic colonies in which the
membranes of the daughter cells
remain enclosed for a long time
within that of the mother-cell.
Forming gelatinous substrata on
moist walls and wet and dripping
rocks.

Fig. 39. Gloeocapsa polydermatica
Kiitzing. X 465. (Original.)

21 (20, 22) Cells enveloped in a common gelatinous matrix.

Aphanocapsa Nageli.

Cells globose, forming irregular colonies enclosed
in a thick, homogeneous integument. Differing from
Aphanothece only in its globose cells. In stagnant
water, on wet rocks, etc.

Fig.

Aphanocapsa grevillei Rabenhorst.
(After West.)

X450.

2 2 (20, 21) Cells globose, reddish purple, arranged in a thin gelatinous stra-
tum Porphyridium Nageli.

Common on damp ground and at the base of damp walls.

23 (12) Cells solitary or a few adhering together in a group, not forming a
definite layer Chroococcus NageH.

Cells globose or somewhat angular, with firm, often thick,
lamellose or homogeneous membrane. Free-floating, or forming
a stratum on wet rocks.

Fig. 41. Chroococcus giganUus West. X 300. (After West.)

BLUE-GREEN ALGAE

107

24 (2) Cells epiphytic; with a distinct base and apex.

Family Chamaesiphonaceae.
Only one genus. . . Chamaesiphon A. Braun and Gninow.

Cells small, ovoid, pyriform, or cylindrical; attached
by their base and generally widening upwards to their
free apex. Solitary or aggregated; sheaths present;
cell walls very thin; cell contents homogeneous, blue-
green, violet, or yellow; reproduction by one-celled,
non-motile cells which are successively cut off from
the upper portion of the plants, gradually escaping
from the open apex. Common on Oedogonium and
other algae in ponds.

Fig. 42. Chamaesiphon incrustans Grunow. X 800.
(After West.)

25 (i) Plants filamentous; filaments simple or branched; consisting of

one or more rows of cells generally enclosed within a more
or less evident sheath. Asexual reproduction by means
of hormogonia, and more rarely by spores.

Order Hormogoneae Thuret . . 26

26 (64)

Filaments cylindrical, sometimes narrowed at the extremities.

Suborder Psilonemateae . .

27

27 (53) Filaments not branched 28

28 (43) Filaments consisting of a single row of cells, seldom {Spirulina)

one-celled; not branched; heterocysts absent; sheaths vari-
able, more or less gelatinous, and sometimes enclosing more
than one filament. . . . Family Oscillatoriaceae . . 29

29 (39)

30 (31)

Never more than one filament within a sheath.

• Subfamily Lyngbyeae .

30

Filaments apparently one-celled, coiled into a regular spiral, often
showing rapid rotatory movements. . . Spirulina Turpin.

Filaments very narrow, consisting of a single
elongated cell, sometimes of great length, regularly
spirally coiled; sometimes showing rapid oscillat-
ing and rotatory movements. Common in stag-
nant water.

. Fig. 43. Spirulina major Kiitzing.
inal.)

X 1000 (Orig-

31 (30) Filaments many-celled 3^

32 (36) Filaments simple, generally showing oscillating and gliding move-

ments; sheaths thin, hyaline, sometimes not evident. . 33

[o8

FRESH-WATER BIOLOGY

33 (34- 35) Filaments more or less confluent by their mucous sheaths.

Phormidium Kiitzing.

Filaments many-celled, straight or bent; en-
closed in hyaline sheaths which frequently become
adherent 10 form an expanded stratum on wet
rocks or moist earth, or entirely submerged.
Usually this stratum is soft and slimy, but it
sometimes becomes hard and leathery. A genus
intermediate in character between Lyngbya and
Oscillaioria.

Fig.

44. Phormidium subfuscum Kiitzing. X 575-
(After Kirchner.)

34 (33 ' 35) Filaments generally without conspicuous sheaths; free, straight, or
with curved extremities Oscillatoria Vaucher.

Tr?=

x

Filaments composed of numerous
short cylindrical cells, the end cell some-
times much attenuated; without a
sheath or with an almost imperceptible
one; generally showing lively creeping
and oscillating movements. Found in
great profusion in all kinds of wet situ-
ations; sometimes free-floating at the
surface of lakes and ponds, or forming
filmy growths on wet soil or rocks.
0. limosa is extremely abundant on the
soil, etc., in greenhouses, while O. Pro-
lifica occurs in the plankton of some lakes in such quantities as to impart
a reddish or purplish color to the water and occasionally to form a "water-
bloom." The latter species has been found in some instances to persist even
into the winter and to color the ice a reddish or pinkish color.

B

Fig. 45. A, Oscillatoria prolifica Gomont. B. Oscillatoria
limosa Agardh. X 465- (Original.)

35 (33' 34) Filaments without sheaths, twisted into a regular spiral.

Arthrospira Stizenberger.

Filaments commonly without a sheath, differing from
Oscillatoria in being regularly spirally coiled, and from
Spiridina in being many-celled. Living singly or form-
ing dark-green slimy strata in stagnant water.

Fig. 46. Arthrospira jenneri Stizenberger. X 500. (After
Gomont.)

36 (32) Filaments not showing oscillating movements; sheaths firm. . 37

37 (38) Filaments free and simple, free-floating or forming an expanded
stratum Lyngbya C. Agardh.

Filaments many-celled, straight or bent,
each enclosed in a firm, generally hyaline,
sometimes lamellose, membrane, i'ree-float-
ing, or forming densely intricate, floccose
masses, or an expanded stratum. Frequently
abundant in plankton.

Fig. 47. Lyngbya major Meneghini. X 465-
(Original.)

BLUE-GREEN ALGAE 109

38 (37) Filaments forming erect tufts, often branched. . Symploca Kiitzing.

Filaments densely interwoven to form a slimy substratum from
which arise erect tufts of variable height. Sometimes more or less
procumbent. False branches solitary; sheaths thin, colorless, firm
or somewhat mucous; apex of the filament straight, sometimes a little
tapering; outer membrane of tlie apical cell slightly thickened in
some species. In hot springs, on damp earth, walls, or trunks of trees.

Fig. 48.

Symploca lucifuga Harvey, a, X 250; b, natural size. (After
Wolle.)

39 (29) Several filaments in a common sheath which is frequently

branched Subfamily Vaginareeae . . 40

40 (41, 42) Sheaths often colored; lamellose; filaments few or many, loosely

aggregated within the common sheath, Schlzothrix Kiitzing.

Several filaments enclosed in a firm
lameUose sheath which is at first
colorless but later becomes yellowish,
brownish, or purpUsh; filaments simple
or variously branched. Forming cush-
ion-hke masses, erect tufts, or a flat
stratum on moist substrata, rarely
free-floating.

Fig. 49. Schizothrix rubella NSgeli.
X 430. (After Gomont.)

41 (40, 42) Sheaths hyahne, fused with adjoining sheaths. Hydrocokiim

Kiitzing.

Filaments composed each of
numberless short cells, the end
cell with thickened cap-like
membrane. Filaments two
to many in colorless, slimy
sheaths, which become fused
with those of adjoining fila-
ments. In brooks and water-
faUs.

Fig. 50. Hydrocoleum homoeotrich-
um Kiitzing. X 390. (After
Gomont.)

42 (40, 41) Sheaths hyaline, not lamellose, containing a large number of

filaments Microcoleus Desmazieres.

Filaments simple, consisting
generally of long cells; closcJy
aggregated in great numbers
in the center of a conspicuous,
hyaline, cyhndrical sheath.

Fig. 51. Microcoleus dclicatulm
W. and G. S. West. X 35°-
(After West.)

no FRESH-WATER BIOLOGY

43 (28) Filaments simple, unbranched; with heterocysts; living singly or in

gelatinous masses, often of definite form. Sheaths very
delicate, mostly confluent. Cells generally torulose, in a
single row Family Nostoceae . . 44

44 (47) Filaments enclosed within a gelatinous mass of definite form. 45

45 (46) Forming delicate, hollow, cylindrical colonies.

Wollea Bornet and Flahault.

Delicate colonies; filaments straight or
slightly bent, arranged in tolerably parallel
rows, with a common gelatinous envelope;
heterocysts intercalary; spores in chains,
bordering on one or both sides of the
heterocysts. IF. saccala Bor. and Flah.
occurs in stagnant water.

Fig. 52. Wollea saccata Bomet and Flahault.
a, X 250; b, natural size. (After WoUe.)

46 (45) Colonies spherical, or of varied form; with the enclosed filament
irregularly interwoven and contorted. . . Nostoc Vaucher.

I

Forming leathery or slimy gelatinous masses, at first spher-
ical or oblong, later of varied form, solid or hollow, and
attached or unattached; filaments contorted and curved in
all directions; the gelatinous sheath sometimes sharply
deUmited, more often fused with the enveloping jelly.
Cells globular, barrel-shaped, or cyhndrical; heterocysts
intercalary, or (when young) sometimes terminal; sp)ores
globular or oblong, formed in rows in varying number be-
tween the heterocysts. Forming free-floating or attached
masses, on damp ground, wet rocks, etc.

Fig. 55. Nostoc commune Vaucher. a, natural size; b, X 465.
(Original.)

47 (44) Filaments more or less straight, free-floating or forming a thin

mucous stratum 48

48 (52) Heterocysts and spores intercalary 49

4Q (50, 51) Filaments naked, or with a thin sheath; single, or aggregated into
formless, flocculent masses; cells equal to or longer than
their diameter Anabaena Bory.

Filaments straight or circinate, naked or enclosed
in a thin sheath, free floating as single filaments or
united to form a thin, slimy stratum; vegetative
cells as long or somewhat longer than thick; heter-
ocysts numerous and intercalary; spores variously
disposed, borne singly or rarely in short chains.
A. flos-aquae Breb. and A. circinalis Rabenh. are
frequently abundant in fresh-water plankton.

Fig. 54-

Anabaena flos-aquae fir^bisson.
(Original.)

X46S.

BLUE-GREEN ALGAE

III

50 (49, 51) FUaments short, straight, densely aggregated in parallel bundles to

form small, feathery, plate-like masses.

. „ Aphanizomenon Morren.

Filaments without sheath,
straight or somewhat taper-
ing at the end; united in
small, spindle - shaped or
plate-like, free-floating bun-
dles; spores much elongated,
cylindrical, solitary, not bor-
dering on the intercalary
heterocyst. A . Jlos-aquac

Ralfs is sometimes found floating in great abundance in the still waters of

ponds and lakes.

51 (49, 50) Filaments free; cells shorter than their diameter.

Nodularia Mertens.

lBc<^.l;^t^MAW^*..mi-j»aiTgg^

Fig. 55. Aphanizomenon Jlos-aquaeRsMs. X 465. (Original.)

ssia^^^

52 (48)

Fig. 57.

Filaments enclosed in a thin, often evanescent sheath;
free-floating as single filaments or united into colonies of
indefinite form; heterocysts intercalary, depressed; spores
almost spherical, in rows, not bordering on the hetero-
cysts.

Fig. 56. Nodularia sp. X 465. (Original.)

Heterocysts terminal and the spores always contiguous to them.

Cylindrospermum Kiitzing.

Filaments without sheath
relatively short, aggregated to
form an expanded film or
colony of indefinite shape;
vegetative cells cylindrical,
longer than the diameter; het-
erocyst terminal; spores gen-
erally soHtary, borne next to
Common on damp earth and stones.

Cylindrospermum
X465.

stagnale Bornet and Flahault
(Original.)

53 (27)

54 (60)

the heterocyst

Filaments with true or false branches 54

Filaments bearing false branches; sheaths firm, of more or less equal
thickness; filaments consisting of a single row of cells, with
heterocysts (except Plectonema).

Family Scytonemaceae . . 55

55 (56, 59) Without heterocysts or spores Plectonema Thuret.

Filaments consisting
only of vegetative cells,
without heterocysts; false-
ly branched, branches
single or in pairs; borne
singly in a firm, colorless
or yellowish sheath. P.
U'ollci Farl. occurs in
some abundance in
ponds, attached to stones,
etc.

Fig. 58. Plectonema uolUi
Farlow. X 260. (After
Kirchner.)

56 (55, 59) With intercalary heterocysts. One filament in each sheath. . 57

112 FRESH-WATER BIOLOGY

57 (58) Branches generally arising in pairs Scytonema Agardh.

Filaments consisting of vegetative cells and
heterocysts; borne singly in a sheath; sheath
tough, lamellose, frequently yellowish or brownish
in color; false branches borne generally in pairs
between the heterocysts. Forming felt-like masses
on wet rocks, etc.

Fig. 59. Scytonema mirabiU Thuret. X 465- (Original.)

58 (57) Branches arising as a rule singly Tolypothrix Kiitzing.

Filaments resembling closely
those of Scytonema, but false
branches arising singly as a rule
instead of in pairs, as outgrowths
in the region of the heterocysts;
the latter 1-5 in a row; spores (in
a few species) elliptical, borne
singly or in rows. Occurring
among various aquatic plants in
ponds and lakes.

Fig. 60. Tolypothrix lanata Wart-
mann. X 465- (Original.)

59 (55' 56) With basal heterocysts. Two to several filaments enclosed in
each sheath Desmonema Berkeley and Thwaites.

Filaments sometimes slightly branched;
heterocysts always basal. On stones, in brooks,
and waterfalls.

Fig. 61.

Desmonema wrangelii Borzi. X 200.
(After Borzi.)

60 (54)

Filaments usually stout, bearing true branches; cells rounded, dis-
posed generally in more than one row; heterocysts present.
Family Stigonemaceae . . 61

61(62,63) Sheaths thick; firm S tigonema \g^rdh.

Filaments free-floating or aggregated
on the substratum to form felt-like
masses; filaments composed partly of two
to several cell-rows, sometimes of a single
row, enclosed in a thick, lamellose, yellow-
ish or brownish sheath, which is often
of irregular thickness. Hormogonia
formed at the ends of the vegetative
branches or in special short branches.
Heterocysts commonly lateral, or less often
intercalary. Vegetative cells rounded,
frequently showing protoplasmic continuity. Growing generally on damp or

Fig. 62

nema

a, Stigonema ocellatum Thuret; b, Stigo-
minutum Hassall. X 440. (After West.)

wet rocks or moss; sometimes free-floating.

BLUE-GREEN ALGAE

113

62 (61, 63) Sheaths thin; branches commonly unilateral. Hapalosiphon Nageli.

Filaments free-floating amongst other algae or subacrial.
Branches long and flexuose, slightly attenuated, generally
narrower than the main axis and borne unilaterally.
Primary axis consisting of a single row, rarely of 2 to 3
rows of cells, enclosed in a strong sheath of uniform
thickness. Spores and heterocysts intercalary. Among
water weeds, in hot springs, etc.

Fig. 63. Hapalosiphon hibernicus W. and G. S. West.
X 440. (After West.)

63 (61, 62) Sheaths thick; fused to form an irregular gelatinous mass.

Nostochopsis Wood.

Forming rounded, Nostoc-like
masses, attached to water plants.
Filaments composed of but one cell-
row; profusely branched.

Fig. 64. Nostochopsis lobata Wood.
X 330. (After Bornet.)

64 (26) Filaments conspicuously attenuated towards one or both extrem-

ities, which are generally piliferous.

Suborder Trichophoreae . . 65

Filaments sheathed, simple or branched, attenuated from the base
to the apex, which is piliferous; heterocysts generally basal,
rarely absent Family Rwularlaceae . . 65

65 (68) Filaments free or forming penicillate tufts or soft velvety expan-

sions 66

66 (67) Branches, when present, distinct and free.

. , Calothrix Agardh.

Filaments simple or
slightly branched, single
in a thick sheath; hetero-
cysts basal or intercalary
or, in a few species,
absent. Forming tufts
or soft velvety expan-
sions on wet or sub-
merged rocks.

Fig. 65. Calothrix thermalis
Haosgirg. X 4t)5 (Origi-
nal.)

67 (66) Branches several (2 to 6) within a common sheath.

Dichothrix Zanardini.

Filaments more or less di-
chotomously branched; hetero-
c>'sts basal or intercalary. On
wet rocks, etc.

Fig. (i6. Dichothrix interrupts W.
andG. S. West. X 4-^0 (After
West.)

68 (65) Filaments forming a hemispherical or globular mass, closely united
by mucus 6q

114

FRESH-WATER BIOLOGY

69 (70) Filaments radiately disposed in a globose or hemispherical, at-
tached mass. Spores unknown Rivularia Agardh.

Forming hemispherical, globular, or hollow
spherical colonies attached to submerged
plants, such as Chara, Myriophyllum, or to
stones in streams and cataracts. Colonies
composed of radiating filaments which are
repeatedly branched; filaments attenuated
and with piliferous extremities; heterocysts
basal; the whole enclosed in a tough, gelat-
inous matrix.

Fig. 67.

Rivularia minutula Bornet and Flahault.
X 300- (After West.)

70 (69) Filaments radiately disposed; colony often free-floating. Spores
regularly present Gloeotrichia J. Agardh.

(Probably not sufficiently
distinguished from Rivularia to
justify its being made a sep-
arate genus.) Colony globose,
free-floating or attached to
submerged water plants; soUd
when young, but inflated and
hollow when old; composed of radiating, branched, attenuated filaments.
Spores elongated, cylindrical, borne immediately above the basal heterocyst.
G. pisum Ag. is a common plankton form and constituent of "water-
bloom."

Fig. 68. Gloeotrichia pisum Agardh. X 465- (Original.)

IMPORTANT REFERENCES ON BLUE-GREEN .\LGAE

Farlow, W. G. 1877. Remarks on some algae found in the water supplies

of the City of Boston. Bull. Bussey Inst., 2: 75-80.
Forti, A. 1907. Sylloge Myxophycearum; in De Toni's Sylloge Algarum

omnium, Vol. V.
Gardner, N. L. 1906. Cytological studies in Cyanophyceae. Univ. of

CaUf. Pub. Bot., 2: 237-296.
Hyams, Isabel F., and Richards, Ellen H. 1901, 1902, 1904. Notes on

Oscillatoria prolifica. Tech. Quarterly, Vols. 14, 15, 17.
Klrchner, O. 1900. Schizophyceae; in Engler-Prantl Nat. Pflanzenfamilien.
Olive, Edgar W. 1904. Mitotic division of the nuclei of the Cyanophyceae.

Beihefte z. Botan. Centralb., 18: 9-44.
1905. Notes on the Occurrence of Oscillatoria prolifica in the Ice of Pine

Lake, Waukesha County, Wisconsin. Trans. Wis. Acad. Sci., 15: 124-134.
Oltmanns, Friedr. 1904-05. Morphologic und Biologie der Algen. 2v.

Jena.
TiLDEN, Josephine. 1910. The Myxophyceae of North America and Adja-
cent Regions, etc. Minneapolis.
West, G. S. 1904. A Treatise on the British Frcshv/ater Algae. Camb.

Univ. Press.
WOLLE, F. 1887. Fresh-water Algae of the United States. Bethlehem, Pa.

CHAPTER VI
THE FRESH-WATER ALGAE

(Excluding the Blue-Green Algae)

By JULIA W. SNOW

Associate Professor of Botany in Smith College, Northampton, Mass.

The fresh-water algae are among the most widely distributed of
plants. They are found in all natural bodies of water, whether
these be rapidly-running streams, brooks, and rivers, or the more
quiet bodies, such as pools, ponds, and lakes. They abound where-
ever there is moisture. All low-growing vegetation in moist places,
the bark of trees, the earth itself, and even snow-covered moun-
tains, bear species, although they may be invisible to the naked
eye.

The forms of the fresh-water algae are most varied, and there are
all gradations from the most minute cell of primitive, spherical
shape to the large filamentous, richly-branched structure, or cell
complex. The difference between the simple unicellular forms and
many of the higher forms is less than would appear at first sight.
The larger forms often instead of being complex organisms with
many organs, each with its own special function, seem to be more
Uke aggregates of unicellular individuals, each capable of perform-
ing all the life functions, and each living independently of its
neighbors. This is manifested in forms where a single cell is sepa-
rated from all others and continues to live and to reproduce. An
example of this is seen in Stigeoclonium and Chadophora, which
under certain conditions fall apart completely, and each cell exists
indefinitely as a unicellular organism undergoing division in three
directions. Such a state is known as the palmella condition.
Each cell in this aggregate, however, when in the right enviromnent,
has the power to reproduce again the original plant, a fact which
would indicate that environment as well as heredity is a factor

Il6 FRESH-WATER BIOLOGY

in the determination of form. It was formerly thought that such
a pol>Tnorphism was characteristic for the majority of the higher
algae, but though frequent it is by no means universal.

Certain of the genera of the unicellular algae must be closely
related to certain genera of the filamentous forms, such as Slichococcus
and Ilormidium. Botrydiopsls and Conjeroa. The structure of
the cell, the color, size, and shape of the chromatophores, the repro-
duction, the chemica substances formed by the cells of the differ-
ent genera, are in each case identical, and practically the only
difference is that in the one case the cells are cylindrical and united
into a filament, while in the other case they may be somewhat
spherical and solitary.

The resemblance is so great between the Chloromonadaceae,
Confen'a, Botrydiopsls, and other forms in reference to the light
color, the small chromatophores, the nature of the zoospores, and
several other points, that many modern writers classify them
together under the head of Heterokontae, in spite of the fact that
some are unicellular, some flagellate, and some filamentous forms.
Though this resemblance is fully recognized by the writer, in this
brief outline of the fresh-water algae the older classification of
Wille will be retained.

The adult algal cell is a typical plant cell, bounded by a mem-
brane, usually of cellulose, but in the Diatomaceae of a siliceous
nature. Just within the membrane is a layer of protoplasm which
encloses one or more vacuoles and in which are imbedded one or
more chromatophores occupying either a parietal or a central
position. The nucleus usually lies near the center. In by far the
larger number of species there is a single nucleus in a cell, but in
the Cladophoraceae and the non-septate Siphonales there are many
nuclei. The non-septate algae are called coenocytes.

The chromatophores of the algae are large in proportion to the
size of the cell, and may be disc-shaped, plate-like, star-shaped,
or spiral. They may be regular or irregular, perforated, netted,
or entire. Nowhere else in the plant kingdom do we find such a
variety of shapes and structures among chromatophores as among
the algae. Within the chromatophores of many species is a body
denser in structure and albuminous in character, the pyrenoid.

THE FRESH-WATER ALGAE II7

This usually is surrounded by starch and is the center of reserve
material.

Davis regards the pyrenoid as the center of activity of the
chroma toph ore. Certain it is that the division of the pyrenoid is
the first visible stage in the division of the chromatophore and of
the entire cell, and takes place in some cases at least before the
division of the nucleus.

On the basis of the color of the chromatophore of the different
forms, together with the mode of reproduction, are formed the chief
divisions of the algae. The different classes are as follows and
each of them is treated separately in a synoptic key at the place
indicated :

Chlorophyceae, color green, page 134.

Cyanophyceae, color blue-green, page 100.

Phaeophyceae, color brown, page 174.

Rhodophyceae, color red or purpKsh green, page 175.

Bacillariaceae, color yellov/, page 125.

In all cases where the color is other than green there is in the
chromatophore a coloring matter which screens the chlorophyll
and gives the characteristic hue to members of the group. In
the Cyanophyceae the coloring matter is phycocyan; in the Phaeo-
phyceae, phycophaein; in the Rhodophyceae, phycoerythrin; and
in the Bacillariaceae, diatomin.

Reproduction in the algae is either sexual or asexual.

Asexual reproduction may take place either by simple cell
division or by the formation of some cell specially modified for
that purpose. Cell division may occur in one of two ways: first,
by fission, where a membrane is formed across a cell, dividing the
original membrane and contents, as in Pleurococcus ; second, by
internal division, where the contents are simply divided into two,
then four, and perhaps eight or more portions, as in Dactylococcus
and Chlorella. The membrane remains for a time unaltered, but
finally becomes ruptured when the daughter cells increase in size,
thus setting free the new individuals. They germinate immedi-
ately and each produces a new plant.

Oblique divisions of cells, so frequently attributed to the algae,
rarely if ever occur. They appear to take place very frequently,

Il8 FRESH-WATER BIOLOGY

2is hi Ankistrodes?nus, Dactylococcus , and CJilamydonionas, but obser-
vation proves that such divisions are ahvays transverse or longi-
tudinal, and that the parts in growing slip by each other and
elongate, producing the diagonal Une of demarcation between
them.

In reproduction by internal division, the new individuals are
called by Artari gonidia, by West autospores, and by Wille akin-
etes, with the akinete character but sHghtly developed. The
contents of such cells may become denser, and possibly be filled
with oil or starch; at the same time the membrane becomes thick-
ened and the whole cell more resistant to unfavorable conditions,
such as heat, cold, or drought. They may remain in this condi-
tion for long periods, and in this way maintain the life of the
organism over conditions which would threaten the existence of
an ordinary vegetative cell. Such cells or akinetes, according to
Wille, may be seen in the palmella condition of Stigeoclonium and
Chaetophora.

The modification of these cells may continue farther, and a
rejuvenescence occur. Each cell becomes invested with a new
membrane and the old membrane is cast off before germination.
These structures Wille would designate as aplanospores. He also
calls attention to the fact that there are many transitional stages
between the vegetative cells and akinetes, and also between the
akinetes and the aplanospores.

In many of the Confervales and Protococcales, instead of
autospores, there are formed motile spores or zoospores. These
are mostly oval in shape, without a membrane, with one, two, or
four ciHa, a reddish pigment spot, one or two chromatophores,
and usually two contracting vacuoles in the anterior end. The
zoosporangium, or cell in whicli they are borne, is in the greater
number of cases developed from an ordinary vegetative cell, but
more rarely from a cell specialized for that purpose. The zoo-
spores originate by the repeated bipartition of the cell contents, by
which 2, 4, 8, 1 6, 32, 64, or even 128 spores are formed, as in the
production of autospores. More rarely a single spore is formed
from a cell. The zoospores are set free either by the entire cell
wall becoming gelatinous, or by its dissolving at a single point,

THE FRESH-WATER ALGAE 1 19

through which the spores gradually press their way. In some
instances the membrane splits and the spores are thus liberated.
If the conditions be not favorable to the liberation of the spores,
however, they may move for a time within the mother membrane,
or may never come into motion at all, but may germinate immedi-
ately without being liberated, and become invested with membranes
of their own. They soon increase in size so that the zoosporangium
wall is broken, but they often remain adhering to each other for a
long time, thus forming a cluster of cells like the parent individual.

Sexual reproduction is always preceded by fertilization. This
process consists in a union of two cells which may be either alike
or unlike, and are known as gametes If the cells are alike they
are called isogametes, but if unlike, heterogametes. The simplest
form of fertilization is seen when two isogametes unite or conjugate
to form a zygospore. These gametes may be two motile cells
resembling zoospores, as n Protosiphon, or they may be non-
motile cells, either distinct individuals as in the Desmids, or as
parts of filaments, as in Spirogyra. Frequently a sKght difference
in size may be detected between these two cells, and undoubtedly
this is a beginning of sex differentiation. In all of the higher
algae this differentiation has advanced much farther and a great
difference exists between the gametes: the female cell, the oosphere
or 'egg cell, being large and non-motile, while the male cell, the
antherozoid or spermatozoid, is endowed with independent motion.
Only in the Florideae does the male cell, the spermatium, lack
motion, and remain dependent upon the action of the water to
transfer it to the egg cell.

The female organ which bears the egg cell is called the oogo-
nium, the male organ which bears the antherozoid is the antherid-
ium. The result of fertilization of an egg by an antherozoid is an
oospore, which is resistant to unfavorable conditions and is usually
dormant for a period before germination.

The female organ of the Florideae is called the procarp. It is
flask-shaped and made up of two parts, the enlarged basal por-
tion, the carpogonium, which contains the egg cell, and a projecting
neck, the trichogyne, for conducting the spermatium to the egg.
The influence of fertiUzation is manifested by a rapid production

I20 FRESH- WATER BIOLOGY

of spores from the base of the carpogonium, surrounded by sterile
filaments; these together form the cystocarp.

Just as in the study of the higher plants attention has been
turned largely from a purely systematic investigation to a physio-
logical study, so among the algae the most important work is done
along the line of physiology. The simpUcity of their structure,
the ease with which many may be cultivated, the readiness with
which they respond to and adapt themselves to external condi-
tions make them a most valuable group with which to experiment.
It would seem that many of the ph\siological phenomena which
in the higher plants are rendered obscure, due to intricacy of
structure and complexity of environment, might be made plain in
these lower forms which lend themselves so readily to manipula-
tion.

Most valuable results in the physiology of reproduction have
already been attained by Klebs w^ho has taken the chief elements
in the environment and studied their effect on the organism. As a
result he has shown that reproduction, at least in the forms studied,
instead of being a phenomenon which, without any determining
cause, occurs simply as a stage of growth, is a phenomenon which is
dependent upon external conditions ; and that as these are altered ,
the one or the other form of reproduction may be originated, per-
fected, or altogether checked, according to the will of the investi-
gator. He has shown most conclusively that the sexual form of
reproduction does not of necessity alternate with the asexual repro-
duction. If the conditions be maintained, it is possible in certain
cases to suppress either form of reproduction indefinitely, or if de-
sired, to call forth the one to the entire exclusion of the other. An
example of this is cited by Klebs in Vaucheria, Protosiphon, and a
number of other forms. These facts would go to prove that an alter-
nation of the sexual and asexual form of reproduction does not exist
in the green algae, though West and others hold that it occurs in
a large number of the Chlorophyceae. The sporophyte generation,
they believe, is represented by the sexual spore which produces
asexual zoospores; each of these in turn, on germinating, ushers in
a gametophyte generation.

In studying the algal flora of any region and the conditions under

THE FRESH-WATER ALGAE 121

which it exists, one notes ecological relations among the algae
quite as much as among higher plants. The forms which may be
found are determined very largely by the nature of their environ-
ment, and many of them cannot be transferred from one set of
conditions to another. A large number of species which live sub-
merged in water soon perish if subjected to the atmosphere, while
others, such as the common Pleurococcus vulgaris, which normally
live exposed to the air, are never found in water. A few forms,
such as Chlorella, Stichococcus and Hormidium, may adapt them-
selves to either environment, and are very widely distributed
under the different conditions where algae are found.

As all forms are dependent on moisture, the geological formations
which determine the amount of moisture must determine the
algal flora of any region. • In localities where there are large tracts
of level land without elevations and depressions, the algal flora is
extremely meager; while in a hilly country where the water accu-
mulates in depressions of the earth this flora is abundant, certain
forms such as Stigeoclonium, Draparnaldia, and Batrachospermum
preferring the rapidly-running water of streams, while the larger
number of species choose the quieter water of ponds and lakes.

From early spring to late fall the algae are most numerous, but
they are also found in winter, even in the vegetative condition, as
many are not injured by freezing. In these cases the chief eft'ect
of cold upon them is simply a retarding of growth and of repro-
duction. But while some forms are found at all seasons, differ-
ent forms predominate at different times, some species being most
abundant at one period and others most abundant at another.
It does not follow, however, that the same date in successive
years will find the same form predominating. Within certain
limits the flora of a body of water is constantly changing, due
probably to changes in temperature, light, and nutrition, or pos-
sibly to other causes too obscure to detect.

Usually the httoral region supports a number of filamentous
algae. Cladophora is one of the most frequent and is especially
abundant in regions where wave action is strong and the current
great. On the other hand, if the water be shallow and exposed to
the direct rays of the sun, such forms as Spirogyra, Zygmma, Oedo-

122 FRESH-WATER BIOLOGY

gonium, and Bulbochactc are found. Char a and Nitella are found in
huge beds at the bottom of lakes at a depth of from one to many feet.

Of the unicellular forms also, different species occur under different
conditions. An especially favorable position for this group is
among the leaves and on the surface of the higher aquatic plants.
Indeed unless higher algae or phanerogams exist in certain locali-
ties but few of the minute forms are ever found. There seem to be
certain preferences on the part of different species of unicellular
algae as to the forms of the higher plants with which they associate.
This may be simply that the shape, texture, and arrangement of
parts of certain of these plants afford a better shelter and protec-
tion for the single cells than do others, but it is more probable that
the plant itself exerts some chemical influence which is attractive
or repulsive to these forms. For instance, enormous numbers of
different species may be found growing among Chara, while in
connection with Ceratophyllum, the leaves of which are very finely
cut, but few species occur.

The endophytic forms, such as Endosphaera and Scotinosphaera,
Kve principally in the tissues of Potamogeton, Lemna, and other
water plants, though they may also be found outside of the tissues.
The discoid forms, such as Coleochaete and Ulvella, are found on the
surface of the broader-leaved types of submerged plants, especially
on Potamogeton; and the unicellular blue-green forms occur abun-
dantly among the Charas, though they are also numerous in most
stagnant water.

In the plankton are always found many species that exist in the
littoral region, but there are also many forms which are distinctively
plankton types. These are characterized by a great surface in
proportion to the mass of the cells, thus rendering them more
buoyant. This is provided for in several ways: by the presence
of long gelatinous or cellulose spines, as in Chodatella and Rich-
teriella; by the union of cells into ribbons or bands, as in Fragila-
ria; and by the production of a homogeneous gelatinous matrix in
which the cells are imbedded, as in Kirchneriella and Sphaerocystis.

In studying the life history of the algae, cultivation is absolutely
essential in order that development may be traced from step to
step without confusing the different phases of the form in ques-

THE FRESH-WATER ALGAE 123

tion with other species which may be found in connection with it.
Aside from this, too, cultures are useful in determining what species,
especially of the unicellular forms, are present in any collection.
Many of these are so minute that they could easily be overlooked
unless they exist in great masses, which is rarely the case. So if
all forms of a locality are desired, it is well to put a small portion
of material gathered, bits of moss, earth, lichen, or washings from
higher aquatic plants into a culture medium and allow it to stand
3 to 4 weeks, when it may be examined; the chances are that
many forms will appear which could not be detected before-
hand. Indeed this is the only way in which certain species may
be obtained.

When a pure culture is desired bacteriological methods for pure
cultures are most useful, but one who is skillful in working under
the low power of a microscope can often, by means of a tiny capil-
lary pipette, isolate a single cell, or a cluster of cells, which he knows
to be all of one kind. If the medium in which the form was grow-
ing contained many other species, the chances are that the lirst
time that the cell or cluster is transferred, a cell of some other
minute form such as Chlorella or Stichococcus, too small to notice
under that power, may be transferred with the desired form; so
to prevent this impurity from being carried to the final culture, thus
making the culture worthless, the better way is to transfer the cell
first to a drop of distilled water on a slide, then sterilize the pipette
in boihng water and, allowing it to cool, transfer the cell again to
a drop of distilled water; the process should be repeated three or
four times, and the cell finally transferred to the receptacle in
which the culture is required.

For this purpose small low glass preparation dishes with loosely
fitting covers are the best. A receptacle that will admit a little
air is better than one that excludes air entirely. These small
receptacles may then be placed directly on the stage of a micro-
scope and the forms studied from time to time without disturbing
the growth in the least.

The bacteriological method for obtaining pure cultures emplo}'s
gelatine or agar-agar plates. These plates are prepared by spread-
ing a thin layer of gelatine or agar-agar mixed with some good

124 FRESH-WATER BIOLOGY

nutrient solution over the bottom of a petri dish or a small glass
culture dish. This must then be sterilized before the culture is
made. In preparing the culture a very minute portion of the me-
dium containing the desired form is mixed with a large drop of
distilled water and then this is scattered at intervals over the surface.
The material must be diluted with enough water so that each cell
will be by itself.

In the course of a few days the single cells will have increased,
and then, while the culture is on the stage of a microscope, the little
colony of cells may be transferred to a Kquid medium by means of a
sterilized needle, the tip of a line brush, or a very fine pipette.

To a very large extent the culture medium must be adapted to
the species to be cultivated. No one medium is favorable to all
species of algae, and the form must be taken into consideration
before a medium is prepared. If the species be a new form, various
different media must often be tried before the right one is deter-
mined. If a quantity of different forms from any collection be
placed in one medium and a second quantity in another, the prob-
abilities are that in the course of three or four weeks but few of
the same species will be found in both cultures. Certain forms will
have died in one while perhaps those very forms have found in the
other medium the substances and conditions for their development.

The media to which the greatest number of forms are adapted
are Moore's solution and Knop's solution:

Moore's solution:

Ammonium nitrate 0.5 gram.

Potassium phosphate^ 0.2 gram.

Magnesium sulphate 0.2 gram.

Calcium chloride o . i gram.

Iron sulphate trace.

These amounts should be dissolved in one liter of distilled water.

Knop's solution:

Potassium nitrate i gram.

Potassium phosphate i gram.

Magnesium sulphate i gram.

Calcium nitrate 4 grams.

Chloride of iron trace.

The first three substances are dissolved in the required amount of water to make from i to
5 per cent of the solution, then the calcium nitrate is added. This solution may then be
diluted as needed; usually a 0.2 per cent or a 0.4 per cent solution is favorable for ordinary
cultures.

THE FRESH-WATER ALGAE 1 25

It should be borne in mind that among the plankton forms
there are many which will not develop in either. For these
the best solution has been found to be a solution made from the
organisms in the plankton itself. In this a perfectly normal de-
velopment may be obtained for many forms, though even in this
some fail of development. Bouillon^_earth decoctions, moist , finely
pulverized earthy bits of bark and cubes of sterilized peat,/ all form
good substances for the ordinary cultivation of the unicellular
algae. The filamentouj_ algae^ are far more difficult to cultivate.
Before satisfying oii?s self with the fife history of any form, that
form should be maintained in culture for an extended period,
when observation can be made from time to time and the efi'ect of
different conditions determined.

An attempt has been made to give the principal genera of fresh-
water algae found in North America, but the fist is by no means
complete. A very few genera of diatoms and desmids here cited
have not been found by the writer and no report of their occurrence
in North America could be obtained ; but these groups are distrib-
uted so universally that they probably will be discovered in this
territory.

KEY TO NORTH AMERICAN FRESH-WATER ALGAE
Class I. Bacillariaceae (Diatoms)

Color yellow; plant a single cell, sometimes united into chains; membrane
silicified, with minute, definite markings.

These are unicellular algae but, by means of a gelatinous substance, are
frequently held together in bands or masses. The membrane is silicified,
making it hard and rigid. It is always composed of two parts, valves, which
may be separated from each other and which are often compared to a box and
itj overlapping cover; the side where the edges overlap is spoken, of as the
ijcirdle^e.. while the outer "surface is referred to as the \ valve side ; this and,
more rarely, the girdle side also are sculptured with Hiie' striations, dots,
dotted lines, and grooves. Many have extending lengthwise a conspicuous
line, the irS^j which frequently bears at its rniddle and both jmds rounded
portions calleanodules.

Reproduction is by auxospores, either sexual or asexual. The asexual
are formed by the contents of a cell collecting, throwing off the membrane,
and forming either one or two spores. The sexual auxospores are formed by
the throwing off of the membrane and the copulation of two cells in one of the
following ways: (a) Two cells divide, making two pairs of daughter-cells; each
individual of one pair fuses with one from the other pair, thus making two
spores, (b) Two cells unite to form one auxospore. {c) Two cells come
together but do not copulate; two auxospores are formed.

126 FRESH-WATER BIOLOGY

1 (9, 10) Valves circular, raphe lacking, markings radial 2

2 (5) Cells cylindrical or ellipsoidal, united into filaments. Valve side circu-

lar, either convex or flat. . . Family Melosiraceae . . 3

3 (4) Cells with no spines or teeth; valves either smooth or punctate, usually

convex; girdle side punctate Melosira Agardh.

-J'..

Melosira is very common in ponds, rivers, lakes, and
reservoirs, and occurs in great quantities in the plankton.
The filaments are often very long.

Fig. 69. Melosira varians Agardh. X 600. (Original.)

4(3)

Cells similar to those of Melosira, but with a circle of tooth-like pro-
jections between the valve and girdle sides.

Orthosira Thwaites.

Van Heurck and West include Orthosira under Melosira, while
many others make a separate genus. The Orthosira forms are
found in the same localities as Melosira but are much less
C abundant.

Fig. 70. Orthosira orichalcea W. Smith. X 600. (Original.)

5 (2) Cells single, disc-shaped, not forming filaments; valves flat, convex, or

undulating, mostly with radial rows of punctulations.

Family Coscinodiscaceae . . 6

6 (7, 8) Valves circular or nearly so, with radiating rows of dots or areola-

tions, the disc with a distinct edge, usually bearing a circle
of inconspicuous submarginal spines.

Coscinodisciis Ehrenberg.

The number of species of Coscinodiscus is verj' large, mostly
marine, although some occur in fresh water with other similar
centric forms.

Fig. 71. Coscinodiscus apiculatus Ehrenberg. X330. (After Wolle.)

7 (6, 8) Valves circular, showing a central smooth or punctate area, and an
outer margin of radiating striations. Girdle view with
undulating ends Cyclotella Kiitzing.

The cells are disc-shaped and are distinguished from other disc-
shaped forms principally by the smooth or punctate center and the
undulating ends. It is found commonly in the plankton.

Fig. 72. Cyclotella compta Kutzing var. affinis Grun. a. Valve side; b,
girdle side. X 408. (After Schiitt and van Heurck-Gninow.)

THE FRESH-WATER ALGAE

127

8 (6, 7) Valves circular, with radial rows of dots, between which are clear
spaces; center either punctate or hyaline; on the margin
a circle of acute spines; girdle view with undulating ends.

Stephanodisciis Ehrenberg.

The length of the spines on the margins of
the cells varies greatly; in S(jme species they
are short and acute, while in others they may
exceed the diameter of the cell many times.
Stephanodisciis occurs frequently in the plank-
ton, but usually not in great quantities.

Fig. 73-

Suphanodiscus niagareoe Ehrenberg.
X 606. (Original.)

9 (i, 10) Valves more or less cylindrical, often in chains, ends greatly ex-
tended, usually forming long spines.

Family Rhizosolexiaceae.
Only one genus Rhizosolenia Ehrenberg.

Fig. 74. Rhizosolenia eriensis H. Smith.
Schrdter.)

X 190. (After

10 (i, 9) Valves not circular or cyhndrical, of different shapes, symmetrical in

reference to a longitudinal or transverse axis; surface marked
by costae or punctate lines making definite angles with a
middle raphe or a median line 11

11 (34, 38) A middle nodule present on the raphe of both valves. ... 12

See also 40 and 65.

12 (32, 36) Girdle view symmetrical with reference to both a transverse and

a longitudinal axis 13

13 (26) Valves not arched or keeled; usually symmetrical with reference to a

straight or a sigmoid raphe. Family Naviculaceae . . 14

Valves symmetrical with reference to a straight or curved middle line; girdle symmetrical

with reference to both axes; a straight or curved raphe; a central and two end nodules present.

14(15) Cells without inner partitions; raphe and valves straight. . . . 16
15(14) Raphe and valves sigmoid Pleurosigma W. Smith.

Fig. 75. Pleurosigma attenuatum W.
Smith. X 300. (After Smith.)

16 (19) Cells linear, oblong, with rounded nodules, the two end ones turned

toward one side, the prominent costae not punctate. . . 17

17 (18) The costae interrupted by a plain band at the center.

Stauroptcra Ehrenberg.

18 (17) The costae not interrupted at the center. . Pinniilaria Ehrenberg.

^■M

E^ilBi«

Fig. 76. Pinnularia viridis
Smith. X600. (Original.)

19 (16) Cells more lance-shaped, the end nodules not turned toward one
side. Striations composed of lines of individual dots. . ^"o

128

FRESH-WATER BIOLOGY

20(23,24,25) Central nodule small, rounded, or slightly elongated. ... 21

21 (22) No lateral longitudinal areas of transverse septa. . . Nmicula Bory.

A form which grows in gelatinous tubes is regarded by some
authors as a different genus Schizonema but others regard it as
a true Navicuki.

Fig. 77. Navicula rhync/tocepftala Kiitzing. X 557- (Original.)

22 (21) Two lateral longitudinal areas of transverse septa. Mostly imbedded

in a gelatinous pseudothallus. . . . Mastogloia Thwaites.

In shape, Mastogloia resembles Xavicula, but is distinguished from it by
the gelatinous envelope and the presence of lateral, transverse, siliceous septa
or plates which divide the lateral regions of the cells into- small compart-
ments. There are transverse striations on the valves. It is not a very
common genus in .\merica.

Fig. 78. Maslogloia smiihii Thwaites. X about 300. (After Smith.)

23 (20, 24, 25) Central nodule broad, extending to near the margin of the valves.

Stauroneis Ehrenberg.

Stauroneis occurs frequently in all
bodies of water and is a constituent of
the diatomaceous flora which forms large
siliceous deposits at the bottom of lakes.

Fig. 79. Stauroneis anceps Ehrenberg.
X 600. COriginal.)

24 (20, 23, 25) Central nodule elongated to a short rod. Borne on gelatinous

stalks Brehissonia Grun.

Fig. 80. Brebissonia
sp. X 580. (Original.)

25 (20, 23, 24) Central and end nodules elongated, enclosed with the raphe
between two longitudinal, parallel, siKccous ribs. Frus-
tules sometimes borne in gelatinous tubes.

Vanheurckia Brebisson.

Fig. 81. Vanheurckia rhomboides Ehrenberg. X 370.
(After West.)

26 (13) Valves asymmetrical with reference to the raphe or to a longitudinal

axis; raphe arched, or nearer one margin than the other.

Family Cymbellaceae . . 27

27 (28) Valves greatly convex; girdle side elliptical or oval.

Amphora Ehrenberg.

A Van Heurck regards A mphora as one of the most difficult
genera of diatoms and notes that over 200 species have
been placed in this genus. It is believed that it origi-
nated from CymbeUa.

^ Fig. 82. Amphora ovalis Kiitzing. a. Valve side; b. girdle
side. X 600. (Original.)

28 (27) Valves flat or only slightly convex 29

THE FRESH-WATER ALGAE

129

29 (30, 31) Raphe straight or bent, ending in tlic middle of the valve ends.

Cells free Cymbella Agardh.

Cymhella varies in shape from that of a typical Naiicula
to one strongly arched, and they have sometimes l)een styled
as asymmetrical Navicidas. Some authors include the genus
Cocconema under Cymbella, but the name Cocconema is the
older name and should be retained. WoUe reports 25 species
of Cymbella.

Fig. 83. Cymbella cuspidala Kutzing. X 600. (Original.)

30 (29, 31) Cells much as in Cymbella, but usually larger and borne on

gelatinous stalks Cocconema Ehrenberg.

Fig. 84. Cocconema lanceolatum Ehren-
berg. X37S. (After West.)

31 (29, 30) Raphe straight, not ending in the middle of valve ends. Cells
living in gelatinous tubes Encyonema Kutzing.

Fig. 85. Encvonema auenvaldii Rabenhorst. X 250.
(After Wolle.)

32' (12, 36) Girdle view asymmetrical with reference to a transverse axis,
the outline being wedge-shaped.

Family Gomphonemaceae . . 33

33 (35) Girdle side straight Gomphonema Agardh.

Fig. 86. Gomphonema acuminatum Ehrenberg. a. Valve side;
b. girdle side. X 600. (Original.)

34 (11, 38) A middle nodule and a raphe present on but one valve. . . 35

35 (33) Girdle side curved; otherwise similar to Gomphonema,

Rhoicosphenia Granow.

The two valves are unlike in shape and in the fact that the lower valve
possesses a raphe, a central and end nodules, while the upper valve possesses
only a pseudo-raphe and is without nodules.

Fig. 87. Rhoicosphenia curvata Grunow. a. Valve side; b. girdle side. X 380.
(After Schonfeldt.)

36 (32, 37) Girdle view symmetrical with reference to a transverse, but not
to a longitudinal axis, the cells being arcuate and attached

to higher algae Family CoccoNEroACEAE.

Only one genus known CVrowf/j Ehrenberg.

Valves oval or elliptical, symmetrical with reference to both axes; raphe
straight, with middle nodules but without end nodules. Markmgs of faint
longitudinal punctate lines; girdle and end views both curved.

Fig. 88. Cocconeis pediculus Ehrenberg. X 600. (Original.)

I30 FRESH-WATER BIOLOGY

37 (36) Girdle side geniculate. Valves straight, linear, or fusiform; frus-

tules either free or stalked. . . Family Achnanthaceae.

Only one genus Achnanthes Bory.

Cells so cun-ed that the two valves arc not alike, the one concave with raphe, middle and
end nodules; the other con\ex, without a middle no(lule, but with a pseudo-raphe. Girdle view
s>Tnmetrical with reference to a transverse axis. Cells single or in bands,
mostly on gelatinous stalks.

The cells may be solitary, though they usually form long, sessile chains or
bands attached tu the surface of green algae. The genus includes both marine
and fresh-water forms.

Fig. .Sy. AchnanUies exUis Kutzing. X 600. (Original.)

38 (11, 34) No middle nodule present on either valve, except in Ceratoneis,

or at most consisting of a slight, ring-hke elevation. . . 39

39(40,41,62) \'alves as>Tnmetrical with reference to a longitudinal axis, in
that on one margin there is a longitudinal row of bead-like
thickenings (keel points) while on the other margin they are

lacking Family Nitzschiaceae.

Only one genus Nitzschia Hassall.

Valves linear, sometimes curved, keeled, with canal raphe. Cells rhomboidal in cross sec-
tion.

"■■'■M»iiiimninmiiii..n.Tm.,..,.,,.,,^,,^ FiG. 90. Nitzschia linearis "Svaxih. X 575-
_- ■ — -^ (Original.)

40 (39, 62) Valves with median, sigmoid keel, compressed, strongly arched,

bearing raphe Family Amphiproraceae.

Only one genus Amphiprora Ehrenberg.

I^^-A^^^

Valves fusiform, with central and two end nodules on raphe.
Girdle side sharply constricted at center.

Fig. 91. Amphiprora sp. X 400- (Original.)

41 (39, 62) Valves symmetrical with reference to a longitudinal axis . . 42

42 (47) Valves each with two wing-like keels, strongly costate, with pseudo-

raphe but no nodules. . . Family Surirellaceae . . 43
Cells mostly large, ovate, or elUptical.

43 (44) Cells bent in saddle shape Campylodisciis Ehrenberg.

Though the shape of the cells seems more or less tri-
angular, they are in reality circular, and their seeming
angularity is due to the cur\'ature of the frustules. It
is a very large genus, some 92 species having been
recorded; the species are mostly marine, though a number
are found in fresh water. Their large size makes them
among the most conspicuous of the diatoms.

Fig. 92. Campylodiscus cribrosus W. Smith. X about 300.
(After Smith.)

44 (43) Cells not bent or spirally twisted 45

THE FRESH-WATER ALGAE

131

45 (46) Valves showing a wave-like margin in girdle view.

Cymatopleura W. Smith.

This is a large diatom which is
easily recognized by the undulat-
ing outline of the girdle side.

The genus is rather small, and
WoUe reports but seven species.

Fig. 93. Cymatopleura apiculata
W. Smith, a. Valve side. b. girdle
side. X 600. (Original.)

46 (45) Girdle view without wave-like margins Surirella Turpin.

UUOUUL'uuuUua

QQoaaninmaa

This genus is widely distributed
■4 and of frequent occurrence in all re-
gions where diatoms are found. Some
species are very large and conspicu-
ous, especially in the plankton.

Fig. 94. Surirella sp. Smith. a.
Valve side. b. girdle side. X 585-

(Original.)

47 (42) Valves without keels. . 4^

48 (59) Cells without deep inner partitions sometimes with imperfect septa. 49

49

(55) Valves with transverse costae So

qo (';4) Valves symmetrical with reference to a transverse axis.

Family Diatomaceae . . 51

Cells symmetrical with reference to both axes, borne in long chains; transverse striations
distinct and uninterrupted except in some cases by a longitudmal plain band.

51 (52, 53) Valve side oval or linear, transverse markings uninterrupted,
girdle side rectangular, cells mostly in zig-zag chams. some-
times in short filament Z)/(2/c7wa de Candolle.

^^^^^<^^^P^aj

Fig. 9 V DiaUma elongaium Agardh. a. Valve
^ side. b. girdle side. X about 300. (After W.
Smith.)

132

52 (51:

FRESH-WATER BIOLOGY

;3) Characteristics similar to those of Diatoma except that the cells
are borne in ribbons Denticida Kutzing.

The valves are marked by heavy ribs which are in reality shallow
septa, between which are delicate striae.

Denticuld occurs on wet rocks and in fresh water; sometimes also m
brackish water.

Fig 96. Denlkula inflata Smith, a. Valve side. b. girdle side.
X 600. (Original.)

52) Characteristics as in Dcnticula except that the striations are in-
terrupted in the middle Odontidium Kutzing.

Many place the members of this genus with Diatoma, while
others regard the interrupted striae and the formation of short fila-
ments instead of zig-zag chains, sufficient differences to place them
in a separate genus.

Fig. 97. a, b. Odontidium mutabile Smith, c. Odontidium tabellaria
Smith. X 570. (Original.)

54 (50)

Valves asymmetrical with reference to a transverse axis.

Family Meridionaceae.
Only one genus Meridion Agardh.

Both valve and girdle sides wedge-shaped, forming ring-
like or fan-shaped bands; striations uninterrupted.

There are imperfect transverse septa which are con-
spicuous on the valve side but show only laterally on
the girdle side. Between these on the valve side are fine
punctate striae.

Van Heurck thinks this genus ought to be suppressed.
It differs from Diatoma only in the cuneate shape of the
valves.

Fig. 98.

Meridion constrictum Ralfs.
Smith.)

X 300. (After

55 (49) Valves without transverse costae. . Family Fragilariaceae

56

Cells of much the same structure as Diatoms.
dots; with or without raphe and end nodules.

Transverse striations composed of separate

56 (57, 58) Cells very slender, not united in bands, either free or attached at
one end, forming clusters on higher algae.

Synedra Ehrenberg.

Fig. 99. Synedra salina W. Smith.
X 588. (Original.)

57 (56, 58) Cells forming bands or zig-zag chains.

Fragilaria Lyngbye.

Fragilaria is a common genus oc-
curring in ponds, reservoirs, and lakes.
F. crotoncnsis has been known to occur
in such quantities as to form water
bloom, producing a thick brown scum
on the surface of a lake.

Fig. 100. Fragilaria crotonensis Kitton.
a. Valve side. b. girdle side. X 225.
(Original.)

THE FRESH-WATER ALGAE 1 33

58 (56, 57) Cells arranged in the form of a star. . . . Aster ionella Hassall.

The radial arrangement of the cells is due to the
presence at the inner ends of small mucous cushions
which unite the cells in this manner. The cells are
linear, unequally enlarged at the ends, capitate in the
valve view and truncate in the girdle view. The
valves are marked with delicate striations.

Asterionella is common in ponds, lakes, and water
reservoirs. It is especially freciuent in the plankton,
probably on account of the radial arrangement of the
cells, which would make it easily buoyed up by the
water.

Fig. ioi.

Asterionella gracillima Heihcxg. X li
(After Schroter.)

59 (48) Cells with interrupted inner partitions.

Family Tabellariaceae

60

Valves linear, oblong, or elliptical, inflated at the center,
or more longitudinal partitions perforated at the center.

Girdle side rectangular, with two

60 (61) Cells slender, valves with only punctate striations.

Tahellaria Ehrenberg.

I

The inner partitions appear in the girdle view
as distinct lines which are not always equally
developed or opposite each other at the two ends
of the cell. At the interruption of the partitions
at the center the valve sides show an inflation.

The zig-zag chains of Tabellaria are conspicu-
ous in almost all collections of algae.

Fig. 102. Tahellaria feneslrata Kiitzing. a. Valve
side. b. girdle side. X 600. c. showing characteristic
arrangement of cell. X about 150. (Original.)

Cells broader, with distinct transverse costae. . . Tetracyclics Ralfs.

Aside from the interrupted inner par-
titions there are also transverse septa
which appear on the valve sides as costae,
between which are very faint striae. The

3

septa are more numerous, and the cells
more cruciform than in Tabellaria; they
occur also in bands instead of in zig-zag
chains.

Fig. 103.
Valve side.
Smith.)

Tetracxclus lacustris Ralfs. a.
b. girdle side. X 300. (After

62 (39, 41) Valves asymmetrical with reference to a longitudinal axis, the
cells being more or less arcuate.

Family Epithemiaceae . . 63

Valves curved, usually with dotted transverse striations, sometimes also with transverse
costae.

134 FRESH-WATER BIOLOGY

63 (64, 65) Transverse costae coarse, converging, projecting inward, often
with lines of dots between. . . Epithemia Brebisson.

Fig. 104. Epithemia lurgida Kiitzing.
X 380. (Original.)

"W

64 (63, 65) Transverse striations punctate; end nodules present, but raphe

wanting . Eunotia Ehrcnberg.

Fig. 105. Eunotia pectinalis Dillw-jn. X 625. (Original.)

65 (63, 64) Valves crescent-shaped, the raphe very near the concave margin,

with end and middle nodules. . . . Ceratoneis Ehrenberg.

There is but a single species.

Fig. 106. Ceratoneis arcus Kiitzing. X 600. (Original.)

Class II. Chlorophyceae

Color, a chlorophyll-green.

This group includes by far the greater number of forms of algae in fresh
water. It is so large and the characteristics of the different members so
varied that no characterization of the group as a whole will be attempted.

1 (253) Plants fine, relatively small 2

In regard to the Characeae the uncertainty of their nature and systematic position is fully
understood, but for convenience they will be considered at the end of the Chlorophyceae.

2 (67) Plants of unbranched, septate filaments, shppery to the touch; or

plants of single cells of two exactly symmetrical parts, some-
times united into filaments. Chlorophyll in spiral bands,
central plates, or star-shaped bodies.

Order Conjugales . . 3

Filamentous or unicellular algae whose reproduction consists only in conjugation, that is
where the contents of two cells which are exactly alike, or at most differing only slightly in
reference to size, unite to form a single cell, the zygospore.

Some authors would place the BaaUariaceae under this group on account of the union which
takes place before the formation of the spore, but as they differ in many respects from the dis-
tinctive members of this group they have been placed in a group by themselves.

3 (59) Plants unicellular, occasionally united into filaments; cells constricted

at the middle or not; one-half of each cell exactly symmet-
rical with the other half; 2, 4, or 8 individuals from a germi-
nating zygospore Family Desmidiaceae . . 4

The membrane mostly furnished with tiny protuberances and pores, both with a definite
arrangement; chromatophore radiating from or including one or more pyrenoids. Asexual
reproduction by the separation of the halves of the cell, between which two new halves are
formed, each attached to and identical with one of the older halves. In sexual reproduction
two cells come together, throw off their membranes, and their contents unite to form a
zygospore. This is usually furnished with conspicuous colorless spines.

4 (22) Cells after division united into filaments 5

THE FRESH-WATER ALGAE I35

5 (11) Cells cylindrical, with no constriction, or at most a very shallow and

broad constriction, giving a slightly undulating outline. 6

6 (7, 8) Cells not longer than broad, sometimes with a very shallow, broad

constriction; chromatophore central, with 6 to 10 rays about
a pyrenoid Hyalotlieca Ehrenbcrg.

Filaments long, often twisted, and slippery to the touch.
=-£=::5^==;«==5=^^^^- Thc diffctent diameters of the cells nearly equal, varying

hi^''''W^I^3^^«^IS- ^''^"^ ^° ^° ^5 ^' ^^^ median constriction often ver>' slight.

A Chromatophore in each cell-half of radiating plates placed
|)it5<»««ti»dks,5j^^]t^- about a pyrenoid.

!t^t4U«^(^i^»;iiig)[><'j^^^^ A broad gelatinous envelop is always present but it is in-

visible without reagents.

Hyalotheca is frequent among filamentous forms of the
B Conjugalcs.

Fig. 107. Hyalotheca dissiliens Brebisson. a. side view. 6. end
view. X 575- (Original.)

7 (6, 8) Cells but little longer than broad, attenuated at the end.

Leptozosma Turner.

Filaments long, cateniform; not twisted, or
but slightly so. Joints united by a strongly
marked suture; near to Bambuscina Kiitzing,
\rA \3A.^ri^ "^ — ^^^^^ ''^^:=:r:^_i^ ^^^ differing therefrom in the suture.

'V\s#ss:^ Fig. 108. Leptozosma catenulata Turner. X 300.

(After Turner.)

8 (6, 7) Cells much longer than broad 9

9 (10) Chromatophore a central plate containing a row of pyrenoids.

Gonatozygon de Bary.

r;^S^^^n^^^S^^^^^^ Length of cells 100 to 200 m; breadth 10 to 20M,

4,;^^^,^,=,,,,,^,,;^,:^.=-.==*. — -•-:■ ''*~^ ~~"'"°^^^^ much like a cell of Mougeotia except that the

membrane is covered with minute projections;
Fig. 109. Gonatozygon ralfsii de Bary. cells sometimes slightly swollen at the ends.

X about 230. (After de Bary.)

10 (9) Chromatophores consisting of several parietal spiral bands.

Genicularia de Bary.

[|^V'<pii:g.^?^-^^'^-^^^ Diameter of cells 17 to 22.5 n', length

i^'^C-;'-^'^?^;;^^^ 10 to 20 times as great. Alembranc cov-

^?> Ivis-uy *.■.'.■. , :fvs . /i^i ^W ^tiJ^i*! Mi,^ )'S,:^^i^f^ ered with fine projections as in Gotiiitozygon.

Fig. no. Genicularia spirotaenia 'Rx€b\sson. X 265. Spiral chromatophores with many pyrenoids.

(After de Bary.)

11 (5) Cells not cyHndrical 12

12 (19) End view of cells circular, oval, or elliptical, rarely triangular. . 13

13 (16) Cells not deeply constricted at the middle 14

14 (15) Cells cask-shaped, placed end to end, with a shallow narrow con-

striction at the middle; end view circular, with two oppo-
sitely placed projections Gymuozyga.

The membrane frequently shows longitudinal stripes.
iii^ l^Q^if^::::-^ Chromatophores in each cell-half composed of a number
^"^^^^ -"""Vj^!^*) ^^^^r'*^ of radially-placeil plates arranged about a pyrenoid at
^51^: ^}j^^^^^^l^ the center.

Fig. III. GymnozygabTtbissoniiNoT(\sieAi. X s6"^- (Original.)

136

15 (i4)

^Mt?0^W:f

FRESH-WATER BIOLOGY

Cells not cask-shaped, with a narrow, shallow, central constriction:
end view elliptical or triangular, ends tapering or round.

Spondylosium Archer.

Cell? 10 to I 2 /J broad: 8 to g/i long, cells tapering toward?
the ends. Membrane smooth or with slight prominences.
A pyrenoid in each cell-half, about which radiate from 4 to 6
chlorophyll plates.

The cells of the filaments are united by the close adher-
ence of the apices of the cells. The filaments are frequently
twisted and enveloped in mucus.

OAOQ

Fig. 112

Spondylosium papillatum \V. and G. West.
(Original.)

X600

16 (13) Cells deeply constricted in the middle 17

17 (18) Cell-halves acutely pointed or oval; upper and lower surface of each
end furnished with a spine which meets a similar one on the
adjoining cell; end view fusiform. . . Onychonema Wallich.

Narrow spines frequently present. In each cell-half a single axial
chromatophore, composed of radiating plates about a central pyrenoid.

Onychonema occurs in swamps and ponds but is not of very fre-
quent occurrence in America.

Fig. 113. Onychonema loeue 'iioxAsXe.dt. X 600. (Original.)

18 (17) Cell-halves oval in outHne, with a deep central constriction; cells
united into filaments by small tubercles.

Sphaerozosma Archer.

Cells 22 to T^in broad and about half as long, end view elliptical;
membrane smooth or with tiny warts near the ends of the cells.

Sphaerozosma is distinguished from Spondylosium by the cells
being united by tubercles instead of by their apices directly.

S. piilchrum var. inflatum VVolle is reported by WoUe as occur-
ring in such quantities as to color the water green.

Fig. 114. Sphaerozosma veriebratum Ralfs. X about 300. (After de Bary.)

mm

[9 (12) End view of cells triangular or quadrangular, seldom oval.

20

20 (21) No space at the center between the transverse septa; cells slightly
and narrowly constricted Desmidium AgSLvdh.

Filaments long, twisted. Cells flat at the
ends, i to i as long as broad, so constricted
at the center as to give a scalloped lateral
outline to each cell. End view with as many
pyrenoids as there are angles, from each of
which radiate two chlorophyll plates.

Fig. 1 15. Desmidium schwartzii Agardh. a. side
view. b. end view. X 5S0. (Original.)

THE FRESH-WATER ALGAE

137

21 (20) An oval opening at the center between the transverse septa.

Aplogonum Ralfs.

A ^ Filament? often twisted, cells sliKhfly

longer than broad, with three or four
projections on each end which exactly
meet others on the adjoining cells, some-
times slightly constricted. Several py-
renoids in each cell, from which radiate
the plate-like chromatophores.

The genus Aplogonum is included by
many under Desmidiiim, but the space
at the center between two adjoining cells,
the lack of the narrow central construc-
tion, and the greater length of the cells
would seem to distinguish it from Ds-
midiunt.

Fig. 116. Aptogonum baileyi "RdXls. a. side
view. b. end view. c. optical section. X 425.

(Original.)

22 (4) Cells not united into filaments.

23

23 {33) Cells not constricted at the center, or at the most only very slightly

so 24

24 (25) Cells crescent-shaped; tapering toward both ends.

Closterium Nitzsch.
Cells varying from short, thick cells swollen in the
middle to very slender cells sometimes bent in the
shape of an S. Membrane smooth, or longitudinally
striated, rarely with a yellow hue. Chromatophores
in each cell-half of several radially-placed plates,
including one or more rows of pyrenoids; at each
end a large vacuole containing moving granules.

Fig. 117. Closterium moniliferum var. concavum
Ehrenberg. X about 200. (Original.)

25 (24) Cells cylindrical or fusiform 26

26 (27, 28) Chromatophore one or more parietal, spiral bands.

Spirotaenia Brebisson.

Cells straight, oblong, cylindrical, or fusiform, with rounded ends. Chroma-
tophores one or several parietal bands with pyrenoids.

Fig. 118. Spirotaenia minuta Thnrti. X 365. (After West.)

27 (26, 28) Chromatophore star-shaped, one in each cell-half.

Cylindrocystis de Bary.

^0^: /M^'^^^J^ % yS^^ ^^'^^ ^^^^ rounded ends, often oval in outline. Chroma-

C^^^^^^ W^m^^^f^0^^'\ tophores two, star-shaped, many rayed, each enclosing a
■^ 'M;'-'.*:^--^ :c;>^S-.;:v.-;^?&)?' II pyrenoid at the center.

Fig. 119. Cylittdrocystis diplosporaLundcti. X 375- (Original.)

28 (26, 27) Chromatophore straight, simple, or multiple .29

138

FRESH-WATER BIOLOGY

29 (30) Chromatophore a single axial plate with one or more pyrenoids.

Mesotaenium Nageli.

Cells cylindrical, with rounded ends, resembling in structure
A cells of Mougeolia but smaller, sometimes adhering to each other
after division but not forming distinct filaments.

'^ — va'--^«*j ^~%v Fig. I2C. Mesotaenium endlkherianum KdigtW. X 625. a. showing

;.^*^^t¥A~«! '^^fi^^'T^^^^J B the surface of the chlorophyll plate, b. showing the edge of the chloro-
phyll plate. (Original.)

30 (29) In each cell-half several chlorophyll plates 31

31 (32) Margins of radial plates entire; pyrenoids central in each cell-half.

Penium de Bary.

Cells sometimes slightly constricted at the middle, rounded or trun-
i^^^^'^^^X cated at the ends; length 3 to g times the breadth; membrane smooth,

jl^ DgCrl punctate, or longitudinally striated; chromatophores radially placed

- about a large pyrenoid in each cell-half.

Fig. 121. Penium cucurbitinum Biss. X 295. (After West.)

32 (31) Margins of the radial plates of the chromatophore scalloped ; pyrenoids

several and scattered Netrium Nageli.

Cells shaped much as in Penium. The scallops of the outer margin of the chromatophores
conspicuous; pyrenoids not large and forming a center about which the chlorophyll plates
radiate, as in Penium, but small and scattered.

Fig. 122. Melrium lamelhsum Brebisson. X 200. (After Kirchner.)

2,2, (23) Cells constricted at the center 34

34 (42) Constriction at the sides slight and usually gradual 35

35 (38) Length of cells usually not more than six times the breadth. . . 36

36 (37) Central constriction very gradual and shallow; a slight incision at

the ends Tetmemonis Ralfs.

Cells straight, fusiform, or cylindrical, slightly and broadly
constricted at the middle; ends rounded, each with a slight
linear incision; length 4 to 6 times the diameter. Chroma-
tophore axial with a single row of pyrenoids.

Fig. 123. Tetmemorus sranulatus Ra.Us. X 465- (Original.)

37 (36) Cells short, ends truncate, constriction rather abrupt, but not deep;

chromatophore of longitudinal bands; pyrenoids many,
scattered Pleurotaeniopsis Lundell.

_ This is regarded by Brebisson as a Calocylindrus, by de Bary

•^W^«!^l^^ «»^^^ ^^ ^ Pleurotaenium and by West as a Cosmarium. Formerly

'^^j»^j£r^^3?^»%«^-^^S^ VVille recognized the genus, Pleuretaeniopsis, but now includes it

• */ j4&_GL#>j?'- 33:, -^ under Cosmarium.

Fig. 124. Pleurotaeniopsis lurgidus Lund. X 130- (After de Baxy.)

THE IRESH-WATER ALGAE
38 (37) Length of cells many times the breadth. . .

139
39

39 (40, 41) Cells before the middle constriction swollen, but without longitu-
din?: flutings; chromatophore of radially-placed plates, with
pyrenoids Pleurotaenium Lundell

Cells straight, cylindrical, somewhat taper-
ing toward the truncate ends. Membrane
smooth or with small warts; at each end a
Fig. 125. Pleurotaenium nodttlosum Rabenhorst. colorless vacuole with dancing particles as in
X 175- (Original.) Closterium.

40 (39, 41) Cells before middle constriction swollen and with longitudinal
flutings; chroma tophores of longitudinal radial plates.

Docidium Lundell.

Cells tapering somewhat towards the ends; no vacuoles with moving granules; membrane
either smooth or with minute protuberances and even with spines in certain regions.

Fig. 126. Docidium baculum Brebisson. X 545. (Original.)

41 (39, 40) Shape of cells much as in Pleurotaenium, but apices broadly cleft
or with bidentate processes Triploceras Bailey.

Cells large, walls covered with rings of furcate processes or small, perpendicular longitudi-
nally-placed plates. Sometimes confused with Docidium.

Fig. 127. Triploceras gracileBa.Hey. One-half of a cell. (After Cushman.)

42 (34) Constrictions at the sides deep and abrupt 43

43 (44) End views of cells 3 to several angled or rayed.

Staurastrum Lundell.

Side view hour-glass shaped ; membrane smooth or with
warts or spines; chromatophores in each cell-half consisting
of radially-placed plates about a central pyrenoid, two
plates extending into each arm or angle

Fig. 128. Staurastrum crenulatumKa.gfi\. X 600. {Original.)

44 (43) End views of cells compressed or elliptical, often enlarged at the
center 45

45 (48) Cells at end with notches or Unear incisions 46

I40

FRESH-WATER BIOLOGY

46 (47) Cells disc-shaped, each cell-half with three or five lobes, the lateral

ones of which are more or less deeply cut . Micrasterias AgSLidh.

Cells brc ■'dly oval or rounded in out-
line. Midai*; constriction deep, some-
times furnished with spines; lateral lobes
often one or more times dichotomously
divided, the last divisions usually fur-
nished with spines. Chromatophore the
form of the cell, in which are scattered
several pyrenoids.

Fig. 129. MicrasUrias papillifera Brebisson.
One half of a cell. X 365. (Original.)

47 (46) Cells at ends with an incision or undulation, end view elliptical with

one or two prominences on the sides. . . Euastrum Ralfs.

Cells oblong or elliptical, with deep, middle constriction, and
variously incised, concave, or undulating margins. End view
oval, with one or more rounded projections. Membrane some-
times with warts or spines. Chromatophore axial.

Fig. 130. Euastrum elegans Kiitzing. X 588. (Original.)

48 (45) Cells at ends without notches or linear incisions 49

49 (54) Cells without spines 50

50 (51) Cells free Cosmarium Corda.

Cells elliptical or circular, sometimes with more or less
undulating or tapering margins; middle constriction deep and
linear; end view oval or circular, often with rounded projec-
tions. Chromatophore in each cell-half, usually of radiating
plates about one or more pyrenoids; membrane often punc-
tate or with minute warts.

Fig. 131. Cosmarium bolrytis Meneghini. X 575- (Original.)

51 (50) Cells united by branched gelatinous stalks, forming colonies . . 52

52 (53) Colonies loose, not encrusted with lime . . . Cosmocladium Nageli.

Cells as in Cosmarium, but borne
by dichotomously or trichotomously
branched gelatinous stalks, which are
united to form free-swimming or
sessile colonies.

The colonies are invested in an
indistinct gelatinous mass, less dense
than the filaments which connect
the cells. It is sometimes found in
large numbers in rivers and lakes.

Fig. 132. Cosmocladium saxonicum de
Bary. X 250. (After Schroder.)

THE FRESH-WATER ALGAE

141

53 (52) Colony a compact cushion;

stalks encrusted with lime.

Oocardium Nageli.

Cells broad, middle constriction slight, chromatophores two,
pyrenoid in each. Stalks closely placed so that the enveloping
cylindrical lime sheaths make a honeycomb-like structure.

They are sometimes branched and imbedded in the free end
of each is a single cell, placed transversely. It occurs where
water trickles over limestone rocks, and is also reported as
being found in mountain streams.

Fig.

133. Oocardium stratum Nageli. X 485. Portion of figure.
(After Senn.)

54 (49) Cells with spines 55

55 (56) Two or four spines on each cell-half . . . Arthrodesmus Ehrenberg.

General characteristics as in Cosmarium, except that each cell-half is fur-
nished with two or four long spines, and the end view shows no lateral
rounded prominences.

The spines in Arthrodesmus are all arranged in one plane, while in Xanlhid-
iutn they may be arranged in two planes.

Fig. 134. Arthrodesmus convergens Ehrenberg. X about 250. (Original.)

56 (55) Two rows of strong spines on each cell-half 57

57 (58) Spines simple Xanthidium Ehrenberg.

Cells oval or nearly round, with deep, narrow, central constriction; end view
elliptical, often with protruding sides; membrane with two rows of strong,
horn-like spines; chromatophore parietal, more or less divided, with several
pyrenoids.

As in Arthrodesmus the presence and the nature of the spines distin-
guish the genus from certain species of Cosmarium.

Fig. 135. Xanthidium fasciculaium Ehrenberg. X about 300. (Original.)

58 (57) Spines branched Schizocanthum Lundell.

Characteristics similar to those of Xanthidium, except that the
spines are thick, short, and branched at the ends.

West believes that Schizocanthum should be included under
Xanthidium as the only difference is in the spines, and there is too
much variation in these, he thinks, to make separate genera.

Fig. 136. Schizocanthum armatum Lundell. X 106. (After Wood.)

59 (3) Plant filamentous, cylindrical, only one individual originating from
a germinating zygospore . . Family Zygnemaceae . . 60

Cells cylindrical, united into filaments, usually found near the surface of the water. Chro-
matophores different in different genera, but all with several pyrenoids. Reproduction .sexual,
occurring by the conjugation of cells in two parallel filaments, ladder-like, or lateral, between two
neighboring cells of the same filament. Parthenogenesis may occur.

142

FRESH-WATER BIOLOGY

60 (64) In conjugating the whole of the contents of the conjugating cells

passes into the zygospore. Subfamily Zygnemeae . . 61

61 (62, 63) Chromatophores two, axial, star-shaped; a pyrcnoid in the center

of each Zygnema de Bary.

Conjugation either ladder-like or lateral: Zygospore within one of the conjugating cells,
or in the conjugating lube. According to Collins aplanospores may take the place of zygo-
spores, also resting akinetes with granular contents and thickened membrane may be found.

Fig. 137. Zygnema sp. X 600. (Original.)

62 (61, 63) Chromatophore one to several parietal, spiral bands, with many
pyrenoids Spirogyra Link.

Conjugation ladder-like or lateral. Zygospore in one of the conjugating cells. Parthenospores
may be formed.

Fig. 138. Spirogyra crassa Kiitzing. a. conjugation of filaments, b. zygospores X 100. (Original.)

63 (61, 62) Chromatophore an axial plate, with several pyrenoids.

Debarya Wittrock.

Cells long; conjugation ladder-like; zygospore between the con-
jugating cells; the middle layer of the spore membrane yellow, with
three parallel longitudinal grooves, connected by radial striations.

Fig. 139. Debarya glyptosperma Wittrock, showing two zygospores. X 95.
(After de Bary.)

64 (60) In conjugation only a portion of the contents of the conjugating cells
passes into the zygospore.

Subfamily Mesocarpeae . . 65

THE FRESH-WATER ALGAE

H3

65 (66) Chromatophore an axial plate, with several pyrenoids. Zygospore
lens-shaped or flattened and angled, in the conjugating tube.

Mougeolia Wittrock.
Conjugation ladder-like or between two adjoining cells of the same filament. Zygospore in
the inflated conjugating tube, separated from the conjugating cells by two or more transverse
walls.

Fig. 140. Mougeotia sp. a. showing the surface of the chlorophyll plate, b. showing the edge of the
chlorophyll plate. X about 500. (Original.)

66 (65) Vegetative portion as in Mougeotia but zygospore not known.

Gonatone^na Wittrock.

Aplanospores produced between two transverse mem-
branes near the center of an elongated cell. .Spore
membrane double.

Fig. 141. Gonatonema veniricosum '^'\ttTocV. X 250.
(After West.)

67 (2) Plants unicellular or of few cells. Chromatophore one or more

parietal bodies, rarely central 68

68 (190, 249) Plants unicellular, or of few cells united into minute famiUes;

frequently imbedded in gelatinous substance.

Order Protococcales . . 69
Each cell carries on all functions independently, and complexes may be regarded as an aggre-
gate of individuals.

Three forms of reproduction may occur: i, purely vegetative; 2, by asexual zoospores;
3, by isogametes. More than one method frequently occurs in one species; the vegetative
reproduction may be by simple fission or internal division.

69 (89) Vegetative cells or colonies for a portion or the whole of their exist-

ence motile Family Volvocaceae . . 70

70 (77) Cells single or in clusters, not forming a definite colony 71

71 (72) Cells spindle-shaped; chromatophores several, indefinite, with two or

more pyrenoids and a pigment spot.

Chlorogoniiim Ehrenberg.

Cells with two cilia; membrane vcr>' thin, pigment spot in
anterior part. Numerous vacuoles and sovcral pyrenoids present.
Division transverse. Reproduction by isogametes. Wille makes
this genus a section under Chlamydomonas.

Fig. 142. Chlorogonium euchlorum Ehrenberg. o. a cluster of cells.
X about 300. (After Ehrenberg.) b. single cell. (After Stein.)

144

FRESH-WATER BIOLOGY

72 (71) Cells ellipsoidal or nearly spherical 73

73 (74) Membrane widely separated from the chromatophore but connected

with it by protoplasmic strands. Two cilia present.

Sphaerella Sommerfeldt.

Chromatophore netted, with two or more pyrenoids and a pigment spot.
Asexual reproduction by longitudinal division, sexual by isogaraetes. A
palmella condition may occur.

Sphaerella often assumes a red color, due to the presence of hemato-
chromc, and is reported in a few cases as being the organism causing "red
rain." It was also supposed that S. nivalis caused the phenomenon of "red
snow," but the form described by Chodat shows the chloroplast as lying
close to the membrane, so this is probably a Chlamydomonas.

Fig. 143. Sphaerella pluvialis Flotow. X about 600. (After Schmidle.)

Membrane not separated from the chromatophore 75

74 (73)

75 (76)

Two cilia and a pyrenoid present.

Color rarely red.

Chlamydomonas Ehrenberg.

Cells ellipsoidal or spherical; chromatophore single, hollow, parietal; a pigment
spot and two ciha at the anterior end. Reproduction by vegetative division, also
by copulation of gametes which are either alike or slightly unlike as to size. Zygo-
spore green or red. The products of the vegetative division may pass at once into
a motile state with cilia, or may be non-motile, according to conditions in the sur-
rounding medium.

Fig. 144. Chlamydomonas ohioensis Snow. X 1000. (Original.)

76 (75) Structure as in Chlamydomonas but with 4 cilia. Some include this
genus under Chlamydomonas Carteria Diesing.

The shape of the cells in the different species differ rather more
than in Chlamydomonas; the structure of the cells, however, is
identical, except for the cilia. Species also occur in much the same
localities as Chlamydomonas but are less frequent.

Fig. 145. Carteria oblusa Dill. X about 475. (After Dill.)

77 (70) Cells united to form a colony of definite shape which is constantly

in motion 7^

78 (79) Colony not surrounded by a gelatinous envelop.

Spondylomorum Ehrenberg.

Colony of 16 cells loosely united, their anterior ends all pointing
toward one point. The cells are obovate, with 4 cilia at their
anterior ends, a pyrenoid, and a pigment spot. A new colony of 16
originates by successive division from a vegetative cell.

Fig. 146. Spondylomorum quaternarium Ehrenberg. (After Stein.)

79 (78) Colony surrounded by a gelatinous envelop 80

80 (83, 88) Colony not spherical or spheroidal 81

THE FRESH-WATER ALGAE

145

81 (82)

Colony a plate of 4 or 16 spherical cells in a single layer, each with
2 cilia. Boundary of gelatinous envelop not distinct.

Gonium Miiller.

Cells oval, with two cilia and a pigment spot. Chroma-
tophore single, parietal, hollow, with one pyrenoid. Re-
production by successive divisions of each cell, forming a
new colony; also, according to West, by isogametes.

Gonium is one of the commonest of the Volvocaceae,
occurring in almost all ponds and lakes. It is also one
of the most beautiful of the group, as the colonies are ex-
ceedingly regular and as they move they revolve, showing
first the surface and then the edge.

Fig. 147. Gonium pectorale Miiller. X 370. (After West.)

82 (81) Colony flattened, anterior portion rounded, posterior portion with

three wart-Uke projections Plalydorina Kofoid.

"The two faces compressed so that the cells of the two
sides intercalate; flagella upon both faces on alternate cells.
Anterior and posterior poles of major axis are differentiated
by the arrangement of the cells and by the structure of the
envelope; long and short transverse axes differentiated by
the flattening of the colony. Cells similar, bi-flagellate,
each with stigma, chroma tophore, and pyrenoid. Asexual
reproduction by repeated division of all the cells, each
forming a daughter colony."

Fig. 148. Plalydorina caudata Kofoid. X 628. (After Kofoid.)

83 (80, 88) Colony spherical or spheroidal, but small. Cells not numerous. 84

84 (85, 86, 87) Colony of 4 or 8 elongated cells with irregular, pseudopodia-like

processes, arranged in a zone around the center of a firm
gelatinous sphere Stephanos phaera Cohn.

Cells elongated, each with cilia at the anterior pole which
penetrate the gelatinous substance. Chromatophores irregular,
with one or several pyrenoids. Each cell gives rise to a new
colony by division; isogametes are also found.

Fig. 149. Slephanosphaera pluvialis Cohn. X 425- (After Hieronymus.)

85 (84, 86, 87) Colony spheroidal, or slightly elongated, of 8 or 16 cells closely

packed at the center of the indistinct gelatinous envelop.

Pandorina Bory.

Cells heart-shaped, with two cilia at larger end, a pigment sjx^t,
and a pyrenoid, the latter in the posterior end of the hollow
parietal chloroplast. Reproduction by successive division m
each cell whereby as many new colonies are formed as there are
cells; reproduction also by the copulation of gametes cither alike
or slightly unlike as to size; zygospore red.

Fig. 150. Pam/oftna morwm Muller. X about 385. (Original.)

146

FRESH-WATER BIOLOGY

86 (84, 85, 87) Colony spherical or ellipsoidal; cells of two types, vegetative and
gonidial, which lie in the anterior and posterior parts of
the colony respectively Pleodorina Shaw.

Colony consists of a spherical or elliptical coenobium of
greenish, bi-flagellate cells of two types, vegetative and
gonidial, in the anterior and posterior parts of the colony
respectively which lie in the periphery of a hyaline gelatinous
matrix and are surrounded by a common hyaline envelop.
Cells each with one reddish stigma which is more prominent
in the anterior part of the colony. No connecting filaments
between the cells; nonsexual reproduction by gonidia which
are formed by increase in size of a part of the cells of a colony.
Daughters escape from parent as small colonies of bi-flagellate
cells which at this stage arc all similar. Se.xual reproduction
not known.

Fig. 151. Pleodorina illinoisensis Kofoid. X 335. (After Kofoid.)

87 (84, 85, 86)

Colony spherical, of 8 or 1 6, 32 or 64 cells evenly scattered near
the surface of a gelatinous sphere. . . Eudorina Ehrenberg.

Cells spheriail or oval, with two cilia and a pigment
spot. Chromatophore single, parietal. Vegetative re-
production .by repeated division, forming at first a
plate-like daughter colony, which later becomes spher-
ical. Sexual reproduction by a pear-shaped anthero-
zoid and a spherical oosphere.

The cells lie at the surface of the gelatinous sphere
and the cilia project at right angles to the surface. All
of the vegetative cells may become transformed into
oogonia and antheridia; in each of the latter 64 anther-
ozoids are formed. The ripe oospores are brownish
with a smooth external membrane. The habitats of
Eudorina are ponds, ditches, and lakes.

Fig. 152. £«<forino e/f|an5 Ehrenberg. (.\fter Stein.)

88 (80, 83) Colony a larger gelatinous sphere with a very large number of
minute cells at the surface Volvox Linnaeus.

Cells very small, round or pear-shaped, connected by protoplasmic filaments, each with a
pair of cilia, a single chromatophore and two or more contractile vacuoles; reproduction sexual
and asexual; in the latter certain cells (parthenogonidia) within the sphere enlarge and through
divisions give rise to a new colony. Sexual reproduction occurs by the union of a fusiform
antherozoid and oosphere; oospore spherical, with red contents and a spiny membrane.

89 (69) Colonies not motile in the vegetative condition 90

90 (95, 131, 175) Cells in colonies, generally sessile and enclosed in a definite
gelatinous envelop, or borne on gelatinous stalks.
Reproduction asexual by zoospores, or sexual by
isogametes. . . . Family Tetrasporaceae . . 91

91 (94) Cells biciliate, at the surface of an inflated, attached colony. Cilia
external and free 92

THE FRESH-WATER ALGAE

147

92 (93) Colonies macroscopic or microscopic, expanded or intestiform, cells
arranged in fours Tetraspora Link.

Reproduction by division in two directions; zoospores
may originate directly from the vegetative cells, and by divi-
sion give rise to a new colony; isogametes with two cilia may
be formed, also resting spores with heavy brown walls.

Fig. 153. Tetraspora explanataK\i\.z\Qg. X 250. (After Nageli.)

93 (92) Colonies pear-shaped, attached, cells irregularly placed near the
surface Apiocystis Nageli.

Chromatophore single, parietal with a pyrenoid. Division in
three directions. A spherical zoospore with two cilia may originate
from each cell and escape from the gelatinous vesicle.

Fig. 154. Apiocystis brauniana Nageli. X 78. (After Nageli.)

94 (91) . Cells spindle-shaped, clustered on the ends of gelatinous stalks.

Chlorangium Stein.

Chromatophore one or two longitudinal bands; the cells may
detach themselves and become zoospores with two cilia and a
pigment spot. Large numbers of motile individuals may be
formed in each cell, though copulation is not known.

Fig. 155. Chlorangium stentorum Stein, a. X about 200. (After
Cieokowski.) b. (After Stein.)

95 (90, 131, 175) Cells with a thick, often indistinct gelatinous covering,

uniting several together into greater or smaller free swim-
ming, rarely attached colonies. Reproduction by fission or
I internal division ; in a few instances by zoospores and
isogametes Family Palmellaceae . . 96

96 (102, 107) Cells embedded in more or less cylindrical and definite gelat-

inous tubes, strands, or stalks which are broader than the
cells 97

97 (100, 10 1) Cells scattered throughout a gelatinous tulje or strand. . . 98

148 FRESH-WATER BIOLOGY

98 (99) Cells at the ends of, or distributed along rather firm, often lamellate

gelatinous strands Hormotila Borzi.

Chromatophore single, granular, without a pyrenoid. Re-
production by cell division, also by bi-ciliate zoospores, eight
of which are formed in a single zoosporangium. The zoospo-
rangia are much larger than the vegetative cells.

Fig. 156. Hormotila mucigena Borzi. X 268. (After West.)

99 (98) Cells distributed throughout a structureless, cyHndrical, branched

gelatinous colony Palmodaciylon Nageli.

Cells spherical; gelatinous tubes branched or
unbranched. single or in clusters. Division of
cells first in one, later in three directions.
Chrom.atophore parietal and often lobed.

The elongated shape of these colonies is
thought by West to be due to divisions occur-
ring more frequently in one direction than in
others. The plant occurs in swamps and quiet
waters.

Fig. IS". Palmodactylon sp.
colony. X about 600.

Portion of young
(Original.)

100 (97)

%S

Cells two or four in series, at the ends of attached, dichotomously
branched stalks; chromatophores several.

Mischococcus Nageli.

Chromatophores one to four, without pyrenoids. Reproduction by
zoospores and isogametes which may or may not unite before germina-
tion.

Fig. 158. Mischococcus confervicola'^sigtli. X about 180. (After Rabenhorst.)

loi (97,

Cells in radiating series, often branched, held together by
gelatinous strands Dictyocystis Lagerheim.

Chromatophore single, central, and radial. Reproduction probably by division.

Though Dictyocystis is reported by several botanists, it seems a somewhat doubtful genus.

102 (96, 107) Cells at the surface of an invisible gelatinous mass and

borne on fine, radiating gelatinous strands 104

103 (104, 105, 106) Cells reniform, four on a stalk, two borne near the adjoin-

ing ends of the other two. . . Dimorophococcus A. Braun.

Chromatophore single and parietal, each group of
cells formed by the internal division of a single mother
cell.

The filaments which bear the cells are thought by some
to be formed from the remnants of the mother membrane,
but this needs further investigation. Large colonies may
become fragmented into smaller colonies. This alga is
not very frequent, and occurs in larger lakes rather than
in stagnant water.

Fig. 159-

Dimorphococcus lunatus A. Braua.
(Original.)

X 600.

THE FRESH-WATER ALGAE 1 49

104 (103, 105, 106) Cells single, spherical, or oval. Dictyosphaerium Nageli.

Chromatophore single, parietal. Reproduction by internal division.
Fig. 160. Dictyosphaerium pulchellum Wood. X 570. (Original.)

105 (103, 104, 106) Colonies much as in Dictyosphaerium except that the cells

are in clusters of four which are held together by the rem-
nants of the mother-membrane Tetracoccus West.

Some regard this as a young stage in Dictyosphaerium.

106 (103, 104, 105) Cells clustered, grape-like, imbedded in the rather firm,

often yellow gelatinous strands. . . Botryococcus Kiitzing.

'^r^^mftS^yVi West's genus Ineffigiata is probably a Botryococcus where the gelati-

Xr> ^ A>vr\ K^Yp nous envelop is somewhat contracted.

CyQ In old cultures of Botryococcus, and often in nature, an orange

^5^2^ or reddish oil is produced which gives the cells that color.

The alga is found very frequently in pools, ponds, and lakes; it
has been known to form the water bloom on lakes of small
dimensions.

\^Y^ Fig. 161. Botryococcus braunii KJitzing. X about 300. (Original.)

107 (96, 102) Cells not at the surface of a gelatinous mass but distributed

through it 108

108 (109) Colonies cyHndrical, branching; gelatinous envelop somewhat

rigid and often lamellate Palmodictyon Nageli.

, - Cells in groups of two and four, the groups sur-

S Q ® ® ^ ^ o -' rounded by gelatinous vesicles which are united to

® ® o® ^ '^ - ^ " "* form the cylindrical colony, and give a more or less

^ ^--o^ o'*' netted appearance to the gelatinous portion. Repro-

. duction by means of resting spores with brown walls;

^ - ^ these spores germinate and produce a new colony.

/ West states that the outer coat often becomes very

^ ' © ^ . ~ tough and of a brown color. Palmodictyon is a

\ 0^_^' very rare alga in America, but Collins reports it

-^ ^3 '*' **o ''' from Massachusetts.

••^ , "> ^^ ' ' Fig. 162. Palmodictyon viridis YMUing. X 210.

,,^ (After West.)

109 (108) Colonies of no definite shape, of the shape of the individual cells, or

more or less angled and showing a dark gelatinous layer be-
tween the cells. Cells often isolated no

110(127,128) Colonies irregular m

111 (120) Cells not in clusters "2

112 (lis) Gelatinous envelop containing concentric lamellae about the

ceUs "3

150 FRESH-WATER BIOLOGY

113(114) Cells spherical Gloeocystis Kaigeli.

The enveloping gelatinous substance showing a concentric lamellate structure.

Reproduction by repeated cell division, several generations of cells often re-
maining enclosed in the original mother-membrane. According to some
authors reproduction also occurs Vjy bicilliate zoospores.

The authenticity of this genus is doubtful as the non-motile stage of certain
species of Chlamydomonas answers this description.

Fig. 163. Gloeocystis vesiculosus K&gtW. X 150. (After Nageli.)

114 (113) Cells elongated Dactylothcce Lagerheim.

Chromatophore a parietal plate lying only on one side of the cell; no pyrenoids.
Gelatinous substance often lamellate.

m

115 (112)

Fig. 164. Dactylothcce braunii Lagerheim. X about 370. (After Lagerheim.)

Gelatinous envelop not containing concentric lamellae about the
cells 116

116 (117) Gelatinous mass containing segments of the antecedent mother
cell Schizochlamys A. Braun.

Cells spherical, scattered in a gelatinous mass together
with the visible remnants of the old membranes which
are split into distinct segments.

West believes that it is the formation of the large amount
of gelatinous material that causes the firmer portion of
the membrane to become ruptured, and that this takes
place previous to the formation of the two or four daughter
cells. 5. gelatinosa is the only species reported in
America, and this occurs as a pale green irregular mass
either free or adhering to water plants.

Fig. 165

Schizochlamys gelatinosa A. Braun.
(Original.)

X 600.

117 (116) Gelatinous mass not containing segments of the antecedent mother-

membrane 118

118 (119) Cells throughout the gelatinous mass formed by the outer layers

of the cell walls Palmella Lyngbye.

Chromatophore parietal, with a pyrenoid. Reproduction by division in three directions,
and according to Wille, by macrozoospores, microzoospores, and isogametes.

119 (118) Cells at the surface of the gelatinous mass.

Dictyosphaeropsis Schmidle.

Cells free or attached, round or elongated. One or two disc-.shaped,
parietal chromatophores present. Reproduction not well known.

Fig. 166. Dictyosphaeropsis palalina Schmidle. X 375- (After Schmidle.)

120 dii) Cells in clusters, usually of eight, sometimes four or sixteen; colonies,
mostly floating 121

THE FRESH-WATER ALGAE

151

121 (124) Cells spherical 122

122 (123) Chromatophore single Sphaerocystis Chodat.

Colonies large; clusters widely separated from
each other. Gelatinous envelop invisible without
reagents. Chromatophore thin, parietal, with a
pyrenoid on one side and an opening on the other.
Reproduction by internal division.

Sphaerocystis is almost universally found in the
plankton and is one of the most conspicuous and
beautiful of all the plankton forms. Sometimes the
colonies are very large, consisting of many clusters.

Fig. 167. Sphaerocystis schraeleri Chodat. X 520.
(Original.)

123(122) Chromatophores many, parietal C hlorobotrys BohVm.

Cells spherical, in a gelatinous matrix, as in Sphaerocystis, but the
chlorophyll in many parietal discs.

Fig. 168. Chlorobotrys regularis Bohlin. X 300. (After West.)

124 (121) Cells not spherical 125

125 (126) Cells crescent-shaped Kirchneriella Schmidle.

Cells in clusters, as in Sphaerocystis, but strongly
crescent-shaped .

In reproduction internal division takes place trans-
versely and the four or eight daughter cells are set
free by the breaking of the cell wall.

Several species occur in the plankton. They also
occur in ponds among water plants.

Fig. 169.

Kirchneriella obesa Schmidle. X 600.
(Original.)

126(125) Cells oval or bluntly pointed Oocysiis N-^ge\l

Cells oblong, single, or two, four, or eight in a gelatinous
envelop; in some cases many clusters in a colorless gclatmous
matrix. Chromatophore single, parietal, with an openmg on
one side or of many small discs. Pyrenoids present m some
species. Cells single or in clusters, as in Sphaerocystis, but
ellipsoidal in shape. , . , , , ,

Oocystis is frequently found m the plankton where it is
usually in large gelatinous colonies similar to Sphacrocyslts
and Kirchneriella. In other localities the cells are generally
solitary.

Fig. 170. Oocystis solitaria Wittrock. X 6cx). (Original.)

152 FRESH- WATER BIOLOGY

127 (no, 128) Colonies somewhat cubical, showing a dark, gelatinous layer
between the cells Gloeotaeniiim Hansgirg.

^|?r< "^ Cells plobose or flattened, colonies of two, four, or eight cells, with

wide lamellate walls. Reproduction by aplanospores.

Fig. 171. Gloeotaenium loitelsbergerianum'Ra.xisghg. X 220. (After Transeau.)

128(110,127) Colonies the shape of the individual cells 129

129 (130) Cells reniform, colony of the same shape or oval.

Nephrocytium Nageli.

Cells single or in clusters, as in Sphaerocyslis, but reniform in
shape.

Nephrocytium resembles Oocystis except that the cells are curved.
It is widely distributed but not very abundant.

Fig. 172. Nephrocytium agardhianum Nageli. X 580. (Original.)

130(129) Cells fusiform ElakatothrixWdle.

Cells elongated, fusiform, gelatinous sub-
stance dense, often lamellate.

Fig. 17.?. Elakatothrix viridis Wille. X 575-
(Original.)

131 (90, 95, 175) Cells without a thick gelatinous envelop holding them

together; sometimes adhering to each other after di-
vision 132

132 (137, 155, 174) Reproduction by fission only, or rarely by fission and

internal division. . . Family Pleurococcaceae . . 133

^33 (134, 135, 136) Reproduction by fission in one direction only, forming
equal cyHndrical cells, the length being one and one-half to
three times the breadth Stichococcus Nageli.

Chromatophore a parietal plate lying only on one side of the cell,
with no pyrenoid. Reproduction by simple fission, the cells sometimes
adhering to each other after the division, but not forming perfect
filaments.

Fig. 174. Stichococcus bacillaris Nageli. X about 400. (Original.)

134 (i33> i35> 136) Reproduction by division in three directions. Cells
spherical or, if in small complexes, somewhat angled.

Pleurococciis Meneghini.

Cells either single or in small clusters of two, four, or more cells which later
fall apart. Chromatophore a thin lining to the membrane with an opening on
one side, and with or without a pyrenoid.

Pleurococciis is the chief constituent of the green coating on the bark of trees,
old wood, and stones.

Fig. 175. Fleurococcus vulgaris Mcaeghiai. X 560. (Original.)

eecis

0

8

00

%

^%

^.

<^

^V

11

0

0

THE FRESH-WATER ALGAE

153

135 {^33i i34> 13^) Characteristics as in Pleurococcus, but sometimes forming
short filaments Pseudo- pleurococcus Snow.

This form may remain indefinitely in either
a filamentous or unicellular state according
to the conditions in the environment. In
the filamentous state it resembles a small
form of Sligeoclonium, but is distinguished
from it by the absence of zoospores.

Chodat regards a form similar to this as
a true Pleurococcus and believes that short
filaments are characteristic of that genus.

Fig. 176.

Pseudo-pleurococcus vulgaris Snow.
X 600. (Original.)

136 (133, 134, 135) Reproduction by fission in three directions and by inter-
nal division Palmellococcus Chodat.

Chromatophore a parietal plate, without a pyrenoid. In addition to reproduction by fission
and internal division, a rejuvenescence of the cell contents may occur, accompanied by a cast-
ing off of the mother-membrane. An orange-red oil is sometimes present.

174) Reproduction by internal division only.

Family Chlorellaceae .

137 (132, 155,

138 (142, 151)

139 (140, 141)

138

Cells spherical, ellipsoidal, or irregular. Membrane
smooth 139

Cells spherical; chromatophore a single, hollow sphere with
one pyrenoid Chlorella Beyerinck.

Cells spherical or somewhat elongated; chromatophore lining the mem-
brane, open on one side, with a single pyrenoid.

The name Zoochlorella Brandt has been given to this same genus and ante-
dates the name of Chlorella by some years, but the name Chlorella seems
more appropriate.

Fig. 177. Chlorella sp. X 600. (Original.)

Cells spherical, chromatophore of many parietal discs, each
with a pyrenoid Eremosphaera de Bary.

Size relatively large; chromatophores many, parietal; nucleus
prominent. Reproduction by internal division.

The cells are large, spherical, and conspicuous. The nucleus is
distinct, suspended in the middle of the cell by strands of proto-
plasm. Two or four daughter individuals may originate by succes-
sive division of the contents and are Hberated by the rupturing of
the mother membrane. Eremosphaera is almost constantly found
among Desmids in Sphagnum swamps.

Fig. 178. Eremosphaera viridis de Bar>'. X 125. (Original.)

141 (139, 140) Cells spherical or irregular; chromatophores many, angular,

radially arranged; many pyrenoids in each.

Exccntrosphaera Moore.

Plant consisting of a single cell, in mature condition var>-inR
in outline from spherical and elliptical to irregular and eccentric
forms. Chromatophores large, angular, usually radiately ar-
ranged, closely lining the wall. Pyrenoids minute, numerous ui
each chromatophore. Multiplication by non-motile sjwres
(aplanospores) which escape by the dissolution of a part of
the cell wall. Reaction to all external stimuli negative.

Fig. 179. Excentrosphacra viridis Moore. X 160. (.After Moore.)

142 (138, 151) Cells spherical or elongated, membrane with hairs, spines, or

reticulate markings i43

154

FRESH-WATER BIOLOGY

143 (147) Cells spherical 144

144 (145, 146) Cells solitary, membrane with short spines or network.

Trochiscia Kiitz.

Cells perfectly spherical, the spines or reticulate markings project-
ing but little.

Chromatophores usually several. Reproduction by internal division.
West also reports reproduction rarely by fission and by zoospores. The
genus needs further investigation.

Fig. 180. Trochiscia vestitus Reinsch. X about 260. (After Reinsch.)

145 (144, 146) Cells solitary, bristles long, rigid, scattered over the entire
surface Golenkinia Chodat.

Reproduction occurs by division in one or two directions and
by autospores. Chodat also reports the formation of zoogonidia
with four cilia.

Golenkinia has been known to occur in great quantities almost
pure in large tanks of water; it also occurs in the plankton,
though not very abundantly. Chromatophore parietal, with one
pyrenoid.

Sir Ray Lancaster believes that his Archerinia bolloni de-
scribed in 1885 and referred to the Protozoa is identical with
Golenkinia radiata described by Chodat in 1894, and with
Richteriella botryoides described by Lemmermann in 1898. If
this be true the name Archerinia claims precedence over the
other two generic names.

Fig. 181. Golenkinia radiata Chodat. X 625. (Original.)

146 (144, 145^

Cells in colonies of eight, sixteen, thirty-two, sixty-four, or
more cells; bristles long, only on the outer surface of a col-
ony Richteriella Lemmermann.

Bristles comparatively coarse and in length many
times the diameter of the cells. Chromatophore single,
parietal, with a single pyrenoid.

The cells are usually clustered in groups of four which
are aggregated into larger colonies. But little is known
of its reproduction except that vegetative division has
been known to occur.

It is found in the plankton of large lakes.

Fig. 182.

Richteriella glohosa Lemmermann. X 556. (After
Lemmermann.)

147 (143) Cells somewhat elongated 148

148 (14Q, 150)

Bristles four, two at each end or one at each end and two at
the center, each with a basal swelling. . Lagerheimia Choddit.

Cells ellipsoidal, with four spines on short pedicels. Chromatophore
single, parietal, with a single pyrenoid. Reproduction by internal
division.

Chodat and West recognize the genus Lagerheimia but it is very doubtful
whether the presence of only four spines with basal swellings is sufficient to
remove it from the genus Chodatella where the spines are more numerous
and have not the basal swellings.

Fig. 183. Lagerheimia genevensis Chodat. X 275- (After Chodat.)

THE FRESH-WATER ALGAE

155

149 (148, 150) Bristles varying in number, without a basal swelling. Cells
single Chodatella Lemmermann.

/ Cells solitary, ellipsoidal; spines evenly distributed over the

surface or in circles about the ends. Chromatophore parietal,
^ / with or without pyrenoids.

Chodatella is occasionally found in the plankton of larger lakes.

Fig. 184. Chodatella cilriformis Snow. X 500. (Original.)

150 (148, 149) Bristles numerous, on the outside of the colony only. Cells
usually united into a small cluster by a gelatinous substance.

Franceia Lemmermann.

Chromatophores two, each with a pyrenoid.

This genus in its general characteristics resembles Richteriella
but it is distinguished from it by the larger size and oval shape
of the cells, the shorter spines and the two chromatophores.

Reproduction takes place by division in a single longitudinal
direction.

Fig. 185. Franceia sp. X about 600. (Original.)

(138, 142) Cells of some other shape than spherical or elliptical; with
points or angles 152

(153, 154) Cells needle-like or fusiform, often variously curved, the length
often many times the diameter. . . Ankistrodesmus Corda.

Ankistrodesmns is found in all ponds,
lakes, and rivers. It is one of the most
common and one of the hardiest of the
unicellular algae.

Fig. 186. Ankistrodesmus. Various species.
X 600. Orl inal.)

151
152

G

153

154

(152, 154) Cells short, fusiform, length two to four times the diameter.

Ddctylococciis Niigeli.

Cells free, short, nine to eighteen n long. Chromatophore with a pyrenoid,
opposite to which there is an opening. In reproduction two to eight cells are
'^J formed by transverse internal division.

Fig. 187. Dactylococcus infusionum Nageli. X 600. (Original.)

(152, 153) Cells distinctly three, to many-angled, angles all in one plane or
not; at the ends often one or more simple or divided spines.

Tetracdron Kiitzing.

Chromatophore single, parietal, usually with a pyrenoid.

In this genus there is the greatest variety in regard to the shape,
of the cells, number of points, and size; the most common one is,
however, a minute form with but few points.

Fks. 188. Tetracdron enorme»de Bary. X 600. (Original.)

156 FRESH-WATER BIOLOGY

155 (132, 137, 174) Reproduction by the formation of zoospores only, or by
isogametes Family Protococcaceae . . 156

156(161, 168) Cells spherical 157

157 (158) Chromatophores many, parietal Botrydiopsis Borzi.

/^^^1?xC/"^ Chromatophores without pyrenoids; zoospores amoeboid, with

itfJ^:5rSs*Sr4, V B ^ single ciHum, a pigment spot, and one (sometimes two) chroma-

l^i^Kl^; V^say tophores; frequently they germinate within the mother-membrane

%'^^^^ ^^^ without a motile period.

^1 mo^ Fig. 189. Botrydiopsis eriensis Snow. a. vegetative cell; b. zoospores.

^ ^ ^^^X^^ Xs8o. (Original.)

158(157) Chromatophore single i59

159 (160) Chromatophore parietal Chlorococcum Fries.

^y- Chromatophore with a circular opening and a pyrenoid; zoospores

^ I g^ oval, with two cilia, a pyrenoid, and a pigment spot. Aplanospores

may' form from non- liberated zoospores. An undescribed form

^ which greatly resembles Chlorococcum has isogametes. It should be

Y placed in a different genus.

§ Fig. 190. Chlorococcum infusionum Rabenhorst. a. vegetative cell.

AS *• zoospores. X 625. (Original.)

160 (159) Chromatophore central with radiating strands.

Radiosphaera Snow.

"^ /^7\ '^-\ Except for the nature of the chromatophore this genus

\ resembles Chlorococcum, but at the center is a pyrenoid

i^'^' Q\ from which the chromatophore radiates. Zoospores

If vt cs^. with two cilia and a pigment spot are formed.

A "^ "^^
^ \ l\ y — Fig. 191. Radiosphaera sp. Snow. a. vegetative cell;

A V I \ ^ *• zoospores. X 580. (Original.)

B

161 (156, 168) Cells more or less irregular, elongated, or tubular. ... 162

162 (163) Cells free, more or less inflated or tubular, usually with a long,

colorless cylindrical portion Protosiphon Klebs.

Chromatophore a parietal, net-like layer, with pyrenoids. Under conditions threatening
drought, red resting spores are formed. In absence of light or mcrease of water bi-ciliated
zoospores are formed which on coming to rest produce spherical cells, or they may copulate and
produce star-shaped zygospores.

Fig. 19a. Protosiphon botryoides Klebs. X 75- (After Klebs.)

163 (162) Cells endophytic, rarely free, irregular, often with cellulose pro-
jections 164

THE FRESH-WATER ALGAE

157

164 (165) Reproduction by zoospores: chromatophore of many radially-

placed rods or segments united beneath the surface.

Scolinospliacra Klebs.
Zoospores fusiform; their production preceded by a
contraction of the chromatophore to the center, about
which there is a granular substance; zoospores penetrate
some water plant or germinate in the water.

Resting cells occur which have one or more thicken-
ings of the membrane.

It was first found in the dead leaves and branches of
Ilypniim, and its normal habitat is probably in the
tissues of some higher water plant, but it occurs fre-
quently in the water and may be cultivated with ease.
Fig. 193. Scotinosphaera paradoxa Klebs. X about 265.
(After Klebs.)

165 (164) Reproduction by copulation of isogametes and in some cases by

zoospores 166

166 (167) Chromatophore a parietal layer with many pyrenoids, later show-

ing a network. Membrane with cellulose projections.

Chlorochytrium Cohn.

Cells spherical or slightly irregular; chromatophore
with many inwardly projecting portions containing
many pyrenoids. The zoospores are liberated singly;
the gametes escape together while still enveloped by the
inner lining to the membrane in which they copulate.

Chlorochytrium occurs in the intercellular spaces of
Lemna. In some species a cellulose projection extends
to the surface of the epidermis at the point of penetra-
tion of the zoospores, but is not found in all.

Fig. 194. Chlorochytrium lemnae Klebs. Cells in the tissues
oi Lemna. X 500. (After Klebs.)

167 (166) Chromatophore dense, with many starch grains: membrane lamel-

late Endosphaera Klebs.

Cells spherical or irregular, found in the tissue of water plants.
In reproduction internal divisions occur, giving rise to eight or sixteen
oval isogametes with two cilia and a pyrenoid. The zygospore {pene-
trates into the intercellular spaces of Patamogetoti if it is present, but
C dies if it cannot be found.

In the spring time it is found as large resting cells in the tissues
of the dead leaves.

Fig,

195. Endosphaera biennis Klebs.
of gametes, a. X about 190; b,

a. young cell; b. gametes; c. union
. X about 400. (After Klebs.)

168 (156, 161) Cells with a thin stalk-like projection on one or both ends,

either free or attached i6q

169 (170) Cells free, Hnear, curved, or spiral, ends with a spine or stalk-like

projection Ophiocytium Niigeli.

Chromatophore single, parietal, with no pyrenoid. Reproduction by
means of zoospores, eight of which are formed in a single cell and are
liberated by the end of the cell being thrown oflf like a cap.

Though the habitat of Ophiocytium is the same as for a number of
other Protococcaceae, it is not so frequently found. When it does
occur, however, in a body of water it may be abundant.

Fig. 196. Ophiocytium cochleare A. Braun. X 600. (Original.)

170 (169) Cells similar, but shorter and attached 171

158

FRESH-WATER BIOLOGY

171 (172, 173)

172 (171, 173)

Cells single, attached; oval, cylindrical, fusiform, or curved
in shape. Chromatophore single and parietal.

Ckaracium A. Braun.

Cells oval, pointed, or rounded at the ends, straight or curved,
sessile or stalked; attached to a substratum with or without a disc.
A pyrcnoid usually present. Reproduction by zoospores which have
two cilia, a pyrenoid, and a pigment spot.

Characium is very common on filamentous algae in all localities. The
shape is greatly influenced by the direction of the rays of light.

Fig. 197. Characium longipes Rabenhorst. X 600. (Original.)

Cells as in Characium, but the chlorophyll in many small,
parietal discs Characiopsis Borzi.

The color is pale green. The zoospores are liberated by the wall of the
upper portion of the cell becoming dissolved. According to West, aplano-
spores may be formed, each of which becomes a gametangium and pro-
duces two or four gametes. Characiopsis is less frequent than Characium
but is found under the same conditions.

Fig.

Characiopsis sp. X 600. (Original.)

173 (171, 172)

174 (132

Cells attached, the new generation clustered at the free tip of
the empty mother cell Sciadium A. Braun.

Thallus of six to eight cylindrical cells, radiating from the tip of
a sessile, empty, cylindrical membrane; reproduction by six to eight
zoospxjres with two cilia each, which attach themselves at the tip of
the mother-membrane after the removal of a cap which liberates the
spores.

Lemmermann unites Sciadium with Ophiocytium because rarely in
Ophiocytium the new generation develops from one end of the parent
cell, but the sessile characteristic and the basal disc of Sciadium
would seem to separate it from Ophiocytium where these characteris-
tics are not found.

Fig. 199. Sciadium arbuscida K.'BraMn. X 600. (After Rabenhorst.)

Reproduction by fission and by zoospores.

Family Chlorosphaeraceae.
Only one genus known Chlorosphaera Klebs.

Cells usually in small cell complexes, originating by fission in
three directions. Chromatophore parietal, with a pyrenoid. Zoo-
spores usually eight in number, originating by successivelnternal
divisions. These have two cilia and a pigment spot. Each vegeta-
tive cell may become a resting spore.

In its vegetative state Chlorosphaera resembles greatly Pleura-
coccus vulgaris, but it is aquatic, rather than aerial. It is a common
form in ponds and lakes, though rarely found in such quantities as
to be noticed, unless developed in culture.

Fig.

Chlorosphaera lacustris Snow. X 585. (Original.)

175 (90, 95, 131) Cells without a gelatinous envelop or stalks; closely united

to form structures of definite shape (coenobia) . ... 176

176 (187) Coenobium usually a cluster of definite shape and structure, formed

by the union of four, eight, sixteen, or thirty-two non-
motile cells arising from internal division.

Family Coelastraceae. . , 177

177 (182, 186) Cells radially placed or forming close clusters 178

THE FRESH-WATER ALGAE

159

178 (179, 180, 181) Cells spherical Coelastrum Nageli.

Cells spherical or slightly angled; chromatophore a hollow sphere, open
at one side, with a pyrenoid opposite the opening.

Coelastrum occurs in all bodies of water, and is found in the plankton.
It is very resistant to unfavorable conditions, persisting long after most
other algae have perished.

Fig. 201. Coelastrum sphaericumK?iigi:]i. X 020. (Original.)

(178, 180, 181) Cells cordate or reniform Sorastrum Kutzing.

Chloroplast parietal, with a single pyrenoid. Cells on short stalks
radiating from a gelatinous center, but both center and stalks usually
hidden by the cells. A new coenobium from each cell.

Sorastrum is of less frequent occurrence than most of the other
members of the Coclastraceac, but is found in most localities where
they are found, especially in the sediment at the bottom of ponds,
and occasionally in the plankton.

Fig. 202. Sorastrum spinulosum Nageli. X 600. (Original.)

180 (178, 179, 181) Cells crescent-shaped, points turned outward.

Selenastnim Reinsch,

Cells acutely pointed. Chromatophore parietal, with no pyrenoid. By many
this is placed near to Ankistrodesmus rather than with the Coclastraceac.

Fig. 203. Selenastrum gracile Reinsch. X 565- (Original.)

181 (178, 179, 180) Cells club-shaped or elongated, forming a star.

Actinastrum Lagerheim.

Rays pointed, each ray composed of a single cell, all of which unite at the center.
Chromatophore single, parietal, often not extending to the ends.

Fig. 204. Actinastrum hantzschii Lagerheim. X SSO. (Original.)

182 (177, 186) Cells in one plane.

^83

183 (184, 185) Cells four, eight, or sixteen in one or two parallel or zigzag
rows Scenedesmus IMeyen.

The cells oval or pointed, the membrane either smooth or
furnished with distinct spines at the ends. Chromatophore
single, parietal, with an opening at one side and a pyrenoid.

This is one of the most common and the best known of
all of the lower algae, it being found in almost all localities
where algae are ever found. Its adaptation to various
environments, and to conditions unfavorable to most other
algae, accounts for its wide distribution.

Fig. 205. Scenedesmus quadricauda Br6b. X 585- (Original.)

184 (183, 185) Cells grouped in fours, forming a rectangular plate of sixteen
or more cells Criicigcnia IMorrcn.

Cells spherical or elongated. Chromatophore thin, parietal, with a circular
opening and one pyrenoid. This is regarded by Schmidle as Staurogema.

Fig. 206. Crucigenia apiculata Chodat. X 1000. (Origin*!.)

i6o

FRESH-WATER BIOLOGY

185 (183, 184) Cells four together, never forming larger plates. From two to

five spines on the external margin of each cell.

Tetrastriim Chodat.
Schmidle regards those forms with spines simply as different species of Staurogenia.

186 (182, 177) Cells four, lying in two planes Tdradesmus Smith.

^^HZi^JSH^Sr^^^ This coenobium resembles a Sccnedesmus rolled up, and in the size, shape,
:,^:-:^j^ and structure of the cells they are the same.
* ® -^ Pjc 207. Tetradesmus wisconsiensis Smith. X 1500. (After Smith.)

187 (176)

188 (189)

189 (ll

Coenobium a coarse net or a concentrically-arranged circular disc of
cells, formed by the joining together of zoospores while within
the mother-membrane, or still within the liberated inner
lining of the same. . . Family Hydrodictyaceae . . i88

Coenobium a free-swimming circular plate of cells, one layer in
thickness Pediastrum Meyen.

The cells arranged either with intercellular spaces or not; marginal
cells with one or two pointed projections; inner cells angled or concave;
chromatophore parietal, with one pyrenoid, and perforated at one side.
Reproduction b}' means of zoospores which are Cast out together with
the inner lining of the mother-membrane, and within which they form
a new coenobium.

An alga which greatly resembles a two-celled Pediastrum was formerly
described as Euaslrum by Schmidle, but Lagerheim places it in a new
genus Euaslropsis. The mode of reproduction is the same as for Pedi-
aslriim; the zoospores, however, arrange themselves in pairs instead of
in a single plate, and form a number of new individuals which are set
free while within the inner layer of the mother-membrane.

Fig. 208. Pediastrum boryanum Meneghini. X 600. (Original.)

Coenobium a coarse net Hydrodictyon Roth.

Nets large, each mesh bounded by five or six
cyhndrical cells; the chromatophore reticulate,
parietal, with numerous pyrenoids; asexual re-
production by zoospores, those from each cell
forming a new net; sexual reproduction by
many isogametes. The zygospore produces
two to five large zoospores which in turn give
rise to a new net when they germinate.

In the early stages the nucleus is single, but
later divides rapidly so that the cell is multi-
nucleate. As the nets are formed within the
cyhndrical mother-membrane they are cylin-
drical in shape for some time, but later become
torn and irregular. The nets occur as a very
thick light green scum on the surface of ponds
exposed to the direct rays of the sun. The dif-
ferent modes of reproduction have been proved
by Klebs to depend largely on the condition in
environment, and that by varying these condi-
ditions the different phases to development can
be produced.

Fig. 209.

Hydrodictyon reticulatum Lagerheim.
X 100. (Original.)

190 (68, 249) Plant of septate filaments, or of closely-arranged cells, forming

plates or cylinders, one or more layers thick; attached or

free-swimming Order Confervales . . 191

Reproduction asexual, sexual, or both in the same species.

191 (196, 246) Plant in adult form a macroscopic, free-swimming plate or

hollow cyhnder of cells; in early stages often filamentous
and attached Family Ulvaceae . . 192

THE FRESH-WATER ALGAE

l6l

:92 (193) Plant cylindrical, flattened, or branched, of a simple layer of cells,
reproduction by zoospores and isogametes.

Enteromorpha Link.

^

Frequently branched and variable in shape; chromatophore
parietal, with one pyrenoid. Zoospores with four cilia and a
pigment spot. Gametes with two cilia.

Both zoospores and gametes are formed in the vegetative
cells except those at the base.

The greater number of species of Enteromorpha are marine,
though E. intestinalis is found in the fresh water. Many of
the salt-water forms are very variable so that the species are
difl&cult to determine.

Fig. 210. Enteromorpha intestinalis L. (Link), a. one-half natural
size. (After West.) ft. X 360. (Original.)

A B

193 (192) Plant in the adult stage a thin, membranaceous plate. ... 194

194 (195) Chromatophore a thin, parietal lining to the membrane, with one

pyrenoid Monostroma Wittrock.

The plant in early stages a hollow sack or cylinder, becoming
torn later, forming a membranaceous plate, near the base of
which certain cells elongate, grow downward and form strength-
ening supports. Reproduction by means of zoospores with four
cilia and smaller gametes with two cilia. These may germinate
without copulation.

The membrane is at first very thin, but later becomes gelati-
nous so that the cells are more or less separated from each other.
Growth is not localized but is intercalary and the cells are often
clustered in groups of four.

Monostroma hullosum occurs in shallow ditches, partially sub-
merged and partially swimming on the surface.

Fig. 211. Monostroma bullosumThMrtt. X 3SO. (After Reinke.)

[95 (194) Chloroplast star-shaped, radiating from the center, with one pyre-
noid Prasiola Meneghini.

Plant at first filamentous, but later a plate of cells grouped in
small areas. Rhizoids frequent at the base. Reproduction, ac-
cording to Lagerheim, in three ways: by isolated iwrtions of the
plant, akinetes, and aplanospores. No zoospores known.

Kiitzing has estabHshed a genus Schizogonium which greatly re-
sembles Prasiola. The chromatophore is stellate and the filarnents
divide longitudinally to form two or more rows. The chief differ-
ence between this and Prasiola is that in the latter genus the
longitudinal divisions continue, while in the former they cease
after the first few times.

Wille makes Schizogonium a subsection under Prasiola and is
followed in this by West.

Fig. 212. Prasiola crispa Mtntghxm. X about 50. (After Oltmann
and Meneghini.)

196 (191, 246) Plant filamentous i07

197 (219) Filaments fine, mostly unbranched 198

198 (217, 218) Filaments generally unbranched. Chromatophore a single.

parietal curved plate or cyhnder, rarely a.xial, or of several

small, distinct discs, rarely more or less united into a network.

Family Ulothrichaceae . . 199

I

1 62 FRESH-WATER BIOLOGY

199 (211, 212, 213) Thcchromatophoresingle, a parietal plate or cylinder. 200

200 (205) Filaments without gelatinous envelop 201

201 (204) Filament always simple, composed of a single row of cells. . 202

202 (203) Cells cylindrical. Reproduction by zoospores and in some cases

by resting spores Hormidium Kutzing.

Zoospores formed singly in each cell; they have two cilia but no pig-
ment spot. Resting spores occur with reduction of moisture.

Fig. 213, Bormidium nitenz Meneghini. X 400. (Original.)

203 (202) Cells but little longer than broad. Reproduction by zoospores
and isogametes. ' Ulothrix Kutzing.

Cells relatively short; chromatophore lining the entire
rnembrane, or only a part, with a pyrenoid. Reproduc-
tion by zoospores and isogametes. Zoospores with four
cilia and a pigment spot; gametes smaller, with two cilia,
capable of germinating without copulation.

Ulothrix occurs frequently among other algae in ponds,
lakes, and watering troughs, though not often in great
quantities.

The resemblance to Hormidium is great, though the
species of the latter genus are apt to be somewhat smaller,
and the length of the cells relatively longer in proportion to
the breadth.

Ulothrix yields readily to cultivation, and different phases
of its development may be controlled by changes in the
environment.

Fig. 214. Ulothrix zonata Kutzing; a. vegetative filament. X
225. 6. macrozoospore. X388. c. microzoospore. (After Klebs.)

204 (201) Filament at first simple, later becoming a solid mass of many cells.

Schizomeris Kutzing.

THE FRESH-WATER ALGAE

163

Plant in early stages like Ulothrix. later forming
a slender, solid parenchymatous filament; reproduc-
tion by zoospores, one from each cell

Quantities of the zoospores are liberated from a
filament at a time, the walls becoming partially gelat-
inous, but showing a parenchymatous structure after
the liberation.

By some European writers the genus is regarded as
the same as Ulothrix, but forms such as are found in
America must establish it as a separate genus. The
zoospores have four cilia and a pigment spot, as in
Ulothrix; the vegetative cells may change into resting
spores.

Schizomeris has been found growing on river banks
and in quiet fresh water.

Fig. 215. Schizomeris leibleinii Kiitzing. a. portion of
filament. X about 625. b. portion of filament showing
division in all directions. X 3°°- c. zoospores. X 625.
(Original.)

205 (200) Filament with gelatinous envelop 206

206 (209) Cells not in distinct pairs 207

207 (208) Cells oval, gelatinous envelop homogenous.

Hormospora Brebisson.

^ This is regarded by many as being but a

phase in the development of Ulothrix, but the
very gelatinous membrane, the rounded ends
of the cells, and the fact that this form is not
known to reproduce by zoospores would indi-
FiG. 216. Hormospora mutabilisBT€hisson. X about cate that it is an independent genus.
600. (Original.)

208 (207) Cells rounded. Gelatinous sheath showing radial fibrillar struc-

ture Radiofiluyn Schmidle.

Chromatophore single, parietal, with one pyrenoid.
Cells spherical, ellipsoidal, or lenticular, in some
species united by short necks. Filaments unbranched.
Reproduction by simple division. Wille includes
Hormospora and Radiofilum with Geminella, a genus
not known to occur in America.

209 (206) Cells mostly in pairs -^°

210 (211) Cells rounded, gelatinous substance lamellate, invested by the

antecedent mother-membrane. . . . Binuclearia Wittrock.
Filaments attached when young; each cell pair
originates from the contents of a single cell, and is
surrounded by a more or less lamellate substance,
about which the original membrane is still visible.
Chromatophore parietal, reproduction by division
and akinetes.
Fig. 218. Binuclearia telrana Wittrock. X about 450.
(Original.)

211 (199, 212, 213) Chromatophore axial, with rounded clear spaces at each

end Phinktoncma Schmidk'.

Filaments short, free-swimming. Cells cylindrical, rounded at the ends, mostly in pairs,
each pair separated from the next by an apparently empty space. Reproduction by division
within the membrane after which the parts become separated, probably by a gelatinous sub-
stance.

Fig.

217. Radiofilum flavescens West.
X 300. (After West.)

164

FRESH-WATER BIOLOGY

Planktonema resembles in many respects the form described by Wittrock as Binuclearia but
Schmidle makes it a new genus. The two genera should be made the subject for further in-
vestigation.

^___ _ ^ . ,, _, .- I .. — 7rr-,r--_ Fig. 219. Planktonema lauter-

(r^^nZsB^±L-i h^'^Q^^ "■ Q O^^Tr^r:?-- — ,^_ _^_ homii Schmidle. X about 1000.

^^"^--^g^ g.^^.-W'-^lIII (After Schmidle.)

212 (199, 211, 213) Chromatophore a parietal network. Microspora Lagerheim.

Chromatophores band-like or netted and thickened at intervals;
membrane often becoming fraii;mcntcd into ll-shaped pieces. Repro-
duction by macrozoospores and microzoospores.

Filaments free, unbranched; sometimes resembling Conferva. Mem-
brane thick, somewhat gelatinous, and distinctly made up of H-shaped
pieces, the ends of the H either just meeting or overlapping. Reproduc-
tion by macrozoospores with four cilia, and microzoospores with two cilia.

Chromatophores many, parietal, disc-shaped. Filaments
fine, unbranched, rarely {Aeronemmn) branched. Repro-
duction by mono-ciliate zoospores 214

Filaments unbranched, at first attached: no pyrenoids.

Trihonema Derbes and Solier.

Filaments light green, soft to the touch. Length of cells one to several times the
breadth,' sometimes shghtly swollen at the middle. Chromatophores from two to many, small,

parietal. Reproduction by zoospores, one or two of
which are formed in a cell and liberated by the
membrane falling into H-shaped pieces. Zoospores
obovate, asymmetrical, with two chromatophores in
the anterior part, one ciUum, and no pigment spot.
Resting cells may occur.

Structure of cells and zoospores as in Trihonema; filaments
composed of segments of 4 to 8 cells; each formed from the
contents of a single vegetative cell, the ruptured wall of
which is visible at the end of the segment. Division rarely

longitudinal Bumilleria Borzi.

Filaments usually short. Zoospores the same as in Trihonema, but liberated through a dis-
solved p>ortion of the membrane, instead of through a circular split dividing the membrane into
two portions. Resting cells may be formed.

Fig. 220. Microspora
amaena Lagerheim.
X 345- (After West.)

213 (199, 211, 212)

214 (215, 216)

Fig.

221. Tribonema minor Klebs.
(Original.)

X800.
215 (214, 216)

Fig. 232. Bumilleria
sicula Borzi. X about
330. (After Borzi.)

216 (214, 215)

Structure of cells and zoospores as in Trihonema. Filaments
minute, richly branched, easily passing into a unicellular
condition Aeronemmn Snow.

Chromatophores pale, sev-
eral in a cell, without pyrenoids
and olosely applied to the mem-
brane. Reproduction by zoo-
spores which have a single cili-
um, a small chromatophore, and
a pigment spot. They move
with an amoeboid motion. This
may be the same as Monocilia
Gemeck, though the branching
is much more abundant than
is described in that form.

Fig. 223. Aeronemum polymor-
phum Snow. X 225. (Original.)

THE FRESH-WATER ALGAE

l6

217 (198, 218) Plants of unbranched, free-swimming, more or less gelatinous
filaments, the cells very long; chlorophyll parietal and sur-
rounding a number of large conspicuous vacuoles which
show as a row of lighter areas; pyrenoids numerous. Re-
production by heterogametes.

Family Sphaeropleaceae.
Only one genus known Sphaeroplea Agardh.

Fig. 224

Sphaeroplea annulina Agardh.
(After Rauvvenhofl.)

II33-

Cells cylindrical, tapering; length
eight to twenty times the breadth,
several nuclei present. Oogonia and
antheridia formed from vegetative cells,
the oogonia containing many oospheres,
and the antheridia a very large number
of antherozoids with two cilia; these are
liberated through holes in the mem-
brane and enter the oogonia through
similar holes; the oospores are red and
have a thick, rough membrane. On
germination each produces one to eight
zoospores with a pigment spot and
two cilia. Spores may be produced
parthenogenetically.

218 (198, 217) Plants of unbranched, more or less gelatinous, filaments,
attached in early stages; cells short, cylindrical, or swollen;
chromatophore single, parietal, with one pyrenoid. Repro-
duction by means of zoospores with two cilia and by hetero-
gametes Family Cylindrocapsaceae.

Only one genus known Cylindrocapsa Reinsch.

Reproduction asexual and sexual; asex-
ual, by zoospores and akinetes; sexual, by
means of oogonia, each with one oospore,
and antheridia, each with two anthero-
zoids; oospore red in color.

This is a very rare alga though it is
reported by Collins as occurring in Massa-
chusetts and by WoUe as occurring from
New York to Florida.

Fig. 225. Cylindrocapsa involuta Reinsch.
a. vegetative filament; h. formation of anthero-
zoids; c. oogonium with antherozoids. X 575-
(After Cienkowski.)

219(197) Filaments coarser, mostly branched 220

220 (233) Chromatophore with irregular, linear, or net-like perforations. 221
221(230) Zoospores biciliate Family Cladophoraceae . . 222

Filaments mostly branched, harsh to the touch, generally attached; chromatophore parietal,
with irregular, net-like perforations; contents granular; numerous pyrenoids. Nuclei many.

22 2 (223) Filaments never branched except at the attachment.

Chactomorpha Kiitzing.

Filaments attached by a branched, rhizoid-like organ. Reproduction by means of zoospores.
The species of this genus are mostly marine.

224

223 (222) Filaments usually branched.

i66

FRESH-WATER BIOLOGY

224 (227) Branches abundant 225

225 (226) Plants large, tufted; reproduction by zoospores. Cladophora Kiitziag.

Plant frequently ver\' large; diameter of the filaments
much greater at the base than at the ends; the length of the
cells one to twenty times the diameter; reproduction by
zoospores, many being formed from a vegetative cell; these
with two or four cilia.

The number of species of Cladophora is very large, and
they are found in fresh, brackish, and salt water, but prob-
ably in the greatest abundance along the shores of lakes
where they are constantly washed by the waves. Some
species are believed to be annual and some perennial.

Fig. 226. Cladophora glomerata Kutzing. X 85. (Original.)

226 (225) Plant forming pulvinate coatings, cells of two kinds, one light and

one dark Chlorotyliiim Kutzing.

Plant of erect, branching, parallel filaments, forming firm, dense tufts imbedded in a gelatinous
mass. In each filament several cells with dense chlorophyll alternate with longer ones contain-
ing less chlorophyll, thus giving a concentric arrange-
ment of light and dark.

Chromatophore band-shaped, asexual reproduction by
Fig. 227. Chlorotylium cataractarum biciliate zoospores which are formed in great numbers
Rabenhorst. X 150. (After Raben- in each zoosporagium. Akinetes are also formed,
horst.)

227 (224) Branches not frequent, rarely wanting 228

228 (229) Branches long, scattered; reproduction by resting spores.

Pithophora Wittrock.
Cells long, cylindrical; akinetes formed
^-v--*^^,^^ ^/i\^^M by the end of a cell being separated by a

membrane, the contents becoming much
thicker and darker, while the membrane
increases in thickness and the whole be-
comes swollen in the middle.

Fig. 228. Pithophora kewen%is'^\\.\.TO(^. a.
vegetative filament; h. formation of resting
npore X 140. (After Wittrock.)

229 (228) Branches short, attenuated, infrequent sometimes rhizoid-like,
sometimes lacking altogether. . . Rhizoclonium Kutzing.

Filaments attached, often curved
and matted, usually with short infre-
quent branches which consist of one
or more cells, sometimes resembling
rhizoids. Cell walls lamellose.

Chromatophore netted, with sev-
eral pyrenoids. Nuclei several Re-
production by biciliate zoospores
and by akinetes. Sometimes occur-
Rhizoclonium hieroglyphicum Kutzing. X 300. ring on damp ground.
(Original.)

THE FRESH-WATER ALGAE

167

230 (221) Zoospores with a circle of cilia near the smaller end.

Family Oedogoniaceae . . 231

Plants of branched or unbranched filaments, attached in early stages; chromatophore with

irregular, linear, or net-like perforations and several pyrenoids; memlirane often with transverse

striations at one end of a cell. Reproduction by means of zoospores with a circle of ciha near

the smaller end and by heterogametes.

231 (232) Plant not branched Oedogonium Link.

■*i ....

Plants either monoecious or dioecious; in the
latter case the filaments bearing antheridia may
be normal filaments, or tiny filaments of single
cells called dwarf males, attached near the oogonia.
These originate from special small zoospores called
androsporcs. But one oosphere in an oogonium;
the spermatozoid enters through a perforation
in the wall or through an opening caused by the
throwing off of a cap; antheridia single or many
together, each containing one or two antherozoids;
oospore brown or red. Asexual reproduction by
zoospores borne singly in vegetative cells; they
have a crown of cilia about a colorless spot at the
anterior end.

Oedogonium occurs in almost all bodies of
water and several species are usually found
together.

Fig. 230. Oedogonium crenulalo-cosiatum Wittrock.

a. oospore. X about 600. b. Oedogonium sp., vege-
tative filament, c. division, .d. formation of antheridia.

b, c, d. X about 520. (Original.)

232 (231) Plant branched

Bulhochaete Agardh.

Most of the cells bear-
ing a long colorless hair,
swollen at the base.
Reproduction as \nOedo-
gonium; the dwarf males
ver>' frequent.

Though not so com-
mon as Oedogonium it
is found all over the
world and sometimes
occurs in great quanti-
ties, completely cover-
ing submerged higher
plants with a feathery
coating.

Small branches which
have been detached are
also often found among
other algae.

Fig. 231. Bulbochiute
mirabilis ' Wittrock. a.
Plant with oospore, b.
dwarf male on oospore.
c. zoospores. X 200.
(Original.)

i68

FRESH-WATER BIOLOGY

Chromatophore a single equatorial band, with one pyrenoid. Fila-
ments branched, attached, frequently with a gelatinous cov-
ering. Reproduction by zoospores and isogametes.

Family Chaetophoraceae . . 234

The zoosporangia of the same form as the vegetative cells; the
larger species usually bearing long hairs.

Subfamily Chaetophoreae . . 235

Plant attached, differentiated into base and apex 236

Filaments imbedded in a firm, gelatinous matrix, forming a
spherical or an irregularly branched, ribbon-liKe thallus
attached at the base Chaetophora Shrank.

■ Filaments radiating from a common center, usually terminating in a colorless hair; micro-
zoospores with two cilia and a pigment spot near the anterior end; macrozoospores also formed.

233 (220)

234 (242;

235 (239)

236 (237, 238)

^-< 4

Fig. 232. Chaetophora pisiformis Agardh. X loo. (Original.)

237 (236, 238) Filaments not imbedded in a firm gelatinous matrix, the
branches irregularly placed, of the same size as the principal
axis Mymn^ma Fries.

Plant either several centimeters long, at-
tached, or verj' minute and free, often passing
into a palmella condition. Sexual reproduc-
tion by means of isogametes with two cilia
and a pigment spot; asexual, by zoospores
with four cilia, and by akinetes.

Myxonema is widely distributed, the mi-
croscopical forms occurring almost univer-
sally on mosses and liverworts in damp local-
ities, while the larger forms are frequent in
running water. They have been known to
completely cover the beds of streams. The
smaller forms are microscopical, and can be
detected only after portions of the mosses
and liverworts are placed in culture and the
Myxonema allowed to develop.

It will then sometimes cover the top of a
culture with a thin film of minute plants.

Fig. 23V , .
portion of branch.
X285. (Original.)

m lubricum Kiitzing. a.
b. isogometes. c. zoospores.

5VTQ^oolov^lo.i^v\

THE FRESH-WATER ALGAE

169

238 (236, 237) Lateral branches in whorls or tufts, smaller than the main
axis Draparnaldia Bory.

Plant attached by a disc of cells. Terminal cells usually ending in a long, colorless hair.
Reproduction by means of zoospores with four cilia and a pigment spot. No fertilization
known.

In Draparnaldia the photosynthesis takes place principally in the tufted branches, as the
chloroplast of the principal axis is reduced to a small, equatorial band in each cell.

All forms of Draparnaldia are large and are found in much the same localities as the larger
forms of Myxonema.

Fig. 234. Draparnaldia plumosa Agardh. X about 50. (Original.)

239 (235) Plant epiphytic adhering throughout to other plants.

240

240 (241) Plant 01 irregularly branched filaments, setae or hairs not abundant.

Herposteiron Nageh.

Plant small, cells with a parietal chromatophore, a
pyrenoid, and frequently a long colorless hair; re-
production by means of egg-shaped zoospores, with
four cilia and a pigment spot, two spores being formed
in a single cell.

This is of frequent occurrence on other filamentous
algae but usually occurs only as small isolated in-
dividuals.

It has long been included under the name of
Aphanochacte, but the name Herposteiron seems to
have priority.

Fig. 235. Herposteiron confervicola Nageli. X 450. (After Hazcn.)

170

FRESH-WATER BIOLOGY

241 (240) Individual cells flask-shaped, each with a long slender hair from

the smaller portion Chaetospliaeridiiwi Klebahn.

Chromatophore
parietal, with one
pyrenoid. Repro-
duction by zoo-
spores, four of
which are produced
in a cell. Horizon-
tal divisions of the
cells also occurs,
the lower of the
daughter cells pass-
ing gradually to the
side of the upper
one.

Chaelosphacridium
is widely distrib-
uted in the United
States though
rarely occurring in
quantities exceed-
ing a few cells at a
time.
These are usu-
._ ally attached to fil-
amentous algae and
are inconspicuous,
though the long
setae are usually
somewhat promi-
nent

Fig. 236. Chaetosphaeridium pringsheitnii Klebahn. X about 425. (After Hazen.)

242 (234) The zoosporangia different from the vegetative cells.

Subfamily Chroolepideae . . 24^

243 (244, 245) Plant minute, tree-like in its branching; reproduction bj

zoospores Microthamnion Nageli

Branches from the upper end of a cell and not sepa
rated by a membrane; obtuse at the tip; color pale
chromatophore a parietal band with no pyrenoid. Zoo-
spores formed in zoosporangia at the ends of filaments

Fig. 237-

Microthamnion kulzingianum Nageli.
(Original.)

X600.

244 (243, 245)

Plant coarse, irregularly branched, partly erect and partl>
creeping on stones and trees; when aerial, often colored rec
by haematochrome. Membrane thick; reproduction b}
zoospores and gametes Trentepohlia Martius

Chromatophores many, irregular discs, without pyre
noids; gameLangia and zoosporangia mostly terminal
gametes and zoospores similar, being egg-shaped, wit!
two cilia and haematochrome, but no definite pigmen
spot. A palmella condition may occur.

These are sometimes referred to as the aerial algat
because they e.xist principally in the air and form oftei
bright-colored incrustations on the bark of trees am
stones. They are not infrequently found in connectioi
with lichen fungi.

As the Trentepohlias are principally aerial, the lib
eration of the zoospores and gametes can occur only a
the time of a rain or in the presence of a heavy dew.

Fig. 238. Trentepohlia wainoi Hariot. X 125. (After
Collins and Hariot.)

THE FRESH-WATER ALGAE

171

245 (243, 244) Structure as in Trentepohlia but many of the cells having
setae Nylandera Hariot.

,. = .. ..===ss;=' There is but one species of this genus described, and the only

point of distinction between this and Trentepohlia is the rather
coarse and unsegmented setae.

Fig. 239. Nylandera tentaculata Hariot. X 140. (After Hariot.)

246(191,196) Plant an attached disc 247

247 (248) Plant a small, attached disc or cushion of cells, made up of radiating
rows of cells either separate or grown together, bearing on
the surface long sheathed hairs. Reproduction by means
of zoospores and by heterogametes.

Family Coleochaetaceae.

Only one genus Coleochaete Brebisson.

Cells with a single, large, parietal chromatophore and a pyrenoid. Any vegetative cell may
give rise to an egg-shaped zoospore. Plants either monoecious or dioecious; oogonia flask-shaped,
at the end of a branch or row of cells; antheridia near the oogonia, each bearing a single anthero-
zoid; a layer of cells develop about the oospore. On germination the oospore divides, producing a
number of cells, in each one of which a zoospore is formed; these reproduce the parent plant.

248 (247)

Fig. 240. Coleochaete scutta Brebisson. Portion of a disc. X about 215.

Plant a disc, of one or more layers in thickness, adhering through-
out to a substratum, often bearing gelatinous hairs. Repro-
duction by means of zoospores, and in some instances by
isogametes Family Mycoideaceae.

Only one genus recorded here Ulvclla Crouan.

/e

\cSf

^cj^^iw^iy'

Fig. 241. Ulvella americana Snow ( =
Pseudulvella americana WiUe). X 150.
(Original.)

Plant a disc of radiating rows of cells, a single
layer in thickness on the margin and several in the
middle; chromatophore single, but thickened so as
to give the appearance of many; pyrenoid single.

Appearance much as in Coleochaete except that mem-
brane and hairs are more gelatinous and the hairs
have no sheaths. Reproduction by zoosjwres only.
These have cilia, and arise first at the center of the
disc and later toward the margin. On the surface of
water plants. Mr. F. S. Collins believes this to be
Chactopeltis but sexual reproduction characteristic for
Chaetopeltis has not been observed in this form.

172

FRESH-WATER BIOLOGY

249 (68, 190) Plants of non-septate, branched filaments, forming felt-like

masses on water or earth; or plants minute, growing on the
surface of moist earth or in the tissues of higher plants;
nuclei, many. Reproduction by zoospores, isogametes, or

heterogametcs Order Siphonales . . 250

Many marine forms; fresh water forms few, diflering greatly in appearance and reproduction.

250 (251, 252) Plant a felt-like mass of branched filaments which contain no

septa except when reproductive bodies are formed.

Vaucheria de Candolle.

Plant branched; chromatophorcs nu-
merous, parietal, disc-shaped; asexual
reproduction either by zoospores or by
akinetes, the former borne singly in ter-
minal sporangia, the latter occurring as
spherical cells on short, lateral branches;
oogonia, each containing one oosphere, and
antheridia, each with many antherozoids
are borne side by side either laterally or
on the ends of short branches.
Fig. 242. Vaucheria repens Hassall. X 300.
(Original.)

251 (250, 252) Plant growing on moist earth, about i mm. broad, erect, green,

balloon-shaped, with branched, colorless rhizoids at smaller
end Botrydlum Wallroth.

Chromatophorcs numerous, minute, parietal, each with a pyre-
noid; reproduction by zoospores; under dry conditions resting spores
may be formed in the branched rhizoid-like organ of attachment.

z;^\..^-^j:

Fig. 243.

Botrydium granulatum Greville.
Woronin.)

X 15- (After Goebel and

253 (i)

Plants growing on the tissues of higher plants.

Phyllosiphon Kuhn.

Plants parasitic in the leaves and stems of aquatic
plants. The lower end is inflated, green, the upper part
colorless. In the vegetative part the chromatophores are
indistinct. Reproduction by internal division or aplano-
spores which are liberated by the rupturing of the cell wall.
In these the chromatophore is distinct.

Fig. 244. Phyllosiphon irisari Kiihn. Cells of host not shown.
X 40. (After Just.)

Plant coarse, at least several centimeters long, with a linear, cylin-
drical, occasionally branched axis, showing nodes and inter-
nodes; at the nodes, whorls of cylindrical leaves which in
turn bear leaflets; sometimes encrusted with lime. Growth
apical Order Charales.

Only one family Characeae . . 254

THE FRESH-WATER ALGAE

173

Leaflets and internodes of both axis and leaf are each of but a single cell, the
walls of which are lined with chloroplasts and in the center of which is a large
sap cavity. In Chara the internodal cell is more or less completely covered by
a layer of cortical cells of the same structure. A swamp-Uke odor is usually
present. Reproduction sexual only; plants either dioecious or monoecious, but
in the latter case the antheridia mature before the oogonia. The antheridium
is spherical, its wall composed of eight ''shields" which contain red chromo-
plasts on their inner surfaces. Attached to the middle of each shield and pro-
jecting inward is a club-shaped cell, the manubrium, which in turn bears a
short cell, the capitulum. To the capitula are attached secondary capitula
bearing four long, slender filaments made up of many cells, each containing
an antherozoid; the antherozoids are spiral in form and have two ciha at their
anterior ends; the oogonia are egg-shaped and are covered by five spiral
cells, the tips of which are divided, once in Chara and twice in Nitella, to form
the "crown." The term sporophydium has been suggested for the structure
including the oospore, its basal cell, and enveloping cells. Below the crown
cells the antherozoids penetrate to effect fertilization. Oospores are brown or
yellowish; on germination they produce first a simple row of cells, the pro-
embryo, on which the new individual arises.

254 (257) Points of the crown of the oogonium two-celled.

Subfamily Nitelleae . .255

255 (256) Leaflets projecting beyond the tips of the leaves, giving the appear-
ance of forked leaves Nitella Agardh.

Axis and leaves never with a cortical covering and seldom encrusted
with lime. Leaves with but one whorl of leaflets, but these in turn
may bear whorls of leaflets, those of the last order always projecting
beyond the leaves, giving them a divided appearance. The antheridium
always terminal on the middle leaf or leaflet. Oogonia either single or
several together, in the place of lateral leaflets.

Fig. 245. Nitella sp. Natural size. (Original.

256 (255) Leaflets not projecting beyond the tips of the leaves, or not present.

Tolypclla A. Braun.

Stem and leaves never with a cortical covering. Leaves with one to
three whorls of leaflets, which in turn may bear other whorls of leaflets,
much smaller than the first. Antheridia single or several together, which
arise from the basal or the first node of a leaf. Oogonia several, sur-
rounding the antheridia. Plants usually monoecious.

Fig. 246. Tolypella nidifica v. Leonh. Three-fourths natural size,
of figure after Wille.)

(Portion

174

FRESH-WATER BIOLOGY

2^1 C2i;A) Points of the crown of the oogonium one-celled.
^' ^ ^-^^ Subfamily Chareae.
Only one genus known in America Chara A. Braun.

Plants mostly encrusted with lime. Principal axis and leaves more or less completely cov-
ered with a layer of cells forming the cortex. Leaves six to twelve in a whorl, each usually
with several whorls of leaflets, mostly with stipular outgrowths. Antheridia and oogonia on
the upper side of leaves. Plants either monoecious or dioecious.

Fig. 247.

Chara fragilis Derv. A. two-thirds natural size portion of figure. (After Wille.) B. portion
of leaf showing cortication. C. Chara coronala Ziz. a. oogonium, b. anthendmm.

In Europe two other genera have been recognized under the Chareae as fol-
lows:

A. Sporophydia borne on the inferior side of the cell which carries the
antheridium Lamprothamnus A. Braun.

B. Sporophydia occupying the place of a leaflet on the anterior side of the
leaf, situated between antheridia Lychnothamnus Leonh.

Class III. Phaeophyceae

Color brown; plant coarse and large; or fine, filamentous.

All species are attached and have a dark or olive green color. Many are
small and resemble the Confervales while others reach an enormous size.
Sexual reproduction takes place by antheridia and oogonia in the larger species,
and by isogametes and zoospores in the smaller.

The members of this class, with a very few exceptions, occur in salt-watef,
and the classification of some fresh-water forms which are often placed in this
group is doubtful.

THE FRESH-WATER ALGAE

175

Only one genus listed here. Plant upright, many centimeters long, differ-
entiated into a pseudo-parenchymatous principal axis and branches, covered
with short, unbranched hairs. Color an olive brown Thorea Bory.

Reproduction asexual only, con-
sisting in the formation of sp)orangia
on the outer surface of the axis,
each containing but a single spore,
without cilia and without membrane.
The position of this alga in the sys-
tem of classitiaition is very doubtful,
but for convenience it is placed with
the Phaeophyceae.

Fig. 248. Thorea ramosissima Bor>-.
Portion of a longitudinal radial section.
X about 150. (After Hedgccock. &
Hunter.)

Class IV. Rhodophyceae

Color red, or a dull, purpHsh green; plant sometimes complex in structure;
reproduction sexual and in most cases asexual also.

Only one order Florideae.

Plants mostly inhabitants of salt water, but represented in fresh water by several genera.
The structure of the different fresh-water genera varies, but the sexual form of reproduction is
essentially the same in all. The male reproductive organs are borne on the ends of filamentous
branches, the contents of each of which produce a single spermatium. The female organ is
flask -shaped, in the larger portion of which, the carpogonium, lies the oosphere; through the
long neck, the trichogyne, the spermatium is conducted to the oosphere at the base, it having
been previously carried by the water to the projecting tip of the trichogyne. As a result of
fertilization, densely branched filaments arise from the base of the carpogonium, on the ends
of which are borne carpospores; these spore-bearing branches, and the sterile branches which
usually surround them, together form the cystocarp. In Chantransia and in many salt-
water species tetraspores are also formed.

1 (8) Plant branched 2

2 (5) Branches simple and not in whorls 3

3 (4) Plants coarse, of simple or occasionally branched, hollow, tapering

bristles with node-like swellings; brownish or dark bluish-
green in color Lcmanca Bory.

Bristles attached to a fine, filamentous structure which is furnished
with rhizoids. Bristles hollow, with a single row of cells through the
center, supported at intervals by transversely placed cells. Anther-
idia borne in great numbers on the surface of the node-like swellings,
a single spermatium in each. Carpogonia imbedded in the outer
wall of the bristles, the tip of the trichog>'ne only projecting. Chains
of carpospores project toward the center.

Fig. 249. Lcmanca torulosa Agardh. One-half natural size. (After
Kirchner.)

176

FRESH-WATER BIOLOGY

4 (3) Plant a steel blue, brownish or red, consisting of a single, branched
row of cells, the branches of the same structure as the
principal axis, irregularly placed and not in whorls.

Cliantransia Fries.

Sexual reproduction resembling that of Batracho-
spermum; carpogonia on lateral branches; tetra-
spores resembling carpospores on the tips of cells.
Plants dioecious.

Fig. 250.

Chantransia chalybea Fries. X igo.
(After Kirchner.)

5 (2) Branches in whorls.

6 (7) Plant purplish or bluish, beaded in appearance, due to whorls of dichot-
omous, accessory branches, composed of a single chain of
cells on a pseudo-parenchymatous axis.

Batrachospermum Roth.

Plant several centimeters long; occasionally dioecious, the antheridia at the ends of acces-
sory- branches, the carpogonia frequently near the axis; the carpospores give rise to a proto-
nema on which the adult form may originate as a branch. The protonema may also give rise
to asexual spores which again may produce protonema.

Fig. 251.

Batrachospermum grabussoniense Sirodot. A . portion of plant.
X 225. C. procarp. X 580. (Original.)

X about 25. B. branches.

7 (6) Thallus erect, richly branched, several centimeters high; beaded
throughout, due to whorls of branches which are so closely
packed and grown together as to form a continuous outer
sheath, the diameter of which is greater opposite these
branches Tuomeya Harvey.

Antheridia at the ends of branches, mostly at the nodes; carpo-
gonia in the axils of branches. This genus is synonymous with
Baileya of Kiitzing.

Fig. 252. Tuomeya fluviatalis Harvey. X 375- (After Sctchell.)

THE FRESH-WATER ALGAE

177

8 (i) Plant an unbranched filament of one or more rows or cells.

Bangia Lyngbye.

Structure simple, hair-like; color of different shades of red; attached
at one end. Found usually in rapidly-flowing water on wood and
stones.

Fig. 253. Bangia atro-purpurea Agardh. X 225. (After Kiitzing.)

IMPORTANT REFERENCES ON NORTH AMERICAN FRESH-
WATER ALGAE

Collins, F. S. 1909. The Green Algae of North America. Tufts College

Stud., Vol. II, No. 3. 191 2. Supplement. Tufts College Stud., Vol.

Ill, No. 2.
Conn, H. W. and Webster, L. W. 1908. A Preliminary Report on the Algae

of Fresh Water of Connecticut. State Geol. Nat. Hist. Surv., Bull.

No. 10.
De Toni, J. B. 1 887-1907. Sylloge algarimi omniimi hucusque cognitarum.

Vol. I, Chlorophyceae. Vol. II, Bacillariaceae. Padua.
Engler, Ad. and Prantl, K. A. E. 1887-1909. Die naturlichen Pflanzenfa-

milien. 4V. in 17. Leipzig.
Hazen, T. E. 1902. The Ulothricaceae and Chaetophorae of the United

States. Mem. Torrey Bot. Club, Vol. XL
Pascher, A. 1912. (See list in Chapter I.)
Saunders, D. 1894. Protophyta-Phycophyta. Flora of Nebraska, i : 1 5-

68. Lincoln.
TiLDEN, J. E. 1909. Minnesota Algae (Schizophyceae) . Mmn. Bot. Survey.
Transeau, E. M. 1913. Annotated List of the Algae of Eastern lUinois.

111. Acad. Sci., 6:69-89.
Van Heurck, H. 1896. A Treatise on the Diatomaceae. London.
West, G. S. 1904. (See list in Chapter V.)
West, W. and G. S. 1904-1912. A Monograph of the British Dcsmidiaccae.

4V. Ray Soc. Publ, Vol. 42. London.
WOLLE, Francis. 1884. Desmids of the United States. 1887. Fresh-water

Algae of the United States. 2V. Text and Atlas. Bethlehem, Pa.
1890. Diatomaceae of North America. Bethlehem, Pa.

CHAPTER VII
THE LARGER AQUATIC VEGETATION

By RAYMOND H. POND

Late Professor of Botany, Texas Agricultural College

Nearly all of the larger plants which have distinct roots, stems,
and leaves grow attached to the muddy substratum. This habit
of the larger plants to grow as attached organisms is so universal
that it can hardly be regarded as an accident and it is reasonable
to suppose that such attachment offers some advantage to the
organism. Even the simple filamentous algae are often attached.

When a plant is floating free any portion of it may be exposed
to the surface hght, or to the air, because the water movements
may turn its body in any direction and such a plant is better off
without specialized organs which would be destroyed by exposure.
It is common to see drifting plants which are dying rapidly be-
cause, among other reasons, the roots are exposed to the intense
light at the surface of the water, The small, free-floating forms
are simple in structure because no portion of the organism has a
distinct en\dronment of its own and changes in position are so
frequent that all parts of the body are equally exposed. The
common duckweed, Lemna, moves with the changing currents and
shows a marked differentiation into an upper and a lower side.
Notable, however, is the fact that its movement is always in a
horizontal direction so that the upper side is uniformly up while
the lower side is down, with its roots in the water, and shaded by
the cap-like upper side. Thus it is that Ceratophylliim, which is
usually regarded as a dicotyledon and which certainly occupies a
much higher station in the natural system than Lemna, shows less
differentiation in outer structure than the latter. In the case of
Ceratophyllum attachment is purely accidental so far as special
organs for the purpose are concerned. Well-developed roots have
never been found on this plant although the rudiment of a root is

178

THE LARGER AQUATIC VEGETATION 1 79

present in the embryo. The rigid segments of the forked leaves
frequently catch on the bottom so that a portion of the stem may
become buried and secure the plant to the soil. Just as often,
however, the plants float free in the water at the mercy of any
influence that may arise to change their relative position. Exam-
ination shows the entire surface of this plant to be so uniform in
structure that it makes no difference what part of the plant body
is vertical or horizontal in the water.

Attachment, therefore, favors and necessitates differentiation
into speciaUzed organs.

In land plants the roots are organs of absorption as well as of
attachment, but until recently the general understanding has been
that the roots of aquatic plants serve for anchoring only. In-
vestigations of the writer have proved that the roots act as organs
for the absorption of mineral matter from the substratum and in
this respect are perfectly analogous to the roots of land plants.

Root-hairs are present on the roots of terrestrial plants with but
comparatively few exceptions. These dehcate structures are uni-
cellular with thin walls and are formed by the enlarging and pro-
truding of the ordinary peripheral cells of the root. Their presence
greatly increases the absorbing surface exposed to the soil and thus
the passage of mineral matter into the plants is provided for with
a minimum expenditure of tissue. Several authors have stated
that root-hairs are absent in the case of submerged aquatics. This
does not seem to be the case, however, as the writer has found them
present on 17 out of the 20 species common in Lake Erie. Even
without experimental evidence it would be reasonable to suppose
that the presence of root-hairs indicates that the roots act as organs
for the passage of mineral matter into the plant. Such delicate
structures can hardly be regarded as lingering rudiments of more
active organs present when perhaps the species was terrestrial.

Land plants have developed a highly specialized tissue system
adapted to the transfer of water from the roots to stem, branches,
and leaves. This conductive tissue is usually called the vascular
system and the necessity for it in land plants is very apparent when
the rapidity with which water passes from the plant is taken into
account. That water plants Ukewise have conductive tissue has

i8o FRESH- WATER BIOLOGY

been known for a long time and a great deal of attention has been
given to a study of its structure. The vascular system of aquatics
is much simpler than that of land plants and seems to represent a
degenerate type of the latter. This general fact has thus far been
interpreted uniformly as indicating that a conductive tissue is
useless in water plants. By logical inference such plants were once
terrestrial but degeneration of the vascular system has accom-
panied adaptation to the aquatic habit. A very different interpre-
tation may, however, easily be made. The significant fact is,
that even those plants which live wholly submerged and are with-
out organs of attachment show at least the rudiments of a con-
ducting system. But why should such plants have any vascular
tissue at all? The epidermis is thin and permeable to solutions of
mineral matter, the tissues are usually only a few cells in thickness,
and in plants \vithout roots, as Ceratophyllum, absorption must take
place in such a large number of the cells that a special tissue system
for the conduction of water is unnecessary.

An aquatic environment does not favor the great differentiation
of tissue characteristic of terrestrial plants. When in water plants
very simple imitations of the land plant structure are found, this
condition does not represent the extreme that has been developed
through a long succession of aquatic ancestors, but is to be re-
garded as indicating the tendency toward simplihcation made
necessary by increasing adaptation to the water life. From this
point of view the conductive tissue is becoming, rather than has
become, unnecessary. So it seems probable from anatomical study
that a simplification of the vascular system is in progress which, if
continued, will eventually lead to a suppression or total disappear-
ance of special conductive tissue. At present, however, it may
safely be said that the majority of our larger water plants have
need of vascular tissue.

The leaves of water plants may be either floating or submerged.
Some plants have only the floating or only the submerged, while
several species have both kinds on the same plant at the same time.
The floating leaves do not show a great variety of form and tend to
be elUptical, oval, or round, while some are shield-shaped. Since
an aquatic environment is more uniform one cannot expect as

THE LARGER AQUATIC VEGETATION

l8l

great variety in leaf form as is noticeable in land plants. The
floating leaves are usually borne on a stalk which in most cases is
flexible, so that the leaf blade may rise or fall with the fluctuating
level of the water. The exposed surface of the floating leaf is
usually waterproof. This is provided for in a variety of ways.
In some cases a waxy coating renders the skin nearly impermeable.

This is true with some of the Potamo- ^i^

gctons. In some cases a coating of
very dehcate hairs so abundant as to
enclose an envelope of air prevents
the water from actually touching the
epidermis proper. This is to be ob-
served in the case of Nelumbo. Some-
times one may see drops of water
standing on the surface of such leaves
and when the leaf is submerged and
then allowed to emerge the water rolls
off leaving the leaf apparently dry.

In striking contrast to the floating
leaves the submerged ones seldom
have a distinct blade and stalk. This
is consistent with the general tendency
to uniformity of structure under a
uniform environment. Vallisneria
(Fig. 254) may be regarded as show-
ing a typical ribbon form which is well
adapted to life under water, because
it is so flexible and is thus able to
endure swiftly flowing currents or
wave movements. In some species, as that of Potamogeton pcr-
foliatus, the submerged leaves are expanded into blades but are
sessile on the stem, that is, are without a leaf stalk. The latter
would be of no advantage to leaves which are not intended
to reach the surface. They would tend to make the plant top-
heavy and easily uprooted by a sudden rush of water. Moreover,
it is quite probable that a greater exposure of leaf surface is nec-
essary because of the diminished hght under water. Linear or

Fig. 254. Vallisneria spiralis. Staminate
and pistillate plants, showing the long rib-
bon leaves which are all blade and have
no apparent stalk. (After Kerner and
Oliver.)

l82

FRESH-WATER BIOLOGY

Fig. 255. Potamogeton natans.
One floating leaf and three
submerged leaves, representing
the thread-like form of the
raonocotyledonous type of sub-
merged leaf. (After Gobel.)

thread-like leaves are very common and may be the only kind occur-
ring on the plant, as in Potamogeton pedinatus, or they may occur
on the same plant together with floating
leaves, as in Potamogeton natans (Fig. 255).
It is to be noticed that most of the monocoty-
ledons conform to some one of the types
mentioned, while the dicotyledons seem to
favor another habit, such as is seen in the
finely dissected leaves oiRanuncnlus aqnatilis ,
Myriophyllum spicattwi, Bidens beckii (Fig.
256) , and Ceratophylliim. Among the dicoty-
ledons in which both floating and submerged
leaves are present, as in Ra-
nunculus and Cabomba (Fig.
257), the tendency to fiinely
dissected leaves is conspicuous, while in the monocot-
yledons, having both floating and submerged leaves
on the same plant, the latter tend to assume the
ribbon-Uke or the long linear outline, as in Fig. 255.
Some of the true water plants, as Bidens beckii and

Myriophyllum spi-
catum, support a
vertical portion of
the main stem con-
siderably above the ^^g,1,i?^S" Lfves
water surface and yrriJd Ssln:
on this emersed
portion ordinary
aerial leaves are
borne. It is some-
times possible in the case of such
plants to find leaves which seem
to be midway in form between the finely cut submerged leaves and
the bladed emersed ones, so it seems probable that the submerged
leaves are to be regarded as exposed leaves which have changed in
form because fife under water requires such modification. Such a
modification has been produced experimentally. Some plants in

tire or slightly ser-
rate. One whorl
shows the transition
stage from the sub-
merged to the
emersed form. ^
natural size.
(After Gobel.)

Fig. 257. Cabomba. Floating leaves, entire and pel-
tate. Submerged leaves with finely dissected
blades typical of Dicotyledons. (After Gobel.)

THE LARGER AQUATIC VEGETATION

183

nature seem to be able to bring forth cither floating or submerged
leaves or both as the conditions imposed seem to require. If grow-
ing shoots of Ranunculus aquatilis are not allowed to reach the
surface of the water only the segmented leaves develop. If speci-
mens of Potamogeton heterophyllus are suddenly left stranded by
receding water the floating leaves may persist and
be succeeded by more floating leaves, thus enabUng
the plant to live for a considerable time, often
persisting until the rising water returns. In such a
case the submerged leaves soon die from exposure,
but the floating leaves have, on the upper surface,
stomata w^hich, in cooperation with the thick
cuticle, are able to regulate the loss of water.

Some of the amphibious species, such as Sagit-
taria natans, are especially variable in leaf form.
The early seedHng leaves are bladeless and ribbon-
like, while the later leaves which rise above the
surface have a distinct blade and stalk (Figs. 258
and 259). From the evident plasticity of these
plants it may be supposed that the form of leaf to
be produced is not predetermined but depends
upon conditions. Wachter has experimented with
Sagittaria natans and
finds that plants hav-
ing the ribbon-like
leaves may be pre-
vented from later pro-
ducing bladed leaves
either by reducing the
intensity of Hght or
by partial starvation.
Plants which have already formed bladed leaves may be induced
in like manner to bring forth the ribbon form. In \iew of such
results it is not unreasonable to suppose that both the floating
and the submerged leaves may easily have developed during the
past from aerial leaves and that both kinds are useful to many
species.

Fig. 258. Sagittaria
natans. Transition from
ribbon-like to bladed
leaves. I natural size.
(After VViichter.)

Fig. 259.

Sagittaria chinensis. Transition
from 'bladed to ribbon-like leaves. The
reversion has been produced by cutting
otT the roots repeatedly, i natural size.
(After Wachter.)

l84 FRESH-WATER BIOLOGY

Many of the delicate submerged plants will wither rapidly when
taken from the water and exposed to the air. This occurs be-
cause the outer layer of tissue or epidermis, as it is called, is thin
and allows the water contained in the plant rapidly to pass into
the air as vapor. If a plant which bears both floating and sub-
merged leaves is exposed it will be noticed that the latter wilt and
dry out much more rapidly than the former. Examination will
show the cuticle of the floating leaves to be thicker and much less
permeable to water, if at all so, than that of the submerged leaves,
while special openings may be discovered through which water
vapor escapes instead of passing oft all over the surface as in the
submerged leaves. These special openings are called stomata and
are the same in structure as those which occur on the leaves of
land plants. The size of these openings may vary from time to
time according to the needs of the plant. Each opening is sur-
rounded by two ceUs, called guard cells, which also vary in size
and shape according to the amount of water they contain. When
turgid they become somewhat kidney-shaped, curving away from
the opening and thus making it larger. When flaccid because
there is little water in the plant they tend to straighten out and
thus make the opening smaller. Thus, by the activity of these
stomata whose action depends upon the amount of water in the
plant, the amount of water passing from the plant by transpiration
is regulated.

The number of stomata occurring on the exposed surface of a
floating leaf may be quite large. One author counted the number
of stomata present in the area of i sq. mm. at five different loca-
tions on the upper surface of the floating leaves of one of the Pota-
niogetons. He found a minimum of 216 and a maximum of 276
with an average of 255 per sq. mm.

It is evident that stomata are intended for leaves which must
endure exposure to the air, but they do occur, though rarely, on
the submerged leaves also (Fig. 260). Sometimes only one or
two submerged leaves of a given plant will have them and
again several specimens of the same species may be examined
without finding any at all. The only explanation for the occur-
rence of such structures on submerged leaves is, that the ancestors

THE LARGER AQUATIC VEGETATION

I8S

Fig. 260. Zannichellia
repens. Submerged
leaf showing stom-
ata. X about 100.
(After Sauvageau.)

of the plants bearing them were adapted to hfe on land or
at least lived under exposure to loss of water by transpiration.

Other openings in the leaf have also been found in
some species. These occur at the apex of the leaf
more frequently in the submerged leaves than in
the floating ones. The opening does not show any
special structure, as is true of stomata, and is formed
by the decay and falling away of the tissue at the
apex, so that the conductive vessels in the veins of
the leaf become exposed to, and in direct communi-
cation with, the water. In some cases this disin-
tegration of tissue at the apex may go so far as to
change to a marked degree the shape of the apex,
making it rounded instead of pointed (Figs. 261 and 262).

The formation of the opening seems to occur before the leaf
matures but is seldom found on the young leaves. In addition to the

species already known as bearing these
openings the writer may mention that
of Vallisneria spiralis on whose half-
grown leaves he has observed them.
Some authors have suggested that the
passage of water through the conduc-
tive tissue is facilitated and that the
This is really a
supposition and has never been proved.
The presence of an earthy coating on the leaves and stems of
some water plants may be commonly ob-
served. This mineral incrustation appears
like a coating of mud on the leaf in many
cases, while in others it is not so conspicuous
and is only noticeable when the plant is
handled. Only the submerged organs seem

. V 1 • . ViG. 2()2. Potamogctondensus. Lesim

to bear the mcrustation, even the lower longitudinal section. The decayed

, tissue has fallen away, leaving the

surface of fioatme leaves beins less favor- vessels e.xposed to the surrounding

° f^ water. X about 135. ^Altef

able to its formation and much less fre- ^''^^-^e^^" '

quently bearing it. Potamogeton peclinatus is seldom, if ever,

incrusted, while other species of this genus usually are. Chara is

Fig. 261. Zosiera nana. Apical portion of
a mature submerged leaf, showing the
change of form at the apex due to decay ^.^^.^^+* „ ,• „:j^j
of apical tissue. X about 40. (After eXCrctlOU IS aided
Sauvageau.)

1 86 FRESH-WATER BIOLOGY

seldom found without an incrustation, while Vallisneria is never
found with it, although the two plants frequently grow side by side
and essentially under the same conditions. The leaves of Vallisneria
are very flexible and almost always bending with the current,
hence, a deposit of soHd matter is prevented. It seems probable,
however, that the physiological processes going on in the plant
determine largely whether or not an incrustation is to be formed.
The coatings are not firmly fastened to the leaf and may be easily
scaled off or loosened by bending the leaf. The presence of the
coatings seems to make little difference to the plant as the tissue
beneath appears of a healthy green color though frequently of
more delicate tint than the unincrusted areas of the leaf.

In all cases known the substance of the incrustation has been
found chemically to be the neutral carbonate of lime, which, of
course, is insoluble. Microscopic examination by polarized light
has revealed the presence of minute crystals in the incrustation
formed on Chara and the same may possibly prove to be the case
with plants of other families. The chemistry of the formation of
this incrustation is 'not known. There is usually present in the
water the soluble bicarbonate of lime which by loss of carbon
dioxid is changed to the neutral or insoluble carbonate. Some
have supposed that as the plants withdraw carbon dioxid from the
water to use in the process of starch manufacture, this insoluble
neutral carbonate is formed and deposited on the leaf. This proc-
ess may be expressed chemically thus:

Soluble Insoluble

CaH2 (003)2 = CaCOa + CO2 + H2O

Another explanation may be that the oxygen liberated by the plant
in starch making acts catalytically upon the bicarbonate to change
it to the neutral carbonate. The former process would more
likely occur in water containing a larger amount of the carbonate
in solution which would be precipitated except for the solvent
action of the carbon dioxid in the water. The latter process
would be more probable in water containing very small amounts
of the bicarbonate which would remain in solution in the absence
of the carbon dioxid.

I

THE LARGER AQUATIC VEGETATION 187

Since the escape of oxygen and withdrawal of carbon dioxid are
simultaneously in progress during the time the plant is making
starch, both processes may operate to precipitate the neutral
carbonate. If the plants secrete an alkaline carbonate this would
immediately upon its escape from the plant decompose the soluble
bicarbonate in the water with the formation of the neutral insol-
uble carbonate. It is uncertain, however, that such an alkaline
carbonate is secreted by the plant and not much emphasis can be
placed upon this hypothesis. The most recent explanation rests
upon the discovery that a soluble calcium salt of succinic acid is
present in the cell sap of Chara. The occurrence of this salt in
the sap of other plants has not been determined, but as succinic
acid is a very probable by-product in the ordinary processes of
plant physiology, its wide distribution may reasonably be expected.
As the calcium salt escapes from Chara by osmosis it is most likely
decomposed with the formation of the insoluble carbonate.

Possibly the incrustation offers protection to the plant in some
way, but this seems hardly probable, and at present one can only
say that its formation is a consequence of processes in the plant
and that its presence is of little benefit or of harm to the plant.

Various plant organs are often found to be covered with a gelati-
nous coating. This may occur on the lower surface of floating
leaves as in species of Nymphaea. Young leaves and growing tips
are often encased with it. In the axils of leaves arising in a
rosette around a shortened stem it is likely to occur. Seed coats
are often slimy and in some fruits the seeds at maturity are em-
bedded in a mass of gelatinous substance which on sweUing rup-
tures the ovary walls and allows the seeds an exit. Some plants, as
Brasenia peltata, have special glands to furnish the slime, but often,
as in leaf axils, there are no distinct structures for furnishing this
substance. Many of the algae are embedded in a mass of slime
just as the eggs of frogs are. Amphibious plants and those sub-
ject to temporary exposure, as in the case of plants which grow in
tide-water, are doubtless protected from too rapid loss of water by
such covering. It may also serve as a protection for young buds
and leaves against devouring animals. It is quite possible tliat
the gelatinous masses in which seeds are found embedded arc of

i88

FRESH-WATER BIOLOGY

very different composition from the slime which occurs on the lower
surface of a floating leaf. The occurrence of the latter may be
accidental so far as the plant is concerned and have little im-
portance in its welfare. In the algae and even with deUcate parts

of higher plants such a coating
may serve to retard the ex-
change of liquids, thus pre-
venting plasmolysis, or in like
manner it may enable the
plant to maintain a cell sap
of much greater density than
''irftnno^^'ATiyTse^^^^^ that of the surrouudiug watcr

(After Gobel.) (Fig. 26^).

Quite a number of terrestrial species are especially adapted for
retaining and digesting as food small animals which are so unfor-
tunate as to wander into the traps borne by the plant. Few
aquatic species have acquired this habit but there are some mem-
bers of the genus Utricu-
laria remarkable for the
special organs developed to
secure animal food. The
bladders are generally re-
garded as modified leaves,
and structures resembling
stomata have been found
on them in some cases.
The bladders have small ,,.,.. ^, ^, , , ,, ,

Fig. 264. Utrtcularta minor. Numerous bladders on the leaves,
nnpninrrc cniarHpH hv hairs >1 , enlarged bladders. L, flower-stalk rising above the water.
OpemngS gUaraeU U> lldirij ,^^^ ^^^^ ^^^^ ^^.^ ^^ ^^^^ .^ ^^ ^^ imagined as horizontal

and closed by a sort of trap- »" ^^^ ^^t«^- ^^^^^ ^'^^""^-^

door which permits small animals in the water to enter but which

prevents any escape for the victims (Fig. 264).

These plants may float free, so far as roots are concerned, but, as
with Ceratophyllum, accidental attachment or rather anchorage fre-
quently occurs through entanglement with other plants or by being
partly buried in the mud.

All of the species raise the inflorescence above the water and
Utricularia inflata sends out whorls of leaves with inflated petioles

THE LARGER AQUATIC VEGETATION

189

from the flower-stalk to serve as floaters. As there are land species
of Utricularia which also have bladders, it seems quite probable that
the aquatic forms have been derived from the land species.

Some authors have suggested that, being without roots and re-
quiring more nitrogenous food than can be obtained from sub-
stances in solution in the water, these bladders have been developed
to secure animal food. It is just as probable that the aquatic
forms are merely using structures that were characteristic of their
ancestors, which were land plants. Why the land species have
developed such structures has never been demonstrated.

Few, if any, of the flowering water plants depend upon seed repro-
duction. Vegetative reproduction by runners, tubers, buds, stem
fragments, etc., is particularly prominent among these aquatics.
Seed reproduction is, however,
common and many are the con-
trivances utilized for securing
the transfer of pollen and cross
pollination. In some few cases,
as Ceratophyllum, Naias, and
Zannichellia, poUination occurs
under water and the pollen
is transferred by the water.
The wind is an important agent
in the transfer of pollen espe-
cially for many of the Potamo-
getons (Fig. 265).

The stamens and pistils of Potamogeton crispus do not mature
on the same plant at the same time. As the pistils mature first
they must receive pollen from some other plant and by the time
the stamens of their own plant are ready to shed pollen, they
have been polhnated and are no longer receptive to pollen. The
poUination of Vallisneria spiralis has become a classic illustra-
tion of the remarkable capacity for adaptation possessed by some
plants. The individuals of this plant are of two kinds — one
bearing stamens and the other bearing pistils only. The staminate
flower cluster is enclosed in a sac which finally ruptures and the
staminate flowers immediately rise to the water surface. After a

Fig. 265. Potamogeton crispus. Pollen distribution by
the wind. (After Kerner.)

IQO

FRESH-WATER BIOLOGY

Fig. 266. Vallisneria spiralis.

short exposure to the air the flowers reflex the sepals to form a
little boat which floats about with the dehiscing stamens exposed
to the air, so that whenever the boat lodges by a pistillate flower

some pollen is deposited upon the
receptive stigma. The pistillate
flower is solitary upon a long stalk,
which, rising from the leaf axils,
elongates very rapidly until the
flower floats on the water surface,
when the stigma is soon exposed
to receive the pollen from the
passing boats of staminate flowers
(Fig. 254, page 181, and Fig. 266).
Sometimes where Vallisneria is abundant the water surface is
completely covered by the staminate flowers, just as Lemna, the
duckweed, often covers certain areas. As soon as the pistillate
flower is fertilized the stalk contracts to a spiral, thus drawing the
flower under water to mature the frviit.

To what extent Vallisneria is propagated by seed is not known.
It has been necessary for the writer to take hundreds of these
plants from the lake for experimental pur-
poses and a seedhng has not as yet been
found. The plants growing in water 2.5 to
3.5 meters deep frequently do not flower at
aU but readily propagate by runners.

As previously mentioned, Zannichellia
palustris conducts its pollination under
water (Fig. 267). The staminate and pis-
tiUate flowers stand in the same axil
filament of the sohtary staminate flower
elongates to raise the anthers above the
stigmas of the pistiUate flowers. The pollen is heavy enough to
slowly sink after escaping from the stamens and in still water
may pollinate the flower of its own plant, but in running water is
usually carried to a neighboring plant.

The pollen grains of aquatic plants differ in one particular from
those of land forms in that they have only one coat. Perhaps this

1 he Fig. 267. Zannichellia palustris.
Pollination occurs under water.
Anthers are raised above the
stiecmas by the loni; filament.
X about 8. (After Gobel.)

THE LARGER AQUATIC VEGETATION 191

is because they are little exposed and do not need protection against
a rapid loss of water.

Very few species develop a showy corolla under water, but Ileter-
anthera graminea is one which has a fairly conspicuous flower under
water.

Most of the attached flowering plants are perennial, and vegeta-
tive propagation is very common. Naias flexilis is an annual.

There is a period of rest for water plants just as for land plants
and as in the latter so in the former this period occurs during the
cold season. Not all of our perennial aquatics make special prep-
aration for passing the winter, and some, as Ranunculus aquatilis,
Ruppia, and Zannichellia, may be found in normal condition even
during the winter. The drifting fragments of Ceralophyllum often
become attached by accidental lodgment and pass the winter in
the vegetative condition.

Some Potamogetons, Ranunculus aquatilis, and others will con-
tinue to grow uninterruptedly all winter if planted in aquaria and
kept at favorable temperature in the greenhouse.

Vegetative reproduction is the conspicuous method of propa-
gation among the larger aquatics, and although many of the species
produce seed there are few which could not easily persist if seed
production were to be discontinued. In some cases fruit formation
has been abandoned. Elodea and Potamogeton rohhinsii rarely fruit.

The rhizomes of most of the water plants are well developed and
represent a considerable portion of the vegetation. In some cases,
as in Potamogeton perfoliatus, if a plant be taken carefully from the
soil fully one-half the fresh weight of the plant will be found to
consist of roots and rhizomes. With
the approach of cold weather the
stems and leaves gradually disin-
tegrate but the rhizomes remain
alive and pass the winter buried in
the mud and in the spring send up j,^^ ^^g p,i,Z,eio» pecUnaius. Rhizomes in

shoots from the buds previously November with winter buds, (.^fter Irm.sch.)

formed (Fig. 268). Heteranthera graminea has long black rhizomes
that are cord-Uke and often quite tough. The young plants seem
in some cases to rise from the nmncrs adventitiously. Among

192

FRESH-WATER BIOLOGY

the Nymphaeaceae large tubers are common and young plants of
Nymphaea alba may sometimes be found floating about attached
to a tuber.

The swamp plants, such as Typha and Scirpus, also have exten-
sive rhizome systems which are important means of wintering and
acquiring new territory.

Some plants have winter buds or hibernacula which form in
autumn, separate from the parent plant, often drift to a new
locality, and finally sink to pass the winter
in a dormant condition only to commence a
new generation the following spring (Fig. 269).
Such winter buds are commonly formed by
Utricularia, Potamogeton crispus, P. zosterijo-
lius, P. pusillus, P.frasii, and possibly others.
The sinking of those winter buds may be ac-
complished by the intercellular spaces becom-
ing injected with water, as is the case with

Fig. 269. Potamogeton crispus. '^ •'

\yinter bud germinating in ^]^g autumu plauts of Lemua mifior.

the spnng. A rhizome with ^^^

TevdoSed''''(Mre?^T??vi;f- Asidc from spccial organs of propagation
""^^ quite a few plants acquire new stations by

means of the fragments of vegetative parts accidentally set adrift.
It is common to find floating stems of Elodea, from the nodes
of which adventitious roots have risen. These roots grow straight
downward and the stem makes Httle growth in length while the
roots are seeking the soil. A fragment of Elodea was found floating
in Lake Erie which had an adventitious unbranched root 45 cms.
in length. The roots do not branch in some species until the soil
is penetrated and then a system of lateral branches develops to
anchor the plant.

In Potamogeton perfoliatus the adventitious roots usually arise
from the nodes of new rhizomes which develop in the leaf axils of
the cutting.

With land plants the development of roots on the seedhng is as
marked as the growth of stem and leaves, but in several water
plants the root development is subordinated to that of the stem
and leaves, while in some species a genuine functional root is not
developed. The rudiment of a root may be present as a part of

THE LARGER AQUATIC VEGETATION

193

the embryo in the seed, but in germination this rudiment is sup
pressed in its development and never gets to be a real root.

The seeds of Ranunculus aquatilis will germinate
either on land or in water but the development of the
seedling is not alike in each case
(Fig. 270). The seed leaves are
similar, except that those of the
land seedling are a little wider in
proportion. The true leaves of
the land plants have broad, seg-
mented blades, while the water

Fig. 270. Ranunculus aqua-
tilis. A. Seedling ger-
minating in water. B.
Seedling germinating on

land. (After Askenasy.) foHii has ouly a icw thread-like

Fig. 271. Potamogeton
lucens. Seedling
with temporary
primary root bearing
cluster of root-hairs.
(After Warming.)

branches with little indication of a distinct blade.

Potamogeton lucens and Naias major send out a primary root
from the seed upon which a cluster of root-hairs soon develops to
help anchor the plant. But this primary root is not lasting and is
soon succeeded by adventitious roots which spring
from the joints of the runners which developed in the
meantime (Figs. 271 and 272).

Ceratophyllum furnishes a very interesting instance
of suppressed root development. There is present
in the embryo of the seed a rudimentary root, but
it never develops into an organ of attachment or
serves for the entrance of mineral salts. When the
seed germinates this rudiment of a root pushes out
far enough to let the plumule rise
from between the emerging cotyle-
dons and then its growth practically
stops (Fig. 273). So far as known,
adventitious roots never appear on ^'j,^lfsum.'''''SZ

J.T-* „1 i. with cotyledon, radi-

tniS plant. cle and tirst leaf pair.

In Nuphar and Brasenia the seed- ^* ^"
ling escapes from the seed by pushing out a plug which before
germination occupies the passage intended for the exit of the
young plant.

The seeds of Utricularia commence to genninate in the muddy
substratum, but as the embryo emerges the newly formed tissues

Fig. 272. Naias major.
Seedling with tem-
porary primary root
bearing cluster of
root-hairs. (After
Irmisch.)

194 FRESH- WATER BIOLOGY

are so buoyant that the seedUng rises to the water surface often
carrying with it the remains of the old seed.

By vertical distribution is understood that which exists in a
plane more or less perpendicular to the earth's surface and may be
illustrated by the distribution one may observe in passing from
valley to mountain-top or by comparison of species found at vari-
ous depths in lake or ocean. Horizontal distribution is, of course,
in a plane more or less conformable to the earth's surface and is
such as one notices in passing from east to west or north to south,
etc. Now the factors which determine the horizontal distribu-
tion of water plants are: first, the chemical composition of the
water, a factor which gives the two large divisions of fresh and salt
water plants; second, temperature which gives zones of plant life
such as arctic, temperate, tropical, etc. ; third, competition among
the plants themselves, a factor which is hkewise influential in
vertical distribution though perhaps to a less degree; and fourth,
the nature of the substratum, which is, of course, most influential in
the distribution of species which grow rooted to the bottom.

To what extent chemical composition of the water is a factor in
the distribution of fresh-water plants cannot at present be stated.
Sulphur springs and waters having unusual composition are not, of
course, fresh water. By the latter term is understood such as
occurs in the rivers and lakes and such as may be used as drink by
the animals, so far as chemical composition is concerned. Such
waters differ, of course, in the quantity and quality of constituents;
but whether such differences are in themselves independent of
other factors, sufficient to determine distribution, cannot at present
be stated.

Suppose we should find that the water of some lake in Wisconsin
is considerably different in chemical composition from that of a
lake in New York and a species of Potamogeton, for example, which
is abundant in the Wisconsin lake but unknown to the waters of
the New York lake, be taken to the New York lake and planted
there. If this plant grows well in the New York lake we would
say that, other conditions being equal, the difference in chemical
composition of the water in the two lakes is not a determining
factor in the horizontal distribution and that the absence of the

THE LARGER AQUATIC VEGETATION 195

Wisconsin species in the New York lake must be attributed to
some other cause or causes. Experimental evidence is lacking for
stating to what extent the chemical composition of the water
becomes a determining factor in fresh water.

The important influence of temperature on distribution is at
once apparent, although the influence exerted by it is much farther
reaching than is at first supposed. Of course, the forms of the
arctic waters would be '' cooked" by the heat of the tropical waters.
It has recently been ascertained that the colder waters support a
more abundant plankton than the tropical waters, and one writer
has explained this fact upon the basis that the colder waters are
richer in nitrates and nitrites because the decomposition of organic
matter proceeds much more slowly and the organisms causing decay
are not so numerous and less active. Such considerations offer a
gHmpse of how indirectly, yet effectively, the various factors may
operate to determine distribution.

The competition of species for space may be considered a factor
in horizontal distribution, although it operates quite locally and
does not work to modify the flora of large areas. Chara is infre-
quent on the alluvial bottoms where other species are present in
abundance, but this is not because it prefers poorer soils but because
it is prevented from occupying the soil of its choice by the other
species.

The character of the substratum is an important factor; in fact,
it is possible to predict the nature of the bottom from the species
that are found growing in it. Among the islands of western Lake
Erie Potamogeton heteropkyllus is common on the reefs and pebbly
shores but is not noticeable in the coves with a good soil substra-
tum and so prominent is it in the former places that its presence
may be considered characteristic of the flora.

Light cannot be counted a factor in horizontal distribution be-
cause there is always sufficient illumination within the limits estab-
lished by other factors. In vertical distribution light is probably
the most important factor. The amount of illuminating power
lost in passing to a given depth is quite variable in different waters.
Fol and Sarasin found in Lake Geneva, in September, hght at
170 meters, and at 120 meters a photographic plate was darkened.

196 FRESH-WATER BIOLOGY

In April they were able to detect light at 250 meters. Of course
the clearness of the water has much to do with the penetration of
light rays. One can see deeper into the water of Lake Superior or
of Lake Huron than into that of Lake Erie. The latter is shal-
lower with much of the bottom clay, so that the water always holds
minute particles in suspension which greatly interfere with the
penetration of light. The red and yellow rays contained in the
beams of sunlight are more readily absorbed than those of higher
refrangibility, as the blue and violet, but whether this is of any
importance in determining the vertical distribution cannot be
stated.

Schimper gives 6 meters as the maximum depth for phanerogams,
although the lower forms, such as Char a and Nitella, are said to
have been found as deep as 30 meters. Temperature is of little
importance because the variations are so slight within the limits
established by light. This is not so much the case with the free-
swimming, lower forms, but only the larger plants are considered
here.

It is impracticable to attempt an elaborate classification of water
plants according to their habitat or adaptation to environment.
In some localities distinct zones of vegetation may be observed
which are apparently determined by the depth of water. Magnin
was able to distinguish four zones in the lakes of the Jura. First
is the littoral, with a maximum depth of 3 meters, which may be
divided into Phragmitetum with Phragmites communis as typical
and Scirpetum with Scirpiis lacustris, sedges, Eqiiisetmn, etc., as
representative. A second zone, the Nupharetum, extending to 3 or
4 meters, is composed of plants with large floating leaves such as are
common among the Nymphaeaceae. The third zone, the Pota-
mogetonetum, in water 4 to 6 meters deep, is characterized by
presence of several species of Potamogeton, especially perjoliatus,
crispus, lucens, and others. The fourth zone, Characetum, occupies
deep water, 8 to 12 meters, where Chara, Naias, and some mosses
cover the bottom.

The flora of almost any lake may be regarded as composed of
zones and even rivers and small streams show plant societies, but
a grouping for one locality is frequently inapplicable to some other,

THE LARGER AQUATIC VEGETATION 197

and the depth oi water for a species varies much according to
clearness and other factors which may be incidental to a particular
region.

It is possible to make a general grouping which will indicate the
important conditions and varieties of environment. To some one
of the groups thus established any aquatic plant may be assigned.

I. Plants without attachment.

((z) Plankton, free swimming, microscopic.
{b) Macroscopic, possibiUty of attachment by accidental
lodgment, as Lemna, Ceraiopliyllum, filamentous algae
common on plants in coves.
II. Plants attached to substratum.

(a) Submerged, algae as Chara and Cladophora, and phan-

erogams as Vallisneria, Elodea.

(b) Partially submerged, usually with floating or emersed

leaves, as Nymphaea, Bidens beckii.
III. Swamp plants or marsh forms with roots and rhizomes under
water but leaves usually emersed though able to
endure inundation and temporary submersion.

Sometimes representatives of each of these three classes may be
found in one small lake, especially if the water gradually deepens
from a marsh or low shore as in Lake St. Clair w^here the wholly
submerged species become so abundant as to form an aquatic
meadow. Potamogeton perfoliatus, P.foliosus, P. zosteraejoliiis, Val-
lisneria, Naias, Chara, Nitella, Elodea, and Myriophyllum may be
found in dense patches covering the bottom. In such formations
the struggle for space must be severe and from observations during
three summers on Lake Erie I should say that Vallisneria is a con-
queror. Naias flexilis may be found in distinct formations in
which other species are very infrequent but being an annual the
creeping rootstocks of Vallisneria may easily invade its territory.

In many of the small inland lakes the water plants are important
agents as soil collectors. The aquatic meadows tend to filter the
water so that suspended matter sinks to the bottom. As the lake
gradually becomes filled and the water grows more shallow a suc-
cession of plant societies occurs. The aquatic meadows >'icld to the

ig8 FRESH- WATER BIOLOGY

Potamogetons with floating leaves and especially the Nymphaea-
ceae which are followed by amphibious species until finally the
bog vegetation appears which may later support the ordinary
terrestrial plants.

It may be supposed that aquatic phanerogams have descended
from aquatic or from land species. The former supposition im-
plies that the plants, as they are now, represent the maximum of
complexity in structure that has thus far developed. The latter
supposition impHes that the simpler vascular system is not to be
considered as foreshadowing a more elaborate structure to be
evolved in the future but is a reduced form of more highly developed
structure present in the terrestrial ancestors. Perhaps some spe-
cies have had land ancestors, while others have descended from
aquatic forms.

Considering the whole list of fresh-water plants, it is noteworthy
that the abundant groups are algae and phanerogams. Bryophytes
and pteridophytes do occur, but infrequently in comparison with
the former groups, the thallophytes and spermatophytes, which
include a large percentage of aquatic vegetation.

Would the great plant groups be represented in this proportion
if the evolution of aquatic forms had proceeded as in the case of
land plants? Does not a water environment insure greater uni-
formity of conditions and would not the evolution proceed more
slowly and the intermediate forms more likely persist in such en-
vironment? How could the great groups of monocotyledons and
dicotyledons ever become differentiated from ancestors living
wholly submerged? How could the seed habit so essentially like
that of land plants ever be acquired by the descendants of sub-
merged forms? On the other hand if water forms have been
derived from land forms, why are not the bryophytes and pterido-
phytes which are frequent in moist locahties better represented
in the aquatic flora? The change from aquatic structure to ter-
restrial must be much more difficult than from terrestrial to aquatic.
When a water plant is suddenly exposed, the loss of water by drying
is so rapid that the plant must die, while a land plant may endure
submersion tor a considerable period. In one case the change of
environment causes a sudden demand for a complex vascular system

THE LARGER AQUATIC VEGETATION 1 99

that the plant Is unable to supply. In the other case the land
plant may persist and gradually reduce in complexity structures
already present. Thus it is that the reduction of the vascular
system has proceeded in the same manner in both the dicotyle-
dons and monocotyledons, so that the simplest stem structure is
alike for members of either group. In Ceratophyllum the vascular
system has become so simplified that its dicotyledonous relation-
ship cannot be established by the stem structure.

How is the presence of stomata on submerged leaves to be ac-
counted for? It can hardly be supposed that they are developing
in anticipation of the time when the species is to have a transpiring
surface. More likely is it that these stomata are reminders of
the time when the species had an exposed surface.

In the genus Utricularia there are land as well as water species
and the presence of bladders characterizes both varieties. It is
hardly probable that submerged plants accustomed to the food
supplied in solution by the surrounding water should acquire an
appetite for animal food and develop such elaborate and unique
organs for securing nitrogenous nourishment.

In some cases, as in Lemna, the ancestry is not so obvious and
convincing evidence is difficult to obtain.

The pollination o£ Zannichellia under water has been previously
mentioned (Fig. 267). In such cases the evolution of stamens and
pistils cannot be regarded as having occurred in wholly submerged
plants. Much less difficult it is to understand how land plants
with stamens and pistils already developed could gradualh' be-
come adapted to an aquatic habit before these organs would dis-
appear by reduction.

It is now known that the roots of several of our genuine aquatic
species bear root-hairs whose presence certainly testifies to the
absorbing activity of the roots and the Ungering terrestrial habits
necessitating such organs.

It must be noted that the foregoing discussion is purely theo-
retical and the intention has been to awaken interest in the study
of the aquatic flora rather than to offer a theory of origin for which
any originahty could be claimed.

Experimental evidence may be obtained that roots are organs

200 FRESH-WATER BIOLOGY

for absorption.^ It is possible by means of very simple apparatus
to actually measure the water which a root absorbs in a given time.
In one experiment of the writer's a small cutting 20 centimeters
long bearing a root 14 centimeters long was used and this un-
branchcd single root absorbed 5 cubic centimeters of water in
24 hours.

Another method can be used to demonstrate that roots are
organs of absorption. A certain substance, namely, Uthium nitrate,
which is soluble in water, is offered in solution to the roots. The
lithium in this compound burns with a rose red flame and very
small traces of this substance in plant tissue may be detected by
burning portions of the tissue and observing the color given to the
flame, and by using the spectroscope the test becomes very deUcate.
In this method it is only necessary to enclose the root in a bottle
containing the lithium nitrate solution by means of a flexible
stopper made by saturating cotton in melted vasehn. After a
time portions of the stem which could not possibly contain lithium,
unless it had passed to it from the roots, are burned and the flame
observed with the spectroscope. Such tests have been made re-
peatedly and the presence of the Uthium may always be traced
through the plant to whatever distance the tissue used in the
test allowed it to travel in the plant. There can be no doubt
then but that the roots are organs for absorption and that sub-
stances absorbed by them are conducted upward into the stem and
leaves. The distance that the lithium travels in a given tissue
probably does not represent exactly the rate of ascent of the up-
ward current but indicates a rate of ascent which is less than that
of the water passage through the plant; that is, water travels
upward a little faster than the lithium which it holds in solution.

Mention has been made of the fact that when cuttings of Ranun-
culus aquatilis are left to drift in the water, new roots arise from
the stem at the nodes. These roots grow directly downward and do
not branch until after penetrating the soil, when they then commence
to branch repeatedly, and as the main root pushes through the soil

1 It is not strictly correct to speak of roots as organs for absorption. The struc-
ture of roots is such that solutions can pass into them. However, the term is so
commonly employed as to make it impracticable to use other phraseology here.

THE LARGER AQUATIC VEGETATION 20I

more branches are formed in succession. The following experi-
ment seems to strongly indicate that light inhibits the formation
of lateral branches of the roots and that the roots of drifting plants
do not branch because of the exposure to the Hght. Five cuttings
of equal length were mounted in bottles so that about 3 nodes of
the stem were inside the bottle. Five similar cuttings were Uke-
wise mounted in bottles which were wrapped with black cloth so
that the roots which developed from the nodes of the cutting
inside the bottle were protected from the light. The darkened
plants developed in all 22 roots having a total length of 1048 centi-
meters and bearing in all 73 branches. The plants exposed to
light developed 28 roots, having a total length of 459 centimeters
and bearing not one single branch. The influence of light is very
evident.

There are two possible reasons why soil may be necessary for
good growth. First, as a source of food and, second, as a substratum
into which the roots can penetrate to anchor the plant. If the
soil is not necessary as a source of food the ordinary water in which
the plant grows should furnish sufficient food. If the soil is neces-
sary only as a substratum to anchor the plant a clean washed
sand substratum ought to do equally as well. Experiments along
this line have been completed by the author and it has been found
that soil is necessary for the good growth of every one of the plants
tested. Clean washed sand cannot be substituted for soil without
sacrifice of growth to the plant. It is reasonably certain that not
one of our common water plants which naturally grows well rooted
in a good soil bottom could live through an entire growing season
if clean washed sand should be substituted for its ordinary soil
substratum.

The behavior of Ranunculus aquatilis is interesting as indicating
(figuratively speaking) an effort on the part of the plant to secure
a soil attachment. This species lives wholly submerged in shallow,
slowly flowing water. The leaves are finely divided and collapse
when the plant is taken from the water. The stem branches
freely, any branch being able to continue the growth of the plant
if the main stem be removed. Roots may arise at any exposed
node, except, perhaps, the terminal one. If a fragment a few inter-

202 FRESH-WATER BIOLOGY

nodes in length be detached and left floating, roots will spring
forth from the nodes or joints of the stem in from 6 to lo days.
While the roots are lengthening toward the bottom the stem does
not increase in length but quickly resumes its growth after the
root has penetrated the soil. More roots then arise from the newer
nodes of the stem and as they also enter the soil the plant is drawn
farther down and fmally becomes firmly anchored. The roots of
such fragments do not branch before reaching the soil but do
so very shortly after the substratum is penetrated. Numerous
lateral roots then arise and form in succession as the main root
advances.

The roots are well supplied with hairs; those arising from the
floating fragments are often covered almost their entire length
with root-hairs. In one instance a root was found to be clothed
with root-hairs for a distance of 45 centimeters, which was practi-
cally its entire length. Since this plant ordinarily grows rooted
in the soil whatever growth it makes under natural conditions
must be regarded as the normal growth and there is no escape
from the conclusion that the growth becomes abnormal when
sand is substituted for soil.

How is the superior growth of plants rooted in the soil to be
accounted for? Is it possible that the soil furnishes plants rooted
in it with food materials that are not available to plants suspended
in the water standing over it? In 1850 it was discovered that
liquid manure loses its color if drained through a layer of soil
sufficiently thick. Not only does the solution lose color but the
organic and inorganic matter originally in it is considerably re-
duced after filtering through the soil. This property or capacity
of soil to withdraw salts from solution is now well established
although not well understood. For a time authors were not
agreed as to whether the retention or fixation of salts by the soil
is a chemical or a physical process. Now it is generally under-
stood that both chemical and physical processes operate to this
end. Some substances seem to be held much more firmly by the
soil than others. Various investigations go to show that most
soils absorb the oxids, salts of the alkalis and alkaline earths of
potassium, ammonium, magnesium, sodium, and calcium in the

THE LARGER AQUATIC VEGETATION 203

order given. It must be remembered, however, that this reten-
tion of dissolved substance by the soil is neither absolute nor per-
manent. We may suppose that in the case of a lake there are two
opposing processes operating in which the soil on the one hand
tends to withdraw salts from the water and retain them, while the
water on the other hand tends to bring salts from the soil into
solution. As a consequence of those two processes the lake water
contains certain salts in much greater proportion than others
which seem to be firmly held by the soil. Just how such condi-
tions influence the plant is only partially known.

It seems as though the substances needed by the plant are the
ones most firmly retained by the soil, — especially the nitrogen,
phosphorous, and potassium compounds, — and yet it is hardly
possible to say that the water does not contain enough of those
substances in solution for the larger plants. While plants cannot
select certain substances and reject others they can to a certain
extent regulate the amount of a substance which they absorb.
It is evident that all of the substances absolutely necessary for
the growth of plants must be present in the water in solution
because there are so many forms which Hve as freely swimming
objects and depend wholly upon the water in which they live for
food. Lemna, the so-called duckweed, Hves in the water and de-
pends upon the water only for food (mineral), but Lemna has
been analyzed and found to contain substances in much greater
proportion than does the water in which it grows. One investi-
gator found the ash of this plant to contain 13.16 per cent of potas-
sium, and 8.73 per cent of phosphoric acid, while the mineral resi-
due obtained by evaporating some of the water in which the Lemna
was growing contained those substances in the respective propor-
tions of 3.97 per cent and 2.619 P^^ cent. However, the fact that
Lemna can obtain all the food necessary from the water alone and
that some other plants must be rooted in the soil to thrive is no
more remarkable than the fact that some animals are herbivorous
while others are carnivorous.

Water plants may be found growing in clayey, sandy, gravelly,
or loamy soil. From field observation one would say that the
loamy soil supports the greatest variety of species. Wherever the

204

FRESH-WATKR BIOLOGY

soil is very sandy the species may be abundant and likewise where
the substratum is distinctively clay or gravel. From field observa-
tion alone it would hardly be possible to say that the quality of
the soil is the determining factor, because sand and gravel are more
common where other factors come in to influence growth and
species selection. The loamy soil is most abundant in the coves
and bayous where the water is quiet and it is in just such places
that plants make good growth and wealth of species abounds.
Plants which would perish in exposed situations make excellent
growth in the protected coves and we cannot be certain from field
observ'ation whether the difference is to be attributed to the soil
or to the more favorable locality. By direct experiment, however,
it is not difficult to ascertain what quality of substratum favors
growth. In such experiments it is very desirable to have condi-
tions as nearly Uke those in nature as possible. Three tyipes of
soil were selected, clayey, sandy, and loamy. A large rectangular
glass aquarium was used to contain a substratum of each one of
the given soil t}^es. Then the three aquaria were placed upon a
submerged platform so that the aquaria themselves were also sub-
merged. This arrangement made the aquaria similar in all condi-
tions except as to the quality of soil, and differences in the growth
of plants in each aquarium could be very easily referred to the
varying quality of soil. Two types of plants were tested in
this way — one was Vallisneria, a t^-pical water plant of the phan-
erogams, and Chara, one of the higher algae. The latter does not
have roots but simple structure called rhizoids which help to secure
attachment. With both of these plants the best growth was
made in the loamy soil and the poorest in the clay soil, while the
sandy soil which of course contained some organic debris supported
a medium growth. In the case of Chara an equal number of plants
of equal size were planted so that the dry weight of the total
growth in each aquarium might be compared. If the poorest
growth in clay be taken as one, then that in sand would be about
2.06, while that in the loamy soil would be about 3.33. The total
dry weight is of course a fair indication of the relative amount of
growth made and there can now be no doubt but that the qaahty
of soil is much concerned with the plant growth upon it and that

THE LARGER AQUATIC VEGETATION 205

of these three types of soil the loamy one is capable of supporting
the best growth.

That soil is necessary for good growth has been previously men-
tioned and explained. The interesting question arises — why is it
that plants artificially anchored but not allowed to root in the soil
are unable to make a good growth? It surely must be a matter
of nutrition, because the soil could hardly be so potent an influence
in any other way. When the plants are artificially anchored all
other conditions are the same as with plants rooted in the soil
except that the roots of the suspended plants are exposed to light
and are unable to absorb nourishment from the soil. That light
in some measure retards root development and thus diminishes the
absorbing capacity of the plant is certain, but this factor is entirely
too small to account for the stunted growth of plants denied a soil
substratum.

Chemical analysis has been employed for the purpose of securing
if possible some clue to the reason why these plants cannot make
normal growth unless rooted in the soil. Vallisneria spiralis, the
eel-grass, whose elaborate arrangement for pollination has been
described, was selected as a typical water plant of wide distribu-
tion. The history of the material to be analyzed must, of course,
be known, and in this case a large number of small plants of
uniform size were carefully taken from the lake bottom and trans-
ferred to submerged boxes which were alike, except that one con-
tained soil and the other did not. The roots of the plants arti-
ficially anchored in the box without soil were not permitted to
touch the box, but dangled in the water, and thus from the water
only could nourishment be taken. After a certain time the plants
were gathered and carefully washed, only the Uving specimens, of
course, being saved. In order to establish a basis for comparison
the volume of each group of plants was obtained b)' immersion in
water and measuring the displacement. The volume of the plants
rooted in soil was taken to be just twice the volume of the plants
artificially anchored. This material was then dried out and the
dry weight taken, which, for the plants rooted in soil, was 52.7
grams and for those suspended 37.2 grams. These figures show at
once that the suspended plants are relatively much heavier than

2o6 FRESH-WATER BIOLOGY

the others. Further analysis discloses the reason for this. The
suspended plants were found to contain relatively twice as much
starch as the others. This means that the suspended plants, though
dwarfed to one-half the normal size, still contained the same weight
of starch that they would have contained if allowed to grow as the
others did in the soil. Evidently the retarded growth cannot be
because of any scarcity of starch. Since this process of starch-
making is one of the very vital processes of the plant it is im-
portant to know that being artificially anchored does not disturb
this fundamental function of the plant. However, as a conse-
quence of this fact, it is evident that the suspended plants must
soon become overcrowded wHlth stored starch and this result in
itself may be a reason for further disturbance of \ital processes
with eventually fatal consequences.

The proteid content of the suspended plants was found to be
smaller, suggesting that sufficient supply of nitrogenous food was
not available for them. This shows that the suspended plants
must have very soon fallen into an abnormal condition in which
the two very fundamental functions of starch-making and of pro-
teid synthesis were not properly balanced.

The analysis showed further that the suspended plants contained
a relatively smaller proportion of mineral matter, which of course
indicates that they were unable to secure and use as much mineral
food as they needed. The elements most deficient in the suspended
plants were potassium and phosphorus, two of the most essen-
tial substances which are no doubt much concerned with the man-
ufacture of food materials.

So far, then, as present knowledge is concerned we can say that
the plants are dependent upon the soil for a sufficient supply of
certain substances, especially nitrogen, potash, and phosphorus.
When the plants are compelled to take all their nourishment from
the water an abnormal condition soon arises by reason of a dis-
proportion between proteid synthesis and starch manufacture which
is manifested by a retarded growth and final death.

That such statements are not conclusively proven must not be
overlooked and just why they cannot be regarded as beyond doubt
would be tedious to explain here.

THE LARGER AQUATIC VIXETATTON 207

The natural conditions of our lakes and rivers are undoubtedly
changing from decade to decade. The extensive destruction of
forests that has occurred in the lake region and along tributary
streams has certainly indirectly affected the plant and animal life
in the lakes, although at present it cannot be stated in any detail
how such influences have operated. The same may be said in
regard to the vast volume of organic matter that constantly comes
to the lakes and rivers as sewage from the cities. The influences
which operate to regulate or determine the food supply of the
water are numerous. Adequate knowledge is only possible by a
thorough study of the food relations among the animals themselves,
between the animals and plants and between the plants and the
soil.

Cycle of matter. — Animals cannot organize food from inorganic
substances but must use, as food, matter that is already organized,
either as vegetable or animal substance. Plants, however, can
and do organize food, using both the mineral salts occurring in the
soil or water, and the gaseous carbon dioxid which occurs in the
air and in the water. The dependence of the animals upon the
plants is at once apparent and the dependence of the plants upon
the earth and air is also apparent. The most important influence
exerted by plants in fresh-water biology is undoubtedly concerned
with their nutrition but they are also important in other ways.

As geological agents in the formation of marl. — The formation of
lime incrustations by water plants has already been considered, so
that it is only necessary to state here that considerable e\idence has
been brought forward to show that the large marl deposits in the
marl lakes have accumulated as already described through the ac-
tivity of plants, especially Chara.

As aerating agents. — Both animals and plants must have air to
breathe, and in running water or open lakes there is usually suffi-
cient oxygen dissolved in the water to support the respiration of
the organisms present. In the still waters of coves and bayous,
however, conditions are different. It is in such places that organic
debris tends to accumulate, and, in decay, overcharges the water
with the gases of decomposition, especially that of carbon dioxid.
Of course, whatever animal life is present under such conditions

2o8 FRESH-WATER BIOLOGY

still further reduces the oxygen supply and increases the carbon
dioxid. The green plants on the other hand during sunlight are
constantly using the carbon dioxid for making starch and giving
off oxygen as a waste product of the process. In this process the
volume of oxygen released equals the volume of carbon dioxid
used, so that an aquatic meadow, growing vigorously in a still-
water cove, would be very efficient in keeping the water well aerated
and much to the advantage of all the animal hfe finding food and
shelter there.

As ajfording shelter and refuge for small animals. — In these
aquatic meadows many kinds of young fish spend their early Ufe
during the period when they require protection from enemies.
Here, too, many of the smaller animals pursued by enemies find
temporary refuge or are able to evade their pursuers.

As a base of attachment for algae. — Wherever the larger plants
occur may be found also many smaller and more lowly organized
forms which use the larger plants as supports. The simple forms,
which are usually algae, would be unable to Hve as free swimming
individuals, and since many of them are used as food by the animals
it is important that they should be allowed to develop abundantly.
The dead as well as the Hving larger plants may be useful in this
way and only direct observation will reveal to one how much of
importance the larger plants are in this one particular.

As organizers of matter and distributors of nourishment for the
plankton. — If, as formerly supposed, water plants take their min-
eral food from the surrounding water and not from the soil at all,
then it is evident that during the growing season these rooting
aquatics would be continually diminishing the food supply of the
free swimming plants, or the plant plankton, and this would, of
course, result in a decreasing food supply for the animals dependent
upon the plant plankton for nourishment. In view of the evidence
now at hand it is certain that these larger plants rooting in the
bottom absorb inorganic matter from the soil and organize this
material into plant tissue which can be used as food by the animals
and also by parasitic and saprophytic plants which can also be used
as food by the animals. This, then, is perhaps the most important
role of the larger aquatic plants, in that their life work results in an

THE LARGER AQUATIC \'EGETATIOX 209

actual contribution of organic matter to the food supply of the
animal Ufe. There is no doubt but that in a body of water like
Lake Erie this contribution of organic matter made from soil and
air constituents that would otherwise remain unused could be meas-
ured in tons even in a single growing season.

In the marshes and shallow places immense quantities of plant
debris are constantly occurring and with changing wind these
masses of organic matter are carried far out into the lake, where,
during the period of slow decay, they furnish food to hosts of small
animals and in the decay yield valuable mineral salts, thus enrich-
ing the water to the advantage of the free swimming forms.

IMPORTANT REFERENCES ON HIGHER AQUATIC PLANTS

Britton, N. L., and Brown, A. 1896-98. Illustrated Flora of the Northern
United States, Canada, and the British Possessions. 3 v. New York.

CoNARD, H. S. 1905. The Waterlilies: a Monograph of the Genus Nym-
phaea. Carnegie Inst, of Wash., Pub. No. 4.

Coulter, J. M., Barnes, C R., and Cowles, H. C. 191 i. Textbook of
Botany. Vol. 2. New York.

Engler, A. 1900+. Das Pfianzenreich. Leipzig.

Engler, A., and Prantl, K. 1887+. (See list in Chapter VL)

Gluck, Hugo. 1905-06. Biologische und morphologische Untersuchungen
iiber Wasser und Sumpfgewachse. 2 v. Jena.

Kerner, a., and Oliver, F. W. 1895. The Natural History of Plants,
their Forms, Growth, Reproduction and Distribution. 2 v. in 4
New York.

Morong, Thomas. 1886. Studies in the Typhaceae. Bull. Torrey Bot.
Club, 15: 1-8, 73-81.
1892-93. The Naiadaceae of North America. Mem. Torrey Bot. Club,
V. 4, No. 2; 65 pp., 55 pi.

Pieters, a. J. 1894. The Plants of Lake St. Clair. Bull. Mich. Fish Com.,
No. 2; 10 pp. Map.
1901. The Plants of Western Lake Erie with Observations on their Distri-
bution. Bull. U. S. Fish Comm., 21: 57-79, 10 pi.

Pond, R. H. 1905. The Biological Relation of Aquatic Plants to the Sub-
stratum. Rept. U. S. Com. of Fish and Fisheries 1003: 483-526.

Warming, J. E. B. 1909. Oecology of Plants; an Introduction to the
Study of Plant Communities. Oxford.

CHAPTER VIII
AMOEBOID PROTOZOA (Sarcodina)

By C. H. EDMONDSON

Assistant Professor of Zoology, University of Oregort

The minute animals consisting of but a single cell throughout
their existence are commonly called Protozoa. They are world-
wide in their distribution, swarming the seas from the surface to
great depths and being found abundantly under almost all condi-
tions of moisture in fresh water as well as in the fluids and tissues
of other animals where many exist as parasites.

The Protozoa may be grouped under the following subphyla:

Subphylum I. Sarcodina. — Moving by means of temporary
extensions of the protoplasm, called pseudopodia.

Subphylum II. Mastigophora. — Pro\ided with one or more
whip-hke processes, called flagella, as organs of locomotion or for
securing food.

Subphylum III. Infusoria. — Locomotor organs in the form of
fine hair-like structures, called cilia, present during the entire ex-
istence or during the embryonic stage only.

Subphylum IV. Sporozoa. — Without true organs of locomo-
tion; usually reproducing by spores. Parasitic. No free living
forms.

It will be observed that the above grouping is based upon the
organs of locomotion. This basis has been found a convenient
one for classification and study, little difficulty arising except in
unusual cases where species are found to possess more than one
kind of motile organs or where species pass through distinct phases
during their life cycle. Of all the Protozoa those representing the
highest degree of simplicity of structure and the greatest general-
ization of life processes, if not the oldest in point of time, are to be
found in the group possessing pseudopodia. These form the sub-
ject of the present chapter, the flagellate and ciliate forms are
considered in the next, and the parasitic Sporozoa do not properly
call for attention in this work.

210

AMOEBOID PROTOZOA (SARCODINA) 21 i

Previously unknown on account of their diminutive size, these
organisms at once attracted the early workers with the microscope.
Although Leeuwenhoek as early as 1675 initiated the study of
Protozoa by his discovery of Vorticella, an infusorian, without
doubt, Rosel's description of Amoeba proteus under the name '' Der
kleine Proteus," in 1755, represents the first recorded observa-
tion of a fresh- water protozoon of the group Sarcodina.

In 1835 Dujardin called the viscid, transparent substance com-
posing the bodies of marine Protozoa, which he then had under
observation, sarcode, but it was not until 1883 that BiitschU first
employed the term Sarcodina and included under it all forms of
Protozoa which move by means of protrusions of protoplasm from
the body proper, called pseudopodia.

Most of the Sarcodina are very minute in size. Very few of
them can be seen by the unaided eye and none can be studied
with any degree of satisfaction without the aid of a compound
microscope. These forms vary greatly in general appearance.
Many of them are naked masses of protoplasm tending to be
globular when first placed under the microscope but soon assum-
ing variable shapes, protruding from the body, w^ith more or less
rapidity, blunt, lobe-like, or filiform pseudopodia, often branching
and sometimes anastomosing. Others are provided with envelopes
or shells, very diverse in form and composition, sometimes secreted
by the animal itself, sometimes consisting of picked-up fragments
firmly cemented together. These envelopes may be compact and
rigid, or flexible, and are provided with one or more apertures
through which the pseudopodia are extended. Still other forms,
commonly known as the HeHozoa or ''sun animalcules," are t}pi-
cally spherical, sometimes with shells of delicate structure and
always with fine ray-like pseudopodia, usually rendered somewhat
rigid by the presence o^ stiffened axial filaments.

Fresh-water Sarcodina may be found in very diverse habitats
and within wide ranges of temperature. They occur from I he
level of the sea to the tops of very high mountains. Perhaps no
other animals have such a vast altitudinal range as certain com-
mon species of Sarcodina. Roadside pools and also ponds, lakes
and rivers are habitats of myriads of these low organisms. In

212 FRESH-WATER BIOLOGY

most of the Sarcodina there is a marked differentiation between
the endoplasm and ectoplasm, the difference consisting in the
greater density and opaqueness of the inner region. This dis-
tinction between endoplasm and ectoplasm reaches a high degree in
certain marine forms, the Radiolaria, where a distinct perforated
membrane, the " central capsule," separates the two regions. None
of the fresh- water forms possess a " central capsule." The greater
density of the endoplasm is accounted for by the character of the
inclusions suspended in it and by the size of the vesicles which
make up its structure.

The inclusions consist of various elements: food which is to
be built into body protoplasm, products which may enter into the
composition of the shell, waste material on the way to the exterior,
or foreign elements which have no part in the physiology of the
animal. In some Sarcodina algae or bacteria are constant features
of the endoplasm, this symbiotic relationship being apparently
essential to the Hfe of the protozoon.

The nucleus is confined to the endoplasm. In a few Sarcodina
condensed nuclear elements have not been observed, but in these
cases the chromatin is without doubt diffused throughout the cell
and has the same functional value as a centralized body.

Usually a single nucleus is present, often two is the normal num-
ber, but in some forms several hundred or even several thousand
have been counted in certain stages.

Commonly the nucleus is spherical, but may be modified in
form, due to the shape of the body and to the flexibiHty of the
nuclear membrane which sometimes permits considerable deformity.

In most Sarcodina the chromatin within the nuclear membrane
is arranged in one or more masses, but in some of the Hehozoa it
is arranged in a network not unlike that of the cell of a metazoon.

Contractile vacuoles, the function of which is the extraction of
waste fluids and gases, are not found in all Sarcodina. These are
absent in many of the marine forms and in some fresh-water genera.
When present, the number varies from one to many. Habitually
the contractile vacuole is spherical but in some species it assumes a
characteristic lobed form. The position of the contractile vacuole
is not always fixed but may frequently be shifted about by the

AMOEBOID PROTOZOA (SARCODINA) 213

flowing protoplasm. In some forms its general position is fixed
and it reappears, after contraction, in the same place. As the
vacuole becomes inflated by waste fluids and gases it rises toward
the periphery and collapses, pouring its contents through the open-
ing formed in the body wall. In some of the Hehozoa are seen
very large contractile vacuoles which rise to the surface and push
the peripheral film outward Hke a bubble before the collapse takes
place.

Many of the shell-bearing forms are capable of raising or lower-
ing themselves in the water. This is believed to be brought about
by the presence of distinct gas vacuoles. The animals seem to be
able to alter the supply of carbon dioxide in these vacuoles and
thereby change their specific gravity.

The ectoplasm, when distinct from the endoplasm, usually ap-
pears as a clear hyaline zone, of greater or less width, at the periph-
ery of the body. In most forms the vesicles of the ectoplasm
are very minute but in some of the Heliozoa they exceed those of
the endoplasm in size and may be arranged in a regular manner
about the periphery, as in Actinosphaerium eichhornii.

The protrusion of the ectoplasm is the initial movement in the
formation of a pseudopodium after which there may be a flow of
the granular endoplasm into the axis of the finger-like extension of
the ectoplasm. At times pseudopodia are but broad extensions
of the ectoplasm with no appearance of endoplasm taking an\' part
in their formation.

Great variation is seen in the pseudopodia which are character-
istic features of the Sarcodina. Among the fresh-water forms
several general types may be observed. The naked and many of
the shell-bearing Sarcodina produce broad, blunt, finger-like, or
more slender, filiform, pseudopodia; the latter may be delicate,
pointed and finely branched, but neither of these fuse or anastomose
when in contact. Another variety is represented by delicate thread-
like pseudopodia which tend to run together and mingle, forming a
great network of flowing protoplasm. This is the anastomosing
type and is seen in a few fresh-water genera, but is characteristic
of many marine forms.

In the Heliozoa is seen another variety. Here the ray-like

214 FRESH-WATER BIOLOGY

pseudopodia are usually supported by "axial filaments" which con-
sist of stiffened protoplasmic supports forming the axes of the
pseudopodia along which the soft protoplasm flows. These axial
supports enter the body, the inner ends apparently resting on or
near the nuclear membrane. The supports permit the flexing of
the rays and at times they may become soft and be absorbed by
the protoplasm of the body.

Shells, which are characteristic of many Sarcodina, may be com-
posed of materials secreted by the protoplasm of the animal itself,
such as chitin, siHca, and calcium carbonate; or may be constructed
of picked-up foreign materials such as sand grains, diatom shells,
dirt, etc.

Shells of chitin are common among fresh-water forms. This
material is deposited about the body as a membrane with one or
more openings for the pseudopodia. It may or may not be applied
closely to the body and is variable in thickness in different species
as well as with age. In young individuals the envelop is usually
thin and transparent; with age it may become thicker and more
opaque. In many forms the envelop is always thin and flexible,
permitting changes in shape of the body from the flowing of the
enclosed protoplasm. When the deposit is in sufficient quantity
a firm, rigid shell is produced. If the body does not completely
fill the shell the former is united to the inner surface of the latter
by protoplasmic threads and is capable of considerable amoeboid
movements within the envelop. Some chitinous shells are very
delicate, transparent and apparently without separate elements,
while others are composed of distinct plates arranged with more
or less regularity.

Species of Dijjlugia and other related forms are provided with
shells composed of foreign materials including grains of sand,
diatom shells, and particles of dirt. These materials are attached
to a thin chitinous layer and cemented together into a compact,
rigid shell with one aperture through which the pseudopodia
extend.

Shells may be composed primarily of siUca. In many fresh-
water forms these siUceous elements are laid down in the form of
regular plates which build up a firm shell. Others, as some fresh-

AMOEBOID PROTOZOA (SARCODINA) 215

water Heliozoa and the marine Radiolaria, secrete spicules which
may be loosely connected, forming an envelop, or cemented to-
gether, building up skeletons of most delicate and beautiful designs.
Sometimes spicules are developed for temporary purposes as the
formation of envelopes during encystment. Calcium carbonate is
the chief constituent of the shells of marine Foraminifera but is not
an element of importance in the shells of fresh -water Sarcodina.

In a one-celled animal the vital processes of the body, though not
different, except in degree, from those of a metazoon, must neces-
sarily be simpler. Here all of the Hfe-forces have their origin and
all of the metabolic changes take place within the confines of a
single cell.

The entrance of food Into the body in the Sarcodina is a simple
process. No mouth being present, material may, in general, enter
at any point on the surface. In naked forms of the Amoeba tj-pe
the pseudopodia flow around the particle to be ingested and in this
way it is enclosed. The pseudopodia of shell-bearing forms draw
in the food through the apertures of the shells where it is engulfed
by the protoplasm.

Most of the Sarcodina are herbivorous, their chief food being
unicellular plants, as bacteria, diatoms, algae, etc. The plant cells
are usually entirely ingested and the soft parts absorbed, after
which the indigestible parts are excreted from the body. However,
in case of Vampyrella, the parasite penetrates the cells of algae and
absorbs their contents.

Some Sarcodina are known to be carnivorous, feeding upon
closely related species. Penard believes that species of Nebcla
may make use of the plates of QuadruleUa, Euglypha, Triucma, etc.,
upon which they feed, in building up their own shells.

Digestion in all of the Protozoa is intracellular. After the ma-
terial enters the body surrounded by a film of water forming a food
vacuole, digestive fluids and enzymes act upon it converting it into
suitable elements for the life of the cell. Excretion in the Sarco-
dina consists, as elsewhere, in the release of waste products. Waste
solids may leave the body at any point of the surface. The
process is the reverse of ingestion, often consisting in the mere flow-
ing away from the material to be discarded.

2l6 FRESH-WATER BIOLOGY

Waste fluids resulting from the metabolism of the cell are col-
lected in contractile vacuoles in most of the fresh-water Sarcodina
and thereby removed. Surplus water which has been ingested is
eliminated at the same time and possibly carbon dioxid may also
be extracted by the contractile vacuole. In those forms, however,
which do not possess contractile vacuoles, the waste fluids and gases
escape from the general surface of the body.

Respiration in the Sarcodina is performed by an interchange of
gases through the body wall. Oxygen is received from the sur-
rounding water and carbon dioxid transmitted to it by osmosis.
The symbiotic relationship between algae and some forms of Sar-
codina, without doubt, has an important respiratory as well as
nutritive function, the plants furnishing oxygen and carbohydrates
to the animals, while the latter supply carbon dioxid and nitroge-
nous waste for the algae.

Reproduction in the Sarcodina takes place either by the division
of the body into two parts, a process commonly called fission ; by
the separation from the parent of one or more small masses of
protoplasm known as buds; or by the production of swarm spores.

In fission, or simple cell division, which is common among fresh-
water forms, the nucleus divides first and this is followed by the
separation of the cytoplasm into two parts, each of which encloses
a portion of the original nucleus. Growth proceeds until maturity
is reached, when the process of division is repeated.

When an envelop is present the enclosed body may divide by
fission after which one portion creeps out at the aperture and con-
structs a new shell about itself. If the envelop be chitin and with-
out distinct elements it is gradually developed at the periphery
of the newly separated individual, but if it be of regular chitinous
or siliceous plates, these elements, in some cases at least, are de-
veloped in the cytoplasm of the parent and pushed out to form the
new envelop of the separating bud.

That the nucleus is concerned with cell division has long been
known. Recent observations, however, have thrown light upon
the presence of extranuclear material scattered throughout the
cytoplasm in many Sarcodina as well as other protozoa. This
material has the form of minute granules termed ''idiochromidia"

AMOEBOID PROTOZOA (SARCODINA) 217

and results from the transfusion of part of the chromatin through
the nuclear membrane or from the breaking up of the nucleus into
small granular bodies which become diffused through the cyto-
plasm.

In some Sarcodina a number of buds may separate from the
parent, each enclosing a quantity of idiochromidia which is built
into a nucleus. This extranuclear material apparently has a
functional value in reproduction and may be compared to the
micronuclei of Infusoria. During the quiescent state of encyst-
ment the bodies of many Sarcodina break into swarm spores.
These are minute organisms each with a portion of the parent
nucleus and provided with fiagella or pseudopodia as motile organs.
The swarm spores may fuse with each other and develop into an
adult form or, in some cases, they may develop without fusion.

Conjugation, in the form of a temporary union or a permanent
fusion of the bodies of two individuals of the same species, has
been observed in some Sarcodina. After temporary union and
separation, in a few cases, swarm spores have been observed to be
developed from both conjugants.

In most of the instances of permanent conjugation reported
there is no clear evidence that the fusion resulted in a union of the
nuclei of the individuals, as is the case in true conjugation. Actual
fusion of the nuclei, however, has been observed in the common
''sun animalcule," Actinophrys sol. Here two indi\iduals come
together, fuse, and become encysted. Nuclear changes take place
which follow in a general way the processes of maturation and
fertilization after which mitotic division results in the formation of
daughter cells.

Many kinds of Sarcodina are exceedingly abundant and collect-
ing them is not a difficult matter. Other forms are rare and only
occasionally obtained. Everywhere among wet mosses and in
sphagnous swamps many fine examples of shell-bearing species
will be found, some inhabiting no other localities. Some prefer
clear, fresh water, while others thrive in stagnant ponds and ditches.

By carefully collecting submerged decaying vegetation from shal-
low water and allowing it to stand in the laboratory for a few days
many of the Amoeba and Difflugia types arc usually found.

2l8 FRESH-WATER BIOLOGY

The ooze at the bottom of ponds or lakes is the habitat of nu-
merous shell-bearing as well as naked forms. Others, like the
Heliozoa, are commonly found among algae, diatoms, or mosses and
may be collected with these plants. Inactive or encysted forms
gathered during cold seasons of the year wil become active on
being placed in a warm laboratory. Shallow aquaria are best
adapted for preserving quantities of living Sarcodina. For those
species which require it, the water may be kept fresh by algae or
other aquatic plants, but for many forms the water may be allowed
to become stagnant, replenishing it only as evaporation takes place.
The Sarcodina may be studied with a considerable degree of satis-
faction, as it is possible to keep them under observation for an in-
definite time, owing to their slow movements. For detailed study
a good compound microscope including an oil immersion lens is
necessary. Concave microscopic slides on which living forms may
be isolated and retained for extended observation are useful.
Methylenblue, used as an intravitam stain, is successful in render-
ing the nuclear elements visible, especially in species without shells
or with transparent envelopes.

When permanent mounts are desired the following method, rec-
ommended by Benedict in the Journal of Apphed Microscopy,
Vol. VI, p. 2647, i^2,y be employed: ''Smear a glass slide with
albumen fixative, as in preparing for the mounting of parafifin sec-
tions. Then place on the surface of the film of fixative a drop or
two of water containing the forms which it is desired to stain.
Let nearly all the water evaporate by exposure to the air of the
room until only the film of fixative remains moist. The slide can
now be immersed in Gilson's or any other fixing reagent and then
passed through the alcohols, stains, etc., in the same way that
mounted sections are handled."

The above method is recommended for other Protozoa as well as
for Sarcodina. As a rapid fixing agent, the fumes of osmic acid
have been found satisfactory. By careful manipulation of fine
dissecting needles under the microscope, the shells of many forms
may be isolated, arranged as desired and, when dried on the slide,
permanently mounted in balsam.

AMOEBOID PROTOZOA (SARCODINA)

219

KEY TO NORTH AMERICAN FRESH-WATER SARCODINA

I (161) Pseudopodia without axial filaments.

Class Rhizopoda

2 (144) Pseudopodia lobose, sometimes pointed but never anastomosing.

Subclass Amoebea . , 3

3 (21) Without shells Order Gymnamoebida . . 4

4 One family recognized. Characteristics of the order.

Family Amoebidae . . 5

5 (6) Body and pseudopodia bristling with minute spicules.

Dinamoeha Leidy.
Representative species Dinamoeba mirabilis Leidy iSy 4.

Very changeable in shape with many tapering pseudo-
px)dia. Papillae-like projections often appearing at the pos-
terior extremity. Entire body sometimes surrounded by a
jelly-like envelop. A contractile vacuole and two nuclei
present. Habitat standing water. Size may reach 200 n,
including pseudopodia.

Fig. 274. Dinamoeba mirahilis

6 (5) Body smooth, without spicules

7 (8) Body usually enclosing symbiotic bacteria

X 100. (After Leidy.)

Large size. Nuclei many.

Pelomyxa Greeff.

Representative species Pelomyxa palustris Greeff 1870.

A very large form moving slowly by broad extensions
of the ectoplasm. Endoplasm enclosing sand, brilliant
corpuscles and bacteri;i; with numerous vacuoles in the ecto-
plasm. Nuclei may number 1000 or more. Habitat ooze
of ponds and sphagnous swamps. Maximum length 20CX3 n.
P. carolinensis Wilson, described in American Naturalist,
Vol. 34, p. 535, is apparently without symbiotic bacteria.

Fig. 275. Pelomyxa palustris. x 25. (After Pcnard.)

8 (7) Body not enclosing symbiotic bacteria 9

9 (10) Ectoplasmic membranes produced between the pseudopodia.

Hyalodiscus Hcrtwig and Lesser,
Representative species. . . . Hyalodiscus rubicund us H. and L. 1S74.

Body discoidal, moving by extending thin sheets of ecto-
plasm which are penetrated by ray-like pseudopodia. En-
doplasm reddish-yellow in color enclosing numerous vacuoles
and one or more nuclei. Habitat ooze of ponds, not common.
Size 40 to 60 At.

Fig. 276. Hyalodiscus rubicundus. X J15 (.•\fter Penard.)

10 (9) Ectoplasmic membranes not produced between the pseudopodia.

Amoeba Ehrenberg . ii

11(14) Pseudopodia sharply distinguished from the body 12

12(13) Pseudopodia lobe-like i mocba proteus Lc'idy iS,-jS,.

Very changeable in form, usually with numerous pseudo-
podia. The nucleus is always single, oval and of large size.
Contractile vacuoles one or more. Habitat both stagnant
and clear water. Size, one of the largest species of the genus;
may reach 300 ^ or more when extended.
Fig. 277. Amoeba Proteus. X loo (Original from a prcixiralion.)

2 20

FRESH-WATER BIOLOGY

[3 (12) Pseudopodia ray-like.

Amoeba radiosa Ehrenberg 1830.

r^:<^«*

Body spherical with pseudopodia more or less rigid, not withdrawn
and retormed rapidly. Nucleus spherical. Habitat, very common
among algae; widely distributed. Size, usually less than icxjm with
pseudopodia extended.

IiG. 278. Amoela radtusa. a, contractile vacuole X loc (After Leidy.)

14(11) Pseudopodia not sharply distinguished from the body 15

15 (20) Contractile vacuole spherical 16

16(17) Posterior extremity villous Afnoeha Umax 'Du]3.rdm 1S41.

Slug -like, usually moving with the broad end forward. Endo-
plasm filled with brilliant granules. Contractile vacuole usually
single. Nucleus changeable in form. Habitat ooze ol ponds.
Size, large individuals usually less than ioom-

Fig. 279. Amoeba limax. x 225. (Alter Penard.)

17 (16) Posterior extremity not villous 19

18 (19) Surface wrinkled, large size. . . Amoeba verrucosa Ehrenberg 1838.

A sluggish species, moving by a slow rolling motion. Pseudo-
podia short, broad lobes. Body proper enclosed by a delicate
membrane. Surface marked by lines crossing each other re-
sulting in a wrinkled appearance. Habitat sphagnous swamps.
Large individuals may reach 3cmd ^ in length when extended.

Fig. 280. Amoeba verrucosa . X 100 (Alter Leidy.)

19(18) Surface not wrinkled, small size. . . ylwoefta gM/Zw/a Dujardin 1841.

Body usually oval in outline, moving with the broad end forward.
Pseudopodia short, broad lobes produced by sudden expansions of the
protoplasm. Nucleus single and one large contractile vacuole. Habitat
stagnant water. Size 30 m-

Fig. 281. Amoeba guttula. X 400. (Alter Penard.)

20 (15) Contractile vacuole not spherical. . . . Amoeba striata Penard 1890.

Moving rapidly by broad extensions of ectoplasm but not changing
form rapidly. Usually from two to four longitudinal lines on the surface.
Two contractile vacuoles often present, the anterior one changeable in
shape. Habitat among algae; not abundant. Size, from 30 to 60 n.

Fig. 282. Amoeba striata. X 250. (After Penard.)

With shells Order Testacea . . 22

Pseudopodia thick, finger-like, rarely filiform.

Family Arcellidae . . 23

Pseudopodia thick, sometimes pointed 24

Shell membranous, more or less flexible 25

Membrane covered with organic or foreign particles 26

Shell membrane double Diplochlamys Greefif. . 27

Hemispherical to cup-shaped, loosely coated with organic and siliceous
particles Diplochlamys fragilis Venard igog.

Color gray, spotted with black. Inner membrane very fragile
but capable of distention. Nuclei usually from 30 to .40. Vacuoles
numerous. Pseudopodia short and thick. Diameter 70 to 125 fx.
Habitat mosses. Not common. Reported from Ontario by Dr.
Penard.

Fig. 283. Diplochlamys jragilis. X 150. (After Penard.)

21

(3)

22

(103)

23

(96)

24

(35)

25

(32)

26

(29)

27

(28)

AMOEBOID PROTOZOA (sARCODINA) 221

(27) Hemispherical to cup-shaped, densely coated with organic particles.

Diploclilamys fimida Penard iqoo.

Yellowish-gray or brown. Inner membrane very delicate, flexible

but resistant. Nucleus single. Vacuoles numerous. PseuflojxKJia

y'\vj^^-/X large at the base, pointed, rarely extended. Diameter 45 ^t. Habitat

'-^^"^a"^ mosses. Reported from Ontario by Dr. Penard.

'^x^ Fig. 284. Diploclilamys timida X 275. (After Pen.ird )

29 (26) Shell membrane single .30

30 (31) Hemispherical; slightly or not at all flexible. . . Parmulina Penard.

Representative species Parmulina cyalhus Penard 1902.

In this species the shell is rigid but in P. obtrcla Gruber it is flexible

about the aperture. Shell is coated with fine particles of sand. dirt. etc.

___. Pseudopodia are broad, rounded lobes extending from the aperture.

/o- '*^ Nucleus and contractile vacuole each single. Habitat among mosses.

.^ '..*"• .^ j)janieter 45 //.

Fig. 285. Parmulina cyalhus. X 27v (After Penard.)

31 (30) Commonly ovoid or hemispherical, but very changeable.

Corycia Dujardin.
Representative species Corycia flava Gtqq^ i^dd.

The membranous covering is dome-shaped but very changeable in
1^^^^^^^ form. Pseudopodia very short and thick. Vacuoles numerous,

i (^ "to^ 0^ Nucleus single, usually concealed by the granules of the endoplasm.

V Vl^®;'^^^,^^ Habitat among mosses. Diameter 80 to 100 m-

^^^i^si^-^"**"^ Fig. 2S6 Corycia flava. X 210 (After Penard.)

32 (25) Membrane without foreign particles; regularly punctate. . . ■ i?,

33 (34) Patelliform; slightly flexible Microchlamys Cockerell.

Representative species.

Microchlamys patella Claparede and Lachmann i860.

Shell circular from dorsal or ventral view convex above with a

very large aperture beneath. Pseudopodium single. Contractile
vacuoles numerous. Nucleus single. Habitat among mosses in
swamps. Diameter 40 n.

Fig. 287. Microchlamys patella. X .^10. (After Penard.)

34 (33) Commonly dome-shaped, but exceedingly flexible and changeable.

Cochlio podium Hertwig and Lesser.
Representative species. . CocJil io podium bilimbosum AueThach 1856.

y^^^X The membranous covering is capable of great expansion, especially at

r>''''^m ^^^ aperture. Pseudopodia pointed, usually numerous. Nucleus and

KilCH contractile vacuole each single and large. Common among algae.

y^^^^'^^^^-r^ Diameter of envelop 25 to 50 fi.

f'"';f''"'\ Fig. 288. Cochliopodium bilimbosum. m, nucleus. X 300. (After Leidy.)

35 (24) Shell membranous, rigid '^^

36(45) Shell discoidal ^^

37 (44) Shell with regular markings more or less distinct. No foreign par-

ticles attached. Aperture central ,^8

38 (43) Shell with regular, distinct punctae. Aperture small.

Arcclla Ehrenberg . . 30

39 (42) Periphery of shell without projecting points 4°

222

FRESH-WATER BIOLOGY

40 (41) Shell strongly convex.

41 (40)

42 (39)

. . . Arcella vulgaris Ehrcnberg 1830.

Shell may be smooth or with re^'ular undu-
lations. Protoplasm united to the inside of the
shell by delicate threads. Pseudopodia long,
straight and very transparent. Contractile
vacuoles numerous. Nuclei two, opposite in
position. This species shows great variation in
size and form. \'ery common in pond water.
Diameter 80 to 140 n.
Fig. 289. Arcdlavul\:,aris. Lateral and interior views

oi the same individual. X 150. (After Leidy.)

Shell very flat Arcella discoides Ehrcnberg 1843.

Shell smooth, regularly punctate, with a large circular aperture. It
is a shy species, the pseudopodia seldom being observed. Contractile
vacuoles numerous. Nuclei two. Common in pond water. Diameter
from 72 to 264 /i.

Fig. 290. Arcella d'ncoide^. X i75- (After Penard.)

Shell periphery with projecting points.

Arcella dentata Ehrcnberg 1830.
When viewed laterally the shell has the appearance of a crown,
the teeth-like points being produced from the base of the low
dome. Nuclei two; contractile vacuoles numerous. Habitat
bogs and swamps. A rare species. Diameter 132 to 184 m-
Fig. 291. Arcella dentata. Lateral and inferior views of the same indi-
vidual. X 100. (After Leidy.)

43 (38) Shell with punctae sometimes indistinct. Aperture very wide.

Pyxidicula Ehrcnberg.
Representative species Pyxidicula cymhalum Penard 1902.

Shell pateUiform, brown in color, with distinct punctae. Aper-
ture round, nearly as wide as the diameter of the shell, bordered
by a narrow rim. Contractile vacuole single. Nuclei probably
two. Pseudopodia not observed in this species. Identified by
Penard in material from Summit Lake, Colorado. The only spe-
cies of the genus thus far reported from North America. Diameter
85 to 90 M- Habitat mosses.

44 (37) Shell without regular markings, but with foreign particles attached.

Aperture eccentric Centropyxis Stein.

Representative species Centropyxis aculeata Stein 1857.

Shell compressed laterally, resulting in both mouth and fundus
being eccentric. Color some shade of brown. Slender spines
usually developed from the fundus. Nucleus single; contractile
vacuoles two or more. The species is very shy, sometimes ex-
tending a single large pseudopodium. A common species among
algae. Diameter 88 to 260 /i-

Fig. 293. Centropyxis aculeata. X 150. (After Leidy.)

45 (36) Shell not discoidal 46

46 (51) Shell spiral, compressed, largely composed of minute, curved, rod-

like plates Lecquereusia Schlumberger . . 47

47 (48) Shell primarily of sand grains, few plates.
^3^ Lecquereusia modesta Rhumbler 1845.

This species has a short, broad neck, slightly turned to one side.
Nucleus single. Pseudopodia few, large and long. Found among
mosses in swamps. Length from 125 to 150 m-

Fig. 294. Lecquereusia modesta. X 125. (After Penard.)

Fig. 292. Pyxidicula cym-
balum. X 210. (After
Penard.)

AMOEBOID PROTOZOA (SARCODINA)

223

48 (47) Shell of rod-like plates 49

49 (50) Plates slender, elongate. . . Lecquereusia spiralis Ehrenberg 1840.

The neck in this species is prominent and turned sharply to
one side. The siliceous plates are cemented very closely to-
gether, forming the shell. Sand and diatoms may sometimes
be incorporated with the plates. Pseudopodia few, long and
large. Habitat sphagnous swamps. Length 125 to 140 ^.

Fig. 295. Lecquereusia spiralis. X 125. (After Penard.)

50 (4q) Plates thick, short Lecquereusia epistomium Penard 1893.

In this species the neck is very sharply distinguished from the
rounded shell and very abruptly turned to one side. The shell is
clear, without foreign particles attached. Habitat sphagnous swamps.
Length 125 yt.

Fig. 296. Lecquereusia epistomium. X 150. (After Penard.)

51 (46) Shell not spiral 52

52 (57) Shell chitinous, transparent, structureless, with no foreign particles or

formed elements attached. . . Hyalosphenia Stein . . 53

53 (54) Surface of shell with undulations. . Hyalosphenia elegans Leidy 1874.

The shell is flask-shaped, compressed, brownish in color,

transparent. Two minute pores, opposite each other, are in
the base of the neck. Protoplasm colorless. Nucleus single.
Pseudopodia few. Common in sphagnous swamps. Length
from 90 to 100 /x.

Fig. 297. Hyalosphenia elegans. X 250. (After Penard.)

54 (53) Surface of shell without undulations 55

55 (56) With pores through the fundus. . Hyalosphenia papilio Leidy 1875.

Shell ovoid or pyriform, compressed, yellowish in color. Slight
variation in size, shape and constitution shown in this species. Pro-
toplasm not filling the shell but attached to the inner surface by pro-
toplasmic processes. Endoplasm always containing chlorophyl.
Pseudopodia often numerous. From two to six small pores a!x)ut
the border of the fundus. Common in sphagnous swamps. Length
from no to 140^1.

Fig. 298. Hyalosphenia papilio. X 200. (Alter Leidy.)

56 (55) Without pores through the fundus. . Hyalosphenia cuncata Stein 1857.

Shell exceedingly transparent and greatly compressed.
Pseudopodia few in number, often but one. Habitat
is reported to be clear water. A rare species. Length
from 60 to 75 n.

Fig. 299. Hyalosphenia cuneata. Broad and narrow lateral
views, ft, nucleus. X 300. (After Leidy.)

57 (52)

58(75) Shell primarily of foreign particles 59

Shell chitinous, more or less densely covered with foreign particles
or formed elements 58

224

59 (72)

60 (6i)

Fig 300.
X no.

61 (60)

62 (69)

63 (66)

64 (65)

FRESH-WATER BIOLOGY

Shell without internal partition or diaphragm.

Difflugia Leclerc . . 60

Aperture not central Difflugia constricta Ehrenberg 1841.

Shells of various forms from nearly spherical to oval and elon-
gate. Aperture always eccentric. Pseudopodium single, rarely
observed. Spines sometimes developed from the fundus. This
:iccaaii>' species is closely related to Centropyxis aculeala. A common

species, widely distributed. Large forms may reach 200 m m
Difflugia constrict. I. length. Most individuals are very much smaller.
(After Leidy. '

Aperture central 62

Shell typically spherical 63

Margin of aperture smooth 64

Neck deeply constricted; aperture small, with margin always re-
curved Difflugia urceolata Carter 1864.

This species is without spines, but a variety, D. urceolata var.
olla, may possess a few short stubby spines developed from the
fundus. The protoplasm does not fill the shell. Pseudopodia
numerous; nuclei many. Found in the ooze of pond water. Large
forms reach a length of 350 ix.

V^?:=;?Clb Fig. 301. Difflugia urceolata. X 75- (After Leidy.)

65 (64) Neck, when present, not deeply constricted;- aperture wide, with
margin seldom recurved. . . . Difflugia lehes Penard 1893.

In many respects this species resembles the preceding one.
The thin, recurved collar is sometimes present but the aperture
is much larger. The shell is very fragile. Nuclei sometimes more
than 100. Found in ooze at the bottom of ponds, lakes, etc.
Very large, some reaching 400 m in length.

Fig. 302. Difflugia lebes. X 60. (After Penard.)

66 (63) Margin of aperture not smooth 67

67 (68) Margin with numerous teeth. . . . Difflugia corona Wallich 1864.

Shell composed of large sand grains but ver>' smooth and regular
in outline. Teeth usually more than twelve in number, very evenly
arranged. Nucleus single. Pseudopodia numerous and large.
From six to nine spines usually developed from the fundus. A very
common species in ooze of ponds. Length, with spines, 200 to 250 /*•

Fig. 303.

lugia corona. Oral view. X 90. (After Leidy.)

68 (67) Margin with few blunt lobes. . . . Difflugia lohostoma Leidy 1874.

Shell ovoid or nearly spherical, usually with a quadrilobate aper-
ture. However, the lobes are somewhat irregular, a trilobate aperture
sometimes appearing. Pseudopodia few. Found among algae and in
the ooze of ponds; common. Average length 150 m-

Fig. 304. Difflugia lobostoma. Oral view. X 105. (After Edmondson.)

69 (62) Shell never spherical 70

AMOEBOID PROTOZOA (SARCODINA) 225

70 (71) Pyriform, with posterior border usually rounded.

Difflugia pyriformis Perty 1852.

This very common species is exceedingly variable in form and
VJAy^SS'H^ size. Penard recognizes six varieties, var. claviformis sometimes
•■:^^i^'^i^^^:sr:^^ reaching a length of 450 m- The posterior border is usually
rounded but some forms may approach the acuminate type.
Fig. 305. Difflugia pyriformis. Found everywhere in the ooze of ponds and lakes.
X 60. (After Leidy. )

71 (70) Elongate, cylindrical, with posterior border acuminate.

Difflugia acuminata Ehrenberg 1830.
Shell cylindrical, the slightly broader posterior extremity taper-
ing to an acute point ending in a knob-like process. Very widely
distributed with other species of the genus. Large forms may reach
a length of 275 m-

Fig. 306. Difflugia acuminata. X 125. (After Leidy.)

72 (59) Shell with internal partition or diaphragm 73

73 (74) Shell with deeply constricted neck and transverse, perforated parti-

tion at the point of constriction. . Pontigidasia Rhumbler.
Representative species. . . . Pontigidasia spectahilis Penard 1Q02.

Resembling Difflugia pyriformis in appearance, except for the
deeply constricted neck. The internal partition has one round
opening and one or two other apertures, the latter being closed by
transparent opercula. Pseudopodia few, long, and move rapidly.
Found with species of Difflugia. Average length 150 m-

Fig. 307. Pontigulasia spectabilis. x 100. (After Penard.)

74 (73) Shell with a short neck; aperture partially closed by a transverse

diaphragm Cucurhitella Penard.

Representative species. . . Cucurbitella niespiliformis Penard 1902.

The neck is quadrilobate with an undulating margin. On the inside

'^Su-H^^ of the neck is a transverse peristome covered with sand grains, resulting

w^ri^'ij in the rounded aperture being much smaller than the diameter of the

f^T^.'^'.a, neck itself. Pseudopodia numerous, straight. Found at the bottom of

)\r^ ponds and lakes. Length from 125 to 140 n.

<l\\X. Fig. 308. Cucurbitella mespiliformis. X 125. (.\fter Penard.)

75 (58) Shell primarily of formed elements 76

76 (81) Shell not compressed, of small siliceous particles, aperture lunate

with inferior and superior lips 77

77 (78) Shell hemispherical or elliptical, superior lip with pores. Large size.

Bull inula Penard.
Representative species Bullinula indica Penard iqc].

?k-'?>^7tcr^i?3(^^ Shell brownish, of small siliceous plates, closely cemcnttxl to-

gether. Superior lip slightly overlapping the inferior lip.
'%\ Nuclei numerous. Diameter igo to 200 m. Habitat mosses.

■^n^'^Rr^^^SrW Fig. 309. Bullinula inJica. X 120. (.■\f tor Penard.)

78 (77) Shell hemispherical, superior lip without pores. Small size.

PI agio pyxis Penard

79

2 26 FRESH-WATER BIOLOGY

79 (80) Inferior lip rounded, dipping far into the interior of the shell.

Plagiopyxis calUda Penard 1910.

Shell gray, yellow, or brown in color, usually smooth and clear. The
lips overlap to such an extent that the aperture is ditlicult to observe.
v\r--l Pseudopodia large at the base with furcate extremities. Nucleus single.
Kj-^K!'] Diameter g2 to 103 /i- Habitat mosses.

Fig. 310. Plagiopyxis callida. X 150. (.^fter Wailes and Penard.)

80 (79) Inferior lip triangular, slightly dipping into the interior of the shell.

Plagiopyxis lahiata Penard 191 1.

Brown in color. Smaller than the preceding species. Nucleus sin-
gle. Pseudopodia not observed by Dr. Penard, who reports the species
from Australia and Vancouver, B. C. Diameter 80 to 88 p.

Fig. 311. Plagiopyxis labiata. X 155. (After Penard.)

81 (76) Shell more or less compressed; aperture not lunate 82

82 (83) Plates quadrangular Qiuidndella Cockerell.

Representative species. . Quadmlella symmetrica F. E. Schultze 1875.

In this species the shell is normally pyriform, one variety

^ being short and another long. The plates are very transparent,

usually regularly arranged in transverse and longitudinal series.

;rt>/J;;'?^^ Pseudopodia few. Common in sphagnous swamps. Length

from 80 to 140 ^l.

Fig. 312. Quadrulella symmetrica, cv, contractile vacuole. X i7S-
(After Leidy.)

83 (82) Plates not quadrangular 84

84 (91) Shell pyriform, sometimes ovoid or rounded, compressed with round,

oval, or irregular plates Nebela Leidy . . 85

85 (88) Shell pyriform 86

86 (87) Neck long, narrow; plates round. . Nebela lageniformis Penard 1890.

Body of shell oval, prolonged as a tubular neck. There are no
'j—onc^ ^^^\ lateral pores through the shell as in some species. The plates are

fo^^^^^^^of'^^^fl round and very clear. Pseudopodia few. Found commonly

\<r£ii22£Q2hxi^^^-Ci.(^^ among mosses; very abundant in some localities. Length 125 n.

^Ss=^ Fig. 313. Nebela lageniformis. X i7S- (After Penard.)

87(86) Neck short; plates round or oval. . . . Nebela collaris Leidy iSyg.

In this species, large, round, and oval plates are usually inter-

A r!^^??3?^?^ySl^^^^ mingled. Sometimes foreign elements enter into the composition

^c^--.>o^ _..{^^4^ of the shell. It is a ver>' common species, found abundantly in

'••o.;,.;^-^M,a.J<9 sphagnous swamps and presents many variations in size and form.

Large individuals average about 1 20 /x.

Fig. 314. Nebela collaris. X 150. (After Leidy.)

88 (85) Shell not pyriform 89

89 (90) Shell rounded, border of aperture smooth.

Nebela flabell urn Leidy 1874.
The transverse diameter usually equals or exceeds the length, but
'pypJ'?^h. apparently transitional forms between this species and the preceding

jm^ooo'^W^ one are sometimes observed. Possibly this is but a variety of Nebela
W^^^OQ^^ collans. The plates are similar in the two species. Habitat sphagnous
'^°-^'?^Sct^ swamps. Length 50 to 100 m-

Fig. 3x5. Nebela Jiabellum. X 150. (After Leidy.)

AMOEBOID PROTOZOA (SARCODINA) 227

90 (89) Shell ovoid; border of aperture crenulate.

f?;^-^ Nebela dentistoma Penard 1890.

The shell is very clear with round or oval plates, the arranRement of
the plates at the margin of the aperture forming the rounded crenu-
lations. Pseudopodia very active. Found in sphagnous swamps.
Length 66 to 130 a*.

Fig. 316. Nebela dentistoma. x 160. (After Penard.)

mm

91 (84) Shell ovoid, compressed with round, oval, or irregular plates. . . 92

92 (93) Aperture oval, terminating a short tube formed by the thickened

oral membrane. Plates irregular.

Awerinzewia Schouteden.
Representative species. . Awerinzewia cyclo^tomata ^choxxitdtn 1902.

Shell a chitinous envelop covered by siliceous plates, some large, scatter-
ing, others small, filling in between the large ones. Sand grains often at-
tached to the posterior border. Color usually violet. Nucleus single.
Closely allied to the genus Heleopera. Length 135 to 1 78 m. Habitat mosses.
Fig. 317. Awerinzewia cyclostomata. X 100. (After Penard.)

93 (92) Aperture elliptical or Hnear, not terminating a tube.

Heleopera Leidy . . 94

94 (95) Chlorophyl always present Heleopera picta Leidy 1874.

The shell is very regular in outline, of a yellowish tint,
usually with little foreign material attached. The presence
of chlorophyl seems to be necessarj^ to the life of the animal.
Pseudopodia numerous. Found in sphagnous swamps.
Length 100 to iiom-

Fig. 318. Heleopera picta. X 150. (After Leidy )

95 (94) Wine-red in color Heleopera rosea Penard 1890.

This species may be known by its color, the tint being of variable
^__^ ,_ depths. Sand grains and other foreign elements cover the fundus of

%'^€.^^^^n the shell. A thin, yellowish lip borders the aperture. Found among
fe^^^^^^"^ mosses in swamps. Length 90 to 100 /i.
~ ^ Fig. 319. Heleopera rosea. X 150. (After Penard.)

96 (23) Pseudopodia sometimes thick, sometimes linear 97

97 (100) Shell chitinous, densely covered with sand grains, diatom shells, and

other foreign elements. . . . Phryganella Penard . . 98

98 (99) Large size; foreign elements large, rough.

Phryganella nidulus Penard 1902.

The shell is hemispherical and usually oi rough contour.
Aperture large. Pseudopodia slender but often accompanied
by broad lobes of protoplasm. Found in the ooze of ponds
and lakes. Large forms are 200 n in diameter.

Fig. 320. Phryganella nuiulus. x 90. (.\ftcr Penard.)

FRESH-WATER BIOLOGY

Small size; foreign elements small. .

Phryganella hcmisphacrica Penard 1890.

Shell hemispherical, composed of small diatom shells
and sand grains. Pseudopodia usually slender, some-
times thick. Found in the ooze of ponds and lakes.
Diameter 40 to 55 /i.

Fig. 321. Phryganella hemisphaerica. X 250. (After Penard.)

100 (97) Shell chitinous, without or sparsely covered with foreign ele-
ments i°i

loi (102) Shell occasionally with foreign elements attached. Aperture ter-
minal Cryptodifflugia Penard.

Representative species. . . Cryptodifflugia ovijormis Penard 1890.

This species has a transparent, yellowish or brownish shell without foreign
elements attached. Ovoid in form. The protoplasm does not fill the shell and
pseudopodia are seldom extended. Found in marshes. Length 16 to 20 m-

Fig. 322, Cryptodifflugia oviformis. X 450- (After Penard.)

Fig. 323. Platoiim parvum
X 725. (After Penard.)

102 (loi) Shell without foreign elements. Aperture terminal or subterminal.

Platoum F. E. Schultze.

In 1875 Schultze described a form under the n-Ame Platoum parvum.
Ovoid with smooth envelop without structure, slightly elastic, aper-
ture terminal or subterminal. Penard, more recently, observed
numerous empty shells and inactive organisms which he provision-
ally refers to this genus. Some had undulating envelopes with
apertures terminal or directed obUquely. Nucleus and contractile
vacuole each, single. Pseudopodia not observed. Length 16 to 21/1-
In preserved material from Alaska, G. H. Wailes found forms
which he considers within this genus, probably P. parvum. Thus
far this is the only record of the genus in North America.

103 (22) Pseudopodia delicate, filiform, usually branched, and pointed.

Family Euglyphidae . . 104

104 (107) Shell flexible, transparent Pamphagus Bailey . . 105

105 (106) Shell spherical Pamphagus hyalinus Ehrenberg 1838.

The aperture of the shell is very large and capable of great
dilation. Protoplasm Is clear, colorless. Nucleus spherical;
contractile vacuole single. Pseudopodia numerous, straight, and
pointed. Found in clear water. Diameter of shell 30 to 48 n.

Fig. 324. Pamphagus hyaltnus. cv, contractile vacuole. X 260.
(After Leidy.)

106 (105) Shell ovoid or elongate.

Pamphagus mutahilis Bailey 1853.

Body very changeable in form. Protoplasm enclosing brilliant
granules. Nucleus large, spherical. Contractile vacuoles, one or
two. Found in clear water. Length of shell 50 to 70 n.

Fig. 325. Pamphagus mutabilis. X 165. (After Penard.)

107 (104) Shell rigid 108

108(113) Shell retort-shaped lOQ

AMOEBOID PROTOZOA (SARCODINA)

229

109 (no) Plates small, round, more or less covered by foreign particles.

Campascus Leidy.
Representative species Campascus cor nut us Leidy i^-j-j.

This species has lateral processes developed from the fundus.
In common with other species of the genus, a delicate, transpar-
ent collar surrounds the aperture, extending perpendicular to it.
In common with the genus Cyphoderia, the bodies of all species
of this genus enclose minute yellow or l^rown granules very re-
sistant to reagents. Apparently a very rare species. Leidy re-
ports it from but one locality, China Lake, Wyoming, at an
altitude of 10,000 feet. Length 112 to 140 /i.
Fig 326. Campascus cornutus. cv, contractile vacuole. x 150.
(After Leidy.)

no (109) Plates small, regular, not covered by foreign particles.

Cyphoderia Schlumberger . . in

III (112) Fundus rounded or mamillate.

Cyphoderia ampulla Ehrenberg 1840.

Plates round or oval, cemented together in diagonal rows,
presenting a hexagonal appearance. The plates do not over-
lap. Minute perforations exist between the plates, appearing
as fine punctae. Pseudopodia few but very long. Found
among mosses, ooze of ponds and lakes. Length Oi to 195 ti.
Several varieties of fnis species are known.
Fig 327. Cyphoderia ampulla. cv, contractile vacuole. X 160.
(After Leidy.)

112(111) Fundus tapering. . Cyphoderia ampidla V3iT. papillata Wsiiles iQii.

This variety resembles the type species except in the shape of the
^-^''^"'^-^ fundus. The plates are sometimes set very close together in this

" ■ \ variety but do not overlap. Found in ooze of lakes. Length 113 to

CT. -3 135 M.

Fig. 328. Cyphoderia ampulla var. Papillata. X150. (From a prepared mount.)

113(108) Shell Straight "4

114 (115) Shell without distinct plates, chitinous, covered with sand, dirt.

etc Pseudodifflugia Schlumberger.

Representative species.

Pseudodifflugia gracilis Schlumberger 1S45.

Shell ovoid, elongate, usually yellowish or brownish. Pseudo-
podia numerous, very long and delicate. Found in the ooze of
ponds, lakes, etc. Length 20 to 65 m-

Fig. 329. Pseudodifflugia gracilis, n, nucleus. X 250. (After Leidy.)

115 (n4) Shell with distinct plates 116

n6 (n9) SheU not compressed, with a short tlattcncd neck. Plates round or
oval 5/>//e;/('(/('r/(2 Schlumberger n;

117 (n8) Margin of neck dentate. . . . Sphcnodcria dcntata \\\r.\Xi.\ x'^oo.

This species may be known by the elongate-oval form of the shell and
the presence of the teeth. The plates overlap givnig the appearance of a
hexagonal design. Found among sphagnum. Length 35 to 50 m-

Fig. 330. Sphenoderia dcnlata. X jio. (After Pcnard.)

230 FRESH-WATER BIOLOGY

1 18 (117) Margin of neck not dentate. Sphcnoderia lenta Schlumberger 1845.

Shell ovoid or rounded with large, round imbricating plates. The aper-
ture consists of a narrow, elongated opening, extending between two lateral
[■t>.'.-i&}yy points opposite each other. Pscudopodia are numerous and very long.
%-lji Habitat sphagnum. Length from .s5 to 50 ti. Leidy describes a species

under the name 5. macrolcpis, dilTering from other species by the angular
plates composing the shell. Habitat sphagnum. Length 24 to 39 n.

^ '"'~' FiG.^31. Sphenoderia lenta. a, contractile vacuole. X 300- (.\fter Leidy.)

119(116) Shell compressed, without a neck 120

120(137) Aperture terminal 121

121(136) Margin of aperture dentate 122

122 (125) Plates elongate-elliptical; margin of aperture finely dentate.

AssiiUna Ehrenberg . . 123

123(124) Large size, rounded l552///«a 5ewJww/MW Ehrenberg 1848.

Adult forms of this species are chocolate brown in color. Con-
tractile vacuole single. Nucleus very large, elliptical. Pseudopodia
•MP -yu\ seldom observed. Common in sphagnous swamps. Length 60 to

Fig. 332 Assulina seminidum. cv, contractile vacuole. X 290.
(After Leidy.)

124(123) Small size, oval l552///;/(Z ;;?/;?or Penard i8qo.

This species is also brown in color but clearer than the preceding one and
l-«Tjf.xi|A the aperture is more regularly crenulate. The hexagonal design formed by the
MM]1 imbricating plates is very symmetrical. Found among mosses. Length 35 m-

w'tvi

^^''^'''^ Fig. 333. Assulina minor. X 30°- (.^fter Penard.)

125 (122) Plates round or oval; margin of aperture with prominent denticles.
Spines often developed. . . . Euglypha Dujardin . . 126

126(133) Aperture circular 127

127 (130) Spines at apex only 128

128(129) Spines, one or two Euglypha mucronata Leidy iSjS.

The shell not compressed; plates imbricating, arranged in
^________,.^_^^ longitudinal, alternating rows. The_ fundus tapers to a point

'r^^^^f^^i^_^^'^^'y^'^^:^^^ which is provided with one or two spines. Found in sphagnous

"^j^^^^i^D^'l^X--.^ ' swamps. Reported from North America only. Length 108 to

Fig. 334. Euglypha viucronala. X 165. (After Leidy.)

129(128) Spines in a tuft Euglypha cristata Leidy iSy 4.

Shell elongated, very little compressed if any, with plates arranged
as in preceding species. Pseudopodia rarely extended. Habitat
i^i^,^, sphagnous swamps. Length 33, to 84 m-

'-^'"^ ^' Fig. 335. Euglypha cnsiata. X 425- (After Leidy.)

130 (127) Spines not at apex only 131

AMOEBOID PROTOZOA (SARCODINA)

231

131 (132) Spines lateral Euglypha brachiata Lcidy 1878.

This species may be known by the straight shell, elongate

and cylindrical. Plates oval, imbricating in a regular manner.
From four to six large, long spines are developed, representing
<i::^3;SJ^Xlt;?Qf=r^ prolongations of some of the lateral plates. Habitat among

\V^^^^^-«-<.i23>^ sphagnum. Length 104 to 128^-

^»^ Fig. 336. Euglypha brachiata. X i8o. (After Leidy )

132 (131) Spines usually absent, scattered when present.

Euglypha alveolata Dujardin 1841.
Shell ovoid, elongated, very slightly compressed if any. Plates
round or oval, imbricating, presenting a regular hexagonal design.
Nucleus large, spherical; contractile vacuoles two in number.
Pseudopodia numerous, long and straight. .\ common species in the
f^^^r^i^T^ ooze of ponds, among algae and mosses. Length 45 to 100 n.

Fig. 337. Euglypha alveolata. X 375- (Original, from a prepared mount.)

133 (126) Aperture oval 134

134 (135) Plates bordering aperture denticulate.

Euglypha ciliata Ehrenberg 1848.

Shell compressed, elongate-oval. Plates oval or round, imbricated.
Needle-like spines are produced from the entire surface or in a line
around the lateral border of the shell. Habitat sphagnum. Length

40 to 90 M.

Fig. 338. Euglypha ciliata. X 250. (After Penard.)

135 (134) Plates bordering aperture lobed. Euglypha compressa Carter 1864.

Shell greatly compressed, formed of elliptical plates, imbricating
and presenting a hexagonal design. Numerous spines, fusiform in
shape, are produced from the lateral border of the shell. Habitat
sphagnum. Length 70 to 132 /i.

Fig. 339. Euglypha compressa. X 225. (After Leidy.)

136 (121) Margin of aperture not dentate. Shell oval, compressed.

Placocista Lcidy.

Representative species Placocista spinosa Lcidy 1874.

This species may be known by the long, awl-shaped spines
which are movably articulated in a line about the lateral border
of the shell. Plates oval, imbricating in a regular manner. Habi-
tat sphagnum. Length 100 to 136 n.

Fig. 340. Placocista spinosa. X 170. (After Leidy.)

137 (120) Aperture not terminal 138

138 (143) Shell elongate-oval, usually compressed; aperture subtcrminal.

Plates rounded Trinema Dujardin . . 130

139 (140) Oral extremity broad.

Trinema camplanatiim Penard 1800.

This species is short and broad, the anterior end usually as broad
as the posterior extremity. Aperture oval. Habitat mosses. Length
30 to 40 n.

Fig. 341. Trinema camplanatum. X 500. (After Penard.)

140 (139) Oral extremity narrow 141

232 FRESH-WATER BIOLOGY

141 (142) Plates distinct, large size. . . . Trincma cnchelys Ehrenberg 1836.

The aperture is circular in this species and surrounded by a num-

^/'^ ^' " »^ her of rows of very minute chitinous plates. Pseudopodia very tine

c'^. ; ■ : . 'v^ iind long, usually few in number. This is the most common species

^^^i^ -' / ' of the genus and is found everywhere among mosses. Length 40 to

/ 100 n.

Fig. 342. Trinema enchclys. X 310. (After Penard.)

142 (141) Plates indistinct, small size. . . . Trincma lineare Penard 1890.

, , The plates of this small form are indistinct except about the edges,

/ where they may appear as minute undulations. The aperture is round.

j^ Habitat as other species. Length 16 to 26 m-

^j^^v^;^ Pig. 343. Trinema lineare. X 500. (After Penard.)

43 (138) Shell shaped as Trinema; aperture subterminal; plates elongate.

Corythion Taranek.
Representative species Corythion dubiiim Taranek 1882.

In this species the shape of the aperture is characteristic, its border rep-
resenting two unequal arcs placed together, the anterior one the longer.
The plates are close together but not overlapping. Habitat mosses.
Length 35 to 40 m-

Fig. 344. Corythion diibium. X 375- (After Penard.)

144 (2) Pseudopodia usually anastomosing 145

145 (158) Pseudopodia very delicate, usually finely branched.

Subclass Foraminifera . . 146

146 (147) Body without a covering; pseudopodia formed from any part of

the surface Biomyxa Leidy.

Representative species Biomyxa vagans Leidy 1875.

The body moves slowly but continuously, no distinction
^ between ectoplasm and endoplasm being observed. Pseu-

dopodia long, branching and anastomosing, always chang-
ing. A granular nucleus and a number of contractile
V <£TS-;^''"^^:::-__.__^ '^'^.cuoles are present. Habitat sphagnous swamps. Large

'°_^<s'.'o( ^^>>.^ individuals may measure 480 ^ between the tips of the

pseudopodia.

'\ P~~^, N ^ Fig. 345. Biomyxa vagans. X 65. (After Penard.)

147 (146) Body with a distinct covering 148

148 (153) Pseudopodia extending from more than one aperture. . . . 149
149(152) Envelop elongate, compressed. . . Amphiirema Archer . . 150

150 (151) Envelop transparent, with no foreign particles attached.

Amphitrema jlaviim Archer 1878.

Pseudopodia straight, unbranched, extending from the opposite
poles of the envelop. Protoplasm always enclosing chlorophyl.
Nucleus single. One or more contractile vacuoles. Habitat
mosses. Length 45 to 55 ix.

Fig. 346. Amphitrema flavum. X 255. (After Penard.)

151 (150) Envelop with foreign particles attached. •

Amphitrema wrightianum Archer 1870.

In this species the apertures at opposite poles are sur-
rounded by short collars. Chlorophyl always present.
•gr,""®*"* "o E- Pseudopodia often branched. Nucleus single. Contractile

vacuoles one or more. Habitat mosses. Length 65 to 70 /x.
Fig. 347. Amphiirema wrighlianum. X 215. (After Penard.)

AMOEBOID PROTOZOA (SARCODINA)

233

152 (149)

Envelop spherical Diplophrys Barker.

Representative species Diplophrys archer i Barker 1868.

In this species the pseudopodia, which are long and branched, extend
from opposite poles of the envelop. The protoplasm always encloses
a large spherical globule usually yellow or brown in color. A nucleus
and one or more contractile vacuoles are present. Habitat sphagnum.
Diameter 8 to 20 /x.

Fig. 348. Diplophrys archeri. X 1200. (.'\fter Penard.)

153(148) Pseudopodia extending from a single aperture 154

154 (155) Envelop very flexible, changeable in shape.

Lieberkuhnia Claparede and Lachmann.
Representative species. . . Lieberkuhnia wageneri C. and L. 1858.

The envelop is normally pyriform but changeable in shape.
Pseudopodia long, anastomosing, extending from a protoplasmic
peduncle at the aperture. Nuclei as many as 200. Contractile
vacuoles numerous. Habitat mosses. Length 96 /i>

Fig. 349. LieberkUh'iii wageneri. X 130. (After Penard.)

155 (154)

156 (157)

Envelop rigid or slightly flexible 156

Body filling the envelop Gromia Dujardin.

Representative species Gromia fluviatil is T>w]diX(]\n i^^i.

Envelop spherical or ovoid, seldom changing shape. The outer

surface of the envelop is covered by a delicate sheath of proto-

/ ".!^ plasm in which minute granules circulate. Pseudopodia numerous,

''..:_^ anastomosing. Habitat among aquatic plants. Diameter 90 to

. - 250 n. This species is identical with Gromia terricola Leidy.

--;."" Fig. 350. Gromia fluvial His. X 25. (After Leidy.)

157 (156) Body not filling the envelop Microgromia R. Hertwig.

Representative species. . . Microgromia social is R. Hertwig 1S74.

Envelop rigid with a short neck. Pseudopodia long, anastomosing, aris-
ing from a peduncle at the aperture. Sometimes colonies are formed.
Habitat standing water. Length 20 m- Conn reports a form from Con-
necticut which he refers to this species with some doubt as to its identity.

Fig. 351.

Microgromia socialis. cv, contractile vacuole; n, nucleus.
(After Hertwig.)

X 545.

158 (145) Pseudopodia ray-like, soft, and anastomosing when touching.

Subclass Proteomyxa . . 1 50

159 (160) Body amoeboid; endoplasm colorless. . . Nuclear ia Cienkowsky.
Representative species. . . . Nuclearia simplex Cienkowsky i^b^.

Body normally spherical but capable of changing shape. Pseudopodia
arising from all parts of the body. Nucleus central, contractile vacuoles
more than one. Diameter 20 to 50 m- Reported by Conn from Connecti-
cut.

Fig. 352. Nuclcaria simplex. X 250. (.Vfter Cona.)

234 FRESH-WATER BIOLOGY

i6o (159) Body amoeboid; endoplasm red or brown.

Vampyrella Cienkowsky.
Representative species. . . Vampyrella lateritia Cienkowsky 1865.

Body spherical or elongated. Pscudopodia arising from all parts of the
body or from one point. The nucleus and contractile vacuole usually con-
cealed by the contents of the endoplasm, A gelatinous sheath sometimes
surrounds the body. Habitat among algae up)on which it feeds. Diameter
25 to 80 n.

Fig. 353. Vampyrella lateritia. X 250. (After Conn.)

161 (i) Pseudopodia with axial filaments Class Actinopoda.

Fresh-water species included in one subclass.

Subclass Heliozoa . . 162
No central capsule between endoplasm and ectoplasm. Pscudopodia ray-like.

162 (165) With no external envelop .... Order Aphrothoracida . . 163

163 (164) Nucleus single Actinophrys Ehrenberg.

Representative species Actinophrys sol. Ehrenberg 1830.

Body spherical with protoplasm highly vacuolated. Usually
one contractile vacuole which rises and pushes out the surface as
a rounded globule before bursting. Pseudopodia extending from
all parts of the body. Habitat pond water among aquatic plants;
very common. Diameter 40 to 50 //.

Fig. 354. Actinophrys sol. cv, contractile vacuole. X 245. (After Leidy.)

164 (163) Nuclei many Actinosphaeriiim Stein.

Representative species.

Actinosphaerium eichhornii Ehrenberg 1840.

Protoplasm vacuolated with very large vacuoles about the
periphery. Nuclei scattered throughout the endoplasm. Pseudo-
podia extending from all parts of the body. One or more con-
tractile vacuoles. Habitat among aquatic plants. Not common.
Average diameter 200 to 300 n. Some have reported individuals
over 1000 M in diameter.

Fig. 355. Actinosphaerium eichhornii. cv, contractile vacuole. X 40.
(After Leidy.)

With an external envelop 166

167) Envelop gelatinous, without plates or spicules.

Order Chlamydophora.

One genus reported in North America. . . . Adinolophus Schultze.
With a pedicel.
Representative species. . . Actinolophus minutus Walton 1905.

Pseudopodia very short, extending from all parts of the body. Nucleus single, in
the posterior region. Contractile vacuole not observed. Diameter of body with en-
velop 12 M- Length of pedicel 70 /i. Habitat river water. Described by Walton
from Ohio. This genus is introduced provisionally. Further knowledge is needed
concerning it, as certain species referred to the genus show marked affinities with
Sucloria.
Fig. 356. Actinolophus minulus. cv, contractile vacuole; ». nucleus. X 350. (After Walton.)

AMOEBOID PROTOZOA (SARCODINA)

167 (166) Envelop with more or less closely united spicules.

235
168

168 (175) With a thick protoplasmic envelop in which are imbedded skeletal
elements in the form of spicules or plates.

Order Chalarothoraca . . 169

169(172) Skeletal elements loosely connected i^q

170 (171) Spicules chitinous, radiating between the pseudopodia.

Hekrophrys Archer.
Representative species. . . . Hekrophrys myriopoda Archer 1869.

In this species the envelop is mucilaginous, its outer border pre-
senting a villous appearance due to the arrangement of the spicules.
Ray-like pseudopodia penetrate the envelop. This organism is
known to take possession of spicules from species of related genera,
probably from discarded skeletons, and make them a part of its
own envelop. Endoplasm usually green with symljiotic algae.
Nucleus single. A contractile vacuole is not always observed.
Habitat marshes and standing water. Diameter 70^.

Fig. 357. Heterophrys myrioPoda. x 190. (After Penard.)

171

(170) Spicules siliceous, scattered through the envelop and surrounding
the bases of the pseudopodia. . . . Raphidiophrys Archer.
Representative species.

Raphidiophrys ekgans Hertwig and Lesser 1874.

The spicules are semicircular, with their convex surfaces
toward the body and pseudopodia. Nucleus single. One
contractile vacuole. Chlorophyl sometimes present. Often
numbers of these individuals are grouped into colonies, joined
by protoplasmic processes. Habitat among aquatic plants.
Diameter 30 m.

R. viridis Archer diflfers from R. ekgans in the fusiform spic-
ules and the constant presence of symbiotic algae.

Fig. 358. Raphidiophrys ekgans. X 150. (After Leidy.)

172 (169) Skeletal elements closely united, forming a compact envelop. 173

173 (174) Spicules siliceous, globular, completely surrounding the body.

Pompholyxophrys Archer.
Representative species. . . Pompholyxophrys piinicca Archer 1869.

The spicules usually in three rows about the body. Endoplasm re<l-
dish. Nucleus spherical, large. No contractile vacuole. PscudojxKlia
very fine and indistinct. Habitat among aquatic plants in ponds antl
in swamps. Diameter 25 to 30 /i. Leidy records this species from
New Jersey as Uyalolampe Jeneslrata Greeff.

Fig. 359. Pompholyxophrys punicea. X 200. (After Penard.)

236 FRESH-WATER BIOLOGY

174 (173) Spicules siliceous, in the form of plates and delicate radiating

spines Acanthocystis Carter.

Representative species. . . Acanthocystis chaetophora Leidy 1874.

The skeletal plates are oval, arranged tangentially. The
spinous rays are of two lengths, the long ones acutely forked,
the short ones widely forked at the distal extremities. Nucleus
large, usually no contractile vacuole. Endoplasm green in
color from enclosed chlorophyl. Habitat among aquatic
plants. Diameter of body 50 to 60 m-

Fig. 360. Acanthocystis chaetophora. X 250. (After Leidy.)

^M^MW^-

175 (168) With a solid envelop, perforated for the pseudopodia. Sometimes
stalked Order Desmothoraca.

One genus reported in North America. . . . Clathrulina Cicnkowsky.

Envelop with a stalk.
Representative species Clathrulina elegans Cienkowsky 1867.

Envelop more or less chitinous, perforated by numerous large, irreg-
ular openings. Protoplasm not filling the envelop. Nucleus single.
One or more contractile vacuoles. Pseudopodia very delicate, appar-
ently without a.Kial filaments. Habitat sphagnous swamps and among
aquatic plants; very common in some localities. Diameter of envelop
60 to 90 M-

Fig. 361. Clathrulina elegans. X 130. (After Leidy.)

IMPORTANT REFERENCES ON PROTOZOA, ESPECIALLY
SARCODINA

BuTSCHLi, O. 1883. Protozoa. In Bronn's Klassen and Ordnungen des

Thierreichs, vol. i, pt. 1-3. Leipzig.
Calkins, G. N. 1901. The Protozoa. New York.

1909. Protozoology. New York.
Cash, J., and Hopkins, J. 1 905-1 909. The British Fresh-water Rhizopoda

and Heliozoa. 2 parts. Ray Society, vol. 75.
COCKERELL, T. D. A. 1911. The Fauna of Boulder County, Colorado.

Univ. Colo. Studies, 8: 227-256.
Conn, H. W. 1905. A Preliminary Report on the Protozoa of the Fresh

Waters of Connecticut. State Geol. and Nat. Hist. Survey, Bull. 2;

69 pp., 34 Pl.

AMOEBOID PROTOZOA (SARCODINA) 237

Edmondson, C. H. 1906. The Protozoa of Iowa. Proc. Davenport Acad.

Sci., II : 1-124; 29 pi.
191 2. Protozoa of High Mountain Lakes in Colorado. Univ. Colo.

Studies, 9: 65-74.
Heaipel, a. 1898. A list of the Protozoa and Rotifera Found in Illinois River

and Adjacent Lakes at Havana, 111. Bull. 111. State Lab. Nat. Hist., 5:

301-388; 5 figs.
Landacre, F. L. 1908. Protozoa of Sandusky Bay and Vicinity. Ohio

Acad. Sci., 4: 421-472.
Leidy, Jos. 1879. Fresh-water Rhizopods of North America. U. S. Geol.

Surv. Territ., vol. 12; 324 pp., 48 pi.
Penard, E. 1902. Faune rhizopodique du bassin du leman. 714 pp., figs.

Geneve.

1904. Les Heliozoaires d'eau douce. 341 pp., figs. Geneve.

1905. Les Sarcodines des grand lacs. 133 pp., figs. Geneve.

1911. Rhizopodes d'eau douce. British Antartic Expedition, 1907-9, i:
203-262. (Includes a Kst of Rhizopods from Canada.)

Wailes, G. H. 191 2. Fresh-water Rhizopods and Heliozoa from the States of
New York, New Jersey, and Georgia, U. S. A.; with Supplemental Note
on Seychelles Species. Jour. Linnean Soc, Zoology 32: 121-161; i pi.

Wailes, G. H., and Penard, E. 191 1. Rhizopoda. Proc. Roy. Irish Acad.,
Clare Island Survey, Part 65; 64 pp.; 6 pi.

CHAPTER IX
FLAGELLATE AND CILIATE PROTOZOA

(mastigophora et infusoria)

By H. W. conn and C. H. EDIMONDSON

Professor of Biology, Wesleyan\U niversity Assistant Professor of Zoology, University of Oregon

By early observers the term Infusoria was applied to all minute
organisms found in water, including not only unicellular animals
but many minute plants and not a few multicellular animals, as
rotifiers, sponges, etc. Later the term was restricted to those one-
celled animals which are commonly found in standing water and
which move by means of long whip-like processes called flagella
or by shorter, hair-like structures called cilia.

At the present time the flagellated forms are included under the
subphylum Mastigophora and those possessing ciHa, throughout
their entire existence or during their embryonic stage only, are
grouped under the subphylum Infusoria. Mastigophora and
Infusoria are of almost universal distribution, occurring in fresh
and salt water, abundant in clear pools and streams as well as
in stagnant bodies of water and also in infusions of plant or animal
macerations. Some are parasitic, Hving upon or within the bodies
of other animals.

In the Mastigophora flagella are the characteristic structural
features. These structures are slender, flexible, whip-Hke processes
drawn out from the body, commonly at one end. The flagellum
when single is usually directed forward, and by a lashing movement,
a corkscrew twisting, or a mere vibration of its free distal end
draws the body forward. Flagella may be numerous and often
one or more are directed backward or trail at the side in addition
to those extended in advance.

That a close relationship exists between flagella and pseudopodia
is easily observed in a number of forms. Some low flagellates

238

FLAGELLATE AND CILLVTE PROTOZOA 239

possess well-defined pseudopodia, and the flagella of these forms have
the appearance of permanent, specialized pseudopodia endowed
With the power of vibration. The interchanging of pseudopodia
and flagella has been referred to in the case of Vampyrella under
Sarcodina. The origin of the flagellum has been traced in some
forms to the region of the nucleus, which may be considered as
evidence in favor of its homology with the axial supports of
pseudopodia.

Cilia, which are the conspicuous and for diagnosis the special struc-
tural feature of the cilia tes, as contrasted with flagella, arc short,
hair-like processes. They arise from the ectoplasm, not origina-
ting from the deeper regions of the body as do flagella. Cilia may
be evenly distributed over the surface of the animal or restricted
to certain regions or zones. Often fusion of cilia takes place form-
ing vibrating membranelles or large bristle-like cirri or setae. By
tufts of cilia certain forms may be temporarily attached to supports.
Suctoria, in transition from the embryonic stages to the adult, lose
the covering of cilia which is replaced by hollow tentacles, capable
of extension and retraction. The tentacles may be pointed or dis-
tinctly capitate, the prey being pierced by them and its protoplasm
drawn through the hollow tubules into the body of the suctorian.

In Mastigophora and Infusoria the protoplasm is similar in
structure to that of lower Protozoa, being alveolar in character.
However, in these groups, the protoplasmic contents of the body
are not arranged in zones to the extent found in Sarcodina. Great
variation exists in the consistency of the body both in flagellates
and in ciliates. In some the body is soft and flexible, the ectoplasm
permitting rapid changes in shape or even the formation of pseud-
opodia; others are enclosed by inflexible membranes, sheaths, or
well-defined plates. Cup-like loricae are sometimes developed,
to the inner surface of which the animal may be fixed, from which
it may project, and into which it may retract. In a few oi the
flagellates a delicate collar is formed about the base of the tlagellum.
The collar is very transparent, variable in size, and capable of being
retracted into the body protoplasm like a pseudopodium.

Many flagellates and ciliates are free swimming, while some may
be temporarily fixed by cilia or flagella or by the adherence of a

240 FRESH-WATER BIOLOGY

surface to some support. Others are attached by stalks or pedicels
which may be rigid, flexible or, in some forms, as Vorticella, may
contract spirally. Special organs of defense are provided in a few
flagellates and many ciliates in the form of trichocysts or stinging,
thread-like structures. In at least one genus of flagellates, Poly-
krikos, the stinging threads are highly specialized, resembling
nematocysts of Coelenterata. As in Sarcodina, one or more con-
tractile vacuoles are usually present in the flagellates and ciliates,
their function being similar in all Protozoa.

Nuclei are present in all Mastigophora and Infusoria but con-
siderable structural variation exists with respect to them in these
two groups. In some flagellates the nucleus consists of scattered
or grouped particles of chromatin without a nuclear membrane,
while in many of the higher Infusoria it consists of a highly differ-
entiated, branched structure. Infusoria differ from other Proto-
zoa, with a few possible exceptions, in the possession of two kinds
of nuclei in each cell, a macronucleus and a micronucleus, the
former being concerned with the vegetative functions and asexual
division, the latter with sexual division. The macronucleus is the
larger and often varies greatly from the regular spherical t>^e; the
micronucleus is usually very small, spherical, and in close contact
with the macronucleus. In but one flagellate, Polykrikos, has this
differentiation into two nuclei been found. In the key which
follows, wherever the term nucleus is mentioned, reference is made
to the macronucleus. In many forms of Mastigophora and In-
fusoria as well as Sarcodina, the nucleus encloses a spherical body
which functions as a division center. During the resting stage of
the cell the division center resembles a nucleolus in appearance, but
during mitosis it elongates, forming a spindle, and indirect division
comparable to that in the Metazoa occurs in some of the more
complex forms.

The endoplasm of many Mastigophora encloses colored corpuscles
or chroma tophores, green, yellow, and brown being the prevailing
colors. The chromatophores themselves often enclose deeply
staining pyrenoid bodies which probably have to do with the con-
struction of starch. Other inclusions as oil droplets, paramylum
granules, allied to starch, and pigment spots are common in those

FLAGELLATE AND CILLVTE PROTOZOA 241

forms containing chromatophores. The red ''eye-spot" is usually
located at the anterior end of the body near the base of the flagellum
and probably functions as a sense organ, being stimulated by rays
of light. Chromatophores, oil droplets, and pigment spots may
sometimes be found in Infusoria but are much less common than
among the flagellates.

Generally speaking, the physiological processes in Mastigophora
and Infusoria are carried on precisely as in Sarcodina. The pres-
ence of chlorophyl in some of the flagellates makes possible the
synthesis of food from inorganic elements, but in many of these
forms and in nearly all of the ciHates distinct mouths are developed,
sometimes permanently open and sometimes open only while food
is being ingested. The symbiotic relationship exists with algae
in some species of ciKates also. Among Mastigophora food is
often whipped down by the flagellum to the soft ectoplasm at its
base where ingestion takes place. The dehcate collars present in
some flagellates assist in food getting. Among ciliates the vibrat-
ing ciHa, membranelles, and membranes serve to draw food toward
the animal by arousing currents of water. In Suctoria the tentacles
are organs for securing food, their distal extremities being provided
with openings through which the protoplasm of the prey is drawn.
Respiration and excretion are similar processes in all Protozoa.
The contractile vacuoles assist in the excretion of waste fluids and
probably of gases. In some Infusoria there are deflnite points on
the surface where waste solids pass from the body.

Among the Mastigophora, longitudinal fission is the predominating
method of reproduction, only a few forms dividing transverse!}'.
Usually the chromatophores, ''eye-spot" and pyrenoids, if present,
divide as well as the nucleus during reproduction. The flagellum
sometimes divides longitudinally, and in other forms is cast oil,
new flagella being developed as the cells separate. In some cases
the "eye-spot," pyrenoids, and flagella arc duplicated before a
division of the ceH commences. Many colonial forms of Masti-
gophora illustrate a highly specialized ty-pc of cell division similar
to that shown in a metazoan ovum. Among Infusoria simjile
division is the predominating method of reproduction. Division
may be longitudinal, transverse, or diagonal, both nuclei dividing

242 FRESH-WATER BIOLOGY

during the process, new stmctures such as mouth parts and con-
tractile vacuoles usually being formed as division goes on. The
production of swarm spores is common among the flagellates, occur-
ring either in the free swimming or encysted condition and develop-
ing into the adult either directly or after the fusion of two of them
has taken place. Swarm spores are produced in a few species of
ciliates during encystment.

Conjugation occurs in both Mastigophora and Infusoria. In
some cases the fusion is permanent; in others it is temporary, the
cells separating after an interchange of micronuclear material.
Conjugation may often be followed by either encystment or the
production of swarm spores, or both. Gametes of unequal size are
frequently produced, in some cases union between two small gametes
taking place, in others a large and a small one uniting. Among
VorticelHdae there is a complete fusion of the free-swimming micro-
gamete with the fixed macrogamete. In some of the more compH-
cated flagellates, as Volvox, phenomena closely resembHng sexual
reproduction occur; sex cells are differentiated from somatic
cells, ova and sperm are developed, and new colonies are produced
as a result of fertilization, Encystment occurs in Mastigophora
and Infusoria as in Sarcodina, the condition sometimes being pre-
ceded by conjugation or followed by the formation of swarm
spores.

In general, methods of collecting, studying and preserving
Sarcodina may be employed for Mastigophora and Infusoria.
However, these latter are often free-swimming, swift-moving forms,
and before any satisfactory study of them can be made their move-
ments must be retarded. An aqueous solution of gelatin will check
the movements without kiUing the animals if a solution of the right
consistency is used and this may be obtained by trial. Egg albumen
may be substituted for gelatin. A drop of very dilute methyl
alcohol added to the water containing Protozoa will usually nar-
cotize them. Evaporation of water from under the cover glass will
gradually retard their movement^ but the larger forms will soon
be crushed by the weight of the cover unless the latter is supported
by wax feet, bits of paper, or very thin glass. Fine capillary tubes
broken into short pieces make useful rollers on which the cover

FLAGELLATE PROTOZOA (MASTIGOPHORA)

243

glass may be supported and the protozoan, if under the proper
pressure, may then be rotated for study from various aspects.

KEY TO NORTH AMERICAN FRESH-WATER MASTIGOPHORA

I (131) Flagellated forms with animal characteristics predominating.

Class Zoomastigophora . . 2

Confessedly a poor definition, but no better can be given. The beginner will often be in
doubt whether forms under consideration are flagellated animals (Mastigophora), or flagel-
lated plants (unicellular algae), or less frequently flagellate stages (spores) of Protozoa and
Protophyta. Even authorities are not in agreement regarding the position which should be
assigned to specific forms; thus the Volvocina are included in both Protophyta and Protozoa
in this book.

2(118) Without protoplasmic collars. . . Subclass Lissoflagellata . . 3

3 (36) Very plastic, often producing pseudopodia. Order Monadida . . 4

4 (15) Not forming colonies and without lorica c

5 (12) Pseudopodia present; flagella, one or two.

Family Rhizomastigidae

6 (9) Flagellum single

7 (8) Pseudopodia lobe-like or pointed, sometimes branched.

Mastigamoeba Schultze.
Representative species Mastigamoeba longifilum Stokes 1886.

Body very changeable in shape, often producing distinct
pseudopodia; movements usually slow, repent, but sometimes
the animal glides forward rapidly without pseudopodia being
formed. Flagellum long, very active. Nucleus small, near
the anterior extremity; contractile vacuole single, anterior in
position. Length 12 to 30 /i. Standing water, among decaying
vegetation.

Fig. 362. Mastigamoeba longifilum. x 1000. (After Conn.)

8 (7) Pseudopodia ray-like, often capitate Actinomonas Kent.

Representative species Actinomonas vernalis Stokes 1885.

Body subspherical, changeable in shape, free swimming or
temporarily attached by a short stalk. Pseudopodia few, radi-
ating from any part of the periphery, simple or branched.
Nucleus subcentral; contractile vacuoles several. Diameter
about 20 n. Shallow ponds in early spring.

Fig. 363.

Actinomonas vernalit. cv, contractile vacuole; n, nucleus.
X 600. (After Stokes.)

More than one flagellum 10

244

FRESH-WATER BIOLOGY

lo(ii) Pseudopodia ray-like with swellings along their course. Flagella

directed forward . Acinetactis Stokes.

Representative species Acinetactis mirabilis Stokes 1886.

Body subsphcrical, soft, and plastic. Short, lobate pseudopodia
often in addition to capitate rays. Flagella subequal arising at
some distance from each other. Nucleus central; contractile vacu-
oles two. Diameter about 1 2 m- Stagnant pond water.

Fig. 364. Acinetactis mirabilis. X 700. (After Stokes.)

11(10) Pseudopodia lobe-like. Flagella two, one trailing. Cercobodo Kvaas.
Representative species Cercobodo sp.

Species not determined.

Fig. 365. Cercobodo sp. X 1250. (After Conn.

12 (5) Plastic but not forming pseudopodia. Flagellum single.

Family Cercomoxadidae

13

13 (14) With a posterior tail-like filament Ccrcomonas Dujardin.

Representative species. . . Cercomonas longicaudata DuisLvdm 1S41.

Body elongate-ovate, fusiform, terminating
posteriorly in a long, tail-like filament about
c o twice the length of the body. Nucleus spher-

ical, subcentral. Length 10 fx. Vegetable
infusions.

Fig. 366. Cercomonaslongicaudata. a;, contractile
vacuole; », nucleus X 1200. (After Stein.)

14 (13) Without a tail-like filament Oikomonas Kent.

Representative species Oikomonas steinii Kent 1880.

Body, in motile condition, exceedingly plastic with a single
flagellum at the anterior end and a lip-like extension which as-
sists in taking food; in sedentary state, pyriform and attached
by posterior extremity. Nucleus posteriorly located. Length,-
when contracted, about 20 to 30 tx. Vegetable infusions. Social.

Fig. 367.

Oikomonas steinii. cv, contractile vacuole; n, nucleus.
X 440. (After Blochmann.)

FLAGELLATE PROTOZOA (MASTK;OPHORA)

245
16

15(4) Often forming colonies and often with lorica

16 (21) Lorica present Family Bikoecidak 17

17 (20) Not forming colonies 18

18 (19) Body attached in lorica by thread-like peduncle; with peristome
process. Two flagella Bicosoeca James-Clark.

Representative species Bicosoeca lepteca Stokes 1885.

/

Lorica subcylindrical with a very short neck in front; drawn out to an acute
point where attachment is made with the pedicel. Body ovate, ol)liquely
truncate in front and projecting slightly beyond the margin of the lorica when fully
extended. Flagella unequal. Nucleus near the middle of the body; two con-
tractile vacuoles. A chestnut-brown color of the lorica indicates old age. Length
of lorica 15 to 18 m- Pond water among algae.

Fig. 368. Bicosoeca lepteca. cv, contractile vacuole; n, nucleus. X 840. (.\fter Stokes.)

Body not attached by thread-like peduncle, no peristome process.

Flagellum single Codonoeca James-Clark.

Representative species Codonoeca inclinata Kent 1880.

Lorica ovate, attached obliquely to a pedicel twice its length. Body attached
to the posterior, inner surface of the lorica without a peduncle. Not projecting
beyond the margin of the lorica. Flagellum extending considerably beyond
the aperture. A nucleus and a contractile vacuole in the posterior regi(jn of
the body. Length of lorica 15 m- Pond water.

Fig. 369. Codonoeca inclinata. cv, contractile vacuole. X 810. (.\fter Kent.)

20 (17) Forming colonies, with peristome projection.

r.^./^ Slylohryon de Fromentel.

~ Representative species. . . ^/y/oftryo/z />t'//(;/(i//<m Dujardin 1838.

Each lorica wineglass-shaped, pointed posteriorly, attached to a pKxliccl
which arises from within the cavity of the associated lorica. Body plastic.
Flagella two, unequal in length. Length of lorica },o to 50 m- I'i>nd water.
Often subdividing by spores.

Fig. 370. Stylobryon pciiolatum. cv, contractile vacuole; «, nucleus. X 75- (After Kent

246 FRESH-WATER BIOLOGY

21 (16) Without lorica; one or more llagella.

Family Heteromastigidae . . 22

22 (29) Not forming colonies 23

23 (26) Flagellum single 24

24 (25) Flagellum directed forward Leptomonas Kent.

Representative species Leptomonas sp.

Body pointed anteriorly and very flexible. Flagellum long and active.
Often parasitic. Fig. 371 represents a form reported by Conn, taken from a
watering trough, and assigned to this genus with some doubt.

Species not determined.

Fig. 371. Leptomonas sp. X 875. (After Conn.)

25 (24) Flagellum trailing Rhynchomonas Klebs.

Representative species Rhynchomonas nasula Klebs 1886.

Body ovate, slightly compressed, anterior end prolonged
into a movable process. Mouth near the anterior end.
Nucleus central. Contractile vacuole anterior. Fresh
water.

Fig. 372. Rhynchomonas nasula. X 1500- (After Conn.)

26 (23) Two or more flagella 27

27 (28) Body free or attached by an attenuated posterior end; spherical to
ovate, with one chief flagellum and one or two secondary
ones. Moderately flexible Monas Ehrenberg.

Representative species M<?wa5/wi(/a Dujardin 1841.

W^^-o°yy^A Fig. 373. Monas fluida. ct, contractile vacuole; m, nucleus; 5, stigma; w, mouth.
"[iavi^^S X 1000.

FLAGELLATE PROTOZOA (MASTIGOPHORA)

247

28 (27) Free, like Monas, but with the anterior end ol^Hque.

Physomonas Kent.
Representative species Physomonas elongala Stokes icS86.

Body elongate-ovate, changeable in shape; free-swimming or temporarily
attached by a very short pedicel. Flagella two, unequal. Contractile
vacuole anterior in position. Length about 1 2 n. Swamp water.

Fig. 374. Physomonas elongata. cv, contractile vacuole; n. nucleus
X 1000. (After Stokes.)

29 (22) Forming colonies. Two flagella -^o

30(33) One zooid upon the end of each branch 31

31(32) Pedicel rigid. . Deudromomis Stein.

Representative species Dendromonas virgaria Weisse 1845.

Body of zooid pyriform, compressed, with an anterior,
lip-like projection from the base of which arise the two
unequal flagella. Nucleus single; contractile vacuole one
or two. Colony branching dichotomously. .\ colony may
include over one hundred zooids. Length of zooid 8 to 10 u.
Pond water.

Fig. 375. Dendromonas virgaria. Colony X 160; single zooid X 935 ,
(After Blochmann.)

32(31) Pedicel flexible Ramosoiiema Kent.

Representative species Ramosoncnia laxum Kent 1871.

Zooids pyriform, compressed, obliquely truncate anteriorly. Pedicel

very slender, threadlike. A colony may include as many as twenty or

XWlVym^/ "i^ more zooids. Length of zooids 8 m- Pond water.

K^UuT r ■ Fig. 376. Ramosonema laxum. cf, contractile vacuole; n, nucleus. Colony X 350;

single zooid X 1000. (After Kent.)

3i (30) Many zooids upon each branch 34

34 (35) Stalk short, branching dichotomously once or twice.

Ccplhdothamuiiim Stein.
Representative species. . Cephalotliamniitm cacspitosum Kent 1880.

Zooids irregularly pyriform, in clusters of two or three
or as many as si.x or eight on the summit of a simple or
slightly branched pedicel. Pedicel very short. Length
of zooid about 6 m- Fresh water, attached to Cyclops.

Fig. 377. Cephalothamniumcacspitoium. X 875. i.Uter Conn.)

248

FRESH-WATER BIOLOGY

35 (34) Stalk long, stout, greatly branched. Anthophysa Bory de St. Vincent.
Representative species Anthophysa vegetans M.\i\[er I'jZt.

Bodies attached in rosette-like clusters, each zooid pyriform
in shape, ohUqucly truncate in front, with two lla^ella of un-
equal length. Clusters attached to a branched pedicel or
free swimming, moving through the water in a rolling motion.
In older stages the pedicel becomes dark brown in color.
Length of zooid 5 to 10 m- In stagnant water.

Fig. 378. Anthophysa vegetans. X 500. (.\fter Miiller.)

36 (3) Sometimes plastic but not producing pseudopodia 37

37 (60) Chromatophores not present; flagella often numerous.

38

38 (49) Flagella usually two, one usually trailing; very minute forms.

Order Heteromastigida . . 39

39 (40) Flagella three in number, one directed forward. . . Elvirea Parona.
Representative species Elvirea cionae Parona 1886.

Body ovate to elongate, laterally compressed. The shorter
flagellum directed forward. Mouth and nucleus anterior.
Fresh water.

Fig. 379. Elvirea cionae. x 1200. (After Conn.)

40 (39) Flagella two in number 41

41 (42) Both directed forward Dinomonas Kent.

Representative species Dinomonas vorax Kent 1880.

Body persistent in shape, subpyriform, widest posteriorly,
slightly curved. Flagella siibequal, longer than the body.
Length 15 ^l. Hay infusions.

Fig. 380. Dinomonas vorax. X 1000. (After Conn.)

42 (41) One flagellum trailing, the other directed forward 43

43 (46) Body spiral or oblique 44

44 (45) Body not spiral, anterior end obhque; very flexible.

PhyUomitus Stein.
Representative species. . . . PhyUomitus amylophagus Klebs 1886.

.~ \--'o'(^ "-"*'«» v-V'.'".Sf3 Fig. 381. PhyUomitus amylophagus. X 137 =

:^f^_2^ \J,jf^^^X2):£^ (After Conn.)

FLAGELLATE PROTOZOA (MASTIGOPHORA)

249

45 (44) Body spiral, elongated.
Representative species.

Spiromonas Perty.

. . Spiromonas angnsta Dujardin 1841,

Body five or six times as long as broad. Fla-
gella subequal, as long as the body, one directed
forward; body sometimes temfKjrarily attached
by one. Length 10 m- Hay infusions.

Fig. 382. Spiromonas angusla. X 1000. (After Conn.)
There is doubt as to the identity of Conn's form.

46 (43) Body neither spiral nor oblique 47

47 (48) Kidney-shaped to spherical; flagella arising from a ventral depres-
sion, one trailing. Food absorbed by a dorsal vacuole.

Pleuromonas Perty.
Representative species Pleuromonas jaculans Fcrty 1852.

Body kidney-shaped, very small; sometimes attached by the pos-
terior flagellum. Contractile vacuole anterior; nucleus posterior.

Length 5 to 9 m- Stagnant water and infusions. Movements
jerking and leaping.

Fig. 383. Pleuromonas j ocularis. X looo. (After Conn.)

48 (47) Pear-shaped to spindle-shaped; flagella arising from the anterior
end, one trailing. Food not taken in by a dorsal vacuole.

Heteromita Dujardin.
Representative species Heteromita ovata Dujardin 1841.

Body ovate, widest posteriorly. Flagella unequal, the
trailing one twice as long as the anterior one. Length
25 to 40 ix. River water with aquatic plants.

Fig. 384. Fleteromita ovata. X 500. (.Alter Conn.)

49 (38) Flagella usually numerous, frequently arranged in groups.

Order Phytomastigida

50

50 (53) Flagella two in number.

51 (52) Body expanded into two wings; flagella long.

Trcpomonas Dujardin.
Representative species Trcpomonas agilis Dujardin 1841.

Very irregular in shape, difTerent ajipcarances being presented
from different points of view. The broad, wing-like lateral lobes
curve backward nearly to the middle of the bo<ly. Length 20 m.
Pond water.

Fig. 385. Trcpomonas agilis. X 450. (.\fter Conn.)

250 FRESH-WATER BIOLOGY

52 (51) Body not laterally expanded, sometimes attached by a stalk. Flagella

arising from the anterior end. . . AmpJiimojias Du}a.rdm.

Representative species Amphimonas globosa Kent 1880.

Body subspherical, attached by a filamentous pedicel. Flagella equal, twice the
length of the body. Diameter 1 2 n. Pond water.

Fig. 386. Amphimonas globosa. X 875, (After Kent.)

Conn reports a form, found abundantly in the fresh waters of Connecticut, which
he assigns to this genus, with some doubt. Although never attached by a pedicel,
the two equal flagella would seem to place it here.

53 (50) Flagella four in number 54

54(55) With a deep, vertical furrow Collodictyon Ca.TiGT.

55 (54) Without a vertical furrow 56

56 (57) With three flagella directed forward, one trailing. Body pear-shaped,

rounded in front, acute behind. . Trichomastix Blochmann.
Representative species Trichomastix sp.

American species observed have not been de-
termined.

Fig. 387. Trichomastix sp. X 7S0. (After Conn.)

57 (56) With all four flagella directed forward 58

58 (59) Body ellipsoidal, with two thread-like processes at the posterior

end Hexamitd Dujardin.

Representative species Hexamita inflata Dujardin 1838.

Body plastic, posterior end bifid, giving rise to the trailing, flagella-like
processes by means of which it may be temporarily fixed. Length 10 to
15 ti. Pond water and infusions.

Fig. 388. Hexamita inflata. X 875. (After Coon.)

59 (58)

60 (37)

61 (87)

62 (69)

63 (68)

64 (65)

65 (64)

FLAGELLATE PROTOZOA (MASTIGOPHORA) 251

Body obovate, obliquely truncate in front; or subpyriform or sub-
spherical with a rounded front Tetramitiis Perty.

Representative species Tetramitus variabilis Stokes i^^b.

Body changeable in form. Fiagella subequal, inserted near the middle of the an-
terior border. Endoplasm granular. Contractile vacuoles two, near the front
border. Food received at any portion of the surface. Length 18 to 25 m- Stand-
ing water with decaying vegetation.

Fig. 389. Tetramilus variabilis. X 250. (After Stokes.)

Chromatophores usually present. Fiagella one or two.

Order Euglenida . . 6 1

Elongated forms usually with pointed posterior ends. Chromato-
phores usually green. Paramylin bodies present.

Family Euglenidae . . 62

Naked or with very thin cuticle 63

Flagellum single 64

Attached by a branched stalk, usually surrounded by a jelly-like en-
velop Colaciuni Ehrenbcrg.

Representative species Colaciuni stein ii Kent 1880.

So far as has been determined, no members of this genus have been reported in
North America. Several species have been reported in Europe. Usually
attached to Cyclops or other fresh-water crustaceans.

Fig. 390. Colaciuni steinii. X 350. (.^fter Kent.)

Not attached and not surrounded by a jelly-like envelop. Large
forms, spindle-shaped, usually green, with an eye-spot.

Euglena Ehrenbcrg . . 66

66 (67) Body rounded anteriorly, surface smooth.

Euglena viridis Ehrenbcrg 1830.

Body usually rounded anteriorly with a colorless, tail-like iwsterior pro-
longation. Surface smooth. Nucleus central; contractile vacuole anterior.
Length 50 to 75 n. Common. The chlorophyl may at times be lost and
the species, no doubt, may then exist on organic substances.

Fig. 391.

Euiilena viridis. cv, contractile vacuole; n, nucleus; pant, paramylum;
st, stigma. X 400. (After Blochmann.)

67 (66) Body cylindrical; surface beaded. Euglena spirogyra Ehrcnhcrg 1S30

392. Euglena spirogyra. X 500- (After Conn.)

Body elongate, cylindrical, with a
jxjinted, tail-like prolongation. IVriplury
covered by oblicjue rows of minute l>cad-
like elevations. Color bright green.
Nucleus central, with an clongate<i starch-
like body anterior and jxistcrior to it.
Kye-spot near the base of the llagcllum.
Length 100 to 200 n. Among algae.

252 FRESH-WATER BIOLOGY

68 (63) Flagella two; body spindle-shaped when extended; chromatophores

disk-shaped Eutreptia Perty.

Representative species Eutreptia viridis Perty 1852.

_ Body very changeable in form. Flagella equalling the

body in length. Eye-spot present. Length, when extended,
100 /x. Pond water.

Fig. 31)3. Eutreptia viridis. X 500- (After Conn.)

69 (76) With a thick cuticle or lorica 7°

70 (76) Lorica present 71

71 (72) Lorica beaker-shaped or tube-shaped Ascoglena Stein.

72 (71) Lorica spherical or cylindrical, smooth or spiny.

Trachelomonas Ehrenberg . . 73

73 (74> 75) Lorica smooth, colorless . . Trachelomonas lagenella Stein 1878.

Lorica colorless, oval or elliptical, smooth. An obliquely projecting neck.
Length 20 to 35 m- Fresh water.

Fig. 394. 1 rachelomonas lagenella. X 600. (After Stein.)

74 (73, 73) Lorica spinous, brown. . . . Trachelomonas hispida Stein 1878.

Lorica elongate-oval, with ends broadly rounded. Surface cov-
ered with minute, sharp-pointed spines. A short, tube-Hke neck
sometimes present Brown in color. Length 30 to 36 n. Pond
water, with other species of the genus.

'nvOTf ^FZ^"^^^ Fig. 395. Trachelomonas kispida. X 400. (After Conn.)

75(73.74) Lorica smooth, brown. . Trachelomonas volvocina Ehrenberg iS2,3-

Lorica nearly spherical, surface smooth, usually without a
neck. Flagellum long. Color brown. Diameter 30 m- Very
^^ - "V^ I y common among algae and other aquatic plants.

Fig. 396. Trachelomonas volvocina. X 450. (After Edmondson.)

76(69) With a thick cuticle but no lorica 77

77 (78) Not flattened, ellipsoidal, with a pointed caudal process.

Chloropeltis Stein.
Representative species Chloropeltis hispidula Stein 1878.

Surface of the body ornamented with mi-
nute spines arranged in longitudinal rows.
4r ■ 't'^ y^ \ CV' Endoplasm green, with an eye-spot. Length

55 p. Fresh water, among diatoms.

Fig. 397- Chloropeltis hisptdula. X 600. (After
Conn.)

78 (77) Flattened 79

FLAGELLATE PROTOZOA (MASTIGOPHORA) 253

79 (84) Posterior border acute or with a caudal appendage 80

80 (81) Ellipsoidal, slightly flattened; posterior end acute. Longitudinally

or spirally marked Lepocindis Perty.

Representative species Lepocindis sp.

This genus is very closely related to, if not identical with, the preceding
one. The form here represented is assigned to this genus by Conn, with
some doubt. Species not determined.

Fig. 398. Lepocindis sp. x 1000. (After Conn.)

Round to pear-shaped, asymmetrical, much flattened; caudal process
present Phacus Nitzsch . . 82

Caudal process moderate; not large.

Phacus pleuronectes Nitzsch 181 6.

Tail-like projection usually curved. Surface longitudinally striateci.
Endoplasm green, enclosing one or more large, amylaceous bodies. Flagel-
lum arises from a cleft-like mouth on the anterior border. Length 25 to
75 M- Among aquatic plants.

Fig. 399. Phacus pleuronectes. X 450. (After Conn.)

83 (82) Caudal process long; size conspicuous.

Phacus longicaudus Ehrenberg 1838.

Recognized by its large size and long caudal pro-
jection. Body frequently twisted on its longitudinal
axis. Length 100 n.

Fig. 400. Phacus longicaudus. x 310. (.Aifter Conn.)

84 (79) Posterior end evenly rounded 85

85 (86) Resembling Phacus but without caudal appendage.

Cydaiiura Stokes.
Representative species Cydanura orhiciilata Stokes 1S86.

Body ovate or suborbicular, thick, compressed, with a longitudmal
keel across the right-hand side. Color green. Contractile vacuole
and eye-spot anteriorly placed. Length about 50 /i. Stagnant pond
water.

Fig. 401. Cydanura orbiculata. X 3^5- (After Stokes. J

86 (85) Oval in outline, rigid, flattened. Chromatophores green, two in

number, lateral in position. . . . Cryptoglcua Ehrenberg.

Representative species Cryptoglena pigra EhTcnhcig \^^i.

Flagellum single, short. Chromatophores band-like, following the
contour of the body. \ scarlet eye-six)t near the anterior extremity.
Length 1 2 ti. Fresh water.

Fig. 402. Cryptoglena pigra. X 1500. (After Conn.)

87 (61) Colorless forms without eye-spots. Often very plastic 88

88 (loi) Body elongate, usually with striped membrane. Nutrition sapro-

phytic. Flagella usually two. Family Astasiidae . . 89

2 54 FRESH-WATER BIOLOGY

89 (94) Body flexible; one or two flagella 90

90 (93) Flagella two 91

91 (92) Secondary flagellum very small, directed backward. . Astasia Stein.

Representative species \ stasia trichophora Ehrenberg 1830.

/yTj^^~^^—~r^~y-^.r~—.^ Body elongate, usually wider posteriorly.

t>>Pi^;^^^^£^s^^ Primary flagellum very thick at the base and

^i^^^^=^=^^^^^ long. Nucleus central; contractile vacuole an-

FiG. 403. Astasia trichophora. X 410. teriorly located. Length, when extended, 30 to

(Alter Conn.) 60 m Common among diatoms and algae.

92 (91) Secondary flagellum about half as long as the primary; both flagella

directed forward Distigma Ehrenberg.

Representative species Distigma proteus Ehrenberg 1830.

Body very plastic; when contracted, distended in one
/ ^^'' or two regions. Endoplasm with dark-colored corpuscles.

^^_^__^^<^^^^^::^^^j^-^ Nucleus central ; contractile vacuole in the anterior region.

^^^;ssss=*ss^^*^^^^^^^v_^^ Length, when e.xtended, 95 /x. Pond water.

* "^ Fig. 404. Distigma proteus. cv, contractile vacuole; n, nucleus;

ph, pharynx. X 33° (After Stein.)

93 (90) Flagellum single; body elongate, tapering posteriorly. A long tubu-

lar pharynx Atractonema Stein.

Representative species Atractoiuma tortuosa Stokes 1885.

Body flexible but persistent in shape, colorless,

enclosing oblong dark-bordered corpuscles. Fla-

^,.^^^55.^^^^ ^<''o'^^3~-^2-^ gellum about half as long as the body. Movements

<i^^^^-'-^^^^>>___^.,('^^ rotary on the long axis. Length 50 to 80 n. In

^""^^^^^S^ vegetable infusions.

Fig. 405. Atractonema tortuosa. X 625. (After Stokes.)

94 (89) Body not flexible 95

95 (98) With longitudinal or spiral ridges 96

96 (97) Elongate or crescentic, with four longitudinal ridges; flagella, two,

unequal Sphenomonas Stein.

Representative species. . . Sphenomonas quadrangular is Stein 1878.

Body subfusiform, with the ridges fopming a quadrate outline in cross sec-
tion. Long flagellum stout, four times the length of the shorter one. A
large amylaceous corpuscle usually enclosed in the endoplasm. Length 40 m-
Fresh water.

Fig. 406. Sphenomonas quadrangularis. X 400. (After Biitschli.)

97 (96) Nearly ellipsoidal, with many spiral ridges. . Tropidoscyphus Stein.

98 (95) Without ridges 99

FLAGELLATE PROTOZOA (MASTIGOPHORA)

:>:)

99 (loo) Resembling Sphenomonas, but without ridges; flagella two, unequal.

Clostonema Stokes.
Representative species Clostonema socialis Stokes 1886.

Body fusiform, with a short, rounded posterior prolongation. Primary flagel-
lum as long as the body; secondary, about one-fourth as long. A long, pha-
ryngeal passage present. Length about 20 m- In standing water.

Fig. 407. Clostonema socialis. X 600. (After Stokes.)

100 (99) Resembling Clostonema, but with a single flagellum.

Menoidium Perty.
Representative species.

Menoidium pellucidum Perty 1852.
Body lunate, obliquely truncated at the anterior extremity. Pos-
terior end rounded. The short side of the body thin and sharp, the
long side rounded. Flagellum equalling the body in length. One or
more amylaceous corpuscles usually present. Length 40 to 60 m-
Fresh water.

Fig. 408. Menoidium pellucidum. X 500. (After Senn.)

loi (88) Body rigid or plastic, usually symmetrical; one or two dissimilar
flagella deeply sunk in the body. Nutrition holozoic.

Family Peranemidae . . 102

102 (109) Body plastic 103

103 (108) One flagellum 104

104 (105) Oval, flattened, very flexible; distinct pharynx and rod-like organ

back of the mouth Peranema Dujardin.

Representative species.

Peranema trichophorum Ehrenberg 1838.

Cuticle finely marked spirally. Flagellum very long, vibratilc at the tip
only. Nucleus central.

Fig. 409. Peranema trichophorum. X 250. (.\fter Conn.)

Conn reports a number of undetermined forms which bear considerable
resemblance to the above species and should, without doubt, be assigned
to the genus Peranema.

105 (104) Flask-shaped; neck-like anterior end with elongated phar>'nx and
rod-like organ io6

256

FRESH-WATER BIOLOGY

io6 (107) Without sand grains attached Urccolus Mereschkowsky.

Representative species Urccolus cyclostomum Stein 1878.

Anterior extremity oblicjuely truncate with an expanded rim about the
mouth. Pharynx nearly reaching the posterior extremity with its distal end
dilated. Surface usually spirally marked. Flagellum about as long as the
body. Length 50 m- Fresh water. Identical with Phialonema cyclostomum
Mereschkowsky.

Fig. 410. Urceolus cyclostomum. X 500. (After Conn.)

107 (106) With sand grains attached Urceolopsis Stokes.

Representative species Urceolopsis sabulosa Stokes 1886.

Body flexible and elastic, with a short, anterior, neck-like prolongation.
Usually densely covered with sand grains. Movements are rapid, the body
being held at an angle with the anterior end downward. The long flagellum
\ibrates strongly at its tip. Food particles are drawn into the oral aperture
with considerable force. Length 20 ^u. Among algae.

Fig.

Urceolopsis sabulosa. X 625. (After Stokes.)

108 (103) Two flagella, one trailing; mouth depression obHque.

Heteronema Dujardin.
Representative species. . Heteronema acus Ehrenberg 1840.

Body very plastic, fusiform when extended. Primar>' flagellum as
long as the body and twice as long as the secondar>% trailing one.
Nucleus central; contractile vacuole in the anterior extremity. Length,
extended, 50 m- Fresh water.

Fig. 412. Heteronema acus. X 500. (After Conn.)

Numerous other forms reported by Conn should, without doubt, be
assigned to this genus. The species are undetermined.

109 (102) Body rigid no

no (hi) One flagellum; body flattened, usually furrowed and keeled.

Pctalomonas Stein.
Representative species. . . PetaJomonas pkurosigma Stokes 1887.

Body ovate, the posterior end pointed; lateral borders sigmoid. Dorsal
and ventral surfaces each traversed by a narrow, longitudinal furrow. Length
IS to 20 M- Standing pond water.

Fig. 413. Pctalomonas pleurosigma. X 625 (After Stokes.)

FLAGELLATE PROTOZOA (MASTIGOPHORA) 257

III (no) Two flagella, unequal 112

112(113) Body with spiral ridges Tropidoscyphus Stem.

113 (112) Body without spiral ridges 114

114 (115) Trailing flagellum very prominent, curving around the anterior

end Anisoncma Dujardin.

Representative species. . . . Anisonema acinus V>\i]diX<\\\\ i?>^i .

ys'^^'-^r'^-^^.^^ Body wider posteriorly, flattened ventrally; anterior vi-

fii^~^ ■ -'^^^vv^^ bratile flagellum short. Mouth near the base of the an-

^^jggliaS^r"^-''^^- terior flagellum. Length 25 m. Among diatoms. Common.

Fig. 414. Anisonema acinus. X scxd. Jhe genus Metanema Klebs resembles Anisonema but is

(After Conn.) flexible.

115(114) Trailing flagellum not prominent 116

116 (117) Primary flagellum carried obliquely forward, vibratile only at its
end. Body ovate or angular with dorsal side concave.

No protrusile pharynx Notosolenus Stokes.

Representative species . . Notosolenus orbicularis Stokes 1884.

Body with a broad, shallow, dorsal concavity; the ventral surface convex.
Movements somewhat eccentric, the convex surface usually directed down-
ward. Nucleus to the left of the center of the body. Contractile vacuole
near the anterior end. Length 10 to 12 /i. Bottom of shallow ponds.

Fig. 415. Notosolenus orbicularis. X looo. (After Conn.)

117 (116) Primary flagellum not carried obliquely forward; pharynx pro-
trusile. A strong furrow on the ventral surface.

Entosiphon Stein.
Representative species. . . Entosiphon sukatus Stein 1S78.

Body oval, flattened; anterior border oblique, with a concavity at the
bottom of which is the mouth leading into a long tubular phar>'nx.
Nucleus posterior. Contractile vacuole anterior. Length 22 ti. Pond
water, among aquatic plants.

Fig. 416. Entosiphon sukatus. X 500. (.\fter Conn.

118(2) With protoplasmic collars. . . Subclass Choanoflagellata . . 119
119(122) Not forming colonies 120

58

FRESH-WATER BIOLOGY

120(121) No lorica, with or without a stalk. Mo>iosiga Kent.

Representative species Monosiga ovata Kent 1880.

Body obovate, the broader end posterior; with a rigid pedicel nearly
equal to the body in length. Length of body about 6 m- Reported by
Conn from the fresh waters of Connecticut.

Fig. 417. Monosiga ovala. X looo. (After Conn.)

121 (120) With lorica, with or without a stalk. . . Salpingoeca James-Clark.
Representative species . . . . Salpingoeca convallaria SiQin iS-jS.

\

Lorica campanulate, pointed posteriorly, slightly constricted anteriorly.
Pedicel very slender and short. Zooid nearly filling the lorica. Length of
lorica IS to 25 M- Attached to Epistylis.

Fig. 418. Salpingoeca convallaria. X 600. (After Kent.)

122(119) Forming colonies 123

123 (128) Without stalks 124

124(127) Colonies enclosed in a gelatinous mass 125

125 (126) Forming a flat colony in an irregular jelly. . Proterospongia Kent.

Representative species. . . . Proterospongia haeckeli Kent 1880.

Zooids pyriform, plastic; collar long, each zooid bearing a single fiagel-
lum. Colony may contain as many as fifty or sixty zooids, but often not
more than six or eight. The gelatinous support very transparent.
Length of zooid 8 n. Fresh water.

Fig. 419. Proterospongia haeckeli. X 37S-

126 (125) Colony disk-shaped or arising from a funnel-like, open jelly tube.

Phalanslerium Cienkowsky.
Representative species. . . Phalansterium digitatum Stein 1878.

NX "N\ jg^ra ^^ z' X' Zooids ovate, plastic. Flagellum two or three

VX \>ni.«R»fB KA ^"^i,^ times the length of the body. Jelly mass coarse,

i'y.'^ftt granular, digitiform, and often branching. Length

of zooid 18 y.. Fresh water.

Fig. 420. Phalansterium digitatum. X 400- (After
ButschU.)

FLAGELLATE PROTOZOA (^IASTIGOPHORA)

259

127(124) Colony free, not enclosed by jelly H irm id i inn Vciiy.

Representative species Hirmidium inane Perty 1852.

As many as eleven individuals may be included in the colony. Un-
der the name Desmarclla irregularis, Stokes describes a form with fifty
individuals. Length of body, reported by Stokes, 8 to 1 2 p. Pond
water.

Fig. 421. Hirmidium inane. Colony X 155; single zooid X 325. (After Stein.)

128 (123) With Stalks \ . 129

129 (130) Stalk simple; many individuals borne at the end of the stalk.

Codosigd James-Clark.
Representative species. . . . Codosiga hotrytis Ehrcnberg 1838.

Bodies ovate; pedicel slender, rigid. Flagellum long. Collar
equalling the body in length. Length of zooid 10 to 15 n. Attached
to aquatic plants.

Kent reports that previous to encystment the collars and flagella
of this species may be withdrawn into the protoplasm of the Ixxlies.
while the latter become covered with radiating pseudopodia. Occa-
sionally the pseudopodia are produced while the collar is still ex-
tended. Spores are formed during encystment.

Fig. 422. Codosiga botrytis. x 350. (After Kent.)

130 (129) Stalk branched, with single individuals or groups on the end of

each branch Codonocladiiim Stein.

Representative species. . Codonocladium umbeUatiim Tatem 1868.

Kent would refer this species to the genus Codosiga, in which
genus some forms possess zooids with short pedicels attached to the
end of the main stalk.

Fig. 423. Codonocladium umbellatum. X 500. (.^fter Conn.)

131 (i) Plant characteristics evident; chromatophorcs usually present; often

producing colonies. Class Phytomastigophora . . i w

132 (205) Body without a shell formed of plates; (.hroniatophores yellow.

brown, or green. . . . Subclass Phytoflagellata . . 13.?

133 (164) Chromatophorcs usually yellow or brown.

Order Chrysoflagellida . . 134

134 (137) Body usually naked but may be enclosed in a jelly mass during

resting stages U5

26o FRESH-WATER BIOLOGY

135 (136) Flagellum single; two chromatophores. . Chromulina Cienkowsky.

Chrysomonas Stein is very closely related to this
genus. Under the name Chrysomonas pulchra Stokes
- describes a species as follows: Body elongate-ovate or
obovate, somewhat flexible, three times as long as
broad, tapering and slightly constricted posteriorly,
curved toward one side anteriorly. Frontal border ob-
liquely excavate. Surface covered with minute hemi-
FiG. 424. Chrysomotun; pulchra. X 400. spherical elevations. Flagellum scarcely equalling the
(After Stokes.) j^^^jy j^ length. Nucleus ovate. Contractile vacuoles

two, anterior. Length 35 to 40 m- Color green. Marsh
water.

1^6(1^0 Flagclla two; two chromatophores. . . . Ochr omonas Wysoizki.
Representative species Ochromonas sp.

Species not identified.

Fig. 425. Ochromonas sp. X 1000. (After Conn.)

137 (134) Body enclosed by a membrane or lorica 138

138 (157) With a membrane ^39

139 (146) Not forming colonies 140

140 (141) With a close-fitting membrane of plates; flagellum single.

Mallomonas Perty.
Representative species Mallomonas sp.

Body elongated, enclosed by a membrane of overlapping
plates which bear long, slender spines. Two elongated, yel-
lowish-green chromatophores are within the body.

Species not determined.

Fig. 426. Mallomonas sp. X 500- (After Conn.)

141 (140) With a firm cuticle; two flagella 142

142 (145) Without chromatophores i43

143 (144) Body oval, truncate or concave anteriorly, enclosing refractive

bodies Cyathomonas de Fromentel.

Representative species. . Cya//jowf)wa5/rw«ca/ade Fromentel 1874.

^.qrasr-^^ De Fromentel identified six or eight species, several of which are

^^rg^'-r\ but slightly distinguished from each other. Length 12 to 20 /x.

^«*^^ll r^*^^^ Fresh water.

^^•JfiSaatf-^ Fig. 427. Cyalhomonas truncata. X 1200. (After Conn.)

FLAGELLATE PROTOZOA (MASTIGOPHORA)

261

144 (143) Shaped as Cyathomonas, but with pharynx and without refractive

bodies Chilomonas Ehrenberg.

Representative species. . Chilomonas Paramecium Ehrenberg 1831.

Body elongatc-oval, anterior margin with a lip-like projection. Flagelia
subequal in length. Endoplasm usually enclosing dark-colored corpuscles.
Length 25 to 40 m- Stagnant infusions; very common.

Fig. 428. Chilomonas Paramecium. X 350. (.\fter Conn.)

145 (142) With two brown or green chromatophores. Shaped as Chilo-
monas Cryptomonas Ehrenberg.

Representative species. . Cryptomonas ovata YAircnhtrg 1831.

ChIoroph>l bands two in number, extending longitudinally through the
body. Length 50 m- Among algae.

Fig. 42g. Cryptomonas ovala. X 350. (.After Conn.)

146 (139) Forming colonies 147

147 (154) Individuals imbedded in a gelatinous mass 148

148 (149) Spherical colonies; individuals usually with two yellow chroma-
tophores and eye-spot. Free-swimming. Flagelia two, un-
equal Uroglena Ehrenberg.

Representative species Uroglena americana Qdl^ms i^(M.

Cells very numerous, arranged around the periph-
ery of a gelatinous mass. Posterior ends of the
cells rounded, with no means of connection with
each other except by the matrix.

Sometimes found in reservoirs, causing the water
to have a fishv taste.

Fig. 430. Uroglena americana. Individual cells X 1500.
(After Conn.)

149(148) Not colored 150

150 (151) Colonies of dichotomously branching lubes. . ClaJomonus Stein.

262 FRESH-WATER BIOLOGY

151(150) Colonies not of branching tubes 152

152 (153) Colony in a gelatinous mass; variable in shape, thread-like, discoi-
dal or round, hollow or sac-like. Individuals with tw^o

equal flagella Spongomonas Stein.

Representative species Spongomonas discus Stein 1878.

Colony discoidal, gelatinous mass granular; zooids subspheroidal.
Flagella two or three times the length of the body. Length of
zooids 8 Ai. Fresh water.

Fig. 431. Spongomonas discus. X lOO. (After Biitschli.)

1 53 (152) Colony formed of jelly-like tubes, closely approximated; individuals

as in Spongomonas Rhipidodendron Stein.

Representative species.

Rhipidodendron splendidum Stein 1878,

Tubules forming an erect branching colony. Zooids ovate or ellipti-
cal, usually in the distal extremity of the tubules. Flagella equal, twice
the length of the body.

The tubes being hollow are probably secreted or excreted from the
entire surfaces, rather than the posterior extremities of the zooids.
The tubes are usually rusty-brown in color and have a granular appear-
ance. Sometimes as many as two hundred tubes are bound together
in one mass.

Length of body 12 //. Fresh water.

Fig. 432. Rhipidodendron splendidum. X 250. (After Stein.)

154(147) Individuals not imbedded in a gelatinous mass 155

155 (156) Forming spherical colonies. About fifty individuals held loosely
together, each with a delicate membrane, often spiny. Fla-
gella two, unequal Synura Ehrenberg.

Representative species Synura uvella Ehrenberg 1833.

Membranes pyriforn,, often with pKJSterior stalk-like pro-
jections; surfaces spiny. Zooids nearly filling membranes.
Color bands two, extending along the lateral borders. Length
of body 30 fi. Pond water.

Fig. 433. Synura uvella. X 6cx3. (After Conn.)

FLAGELLATE PROTOZOA (MASTIGOPHORA)

263

156 (155) Forming annular colonies; individuals closely united. Flagella

two, unequal Cycloncxis Stokes.

Representative species. . . . Cycloncxis annularis Stokes 1886.

From ten to twenty zooids, not in contact in older colonics, leav-
ing a central, circular space. Zooids obovate, about twice as long
as broad. Length of zooid 10 to 15 m- Marsh water.

Fig. 434. Cycloncxis annularis. X 625. (After Conn.)

tXjx

157 (138) With a lorica 158

158 (163) Not forming colonies 159

159 (162) Lorica sessile 160

160 (161) Lorica beaker-shaped; usually with a peristome process.

Epipyxis Ehrcnberg.
Representative species. . . . Epipyxis utriculus Ehrcnberg 1838.

Lorica is truncate or slightly everted anteriorly, widest centrally and pointed
posteriorly. Body occupies about one-half the cavity of the lorica. and is at-
tached by a thread-like pedicel to one side of the lorica. An eye-spot usually
present. Nucleus central; contractile vacuole anterior.

Length of lorica about 40 /x. Attached to water-plants.

Fig. 435. Epipyxis utriculus. X 650. (After Stein.)

161 (160) Lorica urn-shaped. .
Representative species.

Chrysopyxis Stein.

Chrysopyxis urceolata Stokes 1886.

Zooid occupying the center of the lorica, but in no way attached to it.
Flagella two, long, diverging. Yellow chromatophores often present. Nu-
cleus centrally located; contractile vacuole ixisterior. Length of lorica \2 fx.
Attached to algae.

Fig. 436. Chrysopyxis urceolata. x uoo. (After Stokes.)

264

FRESH-WATER BIOLOGY

162(159) Lorica with a pedicel Dere pyxis Stokes.

Representative species. . . Derepyxis amorpha Stokes 1885.

Lorica flask-shaped. Pedicel about one-tenth as long as the lorica.
Zooid occupying the center of the lorica, subspherical, with the front border
pointed. Endoplasm with two greenish-yellow color bands. Length of lorica
25 to 30 M- .Attached to algae.

Fig. 437. Derepyxis amorpha. X looo. ^ After Stokes.)

163 (158) Forming colonies; loricae beaker-shaped. One primary and one

secondary flagellum Dinobryon Ehrenberg.

Representative species. . Dinobryon sertularia Ehrenberg 1838.

Loricae joined to each other without separate pedicels,
the younger individuals being attached by their posterior ends
to the inner, anterior edges of the older loricae. Zooids at-
tached to the bottoms of the loricae by transparent, elastic
ligaments. Chromatophores and eye-spot present. Length
of lorica 20 n. Pond water.

Fig. 438. Dinobryon sertularia. X 750- (After Conn.)

164 (133) Chromatophores green Order Chloroflagellida . . 165

165(168) Flagella four; not forming colonies 166

166 (167) Body enclosed by a lorica Tetraselmis Stokes.

Representative species. . Tetraselmis limnetis Stokes 1887.

Lorica broadly oval, zooid nearly filling the lorica, green in color.
Flagella exceeding the lorica in length. An amylaceous corpuscle pos-
teriorly located. Length of lorica 15 /u. Pond water.

Fig. 439. Tetraselmis limnetis. X 840. (After Stokes.)

FLAGELLATE PROTOZOA (MASTIGOPHORA) 265

167 (166) Body not enclosed by a lorica Carter ia Diesing.

168 (165) Flagella usually two; often forming colonies 169

169 (180) Not forming colonies 170

170(177) Body with closely attached cuticle 171

171 (172) Usually without chromatophores; occasionally a colored eye-spot.

Ellipsoidal, two contractile vacuoles. . Polytoma Ehrenberg.

Representative species Polytoma uvella Ehrenberg 1838.

Flagella two, equal, longer than the body, both extending forward
with loop-like flexures at their bases. Endoplasm usually granular.
Length 20 to 30 m- Animal macerations.

Fig. 440. Polytoma uvella. x iioo. (After Conn.)

172 (171) With chromatophores 173

173 (174) Chromatophores numerous; one flagellum trailing
Representative species. . . .

Treymnia Stokes.
Trentonia jiagellata Stokes 1886.

Body ovate, the anterior border oblique
and somewhat bilobate, the posterior ex-
tremity obtusely pointed. Flagella sub-
equal in length, one extending forward,
often rapidly and spirally vibrating.
. Mouth and pharynx conspicuous. Nu-

nc. 441. Trentonta jiagellata. X 400. (After Stokes.; merous green chromatophores. Length

60 AX. Pond water.

174 (173) Chromatophores few, sometimes wanting 175

175 (176) Spherical or elliptical, with one large chromatophoro. An eye-
spot present Chlaviydomoiias Ehrenberg.

Representative species.

Chlamydomonas pulvisculus Ehrenberg 1883.

Fig. 442. Chlamydomcnas pulvhculu'i. X looo (.\(tcr Coon.)

266

176 (i75)

177 (170)

178(179)

179 (178)

180 (169)

181 (186)

182 (185)

183 (184)

184 (183)

^

185 (182)

FRESH-WATER BIOLOGY

Elongate, spindle-shaped; chromatophores two, ribbon-shaped;

eye-spot obscure Chlorangium Stein.

Representative species.

Chlorangium slentorinum Ehrenberg 1838.

Flagella terminal, subequal. Attached during the sedentary stage by a
short, thick pedicel, singly or in groups up to ten or tvvelve zooids. Length
24 M- Pond water, often attached to various Entomostraca.

Fig. 443. Chlorangium slentorinum. X 375- (After Stein.)

Cuticle separated from body mass 178

Cuticle smooth Haemotococcus Agardh.

Cuticle rough Coccomonas Stein.

Forming colonies 181

Colonies plate-like with flagella upon one face only 182

Colonies in a four-sided plate with envelop closely adherent.
Cells four or sixteen Gonium Miiller . . 183

Four cells Gonium sociale Dujardin 1838.

Sixteen cells Gonium pectomle MiiWer lyy^t-

In this species each of the sixteen cells of the colony produces a
daughter colony of sixteen cells. As the daughter colonies develop, a
secondary shifting of the cells takes place resulting in individuals of
the adult colonies lying in one plane.

Fig. 444. Gonium pedorale. X 350. (After Stein.)

Colonies in a rounded plate with envelop swollen, oval, or spherical.

Stephanosphaera Cohn.
Representative species. . . Stephanosphaera pluvialis Cohn 1853.

Cells four or eight, ovoid or spindle-shaped,
with numerous processes.

This form represents a transition from a
rosette arrangement of cells to a spherical
aggregate, the units being arranged in a
rosette but surrounded by a common gelati-
nous envelop.

Fig. 445. Stephanosphaera pluvialis. /I .copula-
tion of gametes; ^, spore formation; C, cells with
protoplasmic processes; D, colony of eight cells.
A X 1325; B,C,DX 425. (After Hieronymus.)

186 (181) Colonies spherical, ellipsoidal, or flattened, with flagella not confined

to one face ^87

187 (190) Colonies with cells crowded together 188

FLAGELLATE PROTOZOA (MASTIGOPHORA)

267

188 (189) Colony ellipsoidal or spherical with cells reaching toward the center.

Pandorina Bory de Saint Vincent.
Representative species.

Pandorina morum Bory de Saint Vincent 1824.

Cells sixteen or thirty-two; enclosed within a definite
membrane which does not touch the surface of the indi-
viduals. Each cell bears two Ion« llagella.
>

Fig. 446. Pandorina morum cf, contractile vacuole; i/, stigma.
X 250. (After Pringsheira.)

189 (188) Colony ellipsoidal with sixteen cells in four rows around a longi-
tudinal axis. Each cell bears four flagella.

Spondylomorum Ehrenberg.
Representative species.

Spondylomorum quaternarium Ehrenberg 1848.

Reproduction occurs by the cells of the colony separating and
each individual building up a new colony by cell division.

Colonies often produced in large numbers in pond water.
Movements rapid, rotating on the long a.xis. (ireen in color.
Very favorable conditions are necessary in order that the llagella
may be seen and counted.

Fig. 447. Spondylomorum quaternarium. n, nucleus; o, stigma.
X 600. (After Stein.)

190 (187) Colonies with cells not crowded together and not reaching toward

the center iqi

191 (194) Colonies spherical, ellipsoidal, or flattened, with cells uniform in

size IQ2

192 (193) Colony spherical or ellipsoidal; poles not difTcrentiatetl by ar-
rangement or size of cells. No tails present.

Eudorina Ehrenberg.
Representative species. . . . Eudorina clcgans YMri^nhcTg I'^^i.

Cells sixteen, thirty-two. or sixty-four; arranged around the
periphery of the jelly mass but not in contact with each other.
Each cell bears two flagella.

Fig. 448. Eudorina eUgans. X 250. (From a specimen.)

268

FRESH-WATER BIOLOGY

193 (192) Colony flattened, horseshoe-shaped, with poles differentiated by
arrangement of cells. Tails at posterior end.

Platydorina Kofoid.
Representative species Platydorina caudata Kofoid 1899.

Colony slightly twisted in a left spiral. Cells sixteen or
thirty-two imbedded in a transparent, gelatinous matrix and
surrounded by a distinct sheath.

Each cell has two llagella, an eye-spot, a nucleus, and a
single chromatophore. Tails, in sixteen cell colonies, are
three in number; in thirty-two cell colonies five tails are
present. Movement by rotation on the longitudinal axis.
Length 150 /x. Plankton of rivers and lake's.

Fig. 449. Platydorina caudata. X 185. (After Kofoid.)

194 (191) Colonies spherical or elHpsoidal; cells differentiated as to size and

function i95

195 (198) No protoplasmic processes connecting the cells. Small vegetative

cells at the anterior pole, large gonidial cells at the posterior
pole Pleodorina Shaw . . 196

[96 (197) Cells sixty-four or one hundred and twenty-eight, about equally
divided between large and small.

Pleodorina calif or nica Shaw 1893.

Colony spherical, with gonidial cells two or three
times the size of the vegetative cells. Cells bifiagel-
late, not in contact with each other.

Reproduction asexual, by gonidial cells, in this and
other species of the genus.

Found in ponds, ditches, and streams.

Fig. 450. Pleodorina calif arnica. X 300- (After Shaw.)

197 (196) Cells thirty-two, rarely sixteen or sixty-four. Vegetative cells,
four in number. . . Pleodorina illinoisensis Kofoid 1898.

Colony ellipsoidal with cells arranged in five circles;
the polar circles with four cells each, the other three
circles with eight cells each. The gelatinous sheath
enclosing the colony is of two layers.

Gonidial cells much larger than vegetative cells, the
latter always directed forward during movement.

Each cell with two flagella, an eye-spot, a nucleus,
and a single chromatophore.

Average length 113 /x- Plankton of rivers.

Fig. 451. Pleodorina illinoisensis. X 200. (After Kofoid.)

FLAGELLATE PROTOZOA (mASTIGOPHORA) 269

198 (195) Protoplasmic processes connecting cells usually distinct. Polos

of colony not differentiated by arrangement of vegetative
and gonidial cells Volvox Leeuwenhoek . . 199

199 (204) Colonies with distinct protoplasmic processes connecting the

cells 200

200 (203) Protoplasmic processes very stout 201

201 (202) Colonies dioecious Volvox pcrglobator Powers 1908.

•■"■^®<:^^0 0^^'^^^''- Colonies often exceeding i mm in diameter. Ova or

.^I^^^^^Q e 0 ' <3 "^t^^i oosperms not infrequently numbering several hundred in a

•o«'0^'5 G>^^0l®'^.^li^= colony. Very common in the United States.

'•■^0 0'^ Q^^^^ o 0.'^%^^ Fig. 452. Volvox per glohator. Colony with eight daughter coenobia.

'•.0 G ® ■ o^^S® Q ^i>.ci^^j? Cilia and protoplasmic processes not shown. X 50. (From a

■■^oZors^ ^ 'o<^'&^^ prepared mount).

•n.oQ <a .©.??••

202(201) Colonies monoecious Fo/z^o-r g/o6a/(?r Leeuwenhoek 1788.

The common European species. About one-half the size of the preceding species, and con-
taining fewer reproductive cells. This species probably occurs in the United States but, if so,
in much less abundance than Volvox perglobator.

203 (200) Protoplasmic processes slender. . Volvox aureus Ehrenberg 1838.
A typical European species but probably occurring in the United States also. Diameter

about 850 (1.

204 (199) Colonies apparently without protoplasmic processes connecting
the cells Volvox spermatosphara Powers 1908.

Monoecious forms with ripe sperms arranged in bundles
of 32, grouped in sperm spheres in the colonies Mature
colonies often exceed 600 m in diameter. Widely dis-
tributed in the United States.

Fig. 453. Volvox spermatosphara. Colony with two daughter
coenobia, five egg cells and one sphere of sperm bundles.
X 80. (From a specimen.)

205 (132) Usually with an outer membrane or shell in the form of plates;

body usually furrowed; flagclla two. Usually colored.

Subclass Dinoflagellida , . 206

206 (209) Without a membrane around the body 207

207 (208) Cross furrow extending only around the left side; a longitudinal
furrow extending from the central end of the cross furrow to
the under part of the body Uemidinium Stein.

270 FRESH-WATER BIOLOGY

208 (207) Cross furrow extending entirely around the body; often flattened.

Gymnodinium Stein.
Representative species. . Gymnodinium fuscum FAircnherg 1838.

Body oval, compressed, pointed anterioriy. Color light brown. An
eye-spot reported by Perty. Length 60 to 80 n. Fresh water.

^^C^ Fig. 454. Gymnodinium fuscum. X 325. (After Blochmann.)

209 (206) With a membrane around the body 210

210(211) Membrane delicate, homogeneous; body without processes, often

flattened Glenodinium Ehrenberg.

Representative species.

Glenodinium pidvisculus Ehrenberg 1838.

Fig. 455. Glenodinium pulvisculus. X 500 (After Stein.)

211 (210) Membrane of distinct plates 212

212 (213) Plates without horn-Hke processes, polygonal, 21 in number.

Peridiniiim Ehrenberg.
Representative species.

Peridiniiim tahulatmn Ehrenberg 1838.

Body ovate, with convex dorsal and concave ventral surface. Plates
showing a delicate reticulate structure under high magnification. Color
yellow, green, or brown. Length 45 to 60 m- Fresh water.

Fig. 456. Peridinium tabulatum. X 320. (After Stein.)

213(212) Plates with long, horn-like processes Ceratium ^chx^nk.

Representative species. . . . Ceratium hirundiftella MuIIgt ij^G.

Body somewhat quadrilateral, the anterior segment
bearing two nearly straight processes and the posterior
segment a single short one. Color brown or green.
Length go to 170 ij. Freshwater.

Fig. 457. Ceratium hirundinella. X 325. (After Stein.)

CILIATE PROTOZOA (INFUSORIA)

271

INFUSORIA

I (208) Cilia present during all stages of existence. . . Class Ciliata . . 2
2(127) Body usually uniformly covered with cilia 3

3 (104) Cilia similar or slightly lengthened about the mouth; no adoral spiral

zone Order Holotricha . 4

4 (59) Without an undulating membrane about the mouth. Moutli closed

except when taking food. Suborder. Gymnostomina . . 5

5 (6) With a shell of numerous plates arranged in zones around the body.

Ciha projecting between the plates. . . . Coleps Nitzsch.
Representative species Coleps hirtus Ehrenberg 1838.

Ovate, persistent in shape. Mouth terminal, bordered by tooth-like
processes, and surrounded by cilia larger than those of the general
surface. Posterior border usually bearing spines. Length 60 /i- Pond
water and old infusions.

Fig. 458. Coleps hirtus. X 250. (After Conn.)

0 (5) Without a shell 7

7 (12) With tentacle-like processes in addition to the cilia 8

8 (9) Tentacle process single. Ileonema Stokes.

Representative species Ileonema dispar Stokes 1885.

Body flask-shaped, flexible; flattened ventrally, convex dorsally, the
latter surface bearing a row of short, hair-like setae. Tentacle-like proc-
ess thick at the base, twisted, with a filamentous distal half. Nucleus
subcentral; contractile vacuole posterior. Length 1 20 m- Among algae.

Fig. 459. Ileonema dispar. X 185. (After Stokes.)

9 (8) Tentacle processes more than one 10

10 (11) Tentacles very long and numerous, extending between the cilia.

Actinoholus Stein.
Representative species [ct'uioboliis radians Stein 1867.

Body ovate or subglobosc. the anterior extremity pro-
duced as a snout-like projection which carries the mouth
and bears the retractile tentacles and cilia. Nucleus
band-like; contractile vacuole large.

Fig. 460. Actinobolus radians. Figure reprcsentinK indiviilual
with mouth downward. Dimensions undetermined. (.■Vftir
Calkins.)

272 FRESH-WATER BIOLOGY

11 (lo) Tentacles short, few in number, extending from about the mouth.

Mesodinium Stein.
Representative species.

Mesodinium pulex Claparede and Lachmann 1858.

Body turbinate, conical, and tapering anteriorly. A wreath of strong cilia on

a constriction halfway between the middle of the body and the base of the

-jr/ , 1 1 1 V v^ snout-like proboscis. According to Claparede and Lachmann three long stylate

^// W V\ processes e.xtend in front of the mouth. Length 15 /i. Habitat, reported by

Claparede and Lachmann, salt water.

Fig. 461. Mesodinium pulex. X 8io. (After Kent.)

12 (7) Without tentacle-like processes 13

13 (34) Body round, or ovate, or elongate in outhne, symmetrical. . . 14

14 (15) Cilia of body confined to two (rarely one) many-rowed crowns or

circles. Body thimble-shaped, with broad end forward, from
the flattened center of which rises an elevation bearing the

mouth at the apex Didiniiim Stein.

Representative species Didinium nasutum Miiller 1786.

Body oval, broadly rounded posteriorly. One wreath of cilia near the
base of the proboscis, the other posterior to the middle of the body.
Nucleus band-like. Contractile vacuole posterior. Length 100 to 175 m-
Among decaying vegetation.

Fig 462. Didinium nasutum. t:, contractile vacuole. X 95. (.\fter Blochmann.)

15 (14) Cilia not limited to two crowns or circles i6

16 (27) With pharynx absent or slightly developed 17

17 (22) Anterior end rounded, not oblique 18

18 (21) Without a terminal bristle 19

19 (20) Ellipsoidal to ovate, rounded at both ends. Mouth anterior, leading

into a short pharynx. Uniform ciliation.

Holophrya Ehrenberg,
Representative species Holophrya sp.

Species not determined.

Fig. 463. Tlolophrya sp. X 300. (After Conn.)

20 (19) Elongated, cylindrical, narrow in front, mouth terminal or subter-

minal. No pharynx. Cilia longer at the anterior end.

Nucleus divided into small pieces. . . C//«n/z'fl Quenncrstedt.

Representative species Chaenia teres Dujardin 1841.

Forms observed from the fresh waters of Connecticut are
^■^■^ provisionally placed here.

Fig. 464. Chaenia teres. X 350. (After Conn.)

21 (l8)

22 (17)

23 (24)

24 (23)

25 (26)

CILIATE PROTOZOA (INFUSORIA) 273

With a terminal bristle. Similar to Holophrya in shape.

Urotricha Claparecle and Lachmann.
Representative species.

Urotricha Jar eta Claparede and Lachmann 1858.

Body obliquely striated; posterior bristle obliquely directetl
when at rest. Progression by slow forward movement or sud-
den leaps to one side. Mouth on a small circular {)r()mincnce
at the anterior end. Length 20 ^l. Pond water. Bulanlozoon
of Stokes agrees with this genus except that only the anterior
two-thirds is ciliated.

Fig. 465. Urotricha farcta. X 435- (After Conn.)

Anterior end oblique ' 2,5

With a spiral series of long ciHa on either side of a ridge extending
from the anterior border to the posterior extremity.

Perispira Stein.

Representative species Perispira strephosoma Stokes 1886.

Body elongate-ovate. Cilia of the general surface very fine.
Protoplasm filled with dark-colored corpuscles. Length 80 ^.
Standing water with sphagnum.

Fig. 466. Perispira strephosoma. X 280. (After Stokes.)

Without a spiral series of cilia 25

Elongated, with mouth slightly on one side; uniform ciliation. Nu-
cleus single Enchdys Hill.

Representative species Enchelys pupa Ehrenberg 1836.

iP^^^'*'^;^ Body inflated, slender anteriorly. Often colored green.

•J?-^IiP^^?!te«;£. Length about 200 m- Stagnant water.

Fig. 467. Enchelys pupa. X 150. (After Conn.)

26 (25) Elongate, sac-like, mouth occupying the oblique surface. Pharynx

slightly developed, sometimes with rods. Nucleus bead-
like Spathidium Dujardin.

Representative species. . . . Spathidiiwi spatliula Dujardin 1S41.
^^niimiiiiijM^^^a^,,.^^^^^^^^^^.^ Very difficult to distinguish from forms of the genus

:^CCCJM$^''-^'C^^f/ Enchelys.

Fig. 468. Spathidium spathula. X 250. (.\fter Conn.)

27 (16) With pharynx well developed 28

28 (33) Body greatly elongated 29

29 (32) Body flattened 30

30 (31) Flask-shaped with an elongated ncck-likc anterior end. Proboscis

short, retractile. Mouth terminal leading into a long

pharynx. . . . rmc/zf/^^/j/a'/Z/^m Claparetle and Lachmann.

Representative species. . Trachelophyllum tachyblastiim Stokes 1884.

Body eight or ten times as long as broad; neck slender;

'■>^^^,^^;_w-:-_i^..,_^^^^^ pharyngeal passage indistinct, narrow, longitudinally stri-

_2^^|^^^^^^i??t:^2j:gs^^ ate. Cilia of surface long, vibrating indeix-ndently.

''^^^^^^^^^ffT'^^S^^^^^^ Nuclei two, subcentral. Contractile vacuole ix)sterior.

^^Tf./^- ^^ ^^ Length, extended, 120 to 150 /!• Bottom of shallow ptKils.

Fig. 469. Trachelophyllum tachyblastum. cr, contractile vacuole;

macn, macronuclcus. X 250- (After Stokes.)

^74
31 (3o)

FRESH-WATER BIOLOGY

Long, ribbon-like; no proboscis. ^Mouth terminal with an evident
pharynx. Nucleus in the posterior third of the body and a
row of minute vacuoles near one side. . Flcxiphylliim Conn.

Representative species Flcxiphylliim elongatum Conn 1905.

Fig. 470.

Flexiphyllum elongatum.
Conn.)

X 220. (After

32 (29) Body not llattened; with a long, highly contractile neck; a plug-

like projection carrying the terminal mouth which is sur-
rounded by a crown of long cilia. Body longitudinally or

spirally striated Lacrymaria Ehrenberg.

Representative species Lacry;;wrw o/or Miiller 1786.

A common species found in pond water. Its
swan-like appearance was suggested to the early
observers by its graceful movements, as it swims
about extending its neck here and there in search of
food. Length, neck contracted, 50 to 70 m-
Fig. 471. Lacrymaria olor. cv, contractile vacuole; n, nu-
cleus. E.xpanded. X 50. (After Blochmann.) Con-
tracted. X 200. (After Conn.)

33 (28) Body not elongated, spherical to ovate; anterior end not oblique.

Mouth terminal or subterminal, pharynx usually with rods.

Nucleus ovate to ribbon-like. . . . Prorodon Ehrenberg.

Representative species Prorodon ovum Ehrenberg 1833.

Body oval, evenly rounded at both ends; mouth eccentric, open-
ing into a conical phar>^nx which leads far into the body. Rods of
pharynx conspicuous. Cilia of posterior border longer. Nucleus
spherical, central. Contractile vacuole posterior. Length 125 m-
Pond water.

Fig. 472. Prorodon ovum, ct), contractile vacuole; macn, macro-
nucleus; mien, micronucleus. X 170. (After Blochmann)

34 (13) Body asymmetrical with dorsal side arched 35

35 (48) Mouth subterminal or terminal, body greatly elongated.

36

36 (43) Mouth usually open, pharynx often rod-like 37

37 (42)

38 (39)

Mouth subterminal.

38

Anterior end hook-like, bent to the left; elongated, flattened, leaf-
hke. \'entral surface flat with ciliated ribs; dorsal surface
curved, without cilia. Mouth on the left anterior edge, lead-
ing into a pharynx Loxodes Ehrenberg.

Representative species Loxodes rostriim MiiWer lySd.

The body of this species is highly vesicular. Nuclei
'^Pi^'^'^*"?^---'^^''- ' ^^y ^^ two or more. Wrzesniowski has demonstrated a

l5>^!^^^^J^.'^C;^^^ racemose system of nuclei. Length 250 to 400 /!• At the

*^%ii^^^^5S^^^ bottom of old infusions.

Fig. 473. Loxodes rostrum. X 250, (After Conn.)

39 (38) Anterior end not hook-like 40

CILIATE PROTOZOA (INFUSORIA)

Rcprcscntati

275

40 (41) Body not elongated; spherical to ovate, slightly flexible; a short
proboscis at the base of which is the mouth. Pharynx

with rods Trachdiiis Schrank.

"'"'"'" species Trachelius ovum YMxiinhiixg 1^7,^.

Neck highly flexible. Mouth circular; pharynx with rods.
Nucleus central; contractile vacuoles numerous. Endoplasm
at the inner end of the pharynx usually spreads out into four
or five broadly diverging ramifications. Length 500^. J."— "<-
water.

Fig. 474. Trachclius ovum, x 85. (After Blochmann.)

T'resh

41 (40) Body greatly elongated, band-Hke, very flexible; proboscis long with
mouth at the base and a row of long cilia along its ventral

side Dilcptus Dujardin.

Representative species. Dilcptus gigas Claparede and Lachmann 1858.

c>v Body somewhat compressed, often with a pointed,

j) tail-like prolongation. A prominent shoulder or
hump often indicates the position of the mouth.
Nucleus moniliform, very long. Contractile vacuoles
numerous in a dorsal row. Trichocysts on the ven-
tral surface of the neck. Length 500 to 800 n. Pond
water.

Fig. 475. Dileptus gigas. x no. f.\fter Conn.)

Mouth terminal; body elongated with a long proboscis. Nucleus

double Lionotopsis Conn.

Representative species Lionotopsis anser Conn 1903.

Fig. 476. Lionotopsis anser. X 230. (.^ftcr Conn.)

43 (36) Mouth usually closed; pharynx when present, without rods. . . 44

44 (45) With a broad hyaline border; body flattened; proboscis short, mouth

on the left side. Trichocysts well developed on the right

side Loxophyllum Dujardin.

Representative species Loxophyllum rostratum Cohn 1866.

Anterior extremity prolonged into a dorsally re-
flected, uncinate rostrum. Cilia of anterior region
longer. Middle of the dorsal border crenulate, the row
of trichocysts extending from this region forward
nearly to the tip of the rostrum. Nuclei multiple,
central; a number of contractile vesicles {X)sterior.
Length 190 m- Recorded by Conn from the fresh
waters of Connecticut.

Fig. 477. Loxophyllum rostratum.
(After Conn.)

45 (44)

46 (47)

Without a broad hyaline border 46

Body flattened, elongated with an acute proboscis at the base of
which is the mouth. Nucleus single or double.

.1 mp/iilcptus Ehrenberg.
Representative species {mpliilcpliis guttn Cohn iS,66.

Mouth about one-third the length of the body from the
anterior end. Pharynx a short smooth tube. Cilia ev(^n all
^=?^,iii^ over the body. Nucleus-like corjiusclos scattcre<l throughout
the cortical region. Contractile vacuole single, posterior.
Length 125 n. Reported by Conn from Connecticut. Cohn
reports the species from salt water.

Fig. 478. Amp/tileplus gutta. X 335. (After Conn.)

276 FRESH-WATER BIOLOGY

47 (46) Body flattened ventrally, convex dorsally. With a long neck and

usually a tail-like prolongation both of which are hyaline.
Mouth a slit at the base of the neck, often invisible. Nuclei
usually two; contractile vacuole posterior.

Lio)iotus Wrzesniowski.
Representative species Lionotus urzcsniowskii Kent 1882.

■^■^~^'"~~^-~^ Fk;. 479. Lionotus wrzesniowskii. cv, contractile
5- ^.jc^ - vacuole. X 125. (After Kent.)

48 (35) ^louth usually somewhat posterior, and often with a pharynx; body

oval or kidney-shaped 49

49 (50) Body completely ciliated, cylindrical to ovate, rounded posteriorly.

Mouth about one-third of the way from the anterior end;

pharynx with rods Nassula Ehrenberg.

Representative species Nassula oniata Ehrenberg 1838.

Ifl^^l^ Usually some shade of red or brown in color. Nucleus

_ ' W''"^^^ large, spherical, posteriorly located. Contractile vacuole

0' -^ '0K-^ri^^ single. Length 200 m- Among algae

Fig. 480. Nassula ornaia. In act of feeding. X 325. (After
Conn.)

50 (49) Body not completely ciliated; cilia ventral only 51

51 (56) Body flattened 52

52 (55) Mouth in the anterior half of the body 53

53 (54) Body with convex dorsal and flattened or slightly concave ventral

surface. Pharynx with rods Chilodon Ehrenberg.

Representative species Chilodon cucullulus Miiller 1 786.

o The lip-like extension prominent, a groove leading from it to the

mouth. Nucleus oval near the inner end of the pharynx. Contractile
vacuoles numerous. Length 125 to 200 m- Stagnant water and among
algae.

Fig. 481. Chilodon cucullulus. cv, contractile vacuole; macn, macronucleus;
mic, micronucleus. X no. (After Blochmann.)

54 (53) Body with ridges on dorsal and ventral surfaces, crenate in cross

section, pharynx with rods Chilodonopsis Conn.

Representative species Chilodonopsis crenida Conn 1905.

Fig. 482. Chilodonopsis crenula. X 335. (After Conn.)

55 (52) Mouth in the posterior half of the body Opisthodon Stein.

56 (51) Body not flattened 57

CILIATE PROTOZOA (INFUSORIA) 277

57 (58) Body purse-shaped Phascolodon Siein.

58 (57) Body ovate or nearly spherical in outline with a slight lip at the

anterior end. Mouth at the base of the lip with no evident

pharynx. Cilia ventral in six rows. . . . Ilcxotricha Conn

Representative species Hcxotricha globosa Conn u)os.

Fig.

h. nexotricha globosa. Lateral and end views, cv, contractile
vacuole; m, mouth, x 335- (After Conn.)

.SO

Oo (87)

61 (70)

62 (65)

63 (64)

Usually with an undulating membrane or membranes about the mouth

Mouth always open. . . . Suborder Trichostomma . . 60

Peristome usually absent; with or without undulating membranes. 61

Without an undulating membrane; pharynx present 62

One or two broad zones of strong cilia about the body; with a tail-
like tuft of cilia 5,

Two broad zones of strong cilia about the body. Body cylindrical,
with mouth posterior leading into a short pharynx. An-
terior part of the body uniformly ciliated. A band of
strong cilia near the middle and posterior end.

^ . Urocentrum Nitzsch.

Representative species Urocentrum turbo ^m\ev l^?>6.

Body broadly rounded anteriorly, rounded or truncate posteriorly
Movement by a rotation on the long axis or swiftly darting from side
to sidle. Contractile vacuole posterior with the band-like nucleus
curved about it. Length 100 n. Pond water.

Fig. 484. Urocentrum turbo, cv, contractile vacuole; n, nucleus X 200
(After Kent.)

64 (63) With an oblique circle of strong cilia near the anterior end. Body
somewhat pyriform, rigid, finely ciliated. Two groove-like
canals encircling the body. I\Iouth ver^tral, posterior to
the grooves and leading into a short pharynx.

CalccolHs Diesing.
Representative species. . . Calceolus cypripcdiiim James-Clark 1866.

Color light brown. \'crv similar in movement to i'rocnilrum turbo.
Length 80 to 160 ^. Fresh water.

Fig. 485. Calceolus cypripedium. cv, contractile vacuole; moiH, macronucleus
X 200. {.After Kent.)

278

FRESH-WATER BIOLOGY

65 (62) No zones of strong cilia about the body 66

66 (67) Mouth covering the whole oblique anterior end. Body usually oval

or purse-shaped Lciicophrys Ehrenberg.

Representative species Lciicophrys palula Ehrenberg 1838.

Body oval; pharynx tubular, curved. Nucleus banil-
like, central. Contractile vacuole posterior. Length 200 m-
.\mong algae.

Fig. 486. Leucophrys patula. X 150. (After Kent.)

67 (66) Mouth at some distance from the anterior end 68

68 (69) Body ellipsoidal, ciliation regular, mouth a crescent-shaped or spiral

slit leading into a pharynx. . . . Ophryoglena Ehrenberg.
Representative species Ophryoglena atra Ehrenberg 1838.

Body with posterior extremity pointed. Endoplasm usually
opaque, with a dark blue pigment spot in the anterior region.
Nucleus round, posterior; contractile vacuole central. Length 125
to 150 n. Stagnant water.

Fig. 487. Ophryoglena atra. cv, contractile 'vacuole; macn, macronucleus.
X 200. (After Kent.)

69 (68) Body laterally compressed, ovate, with the dorsal surface rounded.
]\louth one-third of the distance from the anterior end, with
a few, long, fine cilia on its superior wall or roof.

Colpoda Miiller.
Representative species Colpoda canipyla Stokes 1886.

Length of body 55/1
leaves.

Standing water with dead
Fig. 488. Colpoda campyla. X 600. (After Conn.)

70(61) With one or more undulating membranes 71

71 (76) One membrane present.

72 (75) Mouth not terminal.

73 (74) Body not flexible; mouth lateral, triangular, following a small peri-
stome and with an undulating membrane in front. Body
similar to Colpoda, but less compressed. . Colpidium Stein.
Representative species Colpidium striatum Stokes 1886.

Body twice as long as broad, striated longitudinally, an-
terior extremity curved ventrally. Nucleus subcentral;
contractile vacuole posterior, often leaving several small
vacuoles after contraction. Length 50 fi. Infusions.

^Mjjl)^^?^*^^^

f^^'""''^-^'

Fig. 48y. Colpidium striatum. X 500. (After Edmondson.)

CILIATE PROTOZOA (INFUSORIA)

279

74 (73) Body very flexible and changeable in shape. Ovate, covered with
fine ciUa, with a long bristle extending from the posterior
border. Mouth ventral with a vibratile and retractile hood-
like velum Saprophilus Stokes.

Representative species Saprophilus agilatus Stokes 1887.

Body twice as long as broad, compressed, obliquely truncate in front;
cilia very short and fine. Body longitudinally striate. Nucleus sub-
central. Contractile vacuole posterior. Length of body 35 to 45 n.
Infusions containing animal matter.

Fig. 490. Saprophilus agilalus. x 390. (After Stokes.)

75 (72) Mouth terminal with a delicate membrane. Body ovate, elastic;

anterior extremity obliquely truncate. . . Trichoda Miiller.

Representative species Trichoda pur a Ehrenberg 1838.

Length 40 m- Often found abundantly in old infusions of pond
water. Swift moving, usually rolling on its long axis.

Fig. 491. Trichoda Pura. macn, macronucleus. X 400. (.^fter Kent.)

76 (71) Two membranes present 77

77 (78) Body elongated, rounded in front, contracting into a tail behind.

One side somewhat flattened, the other convex. Mouth

triangular, near the anterior end Dallasia Stokes.

Representative species Dallasia froutata Stokes 1886.

Body five times as long as broad, ventral
surface convex, dorsal slightly concave: taper-
,^„^^ ing posteriorly to a retractile tail-like prolonga-
^^^^^.-^ >^ ^-^J^ tion. Anterior extremity narrow. Mouth

^ll^\ ^ .,__ jM^'~~ obliquely placed on the ventral surface. Length

'*'^' " '^ 150 M- Still water, with aquatic plants.

Fig. 492. Dallasia frontata. X 335- (After Conn.)

78 (77) Body not contracting into a tail 79

79 (84) With a long, posterior bristle 80

80 (83) Without a spiral row of long cilia 81

81 (82) Body ovate, slightly compressed, broader behind; ventral surface
straight, dorsal surface curved. Mouth near or anterior
to the middle, with an extensile membrane. Cilia densely
arranged in a furrow in front of the mouth.

Uroncma Dujardin.
Representative species Uroncma marinum Dujardin 1841.

The cilia are exceedingly vibratile, their movements being ir-
regular and independent. Nucleus central. Contractile vacu-
ole posterior. Length so n. Fresh water, often associated with
Cyclidium but not so numerous.

Fig. 493. Uroncma marinum. X 400- (After Kent.)

28o

FRESH-WATER BIOLOGY

82 (81)

83 (80)

84 (79)

85 (86)

Body elongate, nearly cylindrical, the anterior extremity truncate
and slightly curved; a short, curved seta borne on either
side near the anterior end. A long, straight bristle extend-
ing from the posterior end Loxocephaliis Kent.

Representative species Loxocephaliis granulosus Kent 1882.

Endoplasm granular, mouth on the obhque anterior bor-
"""',""M<(/f'fnr (ler although quite indistinct. Nucleus spherical, central,

p^ p. ^jfe. Contractile vacuole jiosterior. Length 40 to 70 n. Often
^ ^ -<^ abundant among decaying vegetable matter. Conjugation

readily occurs in infusions.
Fig. 494. Loxocephalus granulosus. X 375. (After Edmondson.)

Like Uro)icma, but with an anterior, spiral row of long cilia.

Dexiotricha Stokes.
Representative species Dexiotricha plagia Stokes 1885.

Body about three times as long as broad, bearing minute
hemispherical protuberances. Cilia setae-like; a row of flexible
^/^p<<r, setae extending from the margin of the mouth obliquely across
<rs "^^^ ^^^ right-hand side of the anterior half of the body. Nucleus
l~ilnrTTX^^ subcentral; contractile vacuole posterior. Length 60 /*• Pond
water.

Fig. 495. Dexiotricha plagia. X 315. (After Stokes.)

Without a posterior bristle 85

Ellipsoidal to elongate, somewhat acute behind. Mouth lateral,
surrounded by a furrow which extends backward. Pharynx
short with rods Frontonia Ehrenberg.

Representative species Frontonia Iciicas Ehrenberg 1838.

Body elongate-oval, wider anteriorly. Mouth a slit anterior to the
middle of the body. Cilia fine, in longitudinal rows. Contractile
vacuoles, usually two. Trichocysts numerous. Length 250 to 300 m-
Stagnant water.

Fig. 496. Frontonia leucas.
V, vacuole.

canal; N, macronucleus; «, micronucleus;
X 165. (After Calkins.)

86 (85) Ovate, flattened, rounded at each end. Mouth triangular or crescent-
shaped, lateral, in front of the middle of the body.

Glaucoma Ehrenberg.
Representative species. . . . Glaucoma scintillans Ehrenberg 1830.

The vibratile membranes extending around the mouth pre-
senting a bilabial appearance. Nucleus large, central. Con-
tractile vacuole posterior. Length 75 /i. Infusions.

Fig. 41)7. Glaucoma scintillans. cv, contractile vacuole; macn, macro-
nucleus; mien, micronucleus. X 350. (.\fter Blitschli.)

-^^^m^\>

CILIATE PROTOZOA (INFUSORIA) 281

87 (60) With a well-developed peristome gg

88 (loi) Mouth not posterior to the middle of the body gg

89 (98) Not surrounded by a lorica or gelatinous sheath qo

go (91) Peristome oblique. Body elongated, slightly flattened, rounded at

both ends or slightly truncated in front. Mouth followed

by a short pharynx; ciliation regular. . Paramoecium Stein.

Representative species. . . Paramoecium caudatum Ehrenberg 1858.

^^^^ Perhaps the most famihar cih'ated protozoon known.

^^^^^^^^gj^*.|pj^^ Body with a large central macronucleus and a small

^^t'^'^%/'^r ■' ' '■' ^^'"^0'^^^ micronucleus, and a contractile vacuole in either

4^^^^^-!:. '^■■^^i^- *'*'^^ extremity. Abundantly supplied with trichocysts.

^'^^^^^■^^^T^^^^'"''''^^'^ Length variable, average 250 ^l. Everywhere in in-

-<»'*:'«aKSiift,Aaiii'.j - ;:-:- - fusions.

Fig. 498. Paramoecium caudatum. X 170. (.^fter Conn.)

91 (90) Peristome not oblique 02

92 (97) With one or more membranes well developed in the peristome. . 93

93 (94) Peristome very broad and conspicuous, occupying the entire right

side. Body oval, flattened ventrally, convex dorsally; an-
terior end oblique, posterior end acute. A tuft of long cilia

extends from the posterior end Lcmbadion Perty.

Representative species Lembadion bullinum Perty 1849.

Nucleus elongated, curved in the posterior region on the left side; con-
tractile vacuole opposite the nucleus. When stimulated the animal swims
rapidly backward rotating on its long axis. Length 50 to 100 m- Among
aquatic plants in pond water.

Hymenostoma Stokes differs from Lembadion in the more posterior, ven-
tral position of the mouth, the greater length of the adoral cilia, the
abruptly narrowing membrane and the double contractile vacuole.

Fig. 499. Lembadion bullinum. macn. macronucleus; mien, micronucleus. x 250.
(.\fter Blochmann.)

94 (93) Peristome not broad and conspicuous 95

95 (96) Without a long, posterior bristle. Peristome parallel to the right

side with a large projecting membrane. Body oval, fat-
tened dorso-ventrally. Cilia very long.

Plciironcma Dujardin.
Representative species. . . . Pleuroncma chrysalis Ehrenberg 1838.

Cilia in length nearly one-half the diameter of the body. stifTcnetl,
setae-like. Nucleus central; contractile vacuole anterior. Length
75 to 125 fx. Fresh water. Stokes rccogni/.es two separate gen-
era, II istriohalantidium. with long setose bristles among the cilia
over the whole body, and Bothrostoma, with a long terminal tuft
of cilia. Biitschli places them both under Phuroncma.

Fig. 500. Pleuroncma chrysalis, wdcw, macronucleus; miV«, micronucleus.
X 225. (.^Ucr Blochmann.)

282

FRESH-WATER BIOLOGY

96 (95) Like Pleuroncma but with a shorter peristome and one or more long

posterior bristles Cyclidium Ehrenberg.

Representative species. . . . Cyclidium glaucoma Ehrenberg 1838.

mm///'-^>-

m

-^

'''//liil^m^

Cilia long and rigid, in longitudinal rows. Nucleus central;
contractile vacuole posterior. Length 20 /i. Very abundant in
stagnant water.

Fig. SOI. Cyclidium glaucoma. X 625. (After Edmondson.)

97 (92) Without an oral membrane. Body ovate; mouth ventral at the
posterior end of a longitudinal groove which bears on its
right-hand border a row of large, arcuately curved setose
cilia diminishing in length toward the mouth. A long
bristle extending from the posterior end of the body.

Ctcdoclema Stokes.
Representative species. . . . Ctedoctema acanthocrypta Stokes 1884.

Often very abundant among fresh-water algae.
Trichocysts are numerous and very stout. Length
of body 25 M-

Fig. 502. Ctedoctema acanthocrypta. X 875. (After Stokes.)

98 (89) With a lorica or gelatinous sheath 99

99(100) Enclosed in a lorica. Animal similar to P/ewr<7W^ma. Lorica oblong-
ovate, hyaline, with tapering extremities, the terminal aper-
tures about half as wide as the center of the sheath. Animal
very active within the lorica. .... Calyptotricha Phillips.
Representative species. . . . Calyptotricha inhaesa Stokes 1885.

Kellicott reports this species from Ontario. Length of lorica 180 to 200 m-
Enclosed animal 30 m- Attached laterally to algae.

Fig. 503. Calyptotricha inhaesa. X 100. (After Kellicott.)

Enclosed in a gelatinous sheath to which the animal is not attached.
Body ovate; mouth ventral, at the end of a groove on the
margin of which is a series of strong cilia. A tuft of long,
curved cilia extends from the anterior extremity.

Cyrtolophosis Stokes.
Representative species. . . . Cyrtolophosis miicicola Stokes 1885.

, _ _ ., A strange form not uncommon among algae. When the animal

comes to rest, a transparent, sticky substance seems to be exuded
from the body which becomes granular, due to excreta, bacteria
and other foreign bodies which adhere to it. When disturbed
the animal glides out of its covering and another is constructed.
A temporary colony may be built up by the adherence of several
gelatinous sheaths. Length of body 25 /i.

Fig. 504. Cyrtolophosis mucicola. X 875. (After Stokes.)

Mouth at the posterior end of the body 102

100 (99)

CILIATE PROTOZOA (INFUSORIA) 283

102 (103) Body flattened, oval, with spiral furrows. Peristome with a vi-
brating membrane posterior leading into the mouth. A
tuft of long bristles at the posterior end of the body.

Cinctochilum Perty.
Representative species.

Cinetochilum margaritaceum Ehreni^erg 1838.

Contractile vacuole posterior, opposite the mouth, with nucleus an-
terior to it. Length 30 ix. Very common in pond water.

Fig. 505. Cinetochilum margaritaceum. x scxj. (After Butschli.)

103 (102) Body neatly oval, ventral surface flat, ciliated; dorsal surface

curved, with three longitudinal grooves. Mouth posterior
on the left side, with a small, vibrating membrane.

Microthorax Engelmann.
Representative species. . . Microthorax sulcatus Engelmann 1862.

Associated with the preceding species. Length 40 to 60 n.
Fig. 506. Microthorax sulcatus. X 310. (After Kent.)

104 (3) An adoral zone present consisting of ciha fused together into mem-

branellae Order Heterotricha . . 105

105(120) With a uniform covering of cilia 106

106(115) Peristome not confined to the anterior border of the body. . 107

107 (112) Peristome a long, narrow furrow 108

108(111) With an undulating membrane 100

109 (no) Body flattened, narrow and hook-like in front. Mouth near the
middle of the body at the end of the narrow peristome.
Membranellae on the left wall of the peristome, on the right
an undulating membrane. Colored. . BUpharisma Perty.
Representative species. . . Blepharisma later itia Ehrenberg 1838.

Body usually truncate behind; nucleus in the anterior half of the body. Contrac-
tile vacuole posterior. Color, peach-bloom. Length 150 /i. .\mong aquatic plants.

Fig. 507. Blepharisma lalcritia. X 180. (.\fter Stein.)

284

no (109)

FRESH-WATER BIOLOGY

Body spiral, cylindrical, somewhat pointed at both ends, but con-
tractile; peristome spiral with the mouth near the middle
of the body. Membranellae on the left side of the peri-
stome, a membrane on the right side.

M do pus Claparede and Lachmann

Representative species Meio pus sigmoides MiXWer ijSO.

Cilia usually longer at the posterior end. A mass of dark pigment gran-
ules in the anterior extremity. Nucleus oval, central: contractile vacuole
posterior. Length 100 to 200 u. At the bottom of infusions. Metapides
acuminata Stokes diflfers from the above species in the posterior, tail-like
prolongation from which extend a number of long bristles. It is also
smaller in size.

\

-CV

Fig. 508. Metopus sigmoides.

CV. contractile vacuole; tnacn, macronucleus. X 220.
(After Stein.)

(108)

Without an undulating membrane. Body greatly elongated, cyl-
indrical, contractile. Peristome reaching to the middle of
the body. Strong membranellae on the left side of the peri-
stome. Body spirally striated. . . Spirostomum Ehrenberg.

Representative species. . Spirostomum ambiguum Ehrenberg 1835.

Body ten to fifteen times as long as
broad, but readily contracting into a short
spiral body. Nucleus moniliform. Con-
tractile vacuole posterior, extending for-
ward as a canal. Extended body may
... reach 2800 m in length. Common among
Fig. 509. Spirostomum ambtguum. ct, contractile vacuole; oQuatic olants
tnacn, macronucleus. X 30. (After Kent.) ^ ^

2(107) Peristome a broad triangular area, deeply sunken 113

113 (114) With an undulating membrane on the right side of the peristorne.
Body cylindrical or purse-shaped, sometimes contractile.
Peristome broad in front extending one-third the length of

the body Condylostoma Dujardin.

Representative species Condylostoma patens M\i\\qv I'j^G.

Body broadly ovate, widest posteriody. Peristome broadly triangular,
extending about half the length of the body. Nucleus moniliform; con-
tractile vacuole irregular. Length 200 m- Stagnant water.

Fig. 510. Condylostoma patens, macn, macronucleus; u, undulating membrane.
X 105. (After Kent.)

CILIATE PROTOZOA (INFUSORIA)

28 =

14 (113)

Without an undulating membrane in the peristome. Body purse-
shaped, oblique in front; peristome funnel-shaped, open
mg on the ventral side by a slit reaching as far as the
middle of the body. Membranellae on the left side of

the peristome Bursaria Muller.

Representative species.

Bursaria truncatclla Muller 1786.

Nucleus band-like; contractile vacuoles numerous. Length 500
to 700 n. Pond water.

Fig. 51

Bursaria truncatella. cv, contractile vacuole: tnacn macronucleus
X 35- (After Kent.)

Peristome confined to the anterior border of the body, with its
plane nearly at right angles to the longitudinal axis of the
body ,j6

115 (106)

116(119) Posterior end not produced into a tail-like process 117

117 (118) Body purse-shaped, slightly flattened, anterior end oblique.

Peristome enclosing most of the anterior end of the body.

Climacostomum Stein.

118 (117) Body funnel-shaped when extended, fixed or free-swimming, some-

times enclosed in a jelly-like lorica. Peristome, the ante-
rior expanded surface with a spiral row of strong cilia
around its border; the left end of the spiral being the lower,
leading into the mouth and short pharynx. Surface fmelv
ciHate sometimes bearing, in addition, long slender bristles.'

Stcntor Oken.
Representative species. . Stcntor polymorphiis Muller 1786.

Body usually containing a cortical layer of chlorophyl granules.
Nucleus moniliform. Length, extended, 1200 n. Among aquatic plants
and in infusions. Sometimes found in gelatinous masses on leaves and
roots of water plants.

Another fresh-water form, S/enlor coerulcus Ehrenberg. blue in color.
is also common.

Fig. 512.

Stentor polymorphus. cv, contractile vacuole; macn, macronucleus
X 30. (.After Kent.)

119 (116) Posterior end produced into a tail-like process; anterior region
helmet-like, rounded anteriorly with a free posterior margin.
Mouth ventral in a ciliated groove. Cilia extending from
the mouth in a spiral across the anterior border and around
the free margin of the anterior portion.

Ciuiiomorpha Perty.
Representative species. Caowmorplia mcdiisula Perty i84().

Movements swift, rotating on the long axis
100 to 130 M. Standing water.

Loncrth. with fail.

Fig. 513. Caenomorplia meJusula. X 200 u\UerMein.)

120(105) Cilia restricted to certain limited areas or zonts 121

121 (124) Body not in a lorica 1^2

286 FRESH-WATER BIOLOGY

122 (123) Equatorial region of the body bearing a circle of long, fine bristles.

Body spheroidal with a spiral wTeath of strong cilia about
the anterior border. Mouth anterior, marginal.

Ualtcria Dujardin.
Representative species Ilallcria grandinella MiXWer 1^86.

, Nucleus round, central, with contractile vacuole near. Moving by a

rotary motion accompanied by sudden leaps. Length 25 m- Common
(^;^ in pond water.

Fig. 514. Ualteruj grandinella. cv, contractile vacuole; macn, macronucleus.
X 400. (After Kent.)

123 (122) Without long, fine bristles, otherwise very similar to II alter ia.

Strombidium Claparede and Lachmann.

v.,V;-,i(.i«//tfi/ Representative species. . Strombidium claparedii Kent 1882.

Body somewhat elongate, tapering posteriorly. Length 80 m- Pond

Fig. 515. Strombidium claparedii. cv, contractile vacuole; n, nucleus. X loo.
(After Kent.)

124 (121) Body in a lorica. . 125

125 (126) Lorica mucilaginous, attached to some support. Body ovate to
pyriform, attached in the lorica by a pedicel. Mouth ante-
rior, surrounded by a wreath of long cilia.

Tintinnidium Kent.
loij^ Representative species. . Tintinnidium fluvidtilisSte'miS6'j. I

fvV? "!'!.:. The lorica has an uneven surface, frequently with incorporated foreign

particles. Body sometimes attached to the bottom, sometimes to the side
of the lorica. Length of lorica 125 n. Attached to aquatic plants.

Fig. 516. Tintinnidiutn fluvialilis. X 200. (After Entz.)

126(125) Lorica chitinous; Otherwise as rm/t7i;z/(f/ww. . . Tintinnus Fo\.
127(2) Body not uniformly covered with cilia 12S

128 (169) CiUa setae-like, usually Hmited to the ventral surface. Dorsal

surface sometimes with bristles. Body flattened.

Order Hypotricha . . i2<)

129 (130) Ventral side uniformly ciliate, except sternum; a group of stronger

cilia behind peristome and near posterior end.

Trichogaster Sterki.

130(129) Ventral surface not uniformly ciliate 131

131 (166) Many border cilia 13-

132 (157) Ventral cilia numerous, in rows 133

133 (152) Ventral cilia bristle-like 134

134 (143) Usually more than two rows of ventral cilia 135

135 (140) Five or more rows of ventral cilia 136

CILIATE PROTOZOA (IXFUSORIA)

287

Fig. 517. Urostyla Irichogaster.
Conn.)

136 (137) Peristome with an undulating membrane, body flexible. Three or

more frontal styles. Five to twelve anal styles in an oblique
row extending to the left. Peristome an elongated triangle.

Urostyla Ehrenberg.
Representative species Urostyla Irichogaster Stokes 1885.

Yentral surface with closely approximated rows
of fine cilia. Anal styles ten or twelve in number.
Nucleus single, according to Stokes. Contractile
vacuole single, to the left of the peristome.
Length 250 to 300 n. Vegetable infusions.
Hemiciplostyla Stokes agrees with Urostyla, but
has no anal styles.
X 1 50. (After Conn found two nuclei in his form and states that
it may be a variety of Urostyla grandis Ehrenberg.

137 (136) Peristome without an undulating membrane 138

138 (139) Elongate, rounded at both extremities, not flexible; five nearly

straight rows of ventral cilia. Peristome on the right-hand
margin, extending back of the middle, with a row of long
cilia or membranellae. Nuclei four to six in number.

Homostyla Conn.
Representative species Homostyla elliptica Conn 1905.

Fig. 518. Homostyla elliptica. X 325. (.After Conn.)

139 (138) Kidney-shaped, with six obHque rows of ventral cilia, the posterior
row the stronger. No frontal, ventral, or anal styles. Border
cilia forming a complete row around the periphery. Peri-
stome reaching to the middle of the body. External para-
sites on Hydra Kerona Ehrenberg.

Representative species Kerona pcdkulus yWiWur I'l^b.

Fig. 519. Kerona pediculus. X 250. (After Stein.)

140 (135) Less than five row^s of ventral cilia 141

141 (142) Body elongated anteriorly into a neck; rounded behind, very con-

tractile. Peristome narrow, extending to or beyond the
middle. Membranellae long. Two or three oblique rows
of ventral setae. No frontal or anal styles.

Stichotricha Perty.

Representative species Stichotricha sccumla Perty 1849.

_______ Marginal setae long and slender. Nuclei two. with

^rf^=7^ ■, ' - ^ ■ \-~.-^rr-^ry:rKP'::!'—^ the contractile vacuole between. Often a mucilaginous
^^<i'<£?<^y<''1^''-^\'*''C-.-;'^^.,,^^^ sheath is secreted by the animal, from which it may
'^^sss^^^ir^?:^, ; project the anterior' half of the body or may entirely

vacate it and swim freely in water. Length about
200 M- Among sphagnum.

Fig. 520. Stichotricha secunJa. X 23s- (After Comi.)

288 FRESH-WATER BIOLOGY

142 (141) Body elliptical to ovate, flexible. Three unequal rows of ventral

cilia; frontal styles numerous. No anal styles. Marginal

setae uninterrupted Eschamustyla Stokes.

Representative species. . . Eschaneiistyla hrachytona Stokes 1886.

Anterior extremity slightly curved to the left with a con-

^^-TjaabUL-l ^'VS'-l'fi'^-"«t^. striction beneath the front border. Frontal styles about

-■jiir^'ViPm^ -^ " qM- "--^^g^Ji^r-. twenty-five in oblique rows. Nucleus not observed. Con-

j^^^Sa^^is^^^qBaflJ^^ tractile vacuole canal-like along the left-hand border. Length

"^^riU^lil 1iliiiii^*'"~'T IT about 200 M- Standing water with dead leaves.

Fig. 521. Eschaneuslyla brachylona. X 200. (After Stokes.)

143 (134) One or two rows of ventral cilia 144

144 (145) One row of about seven large ventral cilia. Long border and anal

cilia ■ Balladina Kowalewsky.

145 (144) Two rows of ventral cilia; body not elongated in front. . . 146

146 (151) Body prolonged posteriorly into a tail-like process 147

147 (150) Body not flask-shaped 148

148 (149) No anal styles; body narrow, elongated, sometimes contractile.

The border setae pushed in on the ventral surface.

Uroleptus Stein.
Representative species Uroleptus musculus MUUer 1786.

Body slightly elastic; tail-like process short, conical. An-
- - -—^ terior end curved slightly to the left, the posterior to the
i:=i:i^^ right. Frontal styles three or four. Length 200 m- Among
aquatic plants.

Fig. 522. Uroleptus musculus. X 150. (After Conn.)

149 (148) With a row of seventeen anal styles upon the left side. In other

respects hke Uroleptus Amphisia Sterki.

150 (146) Body flask-shaped, otherwise very similar to Uroleptus.

Platytrichotus Stokes.
Representative species. . Platytrichotus opisthobolus Stokes 1886.

Frontal styles five. Nucleus single, posterior. Contractile

\acuole single. The posterior tip of the body is changeable

in form. It may be bifid, truncate, or rounded. Long hispid

•^^^^'^^^^''^fuij^^u^^^ bristles are developed from the dorsal surface. Length 190 /i.

Among sphagnum.

Fig. 523. Platylrichoius opisthobolus. X 200. (After Stokes.)

151 (147) Body not prolonged into a tail-like process. Elongated, rounded at

both ends. With two uninterrupted rows of cilia on the

ventral surface Holosticha Wrzesniowski.

Representative species Holosticha vernalis Stokes 1887.

Frontal styles five or six. Anal styles from five to eight,
TS''^''^*-^*,.,^ usually branched. Dorsal bristles numerous. Nuclei two;

^^^^■^^^^^^ contractile vacuole central. Length 190 n. Shallow pools,
observed with algae.

Fig. 524. Uolosticha vernalis. X 225. (After Conn.)

152(133) Ventral cilia setae-like, often in interrupted rows 153

153(156) Ventral setae in more than one row 154

CILIATE PROTOZOA (INFUSORIA)

289

154 (155)

Body elongate-oval, with five to eight frontal styles; ventral setae
usually arranged in two or more rows, the inner rows having
but few setae. Anal styles five or six, two of which are near
the posterior border Plciirotricha Stein.

Representative species. . . Pleurolrichalanceolata¥j\\vQr\hcTg\9>T,^.

Somewhat resembling Stylonychia but without caudal setae and
with anal styles arranged in two groups. Nuclei two in number,
one in front of the apex of the peristome. Length 250 m- Among
algae.

Fig. 525. Pleurotriclia lanceolate. X112. (After Edmondson.)

155 (154)

Body somewhat rectangular in outline with slightly rounded ends.
Three or four obHque rows of ventral setae running from
left to right, and three rows parallel to the peristome Ijorder.
Anal styles five or six. Border ciha uninterrupted.

Onychodromiis Stein.

Representative species Onychodromiis grandis Stein 1859.

Body not flexible. Frontal styles from sixteen to
twenty-eight, in three rows. Anal styles from five to
seven. Nuclei usually four. Length 100 to 300 ti.
Onychodromopsis flexilis Stokes differs from Stein's form
in having a soft, flexible body.

Fig. 526. Onychodromus grandis. x 125. (After Conn.)

156 (153) Ventral setae in one obHque row. Body elongate-oval. Five or
six frontal styles and as many anal. Peristome triangular,
curved, with an undulating membrane.

Gastrostyla Engelmann.
Representative species. . . . Gastrostyla steinii Engelmann i86-\

Body evenly rounded at each extremity. Three very

large frontal styles near the border. Anal styles five,

^ ==^^ i^ ^" obHque row, not projecting beyond the border.

Nuclei four. Contractile vacuole near the middle of the

v>\N body on the left side. Length 250 m- Fresh water.

Fig. 527. Gastrostyla steinii. X 125. (.\fter Edmondson.)

157(132) Ventral cilia few, not in rows 158

158(165) Not produced posteriorly into a tail-hke process 15Q

159 (162) Body flexible 160

160 (161) Border cilia uninterrupted. Narrow, elliptical, rounded^ at both

ends. Five ventral setae and five anal styles. No caudal
bristles. Inner right wall of peristome bent toward outer

left wall Oxytricha Ehrenberg.

Representative species. . . . Oxytricha pell ioftelld MiJUleT lySe.

^^^^^^^^^'^'^'^^'^^^^'r^ Marginal setae set well in on the ventral surface.

■-■o'^-Q-; .' -^^b^/ .Anal styles arising near the iiosterior lK)rdcr and vx-

'" '^^*^<^^ tending' nearly their entire length beyond it. Nuclei

*i;^tf^^!^^P two. Contractile vacuole on the left side. Length So

^^'^ii^iic--''^ \im\ j.^^ jQQ ^ Common in infusions and fresh water.

Fig. 528. Oxytricha peUionella. X 335. Opisthotricha Kent resembles Oxytri<h<i in general

(After Conn.) characteristics but has three caudal setae.

290

i6i (160)

162 (159)

163 (164)

macn

FRESH-WATER BIOLOGY

Border cilia interrupted at the posterior end. Frontal styles,
eight or ten. Five ventral setae and five anal styles. No
caudal bristles. Dorsal hispid setae usually present.

T achy soma Stokes.

Representative species. . . . Tachysoma parvistyla Stokes 1887.

Body narrow anteriorly forming a neck-like region. Ten
frontal styles. Marginal setae scarcely projecting except pos-
teriorly. Dorsal setae minute. Styles in this form are very
^yyyJ;:>'+r^^^^^^ small. Length Oo m- Shallow pools in early spring.

Fig. 529. Tachysoma parvistyla. X 450. (After Stokes.)

Body not flexible 163

With caudal setae. Elongate-oval in shape with eight frontal, five
ventral setae, and five anal styles. Caudal setae usually
three, long. Peristome triangular, with an undulating mem-
brane; the inner wall bent away from the outer wall.

Stylonychia Stein.

Representative species. . . . Stylonychia notophora Stokes 1885.

Front border obliquely truncate on the left side. Peristome
extending nearly to the middle of the body. Caudal setae
widely separated. Nuclei two. Length 120 to 160 m- Pond
water.

Fig. 530. Stylonychia notophora. cv, contractile vacuole; macn, macro-
nucleus. X 300- (After Conn.)

164 (163) Without caudal setae; with inner wall of peristome bent toward the

outer wall. Like Stylonychia in other respects.

Histrio Sterki.
Representative species Histrio erethisticus Stokes 1887.

Frontal styles nine; anal styles five, stout, rigid. Mar-
ginal setae uninterrupted. Length 150/1- Shallow pools,
with algae.

Fig. 531. Histrio erethisticus. X 200. (After Conn.)

165 (158) Produced posteriorly into a tail-like process. Body flexible, with

eight ventral setae and five anal styles at the base of the tail.

Urosoma Kowalewsky.
Representative species Urosoma sp.

Form doubtful as to species.

■^^^^^vrr^^^ Fig. 532. Urosoma sp. X 335- (After Conn.)

166 (131) Border cilia few or none 167

CILIATE PROTOZOA (INFUSORIA) 291

167 (168) No caudal setae. Body rounded or oval, dorsal surface usually
furrowed. Peristome in the posterior region in the left-
lateral border, its right border prolonged into a triangular,
lip-like extension. Usually three frontal styles, four or five
ventral setae, and five or more anal styles.

Aspidisca Ehrenberg.
Representative species Aspidisca coslataT>\i),}iTdm i^^i.

Dorsal surface with five or si.x furrows.
Length 35 n. Common in infusions.

Nucleus band-like.

Fig. 533. Aspidisca costata. x 500. (After Conn.)

[68 (167)

me^n

Caudal setae usually four in number. Body oval, with dorsal
convex surface furrowed. Peristome broad, on the left
side, extending backward to or beyond the middle of the
body. Frontal styles six or eight, a few scattered ventral
setae, and five anal styles Euplotcs Stein.

Representative species Euplotes char on Miiller 1786.

Frontal styles seven; ventral setae three. Nu-
cleus band-like. Length 80 ^. Pond water. Dif-
fering from Euplotcs patella Ehrenberg by its smaller
size and greater number of frontal styles.

Fig. 534. Euplotes cliaron. \'entral view and individual
in process of division. a\ contractile vacuole; macn,
macronucleus. X 300. (After Kent.)

169 (128) Cilia usually limited to the adoral zone, sometimes with additional
rings of cilia. Body cup-like or cylindrical.

Order Peritricha . . 170

170(193) No lorica present 171

171 (180) Without a stalk 172

172 (175) With a permanent secondary ring of cilia at the posterior end

enclosing an adhesive disk 173

Body short, barrel-shaped, with the posterior end discoidal, the
inner border of which is sujiported by a horny ring, the
peripheral zone of which is radially striated and denticu-
late; the outer border surrounded by a wreath of cilia.
Adoral zone extends spirally around the llattened end.
Mouth eccentric. Parasitic forms. . . Triihodimi Stein.

Representative species. . . Trichodiiia pcdicidus Ehrenberg 1S30.

Commonly observed gliding up and down on the tentacles
of fresh-water Hydra. Height of body 70 m.

Fig. 53 s. Tricluidina pediiulus. Individuals adherent lo tcnt.icic of
Uydra. X 50. (After Kent.)

173 (174)

292

FRESH-WATER BIOLOGY

174 (173) Identical with Trichodina, except that the chitinous ring is not
denticulate Urccolaria Stein.

175(172) Without a permanent secondary ring of ciha 176

176 (177) With two rings of stiff, spinous processes. . . Hastatdla Erlanger.
Representative species Hastatella radians Erlanger 1890.

Fig. 536. nastalella radians. mac«, macronucleus. X 500. (.^fter
Erlanger.)

m^n

177 (176) Without rings of stiff, spinous processes 178

178 (179) Posterior end elongated, usually attached; peristome slightly de-
veloped. Ciliated disk small. . . . Scyphidia Lachmann.
Representative species Scyphidia frotnentellii Kent 1S8 2.

Body truncate anteriorly; stalk-like appendafije
longitudinally striated. Length, extended, 80 n.
On water snails.

Fig. 537. Scyphidia fromentellii. ci;, contractile vacuole; n,
nucleus. X 2CX3. (After Kent.)

'^ ^

179 (178) Posterior end not elongated; attached or free. Cylindrical when
extended. Ciliated disk small.

Gerda Claparede and Lachmann.
Representative species Gerda sigmoides Kellicott 1885.

Anterior region narrowed, usually curved. Surface finely striated trans-
versely. Nucleus not observed. Length, extended, 150 m- Adherent to
fresh-water plants.

Fig. 538. Gerda sigmoides. x 160. (After Kellicott.)

180(171) With a stalk. : 181

181 (186) Stalk unbranched 182

CILIATE PROTOZOA (INFUSORIA)

182 (183) Stalk retractile. Body bell-shaped, cuticle often ringed. A series
of strong cilia encircle the central, elevated ciliary disk.
Mouth eccentric between the peristome and ciliary disk.

Nucleus band-like, curved Vorticella Ehrenijerg.

Representative species. . . Vorticella campanula Ehrenberg 1838.

Body broadly campanulate, greatly dilated anteriorly, surface smooth.
Stalk thick, five or six times the length of the body. Endoplasm often
opaque with granules. Length of body 150 m. Pond water. Social.

Fig. 539. VorHcella campanula. X 50. (.\fter Kent.)

183 (182) Stalk not retractile 184

184 (185) With an operculum. Body ellipsoidal to ovate; the ciliary disk
upon a stalk, closing Kke a lid. Nucleus short or band-like.

Pyxidiiun Kent.
Representative species Pyxidium ramosiun Stokes 1887.

Body vasiform, widest cehtrally; surface smooth. Ciliary disk slightly
exserted with two circles of long fine cilia. Pedicel very short. Length of
body about 100 m- Pond water on rootlets of Lemna.

Fig. 540. Pyxidium ramosum. X 335. (After Conn.

[85 (184) Without an operculum. Body elongate-ovate with surface usu-
ally transversely striate, stalk short. . . Rhabdostyla Kent.
Representative species R/iabdosiyla vcnialis Stokes 1887.

Body widest centrally, constricted below the ix?ristomc border. Ciliary
circles'two. Nucleus band-like. Length 50 /i. .\ttach.-.| t.^ (\rlnM and
Cypris in early spring.

Fig. 541. Rhabdoslyla vernalis. cr, contractile vacuole. X OOo. (.-KftiT ^(tokes.)

:86 (181) Stalk branched i^7

294

FRESH-WATER I^IOLOGY

187 (190) Stalk retractile.

188 (189) Zooids contracting independently. Bodies bell-shaped. Central
muscle interrupted at the union of the stalk and the branch.
Ciliated spiral forming about one and a half circles. Nu-
cleus horseshoe-shaped Carchcsium Ehrenberg.

Representative species. . . . Carchcsium polypinum Kent 1882.

Colonics often reachinj? a height of one-eighth of an inch. At-
tached to the under surfaces of stones or floating sticks in fresh-
water pools or running streams. The colony may be the
temporary host of Amphileptus meleagris. Length of zooids

Some interesting work, has been done on the nucleus of this
species by Miss M. Greenwood. (The Journal of Physiology,
Vol. XX, pp. 427-454.) It was found that the normal activity
causes a drain on the organism which, if not offset by sufficient
repair due to the lack of nutrition, results in the more fluid char-
acter of the macrosomes of the nucleus.

Fig. 542.

Carchcsium polypinum.
macn. macronucleus.

Terminal branch with two zooids;
X 300. (After Kent.)

(188) Zooids contracting together. Bodies very similar to Carchcsium
but central muscle continuous, causing all of the zooids to

contract together Zocthamnium Stein.

Representative species. . . . Zocthamnium adamsi Stokes 1885.

Bodies about twice as long as broad, tapering to the
pedicel; finely striated transversely. Length of zooids
60 M- Reported from Niagara River. Attached to
algae.

Fig. 543. Zoethamnium
macronucleus.

cv, contractile vacuole; macn,
100. (After Stokes.)

190 (187) Stalk not retractile , . 191

CILIATE PROTOZOA (INFUSORIA)

bell-shaped, usi
road. Stalk cc

Representative species.

29:

191 (192) ^-^--^ben^^haM^^^ transversely striated; peristomal disk

broad. Stalk contaniuig a canal but no muscle.

I?.- ,■ . Epistylis EhrcnheTR.
J^pislyhs jlavicans Ehrcnberg 1830.

stoI''''ir^Klf' "".Y ^'^ [J'«tinP:"ished by the fact that the

ftee-sw,mm,nK microgamrtes with attache macro™
metes ,s common. Length of zooids 200 to U^ \?

orS'^iteTrciol*"^' ^'°"-' ^'^•' ■" --inl -earns

Fig. 544. Epistylisflavicans. macg, macrogamete- mice
microgamete. x 25. (After Kent.) ^'

19. (.91) ^^^-,^~^^^^ ,,k ,ot broad elevated a con-

Representative species. • : : ; o^.../../.,/.^S:k:'S:.

asbn?a?teT'"°\^''- '"'?'^' 'f * ""1 ^"''^^^' ^^out three times
fnlH™ f -I -^J '''" contracted, zooids are thrown into transverse
n front Pr°n^ l"'' bear longitudinally plicate, snout-like projec ioTs
Siln ■' ■ ,P™^«P'^f "1 enclosing green corpuscles. Cil.arv circles two

to twenf;^' l?nl'ti'T h1'"'"^'- ^"?^'^ '" ^^^^"^ «^«"P^ o! from en
\JZTl^' I . ^^^ °^ ^°'^>' ^50 M. Height of colony 2 5 mm At-
tached to plants m pond water. '

Fig. 545. Opcrciiiaria plicaltUs. x 25. (Aiicr btokes.>

^93 (170) Withalorica.

10}

194 (197) Lorica gelatinous.

10-

296

FRESH-WATER BIOLOGY

195 (196) Animals growing in clusters, attached or free-floating, enclosed in
a mucilaginous jelly. Zooids attached to a branching stalk,
each secreting a jelly-like tube which may remain distinct
or fuse with its neighbor forming a jelly mass. Zooids
similar in anatomy to Vorticella. Usually green.

Ophrydium Ehrenberg.
Representative species. •. . Ophrydium eichhornii Ehrenberg 1838.

Bodies very plastic, finely striate transversely. Clusters hemispherical, of
closely approximated individuals. Some colonies may include as many as one
hundred zooids, although this large size is uncommon.

Division of the body has been observed to take place in a transverse direction,
which is a rare occurrence in this family.

The anterior portion swims away and settles down to form a new colony, or
probably conjugates with some fi.\ed zooid. Length of expanded zooids 250 to
500 n. Fresh water.

Fig. 546. Ophrydium eichhornii

a\ contractile vacuole;
(After Kent.)

I, macronucleus. X $o.

' )6 (195)

197 (194)

198 (205)

199 (202)

200 (201)

Animals solitary; similar in other respects to Ophrydium.

Ophridinopsis Kent.

Lorica chitinous 198

Lorica not decumbent • 199

Lorica sessile 200

Lorica with a hinge-like valve that closes the opening when the
body retracts. Lorica elongate, subcylindrical. Body
elongate with ciliary system as Vorticella.

Thuricola Kent.

Representative species Thuricola valvata Wright 1858.

Lorica four or five times as long as broad, with the valve at some dis-
tance from the aperture. Length of lorica i20m- Fresh water; also
reported from salt water. In Thuricolopsis Stokes the lorica is provided
with a support for the valve. Otherwise as Thuricola.

Fig. 547. Thuricola valvata. X 150. (After Kent.)

201 (200) Lorica without a valve.
Representative species.

Vaginicola Claparede and Lachmann.
Vaginicola leptosoma Stokes 1885.

Lorica broadly vasiform, twice as long as broad, inflated posteriorly. Zooid
elongate, projecting one-third its length beyond the lorica. Peristome twice as
broad as the body. Surface transversely striate. Length of lorica 120 /x.
Pond water.

Fig. 548. Vaginicola leptosoma. ct, contractile vacuole. X no. (After Stokes.)

202 (199) Lorica with a pedicel 203

CILIATE PROTOZOA (INFUSORIA)

297

203 (204) Without an operculum. Zooid like Thuricola; adherent to the
bottom of the lorica in a sessile manner or united by a con-
tinuation of the supporting pedicel. . Cothurnia Ehrenlierg.
Representative species Cothurnia plectoslyla Stokes 1885.

TTldCn

Lorica curved, two and one-half times as long as broad, finely striate
longitudinally, also with transverse markings. Divided posteriorly
into two unequal parts by a curved, chitinous partition to which the
zooid is attached. Zooid not protruding much beyond the aperture
when extended; transversely striate. Length of lorica iio/x. Marsh
water.

Fig.

54Q. Cothurnia plectoslyla. cv
X 250.

contractile vacuole, macn, raacronucieus
(After Stokes.)

204 (203) With an operculum of chitin developed beneath the peristome and
closing the lorica when the animal is retracted.

Pyxicola Kent.
Representative species Pyxicola cartcri Kent 1882.

Lorica subcylindrical, three times as long as broad, anterior margin
slightly oblique, walls undulate. Pedicel very short. Zooid extending
beyond the aperture. Length of lorica 90 /u. Fresh water.

Fig. 550. Pyxicola carleri. X 270. U^fter Kent.)

205 (198) Lorica decumbent 206

206 (207) Animal adherent to the posterior extremity of the lorica.

Plat y cola Kent.
Representative species Platycola decumhcns Kent 1882.

Lorica oval, depressed. Zooid extending considerably
beyond the aperture, the exserted portion being at right
angles to the portion within the lorica. Length of lonca
QO n. Fresh water.

Fig. 551- Platycola decumbens. X 200. (.After Kent.)

207 (206) Animal adherent to one side of the lorica which often has a valvular

aperture. Zooid adherent to the margin of the aperture.

Lagenophrys Stein
Representative species. . . . Lagenophrys vaginocola 'Sic'm \^>,\

Lorica elongate with two semilunar, lip-like processes partially closini: tin-
aperture. The processes are raised when the zooid is extcn<lc<l and lowcrctl
when it is retracted. Zooid adherent by its narrow peristome to the ctlgc of
the aperture. Length of lorica 70 m- Freshwater. 5/y/<j/k-(/ra Kellicolt diflcrs
from Lagenophrys in having an erect lorica with a ^K-dicei.

Fig. 552. Lagenophrys vaginocola. X 210. (.\iter Maupas.)

!98

FRESH-WATER BIOLOGY

208 (i) Cilia present during embryonic stage only. Tentacles in adult.

Class Suctoria . . 209

209 (210) Tentacles branched. Animals solitary, sessile, discoidal, or sub-

spherical, with the sfirface of the integument indurated.
Tentacles flexible, non-contractile, finely perforate at their ex-
tremities. Increasing by gemmation. . Dcndrocometcs '>At'm.
Representative species. Dendfocometes paradoxus Sie'm 1851

Tentacles equal in length to the diameter of thh body,
usually five or less in number. The distal terminations
of the tentacles are capable of great expansion and, by
means of these, other Protozoa are captuicd and the pio-
toplasm of their bodies absorbed into the body of the
host. Nucleus subtriangular. Diameter of body 8c ^i.
Fresh viatei, sometimes attached to Gammarus pulcx, a
fresh-water shrimp.

Fic. SSZ- Dcndrccometti paradoxus. X 170. (After Stein.)

210(200) Tentacles unbranched, contractile 211

211 (220) Without a lorica 212

212(213) With a stalk. Body spherical or pear-shaped. Tentacles knobbed,
scattered, or in groups. In some species the animal may
become detached from the stalk and live a free life.

Podophrya Ehrenberg.
Representative species Podophrya fixa ^ixiWQX !']'&().

Stalk slender but rigid. Tentacles slender,
scattered over the surface of the body, usually
not longer than the diameter of the body. Nu-
cleus oval, central. Contractile vacuoles often
two. Diameter of body 55 m- Attached to aquat-
ic plants.

Fig 554. Podophrya fixa. Active individuals. X 210.
(After Conn.) Cyst. X 230. (Alter Edmondson.)

213(212) Without a stalk 214

214 (215) Forming colonies. Animals fused, forming an erect, branching
colony. Several colonies may be connected by a creeping
stolon. Suctorial, capitate tentacles borne on the ends of

the branches Dendrosoma Ehrenberg.

Representative species. . . Dendrosoma radians Ehrenberg 1838.

Stolon repent, giving rise to a number of erect branches
tapering distally, themselves often branched. Nucleus ribbon-
like, ramifying into the branches. Contractile vacuoles nu-
merous. Height of colony 1000 to 2500 n. Attached to
aquatic plants.

Fig. 555. Dendrosoma radians. X 30. (After Blochmann.)

215 (214) Not forming colonies 216

2i6 (217)

217 (216)

218 (219)

219 (2]

CILIATE PROTOZOA (INFUSORIA) 299

Tentacle one, consisting of a single, movable anterior process.
Parasitic on Cyclops Rhyncheta Zenker.

Tentacles numerous 218

Body spherical, never fixed; knobbed tentacles arising from all

sides Sphaerophrya Claparede and Lachmann.

Representative species. . . . Sphaerophrya magna MdiUpdiS i?>'S>i.

/:.*■

Tentacles not exceeding fifty in number: when fully extended,
equal in length to the diameter of the body. Reproduction has
been observed to take place by transverse division. Diameter
of body 40 ju. Freshwater.

Fig. 556. Sphaerophrya magna. X 500. (After Conn.)

Body irregular; knobbed tentacles arising from the lobes of the

margin of the body. Attached by the broad, lower surface.

Trichophrya Claparede and Lachmann.

Representative species Trichophrya sinuosa Stokes 1886.

Body flattened with lobed margins. Usually not more than five
\|/^6f clusters of tentacles. Nucleus branched. Contractile vacuoles

.3m^^ , numerous. Length 55 m- Attached to aquatic plants

\^/\\\\v^ Fig. 557. Trichophrya sinuosa. X 125. (.\fter Stokes.)

220(211) With a lorica 221

221 (224) Lorica sessile ^^^

222 (223) Usually cup-shaped or subspherical ; tentacles suctorial, sometimes

in groups Solenophrya Claparede and Lachmann.

Representative species Solenophrya pera Stokes 1SS5.

Lorica irregularly cubical or satchel-shaped, hyaline, widest at the base
of attachment, narrowing anteriorly, with the sides somewhat concave.
Zooid oval, not attached to bottom of lorica. Tentacles arising from the
entire frontal border. Two individuals often in the same lorica. Height
of lorica 40 m- Width and length nearly the same as height. Attached to
p.\ aquatic plants in standing water.

Fig. 558. Solenophrya pera. X 225. (After Stokes.)

223 (222) Posterior end of the body prolonged into a projection. Attached

to Epistylis. Two to five long, simple tentacles.

Urnula Claparede and Lachmann.

300 FRESH-WATER BIOLOGY

224 (221) Lorica with a stalk. Body may or may not fill the lorica. The
end of the lorica may be open or provided with slit-like
openings through which the tentacles extend. Tentacles
suctorial, knobbed, scattered, or in groups.

Acineta Ehrenberg.
Representative species Acineta fluviatilis Stokes iSSs-

Lorica subtriangular, compressed, very delicate, widest an-
teriorly, tapering to the attachment with the stalk. Stalk
shorter than the lorica. Two anterolateral openings for the
tentacles. Zooid usually filling the lorica. Length of lorica
40 to 80 n. Attached to aquatic plants.

Fig. 559. Acineta flmiatilis. X 3i5- (After Stokes.)

IMPORTANT REFERENCES ON MASTIGOPHORA AND INFUSORIA

See list of general works under Sarcodina, p. 236; also the following:
Dangeard, p. a. 1902. Recherches sur les Eugleniens. Le Botaniste,

8:97-357; 4Pl., 53 figs.
Kent, S. 1880-1882. A Manual of the Infusoria. 3 vols. London.
KoFOiD, C. A. 1898. Plankton Studies, II. Bull. 111. State Lab. Nat.

Hist., 5: 273-300; 12 pi.
1899. Plankton Studies, III. Bull. 111. State Lab. Nat. Hist., 5:419-

440; I pi.
Palmer, T. C. 1905. Delaware Valley Forms of Trachelomonas, Proc.

Acad. Nat. Sci., Phila., 57: 665-675; i pi.
Powers, J. H. 1907. New Forms of Volvox. Trans. Amer. Micr. Soc.

27:123-149; 4 pi.
1908. Further Studies on Volvox, with Descriptions of Three New Species.

Trans. Amer. Micr. Soc, 2?)'. 141-176; 4 pi.
Roux, J. 1901. Faune Infusorienne des eaux stagnantes des environs de

Geneve, 149 pp., 8 pL, 4to., Geneve.
Stokes, A. C. 1888. A Preliminary Contribution Toward a History of the

Fresh Water Infusoria of the United States. Jour. Trenton Nat. Hist.

Soc, 1:71-344; 13 pi.

CHAPTER X
THE SPONGES (PORIFERA)

By EDWARD POTTS* Meadville, Pa.

The zoophytes or plant animals of the old zoologists or, as they
are now more correctly designated, the separate groups of sponges
and coelenterates, are represented in the fresh waters of North
America through a very narrow range both of genera and species.
Sponges alone constitute the topic of this chapter. The student of
fresh-water sponges must not expect to find them resembling in ap-
pearance the familiar forms of commerce, which in fact are exclu-
sively of marine origin. Nor should he look for shapeless masses of
jelly; such may be found, but they are not sponges. Yet as animal
organisms, sponges, whether fresh-water or marine, are essentially
alike. Infinitely variable in form and external appearance and in
the character and constituents of their skeletal structure, the vital
parts that have clothed them, or do still clothe them if examined
in life, are composed alike of protoplasm or sarcode. This forms
the delicate tissues, structureless except when viewed through
powerful lenses, and builds up the inert framework whether it con-
sists of tough elastic fibers, as in the commercial sponge, or is the
fairy-like structure of flint or lime belonging to other sponges
found in the ocean, or forms skeletons, as in our fresh-water forms
so far as known, always of silex. The active life work of sponges
it is impossible to see with the naked eye and very difficult to study
even under the microscope. Certain collared cells by means ot
waving flagella feed the sponge, reject intrusive matter, and create

* The death of Mr. Potts just after the first manuscript of the chapter liad been
submitted laid upon me the duty of bringing it into conformity with the other chapters
of the book without his help. I have endeavored to do this with the least possible
change from the original. To make sure that no error was committed in the priKcss
I secured the aid of Dr. N. Annandale, Calcutta, India, for whose kind assistance I
am deeply indebted. For the present form of the key Mr. Potts is in no wise responsible.
I am also indebted to Professor Frank Smith for valuable unpublished data in regard
to distribution. — Henry B. Ward.

301

302 FRESH-WATER BIOLOGY

the currents that traverse the canals of the body. While the
action of these fiagella is invisible to the unaided eye, their effect
may be seen if some finely divided carmine is added to the water.
The particles are sucked into the little pores over the surface and
after long wandering, having proved indigestible, are ejected from
the larger orifices.

The skeleton of these siliceous sponges, the only part that can be
easily preserved for study, is composed of spicules or little needles
of "hydrated silica (opal), averaging about one one-hundredth of an
inch in length, fasciculated or bound together side by side, but break-
ing joints, to form threads of considerable thickness along the princi-
pal lines of the sponge growth but thinner in the connecting hnks
that make the interspaces. The binding material along these
threads is not strong and its composition is not certainly known.
The terminal spicules projecting around the sponge uphold the
filmy dermis a little above the firmer body of the sponge. Where
the larger channels unite to form the efferent osteoles the out-
flowing currents stretch this dermis into little cylindrical tubes or
towers, technically called chimneys, with terminal openings through
which one may often see rejected particles shot out as from the
crater of a volcano.

A few fresh-water sponges in some situations seem to be essen-
tially perennial; others die in hot countries at the onset of the sum-
mer season, or among us at the coming of winter, or are broken
up by floods, floating ice, etc., so that for a season they disappear
from view. The ordinary annual revival of sponge life, the growth
after winter or after a period of desiccation, is provided for by the
germination of many seed-like bodies, called gemmules; these may
generally be found when the sponge matures, fixed as a pavement
layer at the base of the sponge or distributed amongst its tissues.
The living cells enclosed in these are protected by a firm chitinous
coat or shell that is again surrounded by a crust composed of
minute air cells, which float the gemmules and promote their distri-
bution to distant places. A variety of minute spicules is normally
found embedded in this crust as described under individual species
in the key.

Whenever the favorable season arrives, that is in most regions

THE SPONGES (PORIFERA) 303

when spring comes or when, in dry regions, the occasional floods
reach them, the gemmules in the pavement layers are supposed to
germinate where they were deposited; the floating kinds, set adrift,
lodge upon any suitable surface and begin their seasonal growth.
Each gemmule is provided with a foramen, or a foraminal aperture,
sometimes plain, but often more or less tubular, through which
the growing cells usually escape by amoeboid action and appear
as a delicate creamy film surrounding the gemmule. Sometimes,
however, they escape by the rupture of the whole gemmule. Where
this is part of a pavement-layer or one of a group of detached gem-
mules the escaping currents flow together as a filmy mass, sometimes
rounded up like a small pea, otherwise as a spreading film or Hke
the wandering trail of slime left by one of the larger snails. The
appearance of the young spicules is nearly coincident with the
escape of the cells and they at once begin to arrange themselves
according to the habit of the species, forming a network over the
supporting surface, upon which is built a superstructure suggesting
that of our modern steel-framed buildings. Special interspaces
become the chambers fined with the coHared flagellate cells already
mentioned. The action of these flagella creates currents of water
flowing in through myriads of almost invisible pores in the cover-
ing, bearing food particles to nourish the growing sponge and then
carrying off and discharging useless matter through the larger canak
by the efferent osteoles already mentioned.

The study of fresh-water sponges should begin here and foDow
the cycle of growth from gemmule to gemmule, watching, if it be
possible, even the development within their own especial cells of
the various classes of spicules, observing in the autumn the gradual
gathering together of the germ cefis before they are shrouded in
chitin or committed to the waters within their floating crusts.
Under favorable conditions and constant as well as careful control
much of this work may be made independent of the seasons, after
germinating the fresh gemmules in shallow glass dishes at home,
and in a small way afford excellent opportunity for study; but it
will not be found practicable to grow sponges in aquaria excepting as
small fragments in very large bodies of water or in vessels in which
the water is constantly or frequently renewed.

304 FRESH-WATER BIOLOGY

Those who wish to gather specimens for their cabinets or design
to determine genera and species must await the maturity of the
various specimens. Observation seems to make it probable that
the rarer, filmy sponges complete their growth and mature their
gemmules earher than the more lusty, massive forms. The gem-
mules of the former have often been seen in August or September
resting in slender lines upon standing or floating timbers from
which the rest of the sponge has disappeared, though the coarser
forms are frequently immature late in November. These dates
hold true for the northern United States generally and would of
course vary in other parts of the world; but there are undoubtedly
individual regions of extreme or atypical climatic conditions within
our own area where the sponge calendar when worked out will show
a distinctly individual aspect.

A hint as to hopeful localities for collecting may suffice. Do not
waste time in hunting along sluggish streams or in shallow, muddy
ponds, where, even if the sponges start to grow, they will soon be j
suffocated by gravitating particles of earthy matter. A reserva- \
tion should perhaps be made in favor of the lower sides of floating
timbers that have long lain in the water, since here gravity protects
instead of injures the sponges. Only one other caution seems neces-
sary. As all known fresh-water sponges are siKceous the student
Vill probably fail to find them in waters strongly impregnated with
carbonate of Hme, though they are recorded from such places.

Perfect drying is to be recommended. The proper classification
can be as readily determined from dry as from fresh sponges and
it is only when a specimen has some novel character or specific
form that it is worth while to preserve it in alcohol. When a
wrapper is necessary for transportation or otherwise, be sure to
use soft paper, rather than cotton or sawdust.

Other features having proved indeterminate or unreliable, the
system is based upon the shapes and positions of the minute spicules
found embedded in the gemmule crust. As these can only be sat-
isfactorily seen when the impenetrable crust is made transparent
or removed, three microsHdes from each specimen must be pre-
pared to determine the forms of the skeleton, the dermal or flesh,
and the gemmule spicules.

THE SPONGES (PORIFERA) 305

Provide a half dozen or more short test tubes with a stand made
by boring holes of suitable diameter in a piece of inch board.
First make sure that you have in hand parts of the same sponge
only. Place in the first tube a dozen or more clean gemmules,
some of them cut in half with a sharp knife, and about an equal
bulk from the remainder of the sponge; cover with a few drops of
strong nitric acid that has been previously brought to a boil in
another tube and set aside, the purpose being to corrode away the
crust but not the chitin of the gemmules. In a few minutes, when
most of the gemmules incline to settle at the bottom, pour off the
acid into the next tube, wash carefully with several lots of pure water,
replace it with alcohol and set the tube aside to settle. Put into
the acid in the second tube a small quantity of all parts of the
sponge, adding more acid if necessary, and boil carefully over a
spirit lamp to thorough disintegration. When that is effected till
this tube also with water and set it aside to settle. The smaller
spicules settle very slowly. It may be well to shake the tube a Httle
in order to separate the darker particles from the pure white. When
the mass has settled, carefully pour off the water with the impuri-
ties, wash the residue with fresh water and let it stand, after which
a mount may be made from this tube. Spread the spicules evenly
and not too thickly on a slide, and let them dry thoroughly before
adding balsam and a cover glass. This amount ^vill of course fur-
nish an epitome of the sponge but will not show the exact relations
of the minor spicules to the gemmules. This can only be seen after
two or more applications of alcohol to the first tube have removed
the acid mixture; to keep out the air, cover with benzol until fully
ready for the balsam. Distribute a few of the gemmules, with some
spicules, upon a second slide and mount in balsam before the air
penetrates them. A fragment of the dry filmy dermis mounted in
balsam will determine the presence or absence of dermal spicules
and fix positively the standing of the sponge according to the key.

If all the smaller spicules distinguished by this process arc accr-
ates, that is, more or less cylindrical, whether straight or cur\'ed,
smooth or spined, pointed or abruptly terminated, the specimen
under examination may unhesitatingly be placed in the genus Spon-
gilla. All others, unless entirely novel, will show some modification

3o6

FRESH-WATER BIOLOGY

of the birotulate form, i.e., two little wheels or rotules connected by
a shaft, and on the numerous variations of these parts depends the
position of the species in the key.

KEY TO NORTH AMERICAN FRESH-WATER SPONGES

I (12) Gemmules with acerate spicules only. . . Spongilla Lamarck . . 2

SpongilHdae with long spindle-shaped skeleton spicules, macroscleres. having pointed or
rounded ends, and often also with minute simple flesh spicules, or microscleres. Gemmules
naked, or with external air-cell layer containing rhabdi, or rod-like spicules.

2 (5) Sponge branching

Abnormal forms of S. lacustris occur in which there are no branches.

3 (4) Flesh spicules smooth Spongilla aspinosa Potts 1880.

Sponge evergreen, encrusting, thin, sending out numerous long,
slender waving branches from a relatively thick basal membrane.
Gemmules few, in scattered branches. Skeleton spicules smooth,
straight or slightly curved, rather abruptly pointed. Dermal spic-
ules minute, smooth, straight or curved, slender, gradually pointed.
From clear standing water in New Jersey and Virginia.

Fig. 560. Spicules of Spongilla aspinosa. Four types of spicules figured
here: ordinary skeleton spicules abruptly pointed at both ends; skeleton
spicule, acute or rounded at one end; malformations of skeleton spicules,
with processes at or near one end; small smooth dermal spicules; globular
or discoidal masses of sUica frequently observed in this species. X loo.
(After Potts.)

o\^

4 (3) Flesh spicules spined Spongilla lacustris (Linnaeus) 1745.

Branches cylindrical or tapering, and rigid. Prefers rapidly running water. Very abun-
dant. Gemmules either apparently wanting or abundant throughout the sponge, with or
without a granular crust. Skeleton spicules smooth. Dermal spicules pointed spined acer-
ates. Gemmule spicules whether few or many generally cylin-
drical, more or less curved, rather sparsely spined. From Boston,
Mass., to McDonald Lake, Alaska, in an infinite number of situa-
tions and variety of forms. The variety paupercula Bowerbank,
made an independent species Spongilla paupercula by Carter, " is
perhaps that one of this group of synonyms about whose identity
with S. lacustris there may be most hesitation. Its character is some-
what anomalous, as its locahty and associations are peculiar. Grow-
ing originalli' in the ponds and reservoirs tributary to the Boston
Water supply, Bailey wrote in 1856 that it grew abundantly in the
waterpipes by which the city was supplied with water from a small
Fig s6i Skeleton and gem- '^^^•" ^^^ minute acerate^ were said to have been smooth which
mule spicules of Spon- would separate it clearly from S. lacustris, but Potts was unable to
gilla lacustris, var. mon- secure material from the original locality which bore out the con-
towa. X 100. (After Potts.) tention.

5 (2) Sponge without branches 6

6 (9) Gemmules in layers or groups 7

THE SPONGES (PORIFERA)

307

7 (8) Tubules of gemmules turned upward or outward from the groups.

Spongilla fragilis Leidy 1851.

Sponge encrusting in subcircular patches, thin at edges, occasionally one or more inches
thick near the middle. In the most varied situations, apparently preferring standing water,
though also in running water. Abundant. Gemmules abundant, primarily in one or more
pavement layers. Also in compact groups surrounded by a cellular parenchyma charged with
subcylindrical spined acerates. Skeleton spicules smooth, slightly curved, rather abruptly
pointed. True dermals wanting. Found in most of the United States.

A B

Fig. 562. Spongilla fragilis. A. Section of group of gemmules; a, curved foraminal tubules, always out-
ward; 6, envelop with acerate spicules. X 12. B. Three types of spicules figured here: skeleton spicules,
smooth, abruptly pointed; variable parenchymal spicules, subcylindrical, subspined: spined, spherical
forms frequently seen throughout the species. X loo. (After Potts.)

8 (7) Tubules of gemmules turned inwards in the groups.

Spongilla igloviformis Potts 1887.
Sponge brown, thin, encrusting. Gemmules in compact hemispherical groups of eight to
twelve or more, resting on the flat side, surrounded by a parenchyma of unequal cells, chargerl
with numerous coarsely spined spicules nearly as long as the rather few, less strongly spined
skeleton spicules. On "the lower side of timbers in cedar swamps, New Jersey. S. mackayi,
described by Carter from Newfoundland, may belong here.

Fig. 563. Spongilla igloviformis. A. Lateral view of dome-shaped group of gemmulp. (Foraminal
tubules open inward and are invisible,) X 25. B. Two types of spicules figured here: skeleton spicules,
weakly spined; "parenchymal spicules" nearly equally long, but more spmous. X 100. (Alter t'otts.)

9 (6) Gemmules not in layers or groups i°

10(11) Dermal spicules birotulate. . . . Spongilla novae-tcrrae Votts iSS6.

Sponge encrusting, gemmules rather numercnis, very large, crust
absent or inconspicuous. Skeleton spicules relatively few, slender,
gradually pointed, smooth or microspmed. Dermal spicules very
abundant, minute, birotulate. Gemmule spicules smooth or irregu-
lar, furnished with long spines, frequently located near the e.vtremi-
ties. Placed by some in genus Ephydalia. tound only in shallow
water of lakes in Newfoundland (4^° N. L.).

Fig. 564. Spicules of Sponiilla novae-terrac. Representing the slender,
smooth or sparsely microspmed skeleton spicules; the dermal spicules birot-
ulates of unequal size; and the spinous gemmule spicules. X 100.
(After Potts.)

V^

3o8

FRESH-WATER BIOLOGY

11 (lo) Dermal spicules acerate S pongilla wagneri Votts iSSg.

Gemmules abundant. Skeleton spicules long, robust, smooth. Dermal spicules very
numerous. Gemmule spicules spined, long, curved. Spines most numerous at extremities.
Recorded only from brackish water of southwestern Florida.

No figure yet published.

12 (i) Gemmule spicules of birotulate type, more or less modified.

Sub-family Meyeninae Vejdovsky . . 13

13 (47) Apertures of gemmules not provided with filamentous appendages 14
14(46) Rotules of gemmule biro tulates nearly equal 15

15 (37) Gemmule birotulates of a single class 16

16 (19) Margins of rotules entire, i.e., smooth, not serrate.

Trochospongilla Wejdovsky . . 17

17 (18) Skeleton spicules smooth. . Trochospongilla leidyi (Bowerbank) 1863.

Sponge of a peculiar light gray or drab color, encrusting thin, persistent. Gemmules numer-
ous, each surrounded by a capsule of skeleton spicules. Skeleton spicules short, smooth,
robust. Dermal spicules wanting. Gemmule spicules short, birotulate, margins entire and
exflected. From Louisiana as well as original field of discovery near Philadelphia. Generally
distributed in the Illinois River from the mouth to La Salle according to F. Smith.

Fig. 565. Trochospongilla leidyi. A. Upper surface of portion of a layer of gemmules, each of which is
surrounded by a lattice capsule (c) of spicules resembling those of the skeleton; at the summit an open
space around the foramina! aperture (a), more than one being sometimes present. X so. B. Four types
of spicules figured here: smooth skeleton spicules, abruptly pointed; same, with rounded terminations;
short birotulates with entire margins; same with rotule twisted or exflected; face of rotule; group of
rotules as they appear upon the surface of the gemmules. X loo. (After Potts.)

18 (17) Skeleton spicules strongly spined.

Trochospongilla horrida (Weltner) 1893.

Sponge encrusting, white, gray, yellow, or brown.
No gemmule spicules except birotulates which are
smooth-margined, low, small. Lives in standing or
flowing water. Rare. F. Smith found one specimen
each in the Illinois River near Starved Rock and in the
Big Muddy River in southern Illinois.

Fig. 566. Trochospongilla horrida. Spinous skeleton spic-
ules. X 180. Birotulate gemmule spicules. X400. (After
W. Kiikenthal.)

THE SPONGES (PORIFERA)

309

19 (16) Margins of rotules serrated or incised. . Ephydatia Lamouroux. . 20

Spongillidae with gemmule spicules of the birotulate type that are uniform or variable in
length but not definitely of two classes, long and short, and that have finely or deeply cut
margins.

20 (35, 36) Dermal spicules if present neither birotulate nor stellate. . . 21

21 (22) Rays and spines of birotulates subdivided and microspincd.

Ephydatia subdivisa (Potts) 1887.

Sponge massive, encrusting, compact. Gemmules few. Skeleton
spicules smooth or microspined, abruptly pointed. Birotulates very
numerous, robust, shafts frequently spined; rays short but subdi-
vided. I'^rom St. Johns River near Palatka, Florida.

Fig. 567. Spicules of Ephydatia subdivisa. Three types of spicules figured
here: smooth and spined skeleton spicules; long, massive geramule birotu-
lates, spined and subspined; rotules of same. X loo. (After Potts.)

22 (21) Rays and spines of birotulates entire 23

23 (24) Margins of rotules very finely serrate

0/

Ephydatia millsii (Potts) 1887,

Sponge encrusting. Gemmules small. Skeleton spicules nearly
straight, slender, rather abruptb' pointed, entirely microspined.
Gemmule birotulates very numerous, very symmetrical, their shafts
usually smooth. Rotules sometimes microspined. From Sherwood
Lake, near Deland, Florida.

Fig. 568. Spicules oi Ephydatia millsii. Three tjTDCS of spicules figured
here: microspined skeleton spicule; mature gemmule birotulates with smooth
shafts; probably immature forms with less notching on the rotules; face
of rotulates lacinulate or delicately notched, and without rays. X loo.
(After Potts J

24(23) Margins of rotules coarsely dentate 25

25 (32) Length of birotulates not more than twice the diameter of rottiles. . 26

26 (31) Shafts of birotulates generally smooth 27

27 (30) Skeleton spicules smooth 28

28 (29) Shafts of birotulates much longer than diameter of rotules.

Ephydatia Jul id! His (auctorum) .

Sponge sessile, massive, rarely throwing out short branches an inch or less in length. Pre-
fers standing water. No vesicular cells in parenchyma. Gemmules numerous throughout.
Skeleton spicules smooth. Dermal spicules wanting. Rotules of gemmule spicules not deeply
indented. Numerous varieties the occurrence of which in North America has not been accu-
rately recorded. The form which Potts describes as present generally throughout the eastern
and middle United States is declared by Weltner to be Ephvdatia miUleri, the secon.l following
species. The true E.flmiatilis is found in Michigan and Illinois, and is fairly common though
not so abundant as E. mulleri {fide F. Smith).

3IO

FRESH-WATER BIOLOGY

29 (28) Shafts of birotulates slightly if any longer than diameter of rotules.

Ephydatia japonica (Hilgendorf) 1882.

Much like E. fluinalUis. Dermal spicules wanting. Birotulates with smooth shaft, short,
never forming more than a single layer on the gemmule. Rotules deeply indented. Gem-
mule with short, straight, broad, very delicate foraminal tubule. In Potomac River, near
Washington, D. C.

Fig. 569. Ephydatia japonica.

%

H

^ ^ ^^ .

Gemmule, X i8; birotulates, X 120; skeieton'spicules, X 120.
(After Annandale.)

30 (27) Skeleton spicules microspined except at tips.

Ephydatia miilleri (Lieberkiihn) 1856.

Sponge cushionlike, rarely branched. Vesicular- cells abundant
in the parenchyma. Dermal spicules wanting. Shafts of gemmule
birotulates not, or barely, longer than diameter of rotules. Rotules
deeply indented. Eastern and Central United States; Nova Scotia;
Newfoundland; Vancouver Island. Found by F. Smith at Douglas
Lake, Mich., and Tolland, Col.

Fig. 570. S'^\cn\t?,oi Ephydatia miilleri. Three types of spicules figured
here: skeleton spicules, X 120; birotulate gemmule spicules; same mal-
formed; group of rotulae; single rotules showing an ordinary distribution of
the rays. X 250. (After Potts.)

31 (26)

Shafts of birotulates with enormous spines.

Ephydatia rohnsta (Potts) li

Sponge massive, encru.sting, thin. Gemmules scarce. Skeleton
spicules pointed, smooth. Birotulates large, generally malformed.
Shafts abounding in spines as long as rays of the rotules. Collected
near Susan ville, California. Perhaps only a variety of E. fluvialilis.

Fig. 571. Spicules oi Ephydatia robusta. Three types of spicules figured
here: smooth skeleton spicules; coarsely spined gemmule birotulates; single
rotules; exceedingly misshapen forms. X 100. (After Potts.)

32 (25) Length of birotulates more than twice the diameter of the rotules.

33

33 (34) Birotulates two or three times longer than the diameter of the rot-
ules Ephydatia subtilis Weltner 1895.

Sponge thin, encrusting. Skeleton needles extremely slender, scantily covered with short
spines. Dermal spicules wanting. Gemmules small, spherical; foramen a simple pore, or a
very short tube. Birotulates delicate, slender, of variable length; shaft thin, smooth, long.
Rotules small, split nearly to the center, with 10 to 20 blunt rays. Kissimee Lake, Florida.

No figure yet published.

THE SPONGES (PORIFERA) ' ^jj

34 (33) Birotulates many times longer than diameter of rotules.

Ephydatia crater ijor mis (Potts) 1882.

Sponge encrusting, thin. Gemmules small, white very numern.,.. Pro 1 , '

mules extremely thick, the foraminal tubes in a Vr'?f?rZT M P^anular crust of gem-

which may be the same as this species The d^sprfSinn " '/ ^ '
ulates^w.th short hooked ra?s; suppSd^i^ii' K" T^'' ^Mill

35 (20, 36) Dermal spicules, minute birotulates.

Ephydatia everetti (Mills)

[884.

36 (20,

Sponge green consisting entirely of slender filaments little more
than a sixteenth of an inch in diameter. Gemmules few but ^?u
smnofh^'n^'^ a thick crust. Skeleton spicules slender! cyHndrkd'
S? I^erma spicules, minute birotulates with slender cyhndncai
shafts and cap-like rotules notched into five or six hooks GemmS
formed'oTfi"''-" '^^- '^""^-^^''^ ^^afts smooth and blender; To^ules
iTr rA K- ^^'^^ ^''''^\' ^^'^"^ved. acuminate hooks. In cdd
water, Berkshire County, Mass., and Nova Scotia.

u ^^^" ^^^- u Spicules of Ephydatia everetti. Four tynes of snirnlp.; f,cn,r.A
formed of hooked rays; minute dermal birotulates. X 100 (After Potts )

35) Dermal spicules stellate Dosilia Grv^y.

Only species yet reported m the United States.

Dosilia palmer i (Potts) 1885.
Sponge massive, subspherical, lobate. Skeleton spicules spar«;elv
microspined, curved, gradually pointed. Dermal spicules star-
shaped, consisting of a variable number of arms of various lengths
radiating froni a large smooth globular body; arms spined through-
out. Gemmule birotulates with long spined shafts, rotules notched
i^rom Colorado River, 60 miles below Fort Yuma, attached to
pendent branches flooded bv spring freshets. •iii'icnea to

In the opinion of Annandale, Potts' var. pdmeri is a different
species from Carter s /^/wm^^o from India. He has seen types of
both and is confident both belong to DosUia

Spicules oi Dosilia palmeri. Five types of spicules figured

lule

rotules of same, irregularly notched; substellate dermal spicules; imperfect
Xi^ (ASerPottsT ^'''° '''^'' amorphous " Scotch terrier ' forms.

37 (15) Gemmule birotulates of two distinct classes t^^

38(41) Dermal spicules stellate Aster omeycn ia Xnus^udviXc. . 39

thf?o?m of^antSerl!"''^'''^^^ ^^"'"'"'' 'P^'"'"' ^^ '^° ^^'''"'^ ^^^^ ^°^ ^'^^ microsderesin

312

FRESH-WATER BIOLOGY

39 (40) Terminal spines of longer gemmule spicules with a simple curve.

Asteromeyenia plumosa (Weltner) 1895.

Sponge massive, though brittle and friable.
Skeleton spicules slender, smooth, sharply pointed
at both ends, nearly straight. Shaft of long birot-
ulates almost smooth, slender, straight; rotules
a circle of curved hooks, joined at the base.
Short birotulates with stouter shafts, profusely,
irregularly, and strongly spined; rotules not mark-
edly convex in profile, irregularly, narrowly, and
deeply serrated. Free spicules very minute,
abundant, resembling those of Dosilia. Gem-
mules large, spherical, with single, very small
aperture having short, straight foraminal tubule.
From Pinto Creek, Kinney County, Tex., and
Shreveport, La.; one specimen measured 29 X
25 cm.

Fig. 575. Asteromyenia plumosa. ^ , gemmule show-
ing aperture in center, X 35 ; ^. short birotulates, X 1 20;
C, long birotulates, X 120; Z), free microscleres. X 120;
£, skeleton spicule, X 120. (After Annandale.)

40 (39) Terminal spines of longer gemmule spicules distinctly recurved.

Asteromeyenia radiospiculata (Mills) if

Resembles A. plumosa. In profile the rays of the longer
gemmule spicule have almost the form of a J. Ohio and Illi-
nois. At Granite City, 111., specimens were taken from settling
tanks of the city water works, measuring 42 x 12x8 cm.

Fig. 576.
mount.)

Spicules ot Asteromeyenia radiospiculata. X 100. (From

41 (38) Dermal spicules acerate if present.

Heteromeyenia Potts . .42

SpongilHdae producing gemmules with birotulate spicules of two distinct classes, long and
short. Margins of rotules not smooth but dentate or incised.

42 (43) Rotules of gemmule spicules of smaller class finely serrated.

Heteromeyenia ryderi Potts

.2.

Sponge massive, often hemispherical. Gemmules numerous, crust
thick, foramina short and inconspicuous. Skeleton spicules grad-
ually pointed, entirely spined except at the tips. Dermal spicules
wanting. Shafts of long birotulates spined, rotules of three to six
short recurved hooks, sometimes umbonate. Rotules of small birot-
ulates nearly as great in diameter as the length of their shafts.
Shafts smooth or with few spines. Shallow flowing water, Florida
to Nova Scotia, and inland at least as far as Iowa.

Fig. 577. Spicules of Heteromeyenia ryderi. Four types of spicules
figured here: skeleton spicule; long gemmule birotulates. hooked and
spined; short birotulates; surface of rotules, margins lacinulate, surface
microspined or granulated; spherical amorphous spicule. X loo. (After
Potts.)

43 (42) Rotules of gemmule spicules of small class coarsely serrate.

44

THE SPONGES (PORIFERA)

313

44 (45) Rotules of gemmule spicules of small class regular mushroom-shaped,
shafts usually smooth. . Heteromeyeniarepens Potts iSSo.

Sponge encrusting, thin. Gemmules not abundant. Skeleton
spicules rather slender, sparsely microspined, gradually pointed
Dermal spicules nearly straight, entirely spined. Gemmule birotu-
lates of longer class comparatively few; shafts, smooth or with one
or a few conspicuous spines often irregularly bent. Rotules dome-
shaped, rays incurved like fish hooks. Small birotulates very nu-
merous, about two-thirds the length of the large ones Quiet
almost stagnant water, New Jersey, Pennsylvania, and Michigan. '

Fig 578. Spicules of E eteromeyenia repens. Five types of spicules
figured here: microspined skeleton spicules; gemmule birotulates of the
longer class, with recurved hooked rays; birotulates of the shorter class
with less pronounced rays; rotules of same; small dermal spicules, coarsely
spined; amorphous spicule. X 100. (After Potts )

45 (44) Rotules of gemmule spicules of small class very irregular, shafts
abundantly spined. Heieromeyenia argyrosperma Potts 1880.

Sponge minute, encrusting, gray. Gemmules abundant and
large. Foraminal tubules somewhat prolonged. Skeleton spicules
rather slender, cylindrical, abruptly pointed, sparsely spined
Dermal spicules apparently wanting. Shafts of long birotulates
sparsely spined. Rays of rotules few, long, stout, and clawlike
Short birotulates much smaller, abundantly spined. From Penn-
sylvania, New Jersey, New England States, and Nova Scotia
Found by F. Smith at Douglas Lake, Mich.

Fig. 57g. Spicules of H eteromeyenia argyrosperma. Three types of
spicules figured here: sparsely microspined skeleton spicules; gemmule
birotulates of the longer class with one to three hooked rays; spined birot-
ulates of the shorter class. X 100. (After Potts.)

46 (14) Rotules of gemmule spicules unequal, the proximal being larger.

Tubella Carter.
Only North American species known.

Tubella pennsylvanica Potts 1882.

Sponge minute, encrusting, on stones or timbers in shallow water.
Gemmules very numerous, small. Skeleton spicules very variable
in length and curvature, entirely spined; spines large, conical. Der-
mal spicules wanting. Birotulates of gemmules numerous with a
large rotule next to the coat and a small distal rotule, varying from
the diameter of the shaft to that of the pro.^imal rotule. Margin of
large rotule usually entire but margin of small often angular and
notched. Shaft smooth. Averse to light and found as a rule under
stones and roots. Eastern United States generally. Found by F
Smith at Rhinelander, Wis., and Douglas Lake, Mich.

Fig. 580. Spicules of Tubella pennsylvanica. Two types of spicuks
figured here: spined skeleton spicules; gemmule "inaequibirotulates." or
trumpet-shaped spicules; group of rotules seen from above, showing the
relative sizes of the rotules; surface of single large rotule. X loo. (.•\fter
Potts.)

47 (13) Apertures of gemmules prolonged and divided into filamentous ap-
pendages Carter ins Potts . . 4S

Gemmules possess a long foraminal tubule, the outer end of which carries an irregularly
lobed disc or is provided with long filaments. Not recognized as a separate genus by some
recent authors (see Annandale, 1909), but distributed among the preceding genera.

314

FRESH-WATER BIOLOGY

48 (49, 50) Foraminal tubule very long and slender, tendrils short, irregu-
larly waving C ar terius tubisperma MiWs iSSi.

Sponge massive. Gemmules numerous. Length of foraminal tubule one-half to once diam-
eter of gemmule. Skeleton spicules rather slender, gradually pointed, sparsely spined. Der-
mal spicules long, slender, entirely spined. Gemmule birotulates abundant, irregular in length,
suggesting genus Ueteromeyenia, shaft smooth or with one or more spines, rotules arched, rays
numerous, long, incurved. Assigned by Annandale to genus Heteromeyenia. In Niagara River,
N. Y., Massachusetts, and Michigan.

Fig. 581. Carierius tubisperma. A. Partial section of gemmule; (a), Foraminal aperture prolonged
into a long tubule flaring and funnel-shaped at its extremity and divided into several short tendrils {d)
or cirrous appendages, (b) . birotulate spicules. X 50. (After Potts.) B. Three types of spicules figured
here: skeleton spicules; gemmule birotulates; face of rotule; long spined slender dermal acerates. X 100.
(After Potts.)

49 (48, 50) Foraminal tubule shorter; tendrils, one or two, enveloping the
tubule C ar terius latitenta Fotts iSSi.

Sponge often encrusting stones in rapidly running water. Gemmules numerous. Cirrous ap-
pendages at first flat and ribbon-like, becoming slender and rounded, and occasionally subdivid-
ing. Skeleton spicules smooth: or sparsely microspined, gradually pointed. Dermal spicules
long, entirely spined. Birotulates stout, shafts with numerous long pointed spines. Rays of
rotules deeply cut and sometimes recurved. Annandale believes this and the following species
should be assigned to Ephydatia. In Pennsylvania, western New York, and Illinois River.

Fig. 582. Carterius latitenia. A. Partial section of gemmule; (a), foraminal tubule short; (6), birotu-
late spicules; {d), one or two long and broad, ribbon-like cirrous appendages. X 3°- (After Potts.) B.
Three tyjies of spicules figured here: skeleton spicules; gemmule birotulates vanable m length; face ol
rotule; spined dermals. Xioo. (After Potts.)

THE SPONGES (PORIFERA)

315

50 (48, 49) Foraminal tubule still shorter; tendrils, three to five, very long
and slender Carterius tenosperma Potts 1880.

Sponge forming irregular masses creeping upon and around water plants and roots, less fre-
quently encrusting stones. Gemmules rather numerous. Foraminal tubules about one fourth
the diameter of the gemmules. Tendrils as much as half an inch long. Skeleton spicules slen-
der, very sparsely microspined. gradually pointed. Dermal spicules slender, nearly straight,
entirely spined. Birotulates with cylindrical shafts, abundantly spined, rotules often irregular.
New Jersey and Eastern Pennsylvania.

Fig. 583. Carterius tenosperma. A. Section of gemmule, (a), short tubule; (d) , long, slender cirrous
appendages. X35- B. Three types of spicules: skeleton spicules; spined gemmule birotulates with
burr-like rotules; ends of same; long, spinous, acerate dermal spicules. X lOO. (After Potts.)

IMPORTANT REFERENCES ON FRESH-WATER SPONGES

Annandale, N. 1909. Report on a Collection of Fresh-water Sponges from
Japan. Annot. Zool. Japon., 7: 105-112, pi. 2.
1909a. Fresh- water Sponges in the Collection of the United States Na-
tional Museum. Part II. Specimens from North and South America.
Proc. U. S. Nat. Mus., 37: 401-406.

1910. Fresh-water Sponges in the Collection of the United States National
Museum. Part IV. Note on the Fresh-water Sponge Ephydatia japon ica,
and its Allies. Proc. U. S. Nat. Mus., 38: 649-650.

191 1. Fresh-water Sponges in the Collection of the United States National
Museum. Part V. A New Genus proposed, with Eeteromeyenia radio-
spicidata Mills as Type. Proc. U. S. Nat, Mus., 40: 593-594.

1911a. Fresh-water Sponges, Hydroids and Polyzoa. Fauna British India.
251 pp., 5 pi.
Carter, H. J. 1881. History and Classification of the Known Species of

Spongilla. Ann. Mag. Nat. Hist., (5), 7: 77-107, pi. 5-6.
Potts, Edward. 1883. Our Fresh-water Sponges. Amer. Nat., 17: 1203-6.
1887. Fresh-water Sponges; a Monograph. Proc. Acad. Nat. Sci., Phila.,

39: 158-279, pi. 5-12.
1890. Fresh- water Sponges. Microscope, 10: 140-143, 1 61-163, 193-
196, 257-263, 307-310; pi. 5-6.
Weltner, W. 1895. Spongillidenstudien III. Katalog und Verbreitung der
bekannten Susswasserchwamme. Arch. f. Naturges., (pt. I), 61: 1 14-144.

CHAPTER XI

HYDRA AND OTHER FRESH-WATER
HYDROZOA

By frank smith

Professor of Zoology and Curator of the Museum, University of Illinois

The student of the animal life of the sea is continually in
contact with a great variety of organisms which have radial sym-
metry and are often striking in appearance, diversity, and abun-
dance. These were formerly included in a great group, Radiata,
but are now separated into two very distinct branches (phyla),
the Coelenterata and Echinodermata. The latter phylum, which
includes the well-known starfishes and sea urchins, is wholly un-
represented in fresh water, while the former, which includes the
hydroids, jellyfishes, and corals, with thousands of species in the
seas of to-day, has in fresh water scarcely a dozen species and
these are relatively insignificant in appearance. The fresh-water
Coelenterata are all included in the class Hydrozoa, and hydra is
the only one which is abundant, widely distributed, and well
known to the ordinary student of zoology. Because of its abun-
dance it is the type form commonly used in zoology classes as an
introduction to a knowledge of the phylum.

Among the more obvious structural or morphological characters
of hydra is the sac-like body with the capacious chamber which
is at the same time body cavity and digestive cavity and of which
the mouth is the only opening to the exterior. The animal is
attached by one end and at the other shows the mouth surrounded
by a circle of tentacles which are evaginations of the body wall
and are hollow, their cavities being continuous with the digestive
cavity. The body wall as well as that of the tentacles is com-
posed of two cellular layers, the ectoderm and entoderm, sep-
arated by a thin, noncellular mesogloea and bounded externally
by a deUcate cuticula. In some species there is an obvious dis-
tinction between an adoral part of greater diameter and more

316

HYDRA AND OTHER FRESH-WATER HYDROZOA 317

granular opaque entoderm, and a narrowed paler aboral part
which is termed the stalk. In other species designated in the
key as " not stalked," there is- no clearly marked division into
such regions. Highly contractile fibers formed by certain cells in
both ectoderm and entoderm may bring about either a great
elongation of the body and tentacles to thread-like proportions or
their contraction to an almost globular form. Certain kinds of
ectoderm cells, which are most abundant in the adoral half of the
body, especially in the tentacles, give rise to the characteristic ne-
matocysts or ^' nettling cells " of difTercnt shapes and sizes. These
contain a fluid secretion which passes out through a thread-like
extension of the sac wall, that is forced out when the cell is stimu-
lated. The combined action of a number of these nematocysts
on the small organisms encountering them results in the loss of
activity or even death of the organisms and so permits their cap-
ture and appropriation as food by the hydra,

Spermaries and ovaries develop in the ectoderm layer and at a
time of year which seems to be fairly constant for a given species
but differs in different species. After fertilization the ovum passes
through the early stages of development while still in the ovary
and becomes enclosed by a chitinous envelop which has a charac-
teristic shape and surface for each species. This en\elop which
often is spiny is referred to in the key as the embryonic, chitinous
membrane. In some species the embryos are freed from the parent
organism and drop to the bottom, while in others they are fastened
by the parent to the substratum to which it adheres. The develop-
ment is direct. In one species {Hydra oligactis) the individuals are
said to be of separate sexes, or dioecious, but in others hermaphro-
ditism prevails. Asexual reproduction by budding is the preva-
lent mode of multipHcation and very rarely the formation of two
individuals by a process of fission has been observed.

Hydra has long been an object of interest and experiment because
of its notable powers of regeneration and form regulation and there
is now an extensive literature dealing with these phenomena.

Hydra individuals ordinarily maintain an independent existence
but in various related groups colonies which often include many
individuals arise by asexual reproduction. In some such colonies,

3l8 FRESH- WATER BIOLOGY

besides hydra-like forms or hydranths, another type of individuals
is produced which become medusae and separate from the colony
as free-swimming forms that develop germ cells which in turn pro-
duce a generation of individuals of the hydranth type. In other
colonial forms the germ cells are formed by individuals that re-
main as members of the colony. All the species of Hydrozoa
which have a complex colonial organization are with one exception
marine.

In the fresh-water colonial hydroid Cordylophora, many of the
individuals or zooids are nutritive and provide food for the colony
and by budding increase its size while other individuals form germ
cells; there are no medusae formed. Among the obvious structural
features in which this form differs from hydra are the following:
the tentacles are not hollow but the entoderm forms a core of large
cells which occupies all the space enclosed by the ectoderm and
mesogloea; the tentacles are more numerous than in hydra and are
irregularly distributed; the cuticula is thick and forms a support-
ing skeleton for the colony.

Four genera of fresh-water Hydrozoa form free-swimming me-
dusae. Two of these occur in Africa but the two following genera
are each known in North America and Europe.

Edward Potts first discovered the Microhydra and it has been
studiM chiefly by him. The hydranth form has no tentacles and
it lives independently or forms simple colonies of two or three
individuals. The medusae have been seen by him to arise by
budding from hydranths but have not been observed when older
than a stage attained two or three days after being freed. They
have but eight tentacles and no marginal sense organs.

Craspedaciista was first found in the Regent's Park Gardens,
London, England, in 1880, and its only occurrence in North Amer-
ica thus far recorded was in Washington, D. C, in 1907 (Hargitt).
Only its medusa stage is known with certainty but what is supposed
to be the hydranth form is very similar to that of Microhydra.
The medusa has more than eight tentacles and has marginal sense
organs.

The hydra is usually found adhering firmly by the base to sub-
merged objects over which it moves slowly and may be found at

HYDRA AND OTHER FRESH-WATER HYDROZOA 319

various distances from the surface, but not infrequently is sus-
pended from the surface film or even drifts about unattached
and thus often becomes a component of the plankton. The hydras
multiply so rapidly when conditions are favorable that they often
take heavy toll from the plankton organisms, especially the ento-
mostracans and small worms. Since they are probably little used
as food by animals useful to man and since they compete with
young lish for food, their economic relations to man are unfavor-
able.

The most favorable conditions for Cordylophora are in brackish
water and there it attains most luxuriant development but it
thrives also in fresh water, although the colonies are there less
stalwart and the ascending branches are usually not more than
half as large as in colonies from brackish water. It was first known
as a brackish water form from Europe and its appearance in fresh
water is of comparatively recent date. It has been known for a
number of years in the United States, near the Atlantic Coast, where
it occurs in both brackish and fresh water. The first recorded
appearance in the Mississippi Valley was in the Illinois River in
1909, but it is now known in several states of that region.

This form is a plankton feeder and thus competes with young
fish for food. Its most vigorous colonies are found where there is
considerable current and in company with Bryozoa it not infre-
quently invades the pipes of water systems, impedes the flow, and
at times vitiates the water itself. ]\{icrohydra is found associated
with bryozoans on the surface of stones in running water near
Philadelphia, and is apparently not an abundant form.

In the search after hydra if pond-lily leaves and coarse sub-
merged vegetation be collected from bodies of water in which
hydra occurs, and allowed to stand a few hours or days in glass
jars, specimens are likely to be found attached to the vegetation
or to the sides of the jar or even suspended from the surface film.
Hydra may be kept in good condition for long periods of time in
well aerated aquaria, if suppHed with suflicient food, preferably
small entomostracans and worms. At the proper season and tem-
perature they may reproduce sexually as well as by budding.
For ordinary purposes a corrosive sublimate and acetic acid

320 FRESH-WATER BIOLOGY

mixture either hot or cold gives sufficiently good results as a fixa-
tive, but for certain cytological studies special methods are recom-
mended; for these one must consult the literature.

Occurring most frequently attached to submerged sticks or twigs
Cordylophora may also be looked for on the submerged surfaces of
walls and piers and also on stems of coarse vegetation. Fixation
may be accomplished as with hydra.

It has recently been shown that the Linnaean systematic names
in common use for species of Hydra must be dropped for the earlier
ones of Pallas. Recent Hterature which deals with the results
obtained by several investigators who have worked on Hydra
shows such conflicting views concerning the status of certain sup-
posed species of this genus, that any classification or key deaHng
with them must be regarded as tentative. The chief difficulty is
with Hydra oligactis Pallas {H. fusca L.), which by some is beHeved
to have been applied in the past to two specifically distinct forms
while others uphold a contrary view.

The treatment of the species of Hydra in the following key is
based chiefly on the papers of Brauer, Downing, and KoeKtz.

KEY TO NORTH-AMERICAN FRESH-WATER HYDROZOA

1 (lo) Hydranths with tentacles; no free swimming medusae at any stage of

the life history 2

2 (9) Tentacles in a circle about the oral end; do not form true colonies;

have power of slow locomotion. . . Hydra Linnaeus . . 3

3 (6) Body not definitely stalked; extended tentacles not very much longer

than the body 4

4 (5) Green; three kinds of nematocysts; embryonic chitinous membrane

spherical, with minute elevations; spermaries limited to

oral third of body; sexual activity more frequent in summer.

Hydra viridissima Pallas {H. viridis L.) 1766.

5 (4) Pale yellow, gray, or brown; four kinds of nematocysts, diameter of

largest 0.0105-0.013 mm.; embryonic chitinous membrane
spherical, with coarse branched pointed spines; spermaries
only on distal third; sexual activity more frequent in sum-
mer Hydra vulgaris VdiWdiS {H. grisea'L.) 1766.

6(3) Body definitely stalked; extended tentacles much longer than body. . 7

HYDRA AND OTHER FRESH-WATER HYDROZOA

321

7 (8) Gray, brown, or reddish; three kinds of nematocysts; diameter of
largest less than 0.0105 mm. ; embryonic chitinous membrane
spherical, with very short spines; spermaries on any part
of body except the stalk; sexual activity more frequent in
winter Hydra oligactis VdXldiS {H. fuscal^.) 1766.

By some it is claimed that //. oligactis is strictly dioe-
cious and is in this way distinct from the following
species.

Fig. 584. Hydra oligactis. (a) Nematocysts. (b) Embryonic
chitinous membrane. X 47- (-'^fter Brauer.)

(7) Gray or brown; four kinds of nematocysts, diameter of largest less
than o.oi mm.; embryonic chitinous membrane plano-con-
vex, with only convex side covered with spines; spermaries
limited to the oral third of the body; sexual activity more
frequent in autumn Hydra polypus Linnaeus i-js^-

Besides the diflferences between H. oligactis and 77. polypus
mentioned above the latter is said to be somewhat smaller and
to have somewhat shorter tentacles than the former. By some
the vaHdity of any of the diflfering characters mentioned above
is disputed, with the possible exception of the difference in the
number of different kinds of nematocysts.

H. pallida Beardsley, a very pale form in Colorado, and H.
corala Elrod, a very large red form in Montana, may prove to
belong to the species listed above, as similar variations of them
are known to occur in Europe.

Fig. 58^^. Hydra polypus, (a)
Nematocysts. (6) Embry-
onic chitinous membrane.
X 36. (After Brauer.)

(2) Tentacles irregularly scattered on the body of the hydranth; form true
colonies Cordylophora Allman.

But one species, C. lacustris Allman, which
occurs in fresh water near Philadelphia. Pa.,
and near Woods Hole, Mass. It has recently
been found in the Illinois River at Havana,
and by Mr. W. Donaldson in the Mississippi
River at Granite City and East St. Louis, 111.,
in the Arkansas River at Little Rock, Ark.,
and in the Red River at Shreveport, La.

Fig. 586. Cordylophora lacustris. (a) A branch from
a colony. About twice as larpe as is common in fresh
water, (b) Female reproductive zooids with embryos
in different stages of development. X 20. (Alter
Schulze.)

10 (i) Hydranths without tentacles; free swimming medusae are formed .

322

FRESH-WATER BIOLOGY

11 (12) Hydranth form most frequently seen; medusae rarely found and

have but eight tentacles Microhydra Potts.

But one species, M. ryderi Potts,
first described from near Philadel-
phia, Pa., but since then found in
different localities in Europe. The
medusae have been seen only when
in a very early stage and the adult
stages are not known.

Fig. 587. Microhydra ryderi. (a) Young
medusa. X 40. (After Moore from
Potts.) (b) Hydranths and embryo.
^ J X 22. (After Ryder from Potts.)

12 (11) Hydranth form rarely seen; medusae have more than eight tentacles.

Craspedacusta Lankester.

But one species, C. sowerbyi Lankester, known in Europe
and America. Found only in aquaria according to earlier
records, but large numbers were collected by Professor H. Gar-
man in September, 1916, in a creek near Frankfort, Kentucky,
the first record of their occurrence in other than artificial sur-
roundings. A second species, C. kawaii Oka, has been found in
a river of China.

Fig. 588. Craspedacusta sowerbyi. X about 4. (After Hargitt.)

Limnocnida Giinther is the only other known genus of fresh-water medusae and its
distribution so far as recorded is limited to the Eastern Hemisphere. Limnocnida
tanganyicae (Bohm) 1883 is found in Africa; Limnocnida indica Annandale 1912, in
India; Limnocnida rhodesia Boulenger 191 2, in southern Africa.

IMPORTANT REFERENCES ON FRESH-WATER HYDROZOA

Brauer, a. 1909. Die Benennung und Unterscheidung der Hydra- Arten.

Zool. Anz., 33: 790-792.
Downing, E. R. 1905. The Spermatogenesis of Hydra. Zool. Jahrb., Anat.,

21: 379-426.
Hargitt, C. W. 1908. Occurrence of the Fresh-water Medusa, Limnoco-

dium, in the United States. Biol. Bull., 14: 304-318.
Nutting, C. C. 1901. The Hydroids of the Woods Hole Region. U. S.

Fish Com. Bull, for 1899: 327.
Potts, E. 1906. On the Medusa of Microhydra ryderi and on the Known

Forms of Medusae inhabiting Fresh Water. Quar. Jour. Mic. Sci., 50:

623-633; 2 pi.
Smith, F. 1910. Hydroids in the Illinois River. Biol. Bull., 18: 67-68.

CHAPTER XII

THE FREE-LIVING FLATWORMS

(TURBELLARIA)

By CAROLINE E. STRINGER

Bead of the Department of Biology, Omaha High School

The Turbellaria or free-living flatworms are among the most
interesting of the simply organized animals because of the re-
markable variety shown in their reactions and behavior. They
are to be found both in fresh and salt water and sometimes in
moist places on land. The fresh-water forms are common in
ponds and streams ahnost everywhere. Many of the smaller
forms resemble infusoria in their minute size, shape, and mo\e-
ments. The larger Turbellaria are more readily recognized as
worms but are often confused with leeches which they resemble
superficially in color and form, although they are easily distin-
guished by their head-like anterior end, non-segmented body, and
lack of posterior adhesive sucker.

Probably the first attempt to describe one of this group dates
back to 1744 when Trembley included in his memoir on Hydra
what was undoubtedly a planarian. As early as 1776 O. F.
MuUer separated the Turbellaria and Nemertinea from the para-
sitic Trematoda, but it was not until 1831 that Ehrenberg gave
to these animals the name Turbellaria because of the tiny cur-
rents in the water created by the delicate cilia which cover the
body. Much confusion existed in their classification until the
appearance of Lang's work on structure and relationships in 1S81
and in the next year of L. von Graff's monograph on the Rhab-
docoelida. Since then considerable attention has been given to the
morphological and physiological as well as to the systematic study
of the group.

Flatworms may be either cylindrical, thread-Hke, spindle-shaped,
or more or less flattened and leaf-like. They range in length
from a fraction of a millimeter to several centimeters. The

324 FRESH-WATER BIOLOGY

larger fresh-water forms are usually inconspicuously colored, gray,
brown, or blackish or are entirely free from pigment. The smaller
forms are often brilliantly colored, yellow, orange, red, or rose;
and a few appear green due to the zoochlorellae or symbiotic
one-celled plants which live within the mesenchyma. The color
is more or less affected by the food contained in the intes-
tine. This is especially true of the non-pigmented or very trans-
parent forms and in many cases examination with a lens will be
necessary to show whether pigment is actually present or not.

The anterior end is often modified so as to suggest the form
of a head, either by the presence of the various special sense
organs, a pair of lobes or cephalic appendages, or by a groove
or constriction separating it from the rest of the body. Eyes
may or may not be present. If present, the usual number is two,
though some forms have four and one genus of planarians,
Poly cells, is characterized by the possession of a large number
of eyes. Accessory eyes or pigment spots are common among
certain species. The normal eyes are usually bean-shaped and
are black in color although there are many exceptions. Acces-
sory eyes are usually more or less irregular in shape as well as in
position.

A pair of sensory pits occurs in the anterior region in many
forms. These may be round, oblong, or sHt-shaped, and very
shallow or deeply sunken. They are connected with special
brain gangHa, are usually provided with long ciha, and are re-
garded as olfactory organs. A few forms possess a statocyst
(otocyst) or balancing organ. It consists of a membranous sac
filled with a fluid in which a strongly light-refracting statoHth
(otolith) is suspended. The non-pigmented, light-refracting organs
found in Stenostomum posterior to the brain and connected with
it by nerves are of three types. They may consist (i) of a va-
riable number of spherical bodies arranged in the form of a
convex organ, the so-called saucer-shaped or pateUiform organ,
(2) of a vesicle which contains a strongly Hght-refracting lens-
shaped body on its wall, or (3) of a hollow capsule-like vesicle.

The epidermis consists of a single layer of ciliated cells. The
dlia are conspicuous in the rhabdocoels, which are enabled

THE FREE-LIVING FLATWORMS (TURBELLARIA) 325

thereby to move freely through the water, and to the unaided
eye look much Hke infusoria. Planarians have a uniform glidin<^
movement but do not swim about unsupported. In addition to
the ciKa, remarkably long sensory hairs are present in a few forms.
The Turbellaria are richly suppHed with various kinds of glands.
Slime glands occur all over the body and are especially numerous
near the anterior and posterior ends. Other glands form the
rod-shaped bodies or rhabdites which are either homogeneous
and uniformly hght-refracting (rhabdoids), or consist of a hyaline
outer layer enclosing a fine granular substance (rhammites). The
former are extremely variable in shape (spindle-, egg-, rod-, or
club-shaped) and originate either in dermal gland cells or in sin-
gle-celled glands witliin the mesenchyma, especially in the anterior
end where the tracts through which they pass to the surface may
appear as conspicuous fines. The rhammites are found onh' in
the mesenchyma. Still other glands produce the pseudo-rhab-
dites which are irregular in shape, granulated in structure, and
have a low light-refracting power. A few forms have nematocysts,
or stinging cells, similar to those of the coelenterates, in place
of rhabdites. Adhesive cells and adhesive papillae are present
in many forms, especially at the posterior end of the body.
The external openings, mouth, genital pore, and excretory pores,
are extremely variable in position.

In place of the usual body cavity of liigher ammals, the space
between the body and internal organs is filled with a peculiar
connective tissue called mesenchyma (parenchyma). In the
smaller forms this tissue consists of a few scattered suspensory
strands and the space between is filled vdih fluid. In others
there is a network which encloses spaces filled with lluid and richly
supplied with cells. The cells may be vacuolated or otherwise
modified. The musculature includes bands of circular, longitudi-
nal, and diagonal muscles in the body wall. There are also mus-
cles which extend through the mesenchyma or connect with the
internal organs. The digestive apparatus includes the mouth,
pharynx, and intestine, all of which play an important ]xirt in
classification and furnish a ready means of distinguishing the two
great groups of fresh-water Turbellaria.

326 FRESH-WATER BIOLOGY

In rhabdocoels (Fig. 589J which include smaller forms, the mouth
may be placed at the anterior end or at various points on the
ventral surface. The pharynx is represented by three general
types, simple, bulbous, and pUcate. In the bulbous t>pe a muscu-
lar membrane divides the pharynx from the surrounding mesen-
chyma; the phcate form does not have the dividing membrane,
but consists of a cylindrical tube lying within a phar>Tigeal cavity
which opens to the exterior through the mouth. The simple and
plicate types of pharynx lie more or less lengthwise and the organ
appears as a tube parallel with the surface of the body. The
bulbous pharynx is more variable and includes three types, the
rosette-shaped, the cask-shaped (dolioHform) , and the variable.
The intestine has the form of a simple sac; it consists of a blind
cyUndrical tube, median in position. It is sometimes provided
with short lateral diverticula. The walls are thin.

In triclads (Fig. 590) the mouth is on the ventral surface usu-
ally just posterior to the middle of the body. The pharyngeal
region ordinarily shows externally about the middle of the body,
either as a more heavily pigmented or as a hghter colored area.
The pharynx is a cyhndrical, very muscular tube which hes within
the pharyngeal ca\dty except when protruded while feeding.
In a single genus, Phagocata, there are many pharyngeal tubes
instead of one. The intestine is thin-walled as in the rhabdo-
coels but has three main branches, a single one extending forward,
and two passing back, one on either side of the pharynx to the
posterior end of the body. Numerous lateral diverticula are
found especially in the anterior region. These may anastomose
with each other or remain distinct.

The protonephridial system (water-vascular system or simple
kidney) possesses one, two, or four principal canals, with a general
antero-posterior direction. The number and position of the open-
ings is variable. The nervous system includes two principal brain
gangha and two main longitudinal nerves with numerous lateral
branches. In many forms the longitudinal nerves may be seen as
two light lines on the ventral surface.

Reproduction is both sexual and asexual. The Turbellaria
are hermaphroditic with the female organs distinct from the male.

THE FREE-LIVING FLATWORMS (TURBELLARIA) 327

Both sets of organs have a common genital pore or are provided
with separate external openings. In many cases the male organs
mature earlier than the female and degenerate as the latter develop
so that a study of various stages of growth is necessary to give
complete knowledge of the organs. The rhabdocoels show great
diversity in structure ranging from those with simple ovaries and
testes to those with an elaborate system of accessory glands and
ducts that much resemble those of the triclads. The male copu-
la tory apparatus or cirrus is often remarkably complex and may,
as in Dallyellia, present the chief characters for identification of
species.

Some rhabdocoels produce two kinds of eggs, the thin-walled
transparent summer eggs which may undergo development within
the body of the parent, and the thick-walled winter eggs which have
a hard, brown shell and develop in the outer world. In other
species only the hard-shelled eggs are produced. In the Catenuli-
dae asexual reproduction by the formation of buds or zooids at
the posterior end of the body is met with commonly. More than
one bud may be produced before separation takes place.

Planarians (Fig. 590) show less variation in the structure of
the sexual organs. The testes, usually numerous, lie both above
and below the digestive tract and extend from anterior to posterior
end. The seminal vesicle opens into the muscular bulb-like
cirrus, the apex of which projects into the male genital atrium,
which in turn leads into the common atrium. Two ovaries are
placed far forward. The numerous yolk glands open into the
oviducts as they pass back and either unite to form a common
duct which enters the genital atrium or open separately into the
posterior part of the uterine duct. Fertilization apparently occurs
in the uterus which lies just back of the pharynx.

Some triclads manifest only sexual reproduction; others have
regular alternating periods of sexual and asexual reproduction;
while a number do not have a definite life cycle since sexual ma-
turity occurs at irregular intervals and often only among a limited
number of individuals. In these forms reproduction is ordinarily
asexual. Dendrocoelum lacteum attains sexual maturity and de-
posits its cocoons during the winter months. Li Planaria maculata

328 FRESH-WATER BIOLOGY

and Planaria agilis sexual organs begin to develop early in the
autumn and mature in the spring. After the cocoons are depos-
ited the reproductive organs degenerate and reproduction is again
carried on by transverse division into two pieces with subsequent
regeneration of the missing parts in each piece. The division
plane in most planarians passes just back of the pharynx. In
Planaria velata there is a division into pieces of various sizes
which encyst in a slime layer in response to unfavorable con-
ditions. This slime layer hardens into a shell-like covering.
Entire animals may also encyst. Asexual reproduction among
planarians may occur at any time of the year and in many species
is the usual method of propagation. The factors which control
the development of sexual maturity are not fully understood
although the food supply unquestionably plays an important part.

Turbellaria undergo no metamorphosis during development but
emerge from the egg, resembling the parent except in the lack
of sexual organs. In viviparous forms the young develop within
the mesenchyma of the parent and make their way to the exterior
through the body wall in the posterior region.

Flatworms are extremely responsive to external influences and
the larger forms especially give interesting and specific reactions
to various kinds of stimuh. If a dish in which they are quietly
gliding about is jarred even very shghtly, it will cause them to
stop and contract until quiet is restored, or if at rest and the dish
is moved they respond by becoming active as soon as the disturb-
ance ceases. Violent disturbance induces a highly excited condi-
tion with a loss of their more delicate reactions. After being
disturbed the animals continue moving about for some time, this
period depending on the strength of the stimulus and the physi-
ological condition of the animal. Naturally it depends also upon
the species since some are more active than others. They come
to rest in some sheltered spot, normally in groups. Light plays
an important part in determining their resting place as they show
decided negative photokinesis . The length of time of the resting
period varies greatly. The animals are much more active at
night than in day time; this is probably due to their feeding
habits.

I

THE FREE-LIVING FLATWORMS (TURBELLARIA) 329

If the worm is in a normal condition a delicate mechanical
stimulus induces a positive reaction, i.e., the animal pauses mo-
mentarily, then turns towards the source of the stimulus and
glides forward in that direction. A negative reaction is usually
given in response to a strong mechanical stimulus. In this case
the animal turns away from the source of the stimulus. The
positive and negative reactions are given not only in response to
weak and strong mechanical stimuli but to changes in tempera-
ture and to various chemical stimuli. The food reaction is essen-
tially a positive one. If food is placed in a dish where planarians
are gHding about, as they pass near enough to receive the stimulus
supplied by the juices of the tissues, they give a positive reaction
similar to that following delicate mechanical stimuli. This reac-
tion brings them to the food and as they pass over it the anterior
end closes over the food as if testing it. This process completed,
the animal moves ahead sufficiently to bring the mouth opening
over the food. The pharynx is extruded and the feeding process
begins. An interesting reaction is given where a planarian falls
dorsal side down, as it rights itself by forming a more or less
complete spiral.

There is a constant secretion of slime over the entire body and
especially on the ventral surface. Irritation causes an increase in the
quantity discharged. The sKme layer and rhabdites probably serve
the purpose of protection to some extent and aid in holding the prey.

Some Turbellaria occur in shallow quiet pools only; others
in larger ponds, lakes, or rivers, while a few species seem to prefer
swiftly flowing spring-fed brooks and streams. They are found
not only in all kinds of water but under varying temperature
conditions as well, since they may be collected during the winter
from beneath the ice and also are found in hot springs with a
temperature of 47° C. They collect on the under side of stones,
sticks, and leaves, conceal themselves among algae and in (lel)ris,
or cHng to the stems of Chara, CeratophyUunu and other h>-dro-
phytic plants. Certain forms are found near the surface in com-
paratively open water, and others in the mud or sediment at
the bottom of ponds or lakes. Peat bogs and swampy places
often furnish a large number of forms.

330 FRESH-WATER BIOLOGY

The regions occupied by different species of planarians are ap-
parently determined by temperature and food supply to a very
great extent. Those species which are adapted to low tempera-
tures become sluggish and inactive in higher temperatures, or
the reverse, and so will be less Hkely to find food than forms
especially adapted to that temperature. If the food supply is
limited this will necessarily lead to a crowding out of those less
perfectly adapted to the environment. The development of any
one species in a particular region is consequently limited by com-
petition with other species already established in the area. In
some cases two or more species may be found in almost equal
numbers in the same pond as Planaria maculata and Dendrocoelum
lacteum. In such cases a variety of food usually seems to be
abundant, thus reducing the competition which would otherwise
lead to the eUmination of the weaker. Cannibahsm sometimes
occurs among individuals of the same species when food is scarce
and different species are especially likely to prey upon each other.
Planaria agilis is a voracious feeder, and will exterminate a culture
of Planaria velata or Planaria maculata in a comparatively short
time even if other food is provided. This may account in part
for the fact that certain species are always found alone.

Ordinarily a pond or stream shows no evidence of the presence
of Planaria even though large numbers of them may be hidden
away under stones or leaves. However, one sometimes finds
them moving restlessly about in great masses, either all in one
general direction or in disorder. Voigt has conducted some inter-
esting experiments with European forms under natural conditions
which would indicate that these apparently concerted movements
are the result of a response to some stimulus which may promise
food, and cannot be regarded as indicating the possession of any
inherited tendency toward periodical wanderings. The marine
Turbellaria, like the fresh-water forms, hide under stones and
among seaweeds. Some find shelter within the shells of molluscs
and a few are parasitic.

The land planarians are in general characteristic of tropical
and sub-tropical regions where they attain a considerable length
and are usually brilUantly colored. In this country one may

THE FREE-LIVING FLATWORMS (TURBELLARIA) 331

sometimes find them in greenhouses and gardens, under flower
pots or boxes, in moist woods under bark and old logs, or in any
moist sheltered place. They are easily overlooked because of the
similarity in their appearance to young snails.

Rhabdocoels are especially abundant in pools or ponds which
contain much algal or other vegetation. A lens is often neces-
sary to distinguish them from other minute organisms. They
may be collected by means of a Birge net or other apparatus used
in collecting small animals or simply by gathering carefully plant
material, sediment, or debris from the ponds where they live
and exposing this material in shallow dishes in the laboratory.
The larger triclads are easily collected as they cling to the stone
or leaf which conceals them when it is lifted from the water and
they may then be removed with the point of a knife, or washed
off into a large-mouthed jar. When algae or debris which con-
tains them is disturbed, they contract, remain motionless until
the disturbance ceases, and then come to the surface and crawl
about excitedly, thus being easily picked up with a large-mouthed
pipette.

Most Turbellaria are easily kept in cultures if the water is kept
pure. Rhabdocoels should have a supply of unicellular and tila-
mentous algae such as diatoms, Spirogyra, etc., and small animals
like rotifers, Crustacea, and insect larvae, as they use both plant
and animal food. Planarians are largely, if not entirely, carnivo-
rous and thrive in aquaria which are supplied with running water
so that they may be given a constant supply of food. If this is
not possible, they may be kept in ordinary aquarium jars or shal-
low dishes with or without algae. They will live for weeks with-
out food but become greatly reduced in size. They take food
readily, especially at night, and should be fed once or twice a
week on earthworms, snails, liver, or almost any soft fleshy animal
tissue. The water should be changed after each feeding.

Small forms are easily studied under the microscope if slightly
compressed by the cover glass through the absorption of the
surplus water with filter paper. A few quince seeds added to
the water are of great assistance as they form a jelly which re-
tards movement without injury to the animal. Cells or hollow

332 FRESH-WATER BIOLOGY

slides are convement for work with large forms. Anesthesia may
be induced by the use of a solution of one-tenth of one per cent
of chloretone, or even less with some species. For preservation
hot corrosive subhmate may be used, or a cold solution of the
subHmate to which five per cent of glacial acetic acid has been
added. Lang's fluid, Chichkoff' s mixture, and 30% HNO3 fol-
lowed after one minute with 70% alcohol, are all useful kilhng
reagents. Formol is useful for preservation of external characters
since the animals retain their shape and color in it better than
in most reagents. The larger planarians are especially valuable
for study in laboratories where attention is given to animal be-
havior. Certain forms also afford excellent training in exactness
of observation.

The lack of well defined and unvarying external characteristics
makes it difficult to identify many Turbellaria. A large part of
the material ordinarily collected is sexually immature whereas, as
has been noted above, a knowledge of the structure of the sex
organs is necessary in certain genera for identification. Preserved
material if immature is especially difficult to identify since the
body becomes distorted in shape and the color is usually so
modified as to be unrehable. The differences in color and form
between several of the species of planarians while definite are
so sHght as to be apparent only after a comparison of Hving
material. In other cases there is a wide variation in color be-
tween individuals of the same species.

Until comparatively recently descriptions of many species of
Turbellaria were extremely meager. The confusion which has
arisen as a result is due to the lack of conspicuous external char-
acteristics which would serve for identification.

THE FREE-LIVING FLATVVORMS (TURBELLARIA)

333

KEY TO NORTH AMERICAN FRESH-WATER TURBELLARIA

Including the Land Planarians

I (78) Intestine a single blind tube, median in position.

Order Rhabdocoelida . . 2

The intestine consists of a simple rod-shaped or sac cavity which rarely has lateral diverticula
and never is divided into two distinct post-pharyngeal branches. Mostly small forms, never
more than a few millimeters in length. The following figures (Figs. 589 and 590) facilitate a
comparison of structure in the two great orders, Rhabdocoelida and Tricladida (p. 354).

Fig. 589. Structure of a Rhabdocoel.
Dalyellia rossi. Compressed, ad, atrial
glands; be, bursa copulatrix; bst, duct lead-
ing from bursa copulatrix; ch, chitinous
part of the male copulatory organ; da, in-
testine; dg, duct of yolk gland; ge, ovary;
go, genital pore; mgc, male genital canal;
mph, retractor muscles of pharynx; ph,
pharynx; pp, cirrus; pr, reddish reticu-
lar pigment; pz, yellow pigment cell; r?,
receptaculum seminis; sph, sphinctor
muscle of the uterus; (e, testes; vd. vas de-
ferens; vs, seminal vesicle; vi, yolk gland; z,
esophageal cells; e, eye; u, uterus. X
50. (After von Graff.)

Fig. 590. Structure of a Triclad.

Diagram of a Planarian. ag,
genital atrium; aw. eye; com, cross
commissures of nervous system;
d', anterior, and d", posterior
branches of intestines; do, yolk
gland; ex. excretory canal; cxp, ex-
cretory pore; gl, brain; gp, genital
pore; In, longitudinal nerve; m,
mouth; od, oviduct; od', common
oviduct; ov, ovary; p, cirrus; pit,
pharynx; pht, phar>-ngeal pocket;
te, testes; ut, uterus; utd, uterine
duct; vd, vas deferens. (After
Bohmig.)

2 (77) Pharynx simple, cask-shaped or rosctte-shapcd. Connective tissue of
body cavity poorly developed.

Suborder Rhabdocoela . . 3

The mesenchyma often consists of but a few strands of connective tissue and contains large
spaces filled with a perivisceral fluid.

3 (30) Reproductive organs simple.

Female organs consist of ovary only.
Section Hysterophora . .

These forms possess no accessory female organs, i.e., no separate yolk glands, uterus, female
copulatory apparatus, etc. Asexual reproduction among rhabdocoels is found only in this
section of the order.

334

FRESH-WATER BIOLOGY

4 (27) Pharynx simple 5

5 (20) Protonephridia with one principal branch, median dorsal in position.

Family Catenulidae . . 6

Without eyes but with ciHated pits, non-pigmented light-refracting organs, and in one genus
a statocyst. The mouth lies on the ventral side of the anterior end. The pharynx opens into
the anterior end of the intestine. Asexual reproduction by budding, thus forming chains of
zooids, known for most species. Testes in front of ovary. Both testes and ovary may consist
of one or more lobes.

6 (7) With one statocyst and pre-oval circular groove Catenula.

But one species supposed to occur in America.

Catenula lemnae (Anton Duges) 1832.

Length of single specimen i mm. Rarely 2 to 4 or
8 zooids in a chain. Delicate, white thread-like. Head
region set off by a circular groove lined with long cilia.
Intestine short and not continuous through chain of
zooids.

Graflf regards the European species C. lemnae as prob-
ably identical with the species which was collected in
the vicinity of Philadelphia and very incompletely de-
scribed by Leidy under the name Anortha gracilis.
Until further collections of the Philadelphia form have
been made this must of necessity be a matter open to
question, and C. lemnae be admitted to the Hst of Ameri-
can species tentatively.

Fig. sqi . Catenula lemnae. {A ) anterior end : J, brain; eg, cili-
ated groove; w, mouth; s/, statocyst. X 75. (After von Graff.)
{B) Chain of two zooids. X 30. (After Mrazek.)

7 (6) Without statocyst or pre-oral circular groove. With ciliated pits. . 8

8(19) Ciliated pits well developed. Without proboscis. Stenostomum . . 9

9 (18) Head region not at all or only slightly set off from rest of body. . 10

10 (17) Integument colorless ii

11(14) Wall of digestive tract free from pigment. ... 12

THE FREE-LIVING FLATWORMS (TURBELLARIA) 335

12 (13) Anterior end bluntly pointed, ciliated pits about as far from end of
body as width of body at that point. Posterior end taper-
ing uniformly to a blunt point.

Stenostomum leucops (Anton Duges) 1828.

Length of single individuals 0.5 to 1.5 mm. .Asex-
ual reproduction by budding 2 to 4 zooids common,
rarely 9 zooids. Intestine continuous through zooids.
Rhabdites small, numerous. Two patelliform organs
which consist of numerous spherical bodies. Male
sexual organs mature in August, female in September.
At this time the animal becomes large, sluggish, and
somewhat reddish-brown in color. The six-lobed
ovary lies under the intestine. The oval-shaped
testes which consist of many closely compacted lobes,
lie above the pharynx and open into the seminal
vesicle which leads through a short canal to the
opening on the dorsal surface. Abundant on plants
in quiet water such as small lakes or ponds. Mass .
N. Y., 111., Mich., Neb.

WV

Op

Fig. 592. Stenostomum leucops. (A) dorsal view of anterior end: b, brain; m, mouth; k, protonephrid-
lum; phd, pharyngeal glands; do, patelliform organ; cp, ciliated pit. X 200. (5) Entire worm, cp,
ciliated pit; c, cilia; b, brain; m, mouth; ph, pharynx; in, intestine; wv, protonephridium; op, external
pore of protonephridium. X 100. (After Ott.)

13 (12) Anterior end very bluntly rounded with ciliated pits very near the end.
Posterior end of body narrow and forming a long slender tail,
somewhat spatulate in shape, except where division has
recently taken place, in which case the tail is shorter and
more pointed. . . . Stenostomum spcciosum Stringer 19 13.
Length 2.25 mm. A large rhabdocoel which moves rather slowly and very gracefully. The
ciliated pits are placed close to the blunt anterior end, much farther forward than in S. leucops,
also are deeper and narrower than in the latter form. The mouth is about as far from the an-
terior end as the diameter of the body at that point, and is surrounded by glands. The pharjnx
has delicate longitudinal striations. The intestine shows many large highly refractive color-
less bodies, probably fat globules. Nothing definite can be said of the light-refracting organs
which were difficult to identify because of the unusual size of the animal. .\ few specimens
collected from pond with S. leucops. Lincoln, Neb.

Fig. 593. Stenostomum speciosum. cp. ciliated pit; 6, brain; ph. pharjnx; m, mouth with surrounding
glands; e. egg. X 45- (Original )

14(11) Wall of digestive tract pigmented 15

33^

FRESH- WATER BIOLOGY

15 (16) Pharynx yellowish-brown. Intestine except gland cells bright yellow.

Stenostomum tenuicauda von Graff 191 1.

Length in cliain«; of 4 zooids 1.5 mm. Slender. Posterior end tapering
to a slender tail (i to ^^ of entire length). Point of tail set with adhesive
cells. Integument colorless and contains masses of small rhabdites measuring
up to 4JM. in length. Excretorj^ pore nearer to intestine than end of body.
Two pateUiform organs 12 m across and composed of loosely joined spherical
bodies. Rochester and Cold Spring Harbor, Long Island, N. Y.

-ep

Fig. 594. Stenostomum tenuicauda. An undivided chain of four zooids: rh, rhabdites;
ig, intestinal glands; ep, excretory pore; ph I, II, pharynx. X 4°- (After von Graff.)

1 6 (15) Intestine yellowish-green between the round glistening oil drops.

Stenostomum agile (Silliman) 1885.

Length of single individual 0.75 mm. Chains of two zooids measure i .5 mm.,
those of five, 4 mm. Light-refracting organs lens-shaped. Rhabdites small.
Posterior end bears adhesive cells. Pharynx long and provided with glands
throughout its entire length. Sexual organs similar to 5. leucops. Monroe
Co., N. Y.

Fig. 595. Stenostomum agile. {A) Anterior end extended; wgr, ciliated pit; lo, lens-
shaped organ; f5c/i, protonephridium; jj/i, pharynx; rfa, intestine; g, brain. X 65. (5)
Lens-shaped organ. X 125. (After von Graff.)

^H^ a

17 (10) Integument bright yellow.

Stenostomum grande (Child) 1902.

Length of chains of 4 to 6 zooids 2 to 2.2 mm. Pre-oral region, especially
the rounded beak-like portion, white. Integument bright yellow, pharynx
somewhat darker yellow, intestine deep orange-yellow. Rhabdites small,
especially numerous in anterior end.

Two patelliform organs composed of about 25 spherical bodies. Posterior
portion of nearly cyhndrical muscular pharynx sometimes shows folds as a
result of contraction. Intestine slightly lobed. Rochester, N. Y. Brackish
water, Falmouth, Mass.

Fig. 596. Stenostomum grande. {A) Anterior end: wgr, ciliated pit; so, patelliform
organ; ph. pharynx; da, intestine. (5) posterior end: ed, excretory pore. X 55- (After
von Graff.)

THE FREE-LIVING FLATWORMS (TURBELLARIA) 337

'enostomiim coluber Leydig 1854.

18 (9) Head region distinct from rest of body

Length 6 mm. Width about one-thirtieth the length. Very
slender, white thread-like with snake-like movements. Head region
broader than the rest of the body with blunt point at anterior end.
Posterior end abruptly rounded. Asexual reproduction not known.
Brackish water, Falmouth, Mass.

Fig. 597. Stenostomum coluber. Anterior end: wj, mouth; ^ pharynx- in
intestine; ov, egg (?); ns, protonephridium. X 20. (After Leydig.) '

A club-shaped proboscis is present.

RhyncJwscolex.
Rhynchoscolex simplex Leidy 185 1.

- (8) Ciliated pits shallow.

Only one species.

Length 4 to 7 mm. Color yellowish-white opaque. Anteriorly abruptly attenuated into a
long cylindrical clavate proboscis; anterior end abruptly narrowed, obtusely rounded Pro-
boscis shows longitudinal and numerous transverse marks. Mouth ventral, at the base of the
proboscis. Intestine straight and capacious. A small wriggling worm found among yellowish
fragments of vegetable matter and confervae at the bottom of clear brooks in the vicinity of
Philadelphia.

Von Grafif regards the European species R. vejdovski Sekera 1888 as probably identical with
this American form.

20 (5) With two lateral branches of the protonephridium.

Family Microstomidae . . 21

Mouth a longitudinal sUt on ventral surface, intestine occasionally with side lobes. Proto-

nephridial branches open in anterior end. Testes and ovary either paired or unpaired, with two

ventral sexual pores, the male posterior to the female. With or without eyes and ciliated pits.

21 (24) The intestine extends dorsally and anteriorly beyond the junction

with the pharynx Subfamily AIicrostominak.

Only one genus Microstomum . . 22

22 (23) With two reddish-yellow pigmented eye spots.

Microstonmm lineare (Miiller) 1773.

Length of single individuals 1.8 mm. In chains
up to 18 zooids with a length of 9 to 11 mm.
Slender. Very active. Color yellowish to grayish-
brown, rarely rose-colored, with the intestine
always darker than the body. Pre-oral portion of
intestine short. Two small ciliated pits. Nettle
cells or nematocysts in place of rhabdites.
Male sexual organs with {xiired testes; slender
chitinous spicule of copulatorj* organ with curved
Doint. Ovary unpaired and median in position.
Hi fresh and brackish water. Monroe Co. and
Ontario Beach, N. V.; West Twin Lake and
Round Lake, Mich.

Fig. 598. Microstomum lineare. M ) anterior jxirtion
of a chain: e, eyes; r/>, ciliated pit; ai. pre-<>r.il por-
tion of intestine; m, mouth; oe, esophagus. X lo.
(After von Grafl.) (B) Chitinous portion of cirrus.
Much enlarged, (.^fter SchuJlze.)

338 FRESH-WATER BIOLOGY

23 (22) Without eyes Microstomum candatum Leidy.

^p-'-t-M^--^/?

Length 1.5 to 3 mm. Commonly in chains of 2 to 8 zooids.
Nematocysts in place of rhabdites. Color of integument white, in-
testine yellow. Ciliated pits directly dorsal to mouth. Pre-oral
portion of intestine short. Anterior end bluntly rounded. Poste-
rior end narrower, bluntly pointed, tail-like, elevated. In standing
water and small brooks, Monroe Co., N. Y.; near Philadelphia, and
in West Twin Lake, Charlevoix, Mich.

Fig. 599. Microstomum caudatum. b, brain; ph, pharynx; cp, ciliated
pit. (After Silliman.)

24 (21) Pharynx opens into anterior end of the intestine, which has short

lateral diverticula Subfamily Macrostominae.

Only one genus Macrostommn . . 25

25 (26) Chitinous portion of copula tory organ a broad straight funnel with

the slender point bent at a right angle or nearly so and
bearing on its convex side the small opening. Vesicula
seminahs and vesicula granulorum connected by a narrow
tube. . Macrostomum appendiculatum (O. Fabricius) 1826.

This is the form known as M. hystrix Oersted
1843. Length 2 mm. Unpigmented, transparent.
Body flattened especially at the ends. The spatulate
posterior end set with adhesive papillae. Rhabdoids
and long sensory hairs conspicuous. Two eyes,
black. Protonephridial tubes open on median dorsal
side back of the slit-like mouth. Testes and ovary
both paired. Asexual reproduction not known. In
running and standing water. Monroe Co., N. Y.; Lin-
coln, Neb.

Fig. 600. Macrostomum appendiculatum. (A) Entire
worm: b, brain; e, eye; ph, pharynx; di, diverticulum of
intestine; i, intestine; ie, testes; vd, vas deferens; vg,
ductus seminalis; vs, seminal vesicle; vg, vesicula granu-
lorum; ch, chitinous spicule of cirrus; $ and 9 < ™^^^
and female genital pores; on, ovary. X 35- (After von Graff.)
(B) Chitinous spicule enlarged. X 3So. (After Luther.)

THE FREE-LIVING FLATWORMS (TURBELLARIA)

3 39

26 (25) Chitinous spicule of cirrus a straight narrow tube tapering to a
somewhat variably curved point. Vesicula seminalis and
vesicula granulorum separated by a short constriction.

Macrostomum sensitivum (Silliman) 1885.

Length 1.5 mm. Color grayish-
white. Intestine yellowish. Broad-
est through middle. Posterior end
narrowed. Rhabdites present in in-
tegument in large numbers, either
singly or in twos and threes. Rhab-
dite tracts conspicuous in anterior
end. Intestine with lateral diver-
ticula. Protonephridium communi-
cates through a pore with mouth
cavity. Chitinous organ somewhat
variable. Monroe Co., N. Y.; brack-
ish water, Falmouth, Mass.

Fig. 601. Macrostomum sensitivum. {A) Anterior end: 6,
brain; e, eye with lens; k, protonephridium which opens
through the pore {p) into the mouth cavity; sh, sensory
hairs. X 150. (After Silliman) (B) Male copuiatory organ
subjected to pressure. (C) Male copulatory organ not under
pressure: w, vesicula seminalis; ig, vesicula granulorum; ch,
chitinous point. Much enlarged. (B, C, after von GraflF.)

27 (4) With a long cylindrical bulbous pharynx. . Family Prorhynchidae.

The pharynx is remarkably large. The mouth is in the anterior end. Testes with numerous
follicles. Ovary not paired. Two sexual pores, the female pore on the ventral side. The male
sexual organs open near the mouth or unite with it.

Only one genus Prorhynchus M. Schultze

28

28 (29) Without eyes.

Prorhynchus stagnalis M. Schultze 185 1.

Length to 6 mm., commonly much smaUer. White, thread-like. Two cili-
ated pits. With numerous pear-shaped glands in the mtegument. 1 haryn.x
about I of total length of body. Protonephridium with four prmcipal branches,
two dorsal and two ventral. Chitinous portion of cirrus straight and stiletto-
shaped. Monroe Co., N. Y.; brackish water, Falmouth, Mass.

Fig. 6c2. Prorhynchus stagnalis. ch, chitinous stUetto; p6 bulb-like cirrus; vs. -^mi-
nal vesicle; ds, ductus seminalis; t, testis follicle; otx;mng of male sexual organ> into
pharyngeal pocket; oi», ovary; e, mature egg. X i5- t.\Uer von uraa.j

-ov

340

FRESH-WATER BIOLOGY

29 (28) With two very small eyes, yellowish by transmitted light, whitish by
reflected light, lying just before the brain in the widest re-
gion of the pharynx. . Prorhynchus applanatus Kennel 1888.

Length 4 mm. White. Body
much flattened at both ends.
Pharynx very muscular. In-
testine a slender straight tube
with one diverticulum extend-
ing anteriorly under the phar-
ynx and numerous slender very
closely set lateral diverticula.
Greenhouse, University of Ne-
braska, Lincoln, Neb.

Fig. 603. Prorhynchus applanatus . From life. X 20. (After Kennel.)

30 (3) Female sexual organs divided into ovary and yolk glands. Male sex
organs complex Section Lecithophora . . 31

Ovary in general small and simple. Yolk glands extremely variable, elongated, lobed, or
forming a network which anastomoses. Chitinous portion of male copulatory organ very
complicated and variable in form.

31 (74) Proboscis either lacking entirely or if present without a definite
sheath Subsection Liporhynchia . . 32

This division contains the greater part of the fresh-water Turbellaria.

32 (61) With a cask-shaped pharynx parallel to the ventral surface or slightly
inclined and with the end directed forward. But one genital
pore Family Dalyellidae . . 2>2>

With the exception of the genus Opistomum, which is not represented in this country, the
pharynx is typically cask-shaped and opens into the anterior end of the intestine. The genital
pore opens on the ventral surface posterior to the mouth. Ovary simple. Yolk glands variable,
female receptaculum seminis and a simple uterus are present. Testes always paired. Chitinous
portion of male copulatory organ often very complex. Pigment eyes usually present, but
without other sense organs. Protonephridium consists of two principal branches which open
on the ventral surface. Rhabdoids and glands of integument prominent.

33 (60) Without a separate pocket for the chitinous part of the cirrus. . 34

34 (59) Sexual pore in posterior third of body. The paired yolk glands un-
branched and separate. . Dalyellia Fleming 1822 . . 35

This is the one commonly known as Vortex Ehrenberg 183 1.

THE FREE-LIVING FLATWORMS (TUR BELL ARIA)

341

35 (36) The chitinous portion of the male copulatory organ is represented
merely by the chitinous tube of the ductus ejaculatorius.

Daly cilia incrmis von Graff 191 1.

Length 0.6 mm. Flattened. Posterior end
modified into a kind of adhesive disk. Color
white by reflected light. Intestine very
broad and yellow in color. Eyes dul^ yellow.
Accessory pigment spots irregularly groui)ed
near the eyes. The locomotor movements
are very quick. Rochester, N. Y.

Fig. 604. Dalyellia inermis. (/I) Ventral view,
slightly compressed: e, eye; m, mouth; vi, yolk
gland; ov, ovary; go, genital pore; co. male
copulatory organ; le, testes. X 115. (B) .Ad-
hesive disk of posterior end. (C) Male copula-
tory organ enlarged: c/i, chitinous tube; ks, vesi-
cula granulorum; vs vesicula seminalis. X 300.
(After von Graff.)

36 (35) Provided with true chitinous organ 37

37 (38) Chitinous portion of cirrus consists of a single chitinous spine.

Dalyellia rochesteriana von Graff 191 1.

Scarcely i mm. long. Closely resembles Z). rheesi. Colorless, transparent
with very small dermal rhabdites. Brownish mesenchymatous pigment not
so abundant as in D. rheesi. Intestine reddish-ocher-yellow. Sexual ix>re
lies just posterior to the intestine in the beginning of the last third of the
body. Rochester, N. Y.

Fig. 605. Dalyellia rochesteriana. Male copulatory organ enlarged: ch, chitinous
spine; vs, vesicula seminalis; ks, vesicula granulorum. (After von Graff.)

38 (37) Chitinous portion of cirrus consists of more than one piece. .

30

39 (44) Chitinous portion of cirrus consists of a number of transverse spines
arranged in a row 4°

342

FRESH-WATER BIOLOGY

40 (41) Spines of unequal size and shape set in a basal piece.

Dalyellia dodgei von Graff 191 1.

Length rarely more than i mm Integument colorless. Intestine greenish from contained
algae. Mesenchyma mottled with sepia-brown pigment. Eyes black. Found very commonly.
Rochester, N. Y.

Fig. 606. Dalyellia dodgei. (.1) Ventral view slightly compressed. X 65. (B) Male copulatory organ
strongly compressed. Explanation of figures: be, bursa copulatrix; cli. chitmous organ; cp. adhesive
papillae; i intestine; e, egg; 6, brain; ois ovary; go genital pore; g/», graspmg papillae of pharynx; vg,
vesicula granulorum; vi, mouth; mgc, male genital canal; ph, phary^nx; pe, cirrus: pi, mesenchyma pig-
ment; rs, receptaculum seminalis; sp, sperm masses; te, testes; vi, yolk gland, vs, vesicula seminalis. Much
enlarged. (After von Graff.)

41 (40) Spines of same size and shape, arranged loosely in a ring without a

basal piece 42

42 (43) With a crown of about 16 spines, tapering from base to the point.

Dalyellia eastmani von Graff 191 1.

Length 0.3 to 0.5 mm. Color of me-
senchymatous fluid pale yellow with
spherical bodies which contain cinnamon-
brown granules in a clear brown fluid.
Rhabdites short and relatively thick and
rounded at both ends. Rochester, N. Y.

Fig. 607. Dalyellia eastmani. {A) Ventral
view uncompressed. X loo. (B) Malecopula-
tory apparatus. X 600. Explanation of figures:
he, bursa copulatrix; be,, blind sack of burs.i;
be,,, opening of blind sac; e, egg; g, brain; m,
mouth; ge, ovary; go, genital pore; rs, recepta-
culum seminis; vs, vesicula seminalis; te, testes;
vi, yolk gland; ag, common atrium; 0, opening
of the male copulatory organs into genital canal;
vg, vesicula granulorum; sp, sperm mass; eh,
chitinous crown of spines; da, intestine; pit,
pharynx; sb, granules of secretion. (After von
Graff.)

THE FREE-LIVING FLATWORMS (TURBELLARIA) 343

43 (42) With a crown of 8 spines, thickened near the middle and tapering
to fine points at both ends.

Dalyellia blodgetti (Silliman) 1885.

OV

Length 0.6 mm. Color light brown.
A number of sensory hairs on anterior
end. Basal piece of the tube which
encloses the spines is not chitinous but
membranous and placed in the male
genital canal which opens into the
atrium. Erie canal, Rochester, and
Monroe Co., N. Y.

_ Fig. 608. Dalyellia blodgetti. {A ) En-
tire: b, brain; vi, yolk gland; g, cirrus; e,
eye; ov, ovary; be, bursa copulatrix; ph
pharynx; s, salivary gland. X 90 (After
billiman.) {B) Crown of spines from chitin-
ous portion of male copulatory organ with
opening {0) into the genital canal. From
a strongly compressed preparation. Very
much enlarged. (After von Graff.)

A B

U (39) Chitinous portion of cirrus bears two longitudinally placed stalks
on one end of which either one or two longitudinal terminal
branches are set. The terminal branches may be set with
spines 4-

45 (46) Each chitinous stalk bears two terminal branches, one set with
spines and one with no spines.

ds Dalyellia fairchildi von Graff 1 9 1 1 .

eae'

Similar in size and color to D. rheesi but more
slender, with a longer tail and the uterus lies pos-
terior to the sexual pore. The egg is round to oval
in shape and measures loS to 140 /i. Yolk glands
open as in D. rheesi through a common yolk duct
but are not lobed, barely notched.

Fig. 609. Dalyellia fairchildi. (.4) Male copulatory
apparatus. X 430. (fi) Chitinous piece enlarged. X
850. ds, ductus seminaiis; eae, outer branch with spines
folded; eai, inner branch with no spines; mv, median
projection; pd, opening of cirrus sheath; pp, cirrus pa-
pillae; .v, double row of spines; st, stalk; vg, vesicula gran-
ulorum; vs, vesicula seminaiis; q, transverse bar; qs,
transverse spines. (After von Graff.)

344

FRESH-WATER BIOLOGY

46 (45) Each chitinous stalk bears a single terminal branch set with
spines 47

47 (so) The spines on the terminal branch are jointed 48

(49) Each spine consists of three joints. Stalk long, somewhat variable
in shape Dalyellia rheesi von Graff 191 1.

Length i mm. When swim-
ming freely the anterior end is
broadly rounded, in crawling,
truncated as shown in figure.
Integument colorless with nu-
m e r o u s delicate rhabdites.
Mesenchyma colored by sepia-
brown to cinnamon-red gran-
ules in a clear yellow fluid. In
the living animal the brain
region appears clear white and
the ventral surface lighter in
color than the dorsal, eyes
black. In pools along Erie
canal.

Fig. 610. Dalyellia rheesi. {A)
slightly compressed: te, testes; vi,
yolk gland; vs, vesicula seminalis;
ch, chitinous portion of cirrus; dg,
duct of yolk gland; be, bursa copu-
latrix; go, genital pore; e, egg; ov,
ovary. X 60. {B) Male copula-
tor>' apparatus: pr, cirrus tube;
meg, male genital canal; 0, open-
ing of genital canal into common
atrium; st, short stalk of chitinous
piece. X 600. (C) Median ventral
grooved piece (mv) turned back;
si, variation in stalk. X600. (After |
von Graff.)

THE FREE-LIVING FLATWORMS (TURBELLARIA)

345

49 (48) Each spine consists of two joints. Stalk much reduced and variable
in shape Dalyellia articidata von Grafi igii.

Similar to D. rheesi in color and general structure. Sexual organs differ as shown by a com-
parison of Figs. 610 and 611. Same localities as D. rheesi.

St

Fig. 611. Dalyellia articulata. [A) Posterior end with sex organs from a strongly compressed specimen:
be, bursa copulatrix; ch, chitinous part of male organs; ge, ovary; gii, genital pore; rs, receptaculura
seminis; «, uterus with egg; vii yolk gland; vs, vesicula seminalis. {B) Chitinous organ with the reduced
stalk (5/). (C) Chitinous portion of cirrus showing variation from (5). Much enlarged. (After von Graff.)

50 (47) The reduced spines on the terminal branch are unjointed and consist

of but one piece 51

51 (52) The dorsal transverse bar bears a row of fine spines.

Dalyellia mohicana von Graff 191 1.

Free swimming, of extremely slender form, similar to D.
rossi. Anterior end of the chitinous portion of cirrus not
sharply defined. Differs from D. rossi chiefly in structure
of the chitinous organ, the stalk of which is not so broad
or flat as in that form. One terminal branch of this organ
bears eleven curved teeth, the other seven of the same
type and one which is larger and three sided. The trans-
verse bar bears a row of straight, sharply pointed spines.
Brackish water, Falmouth, Mass.

Fig. 612. Dalyellia mohicana. (/I) The animal swimmmg.
X 60. (B) Chitinous part of cirrus. Much enlarged, ca, end
branch with a row of spines; si, stalk; qd, dorsal transverse
connecting bar, with a row of spines, as; qv, ventral transverse
bar; mv, median projecting piece. (After von Graff.)

346

FRESH-WATER BIOLOGY

52 (48) The dorsal transverse piece between the longitudinal stalks has a
single median chitinous spine 53

53 (54) The median point is rudimentary; much shorter than the terminal
branches Dalyellia viridis (G. Shaw) 1791.

Length 5 mm. Unpigmented except during the maturing of the eggs
when there is a brownish pigment, but with a continuous layer of zoo-
chlorellae under the integument giving the characteristic green color.
Rochester, N. Y.

Fig. 613. Dalyellia viridis. Chitinous portion of cirrus: si, two-parted stalk;
ea, terminal branch. Much enlarged. (After von Graff.)

54 (53) The median point is as long as the terminal branches 55

55 (56) One terminal branch is not jointed but consists of a single piece
shaped Uke a plow-share, and does not have spines.

Dalyellia armigera (O. Schmidt) 1861.

I

Length 0.6 to 1.5 mm. Color yellowish, reddish, or
brownish-gray. Pharj^nx very large, almost one-fourth
of entire length of body. Anterior end blunt, tail with
adhesive papillae. Swims actively at the surface of stand-
ing and running water. Brooks, Monroe Co., N, Y.;
Lake St. Clair, Mich.

Fig. 614. Dalyellia armigera. ^ (A ) living, uncompressed. X 5°-
(B) chitinous portion of cirrus' m, median point; ea, terminal
branch with 3 to g (mostly 7 or 8) spines; ea2. terminal branch
shaped like a plow-share; g, dorsal and ventral cross pieces;
St, stalk. X 500. (After von Graff.)

56 (55) Both terminal branches bear a row of plates or spines.

57'

THE FREE-LIVING FLATVVORiMS (TURBELLARIA)

347

57 (58) Terminal spine of only one cerminal branch unlike the others in
shape Daly ellia rossi von Grsiii igi I.

Length a little over i mm. Similar in form to D. rheesi. Color of
mesenchyma bright or dark reddish-yellow to cinnamon-brown. Eyes
brown or black. Intestine brownish-yellow. Adhesive cells on short
tail. Common at Rochester, N. Y. In brackish water, Falmouth, Mass.
See Fig. 589 for view of entire animal.

Fig. 615. Dalyellia rossi. Chitinous part of male copulatory organs, st, chitin-
ous stalk; eai and ea2, terminal branches with spines; mv and md, median ventral and
dorsal projections. X 285. (After von Graff.)

58 (57) Terminal spines on both terminal branches unlike the others in shape.

Dalyellia sillimani von Graff 191 1.

Length i mm. Integument colorless with small rhabdites. In heavily pigmented speci-
mens the mesenchyma appears dark brown; those with less pigment show cells hlled with yellow
fluid and containing brown pigment granules. Intestine ocher-yellow. Eyes black. Roches-
ter, N. Y., in brooks and pools.

Fig. 616. Dalyellia sillimani. (A) slightly compressed: bs, bursa seminalis; e, egg; ov, ovar>'; go.
sexual pore; vs, vesicula seminalis. X 70. (B) Male copulatory organ: ea, and eaj, terminal branches of
chitinous organ; kdr, granular glands of one side; ks, granular secretion; nui, median dorsal chitinous
point; mp, retractor muscles; mv, median ventral grooved chitinous piece; />", cirrus opening; vd, vas de-
ferens; vs, vesicula seminalis; Sy last chitinous plate of right terminal branch; sp, last chitinous plate of
left terminal branch; st, stalk. X 330. (After von Graff.)

348

FRESH-WATER BIOLOGY

59 (34) Sexual pore anterior to the middle of the body. Yolk glands branched
and either separate or united to form a network.

Phaenocora Ehrenberg 1836.
This is the genus formerly known as Derostomum Oersted 1843.

Only one species known in this country.

Phaenocora agassizi von Graff 191 1.

Length i to 2 mm. Milk-white. Intestine
greenish-yellow. Eyes reddish-yellow. Between
the eyes and the pharynx or extending over the an-
terior end of it there is a zone of so-called crystal-
loids which appear clear or grayish-brown in
transmitted light. This species is an exception for
the genus in that it possesses rhabdites. Pharynx
cask-shaped, intestine more or less deeply lobed.
In pool, Rochester, N. Y.

Fig. 617. Phaenocora agassizi. (^) slightly compressed:
te, testes; da. intestine; ph, pharyn.x. X 22. (B) An-
terior part, enlarged: ^r, crj'stalloids; 6c, bursa copulatrix;
mm, muscles of bursa; de-^, proximal, and den, distal part
of ductus ejaculatorius; dg, duct of yolk gland; ge, ovary;
go, genital pore; rs, receptaculum seminis; au, eye. X 70.
(After von Graff.)

60 (33) With a separate pocket for the chitinous portion of male copulatory
organ. Sexual pore lies in last third of body . . Jensenia.
Only one species known in this country.

Jensenia pinguis (Silliman) 1885.

Length about 1.5 mm. Color
brown to reddish, darkest in middle
of body. Male genital canal divided
at its connection with the common
atrium, one branch forming the
pocket for the chitinous organ while
the other leads to the seminal ves-
icle. Rochester, N. Y.

Fig. 618. Jensenia pinguis. {A) Entire: m, mouth; vi, yolk glands; /, testes;
e, eye; ph, pharynx; s, glands; i, intestine. X 30. (After Silliman.) {B) Sexual
organs from animal compressed from side: hs, bursa seminalis; bsm, retractor mus-
cles of same; ch, pocket which contains chitinous organ; chm, one of four muscles
for same; e, egg; gd, oviduct; ge, ovar>'; go, genital pore; sd, shell glands; te, testes;
udi, uterus diverticulum of atrium; list, duct of uterus; vd, vasa deferentia; lis, vesi-
cula seminalis; vst, duct from same; wgc, female genital canal. X 60. (After von
Graff.)

61 (32) Pharynx rosette-shaped, standing perpendicular to the ventral
surface Family Typhloplanidae . . 62

The genital pore Hes back of the mouth. Ovary one, testes paired. Other parts of sexual
organs variable. Protonephridium with two main branches which may have either one or two
openings on the ventral surface or may lead to the surface through the mouth or sexual pore.
Eyes, non -pigmented light-refracting organs; cihated pits may be present. Rhabdoids play
an important part in classification. Both summer and winter eggs produced in some species.

THE FREE-LIVING FLATWORMS (TURBELLARIA)

349

62 (63) Genital pore in posterior third of body.

Tribe Olisthanellini

Excretory system opens on ^dorsal surface with one asymmetrical or two symmetrically
placed openings. Testes dorsal to the yolk glands. Without atrial copulatory organ.

Single genus thus far reported in America Olisthatiella.

Only one species in this country. . Olisthanella caeca (Silliman) 1885.

Length 1.3 mm. Without eyes. Without long sensory hairs. Color
grayish-white. Sometimes apparently colored, due to food in intes-
tine. Pharynx rosette-shaped and nearly central in position. Intes-
tine large. Rhabdites and tracts prominent. Female organs only are
known. Sluggish and found only in mud under stones. Monroe Co.,
N. Y.

Fig. 619. Olisthanella caeca, ph, pharynx; t, intestine; b, brain; vi, yolk
pland; oz), ovary; ^o, genital pore; /j, rhabdite tracts. X 35. (After Sillinaan.)

63 (62) Genital pore in anterior two-thirds 64

64 (71) Testes ventral to the yolk glands. Rhabdites only in mesenchyma
tracts Tribe Typhloplanini . . 65

Protonephridia with two main branches which communicate with the exterior through a
transverse branch which leads either to the mouth or to the genital atrium. With or without
atrial copulatory organs.

65 (66) Anterior end of body a retractile proboscis. . . Rhynchomesostoma.
Only one species. . . . Rhynchomesostoma rostratum, (Miiller) 1773.

Length 2 mm. European specimens
reach a length of 5 mm. when extended.
Very transparent. Body t1uid rose or
yellowish-red in color. Intestine contains
yellowish-red oil droplets. \'cntral surface

flat, dorsal convex. Anterior end of body like a telescopic tube.

Pharynx small, lying somewhat before the middle of the body.

Rochester, N. Y.

Fig. 620. Rhynchomesostoma rpstratum. {A) Proboscis partly extended.
(5) Fully contracted. X 40- (After von Graff.)

66 (65) Anterior end of body without retractile proboscis 67

67 (70) Without atrial copulatory apparatus 68

3 so

FRESH-WATER BIOLOGY

68 (69) With a separate receptaculum seminis, whose short duct is closed by a
muscular ring. Dermal rh^-bdites present. . . Strongylostoma.

Only one species known in this country.

Strongylostoma gonocephalum (Silliman) 1885.

Length 1.2 mm. Mesenchyma yellowish, intestine
with yellowish oil droplets. Eyes carmine red. Small
rhabdites are present. This form differs from the
widely distributed European form, Strongylostoma
radiatum Miiller chiefly in the possession of two
shallow oval pits which lie close behind the eyes at
the side. The integument is slightly raised around
them and each bears vacuoles and rhabdoids.
Excretory pore opens into mouth. Erie Canal,
Monroe Co., N. Y.

Fig. 621. Strongylostoma gonocephalum. [A) Entire

animal: tr, tracts of rhabdites; ph, pharynx; ov, ovary;

bs, bursa seminalis; vi, yolk glands; p, cirrus; go, genital

pore; ec, egg capsule. X 40. (After Silliman.) (B) Out- line of anterior

end with eye (ou) and shallow pit (g/) of one side. Enlarged. (After von

Graff.)

69 (68) Without a separate receptaculum seminis Typhloplana.

Only one species known in this country.

Typhloplana viridata (Abildgaard) 1790.

Length 0.5 to i mm. Transparent. Zoochlorellae in the mesenchyma give
it a grass-green color. Tapering at both ends. Without eyes. Anterior
end bluntly pointed, posterior end pointed. Pharynx just anterior to
center. Sexual pore close behind pharynx. Viviparous. The summer
eggs develop within the body of the parent. Winter eggs are as many as
ten in number and yellowish-brown in color.

The pear-shaped bulbous cirrus contains a straight chitinous tube, the
ductus ejaculatorius. The male genital canal is set with small spines; the
small egg-shaped or somewhat elongated testes he near or back of the pharynx.

Luther and von Graff regard the form collected from Monroe Co., N. Y.,
and described by SiUiman under the name of Mesostoma viviparum, also
those collected from West Twin Lakes and Old Channel Round Lake,
Charlevoix, Mich., and described by Woodworth under the names M.
viviparum and M . vividatum, as identical with the European species. There
seems to be no doubt that this is the case, Typhloplana viridata was col-
kcted by von Graff at Rochester, N. Y.

Fig. 6;

Typhloplana viridata. />t, Zoochlorellae; /»A, pharynx; (5 , 9, male and
female genital pore; pe, cirrus. X 70. (After von GraS.)

THE FREE-LIVING FLATWORMS (TURBELLARIA)

351

70 (67) With atrial copulatory apparatus.

Castrada hofmanni (M. Braun) 1885.

Length 1.5 mm. Unpigmented. Colored green from zoochlo-
rellae in mesenchyma. Cylindrical. Anterior end rounded, pos-
terior end running out to a blunt point. Without eyes. Large
rhabdoids in tracts. Pharynx somewhat before the middle of
the body with genital pore shortly back of it. Testes are elon-
gated oval to pear-shaped. Yolk glands are deeply lobed. The
male copulatory organ and bursa copulatrix are entirely enclosed
by the muscular mantle of the atrium copulatorium. Rochester.
N. Y.

Fig. 623. Castrada hofmanni. Cirrus, bursa copulatrix, and atrium
copulatorium. Diagram from preparations subjected to pressure: vs,
vesicula seminalis; ks, granular secretions; sp, spermatophore; rm, cir-
cular muscles; t, teeth-like spines; ac, atrium copulatorium; de, ductus
ejaculatorius. Much enlarged. (After Luther.)

71 (64) Testes dorsal or lateral to the yolk glands. Mesenchyma with

rhabdoids outside of tracts. . Tribe Mesostomatini . . 72

Sexual pore lies in anterior two-thirds of body. Protonephridial ducts open through mouth
to exterior as in most Typhloplanini and in some cases, mouth, protonephridia, and genital
organs have a common external opening. Rhabdites play a very important part in classi-
fication. The larger rhabdocoels belong to this group.

72 (73) With a ventral epidermal pouch and a ductus spermaticus which

connects the bursa copulatrix with the female genital canal.

BothromesostofUd.
Only one species known in this country.

Bothromesostoma personatum (O. Schmidt) 1848.

Length 7 mm. Color on anterior and posterior ends and on lateral margins and ventral
side a clear brown. In mature specimens the pigment is so massed that together with the dark
color of the intestine it gives a dark brown to bluish-black color to the dorsal surface above the
intestine. Some specimens show a mixture of brown and black. The oval eyes are about as
far distant from the lateral margins as from each other. They are i>erceptible only in the
lighter pigmented specimens. The ventral epidermal pouch occurs somewhat posterior to
the eyes. The common opening for mouth, protonephridial ducts, and genital pore is located
about the middle of the ventral surface. Both summer and winter eggs are produced. The
former produce the viviparous young. Ann Arbor, Mich.

A B

Fig. 624. Bothromesostoma personatum. U) entire animal. X 5- (After Schmidt.) (B) Diagram of

sexual organs: he, bursa copulatrix; dsp, ductus spermaticus; pm, opening of cirrus; rs, receptaculum

seminis; pg, genital pore; dg, duct of yolk gland; ph, phar>'nx; no, opening of protonephridium. Much
enlarged. (After Luther.)

352

FRESH-WATER BIOLOGY

73 (72) Without a ventral epidermal pouch and ductus spermaticus.

Mesostoma.
Only one species known in America.

Mesostoma ekrenhergii (Focke) 1836.

This species attains a length of 12 to 15 mm. in Europe. Greatest length recorded for Amer-
ican specimens is 6 mm. Verj^ transparent. Color pale yellowish to brownish. Intestine
yellowish-brown. Thin, flat, and leaf-like in outline. Anterior end tapering, conical. Poste-
rior end tapering sharply and terminating in an acute caudal process. Conspicuous tracts of
rhabdites lead to the anterior end. Eyes black. Two shallow pits occur on the dorsal surface
of the anterior end, one on either side. Both summer and winter eggs are produced but
rarely at the same time. The summer eggs develop and the young embryos may be seen
within the body of the parent. From IlUnois River; Lake St. Clair, Mich.; Ohio; and Elk-
horn River, Neb.

) ^y.

B

1

Fig. 625. Mesostoma ehrenbergii. (A) Diagram from ventral side showing nervous, digestive, and
reproductive systems. Left side shows summer ©ggs, the light, winter eggs: be, bursa copulatrix; da,
anterior branch of intestine; dai, posterior branch of intestine; go, genital pore; ^, ovary; pe, cirrus;
pit, pharynx; ts, receptaculum seminis; le, testes; u, uterus; vd, vas deferens; vi, yolk gland; vs,
vesicula seminalis; wgc, female genital canal; co, subesophageal commissure of ventral nerves; din,
dorsal longitudinal nerve; dn, dorsal nerve of brain; g. brain; Inv, ventral longitudinal nerve; nr, pharyn-
geal nerve ring; us, duct of uterus; ven, ventral nerve of brain; i^d, duct of yolk gland; vtii and dm2, the
two pairs of anterior nerves of brain; x, chiasma of anterior nerves. X 6. (After von Graff, Vogt,
Fuhrmann, and Luther.) (B) From life, showing young worms in left uterus. X Q. (After Woodworth.)

74 (31) With a genuine proboscis which lies within a sheath and communi-
cates with the exterior through an opening at the anterior
end. Pharynx rosette-shaped.

Subsection Calyptorhynchia . . 75

A small group easily recognized by the genuine proboscis. A bursa copulatrix is present.
The cirrus is divided into vesicula seminalis and vesicula granulorum. The rosette-shaped
pharynx lies on the ventral surface.

THE FREE-LIVING FLATWORMS (TURBELLARIA)

353

75 (76) With a single sexual pore Family Polycystididae.

Two ovaries, two yolk glands with finger-like lobes, -and two compact testes. Bursa copu-
latrix small and without a separate external opening.

Single genus thus far found in America Polycyslis.

Only one species known in America. . Polycystis roosevclti von Graff 19 1 1 !

Length 2 mm. Anterior end of body transparent, the rest of the body faintly
reddish. A subcutaneous brown pigment between the longitudinal muscle fibers
gives a more or less striated appearance. The extremely flexible proboscis lies
withm Its sheath just in front of the brain at the anterior end. The mouth
and pharynx lie in the beginning of the second third of the body and the genital
pore lies between the second and last third of the body. Posterior end very
bluntly rounded, anterior end somewhat narrower. Closely resembles the
European species P. gaciti Bresslau except in the structure of the chitinous
portion of male copulatory organ.
Fig. 626. Polycystis roosevelli. Chitinous cirrus tube with bulb (b), ductus seminal]
(ds), and the ducts leading from the granular glands (kd). X 400. (After von Graflf.)

With two sexual pores, the male posterior to the female.

Family Gyratricidae.
One or two ovaries, with yolk glands and one compact testes which lies on the left side.

Only one genus known Gyratrix.

Single species known in America.

Gyratrix hermaphroditus Ehrcnbcrg 1831.
Length 2 mm. White in reflected light. Eyes black. Without rhabdoids or pigment.
Capable of contracting into a ball, or extending to almost double its length as long as it remains
actively swimming. Stiletto-sheath of male copulatory organ a short wide tube. The
very large bursa copulatrix has a separate dorsal opening to the exterior. Egg capsule oval.
From peat bog, Rochester, Monroe Co., N. Y.

One subspecies Gyratrix hermaphroditus hermaphroditus Ehrenberg. Stiletto-sheath with a
hook on the end. The egg capsule is gradually reduced to its stalk and is much elongated.
Rhabdoids occur in the terminal cone of the proboscis.

-po

76 (75)

Fig. 627. Gyratrix' hermaphroditus. {A) Ventral view of compressed specimen, do, dorsal opening
of; be, bursa copulatrix; ch, chitinous tube; chst, stalk of chitinous tube; chg, chitinous stiletto IcidinK
from vesicula granulorum; ec, egg capsule in uterus; ov, ovary; ,i;(/, granular secretor>' glands; ko, external
opening of kidney; ph, pharynx; rltn, attachment of the long prolx)scis retractor muscles; ec, end cone
of proboscis; rm, muscular portion of proboscis; po, external opening of proboscis sheath; If, tester;
vd, yas deferens; vg, vesicula granulorum; vi, yolk glands; vs, vesicula seminalis; cf , male and 9 . female
genital pores. X 30. (After von Graff.) (/?) Stiletto-sheath with straight tube. 0, oiK-nin^ of sliJctta
sheath; ch, chitinous stiletto of cirrus. Much enlarged. (.After Hallez.) (C) Gyratrix hermaphroditus
hermaphroditus. Stiletto -sheath with curved point. Much enlarged, (.\fter von Graff.)

354 FRESH-WATER BIOLOGY

77 (2) Pharynx either variable or cyUndrical and lying within a pharyngeal

pocket. Connective tissue well developed.

Suborder AUoeocoela.

The intestine is an irregular sac mostly with side lobes and an anterior and posterior branch
It divides to form a ring in the median ventral region, thus enclosmg the slender cyhndrical
pharynx which is similar in position and appearance to that of the plananans

No fresh-water representative of this Suborder has been definitely estabhshed for this
country. It seems clear that some must exist in this region and be found on further study ot
the American favma.

78 (i) Intestine consists of three main branches, one an anterior branch

median in position, and two running to the posterior end of
the body, one on either side of the pharyngeal region.

Order Tricladida . . 79

Mostly larger than in the preceding order. Pharynx usually median ventral in position, elon-
gated cyhndrical, and lying within a pharyngeal pocket with the free end directed posteriorly.
Compare figures of a typical Triclad (Fig. 590) and Rhabdocoel given on page 333-

79 (104) Found in fresh-water ponds or streams. . . Suborder Paludicola.

Only one family Planariidae . . 80

Body elongated, flattened, often with conspicuous cephalic appendages. Inconspicuously
colored.

80 (103) Pharynx one • °^

81 (82) With an adhesive disk on anterior end Dendrocoelum.

Only one species known in this country.

Dendrocoelum lacleum Oersted 1844.

Greatest length 22 mm., breadth 2 to 3 mm.
Color milk-white, creamy, yellowish, or in
larger older specimens sometimes roseate. No
pigment except in eye spots. Very translu-
cent. Intestine colored by contained food. A
shght constriction just behind the plane of the
eyes sets off the head and produces the rounded,
cephaUc appendages. Posterior end rounded.
Lateral margins nearly parallel when at rest
or contracted. Median adhesive disk extremely
variable. Usually about one-third of the broad-
est diameter of the head. Inconspicuous in
small specimens. It is not a true sucker but
consists of a depression into which the glands
open and with the margin somewhat raised.
Two eyes normally but from one to six accessory
eyes are common. Mass., Mich., Penn., Wis.
'■ What is probably a variety of this species is

described as a non-pigmented eyeless Dendro-
coelum collected from Mammoth Cave and ad-
joining caves in Kentucky.

^-^

va.df.

gl.sh:-::}

Fig. 628. Dendrocoelum lacleum. U) From life. X4-
(B) Sex organs, dorsal view: brs, copulatory bursa;
dt ej, ductus ejaculatorius; gl sli, shell gland; gl prst,
prostate gland; go po, genital pore; ov dt, oviduct;
pe, cirrus; ut, uterus; va df, vas deferens; vag, va-
gina. X 14. (After Woodworth.)

82 (81) Without an adhesive disk on anterior end 83

J

THE FREE-LIVING FLATWORMS (TURBELLARIA) 355

83 (102) Normal eyes two or none Planaria . . 84

84 (loi) With two normal eyes (sometimes with one or more irregularly
placed accessory eyes) 85

)5 (94) Anterior end more or less pointed with angular cephalic append-
ages 86

86 (91) Anterior end bluntly pointed, angle formed by lateral margins of
head not less than 60°. Cephalic appendages blunt. Body
about as wide just back of appendages as immediately in
front of them 87

87 (88) Angle formed by lateral margins of head much greater than 60^".
Cephalic appendages very inconspicuous, almost entirely
wanting in young specimens.

Planaria joremanii (Girard) 1852.

Length of mature specimens 7 to 15 mm., breadth
2 to 4 mm. Color nearly uniform seal-brown or dark
gray to slate-black, with an inconspicuous gray area
on each cephalic appendage. Eyes gray with a cres-
cent of black pigment on the median side. Body
comparatively thick. Ovaries two, ventral, somewhat
lobed and situated about halfway from anterior end
to phar>'nx. Testes four or five on each side, un-
paired, dorsal and irregularly distributed from region
of ovaries to posterior end of pharynx. Does not
multiply by fission. Found in small streams in
Mass., Penn., Md., Va., and near Washington, D. C.

The species described by Curtis (1900) under the
name Planaria simplicissima and later by Stevens un-
der the same name clearly must be regarded as syn-
onymous with the species establishetl by Girard in
1852 under the name P. foremannii. This species
also appears under the name P. lugubris in various
papers dealing with the physiology of planarians.

ph\

tP

Fig. 62Q. Planaria foremanii. {A) Outline sketch of large mature specimen: gp, genital pore; pk.
pharynx; 5, sensory area on cephalic appendages. X4 (.After Stevens.) (B) Sexual organs, longitu-
dinal section, dorsal view: c, cirrus; d, oviduct; ph, pharyn.x; sv, seminal vesicles; /, testes; ut, uterus;
V, ovary; vi, yolk glands; vl, vas deferens. X 20. (After Curtis.)

88 (87) Angle formed by lateral margins of head about 60°. CcphaHc ap-
pendages distinct. Anterior margin of cephalic appendages
of about same length as posterior margin 89

356

FRESH-WATER BIOLOGY

89 (90) Color blackish to purplish or brownish by reflected light, blackish
or gray by transmitted light. With many irregular spots
entirely free from pigment. . Planaria maculata Leidy 1848.

Length 15 mm. Immature specimens average about 8 to
II mm. In small specimens the pigment occurs in isolated
patches and spots. In larger specimens the pigment patches
are confluent chiefly in the median region leaving the clear
irregular areas which give a ver>' spotted appearance to the
animal. Smaller spots of deep brown or black scattered
among the larger patches. Frequently with a light median
streak. Posterior half of cephalic appendages with non-
pigmented spots. Ventral surface much lighter than dorsal,
almost entirely free from pigment. Reproduces freely by
transverse fission posterior to pharynx. Sexually mature
specimens not common in most localities. Sluggish. Much
less active than those nearly related species which might
be confused with it. Found commonly among algae and
water plants or under stones where water is comparatively
quiet. Mass., Penn., 111., Mich., Neb.

Fig. 630. Planaria maculata. U) From life. X 6. (After Wood worth.) (5) Sexual organs, dorsal
view: u, uterus; co, common oviduct; od, oviduct; a, atrium; gp, genital pore; p, cirrus; vd, vas de-
ferens; m, mouth. X about 35- (After Curtis.)

90 (89) Color dark reddish-brown to grayish-brown. Uniformly pigmented.

Planaria gonocephala Duges 1830.

im

Greatest length 25 mm.
Usually not over 15 mm.
Girard describes the color
of this species as often of
a blackish -brown. Pos-
terior margins of auricular appendages free from
pigment. Much lighter on ventral than on dorsal
side. Eyes in a plane joining the apices of the
auricles. Clear areas around eyes sometimes
elongated in an antero-posterior direction. Re-
production asexually common. Mich., 111.

Fig. 631. Planaria gonocephala. (^) From life. X S.
(After Woodworth.) {B) Sexual organs, longitudinal
section side view: ui, uterus; od, oviduct; de, ductus
ejaculatorius; ^a/), papilla; i'(/, vas deferens; ag, genital
atrium; vs, vesicula seminalis; m, mouth; utd, duct of
uterus; pdr, cirrus glands; pdr^, ducts of cirrus glands;
gP, genitfvl pore. Much enlarged. (After Bohmig.)

91 (86) Anterior end rather sharply pointed. Angle formed by lateral mar-
gins of head not more than 60°. Cephalic appendages long,
slender, sharply pointed, with anterior margin shorter than
posterior margin. Body distinctly narrower back of ceph-
alic appendages than just in front 92

THE FREE-LIVING FLATWORMS (TURBELLARIA)

357

92 (93) Angle of head 50° to 60°. Color a very dark sepia-brown almost
black by reflected light. . . Planaria agilis Stringer 1909.

Length of immature worms usually not over 18 mm. Mature specimens collected have meas-
ured 30 mm. Well fed specimens in aquaria have attained a length of 55 mm. Color usually
very uniform. Ventral surface but little lighter than dorsal. One variety found only in one
locality and with uniformly colored specimens, shows sharply defined non-pigmented spots.
Under lens a clear light-brown ground with fine dark brown, almost black pigment granules,
either quite uniformly distributed or arranged so as to give the appearance of a very close net
work. Circum-ocular spaces either oval or slightly pointed at outer anterior region and placed
just in front of or in line with the anterior margins of cephalic appendages. Some with light
areas on posterior margins of cephalic appendages, others with auricles uniformly pigmented.
A light median streak sometimes present. Lateral margin of head with a (Hstinct inward curve

just back of tip, also at junction of head with cephalic
appendages. Wider just in front of appendages than
at any point posterior to them except in large specimens
which are of about same width through pharyngeal region.
Mature specimens much broader proportionally than
immature. Asexual reproduction the usual method of
propagation in most localities. Very restless and active.
Collected from small ponds and spring-fed brooks either
among algae or on sandy bottom and often where water
flows swiftly. Neb., Mo., S. Dak., Wis., and Cal.

Fig. 632. Planaria agilis. (A) Immature specimen from life.
X8. (B) Sexual organs, dorsal view: m, uterus; «/, uterus tube;
0, oviduct; gp, genital pore; a, atrium; sv, seminal vesicle; vd,
vas deferens; pi, cirrus lumen; la, limit of atrium. Much en-
larged. (After Stringer.)

93 (92) Angle of head about 45°.

Color reddish to yellowish-brown.
Planaria dorotocephala Woodworth 1897.

Length of immature specimens 13 mm. Head about one-sixth of total length of body. Uni-
formly colored. Posterior margins of auricular appendages free from pigment. Sometimes a
narrow light median streak. Pigment in spots or patches, not a network or evenly distributed
as in P. agilis; ventral side much lighter than dorsal. Eyes just anterior to plane joining
auricles. Intestine usually with accessory posterior intestinal trunks which arise either at the
root of the pharynx like the two normal posterior trunks or exist as parallel branches of the
latter. Those of a side usually unite with each other near their posterior terminations. Very
active and restless. Sexual organs have not been described. III., Mich.

Fig. 633. Planaria dorotocephala from life. X 7- (After Woodworth.)

94 (85) Anterior end clearly not pointed 05

95 (loo) Anterior end truncated 06

96 (99) Margin of anterior end with a median anterior and two lateral

rounded projections giving a sinuous outline 97

358

FRESH-WATER BIOLOGY

97 (98) Color gray Planaria velata Stringer 1909.

Length of mature specimens 15 mm. Color of dorsal side to unaided eye varies from almost
white to a very dark gray almost black. Under lens, a colorless groundwork with black pig-
ment granules extremely variable in number. Much lighter in front of eyes and over cephalic
appendages. Lighter on ventral surface, over pharynx, and near lateral margins. Preserved
material often appears colorless and oval in shape. Encystment of the entire animal or divi-
sion into a variable number of pieces followed by encystment of the pieces occurs in response
to unfavorable conditions. The cysts resemble egg cocoons in appearance and are provided
with a shell. Cilia conspicuous. Crete and Omaha, Neb.

3

Fig. 634. Planaria velata from life. X 12. (After Stringer.)

98 (97) Color brownish-red mottled with purpHsh dots except at margins.

Planaria unionicola Woodworth 1897.

Length of the one specimen (preserved) from which the description was made 2.8 mm.,
breadth 1.8 mm. Probably 8 to 10 mm. long when alive and extended. Purple dots occur
in masses. Red color absent over an elongated posterior median area extending nearly to the
p)osterior axis of the animal. Appearance of posterior end suggests an
injury or transverse division. Color of alcoholic material a deep rusty
red. Found creeping on the mantle of Unio alatiis in Illinois River.

Fig. 635. Planaria unionicola from life. About X 3- (After Woodworth.)

99 (96) Margin of anterior end uniformly curved, not sinuous. Color white.

Planaria truncata Leidy 185 1.

Length 10 to 12 mm. Thickness slight. Translucent. Digestive tract variously colored
by food. Two crescent-shaped eyes situated far back and near together. Phar>'nx much
elongated and central in position in sexuallj' mature specimens. Intestine with Httle anas-
>— V tomosis of branches. Ovaries two, sometimes

\,, / lobed. Testes many. Uterus large with stalk

ICVi running to left side, dorsal to vasa deferentia and

// \\ oviducts and entering atrium laterally. Asexual

reproduction by fission. Small stream Bryn Mawr
campus; rivulet at Newark, Delaware.

A comparison of descriptions of P. truncata
Leidy and P. morgani Stevens and Boring leaves
but little doubt that they are identical. The
blackish-white color mentioned by Leidy evidently
was due to food contained in the digestive tract
and not to body pigment since the margin is de-
scribed as translucent.

Fig. 636. Planaria truncata. (^) From life. X 4- (5)
Dorsal view of sexual organs: a, atrium; c, cirrus; gp,
genital pore; oi, oviduct; ph, pharynx; /, testes; «,
uterus; vs, vas deferens. X 7. (After Stevens.)

100 (95) Anterior end rounded in preserved condition (living condition not
known) Planaria simplex Woodworth 1897.

Length 4 mm., greatest diameter 1.8 mm. Color of alcoholic specimen ocher-yellow. Pig-
ment located in spots of nearly uniform size, distributed uniformly over all parts of the body;
no clear areas surrounding eyes or at sides of head. General shape ovate. Broadest at one-
fifth the total length from the anterior end, tapering from here to rounded posterior extremity.
Anterior end rounded, set off from the rest of the body by slight lateral indentions at the levelof
the eyes. No evidence of cephalic appendages. Mouth one-third of total length from posterior

THE FREE-LIVING FLATWORMS (TURBELLARIA)

359

end. Eye spots elongated, crescentic, facing outward and forward at an angle of 45° to the

chief axis of the worm. Intestine of the simple triclad
type; no fusion or anastomoses of posterior stems.

This description is from a single immature alcoholic
specimen. (It is quite possible that the apparent lack
* : of cephalic appendages is due to the eflfect of the killing

'J fluid.) Collected off N. Y. Point, Lake Mich.

Fig. 637. Planaria simplex. From preserved material.
X 10. (After Woodworth.)

101(84) Withouleyes Planaria fidiginosus Leidy iS si-

Length about 5 mm., breadth 4 mm. Body oval, dilated; inferiorly flat, superiorly mo<l-
crately convex, fuliginous. Eyes none; in their ordinary position a slightly greater accu-
mulation of black pigment upon the upper surface. Mouth a little posterior to the center-
I'.sophagus simple. Rancocas Creek near Pemberton, New Jersey.

102 (83) Normal eyes many, arranged so as to suggest a coronet near

the margin of truncated head and extending back near
the lateral margins to a somewhat variable distance.

^ , . , ■ Polycelis.

Only one species known in this country.

, Polycelis coronata (Girard) 1891.

Length 8 mm., breadth 2 mm. Color fuliginous or sooty, uniform, somewhat darker on the

median dorsal region than on margins. Elongated lanceolate. Anterior margin truncated

weakly bilobed or undulating. The numerous eyes are arranged as a coronet or as an arc of

a circle, the arrangement being dependent to some extent

on size. Pharynx elongated, central. Collected near Fort

Bridger, Wyoming. It is quite possible, as Haflcz notes, that

this is a synonym of the European Polycelis nigra.

Fig. 638. Polycelis coronata. From life. X 5. (After Girard.)

103 (80) Pharynges numerous Phagocata.

Only one species known in this country.

Phagocata gracilis (Haldeman) 1840.
yThis species was found and recorded by Haldeman; it was first adequately described by
Leidy to whom it is ordinarily attributed.

Largest specimens 35 mm. long, 4.5 mm. wide. Color shiny black by reflected light, green-
ish-gray by transmitted light. Varies from black to a reddish-brown on one hand or to a light
gray on the other. Small specimens at times almost milky-white. Ventral side lighter than
dorsal. Lateral margins nearly parallel. Widest through pharyngeal region. Anteriorly
sides converge slightly up to about the region of eyes where the diameter increases to form the
head with its rounded cephalic appendages. Posteriorly sides converge to a {wint. Eyes
two with elongated circum-ocular areas. The numerous pharyngeal tubes lie in a common
chamber and open separately into the intestinal tract. When extruded they reach the exterior
through a single orifice. Pools and rivulets, Mass., Penn., Ohio, Wis.

Fig. 639, Phagocata gracilis. {A) Living animal extended. X 4. (B) Partial reconstruction to show
pharynges and their relation to the intestinal tract. X about 8. (After Woodworth.)

104 (79) Found in moist places on land. . . Suborder Terricola . . 105

The so-called land planarians are forms which in a biological sense stand verv near the
water-hving species. They occur only in very moist localities and under circumstances may
^e taken for fresh-water forms. In general appearance they resemble minute, delicate sIurs.

vf^ ^^^.mined under the microscope the structure appears clearly to be that of a flat worm
rather than of a mollusk. The few known species are widely and sparsely distributed. They

360 FRESH-WATER BIOLOGY

are likely to be transported in tropical or subtropical vegetation and to make their appearance
suddenly and in considerable numbers in greenhouses or in moist shady nooks that have been
planted with exotic species. Of one form indeed the proper habitat is not known. Walton
has worked out a key and synopsis of the few species reported from North America and ad-
jacent islands. In modified form this is followed here. Almost no records of the occurrence
of these forms on this continent have been published, and their numbers as well as their range
are sure to be considerably extended when attention is directed to them.

105(110) Eyes either absent or numerous; length more than 40 mm. . . 106

106 (109) Head anteriorly not broader than remainder of body.

Family Geoplanidae . . 107

107 (108) Posterior part of head with eyes in two rows; sides margined with

orange Geoplana nigrofusca (Darwin) 1844.

Length 50 mm. Found in Mexico; reported also from South America.

108 (107) Posterior part of head with eyes in one row; sides margined with

Hght brown Geoplana stolli (von Graff) 1899.

Length 60 mm. Thus far known only from a single specimen collected in Guatemala.

109 (106) Head anteriorly broader than the body. . . . Family Bipalidae.

Only one species Placocephalus kewense (Moseley) 1878.

Color dorsally yellow or greenish-yellow
with five dark violet longitudinal lines.
Length 80 to 250 mm. An introduced
species found in hot houses. Its original
Fig. 640. Placocephalus Kewense. Anterior end. home is unknown
X I. (After von Graff.)

110(105) Eyes two in number; ventral suckers absent; length less than

30 mm. Ill

Rarely the eyes are apparently absent but even here they may be demonstrated in sections.
Ventral" suckers do occur in the related family Cotyplanidae . Known from Africa and New
Zealand.

111 (114) Eyes small, marginal sense organs present.

Family Rhynchodemidae . . 112

112 (113) Color dorsally light brown with two darker longitudinal stripes

and transverse area at posterior two-thirds of body.

Rfiynchodemus syhaticus (Leidy) 1851.
Length not over 10 mm. Common in places de-
scribed by Leidy (1851) in Pennsylvania and redis-
covered in Ohio by Walton (1904). Frequents under
^ side of slightly decayed boards, sticks, etc., in com-
pany with snails, the young
forms of which it closely re-
sembles. Range, Eastern
United States.

B
Fig. 641. Rhvnchodemus syhaticus. {A) Dorsal view of individual from Philadelphia, Pa. X J- (5)
Individual from Newport, R.'l., showing arrangement of esophagus and structure of mtestme. X about
5. (After Girard.)

113 (112) Color dorsally uniformly dark blue.

Rhynchodemus atrocyaneus Walton 191 2.
Length 20 mm. Only two specimens of this form have been reported. Found at Gambler,
Ohio, under decayed boards.
114(111) Eyes well developed; marginal sense organs absent.

Amhly plana cocker elli von Graff 1899.
Color dorsally bluish-black with light yellow median stripe longitudinally and yellow "neck
band." Length 17 mm. Represented only by two known specimens found in Jamaica.

THE FREE-LIVING FLATWORMS ^TURBELLARTA) 361

The following is a list of those forms which are not sufficiently well known
to be given their proper place in the key.

Order Rhabdocoelida
Section I Hysterophora
Family Catenulidae

Microstomiim philadelphicum Leidy 185 1
Microstomum varlahile Leidy 185 1
Section II Lecithophora
Subsection Liporhynchia
Family Typhloplaxidae

Typhloplanid from Canandaigua Lake, N. Y., von Graff igii
Typhloplanid from Irondequoit, N. Y., von Graff 1911
Mesostoma patter soni SiUiman 1885
Family Dalyellidae

Dalyellia hilineata (Wood worth) 1896
Dalyellia marginatum (Leidy) 1847
Derostoma elongatiun Schmarda 1859
Subsection Calyptorhynchia

Rhynchoproholus papillosus Schmarda 1859

The following Rhabdocoels are of very doubtful position and relationships

Vortex (?) cavicolens Packard 1883

Plagiostoma (?) planum Silliman 1885

Acmostomum crenulatum Schmarda 1859
Order Tricladida

Dendrocoelum sp. Pearl 1903

A brief description of these doubtful species will serve to promote their re-
discovery and further study. Each description is taken from the original
account of the species which is also the only record of it yet published.

Microstomum philadelphicum Leidy 185 1.

Body linear, slightly attenuated posteriorly; head conoida! with the apex surmounted by
a small oval papilla; tail obtusely rounded. Respiratory fovea subhemispherical. placed at
the base of the cone of the head. Mouth oval, projectile; esophagus keg-shaped, intestine
narrowed, cyUndroid, dilated at the commencement. Colorless, translucent, ciliated, in-
creasing by transverse segmentation, always observed in the process of forming two segments.
Length 0.9 mm. Found in water of marshes and ditches near Philadelphia.

Microstomum variable Leidy 185 1.

Body broad, linear; anteriorly and posteriorly obtusely rounded. Respiratorj- fovea
longitudinally oval, lateral. Intestine very broad. Colorless, increasing by twos. Length
from 0.3 to I mm. No nematocysts or rhabdites. Found with Microstomum philadelphicum.
Also a chain of 4 individuals was collected in algae culture from shore, Charlevi)ix, Mich., by
Dr. H. B. Ward.

Typhloplanid from Lake Canandaigua, N. Y., von GrafT 191 1.

Length i mm. Anterior end set off from the rest of the body by depressions at the sides, prob-
ably sensory pits. Broadest through middle of body which measures about one-fourth the
length. Spindle-shaped rhabdites in glands and tracts of anterior end. Pigment is present in
the form of large reddish-brown granules which mostly lie lengthwise of the body, stimctimes
branched, and enlarged at posterior end. The pigment forms a reticulation between and passes
over the irregularly shaped eyes. Eyes twice as far apart as they are distant from the margin of
the body. Pigment of eyes the same as that of the body, only much closer compacted so that
they are deeper in color.

The mouth lies in the anterior third of the body. In the uncompressed animal the pharynx

362

FRESH-WATER BIOLOGY

shows as a typical rosette-shaped pharynx. This form is
unusual in that the rosette-shaped pharynx does not lead
into the intestine from its ventral side, but opens into its
anterior end so that when compressed its axis becomes
directed forward. Intestine yellowish and extending
almost to the posterior end, and having the general shape
of the body.

Fig. 642. Typhloplanid from Lake Canandaigua, N. Y. (A)
Swimming freely, showing the dorsal pigmentation. X 55- (B)
Slightlycompressed with pharynx directed forward. X 4°- a",
eyes; da, intestine; ehv, anterior branches of pro tonephridium; g,
brain; ph, pharynx; stz, rhabdite glands. (After von Graff.)

Typhloplanid from Irondequoit, N. Y., von Graff 191 1,

Length 0.5 mm. Without pigment and color»
less apart from the brownish-red eyes and the
oil drops of the intestine. Eyes irregular in shape
and almost twice as far from the side of the
body as from each other. The mouth lies on the
boundary between the first and second thirds of
the body. The anterior end shows many tracts
of rhabdites. Collected from a reedy swamp.

Fig. 643. Typhloplanid from Irondequoit, N. Y. (A >
The animal slightly compressed. X 80. (B) Male
copulatory organ. X 320. au, eye; be, bursa copula-
trix; dr, gland cells; ds, ductus seminalis; /, fat drops;
ge, ovary; go, genital pore; kd, granular glands; ks,
granular secretion; m, muscles; />A, pharynx; j<, tracts
of rhabdites; te, testes. (After von Graff.)

Mesostoma pattersoni Schmarda 1885.

Length 3 to 3.5 mm., 0.6 mm. broad through middle. Color in
reflected light brownish except anterior to the eyes which appears
grayish from the rhabdites. Intestine yellowish. Body fluid with
many cells which contain granules. Eyes directly above the brain.
Pharynx rosette-shaped, not far from middle of body.

Fig. 644. Mesostoma pattersoni. st, tracts of rhabdites; ph, pharynx;
vi, yolk gland; ut, uterus; be, bursa copulatrix; ov, ovary; P, cirrus; t,
testes. X 20. (After SilHman.)

THE FREE-LIVING FLATWORMS (TURBELLARIA)

363

Dalyellia bilineata (Wood worth) 1896.

Length 0.96 mm., breadth 0.24-0.52 mm.
Anterior end truncated, posterior end fKjinted.
Pharynx dolioliform, in anterior third of b(xiy,
traversed by two prominent, lateral, nearly lon-
gitudinal bands of light chocolate-brown, and
numerous other pale indistinct longitudinal
lines. Zoochlorellae in central part of the
body, posterior fifth free from them, trans-
parent-brown. Egg dark chocolate, 120 m X
80 M-

The figures given here are those which
were in possession of Woodworth with the
material when the description was written
and the species named.

Fig. 645. Dalyellia bilineata. i4, compressed. X
about 50. z)d,vas deferens; j)x, vesiculaseminalis; 0,
ovary; c,chitinous portion of cirrus; e, egg; be, bursa
copulatrix; yg, yolk gland. B, chitinous piece. X
about 200. (Unpublished sketch by Ward.)

Dalyellia marginatum (Leidy) 1847.

Blackish, narrow lanceolate, anteriorly truncate; marginate margin delicately striate;
mouth large; pharynx large and oblong; eyes two, anterior, distant, each consisting of two
round masses of black pigment in contact with each other and of which one is larger than the
other; generative orifice one-fourth the length of the body from the posterior extremity.
Length 2 mm. A single specimen found in ditches near Philadelphia, Pa. Digestive cavity
consists of a large capacious sac extending as far back as the posterior third of the body and

having a cecum upon each side of the proboscis. The
cirrus has a yellow color and consists of a round granu-
lar mass with a moderately long and bent spiculum pro-
jecting from its posterior part. This is the form de-
scribed by Leidy under the name Prostoma marginatum.
Fig. 646. Dalyellia mar fiinatum. X about 20. (.^fter Girard.)

Derostoma elongatum Schmarda 1859.

Fig. 647. Derostoma elongatum. X about 25.
(After Schmarda.)

The body is long, ribbon-shaped, flattened.

Posteriorly uniformly tapering. Color red-
dish-gray. Length 2 mm. Without eyes.
Mouth opening elliptical. Pharynx long, cask-
shaped. From brackish water in swamp, New
Orleans, La.

Rhynchoproholus papillosus Schmarda 1859.

n\Uil-lJill-LU.IJiUfUll.'.U.ujj^

tP^S^fei

^^miifnjn'Tnmiwlmmmm^

Fig. 648. Rhynchoprobolus papillosus. X about
9. (After Schmarda.)

Body somewhat compressed, anteriorly
rounded, posteriorly gradually tapering. Color
clear yellow. Length 5 mm. Without eyes.
Proboscis short, round, externally set with
small papillae. Mouth oF>cning central. Phar-
ynx rosette-shaped. From brackish water,
Hoboken, N. J.

Vortex (?) cavicolens Packard 1883.

Found in X cave, one of the Carter caves, Kentucky. Body flat, elongated, narrow lan-
ceolate-oval, contracting in width much more than is usual in Vortex (Dalyellia). Phar>-nx
is situated much farther back from anterior end of body than is usual in Vortex, being placed
a little in front of the middle of the body; it is moderately long, being oval in outline. The
body behind suddenly contracts just before the somewhat pointed end. The genital outlet

364

FRESH-WATER BIOLOGY

is about one-half as wide as the pharynx and orbicular in outline. Apparently eyeless.
White. Length 4 mm., breadth 1.5 mm. Brooks, Carter Caves, Kentucky.

Plagiostoma (?) planum Silliman 1885.

Length 1.5 mm., breadth 0.7 mm. Mouth opening in anterior
end. Pharynx lies within a sheath and has both longitudinal
and transv^erse muscle layers. Radial muscle fibers pass from the
base of the pharj'nx to the body wall. Without eyes or other
sense organs. The poorly developed brain hes in front of the phar-
ynx as a transverse band. The intestine is capacious and has short
lateral diverticula. This species probably belongs to the genus
Prorhynchus.

Fig. 649.

Plagiostoma (?) planum, ph, pharynx; d, intestine.
30. CAfter Silliman.)

X about

Acmostomum crenulatum Schmarda 1859.

0^^^!^^'mmmLL^k

The body is cylindrical, yellowish, i mm. long. Pharynx cylindrical, protractile with six
deep lobes on its margin. Otolith large and spherical contained within a transparent capsule
which is located at the end of the first third of the body.
The ovaries form a large spherical mass in the posterior part
of the body. The cirrus is short knife-shaped and has a
slight double curve. Found in brackish water, Hoboken, N. J.

Fig. 650. Acmostomum crenulatum. From life X about 30.
(After Schmarda.)

Dendrocoelum sp. Pearl 1903.

Agrees with description of Dendrocoelum lacleum, except in respect to the color. Color
ranges from a light grey to nearly black, and is uniform. Found about Ann Arbor, Mich.

IMPORTANT REFERENCES ON NORTH AMERICAN FRESH-
WATER TURBELLARIA

Graff, L. von. 1882. Monographic der Turbellarien. I Rhabdocoelida.

Leipzig.
1904-1912. Bronn's Klassen und Ordnungen des Tierreichs. IV. Bd., Wiir-

mer: Vermes, Turbellaria, Acoela, and Rhabdocoela. Leipzig.
191 1. Acoela, Rhabdocoela und Alloeocoela des Ostens der Vereinigten

Staaten von Amerika. Zeitschr. f. wiss. ZooL, 99 1321-428. Taf. I-VI.
Silliman, W. A. 1885. Beobachtungen iiber die Siisswasser-Turbelarien

Nordamerikas. Zeitschr. f. wiss. Zool., 41 148-78; Taf. Ill, IV.
WooDWORTH, W. McM. 1897. Contributions to the IMorphology of the

Turbellaria II. On some Turbellaria from Illinois. Bulletin Mus. Comp.

Zool. Harvard Coll., 31 : 1-16; i plate.

CHAPTER XIII
PARASITIC FLATWORMS

By henry B. ward

Professor of Zoology in the University of Illinois

The parasitic worms do not all belong to a single systematic
division. Coming in many cases from widely separated groups,
they often show much closer relationship to certain free-living
forms than to each other. But because of a likeness in manner
of Hfe these forms were grouped together by early students of ani-
mal life as the Helminthes and in fact were long regarded as related
by reason of similarities in appearance and habit. There are five
such groups, usually ranked as classes; they are Trematoda or
flukes, Cestoda or tapeworms, Nematoda or roundworms, Acan-
thocephala or proboscis-worms, and Gordiacea or hair-worms.

In any given host only a few parasitic species may be found or
again the number of individuals and species of parasitic worms in
a single host may be very large. I have taken 5000 flukes from a
single fish (Amia), and even larger figures are recorded. At a
given time the variety of species may be Hmited; yet as the kinds
of parasites change with the food, the season, and the region, the
total number found in a certain host may be very large; thus over
one hundred species of parasitic worms are reported from man
and thirty or forty from some well-known and widely-studied fish
or aquatic birds. Some parasites are found in more than a single
host species, a few infest a wide range of animals, and others occur
in one host only; all in all, parasites are far more numerous than
free-living animals both in number of individuals and of species.

The abundance of parasites varies greatly under dilTerent con-
ditions of existence. Desert animals are not without them, but
they are much more numerous and more varied in water-living
animals than in hosts from any other habitat.

Representatives of some or all groups of parasites occur in the
various aquatic vertebrates and invertebrates, and while in a

365

366 FRESH-WATER BIOLOGY

certain sense they are not inhabitants of fresh water, they infest
aquatic animals and their hfe histories form a part of aquatic
biology. To be sure some species of parasites never come into
contact with the external world but are transferred from host to
host with the material in which they are Kving and others are en-
tirely dependent upon terrestrial animals as hosts. Such parasites
have no direct relation to fresh-water life and will be entirely
omitted in the present discussion. However, in the large majority
of parasitic forms the parasitic stage alternates with a longer or
shorter non-parasitic period. During this period of free existence
the species is a dweller in fresh waters alongside of their normal
inhabitants, possessed of similar organs of locomotion and other
adaptations to a free existence, often unrecognized in their true
nature, and properly regarded as members of the shore or bottom
fauna or plankton. This fact alone compels their consideration
in any discussion of aquatic life.

Contrasted with this stage is the parasitic period which is more
extended, usually embracing almost all of the life history. In it
the worm remains with its host, dependent upon the latter for
protection, locomotion, and subsistence, showing structural modi-
fications which aid in maintaining this dependence and indicating
by the absence of organs calculated to provide for successful inde-
pendent activity the changes which the parasitic habit has induced
in its original structure.

As already indicated most parasites show distinct adaptations
to the conditions under which they Hve. To be sure some, such
as certain small parasitic nematodes, are indistinguishable from
their free-living relatives, but such instances are rare. The large
majority have lost organs usually found in free forms and have
gained structures of significance only for a parasitic existence.
Furthermore, both loss and gain are relative and graded, rather
than absolute and unrelated. Thus in some flukes the ahmentary
system is about as well developed as in the free-living Turbellaria,
and of much the same type {cf. Figs. 678 and 639^); in other
flukes the system is greatly reduced {cf. Microphallus, Fig. 697);
and finally in the cestodes it is entirely lacking. The same condi-
tions prevail in the threadworms. Most of the true Nematoda

PARASITIC FLATWORMS 367

have a well-developed and functional digestive system; in Mermis
the system is active during early life and becomes inert and de-
generate in the adult stage. Finally in the Acanthocephala there
is no trace of an alimentary system at any stage in the life-history.
The gains are no less marked. Hold-fast organs, like suckers and
hooks, enable the parasite to maintain its position against the con-
stant and vigorous movements of the host. Such organs of simi-
lar structure appear in widely separated groups, e.g., suckers in
flukes and threadworms.

While these structural likenesses between parasitic worms of
different groups are striking and important, they are in a real
sense superficial and do not serve to conceal more than tempo-
rarily the fundamental differences in structure between the various
groups.

The flatworms (Plathelminthes) are soft-bodied, usually elon-
gate and somewhat flattened forms. In the phylum are included
the free-living Turbellaria (Ch. XII) and Nemertina (Ch. XIV),
as well as two classes of parasitic worms : the Trematoda or flukes,
and the Cestoda or tapeworms. The other three classes of para-
sitic worms named previously are grouped together under the
phylum Nemathelminthes or roundworms, which forms the topic
of a separate chapter. The structure of each group will be dis-
cussed separately, but certain biological features are general enough
to deserve brief mention first.

Aquatic animals possess some external parasites; among them
the species of ectoparasitic flatworms, rare in fresh water, belong
to a single subdivision of the flukes or Trematoda; all other flukes
and the Cestoda which are all parasitic live as endoparasites in
some part of the host organism where they find better protection
than on the surface. The most common place of residence is the
alimentary canal or its adnexa, air-bladder, lungs, liver, etc.
Parasites occur regularly in the body cavity and other serous
spaces, in the kidney and bladder, in the sex organs, in the heart
and blood vessels, encysted in the skin, connective tissue and
muscle, and finally in the nervous system, even entering the eye
or brain and its cavities.

Parasites may be collected by opening an animal in a dissecting

368 FRESH-WATER BIOLOGY

dish of suitable size and examining the contents of various organs.
The parasites usually betray their presence by sluggish move-
ments of the body which make even minute objects conspicuous
in a mass of debris. A watchmaker's lens held in place at the eye
by a spring is of service in recognizing and sorting out the smaller
forms, and long bristles or a camel's hair pencil are useful in pick-
ing out the forms for study and preservation. Doubtful objects
should be examined under a higher magnification whereupon the
firm, definite outline of a parasite enables the student to distinguish
it even when motionless from partly digested fragments of food,
blood clots, or other foreign bodies of similar size and texture.

Parasitic flatworms may be kept some hours in weak normal salt
solution for examination or even in tap water, but deteriorate so
that for careful study material should be preserved as soon as
possible. For preservation an aqueous solution of corrosive sub-
limate is most satisfactory, and the precise method of handhng
suggested by Looss gives results well worth the extra time and
trouble because of the greater ease with which future work may be
carried on. Because of the great similarity in external form be-
tween different types, a determination can be safely reached only
after a worm has been stained and mounted in toto, or sectioned
in case of large and opaque specimens.

The parasitic flatworms have received relatively Httle attention
in North America; it is consequently a difficult matter to prepare
a synopsis that is of value to the student, for from our knowledge
of the group in other parts of the world it is safe to assert that
the known forms do not constitute more than a small fraction
of those that actually exist on this continent. Another difficulty
which presents itself is the impossibihty of defining clearly the
Hmits of the topic. I have endeavored to include in the key all
North American parasitic flatworms thus far recorded from fresh-
water animals whenever the record permits of any reasonable
interpretation. I have omitted a few records so brief or indefinite
that a diagnosis was impossible. There is included also a consid-
erable number of parasites from distinctly land animals, the life
history of which is certainly bound up with stages parasitic in the
fresh-water fauna. On the other hand I have omitted all clearly

PARASITIC FLATWORMS 369

marine species and all from hosts commonly frequenting the sea
and most likely to become infected there.

The parasitic flatworms fall readily into two great classes, the
Trematoda or flukes and the Cestoda or tapeworms. Some authors
would make a third intermediate group out of the few forms which
are known as Cestodaria and resemble the flukes in having a simple
body and the tapeworms in details of internal anatomy. In this
work they are treated with the tapeworms. As apart from these
few cases flukes and tapeworms can be fairly readily distinguished,
it is advantageous for the student to have each group treated sep-
arately in a distinct section of the chapter; and to this treatment
the following brief synopsis may serve as an introduction.

Body soft, flattened, shaped more or less like a simple scale, leaf, band,
or ribbon Phylum Plathelminthes.

The external surface may have hooks, spines, or scales, or be
provided with warts or rugosities, but it does not possess a tough,
shiny, smooth, resistant cuticula. In a few cases the body is cyhn-
drical, conical, or spindle-shaped and does not display the charac-
teristic flattening mentioned in the key.

Intestine present Class Trematoda . . page 369.

Intestine absent Class Cestoda .... page 424.

Sometimes the intestine is so rudimentary or so thoroughly con-
cealed by other organs that its presence is difficult to determine.
It is, however, the only absolute diagnostic characteristic which in
the last analysis separates a fluke from a tapeworm.

Trematoda

The trematode or fluke is usually flattened, oval, seed-shaped,
or rarely rodlike, attenuate, or globular in shape. With few ex-
ceptions one finds on the surface one or more cup-shaped suckers.
The number and arrangement of these constitute a means of sub-
dividing the group. Careful examination under magnification dis-
closes pores or openings and also in some cases hooks or spines on
the surface. Many of the flukes are transparent and permit the
observer to identify the main internal organs.

The alimentary system which usually starts at the forward tip

370

FRESH-WATER BIOLOGY

of the body or close to it and in the anterior or oral sucker is com-
monly shaped like a tuning fork (triclad). More rarely it is rod-
like (rhabdocoel), or branching (dendritic). A sphincter, the
pharynx, is ordinarily found on the esophagus
and the true digestive region consists of the
two branches, the ceca or crura, which vary
greatly in length.

The excretory system (Fig. 651) usually
opens at the opposite end of the body, and
is I-, Y-, or U-shaped. The main branches
are distinct, containing in Hfe a clear fluid
with a shghtly yellowish or bluish tinge.
The finer branches can be traced only with
difflculty. They terminate in the essential
Fig. 6^1. Microphallus opacus. excretory clemcnts known as "flame cells"

Excretory system, dorsal view. -^ ^ ^ .11 ti i •

Reconstructed from senes of which mav bc distmguished readily only m

transverse sections. X 30. (Af- " -^ J ^ . .

ter Wright.) ^^iQ Hviug aulmals under high magnification.

In the larger tubes one finds commonly highly refractive granules
of excretory material.

Of the nervous system one can usuafly see irregular masses
(ganglia) right and left of the aHmentary canal, near its anterior
end. They are joined to form a sort of collar around the esopha-
gus, and from them nerves pass anteriad and posteriad throughout
the body. Further details of structure can be followed only by j
special methods and in well-preserved specimens.

Special sense organs are not common. A few of the ectopara-
sitic trematodes, which are rare in fresh water, have pigmented
eye-spots near the brain, and the free-swimming stages of endo-
parasites show similar structures which with rare exceptions are
wanting in the adult internal parasites.

The reproductive system is the most conspicuous part of the
worm but is exceedingly complicated and often difficult to follow.
Yet it is the most important feature in the classification of the
group. Most flukes are hermaphroditic, and contain complete
organs of both sexes. The arrangement of these organs in a simple,
typical case is given in the accompanying diagram (Fig. 652).
In many species an enormous accumulation of eggs in the uterus

PARASITIC FLATWORMS

371

obscures all other structures in the body. The eggs are covered
with a firm chitinous shell which is often opaque but in other cases
is transparent enough to permit one
to follow the gradual development
of the enclosed embryo.

The development of most ecto-
parasitic trematodes is simple and
not different from that of free-living
flatworms. There emerges from the
egg-shell in due time a ciliated larva
which swims about in the water until
it finds a new host to which it
attaches itself. In endoparasitic
trematodes the life cycle is more
compHcated in all cases and ex-
tremely involved in some. Only a
general outline of conditions can be
given here.

The eggs of the fluke reach the
external world in the feces or dis-
charges from the host. Within the
egg-shell is developed a minute

FiG.6s2. Azygia sebago. Dorsal view. X 16.
larva, the miracidium, evidently ^.^male reproductive system in dorsal aspect.
' ' -' Semi-diagrammatic to snow relation of organs

p ovarian complex, ovarv' drawn in outline only.

acetabulum; exb, e.x-

intes-

adapted by its ciliated covering to JJ«Jf; ^^^^-^^^^

a tree existence. Sooner or later the tin^; u, Laurer's canai- oo, ootype-, ot. ovar>-;

, 1 i-l- T- 11 5g, shell gland; to, anterior testis; /p, posterior

egg arrives m water where the shell testis; «/, uterus; t/.vitciiaria; w.yoikduct;

, , , . . yr, yolk reser\-oir. (Original.)

opens and the larva escaping swims

about in search of a new host. The latter is not the species which
shelters the adult but an intermediate host which for almost all flukes
is a mollusk, in the tissues of which the miracidium changes to an
irregular sac (sporocyst); this produces within itself a new gen-
eration (redia) which also in this host produces a third generation
(cercaria). The miracidium possesses an eye-spot and often a
boring apparatus at the anterior end. These structures are lost
in the metamorphosis into a sporocyst, a stage so simply con-
structed that the young rediae escape by the rupture of the wall.
A redia is characterized by the presence of a rhabdocoel intestine

372 FRESH-WATER BIOLOGY

with pharynx, an oral sucker, and usually a birth pore. The
redia generation may be repeated and either this or the sporocyst
generation be eliminated, so that the cycle may become modified
in either direction.

When development within the mollusk is completed and the
transfer to the adult host takes place, the transfer may be direct
if the mollusk is eaten by a suitable host. Yet this is not the
usual method since the ordinary cercaria possesses a well-developed
swimming organ in the tail which characterizes this stage and is
cast off when the larva reaches a new host or a place of encyst-
ment. This swimming tail is reduced in a few types and wanting
only very infrequently. In other cases various modifications, such
as bristles, folds, branches, lateral membranes, etc., increase its
functional value.

The cercaria usually deserts the snail and actively seeks out its
primary host, but after reaching the outer world it may also encyst
on vegetation or force its way into a second intermediate host, an
aquatic arthropod or small fish, and encyst there. Here it rests,
a small immature encysted distome, until the tissue is consumed
by a suitable host, whereupon it is set free in the afimentary canal
and seeks its final location to attain after a period of growth the
adult form and full maturity. Life histories are known among
trematodes only in the most fragmentary way and the field offers
inviting prospects to the student.

As appears from the account just given two free-living stages
recur in the development of most flukes. The miracidium nor-
mally depends on active migration through the water to reach
and infect the secondary host. In spite of the constant and
abundant production of such larvae their occurrence in plankton
or other fresh-water collections is not recorded. This may be due
to the extreme deHcacy of the larvae which go to pieces almost as
soon as collected.

When infected snails are kept in an aquarium, the cercariae
swarm out at certain times in great numbers and can be seen
swimming actively about in the water. They conduct themselves
under such circumstances like true plankton organisms: protozoa,
rotifers, and entomostraca in the same aquarium. Yet although

PARASITIC FLATWORMS

373

such larvae are produced in great abundance and infected mollusks
are also abundant and widely distributed, there are few records of
cercariae in reports on aquatic life.

Leidy found cercariae free in the Delaware River and in a \V\'-
oming pool. Wright discovered the remarkable anchor-tailed cer-
caria among weeds, and I have taken several forms including the
striking Cercaria gorgonocephala in the tow with a plankton net.
None the less among the fresh-water organisms that are least
known one may well Hst the free-swimming stages of parasitic
worms.

From this survey of the life history it is evident that the degree
of trematode infection depends: first, on the presence of water at
the time when the cercariae or miracidia swarm out; and second,
on the occurrence of mollusks in the region to act as intermediate
hosts. Hence flukes are rare in arid areas and also in regions
lacking in lime where mollusks are all but wanting.

In general, infection is seasonal and may be traced to the climatic
conditions because periods of excessive moisture permit the swarm-
ing of the larvae, whereas during dry months the egg-shells remain
unbroken. The study of the adult parasites has shown that in
most cases observed the flukes produce eggs continually and seem
to display equal reproductive activity in all parts of the year.
The number of flukes found in a given host does not appear to vary
seasonally although it does vary widely in individual hosts.

The fishes, amphibians, reptiles, birds, and mammals that occur
in and around various fresh-water bodies shelter a multitude of
species of trematodes. The group has never been studied care-
fully on this continent and data available include mostly casual or
fragmentary observations on a few of its members. Pratt made
the first general Hst of these species. Since then a number of
students of individual genera or groups of flukes have added to
the count. Even this has only made a start at recording the
North American species in the region which has been studied and
one can hardly venture to predict the number of species in parts
of the country where no collections at all have been made. The
total trematode fauna of North America is greatly beyond any
present records and cannot be estimated from the data at hand.

374 FRESH- WATER BIOLOGY

Even concerning the forms listed it must be confessed that our
knowledge is very imperfect.

In preparing the key I have followed the plan so admirably
formulated by Looss and worked out in various groups by Braun,
Liihe, and Odhner. The data on larval forms (Cercariae) are
adapted from Cort and Faust.

KEY TO NORTH AMERICAN FRESH-WATER TREMATODA

1 (169) Adult forms; sex organs developed and functioning 2

2 (28) Posterior organs of attachment powerfully developed; those at ante-

rior end absent or if present poorly developed and paired.
Chitinous hooks and anchors almost always present.

Subclass Monogenea . . 3

Excretory pores anterior, double, dorsal; uterus short usually containing only a single egg.
Development simple, direct. Most forms are ectoparasitic on body surface or gills. In
fresh-water hosts found in urinary bladder (Amphibia) or respiratory passages (turtles).

3 (8) Posterior organ single. Vagina unpaired. No genito-intestinal canal.

Order Monopisthocotylea Odhner . . 4

4 (5) Two suckers at anterior end, entirely independent of the oral cavity.

A single large posterior sucker.

Family Tristomidae van Beneden 1858.

Monogenetic, ectoparasitic trematodes with a single large round terminal sucker, often
armed with hooks, and with two smaller yet conspicuous lateral suckers at the anterior end.
Mouth ventral just behind anterior suckers. Many forms parasitic on gills of marine fishes;
a few reach fresh water through the movements of migratory fish.

Only species reported from North America.

Nitzschia sturionis (Abildgaard) 1794.

Reported by Linton from gills of sturgeon (Acipenser sturio) at Woods Hole. May be
carried at times into fresh water.

5 (4) Anterior end expanded, bearing special structures of some sort and yet

never true suckers alone.
Family GYRODACXYLroAE van Beneden and Hesse 1863 . . 6

Small, slender, elongate trematodes with anterior end variably provided with specialized
structures, only rarely true suckers and then associated with other special organs. Posterior
disc without suckers, usually with two or four huge hooks in the center and a considerable
number of small marginal booklets.

On the skin and gills of fishes.

The genera reported from fresh water all fall in the section of the family in which the an-
terior end is provided with two or four retractile cephalic tips in which open ducts of numer-
ous dermal glands.

6 (7) Posterior disc with two large central hooks. No eyes.

Gyrodadylus von Nordmann 1832.

Anterior end provided with two lateral contractile lappets. Large central hooks of pos-
terior disc turned ventrad, shaped like fish hooks and bound together at the roots by a special
clamp piece. Marginal hooks sixteen, simple. Viviparous.

On skin and gills of many fresh- water fish, especially Cyprinidae. At times nimierous enough
to destroy the external dermal layer and leave the fin rays naked. May cause death of host.

Reported only twice in North America; from young lake trout in Maine and small-mouthed
black bass, Ontario, Canada. Species uncertain. Cause of serious epidemic among young
fish at hatchery (Craig Pond); also on wild fish in same stream.

PARASITIC FLATWORMS

375

7 (6) Posterior disc with four large central hooks. Two pairs of eyes.

Ancyrocephalus Creplin 1839.

Anterior end bluntly triangular with two inconspicuous lobes on each side, but no distinct
cephalic lappets. Posterior disc bears four large, heavy hooks and clamp, and fourteen or
sixteen small marginal hooks of which two lie before and two behind the large hooks. Ovi-
parous.

On the gills of many fresh-water fish.

Two species, determination doubtful, reported by Cooper from Ontario, Canada. On the
gills of young l3lack bass. Also from rock bass and sunfish.

8 (3) Posterior organs multiple (two to many parted). Vagina double.

Genito-intestinal canal present.

Order Polyopisthocotylea Orlhner . . 9

Suckers at anterior end, if present, open into oral cavity. Posterior end with variable but
well-developed organs of attachment consisting of hooks and suckers grouped on a terminal
field or disc.

9(12) With two oral suckers and with genital hooks 10

10 (11) Posterior disc with eight, less often four (five) small peculiar sucking

organs.

Family Octocotylidae van Beneden and Hesse 1863.

Elongate, flattened ectoparasitic trematodes. The posterior organ of attachment has —
usually in two parallel symmetrical rows — eight, more rarely four or six, small suckers braced
with a characteristic chitinous framework or armed with hooks. Extra hooks occur often on
the disc. Genital pore always armed with hooks. Eggs supplied with one or two long fila-
ments. On gills of marine and fresh-water fishes.

These parasites are rare in fresh water yet no doubt other genera than the two cited here
do occur. The American representatives are not well known and only the first is more than
an accidental member of the fresh- water fauna. For this reason no eflfort has been made to
incorporate them in the key.

Mazocraes Hermann 1782.

One species, formerly known as Odobothrium sagitlatum, is reported by Wright from the
sucker (Catostoniiis teres).

Plectanocotyle Diesing 1850.

Reported from the gills of Roccus americaniis which enters fresh water to spawn so that this
parasite may be taken at times in that habitat.

11 (10) Posterior disc with a large number of small suckers.

Family Microcotylidae Taschcnberg 1879.

Elongate ectoparasitic trematodes with two small anterior suckers connected with the oral
cavity and with the posterior end expanded into a foot-like region bearing a multitude of

minute suckers. Eggs with large filaments at both poles.
Body and posterior organ of attachment symmetrical.

Microcotyle van Beneden and Hesse 1863.

A genus parasitic on the gills of marine fishes. G. A. and \V. G. MacCalluni report three
species from the rock bass {Rocciis Imeatiis) which ascends rivers along the Eastern Coast
for spawning. Hence these parasites might be taken in fresh water, though no record of such
an occurrence has been found.

12 (9) Anterior end pointed, without suckers or other special organs.

Family Polystomidae van Beneden 1858 . . 13

Elongate, flattened monogenetic trematodes with simple anterior end. and with prominent
adhesive disc at posterior end. Posterior disc with hooks and either two or six large ix.wertui
suckers. Mouth subterminal, intestine triclad, often dc-ndntic, with anastomoses. .M.iic
genital pore and uterine orifice median, ventral, postpharyngeal. r,,^

, On body surface, gills, and in urinary bladder of amphibians; in pharynx and cloaca oi rep-
tiles.

376 FRESH-WATER BIOLOGY
13 (27) Posterior disc with six suckers

14

[4 (26) Posterior disc terminal; suckers large.

Poly stoma Zeder 1800

IS

Six suckers in a circle or in two rows somewhat separated in the median Une. In the center
of each sucker a small hook, and others on anterior and posterior margins of shield; between
posterior acetabula two large hooks. Vagina double, one pore on each side near the ante-
rior end. Eggs without polar filament. Genital atrium with circle of hooks.

Several species in reptiles and amphibians. Not common but widely distributed. P.
integerrimum Zeder, type of the genus, is not reported from North America. American species
worked out by Stunkard.

All North American forms fall in the section of the genus characterized by the presence of
a short uterus containing a single egg; to these forms a new subgeneric name should be given.

Polystoma (Polystomoides) Ward.

15 (23) Great hooks present on caudal disc and well developed 16

16 (22) Genital hooks of equal length 17

17 (18, 21)

Not more than 16 genital hooks.

P. (Polystomoides) hassalli Goto 1899.

Length 1.3 to 2 mm.; width 0.4 to 0.65 mm.
Caudal suckers 0.12 to 0.16 mm. in diameter.
Caudal disc with 18 hooks, the largest 0.125
mm. and the smallest 0.033 nun. long. Cir-
rus hooks 0.028 mm. long with a winglike
process at the middle. Uterus contains only
a single large egg measuring o. 11 by 0.25 mm.
to 0.18 by 34 mm.

Urinary bladder of Cinosternum pennsylvan-
iciim, Aromochelys carinatus, A. odoratus, Chel-
ydra serpentina; Maryland, North Carolina,
Texas, Iowa.

Fig. 653. Polystoma hassalli. Ventral view.
(After Stunkard.)

X18.

18 (17, 21) Genital hooks 32 19

19 (20) Acetabula large, adjacent, not contiguous; pharynx smaller than
oral sucker. . . P. {Polystomoides) coronatum Leidy 1888.

Body 3. 1 5 by 0.83 mm. Caudal suckers
0.37 mm. in diameter. Caudal disc with
one pair of great hooks, 0.132 mm. long,
one pair of intermediate hooks, 0.051 nun.
long, and small hooks, 0.02 mm. long.

From the common food terrapin (Leidy).

Fig. 654. Polystoma coronatum. Ventral view.
X 9. (After Stunkard.)

PARASITIC FLATWORMS

377

20 (19) Acetabula small, widely separated; pharynx equal in size to oral
sucker. ... P. {Polystomoidcs) microcotyle Stunkard 19 16.

Body 3 by 0.78 mm. Caudal suckers
0.28 mm. in diameter. On caudal disc one
pair of great hooks, 0.116 mm. long, one
pair of intermediate hooks, 0.061 mm.
long, and small hooks, 0.017 mm. long,
(ienital coronet of 32 equal and similar
hooks.

In mouth of Chrysemys marginata;
Creston, Iowa.

Fig. 655. Polystoma microcotyle. Ventral view
X 9. (After Stunkard.J

21 (17, 18) Genital hooks more than 32 in number.

P. {Polystomoides) megacotyle Stunkard 19 16.

Body 2.5 to 2.7 by 0.71 to 0.78 mm.
Genital coronet 36 to 42 equal hooks.
Caudal suckers large, crowded. On caudal
disc one pair of great hooks, 0.116 mm.
long, one pair of intermediate hooks,
0.058 mm. long, and small hooks 0.017
mm. long.

From mouth cavity of Chrysemys mar-
ginata; Creston, Iowa.

Fig. 656. Polystoma megacotyle. V'entral view.
X 12. (After Stunkard.)

22 (16) Genital hooks Unequal in length.

P. {Polystomoides) ohlongiim Wright 1870.

Up to 2.5 mm. long and 1.5 mm. wide. Caudal suckers 0.2 mm. in diameter. Large hooks
on caudal disc 0.15 mm. and small hooks 0.015 mm. long. Genital coronet of 32 hooks, alter-
nately large and small, with free end sharply curved.

From urinary bladder of Aromochelys odoratus; Canada.

23 (15) Great hooks of caudal disc reduced in size or absent 24

I 24 (25) Genital hooks 16 in number.

P. (Polystomoides) orbicularc Stunkard iqi6.

Length 2.7 to 3.7 mm.; width o.y to
T.2 mm. Caudal suckers 0.3 mm. in
diameter. On caudal disc only a single
minute booklet 0.016 mm. long, in the
base of each sucker; no large ht)oks.
Genital coronet of 16 equal and similar
hooks. Fpg spherical, 0.21 to 0.^4 mm.
in diameter.
-^ In urinary bladder of Chrysemys mar-

FlG. 657. Polystoma orbiculare. E.Uended. Ventral «'"'^/''. and /'.v;H(/rwy5 scripta; North
view. X 10. (After Stunkard.) Carolina, Illinois, Iowa.

378

FRESH-WATER BIOLOGY

15 (24) Genital hooks 32 in number.

P. {Polystomoides) opacum Stunkard 1916.

Length 3 to 4 mm., width 0.8 to i mm. Caudal suckers 0.4 mm. in
diameter. On caudal disc many small hooklets 7 to 9 /x long, and one
larger pair, 75 /x long; no great hooks present. Genital coronet of 32
i.3>c>l) equal hooks. Egg oval, 0.25 by 0.2 mm.

Vitellaria of large compact follicles under dorsal surface from pharynx
to caudal disc except over ovarian complex; so extensively developed as
to obscure internal organs and render body opaque.

In esophagus of Trionyx ferox and of Malacoclemmys lesueurii;
Texas.

Fig. 658. Polystoma opacum.

Extended.
Stunkard.)

Ventral view. X 7- (After

26 (14) Posterior disc overhung by a flap bearing four hooks.

Diplobothrium F. S. Leuckart 1842.

Elongate, ectoparasitic trematodes with slender posterior end. Six short stalked suckers
arranged in two longitudinal rows and armed with chitinous hooks, stand just anterior to
slender caudal tip which carries two hooks on each side.

One species {D. annatum) reported on the gills of the lake sturgeon (Acipenser rubicundus)
from St. Lawrence River.

27(13) Posterior disc with two suckers Sphyranura Wright 18 jg.

Caudal lamina considerably wider than slender body, with two im-
mersed suckers, two large hooks behind them, and sixteen small hooks
arranged seven along each side of the lamina and one in each sucker.
Two contractile bladders anteriorly, each with a dorsal pore. No lateral
vaginae. Oviparous.

Only species known.

Sphyranura osleri R. R. Wright 1879.

On the skin of Nedurus lateralis in the Great Lakes region. Corre-
sponds to larval stage of Polystoma in having only two terminal
suckers.

Fig. 659. Sphyranura osleri.

Ventral surface.
MacCallum.)

X 20. (After Wright and

PARASITIC FLATWORMS

379

28 (2) Organs of attachment one or two suckers of which the anterior is
always single and median; without chitinous hooks or
anchors; accessory suckers rare. Subclass Digenea . . 29

Excretory organs empty by a single pore at or near posterior end. Uterus usually long
containing masses of eggs, rarely only a few. Development complex, with alternation of
hosts and most often also of generations.

With rare exceptions adults endoparasitic in visceral organs, usually alimentary system of ver-
tebrates. Isolated adults occur in moUusks and insects which are the normal hosts for young
stages.

For key to free living larval stages see section on Cercaria, 171 (170) in this key.

29 (30) Anterior sucker not perforate; mouth on mid-ventral surface; no
oral or ventral suckers. . . Order Gasterostomata Odhner.

Pharynx and esophagus present. Intestine sacculate, simple. Vitellaria lateral in anterior
region of body. Germ glands behind intestine, in posterior region. Testes two; cirrus elon-
c:ate; pore ventral near posterior end. Ovary simple, opposite or in front of anterior testis.

Single family Bucephalidae Poche 1907.

Only genus known Bucephalus von Baer 1826.

Anterior end bears large sucker with ventral orifice and small muscular
papillae at lateral angles.

The adult, better known as Gasterostomum, has been reported only from
Canada though to judge from the abundance of the characteristic two-tailed
cercaria it must occur frequently in other regions.

Stomach, intestine, and ceca of black bass and Boleosoma nigrum. Early
stages encysted in young black bass, rock bass, perch, and minnow.

Cercariae parasitic in Unionidae, especially in sex organs. Pennsylvania,
Illinois, Iowa, Canada. Not common; occurring in fifteen species of Unionidae
out of forty-four examined; in susceptible hosts only 4 per cent of individuals
affected (Kelly).

Representative North American species.

Bucephalus pusillus Cooper 191 5.

Fig. 660. Bucephalus pusillus. Ventral view. X 75- (After Cooper.)

30 (29) Mouth at or near anterior tip of body ordinarily surrounded by oral
sucker; another sucker if present median, behind mouth
on ventral surface or at posterior end.

Order Prosostomata Odhner . . 31

31 (36) Intestine simple, rhabdocoel; oral sucker ver>^ poorly developed;
ventral sucking organ a powerful, conspicuous, adhesive
disc or a series of smaller suckers.

Suborder Aspidocotylea Monticelli.

Terminal or subterminal mouth surrounded by funnel-shaped expansion of skin, but not by
true sucker. Holdfast organs ventral, usually in form of large sucking disc distinctly set
off from body and subdivided into numerous sucking alveoli, hut never carrying chitinous
hooks or anchors; or in place of disc single series of small disconnected suckers. .\limentar>-
canal simple, rhabdocoel. Sexual organs simple. Development with or without alternation
of hosts and generations. Endoparasitic, or rarely ectoparasitic, in mollusks and cold-blooded
vertebrates.

Forms not numerous, little known, grouped together at present into
a single family. . . Aspedogastridae Poche 1907 . . 32

380 FRESH-WATER BIOLOGY

$2 (ss) Adhesive organ oval, composed of four rows of alveoli.

Aspidogaster von Baer 1826.

Ventral sucking disc large, equal in breadth and nearly so in length
to entire body; oval in outline with four convergent longitudinal
rows of quadrangular sucking grooves. Margin notched, with sense
organs. Mouth terminal; intestine extending into posterior end.
Sexual pore median; in depression between ventral shield and fore-
body. Ovary small; testis single, same size as ovary. Uterus
moderately long; ova large. In fishes and moUusks.

Representative American species.

Aspidogaster conchicola von Baer 1826.

The common North American species in fresh water, Aspidogaster
conchicola v. Baer, is also the most common parasite of the Union-
idae. From pericardial and renal cavities of various species of the
group; St. Lawrence River; Havana, Illinois; North Judson, In-
diana; Iowa; Pennsylvania. Kelly reported thirty-seven cut of
forty-four species of Unionidae and 41 per cent of the 1577 individuals
examined were parasitized by this species. Occasionally found in
the intestine of various fishes into which it has been introduced
when its proper host, the mussel, was taken as food.

Fig. 661. Aspidogaster conchicola. Anterior end of ventral sucker as seen
from below combined with genital system, partly diagrammatic. Uterus
and yolk follicles left out. Est. X 35- (After Stafford.)

3i

(32) Adhesive disc oval, composed of three rows of alveoH 34

34 (35) Mouth subterminal, not surrounded by buccal disc.

Cotylaspis Leidy 1857.

(

Ventral shield much as in Aspidogaster, save that the alveoU
are in three longitudinal rows, the central alveoli being elongated
transversely. Marginal sense organs present, also two eyes.
Ovary dextral, smaller than single testis in posterior end. Ova
not numerous, large.

Of several species known, Cotylaspis insignis Leidy 1857, is
most frequent. It is adherent to surface of host in angle between
inner gill and visceral mass (Kelly) ; or branchial cavity (Leidy)
of many species of Unionidae: Havana, 111.; Grand Rapids,
Mich.; Lake Chatauqua, N. Y.; Cedar River, la.; SchuylkiU
River, Penn. Kelly examined over 1600 individuals of 44 species
which belong in 24 separate host species and found 18 per cent
infected. The number in a single host is small.

Representative American species.

Cotylaspis cokeri Barker and Parsons 1914-

C. cokeri Barker and Parsons occurs in the intestine of
Malacoclemmys lesueurii.

Fig. 662. Cotylaspis cokeri. Ventral view. X 30. a, X IS*
(Original.)

PARASITIC FLATWORMS

381

35 (34) Mouth terminal, surrounded by expanded buccal disc.

C ot yl ogasier 'MoniicdVi 1892.

Ventral disc composed of single median row of
grooves greatly elongated transversely and sur-
rounded by marginal row of small, circular alveoli.
Mouth in center of discoidal expansion of anterior
tip of forebody. Long prephar>'nx and esophagus.
Ovary and two testes just behind it form linear
series posterior to center of body. Laurcr's can^l
present. Embryo with large posterior sucker;
development unknown.

Parasitic in intestine of fishes.

Single North American species.
Cotylogaster occidentalis Nickerson 1 900.

In intestine of sheepshead (Aplodinolus Rrun-
niens), Minnesota. Rare.

Fig. 663. Cotylogaiter occidentalis. A. Lateral
view of an entire alcoholic specimen in which the an-
terior portion is retracted. X 8. B. Diapram show-
ing relation of organs as seen from the dorsal side, the
animal being represented as straightened horizontally
with the dorsal cone projected backward. Magnified.
(After Nickerson.)

36 (31) Intestine forked; oral sucker distinctly developed; ventral sucker if
present simple 37

In one genus (Cryptogonimiis) the ventral sucker consists of two small acetabula close
together; in a few genera it is more or less intimately connected with a genital sucker sur-
rounding the sexual pore, but in no case does it consist of a series of small sucking organs or
have a complex, many-parted structure.

The forms embraced under this heading in the four suborders which follow, stand in sharp
contrast with those of the suborder Aspidocotylea just preceding. In fact the latter are so dis-
tinct in general appearance, in structure, and in development, that they have regularly been
grouped heretofore apart from the orders which follow. They were generally included under
the Monogenea (p. 374) until Monticelli revived the original view that they should be regarded
as an independent subdivision of equal rank intermediate between the Monogenea and the
Digenea (p. 379). Their very recent inclusion in the latter group has been well justified; yet
even with that the striking differences noted above must be kept clearly in mind.

The forms which follow fall naturally into four groups ranked here as suborders; they are
easily distinguished by a single external feature, the adhesive apparatus, consisting of suckers
which in number and arrangement are characteristic of each group. Thus the holostomes h.ive
in addition to the oral and ventral suckers a special adhesive organ behind the latter ins
special organ is variable in form and character. In the amphistomcs one finds an oral and a
terminal sucker, but no other adhesive organs. The distomes p<issess an oral and a ventral
sucker but none further back, while finally the monostomes have only one sucker and that is
circumoral in location. . . • n

These long recognized groups are already beginning to break up under the influence of more
careful study, and as noted in the next section steps have been taken to eliminate the monostomes
as an independent subdivision, distributing its members among other groups.

382

FRESH-WATER BIOLOGY

37 (48) No ventral sucker present; oral sucker only adhesive organ present.

Suborder Monostomata Zeder . . 38

Endoparasitic trematodes with flattened body and single sucker which surrounds mouth
at anterior end. Intestinal crura often unite in posterior end of body. Genital pore usually
ventral or marginal in anterior region, or rarely rnedian posterior. Life history relatively un-
known. For developmental stages see 174 (183) in this key.

Forms not well known, though frequent especially in reptiles (turtles) and birds; rarely also
mammals. North American records scanty.

Most of the forms described from this continent as " :Monostomum " cannot be located
except generally in this section since the data are lacking on which a more exact determina-
tion depends. It is indeed likely that some of them were wrongly placed in this group and
more complete knowledge of their structure will result in their transfer to some other section.
Until the specimens are restudied they must all be regarded as uncertain. Such doubtful
forms are those hsted as Monostoma sp. in Stiles and Hassall's Catalog (1904) and the following:

Monostoma affine Leidy from muskrat, M. aminri Stafford from bullhead, M. aspersnm
Vaill of Pratt from salamander, M. incommodum Leidy from alligator (which later the author
conjectured to be in fact a distome), M. ornatum Leidy from frog, M. spatulatum Leidy from
"fish."

Odhner contends that the monostomes are isolated members of other groups that have
lost all suckers save the oral and that they should be classed in the various families from which
they have sprung. For practical reasons it will be necessary to retain the group at least until
its forms are much better known.

38 (45) With two compact testes, and follicular vitellaria 39

39 (44) Body elongated. Not parasitic in dermal cysts 40

40 (41) Intestinal crura connected at posterior end. Testes near posterior

end, within crura, asymmetrical. Ovary between testes,
and intercecal but opposite to them.

Family Cyclocoelidae Kossack 1911.

Large monostomes with thick, muscular body, somewhat flattened. Esophagus short, no
pharynx. (Kossack designates the structure which lies near the mouth as the pharynx; I have
called it the oral sucker. He says these forms do not possess an oral sucker.) Intestinal
branches simple or with small ceca on the inner side connected at posterior
end by continuous arch. Genital pore median, ventral to and near oral
sucker. Receptaculum seminis and Laurer's canal wanting. Vitellaria well
developed, lateral and sometimes dorsal to intestine; transverse duct just in
front of posterior testis. Uterine coils numerous, regular, transverse, occu-
pying space between posterior testis and fork of intestine. Eggs numerous,
without polar filaments.

Air passages of water birds; frequently reported as in body cavity.

Only American genus. . . . Cyclocoelum Brandes 1892.

Intestinal crura simple, genital pore near sucker, or at anterior margin.
Cirrus sac small, rarely extending beyond fork of intestine. Vitellaria
extracecal from fork of intestine to posterior end, not continuous with
opposite side. Reproductive glands in posterior region in arch of intestine
at corners of triangle. Ovary smaller than testes, on side opposite them.
Uterine coils do not extend laterad beyond the intestinal branches. Eggs
thick-shelled, large.

The species designated by Leidy as "probably Monostoma mutabile
Zeder" belongs here if his determination be accepted. It was collected
from the gray snipe {Gallinago wilscni).

Fig. 664. Cyclocoelum mutabile. X 3- (After Kossack.)

41 (40) Intestinal crura end blindly at posterior end. Testes symmetrical, in
posterior region, outside of crura. Ovary intercecal, between
testes. . . . Family Notocotylidae Liihe 1909 . . 42

Small monostomes with elongated flattened body tapering and rounded at both ends. On
ventral surface several (3 to 5) rows of small excrescences or papillae with unicellular dermal
glands Esophagus short, no pharynx; intestinal ceca simple, long, not united in posterior

PARASITIC FLATWORMS

383

region. Genital pore median, not far from oral sucker. Cirrus sac elongate enclosing only part
of the convoluted seminal vesicle. Testes symmetrical, near posterior end, outside intestinal
crura. Ovary between te.stes. V'itellaria lateral, anterior to testes. Uterine coils behind
cirrus sac, transverse, regular, not extending outside intestinal crura. Eggs with long fila-
ments at both poles.

42 (43) With conspicuous longitudinal rows of papillae on ventral surface.
Metraterm barely half as long as cirrus sac.

Notocotylus Diesing 1839.

Body attenuated in front, broadly rounded behind. V^entral surface
with three rows (in A'^. quinquesenalis with five rows) of glandular
masses which open into protrusible grooves.

European species reported from cecum of water birds.

Representative American species.

Notocotylus quinqueserialis Barker and Laughlin igii.

In North America one species; in the cecum of the muskrat.
Nebraska, Michigan.

Fig. 665. Notocotylus quinqueserialis. Ventral view. Magnified. (After
Barker and Laughlin.)

43 (42) \>ntral rows of papillae poorly developed. Metraterm about equal

in length to cirrus sac Catatropis Odhner 1905.

Body tapering only slightly, about equally rounded at both ends. \'en-
tral surface with three rows of poorly developed gland masses; the middle
row opens on a low keel or ridge; the lateral rows contain each eight to
twelve small wart-like, non-retractile prominences. Metraterm well de-
veloped, as long as cirrus sac.

European species in cecum and rectum of water birds.

Representative American species.

Catatropis filamentis Barker 191 5.
Only North American species; in the duodenum of the muskrat.

Fig. 666. Catatropis filamentis. \'cntral view. Magnified, (.\fter Barker.)

Nudocolylc novicia, very recently described by Barker from the muskrat, is
placed in this family despite some striking mori)hological dilTerences. The
form is small (0.7 to 0.9 mm. long by 0.5 to 0.65 mm. wide), thick-bodied,
and without ventral glands. The genital pore is lateral and well behind the
middle of the body, being thus far removed from the intestinal bifurcation.
The heavy pyriform cirrus pouch encloses part of the convolutnl seminal
vesicle. Vitellaria in compact masses lie e.xtracecal and just behind the
middle of the body. Transverse uterine coils extend over the intestinal
crura nearly to the lateral margins of the body; they fill the anterior half
and are limited posteriorly by the cirrus pouch and vitelJaria. The eggs
measure 20 to 24^ by 10 to 13/i and have long heavy polar filaments.

Parasitic in intestine of muskrat; Minnesota.

44 (39) Body compressed, broader than long. Parasitic in pairs in dermal

cysts Family Collyriclidae Ward.

Small to moderate sized monostomes with thick but not muscular body, smooth skin; oral
sucker and phaiynx present; ceca long, capacious, not united. C.enital pore ventral near
center of body; vitellaria follicular, scanty, antero lateral. Ovary much lobed. asymmetrical.
Testes oval, symmetrical behind ovary. Uterus in irregular coils showing a tendency to antero-
posterior direction. Terminal region of uterus enlarged.

Parasitic in dermal cysts on abdominal surface. Usually two in each cyst. In birds.

Only American genus 0>//ynV/Mm Kossack loi i.

Submoderate sized trematodes with dorsally arched and ventrally flattened Ixxly. Oral
sucker weak, pharynx small, intestinal crura simple, very broad. Oenital ixjre median, just

3B4

FRESH-WATER BIOLOGY

anterior to center. Vitellaria in seven symmetrical groups, marginal in anterior region.
Testes symmetrical. Ovary in front, strong] v lobed. Coils of uterus irregular, mostly lateral
in posterior half of body. Eggs very small.

Representative American species Collyriclum colei Ward.

The single European species, formerly known as Monostoma
faba, was reported for North America as the cause of an
epidemic among sparrows at Madison, Wisconsin. The life
history is unknown; the supposition that avian insect para-
sites act as the intermediate host is extremely improbable.
It attacks only young sparrows and infected birds are found
only during or just after a wet period (Cole).

The parasite has been found again in Boston, Mass. These
specimens differ clearly from the European form in numerous
minor details, such as ovary, yolk glands, dermal spines, etc.,
and demand recognition as a distinct species under the name
given here.

Fig. 667. Collyriclum colei. X 9- Detail of surface.
(Original.)

Xios.

45 (38) With elongate tubular testes and vitellaria.

Family Heronimidae W'ard

46

Moderate sized monostomes with thick, elongate, soft body somewhat flattened, tapering
both towards pointed anterior and bluntly rounded posterior end. Skin smooth. Oral sucker
weak, pharynx large, esophagus short, ceca simple, extending to but not united at posterior
end. Vitellaria compact, tubular, shaped like inverted V. Uterus in four longitudinal re-
gions. Genital pore ventral to oral sucker near anterior tip. Testes tubular, lobed or with
short branches, vmited into V-shaped organ with apex anteriad. Copulatory apparatus poorly
developed.

Limgs of reptiles. Northern North America.

Two genera imperfectly known which may prove to belong in a single genus.

46 (47) Vitellaria extend only half way
Seminal receptacle present .

from ovary, to posterior end.
. . Heronimus MacCallum 1902.

Oral sucker small, pharynx large, no esophagus, simple intestinal
crura which reach the posterior end but do not unite. Ovary oval
or bean-shaped, lateral in anterior third of body; receptaculum
present but no Laurer's canal. Uterine loops intracecal; terminal
section of uterus sacculate. Vitellaria small, elongate, not follicular,
tubular (?). Genital pore ventral to oral sucker. Testes Y-shaped
with coarse lobes, in median third of body, with median stem
directed anteriad.

Only species known.

Heronimus chelydrae MacCallum 1902.

In lungs and air passages of river snapping turtle {Chelydra ser-
pentina), Ontario, Canada.

Fig. 668. Heronimus chelydrae. From above, combined with dorsal view
showing male genital apparatus. (Excretory vesicle not shown.) Magnified.
(After MacCallum.)

PARASITIC FLATWORMS

385

47 (46) Vitellaria extend from ovary to posterior end of body. Seminal
receptacle absent. . . . Aorchis Barker and Parsons iqi4.

Oral sucker small, weak, pharynx large, esophagus short,
intestinal ceca long, not united at posterior end. Ovary entire,
just behind fork of intestine. \'itellaria compact, tubular^
coarsely lobed or with short irregular branches extending almost
entire length of body. Two divisions of uterus looped or coiled
around intestinal ceca. Other two divisions straight longitudi-
nal tubes. Terminal division conspicuous, heavy, dark band
through length of the body in the median plane. Testes
elongate, tubular, irregularly lobed. Genital pore ventral,
near anterior tip of body. Eggs with short polar stalk at one
end.

Type species.

Aorchis extensus Barker and Parsons 19 14.

Lungs oi Chrysemys marginata, Mississippi River (Minnesota)
and also, in various turtles from Michigan, Indiana, Illinois,
Nebraska.

Fig. 669. Aorchis extensus. Only anterior portion of testes shown
in drawing. X 8. a. Embryos in uterus; note conspicuous eye spots.
X 22. (Original.)

48 (37) Ventral sucker present, usually single though varied in form and

position; never represented by numerous small organs in
series 4g

The acetabulum or ventral sucker proper is a closed organ, not possessing any inner opening
or connecting with any special organ or system. It may be so insignificant in size as to be
difficult to distinguish, in which case the form is erroneously diagnosed as a monostome as has
often occurred. On the other hand it may be as wide as the body or wider and so powerful
as to distort the form of the animal. It may be sessile or be borne on a stalk or peduncle.

In some species a special secondary sucking organ is developed around the genital orifice
and this may even become so highly differentiated as to exceed in size or include the true ven-
tral sucker. Those forms which possess this highly developed adhesive organ ordinarily have
the body divided into two distinct regions.

In location the acetabulum is near the posterior end in the group of amphistomes and at or
anterior to the center of the body in the distomes and holostomes. The latter are readily
recognized by the peculiar adhesive organ and the separate regions of the body even though
the details of form are very variable in different genera.

49 (62) Acetabulum terminal or subterminal and posterior to the repro-

ductive glands Suborder Amphistomata Nitzsch.

Endoparasitic trematodes with oral opening anterior and terminal. Oral sucker powerful,
oval or more elongate, often with two dorso-lateral muscular pockets. Acetabulum conspicu-
ous, much larger than oral sucker, at or very near posterior end. Body muscular, thick, little
flattened and often conical, tapering anteriad. Skin without spines but regularly provided
with sensory or glandular papillae. Excretory bladder sacculate, with median ventral pore
near posterior end. Genital pore ventral, median, in anterior region. Testes large anterior
to small ovary. Vitellaria follicular, lateral, paired. Uterus simple, with few coils. Eggs
numerous, small, plain. Development complex with alternation of generations and hosts.

Only family recognized.

Paramphistomidae Fischoeder iqoi . . 50

50(61) Oral sucker terminal; acetabulum simple, not divided 51

51 (52) No postero-lateral pockets on pharynx.

Subfamily Paramphistominae Fischoeder iqoi.
None of these forms is parasitic as adults in aquatic animals. One species occurs in domes-
tic ruminants in North America. The redia and cercaria develop in some fresh, water snails as
is known of the related European forms. Compare 185 in this key.

386 FRESH-WATER BIOLOGY

52 (51) Postero-lateral pockets present on pharynx.

53

53 (56) Testes two, more or less deeply lobed.

Subfamily Cladorchiinae Fischoeder 1901

54

Amphistomes with more or less strongly flattened body, and with acetabulum usually con-
spicuously ventral, rarely only terminal. Testes branching or lobed. Cirrus sac incom-
plete or nearly wanting.

In this subfamily belongs possibly the "Amphistoma grande Diesing" of Leidy from the terra-
pin which does not seem to conform to the species designated. The description is inadequate
for a final diagnosis.

54 (55) Pharyngeal pockets small, not affecting external boundary of oral
sucker Stichorchis Fischoeder 1901.

Body noticeably attenuated anteriorly, broadly rounded posteri-
orly. Margins rounded, dorsal surface high, arched, ventral flattened.
Acetabulum ventral. Pharynx lacking; crura not much separated
from lateral margins. Cirrus sac small, genital sucker not conspicu-
ous. Vitellaria well developed, mostly behind testes and median
to crura, as well as partly dorsal and ventral to same.

North American species.

Stichorchis siihtriquetrus (Rudolphi) 1814.

One species, St. suhtriquetriis, the true A mphistoma subtriquetrum
Rud. In intestine of the beaver; Quebec, Ontario.

Fig. 670. Stichorchis subtriquetrus. Dorsal view to show arrangement of
parts. Magnified. (After Duff.)

55 (54) Pharyngeal pockets large, conspicuous, modifying greatly outline of
oral sucker Wardiiis Barker and East 191 5.

Moderate sized amphistomes with prominent pharyngeal pockets, and
large subterminal sucker. Esophagus well developed, without differ-
entiated regions; crura long and wavy. Testes shghtly lobed, tandem,
in center of body. Ovary median, behind testes near posterior sucker.
Genital pore posterior to bifurcation of intestine. Vitellaria extend out-
side crura from oral to posterior sucker.

Only one species.

Wardius zihethicus Barker and East k

'15.

In cecum of muskrat. Regarded by these authors as the "^;w-
phistomiim subtriquetrum Diesing" of Leidy (1888).

Fig. 671. Wardius zibethicus.

Ventral view, specimen compressed.
(After Barker.)

Magnified.

56 (53) One or two testes, spherical 57

PARASITIC FLATWORMS

387

57 (58) Vitellaria consist of few large follicles or form i)aired compact organ.
No cirrus sac. . . Subfamily Diplodisci.vae Cohn 1904.

Moderate sized amphistomes with conical body, round in transsection, attenuated ante-
riorly. Terminal sucker very large. Intestinal crura extend to terminal sucker, relatively
broad. Vitellaria a few large follicles on each side which may be
condensed into a more or less compact but lobed organ.
In alimentary canal of Amphibia and Reptilia.

Only North American genus.

Diplodiscus Diesing 1836.

Two testes confluent in older specimens. Genital pore near oral
opening. Esophagus long, pharynx-like enlargement at bifurcation
of intestine, not sharply marked ofT. Excretory vessels looped into
coils, some above and some below intestine.

Only North American species.

Diplodiscus temperatus Stafiford 1905.

Rectum of various frogs,
braska, Minnesota.

Canada, Pennsylvania, Indiana, Ne-

FiG. 672. Diplodiscus temperatus. Adult worm somewhat contracted,
drawn from the ventral side as a transparent object. Magnified. (,.\fter
Gary.)

58 (57) Vitellaria consist of small scattered lateral foUicles. Cirrus sac

present. . . . Subfamily Schizamphistominae Looss 191 2.
Representative North American genus.

Allassostoma Stunkard 1916 . . 59
Large oral invaginations open independently into oral sucker; no preoral sphincter; esoph-
ageal bulb composed of concentric muscle lamellae. Hermaphroditic duct present, (ierm
glands median, near center of body. Both testes anterior to ovary. Vitellaria consist of small
scattered lateral follicles, in posterior region with median follicles also. Laurer's canal opens in
mid-dorsal line anterior to excretory pore.

59 (60) . Large worm (over 10 mm. long) with small suckers.

Allassostoma magnum Stunkard 1916.

Length 10 to 12 mm., breadth 3 to s mm., thickness 1.5 to 2 mm.
Living worm clear, slow-moving, capable of great extension. Acetabu-
lum sub-terminal, ovoid, wider anteriad, 2 to 2.5 mm. long by 2 mm. wide.
Oral sucker terminal, 0.9 to 1.35 mm. long by 0.6 to 0.9 mm. wide; oral
pockets arise at posterior end of oral sucker by separate lateral openings
and extend dorsad and caudad.

Testes oval, 0.27 to 0.35 by 0.45 to 0.9 mm., long axis transverse,
located near center of body and slightly oblique. Ovary median, spheri-
cal or oval, 0.28 to 0.35 by 0.33 to 0.57 mm. in diameter. \'ilelline
foUicles small, sparse, anteriorly extracecal, but posteriorly also intracccal.
No receptaculum seminis and nc vitelline reservoir. Eggs 0.1 by o.ii
mm.

In intestine of Pseiidemys; Illinois, Missouri.

Fig. 673. Allassostoma magnum. W-ntral view. X a. (After Stunkard.)

60 (59) Small worm (length about 3 mm. or less) with large .suckers.

Allassostoma parvum Stunkard 191 6.
From Chetydra serpentina; Urbana, 111.

388

FRESH-WATER BIOLOGY

6i (50) Oral sucker, subterminal ; acetabulum divided by transverse ridge
into two pockets. , . . Subfamily Zygocotylinae Ward.

Differs from all other subfamilies in position of oral sucker and
ofY-yy. peculiar character of acetabulum. Testis lobed; ^cirrus sac lack-

"'""' ing.

Representative American genus.

Zygocotyle Stunkard 19 16.

Acetabulum consists of anterior part extending dorsad and
anteriad into body, and posterior overhanging lip bearing on each
side conical projection. Posterior end of esophagus surrounded
by muscular bulb in which fibers are not arranged in concentric
lamellae as in other amphistomes. Vitellaria well developed, with
large follicles, in extracecal region from oral sucker to acetabulum.
Uterus and germ glands intracecal. Eggs numerous, 0.14 by
0.083 min-

Type species. . . Zygocotyle cerafosa Stunkard 19 16.

From intestine of Anas platyrhynchos; Nebraska.

Fig. 674. Zygocotyle ceratosa. Ventral view. X 5- (After Stunkard.)

62 (49) Acetabulum conspicuously ventral and usually anterior to center of

body. Reproductive organs completely or largely posterior
to acetabulum 63

63 (160) No holdfast organs present except oral and ventral suckers. No

sharp separation between anterior region with holdfast
organs and posterior region with genital organs.

Suborder Distomata . . 64

64 (159) Hermaphroditic distomes 65

65 (148) Ovary anterior to testes 66

66 (107) Coils of uterus do not extend posterior beyond testes, or at most not

beyond the posterior testis 67

Bunodera (see 103 in this key) forms the single exception.

67 (106) Acetabulum a single typical sucker which may be stalked or united

with special genital sucker but is not divided 68

68 (105) Not more than two testes present 69

69 (74) Both ovary and testes dendritic; uterus limited to a restricted

area 70

PARASITIC FLATWORMS

389

70 (73) Large flattened distomes; ovary and testes both highly branched;
uterus median, a short series of transverse coils.

Family Fasciolldae Railliet 1895.

Large distomes with muscular, more or less broad and flattened leaf-shaped body. Ventral
sucker powerful, close to anterior end. Intestinal crura extend to posteror end. Excretory
bladder tubular, extends anteriad beyond testes. Genital pore median, at anterior margin
of acetabulum. Cirrus and cirrus sac well developed. Ovary lateral, in front of acetabulum.
testes symmetrical, postacetabular. Vitellaria extensive, reaching posterior end. Uterus
short, in condensed coil, entirely preovarian. Eggs very large, thin shelled, in moderate num-
bers. Development with alternation of hosts and generations.

Parasites in intestine and gall ducts of Mammalia.

Reported in North America.

Subfamily Fasciolinae Stiles and Hassall 1898 . . 71

71 (72) Anterior tip distinctly set off from main body; vitellaria both dorsal
> and ventral of intestinal branches. F(Z.yc/o/(Z Linnaeus 1758.

Very large distomes with leaf-shaped body having so-called "cephalic
cone" set off at anterior end, and pointed posterior end. Skin spinous.
Acetabulum large, at junction of cephahc cone and main body. Esophagus
short, with pharynx and prepharynx. Intestinal crura near median line,
extend to posterior end, provided on mesial aspect with short branches
and on outer side with long branches which again may be branched.
Uterus in front of acetabulum, forming a rosette. Vitellaria richly de-
veloped in lateral area, and in posterior region also on both surfaces of body.

In the gall passages of herbivores, very rarely in man.

Type species.

Fasciola hepatica Linnaeus 175S.

An introduced species {F. hepatica) common in sheep and cattle in
limited regions; Long Island, N. Y., introduced from Texas, Gulf States,
California. The North American intermediate host is not known. Stiles
suspects Limnaea humilis Say.

Fig. 675. Fasciola hepatica. X 3- (Original.)

72 (71) No distinct anterior conical portion. X'itellaria ventral to intestinal
branches Fascioloides Ward.

Body very large, broad, thick, without separate anterior portion or cephalic cone, iwsterior
end bluntly rounded. Vitellaria confined to region ventral to intestinal branches.

Type species Fascioloides magna (Bassi) 1875,

In liver and lungs of Xorth .\merican herbivores both do-
mestic and wild; usually included in former genus. On the
advice of Odhner anew genus is made for the Xorth .Vmcrioin
form. First discovered in a European zoological garden para-
sitic in the wapiti, it is known to occur in many hosts and to
be widely distributed from Maine to California. It is espe-
cially abundant in parts of the South. Egg and embr>'o are
said by Stiles to agree with those of the last species.

Fig. 676. Fascioloides magna. Intestinal crura and branches
drawn as solid black lines. Natural size. (Original.)

Another genus, Fasciolopsis, common as a parasite of man
in some parts of the East, has been reported in \orth .\nu-rica
a few times as a human parasite. Apparently all these rases
have been imported and the parasite has not so far as known
gained a foothold on this continent.

390

FRESH-WATER BIOLOGY

73 (70) Distomes moderate in size, thick bodied; ovary and testes lobed
or coarsely branched; uterine coil chiefly lateral to acetab-
ulum Family Trogloteematidae Odhner 19 14.

Distomes of small to moderate size with compressed body. Skin with spines in groups.
Ventral surface flat, dorsal arched. Musculature and suckers poorly developed. Intestinal
crura do not reach posterior end. Excretory bladder Y-shaped, or tubular. Genital pore
close to acetabulum. Cirrus sac lacking. Testes symmetrical, postacetabular. Ovary
dextral, immediately in front of testes, lobed or branched. Laurer's canal present. Vitel-
laria very extensive, covering dorsal surface save for narrow median strip. Uterus long, in
open loops, or shorter in tight coil; eggs in first case small, in second moderately large.

Parasites of birds and carnivores, living usually by pairs in cyst-Nke cavities.

The monostome, CoUyriclum colei\{p. 384). is regarded by Odhner as properly a member of-
this family.

Only American genus Paragonimus M. Braun 1899.

Body opaque, thick, nearly rounded in cross section. Skin
with spines. Pharynx ahnost spherical, crura wavy with irregular
walls. Testes lobed, symmetrical, in hindbody. Ovary lobed,
lateral, pretesticular, and postacetabular. Vitellaria extend en-
tire length of body, lateral and dorsal. Laurer's canal and
rudimentary receptaculum present. Uterus in coil, postacetabu-
lar, opposite ovary. Eggs large, thin-shelled, laid before cleav-
age begins.

Encysted, in pairs usually, in lungs of mammals.

Single American species.

Paragmiimus kellicotti Ward 1908.

Parasitic in dog, cat, and pig. Ohio, Illinois, Wisconsin,
Minnesota, Kentucky. Confused in records with the human
lung fluke (P. westermanii Kerbert) which has been positively
determined in North America only in a few human cases, all of
which are probably imported from Asia.

Fig. 677. Paragonimus kellicotti. Total preparation, ventral surface.
The vitellaria are represented on the left side and omitted on the other
side in order to show ovary, testis, vitelline ducts and intestine normally
obscured by them. X 38. a, egg from same specimen. X 150-
(After Ward and Hirsch.)

74 (69) Ovary and testes entire or lobed but not dendritic 75

75 (82) Oral sucker surrounded by a reniform collar open ventrally and

bearing a series of strong spines.

Family Echinostomidae Looss 1902 . . 76

Elongate distomes, very variable in size. Acetabulum powerful, close to anterior end.
Oral sucker small, weak or degenerate; anterior end surrounded laterally and dorsally by
skin fold or "collar" which carries large spines ("spikes") definite in number and arrange-
ment. "Corner spines" on ventro-median lobe usually difi'er from others, i.e., "marginal
spines." Skin in anterior region at least richly provided with fine dermal spines. Pharynx
and esophagus present; intestinal crura extend almost to posterior tip. Excretory bladder
Y-shaped with numerous lateral branches. Genital pore median, near acetabulum or between
it and fork of intestine. Cirrus and cirrus sac well developed. Germ glands postacetabular,
usually median; ovary pretesticular, sometimes lateral. ViteUaria lateral, well developed,
reaching posterior end. Uterus between ovary and acetabulum, with scanty^ lateral loops,
or none. Laurer's canal present, receptaculum seminis absent. Eggs large, thin shelled, not
numerous. Development with alternation of hosts and generations. For characteristic
cercariae see 224 (220) in this key.

Parasites of intestine, rarely of gall ducts, in mammals and birds.

76 (81) With well-developed oral sucker. Parasitic in intestine. ... 77

77 (80) Anterior region not enlarged. Spines in a double row 78

PARASITIC FLATWORMS

391

78 (79) ' Uterus long and much coiled Echinostoma Rudolphi 1S09.

Echinostomes of moderate size with elongate body. Collar with double unbroken row of
spines. Oral and ventral suckers close together. Cirrus sac reaches ordinarily center of
acetabulum. Cirrus long, not spinous, when contracted it lies in coil. Vesicula seminalis
twisted, not bipartite. Pars prostatica present. Vitellaria lateral, posttesticular extendiuL'
in places towards median line. Uterus long, much coiled. Eggs large. '

A mixed group of unplaced and unrelated species, many of which are' not well enough known
to determine their, true place in the family. Several uncertain North American species are
reported under this generic name from chickens (Hassall), and muskrat (Leidy) Some forms
from the muskrat are more perfectly described by Barker et alii.

79 (78) Uterus short, coils few, open. . . . Echinopharyphium Dietz 1909.
Small echinostomes, slender. Much Uke last genus except in absence of pars prostatica

Cirrus sac long, often extending dorsad, or posteriad to center of acetabulum. Uterus short-
eggs not numerous, large. '

The placing of Distomum flcxnm Linton from the black scoter (Yellowstone Lake) in this
genus is probably correct. Another species has been reported by Barker and Bastion from the
muskrat.

80 (77) Spines in a single row. Subfamily Echinochasminae Odhner 1910.

Spines in a single row interrupted at the mid-dorsal line, with 20 to 26
spines only. Cirrus sac when present pyriform. not projecting behind
the center of the acetabulum. Vesicula seminalis not coiled, distinctly
bipartite.

Several genera common in Europe.

Only genus yet recorded from North America.

Stephanoprora Odhner 1902.

Small, elongate echinostomes. Cirrus sac well developed, cirrus short
but muscular, often apparently entirely preacetaljular. Testes median,
close together, in posterior half of body. Vitellaria lateral, never prc-
acetabular, often nearly confluent along median line. Uterus not long;
eggs of moderate size.

Representative American species.

Stephanoprora gilhcrti Ward.

The species reported by Gilbert from the loon iGavia imhrr) and from
Bonaparte's gull {Lams Philadelphia) near Ann .\rbor, iMichigan, probably
belongs to this genus. It cannot be Echinostoma spinulosum Rud., as
designated.

Fig. 678. Stephanoprora gilberti. X 7a (Original.)

Parasitic in gall ducts.

Pcgosomum Ratz 1903.

Echinostomes of moderate^ size with lance-shaped muscular body. Collar poorly developed,
with single row of blunt spines. Skin spinous. Oral sucker entirely degenerate. Pharyn.x
present. Fork of intestine not near acetabulum which is powerful and near center of body.
Cirrus sac large, mostly preacetabular. Testes median, in posterior half of body. Ovary
dextral, postacetabular and pretesticular. Vitellaria from pharynx to posterior end, confluent
in median line, only in front of genital pxire. Uterus short. Eggs large, not numerous.

In gall ducts of Ardeidae. Only one species reported from North America as Distomum
asperum Wright from Ardea minor.

82 (75) Oral sucker without collar and spines ^;^

A condition not represented in the key is found in the AcANTHOcMiASMroAE where the large
funnel-shaped oral sucker opens at the anterior tip and is surrounded by a crown of promi-
nent spines. Acanthochasmus coronarium (Cobbold) was taken from the alimentary canal of
an Alligator mississipicnsis that died in England. According to Odhner Crypto^^onimus and
Caecincola are meml^crs of this family which have lost the crown of spines. Drropristis may also
be related to it.

83 (94) Genital glands median in linear series in posterior region of body. 84

81 (76) Oral sucker degenerate.

392

FRESH-WATER BIOLOGY

84 (91) Uterus between ovary and acetabulum, possessing an ascending

ramus only. Testes ordinarily behind ovary and close to
it, or rarely {Leiiceruthrus) near acetabulum and separated

from ovary by coils of uterus 85

In Deropristis hispida, a peculiar distome found in Acipenser in Europe and reported once
by Stafford in the lake sturgeon from Canada the arrangement of the germ glands differs from
either plan noted in the key line above. Two oval testes are median in posterior end; median
ovary lies near large receptaculum, separated from acetabulum and testes by about equal
distances which are filled by uterine coils. Uterus has short descending ramus which extends
posteriad from ovarian complex to anterior testis, and long ascending ramus from this pomt_ to
genital pore on median anterior margin of acetabulum. Vitellaria are extracecal, in uterine
region. Cirrus sac and seminal vesicle, nearly median and postacetabular, are both well de-
veloped, but rather distinctly separated. The relationship of the genus is not clear and the
American record needs confirmation, hence this form is not included in the key.

85 (88) Body muscular; cirrus sac present.

Family Azygiidae Odhner 191 1 . . 86

Infra-medium to large distomes. More or less elongate, flattened, with thick, muscular
body. Suckers powerfully developed. Skin smooth, on contraction drawn into irregular
transverse folds. No prepharynx. Pharynx powerful, esophagus very short, intestinal crura
reach posterior end. Excretory bladder Y-shaped with very long branches reaching even to
anterior end. Genital pore median, in front of and above acetabulum; genital sinus spacious.
Uterus with ascending limb alone, extending direct from ovary to genital pore in closely laid
transverse loops. Laurer's canal present; receptaculum seminis wanting. Vitellaria follic-
ular, lateral, extracecal, not reaching to posterior end. Eggs 45 to 85 n long, with cap; when
deposited they contain each a ripe embryo, regularly nonciUated.

Stomach parasites of fishes.

86 (87) Germ glands form series in posterior region; ovary anterior, not far

separated from testes Azygia Looss 1899.

Distomes of moderate size or larger, with slightly flattened, much elongate, nearly cyhndri-
cal muscular body, rounded at both ends (Fig. 652). Genital pore close to acetabulum. Cirrus
sac present. Seminal vesicle long and coiled. Uterus intercecal, in center third of body.
Vitellaria extend at least between acetabulum and posterior testes. Ovary and testes behind
middle of body. Main stem of excretory bladder splits behind testes; lateral branches do not
unite in anterior region. Eggs 45 by 21 ^ with thin shell and albumen covering.

Azygia is a powerfully muscular type and is usually much distorted in the process of preser-
vation so that a lot of specimens taken from the same host at the same time present marked
external differences in the preserved condition. Such extreme specimens have been the basis
for various new genera, e.g., Megadlstomum of Leidy and Stafford, Mimodistomum of Leidy
and Hassalliiis of Goldberger. The same factor has led to the separation of too many as species.

Despite many records of its occurrence the common European A . lucii {= A. tereticolle) has
not been found in North America. Several species pecuHar to this continent occur in Amia calva,
Micro pter us salmoides and dolomieu, Esox lucius and reticulatus, Ambloplites rupestris, Salve-
linus namaycush, Lucioperca, Lota lota, Salmo sebago. Maine, St. Lawrence, Great Lakes,
Wisconsin.

87 (86) Testes just behind acetabulum, separated from ovary by coils of

uterus Leuceruthrus Marshall and Gilbert 1905.

Anterior end rounded, posterior end pointed. Oral sucker ventral, promi-
nent, acetabulum one-half as large. Intestinal crura slender, straight, ex-
tending nearly to posterior end. Excretory vesicle forking at ovary. Testes
small, postacetabular, oblique to each other. Uterus at first confined to area
between intestinal crura, ovary and testes, later filUng posterior three-fourths
of body. Vitellaria lateral, in posterior half of body. Laurer's canal present.

One species known (L. micro pter i) from mouth and stomach of black bass
and bowfin in Wisconsin and Indiana.

Odhner advocates the association of this genus with Azygia from which
it differs primarily only in the fact that the testes have moved from their
original place behind the ovary and have been drawn anteriad by the
shortening of the sperm ducts to a location a Httle posterior to the acetabu-
lum. This is the relation they hold in Hemiurus, marine distomes descended
from the Azygiidae.

Fig. 679. Leuceruthrus micropteri. Ventral view showing internal topography.
After a press preparation. Very slightly diagrammatic. Magnified. (After Gold-
berger.)

PARASITIC FLATWORMS

393

88 (85) Body flat, thin, transparent; no cirrus sac present.

Family Opisthorchiidae Luhc 1901 . . 89
Elongate flattened transparent distomcs with weak musculature. Suckers close toRcthcr
and very weak Intestinal crura reach fully or nearly to posterior end. Excretory bladder
Y-shaped with short branches and long stem. Genital pore close in front of acetabulum No
cirrus or cirrus sac. Coiled seminal vesicle. Germ glands in series in posterior region ovary
in front of testes. Vitellaria outside intestinal crura, moderately developed, not reaching
posterior end. Uterus long, preovarian, in transverse loops, mostly postacetabular Ercs
very numerous, small, light yellowish brown in color.

Parasites of gall passages of Amniota.
_ An important parasite of man, Clonorchis sinensis, which belongs to this family has been
introduced several times into this continent but apparently has not gained a footing.

89 (90) Neither uterine coils nor vitellaria extend anteriad beyond

acetabulum Opisthorchis R. Blanchard i'8o5.

Anterior end conical, posterior end broader. Main stem of excretory bladder S-shaped,
passing between testes, anterior forks of Y short. Vitellaria in groups.

In gall ducts of mammals, birds, and (?) fishes. Young distomes encysted in skin and con-
nective tissues, especially subdermal tissue of fishes.

Several species in North America; best known O. pscudojelineus Ward 190 1 in the cat.

Fig. 680. Opisthorchis pseudofelincus. From liver of cat

(( rii,'inal.)

90 (89) Uterine coils and vitellaria both in part anterior to acetabulum.

Metorchis Looss 1899.

Small to moderate sized distomes with short, compressed body tapering anteriad. Skin
spinous. Testes slightly lobed, nearly symmetrical. Coils of uterus compact, extending clearly
over crura to margins. Vitellaria compact, extending anterior to acetabulum.

A single American species M. complexus (Stiles and Hassall) from the liver of cat. New
York, Maryland, District of Columbia. Peculiar in extent and arrangement of vitellaria and in
position of testes. May need to be transferred to a new genus when its structure has been
worked out.

Fig. 681. Metorchis complexus. Magnified, (.\fter Stiles and Hassall.)

91 (84) Ovary anterior, near acetabulum, separated from one or both testes
by coils of ascending and descending rami of uterus.

Subfamily Telorchiinwe Looss 1899. . 92

Small to middle sized distomes with slender, elongate, spinous, somewhat flattened body.
Anterior region very mobile; posterior region stable, .\cctabulum small, in anterior region.
Pharynx present, esophagus variable, crura long. Testes tandem, both in i^)sterior end or
one there and the other not far behind ovary. Laurer's canal and receptaculum seminis pres-
ent. Vitellaria lateral, elongate, outside intestinal crura. Uterus in coils or loops between
ovary and testes or when one testis is near ovary, between ovary and posterior testis. Eggs
numerous, small.

In the intestine of reptiles.

394 FRESH-WATER BIOLOGY

92 (93) Genital pore anterior to and near acetabulum; cirrus sac very long
extending far behind acetabulum to round ovary.

Telorchis Liihe 1899.

Small to middle sized distomes. Musculature light; hence worms translucent. _ Testes
close together, near posterior end, separated from ovary which lies at the end of the cirrus sac
and near the center of the body, by a mass of uterine coils. Excretory vesicle long, median,
extends anteriad about to ovary where it forms two lateral branches.

Species distinguished by length of esophagus and direction and extension of uterine coils.
Cercorchis Liihe with esophagus and having uterine coils entirely intercecal, grades into Telorchis
s..§tr. Liihe (without esophagus and with uterus coiled beyond ceca), and cannot be accepted
as a valid subgenus.

Apparently confined to reptiles; six or more species in North America". Revision of genus
by Stunkard.

(After Stunkard.)

93 (92) Genital pore dorso-lateral, separated by marked interval from ace-

tabulum. Cirrus sac entirely preacetabular.

Protenes Barker and Covey 191 1.
Two species, P. leptus Barker and Covey and P. angnstiis (Stafford) in North America.
From Chrysemys marginata and C. picta.

94 (83) Ovary lateral; testes either median or slightly lateral 95

95 (96) Ovary separated from acetabulum by coils of uterus.

Plagioporus Stafford 1904.

Small, fusiform distomes with acetabulum larger than oral sucker and anterior to middle
of length. Skin smooth. Pharynx and esophagus present; crura extend to posterior end.
Testes median, close together in center of postacetabular region. Ovary small, lateral, just
in front of anterior testis. Uterus from ovary to acetabulum. Genital pore lateral, on level
of intestinal bifurcation. Cirrus sac large, preacetabular, obliquely transverse. Vitellaria
lateral, from esophagus to posterior end.

Only species known Plagioporus serotinus Stafford 1904.

Intestine of large-scaled sucker {Moxosionia macrolepidotum) in Canada.

96 (95) Ovary close to acetabulum, at least not separated from it by coils of

uterus 97

97 (104) Testes large, in posterior region of body, separated from ovary by

small uterus with few eggs; or when eggs are numerous,

they extend beyond testes into posterior end {Bunodera

only). . . Family Allocreadiidae Odhner 1910 . . 98

Distomes of small to moderate size; body attenuated and mobile 'anteriorly. Suckers

well developed. Pharynx and esophagus present; crura long, but not reaching posterior end.

Genital pore near acetabulum or not more than halfway to oral sucker, median or sHghtly

lateral. Ovary lateral, behind but not far from acetabulum. Testes large, proximate, in

posterior region halfway or more from acetabulum to posterior end. Vitellaria lateral. Eggs

large.

Parasites of fishes; rarely of higher vertebrates.

98 (103) Uterus short with few coils, between anterior testis and acetab-

ulum.

Subfamily Allocreadiinae Odhner 1905 . . 99
Acetabulum at end of first third or fourth of total length. Excretory bladder single, un-
divided, sac-shaped, rarely pyriform. Genital pore preacetabular, median or slightly lateral.
Cirrus and sac large, well developed. Testes large, proximate, median or oblique in posterior
region. Ovary spherical or lobed, close between acetabulum and testes, not median. Vitel-
laria lateral, well developed, partly covering crura, often confluent behind testis.
Eggs not numerous, usually large.

PARASITIC FLATWORMS

395

99 (loo) Oral sucker smooth; not provided with muscular papillae around
anterior end • . . . Allocrcadium Looss 1900.

Esophagus long, not dividing, until just before the acetabulum. Ex-
cretory bladder very short, ending at posterior margin of posterior testes.
Ovary spherical, lateral; vitellaria e.xclusively ventral. Cirrus and sac
rather short; prostate well developed. Genital pore median. Eggs
without filament, large (60 to 90 n) with light yellow shell.

Intestine of fresh-water fishes.

Several species from stomach and intestine of sheepshead, pum[>lcin-
seed, sturgeon, sucker, dace, minnow, and gall-bladder of red-finned min-
now. Collected in (ireat Lakes region. Lake Erie, Ontario; Lake
Sebago, Maine. Synopsis of genus by Wallin.

Young forms of A. commune Olsson encysted in Mayfly nymph
(Blasturus ciipidus Say) with eggs and living miracidia in body cavity
of nymph (Cooper).

Representative American species.

Allocreadium lohatiim Wallin 1909.

Length 4 to 7 mm., breadth i to 1.5 mm. Suckers equal, 0.46 to 0.5
mm. in diameter. No prepharynx; pharynx 0.24 to 0.3 mm. long by
0.22 mm. broad.

Testes lobed; cirrus sac extends to center of acetabulum. Ovary
spherical; vitellaria postovarial, profuse, confluent behind posterit)r
testis. Receptaculum large, pyriform, between ovary and anterior testis.
Uterus compact, between anterior testis and acetabulum. Eggs very
numerous, 67 to 85 m long by 46 to 57 ^ broad.

Fig. 683. Allocreadium lohatum. Uterus indicated by dotted area,
added from slide. X 19. (After Wallin.)

100 (99) Six oral papillae surround anterior end loi

loi (102) Genital pore anterior to fork of intestine.

Crepidostomum Braun 1900.

Bifurcation of intestine just anterior to acetabulum. Excretorj' bladder
elongate. Cirrus sac muscular; pore anterior to fork of intestine; testes
large, round, median, halfway from acetabulum to posterior end. Vitel-
laria confluent behind testes. Uterus short, with few eggs, between ace-
tabulum, ovary, and anterior testis. In intestine of fresh-water fishes.

Several species not adequately described.

Representative American species.

Crepidostomum conmtum (Osborn) 1903.

Probably the best known species in the North American fauna is C.
cornutum (Osborn) from the stomach and pyloric ceca of black buss, rock
bass, channel cat, perch, sunfish, darter, etc. Immature forms encysted in
viscera of various crayfish, Ontario, Canada. The worm manifests pre-
cocious sexual maturity as the larger cysts contain many eggs already ex-
truded. Very young forms have been taken from Mayfly nymphs {Hexa^cma)
by Cooper.

Fig. 684. Crepidostomum cornutum. Ventral view; compressed. X 20. (.After
Osborn.)

396

FRESH-WATER BIOLOGY

[02 (loi) Genital pore posterior to fork of intestine. . Acrolichanus Ward.

(Syn. Acrodactyla Stafford 1904 preocc.)

Body uniform in width or slightly constricted behind oral sucker which is
noticeably larger (0.325 mm.) than the acetabulum (0.275 mm.) located
about at center of body. Ovary posterior and close to acetabulum, slightly
lateral. Vitellaria from pharynx to posterior end. Uterus tubular, short,
with few eggs. Genital pore midway from acetabulum to oral sucker.
Cirrus large, with broad lumen at anterior end. Cirrus sac reaching to
posterior border of acetabulum or even a little beyond. Testes spherical,
close together, median, or slightly obUque, halfway from acetabuliom to pos-
terior end.

Representative American species.

Acrolichanus petalosa (Lander) 1902.

One species, A . petalosa (Lander), is common in intestine of Lake sturgeon
{Acipenser rubicundus) in the Great Lakes and St. Lawrence River.

"This is the Z>. auriadatum Wedl of Linton and it is upon the authority of
Looss that I use the above specific demonstration " (Stafford) . The comment
of Odhner that Acr. petalosa is a synonym of Acr. lintoni appears to be in-
correct.

Fig. 6S5. Acrolichanus petalosa; type specimen. X 39- (Unpublished drawing
by C. H. Lander.)

103 (q8) Uterus ventral to both testes, extending nearly to extreme posterior
end Subfamily Bunoderinae Looss 1902.

Small distomes, with elongate body, and smooth skin. Anterior
region small, muscles moderately developed. Oral sucker with circle
of six muscular mammiform processes, often a collar-like expansion.
Acetabulum equal to or larger than oral sucker. Pharynx and
esophagus present, crura long. Genital pore between ventral and
oral suckers. Ovary close behind acetabulum and lateral. Testes
oblique, in posterior half of body. Uterus with descending and
ascending rami in sacculate form, ventral to testes in posterior
region. Laurer's canal and receptaculum seminis present. Vitellaria
lateral, well developed, extending from pharynx to caudal end. Eggs
large.

Type genus Bunodera Railliet 1896.

Esophagus long, forebody narrow. ^ Fork of intestine somewhat
anterior to acetabulum. Cirrus sac without muscular tissue in wall.
Testes obUque, far back in body. Vitellaria not confluent, not
reaching posterior end. Uterus with descending and ascending
rami, greatly enlarged, not coiled, extending to posterior end and
covering testes on ventral side of body.

Recorded in North America.

Bunodera luciopercae (O. F. Miiller) 1776.

One species B. luciopercae (O. F. Miiller) {= Dist. nodulosum
Zeder) reported by Stafford from perch.

Fig. 686. Bunodera luciopercae. Dorsal view. X 47- (After Looss.)

I04 (97)

PARASITIC FLATWORMS 3^^

Testes small, in center of body, separated from ovary by dense

uterine coils with masses of eggs; no eggs posterior to

^^ ^Kfidislomum^Vdaord ic)os.

uuLi, wail tmck. Vitellana continuous from r L'ht to left Ixjth -ilx.v.- mH \J

Only species known. . Aundistomum chelydrae StaffoTcl rgoo.
Intestine of Chelydra serpentina.

Fig. 687. "^""'i^J^f^^^l^^/^ydrae yitellaria changed to correspond with later account
of author. Ventral view. Magnified. (After Stafford.) **ccouni

105 (68) Testes numerous, in two longitudinal series.

Pleorchis Railliet 1896.

Inframedium sized distomes with oval, somewhat flattened bodv Skin
spinous Suckers small equal, separated by only one-fourth bodv 'lenrth
Oral sucker subterminal. Prepharynx prominent, pharynx small, esophaRu^
extended, crura with single branch directed anteriad. Excretory system

, Genital pore preacetabular. Cirrus sac absent (?). Testes numerous
in two rows near niedian plane in posterior half of body, \-itellaria in two
broad lateral bands from acetabulum to posterior end. Other organs con-
hned to small area between anterior testes and fork of intestine mostly be-
hind acetabulum. Uterus short; ova scanty, 48 ^ long.

Reported by Leidy from lungs of musk turtle (Aronwchdys odorata
Latr.) as Monostoma tnplle. Shown by Stiles and Hassall to be distome
somewhat like Distoma polyorchis Stossich. Position and relationship de^
pendent finally on more perfect knowledge of structure which awaits dis-
covery of new material.

Fig. 688. Pleorchis mollis. Magnified, (.\fter Stiles.)

loO (67) Acetabulum represented by two small suckers set close together in
depression on mid-ventral surface near center of bod)-;
genital cloaca opens between the two suckers.

Subfamily Cryptogoniminae Ward.

Very small, spinous distomes of uniform width throughout, with bluntly rounded ends
Oral sucker ver>^ large and prominent. Ventral sucker doul)!e. minute, withdrawn into pocket;
gemtal pore between the two. Prepharynx, jiharynx, and short est)phagus present; crura
extend to anterior margin of testes. E.xcretory vesicle V-shaix-d, fork at oviduct, anterior

398

FRESH-WATER BIOLOGY

branches reach to posterior margin of pharj'nx. Testes elongate, parallel,
dorsal, in posterior third of body; seminal vesicle convoluted, large; no
cirrus or sac. Ovary ventral, proximate to testes, slightly lobed; Laurer's
canal (?); vitellaria lateral, in central region. Uterus with descending
ramus on right, shghtly coiled, extending to posterior end, ascending
ramus returning on left, crossing anterior to ovary and passing on right
to genital atrium. Eggs small, dark, about 20 by 10 ^i.

Type genus.

Cryptogonimus H. L. Osborn 19 10.

The genus has been placed in the Acanthochasmidae; see note under
82 (75). Even if that action be justified it occupies a position suffici-
ently isolated to demand rank in a separate subfamily as indicated
here.

Only species known in North America.

Cryptogonimus chyli Osborn 1903.

In stomach and intestine of Micro ptencs dolomieu and AmblopHtes
rupestris; Lake Chautauqua, New York; St. Mary's River, Michigan;
Canada. Young distomes encysted in small black bass, rock bass, and
minnows (Cooper).

Fig. 689. Cryptogonimus chyli. Ventral view with spines omitted and coils
of uterus simplified. X 9. (After Osborn.)

107 (66) Coils of uterus extend well beyond testes into posterior portion

of body 108

108 (109) Mouth surrounded by a crown of six muscular papillae which

are outgrowths of oral sucker Bimodera.

See note under 66 in this key and description with figure under 103.

109(108) Mouth without crown of papillae no

no (115) Vitellaria represented by small solid more or less lobed organ on
each side of body just anterior to ovary.

Family Gorgoderidae Looss 1901.

Muscular distomes with slender mobile anterior region and flattened posterior region.
Suckers muscular; acetabulum especially projects noticeably beyond surface of body. Skin
without spines but often with fine papillae. Esophagus long without, or short with pharynx.
Crura simple, extend to posterior end. Excretory bladder simple tubular, extending from
dorsal pore near posterior end to region of ovarian complex. Genital pore median, between
acetabulum and fork of intestine; without male copulatory organs. Ovary lateral, post-'
acetabular; Laurer's canal or receptaculum seminis present. Testes lateral, obhque or sym-
metrical. Uterus in numerous open loops chiefly postovarian. Eggs relatively large with
thin, faintly colored shell.

Only one subfamily reported in North America.

GORGODERINAE LoOSS 1 899

III

Small to submedium in size, sometimes slender, sometimes broad in posterior region.
Esophagus relatively long, without muscular pharynx. Testes more or less oblique and within
intestinal crura. Laurer's canal present but no receptaculum seminis. Vitellaria not far
apart.

In urinary bladder and ducts of fishes and amphibians.

i

PARASITIC FLATWORMS

399

Body elongate, lanceolate without conspicuous well marked anterior
and posterior regions j j ^

Testes subdivided, forming on one side a series of four and on the
other five parts; in all nine separate lobes.

Gorgodera Looss 1899.

Testis on ovarian side has five parts; the opposite testis lies further an-
teriad and is divided into four parts only. In well-developed adults these
organs are completely concealed by the coils of the uterus filled with dark
brown, almost black eggs.

Found in the bladder of various Amphibia: Rana and Salamandra (?).
At least two species in North .Axnerica.

Representative American species.

Gorgodera minima Cort 191 2.

Fig. 690. Gorgodera minima. \'entral view. Young specimen with but few
eggs. X 72. (After Cort.)

113 (112) Two simple testes, elongate-oval, not divided.

Gorgodcrina Looss 1902.

Testes are elongate and have irregular notched margins but do not divide into sections.
Vitellaria have only few lobes. Much like the former genus. Adults are difficult to distinguish
' after the uterine coils cover the testes.

Found in the bladder of Amphibia: Bufo, Rana and Sala?nandra (?). Three species known
from North America.

Representative American species.

Gargoderina attenuata Stafford 1902.

Fig. 691. Gogoderina attenuata. Ventral view. X 24. (After Cort.)

114 (ill) Body elongate; slender anterior region distinct from broad poste-
rior region Phyllodistomum M. Braun 1899.

No sharp line of division marks the transition between the two regions
of the iDody. The vitellaria are soHd masses only slightly indented
marginally. The testes are oblique, well separated from each other,
and only weakly lobed if at all.

In urinary bladder of fishes and amphibians.

Representative American species.

Phyllodistomum americanum Osborn 1003.

One species {P. americifmim Osborn) reported from North .\meric.i
in Amblystoma; two others doubtful from pike (Esox liuius), bullhead
(Ameiurus ncbidosiis), and perch (Perca jhivrurns) in Canada.

Fig. 692. Phyllodistomum americanum. Ventral view. X i6. (.\ftcr
Osborn.)

115 (no) V'itellaria composed of distinctly separated follicles.

116

400

FRESH-WATER BIOLOGY

ii6 (119) Vitellaria confined to extreme anterior region of body, not ex-
tending posteriad further than acetabulum 117

117 (118) Vitellaria extend across entire body in anterior region, reaching

nearly to acetabulum.
Genital pore on ventral surface.

Subfamily BRACHYCOELnNAE Looss 1899.
Intestinal crura short, not extending posteriad to acetabulum. Genital pore median, between
suckers. Testes lateral, near acetabulum. Ovary lateral, pretesticular. Uterine coils fill
entire posterior region. Eggs numerous, small.

A single species Brachycoelium hospitale Stafford 1903 is recorded from North America.

Genital pore marginal.

Subfamily Pleurogenetinae Looss 1899.
Intestinal crura of variable length. Genital pore sinistral,^ often marginal. Cirrus sac
large, pyriform, with coiled vesicula seminaUs and muscular cirrus. Eggs 23 to 40 /x long.
Intestines of Anura; a single species in Chamelion.

The family description as written by Odhner will not take in the American genus which
Looss and he think should certainly be included here. Until more data are available it is
unwise to make a new place for this single genus.

Only North American genus yet described.

Loxogenes Stafford 1905.
Small distomes, with broad, thick, heart-shaped body in-
dented at posterior end. Skin spinous. Suckers small, poorly
developed, nearly equal; acetabulum near center of body.
Pharynx present; esophagus very short; crura short, some-
what inflated, not reaching even to center of body. Excretory
vesicle divides near pore, lateral branches inflated, terminat-
ing behind testes. Ovary pyramidal, lobed, preacetabular,
between testes, slightly dextral. Vitellaria ventral, extend
across entire body from pharynx nearly to acetabulum.
Laurer's canal and small receptaculum present. Uterus
chiefly postacetabular, with longitudinal folds in two groups
one on each side of body. Testes oval, small, lateral at ends
of crura, in line with acetabulum or shghtly posterior. Cir-
rus sac long and narrow, preacetabular, sinistral, with coiled
cirrus. Sexual pore dorsal, sinistral, midway between center
and margin at level of fork in intestine. Ova small, 24 by
14 /x, numerous.

In thick-walled closed cysts on pylorus, liver, and bladder
of various frogs. The single species L. arcanum (Nickerson) is encysted in pairs. Massachu-
setts, Minnesota, Ontario.

118 (117) Vitellaria consist of small groups of follicles lateral to pharynx in
extreme anterior region.

Caecincola Marshall and Gilbert 1905.
Very small distomes; anterior end truncate, posterior end bluntly
rounded. Entire body spinous. Oral sucker very large, acetabulum
much smaller. Mouth terminal, prepharynx and esophagus equal, rather
long, pharynx prominent, ceca short but wide. Excretory vesicle Y-
shaped, extending anteriad beyond pharynx. Testes very large, ovoid,
in posterior half; no copulatory organs; seminal vesicle large, bipartite.
Ovary lobed, anterior to right testis; vitellaria scanty, far anterior, lateral
to pharynx. Uterus poorly developed, a few open loops, above and be-
hind testes, extending nearly to posterior end of body. Receptaculum
seminis dorsal to ovary. Assigned by some to the family Acanthochas-
midae; see note under 82 (75) in this key.

Type species.

Caecincola parvulus Marshall and Gilbert 1905.
One species known (C. parvulus) in ceca and stomach of large-mouthed
black bass in Wisconsin.

Fig. 694. Caecincola parvulus. Ventral view; ovary drawn somewhat to one
side to show underlying parts. X 95- (After Marshall and Gilbert.)

119(116) Vitellaria not confined to extreme anterior region 12c

Fig. 69,3. Loxogenes arcanum
Dorsal view. X lo. (After Os-
born.)

40I

121

PARASITIC FLATWORMS

1 20 (123) Intestinal crura short, diverging, not passing acetabulum.

121 (122) Testes symmetrical, lateral, postacetabular.

Subfamily Microphallinae Ward 1901.

Small distomcs having pear-shaped body with mobile anterior rcRion
contammg ahmentary system. Suckers small, prepharynx. pharynx
and long esophagus present; crura short, not surpassing acetabulum
Excretory system V-shaped. (Jenital pore sinistral, rarely pcjst-
acetabular. No cirrus-sac. Seminal vesicle immediately preacetabu-
lar. Testes symmetrical, behind acetabulum. Ovary dextral along-
side of acetabulum. Vitellaria symmetrical, behind testes in form
of a lobcd mass of follicles. Uterus coiled in posterior region ex-
tending anteriad about as far as posterior margin of acetabulum
Eggs small, very numerous.

In intestine of water birds and fishes.

Representative American genus.

MicrophaUus Ward igoi.
One species (M. opacus) in Amia calva, Micropterns dolomieu, An-
gialla chrysypa, Ictalurus pundatus, Percaflavescens; the young dis-
lome encysted in crayfish.

Fig 695. Microphallus opacus. Ventral view; dotted line represents
hnuts of coils of uterus, filled with eggs. X 37. (After Ward.)

122 (121) Testes oblique, in center of body, posterior to acetabulum.

Protenteron Stafford 1904.
Small distomes. Broadest at center, narrowed behind. Skin spinous. Oral sucker termi-
nal, 0.186 mm., acetabulum 0.62 mm. in diameter. Prepharynx longer than pharj-nx or
esophagus. Crura short, diverging, not passing acetabulum. Black eye spots lateral to
pharynx. Testes obhque in center of body behind acetabulum. Ovary in front of left testis
Uterus reaching posterior end. Vitellaria lateral, short, from fork of intestine to near ovary.
Cirrus (and sac ?) extending posteriad to ovary. Eggs 22 by 11 n.

Type species Protenteron diaphanum Stafford 1904.

Intestine of Amhloplites rupestris; Montreal, Canada.

123(120) Intestinal crura extend beyond acetabulum 124

124 (125) Uterus forms rosette in center of body.

Centr ovarium Stafford 1904.

Small distomes, tapering somewhat towards both rounded
ends. Ventral sucker larger than oral, at end of anterior third of
body. Crura terminate opposite center of ovary. Testes behind
ends of crura, not conspicuous. Uterus rosette-shaped, in center
of body. Vitellaria lateral, from esophagus to anterior margin of
testes.

Only species known.

Centrovarium lohotcs (MacCallum) 1S95.

DeHcate worms, i to ,s mm. long. Suckers relatively small and
weak. Ovary deeply iobed. Acini of vitellaria more or less con-
fluent imparting a tubular appearance to the organ. Eggs very
numerous, small, pyriform, 32.5 by 15 /f. with thick brown shell.

Intestine of Esox lucius, Stizostrdion vitrcum, Ambloplitrs
rupestris, Ani^uilla rlirysvpa : Ontario. Canada.

Fig. 696. Centrovarium lobotcs. Dorsal view. Magnified. (After
MacCallum.)

402

FRESH-WATER BIOLOGY

125 (124) Uterus more or less elongated or in coils but not in form of a cen-

tral rosette 126

126 (129) Genital pore near oral sucker on left margin of body.

Subfamily Prosthogoniminae Liihe 1909. . . 127

Small to medium sized distomes with body somewhat flattened and elongate. Skin spinous.
Pharynx present, esophagus variable, crura half or three-quarters length of body. Excretory
bladder Y-shaped, sometimes with caudal vesicle. Genital pore marginal, dorsal or anterior
to oral sucker. Cirrus sac long, slender, cylindrical, extending to or beyond intestinal bifur-
cation. Testes behind acetabulum and ovary. Ovary close to acetabulum, vitellaria extra-
cecal in central portion of body. Receptaculum seminis and Laurer's canal present. Uterus
in coils in posterior region, chiefly behind testes.

127 (128) Testes symmetrical; ovary lobed; uterine coils pass between testes.

Prosthogonimus Liihe 1899.

From the bursa Fabricii of various water birds in Europe. Reported from North America
in a hen's egg and also from two birds.

128 (127) Testes oblique or tandem; ovary entire; uterine coils do not pass
between testes Cephalogonimus Poirier 1886.

Genital pore dorsal or anterior to oral sucker.
Uterus passes from ovarian complex directly
posteriad between crura and testes, on right
side of body, forms mass of coils behind testes
and passes anteriad on left to genital pore.
Vitellaria not always entirely extracecal.
Testes round or irregular. Eggs numerous,
moderate in size, development unknown.

Two species in intestine of frogs, Toronto
and Montreal; and of soft-shelled turtles
(Aspidonedes and Amyda), Minnesota.

Fig. 697. Cephalogonimus americanus. Living
animal, from ventral surface. Magnified. (After
Stafford.)

Fig. 698. Cephalogonimus vescaudus. Entire
worm from dorsal surface, somewhat flattened.
Magnified. (After Nickerson.)

Fig. 697.

129 (126) Genital pore anterior to acetabulum, from nearly median to
marginal in position.

Family Plagiorchiidae Liihe char, emend. . . 130
(Syn. Lepodermafidae Odhner 1910.)

More or less elongate distomes with moderately flattened to cylindrical body; rarely {Oche-
tosoma) strongly flattened. Skin usually spinous over entire body. Prepharynx, pharynx,
and esophagus present; crura very variable in length. Excretory bladder typically Y-shaped
with median stem dividing into two short branches behind complex of Mehlis' gland. Genital
pore usually just in front of acetabulum, slightly left of median line. Cirrus sac crescentic,
powerful, with prominent longitudinal fibers, containing cirrus, vesicle, and prostate; rarely
(Astiotrema) reduced. Ovary on posterior margin of acetabulum, dextral, rarely sinistral
Testes usually oblique, rarely symmetrical or median, close behind ovary. Laurer's canal
present, except in Pneumonoeces; receptaculum seminis variable. Vitellaria lateral, variable
in extent. Uterus extends posteriad to end of body and then anteriad to pore, simple or com-
plicated by coils filling posterior region. Eggs very numerous, small, thin-shelled, measvure
20 to 50 fz.

PARASITIC FLATWORMS

403

130(139) Receptaculum seminis present (except Plagiorchis); crura reach
posterior end (except Styphlodora) j^i

131 (138) VesicuJa seminalis fills greater part of cirrus sac; pars prostalica
follows after it and is very short.

Subfamily Plagiokchiinae Liihe 1909. . . 132

132 (135) Genital pore near oral sucker.

133

133 (134) Testes median or nearly so Pneumonocccs Looss 1902.

Medium sized distomes, with body elongate, thick, and only slightly flattened, tapering an-
teriorly. Acetabulum small. Oral sucker large, pharynx well developed, esophagus short, in-
testinal crura long, extending to posterior end. GenitaJ pore just behind oral sucker, median,
ventral. _ Cirrus sac greatly elongate, reaching acetabulum. Ovary near acetabulum. Testes
postovarian, slightly oblique. Large seminal receptacle between testes and ovary. No Laurer's
canal. Vitellaria lateral in middle region of body. Uterus much coiled, extending to extreme
posterior end. Eggs numerous, small, dark shelled.

In lungs of Anura; widely distributed and abundant. Develop p)erhaps from Xiphidiocer-
cariae. North American species well worked out and described with key by Cort.

Representative American species.

Pueumonoeces colonidensis Cort 191 5.

Fig. 699. Pneumonoeces color adensis. Fully developed specimen, ventral view,
receptacle. X 27. (After Cort.)

ovary; sr, seminal

134 {^2>^) Testes lateral and symmetrical or nearly so. Pnciimobitis Ward.

Much like Pneumonoeces but body larger, thicker, with testes lobed, elongate, lateral and
symmetrical or. only slightly oblique. Extracecal longitudinal folds of uterus pronouncedly
longer than in Pneumonoeces. Ovary lobed. Vitellaria with many very small acini in each
group. Eggs small.

In lungs of Anura. Two species in North America: P. longiplexus, P. brrciplcxus. Cort.
who grouped these in Pneumonoeces, called attention to their close relationship. The i^)ints
of resemblance constitute also characteristic differences from other species in Pneumonoeces
sufficient to justify their being made an independent genus.

Type species Pncumobiks longiplexus (Stafford) 1902.

Fig. 700.

Pneutnobitcs longiplexus. Dorsal view.
(After Cort.)

ovary; sr, seminal reccptacl

404

FRESH-WATER BIOLOGY

135 (132) Genital pore near acetabulum 136

136 (137) No conspicuous pharyngeal glands.

Plagiorchis Liihe 1899.

Body elongate oval, somewhat attenuated at both ends, covered
with minute spines. Pharynx and esophagus of approximately equal
length, crura reach posterior end, or near it. Genital pore just an-
terior to acetabulum, median or slightly sinistral. Cirrus sac curved
around and reaching posterior margin of acetabulum, with large
vesicula seminalis. Testes round to oval, oblique, separated by
uterine branches. No receptaculum seminis. Ovary spherical, at
inner end of cirrus sac. V'itellaria with many closely crowded foUi-
cles usually reaching posterior end. Uterine coils partly pretesticu-
lar, chiefly posttesticular. Eggs numerous.

In intestine of insectivorous vertebrates, chiefly birds, but also
amphibians, reptiles and mammals, infection probably through in-
sects.

Little specialized forms that constitute the type of the family and
from which other genera have diverged in several directions.

North American species.

Plagiorchis proximus Barker 191 5.

Reported from the muskrat in North America.
Fig. 701. Plagiorchis proximus. Ventral view. X 25. (After Barker.)

137 (136) Conspicuous pharyngeal glands present

Glypthelmins Stafford 1905.

Small, oval distomes with rounded ends and cyHndrical body. Skm
spinous. Acetabulum smaller than oral sucker, anterior to middle of body.
Pharynx and esophagus present, pharyngeal glands conspicuous; crura
nearly reach posterior end. Testes small, spherical, at center of body, post-
acetabular, nearly symmetrical. Genital pore median between acetabulum
and fork of intestine. Cirrus sac overlaps acetabulum in part. ^ Ovary small
at left of acetabulum, receptaculum seminis present. Uterus with numerous
short transverse coils within crura between testes and posterior end, spread-
ing somewhat beyond ends of intestine. Vitellaria lateral from fork of in-
testine nearly to end of crura. Eggs small, numerous.

Single North American species known.

Glypthelmins quieta Stafford 1900.

In intestine of Canadian frogs.

Fig. 702. Glypthelmins quieta. Magnified. (After Stafford.)

PARASITIC FLATWORMS

405

138 (131) Vesicula seminalis at inner end of cirrus sac, continued to outer
end by long, tubular pars prostatica.

Styphlodora Looss 1899.

Body somewhat attenuated antcriad, but broadened
posteriorly, with rounded ends. Skin covered with fine
spines. Pharynx and esophagus present; crura do not
reach posterior end. (Jenital pore median, preacetabular.
Cirrus sac encloses coiled vesicula seminalis. Cirrus pcjw-
erful. Testes oblique, close together in center of body.
Vitellaria poorly developed. Receptaculum seminis pres-
ent, but small. Uterus intercecal, but spreading to margin
beyond ends of crura. Eggs numerous.

In intestine of reptiles.

One North American form described by Goldberger as
Styphlodora bascaniensis from the liver (?) of Bascanion
constrictor, Virginia, is a doubtful member of this genus.

Fig. 703. Styphlodora bascaniensis. Ventral view.
(After Goldberger.)

Magnified.

139 (130) No receptaculum seminis, intestinal crura half to three-fourths

body length, at least never reaching posterior end.

Subfamily Reniferinae Pratt 1902 . . 140

Crura of medium length, reaching beyond center of body but not into posterior tip. In
every case an open space or uterine coils intervene between the crura and posterior end of
body.

No receptaculum seminis.

Testes at ends of crura, more or less symmetrical.

In mouth, air passages, lungs, esophagus and stomach of snakes.

A group clearly worked out and defined by Odhncr, richly represented in North America
where occur five out of the seven genera already described.

140 (141) Genital pore marginal or nearly so Rcnijcr Pratt 1902.

Small distomes with elliptical, ventrally flattened body covered with
fine spines. Suckers moderately developed; acetabulum larger, anterior,
to middle. Mouth subterminal; pharyn.x present; esophagus short; in-
testinal ceca reach beyond acetabulum, about to center of body. Ex-
cretory vessel Y-shaped. Genital pore marginal, about level of fork of
intestine. Testes both symmetrical just behind center of body near
ovary which is lateral at right posterior margin of acetabulum. Cirrus
sac large, reaching to or beyond acetabulum with convoluted seminal
vesicle. Vitellaria submoderate in size, lateral, in central third of lK)dy.
Uterus with descending and ascending limb, jiassing between testes nearly
to posterior tip; capacitj' provided by increase in breadth of tube and not
by extension in length and formation of coils.

Representative American species.

Renifcr clliptkus Pratt 1003.

Mouth and air passages of Heterodon platyrhinus. Only one certain
North American species, R. ellipliciis Pratt 190.^, type of the genus.

Fig. 704. Renijer ellipticus. Ventral view. X iS- (.\ftcr Pratt.)

141(140) Genital pore median or nearly so M-

4o6

FRESH-WATER BIOLOGY

142 (143) Testes oblique, separated by greatly enlarged branch of uterus.

Dasymetra Nicoll 191 1.

Body moderately flattened, spinous. Pharynx large, crura wide, not
reaching posterior end. Excretory vesicle Y-shaped, with many side
branches. Genital pore median, slightly preacetabular. Cirrus sac short,
plump; cirrus long. No receptaculum seminis; Laurer's canal present.
Vitellaria branching, lateral. Uterus coiled in posterior end, ascending
ramus wide, nearly straight, metraterm long, muscular. Ova 35 ix long.

Type and only species.

Dasymetra conferta Nicoll 191 1.

Length 3.5 to 4.6 mm., maximum width i to 1.4 mm., near center
Spines long, straight. Oral sucker 0.56 mm. in diameter. Acetabulum
same size or httle less, about 1.7 mm. from anterior end. Pharynx 0.28
mm. in diameter; esophagus short; crura wide, enlarged at ends. Ex-
cretory tubules pigmented. Testes oblique, separated by uterus. Ovary
at right posterior margin of acetabulum. Vitellaria lateral, extend from
genital pore to posterior border of right testis; follicles large. Uterus
spacious; descending ramus dorsal, small; posterior coil behind ends of
intestinal crura; ascending ramus irregular, broad, extending to acetabu-
lum. Metraterm with thick muscular walls. Ova dark brown, Z2> to
37 by 16 to 19 IX.

In mouth (?) of diamond water-snake (Tropidonotus rhombifer); North
America, locality unknown.

Fig. 705. Dasymetra conferta. Ventral view. X i5- (After Nicoll.)

143 (142) Testes lateral, symmetrical 144

144 (145) Topography inverted, i.e., genital pore right and ovary left of
median line Pneumatophilus Odhner 19 10.

Broad, flat distomes of submedian size with moderately de-
veloped suckers. Greatest wadth behind center, tapering to
anterior end, rounded posteriorly. Skin spinous. Suckers in
anterior third of body, acetabulum sUghtly larger. Genital pore
dextral, near fork of intestine, half way between suckers. Oral
sucker slightly subterminal, pharynx present, esophagus very
short. Crura extend to or just beyond testes, with numerous
short lateral projections on outer margin. Excretory vesicle Y-
shaped, slender. Stem reaches to anterior margin of testes.
Testes opposite, just behind center of body, lobed. Cirrus sac
and cirrus moderate in size. Ovary at left posterior margin of
acetabulum. Laurer's canal, but no receptaculum seminis. Vi-
tellaria extracecal, extend from level of genital pore to anterior
part of testes. Uterus with descending and ascending limb pass-
ing between testes; thrown into transverse loops that fill post-
testicular region.

In the lung and trachea of Heterodon platyrhinus and Tropi-
donotus sipedon.

One species in North America, originally described by Leidy
as Distoma variahile var. b., and Usted later by Pratt as Rejtifer
variabilis taken by Odhner as type of the new genus.

Fig. 706. Pneumatophilus variabilis. Dorsal view. X 12. (After Pratt.)

145 (144)

Topography direct,
line. . . .

i.e., genital pore left and ovary right of median
146

PARASITIC FLATWORMS 407

146 (147) Cirrus sac does not extend posteriad beyond acetabulum.

Lechriorchis Stafford 1905.

Distomes of submoderate size oval, narrower behind, ventral sucker
much larger than oral (?), one-third body length from anterior end. Skin
spinous. Pharyn.x and esophagus present; crura extend to [rxjsterior
margin of ?] testes, two-thirds length of body. Testes large, nearly
symmetrical, almost in contact. Cirrus sac large, dorsal and anterior to
acetabulum on right side, (ienital pore at fork of intestine. Ovary
small, spherical, at the end of cirrus sac, on right posterior margin of
acetabulum. Uterus extends directly posteriad to end of body and then
anteriad, ascending limb greatly expanded. Vitellaria [lateral ?], nearly
entire length of ceca. Eggs dark brown.

Two species from North .\merica; type L. primus in lung of garter
snake. The only well-described species is one which Stafford says be-
longs here; it is L. clongalus ( = Renifer elonf^atus Pratt) in mouth of
Heterodon platyrhinus. Renijcr megasorchis Crow 19 13 from the uterus
of Matrix rhombifera may belong here.

Fig. 707. Lechriorchis clongatus. Dorsal view. X 15. (.\fter Pratt.)

147 (146) Cirrus sac extends posteriad beyond posterior margin of acetab-

ulum Zeugorchis Stafford 1905.

Small, elongate elliptical distomes with subterminal oral sucker and spinous skin. Ace-
tabulum near center of body. Pharynx and esophagus present, crura extend to testes only.
Testes oval, lateral, separated. Cirrus sac large, dorsal, extending posterior to acetabulum.
Genital pore in fork of intestine. Ovary small, spherical, at end of cirrus sac. Uterus with
descending and ascending limbs, reaches to posterior end; eggs very numerous. Vitellaria
lateral along crura, but also covering same and approaching median line dorsally. Excretory
bladder median, large, with evident lateral branches.

Single North American form, type species.

Zeugorchis aequatus Stafford 1905.
In esophagus and stomach of garter snake; Canada. This form is very inadequately de-
scribed and its position is somewhat a matter of conjecture. Odhner believes it should be
placed in this subfamily.

148 (65) Ovary posterior to one or both testes 149

149(152) Ovary posterior to both testes 150

150 (151) Uterine coils anterior to ovary, between it and acetabulum; testes

small, oblique, nearly symmetrical, widely separated from
each other, lateral near acetabulum. . . . Lciiccruthrus.
For description and figure consult 87 (86) in this key.

151 (150) Uterine coils posterior to ovary, between it and posterior end;

testes large, oblique or nearly median, forming with acetabu-
lum and ovary almost a continuous median series.

Family Dicrocoi:liid.\i-: Braun 191 5.

Elongate, flattened, transparent distomes of moderate size with weak suckers and ptxjrly
developed musculature. Acetabulum near anterior end. Intestinal crura do not reach jxjs-
terior end. Excretory bladder tubular, reaching anteriad to center of body. Ccnital pore
median, between suckers, near fork of intestine. Cirrus sac small, cirrus conspicuous, derm
glands postacetabular with testes symmetrical, oblique, in median series in front of ovary.
Vitellaria occupy central region of body mostly outside of intestinal crura. Uterus long with
descending and ascending branches in transverse coils, mostly filling area behind t)var>-. Eggs
moderate in size, very abundant, thick shelled, dark brown.

Parasitic chiefly in gall ducts of Amniota.

Type genus Dlcrococlium Dujardin 1845.

Body tapering towards both ends, more anteriad. Testes oblique, close together. Vitel-
laria lateral, symmetrical, small. Genital pore with cirrus sac between ventral sucker and
fork of intestine. Uterus prominent, filling entire body behind germ glands which he between
acetabulum and center of body.

4o8

FRESH-WATER BIOLOGY

The common European species (D. dendriticum, the old Distoma lanceolahim) is said by
Leidy to be frequent in sheep in several western states, but Stiles and Hassall report it as ap-
parently not in North America. I have never seen a specimen collected here. Confusion
with Opisthorchis and similar forms is common in earlier records.

North American genus HaUpegus Looss 1899.

Moderate sized distomes with muscular body, round in cross-section, and powerful suckers.
Pharynx large, esophagus short, crura extending to posterior end. Genital pore close to
pharynx. No cirrus. Testes lateral, near posterior end, symmetrical. Ovary close behind
right testis; vitellaria just behind ovary and composed of group of 4 to 5 large follicles on each
side. Uterus in crowded transverse coils, filling almost entire body. Eggs extremely numer-
ous, small, with long polar filament. In mouth and pharynx of amphibia.

North American species. . . . HaUpegus occidtmlis Stafford 1905.
In mouth and eustachean tube of Rana catesbiana; Canada, Massachusetts.

152 (149) Ovary between testes 153

153 (156) Ovary median or nearly so, hence directly behind anterior tes-

tis.

154

154 (155) Genital pore between acetabulum and pharynx.

Sphaerostoma Stiles and Hassall 1898.

Small distomes with actively mobile, powerful anterior region and broad posterior region.
Suckers powerful. Pharynx present, esophagus long, crura reach into caudal^ end. Cirrus
sac large, cirrus muscular. Testes separate, anterior one near acetabulum on right, posterior
one near caudal tip, median. Ovary intermediate but slightly to left of median line. Vitel-
laria extensive, lateral, from pharynx to posterior end. Uterus in few coils between posterior
testis and acetabulum. With few, large eggs.

This genus has not yet been reported from fresh-water fishes in North America.^ Linton
has found it in marine fishes in the Woods Hole region and it is common in Europe in Cypri-
nidae and many other fresh-water fishes so that it is very likely to be found on this continent
in similar fresh-water hosts.

155 (154) Genital pore some distance behind acetabulum, just anterior to

anterior testis Clinostomum Leidy 1856.

Middle sized distomes with flattened body.
Oral sucker small and retracted at times so that
the body wall rises around it like a collar. Ace-
tabulum near oral sucker, larger, very muscular,
with triangular orifice. No phar>'nx, short eso-
phagus and long crura provided with lateral
pockets. Cirrus sac present. Vitellaria lateral,
strongly developed, confluent behind testes. Uter-
us inverted U-shaped, reaching forward nearly to
acetabulum, with expansion on distal branch of U.
Several species in North America. Not clearly
distinguished in records. Adults are parasitic in
the pharynx and esophagus of fish-eating birds
such as herring gull, various herons, bittern, eagle,
stork. Young forms encysted in frogs and fish
(minnows, perch, bluegill, bullhead, rock bass,
pike, black bass, trout, etc.) . Cort has shown that
the young encj'sted in amphibia are a different
species from those in fish. Widely distributed in
eastern North America at least. The larval stages
are so abundant in some regions that food fish are
rendered unfit for use by the middle of June. The
cysts are deserted by late fall and the fish are free
from infection in winter.

Distoma oricola Leidy from the mouth of Alli-
gator mississippiensis is undoubtedly a related
form as Pratt surmised. It falls in this family
Fig. 708. Clinostomum but too little is known of its structure to justify tomum marginatum. I
marginatum. Larval stage assigning it to a definite genus. Young adult from :

from perch. X i9- (After heron. X i9- (After j

Cort.) Cort.) •'

#^ J

Fig. 709. C linos-

PARASITIC FLATWORMS 409

156 (153) Ovary lateral and slightly posterior to anterior testis but not

directly behind it ^

157 (158) Genital pore at posterior end. . . Uucochloridium Carus 1835.

Small distomes with compressed muscular body. Both suckers and pharynx large and p«jw-
erful. Esophagus short crura very slender, reaching nearly to posterior end Excretory
pore dorsal near caudal tip. Cirrus sac present. Laurer's canal present; rcccptaculum
wanting. Vitellana lateral, conspicuous, extracecal. Uterus in loops ascends on one side of
acetabulum, crosses body, and descends on the other side. Eggs small thick shelled

In the cloaca of birds, not reported in North America. The larval' stage "in Sucdnva is a
si^orocyst which sends into the tentacles of the snail branches that are banded in <ol<,r and
are bitten off by birds Reported in a personal letter by Mr. Bryant Walker who found it in
Succmea ovalis in Michigan.

158 (157) Genital pore ventral, median, just anterior to posterior testis.

Hasstilesia Hall 1916.

Very small oval distomes, nearly round in cross section. Skin
with minute spines in anterior region. Suckers .small, nearly
equal Pharynx and esophagus present, equal in length; crura
irregular, reach to posterior end of body. Excretory bladder
minute with two delicate lateral branches, (ienital pore ventral,
slightly dextral, midway from acetabulum to posterior end. Cir-
rus sac flask-shaped, large; cirrus long. Testes large, one in
extreme posterior region, nearly median, the other near center of
body on left. Ovary small, round, ventral to right intestinal
cecum, near anterior margin of posterior testis. \'itellaria lateral
in anterior half. Uterus in anterior region of body, moderately
developed, mostly pretesticular but with a single loop between
the testes.

Eggs 13 by 20 ^£.

Single American species.

Fig. 710. Hasstilesia tricolor. HasstUesia tricolor (Stiles and Hassall) 1804.

' ^^ ^^ ^''■' ^ In small intestine of 'Lepiis; abundant, Maryland. District of

Columbia, Virginia.

159 (64) Distomes of separate sexes.

Family Schistosomatidae Looss iSqq.

Adults parasitic in blood vessels of man, cattle, and birds; not yet found in North \merica
Cercariae very similar to those of this family occur in North .American snails.
Compare furcocercous cercariae 241 (246) in this key.

160 (63) Special adhesive organ behind acetabulum, .\nterior region with

holdfast organs usually distinctly separated from posterior
region with genitalia Suborder Holostomata Luhe.

The genus Cyathocotylc without diflerentiated regions has not been nvordid in X.irih
America.

Only family represented.

Family HEiUSTOMiDAE Brandes 1888 . . i6r

Distomes with body more or less distinctly divided into two regions. Anterior rcRion sp»K)n
or cup-shaped, serving as adhesive organ. Suckers poorly dcvelo|x-d. but with pi-culiar |>.)st-
acetabular sucking organ. Posterior region cylindrical t)r ovoid. Intestinal crura extend
to posterior end. Excretory bladder in form of subcutaneous network, (ienifal jxirc at
posterior end. Neither cirrus sac nor cirrus. Ovary and testes in series in |>osterior region.
Vitellana conspicuously developed. Uterus short with few, very large, thin-shelKil eggs. .\o
alternation of generations. Develop with intermediate host but without alternation of
generations.

Parasitic in intestine of .Vmniota.

4IO FRESH-WATER BIOLOGY

i6i (i66) Adult forms with developed sex organs.

162

162 (165) Dorsal surface without special suckers 163

163 (164) Anterior region flat, with foliate margins sharply set off from
posterior region Hemistomum Diesing 1850.

Anterior region more or less in the form of a cone opening an-
teriorly and ventrally. Acetabulum often covered by special ven-
tral holdfast organ, not larger than oral sucker, in one case entirely
lacking. Sexual pore dorsal.

North American species.

Hemistomum craterum Barker and Noll 191 5.

Length 0.75 to 1.89 mm. Cephalic region 0.62 to 0.79 mm. long
by 0.41 to 0.49 mm. wide. Caudal region 0.28 to 0.47 by 0.20 to
0.36 mm. Adhesive disk large, flattened cone with crateriform
top, without papillae.

An unnamed species is recorded from Didelphis virginiatia by C.
Curtice.

Fig. 711. Hemistomum craterum. Ventral view.
Barker.)

Magnified. (After

164 (163) Anterior region cup shaped, with anterior circular entrance.

Strigea Abildgaard 1 790.

Frequently called Holosfomum, a name of later date.

Anterior region sharply set off from posterior by circular groove. Flattened lateral region
united ventrally to a cup, with mouth at anterior end. Concealed in this cup small acetab-
ulum and posterior adhesive organ in form of a papilla extending to' mouth of cup. In genital
pore a well developed genital cone; opening terminal.

North American species Strigea cornu (Rudolphi) 1819.

Recorded from Ardea herodias in Alaryland by Stiles and Hassall.

Another species described by Leidy as Holostomum nitidutn from the small intestine of Rana
pipiens is according to Stafford a distome, and if so could not be placed here.

165 (162) With row of suckers on dorsal surface.

Polycotyle WiUemoes-Suhm 1871.

Type species Polycotyle ornata Willemoes-Suhm 1871.

Length 4.5 mm. Posterior region growing larger posteriorly, longer than anterior. In
mid-dorsal line 14 or 15 suckers.

In intestine of Alligator lucius; Charleston, S. C.

Fig. 712. Polycotyle ornata. X 25. (After Willemoes-Suhm.)

166 (161) Larval forms; sex organs wanting or only partly developed. . 167'

Sometimes diflficult to separate from adults and hence noted here as well as later, I

Compare under Holostome Cercariae, 250 (184) in this key. .' I

PARASITIC FLATWORMS

411

167 (168) Larval forms with an oval sucker-like depression on each side of

the oral sucker ZV/rt/ro/v/e Filippi 1854.

Body pyriform or oval. On each side of oral sucker an oval groove, not muscular, with
pores of special (cystogenous ?) glands. '

Encysted in mollusks and vertebrates. European forms belong to various species of Strigea.
Ruttger found these larvae in Limnaca stai^nalis and fed them to ducks; ten days later he
obtained mature holostomids (species not given). Leidy recorded T. typica from Limnae'a
catascopium and Physa heterostropha (cf. 251 in this key). Other undescribed spedes encysted
in North American frogs.

168 (167) Larval forms without sucker-like depressions at the side of the

oral sucker Diplostomulum Brandes 1892.

Body flattened with lateral margins turned ventrad in anterior region; short tip represents
posterior region. On anterior margin near oral sucker group of gland pores on each side.

Several species encysted in body of fishes, or free in optic bulb of similar hosts. Belong to
various Hemistomuni species (cf. 252 in this key).

A form is frequent which has been identified as D. cuticola (v. Nordmann), the larva of
Ilemistomum denticidatum (Rud.) common in Europe. It has been reported from sunfish,
perch, bluegill, pumpkin-seed, minnows, horned dace, rock bass, small-mouthed black bass,
pike, and other fish from Canada to Iowa. Not a few of the larger cysts contain two worms,
one usually much smaller than the other.

Cooper found a form in the optic lens in young Micropterus dolomieu which he identified as
Diplostomulum volvens (von Nordmann).

169 (i) Larval forms; sexual organs entirely wanting or at most only partly

developed 170

A few encysted forms are described that contain eggs and are apparently se.xually mature.

170 (171) Young flukes, encysted or free, always without caudal appendage.

Aganwdistomum. Stossich 1892.

Many immature forms whose relationship to adult types has not yet been determined.
The group is artificial, temporary, and collective, including all agamic flukes with two suckers.
Agamic forms in other groups have been given special names as noted in connection with the
description of the adults.

Forms of this sort are mentioned frequently without specific names. Named forms are also
on record, e.g. A. apodis (Packard 1882) from the ovisac of A pus from Kansas, a unique record
of a distome in a phyllopod crustacean, but without data adequate to fix the species.

All forms described as encysted cercariae belong in this subdivision rather than in the next
since the two marks of distinction between the two are the tail, which is cast otT when the larva
encysts, and the cystogenous glands, pure larval organs, that are emptied in this process and
disappear.

Various species which belong here have been recorded without description under other
names as " Heterostomum echinatum Diesing" of Leidy from the oviduct of Paludina "quite
common," and Distomum centra ppendiculatum of the same author from Helix arborea.

171 (170) Caudal appendage present, usually simple, sometimes modified.

even greatly reduced, rarely absent. . Ccrcaria . . 172

No hard and fast line can be drawn between this group and the last since a few tailless cer-
cariae are known. Furthermore the transition in any case will be instantaneous when the
cercaria under stimulation casts off its tail, which happens normally as well as in cultures.

Small, barely visible, microscopic, free-living forms of simple trematode structure, having
a triclad alimentary canal. A tail, single, double, branched, setose, or otherwise modified is
nearly always present, and is the efficient organ of locomotion. Rarely the tail is rudimentary
or entirely lacking and the form can be classified here only by its strong resemblance in other
features to the tailed larvae. The reproductive organs are always rudimentary, and sometimes
entirely wanting. At most one can distinguish masses or cords of cells that indicate the loca-
tion of future organs. Faust has found that these agree fully with adult conditions. Promi-
nent larval organs are the stylet, a boring spine in the anterior tip al)ove the oral sucker, simple
eyes appearing as pigment spots on the anterior dorsal region usually near the brain. con.-;piru-
ous dermal glands that in one group are designated stylet glands and in another are assigned a
cystogenous function and are perhaps always digestive in character; they present varied features
in different species. All of these constitute useful specific characters.

Very few North American species have been described and the brief records that exist are
in most cases adequate only for the definition of groups rather than species in the true sense.
Most of the following subdivisions of the key are* to be regarded in thai light.

Some names in use like Cercaria bilineata Hald. can have even no general signiQcancc since
the original reference contains no data that will fix the species.

412

FRESH-WATER BIOLOGY

172 (173) Mouth opening some distance from anterior end, near center of

ventral surface. Intestine rhabdocoel.

Gasterostomous or rhabdocoelous cercariae.

Alimentary canal short, simple, rod-shaped. Swimming organ in the form of two long
narrow appendages directed obliquely right and left from posterior end of body in the only
known type. Larval stages of Bucephalidae, such as the well-known Bucephalus polymorphus
von Baer of Europe.

Not yet reported on this continent though the adult (see 29 in this key) is known here.

173 (172) Mouth opening at or very near anterior end of body. Intestine

triclad Prostomatous cercariae . . 174

174 (183) Only one sucker, and that around mouth opening.

Monostome cercariae . . 175
All yet studied have a pair of lateral pigment spots on the dorsal surface, the simple eyes.
Some have also a medium pigment area between the lateral eyes or slightly anterior to them.

175 (178) Cercariae without median eye in cephalic region 176

Under the designation "median eye" is included always an optic cup with pigment lining

and an optic cell; part of these are found in certain developmental stages but in species in-
cluded under this heading disappear so that the structure never becomes complete.

176 (177) Six pairs of large gland cells in tail.

Cercaria urbariensis Cort 19 14.

Length 0.27 to 0.54 mm., width o.ii to 0.2 mm., tail 0.2 to 1.2 mm. long and
0.05 mm. at base. Develops in rediae. An active swimmer. Encysts on soHd
objects. Cysts shaped like thick discs. Moves over surface by aid of two pro-
jections one at each postero-lateral angle of body and with cuticular knob in
tip. Heavily pigmented, especially near anterior end. A pair of lateral eyes;
intermediate pigment nucleus present in later stages, but no optic cup or cell at
any time. Cystogenous glands abundant. From Physa gyrina at Urbana.
lUinois.

Fig.

713. Cercaria urbanensis, mature, ventral view. Cystogenous glands not shown.
X 70. a, posterior locomotor projection. X 216. (After Cort.)

177 (176) Six groups of paired gland cells in tail, each pair dove-taiUng into

the one next anterior Cercaria konadensis Faust.

Cercaria 0.4 to 0.46 mm. in length, o.i to 0.16 mm. in width. Tail 0.4 to 0.45 mm. long by
0.03 to 0.04 mm. diameter at base. This species possesses no median pigment area in cephalic
region. Glands of posterior locomotor organ large and prominent. Cercariae and rediae
aspinose. Germ balls arise from central germinal rachis in subdistal region of redia.

From liver of Lymnaea proxima Lea, Bitter Root River, CorvaUis, Montana.

178 (175) Cercariae with median eye or median pigment area in cephahc

region. Larger species than preceding 179

179 (180) Distinct mobile, evertible spinose pharynx.

Cercaria pellucida Faust.
Length 0.4 to 0.7 mm., width 0.18 to 0.2 mm. Tail 0.5 mm. in length, 0.07 mm. in diam-
eter at base. No large gland cells in tail. Rediae provided with multispinose evertible
piercing organ in prepharynx region. Germ balls arise from central germ cells in distal
region of redia. From liver interstices of Physa gyrina Say, Bitter Root River, Fort Missoula
and CorvaUis, Montana.

180 (179) No evertible spinose pharynx mentioned (imperfectly known

species) 181

PARASITIC FLATWORMS 413

181 (182) Body dark brown, or blackish.

Cercaria hyalocauda Haldcman 1842.

Very imperfectly known. The form described under this name by Evarts (1880) has a body
0.47 mm. long and 0.24 mm. wide with a tail 0.55 mm. long and o.i mm. wide in ma.ximum
Cyst 0.32 mm. m diameter. Body dark brown or blackish. Two eye spots and smaller less
distinct pigment mass between. Tail semitransparent, corrugated when contracted, active
long after detachment from body.

Evarts' description of the living organism shows it is much like C. iirbanensis though easily
distinguishable by greater size of larva and cyst. Haldeman's account is entirely inadequate
to differentiate the form and suffices only to place it in this group. Taken in numbers from
Physa hetcrostropha Say by Evarts.

182 (181) Body white. Doubtful form.

Cercaria {Glenocer carta) lucania Leidy 1877.
Length 0.5 mm. WTiite, ovoid, with conical tail equal to or longer than body and frequently
monihform. Two eyes with intermediate black pigment spot and smaller scattered pigment
spots near them. Produced in bright orange-colored sporocysts which are cylindrical and
bluntly rounded at the ends. Leidy calls this a Monostoma, and all data given agree with
that conclusion except that his description lists an acetabulum which would make it a dis-
tome cercaria. Abundant in Planorbis parvus found near Philadelphia, Pa.

183 (174) JMore than one sucker 1S4

184 (250) Oral sucker well developed; genital atrium not modified. . 185

185 (190) Second sucker ventral and at posterior end of body.

xAmphistome cercariae. . . 186

According to studies on European species the cercaria of Paramphistoma cervis lacks pockets
in the oral sucker and has a connection between the longitudinal e.xcretory vessels. It belongs
to one subfamily. All other known cercariae in this group belong to another subfamily.
They have the pockets in the oral sucker and a muscular enlargement of the esophagus at
the bifurcation of the intestinal crura.

186 (189) Cercariae separate, not attached in bunches 187

Very likely one of the species described below is the larval form of Diplodiscus tempcraius
Stafford, see 57 (58) in this key.

187 (188) Anterior half of body pigmented. . . Cercaria inhabilis Cort 1914.

Large, pigmented form, sluggish in movement. Swims slowly in or)cn
water, does not progress on substratum. Two large eye spots with lenses.
Cystogenous glands thickly developed both dorsally and ventrally. Tail
lightly attached above acetabulum and easily lost. Location of genital or-
gans distinctly indicated by four dense masses of nuclei connected by tine
lines.

From Planorbis Irivohis, Lawrence. Kan., and Urbana. III.

Fig. 714. Cercaria inhabilis, mature, ventral view. Cystogenous glands not shown,
X 44- (After tort.)

414 FRESH-WATER BIOLOGY

i88 (187) Pigment in limited area near eyes.

Cer carta diastropha Cort 19 14.

Smaller than last, eye spots larger in proportion. Pigment confined to
limited area near eyes. Tail always shorter than body. Genital organs dis-
tinctly marked out.

Fig. 715. Cercaria diastropha, mature, dorsal view. Cystogenous glands not shown.
X 60. (After Cort.)

189 (186) Cercariae grouped in bunches with individuals united by tips of
tails, which are very long and slender.

Such forms, designated Rattenkonig-
cercarien by their discoverer, Leuckart,
are as rare as they are striking. C.
daitsii frorn the marine fauna, the only
form of this type known previously,
was determined by Odhner to belong
to Phyllodistomiim folium. The strik-
ing pecuharity in that the cercariae
are joined in groups is evidently not of
fundamental importance as the marine
form (C. ddusii) and the species noted
here belong to different orders of trema-
todes.

North American species.
Cercaria gorgonocephala

Ward 1916.

Fifty or more cercariae in a single
bunch. Tail, i.e., stalk, enlarged at
base with thick wall. Yellow pigment
in body. Stalk marked by two longi-
tudinal lines of dark pigment, attached
to postero-dorsal aspect of worm.

Fig. 716. Cercaria gorgonocephala. Free-
hand sketch from life. X 40. (Original.)

190 (185)

Second sucker ventral, not at or near posterior end of body.

Distome cercariae . .

191

Some distome cercariae are readily recognizable by characteristic features of adult struc-
ture like the collar and spines of the Echinostomidae which are as prominent in the cercaria
as in the adult, and apparently identical in form and arrangement. In the majority of cases,
however, the various groups of distome cercariae at present recognized are purely arbitrary
as they are based on superficial characters. But the system cannot be rewritten until much
more is known of the origin of all of these larval organs and until a large number of species
has been studied.

191 (247) Tail present in larva 192

The name Cercaria is applied strictly only to such larvae as possess a tail, though the tail
may be thrown off at an early period.

[92 (234) Tail not conspicuously modified in form or divided into regions. 193

PARASITIC FLATWOKMS

415

193 (233) Tail slender, never as broad as body of cercaria. .

Cercariae leptocercac . . 194

The long, slender, unbranched tail, which even in maximum contraction does not reach the
width of the body, and in extension is twice the body length or more, is found in the majority of
distome cercariae. The anterior end of the body furnishes data for the subdivision oi these
forms.

194 (199) Anterior end rounded, entirely devoid of spines.

Gymnocephalous cercariae . . 195
So far as known these forms develop in rediae. Many exist on this continent which have
not been reported, for many adults are listed in the earlier sections of this key which must
possess such larvae as one may infer from European studies on related species. These ceitariat
are conveniently subdivided on the structure of the tail which in all is a prominent oigan but
which in some does not function as a swimming organ.

195 (196) Tail simple, not provided with fin-folds or terminal sucking organ.
Three different forms may be noted without attempting to analyze them in the key

Cercaria {Gymnoccphala) ascoidca (Leidy) 1877.

Length 0.25 to 0.4 mm. Body, white clavate; tail long, narrow, cylindrical pointed
Cephahc end triangular and slightly constricted from rest of body. Acetabulum at or behind
center of body often protruded into a cone or expanded into a cup. Xo eyes. In movement
excessively elongated. Rediae white; head distinct from cylindrical body, with birth pore
and caudal prolongation.

Abundant in Planorbis parvus and found free in water containing that species. Leidy is in
error in identifying this form as Cercaria minuta Nitzsch of Europe.

Cercaria agilis Leidy 1858.

Body pyriform, oral sucker large, acetabulum slightly larger, near middle of body. Tail as
long as body, clavate, transversely pHcate. White. Very active.
Found in Delaware River; ordinarily with snails. Common.

Cercaria fasciolae hepaiicae.

Larva of the well-known sheep liver fluke, not yet reported but undoubtedly frecjuent in
certain regions and years as the adult is known to be abundant at certain ix)ints in North
America.

196 (195) Tail modified, having fin-folds or terminal organ.

197

197 (198) Tail provided with dorsal and ventral fin-folds.

Cercaria rcflexa Cort 19 14.

Develops in rediae. Encysts in same snail as redia inhabits or other
snail of the same species. Tail as long as body or longer, provided
with dorsal and ventral fins. Cystogenous glancls abundant. Es<^)ph-
agus long, fine; alst) crura; bifurcation at anterior level of acetabu-
lum. Genital organs marked out by four masses of nuclei. Cort
believes this form is undoubtedly related to the Echinostomcs, but
the spines are not yet developed. .Ml other characters accord with
this view. From Lymnaea rcjlcxa, Chicago, Illinois.

Compare 232 (231) in this key

Fig. 717. Cercaria rcjlexa, ventral view. Cvstogcnous glands not showi
X 60. (.\ftcr Cort.)

4i6

FRESH-WATER BIOLOGY

198 (197) Tail long with terminal organ for attachment.

Megalurous cercariae.
Single American species known.

Cercaria megalura Cort 19 14.

Develops in rediae. Cystogenous glands abundant. Does not swim in open water or use
tail as swimming organ, but as a stalk, becoming attached by the adhesive organ, a group of
unicellular glands at the tip. The tail has the power of elongating very greatly. In this
position the worm waves or wriggles about in a serpentine fashion. When taken up in a pi-
pette it encysts quickly and this seems to be normal on contact with fresh water.

From Pleurocera elevatum, Sangamon River, 111., and Goniobasis virginica, Princeton, N. J.
Adult unknown. Reproductive organs indicated by two masses of nuclei joined by line.

199 (195) One or more spines present at anterior end 200

200 (224) xA.nterior end provided with single median boring spine.

Stylet cercariae . . 201

These forms called Acanthocephala by Diesing and Xiphidiocercariae by Liihe are numer-
ous and perhaps not closely related; even if the stylet cercariae do belong to different adults,
their assemblage in a single group is convenient.

Small, slender-tailed cercariae with rounded anterior margin, bearing a dagger-shaped
boring spine or stylet, usually in the upper lip of the oral sucker. The form of this organ
is very definite in each species and varies between different species distinctly enough to form
in many cases a valuable mark for diagnosis. Eye spots are usually wanting. Development
in sporocysts is most frequent and encystment in a second intermediate host usual in species
of which the development is known.

201 (217) Tail slender, not provided with special organs (bristles, fin-fold)

or regions 202

202 (203) Stylet glands few in number, not more than four on each side.
Tail attached to median posterior extremity, not arising
from distinct caudal pocket. . . Cercariae microcotylae.

Very small. Body less than 0.2 mm. long. Stylet glands 3 to 4 only,
near acetabulum. Excretory bladder small, forking more or less acutely
at anterior end. These forms are all minute and further study may dis-
close the presence of a caudal pocket with minute spines in some or all
species. Two species; not analyzed in key.

Median stem of excretory bladder elongate, club-shaped.

Cercaria leptacantha Cort 1914.

Body oval; circular in cross section, 0.12 mm. long by 0.063 mni- wide.
Tail slender, shorter than body. Stylet small. Not fully developed. Sur-
face in living specimen with highly refractive prominent globules of differ-
ent size.

Produced in oval thin-walled sporocysts from Campeloma decioum
Hartford, Conn.

Fig. 718. Cercaria leptacantha, immature, ventral view, a, stylet, ventral view.
X 320. (After Cort.)

Median stem of excretory bladder short.

Cercaria caryi Cort 19 14.

Very small; stylet glands present, few in number. Acetabulum small;
develops in sporocysts. From Goniobasis virginica, Princeton, N. J.

Fig. 719. Cercaria caryi, ventral view. From Gary's material. X 140. (After
Cort.)

203 (202) Stylet glands more numerous, six or more on each side. Tail aris-
ing from posterior caudal pocket, ventral to excretory
bladder Polyadenous cercariae . . 204

PARASITIC FLATWORMS 417

204(210) Caudal pocket present, distinct, devoid of hooks or spines. . 205

205 (206, 207) Ceca short, lateral trunks of excretory bladder circumscribe
acetabulum C. brcvicaeca Cort 1914.

Body elongate oval, 0.3 mm. long, 0.14 mm. wide. Tail caducous,
slender in length about equal to body. Oral sucker 0.0.S2 mm., ace-
tabulum 0.087 mm. in diameter. Stylet glands 10 to 12 on each side.
Intestinal ceca short. Anterior half of body spinous. A poor swim-
mer.

Found in sausage-shaped sporocysts in liver of Physa anatina
from Manhattan, Kansas.

Fig. 720. Cercaria brevicaeca; a, free hand drawing, ventral view. Cys-
togenous glands not shown. X about 100. b, stylet, ventral view. X 290,
(.\fter Cort.)

206 (205, 207) Ceca arise directly from pharynx region, excretory bladder

muscular, crenate, capable of great distension.

Cercaria crenata Faust.

Body length 0.25 mm., width 0.13 mm. Tail weak, 0.15 to 0.16 mm. in length, 0.02 to 0.03
mm. wide at base. Body oblong-ovate, with deep pocket at posterior extremity for reception
of tail. Stylet glands 13, 8 in outer series and 5 in inner series, minute, extending tu mid-
acetabular region. Esophagus lacking. Sporocysts small oblong-ovate. In hver tissue of
Lymnaea proxima Lea from springs at Fort Missoula, Montana.

207 (205, 2c6) Ceca undeveloped,, excretory bladder bicornuate. . . . 20S

Cort regards these forms as a natural group characterized by development in elongate sac-
shaped sporocysts in Gastropoda, with a slender tail, not usually shorter than the body, with
a small post-central acetabulum, a stylet 30 fx long, with six or more stylet glands on each
side in front of acetabulum, and a bicornuate excretory bladder. He considers that they prob-
ably belong to the Plagiorchiinae. Nothing is known regarding the development of the
American species.

208 (209) Six stylet glands on each side

Cercaria isocotylca Cort i()i4.

Develops in sporocysts. Tail small, vcr>' extensile. Suckers rela-
tively large. Stylet glands just in front of ventral sucker. Excretor\'
pore dorsal, at base of tail. Cenital glands indicated by nuclear ma.ss
dorsal and anterior to acetabulum, and a larger mass dorsal and jx>s-
terior, but connected with the former by a band on left margin of ace-
tabulum.

From Planorbis Irivolvis at Urliana, llliiu)is.

Fig. 721. Cercaria isocotylca; a
side view

ventral
X -'yo.

C.Vfl,

X 20T. b, slylct, vtiilraJ oud
r Cort.)

4l8 FRESH-WATER BIOLOGY

209 (208) Twelve stylet glands on each side. Cercaria polyadena Cort 1914.

Encysts readily. Tail active, easily detached, somewhat larger than
in last species. Oral sucker smaller, stylet glands more numerous. Body
also larger than former species. Genital system marked out by S-shaped
nuclear mass, elongate and dorsal to acetabulum.

Fig. 722. Cercaria polyadena; a, ventral view. Cystogenous glands not shown.
X 207. b, stylet, ventral view. X 290. (After Cort.)

210 (204) Caudal pocket distinct, provided with hooks or spines that are

mostly situated in posterolateral sacs 211

211 (212) Digestive tract naked, ceca rudimentary.

Cercaria dendritica Faust.

Body length 0.38 to 0.40 mm., width 0.16 to 0.17 mm. Tail small, 0.16 mm. in length,
0.04 mm. wide at base. Body obovate, muscular; cuticula thick. Caudal pocket lined with
spines. Excretory bladder large, muscular, bicornuate; tubules dendritic. In long oval sporo-
cysts in liver of Lymnaea proxima Lea, sloughs of Bitter Root River, Fort Missoula, Montana.

212 (211) Digestive tract provided with special glands, in addition to stylet

glands. Ceca developed 213

213 (214) Glands along entire course of digestive tract. Three median

spines on lip of caudal pocket. . Cercaria glandulosa Faust.

Body length 0.45 mm., width 0.2 mm. Tail length 0.3s mm. by 0.05 to 0.06 mm. at base.
Body oblong-ovate, acetabulum shghtly behind center of body, smaller than oral sucker.
Esophagus long, ceca short, unicellular glands along entire digestive system. Cuticula delicate.
Eight cephalic glands. Body filled with cystogenous glands. In sporocysts, in liver of Physa
gyrina Say, Bitter Root River, Corvallis, Montana.

214 (213) Glands in pharynx region only, spines confined to pockets of

caudal pocket 215

215 (216) Ceca attenuate, excretory bladder with long median shank.

Cercaria diaphana Faust.

Body oblong-ovate to ovate. Acetabulum median, about half size of oral sucker. Pharynx
small, surrounded by great mass of unicellular glands. CephaUc glands 8, anterior to cecal
bifurcation. Stylet set with an internal spine at anterior end. Body length 0.2 to 0.2b mm.,
width o.io to 0.12 mm. Tail 0.15 mm. in length by 0.04 mm. wide at base. In oblong
sporocysts in liver tissue of Lymnaea proxima Lea, Bitter Root River, CorvaUis, Montana.

216 (215) Ceca inflated, excretory bladder bicornuate, inflated.

Cercaria micropharynx Faust.

Body minute, ovate, covered with fine spines. Acetabulum mid-ventral, smaller than oral
sucker. Pharynx extremely small, esophagus short, ceca inflated Digestive glands in pre-
pharynx region only. Body length 0.18 mm., width 0.09 mm. Tail 0.14 mm. in length Dy
0.03 mm. at base. In oval sporocysts with well-developed excretory tracts. Liver of Lymnaea
proxima Lea, Rattle Snake Creek, Missoula, Montana.

217 (201) Tail modified, not of simple form 218

PARASITIC FLATWORMS

419

218 (223) Tail provided with fin-like fold, but of normal length.

Cercariae ornatae

219

219(220) Eye spots present Cenaria raconosa FausL

Body length 0.29 mm., width o.ii mm. Tail 0.22 mm. in length by 0.04 mm. wide at base.
Body ovate, oral sucker small, acetabulum somewhat smaller. Esophagus long, ceca short,
e.xtending around acetabulum. Excretory tubules multi-dendritic. Tail with lateral rulUcd
fin-folds. Stylet delicate, attenuate. In polygonal sporocysts in liver of Lymnaca proxima
Lea, sloughs of Bitter Root River, Fort Missoula, Montana.

220(219) Eye spots lacking 221

221 (222) Stylet small, without thickened region.

Cercaria hemiloplmra Cort 19 14.

Body oval, 0.38 mm. long, 0.14 mm. wide, densely covered with
small spines. Tail about length of body, extensile to double body
length, with fin half as wide along ventral surface of distal half. (Jral
sucker 0.065 mm., acetabulum 0.049 mm. in diameter. Stylet small,
without thickened region.

Produced in orange-colored, elongate and non-branching sporocysts,
much twisted together. In Physa gyrina from Rockford, Illinois.

Fig. 723. Cercaria hemilophura; a, ventral view. C ystoRenous f^lands not
shown. X 80. b, stylet, side view. X 2yo. (.\fter Cort.)

222 (221) Stylet heavy Cercaria platyura Lcidy 1S90.

Length 0.8 mm., body 0.4 by 0.12 mm., tail 0.36 by 0.06 mm. at base, width with mem-
branous alae 0.14 mm. Body ovoid, head rounded, oral sucker large (0.08 mm.) with heav-y
stylet. Acetabulum 0.06 mm. Tail nearly as long as body, stout, tapering, corrugated,
with broad, costate, lateral membrane.

Taken free in a pool with Lymnaea, at Fort Bridger, Wyo.

223 (218) Tail short and peculiarly modified. . . . ^Microcercous cercariae.

Tail short, stumpy, with F>owerfulIy developed muscles.
Not a swimming organ, but used as a prop or lever. In
the Cotylocercous cercariae of Dollfus the organ is still
further modified into a type of sucker. This latter group
develops in sporocysts and is mostly marine.

Only species thus far recorded in Xorth
America.

Cercaria trigouura Cort 191 4.

Body 0.24 mm. long, 0.06 mm. wide. Tail 0.05 mm.
long by 0.024 mm. wide. Oral sucker 0.049 mm. long by
0.039 Tirn- wide. Acetabulum just back of center of
body, 0.04 mm. in diameter. Cuticula covered with tine
spines. Tail sht)rt, blunt, easily detached, triangular,
folded into groove. Just anterior i)n)minent gland ojx'n-
jng into the head of this groove. Stylet dorsid to oral
sucker. Stylet glands small but numerous. Elxcretory
system bicornuate, thick walled. Free in tissues of

■ Tf,^ n ■ . ■ 1^1 snails; rediae in s;ime host. No tcndenc>' to encyst

Fig. 724. Cercarta trtqonura.la.teTa.1 =""•".

and ventral views. X 170. Each with noted. . i, rj#-

stylet. X 400. (After Cort.) Found in Campdoma dcctsum from Ilartford. C uon.

420

FRESH-WATER BIOLOGY

224 (200) Anterior end with fleshy collar and crown of spines.

Echinostome cercariae

225

These cercariae develop in rediae which have collar, birth pore, arid posterior locomotor
appendages. They are characterized by the conspicuous collar and spines, also found in the
adult distome. The esophagus is long and the ceca reach to the posterior end of the body.
The tail is long and powerful.

225 (228) Collar spines in a single, if sometimes slightly irregular row.

226

226 (227) Collar spines 42, rounded at both ends; excretory trunks doubly

reflexed in cephahc region Cercaria biflexa Faust.

Acetabulum in posterior third of body. Great number of cephahc glands in 2 series, 50 to
60 in each series, lateral to digestive ceca. Excretory tubes reflexed twice in cephahc region
prehminary to entering lateral trunks. Bladder long, with median swelling; scaleriform anas-
tomosis of excretory tubules in tail. Body length 0.45 to 0.5 mm., width 0.13 to 0.15 mm. Tail
about same length as body, powerful. Encysts within redia. Redia with "feet" in posterior
third of body. In liver tissue of Physa gyrina Say, near Buckhouse Bridge, Bitter Root River,
Montana.

227 (226) Collar spines 36, acute at distal end; excretory trunks arising

from triangular anastomosis in cephalic region.

Cercaria trisolenata Faust.

Deltoid anastomosis of tubules from 3 flame cells in cephalic region, preliminary to entering
lateral trunks. Excretory bladder obtruncate. Acetabulum spinose in posterior third of
body. Readily encysts in free state, easily drops tail. Body length 0.45 mm., width o.i mp.
Tail short, about 0.2 mm. Rediae with lateral "feet" about one-third distance from anterior
end. In Hver of Physa gyrina Say and Planorbis Irivolvis Say. Entire length of Bitter Root
River, Montana.

228 (225) Collar spines in mature cercariae in two alternating rows; excre-

tory trunks reflexed once 229

229 (230) Excretory bladder long, attenuate; 43 equal spines.

Cercaria rubra Cort 1914'

Cysts large, spherical, thick- walled, transparent. Collar has forty-three
equal spines in two alternating rows; four spines on each side of mid-
ventral line point in. Encysted above gills in Canipeloma decisum, Hart-
ford, Conn. No redia found. Known only in encysted stage which is
really an Agamodistomum and not a Cercaria.

Fig. 725.

Cercaria rubra in Agamodistomum stage freed from cyst, ventra
view. X 130. (After Cort.)

230 (229) Excretory bladder ovoid to depressed spheroid, excretory trunk
reflexed almost entire length 231

PARASITIC FLATWORMS 42 1

231 (232) Tail simple, unmodified Cercaria trivolvis Cort 19 14.

Both rediae and cercariae in Planorbis trivolvis, Urbana, Illinois.
Moves actively in free water and on solid bodies; found encysted in
same host with rediae and cercariae. Nuclei of se.x organs in two
masses, connected l)y slender thread. Collar carries thirty-seven equal
spines in two alternating rows; two or three spines near mid-ventral line
point inward.

Fig. 726. Cercaria trivolvis, mature, ventral view. Cystogenous glands not
shown. X 65. (After Cort.)

232(231) Tail with lateral fin-folds Cercaria rejlcxa Cori.

Though without oral spines in the stage originally discovered and described this species
probably belongs here among Echinostomid cercariae.
For description see 197 (198) in this key.

233 (194) Tail simple but heavy, when contracted exceeding in breadth the

body Rhopalocercous cercariae.

Listed from North America.

Cercaria {Rhopalocerca) tardigrada Leidy 1858.

Reported by Leidy from Anodonta species. The true R. tardigrada is Dist. diiplicatum v.
Baer renamed and is the larva of Phyllodistomum folium according to Liihe. Perhaps Leidy's
form is the larva of some American species in that genus.

No North American cercariae have yet been well described which fall into this subdivision
though both of the species listed by Luhe for Central Europe belong to genera, AUocrcadium
and Phyllodistomum, which are reported here. These are not closely related genera and the
group of cercariae does not appear to be a natural one as at present constituted.

Note that Odhner believes that the larva of Phyllodistomum folium occurs in bunches, as
stated in 189 (186) of this key.

234 (192) Tail well developed and highly modified 235

235 (240) Base of tail envelops body of young distome.

Cystocercous cercariae . . 236

The anterior end of the tail is expanded in the form of a bladder into which is folded the
body of the young distome that lies thus in a sac or chamber.

236 (237) Chamber globular, small. Tail simple, slender. Europciin type.

Cercaria macroccrca Filippi 1S54.

These forms of which several have been described in Europe are the young forms of (Tor.co-
derinae (no in this key). The adults have been reported from this country, but this l.irval
form is yet to be identified here.

237 (236) Chamber large; round. Tail fiat, forked, anchor-shaped with

broad terminal flukes; powerful swmimmg organ . . j^*^

These move by rapid alternate lateral jerks of the anchor tlukes. .\s the distome is thus

pulled along by the tail, the usual orientation of a cercaria is r.-versed. The adults arc unknown.

422

FRESH-WATER BIOLOGY

238 (239) Distome fills three-fifths of stem of anchor.

Cercaria wrightii Ward 1916.

Length 0.75 mm., width 0.133 mm. Flukes measure 0.53 by o.i mm. Young distome
0.4s by 0.1 mm. Genital rudiment forms rod-like mass partly preacetabular and partly
postacetabular.

Originally described as a free-swimming sporocyst by R. R. Wright, it was shown by obser-
vations of Braun on the European C. miriabilis to be a highly modified cercaria. Found
in an aquarium at Toronto.

239 (238) Distome fills less than half of stem of anchor,

Cercaria anchor oides Ward 1916.

Length 2 mm., width 0.24 to 0.34 mm.; flukes
curved, tips 0.84 mm. apart. Young distome 0.64
by 0.288 mm. Germ glands already laid down in
middle third of body. Ovary postacetabular, pre-
testicular; testes obHque. Genital pore preacetabu-
lar. Adult unknown.

Fig. 727. Cercaria anchoroides. Young distome just set
free. X 73' o, Cercaria complete. X 27. (Original.)^

240 (235) Tail of cercaria does not envelop young distome, but is modified

in form 241

241 (246) Modification consists in forked end.

Furcocercous cercariae . . 242

The long slender tail is split in its distal region and terminates in two slender branches,
one-third to one-half the length of the entire structure. An unnatural group as this modi-
fication has apparently arisen more than once in different types.

242 (243) Cephalic glands with short ducts, never reaching acetabulum.

Cercaria douthitti Cort 1914.

\

Develops in sporocysts. Tail bifid; nearly twice as long as body. Oral
sucker very large. Two pigment eye-spots with lenses. Eight large cephalic
glands in posterior region with ducts opening into or through oral suckers;
no stylet found. Single genital nuclear mass at posterior extremity of body.
Found in Lymnaea reflexa from Chicago, 111.

Fig. 728. Cercaria douthitti, ventral view. X 98. (After Cort.)

t

PARASITIC FLATWORMS

423

243 (242) Cephalic glands open into ducts posterior to acetabulum. . . 244

244 (245) Cephalic region crowned with spines; two eye-spots present.

Cercaria gracillima Faust.

Body length 0.13 to 0.16 mm., width 0.02 to 0.03 mm. CcphaUc glands in ixjstfrior third
of body. A pair of flame cells (in pockets) in posterior third of excretory trunks. Eyc-sp«jls
lying directly lateral to cephalic ganglia, unpigmented. (Jcnital rudiment extends anterior
to acetabulum. Tail about twice body length, furcae of same length as undivided ix^rtion. In
long attenuated sporocysts in Hver of Physa gyrina Say, near Buckhouse Bridge, Bitter Root
River, Montana.

245 (244) Cephalic region crowned with two small tubercules; eye-spots

lacking Cercaria tuberistoma Faust.

Body length 0.2 mm., width 0.05 to 0.06 mm. Tail about 0.32 mm., furcae equal in length to
undivided portion. Cephalic glands small; excretory system simple, most anterior tubules of
tail refiexed, bladder muscular. In sporocysts, either dumbbell shaped or attached at one
end. No birth pore. Cercariae escape by splitting wall of sporocysts. In liver tissue of
Physa gyrina Say, Bitter Root River, Corvallis, Montana.

246 (241) Modification consists of lateral spines in rows.

Setiferous cercariae.
None yet recorded from North America. A small group, mostly marine.

247 (191) Tail apparently entirely wanting 24S

The tail may be small and easily lost or actually not developed.

248 (249) Develop in rediae or unbranched sporocysts.

Cercariacum.

The young distomes possess no cyst or protective mem-
brane. Found not infrequently in our fresh-water mussels.
Species not described. Adults unknown. One of the Euro-
pean species is thought to be the larva of Asymphylodora.

Cercariacum hclicis (Leidy) 1847.

Total length 0.85 mm.; breadth 0.6 mm., active and vcr>'
extensive. Body white, oval, with oval tail. Oral sucker
marked by radial Hues; acetabulum central, equal in size to
oral sucker, 0.15 mm. in diameter. Pharynx oval. Intestine
large, sinuous, extending to end of body. Excretory bladder
small; lateral vessels double. Oenital pore ix)stacetal)ular.

In pericardial cavity of Helix allcrtiala and //. albolabris.
The "first" and "third" stages of Leidy's later account arc
clearly not the same species as the "second stage" to which
the name Disloma hclicis was originally given.

Called later D. vagans al.st) by Leidy. Die.sing makes it
Cercariacum vagans. Possibly a cercaria which has thrown
off its tail but has not encysted.

Fig. 729. Cercariaeum Ittlicis. Second stage; hiRhly magnific<I.
(.\fter Lciiiy.)

249 (248) Develop in branching sporocysts Lcucochloriiiium

The remarkable species is known in Europe in the adult ft)rm as a fxirasite of sin^ng birds
and in the sporocyst stage in certain snails, Succinea. Sec 157 in this key. It has no free-
living period.

250 (184) Oral sucker rudimentary, much smaller than acetal)ulum. Geni-

tal atrium modified into sucking organ.

I loJostome cercariae . . 251

Genital opening posterior, ventral to excretory pore.

424 FRESH-WATER BIOLOGY

251 (252) Anterior part of body hemispherical to cup-shaped; two lateral

sucking discs also present. . . Cercaria flabelliformis Faust.

Typical tetracotyle form. Body length 0.48 to 0.56 mm., width o.44_mm. Animal slipper-
shaped, with two posterior and two lateral lappets around sucking discs. Anterior part of
excretory system fan-shaped. In rediae or encysted in tissues in liver of Physa gyrina Say,
Bitter Root River, Corvallis, Montana.

Compare 167 (168) in this key.

252 (251) Anterior part of body lamellate or only sUghtly patelliform.

Cercaria ptychocheilus Faust.

Hemistomum larva. Body length 0.48 to 0.63 mm., width 0.17 to 0.37 mm. Posterior
portion abbreviated. Atrial chamber posteriad, well-developed. Varying number of mu-
cous glands, situated in posterior part lateral to genital atrium, empty into the latter. En-
cysted within semitransparent ovoid membrane, with discoid attachment to mesentery of
Ptychocheilus oregonensis Richardson, Bitter Root River, Stevensville and Carlton, Montana.

The encysted form described by Faust is really a Diplostomulum, i. e., the stage succeeding
the true Cercaria. Compare 168 (167) in this key.

Cestoda

The cestode or tapeworm is as the name suggests more or less
like a band or ribbon, and in the majority of cases the band is
subdivided by cross-markings into a series of Hnks or proglottids.
In a few primitive tapeworms the body consists of but a single
link and the general appearance is so similar to that of the fluke
as to make distinction difficult. In some other cases, especially of
fish tapeworms, the ribbon-like body is not subdivided by ex-
ternal cross-markings, but the internal structure shows the poten-
tial presence of proglottids, for the organs are multiplied suc-
cessively in the undivided body as they are in the segmented body
of the ordinary tapeworm. Most tapeworms are distinctly flat-
tened so that one may speak of surfaces and margins. A few
species are, however, so nearly circular in cross section that it is
difficult to use such terms. Abnormal individuals of the flat-
tened species have been described which are three-cornered or
prismatic in cross section; these represent partially fused or par-
tially spHt chains.

One can usually recognize two or three fairly distinct regions in
the ordinary tapeworm: the head or scolex, the neck, and the chain
or strobila. The head is more or less enlarged, globular or oval,
and not infrequently provided with an apical extension designated
a rostellum, which in some forms is held withdrawn in a pocket
under most circumstances. The head is commonly suppHed with
suckers and sometimes hooks also by which it attaches itself to the

PARASITIC FLATWORMS

425

tissue of the host. In some tapeworms the head carries long suck-
ing grooves or bothria, and in others round cup-shaped suckers or
acetabula. More compUcated hold-fast organs are developed on
the scolex in certain groups of cestodes parasitic in marine hosts.
A slight constriction behind the head has been given the name of
^^neck"; many cestodes have no neck. The body usually in-
creases in caliber from the head toward the opposite end. The
partition lines of proglottids are at first very indistinct, and be-
come more marked as one goes backward along the chain. The
form of the proglottids also changes from the scolex toward the
other end of the worm. Much has been made of these and other
minor details of external

appearance in the descrip- Hi exv 9J <^ef tt \\ ^{\^
tions of cestodes. They
are not adequate for the
determination of many
species and moreover are
not of fundamental signifi-
cance. Unfortunately very
few cestodes are transpar-
ent and it is not easy to
study the internal struct-
ure, since the specimen
must first be subjected to
a time-consuming technic.
Methods for the prepara-
tion of cestode material
were outhned briefly in the
general section of this chap-
ter (page 368). . Specimens
must be kept flat and ex-
tended or they are difficult
to study and interpret cor-
rectly.

Each proglottid may be
considered a.^ a unit of structure as it contains a complete set of
reproductive organs (Fig. 730). With rare exceptions tapeworms

Fig. 730. Ophiotaenia filaroidcs. Mature provluttid, un-
flattened, showing relationships of orRans. Abbreviations
used in thi^ and following figures: ci, cirrus; cip, cirrus-pouch;
dej, vas deferens; dj. ductus ejaculatorius; r/, vasa cffcrentia;
ei!>, excretory vi-ssel. ventral; n/, lateral ncr\c; <><)<■, (HKapt;
OT, ovary; m/, uterus; ij, vagina; ri, vitellaria. X 5^- (Af-
ter La Ruf.)

426 FRESH-WATER BIOLOGY

exhibit the same condition of hermaphroditism that was de-
scribed for the flukes, since all organs of both sexes are repre-
sented in a single proglottid. The reproductive organs of one
proglottid have usually no connection with those preceding or fol-
lowing; other organs are continuous throughout the chain. One
may readily observe at the side of the proglottid the main longi-
tudinal nerve trunks which connect with a complicated series of
enlargements or ganglia in the scolex. These main nerve trunks
are joined by cross-connectives in each proglottid. Near them and
parallel to them are the main canals of the excretory system, and
these also are joined by transverse vessels. A network of finer
tubes terminating in flame cells is present in each proglottid and
empties into the main vessels just described. The longitudinal
muscles of the body are sometimes continuous throughout the
chain and sometimes divided at the partitions.

No trace of an aHmentary system has been found at any time
in the entire life history of the cestode.

As one proceeds backward along the chain one can observe the
gradual development of the reproductive organs. These appear
first as faint lines or bands in the tissue, outlining the positions of
the main organs; they grow more definite until at sexual maturity
a complete set of organs of both sexes can be demonstrated (Fig.
730). The organs are very similar in character and interrelation
to those of the trematodes. As one passes further along the chain
other changes take place, primarily the gradual accumulation of
eggs in the uterus and the coincident gradual shrinkage of other
reproductive organs until the latter may ultimately disappear save
for insignificant vestiges. Two different plans are observable
with regard to the production of eggs. The latter may be held for
a time in a uterine cavity and then discharged through a pore, or
they may accumulate indefinitely in a blind uterine sac until they
come to occupy nearly the entire volume of the proglottid. Where
the latter condition prevails, the last proglottids of the chain have
been reduced to mere egg cases that are cut off periodically, either
singly or in groups, and carry to the outer world masses of ova for
the dissemination of the species.

Some cestodes have a free-Hving stage which hatches from the

PARASITIC FLATWORMS

427

egg in the form of a spherical cihated larva (Fig. 731) that for a
short time carries on an existence in the outer world. This larva
occurs among the fish tapeworms. The ex-
ternal layer of large ciliated cells may be
regarded as an embryonic membrane within
which is a narrow fluid filled chamber contain-
ing a smaller spherica mass that in fact is the
true cestode larva, known as an onchosphere.

^■

%.

w

This larva derives its name from the presence '^^^////jiil&v.

of three pairs of long slender hooks arranged fig. 731. mphyiiohoihri.

, . , , 1^1, ""* latum. Free swimming

at equal intervals around one pole of the sphere embryo. MagniSed. (After

■* , , ^ ^ Schauinsland.)

and provided with special muscles that serve

to push the hooks out and then away from the center so as to

open up tissue and force the larva through it.

In most cestodes the onchosphere, surrounded by two or more
membranes characteristic in form in particular groups, is retained
within the egg-shell until the mass is brought passively into the
alimentary canal of a suitable host. Here the onchosphere is set
free by digestion and bores its way out of the alimentary canal
into the body cavity or vascular spaces. It may remain there
free and undergo further development, or by active or passive
migration reach a point where it encysts and remains fixed during
the period of growth. During this period it develops to one of
the larval forms of the group. These forms difi'er in different
subdivisions of the class Cestoda. Among the lower forms they
are small, oval or elongated, spindle-shaped, solid-bodied larvae
known as plerocercoids, and in the highest groups of cestodes
they become large fluid-filled vesicles known as cysticerci or blad-
der-worms. Other types occur among other kinds of cestodes.

These larval forms almost without exception develop in an inter-
mediate host. In some cases the larva wanders out later and
achieves actively the infection of the adult or final host, but in
most instances it is held in the body of the intermediate host
until the latter is eaten. Thereupon it is set free by digestion,
migrates to the organ which is its normal seat, and enters upon
a period of growth that brings it to the fully matured adult
form.

428 FRESH-WATER BIOLOGY

Certain important changes have occurred during this larval
growth period. These are most marked in the bladder- worm ces-
todes. The fully developed cysticercus shows a completely formed
scolex that corresponds in detail with the scolex of the adult ces-
tode save that it is reversed and lies turned into the internal cavity
of the bladder. When the bladder- worm reaches its final location
the head is everted and appears with the armament of suckers and
hooks that characterizes the adult. This scolex attaches itself in
the region appropriate for the adult and the bladder remnant is
lost by digestion while the neck continues to grow in length until
it has produced a full-sized adult worm. The formation of pro-
glottids and the growth within them of the reproductive organs
proceeds slowly as the worm lengthens, the oldest proglottids
being found regularly at the end furthest from the scolex.

The Kfe histories of North American cestodes are entirely un-
known and can only be inferred to be similar to related species
that have been studied in the Old World. The evidence fur-
nished by the latter indicates clearly that tapeworms are not
bound up with an aquatic existence in some stage as are the flukes.
Certain cestodes have aquatic larvae and others bladder-worm
stages in aquatic invertebrates, or vertebrates, but many of the
species parasitic in birds and mammals pass the larval period in
terrestrial hosts (insects, land snails, birds, mammals) and have
no relation to the aquatic fauna at any time. Such forms do not
belong rightly in such a synopsis as this; but the data available
are insufficient to mark out clearly which forms belong to the fresh-
water fauna during some phase of their existence and which are
entirely unconnected with it.

Cestodes are found as parasites in all types of fresh- water verte-
brates. The adults occur most frequently in the alimentary canal
or pyloric ceca. Certain kinds, chiefly larval forms, are found in
the body cavity and the encysted stages, the bladder-worms, may
be encountered in almost any tissue, even in the brain; yet they
are most frequent in connective tissue and seem to find the liver a
preferential location. Usually only a few cestodes are found in
an individual host, but they may occur in such numbers that the
cavity of the ahmentary canal is stuffed full and the wall of the body

PARASITIC FLATWORMS 429

is markedly distended. The distribution of various species is prob-
ably nearly concurrent with that of the particular hosts.

North American cestodes are very imperfectly known and the
large part of the data available concerns species parasitic in ])ir(ls
and mammals. Because of the lack of defmite knowledge it has
been necessary to decide upon somewhat artificial limits, and the
synopsis has been made to include all cestodes reported in North
America from fresh-water hosts and all likely to have develop-
mental stages in fresh-water hosts even though such stages have
not yet been identified on this continent. Among the various
hosts from which tapeworms are reported the water birds are most
difficult to group correctly. Many of them visit both fresh and
salt-water bodies, and most of them feed at times and places on
terrestrial plants and insects either intentionally or incidentally.
Consequently, the source of a given infection is difficult to deter-
mine and some errors have no doubt been made in these cases;
yet, thanks to Ransom's careful and extensive work, avian ces-
todes are better known than those from any other host group in
North America.

The data on North American cestodes are not only scanty but
also so indefinite as to be of Httle value in the attempt to prepare
a systematic outline of the group. Early references are to "ces-
todes" or ''Taenia," and even in later years the same habit has
prevailed. Most existing records of the occurrence of tapeworms
in aquatic hosts cannot be referred to known genera. For these
reasons the appended synopsis must be presented with an apology.
Among the Proteocephalidae I have been able to depend on the
work of La Rue and for bird cestodes I have made free use of Ran-
som's monograph. Outside of these groups there is little definite
knowledge of the North American forms.

KEY TO NORTH AMERICAN FRESH-WATER CESTODA

1 (122) Adult worms; sex organs developed 2

2 (7) Body simple, not divided into joints or proglottids. A single set of

genital organs Subclass Cestodaria . . 3

The few forms included here are often designated the monozootii- cestodes. and sometimes
are regarded as a separate class intermediate in position between Trematoiles and Cestinlcs.
In external appearance they resemble the flukes but are readily distinguished from them by
the entire absence of an alimentary canal. The internal structure is much like that of tape-
worms but the sexual organs are never duplicated.

430 FRESH-WATER BIOLOGY

3 (4) Anterior end not peculiarly modified. No suckers, hooks, or special-

ized scolex region Amphilina Wagner 1858.

Large, oval, flattened forms, parasitic in body cavity of fishes. Anterior end usually notched,
but occasionally extended in the form of a small papilla bearing the pores of a group of uni-
cellular glands. Male genital pore at posterior end. No cirrus sac present. Female pore
slightly anterior to male pore, separate from it. Uterus long, uterine pore at anterior end.
Embryo with circle of ien hooks at one pole.

Not yet reported from North America but present.

4 (3) Anterior end with unarmed, poorly developed adhesive organ, imper-

fectly set off as scolex from rest of body.

Family Caryophyllaeidae Claus 1885 . . 5
Body elongate, flattened, with nearly parallel sides and primitive scolex. Neck may be
present or wanting, as also a caudal appendix. All genital pores ventral, median, near poste-
rior end; cirrus anterior; uterus and vagina open together into a genital atrium.

5 (6) Caudal appendix present in adult. Two distinct sucking grooves on

rudimentary scolex Archigetes Leuckart 1878.

Sexually mature in oligochaetes. A form which undoubtedly belongs here has been described
to me as found in native earthworms. It has not been recorded in the literature. The species
known are 2 to 6 mm. long and parasitic in the body cavity of Tubificidae.

6 (5) No sucking grooves present. Caudal appendix lacking in adult though

present in larval form. . Caryophyllaeus 0. F. Miiller 1787.

Expanded anterior end very mobile, irregularly folded but without definite sucking grooves.
Intestinal parasites of Cyprinid fishes. Larvae parasitic in body cavity of Tubificidae.

7 (2) Body multiplex, usually divided externally into joints or proglottids;

always containing successive sets of reproductive organs
generally corresponding to such subdivisions even in cases
where external proglottid markings are lacking.

Subclass Cestoda s. str. . . 8

Elongate, ribbon-like forms in which the reproductive organs are serially duplicated, each

set constituting a reproductive unit, usually though not always set off from adjacent units by

internal septa and external boundaries. These forms are often spoken of as the true tapeworms,

or polyzootic cestodes.

8 (29, 30) Scolex with a single terminal or with two opposite sucking organs,

never with four suckers or accessory proboscides.

Order Pseudophyllidea . . 9

Scolex rarely armed with hooks, never provided with rostellum, or extrusile proboscides.
The two sucking grooves sometimes combined by complicated growth of their margins into a.
funnel-shaped or tubular organ which may be united with that of the opposite side to a termi-
nal sucker of peculiar form. External jointing is rarely lacking, but often indistinct in certain
regions at least. Uterine pore present, on the surface of the proglottid. Uterus in the form of
rosette-shaped coils or of a large sacculate uterine cavity.

Characteritic fish parasites in one or more stages of the life history.

Liihe places the Caryophyllaeidae (see above), as the first family under this order, grouping
them as monozootic Pseudophyllidea in contrast with all other famiUes as polyzootic. For
practical reasons they are treated here under the Cestodaria.

9 (28) Adult forms with developed reproductive organs 10

The larval forms are sometimes hard to distinguish from adults. Consult also 28(9).

10 (13) Eggs thin-shelled, without Hd. Uterine pore ventral; cirrus and

vagina open dorsal and posterior to uterine pore, or margi-
nal. . . . Family Ptychobothriidae Liihe 1902 . . 11
Scolex with two separate bothria, rarely replaced by a pseudoscolex. No neck; external
segmentation always present but incomplete or obscured by secondary folds in many cases.
Reproductive organs single in each proglottid. Cirrus and vaginal pores posterior to uterine
pore, marginal or median and then on opposite surface from uterine pore. Ovary and shell
gland median; testes in two lateral fields. Uterus in form of a single spacious cavity, never

PARASITIC FLATWORMS

431

of a rosette. Eggs tliin-shelled, without lid. Embryonal development in uterus; all eggs of
an entire worm may be in many cases at the same stage of development, at a given season.
Liihe makes two subfamilies, Ptychobothriinae and Amphicotylinae.

11 (12) Genital pore on surface of proglottid.

Bothriocephalus Rudolphi 1808.

Scolex distinctly elongated, bothria not well developed. External segmentation inc(<mplete
between successive proglottids; serrate marginal incisions distinct but markings on surface of
proglottids often imperfect or wanting. VitcUaria in cortical layer, continuous from pro-
glottid to proglottid, as are also testes. No seminal receptacle. Beginning of uterus a con-
voluted canal (uterine duct) which opens into spherical uterine cavity. Uterine pore median,
ventral; orifice of cirrus and vagina median, dorsal.

Many entries under this name really belong in other genera of the family. A revision of
the group is necessary before one can say which are true species of this genus.

12 (11) Genital pore at margin of proglottid.

Ahothrium van Beneden 187 1.

Scolex not elongate, with two bothria powerful but not deep. Segmentation uncertain
among older proglottids because of surface wrinkles; even oldest proglottids much broader
than long. Nerve trunks near margin, dorsal to cirrus and vagina. Testes exclusively be-
tween nerve cords in two lateral fields. Vitellaria irregular, also in two broad lateral fields,
mostly between longitudinal muscle bundles, "separated at proglottid limits. Ovary
reniform, ventral, median. Shell gland dorsal to ovarj'. Uterine sac in ripe proglottids
filling almost entire medullary region. Uterine pores ventral, in median longitudinal furrow
on strobila.

Representative North American species.

Ahothrium crassiim (Bloch) 1779.

Reported from salmon in Lake Sebago, Maine; not uncommon in the Great Lakes trout.

13 (10) Orifice of cirrus and vagina on same surface as uterine pore and an-

terior to latter or marginal. Eggs thick-shelled, with hd.

Family Diphyllobothriidae Luhc 1910 . . 14

Scolex and sucking organs variable in form, or replaced by pseudoscolex. Segmentation
usually distinct. Receptaculum seminis sharply set oflE from vagina near inner end. Uterus
long, convoluted tube, in form of central rosette; without uterine sac except in Uaploboth-

riuni. Eggs thick-shelled with lid.

14 (27) Genital pore on surface of proglottid 15

15 (24) All genital pores exclusively on one and the same surface of the

strobila 16

16 (19) Scolex very short, not set off from the rest of the worm.

Subfamily Ligulinae Monticelli and Crety 1891 . . 17

Scolex roughly triangular, more or less drawn out to a point with contraction of worm.
Bothria median, small, weak. Genital organs in adult fully develojx^d just behind scolex
Testes form dorsal layer in lateral fields of medullary ixin luhyme. Volk follicles in lateral
part of cortical area. Ovary median, ventral; shell gland median. dt)rsal. . , ,, .

Adult in intestine of water birds; larva in body cavity of tcleosts, attammg full size and
forming advanced rudiments of sexual organs, found occasionally in water, having been set
free by rupture of abdominal wall of intermediate host.

17 (18) External evidences of proglottid formation Hmitcd to anterior end or

entirely lacking I/i,w</ci Bloch 1782.

When fully grown jointed only at anterior end, but the divisions do not agrcx; with the in-
ternal segmentation of reproductive organs. Bothria poorly developed. Lan-ae without
segmentation and without bothria, five chiefiy in Cyprinids. Adults in water birds; stay m
definitive host only brief. , „ . . n . •»

Several species have been reported and described by various authors, all too bncfly to ponnit
of posidve identification. The parasites come from chub, sucker, and trout; .New \ork,
Pennsylvania, Maryland, Yellowstone Park, Arizona.

432

FRESH-WATER BIOLOGY

i8 (17) Proglottid formation evident externally throughout entire worm,
even in larval condition. . . Schistocephalus Creplin 1829.

Apex- of scolex pitted, retractile. Bothria poorly developed. Segmentation complete.
Suckers and proglottids visible in larva. Adults in water birds; larvae in abdomen of Gaste-
rosteus.

At least one adult and one larva are found in North America. No records have been
published.

19 (16) Scolex more or less elongate, distinctly set off from rest of

worm 20

20 (21) Scolex similar in form to first proglottids, separated by sharp boun-

daries; no unjointed region (neck).

Subfamily Haplobothriinae Cooper.

Proglottid formation evident externally only in anterior part of strobila. Large median
dorsal and two smaller ventro-lateral excretory vessels. Both vitellaria and testes medullary.
Cirrus covered with minute spines. Uterus sharply divided into uterine duct and large uterine
sac.

Type and only genus Haplohothrium Cooper 19 14.

Scolex small, simple; rectangular, excavated dorso-ventrally
to form simple bothria, and also slightly laterally. Apex slightly
extended to form low pyramidal disc; posterior end of scolex
modified as auricular appendages which with edges of apical disc
bear minute spines. No neck. Proglottids elongate and auricu-
lae decrease posteriad until segmentation near end is indicated
only by successive sets of reproductive organs. Large median
dorsal and two small ventro-lateral excretory trunks. Testes
small, numerous (80) in 2 lateral fields. No genital sinus. Cir-
rus and vagina open close together well anterior on ventral sur-
face. Uterine pore ventral also, anterior to posterior end of
uterine sac. Ovary horse-shoe shaped, ventral, posterior. Large
yolk-reservoir.

Uterus in 2 regions formed very early, viz. : coiled thin- walled
uterine canal and capacious uterine sac which when filled occupies
almost entire central field of proglottid. Eggs with opercula,
carrying cihated larva.

Type species.

Haplohothrium glohidiforme Cooper 1914.

Intestine of Amia calva. The uterine sac and the armed cirrus
exclude this genus from the family in which it was placed formerly.
It certainly shows some points of resemblance to the Triaenopho-
rinae and has been included in a new subfamily which at present
stands isolated in a position intermediate between that and the
following family.

Fig. 732. Haplohothrium
globuliforme. a, scolex and first
three proglottids; X 20; b,
twenty - third , twenty- fourth,
and twenty-fifth proglottids,
lateral view, showing disappear-
ance of auricular appendages;
X 6; c, young scolex showing
beginning of proglottid forma-
tion; X 11; d, smallest plero-
cercoid observed; Xn- (After
Cooper.)

21 (20) Scolex separated from first proglottids by unjointed region (neck).
Subfamily Diphyllobothriinae Liihe 1910 . . 22

Proglottid formation always evident externally. Genital organs single or double in each
proglottid. Vitellaria cortical; testes medullary in position. Vas deferens with muscular
bulb before entrance to cirrus sac. No spines on cirrus.

Adults in intestine of Amniota; larvae so far as known in fishes, reproductive organs want-
ing at time of transfer to definitive host.

2 2 (23) One set of reproductive organs in each proglottid.

Diphyllohothrium Cobbold 1858.

The most famous member of this genus is the broad fish tapeworm of man, D. latum, commonly
referred to as Bothriocephalus latus, though it is very distinct from that genus as reference to
the section will show. This species has become established on the North American continent,
having been introduced no doubt by immigrants from infected territory in Europe.

Possibly related species [Dibothrium] cordiceps Leidy 187 1.

Length of adult 2 m.; scolex cordiform 2 by 0.6 to 0.8 mm., neck short. Widest about
IS to 25 cm. from head, where proglottids are 7.5 mm. long, 4.5 mm. broad, 0.5 mm. thick.

PARASITIC FLATW'ORMS 433

Genital pores median, ventral, approximated but distinct; cirrus pore most anterior. Cirrus
large, oval. Testes in lateral fields, dorsal. Vagina with vesicle near distal end. Ovary pos-
terior, ventral, transverse to main axis. Shell-gland d(jrsal, near ovary and posterior to it.
Uterus in lateral coils, approaching form of rosette. Ova 70 by 35 /x.

Adult in white pelican; larvae in muscles and body cavity of trout; Yellowstone Lake,
Wyoming.

The name of this form cannot be accepted as Dibolhriiim is only a synonym of Bothrio-
phalus and the location of the genital pores rules this species .out of that genus as at present
dcfmed. Furthermore its exact position and true relationship must remain uncertain until
its structure is better known.

23 (22) Two sets of reproductive organs in each proglottid.

Diplogonoporiis Lonnbcrg 1892.

Very large cestodes parasitic in whales, seals, and occasionally in man.

The human parasite, D. grandis, is reported by Ashford and King from Porto Rico so it may
easily reach the southeastern coast of North America (see also Spargantim mansoni).

24 (15) Genital pores of different proglottids found on both surfaces of

strobila, alternating irregularly from proglottid to proglot-
tid. . Subfamily Cyathocephalinae Luhe 1899 . . 25

Scolcx unarmed, variable in form, not longer than wide, with two median or one apical
sucking organ in form of acetabula. External proglottid limits not marked, or absent. Geni-
tal organs single in each proglottid; all pores median. Vagina and uterus open in common
female genital atrium provided with sphincter and located posterior to male pore. Adults in
fishes.

25 (26) Apical sucking organ single, undivided by transverse fold.

Cyatlwccphalus Kessler 1868.

Scolex with single apical sucking organ in form of a cup, and without evidence in shape or
structure of its origin from fusion of two bothria located on surface. Proglottid limits distinct
externally. Sphincter of female genital atrium poorly developed.

Adults in fishes.

Type species C yatJiocephal us I runcal us (PaWas) 1781.

Reported by Linton from pyloric ceca of common whitefish. Lake Superior.

26 (25) Apical sucking-organ single but divided by transverse fold indicating

its double origin Bothriomonus Duvernoy 1842.

Scolex large, approximately spherical, with single apical sucking organ like acetabulum,
yet divided transversely by a fold which indicates its origin from two bothria typical of family.
No external proglottid boundaries. Sphincter of female genital atrium well developed.

In Acipenser oxyrhynchus; Wabash River, Indiana.

Type species Bothriomonus slur ion is Duvernoy 1842.

27 (14) Genital pore at margin of proglottid.

Subfamily Thiaexofiiokinae Liihe 1890.

Scolex always with typical bothria, not very deep; flattened apex of scolex projects above
bothria as a more or less distinct annular cap. Marginal genital jx)res alternating irregu-
larly; uterine pore, median on ventral surface, anterior to marginal genital |x)re. Repro-
ductive organs single in each proglottid. No muscular l)ulb at inner end «if cirrus sac. Re-
ceptaculum seminis small. Uterus in coils, Init never in rosette form, somewhat enlarged nc;ir
its terminus.

Adults in intestine of fishes and marine turtles; larvae in hshes. mostly unknown.

Type genus Triacnophorus Rudolph! 1793-

Scolex with 4 three-pointed hooks. No external iiroglottid markings. Testes occupy all
medullary layer not taken by other organs. Vitellaria continuous \\\ cortical layer, interrupted
only at genital pores. Ovary and shell gland adjacent to margin bearing genital i>ore. I ter-
ine pore usually not median but on surface at right of median line when marginal ix)re is sinis-
tral and vice versa. . ».t • »

Adults in intestine of fishes; larva encysted in fishes. Present m North Amcnca; no siJC-
cies definitely recorded as yet.

434 FRESH-WATER BIOLOGY

28 (9) Immature forms; sexual organs wanting or at least as yet only partly

developed Sparganum Diesing 1855.

Larval stages, without sex organs; not yet at a period in which specific determination is
possible. Many undescribed forms in various hosts; three known forms are hsted below. The
first named is not yet reported for this continent; the second and third are definitely recorded
for United States of America.

Sparganum mansoni (Cobbold) 1882.

Large forms, 8 to 36 cm. long; o.i to 12 mm. broad. Two longitudinal grooves on dorsal
surface; one median longitudinal groove on ventral surface. In connective tissue and body
cavity of man. Japan. The probable adult, Diplogonoporus grandis has been reported from
Porto Rico.

Sparganum proliferum (Ijima) 1905.

Small form, i to 12 mm. long, 2.5 mm. broad. Body usually irregular in form. Multipli-
cation in cysts by formation of supernumerary heads and transverse division. Encysted in
subdermal connective tissue and elsewhere; in man, Florida, U. S. A., and Japan.

Sparganum sebago Ward 1910.
Length 25 to 36 mm., breadth 1.8 to 0.36 mm. Head with keyhole-shaped bothria. Body
elliptical in cross-section with sUghtly thickened margins. No segmentation developed and
no sex organs. In spleen and body cavity of Salmo sebago; Maine.

29 (8, 30) Scolex with two or four sucking grooves, and also at apex four

protrusile proboscides armed with many hooks.

Order Trypanorhyncha.

The four long slender cylindrical proboscides are conspicuous enough to render the deter-
mination of adult or larva easy. The adults are found in the spiral valve of sharks and rays;
the larval forms occur encysted in migratory fish. They are among the rarest of finds in
fresh-water collecting and are present in North America though no species are recorded as
yet.

30 (8, 29) Scolex with four sucking organs (exceptionally replaced by a

pseudoscolex) but without extensile proboscides. No
uterine pore 31

31 (54) Vitellaria with very numerous follicles, distributed on each side in

longitudinal marginal zone, rarely in the entire surface zone
of the proglottid Order Tetraphyllidea.

Sucking organs 4, cup-shaped, small, or very mobile stalked or unstalked modified bothridia.
Small apical sucking organ frequent. Pseudo-scolex exceptionally present. External seg-
mentation evident, but less conspicuous at end of chain. Genital organs single in each pro-
glottid. No uterine pore, but uterus opens in median ventral line by rupture of wall. Testes
numerous. Ovary posterior, median, usually with two wings. Eggs thin-shelled, without
lid; embryonal development in uterus.

Adults in intestine of cold-blooded vertebrates.

Only family in North America in fresh-water hosts.

Family Proteocephalidae La Rue 1911 . . 32

Heads small. Suckers sessile and without accessory areola. Fifth sucker functional, ves-
tigial, or lacking. No rostellum. Genital organs in general as in other TetraphyUidea.
Genital pores marginal, irregularly alternating. Vitellaria lateral, follicular, follicles closely
grouped about a central conducting tubule. Ovary bilobed, posterior. Oocapt, ootype, shell
gland, and uterine passage present. Uterus with lateral outpocketings and one or more pre- 1
formed ventral uterine openings. Vitellaria, testes, ovary and uterus within the inner longi- i
tudinal muscle-sheath.

Habitat: In fresh-water fish, amphibians, and aquatic reptiles.

32 (53) Head without lappets or folds of tissue around suckers ^t, \

2,2> (46) Testes in one broad mass between vitellaria; parasitic in fresh- '
water fish Proteocephalus Weinland 1858 . . 34 i

Head globose or conical, flattened dorsoventrally. No rostellum. No spines or hooks. ,
Suckers circular or oval. Fifth sucker functional or vestigial, rarely lacking. Musculature '
well developed. Eggs with three membranes. '

PARASITIC FLATWORMS

435

34 (41) Functional fifth or apical sucker, absent or vestigial 35

35 (t,8) Testes number 100 or more 36

36 (37) Genital pore on lateral margin near center of proglottid.

Proteoccphalus macrocephaliis (Creplin) 1825.

As much as 40 cm. lonR by i to
1.8 mm. broad, or perhaps more.
Proglottids very numerous; first
much l)r(>ader than lonj,'; maturi.*,
broader than lonj,' or nearly cjuad-
rate; ripe, longer than broad.
Suckers 0.095 to 0.106 mm. in
diameter. Fifth sucker vestigial.
Testes 100 to 120, irregularly
scattered between vitellaria, ly-
ing in one or two layers, usually
one. Cirrus-pouch short, about
0.16 mm. long; ratio to proglot-
tid breadth i : 6 to i : 8. Uterine
pouches 7 to 14 on either side.

Habitat: In intestine of An-
gxiilla vulgaris and A. chrysyPa
Raf.

^ Fig. 733. Proleocephalus macrocephalus. a, Head. X 70; b,
ripe proglottid showing female reproductive organs. X 40. (After
La Rue.)

37 (36) Genital pore on lateral margin anterior to center of proglottid.

Proleocephalus per plexus La Rue 191 1.

Length as much as 155 mm.; maximum breadth 1.7 mm. First proglottids much broader
than long; mature proglottids 1.70 mm. broad by 0.595 mm. long; ripe proglottids quadrate
or longer than broad. Suckers, 0.340 to 0.459 "im. long by 0.255 to 0.272 mm. broad. \o
vestige of fifth sucker.

Genital pore at end of
first fourth or half of
proglottid. Cirrus-fM)uch
0.30 to 0.344 mni. long,
extending to one-third or
one-fifth width of proglot-
tid. Testes 135 to 155 in
number, in one layer an-
terior to ovar>'. \'agina
anterior to cirrus-pouch,
never crossing same. Vi-
tellaria extend to posterior
margin of proglottid and
parallel to it. L'teruswith
20 to 25 lateral pouches
on each side.

Hal)itat: In intestine of
Fig. 734. Proleocephalus perplexus. a. Head. X 36; b, ripe proglottid, -^'"i^ ^^^^'^ and Le pi so stats
reconstruction showing male reproductive organs (U, testes), and ovary. Piatosiomus. llunois,.^orin
Note also position of sphincter vaginae (I'aj). X 36. (.\fter La Rue.) Carohna.

38 (35) Testes number less than loo 30

39 (40) Suckers with pointed apex and shallow cavity.

Proleocephalus singular is La Rue 191 1.

Strobila long, slender, up to 170 or even 250 mm.; maximum breadth 0.90 to i.o mm. Head
small, suckers large. No vestige of fifth sucker. First prt)gli)liids brt)ader than long; mature
proglottids 0.85 mm. broad by 0.34 to 0.37 mm. long; riin- proglottids longer than bri>ad or
quadrate. Old spent proglottids up to 2.0 mm. long by 0.4 mm. broad.

Genital pore at end of first one-fourth to one-half of proglottid. Testes 75 to So or 90, m a

43^

FRESH-WATER BIOLOGY

single layer. Vas deferens large mass of coils in mid-field. Cirrus-pouch slender, nearly
straight, muscular, length two-fifths to one-third proglottid width.

Vagina always anterior to cirrus-pouch, never crossing latter. Beginning region of vagina
narrow. Uterus with 20 to 25 lateral outpocketings.

In intestine of Lepisosteiis platostomus. Illinois.

Fig. 735. Proteocephalus singularis. a, Head; apical prominence contracted; 6, apical prominence
extended, X 50; c, ripe proglottid, frontal section showing arrangements of testes, vitellaria and ovary;
vagina and cirrus-pouch not shown, X 36. (After La Rue.)

40 (39) Suckers round or oval with smooth contour.

Proteocephalus ambloplitis (Leidy) 1887.

Large, 280 to 410 mm. long, 2 to 2.5 mm. in maximum breadth. Surface of body rough,
with transverse and longitudinal furrows. Scolex prominent. Fifth sucker vestigial. Young
proglottids 12 to 15 times broader than long. Mature and ripe proglottids broader than
long, about quadrate, or rarely longer than broad. Vitellaria not posterior to lobes of ovary.
Genital sinus at end of first fourth of proglottid. Uterus with 15 to 20 lateral outpocketings
on each side. Cirrus-pouch pyriform, muscular, two-sevenths to two-fifths of proglottid
breadth. Coils of vas deferens many, extending to middle of proglottid. Testes 70 to 100 in
number.

Intestine of Ambloplites rupestris, Micropterus salmoides, M. dolomieu, Amia calvor New
York, Michigan, Minnesota, and Wisconsin.

vas

Fig. 736. Proteocephalus ambloplitis. a, Head, X 25. (After La Rue); b, ripe proglottid, frontal
section showing main parts of male and female reproductive systems, magnified, (After Benedict.)

41 (34) Well-developed (functional) fifth sucker present 42

PARAS [TIC I LATWORMS

437

42 (43) Cirrus-pouch extends half way across proglottid.

Proteocephalus exiguus La Rue 191 1.

Stroliila short, slender, lenKth 9 to 38 mm.,
maxmnim breadth 0.425 to 0.8 mm. First
proglottids longer than broad or nearly quad-
rate; mature and ripe proglottids longer than
broad, ripe proglottids considerably larger, 0.680
to 1. 190 mm. long by 0.460 to 0.595 mm. broad.
Suckers 0.058 mm. broad, 0.069 to 0.085 mm.
long. Genital pore near middle of lateral mar-
gin of proglottid. Testes .:i4 to 54 in number,
in one layer. Vas deferens forming mass of
coils in mid-field. Vagina anterior to cirrus-
pouch, crossing it near middle. Uterus with 9
to 14 lateral pouches on either side.

In intestine of Coregonus ni^ripiiuiisX- Prog-
nathus, and C. artedi, Lake Michigan.

Fig. 737. Proteocephalus exiguus. a. Head, su,
fifth sucker, X 93; b, mature proglottid, X 60
(After La Rue.)

43 (42) Cirrus-pouch less than one-third breadth of proglottid.

44 (45) Testes in one layer Proteocephalus pingiiis La Rue

44

IQI I.

Fig. 738. Proteocephalus pinguis. a. Head in dorsal or
ventral view, X 45; b, ripe proglottid, till, lateral uterine
pouches, ventral view, X 63. (After La Rue.)

Strobila short, .slender, length up to
90 mm., ma.ximum breadth 1.24 mm.
First proglottids very short. .Mature
and ripe proglottids nearly quadrate or
in a few ripe proglottids length exceed-
ing the breadth.

(ienital pore at or near middle of
lateral margin of proglottid. Testes
54 to 70, in a single layer. Cirrus-
pouch short, stout, 0.13 to 0.14 mm.
long by 0.05 to 0.06 mm. broad, i : ^
or I :4 in breadth of proglottid. Va-
gina anterior, but vaginal ojx'ning al-
ways dorsal to cirrus-pouch. Vagina
crossing inner end of cirrus-sheath.
Uterus with 10 to 14 lateral pouches
on either side.

In intestine of Esox reticidatus Le
Sueur, and E. Indus Linn., Maine,
Michigan, and Wisconsin.

45 (44) Testes in two layers Proteocephalus pus ill us Ward iqio.

Very small, weak; length 30 to 50 mm.,
maximum breadth 0.350 mm. Proglottids
few. First proglottids broader than long,
mature proglottids longer than broad, rijx^
proglottids much longer (0.84 to 1.4 mm.)
than broad (0.18 to 0.35 mm.)

Genital sinus at end of first one-third to
two-fifths of i^roglottid. Testes 44 to 70 in
number, in two layers. Coils of vas deferens
few, anterior to cirrus-ix)uch. Vagina never
crossing cirrus-pouch. Uterus with 10 tt) 16
lateral pouches on each side.

Habitat : Intestine of Satmo srbago Girard
and Crislhomrr ttamaycush \Vall)aum; Se-
bago Lake, Maine, Lake Temagami, On-
tario.

Fig. 739. Proteocephalus pusillus. a. Head, showing
fifth sucker, X 70; b, mature proglottid, toto, X 63.
(After La Rue.)

438

FRESH-WATER BIOLOGY

46 (33) Testes lie in two lateral fields between vitellaria; parasitic in am-
phibians, aquatic snakes, and lizards.

Ophiotaenia LiSi Rue igii . . 47

Head globose or somewhat tetragonal. No rostellurn. ^ No hooks or spines. Suckers dr-
cular or oval, with margins entire. Fifth sucker vestigial. Neck usually long. Testes in
two long lateral fields anterior to_ ovary. Musculature weak.

In aquatic snakes and Amphirbia.

47 (48) Vagina always anterior to cirrus-pouch, not crossing latter.

Ophiotaenia filaroides La Rue 1909.

Worms attenuate, small, thin, flat. Length 80 to no mm., maximum breadth about 0.80
to OQO mm Suckers deep, muscular, oval, maximum diameter 0.165 to 0.184 mm First
progiottids o 30 to 0.36 mm. broad by o.io to 0.17 mm. long; mature proglottids quadrate or
longer than broad; ripe proglottids from 1.6 mm. to 4.0 mm. long by 0.8 mm. to 0.75 mm.

Genital pore at end of first fifth of proglottid. Testes 70 to 114 in number.
Few coils in cirrus-pouch. Cirrus-pouch about 0.22 mm. long by o.ii mm.
broad. Vitellaria with large follicles. Uterus with 25 to 35 lateral pouches on
each side. (For structure of mature proglottid consult figure 730, page 425.)

Intestine of Amblystoma tigriniim (Green); Nebraska and Kansas.

Fig. 740. Ophiotaenia filarioides. Head of adult, magnified. (After La Rue.)

48 (47) Vagina either anterior or posterior to cirrus-pouch 49

49 (52) Genital pore anterior to middle of margin of proglottid 5°

50 (51) Testes number 90 to 160. Ophiotaenia Idnnbergii (Fuhrmann) 1895.

Fig. 741. Opkwlaenia idnnbergii. a. Head, b, mature
proglottid, magnified. (Alter Fuhrmann.)

posterior to it. Vagina never crosses cirrus-pouch

Length 170 to 190 mm., breadth up to
1.35 mm. Scolexo.50too.60mm. broad.
Suckers measure 0.24 to 0.26 mm. long
by 0.14 to 0.22 mm. broad. First pro-
glottids about 0.5 mm. long by 0.50 mm.
broad; mature proglottids 0.85 to i.o
mm. square, or longer than broad,
measuring as much as 2.5 mm. long by
0.45 to 0.5 mm. broad. Ripe proglottids
not observed.

Genital pore situated at end of first
one-third or two-fifths of proglottid.
Testes 90 to 160 in number, extending
lateral of excretory vessels and a few
into midzone. Cirrus-pouch 0.185 to
0.280 mm. long by 0.05 to 0.085 or o.io
mm. broad, with large mass of coils
Uterus with 25 to 40 lateral pouches.

In intestine of Neciurus maculosiis Raf.; Ohio, Indiana.

PARASITIC FLATWORMS

439

51 (50) Testes number 150 to 215

Ophiotacnia pcrspicua La Rue 191 1.

Length up to 360 mm., maximum breadth
about 2.0 mm. First proglottids short, mature
proglottids quadrate (2.0 mm.) or somewhat longer
than broad, ripe proglottids as much as 3.8 mm.
long by 1.2 mm. broad.

Genital pore situated near middle or at end of
first third of proglottid. Testes 150 to 215. Vas
deferens in ripe proglottids heavy mass of coils
reaching from end of cirrus-p<juch to mid-field.
Ratio of length of cirrus-pouch to proglottid
breadth i : 4 to i : 3. V'agina anterior or pos-
terior to but not crossing cirrus-pouch. Uterus
with 20 to 30 lateral pouches on each side.

Habitat: Natrix {Nerodia) r hombifer HaWowcW;
Illinois, Oklahoma.

Fig. 742. G;ilnolaenia pcrspicua. a, Head. X 23;
b, ripe proRlottid, showing uterine pouches, and testes.
(After La Rue.)

52 (49) Genital pore at or near center of margin of proglottid.

Ophiotaenia gra^idis La Rue 191 1,

utvp

Very long (fragments 200 mm.), 2.75 to 4.25
mm. broad in ripe proglottids. First proglottids
much broader than long; proglottids with develop-
ing sexual organs quadrate or nearly so; ripe pro-
glottids quadrate or much longer than broad.
Head large, i.o to 1.2 mm. broad at base of suck-
ers. Suckers about 0.34 by 0.36 mm. Testes
large, numerous, 200 to 250. Cirrus-pouch 0.24 to
0.26 mm. broad, 0.64 to 0.75 mm. long, enclosing
few or no coils of ductus ejaculatorius. Uterus
with 40 to 60 lateral outpocketings on each side.

In intestine of Ancislrodon piscivorus Holbr.,
locality not known.

Fig. 743. Ophiotaenia grandis. a, Head, showinR
swollen region back of head, X S; b. mature pro-
glottid, ventral view showing reproductive organs and
ventral uterine pores {utvp). X 10. (After La Rue)

S3 (32)

Many lappets or folds of tissue about suckers.

Corallobotliriiim Fritsch

[886.

Scolex with four suckers situated on the flat anterior face of the head. .Many irregular
folds and lappets of tissue about margin of anterior surface; may enclose suckers as in a corolla.
Norostellum. No hooks nor spines. Neck broad, short. Habitat. In Siluridae.

Marshall and Gilbert report the occurrence of two species m the lonuiion bullhead. I have
an undescribed species taken from a channel-cat at Milford, Neb.

54 (31) Vitellaria condensed, in a single mass, in medullary layer, usually
immediately posterior to ovary, rarely anterior to it.

Order Cyclophyllidea . . 55

Scolex with 4 cup or saucer-shaped suckers and in the center an apical organ or rostcllum of
varied form. Hooks common on rostellum, very rare on suckers. Segmentation well devel-
oped, only rarely absent (Fimbriariidae); proglottids set free after lull maturity. No uterine
pore; rarely a secondary connection to the exterior permits the escape of ova. Testes m nuxlul-
lajy layer, ordinarily numerous. Ovary bilobed; vitellarium compact, smgle. near ovary

440

FRESH-WATER BIOLOGY

with shell gland between. Eggs thin-shelled, no lid; onchosphere with one or more mem-
branes. Bladder-worm in vertebrates and invertebrates.

The great majority of forms commonly designated Taenia are included here. Number
and form of hooks on which older systems are based form unrehable means for the distinction
of species. In immature forms the organs utilized in this key are undeveloped and a deter-
mination can only be approximate.

55 (117) Body flattened. Distinct and regular external boundaries corre-

sponding to internal grouping of organs in the strobila. 56

56 (57) Suckers carry on anterior and lateral surface auricular appendages.
Vitellarium anterior to ovary.

Family Tetrabothriidae Fuhrmann 1907.

Scolex unarmed, without rostellum. Neck short. Proglottids
except oldest always much broader than long. Reproductive organs
single in each proglottid. Genital pores unilateral; genital cloaca
deep. Cirrus-pouch small and nearly spherical, united with genital
cloaca by muscular cloacal canal. Eggs with three transparent en-
velopes. Adults in birds and mammals.

Type genus.

Tetrabothrius Rudolphi 18 19.

Fig. 744. Tetrabothrius
macrocephalus . Scolex; mag-
nified. (After Liihe.)

With characters of the family.

Scolex unarmed, quadrate. Suckers large. Sexual pore always
dextral.

The hosts are aquatic birds, largely marine. Nearly twenty species
are described, a number of which occur in North American birds:
(gull, grebe, heron, loon), that frequent fresh-water bodies.

57 (56) Suckers simple without appendages of any sort. Vitellaria not

anterior to ovary but posterior to it, or in the same trans-
verse plane with it 58

58 (59) Genital pores median, on flat surface of proglottids.

Family Mesocestoididae Fuhrmann 1907.

Scolex without rostellum or hooks. Suckers unarmed. Reproductive organs single in
each proglottid. Genital pores median on ventral surface. Vagina opens in front of or beside
cirrus-pouch. Eggs in terminal proglottids inclosed in single thick-walled egg-capsule. Adults
in mammals and birds.

Type genus Mesocestoides Vaillant 1863.

With characters of the family.

Few species; almost never in aquatic forms. No North American records although the
genus occurs here.

59 (58) Male genital pores at margin or very close to it. Female pores

when present similarly located 60

60 (104)

61 (103)

62 (102)

63 (64)

Female genital pore present and located near male pore. ... 61

Uterus transverse or irregular, not elongated in median line of
proglottid 62

Reproductive organs simple in each proglottid or if genital pores
are double, the organs are also double 63

Scolex provided with three to many rows of hooks.

Family Dipylidiidae Liihe 1910.

No forms in fresh-water hosts.

64 (63) Scolex provided with one or two rows of hooks or without any
hooks 65

PARASITIC FLATWORMS 441

65 (70) Rostellum hassock-shaped with a muhitudc of very small hooks

arranged in a double row.

Family DavaIxNEidae Fuhrmann 1907 . . 66

Scolex with rostellum usually broader than hi^h and armed with very many minute hammer-
shaped hooks. Margins of suckers usually with small hooks, (lenital organs usually single,
rarely double in each proglottid. Testes numerous. Onchosphere with two thin membranes.'

66 (67) Uterus divides into numerous separate parenchyme-capsules.

Davainea R. Blanchard i8qi.

Rostellum armed with double row of hooks; dorsal excretory vessels present. RcprcKluctivc
organs single in each proglottid. Genital pores unilateral or occasionally irregularly alternate.
Uterus breaks down into egg capsules each containing one or several eggs. .Adults in mam-
mals and birds. Numerous species; mostly in scratching birds. D. anatina is reported from
the domestic duck in Europe. No North American records.

67 (66) Uterus not breaking up into separate parenchyme-capsules. . . 68

68 (69) No parauterine organ; uterus sac-shaped. Rostellum broader than
_ scolex with several thousand booklets.

Opiiryocotyle Friis 1870.

Rostellum broader than rest of scolex; suckers
armed only near anterior border. Reproductive or-
gans single in each proglottid. Uterus sac-like, per-
sistent.

Three species in European shore and water birds
some of which occur in North America.

Fig. 745. Opiiryocotyle proleus. Head and neck with
retracted and extended infundibulum; magnified. (.After

Stiles.)

69 (68) Uterus coiled in posterior end of proglottid; thick-walled para-
uterine organ in anterior region. Rostellum small; with
not to exceed a few hundred booklets.

Idiogenes Krabbe 1868.

Small cestodes. Genital pores unilateral. Cirrus-pouch very large, with retractor. Para-
uterine organ develops in front of uterus; eggs finally pass directly into it from uterus and it
is transformed into single thick-walled egg capsule. Adults in birds.

A few species in water birds; none recorded as yet in North .Vmerica.

70(65) Rostellum sac-like, or lacking 71

71 (82) Not more than four testes in each proglottid.

Family Hymenolepididae Fuhrmann 1007. . . 72

Scolex armed with 8 to 40, usually 10 hooks, with points directed i^)steriad when at rest,
on a more or less elongated rostellum which rarely is rudimentary and unanned. Genital
pores strictly unilateral in entire strobila. Genital ducts dorsal to e.\cretor>- ducts and longi-
tudinal nerve. Female glands median. Onchosphere with three membranes, .\dults in
birds and mammals.

72 (73) In each proglottid normally 4 testes. . . Oligorchis Fuhrmann ioo().
A single species in North America; not reported in aquatic birds.

73 (72) In each proglottid normally less than four testes 74

74(79) In each proglottid normally three testes 7^

442

FRESH-WATER BIOLOGY

75 (76) Strobila broad, lancet-shaped. Ovary and vitellarium ante-poral,

alongside of testes Drepanidotaenia Railliet 1892.

Scolex very small, with 8 hooks. Neck wanting. No accessory sac in genital atrium.

Type species Drepanidotaenia lanceolata (Bloch) 1782.

Adult in intestine of ducks and geese; cosmopolitan. Bladder-worm in various Cyclopidae
and Diaptomus.

Fig. 746. Drepanidotaenia lanceolata. Transverse section of proglottid; u, uterus; vt, vitellaria;
ov, ovary; t, testes; vd, vas deferens; sr, seminal receptacle; v, vagina; magnified. (After Wolffhiigel.)

76 (75) Strobila slender or even filiform. Ovary and vitellarium ventral to
testes or between them 77

77 (78) Suckers entirely unarmed, or at most armed with hooks on margin
only Hymenolcpis Weinland 1858.

Rostellum well developed, rarely rudimentary
or absent. Accessory sac generally wanting in
genital atrium. Rarely as abnormality 2, 4,
5, or 6 testes in a single proglottid. Chiefly in
land and water birds; some species in mam-
mals.

A very large genus; about 50 species occur in
aquatic hosts found in North America. Among
them a few are definitely reported for North
America. H . compressa (Linton) 1892 from the
scoter and canvas-back. H. fusus in which
Fig. 747. Hymenolcpis megalops. Dorsal view Fuhrmann places Linton's Taenia filum from

of mature segment (no. 172). Reconstruction from gulls at Yellowstone Lake

rri°t?ako^%rdSS?.5 ^..,»e,a/.^.describedby Ransom (withother

genital cloaca; nt, main lateral nerve; sg, shell species from land birds) from the pintail duck;

gland; /, testis; tm, transverse muscles; tit, uterus; Missouri River, Mo.

vc, ventral excretory canal; vg. vagina; vs, seminal

vesicle; vs', seminal vesicle of cirrus-pouch; xpl,

plexus of excretory vessels; yp, yolk glands. X 90.

(After Ransom.)

78 (77) Suckers armed on borders and also in cavity with small booklets;
sacculus accessorius always present.

Echinocotyle Blanchard 1891.

Rostellum armed with single crown of ten slender hooks with dorsal
root and blade about equal in length and ventral root rudimentary.
Suckers large, flat, oval, poor in musculature, armed on borders and in
middle with several rows of small booklets. Muscular, spinous sacculus
accessorius always present. Adults in birds.

Type species. . Echinocotyle rosseteri'EXainchdiTdiZgi.

Five species in shore and water birds of Europe. Hosts mostly found I
in North America also.

Fig. 748. Echinocotyle rosseteri. Head with extended rostellum; X 250.
(After Blanchard.)

PARASITIC FLATWORMS
yg (74) In each proglottid normally less than three testes.

443

80

80(81) Two testes in each proglottid -O/Wc///^ Clerc 1903.

Rostellum with single crown of ten hooks having long dorsal and short ventral roots or
exceptionally very short dorsal root and ventral root nearly as lung as the hladc. Entire
surface of suckers may be armed with minute spines. Inner longitudinal muscle layer con-
sisting of 8 bundles, 4 dorsal and 4 ventral. Two testes in each proglottid. Ovary and vitel
larium always median. Adults in birds.

Four or more species in European water birds. Most of the host species occur in North
America. D. acuminata and D. americana were both collected by Ransom from the coot in
Nebraska.

Fig. 749. Diorchis acuminata, a. Hook from rostellum; sexually mature scRmcnt; cp, cirrus-
pouch; ov, ovary; t, testis; ves sent, seminal vesicle; yg, yolk gland; magnified, (.-^fter Ransom.)

Fig. 750. Diorchis americana. a. Hook from rostellum; magnified; se.xually mature segment at
high focus to show male organs, dorsal view; magnified; cp, cirrus-pouch; ov, ovar>-; /, testes; vts sem,

seminal vesicle; yp, yolk gland; magnified. (After Ransom.)

81 (80) One testis in each proglottid \ploparaksis Clerc 1Q03.

Fig. 751. Aploparaksis filum. Transverse section
of proglottid, female reproductive organs not shown;
X 3,6. (After Clerc.) Hook from rostellum, X 75°-
(After Krabbe.)

Strobila small and slender. Rostellum
armed with a single crown of lo hooks, with
ventral root as long or nearly a.s long as
blade. Suckers unarmed. One testis dors;il.
Seminal vesicle large. Ovary and vitcUa-
rium always median. .Vdults in birds.

Type species.
Aploparaksis Jil urn (Goczc) 17S2.

.V dozen species described from avian
hosts both terrestrial and aquatic: nearly
all of the species arc found in North .\mcri-
can host s]K*cies.

82 (71) At least six testes normally in each proglottid 83

444

FRESH-WATER BIOLOGY

83 (83a) Rostellum entirely lacking. Scolex unarmed, very muscular.

Family Anoplocephalidae Kholodkovsky 1902.
Not found in fresh-water hosts.

83a (83) Rostellum present and armed with one or two rows of hooks.

Family Dilepididae Fuhrmann 1907 . . 84

With rostellum armed with single or double crown of hooks rarely in broken zig-zag row,
exceptionally rudimentary. Points of hooks directed posteriad. Suckers unarmed. Genital
pores marginal (see 84 just below). Sex organs in each proglottid simple or double. Uterus
sacculate or lobed, simple.

Onchosphere with three membranes. Many genera chiefly found m birds, rarely m rep-
tiles or mammals.

84 (85) Genital pores submarginal, dorsal, but never as far as half way

from margin to median hne.

Trichocephaloides Ssinitsin 1896.

Rostellum powerful with single crown of hooks. Genital pores unilateral, subdorsal. Cirrus
short and thick with long bristles; no seminal vesicle. Testes few, in posterior region of seg-
ment. Uterus sac-like; eggs few. Adults in birds.

Few species in shore birds; parasites not reported from North America.

85 (84) Genital pores distinctly marginal 86

86 (93) Genital pores uniformly unilateral 87

87 (88) Rostellum with single crown of hooks. Lateriporus Fuhrmann 1907.

Rostellum armed with single crown of 12 to 16 hooks (120 to 170M long), with long dorsal
and short ventral root, and well-developed blade. Proglottids broader than long. Genital
canals pass dorsal of longitudinal excretory vessels. Testes 12 to 30 in number, situated pos-
terior and lateral to ovary and xntellarium. Uterus sac-Hke, filling entire medullary paren-
chyma in terminal proglottids. Adults in birds.

Five or more species, found in Europe in Anseriformes; not yet reported for North America.

88 (87) Rostellum with double crown of hooks; rarely rudimentary and un-

armed 89

89 (92) No spines on base of cirrus 9°

90 (91) Testes not in front of but behind ovary and vitellarium.

Dilepis Weinland 1858.

Rostellum armed with double crown of hooks having long dorsal and short ventral root and
long blade. Inner longitudinal muscle layer consisting of numerous bundles. Proglottids
broader than long. Genital canals pass dorsal of the longitudinal excretory vessels and nerve.
Vas deferens coiled, seminal vesicle not developed. Testes in medullary portion typically
numerous (40 to 50), but may be reduced in number (7). Uterus sac-Uke with few or numer-
ous outpocketings. Adults in birds and mammals.

Many species from various birds including fresh-water types found in North Amenca.
D. transfuga from the spoonbill determined for North America by Ransom. D. unUaterdis
for the green heron by Stiles and Hassall, and by A. J. Smith; also for the httle blue heron by
Leidy.

91 (90) Testes very numerous, entirely surrounding the female glands.

Cydorchida Fuhrmann 1907.

Rostellum armed with double crown of hooks, which have a very large dorsal root and small
hook portion. Genital canals pass between longitudinal excretory vessels. Cirrus-pouch
communicates with genital cloaca by narrow canal opening upon large papilla. Uterus ventral,
growing laterally between the excretory vessels into the cortical parenchyma and fiUing entire
proglottid. Adults in birds.

In heron, crane, etc., in Europe. Not recorded for North America.

PARASITIC FLATWORMS

445

92 (89) Root of cirrus with one or two pairs of powerful hooks lying in
special pockets; genital canals pass between longitudinal
excretory vessels.

Gryporhynchus Xordmann 1832.
(Syn. — Acdnthocirrus Fuhrmann 1907.)

Genital canals pass between the longitudinal excretory vessels.
In genital atrium lateral to root of cirrus two special pockets with one
or two pairs of powerful hooks in each. Uterus sac-like. Adults in
birds.

Three species or more in herons; not reported from North America.

Fig. 752. Gryporhynchus cheilancristrolus. Proglottid with contracted
cirrus-pouch; short heavy hooks in pockets at opening of cirrus-pouch into
genital cloaca. Magnified. (After Clerc.)

93 (86) Genital pores not unilateral but alternating 94

94 (97) Genital pores regularly alternating 95

95 (96) Rostellum with single crown of hooks. Less than 30 proglottids;

scolex large; no neck Amocbotaeuia Cohn i8qq.

Proglottids much broader than long. Testes rather numerous (12 or more), in posterior
portion of segment. Uterus sac-like, fills entire medullary portion of terminal proglottids.
Adults in birds.

Four or five species, some in shore birds that occur in North America.

Fig. 753. Amoebotaenia.
Anterior end, magnified.
(After von Linstow.)

Fig. 754. Amoebotaenia cuncata. a. dorsal view;
b, ventral view; magnified, (.\fter Cohn.)

96 (95) Two rows of hooks on rostellum.

Cvclustcra Fuhrmann iqoi.

Rostellum with double crown of hooks. Longitudinal musculature in three layers, (icni-
tal canals pass between the longitudinal e.\cretor>' vessels and ojx'n into a very muscular cloacal
canal. Testes numerous, scattered throughout entire dorsal medullar>' portion of proglottid.
Ovary and yolk gland surrounded by ring-like uterus with secondar\' branches. Eggs with
two shells. Adults in birds. C. capita, the type species, is reported by Ransom as found in
the roseate spoonbill in North America.

97 (94) Genital pores alternate irregularly 9S

446

FRESH-WATER BIOLOGY

98 (99) Uterus sac-like

Anomotaeiiia Cohn 1900.

Rostellum with double crown of hooks, w'ith long dorsal and short
ventral root, and long blade. Genital pores near anterior border of
segment. Genital canals pass between the longitudinal excretory
vessels and dorsal of the nerve. Vas deferens coiled, seminal vesicle
absent. Testes numerous, in posterior portion of segment (or rarely
laterally on both sides of the female glands). Adults in birds and
mammals.

]Many species from both land and water birds in Europe. A . con-
stricta from the fish crow, determined for U. S. A. by Ransom. [Many
European hosts of other species are found in North America.

Fig. 755.

Anomoiaenia constricta. Male and female reproductive organs,
magnified. (After Volz.)

99 (98) Uterus branching and in ripe proglottids incompletely divided intp
numerous small communicating compartments .100

loo ^loi) One crown of hooks on the rostellum. Choanotaenia Railliet 1896.

Scolex small. Rostellum armed with single crown
of hooks usually with long dorsal and short ventral
root. Proglottids numerous, rarely less than 30;
oldest often longer than wide. Genital pores irregu-
larly alternate near anterior border of proglottid,
(ienital canals pass between longitudinal excretory
vessels and dorsal of nerve. \^as deferens coiled,
seminal vesicle absent. Testes numerous, in posterior
region of, or more rarely laterally on each side of, the
female glands. Uterus subdivided into numerous
small communicating chambers incomplctelj' sepa-
rated by partitions infolded from wall so that in some
cases eggs appear almost as if isolated in parenchyma.
Adults in birds and mammals.

A dozen species or more from North American

hosts; land, shore and water birds represented. Ch.

^ ^ ^, . . ^ ,., , zWzmtfj&H/HW is common in chickens and is recorded

Fig. 756. Choanotaenia mfundibulum for North America generally. Ch. porosa occurs in ?.

a, Hook irom rostellum; magnmed; seg- , r ^. °, . , •'., . ^ ^ j v t • i.

ment showing reproductive organs; magni- number of aquatic birds; it is reported by Linton

fied. (After Ransom.) from gulls at Yellowstone Lake.

loi (100) Rostellum armed with double crown of hooks.

Monopylidium Fuhrmann 1899.

Reproductive organs single in each proglottid. Genital canals pass between longitudinal ex-
cretory vessels and dorsal to longitudinal nerve or to both excretory vessels. Testes numerous
(20 to 40 or more), behind ovary and vitellarium or laterally on both sides of latter. Vas
deferens coiled; seminal vesicle absent. Uterus breaks down into egg capsules, each con-
taining usually one egg. Adults in birds.

A dozen species in European hosts which include some shore birds found in North America.

102 (62) Reproductive glands simple, central in each proglottid; ducts
and pores double, one set on each side.

Diploposthe Jacobi 1896.

Rostellum armed with single crown of ten hooks. Suckers unarmed. Inner longitudinal
muscle layer, except for two or three small bundles lateral beyond excretory vessels, developed
in median portion consisting of about ten dorsal and ten ventral bundles of unequal size.
Outer longitudinal muscle layer of numerous equally developed bundles, interrupted where
genital canals pass through. Outside thin layer of diagonal fibers, at posterior end well-
developed muscle ring. Genital pores marginal, one on each side. Testes few (3 to 7) in
posterior portion of proglottid. Two vasa deferentia. Seminal vesicles present on each side

PARASITIC Fl.ATWOKMS 4^7

armed with strong hooks. Female glands single, median; two vaginae. Eggs with ilirtc
membranes.

The type species, D. laeyis, from various ducks and geese found in North .\mcrica .\o
record of any species on this continent.

vt ov vi

Fig. 757. Diplopostke laevis. Optical section of ripe proglottid; vd, vas deferens; /, testes; u, uterus
vt, vitellaria; ov, ovary; vs, seminal vesicle; v, vagina; X 22. (After Jacobi.)

103 (61) Uterus with median stem and lateral branches; female genital

glands in posterior end of proglottid.

Family Taexiid.ve Ludwig 1886.
Splex usually with well-developed rostellum armed with double crown of hcxjks, rarely with
rudimentary unarmed rostellum. Suckers unarmed. Terminal segments longer than broad.
Reproductive organs single in each proglottid. Cicnital pores irregularly alternate. Vas
deferens coiled, seminal vesicle absent. Testes numerous, scattered. Double ovary poste-
rior, median, posterior to which is the yolk gland. Egg with thin outer membrane, and thick
brown radially striated inner shell. Adults in mammals and birds.

Taenia Linnaeus 1758.

Forms rightly included here are as adults characteristic parasites of higher carnivorous land
animals and the larval forms (cysticerci) also occur in land-living herbivorous or omnivorous
mammals.

Eggs are distributed widely by surface waters. Larval stages occur rarely in aquatic mam-
mals, e.g., Cysticcrcus fasciolaris the bladder-worm of Taenia crassico/lis of the cat wliich Stiles
and Hassall, and later Linton also, have reported from the muskrat.

104 (60) Female genital pore not adjacent to cirrus and male pore. . . 105

105 (112) Proglottids without lateral appendages. Female genital {xjre is

entirely lacking.

Family Acoleidae Fuhrmann 1007 . . 106
Thick-bodied cestodes with rostellum usually armed. Proglottids short. Musc-ulature
very powerful. Cirrus sac very large; cirrus armed with strong spines. Eggs with 3 mem-
branes. In birds.

106(111) Hermaphroditic forms 107

107(110) ]\Iale and female genital organs simple 108

108 (109) Testes numerous; seminal receptacle very large; uterus a trans-

verse tube anterior to ovary. Male genital pores regularly

alternate icolcus Fuhrmann 1809.

Scolex small with armed rostellum. Reproductive organs single. Cirrus-pouch passes
ventral of longitudinal excretory vessels and nerve. V'^agina closed, functions as very large
seminal receptacle. Adults in water birds.

Type species lr()/(7/.s (/rmc;///.? Fuhrmann 1899.

From the black-necked stilt; parasite not reported from North .\merica.

109 (108) Testes few; seminal receptacle very small; uterus encircling

ovary; male pores irregularly ahernate.

Ciyrococlia Fuhrmann iSoo.
Rostellum armed with single crown of hooks arranged in zig-zag row having eight angles.
Reproductive organs single in each proglottid. Cirrus |>nuh jKisses In-tween longitvidina!
excretory vessels and dorsal of nerve. Cterus ring-like, with numerous outixHketings. and
with opening in terminal proglottids both dorsally and ventrally in median line of posterior
margin. Adults in birds.

In water birds; not reported in North .Vmerica.

448 FRESH-WATER BIOLOGY

no (107) Male reproductive organs double and female single in each pro-
glottid with two vaginae functioning as large seminal re-
ceptacles Diplophallus Fuhrmann 1900,

Large forms with small scolex and armed ros-
tellum. Testes numerous, in two lateral fields
fully separated by median female glands. Cir-
rus sac powerful, cirrus slender, very long.
Vagina a blind transverse canal. Uterus at
first transverse tube: later irregular, and finally
taking in entire medullary region.

Type species.

Diplophallus polymorphus

(Rudolphi) 1819.

Fig. 758. . Diplophallus. Schematic transverse Yxom the black-necked stilt; parasite not re-
section of ripe proglottid; /.testes: «, uterus; sr, ^^^ r „ -^t ,i »„ . '^

seminal receptacle; .., ovary; vt, vitellaria. (Afte^ ^^rded from North America.
Wolffhugel.)

111 (106) Dioecious, entire strobila male or female; male with a double

set, female with a single set of reproductive organs in each

proglottid Dioicocestus Fuhrmann 1900.

Female thicker and broader than male. Vagina irregularly alternating, reaching almost to
the edge of the segment. Testes numerous, divided more or less plainly into two symmetrical
groups. Eggs with three envelopes. ]Male ducts paired in every proglottid. Adults in
birds.

Type species Dioicocestus paronai Fuhrmann 1900.

Several species from grebe and ibis; parasite not recorded from North America.

112 (105) Proglottids carry lateral foHate or digitate processes. Female

genital pore, when present, separate from marginal male
pore. . . Family Aimabiliidae Fuhrmann 1907 . . 113

Rostellum with simple crown of hooks. Proglottids short with lateral margins prolonged
into processes. Musculature weakly developed. Cirrus sac large; cirrus spinous. Duct
united with receptaculum seminis, designated as accessory vagina, opens in cases on surface or
on margin opposite male pore.

In water birds.

113 (114) Male sexual organs double in each proglottid. Accessory vagina

with surface opening. Uterus a network.

Amahilia Diamare 1893.

Scolex very small with armed rostellum. Male reproductive organs double with one pore
on each side of proglottid. Cirrus armed with strong spines. Testes numerous, in median
field. Female organs median, single set in each proglottid. Uterus forming network con-
sisting of dorsoventral ring with dorsoventral anastomoses. Accessory vagina opening ven-
trally, communicating (?) with canal from excretory system opening on ventral surface of
proglottid in median line. Adults in birds.

Type and only species imabilia lafnelligera (Owen) i8$2.

114(113) Male organs single in each proglottid. Uterus sac-like. . . . 115

115 (116) Rostellum thick, powerful. Male pores alternate irregularly.
Female pore, when present, on surface of proglottid.

Schistotaenia Cohn 1900.

Rostellum very large, armed with heavy hooks. Between rostellum and suckers an annular
thickening covered closely with small three-cornered hooks. Testes numerous, dorsal, poste-
rior, across entire width of proglottid, reaching maturity later than female glands. Ovary
and vitellarium large. Male duct runs between excretory canals, accompanying vagina which
ends blindly near cuticula.

Tj^e species S. macrorhyncha in the horned grebe. Parasite not recorded from North
America.

PARASITIC FLATWORMS

449

ii6 (115) Rostellum long, slender. Male pores alternate regularly. Female
pore, when present, always marginal.

J atria Kowalewski 1904.

Rostellum with single crown of 10 to 14 large hooks and behind them
numerous rows of small conical hooks. Suckers and fKjsterior p<jrtion
of head covered with minute spines. Segments not numerous. Cirrus-
pouch large. Testes not numerous. Male and female canals pass be-
tween longitudinal excretory vessels. Distal end of vagina instead of
opening to exterior turns postenad into next following progh^ttid and
opens into seminal receptacle there. Seminal receptacles median; ac-
cessory vagina present opposite cirrus-pouch, sometimes with ojx-ning.
Adults in birds (Urinatores).

The type species (Tatria biremis Kowalewski iqo4) occurs in the
horned grebe and has not been reported for North America. In 1887
Leidy reported Taenia scolopendra Diesing from this host and that species
is placed here by some authors.

Fig. 759-

Tatria biremis. Forma major; proglottids with lateral appendages,
X 30. (After Kowalewski.)

117(55) External division of strobila into proglottids lacking 118

118 (119) Anterior portion of strobila folded and coiled to form large pseudo-
scolex; strobila grooved transversely, without true pro-
glottid limits. . . Family Fimbriariidae Wolfifhiigel 1898.

Scolex small, imstable, frequently lost, with rostellum armed with single row of hooks.
Pseudoscolex conspicuous. Strobila with transverse grooves which produce appearance of
segmentation. Three pairs of longitudinal excretory vessels. Reproductive
organs not segmentally arranged. Genital pores marginal, irregular, generally
unilateral. Testes numerous, arranged in transverse rows. Uterus not persist-
ent, breaking down into a large number of egg sacs. Egg spindle-shaped with
thin transparent shell. Adults in birds (Anserif ormes) .

Type genus Fimhriaria Frolich 1802.

(Syn. — Epision Linton 1S92.)

Two well-known species both occur in North American water birds; a third,
F. plicata (Linton) 1892 is recorded from the American scoter.

Fig. 760. Fimhriaria plicata. Lateral view of head and anterior part of body of
smallest specimen. X 8. (After Linton.)

119 (118) Scolex small, simple. Strobila round or nearly so. Without pro-
glottid boundary except at extreme posterior end.

Family Nematot.venudae Liihe 1910 . . uo

Scolex unarmed, without rostellum. At extreme ix)stcri(.r lilifomi end of strobila a few
separate proglottids visible externally; these are much longer than thick, sciviratc readily, and
move about independently a long time. Genital pores alternate irregularly. Cirrus and
vagina pass dorsal to excretory canals and nerve trunks, open into genital atrium marginal
in location. Male organ dorsal, female ventral.

In intestine of .\mphibia.

450

FRESH-WATER BIOLOGY

20(121) Two testes in each proglottid N emafo taenia Luhe iSgg.

Strobila thicker near anterior end becoming thinner
and eventually filiform, circular in cross-section. Neck
short, cirrus-pouch long, passing within longitudinal
muscle layer. Vas deferens long, with ventral loop
between ovary and excretory canals. Two testes,
dorsal and symmetrical. Vitellarium almost exactly
in center of body. Ovary ventral, nearly median;
uterus horseshoe-shaped, breaks up early into numer-
ous capsules with 2 to 4 eggs, usually 3, in each cap-
sule becoming ultimately 13 to 30 small dark uterine
capsules.

Records of its occurrence in'North America are open
to question. '

T>^e species.

N ematotaenia dispar (Goeze) 1782.

Fig. 761. Nematotaenia dispar. Transverse section of
ripe proglottid; c, cirrus; t, testes; m, retractor muscle of
cirrus; t'/, vitellaria; oi', ovary; vd,wa.s deferens; i', vagina.
Magnified. (After Fuhrmann.)

121 (120) One testis in each proglottid.

Cylindrotaenia Jewell 191 6.

Strobila thickest near center, becoming thinner
towards both ends. Neck long. Single testis
round, on aporal side of proglottid just dorsal to
transverse diameter. Cirrus-pouch short, ending
at longitudinal muscle layer. Vas deferens short,
nearly straight. Uterus breaks up into capsules
each containing 4 to 6 eggs, becoming enclosed
later in two conical organs, one dorsal and one
ventral, which are large transparent uterine cap-
sules.

Type species.

Cylindrotaenia americana Jewell 1916.
Perhaps Taenia pulchella Leidy 1851 belongs
here.

Fig. 762. Cylindrotaenia americana. Transverse
section of ripe proglottid; t, testes: vd, vas deferens; c,
cirrus; v, vagina; ov, ovary; vt, vitellaria. Magnified.
(After Jewell.)

122 (i) Larval forms; reproductive organs undeveloped 123

Usually small and unsegmented though some bladder-worms reach considerable size and
even show the beginning of proglottid formation. On the whole these larvae show little or no
organ differentiation and are distinguishable from adults by the absence of characteristic
structures. Most larvae are encysted but there are numerous free forms.

123 (124) Four long proboscides covered with hooks.

Very rare but easily recognized.

Trypanorhyncha (p. 434)-

124(123) No proboscides with hooks present 125

125 (126) Scolex and sucking organs hardly differentiated at all and the
latter when present never more than two.

Larvae of Pseudophyllidea.

(See also Sparganum, p. 434.)

The anterior end of these and other larvae is often rolled in so that its exact character is
difficult to determine.

PARASITIC FLATWORMS
126 (125) Four suckers on the scolex of the larva.

Cystlcercus

451

127

The head of the larva is inverted so that these suckers are in the center „f the mass and mav
easily be overlooked. In the narrower sense the term cystlcercus is applied to the lar^'e thin-
walled bladder-worm having a cavity of considerable size filled with watery fluid in which the
scolex grows from a polar papilla that subsequently hollows out giving in reverse the srolov Af ih..
adult This larva belongs to the terrestrial fauna and occurs only SJnl^lly in aquatc form
hke the muskrat which have become a part of the acjuatic fauna secondarily.

127 (128) Entire larva solid parenchyma tissue,
apex at bottom of infolding.

Scolex invaginuled with
Plcroccrcoid.

Caudal region not differentiated at all or only very poorly indi-
cated. In general structure the Bothriocephalid larvae with two
sucking grooves are like the true plerocercoids with 4 acetabula

Larvae prominently of Proteocephalidae, also of Cycloi)hyI!idea
from reptiles. One special form known as Gryporhynchus has been
identifaed as the larva of Dilepis or some allied genus.

Fig. 763. Proteocephahis plerocercoid; a, from the body cavity b from
cyst suckers drawn within body. Note iar-e end organ, shaded; c\ from
intestine; optical sections, X 10. (After La Rue.)

(127) Spaces in larva between folds of tissue,
surrounded by cyst

Scolex in natural position,,
Cxsticcrcoid.

Usually with caudal appendage in a posterior hollow of the cyst, and on the tail the embrv-
onic booklets of the onchosphere. In form and texture the cyst varies greatly. Calcareous
bodies abundant, mostly on the invaginated layer between the cyst and the scole.x which corre-
sponds to the neck when the larval head is evaginated.

Very frequent among Cyclophyllidea. Relationship between the cysticcrcoid and the adult
may be inferred from careful e.xamination of the scolex and its armature.

No records exist of the
presence in North .Ameri-
ca of these forms. I-'or
convenience in recogniz-
ing them a figure is in-
cluded of an abundant
European form likely to
occur here also in similar
aquatic hosts. W hile
these cysticercoids are
most fretjuently recridid
from t\)pepoda. Ostra-
coda, and other small
aquatic Crustacea, they
occur also in l.unibruu-
liis and other .'■mall an-
nelids, and more rarely in
small snails and slugs.

Fic. 764. Drttanidotantia
fiiu idtd. a, IkkIv of Cyili^t's
<m;»/«5. containlru- l.tx .1
i.i|><."worm (c\ ■
simc Iar\-a wi;
lon>: tail, isol •
crustaci-an;
with cxtrndf
nil'iol. (.\ft( :

452 FRESH-WATER BIOLOGY

REFERENCES ON NORTH AMERICAN PARASITIC WORMS

IMPORTANT GENERAL WORKS

CoBBOLD, T. S. 1864. Entozoa. 480 pp. 82 figs. London.
1879. Parasites. 508 pp. London.

DiESiNG, C. M. 1850, 185 1. Systema helminthum. Vienna. 2 vols.; 679
and 588 pp.

DujARDiN, F. 1845. Histoire naturelle des helminthes, ou vers intestinaux.
Paris. 654 pp. Atlas, 12 pi.

Leidy, J. 1904. Researches in Helminthology and Parasitology. Smith.
Inst., Misc. Coll., vol. 46, Art. Ill, 281 pp. (Reprint of Leidy's contribu-
tions from 1845 to 1 89 1. With a' bibliography.)

LiNSTOW, O. VON 1878. Compendium der Helminthologie. 382 pp.
1889. Nachtrag. 157 pp. Hannover.

Looss, A. 1901. Zur Sammel- und Conservirungstechnik von Helminthen.
Zool. Anz., 24: 302-304, 309-318.

Smith, A. J. 1908. Synopsis of Studies in Metazoan Parasitology. Univ.
Penn. Med. Bull., Feb., 68 pp. 10 pi.

Stiles, C. W., and Hassall, A. 1894. A PreUminary Catalog of the Para-
sites Contained in the Collections of the U. S. Bureau of Animal Industry,
U. S. Army Medical Museum, etc. Vet. Mag., i: 245-253, 331-354.
1902-1912. Index-Catalog of Medical and Veterinary Zoology. (Authors.)
Bur. An. Ind., Bull. No. 39; 36 parts, 2766 pp.

Wright, R. R. 1879. Contributions to American Helminthology, Proc,
Can. Inst., n.s. i: 54-75, 2 pi.

trematoda

Braun, M. 1879-93. Trematodes. Bronn's Klass. u. Ord. d. Tierreichs,

Vol. 4, 925 pp., 34 pi. Leipzig.
Cooper, A. R. 191 5. Trematodes from Marine and Fresh-Water Fishes.

Trans. Roy. Soc. Can., (3) 9: 181-205, 3 pi.
Cort, W. W. 191 5. Some North American Larval Trematodes. 111. Biol.

Monogr., i: 447-532; 8 pi.
Looss, A. 1894. Die Distomen unserer Fische und Frosche. Biblth. Zool.,

Heft. 16, 296 pp., 9 pi.
1899. Weitere Beitrage zur Kenntniss der Trematoden-Fauna Aegyptens,

zugleich Versuch einer natiirlichen GHederung des Genus Distomum Ret-

zius. Zool. Jahrb., Syst., 12: 521-784, 9 pi.
Luhe, M. 1909. Parasitische Plattwiirmer. I: Trematodes. Susswasser-

fauna Deutschlands, Heft 17, 217 pp., 188 figs.
Odhner, T. 1 9 10. Nordostafrikanische Trematoden. I. Fasciolidea. Swed-
ish Zool. Exp., 23 A; 170 pp., 6 pi.

PARASITIC FLATWORMS 4^3

1911-1913. Zum naturlichen System der digcncn Trcmatodcn I-VI.
Zool. Anz., vols. 37-42.
Pratt, H. S. 1900. Synopses of North American Invertebrates, XII. The
Trematodes. Part i. Heterocotylea. Am. Nat., 34: 645-662; 50 ligs.
1902. Part 2. Aspidocotylea and Malacocotylea. Am. Nat., 36: 887-910,
953-979; 8 pi.
Stiles, C. W. and Hassall, A. 1908. Index-Catalog of Medical and \'eter-
inary Zoology. Subjects: Trematoda and Trematode Diseases. Hyg.
Lab., Bull. No. 37, 401 pp.

CESTODA

Braun, M. 1894-1900. Cestodes. Bronn's Klass. u. Ord. d. Tierreichs,

Vol. 4, p. 927-1732, 25 pi. Leipzig.
La Rue, Geo. R. 1914. A Revision of the Cestode Family Proteocephalidac.

111. Biol. Monogr., i: 1-350, 16 pi.
LtJHE, M. Parasitische Plattwurmer. II. Cestodes. Susswasserfauna

Deutschlands, Heft 18, 153 pp., 147 figs.
Ransom, B. H. 1909. The Taenioid Cestodes of North American Birds.

U. S. Nat. Mus., Bull. 69, 141 pp.
Stiles, C. W. and Hassall, A. 191 2. Index-Catalog of Medical and \'cteri-

nary Zoology. Subjects: Cestoda and Cestodaria. Hyg. Lab., Bull.

No. 85, 467 pp.

CHAPTER XIV
THE NEMERTEANS

By WESLEY R. COE

Sheffield Scientific School of Yale University

Among the fresh-water animals of the northern half of the
United States occurs a slender Httle worm of a beautiful reddish
color belonging to the group of Nemerteans. These worms can be
easily distinguished from the other flatworms (Platyhehninthes)
by the slenderness of the body, and from the other groups of worms
by their perfectly smooth, ciliated bodies and their leisurely creep-
ing movements. The presence of the proboscis armed with a
formidable calcareous stylet which can be thrust out of the opening
at the anterior end of the body is proof that the worm is a ne-
mertean.

These nemerteans live along the shores of lakes and streams,
as well as in pools and artificial basins of water and aquaria. Quiet,
shallow areas of water with a dense growth of water plants are
particularly favorable. The worms may be found creeping over
the stems and leaves of the water plants, among the dead
leaves and debris at the bottom, on stones and objects in the
water, and oftentimes beneath the stones along the shore. The
under sides of floating leaves, as Hly pads, particularly those par-
tially decayed, often harbor numbers of these tiny worms. They
are, however, local in distribution and are seldom found in abun-
dance over a very wide area. When common in a shallow inlet a
few yards wide, a further search for a mile along the shore of a
lake or stream may fail to reveal a single specimen.

The worms are usually from lo to i8 mm. in length when fully
extended, but may contract to a small fraction of their former
length. They rarely exceed i mm. in diameter. The color varies
considerably, shades of red, orange, or vermiUon being most com-
mon, while the smaller specimens are often pale yellowish or flesh
colored. The anterior half of the body is more brightly colored

454

THE NEMERTEANS

455

CP

cc

— LI\J

than the posterior portion, where the in-
testinal lobes and reproductive glands
modify the brilliancy of the coloring.
Some individuals have a cast of reddish
brown.

On the anterior end of the bod>' arc
usually six black pigment spots, or ocelli,
arranged symmetrically in three pairs {o,
Fig- 765). Smaller specimens may have
but four ocelli, and occasional irregularities
occur in which the number may be live,
seven, or eight.

It is to the internal organization of the
body, however, that one must look for
those characters which are mainly used
in the classification of the nemerteans.
These structures must be studied in most
species by means of serial sections, but,
fortunately, the fresh-water forms arc so
nearly transparent that the principal or-
gan systems of the body may be studied
in the Hving animal. It is only necessary
to place the worm on a slide with a small
drop of water and flatten the body be-
neath a cover glass. When such a speci-
men is examined under the low powers
of a microscope the principal anatomical
features are easily made out.

Particularly characteristic is the probos-
cis, a strong muscular organ (/>. Fig. 7O5)
contained in the rh>-nchococl and en-
closed by the proboscis sheath. This
organ extends from the anterior extrem-
ity nearly to the posterior end of the bod)-.

Fig. 765. Sticlwstcmma ruhrum (Ix-idyl. Diapram of Ii\ i;:.- in !i-
vidual flattened beneath a cover plass. showinR inli r
i4,anus; C, pyloric cecum; Ct\ cephalic furnnv;
ganglia: Cponad; /.intestine; LiV. lateral nerve; (>.•>
boscis; i?, rhynchodaeum; /?C,rhynchocoel; /^A/, retractor muscle of proboscis; 5, centr.il styUt .m ! •iv-;

- RM

— A

456 FRESH-WATER BIOLOGY

Back toward its posterior third, the proboscis is armed with a
needle-like calcareous stylet (s) resting upon a solid conical basis.
Beside the central stylet there are two lateral pouches each con-
taining 2, 3, or 4 accessory stylets of size and shape similar to the
central stylet. The proboscis is considerably longer than the sheath
in which it hes coiled and to which it is attached at both ends.
By means of its powerful musculature it can be thrust out of the
anterior end of the body. This process of eversion turns the ante-
rior part of the proboscis inside out and brings the central stylet
to the end of the everted organ, where it constitutes a formid-
able weapon of defense or offense. After eversion the retractor
muscle at its posterior end withdraws the proboscis to its original
position.

The mouth and proboscis open together through the rhyncho-
daeum (;-) at the anterior end of the body. The esophagus leads
into a broad stomach, and this into the intestine with its numer-
ous lateral lobes. At the anterior end of the intestine a pair
of pyloric ceca (c) extend forward to the brain. The short rec-
tum leads to the opening at the posterior end of the body. The
nemerteans feed upon other worms and soft-bodied animals of
various kinds.

The central nervous system consists of the four cerebral gangHa
and a pair of large longitudinal lateral nerves (In). These are
easily seen in the Hving worm.

The excretory system extends the entire length of the body as a
series of dehcate tubes with several efferent ducts leading to each
side of the body. The three longitudinal trunks of the blood
vascular system are often distinctly seen in the Hving animal.

The fresh- water nemerteans are hermaphroditic, and usually
protandric. The gonads are arranged serially along each side of
the body between the intestinal lobes. Each gonad bears both
male and female genital products, which are discharged when
mature through a small pore opening on the side of the body.
The male sexual elements are formed first, and in the smaller and
evidently younger worms the gonads are filled with developing
spermatozoa. Later, and after the discharge of a portion of the
spermatozoa, the eggs begin their development.

THE NEMERTEANS

457

As a rule a single egg is formed in each gonad, although some-
times there are two. Even when the eggs are fully formed there
remains in each gonad a portion of the spermatozoa i)revi(jusly
formed. This fact has led certain investigators to conclude that
self-fertilization may sometimes occur. The eggs are fertilized after
deposition, however, and the gregarious habits of the worms pre-
sumably insure the presence of spermatozoa from other individuals
which may effect cross fertilization in whole or part.

The eggs are deposited in a double string embedded in a jelly
which attaches them to the water plants or other objects on which
the worms are found. They are beautiful objects by which to
illustrate the processes of fertilization, maturation, cleavage and
the development of the embryo.

The worms may be kept ahve for a long time in aquaria contain-
ing water plants, and under suitable conditions will continue to
live and breed year after year. They thrive under the conditions
found in botanical gardens, where large basins of water are used
in the cultivation of exotic water plants.

Although the nemerteans are represented by numerous genera
and species in the oceans in all parts of the world, only a few forms
occur in fresh water and a few others in moist places on the land.

In North America only a single genus is known from fresh water,
and of this genus the described species are so closely similar as tc
lead to some doubt as to whether more than a single .species is
actually represented.

In 1850 Leidy published a brief and imperfect descrii)tion of a
nemertean found in the vicinity of Philadeli^hia, which sj)ecies he
described as Emea rubra. Silliman later found the same or a
very similar species in New York State, to which he gave the name
Tetrastemma aquarium dulcium, and included Leidy's species therein.
Montgomery, in 1896, described under the name Stichostcmma
asensoriatum, a similar species from Pennsylvania, while aj-Jixir-
ently similar forms have been recorded from Connecticut, Illinois,
Nebraska, and Washington. The worms are thus known to occur
from the Atlantic to the Pacific coasts and have probably i)een
observed at numerous unrecorded localities in the intervening
territory.

458 FRESH-WATER BIOLOGY

But whether the nemerteans from these widely separated local-
ities represent a single or several distinct species is not yet defi-
nitely known. Since fresh-water nemerteans similar to ours are
found in England, Germany, and other parts of Europe, and in
Asia and Africa, a careful study of specimens from many Ameri-
can localities is necessary to settle the question of nomenclature.
For it is not improbable that some of the locaHties mentioned
have been stocked with forms transported from other parts of the
country, or from other quarters of the >^orld. The importation
of cultivated water plants furnishes ideal conditions for the intro-
duction of the nemerteans associated with them.

A recent study indicates that the species found in Connecticut
is identical with that recorded by Montgomery from Pennsylvania.
This species differs in certain anatomical details from any of the
described exotic forms, but is evidently synonymous with Leidy's
Emea rubra. Since there is nothing in the pubHshed descriptions of
specimens from other North American localities to indicate a spe-
cific distinction it is at present possible to recognize but a single
species, to which the name Stichostemma rubrum (Leidy) should be
applied.

IMPORTANT REFERENCES ON FRESH-WATER NEMERTEANS

BoHMiG, L. 1898. Beitrage zur Anatomic und Histologic der Nemertinen.
[Stichostemma graecense (Bohmig), Geonemertes chalicophora (Graff).] Zcit.
f. wiss. Zool., 64: 479-564.

Detailed account of the structure of a fresh-water form.

BtJRGER, O. 1895. Die Nemertinen dcs Golfcs von Ncapel und der an-

grenzenden Mecres-abschnitte. Fauna u. Flora v. Ncapel, Monogr. 22.

Important monograph on the European nemerteans.

Child, C. M. 1901. The Habits and Natural History of Stichostemma.

Am. Nat., 35: 975-1006.
Hartmeyer, R. 1909. Nemertini. Die Siisswasserfauna Deutschlands, Heft,

19: 47-48.
Montgomery, T. H., Jr. 1895. Stichostemma eilhardi nov. gen. nov. spec.
Ein Beitrag zur Kenntnis der Nemertinen. Zeit. f. wiss. Zool., 59: 83-146.
Anatomical study of a fresh- water nemerteau.
1896. Stichostemma asensoriatum n. sp., a Fresh -water Ncmertean from
Pennsylvania. Zool. Anz., 19: 436-438.

Description of a fresh-water nemertean from Pennsylvania.

CHAPTER XV
FREE-LIVING NEMATODES

By N. a. COBB

U. S. Department of A zricullure

Practically any collection of sand, mud, debris or aquatic vege-
tation, from standing or running water, in any part of the coun-
try, will yield, on examination with a hand lens, minute slender
organisms which whip themselves about by means of more or
less rapid contortions of the whole body. This t}pe (jf
movement identifies them as nematodes; it dilYers from that
of other small organisms in that, though often vigorous and con-
spicuous, it is in one plane only, the dorso- ventral plane of the
body, and in that the length and proportions of the body mean-
while remain unchanged. In pure water, moreover, this thrash-
ing about seems to produce no locomotion; the animal remains
in the same spot unless among vegetation, debris or particles
of soil. When quieted by stupefying or killing, these fresh-
water nematodes ("threadworms" or "roundworms") are seen
to be more or less cyUndroid unsegmented, without locomotor
appendages, varying in length up to a centimeter or more.
They belong to a group in the animal kingdom comparable in
number and importance with the insects; nematodes of other
sorts live free in the soil, and in the sea, r.nd infest as parasites
an immense variety of plants and other animals. They arc in-
conceivably abundant. A tablespoonful of ooze from the bottom
of the ocean may contain thousands of specimens. The number
of nematodes in the top six inches of an acre of ordinary arable soil
is shown by statistical calculations lo reach thousands of nu'llions.
The number of eggs vastly exceeds even that of adults; for they
are usually very prolific, a single female somelinies producing
hundreds of thousands of eggs.

Even the free-living soil and water nematodes have become
adapted to an astounding variety of habitats; they occur in arid
deserts, at the bottom of lakes and rivers, in the waters oi hot

459

460 FRESH-WATER BIOLOGY

springs and in polar seas. They were thawed out alive from
Antarctic ice by members of the Shackleton expedition. An exam-
ination of beet seeds imported into the United States disclosed
the presence on them of several species of nematodes. The tap
water of even well-conducted cities often contains nematodes.
Their microscopic eggs and larvae, even more readily than the
adults, are transported from place to place by an exceedingly great
variety of agencies. They are carried by the wind, by flying
birds and running animals, they float in ah the waters of the earth,
and are shipped from point to point throughout the civilized world
in vehicles of traflic. Sometimes the eggs and larvae are so re-
sistant to dryness that if converted into dust they revive again
when given moisture, even after as long a period as a quarter of
a century. There are beneficial nematodes, though knowledge of
this phase of the subject is in its infancy. Some nematodes feed
exclusively on their injurious brethren. Others devour baneful
micro-organisms. Their adaptations in these respects appear to be
similar to those of insects.

The smaU fraction of the fresh-water nematodes of North America
at present known, comprises only about thirty genera, but these
present such a variety of form that a thorough knowledge of them
insures a fair understanding of all the free-living nematodes.*

The number of nematode species is enormously greater than
commonly supposed. Since most species of vertebrates are in-
fested by one or more nematodes, and with comparatively few ex-
ceptions a given parasitic nematode infests but one host, it may be
estimated that more than 80,000 nematode species infest the forty
odd thousand species of vertebrates. Insects, also much infested,
will add many thousands of species. The molluscs, crustaceans,
and various groups of worms are also infested, and investigation
continues from this source also to augment the number of known
species of parasitic nematodes.

Numerous as the parasitic species are, it is certain that
the species of nematodes living free in soil and in water far

* In an attempt to distinguish the parasitic nematodes from the aquatic and soil-
inhabiting nematodes, the latter are usually assigned to the group of free-living nema-
todes, — an arbitrary classification not based on natural relationships.

FREE-LIVING NEMATODES

461

outnumber them; and the number of free-Uving individuals is
so great that they probably constitute one of the important
mechanical as well as biological factors in soil, and in the bot-

Lip ,

Lateral field
Pharyngeal bulb

Pharynx ,

Salirary gland
Muscular layer

Cuticula

Hair

Esophagus

Cuticula

Nerve-ring

Duct of ventral gland

Esophagus.

Nerve ring

Ridge in cuticula

Esophagus

Stria of cuticula

Sub- cuticula

Wing of cuticula

Cuticula

Cardiac bulb ...
Dorsal field

Valvular apparatus
Its radial muscles
Muscular layer
Wall of intestine
Wing of cuticula
Ovum fit to fertilize

29. Blind end ovary

30. Intestine

31. Yolk of egg

32. Nucleus of egg

33. Shellofegg...

34. Internal lateral field ,.

35. External lateral field

36. Intestine

37. Copulatory muscle

38. Wing of cuticula.

39. Copulatory muscle

40. Intestinal cell

41. Accessory male organ

42. Ejaculatory duct

43. Copulatory muscle

44. Wmg of cuticula

45. Constriction in spiculum

46. Right-hand spiculum

47. Distal end spiculum

48. Accessory piece

49. Caudal gland . . . .
60 Left wing of bursa

61. 1st caudal gland

62. 2nd caudal gland

63. 3rd caudal gland

64. Muscular wall

56. Right wing of bursa

. Cephalic seta
. Labial papilla
, Pharyngeal rib
. Pharynx or throat
. Pharyngeal tooth
. Pharyngeal bulb
. Salivary gland
. Lateral organ
, Esophagus tube

Eye, with lens
, Excretory pore
. Ampulla
. Median bulb
. Nerve-rmg

Ganglion cells
, Duct of ventral gland
. Duct of lateral gland

A lateral gland

Cardiac bulb

Valvular apparatus
, Wing or ridge in skin

Cardiac coUum

Cardia

Stomach or intestine

Tessellation of same

Cuticula

Wall of intestine

Ventral gland

Striation in cuticula

Ripe ovum

Uterus

Unripe ovum in ovary

Spermatoioa

Fertilised egg in uterus

Blind end of ovary

Yolk of egg

Vaginal glund

Vulva

Vagina

Vaginal gland

Lateral field

Seminal vesicle

Wall of same

Spermatozoa

Copulatory muscle

Accessory male organ

Ductus ejaculatoriuB

Three pre-anal papillao

Copulatory muscle

Proximal end spiculum

Pylorus

Anterior ribs of bursa

Anal gland

Anus

Post anal papillae

Caudal gland

Median ribs of bursa

ursa
Posterior ritis of bursa
Duct ofraudul glandt
Terminus

Diagram of Nematode structure.

Fig. 766.
Above, anterior end of female. Below posterior end of male.
(After Cobb.)

toms of lakes and oceans. The aquatic nematode species exist
in enormous numbers, in both fresh and salt water, while tlic
number of individuals is past computation. The unavoidable con-

462 FRESH-WATER BIOLOGY

elusion is that there must be hundreds of thousands of species of
nematodes.

Nearly all the tissues of the fresh-water nematodes are compara-
tively colorless and transparent, and whatever decided color the
body possesses is usually confined to the intestinal region. The
cells of the intestine itself are sometimes colored by the presence
in them of granules of a faint yellowish or brownish tint, and
the middle portions of the body are thus rendered yellowish or
brownish. The color of the ingested food, showing through the
tissues of the body, is also sometimes a color factor. The food
varies in color from nearly black to colorless, and the body is
correspondingly tinted. Species feeding on the juices of plants
are usually nearly colorless, e.g., species of Tylenchns and Aphe-
lenchus. A few species possess colored eye-spots near the head.
In some species the esophagus contains yellowish or brownish
pigment.

Most genera, and even some species, of fresh-water nematodes
have a world-wide distribution. The small size and the vitaHty
of the individuals favor their transportation in a great variety of
ways, one of the most efficient vehicles being the feet of flying
water-fowl. Possibly some of the aquatic species are as resistant
to dryness as are rotifers, and, as "dust," are blown about in the
same manner. Certain species of plant-infesting nematodes will
revive after many years of desiccation.

Another cause of this wide distribution is the fact that fresh-
water nematodes adapt themselves to a great variety of depths and
temperatures. They are found as near the poles as are any other
organisms. They occur in practically every body of water where
extreme conditions do not preclude Hfe of any kind. Few organ-
isms are so easy to find.

The outer covering of a nematode is composed of a non-cellular
layer usually divided into two parts, the cuticula and the subcutic-
ula. These groups are not easily defined, but the natural division
line is probably between the outer layers that are to be shed at the
next moult, and all the other layers. Thus the subcuticula in turn
becomes the cuticula. The cuticula is composed of about three
layers and the subcuticula of about an equal number. Though

FREE-LIVING NEMATODES

463

some of the markings usually to be seen in the cuticula are due to
sense organs or to pores, most of them are inherent structural
markings. These markings are used as specific, and in some cases
as generic, characters.

The cuticula of almost any species, if examined with sufficient care
will show transverse striations, ranging in the various species from
a few score to upwards of a thousand. m

Many species described by earher writers
as destitute of these striations really
possess them. When very fine the
transverse striae are best seen at the
extremities of the organism. In some
genera the striae are apparently due to
the constant bending of the body in the
dorso- ventral plane. This pecuhar mo- ^ "^

. . I'iG. 767. Diagrammatic cross-section

tion, which IS universal amongr nema- ti^^ugh the middle of a nematode.

° "". ovary; tnt, mtestme; m. median

todes, and continuous from birth to fidd^; i:t'cutVS^=-S;^^^^
death, unceasingly stretches and then !u!d"tbmSbn''its":?ri^
compresses the dorsal and ventral sur- '^S^:^''^^^<:'\:S:^:'li

r A ^ ^T- J.* 1 J^ • course, in no sense organs, but only

laces. At tne time when the one is convenient descriptive terms. The

, , , , , , . , ,_^^ , line shading between the fields repre-

stretched the other is compressed. This ^^°ts muscle ceiis. (After cobb.)
results in characteristic appearances, such as the more pronounced
striation of the dorsal and ventral surfaces, the interruption and
variation of the striations near the lateral lines, and the presence on
the lateral fields of various longitudinal striations. In some genera
the striations are compound, that is, each transverse striation is
resolvable into a row of dot-like markings, either round or elongated.
These secondary markings may be again resolvable, the result being
a very complex series of exceedingly minute markings. The trans-
verse striations are usually more or less plainly interrupted near the
lateral fines. Obhque striae, such as are to be found in the large
parasitic nematodes, sometimes occur in the fresh- water species,
in some Mermithidae, for instance.

The longitudinal striations are of two kinds: (i) True stria-
tions of the cuticula due to certain stiffening structures or ^' wings,"
and (2) internal markings due to the attachment of the cells of the
muscular layer and of the lateral fields. The longitudinal stria-

464 FRESH-WATER BIOLOGY

tions, when they are really cuticular structures, are likely to appear
in some multiple of four. Since they occur on each side of the two
lateral lines, and, naturally, in a symmetrical way, the smallest
number possible is four. Two on each side of each lateral line
would make eight in all, a state of things exemplified in Iota. In
Diplogaster the number is about sixteen to thirty-two, and ap-
parently these numbers also prevail in some Dorylaimi.

The various elements of the cuticula originate in certain cells in
the longitudinal fields, which early in the development of the em-
bryo become separated from the ectoblastomere group of cells. One
of the first two somablastomeres, the primary ectoblastomere, divides
and spreads systematically over the endoblastomeres. By further
divisions the primary ectoderm thus formed gives rise among other
things to the cuticula. The nuclei of the ectoblast cells destined
to form the cuticula of the embryo arrange themselves in longitudi-
nal Hnes. Increasing, and functioning from these Hnes they become
specially active at each moult in producing a new layer of cuticula.
At moulting time the activity of the cuticula-forming cells in the
lateral fields is indicated by an increase in the size of the nuclei
and the growth from them of excessively fine elements forming the
cuticula. The lateral fields appear to be the leading members of
this group of cuticula builders. This is in harmony with the greater
abundance and variety of the lateral cuticular structures.

In the course of its development a nematode sheds its skin
about four times, — and often appears to be about as active
during the moulting period as at other times. In some species
the changes that take place at the time of moulting are of a
striking character, reminiscent of the metamorphoses in other
groups, though no true metamorphosis takes place. Thus we have ;
in the last moult of the males in some species of Iota a marked alter-
ation, viz., the loss of the oral spear. This so alters the appear-
ance of the male that one unfamiliar with the facts would not >
class the adult males in the same genus as the females.

During the moulting period the cuticula is thicker and looser, — j
sometimes very loose. The lining of the mouth and esophagus, j
as weU as that of the rectum, is shed at the same time as the outer [^
cuticula. At this time, therefore, the mouth parts take on unusual

FREE-LIVING NEMATODES 465

appearances. If the pharynx is armed with teeth these are often
seen in dupHcate. In a moulting Dorylaimus, for instance, one may
see the old spear or tooth and behind it a second smaller one, and
in some cases even a third. The nature, or the presence, of stria-
tions may become more evident, or less evident, at the moulting
period than at other times. Remnants of old skin attached to
newly moulted individuals have sometimes given rise to erroneous
deductions and to errors in taxonomy.

The nervous system centers in the so-called nerve-ring, which in
free-living species encircles the esophagus near the middle of the
neck. This ring is composed of interwoven nerve-fibers which,
taken together with the groups of nerve cells immediately in front
of and behind them, form what is undoubtedly a rudimentary
brain. (See Rhahdolaimus)

Eyes, or rather eye-spots, are known in one or more species of the
following fresh-water genera: Dorylaimus, Diplogaster, Spilophora,
Cyatholaimus, Chromadora, and Monhystera. The visual organs
in their most complete form consist of well-defined subspherical
cuticular lenses placed in front of collections of reddish, violet, or
blackish pigment-granules. Usually two such organs are placed
symmetrically, one on either side of the esophagus, between it and
the body wall, and in a dorsally sublateral position. Nerves pass
backward from the eyes to the nerve-ring. It is doubtful whether
the lenses form images that are perceived, though no doubt the
more perfect of the lenses found in nematodes are capable of form-
ing excellent images. Probably the lenses serve merely to collect
and condense light. Usually the eye-spots are mere collections of
pigment without lenses. Eye-spots, or what appear to be such, may
occur embedded in the esophagus. It is probable that the great
majority of species, even when without specialized visual organs,
perceive light by its direct action on the nervous system. A
few experiments will convince anyone that many eyeless species
distinguish the direction from which the light comes. There is no
satisfactory evidence that nematodes hear.

At various points on the surface of the cuticula there are found
innervated papillae and setae, which appear in most cases to be tactile
organs. Sometimes, however, they are associated with glands, as,

466 FRESH-WATER BIOLOGY

for instance, in the case of the supplementary organs of the males.
These papillae, hairs, and setae all belong to the same general class of
structures, but various terms are applied to them in accordance with
their size and location. The special hairs found on and near the
lips are known as cephaHc setae, in contradistinction to the large
hairs or setae sometimes found at the posterior extremity, the

caudal and terminal setae. The
setae are no doubt mainly tac-
tile in function, though it seems
certain that some of the ce-
phaHc setae and papillae serve
2 also as organs of taste and

_ Fig. 768. Head of a nematode (diagrammatic), i , side smcll.
view; 2, front view, showing triangular mouth opening

in the middle. The ventral side to the right in i shows Xhc similar OrSTanS fOUnd On

the ampulla and excretory duct. As the right side 01 the o

head is towards the spectator the lateral organ appears ^^iC general SUrfaCC of thc bodv

as a left-handed spiral. The arrangement of the cephalic ^^ ^ ^v.xxv.it*.i ow.j.iu,«^v. v^i i,j.xv. kj\j\j.j

setae is characteristic, the lateral ones being single, while rjillpH liPirQ r%r cOmatir

the submedian are in pairs whose members are of un- **J-C i-dllCU llclllb Ui SUlllctLlU

equal size. (After Cobb.) ^^^^^^ ThcSC probabty foUoW a

definite law in their distribution, but are so small that the exact
distribution is difficult to make out and has been studied in but
few cases. While it is not estabhshed that their distribution
accords with a segmentation theory, this matter is worthy of care-
ful study. Sometimes the hairs occur in harmonic repetition on
successive groups of annules. The papillae of the cuticula are setae
that do not project beyond the surface, or not far enough to entitle
them to be called setae. They should not be confounded with
pores, or with mere projections of the surface of the cuticula.
Neither of these latter are innervated. Tactile structures sup-
plementary to the sexual organs are found on the tail end of the
male both in front of and behind the anus, generally toward the
ventral side. They are much more rare in the female, being
located, when present, near the vulva.

What are known as the amphids or lateral organs are of such
widespread occurrence among free-Hving nematodes as to make it
seem certain that their function is of fundamental importance, but
what the function is remains a mystery. The amphids are two
lateral, symmetrically-placed external cephaUc organs. The ex-
terior part has the form of a circle, spiral, helix, or elongated figure,

FREE-LTVING NEMATODES

467

the helix or spiral being the fundamental form of the main cuticular
outer lateral markings that serve so good a purpose in characterizing
species. These external markings are undoubtedly in some species
connected with internal series of lateral organs arranged in two rows,
one along each lateral field, extending throughout the length of the
body. One more or less plausible theory concerning the amphids is
that which proposes to regard them as breathing organs. It is only
very exceptionally that they are known to have special direct con-
nection with the central nervous system. Such connection would
be expected, if, as some suggest, they are organs of sensation.
Their apparent homologues found in some parasitic nematodes
seem rudimentary. Possibly they are organs of equiUbration.

In describing the digestive system it is necessary to consider the
mouth parts, the saHvary or mouth glands, the esophagus, the in-
testine, and the rectum. Roughly speaking, the mouth parts may
be divided into two main groups: those adapted to biting and those
adapted to sucking. The various forms of the pharyngeal cavity
in the biting group are shown in the adjacent illustrations, together

None Conoid Concave- Cyathiform Cyathiform,

conoid then Cylindroid

Fig. 769. Forms of the pharynx. (After Cobb.)

Cylindroid

Compound

with their corresponding nomenclature (Fig. 769) . The formation of
the pharynx in the sucking groups is more uniform. The soft- lipped
species are intermediate in form and are adapted to seizing and
swallowing various microscopic organisms, both plant and animal.
The mouth cavity or pharynx is usually more or less strongly
lined with cuticula, and often furnished with cuticukir parts serving
various purposes according to the food habits of the species. Where
the lips are muscular and mobile, not infrequently they are sup-
plied with rather complicated gripping organs arranged like the
jaws of a lathe chuck. This arrangement of the mouth parts is
well illustrated in Enoplus; the reverse motion for ripping tissues
open is shown in Ironus (Fig. 781). Mononchus (Fig. 782) shows
the development of six muscular lips with opposing pharyngeal

468 FRESH-WATER BIOLOGY

teeth used in seizing prey. There are a number of genera in which the
pharynx is armed with from one to three prominent teeth of prob-
lematical function. In some of these cases the teeth are the outlets
of an equal number of glands located in the wall of the esophagus.
The secretions of these glands are probably saUvary in nature, or
possibly in some cases venomous, or even, as has been suggested,
excretory. These suppositions rest on structural and food-habit
considerations, rather than on an examination of the nature of
the secretions. The saliva theory is strongly supported by the
nature of these glands, whether their form, number, position, or
structure is considered, but they sometimes empty through fang-
like projections in carnivorous species that one would think could
profit by the use of venom in much the same way that serpents do.

The nematode esophagus is an organ of which every cross-section
is usually substantially circular, though the diameter may vary
much in the various parts. The central canal is usually trique-
trous in cross-section (Fig. 766). The lining is uniformly cuticular
and varies considerably in thickness in the various species. In the
simple cylindrical form of esophagus, radial muscles, the contraction
of which accomphshes the act of swallowing, everywhere pass from
the lining of the organ to the exterior cyHndroid wall. The action of
these muscles is peristaltic, first creating the necessary suction, and,
after the food is sucked in, rapidly forcing it along toward the intes-
tine. The act of swallowing is often lightning-like in its rapidity.

In addition to this general radial musculature the esophagus some-
times presents spherical or ellipsoidal muscular swellings, or bulbs,
often suppHed with a central cuticular valve, for exerting more pow-
erful suction than could be produced by the narrower tubular part.
The presence of bulbs denotes certain methods of feeding, — either
the lips need to be fastened securely to the source of food in order
to facilitate the stabbing action of the oral spear, or it is necessary
to exert unusual suction in order to ingest the food. There may be
one, two, or three of these bulbs, or none. The corresponding forms
of the esophagus are shown in the accompanying illustration
(Fig. 770), to which the appropriate names are appended. In rare
cases the esophagus is not clearly marked off from the intestine,
but there nearly always exists between these two parts of the ali-

FREE-LIVING NEMATODES

469

mentary canal a distinct constriction, known as the cardiac con-
striction. In the immediate vicinity of this constriction small
organs are sometimes found, apparently of a ^dimdular naturr,
though their functions are still veiled in obscurity. Here also (Kcur
definite nerve cells which are probably to be regarded as the center
of an involuntary nervous system.

Cylindroid Conoid

()

&

Fusiform Clavate Dorylaimoid Oxyuroid Rhabditoid lylcnthui.! Apbclcndnid
Fig. 770. Forms of the esophagus. (After Cobb.)

The intestine is a tubular canal extending from the csophap^J^ to
near the anus. Usually rather uniform in diameter, it is occasion-
ally somewhat expanded just behind the esophagus to form a
rudimentary stomach, if one may judge from the histoloi^y (^f this
part of the organ. The cells at this part of the intestine are often
markedly different in structure and chemical reaction from thosc^
farther back. In almost any species a sufficiently careful examina-
tion will show that some of the anterior cells of the intestinal tul)c
differ from those farther back, and hence it appears certain that the
anterior part of the intestine serves a digestive function, while the
remaining part serves as an intestine proper. There are also well
differentiated cells in the wall of the posterior part of the intestine,
indicating here also a subdivision of functions.

The intestine ends in a short tubular conoid region leading to
the anus, and known as the rectum. This part is more or less
muscular and serves to extrude the feces. In Dor vidimus and its
congeners, just preceding the rectum there is a short \ery distinct
part of the alimentary canal known as the prc-rectum. In spite oi
the definiteness of its structure its function is unknown. Kmpt\in-
near the anus there are usually to be found a number of small unicel-
lular glands, called anal glands, perhaps ser\'ing as accessories in defc-

470 FRESH-WATER BIOLOGY

cation. The anal muscles are muscular strands passing from tne
transverse slit-like anus to the body walls near the lateral fields.

There is no vascular circulatory system. These organisms are so
small that the colorless "blood" is aerated without the need of special
vessels. The movements of the body serve to propel the body-fluid
irregularly about through the body cavity and among the organs.

The main locomotive movements of nematodes are due to the
alternate action of two antagonistic sets of muscle, dorsal and
ventral, extending nearly the full length of the body, and acting on
the lateral thickening of the cuticula as a fulcrum. The move-
ments are serpentine, but in a dorso- ventral plane. As the result-
ing body-curves are usually wider than the space between the
cover glass and the microscope shde, it follows that the micro-
scopical view of these nematodes is usually a lateral view.

Locomotion is accompHshed by the aid of friction on surrounding
solid objects, such as the stems or roots of plants, grains of sand
or other particles. Comparatively few of the aquatic species can
swim, and even these seem uneasy and frightened when they find
themselves floating free in the water. ]\Iost of the aquatic species
are supplied with three unicellular caudal glands and a terminal
spinneret, whose main, and probably sole, function is to cement
the tail temporarily to various objects. From this attachment
as a base the nematode moves its head in various directions in
search of food, or of its mates. Some species, for instance some
species of Chromadora, attach themselves alternately first by the
head by suction, and then by the spinneret, executing movements
like those of the common caterpillars known as ''inch- worms."

The excretory organ of the f ree-hving nematodes consists of a uni-
cellular* gland, the renette, lying in the body cavity, not far from the
junction of the intestine and esophagus. It empties through a duct
leading forward to a ventral excretory pore, usually located some-
where between the Hp region and the intestine. There are a number
of genera in which the renette has not yet been seen. Its homologue
in the large parasitic species is renal in nature, — at least in one case.

Through the study of the free-Hving species the supposed excre-
tory function of the lateral fields, long beheved in, has been dis-

* Rarely two to many-celled and double .

FREE-LIVING NEMATODES ^y j

een

proved. The apparent connection in the parasitic species Ijctw
the excretory organ and the lateral fields is incidental, the action
of the body muscles tending to locate such long slender tubular
organs in the region of least motion, namely the lateral region.
In these parasitic species the organ is often bifurcated a little be-
hind the excretory pore (apparently on account of the increased
size of the whole organism), and thence backward the tubular
elements are attached to or lie in or near the lateral fields. This
suggests that the mystery surrounding the excretory organ in
some of the free-living species may perhaps be solved by search
directed toward the discovery of a bilaterally symmetrical renette.
Dorylaimus, a genus containing some of the largest free-living
nematodes, is a case in point. The renette cell often has smaller
companion cells in its immediate rear.

The caudal glands, so common in the tail end of the free-living
nematodes, serve to cement the tail end to any convenient object.
In thus attaching themselves nematodes sometimes show great skill
and pertinacity. The terminus of the tail bears a minute spinneret
through which the secretion of the glands is forced out, and by means
of which its flow may be regulated, much as in the case of spiders.
The secretion is a cementing substance insoluble in water. The
caudal glands are normally three in number and are usually located
single file in the anterior part of the tail, or somewhat farther forward
in front of the anus. Two of the ducts often unite to form one duct ;
sometimes all three unite. Just in front of the pore in the spin-
neret the ducts may enlarge to form one or more ampullae. Caudal
glands are absent in most of those species in which the males are
supphed with lateral caudal flaps constituting the bursa. It is
possible that the secretion of the bursal ribs, or tubes, is of the
same general character as that of the three caudal glands, and that
these two sets of glands are homologous. The ribs of the bursa,
when the full complement is present, consist of three groups. This
is at least suggestive. The females of such species sometimes have
lateral pores on or near the tail.

The sexual organs originate from a few cells set oil for the pur-
pose early in the development, which for a time remain rather
quiescent near the center of the body. As tlie nematode ap-

472 FRESH-WATER BIOLOGY

proaches maturity these sexual cells resume their activity and
begin to divide and to produce a symmetrically two-parted elon-
gated group of cells, one part extending forward and the other
backward. Primarily the sexual organs of both sexes are double,
and the normal development at first always forecasts a double
organ. This forecast is often fulfilled, but in many species one of
the halves has deteriorated or become vestigial. Where this is
the case the symnietry of the early development is soon lost and
the group of developing sexual cells then becomes one-sided.

At the last moult, or the penultimate, the sexual opening in the
cuticula makes its appearance. This is always on the ventral side,
and in the male invariably corresponds with the anus; in the female
it is independent and nearer the middle of the body, usually very
near the middle when the internal organs are double and symmet-
rical, and farther back, or more rarely farther forward, when there
is only one ovary.

The female sexual system is very commonly double, each half of it
being tubular and consisting of (i) an ovary, (2) a seminal receptacle,
(3) a uterus, (4) a vagina ; this latter of course in common with the
other half of the apparatus. These parts may lie in linear succession
in the body cavity, or, as is more often the case, the series may be
folded near its middle, that is, between the ovary and the uterus,
so that the ovary is reflexed and extends back toward the vulva.

The more usual forms of female apparatus are as follows:

1. Of two parts, each reflexed.

2. Of two parts, each outstretched.

3. Single and reflexed.

4. Single and outstretched.

When the organ is single it may extend either forward or back-
ward from the vulva, though it usually extends forward. Letting
F represent the vulva, - an outstretched organ, and ' a reflexed
organ, the various forms may be abbreviated as follows :

*F' -F- 'F F» -F F-

and this is the form in which the facts are presented in the measure-
ment formulae for the females, except that F is replaced by the per-
centage measurement figure representing the position of the vulva.

FREE-LIVING NEMATODES 47.

As the male organ may be either double or single, outstretched
or reflexed, the corresponding abbreviations for the usual forms of
male apparatus are as follows:

-M =M *M -U -M-

and this is the form in which the facts are presented in the formulae-
for males. As the testes always he in front of the sexual opening,
the datum point of the reference signs in this case is the point
where the testes join the vas deferens, not the sexual opening, as
in the females. The percentage figure representing the extent
of the male sexual organs dates from the anus. Species with re-
flexed testes are comparatively rare among fresh-water nematodes,
the commonest forms being -M- and -M.

The bhnd, free, or distal end of the female sexual tube is usually
found to contain only cells of extremely small size, observable with
difficulty. In consequence Kttle is known about the primordial
sexual products in these free-living species. The interior of the
main part of this segment of the tube, the ovary, is filled with devel-
oping oocytes, which generally soon arrange themselves in single file.
The oocytes increase rapidly in size, so that they are ripe by the time
they reach the entrance to the uterus. At this point they undergo
synapsis, meet the spermatozoa, and are fertihzed, and then receive
their shells, cuticular coverings acquired in the uterus. The sper-
matozoa usually collect together at the end of the uterus, which, in
some instances, has a special form adapted to their reception, and
in all cases must be at least physiologically adapted to attract and
retain them. Some species have special receptacles for the sper-
matozoa in the shape of large tubular branches of the uterus, —
genuine spermathecae.

The entrance to the uterus from the ovary is narrow, and this
slender part of the sexual tube is armed with delicate annular
muscles adapted to moving the ova on into the uterus. The
uterus varies much in size. Frequently in the small species a
single egg completely fills it; in the larger fresh-water species each
uterus may become large enough to carry a score or more of eggs.
In the larger parasitic species this capacity is enormously greater,
so that the number of eggs in the uterus may reach tens of thou-
sands, or even hundreds of thousands.

474

FRESH-WATER BIOLOGY

The vagina is usually short and more or less muscular, especially
near the vulva, where its wall is usually thicker. At the thickest
part it suddenly diminishes in massiveness, and in the case of the
double-ovaried species forks to form two short tubular branches
which join the uteri. The walls of these two short tubes, as well
as those of the part nearer the vulva, are suppHed with encircHng
muscle fibers which by their peristaltic action force the egg onward
and outward in the process of deposition. The vulva is a trans-
verse sHt-like opening whose length varies up to about one-half the
width of the body. Muscular fibers radiate from its cuticular
margin to the ventral submedian parts of the body wall, and serve
by their contraction to open the orifice.

The subspherical to elongate eggs are covered with cuticular
shells of varying thickness, usually smooth, but sometimes bearing
projections. In the greater number of fresh-water species the eggs
are deposited before segmentation begins, but in some genera fully
developed embryos are formed in the eggs before deposition. A
few species are viviparous. The period of gestation varies widely.
In some cases the formation of the embryo occurs within the
space of a few hours to a day or two, in other cases weeks are
necessary.

The structure of the testes resembles that of the ovaries, but
the resulting sexual cells, the spermatozoa, are smaller. The pri-
mordial germ cells at the bHnd end of the testis multiply to form
the grandmother-cells of the spermatozoa, which grow to a con-
siderable size, so that it is usually easy to locate the part of the
testis where they are maturing, — generally the middle or proximal
part. These grandmother-cells, or spermatocytes, have the num-
ber of chromosomes characteristic of the males of the species, and
they proceed to the formation of the spermatozoa by a process of
sudden double division of the chromosomes such that each sper-
matocyte gives rise in most of the known cases to four spermatozoa,
two with half the number of chromosomes characteristic of the
females and two with one less chromosome than this. All these
spermatozoa are supposed to be potent, but there is a dearth of
experimental evidence.

The oocytes follow a similar course but only one of the last

FREE-LIVTNG NEMATODES 475

four female cells is potential, the other three being the so-called
polar bodies which are left at the periphery of the egg to disinte-
grate and disappear. The polar bodies are to be looked for in
eggs that have just entered the uterus, and can be observed to
advantage only in stained specimens, though they may sometimes
be seen in the living material. The fundamental facts connected
with fertilization and inheritance in animals were first worked out
largely through the instrumentality of the eggs of various species
of nematodes. In this respect they are classical objects.

V

Fig. 771. Forms of spicula. i. Broad, tapering, blunt. 2. Elongate. 3. Slender. 4. Setaceous.
5. Elongated, tapering. 6. Elongated, arcuate. 7. Elongated, bent. 8. Fusiform, slightly arcuate.
9. Arcuate, strongly cephalated. 10. Sickle-form. 11. Hamate. 12. L-shaped. (.^fter Cobb.J

The male intromittent organs, the spicula, are usually two in
number, and in nearly all free-living species the two are identical
in form and size. Each spiculum is usually a straight, curved, or
bent, elongated framework of cuticula, commonly one to two times
as long as the anal body diameter. Exceptionally it may be very
long and slender. The main portion of its shaft is usually of uni-
form size, while the free or distal end commonly terminates in a
somewhat blunt point, which, however, may be variously modified.
The anterior or proximal end is often swollen or cephalated, for the
attachment of muscles.

The muscle for protruding the spiculum more or less insheaths
it, and is attached to the proximal end of the spiculum and to the
body wall, or to an accessory piece, near the anus, so that its con-
traction moves the spiculum toward the anus and thus protrudes
it. The retractor muscle is attached to the proximal end oi the
spiculum and thence usually passes forward and toward the dorsal
side of the body, where it is attached to the body wall; its con-
traction thus tends to pull the spiculum back into the body. It is
usually rather easy to observe these retractor muscles of the spicula.
but difficult to observe the protruding muscles.

In order that these muscles may act to better ad\'antage the
spicula often sHde in grooved pieces of cuticula named the acces-

476 FRESH-WATER BIOLOGY

sory pieces. These accessory pieces are usually from one-fourth to
two-thirds as long as the spicula themselves, and not uncommonly
possess an inward or backward extending apophysis whose function
is to anchor them firmly in position, or serve for the attachment
of special muscles. Long-necked unicellular glands are often
seen to empty into the cloaca near the distal ends of the spicula.
These probably serve a special purpose at mating time. The
form of the spicula and of their accessory pieces is useful in
distinguishing the various species, and as these organs are usually
viewed in profile the various terms used to describe them are
understood to apply to this aspect. The various forms and terms
are shown in the accompanying illustrations, Fig. 771.

Among the male accessory organs the bursa is, in a number of
genera, the m^ost important, though there is no trace of it in the
greater number of the fresh-water genera. The bursa is a thin, trans-
parent flap-like expansion of the lateral cuticula of the tail end of the
male, and serves as a copulatory clasping organ. It may consist of
two distinct halves, one on each side of the tail, and each ending short
of the extremity, or the two parts may extend to the extremity
and coalesce to form a continuous flap encompassing the tail.
The bursa springs from the submedian or lateral regions, though it
is usually on the ventral side of the lateral lines and, furthermore,
is bent toward the ventral side. Typically the flaps spring from
the body somewhat in front of the anus, grow wider as they pass
backward, and reach their maximum development about opposite
the anus; thence onward they usually diminish, — though in some
cases not very much. In its maximum development the bursa may
possess flaps as wide as the body itself; from this maximum it
varies to rudiments that may easily be overlooked (pp. 484, 493).

The bursa functions as a male clasping organ through the pres-
ence of muscular fibers adapted to close it ventrally, and through
the presence of so-called ribs which appear to be in the main, if not
altogether, tubular outlets for a cement-like secretion used to
fasten the male more or less permanently to the female at mating
time. No chemical examinations have been made of the cement
substances of the bursa and the caudal glands, but both are insol-
uble in water and seem otherwise similar. Some genera in which

FREE-LIVING NEMATODES 477

no bursa is developed, nevertheless have papillae, as they ha\e been
called, located according to the same general law as the riljs of the
bursa. (Diplogaster, Cephalobus.)

One striking fact will be forced on the attention of the collector of
nematodes early in his work, and that is the comparative rarit\- of
the males. In many of the species the males have never been seen,
and in most species the females are from five to twenty times as
common as their mates. There is reason to think that in some
species the males are very short-hved, and that this is the reason
they are so rarely seen. The males are often so much smaller than
the females that they are easily overlooked, or mistaken for young,
so that in such cases the rarity of the males may easily be over-
estimated. In a few species the males appear to be more common
than the females, at least at times. Hermaphroditism and par-
thenogenesis are frequent. (See p. 495.)

As the ova approach the narrow duct leading to the uterus they
rapidly acquire yolk of a distinctly granular character. In the case
of the numerous species having refiexed ovaries, the oviduct is
located near the flexure, and is so small and short that it is usually
impossible to see it except when the organs are immature. Passing
through the oviduct, the ovum enters the uterus, where for a short
distance the cells of the uterine wall are unusually well developed,
apparently to furnish the material for the shells of the eggs. Here
too the eggs are fertilized. The proximal limit of the shell-gland
is often very definite. The rest of the uterus is thin-walled and
connects with the vagina through a narrow muscular duct, mainly
responsible for forcing the eggs into the outer world. The eggs
at the time of deposition are usually soft and pliant, so that they
easily pass through the vulva, even when relatively large.

The fresh-water nematodes are t>T3ical of the entire group of
free-living nematodes in that while most of them arc oviparous,
some are ovi- viviparous and others viviparous. The eggs in most of
the known fresh- water species are smooth shelled. In the segmen-
tation the first division is a slightly unequal one, one blastomere giv-
ing rise to the somatic tissues, the other to the sexual organs.

There are various organs that have been observed in the free-
living nematodes whose functions are problematical, such as (i) the

478 FRESH-WATER BIOLOGY

double organ in the females only of some species of Oncholaimus,
located in the posterior part of the body and connecting with the
exterior through openings in the subdorsal region; (2) the gland-
Uke pair of organs seen in the females of Diplogaster, and apparently
also of Rhahditis and other related genera; and (3) the long-necked
paired glands sometimes emptying into the male cloaca. It is
conceivable that some of these serve a sexual function, such as
the secretion of a substance whose odor or taste is of service in
enabUng the nematodes to locate their mates.
< 88 >

< 28>

< 14>

< - - 7'^^^_..-,,,-----——--'^^rzzzzz^,_.---... V ,---, :

^3 17? a C>-CjO'''..x'l^) m

— "^ oii/ •

Fig 772. Diagram in explanation of the descriptive formula used for nematodes; 6, 7,8, 10, 6 are
the transverse measurements, while 7, i4> 28, 50, 88 are the corresponding longitudmal measurements.
The formula in this case is:

7. 14. 28. 50- 88.
6. 7. 8. 10. 6.
The measurements are simply percentages of the length, and the formula, as printed in the key, may
be regarded as somewhat in the nature of a conventionalized sketch of the nematode with dimensions

The measurements are taken with the animal viewed in profile; the first is taken at the base of the
pharynx the second at the nerve-ring, the third at the cardiac constriction (base of the neck ), the
fourth at the vulva in females and at the middle (M) in males, the fifth at the anus. (After Cobb.)

It seems reasonably clear that fresh-water nematodes have
marked seasonal development, at least in some species. Adults
of many species can be found at all times of the year. Freezing
does not necessarily kill them. Although the fresh-water nema-
todes are so widespread, and so abundant at all seasons, it is not
always easy to isolate them for examination without the use of
special methods. Few of these nematodes exceed two to three milH-
meters in length, and they are so slender and transparent as to make
it practically impossible to examine them without the aid of a lens.

However, when special methods are employed they may easily
be collected. A few centigrams of mud or sand from a place where
nematodes are beHeved to exist is disseminated in a watch glass of
water, and the sediment examined carefully for the characteristic
wavy non-progressive motion exhibited by these Httle organisms.
When discovered, the specimens are captured with a fine-pointed
pipette or medicine dropper and ejected with a minimum of other

FREE-LIVING NEMATODES

419

material into a second watch glass, from which Ihcy are removed on
a very fine-pointed needle and placed in a drop of clear water on a
microscope slide. These operations are best performed on the stage Jf
a dissectingmicroscope, under a lens magnifying five to ten diameters.
To collect specimens in large numbers it is best to make use of
more elaborate methods. A coarse sieve with meshes two to three
millimeters across is used to remove objects larger than nema-
todes. To gather the nematodes, the material that comes through

Fig. 773. Measuring the length of
the camera lucida drawing of a nema-
tode. The head end of the drawing
lies near the left-hand cuff. The
pharynx is shown, and near it, next
the knuckle of the httle finger, is the
oblique nerve-ring. The cardiac con-
striction lies this side of the end of the
forefinger, and the vulva on the
farther side. Mention should be made
of the presence of the error resulting
from the attempt to measure a curved
line with a straight measure. The
aim should be to reduce this error so
much that it can safely be neglected.
One means of reducing this error may
here be mentioned, namely, reducing
the "step" of the divider legs in pro-
portion to the sharpness of the curv^e
to be measured. Another method
may also be mentioned, but it is to be
used with caution, and only as the
result of experience. By a number of
careful trials it will be found that a

measurement nearer the truth can be obtained by fbllowing a path somewhat on the outside of the curve*
of the median line on the drawing or image being measured, but care must be exercised in adoptinK this
method not to overshoot the mark. Where the curve is sharp it is of course safer to go always a liltlr on
the outside of the curve. I consider it to be sufficiently accurate after a little practice to dispense with
actually drawing in a median line on which to measure It is easy to keep sufficiently near the miildle
by eye. Of course, with a reliable map-measure all these difficulties dis ip:ie:ir. The map measurer, an
instrument to be had from most dealers in drawing instruments, has a small milled wheel that may be st-
rolled along a crooked line as to measure its exact length.

To obtain the percentage figures used as terms of the formula simply divide each of the various trans-
verse and longitudinal measurements by the total length. Using a slide rule these divisions iKcupy
only two to three minutes. (After Cobb.)

this coarse sieve is passed through sieves of finer and finer mesh
until the limit of fineness is reached. About the finest mesh ob-
tainable is that of the finest miller's bolting silk (0.25 to 0.5 mm.),
which, when stretched over appropriate rings made of ])ottomless
dishes will allow fine mud to pass through while it will retain all
but the smallest nematodes. By successive sif tings practicall>- all
the nematodes can be secured.

The sifting can be supplemented by gravity methods. Aquatir
nematodes are lighter than sand and heavier than water. It tlu'
water containing the nematodes be violently agitated and then be
allowed to rest for a few seconds the sand will have subsided to the
bottom, and the nematodes may be decanted off if the pouring be
managed expeditiously. Then, if the nematode-containing water

480 FRESH-WATER BIOLOGY

be allowed to rest for from two to four minutes in a vessel two to
three inches deep the nematodes will have largely settled to the
bottom and the supernatant muddy water may be carefully de-
canted away. The residue will contain an abundance of nema-
todes that may be captured as described above.

Fresh-water nematodes are so active that it is practically impos-
sible to examine them without first anesthetizing or kilHng them.
They may be rendered unconscious by the use of a small amount
of chloroform dissolved in water. Ether, chloral hydrate, tobacco
smoke and other anesthetics and narcotics are also used in this
way. Specimens treated thus are wonderfully transparent, and
display to a maximum advantage certain features of the anatomy.

Permanent preparations may be made by kilUng and fixing with
Flemming's solution or Bouin's solution, washing, and then chang-
ing to water containing 5 per cent glycerine and very slowly evap-
orating in a closed, preferably warm, space such that the solution
becomes fully concentrated in the course of a few days. The
cuticula of some nematodes is so thin and flexible, and at the
same time so impervious, that this evaporation process sometimes
has to be prolonged to several weeks to prevent crumpling, but
many kinds can be successfully treated in two to three days. If
the specimens have been blackened by the Flemming's solution,
they may be satisfactorily bleached in a few hours or days by
adding a few drops of dioxide of hydrogen solution to the glycerine
in which they lie after evaporation. They are removed to pure
glycerine one by one as they become bleached, and then are
mounted in glycerine jelly. Specimens treated in this way make
excellent material for examination, but may deteriorate in the
course of years. Again, the specimens may be killed by suddenly
heating in water on a glass slide until they become motionless,
and can then be examined at once, or evaporated as above de-
scribed in 5 per cent glycerine.

The residue from the subsidence and sifting methods, already
described, may be added suddenly to an equal volume of boihng-
hot concentrated solution of corrosive sublimate and allowed to cool.
When the specimens have remained in chis solution for twenty-
four hours or more they may be picked out one by one on the point

FREE-LIVING NEMATODES

481

Fig. 774. Skeleton camera lucida drawitiR used to
compute the nematode formula. (.After Cobb.)
The head end lies to the left. This gives the
following formula.

1-9

[4.8 46 9S

,81 mm.

of bamboo splinters and differentiated into alcohol, and thence
successively into acid carmine in 70 per cent alcohol, 70 per cent
alcohol with i to 2 per cent hydrochloric acid, absolute alcohol, oil
of cloves and Canada balsam. The specimens thus treated arc
more permanent than those resulting from the glycerine treatment
described above and are the only
satisfactory ones for many cyto-
logical studies. These various
treatments may affect the relative
proportions of the organism dif-
ferently, especially those of the
neck. It is therefore best when
noting measurements of specimens ^.8 52 7.4 10.4 4-3

for descriptive purposes to indicate how the specimens were treated.

The student cannot expect to examine the finer details of the
anatomy or indeed to make satisfactory progress without the i)atient
use of a good oil immersion objective under favorable conditions.

The formula is made to convey much additional information, by
interspersing suggestive signs. Thus the successive signs in the ad-
/_ ii_ _iL_^i7 '^rL—^L<i- , 8 mm jaccut formukc indicate lips,' papillae

< — I 2 3 J ' ' 4_i 4 9 1 6

on the lips,- a pharynx of uniform
i= il--tr/^~3i5 T7~~^2jri ' "^ (diameter without armature of any

kind,^ no amphids,'* a rcnctte whose
excretory pore is located a little behind
the nerve-ring,^ about 600 transverse
striae resolvable into rows of dots,®
no wings to the cuticula,'^ a median
esophageal bulb two-thirds as wide as the middle of the neck,'** a
cardiac bulb three-fourths as wide as the base of the neck,'' two
symmetrically reflexed ovaries, occupying 71 per cent of the length
of the body,^^ no caudal glands or spinneret, '^ a single outstretched
testis occupying 63 per cent of the length of the body,'- a bursa
beginning in front of the anus and including the entire tail,'^ 4
bursal ribs or supplementary organs on cither side in front of the
anus, and 5 ribs on either side behind the anus.'^

1 Conventionalized contour of the front of the head. - Conventionalized ((.iin.ur
of the lips. 3 Conventionahzed outline of the pharynx. * Absence of mark indicat-

TABLE
Terminology Relating to Strlatlon of Cuticula.

100 down

260 ±

SOO ±

760 ±
1000 ±
1500 up

Very coarse

Coarse

Rather coarse

Rather fine

Fine

Very fine

Hone

482

FRESH-WATER BIOLOGY

KEY TO NORTH AMERICAN FRESH-WATER NEMATODA

1 (64) Intestine normal and functional throughout; anus present in both

sexes 2

The forms which are included here are typical nematodes. They possess an alimentary
canal which is complete and functional during the entire life of the individual. They are
free living in the adult as well as in the larval stage of existence. With the free-living forms
are sometimes found parasitic forms so similar in structure that a knowledge of their source is
needed to determine whether the species is parasitic or not. No note is taken of the parasitic
forms and the following statements apply only to the true free-living nematodes.

They are all relatively small in size and so transparent that the internal structure can be made
out clearly in the Uving animal. In these respects as well as in detail of internal structure they
stand in distinct contrast to the other group included under the alternative heading in the
key. Famihes which include only parasitic species are not mentioned in this key.

2 (13) Oral end armed with roptrusile spear or sting 3

3 (8) Spear with bulbous base 4

4 (s) Cuticula with 70 to 100 coarse, retrorse annules Iota Cobb.

Genus consisting of a considerable number of species, found in swamps and in acid
soils. These nematodes are covered with retrorse scales, or bristles, so that it is practically im-
possible for them to move in any other direction than forward. ^ Near the head the remarkably
large and powerful spear can be seen through the skin. When, in order to make punctures, this
spear is thrust out, the nematode is not pushed backward, because of the friction which its
scales offer to surrounding soil particles. But often the males of Iota lose the spear at the last
moult and become relatively longer and more slender and smoother, and then they look very
unlike the females.

Representative species Iota octangular e Cobb 19 14.

^ 14 21 .__2i_ -85" 92^ ^^ Male unknown. Habitat: Dismal Swamp, Va.

C"^ II 12 12./ 9 6. '""'■

Fig. 775. Iota ocfangulare.
a, mouth opening; b, lip region; c, spear muscles; d, shaft of spear; e, base of spear; /, cuticular tube
ol esophagus; g, nerve-ring; k, posterior portion of esophagus; i, flexure in ovary; j, body muscles;
k: cuticula; I, one of the eight longitudinal rows of modified cuticula; m, ovum; n, muscles of body wall;
0, sublateral modification of the cuticula; p, uterus; q, subdorsal modification of the cuticula; f, vulva;
s, muscles of the body wall; t, rectum; u, anus; v, terminus. (After Cobb.)

5 (4) Cuticula with 200 or more finer or almost invisible annules 6

ing amphids. ^ Oblique line, conventionalized drawing of the outlet of the excretory-
duct, placed just behind the measurements relating to the nerve-ring. ^ Character
of the hne running through the formula (see adjacent table) , and dots placed on either
side of the Hne. ^ Absence of short horizontal Hnes above and below main line, such
marks being used when wings are present. ^ Horizontal stroke under two-thirds of
the nerve-ring \vidth measurement. ^ A corresponding stroke under three-fourths of
the width measurement for the base of the neck. ^^ Single quotation marks around the
measurement indicating the position of the vulva, and 71 used as an exponent. ^^ Ab-
sence of spinneret mark, — an angular sign used to indicate spinneret. ^ Dash in
front of the M and 63 used as an exponent. ^^ Curved marking under the transverse
anal measurement, extending to the end of the formula line of the male, ^^ 4 and 5
used as sub-figures before and after the anal diametral measurement with ditto marks
to indicate that the ribs occur on both sides.

FREE-LIVING NEMATODES

483

Esophagus with a distinct median bulb, and a more or less distinct
posterior swelling. Males with bursa. . Tylenclius Baslian.
Genus consisting of numerous species, many of them iwrasilit
in plants and sometimes highly injurious. Aquatic species are rather
uncommon. A single species found parasitic in a marine alsa
I nncipally owing to its economic importance the genus has a very
extensive literature.

Representative species.

/l^ 9 8. __ 13. -81

V '.i ' 'l.8'/~ 2._ ■ ■ '2 2

(- :

7(6)

Tylenchus dipsaci Kahn 1857.

8= 2_ ■ "22 '12' I 5 mm '^ ''|^. S[K'cieS is fouod

parasitic in onion and hya-
, — *]■■ • -^1 ••'•'.. Mmm. ^'"^'1 \i\i\h>, and in a num-
1' '9 .2. -NU ber of other plants, and is

very harmful. The spear, h, i, Fig. II, is shot forth hy the musiles.
/, and is used to puncture the cells of the h(jst plant. The sjiear is
tubular, and the juices of the host are sucked through the siK-ar into
the intestine by means of the bulb, c. Often referred to in literature
as Tylenchus devaslalrix.

Habitat: Europe, America, Australia, and probably throughout
the temperate regions.

Fig. 776. Tylenchus dipsaci. Kiihn.

I, a female; II. head of the same more highly magnified; III. Uil of
a male; IV, view from below, of the female sexual oi)cnin)z; \". cross-
section of the neck passing through the median sucking-bulb; \ I. front vktw
of the penes and their accessory parts; VII, cross-section through the middle of
a female, showing how the body-cavity is filled completely by the ovary- (»)
and the intestine (3).

a, lip region; b, tip of spear; c, median sucking-bulb; <f, ncr%T-rinK;
e, excretory pore; /, muscles for moving the spear forward; /t, ixwtcrwr
esophageal swelling; A, excretory' gland; i, hind end of si)car. thrre-bulbrtl:
i, loop in ovary; k, right spiculum; /, muscles for ojjcning the vulva;
m, the vulva; n, glandular (?) bodies; o, bursa; p. hind end of ovar>-;
q, uterus containing spermatozoa and one segmenting egg: r. segmentrnK
egg; 5. vagina; /, the vulva or female sexual opening: «, blind end of ixsterio'
rudimentary ovarv; v, intestine, showing its cellular structure; ir. cross-
section of an egg; x, anus; y, wings of the cuticula; z. cross-section o( the
intestine. (After Cobb.)

Esophagus with only one swelling, corresponding to the median l)ulb i)f
Tylenchus. Males without bursa. . . Aphdcnchiis l^Asu^n

Genus consisting of numerous species, the niajority parasitic in
plants, and often highly injurious. Some sjx-cics prthenoKenetk-.
This genus closely resembles Tylenchus. frt)m which it is distin-
guished by the absence of the bursa on the males, and by the less
developed posterior portion of the esophagus. Thi> latter Ls so
deteriorated that it cannot be distinguished from the intestine.
The oral spear also is usually less strongly deyeloix-d than in
Tylenchus, and its posterior extremity is less likely to pn-si-nt
bulbous swelhngs. .\s in Tylenchus, so here, some of the spitics
are known to revive years after haWng been dried up and con-
verted into "dust." In the dirt or dust adhering to seeds and
plants they are often transported long distances, -'^•anv «' ln«
species, therefore, are now cosraoiJoUtan. Like I yUtuhus, ihii genu*
has an extensive literature.

Representative species. ^ , u o

Aplielenchns viicrohiimus Cohh 1891.

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' °^ Habitat: Douglas Lake,
Michigan.

Fig. 777. Aphelcnchus microlaimus.
a, the lips; b, the spear; r. the nerve-ring; J sucking-bulb; ''J-f"*^^
vote- f ventral gland; g, blind eivl of testicle; h. inloslinc; i. cuticwU or
skS ;•; spStozoonf*. right spiculum or penis; /. piece accr^oo' »
the spicula; m, anus; n, papiUa; o, terminus. (.Vflcr Ujbb.)

484

FRESH-WATER BIOLOGY

Representative species.

'i-:

,3 4)

7 1

9 1

-52-58

97 2

(M)

1 6/

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2 1

1 2

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8

12/

11
1.4

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1 7

99 3

8 (3) Spear without a bulbous base 9

9 (10) Esophagus with a median bulb; males with bursa.

Dolichodorus Cobb.

This genus is distinguished from Tylenchus by the peculiar lobed bursa without ribs, by the

relatively long and slender oral spear and peculiar lip region, and by the presence of a double

sexual organ in the female. There are few Tylenchi the females of which possess two ovaries.

. . Dolichodorus heterocephalus Cobb 19 14.

The transverse striie are resolvable with high
powers under favorable conditions into rows of
exxeedingly minute, somewhat irregular elements.
The flaps of the bursa are striated in much the same
manner as the cuticula, and the margins of the
flaps are distinctly thickened. The sper-
matozoa are small and numerous and it ap-
pears that the reduction divisions take place
in a short segment of the testis not far from
the blind end. The organs obscurely figured
in connection with the head appear to be the
outlets of glands located in the neck.

The "cardiac swelling" h appears to have
the same structure as in some species of Ty-
lenchus, in which it is known to be caused by
the presence of glands exterior to the esoph-
agus, and therefore not properly to be re-
garded as a cardiac swelling of the ordinary
kind. In the Tylenchi mentioned, these
glands empty through a minute duct which
enters the esophagus, passes through the
median bulb on the dorsal side of its valvular
apparatus, and, continuing, empties into the
pharynx at the base of the spear. These so-
called salivary glands are designated at g in
I, under Tylenchus dipsaci (Fig. 776). Similar
structures may occur in the present species.

Inequality of the ovaries is characteristic
of a vast number of species of nematodes
and may have a deep morphological signifi-
cance. It is nearly always the posterior
ovary which is the smaller. Every degree
of inequality exists even to the extinction
of one ovary. The smaller branch may pro-
duce smaller and what appear to be inferior
eggs, and may even cease to function as a
reproductive organ and function merely as a
minor part of the other branch, serving, for
instance, either as an extension of the uterus,
or as a seminal receptacle.

Habitat: Douglas Lake, Michigan; Silver
Spring, Florida.

Fig. 778. Dolichodorus heterocephalus.
I, nearly side view of a female; II, lateral view
of surface of head, more highly enlarged; III,
sagittal section of head; IV, dorso-ventral view
of head; V, front view of head; VI, side view,
posterior extremity of male; VII, ventral view of
posterior rxtremity of female; VIII, ventral view
of posterior extremity of male.

a, papilla; b, cephalic organ of unknown signiQ-
cance; c, spear; d, base of spear; e, median bulb;
/, nerve-ring; g, excretory pore; //, cardiac swell-
ing; i, intestine; j, anus; k, lateral caudal pores;
/, terminus; m, blind end of posterior ovary;
n, ovary; o, left spiculum; p, accessory piece;
q, distal end of accessor^' piece; r, left flap of
bursa; s, terminus oE male; t, ovum; u, sperma-
tozoa; ;•, vaginal muscles; w, uterus; x, vulva;
i', anus. (After Cobb.)

10(9) Esophagus with only an elongated posterior swelling; no bursa. . 11

FREE-LIVING NEMATODES

4S5

(12) Pharynx simple, male supplementary organs not in fascicles.

Doryldimus Dujarciin.
Genus consisting, no flouht. of hundreds
of species, and inhabiting stjii. frt-sh water,
and, to a limited extent, brackish water.
They feed so far as known on vcKetahIc
matter, most commonly, it is hclieve<l. on
the roots of jilants which they pierce by
means of the hollow oral sf>car.

Representative species.

Dorylaimus Jccuudiis Cobb 1914.

[-'

Habitat:
ington, D. C.

Fig. 779. Dorylaimus fecundui.
At the right, head and tail of a fi-m.ilc; al the left,
tail end of a male,
a, apex of spear, showing' ohlique opening:
b, papilla of the anterior circlet; c, pantUa of
the posterior circlet; d, guidint'-rinR for the
spear; e, commencement of the esophaRus,
/, pre-rectum; g, rectum; //, anus; i, anai
muscles; j, caudal pai)ilhi; k. outer cuticub;
/, inner cuticula; m, muscular layer; n, prr-
rectum; o, one of the numerous oblicjuc a>|m-
latory muscles; P, one of the ventral scries of
r, pair of pre-anal papillae; 5, retractor muscles of the
accessory piece. (.After Cobb.)

4 4

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Algae, Potomac River, Wash-

male supplementary organs; q, ejaculatory duct
spicula; /

(11)

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19

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muscular layer; u, right spiculum

Pharynx with complicated radiate framework, male supplementary
organs in fascicles Aclinohiimus Cohh.

Genus represented in all parts of th world, and proposal for
species similar to Dorylaimus labyrinthoslonius, in which the
pharynx is more or less immobile, radially striated and elabo-
rately constructed.
Representative species.

Actinolaimus nidiatus Cobb 1913.

The esophagus bcjjins

e.9 13. 41. -M- ^1 4 I mm "'^ ^ ^"'**^ alx)Ut OnC-

'' I "8 T. n T. tmI" third as wide as the cor-

responding portion of the neck. It continues to have this width
for some distance. Considerablv in front of the middle of the
neck it expands rather suddenly. The cells of the brownish intc-^-
tine contain granules of variable size, arranged so as to give n.sc
to a rather obscure tessellation. The tail of the female is concave-
conoid to the hairfine terminus. The tail of the male is hemi-
spherical-conoid. Immediately in front of the anus are two ven-
tral papillae placed side by side. In addition t(^ these there are
ventral papillae arranged in three raised and conspicuoiis groups
or fascicles. These three groups form a .scries whose length is
about equal to the distance from the jx.stenor group to the end
of the tail. The two equal, slightly arcuate rather aculc
spicula are about twice as long as the anal IkkIv diameter The
surface of the tail carries a number of innervate<i |upillac. at
least as many as six, and probably c|Uite a number of others.

Habitat: Roots of plants and among algae Potomac River and
its banks, Arlington Farm near Wiushington, DC; Douglas

Lake, Mich. ... ,. ,

Fig. 780. Actttwlamus radiatus
lb, lip region; />/>. innervated ixipillae; ph, phao'nx; on. oncho, of
spear; or, mouth opening, (.\ller Cobb.)

13(2) Oral end without protrusile spear or Sting. '-^

14 (37) Pharynx armed with one or more refractive,

Xv5/^

cutKular tecti

486

FRESH-WATER BIOLOGY

15 (16) Number of teeth three, equal, small, mobile, well forward near the

mouth. . Ironus Bastian.
Genus with about six known
species, confined to fresh water,
though there is a very similar
genus, Thallasironus de Man, for
the reception of similar marine
forms. Some species hermaphro-
ditic. Salivary glands in esophagus.

Representative species.

Ironus americanus
Cobb 1914.

16 23 27 29 1.3

From the size of the apparently
matured ova it is assumed that the
eggs are considerably elongated.
It is unlikely that more than one is
contained in the uterus at a time.

Habitat: Deer Bottom, Pikes
Peak region, Colorado.

Fig. 781. Ironus americanus.

I, head and anterior portion of neck;
II, head, lateral view "teeth" ex-
truded; III, head, " teeth " withdrawn
with second set formed in preparation
for the next moult; IV, tail end of
female.

a, one of the three pharyngeal
teeth, shown extruded; h, papilla; c,
cephalic seta; d, amphid; e, pharynx;
/, toothlet; g, toothlet; h, esophagus;

f, lining of esophagus; j, nerve-rmg;
k, intestine; /, anus; in, caudal gland;
n, terminus. (After Cobb.)

16 (15) Number of teeth one; or more than one, and unequal 17

17 (22) Teeth, at least one of them, usually massive; thick, more or less
papillate lips closing over the capacious pharynx. • • • 18

Main tooth dorsal (sometimes all nearly obsolete) ; Hps thick, armed

with papillae; no setae Mononchus Bastian.

Genus of a score or more species, some in fresh water, others
in soil, where they hunt and devour nematodes and other small
organisms. The movements, especially those of the head, are often
very active. The males are very rare. The name Mononchus
indicates the presence of a single pharyngeal tooth, but sometimes
there are one or two additional teeth; sometimes all are absent.
The relatively powerful lips can be everted, and are utilized to
grasp the prey and force it against the pharjmgeal teeth. In some
species the wall of the pharynx bears series of minute rasp-like
denticulations. Some species are hermaphroditic.

Representative species. Mononchus major Cobb 1893.

1.6

6.

19

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95

16

2 2 ■

26

2 9

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19

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95

15

23

2.9

2 8

12-N2 3

> 3 4nua., ^y^ elegant species is
a soil inhabitating form

> 3 4 mim sometimes found in wet
places. No American species are figured as yet. The adjacent il-
lustrations are derived from Australian specimens.

Fig. 782. Mononchus major.
I side view of male; 11, side view of head of same; III, front view of
head; IV, side view of tail; V, details of male papillae.
a mouth; h, lip-papiUa; c, lip; d, esophagus; e, nerve-ring; /, phar-
yngeal tooth; g, inner^'ated papilla of skin; U, esophagus; t, base of
phSnx;i, cardiac collum; k, intestine; /, flexure in testicle ;. m blind
end of testicle; «, vas deferens; o, lip; p, mouth opening ; 9, ejaculatory
duct- T spicula; s, ejaculatory duct; t, accessory piece; w post-anal
papillae! %, spicula; w, ejaculatory duct; x, ventral row male papillae,
y, anus; 2, three anal glands. (After Cobb.)

FREE-LIVING NEMATODES

487

19(18) Main tooth submedian. Lips thin; setae present 20

20(21) Males without bursa 0)ic/iolui, nus DuinuWn.

%t/Il/ I Genus of numerous siK-cics. nearly all

marine. A few six-cies only in Ijrackish
and fresh water. C'osmoixjiilan. i-xt<ii(J
ing well into the ix>lar sc-as. Some attain
a length of 25 to 30 mm. The individuals
sometimes occur in enormous numln-rs

The pharyngeal teeth vary in iiumUT,
form, and size, and atTord g(M)d n|m-. ilk
characters. The segments of the ev.pha-
gus frequently contain much-hramhcd
"salivary" glands emptying through the
pharyngeal teeth.

The female sometimes possesses a pecu-
liar pair of relatively large organs of un-
known .significance emptying through
pores toward the tail end.

Representative species.
OncholaimHs piinctatiis Cobb 1914.

7 19 10 ;i -M.«« tj

L-** 1.T7 n Ti n ^Tl~' ' ' ■•

X897

Fig. 783. Oncholahnus
punctatus.

a, thin flaps on margins
of lips; b, lips; c, anterior
circlet of papillae; d, poste-
rior circlet of papilla-like
cephalic setae; e.J, subme-
dian tooth or onchus; g, wall
of pharynx; k, intestine; i,
ejaculatory duct; j, spic-
ulum; k, dorsal tooth or
onchus; /, amphid; m, am-
pulla of gland, emptying
through dorsal onchus, k;
n, rectum; 0, beginning of
esophagus; ^, anus; 9, lin-
ing of esophagus; r, caudal
gland; s, caudal papilla;
t, ducts of the three caudal
glands ;m, spinneret. (After
Cobb.)

21 (20) Males with bursa.

Oncholaimellus de Man.

Much like Oncholaimus, but males have narrow

bursa. Spicula unequal, or equal. Two species

known; the type 0. calvadosicus de Man is marine.

Representative species.

Oncholaimellus heterurus Cobb 19 14.

It is rather difficult to obser\'c the finer
details of the cuticul.i on account of the
presence in it of numerous, dot-like eU-
ments, which are arranged in loni,itudinal
groups, of which the wiclest are the lateral
groups. The longitudinal arrangement of
the granules is continuous throughout the
body, but it is most marked on the lateral
fields. There are six lips.

Habitat: Fresh-water pt)nds. Cape
Breton Island, Dominion of Canada.

X4.57

There are six lips, each bearing on its anterior sur-
face, near the margin of the head, a somewhat out-
ward pointing, minute, innervated papilla. The cells
composing the intestine contain scattered granules,
which give rise to a very obscure tessellation, and also
certain doubly refractive granules. The posterior
testis is the smaller. This is a doubtful Oncholaimel-
lus, since there are no pharyngeal teeth, and the
amphid varies from that of the type species, as do
the spicula, which in the type species are unequal.

Habitat: Fresh-water pond near Ocala, Fla.

Fig. 784. Oncholaimellus heterurus.
I, side view of head; II, ventral view of head; III, side
view of tail end of male; IV, ventral view of anal region of
male, o, excretory pore; b, submedian cephalic seta; c,
pharynx; d, left flap of bursa; e, esophagus; /, left spiculum;
g, accessory piece; h, amphid; i, male [X)st-anal seta and pa-
pilla; j, lateral seta; k, spinneret; /, thin lips. (After Cobb.;

488

FRESH-WATER BIOLOGY

22 (17)

23 (36)

24 (25)

Teeth small, often only one, then dorsal; lips with inconspicuous

papillae; pharynx of moderate size 23

Esophagus with one or two bulbs 24

Bulbs two, spinneret absent Diplogaster M. Schultze.

Genus with more than a score of
known species, mostly found in fresh
water but also in many moist situations
in soil and between the sheaths of
grasses, etc. Some species hermaphro-
ditic. A number of the species appear to
be at least facultative parasites. They
are often found in dead insects and cater-
pillars, whose death they apparently
have caused. Other species are found
in decaying mushrooms, animal excreta
and foul pools. Many of the species are
easily reared in decayed meat and va-
rious other culture media. Many thrive
best in the presence of bacteria.

Representative species.
Diplogaster fictor Bastian 1865.

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then cardiac, or none; spinneret present

Striae resolvable near the head into
rows of refractive dots arranged in lon-
gitudinal as well as transverse Hnes. A
short distance behind the head the longi-
tudinal rows arrange themselves in pairs.
These pairs indicate the locus of about
twenty-four longitudinal cuticular ribs
or wings, which extend from the middle
of the neck to near the anus. On the
tail these ribs again resolve themselves
into double rows of dots. The thin-
shelled eggs appear to be deposited
before segmentation begins, something
rather unusual in this genus.

Habitat: Spring, Washington Coun-
try Club, Chevy Chase, Md.

Fig. 785. Diplogaster jidor.

I, side view of female; II, head of the
same, seen in dorso-ventral view, lips nearly
closed; III, head of the same, lateral view,
lips nearly wide open; IV^ head of the same,
lateral view, lips partially closed; V, front
view of mouth, partially closed; VI, lateral
view, posterior portion of a male specimen;
VII, somewhat diagrammatic perspective
view showing markings of the cuticula.

a, one of the lips; b, one of the six cephalic
setae; c, amphid; d, one of the two more or
less evertible pharyngeal hook -shaped teeth;
e, median esophageal bulb; /, nerve-ring;
g, anus; h. rectum; i, intestine; j, terminus;
k, posterior esophageal bulb; /, nerve cells;
m. renette cell (?); n, left spiculum; o, lumen
of the intestine; p', pre-anal male seta;
P",P"', ^"", post-anal male setae and papil-
lae; q, one of the cells of the intestine; r,
accessory piece; s, flexure in anterior ovary;
/, blind end of anterior ovary; y, vagina;
w, synapsis in egg in the anterior uterus;
.T, one of the spermatozoa in the vagina;
y, uterus; z, vulva. (After Cobb.)

26

FREE-LIVING NEMATODES

489

26 (27) Lateral dots much accentuated Spilophoni HjLsiian.

The striae arc rcs^jlvah'e into ruw< ..f dots

which are much accentuated on the latir.il lu-lds.

/' \ _ ' Genus of a score or more known siKxics,

aquatic, mostly marine.

Representative species.

Spilophora canadensis Cobb 19 14.

Cs .5. . . .8. . . i '5 -MM U4

(^ 2. 4.3/ ■■ . ij i.- • •■\yi ■> '■*

Lateral wings (j) are very prominent, and pos-
teriorly are somewhat scalariform. The females
have symmetrically reflcxed ovaries.

Habitat: Fresh-water ptjiids, Cape Breton Is-
land, Dominion of Canada.

Fig. 786. Spilophora canadensis.

a, mouth opening; b, dorsal tooth; c. pharj-nx; d.
base of the pharynx; e, esophuKus; f, nerve celL»; t,
nerve-ring; //, excretory imre; /, valvular api«ratu<i
of the bulb; j, longitudinal row of cuticular markings
characteristic of the genus; k, intestine; /, rencttc cell;
m, nucleus of renette cell; n, cell access<jrv to the
t » ti X300 renette cell; o, blind end of testicle; p, reversed of the

striationsof thecuticula; (/, vas deferens; r, spiculum; i,
anus; /, caudal gland; u, spinneret, (.\fter Cobb.)

Striae composed of dots; the lateral ones Httle if any accentuated. 28
Pharynx without esophageal bulb Cyatholaimus ^iisiv^n.

PharjMix is cup shaped then conoid, and
longitudinally ribbed.

Genus of a score or more of aquatic
species, nearly all marine but found also
in brackish and fresh waters. Cyatho-
laimi are found in all trojiical and tem-
perate seas, and the individuals are nu-
merous. In most habitats lx)th sexes
will be found. Diatoms are sttmetimcs
found in the intestine. Thoush not
shown in the species here figured, the re-
nette seems always present, and is often
well developed.

27 (26)

28 (29)

Representative species.
Cyatholaimus truncatus Cobb 1914.

i-

Habitat: Silver Springs, Fla.

Fig. 787. Cyatholaimus trumatui.
I, side view of a female; II. side view of
head; III, front view of the same head;

IV, ventral view of anal region of male;

V, lateral view of the siime; VI. lateral view
in tl>e middle of tiie body showing cuticular
markings and pores.

a, suhmedian cephalic seta ; h. lal>ial
papilla; c, amphid; d, dorsal to<nh: <■, lat-
eral cephalic seta; /, one of the twelve ribs
of the vcstihulc; .?, small sul)nie«lian phar;k-n-
goal tooth; //, base of the pliar>nx; i. ejac-
ulatory duct; j. intestine; k. one of the
four male pre-anal supplementary orRan.*;
/, one of the spicula; m, anal muscles; ». one
of the accessor>- pieces; o, ner\c ring; p.
one of the cells of the intestine; q. lumen oA
the intestine; r, anus; s, blind end of re-
flexed ovar\-; /, egg; u. vulv.i; r. llexurr
in anterior ovan.'; w, junction <>l tlir .ivarv-
and uterus; J. pores in the cutKiila: y cme
of the three caudal glands; :. male gland (i).
(After Cobb.)

490

FRESH-WATER BIOLOGY

29(28) Pharynx less conspicuously ribbed; cardiac bulb distinct. ... 30

30 (35) Dorsal tooth well developed 31

31 (34) Pharynx cyathiform then conoid, joining esophagus indefinitely, s^
32(33) Amphids spiral, inconspicuous sUts or none. . .Chromadora BsiStia.n.

Y«j Genus, aquatic, mostly marine but abundant in fresh waters.

Twenty to thirty species known. Found in American fresh waters,
no species yet described. Species highly developed, usually of small
size. Many possess eye-spots near the head. The males usually
have a number of pairs of special unicellular glands emptying through
slender ducts into the cloaca. These glands are usually arranged in
series of pairs toward the dorsal side of the body some distance in
front ot the spicula. Amphids, fairly well developed, usually difficult
to see because of their peculiar form and position; far toward front
of head, usually seen more or less in profile. Cardiac bulb relatively
shorter than in Spilophora, and not so distinctly subdivided. Males
usually- have well-developed series of ventral supplementary organs;
such organs are less common and less well developed on males of Spilo-
phora. Lateral elements of the transverse striae sometimes modified,
but rarely reaching degree of dififerentiation shown in Spilophora.

Representative species. . Chromadora minor Cobb 1893.

^ .6 9. . tS. '48' 86. .

£ \.i'"yir'-u 48 28 • Habitat: Pacific Ocean,

^ 6 8 3 ,4 _M 89 California, and Australia.

e \.i • ■ a:?/-- • ij 3'.8 • ic^i.i ■> '-'^ °^

Fig. 788. Chromadora minor.
I, male of Chromadora minor; II, one of the ventral accessory organs of the
same nematode; III and IV, head and anal region of the same nematode.
a, pharj^nx; b, eye-spots; c, esophagus; d, h, ventral supplementary organ;
e, nerve-ring; /, excretor>' pore ; g, gland of supplementary organ; f, renette
cell; j, organ of unknown nature, accessorj- to the renette cell; k, blind end
of testicle; /, cephalic seta; m, ribs of pharyngeal opening; n, papilla;
0, dorsal tooth; p, pharynx; g,one of the striae of the cuticula; r, subcephalic
seta; s, dorsal eye-spot; /, intestine; z<,one of the ventral male supplementary
organs; v, ejaculatory duct; u\ one of the supplementary organs; x, anus;
y, left spiculum; s, accessory piece.

33 (32) Amphids spiral, well developed Achromadora Cobb.

Genus proposed for the reception of Chrom-
adora minima Cobb and similar soil and fresh-
water species. Distinguished from Chromadora
by the presence of well-developed spiral am-
phids. The dorsal tooth is farther back and
is opposed by a small ventral "pocket" as
shown in the figure of Achromadora minima.
Species found, probably, in all parts of the
world. Known from Australia, Fiji, and
various parts of United States and Europe.

Representative species.

Achromadora minima (Cobb) 1914.

E>.

10 _ .

Male unknown. Habitat: Soil, El Paso,
Texas. Potomac River, Washington, D. C.
Fig. 789. Achromadora minima.

I, lateral view of a female; II, lateral view,
cuticular markings; III, lateral view of head.

a, cephalic papilla; h, cephalic seta; c. one of
the ribs of the pharynx; d, dorsal pharyngeal
tooth; e, subventral (?) phar>mgeal tooth; /,
pharynx; ,5, cuticular markings; h, amphid; f,
nerve cell; j, nerve-ring; k, spinneret; /, excretory
pore; m, flexure of ovar^^; n. one of the caudal glands;
0, blind end of posterior ovary; p, anus; q, intestine;
r, vulva; s, one of the granules of the intestine; /.
egg. (After Cobb.)

FREE-LIVING NEMATODES

491

34 (31) Pharynx cyathiform then prismoid, ending behind very definitely;

amphids distinct. . Etkmolaimus de Man*

Genus of two known sf)ccu>s. one Kuroiican one
American. Closely relatod to Chromadora. from
which It IS readily distinguished by the narrow uniform
posterior portion of the pharynx, which is usually
surrounded by a comparatively distinct pharyngi-al
bulb.

Representative species.

Ethmolaimus amerkanus C obb 1Q14.

[-

35 (30)

Labial papillae, apparently 12. Onchus thumb-
shaped, forward pointing, attached to a distinctly
thickened rib of cuticula which extends from the lip
region back to the base of the pharynx, and is thicker
anteriorly than posteriorly. Fully dcvdoiR-d ov.i arc
nearly twice as long as the body is wide, and one-third
as wide as long. Form, size, and number of eggs un-
known.

Habitat: Spring, Washington Country Club, Chevy
Chase, Md.

Fig. 790. Ethmolaimus americanus. Lateral view of a
female, a, lips; b, minute dorsal and ventral pharyngeal
teeth; c, one of the four cephalic setae; d. amphid: t,
pharynx; /, nerve-ring; g, excretory pore; h, nerve cells;
i, cardiac bulb; 7", beginning of the intestine; *, rcnclle
cell (?); /, beginning of main portion of the inicstinc; m.onc
of two pairs of unicellular organs of unknown significance;
w, cuticula; 0, one of the cells of the intestine; p. su(x:uticuU;
q and r, body cavity; s, vulva; /, nucleus of one of the
muscle cells; «, spinneret; v, one of the caudal glands;
w, anus.

Dorsal tooth minute, amphids circular. . . . Mkrolaimus de Man.

Amphids well developed.
Genus of few species from Europe
and North .America.

Representative species.

Idkrolaimus jhrciatilis
Cobb 1914.

as
ii'

The eggs appear to be deposited be-
fore segmeiitatinn begins. Sfxvimens
with one, and thn.se with two. (Svarics.
appear to be about cnjually numerous;
as no other dilTerence has been detected,
they are included for the present under
the same name and description.

Habitat: Maple River, .Michigan.
Fig. 791. Mkrolaimus ilutidtilis.

I. lateral view of female; II. head of
the same. / u •

a. mouth opening: b. one ol the six
cephalic papillae; c. one of the four cephalic
setae; </, one of the small phar>n»:c.il tcrlh;
e, excretor\- iwre; /. spiral amphid. f.
esophagus; A. ner\-e-nng; 1. car.luc
bulb: j. preliminar>- portion ol the in-
testine: k. renctte cell; /. bodv i-ivity;
m lumen of intc->itinc: w. one of the cclU
of the intestine; 0. anus: /. lie mi re in
posterior ovar>'; Q. uterus: r. blind rn.l o
posterior ovar^-; s, one of the tl.n-r v.uid*!
glands; /. spinneret: u, ckk>
w, cuticula.

.Iva:

(After Cobb.)

492

FRESH-WATER BIOLOGY

36 (23) Esophagus plain Cryptonchus Cobb.

Iff Y^^^y^^ PP Differs from Cylindrolaimns de Man in the form of the amphids,

and the strongly developed esophagus with its various regions, in
the presence of a dorsal tooth at the base of the pharynx and in
the absence of setae.

ccm

Single species.

Cryptonchus nudus Cobb 1913.

H

9 ...^..26; .'?.3'* ?.!.... ..> I 9 mm At a point about two

" ^ ^^ '^ body widths in front of

the cardia the nature of the esophagus suddenly changes, the
lining becoming notably less massive, and the radial structure
becoming relatively more massive, and at the same time changing
its character, so that there is a rather striking contrast between
this short posterior section and the main portion of the esophagus.
Wing space one-third as wide as the body. The anterior part of
the intestine for a distance equal to the body radius consists of
small cells packed wnth granules and possessing larger and differ-
ently formed nuclei. Eggs four times as long as the body is wide,
one-fourth as wide as long, and comparatively thick shelled;
uterus contains one at a time.

Habitat: Found about the roots of aquatic plants, Potomac
River, Arhngton, and in Douglas Lake, Mich.

Fig. 792. Cryptonchus nudus. lb, lip region; pp, labial papillae; am,
amphid; ph, pharynx; on, onchus or tooth; oe, esophagus; sp, spinneret.
XI81 '^^^^^^ Cobb.)

Pharynx without teeth 38

Esophagus with bulbs 39

Amphids circular or nearly so ; pharynx compound, much elongated. 40
Cuticular external marking of amphid circular. . . Plectus Bastian.

Genus of about thirty species mostly about plants. Some aquatic, none marine. Some
species, perhaps most, parthenogenetic or hermaphroditic. Obscure labial papillae usually present.

Representative species Plectus tubifer Cobb 19 14.

74 mm First lateral pore of the
cuticula immediately behind
the lateral organs, whence
79 mm. similar, somewhat smaller
pores, totaUing about two
hundred, form four subme-
dian rows. Six rounded, rather massive hps sur-
round the short, napiform vestibule leading to the
pharynx. Amphids transversely elongated or
roundish, open behind. There is an obscure, pos-
terior, more or less closed, elon-
gated, triquetrous pharyngeal
^ J k

sp

37 (14)

38 (49)

39 (42)

40 (41)

2.

II. 19.

■49"«

926

2.1

3.4 /— 3_5

3 2

2.3

I 9

10. 19.2 ■

'-Mi*

91 5

2.

•31.^ -3 A

36

}'-\i 3

XZ20

Fig. 793-
a, mouth; 6, papilla-like cephalic setae; c, lateral organ; J, pharynx; e, posterior chamber of phar\'nx;
/, esophagus; g, nerve-ring; h, excretory pore; i, renette cell; j, glandular (?) cell; k, cardiac bulb;
/, cardia; m, intestine; n, blind end of anterior testicle; o, spermatocyte; p, flexure in posterior testicle;
q, blind end of posterior testicle; r, junction of testicles; s, vas deferens; /, glandular (?) organ; «,
muscle to one of the three supplementary organs; v, anterior supplementary organ; w, spiculum; x, anus;
y, one of the caudal papillae; 2, spinneret, (.\fter Cobb.)

Plectus tubifer. Male,
lateral organ; J, pharynx;

FREE-LIVING NEMATODES

493

41 (40) Chitinous marking of amphid not circular. . . . Clironogast€r Cobb

Genus closely related to Plectus, differing in much elongated cardia. connecting mstcrior
esophageal bulb and intestine. Ovary single in Chrono^asler, double in PUclus ^''''^'■^^'

ra^ Single species known. . Chronogaster gracilis Col^b 1913. ^^ ^

5

II. .

25.

•56"

89

2

2 3'-

2.6

• 5.

16

2

12

25.

-M-"

92 7

9

1.9 / ■

2-i

2 4

9~XI 9

Male unknown. Habitat: Potomac
River; Douglas Lake, JNIichigan.

%,

Figs. 794 and 795. Clironogastrr Rraulis.
a, lips; b, papilla; c, cephalic seta; </. phar>'n\:

e, esophagus; /, posterior chamln-r of i)har>iut;
g, problematical organs; //, ner\'e-rin);; 1, excretory
pore; j, renette cell; /, valvular a|>i>aratus in
cardiac bulb; m, cardia; n, intestine; o. llcxurc in
ovary; p, nucleus of ovum; q, bliml end of ovarj-;

f, egg; s, vulva; /, anus: u. c.iuil.il uLind; r,
spinneret. (After Cobb. 1

42(39) Amphids apparently absent; pharynx simple 43

43 (44) Esophagus with two bulbs; males with bursa.

Rhahditis Dujardin.

Genus of numerous species, some parasitic, especially in insects.
Several marine species and a number in fresh water. Conimon in
decaying matter. Reproduction wonderfully varied, ranging from
parthenogenesis, through hermaphroditism of varying degree to com-
plete bi-sexuality. Many species microbivorous. In some siiecies
there is a marked alternation of generations.

Bursa better developed in species of Rhahditis than in any other
fresh-water nematodes. Other genera presenting this feature are
Tylenchus, Dolichodorus, and Oncholaimellus. Bursa (Fig. Ill)
consists of two thin lateral extensions of cuticula containing rays or
ribs, often tubular, constituting outlets of cement glands, always
well supplied with nerve endings. Form of bursa and arrangement
of its rays form good generic and specific characters.

Representative species. Rhahditis cylindrica Cobb 1S9S.

<-_ 12 n _ ^ J7_ 'Ji'l 91L \%mm.

<.— I 2 3J/ 4_3 4 9 1.6

Habitat: Wet soils.

(=

J6_
3.5"

3.7 4 2^5

Fig. 796. Rhahditis cvUndrica Cobb.

I, side view of female; II, side view of attached male; III, ventral view
of male tail. . . ,

a, pro.ximal end of spiculum; h, lip; c, base of pharynx; d, right spiculum;
e, bursa; /, anus; g, median bulb; h, nerve-ring; i, excretory pore; j, cardiac
coUum; k, intestine: /, one of the ribs of the bursa; w, egg containing
embryo; m, flexure in ovary; o, lips; p, pharynx; 9, segmenting egg;
r, median bulb; s, vulva; /, intromitted spicula; u, ejaculatory duct: r.
testicle; w, blind end of testicle; x, blind end of reflexed ovary; y, intestine,
z, anus. (After Cobb.)

wy^

494

FRESH-WATER BIOLOGY

44 (43) Esophagus with only one well-developed bulb; males without

bursa 45

45 (46) Pharynx long and narrow Rhahdolaimus de Man.

Genus of four known species, three European, one American.

Representative species Rhahdolaimus minor Cobb 1914.

c=

77 »

.......

The cuticula appears to be destitute of any but very
fine transverse striations, most clearly visible near the
head. Careful focussing appears to indicate the
presence on the outer margin of the head of almost
invisible papilla-like organs which may perhaps be
the representatives of cephalic setae. There are no
hps. The thin-shelled, smooth eggs are relatively
large and elongated and have been seen in the uterus
one at a time. They are about four to five times as
long as the body is wide and about one-fifth as wide as
long. They appear to be deposited before segmenta-
tion begins. The eggs are so large in proportion to the
size of the ovaries that they push the ovaries first to
one side and then the other as they develop, so that
both ovaries may occasionally appear to be either in
front of or behind the vulva. The specimen figured
was so twisted that the head presents the dorso-
ventral view, and the tiny amphids (a) therefore
appear in profile. The figure shows well the typical
distribution of nerve cells, large numbers in front of
and behind the nerve-ring, a smaller collection in the
cardiac region, and other collections in the anal region.
The long, slender spirmeret is characteristic of the
genus.

The figure illustrates the general features of the cen-
tral nervous system, which in nematodes consists of a
ring of ner\^e fibers encircling the esophagus,'and hav-
ing connected with it a number of more or less spherical
nerve cells, shown dark in the figure. Under favorable
circumstances each one of these cells can be seen to be
connected with others, and directly, or indirectly, with
the ring of fibers. The whole, therefore, constitutes a
rather complicated, coordinated system of nerve cells.
In many species the cells, such as those shown at c and
h, are arranged in longitudinal groups, and even where
the groups are not apparent, as here, the connections
among the cells are undoubtedly systematic and cor-
respond with the longitudinal grouping that is evident
in other genera. From the central nervous system
extend forward and backward nerves, — ventral, dor-
sal, lateral, and to a lesser extent submedian, connected
by commissures. Special collections of nerve cells
occur on the ventral side near the cardia, vulva, and
anus. The exterior indications of the nerves are found
in papillae and setae, usually corresponding in position
with the main branches of the ner\'ous system.

Habitat: Mud, Beach pool, Pine Point, Douglas
Lake, Michigan.

Fig. 797. Rhahdolaimus minor.

I, lateral view of female; II, head of the same, showing
amphid. The head m I is twisted, so that the amphid
appears as if ventral, or nearly so.

a, amphid; b, long, narrow phar>-nx; c, anterior group
ot nerve cells; d, nerve-ring; e, cardiac bulb; /, wall of
the mtestine; g, fle.Yure in anterior ovarj^; h, posterior
group of nerve cells; i, body cavity; j, lumen of intestine;
k, ovum; /, blind end of posterior ovary; w, egg; w, flexure
in posterior ovary; o, cuticula; /), caudal glands; 9, subcuticula;
r, vulva; s, rectum; t. anus; u, nerve cells (?); v, duct of
caudal glands; w, spinneret; x, lip region. (After Cobb.)

FREE-LIVING NEMATODES

495

47

46 (45) Pharynx not long and narrow

47 (48) Striae not resolvable into rows of dots Cephalohns Baslian.

Genus of numerous species, frequent about the higher plants, doubtless often at least "semi

parasitic.' Occasionally species in fresh water. Common in deaiying veirctable maticr
Some species are parthenogenetic, others hermaphroditic. Found on iht- surface of iiw( t^

Cephalobus resembles Rhabditis, but may readily be distinguished by the form of the r,l,ir\nx
and the nature of the male caudal armature. The pharynx of Cephalobus is ahnosi m-v.-r
cyhndroid or prismoid as in Rhabditis. On the contrary it tends to tafK-r more or less reKularlv
from the base of the hps backward. Though simple in form the pharynx is usually comixjuiKled
of two or three series of short cuticula elements separated from each (jtluT by transverse
breaks. In a considerable number of species the lips a.-j mjdiiied so as to bear more or less
complicated forward pointing cuticula appendages.
Such forms are intermediate between the typical
Cephalobi and other genera, such as Acrobelcs and
Wilsonema. The males of the Cephalobi do not
possess a bursa, at most showing faint indications of
such a structure. Nevertheless the papillae or ribs
found accompanying the bursa in Rhabditis are present
in Cephalobus, though they sometimes are less numer-
ous than on typical Rhabdites.

Not infrequently the ovary functions in the first
instance as a testis. Spermatocytes appear in the
young ovary even before an external sexual opening
exists. The developing spermatozoa descend the
oviduct and enter the uterus. Later the oocytes de-
velop and are fertilized by the spermatozoa previ-
ously produced in the same organ, — at least this
happens in some instances, and hence is assumed to
happen in all. So far no differences have been dis-
covered between spermatozoa produced in this way
by these syngonadic females and those produced by
the rarely occurring males. It is therefore fair to as-
sume that the sperm cells so commonly produced
in this way are potent. As in Rhabditis the renette
often takes the form of two long slender lateral ducts
ending bhndly near the anus. Some species may be
revived after remaining months or even years in a dry
condition.

Representative species.

Cephalobus suh-elongatus Cobb 19 14.

^

The thin, transparent, colorless layers of the naked
cuticula are traversed by about seven hundred plain,
transverse striae, resolvable with high powers without
very much difficulty. There are three rather distinct,
bluntly conoid lips, which are rounded in front; each
of them apparently has two inconspicuous innervated "^

papillae. The intestine is composed of cells of such a
size that probably only about two are recjuired to build
a circumference. The nerve-ring surrounds the esoph-
agus obhquely, and is accompanied by nerve cells, of
which the greater number are behind the nerve-ring
and in front of the cardiac bulb.

Habitat: Moss Bog, VV. End of Douglas Lake, Mich.

_ Fig. 798. Cephalobus sub-elongatus.
Lateral view of a female.
a, lips; h, pharynx; c, anterior portion of esophagus;

d, posterior extremity of anterior portion of esophagus;

e, nerve-ring; /, cardiac bulb; g, beginning of intestine;
//, one of the cells of the intestine; /, lumen of the
intestine; j, excretory pore; k, cardiac valve; /, re-
nette cell; m, flexure in single ovary; n, cuticula; o,
ovary; />, spermatozoon in uterus; q, vulva; r, nucleus in ^^^
ovum; 5, body cavity; t, anus; u, ripe ovum; v, unripe
ovum; w, oocyte; x, blind end of ovary; y, rectum; 2,
terminus. (After Cobb.)

t 8

15.

23.

•6151

94.

1.6

3./

J-6

■■4.3"

M

496

FRESH-WATER BIOLOGY

48 (47) Striae resolvable into rows of dots, altered on lateral fields.

Teratocephalus de Man,

Interesting genus of few species, with movable cuticular lips. Species have thus far been
found only in fresh water and wet soils, but the genus appears to have a world-wide distribution,
at least in temperate regions. Teratocephalus seems related to Cephalobus from which, how-
ever, it differs strikingly in the formation of the lips and pharynx. It is difficult to determine
the functions of the movable cuticular labial elements {a). The most reasonable assumption
appears to be that they are biting organs.

-Representative species Teratocephalus cornutus Cobb 1914.

The cuticula is traversed by about 1500 transverse
striae, resolvable into rows of minute dots, which are
modified on the lateral fields. The movements of
which the lips are capable are plainly indicated in
Figs. II and IV. The relatively large eggs are ex-
tremely mobile, so that they pass out through the
relatively small vulva without difficulty. Contact
with water, however, appears to harden the shell so
that after deposition the eggs have a more definite
and rigid form. These phenomena are characteristic
of the eggs of many genera, especially those in which
the eggs are of relatively large size. In the present
species the eggs are deposited before segmentation
begins. The general form of the tail, and its termi-
nus, would seem to suggest the presence of caudal
glands, but none have been seen.

The cardiac bulb so strongly developed in this
species is similar to that found in Rhabditis, Plectus,
Cephalobus, etc. It consists of three movable valves
rolling against each other, that can be pulled back-
ward by appropriate muscles. The arch over them
meanwhile remains rigid; thereby a vacuum (suction)
is produced. The minute striation on these valves
has suggested that they are triturating organs, but
the food habits would not seem to necessitate such
an assumption. It seems more likely that the
striations are due to such a disposal of the cuticula
as will give to the organs the necessary strength and
eflficiency. These valves act rapidly, often several
times per second.
Habitat: Maple River, Michigan.

Fig. 799. Teratocephalus cornutus.
I, lateral view of a female; II, lateral view of head,
more highly magnified; III, front view of head; I\',
dorso-ventral view showing lips wide open; V, cuticula
showing lateral field.

a, one of the six movable, cuticular lips; b, one of
the four submedian cephalic setae; c, amphid; d, nerve-
ring; e, excretory pore; /, organ of unknown signifi-
cance; g, cardiac bulb; h, intestine; i, anus; j, rec-
tum; k, cuticula; /, one of the cells of the intestine;
m, lumen of the intestine; nn, flexures in ovary; o, egg;
p, vulva; q, blind end of posterior ovary; u, terminus.
(After Cobb.)

49 (38) Esophagus without bulbs .... 5c

50 (57) Pharynx none.

51

51 (56) Caudal glands and cephaHc setae present 52

FREK-LIVING NEMATODES

52 (55) Amphids spiral.

4Q7
53

53 (54) Male supplementary organs papillate Hastiana dc Man.

Named in honor of the English nematologist Henry CharRon liastiaii, iSj7-igi4

Genus of slender nematodes with rather simple mouth parts. M:iK-s with a ventral row of
small supplementary organs extending over the greater part of the length of the body Half
a dozen species known. Occurs in Europe, America, JajKin, and .\ustralia.

Representative species Basliana exilis Cobb

[914.

P .4 6 _ 19. -M-O" 92.

£ ^ T — r2--^-i:4 2:--o^i.T ''"""•

The moderately thick layers of the
transparent, colorless, naked cuticula
are traversed by about eight hundred
transverse striae, which do not appear
to be further resolvable. These striae
exist in the outer as well as the inner
cuticula, so that the entire contour of the
body is crenate. Rather conspicuous
lateral wings are present, the optical
expression of which is two distinctly re-
fractive longitudinal Hues opposite the
lateral fields, separated from each other
by a distance somewhat greater than the
width of one of the annules of the cuticula.
There is a circlet of at least six cephalic
setae, of which the four submedian are
the longer, and are somewhat longer than
the head is wide. Possibly each of these
latter is accompanied by a shorter seta,
thus making ten in all. Apparently
labial papillae are present, but they have
not been sufficiently clearly seen to per-
mit of enumeration. From the rather
raised anus the conspicuous rectum,
which is twice as long as the anal body
diameter, extends inward and forward.
The tail is conoid, but tapers more rapidly
near the acute terminus. Nothing is
known concerning the renette.

Habitat: Fresh water, Tynne Station,
Fla.

Fig. 800. Bastiana exilis.

Lateral view of a male specimen.

a, one of the six cephalic papillae; b, one of the
posterior set of four submedian cephalic setae;
c, one of the anterior set of si.x cephalic setae; d,
esophagus; e, cervical seta;/, amphid; g, one of
the cells of the intestine; //, one of the numerous
male supplementary organs; /, blind end of the
two testes; the two testes join each other at n, the
complete development of the spermatozoa tak-
ing place between the locations indicated by /
and «; the junction of the testes with the vas
deferens is on the far side of the body and is
not shown; j, nerve-ring; k, posterior extrem-
ity of esophagus (pseudo-bulb); /, left spicu-
lum; m, cuticula; n, spermatozoon; o, anal mus-
cle; p, terminus; g, vas deferens; r, intestine.
(After Cobb.)

498

FRESH-WATER BIOLOGY

Male supplementary organs protusile tubes. Aphanolaimus de Man.

Genus of fresh-water nematodes,
of which nearly a dozen species are
known. Hermaphroditism occurs.

Representative species.

Aphanolaimus spiriferus
Cobb 1914.

X

.5

'7

9. _ 20.
■|.5' ■ 2.1

•50"«3 &
■31'

.2
.7

10. _ 14 (?)
l.l' ■ 2.

2 4 71

9

55 (52)
i

-V c

Viviparous. Two embryos and de-
veloping egg have been seen in each
uterus at the same time. Eggs,
about as long as body is wide, and
less than half as wide as long.

Habitat: Potomac River, Wash-
ington, D. C.

Fig. 801. Aphanolaimus spiriferus.

I, lateral view, anterior end of female;

II. lateral view, posterior end of female;

III, lateral view of head, more highly
magnified; IV, male supplementary
organ; V, lateral view of posterior ex-
tremity of male.

a, mouth opening; b, amphid; c, lumen
of esophagus; d, pigmented eye-spots (?);
e, intestine; /, nerve cell; g, rectum; h,
nerve-ring; /, anus; k, esophagus; /, cau-
dal gland; m, duct of caudal gland; n,
glandular body at base of neck; 0, spin-
neret; p, ejaculatory duct; q, intestine; r,
anterior end of cloaca; 5, right spiculum;
t, backward pointing accessory piece; u,
nerve cells (?); v, male supplementary
organs. (After Cobb.)

Amphids circular or ellipsoidal Tripyla Bastian.

Genus of toward twenty fresh-water
species, some at least carnivorous.

Representative species.

Tripyla lata Cobb 1914.

r ^ I J 7_ 20 '»'*'> 8_5_^ 2^ ^^,

7. „ .7 7_ 20 -M-5» 82 8 . , , ^^

p ' 2 1 — 3-2 Ji Ts — I?sTr\ ^■*'^'

In lumen of pharynx at a point re-
moved from anterior extremity a distance
a little greater than radius of head,
minute inward-pointing dorsal tooth,
having a length about equal to width of
one of the annules of cuticula, proving
that pharynx extends backward a dis-
tance equal to width of head. In some
specimens not far behind this point dis-
tinct transverse fold in lining of esopha-
gus.

Habitat: Alpine Lakes, Bald
Mountain, Colorado.

Fig. 802. Tripyla lata,
a, labial papilla; b, lip; c, amphid; d, sper-
matozoon; e, spermatocyte of anterior testis;
/, base of esophagus, pseudo-bulb; g, nerve-
ring; h, cuticula; j, esophagus; j, lining of
esophagus; k, intestine; /, posterior testis;
w, male supplementary organ; n, vas def-
erens; 0, retractor muscle of spiculum;
p, right spiculum; q, intestine; r, duct of
caudal gland; s, caudal gland; /, spinneret.
(After Cobb.)

FREE-LIVING NEMATODES

4og

56 (51) Caudal glands and cephalic setae absent

. . Alaimus de Man.
The species of this small kciius have a
rather simple structure. All are slender.
Some appear to be parthenoKeiictic.
Representative species.

Alaimus simplex Cobb 19 14.

r . I?.. . "■ r- " »■«• 92

I. .J .e'^"':9 i i 6 ' ■■

r . ;2. . 7. _ 1$ M 94

Very minute striations in subcuticula at
extremities, under favorable conditions.
Obscure traces of lateral winRs. Krks ap-
parently deposited before segmentation be-
gins. Whether two testes or only one not
determined. Broad, nninded, blunt end of
testis, located as far behind base of neck as
latter is behind anterior extremity.

Habitat: Big Lake, Fla.

Fig. 803. Alaimus simplex.

I, lateral view of a female; II, anterior ex-
tremity, lateral view; III, posterior extremity
of a male, lateral view.

a, lip region; b, phar>'nx; c, amphid; d,
amphid, enlarged; e, group of spermatozoa at
posterior portion of ovarj- ;/, blind cnfl of ovary;
g, male supplementary paijillae; h. left spicu-
lum; i. terminus; 7, submedian elevation or flap
indicating rudimentary bursa; k, egg; /. vulva;
w, nerve-ring; «, posterior extremity of esopha-
gus; p, modified cells of anterior intestine; (j,
cuticula; r, wall; 5, lumen of intestine; /, flexure
in single ovary. (After Cobb.)

57 (50) Pharynx present 58

58 (59) Pharyngeal cavity relatively large, amphids very small if any.

Prismatoldimus de Man.

Well-characterized genus consisting at present of four
or five species. This genus resembles Monhystera to a
certain extent.
Representative species.

Prismatolaimus stenurus Cobb 1914.

£=

Behind each amphid, at a distance equal to the width
of two to three annules of the cuticula, there is a short
seta. The ovaries are moved backward and forward
in accordance with stage of development of eggs. These
latter appear to be deposited before segmentation begms.
Notwithstanding the slenderness of the tail caudal glands
and a spinneret are present.

Habitat: Roadside pool, Douglas Lake, Michigan.

Fig. 804. Prismatolaimus stenurus.

side

I, lateral view of a female; II. front view of head: III,

Tone'ofthe six cephalic papillae; 6, one of the ten ccphalk
setae; c, one of the six thm lips; d, pharynx; e ^mph 1 /.
lumen of the esophagus;..^- nerve-nng; h cu .cula; •• n"-;''^
of ovum; j, vulva; ^, bhnd end of l>«Jt«-"r'«^,^."^;'^J ; '■ ^ ^
beginning of the intestine; n. one of the cells of the ^^i'"' -;'/f«^
Einef ., rectum; />• ^""^^'Z' «"^ "^^i7,^■:'Sl^l3t"^*'• ''
flexure in anterior ovary; 5, spinneret. (After Lobb.)

500 FRESH-WATER BIOLOGY

59 (58) Cavity small, amphids usually well developed.

60

60 (61) Form of cavity conoid, open in front; circular amphids considerably
behind it • Monhystera Bastian.

A large, aquatic genus of which about one hundred species are known. Many marine.
Some found in soil. Many species feed upon diatoms. Probably no other nematode genus
is so widespread as Monhystera. In any collection from land or from fresh or salt water the
first specimen to come to view often proves to be a Monhystera. The species are very numer-
ous and the individuals surprisingly so. Brightly colored eye-spots are more common than in
any other fresh-water genus.

Representative species Monhystera sentiens Cobb 1914.

t=»,i

6

7

. 22.

-7262

88.

6

■3 1

43

48

31

7

9

. 22

-M-71

87.

6

29

3 5

4 2

^33

The striae are more readily visible
toward the extremities, especially the
posterior extremity. The lips appear
to be three in number, and are longi-
tudinally striated or fluted. The
anterior portion of the intestine is
somewhat bulbous in form, and is
separated from the esophagus on
the one side and the true intestine on
the other, by a pair of constrictions.
This portion may perhaps be looked
upon as a strongly developed cardia.
The lateral fields vary in width in
different parts of the body. A httle
in front of the anus they are about
two-fifths as wide as the correspond-
ing portion of the body, and contain
rather numerous scattered nuclei of
such a size that about eight would be
required to reach across the field.
A Httle farther forward the field is
narrower. Anteriorly it is wider
again. The blind end of the anterior
testis is located a short distance behind
the nerve-ring, while the blind end of
the posterior testis is located about as
far in front of the anus as the ter-
minus is behind it. The testes are
broad and in some parts appear to
fill up the main portion of the body
cavity.

Habitat: Sand bar off Plummer's
Island, Potomac River.

Fig. 805. Monhystera sentiens.

I, side view of a female; II, side view of head of the same; III, side view of posterior extremity of a
male.

a, pharynx; b, submedian cephalic seta; c, lateral cephalic seta; d, spermatozoon; e, amphid; /, lining
of esophagus; g, esophagus; /;, subcephalic setae; i, lumen of intestine; j, nerve cells; k, nerve-ring;
/, striated lip region; m, left spiculum; n, cell-nucleus associated with amphid; _ o, blind end of
single ovary; pp, the three caudal glands; q, anal muscles; r, spinneret; s, beginningof intestine; t, anus;
u, one of the cells composing the intestine; v, vulva; w, egg, the spermatozoa "d" being outside of the egg
"w"; *, egg in synapsis; y, vaginal glands; 2, ovum. (After Cobb.)

FREE-LI\^NG NEMATODES

;oi

6i (60) Form of cavity various, closed in front, amphids opposite it. . (ji

62 (63) Lateral organs or amphids inconspicuous Trilolnis Bastian.

Fresh -water genus of which about half a dozen species are known. Known to fee.l u[xjn
diatoms in one case and upon rotifers in anotlier. Hermaphroditism occurs.

Representative species Trilobus longus {W\i\y) 1)^,-^1.

.3

7.

19.

'Ab'iO

89.

2 8/

3.8

4.6

2.3

3

8.

14.

-M-

92.

2,6/

3.2

3.8

t"N2.7

source of nourishment of this species,
about one-fourth as wide as the body.

The lips bear papillae but their numlier i.<i not
„ known. The intestine frequently contain.s rliatoms
in large numbers, indicating that these are a comm<jn
The longiitudinal fields are distindly develoi)cd, and
From the slightly elevated vulva the vagina leads in-
ward at right angles to the ventral surface fully half way across the body. The rcllexwl
ovaries pass about two-thirds of the way back to the vulva. Two or tiiree eggs may <Kcur in
each uterus at one time. These are somewhat ellipsoidal and thin shelled, being al)out two-
thirds as long as the body is wide and about two-thirds as wide as long. The eggs ap[X'ar to
pass through at least the early stages of segmentation before being deposited. The waits of
the vagina present the peculiarity of being very thick, and composed of six to .seven tun-
centric layers so that the organ is considerably broader than it is deep. Its intcrnAl wall
presents the peculiarity of staining strongly with carmine.

Trilobus longus, the only American fresh-water nematode outside the Mcrmithidac that had
been adequately characterized previous to the inception of this chapter, was de.scribed by the
famous Philadelphia naturalist, Dr. Joseph Leidy, in 185 1. At that time extremely little wa^
known about the free-living fresh-water nematodes, and no one dreamed of their vast numlxrr
and variety. The peculiar male supplementary organs of Trilobus did not fail to attract atten-
tion, and it is owing to this fact that Leidy's name is associated with the striking sp)ecic3
selected as a representative of the genus.

Habitat: Mud about the bases of aquatic plants, in pools, ditches, rivers, and lakes through-
out the country.

Trilobus longus.

T, male; II, head, lateral view; III, head, lateral view; IV, head, ventral view; V. anterior supple-
mentary organ; VI, posterior supplementary organ; VII, two supplementary organs from an exceptional
female.

a, lateral seta; b, papilla; c, submedian seta; d. pharynx; r, lateral organ; /, toiUh; .c. toj)lh; *• «^Jj|J':
agus; /, nerve-ring; i, excretory pore; k, body muscles; /, glandular!?) organs; w. intestine; «• W'"'|
end anterior testicle; 0, testicle; p, junction of testicles; q, blin.l-cnd posterior testicle; r. va> *>^'^'^:
5, nerve of supplementary organ; t, cavity of supplementary^ organ; u, left spiculum r. acccs^ r> piece,
w, the three caudal glands; x, anus; y, terminus; z, aix-x of supplementary organ. K.\\\cx Couu.;

;o2

FRESH-WATER BIOLOGY

63 (62) Lateral organs or amphids more or less conspicuous spirals or circles.

Anonchus Cobb.

Genus of which a single species is known. There are indications of folds surrounding the
mouth opening, so that in all probability the lips may be opened outward as in Mononchus.

Single species known Anonchus monhystera Cobb igis ■

pe jy--3------3 7--'^j--®|^^-> I mm. Lateral fields occupied by about forty internal

ellipsoidal bodies, rather equally spaced in two series.

Y=<f *---i^^^^: ?* ^^-> I. mm. Cardia slender, as long as the neck is wide. The

~ ^' ■' '' ^' ''^^' twenty tubular male supplementary organs are con-

tinued to the head by a series of about seventy minute ventral depressions.
Habitat: Mud about the roots of aquatic plants, Potomac River.

XI39

Fig. 807. Anonchus tnonhystera.

Fig. 808. Anonchus monhystera.

a, mouth opening; b, pharynx; c, cephalic seta;
d, lateral organ; e, esophagus; /, cellular body in
lateral field; g, nerve-ring; h, excretory pore;
i, cardia; j, anterior end of intestine; k, renette
cell; /.lumen of intestine; m, blind end of testicle;
n, testicle; 0, spermatozoa; p, one of the numerous
supplementary organs; q, anus; r, accessory piece;
s, one of the caudal glands; /, terminus; u, right
ppiculum. (After Cobb.)

a, mouth opening; b, cephalic seta; c, chitinous
element, anterior portion of pharynx; d, pharynx;
e, spiral amphid; /, radial musculature of esoph-
agus; g, lumen of esophagus; h, cuticula; i,
ampulla of gland (?); j, body wall. (After Cobb.)

FREE-LIVING NEMATODES -o^

64 (i) Posterior region of intestine atrophied; anus vestigial or absent.

Family Mermithidak . . 65

The forms included in this group are of some size, being notably larger than those in the
first section of the nematodes. These often reach lo to 20 cm. in length They are more
or less opaque so that the mternal structure cannot usually be determined by sut>cr
fjcial exammation of the living ammal. The intestinal region of the alimentary canal' is re-
duced to a mere cord of cells without any cavity, or may be entirely wanting for a |>ortion of
the length. The anus if discernible at all in the female has the form of a mere shillow dcnl
in the external surface of the cuticula to which the vestigial remnant of the intestine is attachctl
In the male the terminal portion of the intestinal canal persists as the genital duct cloaca an<l
the anus functions as its orifice, but the intestinal tube is atrophied in front of the ixiint at
which the sexual canal joins it. These forms are parasitic in larval life and do not feed during
the adult stage of their existence. The latter may be passed either in water or in the stA\
though the species are more frequently reported from the latter. By virtue of likeness iti
habit and to some extent also in external form Mermithidae are often regarded as related to the
"hair snakes" (Gordiacea) to which, however, they bear no real structural resemblance. They
are the so-called "cabbage worms " which from time to time enjoy transient newsjjaper notoriety
on account of their supposed poisonous character whereas really they are harmless.

The American Mermithidae are very little known. The following key to the cstablishwl
genera will be of service to the student in allotting any of his discoveries to the proper genua

65 (66) Hypoderm with only two longitudinal fields; cuticula with criss-

cross fibers; spicula two N comer mis von Linstow.

66 (65) Hypoderm with more than two longitudinal fields 67

67 (78) Longitudinal fields six 58

68 (73) Cuticula without criss-cross fibers 69

69 (70) Spicula two Mesomermis Daday.

Representative species Mesomermis virginiana Cobb iqi 4.

There are minute longitudinal striations throughout the body. These are interrupted on the
lateral jines where there is a distinct wing. There is no distinct pharynx. The mouth pore is
very minute and is located a little toward the ventral side of the middle of the front of the head.
The cuticula is penetrated on the head by a number of innervations which end in minute depres-
sions on the surface of the head. Near the mouth opening there is one of these depressions on
the dorsal side, and apparently a similar one on the ventral side, while nearer the outer margin
of the head there are two ventral submedian and two dorsal submedian similar depressions.
Pores occur also here and there on the body, as well as on the neck. The lateral organs present
the following appearance when seen from the side: They appear to project from the surface
of the body very slightly, beginning as a tube having a length about one-third as great as the
corresponding diameter of the head. This tube has very thin walls, and, a short distance in.
apparently near the surface of the body, a second element appears in the form of a circle inside
that representing the contour of the outer tube. This appears to constitute a sort of core In
the midst of which are a number of refractive elements, resembling ner\x- fibers, which pass in-
ward and backward toward the lumen of the esophagus. Some of these elements are longer
than others. The focus passing inward picks up one, then two, then several more, st) that by
the time a view is obtained that is wholly inside the body there are seen a half dozen or more
of these elements. It is impossible in this view to pick up the internal connections of thes<-
refractive elements. The lateral fields are about one-third as wide as the body. The tail of
the male bears several series of innervated papillae. These papillae are arranged on the ventral
submedian Hnes as .well as on the ventral line. The ventral papillae just in front of and jii^t
behind the anus are double. In the submedian rows there are four on the tail — one opjjosite
the anus, one a little farther back, a third near the middle of the tail, and a fourth considerably
farther back. In front of the anus on each side there are eight submedian papillae occupying .1
distance more than twice as great as the length of the tail; the distance between the successive
papillae increases with the distance from the anus, so that the space between the st-venth and
eighth is about two-thirds as great as the diameter of the body. Of the median papiltu; on the
tail there are three, two near the anus and one just in front of the middle of the tail, with |x)s
sibly a fourth farther back. Of the median papillae in front of the anus there are two near the
anus, and ten additional ones about coextensive with the submedian papillae, and distributiti in
the same manner. There are two outstretched testes, the posterior a little shorter tli.m tin-
anterior.

Co A 6 - " -M-« %. Habitat: Cranberry bog, Arlington Farm, \irpini.i.

504

FRESH-WATER BIOLOGY

^

m

mi

rx 334 ,

Fig. 809. Mesomennis virginian.i.

a, mouth opening; h, anterior circlet cephalic papillae; c, posterior circlet
cephalic papillae; d, pharyngeal tube; e, outer margin lateral organ;/, strands,
lateral organ; g, esophagus; h, papilla; i, unicellular organs of uniinown signif-
icance; j, nerve-ring; k, esophagus; /, intestine; m, ejaculatory duct; n, body
wall; 0, one of the oblique copulatory muscles; p, one of the submedian sup-
plementary organs; q, one of the ventral supplementary organs; r, spiculum;
5, one of the caudal ventral supplementary organs; t, subventral caudal sup-
plementary organ. (After Cobb.)

X 120

Fig. 810. Mesomermis virginiana.

a, mouth opening; b, lateral organ; c, esophagus; d, nerve-ring; e, posterior end esophagus; /, intestine;
g. blind end anterior testicle; h, testicle; i, junction of testicles; ;, intestine; k, blind end posterior
testicle; /, ventral supplementary organs; m, submedian supplementary organs; », oblique copulatory
muscles; 0, spiculum. (.After Cobb.)

FREE-LIVING NEMATODES

70 (69) Spiculum single.

71

71(72) Vagina of the adult cylindroid, S-shapcd. . . Li mnomcrmis D.i&^y.

72(71) Vagina tubular (?) not S-shaped P sc ud 0 mc rm i s ^kM^n

73 (68) Cuticula with criss-cross fibers. ...

/4

74(77) Vagina of the adult S-shaped

75 (76) Spiculum single Paramermis von LinstoNv.

76 (75) Spicula two Mermis Dujardin.

77 (74) Vagina of the adult not S-shaped BaUiymcrmis Daday.

78 (67) Longitudinal fields eight -g

79(80) Cuticula without criss-cross fibers H ydromcrmis CorU.

80 (79) Cuticula with criss-cross fibers Eiuncrmis Dadav.

IMPORTANT REFERENCES ON FREE-LIVING NEMATODES

Bastian, C. 1865. Monograph of the Anguillulidae. Trans. Linn. Soc,

Lond., 25: 73-84; 5 pi.
BuTSCHLi, O. 1873. Beitrage zur Kenntnis der freilebenden Nematodcn.

Nova acta caes. leop., 36: 144; 11 pi.
Cobb, N. A. 1913. New Nematode Genera Found Inhabiting Frc-sh-

Water and Non-Brackish Soils. Jour. Wash. Acad. Sci., 3: 432-444.
1914. The North American Free-living Fresh-Water Nematodes. Trans.

Amer. Micr. Soc, 2>i\ 69-134; 8 pi.
De Man, J. G. 1884. Die frei in der reinen Erdc und im susscn Wasser

lebenden Nematoden d. Niederlandischen Fauna. 206 pp.; 34 pl-
Jagerskiold, L. a. 1909. Freilebende Siisswasserncmalodcn. Siisswasscr-

fauna Deutschlands, Heft 15; 46 pp.; 65 figs.
Maupas, E. 1899. La mue et I'enkystement chez les Nematodes. Arch.

zool. exper. (3), 7: 562-628; 3 pl.
1900. Modes et formes de reproduction des Nematodes. .\rch. zcx>I.

exper. (3), 8: 462-624; ir pl.
MicoLETZKY, H. 19 13. Freilebende Susswassernematoden der O.^talpen

Sitzber. Kais. Akad. Wiss. Wien, Math.-natunv. Kl., Abt. I, 122 : in

122, 543-548.
Steiner, G. 1913-1914. Freilebende Nematoden aus der Schweiz. Anluv.

Hydrobiol. und Planktonk., 9: 259-276, 420-438.

CHAPTER XVI
PARASITIC ROUNDWORMS

By henry B. ward

Professor of Zoology in the University of Illinois

The roundworms or Nemathelminthes constitute a group of
convenience into which are put three classes that have Httle in
common except general external appearance. But even in this
feature differences of a real character appear on closer examination
and the study of internal anatomy fails to show any intimate
agreement in the fundamentals of structure. The three classes
embraced in this phylum are the Nematoda or true roundworms,
the Gordiacea or hairworms, and the Acanthocephala or probos-
cis roundworms. All agree in the elongated generally cyKndrical
form, and in the uniform or monotonous external appearance.
The Nematoda show nearly always some taper toward one or both
ends, being thus spindle-shaped rather than truly cyKndrical, and
possess a smooth, glistening, colorless external surface. The Gor-
diacea are larger, more uniformly cyKndrical with blunt rounded
ends and an exterior at least faintly colored in whole or in part.
The Acanthocephala show a roughened surface sometimes with
imperfect rings around the body, and the form usually Kke a
carrot is always somewhat irregular. These differences are general
and subject to exception but with practice one can usually separate
members of the three groups at sight, and the structure is so differ-
ent that it is wise to consider each group separately in an inde-
pendent section of the chapter.

Biologically the three classes show certain contrasts. The Nema-
toda include many free-Kving forms and many others purely
parasitic, but most of the latter have brief free-living stages during
which they achieve the transfer to a new host. The Gordiacea are
parasitic during early Kfe and spend the adult existence free in
water bodies. The Acanthocephala are among the most highly
specialized of parasites as they have no free-living stages at all

506

PARASITIC ROUNDWORMS .q-

and as there is no trace of an alimentary canal at any sta^c of
development.

In collecting parasites one may find adult Xcmatoda and
Acanthocephala side by side in the same intestine but the latter
rarely occur outside the alimentary canal and nematodes often do.
The Gordiacea are parasitic in larval stages normally in the Ixxly
cavity of Insecta and are found only infrequentl\- in other hosts.
They are most commonly found as adults in general a(|uati( col-
lecting and are well known even to the casual observer of life in
ponds and ditches under the popular designation of " Hair Snakes."

The technic of handling the roundworms is not simple. Para-
sitic nematodes are collected in the manner already described for
parasites in general (p. 368), but owing to the very resistant cutic-
ula and delicate structure of these worms great care is necessary
to avoid injuring specimens seriously. Those which are loose can
be picked up with a fine camel's hair brush. This instrument is
most convenient in the handling of small species. Many species are
so firmly attached to the intestinal wall that it is difficult to remove
them without injury. Gentle manipulation if prolonged will usu-
ally loosen the hold, but the body is easily lacerated by grasi)ing
it with forceps other than very lightly or the mouth parts are often
torn by pulling the worm too hard. Encysted forms should be
freed from the cyst under a dissecting lens with fine, sharp needles.
A very good needle is made of a glass rod drawn out to a point.
Most nematodes are very sensitive to changes in osmotic pressure
and are badly disfigured by rapid changes. Living specimens
should not be put into distilled water or normal salt solution.
Tap water is fairly good and for nematodes from fresh- water fish
a 0.3 per cent salt solution is best, but material should not be
left in such a fluid longer than absolutely necessary.

The resistant cuticula prevents the entrance of cold killing
solutions so thoroughly that these worms live even hours in lluids
that kill other parasites promptly. Hot fluids coagulate the body
proteins and preserve specimens well extended. Xo successful
methods of narcotization have yet been worked out. The killing
fluid recommended by Looss is all in all most useful; it is made
by adding to alcohol (70 to 85 per cent) from 5 to 10 [>er cent

5o8 FRESH-WATER BIOLOGY

glycerine. This fluid is heated over a flame in a beaker or thin
watch glass until it begins to volatiUze, or more precisely to a
temperature of 56° to 60° C. The worms in a minimum amount
of fluid are dropped into the beaker, whereupon most forms
straighten at once. Specimens are preserved permanently in this
mixture and by allowing it to evaporate slowly one can bring them
gradually into strong glycerine in which they can be studied. This
method is especially good for mounting in to to. For histological
details nematodes should be killed in a mixture containing equal
parts of acetic acid, alcohol, and water, which has been saturated
with corrosive subHmate and to which has been added 0.25 per cent
osmic acid.

Formol can be used to advantage only in the lactophenol quick
method. Nematodes are killed in 2 to 5 per cent formol and after
lying there 2 hours are gradually transferred to a solution com-
posed of I part glycerine, i part lactic acid, i part phenol, and 2
parts water. The transfer should be timed to bring them at the
end of 6 hours into the pure solution.

Lactophenol specimens are mounted in the same fluid in a pre-
pared cell. Glycerine-alcohol material is mounted in strong glycer-
ine into which it has been carried gradually by evaporation. When
material must be stained and embedded for sectioning, or mounted
in balsam, treatment is very difficult and results are uncertain. In
general ah changes must be gradual and as deliberate as possible.
The simplest method is to employ a string siphon made by placing
three stender-dishes in a stair-step series, with the worms in the
middle dish and the fluid into which they are to be transferred in
the top dish while the waste flows into the bottom dish. String
siphons lead into and out of the center dish and the amount of the
flow is regulated by the size of the string.

The differentiator (Fig. 811) is a very valuable aid in nematode
technique. Worms are placed in the small tube a and the tube h
is filled with the fluid into which they are to be transferred. The
very fine tip regulates the flow of the fluid. When in absolute
alcohol they can be taken out and brought into a clearing fluid
by the siphon method, or the differentiator may safely be used
by extending the fine tip e, and leaving out the mixing

PARASITIC ROUNDWORMS

509

chamber. The best clearing fluids are synthetic oil of wintcrgreen
(methyl saHcylate) and xylol. As stains, Delal'icld's hematoxylin,
EhrHch's acid hematoxyUn, and Mayers' para-
carmine give good results. For sections the first
two are advised, also a stain made by saturating
a one per cent phenol solution with thionin.
Special methods were worked out on the nerv-
ous system by Goldschmidt. Nematodes may
also be studied by staining intra vitam by
thionin without phenol and by methylene
blue.

When specimens are to be transferred to bal-
sam or damar, it is wise to pierce the body
wall with a fine needle. Some skill is necessary
to avoid injury to internal organs. When
transferring the worms to thin balsam place
them in paper cups and allow the medium
to dialyze into them. Sections are difficult to
make but possible by the use of very hard
parafhn and great care in making the transfers.
Vacuum embedding is helpful in securing good
infiltration.

For Gordiacea the alcohol-glycerine method

Til • II- iiG.Bii. iJin

IS useless; on the whole the corrosive subli- for dchydratin*:.

voir; b. ol)jcct holders; c,

mate-acetic mixture works best, but should be ^^^}-" ^"'' r^Kuiation dr-

^ vice; J. s;ifclv tube; *.

used warmed to 56° or 60° C. In other respects J^^iShoriu-i Jl

Fig. 81 1. Differentiator

here also.

The re»-
I meters

the instructions for nematode technic apply ISdTn'^thc &". Tui

filling avoid bunhlcs t.
end piece of ditTerentiator

The Acanthocephala are best killed and fixed pi[-ce \i"diiTcrcntutor fJr

^ . . . alcohols. (After MaK'.ith.)

in the corrosive sublimate-acetic mixture and

In general methods

do not come out well in glycerine-alcohol,
used for flatworms work well with these forms also, but for
more precise results on any of the roundworms each worker
must develop a special technic. (Compare further Looss,
Ransom, Magath.)

The following distinctly artificial key ma\' be used to separate
the three classes of Nemathehninthes; it must be supplemented by

5IO

FRESH-WATER BIOLOGY

reference to the longer discussion in the opening paragraph of

this chapter.

A (B) With anterior, protrusible proboscis covered with rows of recurved

hooks Class Acantbocephala (page 542)

B (A) Without proboscis at anterior end C

C (D) Adult free-living, aquatic, long, cylindrical, with posterior end bifid

or bluntly rounded Class Gordiacea* (page 535)

The family of the Mermithidae (page 534) agrees in some of
these particulars with the Gordiacea, although the structure shows
that these species are true Nematoda and not Gordiacea; they are
readily distinguished by the acutely pointed posterior end and
terrestrial habit.

D (C) Adult usually spindle-shaped, tapering rather than cyHndrical. Pos-
terior end never bifid or bluntly rounded, usually acutely
pointed, occasionally peculiarly modified in form.

Class Nematoda . . E
E (F) Free-living during entire life cycle. Adults small, transparent.

Free-living Nematoda (page 459)
F (E) Parasitic during most or all of the life cycle. Larvae small, transpar-
ent; adults variable in size, often more or less opaque.

Parasitic Nematoda
Parasitic Nematoda

The nematodes are easily recognized by their appearance, which
has given them the common name of round- or threadworms.
Most of them are small, measuring only a few millimeters in length
and a fraction of a milhmeter in diameter, and resemble a fragment
of a violin string. A few of the larger sorts reach a length of
several centimeters or even a meter. . The external surface is usu-
ally smooth and glistening and the body is not divided into joints
or segments. In some cases a fine surface striation is present
which appears under a lens as delicate circular grooves; the
exterior may also bear irregular beaded tubercles or fine scales,
spines, or hairs. When present these are usually confined to
certain regions and the remainder of the surface has the typical
nematode appearance.

The body tapers slightly towards one or both ends and only
very rarely can one find marked differences in diameter or dis-

* Some authors designate the class Nematomorpha and rank the Gordiacea as an
order under it.

PARASITIC ROUNDWORMS

tinguish adjacent regions by other prominent features. As a rule
the anterior end is sHghtly blunter whereas the posterior end i> more
pointed. The uniformity of external appearance is very charac-
teristic of nematodes. This creates an impression of monotony
in structure and renders their classification difficult. The smaller
forms are somewhat transparent in life but the larger species are
opaque.

One may also recognize a nematode easily by its peculiar type
of movement, which in a Hquid medium consists of a more or less
rapid and violent coifing and twisting alternately right and left
without appreciable progress, but is modified by the presence of
sofid particles in the fluid into a powerful serpentine nioxemcnt
winding in and out among the debris. This grows in etTectiveness
as the material becomes more nearly sofid and the particles are
less readily pushed aside by the twisting of the worm.

In external features the parasitic species appear somewhat dif-
ferent from the free-living forms. On the whole they are much
larger, thicker and more opaque. Few species are as minute as
free forms and only these minute types approach the free species
in transparency. The external form is also more monotonous
since the delicate hairs and scales that distinguish free species arc
almost entirely wanting. Eyes, amphids, and setose tactile organs
such as already described for free-Hving t>pes are not present in
parasitic species.

Parasitic nematodes occur in nearly afi w^ater-living vertebrates;
they are also often found in insects. In crustaceans and worms they
are much less frequent and in any other forms their presence is un-
usual. While adult forms are found in aU hosts, yet the immature
stages are more frequent in hosts from the lower groui)s nuntit)netl
and less common in the higher vertebrates. The encysted worms
are usually larval forms. The adults frequent commonly the
alimentary canal, though some species occur regularly in con-
nective tissue and rarer types in other parts of the bodw IjicxstiMl
larvae may be found almost anyw^here.

In structure the parasitic threadworms manifest great similar-
ity to the free-living species and in view of the detailed treatment
given the latter in the last chapter it will be necessary in the prcs-

512

FRESH-WATER BIOLOGY

ent general discussion to refer prominently only to points of con-
trast or to features peculiar to parasitic forms. For further
structural details the student should consult that discussion which
should be read in connection with the following description. Some
parasitic nematodes are apparently indistinguishable from free-
living species, others are classed in the same genera or families,
but there are also large groups that contain no free-living species
and are highly modified for a parasitic existence. In general the
smaller transparent species show the greatest similarity to the free-

FiG. 8i2. Ascaris lumhricoides . a, top view of head; dorsal Up with two sensory papillae and ventra
lips with one each; the shaded areas indicate the muscle attachment, b, lateral view, showing ventral
lips. Magnified. (After Leuckart.) Camallanus ancylodirus. c, ventral view of head, X i35; <^> lateral view
of head, X 135. (Original.) Necator americanus. e, head of young male, dorsal view, X 160; /, head of
young female, from the right, X 160. (After Looss.)

living species whereas the large opaque forms depart most widely
from that type. In general organology, microscopic structure of
cells and their arrangement in layers, as well as in fundamental
features of reproduction and development, the parasitic nema-
todes agree substantially with the free-living forms and manifest
their recent differentiation from them.

The anterior end or "head" of a nematode is usually slightly
truncated or bluntly rounded and shows under a lens the presence
of lips, papillae, spines, teeth and other special structures.

In reality the numerous modifications of the anterior end may

PARASITIC ROUNDWORMS

513

be reduced to a few fundamental types (Fig. 812). In the first
the tip of the body is unarmed or at most provided wiili a few
minute papillae arranged around the mouth opening wliich is a
minute circular orifice. In a second, three lips are present, a large-
dorsal and two smaller ventro-lateral, which border a l.rian;;ular
mouth. In a third, the oral aperture is a dorso-ventral slit guar(le<l
by two lateral jaws often called lips but very distinct in form and
function from the triple labia of the second type. In the fourth
class one finds a hollow cup-shaped capsule with an entire margin
which in lateral aspect resembles the jaws of the third type but is
very unlike them in general plan. The capsule is a powerful
sucking organ, the jaws act as a grasping organ like a vise or pin-
cers, the lips are weaker and more varied in movement. These
main types of oral apparatus are modified in so manv directions
that it is often difficult to comprehend the general t}'pe inNoKcd
in a compKcated case.

The mouth cavity may be tubular, funnel-shaped, or even ex-
panded into a globular or oval capsule or pharynx. Following
this region comes the esophagus which is either muscular or
capillary. The muscular type is prominent, thick walled, and tri-
angular in cross section (Fig. 813, a), with the muscle fibers perjKMi-
dicular to the lumen. By the contraction of these tibrrs the
cavity is enlarged and the a

organ acts as a pump to
draw in food. The esophagus
may be differentiated into
two regions, one clearly mus-
cular and the other granu-
lar, or the single muscular
region may have large (sali-
vary?) gland cells in its wall.
It is frequently terminated by a spherical bulb which contain>> a
valvular apparatus. In some cases this bulb is double. The
cavity is fined by an inturned layer of the external cuticula wliieh
terminates at the bulb. This is the type of esophagus found in
free-living forms (see Chapter XV, p. 461, Fig. 766). The
capifiary esophagus (Fig. 813, b), consists of a minute clfitinous tube

Fig. 813. a, Aiuylosiomu diunlcnaU. Trans-srction vi
the esophagus, magnified, (.\ftcr Looss.) b. Truknuima
conlortum. Transverse section of esophagus, magnified.
(After von Linstow.)

5U

FRESH-WATER BIOLOGY

surrounded by a row of granular cells but without muscle elements.
It does not terminate in a bulb though the end of the cell row may
be slightly enlarged.

The esophagus opens directly into the following region which is
commonly termed the intestine. It is the digestive portion of the
canal and is without any cuticular Hning. The cavity is of con-
siderable size and Hned by large cells rich in protoplasm. This
region changes gradually into the narrow terminal section of the
canal, known in the female as the rectum, or in the male as the
cloaca, since the duct of the sex gland joins it to form a common
passage way.

The tail is ordinarily sharply pointed though sometimes the
point is short and in other cases long drawn out. The anal open-
ing is ventral, a Httle anterior to the tip of the body. In a few
instances the anus is terminal and the tail is rounded or of peculiar
form. In several families its true character is obscured in the
male because lateral wings or folds of cuticula cover it. These
folds may be low, narrow, keel-hke ridges along the sides or may
have developed into wide semi-circular wings forming together a
clasping organ known as the bursa. Protoplasmic strands in the
wings appear like ribs of an umbrella; they vary in form and
number and are much used in the diagnosis of species. Numerous
papillae occur on the ventral surface of the male both in front of
and behind the anus. They vary greatly in size and arrangement
in different species and constitute another useful feature in the
determination of genera and species. A prominent cup-shaped
sucker is found on the ventral surface in front of the anus in some
species and one can often see in the body behind the anal orifice a
few large unicellular structures which are interpreted as glands.

Between the head and the tail there are very few external fea-
tures to be noted. A minute excretory pore Hes in the mid- ventral
line not far from the middle of the esophagus. In the female the
sexual pore also is found on the ventral surface; in some famiUes
it is near the head, in others near the tail, and again in the center of
the body. Its location is an important characteristic in defining
the various groups.

A circumesophageal nerve ring with lateral gangha is a conspic-

PARASITIC ROUNDWORMS -j-

uous feature in most nematodes. It lies not far from the excretory
pore, a short distance behind the anterior end of the esophagus.

A cross section of the body shows on the exterior the thick
non-cellular cuticula; within it the hypoderm or sub-cuticuhi
which is cellular but without cell walls. This layer is thin except
at the median and lateral fields which arc visible externally as
faint streaks and hence often called "Hues''; here it projects inward
between the muscle cells. The major part of the body wall con-
sists of the muscular layer, a single layer of large cells with hjngi-
tudinal but no circular or cross fibers; these cells have a con-
spicuous protoplasmic body on the inner side next the body cavity.
The muscle layer is divided into four areas separated by the median
and lateral fields of the hypodermis; rarely the presence of sub-
median fields makes eight such muscle areas. Each of the four
muscle areas may contain many muscle cells (the Polymyaria)
or be limited to a longitudinal series of two muscle cells (the
Meromyaria) .

The cuticula of nematodes is usually said to be " chitinous '' but
as this layer is soluble in alkalis, digested by the action of en-
zymes, and contains a very high percentage of nitrogen, it is not
chitin; it has been correctly designated as cornein by Reichard.
Glycogen occurs in large amount in nematode tissues and is sup-
posed to furnish them oxygen and energy.

The body cavity is large but not lined by a peritoneal epithe-
lium. It is in fact formed by the breaking down of connective
tissue cells, the remnants of which may still be observed in well
preserved specimens, especially at the anterior end. Both repro-
ductive and digestive organs are free in this ca\'ity since mesen-
teries are lacking. In full-grown worms the space of the body
cavity is almost entirely filled by the greatly enlarged and nuich
convoluted reproductive organs which press upon each other, the
ahmentary canal, and the body wall so as to leave only small
irregular cavities here and there.

The reproductive system is exceedingly simple. In both sexes
it has the form of a long tube in which the various regions are
continuous and only slightly distinguished from each other in form.
The fine inner end of the tube produces the reproductive cells.

5l6 FRESH-WATER BIOLOGY

eggs or sperm. In the female the fully developed eggs are pushed
into a slightly larger region in which fertiHzation takes place.
Sometimes the fertihzed eggs are provided with a heavy shell and
are soon ejected to carry out their development in the outer world.
In other cases they are retained in a sac-like uterus until devel-
opment is more or less advanced. In certain families the entire
development is carried out within the uterus and the female brings
forth living young. The organs in these cases differ in length
and capacity rather than in fundamental structure.

In the male the reproductive system consists of but a single
tube, emptying as already stated into the cloaca, whereas the
windings of the tube lie in the body in front of this region. In
the female the tube may be single but is most frequently double
or Y-shaped. The short stem of the Y connects with the female
pore, the branches extend in coils into the body. One branch
may pass anteriad and the other posteriad or both may He nearly
parallel in the same part of the body. One branch may be greatly
reduced and by its final disappearance give to the system the form
of a single tube such as is found in the male. Various intermediate
stages occur.

In connection with the terminal portion of the male duct are
usually found pieces of cuticula shaped like hooks or needles, and
known as the spicules. There may be only one spicule or if two
are present they may be equal or unequal. Finally an accessory
piece furnishes in some species a link or groove in which the spicules
proper are held and through which they are extruded. These
spicules are easily seen both on account of their high refractive
index and because in many preserved specimens they project
conspicuously from the anal opening. In transparent forms the
student may detect under the microscope the spicule sac, dorsal
to the intestine, in which the spicules are housed and also special
sets of muscles by which they are operated. The number,
length, and exact shape of these organs serve as features for specific
diagnoses.

The development of parasitic nematodes introduces all varia-
tions from extreme simpUcity to some of the most complex life
histories known among animals. The early development is simple.

PARASITIC ROUNDWORMS 517

Within the egg-shell is formed in direct fashion a minute worm
which on hatching displays the main features of nematode struc-
ture. This embryo may require weeks or months for its growth
and may wait within the shell for years before it is passively intro-
duced into a new host; or it may break out from the shell and spend
a period in moist earth or water awaiting the time when in one
way or another it is brought into a suitable host. In most cases
the embryo of a parasitic nematode spends a brief i)eri(Kl at least
as a free-living larva, and always in an aquatic environment, but
this may be semi-fluid mud as well as open water. Frecjuently it
undergoes in this stage or earlier the first of the four character-
istic molts and within the cast cuticula of the embryonic form
enters upon a resting stage well protected against drying out.
In this condition it may be transported by wind or water, or at-
tached to other objects, even such living agents as the feet of
reptiles^ birds, or mammals, and thus be carried far in attaining
the location where by some chance it is introduced into the body
of a new host. When this new host is reached it may be the same
as the original host in which case further molts bring the wonn in
a short time to the adult condition. In other instances the larva
reaches an intermediate host in which it becomes cnc\sted in
muscles or viscera and after a period of growth is read}- for transfer
to the final host. This change involves the consumption of the
flesh with the encysted larva by a suitable final host, whereupon
digestion sets the worm free, the active development is resumed,
and the adult form reached after a period of growth.

Most often the larval parasite is taken into a new host with
water or food. In some cases the free-living larva docs not
depend on chance to carry it but gains entrance by its own activ-
ity. Thus the hookworm larva, Hving in moist earth, when brought
suitably in contact with the skin of an available host burrows into
it and completes its Ufe history during its devious wanderings in
that host.

As an illustration of the life history of a typical aciuatic species
may be taken the development of Camallaniis lacustris, formerly
often designated Cucullanus elegans. This development was worked
out and described by Leuckart somewhat as follows:

5i8

FRESH-WATER BIOLOGY

The female is viviparous and produces myriads of young. The
larva at birth (Fig. 814, a) has an awl-shaped tail equal to one- third
the total length; no trace of the adult lips are seen; the esophagus
is simple, as also the intestine, and a single cell is the only trace of
genital organs present. A boring spine lies dorsal to the mouth.

Fig. 814. Development of Camallanus lacuslris; a, youngest stage of larva; b, second stage from body
cavity of Cyclops; c, at end of second stage showing jaws forming; d, third stage with larval jaws complete.
Magnified. (After Leuckart.)

The larva soon gains entrance to a small aquatic animal {e.g.,
Cyclops) through the mouth and bores its way into the body
cavity where the first molt occurs. After this the worm {h) has
grown in size, lost its long tail in part and acquired a bipartite
esophagus. A period of growth follows towards the close of which
the Hps of the adult are laid down (c) and the second molt dis-
closes an oral armature {d) which though smaller and differently
marked than that of the mature worm, yet displays its likeness
even to the beginning of the dorsal and ventral labial tridents so
conspicuous in the adult Camallanus. The genital area is still in-
significant and the tail carries three small spines near the tip which
survive in the adult female only. The double esophagus is fully
differentiated even to the valve cells at the lower end and the
nerve ring is well developed.

In summer these changes require only 3 days but in winter they
may last 3 weeks. No further change ensues until the parasites are
brought into the alimentary canal of a suitable fish host. Here
set free from the larval host by digestion, the worm grows rapidly
to I mm. in length, molts and assumes the sexually differentiated

PARASITIC ROUNDWORMS

form of the adult. Ten to fourteen days after introduction into i
fish the young worms have become fully matured and pair.

In most cases the larval Camallanus is introduced directly into
the final host from the first intermediate host, but in others cn-
cystment in a second intermediate host becomes an enforced pre-
liminary to the attainment of the final host. This takes place
when the intermediate host is eaten by some species other than
the final host; the larva is set free by digestion but immediately
encysts again, usually in the intestinal wall. Such erratic encysted
larvae occur in a wide variety of unusual hosts (Seurat).

Too many complications enter into individual cases to be dis-
cussed in detail here. It is necessary to mention briefly, however,
one type of Hfe history of a different character. Among the
Filariidae, the adult is parasitic in the connecti\'e tissues or body
cavity of the host and is viviparous. The embryos are produced
in enormous numbers and invade the blood stream from which
they are drawn out by biting insects such as the mosquito. After
a period of development in the mosquito they escape into the final
host when the insect is biting again, and now are ready to develoj)
into the adult parasite. In this case no part of the life-history is
spent in the outer world and the only link which connects the life-
history to aquatic biology is the intermediate host which may be,
like the mosquito, a typical aquatic organism in early life.

The nematode life histories which have been parti}- worked out
are mostly those of the parasites of man and the domestic animals.
Almost nothing is known of the development of j)arasites from
characteristic aquatic hosts and the held offers enticing oppor-
tunities to the student.

Concerning other phases in the biology of parasitic nematodes
little or nothing has been ascertained. Observations are too
scanty to furnish data on their length of life, on seasonal variation,
or on factors that influence their frequency. Their distribution
evidently cannot transcend that of the hosts and in many cases
falls far short of conforming to that, but the conditions which
aftect such variations are beyond safe conjecture.

No satisfactory outline for the classification of parasitic nema-
todes has yet been worked out and the very imperfect knowledge

520 FRESH-WATER BIOLOGY

of North American forms makes it impossible to do more than
group the few records available into an arbitrary key. A natural
classification lies far in the future and collecting in any region will
surely result in extending greatly the Hst of species included in the
subjoined key. Parasites from terrestrial hosts have not been
included in the synopsis; doubtless many of them depend upon
water for their transfer during a free-living stage from one host to
another and some of them may even utilize aquatic species as in-
termediate hosts, just as the guinea worm larva occurs in a fresh-
water copepod and reaches the human host in drinking water.
The nematode parasites of fishes, amphibians, and aquatic species
among reptiles, birds, and mammals may safely be assigned to the
fresh-water fauna. They are included here so far as described from
North America.

Undoubtedly the larvae of the hookworms {Ancylostoma duode-
nale and Necator americanus of man; Uncinaria stenocephala of
the dog), of the parasite of Cochin China diarrhoea {Strongyloides
stercoralis), and of many other parasites which occur in North
America are aquatic organisms and live for considerable periods
in pools of water or in moist earth, awaiting an opportunity to
gain entrance into a suitable host. Yet as immature forms they
can be differentiated with great difficulty if at all, and do not show
the structural features that characterize the adults to which they
belong. Hence they are only noted collectively in the subjoined
key. The adults which parasitize land animals are not included
in the list.

KEY TO NORTH AMERICAN PARASITIC NEMATODA

I (4) Immature. Sexual organs only partly developed, if at all.

Agamonema Diesing 185 1 . . 2

A collective name for the group of imperfect, larval nematodes not yet developed so that
the worms can be definitely classified. Many such forms occur encysted in fish, and the group
was originally proposed to hold fish parasites. Now it is used to include all agamic nema-
todes that cannot be referred to a more definite group. The rudiment of the sexual organs
can usually be seen as a large cell or a discrete mass of a few cells, lying near the center of the
worm. In older individuals this sexual rudiment has begun to grow out into a long cord of
cells which marks the place of the future reproductive system. In these forms the Hps, papil-
lae, and other features of special adult structure are wanting or only generally and indefinitely
laid down. Sometimes distinct characters, such as the three lips of the Ascaridae which are,
nowever, easily confused with similar conditions in other groups, may enable one to assign
these immature forms to a definite family, subfamily, or genus, and other collective names
are then applied to such forms, e.g., Agamomermis. These larval forms are very similar and
are apt to be confused because of their general resemblances.

PARASITIC ROUNDWORMS rji

2 (3) Free-living in moist earth or water. Many embryonic and lar\'al

stages of parasitic nematodes.

Not distinguishable from free-living nematodes except by exact data cotK erninc sneiific
forms which are available only in a few cases. Such are the larvae of the human h(.<.kif.,rms
{Ancylostoma duodenale or Necator amertcanus), of Strongyloidcs stcrcoraiis known to Ik- nrcsi-nt
generally in infected areas. They depend for their development uixjn the opixjrtunilv of
entering a new human host. '

3 (2) Encysted in the viscera or flesh of various fishes.

Agamonema capsular ia ( Rudolph i) 1802.

The name covers what is probably a wide variety of different species from difTert-nt source*
Thus worms under this name are listed from migratory fishes, and these arc very likely to
represent encysted larvae of marine adults; and also from fresh-water fishes in which case
they are doubtless of fresh-water origin. The descriptions of these forms arc brief. Rcneral
and inadequate to differentiate larval forms of different genera.

Among the other species recorded from North America are:

Agamonema papilligerum, a single specimen of which was found by Leidy in Philadelphia,
in the body cavity of a pike. Later regarded by him as young FUaria solilaria.

Agamonema piscium from the white fish, listed by Stiles and Hassall in the collection of the
Army Medical Museum.

Such forms may be found in other hosts than fishes like the embryos recorded by Ix-idy as:

Nematoideum integumenti lumbriculi limosi, encysted in the skin of a mud-inhabiting annelid.

4 (i) Mature. Sexual organs developed; worms active, not encysted. . . 5

Most adults are easily recognized as the eggs can be seen in the female and the sperm ma.s8
in the male. The open sexual pore in the female and the spicules in the male when exsertcd
aid in reaching a diagnosis.

5 (6) Small transparent nematodes; in general appearance identical with

free-living forms. Few eggs in uterus.

Not a very satisfactory means of separating this group from certain species in the subse-
quent divisions which approach rather closely to the brief description of the key line above.
In case of doubt regarding a specimen the student should try also the latter alternative, 6 (5)
of the key.

These forms are all minute (less than S to 6 mm. long). Furthermore they are simple in
structure and not easy to differentiate from free-living species. They possess a double es<iph-
ageal bulb and ventral glands often in lieu of lateral excretory canals. The male has two
similar spicules and in some cases a bursa. The female sexual pore is found in the posterior
half of the body and the uterus contains only a few thin-shelled eggs.

One family, the Anguillulidae, includes the vinegar eel, the paste eel, various plant para-
sites of some economic importance, and many free-living forms. These do not show any alter-
nation of generations in the life history.

Only group containing animal parasites.

Family Angiostomid.ak iiraun 1S05.

Characterized by heterogony. Otherwise very much hke the .\nguillulidae. and united
to them by many authors. Parasitic generation contains no males.

Only genus recorded for North America. . Angiostomd Dujanlin 1845.

Representative species in North America.

Angiostoma nigrovcnositm ((ioczc) iSoo.

In Biifo lentiginosiis; lung. District of Columbia. Listed by Stiles and Hassall under the
name Rhahdonema nigrovenosum as in the Bureau of .\nimal Industry C»»llection.

6 (5) Nematodes larger than free-living species; almost always distinctly

less transparent and often even oi)aque. I'tcrus contains

many eggs ^

The unsatisfactory character of the key at this point has already been noted. The n«na-
todes which follow are usually well differentiated parasites, recognizable by one or another
typical structure not present in the previous group. They are, however, distinguishable irora
the latter only in general aspect and the key is open to doubt in a few cases.

522 FRESH- WATER BIOLOGY

7 (75) Esophagus prominent, muscular, with triradiate lumen.

Suborder Myosyringata . . 8

8 (15) Bursa present in male and conspicuously developed 9

9 (14) Male with broad bursa traversed by system of rays. Buccal cap-

sule usually well developed in both sexes.

Superfamily Strongyloidea Weinland 1858 . . 10

With the spherical buccal capsule may easily be confused the bivah^e oral armature of
some of the Spiruroidea. The former presents in cross-section an unbroken circle, or oval.
The latter is distinctly composed of two pieces interrupted along Unes of division. In the
former the mouth opening is a ring that may be dentate or serrate but is still complete; in the
latter the mouth opening is a sht having at opposite points two deep acute angles. A buccal
capsule is wanting in the three forms described here.

The bursa in the strongyles is a conspicuous broad flaring organ, supported generally by
six paired rays and one unpaired median ray, all extending outwards from a common center
much Hke the ribs of an umbrella.

Only a very few strongyles have been reported in North America from aquatic hosts and these
few are not representative of the majority of the group to which belong the hookworms and
other well-known and abundant parasites of land animals. The three species cited here are in
truth so unlike typical strongyles that it is difficult to bring them into the key.

Since the group is very large and complex and only three species are to be considered here
no effort has been made to outline the famihes or the numerous other subdivisions. The
key is merely a convenient way of separating these few species. It is not unlikely that other
genera are represented in the same and other aquatic hosts.

10(11) In reptiles and amphibians. . . . Strongylus auricularis Zeder iSoo.

No buccal capsule; 30 longitudinal ridges on the body. Spicules bifid or trifid at the distal
end.

Reported by Leidy in 1856 from the intestine of Bufo americana and Cistudo Carolina in
Philadelphia. No other data accompany the record so that it cannot be verified at present.
At least two species are included in European records under this name.

The genus Strongyliis is grouped by Railliet and Henry under the family Strongylidae, sub-
family StrongyUnae, tribe Stronglyeae.

Ransom is uncertain as to the genus in which Zeder's or Schneider's species should be placed
but thinks they evidently belong in the family Trichostrongylidae. Probably Leidy's form
will fall in the same group.

11 (10) In mammals 12

12 (13) From frontal sinus of aquatic carnivore.

Filar Old es van Beneden 1858.

Railliet and Henry include this genus in the subfamily Metastrongylinae.

Only species known . . Filaroides mustelarum van Beneden 1858.

No description of the North American form has been given as yet. Identified as European
species from host and effect.

In frontal sinuses of various Mustelidae: skunk, weasel, mink, and otter, from northeastern
North America. Produces large asymmetrical postorbital swellings.

13 (12) From intestine of aquatic rodent.

Trichostrongylus jiherius Barker and Noyes 191 5.

Capsule absent in both sexes. Male 2.8 mm. long, 0.013
to 0.09 mm. broad. Bursa with broad lateral lobes and
narrow dorsal lobe. Spicules short and heavy.

Female 4.7 mm. long, 0.03 to 0.135 mm. broad. Vulva
near posterior end. Eggs oval, 0.059 by 0.036 mm., shell
thick.

Intestine of muskrat. Nebraska.

The genus Trichostrongylus is type of the subfamily Tri-
chostrongylinae.

Fig. 815. Trichostrongylus fiberius. Posterior end of male. X iSo*
(After Barker.)

PARASITIC ROUNDWORMS 3,3

14 (9) Male with bell-shaped bursa encircling posterior end; no sunrwrlinu

ribs in bursa. No buccal capsule.

Family Dioctopiiymidae Raillici 1015.

Mouth surrounded by one or two circles of papillae, 6. ,2. or ,8 in number. Ks.,phi«u.
very long, without bulb. One ovary; vagina very lonL-. Vulva near anleriur n.d anu^
terminal in female. One long spicule. Eggs with very Lhick pitted shells Lar«c worms
in some genera armed with spines near anterior end. '

Only genus parasitic in North American aquatic hosts.

Dioctopliymc Collel-.Meygret i.Ho:.

Anterior end unarmed; mouth surrounded by six papillae.

Only species known Dioctophytnc rcualc (Coc^.q) i-jSi.

Color blood red; six circumoral papillae and 150 al..ng latrral lines
Male up to 40 cm. long, 4 to G mm. broad. Anus terminal, surmundcd
by circular bursa without ribs. Spicule 5 to 6 mm. long. Female up
to I m. long, and 12 mm. broad. Anus crescentic, terminal. Sex p.irc
only 50 to 70 mm. from anterior tip. Uterus single. Eggs oval- shell
brown, very thick, deeply pitted except at poles.

In pelvis of kidney of seal, otter, dog. wolf, etc. Rare in man
Reported from mink and dog in Pennsvlvania bv Leidy. Found in
dogs at Chicago, Illinois. Intermediate host probably a fish.

The giant among nematodes; a dangerous and little known para>itc

Another form which may belong here was collected in Florida by

Wyman from the water-turkey or snake-bird and described as -nearly

Fir Srfi ninrfnt,hv,„P ^f ^^t i(ientica.l With Eustrongylus papillosus lYxv^lnK \n Plolus ankiniia

renal^. ' Ante^Sr^nd of ^JP^, Brazil." The species last mentioned was included in the genus

female. X3. (After Riley ^ystnchis by Mohn, but as the identihcation of Wvman was not final

and Chandler.) it is impossible to enter Uystrichis papillosus definitely among North

American species.

15 (8) Bursa absent or weakly developed in male. True buccal capsule

wanting 16

Compare the discussion under 9 (14) in this key. The caudal alae, often but incorrectly
called a bursa, when present consist of long, narrow wings not projecting conspicuously from
the body but parallel to it and not supported by radiating ribs, but having at most a scries
of canals at right angles to the body.

16(51) Very long, slender forms, with or without lips 17

17 (26) Esophagus slender, simple, no bulb.

Superfamily Filarioidea Weinland 1858 . . 18

The anterior end is usually plain and no lips are present though in some cases a few minute
oral papillae can be recognized. The esophagus has only a single region. The posterior end
of the male is rolled into a close spiral of two or more coils. The vulva lies far anteriati and
the forms are usually ovoviviparous. The group as now conceived is much m»tre sharply lim-
ited than formerly.

18 (19) Anus wanting in adult; vulva lacking in adult female.

Family Dracunculidae Lcipcr iqi.:.

The famous guinea-worm of man known since ancient times belongs in this group. After
impregnation the sexual pore disappears and no trace of it has been found in the adult. I he
females grow to a relatively enormous size coincident with the development of great numliers
of minute embryos which fill the uterus. The larvae develop in aquatic organisms, prob-
ably Copepoda, Ostracoda, etc.

Only North American genus 7r///// wmvmj Diesing 186 1.

Mouth surrounded by four low papillae. No buccal cax-ity. Esophagus funnel-shaped at
origin. One esophageal gland with large nucleus. Polymyarian. I'terus broad, traversing
entire body, with short ovary at each end. Embryos develop in uterus. No anus, vulva, or

524 FRESH-WATER BIOLOGY

vagina present in adult. Male much smaller than female; with two spicules and accessory
piece. Females parasitic in body cavity of Teleostei.

Single North American species recorded.

Ichthyonema cylindraceum Ward and Magath.

Male unknown, probably minute. Mature female loo mm. long, of nearly equal diameter
(0.48 mm.) everywhere. DeUcate, semi-transparent, and very fragile owing to thin body
wall. Lateral lines broad, light colored, conspicuous. No hps or papillae. Esophagus 1.09
mm. long, 0.066 mm. in diameter. Vulva and vagina atrophied, no vestiges discernable.
Female impregnated; uterus crowded with undeveloped ova almost spherical, 44 m in diameter.

In abdominal cavity of Perca flavescens; Lake St. Clair.

Fig. 817. Ichthyonema cylindraceum. Anterior end of female. X 35- (After Ward and Magath.)

19 (18) Anus present in adult; vulva persistent in female.

Family Filariidae Claus 1885.

A large group not well known and imperfectly subdivided into a number of subfamilies,
leaving many other forms still unplaced. Most of the species are connective tissue parasites
and the majority inhabit terrestrial hosts.

Forms that have not been described from this family exist in North American aquatic hosts.
Those recorded are few in number and imperfectly known. The following classification is
purely temporary. The genus Filar ia has been used as a convenient receptacle for all slender
roundworms that did not show conspicuous features of external anatomy adequate to place
them definitely elsewhere. Unless the proper location of a species could be determined clearly
it has been left imder this general heading even though its original location in this genus appears
to have been an error.

Type genus FzYar/a 0. F. Miiller 1787 . . 20

Among the forms recorded as "Filaria^' are some that have no usable description or in a
few cases none at all and must be recognized, if at all, by their host, habit, or geographic
location. Such are ^^Filaria ardearum" Stiles and Hassall 1894, cited from Ardea herodias,
in Leidy Collection.

Filar ia atnphiumae Leidy 1856 encysted in the stomach wall of Amphiiima means; alcoholic
specimens in Philadelphia.

Filaria cistudinis Leidy 1856 from the heart of Cistudo Carolina, Pennsylvania.

Filaria spec. Leidy 1882, a red worm from the musculature and peritoneum of the black bass.

Filaria nitida Leidy 1856 from Rana pipiens; later from fish and reptiles. "Probably
yoimg of F. solitaria." (Two species ?)

20 (25) Anterior end without lips 21

21 (22) Anterior tip lacks both lips and papillae.

Filaria wymani Leidy 1882.

No lips or papillae. Female 65 by 0.5 mm., sexual pore near center (?); viviparous. Eggs
0.02 mm. long; embryos 0.15 mm. Male half as large, with coiled caudal end; one spicule.

Coiled on back of cerebrum of Plotus anhinga in Florida. Males rarer than females. Prob-
ably not Pelecitiis {Filaria) helicinus (Molin i860) with which Leidy later identified it.

22 (21) Anterior tip with minute papillae 23

23 (24) Oral papillae in two series of 4 to 6 each.

Filaria solitaria Leidy 1856.

Body cylindrical, rose-red with more deeply tinged extremities. Length up to 150 mm.,
breadth i mm. Slightly narrower towards both ends. Tail obtuse; anus terminal, trans-
verse, with prominent lip. Esophagus tortuous, one-sixth length of body.

Beneath dorsal skin of Rana pipiens; also in muscles of Anguilla chrysypa in Delaware
River. In peritoneum of Chelonura serpentina, Emys serrata, and Esox reticulatus. Most
frequent during winter and spring. Railliet thinks two species are involved.

PARASITIC ROUNDWORMS

24 (23) Only two small conical papillae near moulh.

Filaria physdura Bremser 181 1.

Living worm pink with brown intestine and white uteri prominent Femak- 10 f
long, I to 1.5 mm. broad Head obtuse. Mouth with two small conical pa.X- ' MaTil
35 mm. long, 0.615 mm. broad; tail curved with short quinquecostatc alac which arc oil
mm. long. Spicule recurved. ^^ °--*S

In abdomen of kingfisher; Pennsylvania. "Determination not positive" (Lcidy).

25 (20) Anterior end provided with two lips. Each lip carries two blunt

hooks Filaria cingula von Linslow u)02.

Length 15 to 25 cm., diameter 0.53 mm. Anterior end bluntlv rounded; dorsal and vi-ntraJ
triangular hps with two blunt hooks in each. Cuticula embossed with low rounded trans^
verse ridges on dorsal and ventral surfaces. Pharynx narrow, 0.375 mm. Iomk with bulbous
enlargement at end. Esophagus triangular, 15 by 0.13 mm. Lateral fields broad Two
ovaries. Vulva? Embryos 0.33 by 0.014 mm. Viviparous.

In skin of Cryptobranchus allegheniensis; Ohio river. Identification with von Linstow'j
meager description uncertain.

Fig. 818. Filaria cingula. Optical section of the two anterior millimeters; /, lips; p. pharyngeal bulb;
0, ovary; e, esophagus; u, uterus; h, hooks; r, ridges. Magnified about 50. (After Kreckcr.J

26 (17) Esophagus with two separate regions, more or less difTercntiatc<I.

Superfamily Spiruroidea RaiUiet and Henry 10 15 . . 27

The mouth has two lips, or is without any. Esophagus with partition dividinR it int<j two
regions which may be differentiated as anterior muscular and posterior granular region, and
may be much alike in appearance.

Male with lateral alae near posterior end of body. Alae in general long, not much if any
wider than body, without ribs or radiate, branching supports.

Most of these forms were previously included with the Filarioidea from which they an- most
easily distinguished by the double esophagus.

27 (42) Anterior end simple, without prominent lateral valve-like lips. . 28

28 (41) Tail in female simple, not modified in the form of a sucker-like

structure

29(40) Male with preanal papillae and without vent nil ridges. 30

30 (37) Preanal papillae in male single not stalked and paired, also tew in

number Family Spiruridae Oerley 1SS5 . . 31

There are several subfamilies which contain numerous parasites of terrestrial hosts.

31 (34) Anterior end plain, unornamented by external ridges or frills.

Subfamily Spirurinae Raillict IQ15 ■ • ^^
The mouth has two small lips, or none. The pharynx is simple or wanting. The \ulva is
at the center of the body, or anterior.

526

FRESH-WATER BIOLOGY

32 {^7,) Mouth without lips.

Fig. 818. Haplonmea im-
mutatum. Anterior end show-
ing lateral alae. X 22. (After
Ward and Magath.)

Male without caudal alae.

Haplonema Ward and Magath.

Anterior end flexed or coiled, provided with lateral alae.

Esophagus muscular, without bulb, divided into two regions by-
partition near center. Posterior end of male without bursa, with
two pairs of preanal papillae and three pairs of postanals.
Spicules two, equal. Vulva near center of body; ovary double,
laid in transverse loops near anterior and posterior ends. Ovipar-
ous.

Only North American species.

Haplonema immutatiim Ward and Magath.

Body moderately robust. Males 10 mm. long, 0.2 mm. broad;
females 15 mm. long, 0.31 mm. broad. No lips present; three
minute oral papillae. Esophagus divided about equally; anterior
and posterior regions not distinctly differentiated. Spicules 0.75
mm. long, 0.02 mm. broad, fiat, ribbon-shaped. Eggs 65 by 45 tx, '
with moderately thick, smooth shell. Vulva five-eighths of
length from anterior tip.

From intestine of Amia calva; Lake St. Clair, Michigan, and
Fairport, Iowa.

33 (32) Mouth with w^ell-developed lips. Male with caudal alae joined

anteriorly across ventral surface of body.

Physaloptera Rudolphi 1819.

Mouth elongated dorsoventrally; bounded by 2 lateral, thick Hps each carrying a toothed
process and 2 broad submedian papillae. Caudal end of male with lateral alae and 10 pairs
of papillae, of wnich 4 are stalked and in each ala, whereas 6 are sessile and on body. Spicules
2, unlike. Vulva in anterior region. Eggs very thick-shelled.

Species reported in North America but not adequately known.

Physaloptera constrida Leidy 1856. In stomach of Tropidonotus sipedon; Pennsylvania.
Also Physaloptera contorta Leidy 1856. In stomach of numerous turtles; Pennsylvania.

34 (31) Anterior end with sinuous cuticular thickening or cervical frill.

Subfamily Acuariinae Railhet, Henry, and Sisoff 191 2.

Anterior end provided with bands, epaulets, or similar ornaments. Mouth with two simple
lateral Ups, pharynx and esophagus differentiated into two distinct regions. Caudal end of
male with lateral alae; four pairs of preanal papillae; postanals variable. Eggs with thick
shell, containing embryos when deposited.

In digestive tract of birds. A numerous and varied group.

Only genus yet recorded in North American aquatic hosts.

Acuaria Bremser 181 1

ZS

The cervical frill consists of two or four simple or complex loops draped from the tip of the
head back over the anterior region of the body. Vulva in posterior region. Two imequal
spicules. In esophagus, crop, or gizzard of birds. Often called Dispharagus in records.

35 (36) With trifid cervical papilla.

Acucria triaenucha (Wright) 1879.

Male unknown. Female 10 mm. long, 0.43 mm. broad. With cervical frill;
lateral loops 0.18 mm. from anterior end at top and extend 0.405 mm. posteriad.
Cervical papilla a trident spine, at base 0.06 mm. from end of frill, and 0.06
mm. long. Eggs 27 by 18 fx.

Single female taken from gizzard of Botaurus minor in Canada by R. Wright
and described as Filaria triaenucha.

Fig. 819. Acuaria triaenucha. Cervical papilla. X 233. (After Wright.)

PARASITIC ROUNDWORMS -27

36 (35) No trifid cervical papilla present.

Acuaria ardcac (A. J. Smith) i.^o^.

Male unknown. Female 17 by 0.7 mm. Two lateral lips, each with double papillae From
base of each lip two promment submedian ridges on surface extend posteriad nearly to ccntt-r lA
body, then dorsad and ventrad respectively to join similar lines on opixjsiic side. Ksi.phaifu*
2 mm. long, in two sections: anterior narrow region o.S by 0.05 to o.oy mm., ixjstrrior widrr
region 1.2 by 0.2 mm. Anus 0.35 from tip of tail which is bent strongly dorsjid. Vulva nt-.ir
center of body; no eggs developed.

In Ardea herodias. Described originally as Dispharagiis ardeae by A. J. Smith.

37 (30) Preanal papillae in male numerous, grouped in pairs and stalked.

Family Thelaziidae Raillict 1916.

Head naked or provided with cuticular thickenings or helmet-like covering. Mouth with
2 to 6 very small lips or without any, followed by a long vestil)ule or a short butial capsule.
Esophagus composed of two distinct regions. Males with or without lateral alac in caudal
region, with a linear row of numerous preanal papillae, often paired; postanal i)apillae lc*«
numerous; 2 spicules, almost always unequal. Female with double uterus; vulva variable
in location. Oviparous or viviparous.

Only genus in North American aquatic hosts.

Cystldicola Fischer 1797 . . 38
No valid record exists for the European C. Jarionis in North .\merica.

38 (39) In air-bladder of salmonid fishes.

Cystldicola stigmatiira (Leidy) 1886.

Length: male, 12 to 25 mm.; female, 20 to 40 mm. Width: male, 0.25 mm.; female, 0.4s
mm. Mouth circular with 2 minute lateral teeth. Buccal capsule tubular, 0.12 to 0.2.J mm.
long. - Anterior region of pharynx 0.5 to 0.6 mm. by 0.054 Tnm., posterior region 2.1 to 2.\

mm. by o.i mm. Male with

narrow lateral membranes on

caudal end ; 5 pairs of single

postanal papillae, 9 pairs of

double preanal papillae. Two

unlike spicules; one slender oS

to 0.9 mm. long, o.oi mm. wide;

other trowel-shapeti, 0.16 mm.

Fig. 820. Cystldicola stigmatura. Anterior end of female. X 85. \q^^ q jg ^im wide Female

(After Ward and Alagath.) s^^^;^, ^^^e near center of Ixxly ;

uterus with anterior and posterior branches both well developed and symmetrical. Ova thin

shelled, containing developed embryo when laid, 44 by 27 /x.

In air-bladder of Great Lakes trout, white fish, and lake herring. Lake Eric, Lake St.
Clair, Lake Michigan, Lake Ontario (Leidy).

In half or more of fish examined. Reported by Wright as Ancyracanthus cystidkola and by
Leidy as Filaria stigmatura.

39 (38) In heart of white fish Cystldicola scrrata (Wright) 1S79.

Length 11 mm. With several small teeth around anterior end instead of two as in former
species. Only a single specimen found by Ramsay Wright at Toronto. I'erhaps an imma-
ture specimen, either migrating in blood stream, or accidentally introduced into this peculiar
location.

40 (29) Male with conspicuous ventral ridges near posterior end; preanal

papillae absent or inconspictious. Body spinous.

Splnltcctiis Fourment 1S83.

Mouth without lips or papillae. Except at extreme tip the body is encircli«d in the ante-
rior half or more by rows of spines pointing backward. The ventral surface in the male carnes
several parallel series of rugosities just anterior to the anus.

Representative North American species.

Splnltcctiis gracilis Ward and ALigalh.

Mature female 17 to 19 mm. long, 0.14 broad; male 12 mm long, 0.075 mm broad. ^}^^f
130 rows of spines with 40 to 50 in each row. .Interior tip free from spmes for o.n mm. in

5^8

FRESH-WATER BIOLOGY

female, o.i in male. Vulva one-fourth total length from caudal tip. Spicules two, large,
heavy, unequal. Ova 41 by 24 n, thick- waUed.
In intestine of black crappie, sheepshead, and white bass at Fairport, Iowa. Abundant.

Fig. 821. Spinitectus gracilis. Anterior end of female. X 220. (After Ward and Magath.)

41 (28) Posterior end in female modified to form a sort of sucker by which
the parasite is attached to the stomach wall.

Hedruris Nitzsch 1821.

Head with 4 lips: 2 lateral, slender, each with 2 papillae; 2 median, thinner, overlapping
laterals almost completely. Vulva near anus. Tail of female modified to form with included
spine, the caudal tip, an adhesive organ or sucker. Eggs elhptical, with lid-like areas at both
pointed poles, contain developed embryos. Male spirally wound around female. Tail strongly
compressed laterally: 6 pairs postanal papillae, i pair just preanal. Spicules 2, similar, very
short, apparently grown together.

Tj^e species Hedruris androphora Nitzsch 1821.

RefX)rted from Amhlystoma mexicana and Nanemys guttata by Stiles and HassaU. The form
described by Leidy in 1851 as Synpleda pendula certainly belongs in this genus if not in this
species.

Also recorded Hedruris siredonis Baird 1858.

In British Museum collection. From "stomach of Siredon mexicanus from Mexico." Male
not found.

42 (27) Anterior end provided with heavy, lateral, valve-shaped lips.

43

43 (48) Lips red or brown, very conspicuous. Esophagus with two well
differentiated, distinctly separated regions. No preanal
sucker in male.

Family Camallanidae RaiUiet and Henry 1915 . . 44

Body nearly cylindrical, with heavy oral armature having the appearance of a bivalve shell,
which is really 2 thick, lateral, valve-hke lips probably functioning as jaws and not a buccal cap-
sule. Each valve marked by longitudinal ridges terminating at the inner margin of the mouth
in minute teeth. Mouth an elongated oval; inner opening of oral cavity to esophagus round,
encircled by hea\y basal ring of chitin. Several (2 to 4) hea\y chitinous rods diverge from
common center at each side of capsule along sides of body beneath cuticula, forming a fork
or "trident."

Esophagus bipartite, anterior region muscular, club-shaped; posterior dark, granular (gland-
ular?); valve to intestine.

Tail of male surrounded by narrow, poorly developed caudal alae with stalked papillae. A
single spicule with accessory piece or two nearly equal spicules. Female sexual pore towards
center of body. Viviparous; embryos develop in Crustacea and insect larvae.

Parasitic in aUmentary canal of fishes and reptiles.

Single genus known Cawa//awM.y RaiUiet and Henry 191 5.

These forms are often cited as Cucullanus and Dacnitis. RaiUiet and Henry have recently
cleared up the confusion previously existing in the group.

PARASITIC ROUNDWORMS

520

44 (45) With anterior end bent ventrad.

Camallaniis ancylodirus W ar.l and Maguih.

Mature female 25 mm. lonp, 0.56 mm. broad: male iq mm l.mir o ..s
mm broad. Oral armature in female 0..42 to o.hH mm. Iohk by o"ih to
0.187 mm. broad; in male 0.126 mm. lonK by 0.12 mm. bn.a.i. Trident
with 3 or 4 roots, in female 0.21 and in maleo.iSmm I..11L' si.i. nl.-, „.- .rl.
equal. Vulva three-fifths of length from anterior end

In intestine of German carp. Fairport, Iowa.

Fig. 822. Camallanus ancylodirus. Head of male.
Magath.)

X 70. (.After W ar.l and

45 (44) With anterior end attenuated, not bent ^6

46 (47) Vulva one-third total length from anterior tip. No spines on caudal
tip Camallanus oxycephalus Ward and Magalh.

Female slenderer than preceding species, 25 mm. long, 0.27 mm. broad, straight through
entire length. Oral armature smaller. First esophagus 0.47 by 0.085 mm.; second 0.57 mm.
wide. Male unknown. In intestine of white bass and black crappie.

Fig. 823. Camallanus oxycephalus. Anterior part of female. X 70. (.After Ward and Magath.)

47 (46) Vulva behind center of body. Three small spines on caudal lip of
female Camallanus trispi)wsus (Xa:'\(\\) 185 i.

Mouth large, valves with 8 radiating lines on each side of unstriated median band, makins
16 rays on each valve. Male 6 mm. long, 0.12 to 0.16 mm. broad. .\nus o.oS mm. from laudal
tip. Two spicules, 0.12 and 0.43 mm. long. Fem.ale 12 mm. long, 0.24 to 0.27 mm. liroad
First esophagus 0.38 by 0.12 mm; second 0.46 mm. long. .\nus 0.022 mm. from caudal tip
which bears three minute points. Vulva with prominent lips.

In small intestine of Emys guttata, E. reticulata, E. scrpala, Chclydra .urpcutitta. Thiladcl-
phia (Leidy).

48 (43) Lips not conspicuous; esophageal regions similar in structure, mn
sharply separated. Male with preanal sucker.

Family Cucullaxid.ae Slossich iSgS

Mouth eUiptical, with long axis dorso-ventral, bounded by two lateral valves recalling those
of Camallanus. Esophagus pestle-shaped but without bulb, two regions appear alike in
structure, short, separated only by transverse partition. Male without caudal alae; two
equal spicules; preanal sucker without horny ring. Female with vulva not far from center
of body.

In intestine of fishes.

There are in North America numerous species of this genus. Only a few have been descrihcd
adequately. In the past these forms have often been recorded as Dacnilis Dujardin 1S45
and assigned to the Heterakidae.

530

FRESH-WATER BIOLOGY

49 (50) With anterior end bent dorsad. No intestinal cecum present.

Cucullanus O. F. Miiller 1777.
Anterior end flexed dorsad 60 to 90 degrees. Spicules with accessory piece. Ovary double.

Representative species in North America.

Cucullanus clitellarius Ward and Magath.
Body uniform in diameter except for clitellar-like swelling i mm. long, and 1.5 mm. from
anterior tip. On each oral margin three small papillae. Male 10 mm. long by 0.38 mm.
broad. Esophagus 1.45 by 0.12 to 0.22 mm. Spicules gouge-shaped, 1.62 by 0.035 mm.;
accessory piece dagger-shaped, 0.06 by 0.015 mm. Two small preanal papillae; 4 pairs of
postanals. Females 12 to 17 by 0.5 mm. Esophagus 1.6 by 0.13 to 0.32 mm. Vulva two-
thirds of length from anterior end. Uterus and ovary double. Ova 63 by 46 /x.
In intestine of lake sturgeon; Lake St. Clair.

50(49) Anterior end straight :

well-developed intestinal cecum present.

Dacnitoides Ward and Magath.

Much like Cucullanus except that anterior tip is not flexed, an accessory
piece is lacking and only a single ovary is developed. The intestine pos-
sesses a prominent cecum extending anteriad to the nerve ring.

Representative species in North America.

Dacnitoides cotylophora Ward and Magath.

Male 4 to 6 mm. long, 0.2 mm. broad. Each lateral valve with anterior
marginal cuticular thickening bearing 3 papillae. Esophagus 0.5 to o.6_ by
0.06 to 0.12 mm. Boundary between esophageal regions at nerve ring.
Spicules 0.89 by 0.005 mm. Caudal papillae: one pair on anterior margin
of sucker, four pairs between sucker and anus, a single medial papilla just
in front of anus and four pairs postanal.

Female 4 to 5.5 mm. long, 0.28 mm. broad. Anus 0.14 from posterior
tip with 4 slender spines midway between. Vulva one-eighth of total length
behind center of body. Posterior uterine branch has no ovary. Ova 65
by 40 jLt.

In intestine of yellow perch and wall-eyed pike; Lake St. Clair.

Fig. 823a. Dacnitoides cotylophora. Head of female, showing oral armature,
esophageal regions, intestine, cecum, and anterior coils of ovary. X 57- (After
Ward and Magath.)

51 (16) Stout bodied forms with conspicuous lips 52

52 (55) Two heavy lips. Body covered on anterior region at least with

dentate or spinous plates.

Family Gnathostomjdae Railliet 1893.

Body covered in whole or part by circles of dentate cuticular plates. Anterior tip enlarged,
provided with simple spines, separated by nuchal constriction. Two large fleshy lips.
Esophagus large, muscular. Vulva behind middle of body. Two equal spicules. No bursa.
In male two pairs of preanal papillae and two postanals.

Type genus Gnathostoma Owen 1836 . . 53

Entire body or anterior end covered with abundant spines, often many pointed. Head
separated by circular constriction, with circles of simple spines. Two large, fleshy lips. Spic-
ules 2, unequal; vulva behind center of body. Male with two pairs of postanals.
Two species reported from North American.

53 (54) Anterior plates palmate with eight spines each.

Gnathostoma horridum (Leidy) 1856.
Female 66 mm. long, 3 mm. broad. Male unknown.

Taken from stomach of Alligator mississippiensis in Georgia and originally described by
Leidy as Cheiracanthus horridus.

54 (53) Anterior plates tridentate. . . . Gnathostoma sociale (Leidy) 1858.
Female 30 mm. long, 1.5 mm. broad. Male 24 mm. long, i mm. broad.

Taken from stomach of mink {Putorius vision) in Philadelphia and originally described by
Leidy as Cheiracanthus socialis.

PARASITIC ROUNDWORMS

531

55 (52) Relatively thick, heavy-bodied forms. Mouth with three lips, more

or less conspicuous. Always oviparous.
Superfamily Ascaroidea Railliet and Henry U)is

One large dorsal and two smaller ventral lips, right and left of medial line; secondary lips
(mterlabia) may be uitercalated. Buccal capsule never present. Dorsal lip l>car8 rcinilarlv
two papillae and ventral lips one each. Lips rarely greatly reduced {or aljscni:-').

56 (68) Polymyaria. Usually 'arge opaque species 57

For discussion of term Polymyaria see page 515.

57 (67) Lips prominent. No ventral sucker in male.

Family Ascaridae Cobbold 1864 . . 58
Male usually has two spicules. Female with abruptly conical posterior end.

Type genus l^a/m Linnaeus 1758.

No fringes or tentacles on the lips. A large and complex group. DilTcrontiatcd usually on
the basis of the form of the lips which present many modifications in minor details.

A number of forms have been recorded under the name Ascaris which are so inade(juatcly
described that their exact systematic position must depend on their redi-scovt-ry and further
study. Such are:

Ascaris longa Leidy 1856 of which a single female specimen was taken from the intestine
of the wood ibis in Georgia.

Ascaris penita Leidy 1886 from the intestine of the terrapin.

Ascaris cylindrica Leidy 1849 from the intestine of Helix allernata in Pennsylvania.

Ascaris entomelas Leidy 185 1 from the lungs of Rana halecina, which the description says
is "not Ascaris nigrovenosa Zeder" ( = Angiostoma nigrovenositm q.v.).

Ascaris tenuicollis Rudolphi 1819, from the stomach and intestine of Alligator mississippi-
ensis or encysted on viscera. Reported frequently.

Probably most of these do not belong in the genus Ascaris in the strict sense and ver>' likely
not in the family of the Ascaridae as at present defined. These species are not well known
and often determinations have evidently been based on general factors that are not truly
diagnostic.

58 (59) Lips relatively small, without intermediate lobes; dental plates with

serrate edges on inner margins.

Ascaris lanceolata Molin i860.

Male 20 to 25 by 0.5 mm.; female 25 to 40 by 0.8 mm.

Lips much like those of Ileterakis. Tail of male with
oval groove on ventral surface, and parallel longitudinal
furrows on dorsum; lateral to these merely cuticular folds
(weakly developed alae?). Papillae: about ly |)reanal
and 12 postanal with one row of long papillae in an arc.

In stomach of Alligator mississippiensis. (leorgia.

Fig. 824. Ascaris lanceolata. Dorsal lip, inner aspect. X 80.
Ventral view of tail of male. X 6. (After von Draschc.)

59 (58) Lips well developed; with intermediate lobes or interlabia. . . 60

60 (64) With serrate dental plates on inner border of lips 61

61 (62, 63) Tail of male with 6 pairs of postanal papillae.

Ascaris sidcata Rudolphi 18 10.

Male 35 mm. long; female 97 to too mm. lon^.
Body attenuate anteriorly, distinctly ringixl. Lijw
very large, hexagonal; lobes indistinct; interlabia
very small. Tail of male with 6 postanal papillae
and many (±64) preanals. Bursa broad. Eggs
irregularly elliptical, large.

Reported in 1887 by Leidy from the stomach i^
terrapin, Pennsylvania.

Fig. 825. Ascaris sulcata. Dorsal \ncw of lips, and po*"
tenor end of male. Magnified. (After Sio&ucb.)

532

FRESH-WATER BIOLOGY

62 (61, 63)

Tail of male with 4 pairs of postanal papillae.

Ascaris ardeae Smith 1908.

Female up to 80 mm. long and 1.8 mm. broad.
Head rounded with 3 prominent lips and well-marked
interlabia, Superior lip with finely denticulate anterior
and lateral borders. Tail acutely conical, vulva 30 mm.
from head. Ova 0.105 to o.ii mm. by 0.096 too. x mm.;
shell colorless marked by thick-set pits.

Male 72 mm. by 1.5 mm. Spicules double, equal,
brownish, 1.3 mm. long. Tail incurved, bluntly rounded
with small acutely conical tip. Papillae: 2 pairs on
conical tip also 2 pairs postanal and 5 pairs or more
preanal.

In Ardea herodias.
^ „ . . . , - , . Much like A . serpentulus Rudolphi reported by Leidy

Fig 820. Ascans ardeae Lateral view f ^^^^ j^ ^ Probably Leidy 's record concerns this
of anterior end, showing two of the lips • t-u*. a i t i iii.ju/\

(partly in profile) and two of the interlabia. ^P^i^^^?-, J^e true A . serpentulus was collected by A.
Ventral surface of male tail. (Note the J- Smith from a European crane m the Philadelphia
second pair of papillae from tip of tail as Zoological Gardens,
uncertain.) Magnified. (After A. J. Smith.)

63 (61, 62) Tail of male with 3 pairs of postanal papillae.

Ascaris microcephala Rudolphi 1819.

Male 15 to 45 mm., female 45 to 70 mm. long. Body greatly
attenuated anteriorly. Lips quadrangular, with anterior margin
concave and angles projecting. Interlabia as long as lips. Cer-
vical papillae in dorsal and ventral lines. Tail of male obliquely
truncated; papillae small, 3 postanal and 31 preanal. Ova 72 by
59 M-

In crop, esophagus, stomach and intestine of various herons,
and bittern. Florida to Canada.

Fig. 827. Ascaris microcephala. Dorsal view of head.
(After von Linstow.)

Magnified.

64 (60) Without serrate labial plates 65

65 (66) With interlabia Ascaris helicina MoHn i860.

Male 6 to 8 by o.i to 0.2 mm.; female 13 to 28 by 0.3
to I mm._ Three interlabia. Lips almost quadrangular
with auricles on anterior corners. Tail of male with 5
postanal and 4 large lateral preanal papillae. Vulva an-
terior, or almost in center of body.

In stomach of Alligator mississippienis.

Fig. 828. Ascaris helicina. Dorsal lip, inner aspect. X 55-
Tail of male. X 85. (After von Drasche.)

66 (65) Neither interlabia nor dental plates in oral armature.

Ascaris miicronata Schrank 1790.

Length 52 mm., breadth 0.75 mm. Body much attenuated anteriorly. Lateral membrane
broad on head, disappears on neck. Greatest breadth of upper lip twice its length; base
broader than anterior margin; lateral margins divided into anterior straight and posterior
arcuate portion. Tail of male with 2 rows of preanal papillae on each side.

From Alligator mississippiensis. Listed by Stiles and Hassall in Leidy Collection.

67 (57) Lips distinct, not large. Male with ventral sucker near anus.

Family Heterakidae Railliet and Henry 1914.

None known from aquatic hosts. Likely to be confused with Cuadlanus {cf. page 530) which
has a preanal sucker without horny ring. There are in North America numerous species of
this genus.

PARASITIC ROUNDWORMS 533

68 (56) Meromyaria. Small transparent forms 6^

For discussion of term Meromyaria sec page 515.

Lips simple, inconspicuous. Vulva anterior. Caudal end of female distinctly clorujale
separated from Ascands by some authors. ' wunRaic.

69 (70) Without esophageal or intestinal cecum.

Family OxvuRroAE Coblx)ld 1864.

The few North American records cannot be safely assijmed on the basis of the pn-vnt div
tmction between this family and the next. Consequently they are left where they were olacrd
originally. '

Among forms recorded from North America which cannot be placed at present owing to
imperfect knowledge of their structure are:

Oxyuris dubia Leidy 1856 reported from Bufo americanus and SaJamatuIra rubra. .Male
unknown.

North American genus Spironouni U-idy 1856.

Mouth surrounded by circular, papillated lip. Tail of male spiral, acute. tulxTcubtc.
Spicules two, curved, ensiform, costate. Tail of female conical, acute. Vdva at posterior
third.

Type species Spironoura aracilc WuW \^s6.

Female 16 by 0.25 mm.; male 8 by 0.25 mm. with two rows of three papillae on tail. Found
in stomach of Emys serrata and Siredon mexicanus.

Also recorded Spironoiira affiiic Lcidy 1858.

Female 9 by 0.4 mm.; male 6 by 0.3 mm., with two papillae on each side of tail near end.
Foimd in cecum of Cistudo Carolina.

70 (69) With cecum on esophagus or intestine, or on both.

Family Heterocheilidae Railliet and Henry 1915 . . 71

71 (74) With papillae on tail of male and with ceca on both esophagus and

intestine Co»/racoec«w Railliet and Henry 191 2.

72 (73) Without circle of spines on tail.

Contracoeciim spicidigcnim (Rudolphi) i8oq.

Male 18 to qo mm., female .^o to 154 mm.
long. Lipssinall; interlabia well dcvel»»pcd
with a small notch at outer margin. Intes-
tine with diverticulum at anterior end. Tail
of male with 7 postanal pajiillae many ( ± 40)
^^\\%J^ lyyy preanals in 2 lateral series. Spicules very

long, usually well extended, and recur\'«i.
V^ulva anterior. Ova irregularly reticulate
0.1 1 to 0.12 mm. long.

Reported by Leidy in iS5r>. 1SS2. and i8<>8
^ „ ^ . ,. » . J from the stomach of ct)rmorant. white and

Fig. 82g Contracoecum spiculigerum Anterior end j pelicans, and water turkev, \l,r^A.,

and tail of male. Magnified. (After Stossich.) t n k ta

73 (72) With circle of spines on tail.

Contracoecum adunca (Rudolj^hi) 1809.

Male 30 to 31 mm., female .^o to 65 mm. long. Weak lateral
cuticular membranes. Linstow says interlabia are present. hM.ph-
agus with cecum extending posteriad o.h mm., and intestme with
similar extension 0.41 mm. anteriad. Tail of male sh..rt. conical
coiled; 27 preanal papillae in simple series, and 3 postanals. I ip ol
tail ringed with tine spines. Spicules long (1.92 mm.). c«jual, some-
what enlarged at proximal end. , , . « 1 •
In intestine and pyloric appendages of shad I ^"^V"^-'"'**
Fig. 830. Coniraoecum Maine Probably of marine origin though taken from tish m ircsn
adunca. Dorsal view of „„f_-. '
upper lip. Magnified. (After wai:er.
von Linstow.)

534

FRESH-WATER BIOLOGY

74 (71) Without papillae on tail of male and with single intestinal cecum.

Hysterothylacium Ward and Magath.

Anterior end with narrow lateral wings. Lips three, not prominent. Esophagus long,
slender, with terminal bulb. Intestine with short simple cecum at anterior end, extending
posteriad. Males with two equal spicules. Females unknown.

Type species. . . Hysterothylacium hrachyuriim Ward and Magath.

Male 32 mm. long; maximum width 0.66 mm. Lateral ala one-quarter width of body.
Esophagus 3.1 mm. long, o.i to 0.13 mm. broad; bulb with three teeth; cecum 0.94 by 0.08
mm. Spicules 0.72 mm. long, 0.045 mm. wide. Pyriform sperm vesicle prominent.

In stomach of black bass; Lake St. Clair.

75 (7) Esophagus slender, non-muscular; lumen a capillary chitinous tube

traversing a row of granular cells.

Suborder Trichosyringata . . 76

76 (77) Anus lacking; alimentary canal non-functional in adult. Adults

free living Family Mermithidae Braun 1883.

These forms are only distantly related to aquatic biology as the adults occur free in soil, or
less often on plants as the famous "cabbage-snake." The early hfe is spent as a parasite in
the body cavity of some insect or crustacean from which they occasionally escape into an
apple or other peculiar environment.

They are very slender, greatly elongated, threadworms in which the ahmentary canal is
transformed in the adult into a fat body. The eggs are spherical, with two peculiar stalked,
tasselated appendages at the poles. The adults are fully considered in the chapter on Free-
living Nematodes (consult page 503).

The Mermithidae are often confused with Gordiacea to which they bear a certain superficial
resemblance. The differences are discussed later (page 535).

77 (76) Alimentary canal complete and functional. Adults always para-

sitic. . . Family Trichinellidae Stiles and Crane 1910.

Esophagus formed by capillary tube traversing chain of cells. Anterior region of body
slender, posterior region swollen. Anus terminal. Male with single spicule (or none?).
Female with one ovary. Vulva near junction of anterior and posterior body regions.

The well known human parasite, Trichinella spiralis, commonly called trichina, is included
in this group though in another subfamily from the following.

Subfamily Trichurinae Ransom 191 1 . . 78

78 (79) Anterior region of body very slender and much longer than posterior

region Trichuris Roederer and Wagler 1761.

In North American aquatic host.

Trichuris opaca Barker and Noyes 191 5.

Male 22 to 28 mm. long; anterior region 13 to 19 mm.
long, 0.06 to o.oS mm. thick; posterior region 7 to 9 mm.
long, 0.14 to 0.16 mm. thick. Spicule 2 mm. long; sheath
0.18 mm. long, 0.07 mm. in diameter.

Female 22 to 30 mm. long; anterior region 18 to 19
mm. by 0.06 to 0.07 mm.; posterior region 10 to 11 mm.
by 0.23 to 0.25 mm. Vulva between first and second an-
terior eleventh of posterior region.

Duodenum of muskrat. Nebraska.

Fig. 831. Trichuris opaca. Posterior end of male. X 20.
(Atter Barker )

/m m.

PARASITIC ROUNDWORMS 5^j;

79 (78) Anterior region not much slenderer than posterior region and equal

to it in length or shorter Ca pillar id Zv^lt i>kx^.

In North American aquatic host.

Capillaria ransomia Barker and Xoyes 1915.

Length 19 to 20 mm.; breadth of male o.oi to 0.03 mm., of female 0.02.' to 0065 mm
Bursa of male small, with 2 lateral lobes. Spicule 1.36 mm. Ions, 0.007 mm. bruad. Vulva
in anterior fourth of body. Eggs 0.05 by 0.02 mm. with prominent plugs.

Duodenum of muskrat. Nebraska.

GORDIACEA

The Gordiacea are familiar to all as the hairworm.s or "hair
snakes" frequently found in the country in drinking' trou-^dis.
springs, brooks, ponds, or indeed any body of water, lar<^c or sfikiII.
In general appearance these worms are very much like the nema-
todes but the more fully their internal organization has become
known by study the less they seem to resemble that group in de-
tail, and the present tendency is to separate them as an independ-
ent class. Some even make the group an independent phylum.

The body resembles a bit of fine wire or a tough root libir in
appearance. It is nearly cylindrical, usually with blunt or rounded
anterior end and a caudal extremity of modified form, often swollen,
lobed, or curled in a loose spiral.

Certain nematodes, especially Mermis which occurs free in soil
in the adult stage, resemble the hairworms so much externally that
they are often confused with them. The two ditTcr greatly in
internal structure and somewhat in less important external lea-
tures; but by their pointed anterior end, tapering body, and
smooth, finely striated and somewhat transparent cuticula the
true nematodes are usually easily distinguished from the Ciordi-
acea with blunt head, cylindrical body, and roughened, ordinarily
also papillate, irregular cuticula. Mermis in particular is most
readily distinguished by the pointed posterior end and when alive
by the active anterior region.

In the Gordiacea a single orifice serves as the common outlet of
the reproductive and alimentary systems, alike in both sexes; it is
located near the posterior end. There are no lateral lines and the
male never possesses spicules.

These animals are so opaque that little or no internal structure
is visible on examination either with the naked eye or with the

536

FRESH-WATER BIOLOGY

aid of a microscope. The most of the features on which classifi-
cation is based are external and must be regarded as arbitrary
and trivial. The internal structure can be studied only with
difficulty by complicated technic and may be passed here without
description.

In one respect the Gordiacea differ from the parasitic worms
heretofore considered: the adults are free-Hving and it is only the
young stages which carry on a parasitic existence. Probably the
free aquatic stage is merely a reproductive period, even though it
is prolonged for several weeks or months. The worm when loaded
with eggs is round and plump, but the spent female is often wrinkled
and flattened.

Gordius deposits its eggs in a long white or grayish cord which
may be several feet long and apparently many times the bulk of
the female worm. In some species the cord breaks up into shorter
pieces. The vv^orms are often observed in knotted masses, con-
sisting of two or more worms coiled together. In some cases at
least they are coiled about the egg strings and remain for many
days in this position, thus in a sense exercising protection over the
developing embryos. It is commonly said that the Gordiacea de-
posit their eggs in brooks or other running water, but I have found
some species in abundance on water plants and in knotted masses

along the shore of Lake St. Clair, Lake
Erie, and Lake Michigan. Rarely I
have seen a conspicuous windrow of
adult worms and egg masses extending
for some distance along the water's
margin of an inland lake and probably
washed up there by wave action. The
minute embryo (Fig. 832) which hatches
from these eggs after a brief period
possesses a conspicuous proboscis and
set of hooks at the anterior end. By
this powerful boring apparatus the em-
bryo forces its way into some aquatic
insect, often the ma3^y larva. Further changes are not known
except that in the body cavity of various adult insects, such as

Fig. 832. Enibroyo of Paragordius
varius with extended proboscis, X looo.
(After Montgomery.)

PARASITIC ROUXDWOkMS -,-

beetles, grasshoppers, and crickets, are found well-^rown and iKMrl\-
mature larvae of the hairworms. On escaping into the water from
these insects, the worms become sexually mature and the lyclc is
completed. Villot denied the necessity of an intermediate hcjst,
but others have held that the hairworm undergoes two and pt-r
haps more changes of host during the complete life cycle. When
the worm escapes from an insect it swims about actively in the
water but even where the capillary esophagus is not closed so that
the taking of food is absolutely precluded, the worms i)rol)ahly
take no nourishment in the aquatic stage.

Hairworms in an early or late larval condition have been re-
corded as parasites not only in the insects cited above but also less
frequently in spiders, oligochaetes [Lumbriculus) , snails, and rarely
in distomes, fish, and amphibians (?). In the last three t>pes their
presence is no doubt purely accidental. Adults in the free-living
stage have been reported a number of times as human parasites.
Here their presence is also fortuitous and is doubtless due to the ac-
cidental swallowing of specimens in water or in food eaten uncooked.

The number of species of Gordiacea in North America is not
large and thanks to the splendid work of Montgomery the group
is well known. The following synopsis is based on his papers.
The range of species has been somewhat increased b\' my own col-
lections from regions not represented in his records. I have also
been given valuable unpubHshed data by H. G. May. Even yet
there are no records from the southeastern or northwestern United
States and only a single record each from Canada and Alaska.
The absence of records from any region indicates lack of study in
that region rather than scarcity of material.

Only three well-marked genera are known: Gordius, Ghordodcs,
and Paragordius, all of which are represented in this continent.

KEY TO NORTH AMERICAN GORDIACEA

I (8) Anterior region distinctly attenuated, coming nearly to a point ; usu-
ally lighter than the rest of the body and without a dark

ring Clwrdodcs Crcplin 1847 . . 2

Caudal end simple, not lobed; in female somewhat enlarged. External surface complicatctl;
several types of areoles present. ,

Because the males and females are distinctly unlike in external appearance thoy come oui .1^
separate groups in the key. The cross references carry the student back to the other >ex n
each case. It will be noted that the key Une which ultimately determmes the sik-ocs is usually
alike in both sexes.

538

FRESH-WATER BIOLOGY

2 (5) Caudal end slenderer than preceding region of body, with tendency to
roll into spiral form (Males of Chordodes) . . 3

The cloacal orifice is ventro-median and the ventral surface possesses a shallow furrow or
groove from this orifice to the posterior extremity.

(4) Cuticular areoles longer than high; small circular pits upon and be-
tween them. . . Chordodes occidentalis Montgomery 1898.

For female of this species consult 6 in this key.

Male up to 255 mm. long, 1.5 mm. broad. Color light brown to
black; tip of head yellowish white. A western species; Montana,
Wyoming, CaHfomia, Arizona, Texas, Mexico.

An Acridiid is known to serve as host for this species.

Fig. 833.

Head and surface areoles of Chordodes occidentalis J . Highly
magnified. (After Montgomery.)

4 (3) Cuticular areoles higher than long.

Chordodes morgani Montgomery 1898.

For female of this species consult 7 in this key.

Male 64 to 220 mm. long. Color dull chocolate brown, except anterior end which is always
white. Papillae of several types; the most regular conical with short spine, and the highest
papillae with a few spines on the summit of each being typical.

The species manifests a high degree of individual and sexual variation. Recorded from
Pennsylvania, Maryland, Michigan, Ohio, Florida, Iowa, and Nebraska. C. puerilis, origi-
nally described from two males, belongs here.

A Blattid is known to serve as host for this species.

.'^HMXV^AvUvHV^

■^'^--''^--A M^ fui^

Fig. 834. Cuticula of Chordodes morgani 9
in transverse section. Highly magnified. (After
Montgomery.)

Fig. 835. Cuticula of Chordodes morgani
J in transverse section. Highly magnified.
(After Montgomery.)

5 (2) Caudal end swollen, somewhat knob-shaped; also marked off by a
slight constriction. No tendency to roll into a spiral.

(Females of Chordodes) . . 6

The females of Gordius, which may easily be confused with these, never have more than a
sHght swelling at the caudal end and this is not marked off by a constriction.

(7) Cuticular areoles longer than high; small circular pits upon and be-
tween them . . Chordodes occidentalis Montgomery 1898.

For male and range of this species consult 3 in this key.
Anterior region much attenuated; head pointed. Areoles low.
darker neck ring and black mouth spot.

Color yellowish brown with

7 (6) Cuticular areoles higher than long.

Chordodes morgani Montgomery 1898.

For male and range of this species consult 4 in this key. The variable papillae are also
noted there.

Female up to 222 mm. long. In the largest females the cuticula in surface view is like that
of the males, except that the large papillae are less numerous. Color averages lighter than in
the male.

PARASITIC ROUNDWORMS

539

« (i) Anterior region very slightly or not at all attenuated. Tir, white usu-illv
followed by a distinct dark ring ' ' '

Caudal end lobed; in feniale if not lobed then of uniform caliber with Ixxly or sliKhily en-
larged, but not set oflf by a distinct constriction. MiKnii> cn-

9 (lo) Anterior region slightly attenuated, tip obliquely truncate- dark
ring very broad Paragordius Camerano iSg;.

Caudal end trilobed in female and only bilobed in male. All males of Gordius also have the
caudal end bilobed.

Montgomery rightly emphasized the absence of cloacal musculature in the male and the
exceedingly long cloaca in the female as most significant generic features to which the taudaJ
lobes were subordinate in value. For mere diagnostic purposes the latter are convenient.

Only species in North America. . . Paragordiiis varius ''Leidy) 185 1.

Males more slender and considerably longer than females; up to 350 mm. lonR. o 9 mm
wide; female up to 290 mm. long, 2 mm. wide.

The long trilobed tail of the female, the long cylindrical caudal lobes in the male, the obliquely
truncated head, and the usually very dark-colored ring around the head make its identification
easy.

Montgomery found the larva only in Achaeta abbreviala (Gryllus assimilis). Found by
Minnie E. Watson in the same host at Urbana, Illinois, and by H. G. May in the same host
and also in Nemobius Jasciatus at Douglas Lake, Michigan.

From New England to New York, Virginia (and southward?; it is reported from (;uatemab):
also Kansas and CaUfornia. I have specimens from Lake Erie, Lake St. Clair, Lake
Michigan, and Nebraska.

e

Fig. 836. Paragordius varius. a, lateral aspect of head. X 25. (Originat) ft. vfnlr.il view of uil.
X 25. (Original.) c, dorsal view of tail (female). X 25. (After Stiles.) «/, surface view of cuticulm in
male and e, in female. Highly magnified. (After Montgomery.)

10 (9) Anterior region not attenuated, tip usually rounded.

Gordius lAwnwcns \-]S^ • ^^
Caudal end bilobed in male; simple, not enlarged in female.

11(22) Caudal end bilobed, spirally inroUed. . (Males of (TorJ;;/^) . . i:

12 (13) Arcuate cuticular ridge anterior and lateral to cloacal p<irc.

Gordius alasccnsis Montgomery kx)?.
Female not known; male 120 mm. lonp. slen-
der, cylindrical. Head roundi-tl. Cau<l.il lol>os
without hairs or spicules. .Aretiles irreRular. in-
terconnected. Color dark brown with darker
[Oj'^J neck ring.

Fig 8?7. Gordius ulufcrnsis. CuticuUr arrolr*.
lateral and ventral views of tail. Magnifictl. l-Mtcr
Montgomer>'.)

S40

FRESH-WATER BIOLOGY

13(12) No cuticular ridge anterior and lateral to cloacal pore 14

14 (15) Behind cloacal pore sharp V-shaped ridge.

Gordius villoti Rosa 1882.

For female of this species consult 23 in this key.
This species was described by Montgomery as G.
aquaticus. Several subspecies have been distin-
guished. In the typical form the cuticula is marked
with large light spots.

Male up to 655 mm. long, 1.3 mm. broad, equal
in diameter throughout; both ends obtuse; no true
areoles present.

From Canada, New England, New York to South

Carolina; westward to South Dakota, Montana, and

California; south to Oklahoma, Texas and Mexico.

1 iG. 838. Gordius villoti $ ; ventral view of Various Acridiidae serve as hosts for this species.

anterior and posterior ends of body. Magnified. Also found in Locustidae by H. G. May.

(After Montgomery.)

15 (14) Cuticula behind cloacal pore without sharp, V-shaped ridge. . . 16

Paragordius varius which miglit be confused here is readily distinguishable by the trun-
cated anterior end.

16 (17) On each side of cloacal pore a longitudinal Hne of hairs.

^-N Gordius lineatus Leidy 1851.

For female of this species consult 28 in this key.
Male up to 278 mm. long, 0.6 mm. broad; very slender. Pale
yellow or buff in color; areoles small. Perhaps only a young
form of G. villoti. Most of the specimens taken from springs.
Fig. 839- Gordius lineatus $ ; j^g^ York, Pennsylvania, Maryland, Michigan,
anterior and posterior ends, and
surface view of cuticula. Mag-
aified. (After Montgomery.)

17 (16) No line of hairs along side of cloacal pore; head not obliquely trun-

cated 18

18 (21) Conical spicules behind cloacal aperture 19

19 (20) Caudal lobes short, thick, and nearly conical.

Gordius densareolatus Montgomery 1898.

For female of this species consult 29 in this key.

Male up to 290 mm. long, i .1 mm. broad. Body robust. Conical spines
on ventral surface of caudal lobes. Color deep chocolate, with black
ring about cloacal aperture. Wyoming, Montana, California.

Fig. 840. Gordius densareolatus $ . \'entral view of posterior end.
(After Montgomery.)

Magnified.

20 (19) Caudal lobes nearly cylindrical.

Gordius longareolatus Montgomery 1898.

Female of this species unknown.
Male 115 mm. long, 0.5 mm. broad. Longitudi-
nally arranged elongate areoles characteristic and
^^ = ==^^ of rounded-conical form without median groove.
'=^^^'^.^=' No hairs between areoles. Color deep olive brown;
'^ •=-^- ^= tip of head white. California.

Fig. 841. Gordius longareolatus $ ; head, tail in ven-
tral aspect, and cuticular areoles. Magnified. (After
Montgomery.)

PARASITIC ROUNDWORMS

21 (i8) No conical spicules behind cloacal aperture; caudal lobes cylin-
^^^^^^ Gordius pliilyccp/uilus Monigomcry iii()».

For female of this spcdcs n.Msult ^o in tlii> key
Male up to 216 mm. Iomk, i mm. broad. The flattened
anterior end is characteristic, l.ut MontRomery fuund one
specimen apparently of G. densarrolalus with this feature and
could explain it only as a hybrid form. Canada. iVnnsvl-
vania, and Guatemala. '

Fig. 842. Gordius plalycephalus t
aspect. Magnified. (Aft

^ , head and ui! in vcntr&I
ter Montgomery.)

2 2 (11) Caudal end straight, not enlarged nor lobed.

(Females of Gordius) . . 23
Compare 5 in key.

2;^ (24) No elevated cuticular areoles on surface of body.

Gordius villoti Rosa 1882.
For male and range of this species consult 14 in this key.
. Largest female 705 mm. long, 1.9 mm. broad. One variety {G. villoti diffifilis .Mont-
gomery) has cuticular areoles at the ends of the body only. The other varieties arc like the
males marked with hght spots or plain. Montgomery found some points of difference from
the European type, and the American form may prove on further study to be a sep.-irale
species.

24 (23) Elevated cuticular areoles cover the entire surface of the body. 25

25 (26) Paired dark stripes occur in median lines.

Gordius leidyi Montgomery i8q8.

Male of this species is unknown. Female
295 mm. long, 1.5 mm. broad. .Sharply dis-
tinguished from all other species in the genus
by the peculiar truncated form of the jxtstcrior
end and the two narrow parallel stripes of
intense reddish brown in the median line of
the dorsal groove.

In the Leidy collection; source unknown.

Fig. 843. Gordius leidyi 9 ; head and tail in (lor-
sal aspect. Magnified, (.^fter Mont^jomco')

26 (25) Dark stripes in median lines arc lacking ^7

The tmknown female of Gordius longareolatus probably falls here.

27 (30) Areoles not elongated in long axis of body; head not tlailened. . i8

28 (29) Areoles close-set, tending to produce longitudinal ridges.

Gordius lineatus Leidy ii^5i.
For male and range of this species consult 16 in this key. . « 1

Female up to 283 mm. long, 0.8 mm. broad; Hke male very slender. Deeper buff color as

against the pale, transparent yellowish white of the male. In the female the cloacal onticc u

surrounded by a narrow reddish-brown ring.

29 (28) Areoles more or less confluent, tending lo produce transverse rows;

head usually cylindrical. , ^

Gordius dcnsareoliilus yUmif^omvry iSgS.

For male and range of this species consult 19 in this key. .... , ,, .1 u^u*

Female up to 3Q5 mm. long, 1.7 mm. broad. Body roI)ust. Head white followi-d by I Rht
buff ring and broad reddish brown ring; cloacal pore surrounded l>y thm black ring and "r.ua« r
circular reddish brown area; body generally chocolate or yelU)wish brown, t l.vu.ii ■■-
in a ventral depression.

o-PA

542 FRESH-WATER BIOLOGY

30 (27) Areoles not elongated, usually separated; head usually flattened;

interareolar groups of fine hairs.
Gordius platycephalus

Montgomery 1898.

""^oc^j" Yor male and range of this species cbnsult 21

in this key. Female up to 335 mm. long, 1.4
mm. broad. Posterior end slightly enlarged.
Color brown; tip of head lighter; dark ring
around neck.

Fig. 844. Gordius platycephalus ^ ; head in dorsal
aspect, tail in ventral aspect, and surface view of
cuticula. Magnified. (After Montgomery.)

ACAN THO CEPHALA

The Acanthocephala or proboscis roundworms constitute a most
remarkable group both in the extreme adaptation to the parasitic
habit which they manifest and in the unique structure which pre-
sents Httle or no parallel to any other type of animal. Most of
them are small, measuring only a few millimeters in length although
the common parasite of the pig, Gigantorhynckus hirudinaceus
(commonly called Echinorhynchus gigas), reaches a length of 15
cm. in the male and 30 to 50 cm. in the female.

In form they are elongate, roughly cyUndrical, or spindle-shaped
but with several distinct regions that give the body an irregular
form. These regions are a retractile proboscis armed with hooks,
a neck, and a body proper. When examined living the body is
often flattened or slightly bent, and displays a surface irregularly
roughened or marked by transverse ridges of varying size. When
removed to normal salt solution or preserved in other fluids, they
tend to assume a smooth rounded form, sometimes with slight
regular annulations that suggest segmentation but in fact do not
extend beyond the dermal layer.

At the anterior end the proboscis, which is retractile and in pre-
served specimens often partly or wholly withdrawn into the body,
presents a variable form being in various species cyHndrical, glo-
bose, filiform, spindle-shaped, and even more complex; it may be
long or short, straight, oblique, or at right angles to the long axis.
The particular form is characteristic of the genus or species and useful
in diagnosis. The proboscis bears always a considerable number of

PARASITIC ROUNDWORMS -43

recurved hooks which are arranged in rows. One can distinguish
both longitudinal and circular rows and as the hooks alternate
they form a quincunx pattern. The number, form, and arrange-
ment of the hooks are again diagnostic features. Usually the hooks
are strongly recurved but they may be almost straight and often
the form varies from tip to base of the proboscis. The form of the
root is also subject to variation in different species. In a few cases
the hooks differ on the dorsal and ventral sides of the proboscis.

In most species a neck intervenes between the proboscis and the
body proper. It is nearly always unarmed and usually short. At
times it is externally very sharply marked off from the \hhW or
again difficult to distinguish. Internally a cuticular fold or >rp-
tum divides the hypoderm of the proboscis and neck completely
from that layer in the body. The circular insertion of a retractor
muscle at this point also separates these regions from each other.

The body proper forms the major part of the animal. It is
usually unarmed but may bear small spines of definite form and
arrangement on some portion of the external surface.

The body wall has on the exterior a thin cuticula which is not
conspicuous as in nematodes. The subjacent hypoderm possesses
in one group a few very large and prominent nuclei which were
seen by early investigators though their true nature was not divined.
These nuclei usually show as sweUings or prominences on the sur-
face. In most Acanthocephala, however, the hypoderm has many
small nuclei which cannot be seen on casual observation. Two
elongate organs, the lemnisci, are projections of the h>poderm
posteriad into the body cavity. They originate at the line be-
tween neck and body proper and vary in size and form in dilTerent
species. Their function is unknown. The body wall contains a
system of lacunae which is conspicuous both in living and pre-
served specimens as two longitudinal vessels with smaller anasto-
moses usually numerous and irregular.

The proboscis sheath, usually a closed muscular sac. is attached
at the base of the proboscis, or rarely inside that organ. The j>ro-
boscis can be inverted into the sheath. The brain lies within thr
sheath concealed between the retractor muscle-. Its precise loca-
tion may be determined by the retinacula, a pair of nerve cords

544 FRESH-WATER BIOLOGY

passing from it directly through the sheath and obhquely to the
body wall.

No trace of an alimentary system has been found in the adult
or in any stage of development. Nutrition is thus provided for
entirely by absorption.

The sexes are separate in all cases. The genital pore in both is
at or very near the posterior tip. The male is smaller and more
slender than the female and often distinguished externally by a
bell-shaped bursa that surrounds the genital pore. This is a mus-
cular fold which is held within the body except at coition and
may be forced out by the contraction accompanying the preser-
vation of the specimen. Two oval testes He usually in the center
of the body one behind the other. Farther back is a group usu-
ally of a few large cells, the cement glands.

Fig. 844. Acanthocephalus ranae. Entire female, br, brain; bu, copulatory bursa; c? cement glands;
cr, cement receptacle; inr, invertor of neck region; /, lemniscus; pr, proboscis receptacle; /»/, postenor
testis; re, retinacula; rpr, retractors of proboscis receptacle; si, suspensory ligament; ta, anterior testis.
X 30. (After Van Cleave.)

In the female a Hgament extends through the center of the body
cavity from end to end. The ovary, which is present only in the
larval stage, produces great numbers of ova that later, surrounded
by a heavy covering of three distinct membranes, float free in the
body cavity. A complicated apparatus known as the uterine bell,
located in the body cavity near the posterior end, performs rhyth-
mic contractions that discharge from the body all well-developed
embryos and return to the body cavity all that are not sufficiently
matured.

The Hfe history of Acanthocephala is almost unknown. Those
parasitic in terrestrial hosts develop probably without any rela-
tion to the aquatic fauna as Gigantorhynchus hirudinaceus of the

PARASITIC ROUNDWORMS

545

pig finds its intermediate host in terrestrial beetle larvae. Of
forms from aquatic hosts it is inferred that the ripe embryos dis-
charged into the water with the feces of the host attain by chance
a suitable intermediate host which is probably a crustacean or in-
sect and in that develop to the end of the larval stage. When
this intermediate host is eaten by the final host the parasite reaches
the place in which it can complete its development.

Almost no records have been pubUshed of Acanthocephala from
North American fresh-water hosts. My own collections and re-
cent papers by Van Cleave, to whom I am indebted also for valu-
able unpubUshed data, give at best an imperfect survey of the
field. The system used, which follows in the main Llihe's work, is
also confessedly artificial and incomplete.

KEY TO NORTH AMERICAN ACANTHOCEPHALA

1 (lo) In hypoderm and lemnisci only a few giant nuclei.

Family NEOECHiNORHYNCHmAK Ward .

Primitive Acanthocephala with hypoderm consisting of a syncytium in which arc six giajil
nuclei, ordinarily arranged so that five lie in the mid-dorsal line and one in the mid- ventral.
One lemniscus contains two giant nuclei and the other only one. These nuclei are usually
conspicuous on external examination.

Proboscis sheath contains only a single layer of muscles. Cement gland a compact maf s.
Neck lacking. Muscles weakly developed. Lacunar system with simple circular connec-
tions.

2 (9) Proboscis globose, or nearly so; with three circles of hooks.

Neoechinorhynchus Stiles and Hassall 1005 . . 3

Proboscis short, globose, with few hooks. Hooks of anterior row much larger than those \j.
center and basal rows. Cement gland with eight nuclei.

3 (4) Twelve hooks in each circle.

Neoechinorhynchus gracilisentis (Van Cleave) IQI.^

Body small, tapering slightly toward both ends, bent
into a crescent. Mature females 1.7 to 4 mm. lonff:
maximum width 0..5S mm. just anterior to centi-r of
body. Males 1.5 to ,^ mm. long, ma.xinuim l)rcadth o.j
mm. Proboscis slightly longer than wide w^ilh con-
striction between second and third row of hooks.
Hooks delicate, in anterior rt)W curved 15 ui 17^
long, in middle row 1 2 to 1 5 M long, m basal row nearly
straight, 15 to 20/i lonK- Knibryos spmdlo shaped. 36
to 40 M long by 10 m broad . . ,„• • u-

. . In intestine and ceca of hickory shad; llUnois Kirer.
Fig. 845. Neoechinorhynchus gracilisentis. n^fr^Kf^r tr^ \Ttv
Proboscis. X9S; hooks and embryos, X OctoDer lo iua\ .
310. (After Van Cleave.)

4 (3) Six hooks in each circle.

546 FRESH-WATER BIOLOGY

5 (8) Terminal hooks over go (x long. Embryos under 50 ju long 6

6 (7) Body 8 to 32 mm. long. Embryos very small.

N eoechinorhynchiis emydis (Leidy) 1852.

Fig. 846. Neoechinorhynchus emydis.
X 75; hooks and embryos, X 230.
Cleave.)

Proboscis,
(After Van

Body much elongated, cylindrical. Female

10 to 32 mm. long, 0.7 mm. in maximum
width. Male 8 to 11 mm. long by 0.7 mm.
broad. Proboscis globose, 0.175 mm. long.
Hooks large, in anterior row strongly recurved,
95 to 103 /x long, in middle row 49 to 59 /x
long, in basal row 35 to 54 11 long, nearly
straight. Embryos very small, oval, 16 by

11 fX.

Originally described by Leidy from the in-
testine of various species of Emys from
Pennsylvania and Maryland. Frequent in
M alacoclemmys geographicus (Lesueur) and
Pseudemys elegans Max from the lUinois
River.

7 (6) Body 2 to 13 mm. long. Embryos about 40 n long.

Neoechinorhynchus tenellus (Van Cleave) 1913.

Neoechinorhynchus tenellus.
75; hooks and embrj-o,

Body small, both ends curved strongly ventrad.
Posterior two-thirds of body markedly attenuated.
Female 3.5 to 13 mm. long, 0.6 mm. in maximum
breadth; males 2 to 8 mm. long, 0.5 mm. broad. Pro-
boscis nearly cylindrical, 0.150 mm. long by 0.135 vara.
wide. Anterior hooks 90 to iio^u long, heavy; middle
hooks 38 /i long; basal hooks 27 /x long. Embryos
37 to 45 by 12 to 16 M-

Intestine of Esox lucius L. from Lake Marquette
near Bemidji, Minnesota.

X 230. (After Van Cleave.)

8 (5) Terminal hooks usually less than 90 ix long. Embryos over 50 m long.

Neoechinorhynchus cylindratus (Van Cleave) 19 13.

Fig. 848.
X75
Van Cleave.)

Large, straight-bodied. Female 10 to 15 mm.
long, 0.7 mm. in maximum width, just behind
proboscis. Male 4.5 to 8.5 mm. long, 0.5 to 0.7
mm. in maximum breadth near anterior end.
Proboscis slightly broader (0.172 mm.) than
long (0.15 mm.). Anterior hooks 79 to 97 ^
long, heavy, strongly recurved, center hooks
37 /x long, basal hooks 21 to 25 /x long. Em-
bryos 49 to 51 )U long by 15 to 21 fx broad.

In intestine of Micropterus salamoides (La-
cep.). Pelican Lake, Minnesota, and of An-
guilla chrysypa, Woods Hole, Massachusetts.

PARASITIC ROUNDWORMS

547

9 (2) Proboscis long.

Numerous irregular circles of about six hooks each.

Tanaorhamphus Ward.

The extreme length of the proboscis and the larRc number of hooks
serve to contrast this with the previous closely related genus H.xAs
in the anterior row are not conspicuously larger than those following.
The cement gland has 16 nuclei.

Only species known.

Tanaorhamphus longirostris (Van Cleave) igij.

Body robust, posterior end flexed slightly ventrad. Females
average 6.2 mm. long, and 0.63 mm. in maximum bn-adth Males
average 4 mni. long, and 0.47 mm. in ma.ximum breadth, i'roboscis
cyhndrical with slight constriction one-third distance from ba.se to
outer end, bent ventrad 60 degrees. Hooks in about 20 circular
rows of six to ten hooks each. Anterior hooks 54 M long, successive
hooks gradually smaller until within a few rows of the base where
they become abruptly smaller; basal hooks 16 m long. Embryos
oval 27 ^i long by 8 to 10 )u broad.

In intestine of hickory shad from Illinois River; not abundant but
probably most frequent in summer and wanting in January to .April.

Fig. 849. Tanaorhamphus longirostris. Proboscis, X 75; embroyos X210
(After Van Cleave.)

10(1) In hypoderm many small nuclei, not conspicuous externally. . . n
The proboscis sac has a double muscular wall.

11 (36) Proboscis and neck simple, without bulbous enlargement even in

fully developed specimens 12

12 (27) Hooks in each circular row all alike; no contrast between different

sides of proboscis 13

13(24) Proboscis sheath attached at posterior end of proboscis 14

14(19) Body of parasite entirely free from spines at all points 15

15 (16) Retinacula emerge from proboscis sheath at blind posterior end

which contains ganglion. Acanthocephalus Koelreuter 1771.
In marine and' fresh-water fishes and Amphibia, larvae in Isopoda.

Representative North American species.

Acanthocephalus ranac (Schrank) 17S8.

Body elongate, club-shaped, largest near neck. Proboscis short, cylindrical. Twelve rows
each with 6 or 7 hooks which are 60, 70, 80 and 50 fi long. Embryos \io ^l long by 13 ^ broad.
This European species has been identified by Van Cleave who showed that it is apparently
rare in this country.

From intestine of Diemydylus viridescens taken near Baltimore, Maryland.

16 (15) Retinacula emerge from lateral walls of proboscis sheath; ganglion

distinctly anterior to bhnd posterior end of sheath.

Echinorhynchus Zocga ly-jO . . 17

Neck wanting or very short; proboscis long, cylindrical, bent ventrad. Hooks numerous,
much alike throughout except that roots grow shorter and disappear in later rows.

In marine and fresh-water fishes.

Nearly every new species described from this continent has been assigned to this genus,
many of them erroneously. Several good species in North America. Abundant in whitefish
and lake trout from the Great Lakes.

548

FRESH-WATER BIOLOGY

17 (18) Embryos from
a e

5 to 108 M long.

Echinorhynchus thecatus Linton 1892.

Body cylindrical , slightly curved; proboscis curved also.
Female 11 to 26 mm. long; width 0.51 to 0.89, anteriorly 0.8
to 1,4 mm. in maximum, 0.52 to i mm. posteriorly. Male 7
to 12 mm. long; width 0.39 to 0.69 anteriorly, 0.59 to 0.95 in
maximum, 0.37 to 0.75 posteriorly. Hooks in 24 to 31 trans-
verse and 1 2 longitudinal rows surrounded by prominent collars.
Embr>'os 85 to 108 fx long by 18 to 22 fx broad. (Graybill.)

In ahmentary canal and body cavity of Micropterus dolo-
mieu, Ambloplites rupestris, Amia calva, and Roccus lineatus.
Great Lakes and eastern waters.

Fig. 850. Echinorhynchus thecatus. a, hooks from ventral side of
proboscis near base; b. hook from ventral, i.e., concave side of probos-
cis; c, hooks from dorsal, i.e., convex side of proboscis. X 150- (After
Linton.)

18 iiyj Embryos from 115 to 165 ix long. . Echinorhynchus salvelini Linkins.

Male 7 to 9 mm. long, 0.82 to 1.27 mm. broad. Fe-
male loto 17 mm. long, 1.2 to 1.6 mm. wide. Proboscis
armed with 26 circular rows of 8 hooks each. Hooks
alternate in adjacent rows. Basal hooks 39 to 50 /x
long; hooks in middle and anterior regions 44 to 68 /i'
long, those with basal processes 83 fj. long. Embryos
115 to 165 ^l long by 20 to 25 fx wide.

From lake trout; Lake Michigan.

Fig. 851. Echinorhynchus salvelini. Optical section through
anterior region of bodJ^ X 60. (After Linkins.)

19 (14) Spines on body at some point at least, usually at anterior end. . 20

20 (23) Body tapers regularly towards both ends. Proboscis in line with

axis of body. Posterior limit of spines alike on dorsal and
ventral surfaces 21

21(22) Cement glands tubular Poly morphus Liihe igii.

Fine spines on skin of anterior body. Just behind the limit of these spines a conspicuous
annular constriction. Type species P. minutiis (Goeze) from various European water birds.
At least one species yet undescribed from North American Anseriformes.

22 (21) Cement glands irregularly ovoid. (Males and some females or
young specimens.) Filicollis Liihe 191 1.

Compare number 37 in this key.

The males, the young females and even some adult females of certain species have a proboscis
that departs only slightly from the usual type, being a little enlarged but not conspicuously

PARASITIC ROUNDWORMS

549

set off from the neck. In the type species, FilicoUis analis, a European form not yet definitely
reported for North America, the adult female has the proboscis enlarged to a thin-walled
spherical bladder which bears the hooks on its anterior aspect in a series of radiating lines.
Representative North American species.

FilicoUis bolulus Van Cleave iqi6.
This peculiar form found in water birds has been reported from the eider (Somatcria dresseri)
from Maine. Although the range of the bird carries it (rarely) as far west as Colorado, yet
the particular parasite may not be native to fresh waters. Acanthocephala of this general
type have been reported from North .\merican ducks under the name of '' Echinorhynchus
polymorphus."

Fig. 852. FilicoUis bolulus. Female with tip of proboscis slightly inturned. X 10. Male, neck re-
tracted, body spines not shown. X i7- (After Van Cleave.)

23 (20) Body club-shaped, anterior end enlarged. Proboscis bent ventrad.

forming an angle with axis of the body. Spines extend
further posteriad on ventral surface than on dorsal.

Corynosoma Liihe 1004.

The peculiar form and the unusual distribution of spines on the body serve to identify the

members of this genus which is apparently limited in the adult stage to fish-eating birds and

mammals, chiefly seal. The genus is mainly marine but Van Cleave has a record of a species

from birds at Yellowstone Lake.

24 (13) Proboscis sheath attached at center of proboscis.

Family Centrorhynchidae Van Cleave 1916 . . 25
The proboscis sheath starts from near the center of the proboscis wall. The mature forms
are parasitic in the intestine of birds.

25 (26) Proboscis receptacle two layered: retractors penetrate its posterior

rounded tip Centrorhynchiis'Luhc iqii.

Three long tubular cement glands.

Only North American species.

Centrorhynchiis spinosus \'an Cleave 1Q16.

Female 20 mm. long, 0.6 mm. broad anteriorly. 0.5
mm. posteriorly. Proboscis 0.65 mm. long constricted at
insertion of proboscis receptacle with hooks of 2 tyjx^s in
30 longitudinal rows of about 24 hooks each.

In intestine of Ilerodias egretla from District of Colum-
bia (?).

Fig. 853. Ccntrorliyiultus spinosus. Proboscis and anterior
region of body, showing also insertion of [iroboscis receptacle
and location of the retractors of the receptacle with reference
to the wall. X 26. (After Van Cleave. )

26 (25) Proboscis receptacle single layered; retractors pass through its sides

some distance anterior to posterior tip.

Mcdiorhynchus Win Cleave 1Q16.
Nerve gangUon near center of proboscis receptacle. In male 8 round or pyriform cement
glands. Proboscis hooks distinctly of two types. Proboscis receptacle not cylindrKal in form.
Known species mostly in land birds but one record concerns the Carolina rail, / orzana Caro-
lina, that might have been infected from an aquatic intermediate host.

550 FRESH-WATER BIOLOGY

27 (12) Hooks not alike on ventral and dorsal surfaces of proboscis. . . 28

28 (29) Hooks differ in form, especially of root, but not in size. Body uni-

formly cylindrical or nearly so.

Rhadinorhynchus Liihe 191 1.

Hooks of dorsal surface with much shorter root, also slenderer and less curved than those on
ventral surface. In marine fishes almost exclusively, but present in trout from eastern states.
Species yet undcscribed.

29 (28) Hooks differ noticeably both in form and size. Body very large

and slender, with marked enlargement near anterior end.

Arhythmorhynchus Liihe 191 1 . . 30

Body in front of enlargement covered with fine spines. Proboscis very long, enlarged at
center, oblique to body axis. Adults in intestine of birds.

30 (31) Hooks on mid- ventral surface of proboscis conspicuously larger

than any others.

Arhythmorhynchus trichocephalus (R. Leuckart) 1893.

Body very slender. Length 5 to 8 cm., diameter 0.5 to 0.8 mm. Ovoid swelUng 2.3 to 2.9
mm. behind neck with length of 1.6 to 2.4 mm. and breadth of 0.6 to 1.4 mm. Anterior to
swelling many dermal spines 28 to 35 ju long. Proboscis with 20 longitudinal rows and 19 or
20 transverse rows of hooks.

From Florida; host unknown.

31 (30) Hooks on mid-ventral surface of proboscis not conspicuously larger

than others 32

32 {t,2,) Large hooks exceed 100 ^t in length.

Arhythmorhynchus uncinatus (Kaiser) 1893.

Length 4 to 6 cm., diameter i to 1.2 mm. Ovoid sweUing about 5 mm. behind neck; 0.6
mm. in front of sweUing prominent annular enlargement i to 1.4 mm. long, 1.7 to 2 mm. in
diameter and covered thickly with small spines. Proboscis with 18 transverse and 18 longi-
tudinal rows of hooks.

From Florida; host unknown.

33 (32) Large hooks not more than 50^1 long.

34

34 (35) Eighteen longitudinal rows of hooks.

Arhythmorhynchus hrevis Van Cleave 19 16.

Female 6 to 12 mm. long, 3 mm. wide. Male 5 to 6 rrm.
long, I to 1.5 mm. wide. Neck naked. Body just back of
neck with few small spines. Proboscis 0.665 mrn- long, 0.23
mm. wide at base, 0.19 mm. at tip, 0.34 mm. at center. Em-
bryos 76 to 100 n by 24 to 30 ju. Middle shell heavy, with
rounded swelling at each pole.

From bittern {Botaurus lentiginosus); Baltimore, Mary-
land.

Fig. 854. Arhythmorhynchus brevis. Anterior end of body. X 40-
..(After Van Cleave.)

PARASITIC ROUNDWORMS

551

35 (34) Proboscis with sixteen longitudinal rows of hooks.

Arhythmorhynchus pumilirostris Van Cleave 1916

Female up to 30 mm. long, and 1.5 mm. broad. Proboscis 0.45
mm. long, 0.114 mm. wide at base, 0.095 mm. at tip, 0.18 mm at
center. Embryos 65 to 89 /* long, 18 /x broad. Middle shell with
evagination at each pole.

Yrova. hiti^xn {Botaiiruslentiginosus); Washington D. C.

Fig. 855.

Arhythmorhynchus pumilirostris. r ofile, anterior end
body. X 95- (After Van : leave.)

36 (11) In anterior region of mat'\e specimens prominent bulbous enlarge-
ment, separated Irom body by slender cyHndrical neck. 37

The bulb is embedded in the intestinal wall or may even be in the body cavity when the
slender region traverses the wall connecting with the body of the parasite in the intestine. In
handling such material the proboscis may easily be partly or completely torn ofiF, and the para-
site is then difficult to identify as the characteristic bulb at least is gone.

37 (38) Bulb consists of the proboscis,
bulb in radial lines.

Hooks on the anterior face of the
(Females of) FilicoUis Liihe 191 1.

Representative North American species.

FilicoUis hotidus Van Cleave 1916.

In females thus far reported under this name for North America the bulb is wanting; it may
be present in older specimens and in fact is described in specimens recorded under the name
E. anatis which may belong here.

Compare number 22 in key.

38 (37) Bulb consists of anterior part of neck only. Proboscis extends an-
teriad from bulb. . . . Pomphorhynchus MonticelH 1905,

Proboscis long, cylindrical, with many hooks. Neck very long, expanded in anterior region,
slender, cyHndrical in posterior portion. In intestine of fishes; one of the commonest types
in European fresh-water hosts. Not infrequent in North American fresh-water fishes; species
not described.

IMPORTANT REFERENCES ON NORTH AMERICAN PARASITIC

ROUNDWORMS

GENERAL WORKS

See also list in Chapter XIII, page 452
1 89 1. Die Nemathekninthen. Heft i, 120 pp,

Hamann, 0

Heft 2, 120 pp., II pi. Jena.
Leuckart, R. 1876. Die menschliche Parasiten.
Acanthocephala]. 882 pp., 401 figs. Leipzig.

Vol.

, 10 pi. 1S05.
2 [Nematoda,

552

FRESH-WATER BIOLOGY

NEMATODA

Brasche, R. von. 1882-3. Revision der in der Nematoden-Sammlung des
K. K. zoologischen Hofcabinetes befindlichen Original-Exemplare Die-
sing's und Molin's. Verb, zool.-bot. Ges. Wien, 32: 1 17-138, 4 pi.; ^t,:
107-118, 3 pi; 33: 193-218, 4 pl-

Hagmeier, A. 1912. BeitragezurKenntnisder Mermithiden. Zool. Jahrb.,
Syst., 32: 521-612, 5 pl.

Hall, M. C. 1916. Nematode Parasites of ^Mammals, etc. Proc. U. S.
Nat. Mus., 50: 1-258, I pl.

LiNSTOW, O. von. 1909. Parasitische Nematoden. Siisswasserfauna Deutsch-
lands, Heft 15, p. 47-81.

Magath, T. B. 1916. Nematode Technique. Trans. .Amer. Mic. Soc, 35:
245-256.

Railliet, A. and Henry, A.

191 5. Sur les Nematodes du genre Camallanus Raill. et Henry, 191 5
(Cucullanus auct., non Mueller, 1777). Bull. soc. path, exot., Paris, 8:
446-452.

Ransom, B. H. 1911. The Nematodes Parasitic in the AHmentary Tract of
Cattle, Sheep, and other Ruminants. Bur. An. Ind., Bull. 127, 132 pp.

ScHNEroER,A. 1866. Monographic der Nematoden. 357 pp. 28 pl. Berlin.

Seurat, L. G. 1916. Contribution a I'etude des formes larvaires des Nema-
todes parasites heteroxenes. Bull. sci. France et Belgique, 49: 297-377.

Stossich, M. 1896. II genere Ascaris Linne. 1897. Filarie e Spiroptere.
1899. Strongyhdae. Trieste.

Ward, H. B. and Magath, T. B. 19 16. Notes on Some Nematodes from
Fresh- Water Fishes. Jour. Parasitol., 3: 57-64, i pl-

gordiacea

Montgomery, T. H., Jr. 1898. The Gordiacea of Certain American Col-
lections. Bull. Mus. Comp. Zool. Harvard, 32: 23-59, 15 pl.

1898a. The Gordiacea, etc. Pt. H. Proc. Cal. Acad. Sci., (3) i: 333-344,
2 pl.

1899. Synopses of North American Invertebrates. II. Gordiacea (Hair
worms). Amer. Nat., $$: 647-652.

ACANTHOCEPHALA

LiJHE, M. 191 1. Acanthocephalen. Siisswasserfauna Deutschlands, Heft

16, 60 pp., 87 figs.
Van Cleave, H. J. 1913. The Genus Neorhynchus in North America.

Zool. Anz., 43: 177-190.
1915. Acanthocephala in North American Amphibia. Jour, Parasitol., i:

175-178.

CHAPTER XVII
THE WHEEL ANIMALCULES (ROTATORL\)

By H. S. JENNINGS

Professor of Zoology, Johns Hopkins University

The Rotatoria or Rotifera are perhaps the most characteristic
group of fresh-water animals, and at the same time the most
attractive and beautiful. They are everywhere abundant in fresh
water, but are rare elsewhere. With their varied and fantastic
forms, their brilliant colors and lively manners, the}- have long
been the favorites of amateur microscopists. Some of the older
observers have expressed themselves with great enthusiasm in
regard to these creatures. Eichhorn (1781) who discovered Sieph-
anoceros in 1761, calls it the "crown polype," and Kkens this "in-
comparable animal" to a pomegranate blossom. Of Floscidaria he
says, "Now I come to a very wonderful animal, which has very
often rejoiced me in my observations: I call it the Catcher: ex-
traordinarily artistic in its structure, wonderful in its actions, rapid
in capturing its prey." Eichhorn's account of the capture of prey is
excellent: "Its head was a widespread net . . . with points which
had little round balls on their tips; so it awaits its prey; when a
little animal came into this net or hollow basin, then it conMil-
sively drew the neck a little together, as if to find out, as it were,
whether it had really gotten its booty; then it suddenly folded the
net together and pushed the prey into its body, where one could
still see it plainly. . . . And I have often seen it exactly as in
[Fig.] K\ then it looked terrible, no lightning stroke can rush from
the clouds into the air so quickly as this little animal fiercely struck
together the two hooks when it noticed a prey in its outspread
net."

The rotifers are minute, chiefly microscopic animals. Their
most characteristic feature is the ciliated area at or near the ante-
rior end of the body, serving as a locomotor organ or to bring food
to the mouth. Taken in connection with the lack of cilia on other
parts of the body (save in rare cases at the posterior end), this

553

554 FRESH-WATER BIOLOGY

ciliated area or corona serves as a rule to distinguish a rotifer at
once from any other many-celled animal Hving in fresh water.

The extreme diversity of form and organization in different
rotifers, though constituting the greatest charm of their study,
makes it almost impossible to give a formal definition of the group.
Even the most characteristic feature, — the cihated corona, —
is in a few cases lacking. The form of the body varies extremely,
from spherical in Trochosphaera (Fig. 947) to the excessively atten-
uated form of Rotifer neptunius (Fig. 960), the fiower-Hke shape of
Stephanoceros (Fig. 937), or the spiny, turtle-like figure of Poly-
chaetus (Fig. 905).

Yet one can give a characterization that will be true for the great
majority of the rotifers. The body is as a rule somewhat elon-
gated, with the cihated corona at the anterior end ; it is extended at
the posterior end, behind and below the cloacal opening, to form a
stalk, or tail-like appendage known as the foot. This frequently
ends in two small pointed toes. There is a well-developed ali-
mentary canal, with a muscular pharynx, containing complex jaws.
There is a simple excretory system, while circulatory and respira-
tory systems are lacking. The nervous system consists of a prom-
inent brain and of certain nerves and sense organs. The sexes are
separate, and the male is usually a minute, degenerate creature,
lacking the alimentary canal.

Rotifera may be found wherever there is fresh water. Lakes,
pQnds, and streams harbor them in immense number and variety.
Swamps and marshes swarin with them. Wayside pools, drains,
and even the dirty water that stands in barnyard holes about
manure heaps, are proKfic sources of rotifers. The mud of eave-
troughs, the bottoms of funeral urns, the cavities found in the axils
of the leaves of certain mosses, — all these are famous collecting
grounds for the rotifer hunter. A few rotifers are parasitic, some
externally, some internally. A few live in salt water, but they are
much less abundant in the ocean than in fresh water.

In giving an account of the structure and life of the rotifers, it
will be well to have in mind at first some representative type ; then
the variations found in other rotifers may be traced. The typical
rotifers, as well as the commonest ones, are those belonging to the

THE WHEEL ANIMALCULES (R0TAT0RL\)

:>:>:)

great family of Notommatidae, and there is much reason to believe
that all other rotifers have been derived from forms essentially
similar to those found in this family. The different members of
the Notommatidae are so much alike that it is hardly necessary
to select precisely some one species for a type. But it will be well
in following this account to have in mind such an animal as Proalcs
(Fig. 856), or Notommata truncata (Fig. 857, yl and B), or Co pens

o —

OM

mg-

^m

Fig. 856. Proales werneckii Ehr., a typical notommatoid rotifer. A, Female, dorsal view. X 400.
B, Male, side view. For explanation of letters, see Fig. 857. X 600. (.\fter Rousselet.)

pachyurus (Fig. 857, C). For convenience one can refer to any
member of the Notommatidae as a notonimatid.

The notommatids, though the most abundant, are as a rule the
least conspicuous of the rotifers. They have usually a nearly
cylindrical body, often somewhat swollen behind, and with a
slender posterior foot (/) ending in two toes (/). Most of them are
found swimming about amid vegetation or creeping o\'er its sur-
face. Like all other living things, these rotifers are bundles of
activity. They are busily engaged in carrying on many processes.

556

FRESH-WATER BIOLOGY

internal and external; in meeting and solving the problems which
the world presents. And it is almost surprising to note, when the
matter is first examined from such a standpoint, how nearly the
objects of the stri^ ings of almost any lower group resemble those
of the highest. To get proper food and oxygen; to find or construct
a proper place to dwell; to arrange for the production and growth
of the young; to protect one's self and one's progeny from ene-

FlG. 8s7. Notommatoid rotifers. A , Notommata truncata Jennings, side view. X 300. B, same, dorsal
view. X 300. C, Copeus packyurus Gosse. X 150. The letters in Figs. 856 and 857 have the follow-
ing signification: 6r, brain; c, cloaca; co, copulatory organ; ct, contractile vacuole; e, eye; ea;, excretory
organs; /, foot; fc, flame cell; gg, gastric glands; in, intestine; la, lateral antennae; m, mouth; mg,
mucous glands of foot; ms, muscles; mx, mastax; 0, esophagus; ov, ovary; sg, sahvary glands; sp,
spermarium; st, stomach; t, toes. (.After Weber.)

mies and from the forces of nature, — these, and the activities
growing out of them, form the groundwork of Hfe in the lowest as
well as the highest creatures. In studying the rotifers, it will be
best to look upon them as Hving things and to ask: What processes
and activities are they carrying on? And what apparatus do they
use in these activities? Thus, one is led to take up in order the

THE WHEEL ANIMALCULES (ROTATORIA) 557

various systems of organs, to notice their variations and modifica-
tions, and the uses they serve.

Perhaps the chief concern of all organisms is to provide material
for carrying on the complicated chemical processes that are going
on within, — that is, to get food and oxygen. How does the
rotifer accomplish these ends?

This is done mainly by the aid of the ciliated surface at the
anterior end, — the corona. The cilia of this region are fine, hair-
like processes which are in constant motion. They strike back-
ward more strongly than forward, so that they cause a current to
pass backward from in front of the animal to its mouth, and thence
over the surface of the body (Fig. 858). In the simplest notommatids

\ \ N

N ^

*^

Fig. 858. Currents of water caused by the cilia of a rotifer. The dotted area shows how material lyin?
in front of the rotifer is drawn out in the form of a vortex to its mouth. (The rotifer is Proales sordida Gosse,
from a figure by Dixon-Nuttall.)

the corona is a mere flattish disk on the ventral side of the anterior
end, covered uniformly with short ciha (Fig. 859). In other rotifers
there are great variations in the size and arrangement of the cilia;
these variations will be taken up later. The water current pro-
duced by the corona has a number of different uses:

1. It continually renews the water that bathes the surface of the
animal, thus insuring a constant supply of fresh oxygen. The
oxygen thus supplied is absorbed by the entire surface of the ani-
mal, apparently, for there are no special respiratory organs.

2. The current brings to the mouth any particles of food that

558

FRESH-WATER BIOLOGY

may be floating in the water, or that are easily washed from sur-
rounding objects. The mouth, situated in the posterior part of
the corona, opens, and so admits or seizes such food as is adapted
to the rotifer. In many rotifers the cilia are the chief direct agents
in obtaining food, and in practically all species they are either
directly or indirectly of the greatest importance for this function.
A

Fig. 859. Corona of Proales tigridia Gosse. A, surface view, from ventral side. B, side view.
m, mouth. (After Wesenberg-Lund.)

3. In place of bringing food and oxygen backward to the rotifer,
the cilia may carry the animal forward to new supphes of these
necessities. This is the case in all free-swimming rotifers; the ciha
are the main organs of locomotion. In thus moving the animals
about, the ciha of course play as important a part in food-getting
as when they bring the food to the rotifer. In most species the
ciha act in both ways at once, bearing the animal forward and the
food backward, so that the two meet.

4. The water currents remove the products of respiration and
excretion, which the rotifer, Hke other animals, is continually
giving off. Carbon dioxide is doubtless given off over the whole
surface of the body, while other waste products are discharged by
the contractile vesicle (see p. 561). If these waste products were
allowed to accumulate, they would be most injurious.

While these are the main uses of the cilia, they assist, in a num-
ber of rotifers, in other important operations, such as the con-
struction of a tube or nest.

The further course of the food may now be followed. The mouth,
situated in the posterior part of the corona (Fig. 859, w), leads into
a cavity with thick, muscular walls, known as the mastax (Figs. 856
and 857, mx) . The mastax is armed with a complicated set of jaws,
which have little resemblance to jaws found anywhere else in the
animal kingdom. They are known as the trophi (Fig. 857, i4, tr).

THE WHEEL ANIMALCULES (ROTATORIA) 559

The trophi consist of a number of pieces, so arranged that two main
parts may be distinguished. There is a middle portion, somewhat
fork-shaped, which is known as the incus (Fig. 860, in), and two
lateral parts known as the mallei {ma).

In the middle portion or incus may be distinguished a single
basal piece, comparable to the handle of the two-tined fork; this
basal piece is known as the fulcrum {fu, Fig. 860). The two blade-
like pieces resting on it, i.e, the tines of the fork, are the rami ira).
A B

ma.:
-rnu.

~mu.

Fig. 860. Trophi or jaws of rotifers. ^, Malleate type. (From Wesenberg-Lund, after Hudson and
Gosse.) B, Forcipate type, from Z)ig/e«a/orc//>a/a Ehr. (After Gosse.) /m, fulcrum; in, incus; m<i, mallei;
mil, manubrium; ra, ramus; un, uncus.

The rami are joined to the fulcrum in such a way that they may
move back and forth, like the blades of a pair of shears. They
often bear teeth.

In the lateral parts or mallei one may likewise distinguish two
parts. The basal piece, serving as a sort of handle, is known as the
manubrium (Fig. 860, mu). Joined to the top of this, but placed
nearly at right angles to it, is the piece known as the uncus {iin)\
the two unci usually lie across the tops of the rami, their points
meeting in the middle. Each uncus may bear one or more points,
or a number of sharp ridges serving as teeth. The food passes
between the teeth of the unci and rami and is cut and ground by
them. The jaws are worked by muscles which are attached to
the manubria and to other parts of the apparatus; these muscles
make up the main part of the mastax.

In different rotifers the trophi vary much in the form and rela-
tive development of the t>T)ical parts; this is true even within the
Notommatidae. There are two main lines of divergent develop-
ment: (i) In many rotifers the parts of the trophi become thick
and stout; the unci are broad plates bearing a number of ridges.
Such jaws are used mainly for grinding, and are said to belong to the

560

FRESH-WATER BIOLOGY

malleate type (Fig. 860, ^), on account of the great development of
the mallei. (2) In other species all parts of the trophi are long and
slender; the unci end in a single sharp point, which may be thrust
out of the mouth to seize upon living prey. The two rami Hke-
wise form a pair of strong, blade-Kke jaws. Such trophi are said
to belong to the forcipate type (Fig. 860, B) ; they are found in active
rotifers of predatory habits. There exist many modifications of
these two types, and many jaws intermediate between the two.
Both types of jaws are found in the Notommatidae.

The mastax usually bears near its posterior end a pair of small
glands that are known as salivary glands (Fig. 856, sg). From the
mastax the food passes into the slender esophagus (Figs. 856 and
857, 0), which leaves the mastax on its dorsal side. Through the
esophagus the food reaches the large stomach (st), where digestion
takes place. Attached to the anterior end of the stomach are the
two large gastric glands (gg). From the stomach the undigested
remnants of the food pass back into the straight slender intestine,
and thence to the outside at the cloacal opening (c). This lies on
the dorsal side of the body, above the foot.

The body cavity is enclosed by but a single layer of cells, which
form the body wall, so that each cell is bathed on its outer surface
by the outer water and on its inner surface by the fluid of the body
cavity. By this arrangement the processes of respiration are
made very simple. Oxygen doubtless passes from the surround-
ing water through the single layer of cells into the body fluid, while
the waste carbon dioxide produced within is given off in the same
way to the outside.

The nitrogenous waste products are not so easily eliminated as
is the carbon dioxide; for removing these the rotifers have a set of
excretory organs. These consist of fine tubules running through
the body cavity at the sides of the alimentary canal (see Fig. 857,
ex, and Fig. 861). On each side there are usually two tubes, one
with thick walls (a), the other with very thin ones (b). These two
are usually connected (c) in the anterior part of the rotifer. They
commonly bear at intervals along their course certain minute
club-shaped organs (Figs. 85 7 , 5 ; 86 1 ,/c) . These are closed at their
free ends, and contain within them either a vibrating membrane

THE WHEEL ANIMALCULES (ROTATORIA)

561

or a bunch of long cilia. The membrane or the bunch of cilia is
always in rapid movement, giving the appearance of a minute
flame, so that these structures are called flame cells. The cilia or
membrane doubtless serve to propel a current through the tubes.
In many rotifers a transverse tube in the head region unites the

Fig. 86r. Excretory organs. .1, LAcinularia socialis Ehr., showing the thin-walled tube a, the thick-
walled tube b, the transverse connecting tube c, and the flame cells /c. Modified from a figure by Hlava.
B, Excretory tubules of right side in Floscularia campanulata Dobie. cv, contractile vesicle; fc, tlame
cells. (After Montgomery.)

thin-wafled tubes of right and left sides. Often all the tubes are
convoluted in their course.

There is reason to believe that the walls of the tubes absorb the
nitrogenous waste matter from the fluid of the body cavity. This
waste matter passes backward, driven by the flame cells, to the region
of the cloaca (Figs. 856, 857, c). Here is found in most rotifers a
small sac into which the tubes from both sides enter. This sac opens
along with the intestine into a small cavity known as the cloaca.
The sac, or contractile vesicle (cv), as it is called, contracts at
intervals, expelling to the outside the fluid with which the tubes

a

Fig. 862. Spiral path followed by swim

— ■ ■'ifer. as seen in D' " '' '

(After Jennings.;

ming rotifer, as seen in Diurella tiKris
MUller. -■- - -

FRESH-WATER BIOLOGY

have filled it. The contractions take
place frequently, so that a large amount
of fluid is expelled.

Besides its organs for the nutritive
processes, the rotifer has of course or-
gans for causing and controlling move-
ments. The chief organ of locomotion
is the cihated corona. By its aid the
rotifer may either creep along over
surfaces, or swim freely through the
water. When swimming freely the ro-
^ tifer usually revolves on its long axis,
so as to follow a spiral course (Fig. 862).
Changes of form and movements of
parts of the body are brought about
i by many slender muscles (Fig. 857, C,

I ms). These muscles are either applied

closely to the body wall or pass from
the body wall through the body cavity
to other parts. The muscles are often
striated.

An important organ for producing or
guiding motion is found in the foot
with its toes. The foot of the notom-
matid is usually short; it is nothing
more than that part of the body be-
hind the cloaca. It usually tapers
somewhat, but is not clearly marked
off from the rest of the body, as it is
in some rotifers of other families. At
its posterior end it bears side by side
the tapering, pointed toes, which are
usually small in the Notommatidae.
The toes serve as a steering apparatus
in swimming, and as points of sup-
port and attachment in creeping. For
attachment the toes are supplied with

THE WHEEL ANIMALCULES (ROTATORL\) 563

two glands lying in the foot (Figs. 856 and 857, mg); these secrete
a sticky, tenacious mucus, which may be discharged either at the
tip of the toes, or at their base, so as to flow out over their surface.
By this mucus the rotifer may attach itself loosely to objects of
various sorts, so that the movements of its cilia may continue to
bring food to the mouth without carrying the rotifer away from
its anchorage. Often the mucus is drawn out to form a long
thread, like that produced by a spider; from this thread the rotifer
remains as it were suspended, swinging about from side to side at
a distance from the point of attachment, but not breaking away
from it completely. At times the rotifer spins out behind it a
thread of mucus "as it progresses slowly through the water; this
thread steadies its course and keeps it connected with its point of
departure. The foot and toes are modified in many ways in other
groups, as will be seen later.

For controlling motion the rotifer has a nervous system and a
number of sense organs. The chief part of the nervous system is a
large gangHon known as the brain (br), lying on the dorsal side,
just above the mastax, at the anterior end. From the brain
nerves pass in many directions to the various organs of the body.

Several different kinds of sense organs are found in the rotifers.
In some part of the anterior end, usually attached to the brain,
there are usually one or two red pigment spots; these are supposed
to be organs of light perception, and are known as eye-spots (e).
In a few cases three or more of these are found. Sometimes the eye-
spots are not attached directly to the brain, but are connected with
it by nerves (for example, in the genus Rotifer). The eye-spots
sometimes bear on their anterior surfaces hemispherical cr}'stalline
lenses. In some rotifers eye-spots are lacking.

Many rotifers bear sense organs of various kinds on the corona
(see for example the corona of Synchacta, Fig. ^S^, or of Ilydatina,
Fig. 906, B). Such sense organs are less common in the Notomma-
tidae than in more specialized rotifers.

Almost all rotifers have a pair of sense organs on the sides of
the body behind the middle; these are known as the lateral an-
tennae (Fig. 857, C, la). Either another antenna, or a pair of ihem,
is found on the dorsal surface of the head, just above the brain;
these are known as the dorsal antennae (Figs. 856 and 857, da).

564 FRESH-WATER BIOLOGY

The organs of reproduction are still to be considered. Most of
the rotifers commonly seen are females, as the males are very
minute and rare. In the Notommatidae, as in most other rotifers,
there is a single large reproductive body, commonly spoken of as
the ovary, or sometimes as the germarium. This Hes ventral to the
intestine, in the posterior third of the body (Figs. 856 and 857, ov).
It consists of two portions, of different functions. The large part
contains a small number of large nuclei, often just eight; this por-
tion prepares the yolk for the developing Qgg, so that it is called
the vitellarium. At one end or side of this vitellarium is a small
mass containing many minute nuclei. From this part the egg
develops, the small nuclei becoming each the nucleus of an egg.
This part is known as the germarium, since it produces the egg or
germ. From the ovary a thin-walled, sac-like passageway, the
oviduct, leads backward to the cloaca; by it the egg is discharged.
The oviduct can be seen, as a rule, only with great difficulty.

In most rotifers the males are small and degenerate. But in
some of the Notommatidae, as well as in a few other species, they are
nearly as well developed as the females, and resemble them in
structure. In Proales werneckii (Fig. 856), which lives within Vau-
cheria filaments, the male is as large as the female, but the ali-
mentary canal is not quite so well developed. In Rhinops vitrea
(Fig. 863), the male is smaller than the female but not otherwise
degenerate, while in the aberrant rotifers known as the Seisonacea
males and females are alike, save for the reproductive organs. In
most other rotifers the minute males either lack the ahmentary
canal entirely or have only vestiges of it (see Fig. 864). In all
cases in the male in place of the ovary is found a sac, the sperma-
rium (sp), in which many spermatozoa are seen swimming about.
The sac extends backward as a large tube, ending in a ciliated
opening from which the spermatozoa are discharged. That por-
tion of the tube bearing the opening may be protruded as a copu-
la tory organ.

The chief structures of a typical rotifer have now been described,
mainly as shown in the Notommatidae. Next, the Rotifera as a
whole will be surveyed and the different groups examined rapidly
to note how these differ from the notommatids and from one an-

THE WHEEL ANIMALCULES (ROTATORIA)

565

other. Such a survey gives strongly the impression that the other
rotifers have been derived by various modifications from rotifers
having in general the characteristics of the Notommatidae. Space
will not permit setting forth in detail the grounds for this impres-
sion, nor will it allow describing the many forms transitional be-
tween the Notommatidae and other groups. But in giving an

Fig. 863. Male oi Rhino ps vitrea,
Hudson, showing presence of
the alimentary canal, co, cop-
ulatory organ; mx, mastax; 0,
esophagus; sp, spermarium;
St, stomach. X 400. (After
Rousselet.)

Fig. 864. Male of Copeus pachyurus Gos.se,
showing absence of alimentary canal, br,
brain; co, copulatory organ; 5/>, sperma-
rium. X 260. (After Dixon-Nuttall.)

account of the other rotifers, they will be grouped about the No-
tommatidae in the way which appears to be called for by the facts.^

1 This follows mainly Wesenberg-Lund (1899), who has developed a classification
of the Rotifera based on their origin from Notommatoid forms. While this classifi-
cation has not thus far been commonly employed, the same can be said of any other
classification that has been proposed. The writer is convinced that the classification
given by Wesenberg-Lund is the only really natural one and that its use is a great
aid to an understanding of the Rotifera; he has therefore employed it. It should be
noted, however, that the arrangement here given differs in many details from that of
Wesenberg-Lund, as the advance of knowledge, or the writer's own experience, seems
to require. No scheme of classification can be completely li.xed until knowledge of
the organisms to be classified is infinitely more complete than is the present knowledge
of the Rotifera.

566 FRESH-WATER BIOLOGY

1. Notommatidae. It will be helpful first to notice some of the
chief variations of type among the Notommatidae themselves.
The simplest, most undifferentiated rotifiers that exist are those
commonly classed in the genus Proales. They have small, soft
bodies, nearly cylindrical, and obscurely segmented externally
(Fig. 856). The foot and toes are short. The corona is a uniformly
ciliated, nearly plane surface on the ventral side and anterior end
(Fig. 859). These rotifiers are small, sluggish creatures, very numer-
ous, but not differing greatly among themselves, so that the species
are hard to distinguish and students of the rotifiers have paid
little attention to them. In other species of the Notommatidae
the corona has become differentiated in a peculiar way, forming
the so-called auricles; these species are classed mainly in the genus
Notommata. The auricles are portions of the ciliated area set off
prominently on each side of the corona and bearing stronger cilia
(Fig. 857, jB) ; they serve to enable the animal to move more rapidly.
In the simplest cases the auricles are directly continuous with the
rest of the ciliated disk, as in Notommata aurita (Fig. 878) . In other
cases there i*s a space without ciHa between the disk and the auri-
cles (Fig. 881). The auricles are commonly kept contracted when
the animal is creeping about, so that their existence would not be
suspected. But when the animal prepares to swim through the
water it unfurls these auricles and sails away. The species of
Notommata are more active than Proales, and there are greater
differences among the different members of the genus.

2. Synchaetidae. A Kne of divergence, consisting essentially in a
greater development of those characteristics of Notommata which
give it rapidity of movement, leads to the production of what
is commonly classed as a different family, — the Synchaetidae
(Fig. 880). In Synchaeta the entire corona is very large,
occupying the large end of the cone-shaped body, while the
auricles are highly developed, forming powerful swimming organs
which are set off at a distance from the remainder of the co-
rona. By the aid of these auricles the species of Synchaeta dash
about with such rapidity that they can hardly be followed with the
microscope. (See the monographic study of the Synchaetidae by
Rousselet, 1902.)

THE WHEEL ANIMALCULES rROTATORL'\) 567

A further development of this line is seen in Polyarthra (Fig. 882).
Here powerful swimming organs have developed in the form of
appendages along the sides of the body, while the auricles have dis-
appeared. The animal never attaches itself, so that the disap-
pearance of the foot is complete. In Anarthra (Fig. 885) we fmd
precisely a Polyarthra that has not yet developed the appendages,
or that has lost them (?).

Synchaela and Polyarthra are typical open-water rotifers, consti-
tuting important elements of the plankton.

To introduce the families of Rotifera next to be considered, it
is necessary to return to certain features of the Xotommatidae.
Many of the species of that family show a very slight tendency to
a stiffening of the cuticula, so that the body retains a somewhat
definite form, often a little angular. Such notommatids are classed
in the genus Furcularia (Fig. 870). These are usually more active
than Proales or Notommata, and have longer, stiffer toes. By
accentuation of these features of Furcularia, and by further spe-
cialization, there are formed several families of free-swimming
rotifers :

3. Salpinidae. The cuticula becomes more hardened, and three
or four longitudinal furrows are formed, one in the dorsal middle
line, one on each side, and sometimes a weak one in the ventral
middle line. Thus there is produced a sort of armor or lorica,
composed of three or four plates (Figs. 886, 887). Such loricas are
seen in most pronounced form in Salpina (Fig. 886). But every
possible intermediate gradation exists, leading from Furcularia to
Salpina. The intermediate steps are mostly classed in the genus
Diaschiza (Fig. 887); here the cuticula is only sHghtly stitlened, and
the longitudinal clefts are httle marked. The species of Diaschiza
are many of them hardly distinguishable from Furcularia or even
from Notommata; they were formerly classed in these two genera.
In Salpina the lorica is strongly developed and bears long spines
or teeth. Diplois and Diplax stand between Diaschiza and
Salpina, having strong loricas but no teeth. There is thus a
continuous series from the Notommatidac to Salpina. The Sal-
pinidae are common amid vegetation. (See the Monograi)h on
Diaschiza by Dixon-Nuttall and Freeman, 1903.)

568 FRESH-WATER BIOLQGY

4. Euchlanidae. Another line of divergence leads from the No-
tommatidae, probably likewise through Furcularia, to Distyla^
Cathypna, Monostyla, and Euchlanis, — forming the family Euch-
lanidae. The first steps in this series are seen in those species of
Distyla in which the body is soft, wrinkled, and only a little flat-
tened (Fig. 890). In the extended condition these are hardly to be
distinguished from small species of Furcularia. But when re-
tracted there is a tendency to form lateral furrows along the side,
while a sharp edge is seen in front (Fig. 890, B). In other species of
Distyla (Fig. 891) these differentiations are permanent and the cutic-
ula forms an evident lorica, consisting of a dorsal and a ventral plate.
This line of evolution shows its highest development in Euchlanis
(Fig. 893). The Euchlanidae are common among aquatic vegetation.

5. Coluridae. This group resembles the Euchlanidae, but has
probably developed from the Notommatidae separately. The
hardened cuticula here forms a soHd lorica, open at each end for
head and foot; sometimes the cuticula is not hardened on the
ventral surface. A portion of the lorica extends out over the
head as a sort of hood (Fig. 901). Metopidia (Fig. 901), Colurus
(Fig. 900), and Stephanops (Fig. 899) are the principal genera; they
are all minute, creeping about among plants and debris.

6. Rattulidae. A fifth Hne of divergence leads from the Notom-
matidae to thegenera Diurella (Fig. 895) send Rattiilus (Figs. 896, 897).
The cuticula of the nearly cylindrical body becomes hardened over
nearly the entire surface, so as to form a curved, pipe-like structure,
with openings for the protrusion of head and foot. The less differ-
entiated RattuHdae (Diurella, Fig. 895) resemble greatly the lower
Notommatidae, ha\dng the cuticula only a httle stiffened and toes
differing but Httle from those of Furcularia. But this Kne runs into
extremely bizarre forms. The animals tend to become unsymmet-
rical, the organs of the right side being smaller, while the body
becomes in some cases twisted into a segment of a spiral. The
right toe becomes enormously extended to form a long rod-like
structure, while the left toe nearly disappears (Figs. 896, 897). The
right side of the tifophi (Fig. 898) becomes smaller than the left.
The Rattulidae are common among vegetation. (See the mono-
graph of this family by the present writer (Jennings, 1903).)

THE WHEEL ANIMALCULES (ROTATORIA) 569

7. Dinocharidae. Scaridium (Fig. 903) is perhaps essentially a
Furcularia which has developed a long foot and long toes, for leap-
ing (compare Furcularia longiseta, Fig. 871). Dinocharis (Fig. 904)
and Polychaetus (Fig. 905) are perhaps further developments, some-
what divergent, along the same line. All these animals are given to
springing about wildly by the aid of powerful strokes of the foot
and toes; the same habit is found in various species of Furcularia.

Next may be taken up a line of divergence from the central
Notommatidae that leads to some extraordinary forms. It pro-
duces the great families of the Hydatinidae, the Notopsidae, the
Ploesomidae, and the Brachionidae, with their relatives. Here de-
velopment has proceeded both toward greater strength and activity
and toward protective armor, so that the result is to produce some
of the most powerful and ferocious rotifers that exist.

8. Hydatinidae. The close connection with the Notommatidae
is seen in the Hydatinidae. The well-known rotifer Hydatina senta
(Fig. 906) was formerly classed with the Notommatidae. It has a
soft, segmented body, small foot and toes, ventral corona, — all as
in the primitive genus Proales. But the corona (Fig. 906, B) is
large and differentiated in a way that is characteristic for the
families making up the present group. Around the outer edge of
the corona the cilia form a prominent wreath, while about the
mouth is another series of ciHa so interrupted as to form three
groups, one dorsal and two lateral (Fig. 906, B). In the region
between the outer and inner series of cilia are certain prominences
(three in Hydatina), on which the cilia have become long, stitT
setae, doubtless serving as sense organs. The coronal area between
the parts thus far mentioned retains in Hydatina senta a portion of
the covering of fine ciHa primitively found in Proales; in most other
members of this group these fine cilia have quite disappeared.
The jaws are of the peculiar type shown in Figure 906, C.

9. Notopsidae. The next step in differentiation is seen in Notops
{ox Hydatina) hrachionus (Fig. 909). The cuticula, while still soft,
has become a little stiffened, so that the body tends to hold its
form; the foot is more prominent.

The next steps seem to be as follows: Notops clavulatus (Fig. 912)
and Triphylus lacustris (Fig. 908) are rotifers showing still the soft

570 FRESH- WATER BIOLOGY

body of the Notommatidae, but approaching the definite permanent
form found in Ploesoma. The corona (Fig. 912, ^) is much like that
of Hydatina, save that the fine ciliation of the general surface has
disappeared. Notops pelagicus (Fig. 910) shows a further step in
the same direction; the cuticula is here stiffened to form a thin
transparent lorica, of sufficient stiffness to form angles and teeth,
though with by no means the thickness and soHdity found in
Ploesoma and Brachionus.

From Notops pelagicus it is but a short step in one direction to
Gastropus and Ploesoma, in another to Brachionus.

10. Gastropodidae. The transition from Notops to Gastropus is
shown hy Gastropus hyptopus (Fig. 915), which was originally con-
sidered a species of Notops, and which if it stood by itself would
still be placed in that genus. The lorica is here soft, the body
short and thick. The lorica becomes more marked, and the other
pecuHarities more pronounced in the other species of Gastropus,
Gastropus stylifer (Fig. 917) forming the extreme in this direc-
tion.

11. Anapodidae. Probably derived from forms similar to Gas-
tropus by a process of reduction are the species of Ana pus (Fig. 911),
in which the foot is lacking, the corona small and simple.

12. Ploesomidae. The species of Ploesoma (Figs. 918 to 920) are
closely related to Notops and Gastropus. Ploesoma truncatum (Fig.
920) shows a lorica only a little stronger than that of Notops pel-
agicus, and resembhng that of Gastropus hyptopus, though it has
many irregular wrinkles. In other species of Ploesoma the lorica
becomes stronger and marked in very pecuHar ways. Ploesoma
lenticulare (Fig. 918) and P. hudsoni (Fig. 919) are among the most
active and powerful of the predaceous Rotifera. They tear their
w^ay through the water at a furious rate, darting from side to side,
and seizing and devouring with their powerful jaws other rotifers
with which they come in contact. The Ploesomidae are among the
most important plankton organisms.

13. Brachionidae. From Hydatina and Notops to Brachionus
the step is perhaps still shorter than to Gastropus and Ploesoma.
In Brachionus (Figs. 922, 923) the three prominences that surround
the mouth in Hydatina and Notops (see Figs. 906, 910) have become

THE WHEEL ANIMALCULES (ROTATORIA) 571

much developed, so that they stand high above the general surface
of the corona (Fig. 923). They partly enclose a sort of funnel,
open on the ventral side, which leads down to the mouth. In
most species of Brachionus the integument has become very thick
and hard, so as to form a stout lorica, often bearing spines or teeth
(Fig. 921). But Brachionus mollis Hempel (Fig. 925) marks the
transition in this respect, the integument being merely a little
stiffened and without spines or teeth. In Brachionus, as in Ploesoma
and Gastropus, the stout foot is marked with rings. The jaws are
constructed on much the same plan throughout all these groups.

The Brachionidae are among the most numerous of the rotifers
found in ponds and pools amid vegetation. Some of the species
are extremely variable.

14. Anuraeidae. An offshoot of the Brachionidae is found in the
Anuraeidae (Figs. 913, 916). The general organization is the same
as in Brachionus, but the foot has been lost, though in the males
(Fig. 913, C) it is retained. The lorica shows in some species of
Notholca a tendency to run into bizarre forms (Fig. 916). The
Anuraeidae are among the commonest of the rotifers of the plank-
ton; they vary extremely with seasonal and other changes.

15. As plane hnidae. The group diverging by way of Hydatina
is now left, and another offshoot of the Notommatidae taken u[).
In the Asplanchnidae the body remains soft, but becomes large and
inflated, while the foot disappears; the jaws are of a remarkable
type known as the incudate (Fig. 929, B), and the alimentary canal
loses its posterior opening (see Fig. 929, A), the undigested waste
being disgorged through the mouth. But one finds in all these
respects forms transitional between the Notommatidae and the
Asplanchnidae. Thus, Asplanchnopus (Fig. 927) retains the foot,
though it lacks the intestine, and has the characteristic jaws of this
family. Harringia (Fig. 928) retains not merely the foot, but like-
wise the intestine. Its corona is like that of As plane Jnia while its
jaws (Fig. 928, B) are squarely intermediate between the usual form
and the incudate type characteristic of Asplanchna. The t}pical
incudate jaws consist mainly of the very large incus (fulcrum and
rami), the mallei having nearly or quite disappeared; but in Har-
ringia all the typical parts of the jaws are clearly seen.

572 FRESH-WATER BIOLOGY

The typical Asplanchnas are beasts of prey, the jaws forming a
great pair of forceps which can be thrust from the mouth to seize
other large animals. Asplanchna herrickii de Guerne and A. pri-
odonta Gosse (Fig. 929) are important elements of the plankton of
lakes. In the Great Lakes they sometimes swarm so densely that
a net dipped into the water captures thousands. Other species of
the Asplanchnidae Hve among water plants.

16-18. Floscularida. Now come certain groups of rotifers that
seem at first view to differ markedly in almost every respect from
the notommatids. The Flosculariidae (Figs. 933 to 936) live attached
in tubes. The foot has become a stalk for attachment; there are
no toes. The corona is immensely large, forming a great lobed
net of thin membrane, which can be spread widely and serves to
capture Hving prey; the mouth Hes in the center at the bottom of
this net. The ciUa about the edge of the corona have become enor-
mously long and slender rods or threads, which do not beat as cilia
usually do, but may be moved about so as to aid in entanghng prey.
In connection with the method of feeding on large animals thus cap-
tured, the alimentary canal (Fig. 934) has become greatly devel-
oped. The upper part of the coronal net forms a great funnel, called
the infundibulum (i), partly closed off below by a ring-like fold,
the diaphragm (d), which has about its edge an interrupted cir-
clet of cilia. The opening through the diaphragm leads into a
second chamber, the vestibulum (v), at the bottom of which is the
mouth (w). From the mouth there hangs the slender esophageal
tube (o) ending freely below. The food after passing through this
reaches a third large cavity, the proven triculus (pr) . It is only at
the posterior part of this that the mastax (mx) and jaws are reached;
so that all thus far seen corresponds merely to the short mouth
cavity lying in front of the jaws in other rotifers. The trophi
(Figs. 934 and 933, D) are pecuKarly modified, the unci forming a
pair of two-tined forks which are the main part of the jaws, though
the other typical parts can be distinguished.

The Flosculariidae include two genera, Floscularia (Figs. 933 to
936) and Stephanoceros (Fig. 937). The numerous species are found
abundantly seated in transparent tubes attached to plants; they
are among the most attractive objects known to microscopists

I

THE WHEEL ANIMALCULES (ROTATORL\) 573

(cf. p. 553). Of Stephanoceros there is but one species (Fig. 937),
while of Floscularia there are many, varying extremely in the form
of the corona. A few species have become free and swim about
in the open water (Fig. 935). The fact that they bear their tubes
with them shows that the free Hfe has been secondarily acquired,
after the animals had become adapted to the attached condition.
All young Floscularias swim about for a time by means of moving
cilia, just as do other rotifers. The males (Fig. 933, B) are free-
swimming throughout life.

What relationship have the Flosculariidae to the typical rotifers
found in the Notommatidae? It must be remembered that not
all Flosculariidae have the extraordinary forms shown in Figs. 933
and 937. In some, the borders of the corona are not drawn out
into lobes, but are smooth, as in other rotifers (see Fig. 936). In
others the ciha of the coronal edge are all, or partly, short and beat
regularly, like those of other rotifers; and about the mouth is the
same circlet of cilia found in other rotifers. Such Floscularias
approach much more nearly to the typical Notommatidae than do
the extreme developments along this Hne seen in Stephanoceros
and certain species of Floscularia.

Furthermore, among close relatives of the notommatids are cer-
tain rotifers that seem to show transitional stages leading to the
Flosculariidae.^ In Microcodides and in Microcodon (Fig. 931), the
corona is formed on essentially the same plan as in the Floscularias,
and there are other peculiarities that seem to show that these are
transitional forms. In Microcodon, as in Floscularia, the corona
is the broadest part of the body; it has elevated edges, approaching
the net formation, and the mouth is in its center, with an inter-
rupted circlet of cilia about it. The foot in Microcodon as in Flos-
cularia forms a sort of long slender stalk, not ending in toes. But
in Microcodon it ends in a sharp point, while in Floscularia it ends
in a disk; this is doubtless because the fonner is still a free animal,
while the latter is attached. It is a most suggestive fact that Mi-
crocodon frequently places itself in the upright position, with the toe
attached by a thread of mucus, and thus remains for a time in a cer-
tain spot; such habits might readily lead to pemianent attachment.
1 These important considerations are due to VVeseaberg-Lund (1899) •

574

FRESH-WATER BIOLOGY

All together, Microcodon seems to form a link between the Flos-
culariidae and the Notommatidae. Microcodon itself is closely
connected with the Notommatidae by the transitional species be-
longing to the genus Microcodides (Fig. 932). These have corona,
body, and toes more nearly on the notommatoid plan. The two
genera make up the family Microcodonidae.

Specialization going even beyond that in the Flosculariidae is
seen in Apsilus (Fig. 938) and AtrocJms (Fig. 939). In these ex-
traordinary rotifers the ciha have been completely lost. The
comphcated structure of the alimentary canal shows their close
relationship to the Flosculariidae. In the young the ciha still
exist, and the animals swim about by their aid.

19-22. Melicertida. Another group of extraordinary and at-
tractive rotifers is that of which Melicerta (Fig. 948) is the repre-
sentative. These were formerly classified with the Flosculariidae,
the two forming the group Rhizota. But it is evident that the
two famines differ widely, and that the group Rhizota is not a
natural one. The Mehcertidae are found, hke the floscules, at-
tached to aquatic plants, often in great numbers. Many live in
tubes, and the species of Melicerta manufacture their tubes in a
most interesting manner, as is well described in Hudson and Gosse

(1889).

The most important peculiarity of the Mehcertidae is perhaps
the corona. This is a large disk, bare within, but having around
its outer edge a series of strong ciha, just as in many other rotifers.
But in this group is found a special pecuHarity. This outer wreath
is differentiated into two series of cilia, running parallel around the
disk (Fig. 865). The inner series has much larger ciha than the
outer one, and between the two is found, in most cases, a groove.
This groove is often hned with fine ciha. Along the groove small
food particles are carried to the mouth, situated on the ventral
side. In some genera the disk is drawn out to form two, four,
or eight lobes, giving the animal an extraordinary appearance
(Fig. 950); in other cases it is nearly circular (Figs. 865, 951, 952).
Throughout this group the jaws are of a pecuKar type (Fig. 866),
known as the malleo-ramate. As a rule the animals have two eyes.

The more extreme types of this group seem to stand far from

THE WHEEL ANIMALCULES (ROTATORIA)

575

the typical free-swimming rotifers. Yet again, as in most other
cases, free-swimming species form a transition to these extreme
types. One finds the same peculiar corona, the same remarkable
type of jaws, and various other features in common with the
MeHcertidae, in a number of free-swimming rotifers. These in-
clude the gmQrsiPterodina (Fig. 942), Pomp holy x, Pedalion (Fig. 946),

Fig. 865. Corona of Lacinularia socialis Ehr., to show the two wreaths of cilia.
B, Side view. (After Wesenberg-Lund.)

A, Dorsal view.

Triarthra (Fig. 944), and Tetramastix (Fig. 945). These rotifers are
the only ones that have corona and jaws Hke those of the Meli-
certidae, and they agree with them in many other particulars.
Thus, all have two eyes, while most other rotifers have but one.
In all there is either no foot, or it is a pecuhar one, lacking the
characteristic toes. In Pterodina the foot ends in a bundle of
cilia, and this is Hkewise true of the young of the jMeHcertidae. In

Fig. 866. Malleo-ramate jaws. A, Jaws of Melicerta ringens Schrank. (.\fter Weber.) B, Jaw3
of Pterodina caeca Parsons. (After Rousselet.)

many MeHcertidae there is below the mouth a peculiar fold of in-
tegument forming the so-called ''chin" which plays a part in the
formation of the pellets used for building the tubes. This chin
is hkewise found, in a sHghtly less developed condition, in Pedal-
ion (Fig. 946, ch) and in Triarthra, while nothing of the sort is
found outside the present group. The remarkable similarity of
corona, jaws, eyes, and other features seems to demonstrate clearly
that all these free-swimming rotifers are closely related to each
other and to the MeHcertidae.

576 FRESH-WATER BIOLOGY

The free-swimming members of the group have developed a
number of striking external peculiarities, due to differences in the
mode of life. Pterodina (Fig. 942) has a flat body, protected by a
hard cuticula forming a lorica; this shape aids it greatly in swim-
ming. Pedalion (Fig. 946) has developed six great limbs which Hke-
wise aid it in swimming. Similar Hmbs, but in a simpler condition,
are seen in Triarthra (Fig. 944) and Tetramastix (Fig. 945). In these
genera the function of the limbs seems to be mainly to protect the
animals from being swallowed by such predatory beasts as As-
planchna. One often sees an Asplanchna attempt to swallow one of
these at a gulp, but the prey at once extends its long appendages in
all directions, and these frustrate the attempt. The male of Pedalion
(Fig. 946, B) has simple appendages and bears a striking resemblance
to one of the simpler species of Triarthra (Fig. 944, B).

An extraordinary offshoot of the Meticertidae is seen in the
spherical rotifer Trochosphaera (Fig. 947). In the corona, the jaws,
the lack of a foot, and various other features it agrees essentially
with the MeHcertidae, though its external form is very different.

23-25. Bdelloida. This, the last group of rotifers, includes mainly
the genera Rotifer (Figs. 958, 960), Philodina (Fig. 959), Callidina
(Fig. 961), Microdina (Fig. 962), and Adineta (Fig. 957). They are
somewhat worm-Hke animals, often creeping like leeches, and found
in great numbers amid aquatic vegetation. They are specially
abundant in Sphagnum and other wet moss or moss-like plants; an
immense number of species particularly of Callidina are found in
such places.

This group differs widely from the typical rotifers in many points.
The typical corona of the Bdelloida is a highly differentiated struc-
ture consisting mainly of two flat disks borne on stalks and with
cilia about their edges (Fig. 959, etc.). When the ciHa are in mo-
tion these two disks give the appearance of two revolving wheels.
It is to this that the name wheel-animalcule, and the Latin terms
rotifer and rotator are due; the Bdelloida were the first rotifers to
attract the attention of microscopists. The base of the stalks
bearing the disks is often clothed with short ciha. On the dorsal
side of the corona there is a long tentacle.

The foot ends as a rule in three or four minute projections, by

THE WHEEL AmMALCUI.ES (ROTATORTA) 577

which the animals attach themselves; it bears also a pair of ''spurs "
on its dorsal side, a short distance from the end. These spurs
perhaps represent the two toes of other rotifers.

The trophi (Fig. 867) present perhaps the most modified type
found in the Rotifera; they show clearly that this group is not a
primitive one. In most species the trophi are represented by two
pieces shaped like a quarter of a sphere and placed side by side
(Fig. 867, A). Across the free surface of these pieces extend two or
more ridges. These jaws may be opened and closed by the mus-
cular mass in which they are imbedded, the ridges fitting together
in such a way as to serve as grinding teeth. The two halves of the

Fig. 867. Jaws of Bdelloida. ^, Jaws of P/n'Wina Sryce/ Weber (typical ramate jaws).
Microdina paradoxa Murray. (After Murray.)

B. Jaws of

trophi represent the two rami of other rotifers, the remainder of
the apparatus having almost completely disappeared. But tran-
sitional forms (Fig. 867, B) show clearly how these trophi are de-
rived from the typical structure.

The point in which the Bdelloida differ most from other rotifers
is in the fact that they have two ovaries in place of one. This
pecuharity is shared with the Bdelloida only by a bizarre group of
parasitic marine rotifers, the Seisonacea (Fig. 868) which live at-
tached to the marine crustacean Nehalia. On account of this pecu-
liarity the Bdelloida and Seisonacea are commonl}' classed apart
from all other rotifers as the Digononta, the others being called the
Monogononta.

The Bdelloida include an immense number of species, the greater
part of them belonging to the genus Callidina. The difference
between species is often only slight, and the animals change form
almost continually, so that their systematic study is perhaps more

578

FRESH-WATER BIOLOGY

difficult than that of any other group of rotifers; it has been con-
fined mainly to specialists in this particular group.

Many species of the Bdelloida possess
a remarkable power of withstanding dry-
ing. Philodina roseola is often found as
Httle pink balls in the dry deposits in
the bottoms of urns and eave-troughs.
When this material is placed in water,
the pink balls quickly swell, take the
rotifer form, and continue their inter-
rupted life activities where these were
stopped. Many species may be ob-
tained for study in the Hving condition
from dried moss and other vegetation
brought from a distance. No males are
known in the Bdelloida.

26. Tlie Seisonacea (Fig. 868) are ex-
traordinary rotifers parasitic on marine
Crustacea. Their relationships are un-
certain, but, having two ovaries, they
are usually placed near the Bdelloida.
In the Seisonacea male and female are
Since they are exclusively marine, these
forms are omitted from the synoptic key.

The studies thus far made of the rotifers of different regions
seem to indicate that in general these animals may be said to be
potentially cosmopolitan, any given species occurring wherever the
conditions necessary to its existence occur. Whether any given
rotifer shall be found in a given body of water depends mainly,
not upon the locahty of this body of water, but upon the precise
conditions there found. Studies on the rotifers of Europe, Asia,
Africa, America, and AustraHa show, not different faunas in these
regions, but the same common rotifers found everywhere, with
merely a new form here and there, and it is an extraordinary
fact that when a new rotifer is described from Africa or Australia,
its next occurrence is often recorded from Europe or America. In
stagnant swamps all over the world appear to be found the char-

FiG. 868. Seison annulatus Glaus, female.
(After Claus.)

similar and of equal size.

THE WHEEL ANIMALCULES (ROTATORLA) 579

acteristic rotifers of stagnant water; in clear lake water arc found
the characteristic Hmnetic rotifers; in sphagnum swamps every-
where, the sphagnum rotifers. Variation in the rotifer fauna of
different countries is probably due mainly to differences in the con-
ditions of existence in the waters of these countries, rather than to
any difficulty in passing from one country to another. The num-
ber of different sorts of Rotifera to be found in any given region
depends upon the variety of conditions to be found in the waters
of this region. Two bodies of water half a mile apart, presenting
entirely different conditions, are likely to vary more in their rotifer
fauna than two bodies of water 5000 miles apart that present
similar conditions. Of course, the tropics will have characteristic
species not found in cooler regions, since they present conditions of
existence not found elsewhere, and the same may be true of Arctic
regions. The problem of the distribution of the Rotifera is then
mainly a problem of the conditions of existence rather than of the
means of distribution. The ability of the eggs to live in dried
mud, which may be carried about on the feet of birds or I)l()wn
about as dust by the winds, seems to give sufficient opportunities
for any species to multiply wherever occur the conditions neces-
sary for existence. Most rotifers seem adapted to a rather nar-
rowly limited set of conditions.

Many species of rotifers vary extremely in the external details
of their structure. This is particularly true of loricate rotifers
that bear teeth, spines, or other projections. Extreme examples
of such variation are seen in Brachionus bakeri Ehr. and in Anuraca
cochlearis Gosse (Fig. 913). Lauterborn shows that the variations
of Anuraea cochlearis are by no means haphazard, but depend upon
the seasons and upon changes in the conditions of existence. In
the course of a year this species undergoes a cycle of regular changes
from month to month, and this yearly cycle was found to be essen-
tially the same during a period of study of twelve years. In the
colder months of the year appear individuals of greater size, with
smooth loricas and long prominent spines. As the waters become
warmer, in spring and summer, the individuals found are smaller
in size, the surface of the lorica becomes roughened, and the spines
grow shorter, until the caudal one disappears completely. As cold

^8o FRESH-WATER BIOLOGY

weather approaches there is a return to the stouter forms. There
results an immense number of different forms, many of which have
been described as different species. Apparently these changes are
adaptive in character. At the higher temperatures of summer the
inner friction of the water decreases much (as Ostwald has shown) ,
so that swimming animals tend to sink more readily than be-
fore. The decrease in size of the body, with the roughening of its
surface, increases greatly the proportion of body surface to body
weight, so that the animals sink less readily; the tendency to sink
due to the warmth of the water is compensated. The small, rough
forms are therefore adapted to warm ,weather. But the decrease
in size of the spines cannot be accounted for in this way; it must
depend on other relations.

In the Rotifera the males are usually minute, degenerate crea-
tures, — the race being represented mainly by the females ! The
males usually have no alimentary canal, and thus during their
entire life they never take food. They are, of course, therefore,
condemned to an early death. They usually swim about rapidly,
often swarming about the females. Fecundation takes place in
some cases by the insertion of the copulatory organ of the male
into the cloaca of the female; this has been seen in many cases.
In other cases apparently the male pierces the body wall of the
female, injecting the spermatozoa directly into the body cavity.
This takes place in Hydatina.

In a few of the Rotifera the males are of the same size and struc-
ture as the females (in the Seisonacea). In Proales werneckii the
male is of the same size and form as the female, but the aHmentary
canal, while present, is simplified and reduced in size. In other
species, various vestiges of the alimentary canal may be present,
but they are not functional. In certain groups no male is known
to exist; this is true for the entire suborder of the Bdelloida. In
the Rattulidae likewise no males have as yet been seen. Much
further study of the existence, structure, and activities of the males
is needed. If they are actually non-existent in some groups, then
of course the reproduction is throughout by parthenogenesis, —
fertilization of the egg not occurring even at long intervals.
Most rotifers produce several different sorts of eggs. These are

THE WHEEL ANIMALCULES (ROTATORL\) 581

the following: (i) large eggs, without a thick shell, from which
females are produced; (2) small eggs, similar to the last in ap-
pearance but producing males; (3) eggs which have a thick shell,
often armed with spines or projections. These are often spoken
of as ^'winter eggs" or ''resting eggs." They may apparently
live a long time under all sorts of unfavorable conditions, devel-
oping when favorable conditions are restored. The relation of
these different sorts of eggs to the appearance of the males, and to
fertiHzation, has been much discussed and investigated. In Ilyda-
tina, according to Maupas, and in Asplanchna priodonta, according
to Lauterborn, the following is the state of the case. There are
two sorts of females, not distinguishable externally, but one pro-
ducing large eggs, the others small ones. The large eggs cannot be
fertilized, and they always develop into female rotifers. The small
eggs, if not fertiHzed, develop into male rotifers, but they may be
fertilized, and if this occurs they become transformed into the
*' resting eggs," from which there later develop female rotifers.
In Hydatina, according to Maupas, fecundation can occur only
when the female is young, before any of the eggs develop, and the
female so fecundated produces only resting eggs. But in As-
planchna and in various other rotifers the same female produces
both male eggs and resting eggs, although only the latter are
fertilized. According to Mrazek, in Asplanchna herrickii the same
female bears at the same time ordinary female eggs, male eggs, and
resting eggs. There is apparently much variation in these rela-
tions among different rotifers.

Males and resting eggs are as a rule not found at all times of
the year, but appear at certain periods, — the resting eggs of
course following the appearance of males. In the pelagic Rotifera,
Lauterborn has made a study of the periodical appearance of males
and of resting eggs. He finds that these rotifers may be divided
into three classes: (i) perennial rotifers, which occur in greater
or less numbers all the year round; (2) summer species, found
only in summer; (3) winter species, found only in winter. In the
perennial species parthenogenetic reproduction continues through-
out the year; but males appear as a rule only twice a year, in
spring and fall. In the summer rotifers, males appear in the fall,

582

FRESH-WATER BIOLOGY

and the species is carried over the winter in the resting eggs re-
sulting from fertilization by the males. In the winter rotifers, the
males appear in the spring, and the species is carried over the sum-
mer by the resting eggs.

By the greater number of rotifers the eggs are laid as soon as
they are completely formed, development taking place outside the
body of the mother. But some rotifers are viviparous, the egg
being retained in the mother's body until it is partly or completely
developed. It is remarkable that the viviparous condition is found
in several different groups of rotifers that are not closely related,
so that it must have been developed independently several times
within the Rotifera. Asplanchna and Rotifer are among the best-
known viviparous genera. Philodina and Callidina, closely related
to Rotifer, as a rule deposit the eggs undeveloped, though certain
species in both these genera produce living young. Thus ovi-

parity and viviparity, which in
some higher animals distinguish
grand classes, are among the
rotifers both found in the limits
of a single genus.

It is a rather remarkable fact
that the cleavage and early de-
velopment of the rotifer egg does
not resemble that of the animals
to which the rotifers have often
been considered the nearest rela-
tives. In annelids and lower
mollusks the early development
shows a remarkable similarity

Fig. 869. Developing egg of a rotifer Asplanchna eVCn in thc dctails of tllC Spiral

herrickii de Guerne. a. Single cell stage; b, four _ . . . -

cells; c, twenty cells; d, ninety -four cells; e, optical clcaVagC. But m thC rOtllCrS
section through embryo formed of many cells.

(After Jennings.) the clcavage f ollows a Completely

different type (Fig. 869). The developing rotifer forms a soKd mass,
which contains no cavity until the organs formed within this mass
begin to separate, just before the rotifer takes its final form and
becomes active.

When living the body of the Rotifera is usually transparent and

THE WHEEL ANIMALCULES (ROTATORIA) 583

all the organs are sharply defined, so that they are readily seen.
After death, the transparency and sharpness are as a rule lost, and
most methods of killing the rotifers cause them to become strongly
contracted, so that the structure is no longer clear. Direct obser\'a-
tion of the hving animal will therefore always remain one of the most
important methods of studying these forms, for whatever purpose.
By Rousselet's method, however, it is now as easy to pre-
serve most of the Rotifera in natural form as any other lower
animals. This method is essentially as follows: The animals
are killed uncontracted by the aid of a narcotizing fluid, the essen-
tial feature of which is a | to i per cent solution of hydrochlorate
of cocaine. The cocaine may be used in a simple watery solution,
but better results are reached by using the following mixture:

Hydrochlorate of cocaine (2 per cent solution) . . 3 parts

Methyl alcohol i part

Water 6 parts

The rotifers are brought into a small volume of water, and a
little of this narcotizing fluid is mixed with it. The proper amount
must be learned by trial, but it is always best to begin with a very
small proportion of the fluid, ^o or less, and to add more as required.
This fluid causes the rotifers to swim slowly and gradually to sink
to the bottom. They will soon die, and if allowed to die unfixed
will be quite worthless for study, destructive changes taking place
in the tissues at the moment of death. As soon therefore as the
ciliary movement has nearly ceased, as much as possible of the
water should be drawn off, and a small amount of 0.25 per cent
osmic acid introduced, which kills and fixes the rotifers at once.
Now the osmic acid should be drawn off at once and water added
or the rotifers removed with a capillary pipette to fresh water;
they should be washed several times in distilled water. If the
osmic acid is allowed to act too long the rotifers will be blackened.
The blackening may, however, be later removed, if necessary, with
hydrogen peroxide. After washing, the rotifers should be pre-
served in 3 to 6 per cent formahn. They cannot as a rule be pre-
served in alcohol without extensive shrinkage, rendering them use-
less for further study.

584 FRESH-WATER BIOLOGY

If desired, the specimens may be permanently mounted in hollow
ground slides. The slides should be thin and the concavities shal-
low, so that high powers of the microscope may be used. The
specimens are transferred to the concavities along with some of the
formalin and covered with a circular cover-glass. It is best not to
leave any bubbles of air beneath the cover. The superfluous for-
malin may be withdrawn from the edge of the cover with a bit of
filter paper, and the cover is then sealed by the aid of a revolving
stage. It is, of course, necessary to use some sealing material that
will not allow water to evaporate through it. Rousselet recommends
the following for seahng the mounts: After fixing the cover with a
layer composed of a mixture of two-thirds gum damar with one-
third gold size, there are added two coats of pure shellac, followed
by three or four coats of gold size, allowing twenty-four hours for
each coat to dry before another is added.

Extensive collections containing many species of Rotifera may
be made by travelers and others by the use of the method given
above. The rotifers, taken with a net or otherwise, are brought
into as small an amount of water as possible, in a watch-glass.
Then a considerable quantity of the narcotizing fluid is introduced
and the rotifers are watched till most of them have sunk to the
bottom. Thereupon the water is removed, so far as possible, and
the J per cent osmic acid added. This is removed as quickly as
can be done without taking up too many of the rotifers; they are
then washed and preserved in formalin. It is very desirable to kill
a certain proportion of every collection in osmic acid without previ-
ous narcotization, as some of the loricate rotifers are more easily
determined from contracted specimens than from extended ones.

A method of mounting Rotifera in the ordinary mounting media,
such as Canada balsam, has been given by Zograf. It does not give
such perfect results, in most cases, as does Rousselet's method, but
it is useful for some species. The rotifers are stupefied and killed
in the way given above. After they have been in the osmic acid
from two to four minutes, this is removed as far as possible, and a
considerable quantity of 10 per cent pyroHgneous acid is added.
This is allowed to act five or ten minutes; then the rotifers are
washed several times in distilled water. As a result of the harden-

THE WHEEL ANIMALCULES (R0TAT0RL\) 585

ing action of the pyroligneous acid, they may now be passed, like
other objects, through successively stronger grades of alcohol till
absolute alcohol is reached. They may then be cleared in clove or
cedar oil, in the usual way, and mounted in Canada balsam, or
gum damar, or they may be mounted in glycerine.

In America the systematic work on the Rotifera has consisted
largely in the publication of lists of species found in certain regions.
While this work undoubtedly has its uses, there are other lines of
study which would at the present time be of much greater value
even for purely systematic purposes. On account of the very
large number of species of Rotifera, their minuteness, and the
unsatisfactory work that has been done upon them, it is often
almost impossible to determine with certainty even common spe-
cies. This can best be remedied by studying carefulh' circum-
scribed groups, such as single genera and families, collecting them
extensively, describing and figuring all the species, and going criti-
cally over the literature of the group in such a way as to set the
synonymy in order.

Careful comparative studies of certain organs or sets of organs,
such as the corona, the trophi, etc., throughout varied groups,
would help much in understanding the interrelationships of the
Rotifera. If possible a study of the habits should be made in their
relation with the structures, since these matters are closely con-
nected. Monographic anatomical studies of certain species are
always of value. They would be especially useful if a thorough
study of the habit and physiology could be made at the same time.

A most important field, and one little cultivated, lies in the
study of the activities by which the rotifers respond to their en-
vironment. Thorough studies of the movements and habits, the
reactions to stimuh, ''tropisms," and the like, would be of great
interest. Disconnected observations on these matters are of com-
paratively Httle value; definite problems should be taken up and
followed to the end.

The variations induced in a single species, and in an entire
fauna, by changes in seasons, temperatures, and in other features,
have received some study and deserve much more. One of the
most interesting lines of work for which the rotifers present oppor-

586 FRESH-WATER BIOLOGY

tunity lies in the study of the various problems connected with
reproduction and the diversity of the sexes. Few groups of organ-
isms present conditions so favorable for the study of these funda-
mental matters.

The relationships of the Rotifera to other groups, and their
interrelationships among themselves are subjects which have been
much discussed and on which there is wide divergence of opinion.
As a result, the classification of the group differs greatly with
different authors. The classification perhaps most commonly
employed is that given in Hudson and Gosse's Monograph of the
Rotifera. Wesenberg-Lund's classification, based on that view of
the interrelationships of the Rotifera set forth in the foregoing
paper, has been Httle used; yet it appears to be that to which a
careful and unprejudiced study of the members of the group leads.
Most earlier classifications have found their guiding principles in
matters quite extraneous to the Rotifera as such. Led by theo-
retical considerations, the primitive rotifers have been looked for
among highly specialized species. Huxley compared the two ciliary
wreaths of Lacinularia to the two wreaths of certain larvae of other
groups, — of echinoderms, annelids, and the Hke, — thus indicating
a possible close relationship between them. This suggestion was
eagerly followed up, and the primitive organization of the Rotifera
has been sought in such highly differentiated, untypical forms as
the Melicertidae, the Philodinidae, and the Hke. Even that bizarre
side-shoot of one of the most highly specialized families, Trocho-
sphaera (Fig. 947) , has been considered a primitive rotifer of special
significance, from its superficial resemblance to the trochophore
larvae of annehds, etc. Less popular, but still enjoying consider-
able repute, have been the theories which held that such forms as
Pedalion (Fig. 946) show a close relationship of the Rotifera with the
larvae of Crustacea. Careful comparative study of the Rotifera
themselves seems to show clearly that Lacinularia and the Meli-
certidae,. Trochosphaera and Pedalion are alike terminal twigs of
the rotatorian tree — highly speciaHzed forms, whose origin is to
be sought in such rotifers as the primitive Notommatidae.

Note. — For recent changes in the names of many rotifers, in accordance with the
strict rules of priority, the paper of Harring ('13) should be consulted.

THE WHEEL ANIMALCULES (ROTATORL\) 587

KEY TO NORTH AMERICAN FRESH-WATER ROTATORIA

I (138) One ovary. Do not creep like a leech.

Subclass Monogononta . . 2

This subclass includes all the rotifers commonly met, save the Bdelluida (q.v.), which are
distinguishable by their habit of creeping Uke leeches.

2 (109) Corona of various types. Where there are two wreaths of cilia, those
of outer wreath never shorter than those of inner. ... 3

3 (97) Mouth not near center of corona. . . . Order Notommatida . . 4

Free-swimming or creeping rotifers, but never creeping like a leech; corona ventral or ter-
minal, consisting of a disk which is either uniformly ciliate or has a wreath of cilia about its
circumference with usually two or more groups of cilia close to the mouth, or shows some inter-
mediate condition. Where there are two wreaths of cilia, the outer is never shorter than the
inner. Mouth not in the center of the disk. Jaws never ramate (Fig. 867, .4) nor malleo-
ramate (Fig. 866). Foot usually ending in two toes placed side by side; rarely ending in one;
sometimes absent; never forming a disk for attachment nor ending in a bunch of dlia. Lorica
present or absent.

4 (90) Jaws not incudate. Intestine and anus present 5

5 (31, 64) Without lorica. Corona when as broad as other parts of the body,
not consisting of an outer wreath, a partial wreath about
the mouth and styligerous prominences between.

Suborder Notommatina . , 6

Body usually soft and somewhat segmented. (See also family Hyd.\tinidae, 66.)

6 (26) Corona without long antenna-like bristles and setigerous prominences.
Foot present Family NoTOJiiiATiD.\K . . 7

Soft-bodied rotifers, usually elongated, cuticula more or less distinctly segmentetl; ioot not
distinctly marked ofif from the remainder of the body, usually short and endmg m two toes
placed side by side, or rarely but one toe. Corona usually not so wide as the remamder ot the
body. Living mainly amid vegetation of the shores and bottom. ,,,__,.., t,.

This family cannot be sharply marked oflf from others; see particularly Hydatmidae. Ihc
genera of the Notommatidae are likewise not sharply definable; they are merely more or less
convenient subdivisions of a group that would be too unwieldy if taken as a unit.

7 (19) Without auricles

N.B. Auricles are often contracted and are then invisible.

8 (16) With one or more eyes ^

9 (r2, 15) With a single eye only ^°

S88

FRESH-WATER BIOLOGY

Fig. 870. Furcularia Fig. 871. Furcularia
Jorficula Ehr. X 300. longiseta Ehr. X 400.
(After Weber.) (After Dixon-Nuttall.)

Fig. 872. Diglena ros-
trata Dixon - Nuttall.
X 320. (After Dixon-
Nuttall.)

Fig. 873. Distemma set-
igerum Ehrenberg.
X 166. (After Ehren-
berg.)

Fig. 874. Triophthalmus Fig. 875. Alhertia iw Fig. 876. Pleurotrocha Fig. 877. Taphrocampa

dorsualis Ehrenberg. trusor Gosse. X 13S. grandw Western. X 125. annulosa Gosse. X I4»

X80. (After Ehren- (After Gosse.) (After Dixon-Nuttall.) (After Weber.)
berg.)

THE WHEEL ANIMALCULES (ROTATORL\) 589

10(11) Eye in neck region Proalcs Gosse

Small, slow-moving, soft-bodied species, with partly ventral corona. Many species.

Representative species( Fig. 856, page 555) . Proaleswerneckii Ehrcnberg.
(Fig. 858, page 557). . . . P. sonlida Coasc.
(Fig. 859, page 558). . . . P. tigrida Gossc.

11(10) Eye near front Furcularia EhrcnhcTg.

Cuticula a little stiffer, so that the form is retained; shape at times a little prismatic; toes
longer and stiflfer than in Proales; active. Species numerous.

Representative species (Fig. 870). . Furcularia jorficida Y.\\mi\\)<:rg.
(Fig. 871) F. longiscta Ehrcnberg.

12 (9, 15) With two eyes 13

13(14) Eyes near front Digloia Ehrcnhcvg.

Strong predacious species with forcipate jaws; toes usually large. One or two species.

Representative species (Fig. 872). . Diglena rostrata Dixon-Nuilail.
(Fig. 860, B, page 559). . D.forcipata Ehrcnberg.

14 (13) Eyes in neck Dlstemma Ehrcnberg.

Representative species (Fig. 873). . Distemma setigeriim Ehrcnberg.

15 (9, 12) With three eyes in a transverse row. . Triophthalmiis Ehrcnberg.

One species only (Fig. 874) Triophthalmiis dorsualis.

16 (8) Without eyes.

17(18) Internal parasites ^/6er/w Dujardin.

Few species.

Representative species (Fig. 875) ilbertia intrusor Gossc.

18 (17) Free, or external parasites Pleurotrodm Ehrcnberg.

Few species.

Representative species (Fig. 876). . . Pleurotrocha grandis Western.

19 (7) With auricles ■^o

N.B. Auricles invisible when contracted.

20 (25) With one eye - ^^

21 (24) Smaller, soft-bodied forms 22

22 (23) Cuticula with many transverse folds Taphrocampa Gosse.

Representative species (Fig. 877). . Taphrocampa annulosa Ciossc.

590

FRESH-WATER BIOLOGY

Fig. 878. A, Notommata aurita
Ehr. X200. (After Weber.)
B, corona. (After Wesen-
berg-Lund.)

Fig. 878.^.

Fig. 880. Male of Synchaeta tremula Ehr.
X300. (After Rousselet.)

Fig. 879. Eosphora dtgitata
Ehrenberg. X 78- (After
Weber.)

Fig. 881. Notommata Fig. 882. Polyarthra platyptera
torulosia Duj. X 200. Ehr. X 200. (After Weber.)
(After Cohn.)

Fig. 883. Female of 5y»cAa6/a Fig. 884. Corona of 5ynctoe/a 6a//tca Ehr. ^^f; 885.;4 «ar/Ara a ^
styla^ Witrz. X225. (After seen from above. (After Rousselet.) ^6ra Hood X 220.

Rousselet.) ^^^^^ ^'^'^•^

THE WHEEL ANIM.\LCULES (ROTATORIA) 591

23 (22) Cuticula without many transverse folds. . Notoinmata Ehrenberg.
Many species.

Representative species (Fig. 878). . . Notommata auritaEhrnnhQr^.

(Fig. 881) N. torulosia Dujanlin

(Fig. 857, A and 5, page 556).

N. truncata Jennings.

24(21) Very large, thick-bodied forms Co/>ew5 Gosse.

Corona extending far on ventral surface. Few spedes.

Representative species (Fig. 857, C, page 556, and Fig. 864, page 565).

C opens pachyurns Gossc.

25 (20) With three eyes Eosphora Ehrenberg.

One large eye on brain; others small, in front. Few species.

Representative species (Fig. 879). . . Eosphora digitata Ehrcnhcrg.

26 (6) Two or four long bristle-like antennae on corona. Foot present or

absent Family Synchaetidae . . 27

Open- water rotifers; bodies short; foot short or absent; corona as broad as the broadest
part of the body, consisting mainly of a row of large cilia about the circumference.

27 (28) Auricles present Synchaeta Ehrenberg.

Body usually conical, largest at the head; foot short, rarely absent. About a dozen spedes.

Representative species (Fig. 883). . . Synchaeta stylata Wierzcjski.

(Fig. 880) S. tremuhi Ehr(.Til)crg.

(Fig. 884) S. baltica Ehrenberg.

28 (27) Auricles absent. No foot 29

29 (30) With lateral oar-like swimming appendages. . Polyarthra Ehrenberg.
One species only (Fig. 882). . . . Polyarthra platyptera Ehrenberg.

30(29) Appendages lacking \narthr a Hood.

One species only (Fig. 885) Anarthra aptcra Hootl.

31 (5, 64) Lorica always present. Corona small, not so broad, as a rule, as

the broadest part of the lorica. Suborder Loricatina . . 32

Foot present, short, not ringed; ending in two toes, or rarely one.

32 (47) Lorica divided into plates by longitudinal furrows ^i

592

FRESH-WATER BIOLOGY

Fig. 886. Salpina spinigera Ehr. X 200.
(After Weber.)

Fig. 888. Diplois daviesiae Fig. 889. Diplax mdens
Gosse. X87. (After Levander. X 267. (After
Weber.) Lucks.)

Fig. 887. Diaschiza hoodii Gosse.
/I, Female. B.Male. X 300.
(After Dizon-Nuttall and Free-
man.)

Fig. 890. Distylainermis Bryce. A, Dorsal view; 5, con-
tracted; C, side view. X 225. (After Dixon-NuttaU.)

Fig. 89 1 . Distyla ohioensis Herrick .
X 420. (After Jennings.)

THE WHEEL ANIMALCULES (ROTATORLV) 593

33 (40) Lorica of three or four plates. Furrows arc one mid-dorsal, two
lateral; sometimes one mid- ventral.

Family Salpinidae . , 34

34 (35) Lorica with teeth or spines in front, or behind, or both.

Salphia Ehrcnbcrg.
Representative species (Fig. 886). . . Salpina spinigcra Ehrcnbcrg.

35 (34) Lorica without teeth or spines 36

36 (39) One eye present 37

37 (38) Lorica not strongly marked, the furrows and plates noticeable only

on close examination Diaschizn Gosse.

Representative species (Fig. 887) Diaschiza Iwodii Gosse.

38 (37) Lorica distinct and strong Diplois Gosse.

Two species.

Representative species (Fig. 888) Diplois davi^siae Gosse.

39 (36) No eye; lorica distinct Diplax Gosse.

Representative species (Fig. 889) Diplax viiiens Lii\'i\n{\{:r.

40 (33) Lorica of two plates. Furrows lateral. Family Euchlanidae. . 41
One plate dorsal, the other ventral.

41 (46) Two toes 42

42 (45) The two plates connected by a membrane which folds into the lateral

furrow 43

Small species, not specially clear, lorica often marked in various ways.

43 (44) Lorica narrower Distyhi Eckstein.

Many species.

Representative species (Fig. 800) Distyla imrmis Br>'ce.

Representative species (Fig. 891) D. ohioaisis Hcrnck.

594

FRESH-WATER BIOLOGY

Fig. 895. Diurella sulcata
Jennings. X 35o. (After
Dixon-Nuttall.)

Fig. 897. RaUulus latus
Jennings, r, right toe;
I, left toe. X 225.
(After Jennings.)

Fig. 898. A, RaUulus
longiseta Schrank. X
200. B, Trophi of same.
(After Jennings.)

THE WHEEL ANIM.\LCULES (ROTATORIA) 595

44 (43) Lorica broader Cathypna Gossc.

Several species.

Representative species (Fig. 892). . . . Cathypna liina Ehrenberg.

45 (42) The two plates not connected by membrane. . Euchlanis Ehrenberg.

Large, conspicuous, clear species; lorica not sculptured or otherwise markc*!. Many s|x.-Lifs.
Representative species (Fig. 893). . Euchlanis macrura Khrcn\KTi:,.

46 (41) One toe Monostyla Ehrenberg.

Many species.

Representative species (Fig. 894). . Monostyla lunaris Ehnjiiberg.

47 (32) Lorica undivided, of a single piece 48

48 (51) Lorica somewhat pipe-shaped, often unsymmetrical.

Family Rattulidai: . . 49

Lorica closed all around, cylindrical, fusiform, ovate, or conical, with an opening at each end
for head and foot; often unsymmetrical and with oblique ridges or furrows. Toes bristle-
like; sometimes equal, then short; sometimes very unequal, so that but one is noticeable, this
then very long.

49 (50) Toes equal, or, if unequal, the shorter one more than one-third the

length of the longer Diurdla Bory.

Many species.

Representative species (Fig. 895) Diurclla sulcata Jennings.

(Fig. 862, page 562) D. tigris Miiller.

50 (49) Toes unequal. The smaller less than one-third length of longer.

Rattulus Lamarck.

Many species.

Representative species (Fig. 896). . . . Rattulus cylindricus Imhof.

(Fig. 897) i?. /(i/;<-v Jennings.

(Fig. 898) R- longiscta Schrank.

51 (48) Lorica not pipe-shaped. Symmetrical 52

K2 Uq) Foot and toes not exceptionally long. No spines.

^ ^^^^ Family Coluridae . . 53

Lorica of a single piece, either covering both dorsal and ventral surfaces, or only the dors;i!.
53 (58) Head surmounted by a chitinous shield 54

596

FRESH-WATER BIOLOGY

Fig. 899. Stephanops in-
termedius Burn. X 350.
(After Weber.)

Fig. 900. Colurus grallator
Gosse. X37S. (After Weber.

Fig. 902. Cochlearet urbo Gosse.
X 200. (After Gosse.)

Fig. 901. Metopidia ehren-
hergii Perty. X 400- (After
Jennings.)

Fig. 903. Scaridium longi-
caudutn Ehr. X 200.
(After Dixon-Nuttall.)

Fig. 904. Dinocharis pocillum Ehr. A, Female. B, Male.
X 300. (After Weber.)

THE WHEEL ANIMALCULES (ROTATORIA) 597

54 (55) Head shield broad, flat, appearing from above like a halo.

Skplianops Ehrenberg.
Several species.

Representative species (Fig. 899). . . Skplianops intermedins Burn.

55 (54) Head shield arched, in side view appearing like a hook 56

56 (57) Lorica arched and laterally compressed Colurus Ehrenberg.

Many species.

Representative species (Fig. 900) Colurus grallator Gossc.

57 (56) Lorica flattened, wider than high Metopidia Ehrenberg.

Representative species (Fig. 901), . . . Metopidia clircnbergii Wny.

58 (53) No head shield Cochleare Gosse.

Lorica shaped like a coat, covering only the anterior half or less of the dorsal surface. One
or two species.

Representative species (Fig. 902) CocJilcare turbo Gossc.

59 (52) Foot and toes usually long; if not, upper surface of lorica with long

spines Family Dixochakidak . . 60

Lorica entire, covering head as well as body. Movements often of a leaping character.

60 (63) Lorica without spines on dorsal surface 61

61 (62) Lorica weak, hardly noticeable Scaridium Ehrenberg.

No sculpturing of any sort; toes very long. Two species.

Representative species (Fig. 903).

Scaridium longicaudum EhrenlK-rg.

62 (61) Lorica rough Dinocharis Ehrenberg

Two species.

Representative species (Fig. 904). . Dinocharis pocillum EhrenJKTg.

598

FRESH-WATER BIOLOGY

Fig. 905. Polychaetus collinsii
Gosse. X 250. (After
Jennings.)

B

Fig 906. Hydatina senla Ehr. A, Dorsal view of female.
X 150. (After Weber.) B, Corona. (After Wesenberg-
Lund.) CTrophi. (After Weber.)

Fig. 907. Cyrtonia tuba
Ehrenberg. X 200.
(After Rousselet.)

Fig. 908. Triphylus lacustris Ehrenberg. X 134. (After Western.)

THE WHEEL ANIMALCULES (ROTATORL\) 5Q9

63 (60) Lorica bearing long spines on dorsal surface. . Polychadus IV-rty.
Lorica turtle-shaped. Two species.

Representative species (Fig. 905). . . . Polychactiis collinsii Gossc.

64 (5, 31) With or without lorica. Corona usually as broad as broadest
part of body and consisting of an outer wreath of cilia and
an inner interrupted wreath about the mouth, with sty-
ligerous processes between them.

Suborder Hydatinina . . 65

A heterogeneous group in external characters but showing eviflcncc (jf dost- rtlation-ship
throughout. Corona never a perfect circle of two wreaths, with mouth in center. .Ml loricate
forms without foot belong here. In all non-loricate forms foot present and ending in two U)C%,
side by side. In loricate forms foot when present ends in two toes, side by side, .save in one
species, Gastropus stylifer, where there is but one toe. The families of this order are greatly
in need of a revision based on thorough comparative study of all the species.

65 (73) Without lorica 66

66 (70) Foot not sharply separated from body.

Family Hydatinidae . . 67

Large rotifers, body soft and segmented, of notommatoid characteristics, not greatly swollen
dorsally, nor compressed sidewise. Corona of typical form of suborder, or having a large
dorsal proboscis that bears two eyes. Foot lying in the body axis, not ventral; ending in two
short toes.

67 (68, 69) No eye Hydatina Ehrenbcrg.

Only one species (Fig. 906) Hydatina scuta Ehrenberg.

68 (67, 69) One eye Cyrtonia Rousselet.

Only one species (Fig, 907) Cyrtonia tuba Ehrenberg.

69 (67, 68) Two eyes; corona with dorsal proboscis. . . . Rhino ps Hudson.
Only one species (Fig. 863, page 565). . Rhinops vitrca Hudson.

70 (66) Foot decidedly set off from remainder of body.

Family NoTOPsroAE . . 71

Body much swollen dorsally, flatter ventrally; cuticula slightly stitTer .st) that the Ixxly holds
its shape, or sometimes forming a weak but evident lorica. Foot forming a prolongation oi'
the ventral surface or extending ventrally; two small toes.

71 (72) Two eyes Triphylus Hudson.

Only one species (Fig. 908) Triphylus lacustris Ehrenberg.

6oo

FRESH-WATER BIOLOGY

Fig 909. Notops brachionus
Ehr. Xioo. (After Weber.)

Fig. 910. Notops pelagicus Jennings. A, side
view; B, Corona. X 400. (After Jen-
nings.)

B

FlG.gii. Anapusovalis
Bergendal. X 240.
(After Weber.)

Fig. 912. A, Notops clavulatus Ehr. X 100.
(After Hudson and Gosse.) B, Corona.
(After Jennings .)

Fig. 913. A and B, Forms of Anuraea cochlearis Gosse.
A, variety macracantha. B, Variety tecta. X 300.
(After Lauterborn.) C Male of Anuraea brevts-
pina Gosse.

THE WHEEL ANIMALCULES (ROTATORL\) 6oi

72 (71) One eye Notops Hudson.

Slight indication of lorica sometimes. Several species.

Representative species (Fig. 909). . . Notops hrachionus Ehrcnlx^rg.

(Fig. 912) N . clavulatus V.hritnXmrg.

(Fig. 910) N. pelagkus Jennings.

73 (65) Lorica present ^^

74 (81) No foot 7

75 (76) Lorica of two convex plates, placed together at their edges.

Family ANAPOoroAE.
Lorica ovoid or oval.

Only one genus ^na/»«5 Bergendal.

One or two species.

Representative species (Fig. 911) ^«a/>w5 ora//^ Bergendal.

76 (75) Lorica of a convex dorsal and a flat ventral plate, or sometimes
irregular Family Anuraeidae . . 77

Open in front for head and behind for cloaca; usually armed with spines or teeth.

77 (80) Spines or teeth at the anterior or posterior edges of the lorica, or
none 7^

78 (79) Lorica not longitudinally striated Anuraea Ehrcnberg.

Representative species (Fig. 913, A and B). Atturaea coc/dairis Closse.
Many species. Lorica of convex dorsal and flat ventral plate.

(Fig. 913, C) ■{. brr.'is pi tui Gossc.

6o2

FRESH-WATER BIOLOGY

Fig. 914. Eretmia trithrix Gosse.
CAfter Gosse.)

Fig. 916. Nothol-
ca longispina
Kellicott. X
170. (After
Weber.)

Fig. 917. Gastropus stylifer
Imhof. X 200. (After
Weber.)

Fig. 915. Gastropus hyptopus Ehr.
X 170. (After Hudson and Gosse.)

Fig. 918. Ploesomalenticulare
Herrick. X 300. (After
Wierzejski and Zacharias.)

Fig. 919. Ploesoma hudsoni Imhof. X 150. (After
Wierzejski and Zacharias.)

Fig. 920. Ploesoma truncatum Le-
vander. X 160. (After Weber.)

THE WHEEL ANIMALCULES (ROTATORIA) 603

79 (78) Lorica longitudinally striated Notholca Gosse.

Sometimes very long and slender. Three or four species.

Representative species (Fig. 916). . . Notholca longispina KcWkuw.

80 (77) Lorica with long bristle-like outgrowths from its surface but not
from anterior or posterior borders Erctmia Gossc.

Few species, all more or less doubtful.

Representative species (Fig. 914) Eretmia irithrix Gossc.

81 (74) Foot present 83

82 (85) Foot projects from ventral surface 83

83 (84) Lorica entire, not wrinkled Family Gastropodidae.

Lorica flask-shaped with small foot projecting from ventral surface. Foot ringed, ending
in one or two toes.

One genus only Gastropiis Imhof.

Several species.

Representative species (Fig. 915). . Gastropus hyptopits Ehrcnbcrg.
(Fig. 917) G. stylijcr Imhof.

84 (83) Lorica open along mid-ventral line; marked with wrinkles or vesi-
cles Family Ploesomidae.

Lorica stout, widely open in front for the large head, and open ventrally for the foot. Foot
strong, ringed, ending in two toes. Strong, active rotifers.

Only one genus Plocsomu \\<:n\c^.

Three or four species.

Representative species (Fig. Q2o). . Plocsoma trumatum Levandcr.

(Fig. 918) P- Icfiticuhirc Hcrrick.

(Fig* 919) ^^- ^'n^^-'^oni Imhof.

6o4

FRESH-WATER BIOLOGY

A

Fig. 921. A, Brackionus punctatus'Hempel. X 400. (After
Dixon-Nuttall.) B, Male of Brachionus quadratus Rousselet.
(After Marks and Wesche.)

Fig. 922. Brachionus pala Ehr.
X 160. (After Weber.)

Fig. 923. Corona of Brachionus
annularis Gosse. (After Wesen-
berg-Lund.)

^v^_

Fig. 924. Schizocerca dkersicornis
Daday. X300. (After Wier-
zejski.)

Fig. 925. Brachionus mollis Hempcl.
X 280. (After Hempel.)

FlG. 926. Noteus quadricornis
Ehrenberg. X 144. (After
Hudson and Gosse.)

THE WHEEL ANIMALCULES (ROTATORIA) 605

85 (82) Foot projects from posterior end. . Family Brachiontoae . . 86

Lorica consisting of a convex dorsal plate and a flat ventral one; usually stout and armed
with spines, though not always. Lorica opened behind for the long, strong f(X)t which is often
covered with close rings. Foot either ending in two toes or forked at its free end

86 (89) Foot not forked 87

87 (88) Lorica very convex dorsally Brachionus Ehrenberg.

Many species.

Representative species (Fig. 922). . . Brachionus pala EhrcnlKTR.

(Fig. 921,. 4) B. piimtatiis WiimpuX.

(Fig. 921, -B). . . . B. qiuuiratus KousscXtii.

(Fig. 923) B. annularis iiossQ.

(Fig. 925) B. mollis Hempcl.

88 (87) Lorica flat ^otciis Ehrenberg.

Foot not ringed.

Representative species (Fig. 926). . Noteus quadricornis Ehrenberg.

89 (86) Foot forked at its end Schizoccrca Dadny.

Only one species (Fig. 924). . . . Schizoccrca diver sicornis Daday.

6o6

FRESH-WATER BIOLOGY

Fig. 927. Asplanchnopxis myrmeleo Ehr. A, side
view. X 80. (After Weber.) B, jaws. (After
Wierzejski.)

Fig. 928. Harringia eupoda Gosse. ^, side view.
X 100. (After Western.) B, jaws. (After
Wierzejski.)

Fig. 929. Asplanchna priodonta Gosse. A, Dorsal view.
J< 100. (After Weber.) B, jaws. (After Wierzejski.)

Fig. 930. Ascomorpha ecaudis Perty.
X 200. (After Hudson and Gosse.)

THE WHEEL ANIMALCULES (R0TAT0RL\) 607

90 (4) Jaws incudate, save in Ascomorpha. Intestine and anus lacking save

^^ ^''''P' Suborder Asplanchnina.

Sac-shaped rotifers, usually without a foot, though in some cases a sm-ill f.w.f Jc r.r». ^.
the posterior part of the ventral surface. ' "^'^ '^ P*^^"^ "°

One family only Family Asplanchmdal . . 91

91 (94) Foot present

92 (93) Intestine absent Asplanchnopus de Guerne.

Two or three species.

Representative species (Fig. 927)

Asplanchnopus myrmcico Ehrenlx-rg.

93 (92) Intestine present Harringia Bcauchamp.

Only one species (Fig. 928) Harringia eupoJa Gosse.

94 (91) Foot absent q5

95 (96) Large clear rotifers w^ith incudate jaws Asplanchna Gosse.

Many species.

Representative species (Fig. 929). . . Asplamhna priodonUi Ciosse.
(Fig. 869, page 583). . .1. hcrrickii de Gucrnc.

96 (95) Very small rotifers, usually colored or opaque; jaws not incudate.

Ascomorpha I'erty,

, One or two species.

Representative species (Fig. 930) [scovwrpha ccaudi< V^^^^^'

6o8

FRESH-WATER BIOLOGY

Fig. 931. Microcodon

clavus Ehr., ventral Fig. 932. Microcodides robustus

view. X 260. (After Glasscott, with corona (c). X

Weber.) 300. (After Rousselet.)

Fig. 933. A . Floscularia proboscidea
Ehr. Female. X 100. (After
Weber.) B, Male of the same.
D, Side view of jaws of Floscu-
lariidae. (After Wierzejski.)

Fig. 934. Alimentary canal of Floscu-
laria campanulata Dobie. (Modified
from Montgomery.) d, diaphragm;
i,infundibulum; w, mouth; mx, mastax;
0, esophagus; pr, proventriculus;
V, vestibulum.

Fig. 935. Floscularia uni-
loba Wierz. X 125.
(After Wierzejski.)

Fig. 936. Floscularia edentata
Collins. X 150. (After Weber.)

THE WHEEL ANIMALCULES (ROTATORL\) 609

97 (3) Mouth nearly in center of large corona. . Order Floscularida . . 98

Corona circular or drawn out into lobes, points, or arms. Foot never ending in two toes
placed side by side. Mostly attached or tube-bearing rotifers, the foot formins a disk for
attachment; a few free-swimming species in which the foot ends in a single toe, sometimes
accompanied by a dorsal spur.

98 (loi) Free swimming; foot ending in a single toe.

Family IVIicrodonid.\e . . 99

Corona circular, with mouth in center, an outer wreath of active cilia; cilia about the mouth
larger and bristle-like. One eye.

99 (100) Foot as long as body Microcodon Ehrenberg.

Body slender, corona with raised borders, slightly bilobed; foot slender, straight, ending in
a single toe; no dorsal spur.

Only one species (Fig. 931) Microcodon claims Ehrenberg.

100 (99) Foot not more than half as long as body. . Microcodides Bergendal.

Body not so slender; foot ending in one toe which is sometimes accompanied by a dorsal
spur.

Representative species (Fig. 932). . Microcodides robust us Gkisscolt.

10 1 (98) Attached, or bearing tubes if free swimming 102

102 (105) Cilia around corona Family Floscularhdae . . 103

Corona large, forming a net for the capture of prey. Cilia about its edge usually forming
long threads or bristles which do not beat Hke those of other rotifers, though they may move
rather slowly. Jaws uncinate (Fig. 933, D).

103 (104) Corona circular, or drawn into lobes, or pointed; its cilia not in
whorls or regular groups Flosculana Okcn

Many species.

Representative species (Fig. 933, A and B).

Floscularia prohoscidca EhrcnhtTg.
(Fig. 934 and 861, B, page 561).

F. campanuhita Dohic.

(Fig. 935) F.;/;//A;/>c;\yier/.cjski.

(Fig. 936) P' cdcnldtd i oUin^.

6io

FRESH-WATER BIOLOGY

1-iG. 938. Apsilus bucinedax Forbes.
Ventral view. X65. (After Stokes.)

Fig. 937. Stephanoceros eich-
hornii Ehr. X 60. (Alter
Weber.)

Fig 939- Alrochus tenlaculatus
Wierz. X35- ( After Wierzejski.)

Fig. 941. Acyclus in-
quietus Leidy. X 12.
(After Leidy, from Hud-
son and Gosse.)

Fig. 940. Pompholyx
complanata Gosse.
X24S- (After Hud-
son and Gosse.)

Fig 942. Pterodvna pattna Ehr. ,^- .I^^^f .u^mak ^(Aft'r
V o« (After Weber) B, Dorsal view of the male, ^mier
Sarki and w'eschS C\ Corona, showing the two wreaths of
cilia. (After Wesenberg-Lund.)

THE WHEEL ANIMALCULES (ROTATORLK) 6ll

104 (103) Corona drawn out into long pointed arms, which bear cilia arranged

in whorls Stephanoceros Ehrenberg

One species only (Fig. 937). . Stephanoceros eichhornii Ehrcnbcrg

105 (102) No cilia on corona Family Apsilidae

106

106 (107, 108) Body short, sac-like Apsiliis MetschnikofT.

Corona a large sac or chamber; no foot; attached by an adhesive disk. Two or three spedes.

Representative species (Fig. 938). . . . Apsiliis hucincdax Forbes.

107 (106, 108) Body longer, fusiform, a narrowed neck separating off a

conical anterior part Atroclnis Wicrzcjski.

Corona a membranous ring with five short lobes bearing tentacles.

Only one species (Fig. 939). . Atrochus tentaculatus VVierzejski.

108 (106, 107) Body long, with a long, slender, tapering stalk.

Acyclus Leidy.
Corona with but one large dorsal lobe. Living in colonies of Megalotrocha dboflavicans .

Representative species (Fig. 941) Acyclus inquictus Leidy.

109 (2) Corona surrounded by two parallel wreaths of cilia with a furrow be-

tween. CiUa of outer wreath always shorter than those of
inner.

Order Melicertida . . no

The furrow between the wreaths of cilia sometimes clothed with short cilia. Jaws malleo-
ramate (Fig. 866). Foot never ending in two toes side by side; sometimes lacking. Eyes two,
rarely absent. Fixed or free swimming; the free-swimming species often without foot and
frequently bearing appendages on the body.

no (121) Free swimming and not in tubes or in colonies. .... n i

111 (120) Not spherical . . iii

112 (115) With a lorica. Without appendages.

Family Pterodinid.\e . . nj

113 (114) Foot present, long, ringed, ending in a bunch of cilia.

Pkrodina Ehrcnbcrg.

Lorica more or less flattened dorso-ventrally. Many species.

Representative species (Fig. 942). . • Pterodina pal i mi EhrenUTc
(Fig. 866, B, page 575)- • ^' <''^'<''' Parson.v

n4 (n3) No foot Pompholyx Gosse.

Lorica not flat. Two or three species

Representative species (Fig. 940). . . Pompholyx com pUfUa i.)o6&c.

Fig. 943. Pedetes sal-
tator Gosse. X 290.
(After Hudson and
Gosse.)

Fig. 944. Triarthna. A.Triarthralongisela
Ehr., side view. X 190. (After Weber.) B,
Triarlhra brachiata Rousselet. X 200.
(After Rousselet.)

Fig. 945. Tetra-
mastix opoli-
ensis Zach.
X ISO. (After
Rousselet.)

Fig. 946. Pedalion mirum Hudson. A, Ventral view of female, ch,
B, Male. (After Wesenberg-Lund.)

'chin." X 70. (After Weber.)

6X3

Fig. 94^. Trochosphaera solstilialis Thorpe. X 80. (After Rousselet.)

THE WHEEL ANIMALCULES (R0TA'1XJRL\) 613

115 (112) Without lorica. With spinc-Ukc or limlj-like appendages. No
foot Family rEDALioNiD/VE . . 116

116 (117, 118, 119) Appendages, two, very long Pcddcs Gosse.

Representative species (Fig. 943) Pcddcs sallalor Ciossc.

117(116,118,119) Appendages, three, spine-like. . rr/flr/Aro Ehrenberg.

Two or three species.

Representative species (Fig. 944, A). . Triarthra lon^iscta Ehrcnberg.
(Fig. 944, 5) T.brachiata RoxxssiiXci.

118(116,117,119) Appendages, four; spines or bristles.

Tctramastix Zacharias.

One species only (Fig. 945). • • Tctramastix opolicnsis Zacharias.

19 (116, 117, 118) Appendages, six, branching, somewhat crustaccan-like.
^ ^ ' " Pcdalum Hud.son.

Two species.

Representative species (Fig. 946). . . . Pedalwn mirum WuiX^Vi.

Representative species (Fig. 947). • Tmhosphacra sol sti I tohs Thorpe

Fig. 948. Melicerta ringens Schrank. A, Animal in
its tube. X 60. (After Hudson and Gosse.) B,
Side view of animal removed from its tube. (After
Weber.) C, Male. X 45- (After Joliet, from Weber.)

S'

Fig. 949. Limnias
ceratophylli Schrank,
X87. (After Hlava.)

Fig. 9SO. Octotrocha sPeciosa Thorpe. X 40.
(After Thorpe.)

614

Fig. 951. Oecistes brevis Hood.
X 300. (After Rousselet.)

THE WHEEL ANIMALCULES (ROTATORL\) 615

121 (no) Fixed by the tip of the stalk-Uke foot, or with tubes, or in colonies
Secondarily free in a few cases, then distinguishable by the
soft elongated body, without lorica or appendages.

Family Melicertidae . . 122

122 (130, 133) Individuals attached, separate, or in branching, non-spherical
colonies of few specimens (1-30) 123

123(124,125) Corona four lobed Melicerla Schmnk.

Two lobes in one species. Living in tubes. Several species.

Representative species (Fig. 948 and Fig. 866, .1, page 575).

Melicerta ringcus Schrank.

124 (123, 125) Corona eight lobed Octotrocha Thorpe.

Representative species (Fig. 950). . . . Octotrocha spcciosa Thorpe.

125(123,124) Corona more or less two lobed 126

126(129) Dorsal antenna minute or absent 127

127 (128) Corona broad, of two lobes, with a wide dorsal gap.

Limn'uis Schrank.

Dorsal antenna minute, ventral antennae long; living in tubes not made with ix-llots. Sev-
eral species.

Representative species (Fig. 949)- • • Limnias ccratophylli Schrank.

128 (127) Corona a wide oval or nearly circular, indistincUy t^yo lobed.
Dorsal gap minute Occistes YMvQnhcig.

Dorsal antenna inconspicuous or absent. Ventral antennae obvious. Living attached in
tubes. Many species.

Representative species (Fig. 951) Occistcs brcAs Wood.

Fig. 9 < 2. Conochilus unicornis Rousselet. ^, Colony. X40
5, Single animal isolated. X 150. (After Weber.)

Fig. 953. Conochiloides nutans
SeUgo. X87. (After fflava.)

Fig. 956. Cephalosiphon

Fig. 954. Pseudoecistes rotifer Sten- Fig. 955- Megalotrocha alboflavkans ^l^^f^^^^^'Ji^f^'
toos. X150. (After Stenroos.) Ehrenberg. Single individual. (After Dixon Wultau.;

^ X87. (After Hlava.)

616

THE WHEEL ANIMALCULES (ROTATORIA) 617

129 (126) Dorsal antenna very large, with two projections or hooks :ii its

side Ccphalosiphon Ehrcnbcrg.

Corona nearly circular with a distinct dorsal gap. Ventral antennae small or absent.

Representative species (Fig. 956). . Ccphalosiphon limnias EhrcnherK.

130 (122, 133) Not attached nor forming colonics, save that one adult may
be grouped with its young 131

131 (132) Not forming tubes Psciidoccistcs Stcnroos.

In other respects like Cephalosiphon. One or two species.

Representative species (Fig. 954). . . Psciulocc isles rotifer Sicnroos.

132(131) Inhabiting a tube Cojiochiloides Uhva..

Individuals separate or one grouped with its young. One or two species.

Representative species (Fig. 953). . . . Conochiloides nalans Seligo,

133 (122, 130) In clusters of many individuals, forming usually a spherical
~~ colony appearing to the naked eye as a yellowish ball. . 134

134 (137) Clusters attached US

135 (136) No tubes Mcgalotrocha Ehrcnbcrg.

Colonies often several millimeters in diameter, attached to plants Individuals not imbedded
in a gelatinous mass; corona broad, kidney shaped. Body usually with two or four opaque
warts. Several species.

Representative species (Fig. 955). .,1

Megalolrocha albojlavieans Ehrcnbcrg.

136 (135) Dwelling in transparent gelatinous tubes. . Laciuidarui Schwcigger.

Colony, a mass of some mm. in diameter, often appears to 1)C imbeddeii in a mass of jelly.
Corona heart shaped (Figs. 861, A, and 865). Several species.

Representative species (Fig. 86i,.4, page 561. and Fig. 865. page 575).

Lacinularui socuilis Ehrcnbcrg.

137(134) Clusters or colonies free swimming. . . . C(7wor//;7w;y Ehrcnbcrg.
Two or three species.

Representative species (Fig. 952). • ConochUus unuornis Roussclet.

Fig, 958. Rotifer

citrinus Ehr.

X 170. (After
Weber.)

Fig. 962. Microdina paradoxa
Murray. X 400. (After Murray.)

Fig. 060, Rotifer neptunius Ehr. X 100.
(After Weber.)

6x8

Fig. 961. Callidina angustt-
collis Murray. X 325-
(After Murray.)

THE WHEEL ANIMALCULES (ROTATOR L\) 619

138 (i) Two ovaries Subclass Digononta,

In fresh water; only one group Order Bdelloida . . 139

Free-living. Swimming with the corona or creeping hke a leech, or Ixjth. Bo^ly without
lorica, usually nearly cyHndrical, dorsal and ventral surfaces not being conspicuously differ-
entiated, and composed of rings which may be drawn one within the other in telescopic
fashion. A dorsal proboscis behind the corona; jaws ramate (Fig. 867).

139 (146) Corona present i

40

140 (145) Corona of two nearly circular disks raised on short stalks, present-
ing the appearance of two wheels.

Family Philodinid.vk . . 141

141 (144) Eyes, two 142

142 (143) Eyes in the dorsal proboscis Rotifer Schrank.

Several species.

Representative species (Fig. 958). . . Rotifer citriniis KhrcnbcrK.
(Fig. 960). . . . R. neptunius Ehrcnberg.

143 (142) Eyes in the neck, directly over the brain, just above the jaws.

Philodina Ehrenberg.

Several species.

Representative species (Fig. 959). . . Philodina roseola Ehrenberg.
(Fig. 867, A, page 577). . . P- brya-i Weber.

144 (141) Eyes, none CaUidina Ehrenberg.

The genus CalUdina when revised will be broken into several genera. Many species.

Representative species (Fig. 961). • CaUidina angusticollis Murray.

I4< (140) Corona a flat surface covered with cilia on the ventral side of the

anterior end Family Vdinktidak.

One genus only IJ/m/.i Hudson.

Representative species (Fig. 957) Ulmeta vaga \hxy\,^.

146 (139) No corona Family MICRODIMD.^K.

The mouth has a group of cilia about it.

One genus only ; ^. ' « ' „ "•''"""'{ ■""'">■•

Representative species (Fig. <,6. and ^^^^^^Jj^Jii;^^,^,^,

620 FRESH-WATER BIOLOGY

IMPORTANT REFERENCES ON FRESH-WATER ROTATORIA

DixoN-NuTTALL, F. R., and Freeman, R. 1903. The Rotatorian Genus

Diaschiza; a Monographic Study. Jour. Roy. Micr. Soc, 1903: 1-14,

129-141.
Harring, H. K. 1913. Synopsis of the Rotatoria. U. S. Natl. Museum,

Bull. 81. 226 pp. (Changes some of the generic names here employed.)
Hudson, C. T., and Gosse, P. H. 1889. The Rotifera or Wheel Animalcules.

2 vols. London.
Jennings, H. S. 1900. Rotatoria of the United States with especial reference

to those of the Great Lakes: Bull. U. S. Fish Com., 1899: 67-104.
1901. Synopsis of North American Invertebrates XVII. The Rotatoria.

Amer. Nat., 35: 725-777; 171 figures.

1903. Rotatoria of the United States, II. A monograph of the Rat-
tulidae. Bull. U. S. Fish Com., 1902: 273-352.

1904. Reactions to Stimuli in certain Rotifera. Carnegie Institution,
Publ. i6: 73-88.

Montgomery, T. H. 1903. On the Morphology of the Rotatorian Family

Flosculariidae. Proc. Acad. Nat. Sci., Phila., 1903:363-385.
RoussELET, C. F. 1902. The Genus Synchaeta; a Monographic Study.

Jour. Roy. Micr. Soc, 1902: 269-290.
Surface, F. M. 1906. The Formation of New Colonies of the Rotifer Mega-

lotr ocha alboflavicans Ehr. Biol. Bull., 11: 182-192.
Wesenberg-Lund, C. 1899. Danmarks Rotifera I. Grundtraekkene i Roti-

ferernes Okologi, Morfologi og Systematik. Kobenhavn.

I

CHAPTER XVIII
GASTROTRICHA

By henry B. ward

Professor of Zoology, University of Illinois

Among the microscopic animals common in fresh water and
limited in distribution to that environment are certain minute
organisms known as the Gastrotricha. Though limited in variety
of species they are so abundant, so widely distributed, and so strik-
ing in appearance as to command the attention of every student
of aquatic Hfe. They live in numbers among algae and debris and
in almost every bottom collection appear in
company with the rotifers and protozoans. In
movements and habits they resemble closely
the ciliate Protozoa, and are easily confused
with them. Ehrenberg, who first described in
detail the structure of these organisms, placed
them among the Rotifera and many later
investigators have followed this suggestion.
Others incline to regard them as Nematoda
Irom which they differ most strikingly in pos-
sessing ciHa which are not known in other
worms of that group. In size they are strictly
microscopic, varying from 0.54 mm. in maxi-
mum length to only one-eighth of that. They
constitute a distinctly uniform group not
closely related to any other existing t^-pes of
animal life. Our knowledge of the anatomy
of these organisms is due principally to the
investigations of Stokes in this country 2ind^'V^i^s£:!''E:rS:^.

ry ^• ^ • rx. ^l/, muscles; /J, brain; /-^crk.

Z-elmka m Germany. O. esophagus; /. intestine;

Ine general structure of the group is well zeiinka.)
illustrated in the figure of Chaetonotus maximus taken from Zeiinka 's
monograph (Fig. 963). While the form of the body api)roachcs a
cylinder, there is usually an expanded area in front known as the

621

62 2 FRESH-WATER BIOLOGY

''head," a narrower part just behind it called the ''neck" and the
larger "rump," or body proper, which constitutes the major portion
of the animal. These regions are not sharply limited and sometimes
can not be distinguished at all. They do not correspond to any
internal structures. The ventral surface is more or less flattened
and the dorsal surface arched as is conspicuously seen in side view.

The head bears at its tip an opening, the mouth, surrounded by
a row of deUcate oral bristles which point forward. The sides of
the head are often lobed and carry two circles or series of groups
of fine sense hairs; those of the anterior series point outward and
forward while the others are usually directed backward. Some-
times the entire body is smooth, or it may be partly or entirely
covered with plates, spines, or hooked bristles. These furnish
the criteria for the distinction of species and are carefully described
in the key.

The posterior end of the body may be bluntly rounded, pointed,
or forked. The caudal processes, often spoken of as "toes," carry
special bristles and contain cement glands, the secretion of which
is expressed through terminal pores and enables the animal to
attach itself temporarily to objects in the water.

On the ventral surface are two bands of ciHa near the median
line, extending nearly the entire length of the body. These con-
stitute the chief organs of locomotion. The movements of the
Gastrotricha are so graceful as to eUcit admiration from every
observer. In motion they recall the long-necked infusoria, though
excelhng the latter in speed and variety of movement. By bend-
ing the body sharply on itself the animal may instantly reverse its
course. Those species possessed of long bristles utilize them in
moving by leaps like jumping rotifers. Other species employ the
caudal processes in movement, looping the body and attaching the
tips of these toes successively in different places.

The internal anatomy is simple. From the mouth (Fig. 964, A),
a straight ahmentary canal traverses the length of the animal
terminating in a simple anal orifice just above the posterior end of
the body. One can distinguish an anterior muscular region, the
esophagus and a posterior portion, the intestine (Fig. 964, C), which
is lined by large digestive cells, rich in protoplasm. Small gland

GASTROTRrCHA 627

cells on the esophagus are designated as salivary in character
and other gland cells in a fringe at the beginning of the intestine
have been regarded as hepatic or liver cells. The food of the
Gastrotricha consists mainly of unicellular algae, the tests of wliich
can often be recognized in the intestine.

Six pairs of delicate longitudinal strands constitute the entire
muscular system as there are neither circular nor oblique muscles.

the body; ^ c:

One pair of muscles extends nearly
the entire length of
the others occupy only the ante-
rior or the posterior region meeting
near the center. They He in the
body cavity which is devoid of
any special lining epithelium. The
head region of the body cavity
is almost completely filled by a
saddle-shaped mass (Fig. 964,^) of
nerve cells dorsal and lateral to
the esophagus which constitutes
the brain. From it nerve fibers
go out to the anterior sense hairs
and lateral strands follow the
alimentary canal to the posterior
end of the body. Minute pigment
spots which may be designated as eyes certainly occur in some
species despite the doubts expressed by Zelinka.

Excretory organs are present in the form of a pair of lateral
much coiled tubes near the center of the body. The inner end of
each tube is closed by a long flame cell and the outer end opens
on the ventral surface near the median fine and just behind the
center of the body. Just behind these coils, in the mature females,
lie the large eggs that mark the anterior limit of the simple ovary.
These eggs become so large that they extend over one-third to
one-half the length of the entire body and increase its normal
transverse diameter noticeably so as to modify greatly the form of
the gravid female. The large, oval eggs are laid on algal threads
or empty shells of other animals. When deposited they ha\e a

Fig. 964. Chaetonotus maximus. i4, optical longitu-
dinal section through anterior tip of the body
showing mouth, oral bristles, frontal plate, and
esophagus. X 535- B, cross section through
posterior extremity of A, showing tripartite
esophagus and above it the saddle-shai>eti brain
while below are the two ventral cilian bands.
X 690. C, longitudinal section through the pos-
terior region of the body showing below the in-
testine, rectum, and anus; above in the ovary a
single ripe egg; on the up[)er surface fine
bristles, and at the pxisterior tip one of the toes
with its adhesive gland. X 430. (.\fter Zelinka.)

624 FRESH-WATER BIOLOGY

tough thick shell, often covered with hooks and knobs, that seem
to anchor them in place. When the embryo has reached its full
development its vigorous movements burst the shell and a full-
grown animal emerges.

No one has yet described a male and it is uncertain that any
other t^pe than the female exists. This form may have a sperm-
producing organ yet undiscovered and thus be in reality hermaph-
roditic or may reproduce exclusively by parthenogenesis.

The Gastrotricha have been studied but Httle in North America.
Of the seventy-five species thus far described only sixteen have
been recorded from the United States. Most of these were found
and described by Stokes at Trenton, New Jersey. While this dis-
tribution appears highly local there is no doubt that search in
other places will demonstrate for American species the same wide
general distribution that has been shown for European forms.
Further study will doubtless result also in the discovery of many
other species on this continent, since the evidence thus far secured
indicates that, like most minute aquatic organisms, these forms, too,
are cosmopolitan in distribution.

KEY TO NORTH AMERICAN FRESH-WATER GASTROTRICHA

1 (31) Caudal end prolonged into two prominent lateral processes.

Suborder Euichthydina . . 2
Each caudal process encloses a glandular apparatus and bears a pore at the tip.

2 (11) Body naked, scaled, or covered with rugosities or papillae, but never

bearing spines Family Ichthydidae . . 3

s(6) Body without scales; cuticula smooth.

Ichthydium Ehrenberg 1830 . . 4
Seven or eight species described; only two reported from North America.

4 (5) Surface of body entirely smooth, no constant furrows or ridges.

Ichthydium podura O. F. Miiller 1786.

Total length 0.075 mm.; esophagus 0.0188 mm., caudal process 0.00875 mm.
long. Breadth of anterior region 0.0163 mm. The cuticula is thin and is
often laid in deep wrinkles, but these are entirely inconstant. The lateral
margins show no trace of being flattened. The caudal processes are sharply
set off from the body. Eggs smooth.

Fig. 965. Ichthydium podura in dorsal view. X 360. (After Zelinka.)

GASTROTRICHA

625

5 (4) Dorsal and lateral surface with deep transverse furrows. Posterior
region of body narrow and elongated.

Ichthydium sulcatum Slokes 1.S87.

Total length 0.107 to 0.187 mm.; esophagus not more than one-si.xlh the
entire length. The body is unusually soft and flexible. The lateral mar^in-s
are so flattened that they impart to the body the effect of wings. The i)os-
terior region is narrow and very much longer than in other species.

Fig. 966. Posterior region of Ichthydium sulcatum in dorsal :isi>ect.

(After Stokes.)

X alxjul 600.

6 (3) Body covered with smooth scales or with rounded papilhu-, hut wit hout

spines Lepidodcrma Zelinka iSSc, . . 7

Six species described; three reported from North America.

7 (10) Minute soft scales present 8

8 (9) Scales shield-shaped.

Lepidoderma squamatum (Dujardin) 1841,

Length of body from 0.119 to 0.2 mm., of esophagus 0.042 to 0.044 mm.; breadth of anterior
region 0.033 mm., of posterior body also 0.033 mm. Large smooth scales near the posterior
end seen in profile simulate curved bristles or spines. Scales on body and neck in seven alter-
nating longitudinal rows; on posterior region eight rows present. New Jersey.

(05DD

Fig. 967. Lepidoderma squamatum in dorsal aspect with characteristic dorsal scales of head. neck, and
trunk. X 375- (After Zelinka.)

9 (8) Scales rhombic, pointed.

Lepidoderma rlwmlwidcs (Stokes) 18S7.

Fig. 968. Lepidoderma rhomboides. A, ventral
view of head. B, caudal branch. C, portion of the
scale pattern. X 350- (After Stokes.)

Length 0.295 mm.; breadth of anterior region
0.036 mm. Body long, slender. Esophagus
short, " not over one-sixth total length." Scales
0.00506 mm. long, thickened along the margins.

Posterior margin of each scale appears to carry , , , 1 111, .i...,.f -,«

a small triangular supplementary scale. Caudal process remarkably long, markeil b> aln.ut ao
delicate rings. New Jersey.

626

FRESH-WATER BIOLOGY

lo (7) Body covered with hemispherical papillae.

Lepidoderma concinnum (Stokes) 1887.

Length 0.096. Body cylindrical. Back and sides covered with
small half-round papillae arranged in thick -set oblique rows. Egg
smooth, 0.055 mm. long. New Jersey.

Fig. 969.

Posterior region of Lepidoderma concinnum in dorsal view.
X about 525. (After Stokes.)

11 (2) Body provided with spines either attached to the dermal scales or

springing directly from the surface.

Family Chaetonotidae . . 12

12 (30) Caudal process simple; spines attached to dermal scales.

Chaetonotus Ehrenberg 1830 . . 13
A large and complicated group; more than forty species already described; ten species re-
ported from North America by Stokes.

13 (20) Dorsal spines nearly uniform in length, at most twice as long on

posterior region as on anterior region, and without any
marked transition from one size to another 14

14 (15) Dorsal spines with accessory barbs or points. Anterior region

sharply set off from so-called "neck."

Chaetonotus similis Zelinka 1889.

Length of body 0.12 to 0.22 mm., of esophagus 0.05 mm. Body
covered dorsally and laterally with triangular scales carrying spines
with accessory point. Oral funnel plicate. Originally described
from Trenton, New Jersey, as Ch. maximus which it closely
resembles in head and body. Under a high magnification differ-
ences in the spines appear. All of them are forked and have
a fine lateral point near the tip.

ml

Fig. 970. Chaetonotus similis in dorsal view. X 375- A, body spine
from the side, X 1600. (After Zelinka.)

GASTROTRICHA
15 (14) Dorsal spines simple; i.e., without lateral barbs

627

or pointb.

16 (17) Anterior region sharply set off from narrow "neck" region.

Chaetonotiis Jormosus Stokes 1887.

Length 0.169 mm. Oral ring minutely beaded. Head thn-e l<,l,cd. I)„rsal and lateral
aspects of body covered with short tine recurved spines with slight basal cnlarRcmcnls -but
without scales.^. Spines all subequal, in length 0.0292 mm., or less. Trenton. New Jcr«v

No figure pubhshed. j ■ ^> •

17 (16) Transition from anterior region to body gradual, not sharply market!
at any point ' ,^

18(19) Head rounded Chaetonolus brcvispi)wsus ZcV\n\i-d iHH(}.

Length of body 0.095 to 0.149 mm., of esophagus 0.0223 mm-
Spines somewhat curved, remarkably short, slightly larger poste-
riorly, arranged in eleven rows Head circular in front, with four
eye-spots. The only American species reported ni(jrc than ontc.
Orono, Me., and Trenton, New Jersey. It is the C. larus of Stoke-,
also of Fernald.

Fig. 971.

Chaetonolus brevispinosus in dorsal view, X a^K), with spioiMC
scale more highly magnified, (.\fter Zelinka.)

19(18) Head five lobed Chaetonof us ncdnt/iodes Siokcs i^S-;.

Length 0.1411 mm. Body covered with scali-s which In-ar eaih a
small supplementary scale; the latter in the anterior region iios-st-s-^t-i
a short, curved spine; just behind the middle of the IhkIv these trrnu-
nate in a cross row of larger spines. t)n each side near the laudal
processes are two larger curved spines. Trenton, New Jer>cy.

Fig. 972. Posterior end of Charlonotus acanlht>dfs in dor^;d virw.
X about 570. (After Stokes.)

628 FRESH-WATER BIOLOGY

20 (13) Certain dorsal spines of much greater length than others. ... 21

All species in this group thus far reported from North America have large bifurcate spines.
A number of European species have simple spines without a lateral point near the tip. Griin-
spann classes the ne.xt species among the latter despite Stokes' positive statement that the
spines are bifurcate.

21 (26) Head and neck free from covering of small spines. Large spines on
body proper 22

22 (23) Large dorsal spines in longitudinal rows and of approximately equal
length Chaetonotus octonarius Stokes 1887.

Length 0.0862 to 0.1034 nun. Breadth of distinctly five-lobed head
0.0206 mm. Large spines unequally furcate arranged in two lateral
rows of three spines each and a median row with one anterior and one
posterior spine. The figures and descriptions given by Stokes and
Griinspann do not agree fully and may belong to separate species.
Rare; Trenton, New Jersey.

Fig. 973. Chaetonotus octonarius mdorsaXw'xtwi. X about 580. (After Stokes.)

23 (22) Large dorsal spines in two distinct transverse row^s, with spines in

one row clearly longer than those of the other 24

24 (25) Eight (rarely fewer) large spines in two transverse rows set close

together Chaetonotus longispinosus Stokes 1887.

Length 0.0736 mm. Large spines usually eight, four in each row, or
five in one and three in the other; sometimes only four spines in all
(the others lost?); longer spines in posterior row. The figure in
Griinspann is really the next species. The European form identified
as this species is twice as large. Trenton, New Jersey.

Fig. 974. Chaetonotus longispinosus in dorsal view. X 6io. (After Stokes.)

GASTROTRKI

()2Q

25 (24) Seven (rarely fewer) large spines in tuo ui.idy sq>aratc.l irahsvcrse
^^^^ C/iaclunolus spinulosus Slokc:, iHii?.

Length 0.0675 to o 089 mm. I'sually four larRc spine in antcri.r
row and three m posterior. Some may Iw supprcsswl („r l.,Ht'> Icav-
ing three m front and only one in the center U-huM <ui-,ns o(
anterior row distinctly longer. ICgg o.o.i.}«; mm. 1,,. ' .,n

one side with short hairs. The embryo esta|>e> in 11 .,»d

thirty hours later the young individual shows an ovan 1 „ h

the nucleus becomes conspicuous si.\ hours later.

Fig. 975. C/iaetonolus spinulosus IthIots^A view. X 665. (After Stokes.)

26 (21) Spines

present on
body. . .

head and neck much smaller than those

on
27

27 (28, 29) Four transverse rows of large dorsal spines on posterior region
of body. Also one large lateral spine on each side at caudal
process Chaetonotus acanthophorus Stokes 1887.

Length 0.108 mm. Head and neck covered with short spin«.
Large spines on body in four cross rows of five each, not altrrnalinjt
so that they appear also as five longitudinal rows of four spines each.
The last lateral spine at the base of the caudal process is large and much
like those in the dorsal rows. Trenton, New Jersey.

Fig. 976. Chaetonotus acanthomorphus '\n dors>a.\ \'\cy; ■ X 415- \Suhdork*i
spine. X about 1165. (After Stokes.)

28 (27, 29) One transverse row of large spines just in front of the caudal end
of the body C/iai'io)iolus spinifcr Siokcs iSS-;.

Length 0.1954 mm. Back and sides covered by
rounded imbricated scales, each with stout n-oirved
spine minutely furcate at tip. The f' -^ »

smgle series immediately in front of tlu nw

are much larger and stouter than tho- ' ol

the body. Egg ornamentetl with provc.-v<-.s \Aiyu\K
in length and sha|)e in dilTerenl s|>et-imcns. Stoke*
distinguishes eggs with three se|wirate i>attcrn» rrM»ri--
tively, 0.0705. o.o7,i5. and o 0793 mm. lon^. Trenton.
New jersey.

Fig. 977. CItaelotuUus spinifrr. A •'J^

tion of egg. showing tnfi.l .in.l -i ■
and surface asi^ecls. Highly ma>;i.

630

FRESH-WATER BIOLOGY

29 (27, 28) Five transverse rows with thirteen large spines. Also two con-
spicuous lateral spines on each side near the end.

Chaetonotus enormis Stokes 1887.

Length 0.0846 mm. Of the thirteen large spines three stand in the ante-
rior row, four in the next, one at the extreme on each side in the next, three
in the fourth row, and one at the center in the fifth row. On each side
near the caudal process are two forked spines easily confused with those of
the five rows which they much resemble. Trenton, New Jersey.

Fig. 978. Chaetonotus enormis in dorsal view. X 530. (After Stokes.)

30 (12) Caudal process branching or notched. A transverse row of large

spines near its base. Body surface rough.

Chaeturina Ward.
Only one species known.

Chaeturina capricornia (Metchinkoff) 1864.

A swamp animal not yet reported from North America.

31 (i) No caudal processes. Posterior end simply rounded or lobed, in the

latter case provided with long fine spines.

Suborder Apodina.

Reported from North America Family Dasydytidae.

'Iwo genera described for Europe.

Single North American genus Dasydytes Gosse 185 1.

Several species listed from Europe.

Only species reported from North America.

Dasydytes saltitans Stokes 1887.

Length 0.085 mm. Head three lobed, distinctly separated from body by
slender neck, provided with two rows of cilia which vibrate alternately.
Four long heavy spines arise on each side near the neck and cross the back
obliquely. Two long straight spines, and two others long and curved,
project from the posterior end. This species swims rapidly but also moves
by sudden leaps to one side or the other, covering a distance equal to
double its length or more in a single jump. Trenton, New Jersey.

Fig. 979. Dasydytes saltitans in dorsal view. X 4iO' (After Stokes.)

GASTROTRICHA 6^,

IMPORTANT PAPERS ON NORTH AxMERICAX GASTROTRICHA

Fernald, C. H. 1883. Notes on the Chactonolus larus. Amcr. Nat., 17:

12 17-1220; 2 figs.

Interesting biological study on Ch. breiispiitosus.
Grunspann, Th. 1910. Die Susswasser-Gastrotrichen Europas Ann. Biol.

Lacustre, 4: 211-365; 61 figs.
Stokes, A. C. 1887. Observations on ClnidonotHs The MicroscoiH?, 7:

1-9, 33-43; 2 pi. Translated in Jour. Microg., 11: 77-85, 150-153, 560-

565; 2 pi.
1887a. Observations on a New Dasydyles and a New Chaetomtus. T!ic

Microscope, 7: 261-265; i pi. Translated in Jour. Microg., 12: 19-22.

49-51; I pi.
1896. Aquatic Microscopy for Beginners. Third edition (Gastrotricha, pp.

178-193).
Zelinka, C. 1889. Die Gastrotrichen. Zeit. f. wiss. Zool., 49: 209-3S4:

5P1.

CHAPTER XIX

AQUATIC EARTHWORMS AND OTHER
BRISTLE-BEARING WORMS
(CHAETOPODA)

By frank smith

Professor of Systematic Zoology and Curator of the Museum of Natural History, University of Illinois

Earthworms, with their flexible segmented bodies and four
double rows of bristles, or setae, are objects familiar to all students
of animal hfe. Although most species are terrestrial there are also
aquatic ones and these are abundantly represented in our fresh
waters. Closely related to the earthworms and similar in structure
are numerous other worms which are essentially aquatic. These
also, with certain exceptions, are provided with setae and are
included with earthworms in the group Oligochaeta. The setae-
bearing worms of the sea (Polychaeta) commonly bear the setae on
lateral muscular outgrowths of the body wall, the parapodia. The
Oligochaeta and Polychaeta collectively are often referred to as the
Chaetopoda.

The Chaetopoda, Hirudinea (leeches), and certain strictly marine
worms which are not under consideration here, are included in the
phylum Annelida.

Fresh-water Polychaeta

Although the Polychaeta are essentially marine in habit, a few
species in various parts of the world have become adapted to
fresh-water conditions. Manayunkia speciosa Leidy is found in
the Schuylkill River and in other fresh-water situations near Phila-
delphia, and Johnson has described two fresh-water species from
the western coast region, — Nereis limnicola Johnson from Lake
Merced, near San Francisco, and Lycastoides alticola Johnson from
Lower California.

These are stray intruders from the rich, marine fauna of this
group in adjacent salt water, and none have yet been discovered

632

AQUATIC EARTHWORMS 6^3

at any great distance from the sea. Further, more careful study
of the Hfe in brackish water estuaries and fresh-water bodies in
close contiguity with the ocean is Hkely to reveal the presence of
such forms in other locahties.

Fresh-water Oligochaeta

The Oligochaeta, including the earthworms and related aquatic
forms, are segmented worms which have a somewhat extensive
and well-defined body cavity separating the alimentary tract from
the body wall. They are hermaphroditic, with the reproductive
organs limited to a few definite segments or somites. The bristle-
Hke setae in the body wall aid in locomotion, but such setae are
absent in the family Discodrilidae which are parasitic on the ex-
ternal surfaces of crayfishes. The majority of the species are
terrestrial, and the aquatic forms are nearly all confined to fresh
water. Seven families of aquatic Oligochaeta are found in the
northern hemisphere and are all abundantly represented in the
United States.

Morphological Relations. The general plan of structure of the
aquatic forms agrees essentially with that of the earthworm.
External metamerism is indicated by the transverse grooves and
by the segmentally arranged setae, and the corresponding internal
metamerism is recognizable in the septa, nephridia, transverse
blood vessels, and in the ganglia of the ventral nerve chain. The
prostomium — the dorsal part of the anterior somite extending
anterior to the mouth — is very flexible and sensitive, and is an
important tactile organ which in some species is prolonged into a
proboscis (Fig. 984.) The somites are numbered consecutively from
the anterior end, and are designated in these pages by Roman nu-
merals in accordance with a common practice. The boundary
between two somites is indicated thus: X/XI.

The setae are usually conspicuous and are of taxonomic impor-
tance. They are commonly grouped into dorsal and ventral bundles,
the most anterior ventral pairs being always on the second somite.
Figure 991 illustrates some of the more usual types of setae.

The nephridia are the segmental excretory organs, which t>iM-
cally are paired and are usually present in all somites of the body

634 FRESH-WATER BIOLOGY

except a few anterior ones and one at the posterior end. Not infre-
quently some of the nephridia may fail to develop, when a more or
less irregular and asymmetrical distribution results.

The reproductive organs of the fresh-water OHgochaeta are simi-
lar to those of the terrestrial earthworms. One or two pairs of
male gonads (spermaries or testes) are attached to the anterior
septa of certain somites and extend freely posteriad into the cavities
of the somites. One or two pairs of ovaries are correspondingly
situated in somites posterior to those which contain the spermaries.
The sperm, ducts of most species have their internal openings or
spermiducal funnels in the somites which contain the spermaries,
and the external openings, or spermiducal pores, on some somite
posteriad; but in a few species both openings may be in the same
somite. In many species the sperm ducts are modified in various
ways, giving rise to prostates, atria and storage chambers (Fig.
990). The internal openings of the oviducts, the oviducal funnels,
are in the ovarian somite, and the oviducal pores are either at the
posterior boundary of the same somite or, more commonly, on
the following one. Accessory reproductive organs are commonly
present. Evaginations of the septa of the somites which contain
spermaries form sperm sacs in which the sperm cells may complete
their development and be temporarily stored before they pass out
through the sperm ducts during copulation. Evaginations of the
posterior septa of the ovarian somite form ovisacs. Invaginations
of the body wall of certain somites produce spermathecae, usually
paired, which serve for storage of the sperm cells received during
copulation, from another individual.

Sexual reproduction occurs in all famihes of fresh-water OHgo-
chaeta at more or less definite seasons of the year. In the two
famines Naididae and Aeolosomatidae, asexual reproduction by
budding is the mode by which the majority of new individuals
are produced. Figure 980 exhibits the main features of the process
and renders an extended description unnecessary. The body wall
thickens anterior to the middle of the budding somite and forms a
budding zone, the anterior half of which gives rise to an indefinite
number of new somites which form the posterior part of the ante-
rior daughter-worm. The posterior half of the budding zone

AQUATIC EARTHWORMS

635

gives rise to a definite number of new somites (five in most species
of Naididae), which form the anterior part of the posterior daughter-
worm. The daughter-worms, before separation, may in turn de-
velop budding zones, and in some cases even a third series oi these
zones may appear and
thus give rise to chains
of incipient individuals,
or zooids. In some spe-
cies ehains of eight zooids
are of ordinary occur-
rence. In the genus
Chaetogaster the plane
of division is in a septum
between two somites.
Although many aquat-

\r Olicrnrhaptn Vin\7-p tViP ^^^- 9^°- Development of budding zones in Stylaria lacuslris.
IL WilgUeildeLcl nave Uie ^, An early stage. 5. A later stage. C. Still later sI;,kc with

power to regenerate a second budding zone weU started. X. 5. (.-Vfter UuckarU

missing parts, greatly developed, there is lack of evidence that it is
of much importance in normal reproduction.

Environmental Relations. The well-known investigations of
Darwin and others, on the action of terrestrial earth worm.s on the
soil and its organic contents, have led to a general ai)preciation of
the importance of the relations of these animals to their surround-
ings. It is less generally understood that their aquatic relatives
play a very important part in reducing the great masses of aquatic
vegetation to a finely-comminuted condition. Oligochaeta of
various species abound in the mud at the bottom and along the
shores of most bodies of fresh water, and an almost continuous
stream of this mud with its decaying organic contents is passing
through their bodies and being still further subdivided and de-
prived of organic material and its available energy. Numerous
other species swarm in the decaying leaves and stems of coarse
vegetation of swampy areas and materially aid in their disintegra-
tion, while still other kinds populate the floating masses of algae,
which they rapidly devour as decay progresses. Since under
favorable conditions it requires but two or three days for Xauh-
form worms to reproduce by budding, they multiply with such

636 FRESH-WATER BIOLOGY

rapidity that they can extensively populate large masses of mori-
bund algae in a very short time, and their activity accounts in
part for the speedy disappearance of such masses in the autumn.
Although many of these worms will not thrive in polluted water,
others are adapted to foul conditions where fermentation is rife,
and, in fact, multiply most rapidly in such situations. Some
species of this sort feed extensively on the zoogloeic masses which
abound where fermentation is active. The food of most Oligo-
chaeta consists chiefly of decaying vegetable matter, but worms of
a common Naid species, Chaetogaster diaphanus, have a marked
preference for Chydorus sphaericus, a Cladoceran species which they
capture and devour in large numbers. Worms of the family Dis-
codrilidae are parasitic on crayfishes.

Certain of the Naididae can swim effectively in open water, but
a great majority of the Oligochaeta are limited to crawling move-
ments for locomotion.

Striking structural adaptations are not numerous in the group,
but the pecuHar modification of the posterior end in Aulophorus
and Dero for purposes of respiration, deserves mention. These
worms live chiefly in tubes of their own making or with their
bodies almost wholly buried in masses of vegetable material, and
respiration is aided by well-developed gill structures (Fig. 985).
The Discodrilidae in adaptation to their peculiar mode of life, have
become so leech-like in action and external appearance that for-
merly it was usual to treat them as belonging to the Hirudinea
rather than to the Oligochaeta.

Collection and Preservation. The larger specimens may be ob-
tained by carefully screening mud from bottoms and shores and
from about the roots of coarse plants through fine-meshed nets or
sieves. Others may be obtained by carefully pulling to pieces
decaying rushes and masses of algae. Smaller specimens often
may be obtained from the sides of aquaria in which mud and vege-
table material have been allowed to stand for a few days. During
the fermentation of such masses large numbers of small worms
appear in the surface layers and about the margins.

The most successful methods of preservation vary with different
species, and must be gained by experiment, but some general hints

AQUATIC EARTHWORMS 637

may be given here. Specimens intended fur secLloning must be
kept in water and material which is free from grit until the alimen-
tary tract is cleansed from mud and sand. The methods necessary
for securing straight and well-extended specimens for fixation vary
greatly with the species. Dilute solutions of the fixing agent
when of the right strength will often cause the worms to (h'e in a
properly extended condition, and this is esi)ecially true of some (jf
the Tubificidae when corrosive sublimate is used. Commonly some
means of narcotization is required to secure the relaxation neces-
sary for the preparation of well-extended specimens. Oood re-
sults are often obtained by the gradual addition of a solution of
chloretone until the worms no longer respond to stimuli and fail
to contract excessively when placed in the iixing lluid. Another
common expedient used with success for some species is to inmierse
the worms in water within a closed vessel and there subject them
to the action of the vapor of chloroform, which is put into the same
closed vessel but in a separate container. Only the vapor should
be allowed to reach the water that contains the worms.

When properly narcotized the specimens may be immersed in
the fixing agent and kept straight by holding them against any
convenient straight edge until they have become sutTicientl)' rigid.
A rectangular glass candy-tray is a convenient vessel for fixation
purposes since the angles formed by the sides and the bottom
furnish good opportunities for keeping the worms straight. It is
often advantageous to use a small amount of hxing lluid at lirst
and to keep the worms only partially submerged until the\- have
become stiffened and then completely immerse them. Small speci-
mens like tubificids and enchytraeids may be con\'enientl\- fixed on
a glass plate with the aid of square-edged toothpicks which have
been soaked in the fixing agent. A toothpick with the adhering'
fluid is placed on the glass, an anesthetized worm stretched along
one edge of the toothpick, another toothpick placed against the
other side of the worm and a second worm stretched along the free
edge of the second toothpick. A repetition of this process will
enable one to prepare a considerable number of specimens in a
brief time. Subsequent treatment is like that for other material
of similar nature.

638

FRESH-WATER BIOLOGY

KEY TO NORTH AMERICAN FRESH-WATER OLIGOCHAETA

1 (45) Well-developed setae present on most somites 2

2 (24) Reproduction chiefly asexual, by budding; sexual reproduction

less frequent. Clitellum, when present, on some somites of
V-VIII. Length less than 25 mm. in most species. . 3

3 (4) Setae of ventral bundles as well as dorsal setae capilliform; septa

imperfectly developed; prostomium broad and ciliated ven-
trally; integument of most species contains conspicuous
colored bodies of some shade of red, green, or yellow. Usu-
ally 1-2 nmi. long Family Aeolosomatidae.

A eolosoma Ehrenberg is the only North American
genus and the species of the U. S. have not been
much studied. A . tenehrarum Vejdovsky has pale
yellow or greenish integumental bodies. One or
two species with colorless bodies are known. A.
hemprichi Ehrenberg has salmon-colored bodies.
This last named species thrives exceptionally well
in hay infusions and in similar cultures from wheat
and thus large numbers are readily obtained for
experimental purposes.

Fig. 981. Aeolosoma hemprichi.
Lankester.)

X 20. (After

4(3)

Ventral setae all uncinate (Fig. 991); septa well developed; no
brightly colored integumental bodies.

Family Naididae . . 5

5 (8) No dorsal setae 6

6 (7) Ventral bundles of setae on III-V as on other somites.

Schmardaella Michaelsen 1900.
The South American species 5. filiformis (Schmarda) has recently been reported from Lake
St. Clair (Moore, 1906).

7 (6) No setae on III-V. Somite III much elongated.

Chaetogaster K. von Baer 1827.

Several species are known
from North America, of which
C. limnaei K. von Baer, which
lives in mollusks, and the large
transparent C. diaphanus
(Gruithuisen), 10-15 mm. long,
are easily recognized.

Chaetogaster limnaei. X 40.
(After Lankester.)

8 (5) Setae in both dorsal and ventral bundles 9

0(12) No capilliform setae in dorsal bimdles. .......... ip

AQUATIC EARTHWORMS 639

10 (11) Setae of dorsal bundles all uncinate. . Paratmis Czerniavsky 1880.
P. litoralis (Muller) reported as abundant on the New England coast and may occur in adja-
cent fresh waters. The first dorsal setae are on V.

11 (10) Dorsal setae nearly straight, slightly toothed or simple-pointed.

Ophidomiis Gervai.s 1.H38.

B«an^(ii<f.^!i'!JBrl"llL_Mi ^" ^^>'P^"^^'^'^ (Miiller) may be easily rccoKnizcd by the

^^^1^^^^"^' ■W^^HtefcrK. small irregularly distributed dorsal sctar; by the four larKC

^P^^^I''l^^o''^o-^^^^^^ transverse pigmented areas on the anterior resion, and

-li^To- '■ ''Wl ! *? '' °o 0 J^ by the relatively large size. Length 25-30 mm.

'^j ^ ''^-,>;>.U^^>-W^.,^ sjf Fig. 983. AnterioT tndolOphidonais serpentina. X 40. (After

""""T '' ^ Piguet.)

12 (9) CapiUiform setae present in dorsal bundles 13

13(21) First anterior dorsal setae on V or VI 14

14 (18) Posterior end not modified into a gill-bearing respirator}- organ;

first anterior dorsal setae on \'1 15

15 (16, 17) One or more capilliform setae of VI much longer than those of

other somites and equal to three or four times the diameter
of the body Slavimi Vejdovsky 1883.

S. appendiculata (d'Udekem), common in some parts of the United States, has Ixidy surface
studded with sensory papillae and with foreign bodies.

16 (15, 17) Prostomium elongated to form a proboscis; dorsal setae of \'I similar

in length to those of other somites. Stylaria Lamarck 1816.

S. lacustris (Linnaeus) has proboscis flanked by promi-
nent lateral prostomial lobes (Figs. 980 and 9!^4);. -*>• foi-
sidaris Leidy lacks the lateral prostomial lobes (Fig. 984).
The former' is abundant and widely distributed in the
United States while the latter is reported only very infre-
quently.

Fig. 984.

Prostomium and proboscis, Stylaria. A, S. laeuitrii

B.S./ossularis. X40. (Original)

17 (iK, 16) Without proboscis; dorsal setae of VI similar in length to those of

other somites A'd/^ Muller 1774.

Several species without conspicuous differences are reported from the United States. A'.
elinguis Muller is one of the best-known species and A^. communts I>.guet is very common.

18 (14) Posterior end modified into a gill-bearing respiratory organ, the

branchial area ^^

10 (20) Ventral margin of the branchial area with a pair of long processj-s.
^^ ^ .l;</()/)//t;r//5 Schmarda iSoi.

A Jurcatiis (Okcn) has the first dorsal setae on V and
has two pairs of well-develo,R'd gills

A vagus Leidv crawls or tloats about m a tube made
; ^i;:'^^-. from bryozoan statoblasts and bits .)f vegetation It hw

the first dorsal setae on VI and has only slightly devel-
oped gills.

Fig q8s. Posterior end of .1 ulo Chorus /urcaius.
^ Bousflicld.)

X 40. (After

640 FRESH-WATER BIOLOGY

20 (19) Ventral margin of the branchial area without long processes.

Dero Oken 181 5.

D. limosa Leidy is abundant and the best known of the North
American species. D. obtusa d'Udekem and a species which prob-
ably is D. perrieri Bousefield are of frequent occurrence, but a careful
study of the North American representatives of this genus, as well
as of Nais, is necessary before we can be sure of their exact relation
to European species.

Fig. 986. Posterior end of Dero limosa. X 25. (After Bousefield.)

21 (13) First anterior dorsal setae on II 22

22 (23) Dorsal setae of two kinds: capilliform and shorter needle-form setae

which commonly have cleft distal ends,

Naidium O. Schmidt 1847.
N. osborni Walton has been described from Lake Erie (Walton, 1906). This genus is united
with Pristina by some writers.

23 (22) Dorsal setae all capiUiform, mostly with very fine teeth on convex

side; prostomium commonly elongated into a proboscis.

Pristina Ehrenberg 1831.

P. longiseta var. leidyi Frank Smith has the capiUiform setae of III greatly
lengthened (.700 mm.) and without serrations. The typical form of this
species as found in Europe has extremely minute inconspicuous serrations
on the capilliform setae of dorsal bundles of somites other than III. In the
variety P. I. leidyi, which is found in the United States and certain other
parts of the world, the serrations are coarser and more easily seen.

d.s.

Fig. 987. Pristina longiseta ya-r. leidyi. r. 5., ventral seta; X 3oo- (i. 5., part of seta
from dorsal bundle. X 450. (After Smith.)

P. flagellum Leidy has a very characteristic posterior end. Specimens of
this species have been met with by the writer but once and when there was
no opportunity for study beyond enough to convince him of the general accu-
racy of Leidy's description and that the species really belongs to Pristina.

Representatives are sometimes found of certain species in which the dorsal
setae of III are not especially elongated but their exact relationship to Eu-
ropean species is uncertain.

Fig. 988. Posterior end of Pm/ma^ageWMW. X 16. (After Leidy.)

24 (2) Reproduction sexual, never by budding; clitellum ordinarily poste-

rior to VIII 25

25 (34i 35) Ordinarily more than two well-developed setae in each of some or

all of the bundles; ventral setae ordinarily cleft (exc. Telma-
todrilus: see below); clitellum ordinarily on X or XI and
one or more adjacent somites; $ pores ordinarily on XI, ex-
ceptionally on XII; spermathecal pores on somite anterior
to one bearing <? pores (in North American species) ; length
commonly more than 25 mm.; blood vessels usually with con-
spicuous red contents. . . . Family Tubificidae . . 26

^ Accurate identification of species in this family usually requires the aid of careful dissec-
tions or of serial sections, and depends largely on a careful study of the reproductive organs.
(Fig. 990.)

AQUATIC EARTHWORMS

641

Sperm-ducts without definite prostate glands and opening into a
common median chamber with single ventral median <>|K-n-
ing on XI; spermathecal pores on X; setae of dorsal bundles
all cleft RJiizodrilus Frank Smith u/x).

One species thus far known in North America, R. latUus Frank Smith,
found in roots oi Sagittaria in Illinois. Has two kinds of jjcnital setae
on IX and XI; length 75-100 mm.; whitish in ap[)carancc (Smith, lyoo).
Michaelsen includes this species in Monopylephorus Levinscn.

Fig. 989.

Rhizodrilus lacteus. a, ordinary uncinate seta; b and c, Kcniul N<-ta.
from IX and XI. X 150. (After Smith.)

27 (26) Sperm-ducts with definite prostate glands 28

28 (29) Ten or more small definite prostates on each sperm-duct; no capil-

liform setae; setae indistinctly cleft and sometimes simple-
pointed Tclmalodrilus Eisen iHyg.

Two species, T. vejdovskyi Eisen and T. mcgregori Eisen, are found in California.

29 (28) Sperm-ducts each with one definite prostate gland (Fig. 990). . 30

30 (31) Dorsal setae all uncinate and similar to ventral setae; penis with
chitinous sheath Limnodriliis Clapartkie 1S62.

Several species have been descrif>ed from
California (Eisen, 1885).

L. gracilis Moore has recently been described
from Lake Erie (Moore, 1906). In L. clapare-
dianiis Ratzel, an abundant si)ecies of wide
distribution, the length of the chitinous penis
sheath is 8-50 times its diameter.

Fig. 990. Reproductive organs of Limncdritus
gracilis. I, spermary: sp. spermatheca; /. spenni-
ducal funnel; r, :, sperm-duct; 6. prostate kIuxI;
r, atrium; at, penis and jx-nis sncath; av, ovary.
X 20. (.\fter Moore.)

31 (30)

Dorsal bundles ordinarily contain capilliform setae and also jx-cti-
nate or paknate setae. (Fig. 991.) 32

Fig 991 a and fi, uncinate setae from 7'M/>f7rx»»ik//i5r/<ir«»J,f and
d, palmate setae. T. tnultisrlosus; e and /. jKCtinatc setae. T.

tubifex. <i, ft, and <, X 150. (DriKinal.)

?2 (s3) Length of atrium and penis combined, at least two-thirds that of
the remainder of the sperm -duct. . Ilyodnlus Eisen iNTQ-

Three species described from California (Eisen, 1S85).

642 FRESH-WATER BIOLOGY

^^ (32) Atrium and penis combined, much shorter than the remainder of
the sperm-duct Tubifex Lamarck 1816.

■^\\ v\i ^\ ^\ Several species have been described from North America.

^ -^^^''^^JL^L^L^ T. tubifex (Muller) is a widely distributed species and

^^^> — \ ■- ^ \: " " "- abundant both in Europe and the United States. An-

^^ t_ ^ J' ^--^"z -ijji, other species, T. multisetosus (Frank Smith) from Illinois

'^^^-^jM^M^W' ^^ ^^^ ^^^^^ integumental papillae and conspicuous clusters

^"' •^^^nn'^*Pp*?5p^;i^5-4^; ^j capilliform setae (Smith, 1900). (Figs. 991 and 992.)

Fig. 992. Anterior somites oi Tubijex multisetosus. X i3- (Original.)

34 (25. 35) Ordinarily with more than two setae in each of some or all the

bundles; setae simple-pointed and usually nearly straight;
clitellum on XII and on more or less of adjacent somites;
Spores ordinarily on XII; spermathecal pores on IV/V.
Ordinarily whitish in appearance and seldom more than
25 mm. in length. Both terrestrial and aquatic species
abound Family Enchytraeidae . . 35

There are numerous species of this family represented in the fresh waters of North America,
which have only recently received attention from the systematists of the group. Eisen
(1905) has described several fresh-water species from the Pacific Coast states belonging
to Mesenchytraeiis Eisen, Enchytraeus Henle and Lumbricillus Oersted. Smith and Welch
(1913) have described Marionina forbesae from Illinois and Welch (1914) has described
Luynbricillus rutilus from IlUnois.

35 (25. 34) Ordinarily with not more than two well-developed setae per bundle,

or eight more or less separated setae per somite. ... 36

36 (37.42) Setae simple-pointed; J pores, 2 pairs on XI and XII or both

pairs on XII; spermaries in X and XL

Family Haplotaxidae.

Haplotaxis (Phreoryctes) emissarius (Forbes) is the only representative of this family thus far
known in North America. Has two large isolated ventral setae and two small dorsal setae
oer somite; many somites without dorsal setae; length 150-200 mm.; diameter, scarcely i mm.;
subterranean habit.

37 (36, 42) Setae either simple-pointed or cleft; S pores on one or more somites

anterior to XII, with spermiducal funnels in same somites;
cecal diverticula of the dorsal vessel or its branches, in the
mid-body region Family Lumbriculidae . . 38

38 (39) Setae cleft at distal extremities; prostomium without distinct pro-

boscis; spermathecae and spermathecal pores paired or
asymmetrical in three or more somites posterior to somite
bearing ^ pores Lumbricillus Grube 1844.

L. inconstans (Frank Smith), common in the Mississippi Valley, has Z pores on X or XI and
spermathecae in XI-XV or XII-XVI (Smith, 1905)

39 (38) Setae simple-pointed; spermathecal pores on but one somite ante-

rior to $ pores 40

40 (41) Large median spermathecal sac with numerous tubular diverticula

in VIII; with single median external opening.

Siitroa Eisen 1888.

Two species. 5. rostrata Eisen and 5. alpestris Eisen, each with distinct proboscis, are
found west of the Rocky Mountains.

AQUATIC EARTHWORMS 6^^

41 (40) Spermathecae withoul diverticula, paired or two unpaired ones

opening separately; long, highly muscular, ejaculatorv
chamber forms part of each otherwise highly difrcrcntiatcd
sperm-duct EclipiJrilus Eisen 1881.

A genus of peculiar North American Lumljriculida,- which includes /•. fnnJus Fism
from Cahfornia, with paired $ pores on X; E. asymmetricus (I-rank Smith/ from IIIinST
with single median ^ pore on X; and t. palustns (Frank Smith) fr(.m Florida with wirH I
pores on IX (Smith, igooa). i^ucu ,5

42 (36,37) Earthworms, essentially aquatic in habit. Setae simple-[M)intcd

and paired in each of four bundles per somite; i jM^res ex-
ceptionally on XII or XIII, commonly further jxjsterior-
spermaries in X and XI; ovaries in XIII 43

43 (44) Clitellum beginning on XIV to X\T and extending over 10-12

somites; $ pores on XVHI/XIX or on XIX. recognizable
only in sections; few or no dorsal [)()res; without well-
developed gizzard Sparganophiliis Benham 1892.

Several North American species, of which S. eiseni Frank Smith is found in the Mi«isissinpi
Valley, Great Lakes region, and Florida; S. smithi Eisen and subspecies occur in Caiifomia
6". benhami Eisen and subspecies in Mexicoand Central America (Eisen, i8g6).

44 (43) Clitellum beginning on XVIII-XXIII and extending over 4-6

somites; ^ pores on XII, XIII, or X\', conspicuous; gizzard
limited to XVII; first dorsal pores on I\'/\'.

Hdodrilus Subgenus Eiscnidla Michaelsen kjoo.

The highly variable species, H. (E.) tetraedriis (Savigny), is represented in North A merit a
by several of the subspecies indicated in the diagram from Michaelsen (Fig. 9^3).

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 2S

furm tjfica

furm hcrcynxa
form tura/x^itiina
furm .\'iHnii

fulin ylv/ii

Fig. 993. Different forms of Heloirilus {Ehenidla) tctraedrus (SaviRny). The diaKram shows
the positions for the spermiducal pores and the tubercula pubertalis. (.\ftcr Michaclicn.)

A specimen which is presumably the type of Ilclodrilus tclrarJrus forma pupj (Eis<-n)
was deposited in the United States National Museum and has been studittl by the writer
It is almost certainly a regenerated individual and is hii^hly abnormal and hence the form
presumably has no systematic status except in synonomy. References in |>ara>iraphs 42 and
44 of the above key and in Fig. 993, to spermiducal pores on XII, have therefore lost their
significance.

Beside these essentially aquatic forms, several species ji Diplocardia and HciodrUus live
in bottomlands and low-lying banks of streams which are subject to overflow for prolonged
mtervals

— • ^^

^^ f~

— ;• ^

-p* ^ ^^ —

-y II —

644

45 (i)

FRESH-WATER BIOLOGY

Without setae; pharynx with two chitinous jaws, dorsal and ven-
tral. Small leech-like worms, parasitic or symbiotic, on
crayfishes Family Discodrilidae . . 46

The family name Branchiobdellidae is preferred by some writers.

46 (49) Two pairs of spermaries and two pairs of sperm-ducts in the fifth
. and sixth post-cephaHc somites 47

47 (48) Without conspicuous dorsal appendages on post-cephalic somites.

Bdellodrilus Moore 1895.

B. philadelphicus (Leidy) and B. illuminatus (Moore)
resemble each other in having the anterior pair of nephridia
open to the exterior through a common pulsatile vesicle on
the mid-dorsal line of the third post-cephalic somite and in
having the dorsal and ventral jaws quite dissimilar. The
former has the head much broader than the anterior body
somite and enjoys a wide distribution in the eastern half of
the United States. The latter has nine pairs of conspicuous
lateral glands, the head narrower than the following somite and is less common.

Fig. 994. Bdellodrilus phiiadel-
phicus. X 9- (After Moore.)

B. pulcherrimiis (Moore) and B. instahilis (Moore) re-
semble each other in having the anterior nephridia open
separately and in having the dorsal and ventral jaws simi-
lar. The former has all post-cephalic somites evidently
biannulate; ahmentary canal straight; jaws small, each
bearing three teeth. The latter has biannulation con-
spicuous on only anterior four post-cephalic somites; ali-
mentary canal with transverse loop in seventh somite;

and dark-brown jaws, each bearing four teeth. They have been described from North CaroUna

and Pennsylvania (Moore 1893).

Under the name Cambarincola macrodonta, Ellis (191 2) has described a species from Colorado

which is closely allied to B. philadelphicus but which has the head narrower than the greatest

width of the body and different shaped jaws. It also lacks the conspicuous glands of B.

illuminatus.

Fig. 995. Bdellodrilus instahilis.
X 9. (After Moore.)

48 (47) W'ith conspicuous dorsal appendages on each of several post-
cephalic somites Pterodrilus Moore 1894.

P distichus Moore, with simple cylindrical dorsal append-
ages on each of post-cephaUc somites II to VIII, and P.
alcicornus Moore, with dorsal appendages of complex form
on post-cephalic somites III and VIII and simple ones on
IV and V, have been described from crayfishes of eastern
United States (Moore 1894).

Under the name Ceratodrilus thysanosomus. Hall (1914)
has described a species from Utah which resembles the
above described species of Pterodrilus closely, but has the
antero-dorsal border of the head furnished with a membran-
ous border deeply incised to form four tentacular append-
ages. The dorsal appendages are transverse bands with edges bearing six to eight points.

Fig. 996. Pterodrilus alcicornus.
X 50. (After Moore.)

49 (46) But one pair of spermaries and one pair of sperm-ducts and these
in the fifth post-cephalic somite.

Branchiobdella Odier 1823.

B. americana Pierantoni has the prostomium entire and the jaws dissimilar. It has been
collected in Texas and North CaroUna. B. tetrodonta Pierantoni has the prostomium divided
into dorsal and ventral lobes and the jaws similar. It is found in California (Pierantoni 1912).

AQUATIC EARTHWORMS 645

LITERATURE ON FRESH-WATER OLIGOCHAITA

EiSEN, G. 1885. Oligochactological Researches. Rcpt. U. S. Fish Com. for
1883, 11: 879-964; 19 pi.
1896. Pacific Coast Oligochaeta II. Alem. CaHf. Acad. Sci., 2: 123-198;
12 pi.

1905. Enchytraeidae of the West Coast of North America. Harriman
Alaska Expedition, 12: 1-166; 20 pi. New York.

Ellis, M. M. 1912. A New Discodrilid Worm from Colori.lo. Proc.

U. S. Nat'l Mus., 42: 481-486.
Galloway, T. W. 191 i. The Common Fresh- Water Oligochada of the

United States. Trans. Amer. Micr. Soc, 30: 285-317; 14 figs.
Hall, M. C. 1914. Descriptions of a New Genus and Species of the

Discodrilid Worms. Proc. U. S. Nat'l Mus., 48: 187-193.
Michaelsen, W. 1900. Oligochaeta. Das Tierreich. No. 10. Pp. .x.xi.x and

575.
Moore, J. P. 1893. On Some Leech-like Parasites of .American Crayfishes.
Proc. Acad. Nat. Sci. Phila., 1893: 419-428; i pi.
1894. Pterodrilus, a Remarkable Discodrilid. Proc. Acad. Nat. Sci. Phila..
1894: 449-454; I Pl.

1906. Hirudinea and Oligochaeta Collected in the Great Lakes Region.
Bull. Bur. Fish., 21: 1 53-171; i pl.

PiERANTONi, U. 191 2. Mouografia dei Discodrilidae. Ann. Mus. Zool.

Univ. Napoli, n.s., 3, No. 24, 28 pp.; i pl.
Smith, Frank. 1900. Notes on Species of North American Oligochaeta IH.

Bull. 111. State Lab. Nat. Hist., 5: 441-458; 2 pl.
1900a. Notes on Species of North American Oligochaeta I\'. Bull. III.

State Lab. Nat. Hist., 5: 459-478; i pl.
1905. Notes on Species of North American Oligochaeta \'. Bull. 111.

State Lab. Nat. Hist., 7: 45-51-
Smith, F., and Welch, P. S. 1913. Some New Illinois Enchytraeidae. Bull.

111. State Lab. Nat. Hist., 9: 615-636; 5 pl.
Walton, L.B. 1906. Naididae of Cedar Point, Ohio. Amer. Nat., 40: 683-706.
Welch, P. S. 1914. Studies on the Enchytraeidae of North America. Bull.

111. State Lab. Nat. Hist., 10: 123-212; 5 pl.

CHAPTER XX
THE LEECHES (HIRUDINEA)

By J. PERCY MOORE

Professor of Zoology in the University of Pennsylvania

The Hirudinea or leeches are predatory or parasitic annelids
with terminal suckers serving for attachment and locomotion.
Quite nearly related to the Oligochaeta and closely resembled by
the semi-parasitic Discodrilidae in the possession of suckers, jaws,
and median genital orifices and in the absence of setae, they are
characteristically modified for procuring and digesting their pecul-
iar food, consisting typically of blood and other animal juices.

The body of a leech is generally constituted of thirty-four meta-
meres (designated I to XXXIV), each represented in the central
nervous system by a ganglion usually consisting of six capsules or
groups of nerve cells. Externally superficial furrows divide each
fully developed somite into from two to sixteen rings or annuli.
One of these, lying at the middle of the somite, contains the gangKon
and usually bears three or four dorsal pairs and three ventral pairs
of eye-like sense organs or sensillae and is termed the neural or
sensory ring. Segments having the full number of annuli charac-
teristic of the genus are termed complete, and are always found in
the middle region. Incomplete or abbreviated segments occur at
the ends of the body and may have any number of annuli less
tlian the complete somites into which they grade. Recognizing
the triannulate somite as basic for most leeches and considering
that more complex somites may be derived by repeated binary
division of its annuli the following symbols are employed for the
precise designation of particular rings. Counting from the head
end the rings of the triannulate somite are A'^, A"^, and A^, where
A^ is the neural or sensory annulus. These, bisected, give col-
lectively the secondary annuli B^ to B^. Repeated subdivisions
give tertiary annuH C^ to O^ and quaternary annuh D^ to D^\
But the full theoretical number of the fourth order is never

646

THE LEECHES (HIRUDINEA) 647

developed and the neural annulus is usually less divided than the
others.

Setae are always absent, except in AcantJiobdella, and suckers
always present, except in a few exotic, chiefly burrowing, genera.
The oral sucker surrounds the mouth, sometimes forming mere
lips- and being widely expanded only in Ichthyobdellidae and a few
Glossiphonidae. The caudal or subanal sucker is larger, discoid or,
more rarely, deeply cupped, and widely expanded beyond its con-
stricted central pedicle. There is a powerful and elaborate muscu-
lar system, consisting of circular, oblique, and thick, longitudinal
coats, as well as vertical and radial sheets and fibers.

The digestive tract is divided into buccal chamber, pharynx,
esophagus, stomach or crop, intestine and rectum. In the jawed
leeches the mouth is large; in the proboscis leeches a mere pore in
the disk of the sucker. In the former the buccal chamber usually
contains three compressed muscular jaws bearing serial teeth on
the ridge. The pharynx is a muscular bulb, a straight tube, or a
slender, exertile proboscis moving within a sheath. Salivary glands
may open into the short esophagus or on the jaws. The large
stomach or crop varies with the nature of the food and may be a
straight tube, or compHcated by from one to twenty pairs of simple
or branched lateral ceca, of which the posterior pair is largest and
most constant. Generally short and simple, the intestine may
bear four pairs of simple ceca (Glossiphonidae). A short, narrow
rectum opens by a small dorsal anus usually behind XXVI or
XXVII, but rarely behind XXIII.

Leeches are hermaphroditic. The genital orifices are median, with
the male pore preceding the female. The testes (really coelomic
sacs enclosing the testes) vary from one elongated pair in Acafi-
thobdella to usually six (five to nine) pairs in the Rhynchobdelhie,
nine or ten (five to nineteen) pairs in the Hirudinidae. and very
numerous small ones in the HerpobdcUidae. A vas deferens on
each side continues into an epididymis and an ejaculatory duct
which may be provided with a sperm sac and a glandular region
for forming the horny spermatophores. The two ejaculatory ducts
open into an unpaired genital bursa or a more complex atrium
. which may be elongated into a highly muscular sheath cnclosmg a

648 FRESH-WATER BIOLOGY

penis and provided with a prostate gland. The ovaries, also
coelomic sacs, are a single pair, usually elongated and folded and
opening directly into a small median bursa. In the Hirudinidae
they have special ducts provided with an unpaired albumen
gland and a muscular vagina. Accessory copulatory glands may
occur.

A most striking characteristic of leeches is the great reduction of
the body cavity which, besides the ovarian and testicular coelom, is
represented only by a system of sinuses, the extent and arrange-
ment of which vary in the several famiKes. In addition there is a
true blood vascular system consisting of dorsal and ventral longi-
tudinal trunks and a peri-intestinal sinus united by transverse
loops and in the caudal sucker by a circle of radiating loops. Ex-
cept in some Ichthyobdellidae, which have lateral gills or pulsating
vesicles, leeches respire solely by virtue of the capillary network
underlying or even penetrating the hypodermis.

The nephridia in general resemble those of the OHgochaeta, but
the funnels especially are more complex and variable, being some-
times branched and sometimes having the opening occluded. Not
more than seventeen pairs usually occur, they being absent from
both ends of the body and often from one or more clitellar segments.

Pigment occurs in the form of excreted matter contained in
wandering cells and reserve cells and is usually deposited along
the line of muscle bundles in either metameric or non-metameric
spots or bands. The eyes are highly developed sensillae, several
of which are sometimes united in a common pigment mass. They
occur rarely on the caudal sucker as weh as on the head.

Leeches are among the most interesting and beautiful of the
invertebrate inhabitants of our fresh waters. They abound in
ditches, pools, ponds and lakes, few species occurring in swift, cold
streams. In the small lakes of our northern borders they fairly
swarm.

They are predatory hunters or scavengers, temporary or nearly
permanent parasites, or they may change from one mode of life
to another. The few fresh-water Ichthyobdellidae attach them-
selves chiefly to the fins and gills of fishes. Several Glossiphonidae
have similar habits and one remarkable species is a nearly permanent

THE LEECHES (HIRUDINEA) 649

parasite on the sheepshead of the lakes of Minnesota, its sucker
becoming fixed into deep pits in the inflamed tissues of the isthmus.
Many of this family are temporary parasites on turtles, frogs,
salamanders, etc., but also Hve free and subsist upon a([ualic
worms, mollusks, etc. Because of the nature of their food the
smaller species are known as snail leeches. The Herpobdellidac are
voracious destroyers of aquatic worms, larvae, insects, and even of
their own kind. Many of the Hirudinidae have similar habits but
also burrow into mud. Some even habitually leave the water in
quest of earthworms and one, Haemopis lateralis tcrrcslris. inhabits
garden soil several miles from water.

While most species will partake of vertebrate blood, especially
just before the breeding season, Macrobdella is our only native true
sanguivorous jawed leech. While young it feeds upon larvae and
worms and attacks vertebrates only when mature, and even then
varies the blood diet with an occasional meal of frogs' eggs. This
and other jawed leeches painlessly make a trifid incision in the
skin and quickly extract more than their own weight of blood, the
flow of which is faciUtated by a ferment which prevents coagula-
tion. As the blood fills the gastric ceca its fluid constituents are
drawn off through the walls and exude in droplets from the ncph-
ropores. The solid parts remain and, protected from decay by a
preservative secretion, may not be completely digested for upwards
of a year.

The short, flat triannulate Glossiphonidae are poor swimmers
but sometimes active creepers. When disturbed they roll into a
ball, pill-bug-like, and fall to the bottom, soon to creep hastily to
shelter. Species with longer, more complex segments are better
swimmers and the elongated and muscular HerpobdcUidae and
Hirudinidae swim powerfully, moving rapidl}' with graceful undu-
lations in either the vertical or horizontal plane. Their resting
attitudes are varied and characteristic. Probabl>- in order to facili-
tate respiration many species attach one or both suckers and wave
the body with an undulatory motion. Most leeches are nocturnal
and except when stimulated by hunger and the proximity of food
they avoid the light by hiding beneath stones, among plants or in
the mud.

650 FRESH-WATER BIOLOGY

Reproduction takes place in the spring and summer, some species
continuing to produce batches of eggs for five or six months. In
the Rhynchobdellae and HerpobdelJidae copulation consists in the
implanting by one individual of a horny, usually two-chambered
spermatophore on the skin of another. From this the spermatozoa
issue in a stream and, by a process that Professor Whitman has
aptly termed hypodermic injection, penetrate the tissues to the
ovarian sac where impregnation occurs. Among the Hirudinidae
a more definite act of copulation and reciprocal fertilization takes
place during which the filamentous penis of one individual
deposits a spermatophore within the vagina or at the genital
orifice of the other.

The Glossiphonidae carry their eggs in several membranous
capsules attached to the venter, maintaining an undulatory move-
ment for their aeration. The young also remain for a time fixed
by a sort of byssus thread and later by the sucker, and are said to
be partly nourished by an albuminous secretion of the parent. All
other leeches form chitinoid cocoons or egg capsules from the secre-
tion of the deeper glands of the clitellum which hardens on exposure
to the water. The Ichthyobdellidae deposit a single ovum in a
small stalked capsule, the Herpobdellidae and Hirudinidae several
in an albuminous mass within a larger capsule, which in the case
of the former is a flat pouch attached by one side and in the
latter an ellipsoidal case with a thick, spongy, vesicular wall buried
in wet earth.

Leeches have rather dull senses which arise in three sets of
cutaneous organs. Numerous goblet cells located in the lips are
taste organs and guide the leech on the trail of its prey. Tactile
organs are scattered all over the skin but are especially numerous
on the lips. Wave movements and light stimuli appear to affect
all parts of the body. The eyes are strongly sensitive and the
sensillae much less so to changes in the intensity of light.

Leeches may readily be found by searching in the situations indi-
cated above. Sanguivorous species are easily collected by stirring
the mud in their haunts with one's bare feet and removing them
from the skin as they become attached, or by attracting them with
fresh blood placed in the water. They may be kept and studied

THE LEECHES (HIRUDIXEA) 651

indefinitely in aquaria. For examination alive under a microsa)pe
they should be stupefied and relaxed by placing a little carbon
dioxide (as soda water), chlorotone, or cocaine in the water.

For preservation they should always be tirst relaxed with similar
reagents and extended before fixing. Chromic acid in one-cjuarter
to one-half per cent solutions, picro-sulphuric acid. Gilson's fluid,
corrosive-sublimate-acetic mixture and Fleming's fluids are all
good fixatives, but great care should be taken to wash out the
acids in order to prevent sweUing of the connective tissues. Forma-
lin is a good preservative for general purposes.

KEY TO NORTH AMERICAN FRESH-WATER LEECHES

I (36) Mouth a small pore in oral sucker from which a muscular pro-
boscis may be protruded; no jaws.

Suborder Rhynchobdellae . .

2 iss) Body not divided into two regions; usually much depressed; eyes
near median line; stomach usually with well developed lateral
ceca Family Glossiphonid.vk . . 3

3 (28) Complete somites essentially triannulate 4

4 (13) Epididymis and ejaculatory duct forming a long. open, backward

loop; salivary glands diffuse; eyes simple; size small; chiefly
under stones and on plants in ponds and lakes.

Glossip/ionia Johnston iSib . . 5

5 (10) Eyes one pair, well separated. Genital pores separated by one

annulus ^

6 (7) A brown chitinoid plate and underlying nuchal ghunl on dorsum

of VIII -. Glossip/ionia sldgHiilis {LmnM-ns) i-js^'

7 (6) No nuchal gland or plate ^^

8 (0) Greatly elongated, slender and neariy terete; without papiUae;

very transparent; colorless; gastric ceca one pair.

Glossiphonia mphcloidca (Graf) 1S99.

FRESH-WATER BIOLOGY

12 (ll)

13(4)

14 (27)

15 (16)

16 (15)

Relatively short, broad and flat; cutaneous papillae absent or in
I to 5 series, small or large, often double; deeply pigmented
in narrow longitudinal lines, or diffusely with metameric

'° white spots on neural annuli; gastric ceca six pairs, simple.

Glossiphonia fusca Castle 1900.

This species is very variable, especially in the character of
the dorsal cutaneous papillae which may be scarcely evident
and limited to a median series on a few segments, or large and
conspicuous and arranged in five series extending for the en-
tire length, or in any intermediate condition. Those of the
median series are formed of a pair of papillae more or less
completely coalesced. Usually they are deeply pigmented
and contrast strongly with the clear white spots flanking
them. The eyes are unusually large and conspicuous. It
lives in ponds but also in colder waters than most species of
the genus, even in springs, and attaches itself to the larger
water snails and more rarely to leeches. The eggs, Hke
those of Glossiphonia complanata, are laid in a few large
gelatinous capsules borne on the venter of the parent leech
and breeding is continued to midsummer. Glossiphonia fusca
is much less active than Glossiphonia complanata and feeds
less frequently upon worms and larvae, preferring snails.

Fig. 997. Glossiphonia fusca. General anatomy showing external
outline, segmentation and annulation, alimentary canal, re-
productive organs, etc. I-XXVII — somites; 2-70, annuli; pro,
proboscis; Po $ , male orifice; Po 9 , female orifice; ov, ovary;
oe, esophagus; iglv, stomach or crop; te, testes; ga and in, in-
testine; an, anus; dt. ej, ductus ejactulatorius. X 10. (Modified
from Castle.)

Eyes three pairs n

Genital pores separated by one annulus; eyes in three groups of
two, in a triangular figure; body transparent, with little
pigment; no papillae; gastric ceca six pairs, nearly or quite
unbranched. . . Glossiphonia heteroclita (Linnaeus) 1758.

Genital pores separated by two annuli; eyes in two nearly parallel
rows; body rather thick and opaque, usually deeply pig-
mented, a pair of dorsal and ventral dark, narrow lines run-
ning for nearly entire length; gastric ceca seven pairs,
slightly branched. . Glossiphonia complanata (Linna-eus) ij $8.

Epididymis more or less complexly and compactly folded in vi-
cinity of atrium ; salivary glands usually compact. . . 14

One pair of anterior compound eyes; gastric ceca seven pairs,
usually much branched; saUvary glands compact; size mod-
erate to large. Temporary parasites on water turtles, frogs
and fishes; most species also free-living.

Placobdella R. Blanchard 1893 . 15

Somites I-V distinctly widened to form a discoid "head." Somites
I and II biannulate; dorsum with three strong papillated
keels. On fishes and frogs. . Placobdella monHferaMooieigi 2.

Somites I-V not especially widened 17

THE LEECHES (HIRUDI.VEA)

17 (18)

18 (17)

19 (22)

20 (21)

I

653

I'lacobdelh pediculata I k-miiiKway 1008
Anus behind XXVII; posterior segments normal.

Placobddla is. sir.). . ,g

Cutaneous papillae smooth and round.

Integuments opaque, deeply niemonfr.rl ."n .. ^

leii ^ ^ ' ^y pigmcnicd m a conspicuous pattern

ol ohvc green and yellow; annulus
^ without trace of a secondary
furrovv; size large. Common on
Lnelydra, etc.
Placobddla parasitica (Say) 1824.

One of the best known of our leeches
most often found clinKinK in lanrc
numbers to the naked skin at the base
of the hind leRs of the .snapping turtle
whose I)lood they suck. LarRe in.li-
yiduals measure fn.m , to 4 inches
ong in partial e.xtension and arc very
broad, thm, and fohaceous. When
bearing eK«s or young the>' often leave
the host and for a time lead a free li/e
m ponds and streams, feeding ofj
worms and lar\ae. Eggs and youn«
are borne m large numbers and it is
an mterestmg sight to obser\-e the
crowded family of youngsters actively
bending and turning on the venter of
the parent, the thin margins of whose
body are mrollefi to form a i)rotccting
fold. The color patti-rn is rich and
striking, theground color of dull green
or ohve green standing in sharj) con-
trast to the bold and characteristic
markings of yellow by which it is re-
placed to a varjing degree.

Fig. 998. PlacobdrUd parasitica. Kxtemai
metamerism, central lunous system, re-
productive organs, etc. l-.VXVII —
somites; mg, ol. I. m. marjiinal. outer
lateral, lateral and median srasill.ic re-
spectively; pkg.^ \ i.h.ir>n>:c.il kLiwIs;
0€, esophagus; v, atrium or s|irrma(o-
phore sac; d, ductus eiaculatorius; ri,
vesicula seminalis; <J and 9. male
and female jwrcs; tdc. vas deferens. /.
testes; ov, ovary. X J. (Redrawn
from Whitman.)

, 'XAIV
t • ' XXV

XXVI
XXVII

21 (20)

22 (19)

23 (26)

Integuments translucent, brightly but not deeply pigmented with
green, orange, and white; a^ of complete somites with a
distinct secondary cross-furrow; size medium.

Placohdclla picta (\'crrill) 1S7J

Cutaneous papillae prominent and rough or pointed ::

No marginal papillae on caudal sucker

654 FRESH-WATER BIOLOGY

24 (25) Much depressed; papillae numerous; no accessory eyes; size large.

Placohdella riigosa (Verrill) 1874.

25 (24) Moderately depressed; papillae less numerous; neural annulus with

much dark pigment; several pairs of simple accessory eyes
succeeding compound eyes; size medium.

Placohdella hollensis (Whitman) 1892.

26 (23) Numerous minute papillae around margin of caudal sucker. Mod-

erately depressed; dorsal papillae usually in a median and
two paired series, small, acute and pale yellow or brown; a
very conspicuous and constant pale band across somite VI;
size small Placohdella phalera (Graf) 1899.

27 (14) Eyes four pairs, all simple; gastric ceca nine or ten pairs; salivary

glands diffuse; body very soft and almost oedemous ; genital
pores at XI-XII and XII a^/a^; color green with three series
of pale yellow spots. On fishes and free in streams.

Protoclepsis occidentalis (Verrill) 1874.

This leech and others of the genus are noteworthy
among the members of their family for their transparency
and activity. No other glossiphonids creep with any
approach to the same speed and none swim so well. So
far as has been observed the eastern species is exclusively
sanguivorous, pursuing and attacking frogs and fishes.
Nothing is known of the breeding habits beyond the fact
that spermatophores are formed and attached to the skin.

Fig. 999. Protoclepsis occidentalis. Dorsal view of anterior
seven segments, showing annuli, eyes, and sensillae. X 20.
(Original.)

^"CC

^

>'/^-~— .

__ — "-K

I'v^;/--,^

—'9 9;^-

2jA

"^'■7° ~

■ 9 ©_^

■~\

vi('^^

. . '

»

0 i\

J

-"^

'^II;' • .

0

• -_J

-J

Complete somites not triannulate 29

Complete somites of two annuli, the anterior much the larger.
Salivary glands compact; gastric ceca seven pairs; epidid-
ymis a short, wide, U-shaped sperm-sac; eyes one pair,
united; genital pores separated by the large annulus of
XII; size small. On salamanders, North Carolina.

* Oligohdella hiannulata (Moore) 1900.

(* Oligohdella nom. nov. for Microbdella Moore preoccupied.)

An interesting and Httle known leech taken on only one
occasion in a cold mountain stream. Nothing known of
breeding habits. Color green.

Fig. 1000. Oligohdella hiannulata. General anatomy: boundaries of
middle somites indicated; g, salivary gland; at, atrium; pg,
spermatophore sac; 55, sperm sac; $ male and 9 female orifices;
Ci to cv, gastric ceca; ov, ovar\'; vd, vas deferens; /i to to, testes; i,
intestine; a, anus. X 10. (After Moore.)

THE LEECHES (mRUDIXEA)

655

30 (29) Complete somites of six unequal annuli; salivary glands difluse-

gastric ceca seven pairs; caudal sucker wiih marginal circle'
of glands and papillae; eyes one pair, united; size small
Probably fish parasites. . ActinobdellaMvvTi: u)Oi . . 31

31 (32) Sucker papillae and glands about 60; five series of dorsal i)apillae.

Actinohdrllti anucclens Moore i<;oi.

32 (31) Sucker papillae and glands about 30; median dcjrsal series of t)a-
pillae alone developed.

Actinobddla inajuiannuluta Moore i.^Os.

Fig. iooi. Actinohdclla inequian-
nulata. Annulation, s^-nsilUc
and (lursal cutaneous ^lapilUc of
anterior twelve Mimites. Pov
terior en(l with sucker from the
side. X 20. (After Moore.)

33 (2) Body divided into a narrow anterior and a wider posterior region;

little depressed; eyes when present usually well separated;
stomach usually with only a posterior pair of more or less
coalesced ceca. . . , Family Ichthyobdellidak . . 34

34 (35) Complete somites of 12-14 very short annuli; no distinct lateral

vesicles; eyes one or two pairs; size small. Parasitic on
small fishes Piscicola punctatii iW'TnU) iS-ji.

35 (34) Complete somites of six annuli; strongly divided into two regions;
lateral pulsating vesicles in somites XII to XXIII; eyes
two pairs; size medium. Parasitic on Fundulus in fresh and
saltwater Trachclobdelld viviJa {\crTill) iS-j 2.

The anterior region is formed of eleven somites of which the first
five comprise the head and the last three the clitellum. which is
somewhat sunken into the widened jxisterior rcRioii. .X little known
leech which has been taken only in southern New Kn^land.

Fig. 1002. Trachelobdellavivida. Annulation from dorsum. Somites al the
ends of the body are numbered and the annuli l)et\vecn which the male
and female orifices lie are indicated. X j. (After M.x.n- >

656 FRESH-WATER BIOLOGY

36 (i) Mouth large, occupying entire cavity of sucker; pharynx not

forming a proboscis; jaws often present.

Suborder Gnathobdellae . . 37

37 (54) Eyes typically five pairs on somites II- VI, arranged in a regular sub-
marginal arch; complete somites five-ringed; toothed jaws
usually present; genital ducts complex, usually with a pro-
trusible penis and muscular sheath (atrium) and a vagina
of corresponding length; testes strictly paired, usually nine or
ten pairs; stomach with at least one pair of spacious ccca;
size generally large Family Hirudinidae . . 38

38 (43) Jaws prominent, teeth numerous, in one series; ceca along entire
length of stomach. True blood-suckers 39

39 (42) Copulatory gland pores on somites XIII and XIV; penis conical;

dorsum with metameric median red and lateral black spots.

M acrobdella \'Gr rill 18^2 . . 40

40 (41) Genital orifices separated by five annuli.

Macrobdella decora (Say) 1824.

The species of Macrobdella are the nearest approach in our
fauna to the medicinal leech of Europe but at times vary the
diet of blood with frogs' eggs and worms. M. decora is well-
known as a voracious infester of swimming holes and of drinking
places for cattle and has received the name of "blood-sucker."
After coitus, during which the copulatory glands function,
spongy cocoons are formed and deposited to hatch in the mud
by the side of ponds and streams. Widely distributed; reported
from ]\Iaine to Minnesota and from Pennsylvania to Kansas,
northward into Canada. Frequently used by physicians instead
of imported leeches for blood-letting. Said to be equally eflBca-
cious of the smaller capacity, about 5 gm. It is so powerful that
serious results have followed its attacks on legs of children wading
in ite haunts.

Fig. 1003. Macrobdella decora. Reproductive organs (in part) dissected.
at, atrium; cgl, copulatorj' gLnds; de, ductus ejaculatorius; ep, epidi-
dymis; gXI-XIV, ganglia XI to XIV; os, ovisac; od and ode, oviduct;
ov, ovary; ij and ^, first and second pairs of testes; vd, vas deferens.
X 3. (After Moore.)

41 (4c)

Genital orifices separated by two and one-half annuli.

Macrobdella sestertia Whitman 1886.

THE LEECHES (HU^UDINEA)

657

42 (39) No copulatory glands; penis lilamcntous; colors variable, dorsum
usually green with six or four brown stripes, sometimes
broken. European medicinal leech; introduced.

lliriidu medUinalis Linnaeus 17 58.

Fig. 1004. Htrudo medicinalts. External morphology from the dorsum. The numerals on the rishl
indicate the annuli, those on the left the somites, the index lines running to the ncuml annul!-
1st P. and 17th P., first and last nephridiopores. Natural size. (After Whitman.)

43 (38) Jaws variable, sometimes rudimentary or absent; teeth when

present all or partly in double series; gastric ceca one large
posterior pair only. Chiefly predaceous 44

44 (47) Jaws short and high; teeth small, only partly in two scries; no penis;

genital orifices separated by three or four rings, surrounded
by systems of gland pores. . Philobdella W-rriW iS-j 4. . 45

45 (46) Denticles about 35; narrow median dorsal and broader marginal
yellow stripes and a few brown spots.

Philobdella gracUe Moore igoi.

Philohdclla takes the place of Macro-
bdella in the Gulf States and has
singular habits. It is the native
"blood-sucker " of that ri-gion.

Fig. 1005. Philobdflla gracile. A , external
genital orifices { $ , 9 ) wi'h their re-
spective svstems of pland (K)rcs icj;p J
and cppy); np, ncphridit>pt>rrs; tbrn.
vl, vm, submargmal, lateral, and mnlian
sensillae. X .^}. (After M.iorc.) /».
outlineof a jaw with te«lh. X .?S- <.\ftcr
Moore.)

46 (45) Denticles about 20; no median dorsal stripe and no spots; two

faint stripes of reddish brown separated b\- a narrow line of
blackish on each side of dorsum.

Philohdelhi jloridana X'errill 1S74.

47 (44) Jaws rather small and retractile into pits or absent; teeth when

present coarse and all in double series; penis filamentous;

genital orifices separated by live rings; no copulatory glands.

IJiumopis Savigny 1S20 . . 48

48 (51) Jaws and teeth present.

49

658

FRESH-WATER BIOLOGY

49 (50)

Teeth 12-16 pairs; annuli VII a* and VIII a' enlarged, but only
slightly subdivided; color variable, usually blotched.

Haemopis marmoratis (Say) 1824.

Fig. 1006. Eaemopis marmoratis. External morphology,
showing sensillae, annulation, and limits of somites.
c, clitellum; V-XXVII, somites; 61, 62, <h, h, h, the five
annuli of somite XV. X ij. (Original.)

Fig. 1007. Haemopis marmoratis. Reproductive organs,
dissected, al, atrium or penis sheath; de, ductus ejacula^
torius; ep, epididymis; gXI-XVI, ganglia XI-XVI
ga, albumin gland; gp, prostate gland ; os, ovisac; ode,
common oviduct; ffv, ovary; ss, sperm sac; /1-3, testes
va, vagina; vd, vas deferens; $ male orifice; 9 female
orifice. X 2. (After Moore.)

50 (49) Teeth 20-25 pairs; annuH VII a^ and VIII a', completely subdivided;

color gray or plumbeus with no or few spots, usually a
median black and marginal orange stripes; size very large.
An aquatic and a terrestrial variety.

Haemopis lateralis (Say) 1824.

51 (48) Jaws absent or rudimentary; no teeth 52

52 (53) Upper Hp relatively narrow and arched; ^ orifice XI ftV^S 9

XII h^/h^; protruded penis very slender and straight; ven-
tral ground color paler than dorsal; dark blotches always
present; size very large. . Haemopis grandis (Verrill) 1874.

53 (52) Lip relatively broad and flat; genital pores near middle of XI b^

and XII b^; protruded penis very long, rather thick and
twisted; ground color nearly uniform; dark blotches fre-
quently absent or few; size moderate.

Haemopis plumbeus Moore 191 2.

THE LEECHES (HIRUDIXKA)

^59

54 (37) Eyes three or four pairs (rarely absent), usually one or two pairs
on II and two pairs at sides of mouth on I\'; no jaws, no
gastric ceca; genital ducts relatively simple, with small
atrium produced into a pair of dorsal cornua and no jK-nis;
testes numerous, not paired. Predaceous.

Family Merpoudlli.idai: . . 55

55 (56) Som

gxu.

ites strictly five-ringed, none of the annuli obviously enlarged
or subdivided. Eyes three pairs, the first largest; genital
pores separated by two annuli; atrial cornua simply cur\'ed;
vasa deferentia reaching forward to ganglion XI.

Ilcrpohdclla punctata (Leidy) iSyc.

The largest, bi-st known and most widely di^^tributcd
member of the family in North America. The color variw
considerably according to the amount of black i)i>s'mfni
present. A very active leech which feeds voraciously on
small worms, other leeches, and aquatic insect laivae. It
will take human blood when opiKjrt unity offers. Kgg
capsules found abundantly attached to stones, etc.

Fig. 1008. Eerpobdella Punctata. Atrium and nciRhborinK parts
of reproductive organs. at, atrium; df. ductus cjacuiatoriur;
iXI, ganglion XI; 9 . female orifice; of, fundus of ovary;
ov, ovary; p, atrial horn. X 7 J. (After Moore.)

56 (55) Annulus b obviously enlarged and subdivided 57

57 (58) Atrial cornua spirally coiled, vasa deferentia with anterior l{X)ps
reaching to ganglion XI; eyes four pairs; genital orifices
separated by two annuli; colors plain or irregularly blotched.

Nephelopsis obscura \'errill 1.S27.

Fig. 1009.

Nephelopsis obscura. Dorsal and lateral aspects of atrial
region. X 3- (Ori^'inal.)

58 (57) Atrial cornua not spirally coiled, l)ut short and merely curved.

Dina R. liianchard iSc): . . 50

59 (62) Vasa deferentia with anterior loops reaching to ganglion XI. . 60

60 (61) No pigmented eyes; genital pores separated by two annuli; longi-

tudinally striped. California. . Dina atioculata'SlooTC i^S>.

61 (60) Eyes four pairs; genital pores separated by three to three and one-

half annuli; nearly pigmcntless. . Dina parva Moore 1Q12.

62 (59) Vasa deferentia not extending anterior to atrium 6j

63 (64) Eyes, three pairs; genital pores separated by three annuli; atrial

cornua very small; pigment nearly absent.

Dina microstoma Moore looi.

66o FRESH-WATER BIOLOGY

64 (63) Eyes, three or four pairs; genital pores separated by two annuli;
atrial cornua prominent; pigment absent or in scattered flecks.

Dinafervida (Verrill) 187 1.

Fig. ioio. Dinafervida. Reproductive organs except testes, at, atrial cornua; de, ductus ejaculatorius;
gXI-XVIII, ganglia XI to XVIII; of, closed end of ovary; ov, ovary; ss, sperm sac; vd, vas deferens.
X .35. (After Moore.)

IMPORTANT PAPERS ON NORTH AMERICAN LEECHES

Bristol, C. L. 1899. The Metamerism of Nephelis. Journ. Morph., 15:
17-72.

Castle, W. E. 1900. Some North American Fresh-water Rhynchobdellidae
and their Parasites. Bull. Mus. Comp. Zool. Harv., 36: 18-64.
1900. The Metamerism of the Hirudinea. Proc. Amer. Acad., Arts and
Sci., 35: 285-303.

Forbes, S. A. 1890. An American Terrestrial Leech. Bull. 111. State Lab.
Nat. Hist., 3: 1 19-122.

Graf, A. 1899. Hirudineenstudien. Nova Acta Leop. Carol. Akad. Natw.,
72: 215-404.

Hemingway, Ernest E. 1908. Placobdella pediculata n. sp. Amer. Nat.,
42: 527-532.

Leidy, Joseph. 1868. Notice of Some American Leeches. Proc. Acad. Nat.
Sci., Phila., 20: 229-230.

Moore, J. Percy. 1901. The Hirudinea of Illinois. Bull. 111. State Lab.
Nat. Hist., 5: 479-546.
1905. Hirudinea and Oligochaeta collected in the Great Lakes Region.
Bull. U. S. Bur. Fish., 25: 153-171.

Nachtrieb, Hemingway, and Moore. 191 2. Report on the Leeches of
Minnesota. Geological and Natural History Survey of Minnesota,
Zoological Series No. V. Part III., Classification of the Leeches of Min-
nesota, by J. Percy Moore, pp. 65-150. Frontispiece and Plates I-VI.

Verrill, A. E. 1874. Synopsis of the North American Fresh-Water Leeches.
Report U. S. Comm. Fish., 2: 666-689.

I,

CHAPTER XXT
THE FAIRY SHRIMPS (PHYLLOPODA)

By a. S. PEARSE

Associate Professor of Zoology, University of Wisconsin

Phyllopod crustaceans are among the most graceful and attrac-
tive of the inhabitants of fresh- water pools. A familiar example
is the fairy shrimp {Euhranchipus) that is a harbinger of spring
throughout the eastern and central United States. No ph}'llopods
are of great size, the largest usually not exceeding a couple of
centimeters in length, though one species of A pus reaches seven.
Certain genera of this group ^ of crustaceans existed in Devonian
times but recent species were first described by scientists early in
the eighteenth century, and were, with the cladoceran Daplniia^
made the subject of a series of remarkable memoirs by J. C. SchatTer
(1752-1756). Up to the present time forty-one species have been
described from North America and a large number from other
continents, for phyllopods occur in every part of the world and are
found from sea-level to altitudes of more than 10,000 feet. But
the animals that are to be discussed in this chapter are interest-
ing not only on account of their ancient lineage and wide distribu-
tion. Their primitive structure has been much studied by those
who sought to solve the riddle of the origin of the arthropods, and
their remarkable ability to withstand striking changes in temper-
ature and humidity, as well as the various forms that some species
assume under different conditions, have made them equally attrac-
tive to naturalists and those interested in the experimental side of

zoology.

The different suborders of phyllopods present considerable
diversity in general shape. Such diversity is due largely to differ-
ences in the development of the carapace, which may form a shell-
fold, and these differences are curiously correlated with variations

1 Caiman rejects the suborder Phyllopoda and divides his subcla,«vs Rranchiopoda
into four orders: Anostraca, Notostraca, Conchostraca, Cladocera. Iherr ,s much m
favor of such a system.

661

662

FRESH-WATER BIOLOGY

in the position of the eyes. In the Anostraca (Fig. loii) there is
no shell-fold and the body, composed of many distinct somites, has
an almost worm-like aspect; the Notostraca (Fig. 1012) are also
elongated and composed of numerous somites, but are flattened, and
their anterior portion is covered dorsally by a broad arched carapace ;
the bodies of the Conchostraca (Fig. 1013) tend to be laterally com-
pressed and are enveloped in a bivalve shell that makes them look
like a small clam. The shell-fold is not attached to the trunk
somites which it envelops. It may be more or less corneous but
is never calcified. The eyes are elevated on movable peduncles in
the Anostraca but are sessile in all other phyllopods. A pecuhar

ttJ ..

Fig. loii. Branchineda paludosa, ma-le and female, ai, first antenna; a2, second antenna; d, cerco-
pods or furcal rami; p, penis; t, telson. X 3. (After Packard.) ,

structure, the frontal (or haft) organ, is variously developed in
the different groups; in some it is only a sensory area and in others
it has a knob-Hke pediculated form.

The head is distinct from the trunk and the number of trunk-
somites is variable. Some notostracans have as many as forty-two
trunk-somites; the Conchostraca have from thirteen to twenty-
eight, and the number in the Anostraca ranges from nineteen to
twenty-three. Apart from the head, the trunk of phyllopods
shows no differentiation into distinct regions. The terms "thorax"
and ''abdomen" have been variously used to designate the pre-
or post-genital, or the limb-bearing or limbless, regions respectively.
But the Hmits of these regions do not coincide, even approximately,
except in the Anostraca; and ''thoracic" and "abdominal" are
therefore not appHcable to the group. The last segment, or telson,
usually bears a pair of appendages, the furcal rami or cercopods.

The appendages are fairly uniform in character, except as they
are modified by sexual dimorphism. The first antennae are always

THE FAIRY SHRIMPS (PHYLLOPODA)

663

small and often unsegmented. The second antennae are vestigial
or absent in the Notostraca; in the male anostracans they form
variously modified clasping organs; and in the Conchostraca they
are biramous swimming appendages. Male Anostraca uften bear
frontal organs which may arise from the bases of the second anten-
nae or from the front of the head. The trunk-limbs are leaf-like
in form (hence the name Phyllopoda) and are remarkable for ha\-
ing gnathobases, or '^ chewing bases," far removerl from the mouth.
The first or the first and second pair are modified in male Con-
chostraca for clasping the female. In female Notostraca the limbs
of the eleventh trunk somite are
modified to form brood-pouches, or
''oostegopods," for carrying eggs. The
females of some Conchostraca have
the flabella of two or three limbs near
the genital aperture enlarged and the
egg masses are attached to these. In
the Anostraca the appendages of the
somites on either side of the genital
opening are modified for reproduction
in both sexes.

In addition to the various appendages
which serve as accessory reproductive
organs, the oviducts unite to form an
external uterine chamber in the Anos-
traca, and the males of the same suborder have a copulatory organ
formed by the fusion of the extremities of the vasa deferent ia.
All phyllopods are of separate sexes. Males are much less conmion
than females, in fact some species are known onl\- from female
specimens, and the development of several is believed to be usu-
ally parthenogenetic. The gonads are paired and have a simple
tubular structure, except in the Notostraca where the\' are much
ramified. In the Anostraca the eggs are carried in the female's
brood-pouch, the uterine portion of the oviduct, sometimes until
they hatch. The Notostraca bear the eggs in the special receptacles
formed by the eleventh pair of trunk-limbs, and the Conchostraca
carry them enclosed in the valves of the shell.

Fio. 1012. A pus aequaiis. c, caraf>acr:
/, telson; d, ccranxids or furcal rami.
X 3. (After Packard.)

664

FRESH-WATER BIOLOGY

Fig. 1013. Estheria morsei, with left valve of shell removed. X 9-
ai, first antenna; 02, second antenna; c. carapace; d, cercopods
or furcal rami; /, flabella; u, umbone. (After Packard.)

The alimentary canal of phyllopods consists of a large mastica-
tory and glandular atrium produced by an overhanging labrum

c in front of the mouth;

this is followed by a
buccal cavity, a ver-
tical esophagus and a
small globular stom-
ach within the head;
and, behind these, is a
long straight intestine
which terminates in a
short rectum at the
posterior end of the
body. The heart is
greatly elongated in
the Anostraca, oc-
cupying nearly all the trunk-somites, with a pair of ostia opening
in each somite. In the Notostraca and Conchostraca it is more
restricted — and extends through only three or four segments in
the latter. There are no definite blood vessels. A maxillary gland
(consisting of an end-sac, glandular coiled tube, and short terminal
duct) serves as an excretory organ in phyllopods. The ladder-like
structure of the ventral nerve chain shows the primitive character
of the nervous system.

After leaving the egg, all American
phyllopods begin their development as a
free swimming nauphus or metanaupHus
(Fig. 1014). Some differences exist even
in closely allied forms in regard to the
stage ot development reached at hatching.
The larvae of the Notostraca and Anos- ^'f;iformis, ^sfh^Sd!^ ^MtRiaus,

, , 1 • .. J.1 i.* from Lankester's Treatise on Zoology.)

traca are typical metanauplei at the time

of hatching, with an oval body that shows the beginning of several
trunk-somites posteriorly and sometimes the rudiments of their
appendages. The first antennae are well developed but uniramous,
the second antennae have a movable masticatory process and the
mandibles are but feebly developed. The earliest conchostracan

THE FAIRY SHRIMPS (PHYLLOPODA) 665

larva has no trace of trunk-somites; the first antennae are greatly
reduced and the labrum is very large. The trunk-somites and thc-ir
appendages become differentiated in regular order from before
backwards. The single median eye of the larva persists in adult
phyllopods.

All Phyllopoda, except Artemia, live in small fresh-water jxiols.
especially those that are formed during spring rains and dry up
during the summer. In such situations they often occur in enormous
numbers. The writer once saw in Nebraska nearly half a bushel
of dead Apus bodies on the bottom of a shallow dried-up depression
about twenty feet in diameter. The eggs of most genera can re-
sist prolonged desiccation; indeed it seems necess:iry for the develoi)-
ment of many species that eggs should first be dried and afterwards
immersed in water. Many eggs float when placed in water and
development takes place at the surface. The mud of dried pools
often contains large numbers of eggs that may be carried long
distances by winds, birds, or by other means. Many exotic species
have been reared from dried mud brought home by travelers.

On account of the rapid evaporation of the pools in which they
live, phyllopods are able to withstand considerable changes in the
amount of mineral salts in the water. It is remarkable that,
though none of these crustaceans are marine, Artcmia salina lives
in salt lakes and salt evaporating basins where the salinity far ex-
ceeds that of the ocean. One instance has been recorded where
the salts in solution were 271 grams per liter, and where the watrr
was of the color and consistency of beer. Artcmia salina is subject
to marked form variations that are more or less correlated with
sahnity, and both Kellogg and Artrom have observed that this
species tends to assume a reddish color as the water about it .^rows
denser.

Phyllopods usually swim on their backs with the ventral surface
uppermost. Eubranchipus swims easily about when it is not rest-
ing on the bottom; Apus is a graceful swimmer but often creeps on
its ventral surface over the bottom and upon vegetation; Esthcria
commonly burrows in the mud. Food is collected in the ventral
food-groove between the post-oral limbs whose gnathobases drive it
forward to the mouth. It consists of suspended organic debris,

666 FRESH-WATER BIOLOGY

together with diatoms, other algae, and Protozoa. Large species,
however, are able to gnaw objects, and Apus is said to nibble
insect larvae and tadpoles. No parasitic phyllopods are known.

The distribution of all species is apt to be local and irregular.
A certain pool may swarm with phyllopods, while others near at
hand will not possess a single individual. A particular species may
be extremely abundant for one season and then be infrequent or
entirely absent for several years, or it may appear regularly in a
certain spot season after season. No Notostraca have been found
in eastern United States and none of the genus Estheria in the
Conchostraca are found east of the Mississippi River. The greater
part of the North American species are found on the great plains.

Collecting phyllopods is usually a simple matter. They are
easily captured with a hand net or picked up with the fingers.
For ordinary purposes 70 per cent alcohol is a satisfactory preserv-
ative; specimens may be kept for future reference by dropping
them into it and keeping them in a tightly stoppered bottle. Dilute
formol may also be used, but is not as satisfactory as alcohol because
it often makes specimens so brittle that they break up easily.
These crustaceans are admirable aquarium animals and make
attractive objects for a school room or private study. With a
few water plants for company they may Hve for weeks. They
should not be put in aquaria with predaceous animals for usually
they will be quickly devoured.

ElEY TO NORTH AMERICAN FRESH-WATER PHYLLOPODA

1(36) Body elongated, without carapace (Fig. loii) . Suborder Anostraca . 2

2 (5) Seventeen to nineteen pairs of pregenital ambulatory limbs.

Family Polyartemudae.
Only one genus in America Polyartemiella. . . 3

3 (4) Male frontal appendage tuberculiform ; male clasping antenna quadri-

ramose Polyartemiella hanseni (Murdoch) 1874.

Described from Alaska. This and the following species are remarkable
for the large number of ambulatory limbs which exceeds that of any other
anostracan. Apparently common in portions of Alaska and Yukon
Territory that border on the Arctic Ocean.

Fig. 1015. Polyartemiella hanseni. Side view of head of male. X 6.
(After Daday.)

THE FAIRY SHRIMPS (PHYLLOPODA) 067

4 (3) Male frontal appendage wanting; male clasping antenna triramose.
^ ^ Polyarttmidla jmlayi Daday ic^oy.

^ ;?\ The copulatory appendages of this form arc thick, spiny, and shapcti like

/^V. \ ^ t^sh-hook; the female has a long median fmKcr-Iike apiK-nda«e on the

dorsal surface above the egg sac.

PribylofT Islands and Alaska. The genus to which this species belonw is
entirely arctic in its distribution.

Fig. 1016. Polyartemiellajudayi. Dorsal view of head of male X S- (After Daday.)

5 (2) Eleven pairs of pregenital ambulatory limbs 6

6 {t,^) Clasping antenna of male biarticulatc

7 (16) Head of male unarmed in front, basal segment of clasping antenna with-
out a laminar appendage. . Family BKANcmNKCTiDAK . . 8

8(15) Post-genital region 9-segmented, apical article of male clasping antenna
triangular and falciform Bramliiiieclii . . 9

9 (10) Basal segment of male clasping antenna serrate on inner margin.

Branchinccta paludosa (O. F. Muller) 1788.

The egg sac of the female is very long and slender. The c(ipulator>'
appendage of the male is thick antl arcuate.

This is an arctic species and occurs in northern Elurope as well as in
Greenland, Labrador, and Alaska, in North America. See also Fij?. 101 1

Fig. 1017. Branchinccta paludosa. Head of male, dorsal view X s-
(After Daday.)

10 (9) Basal segment of male clasping antenna not serrate on inner margin. 1 1

11 (14) Basal segment of male clasping antenna with a spiny area on

inner margin 12

12 (13) Inner margin of basal segment of male clasping antenna with a

rounded tubercle near base and a swollen spiny area
just proximal to middle.

Branchineda coloradoisis Packard 1S74.

The segmentation and early development take place under the ice in
Alpine Lakes, The eggs of this species are much larger than those of
others in the genus. This fact may account for the ability to devdop
so early.

Reported from Colorado where it occurs at an altitude of 11.000 ft.
The larvae appear as soon as the ice melts in the spring.

Fig.

branchinccta cnloradensis. He.-id of male, fro
(After Shantz.)

13 (12) Basal segment of male clasping antenna armed with a large spmy
process, one third as long as the segment, which arises just
distal to the middle of the inner margin and projects pro.xi-
mally, a prominent finger-like process with a tiiberculatol
tip near inner proximal angle.

Branchincdii packanli Pearse ioi3-

The five pregenital segments of female produce*! laterally into strong
spinous processes; these grow larger posteriorly. Colltvte<l at La Junta,
Colorado.

Fig. 1019. Branchinccta packardi. Basal segment of iccond ititconi ol mxle.

FRESH-WATER BIOLOGY

Inner margin of basal segment of male clasping antenna without a
tubercle but with a spiny area near proximal end.

Branchinecta lindahli Packard i88^.

The body is robust; the caudal appendages are comparatively long;
the eggs are small, and the ovisac usually contains about fifty of them.

A plains species recorded from Kansas, Nebraska, Colorado, and
Wyoming. It is known to occur as high as 7500 ft. above sea level.

Fig. 1020. Branchinecta lindahli. Headof male, front view. X 3. (After Shantz.)

15 (8) Post-genital region 8-segmented, apical article of male clasping antenna
compressed Artemia.

Only one species. . . . Artemia salina (Linnaeus) 1851.

Connecticut, Utah, California, Lower California. This species is
remarkable for its ability to live in extremely saline water. It is
frequently found in salt evaporating basins. The form is variable,
and several varieties have been described.

Fig. 1021. Artemia salina. Head of male, dorsal view. X 4. (After Daday.)

16 (7) Head of male often bearing a frontal appendage or a laminar appendage

on the basal segment of the clasping antenna.

Family Chirocephalidae . . 17

17 (30) Frontal appendage of male variable, rather short; terminal segment

of copula tory organ smooth Euhranchipus . , 18

18 (25) Body segments of male and female all superficially unarmed. . . 19

19 (20) Frontal appendage of male short, about as long as basal joint of sec-

ond antenna; lanceolate, margin denticulate.

Euhranchipus vernalis Verrill 1869.

Massachusetts, New Jersey, Indiana, Michigan. This species
appears in small quiet pools soon after the snow disappears in spring,
or even in mid-winter, but has not been observed during the summer
months.

Fig. 1022. Euhranchipus vernalis. Head of male, side view. X 4.
(After Packard.)

Frontal appendages of male when extended longer than basal joint
of second antenna 21

Frontal appendages of male attenuate, middle fourth serrate.

Euhranchipus holmani (Ryder) 1879.

This species was first discovered in
New Jersey and has since been ob-
served on Long Island, New York.
Packard ('83) confused this species
with Branchinella gissleri Daday.

Fig. 1023. Euhranchipus holmani. Head
of male; yi, side view; 5, front view.
X 4. (After Daday.)

22 (21) Frontal appendages of male broad, lanceolate, lobate on margins. 23

THE FAIRY SHRIMPS (PHVLLOPODA) ,...;

23 (24) Terminal segment of male clasping antenna with a small process near

base that is one-eighth as long as the segment.

Eiibninchipus ornatus Holmes k^i.

lliis s p {_• c i c s was dc-
stril>L«l from sixrcitncns
taken in Wisconsin. The
frontal apiK-ntla^t-s are re-
markably l>roa«l. In the
left-hand fij^urc the male
frontal appendages arc
rolled up.

Fig. 1024. Eubratuhipu\ or-
nalus. Male. A. i«»Ntcrior
view of head; B. (r«»ntal
orRan; C, second antrnria.
X 10 (AhcT Hnlmr^.,

24 (2^) Terminal segment of male clasping antenna armed with a i)rocess

near its base that is half as long as itself.

Euhranchipiis dadayi Pcarse 10 1.^.

Recorded from eastern
Nebraska and Missouri.
Some sfx-cimens arc re-
markably transparent.
This sjxries appears in
small p<jols durinc April
and NIay. The females
are more reddish than the
translucent male^.

Fig. 1025. Euhranchipui da-
dayi. Male. A. ix>sterior
view of head; fi, frontal
organ; C, second antenna.
X8.

25 (18) Some body segments produced into lateral processes 26

26 (27) Body segments 9 and 10 of female produced into latcnil processes;
post-genital segments unarmed.

Eiibrauchi pus gel id us (Hay) IvSSq.

Records from New York. Massachusetts.
Indiana, Alaska, and Yukon Territor>-. Canaila
Usually abundant where it is found. The proc-
esses on the .somites just in front of the epR sac
on the female distinguish this six-cies from al!
others in the genus. The Hay's (Syl haliheil
the eggs of this anostracan from driisl mud.
without freezing, and describi^l development.il
stages. The wide range is remarkable for a
member of this genus.

Fig. 1026. Eubrandtipus grOdus. A. side view of
head of male; H, side view of posterior jvirtion ol

female. X 4-

27 (26) Body segments 9 and 10 of female not produced laterally
genital segments acutely produced on both sides. .

p<ist-
. 28

670 FRESH-WATER BIOLOGY

28 (29) Post-genital region 8-segmented; cercopods ensiform.

Euhranchipus serratus Forbes 1876.
Described from specimens taken in Illinois.

29 (28) Post-genital region 9-segmented; cercopods dilated with obtuse

apices Euhranchipus bundyi Forbes 1876.

Described from specimens collected in Wisconsin.

30 (17) Frontal appendage of male either vertical or extending out from the

middle of front of head; terminal segment of copula tory
organ spiny 31

31 (32) Post-genital segments distinct in both sexes, cyUndrical, cercopods

always distinct Branchinella.

Only one species in North America. . Branchinella gissleri Dadsiy 1910.

This interesting phyllopod has been recently described
from specimens collected in New York. Packard ('83)
confused it with Euhranchipus holmanii (Ryder). The
male frontal appendages are usually twisted, and coiled
together.

Fig. 1027. Branchinella gissleri. Dorsal view of head of male.
X 5- (After Daday.)

32 (31) Post-genital segments fused in both sexes; cercopods confluent.

Thamnocephalus .
Only one species Thamnocephalus platyurus Packard 1879.

A peculiar species that has been recorded from Ellis,
Kansas, where it frequented temporary pools in the
bottoms of ravines, and from La Junta, Colorado,
where it w^as found in a "cattle pool."
Fig. 1028. Thamnocephalus platyurus. Dorsal view of
male. X i. (After Packard.)

Z2> (6) Clasping antenna of male triarticulate. Family Streptocephalidae.
Only one genus in America Streptocephalus . . 34

34 (35) Anterior digit of male clasping antenna broad, undulate, bifid at tip.

Streptocephalus texanus Packard 187 1.

The second antennae of the female scarcely exceed the first in length;
her cercopods are stouter than those of the male.

The appendages beneath the head of the male are root-like and give the
animal a very pecuhar appearance.

Texas, Kansas, Colorado, Nebraska. This species occurs in the spring or
fall in pools on the open prairie.

Fig. io2g. Streptocephalus texanus. Head of male. X 4- (After Packard.)

35 (34) Anterior digit of male clasping antenna nearly straight, hnear.

Streptocephalus sealii Ryder 1879.

New Jersey. This species has been known to appear twice in the same pool
during a summer, in June and August, following rains.

Packard described another species, S. floridanus, but the description was
not definite enough to differentiate it from other American species.

Fig. 1030. Streptocephalus sealii. Head of male. X 3- (After Packard.)

THE FAIRY SHRIMPS (PHYLLOPODa) 671

36(1) Body with a well-developed carapace .^

37 (52) Body depressed, covered dorsally by a depressed shield.

Suborder Notostraca 38

38(45) Telson ending in a long, paddle-shaped outgrowth. . Lcpidurus . 39

39 (40) Telson short, obtusely pointed, spiny on edge.

Lepidurus glacialis Kroyer 1847.

|?f~5J| ^^ arctic species recorded from Greenland and Labrador. The larapace

11^ nIS ^^ ^^'^^ '^""^^ ^"^^ regularly ovate; twelve segments are exposal behind it.

^'ff V.Wp Fig. 1031. Lepidurus glacialis. Telson. X 6. (After Packard.)

40 (39) Telson spatulate. ^ i

41 (42) Telson carinate dorsally; carapace large, leaving only five body seg-

ments and telson uncovered.

Lepidurus coucsii Packard 1S75.

This species occurs in Utah where it frequents prairie p(x>ls of
various sizes.

Fig. 1052. Lepidurus couesii. Telson. X 6. (After Packard.)

42 (41) Telson not carinate dorsally 43

43 (44) Telson long bilobed; carapace short, without spinous crest.

Lepidurus bilobatus Packard 1S77.
This species has not been recorded since the Hayden survey, when it was taken in Colorado.

44 (43) Telson long, not carinate, sometimes bilobed; carapace with a median

spinous crest Lepidurus lemmoni llolmvs iS(j4.

California. The cercopods are very long in this species.

45 (38) Telson short, cyHndrical, simple ipus . . 46

46 (47) Carapace as long as the portion of the abdomen projecting beyond

it; telson short with two median and two lateral spines on
its dorsal median third. . . . A pus acqualis FacksiTd iSyi.

V^ >l\ A widely distributed species occurring in Mexico. Lower California. Texas,

t^> ,^\ Nebraska, and Kansas. It [has 23 segments exposed behind the carapace.

^'^^^-■'^ Fig. 1012 shows the form of this species.

Fig. 1033. Apusaequalis. Telson. X 6- (After Packard.)

47 (46) Carapace shorter than the portion of the abdomen exposed behind

it 48

48 (49) Telson long, with three median and two lateral spines on its dorsal

median third; 29 segments exposed behind carapace.

Apus nnvhcrryi V:icka.Td 1S71.

% '^ "^ Recorded from Utah and Colorado. The hairs along the cercopods arc

I y J> , \ said to be remarkably fine.

pr^^l Fig. 1034. A pus ncu'bcrryi. Telson. X 6. (After Packard.)

49 (48) More than 30 segments exposed behind carapace.

^0

672

FRESH-WATER BIOLOGY

50 (51) Carapace short, three-fifths as long as exposed abdomen; telson with

one (or two) median and two lateral spines on its dorsal
median third A pus lucasanus Fs-cksnd iSyi.

An abundant and widely distributed species; reported from Lower Cali-
fornia and Kansas.

Fig. 1035. Apus lucasanus. Telson. X 6. (After Packard.)

51 (50) Carapace even shorter than in A. lucasanus; telson very short with

one median and four lateral spines on dorsal median third.
Apus longicaudatus Leconte 1846.

This form occurs in Colorado, Nebraska, Texas, and along the Yellowstone
River.

Fig. 1036. Apus longicaudatus. Telson. X 6. (After Packard.)

52 (37) Body compressed, carapace forming two lateral valves which enclose

the body Suborder Conchostraca . , 53

53 (60) Only the first post-cephalic Umbs prehensile in the male; carapace

spheroidal, without Knes of growth; head not included

within carapace-chamber Family Limnetidae.

Only one genus Limnetis . . 54

54 (57) Shell subspherical 55

55 (56) Length, 3 mm.; front of male's head narrow; second antenna i6-seg-

^ ^ mented; flabellum very large. . Limnetis gouldii Baird 1862.

A form widely distributed through Massachusetts, Nevr
Hampshire, Rhode Island, New York, Illinois, and Canada.
It is very hardy and will live for months in aquaria.

Fig. 1037. Limnetis gouldii. ^ , head of male, dorsal view. X 21;
B, shape of shell. X 7. (After Packard.)

56 (55) Length, 4.2 mm.; front of male's head very broad; antenna 20-seg-

mented Limnetis gracilicornis Packard 187 1.

This species was described by Packard from specimens collected
at Waco, Texas.

Fig. 1038. Limnetis gracilicornis. Head of male, dorsal view. X 18.
(After Packard.)

57 (54) Shell suboval 58

58 (59) Length, 4 nam.; front of male's head broad and square; second an-

A B tenna 14- and 17-segmented; flabellum very narrow.

Limnetis mucronatus Packard 1875.

This species has been reported from Montana and Kansas.
It is easily recognized by the mucronate, tridentate front.

^3

Fig. 1039. Limnetis mucronatus. ^ , head of male, dorsal view. X 20;
B, shape of shell. X 4. (After Packard.)

59 (58) Length, 4 (to 6) mm.; front of male's head rather broad; second
A B antenna 29-segmented; flabellum short and broad.

Limnetis brevifrons Packard 1877.

This is the largest known species of this genus in North
America. It has been observed only at Ellis, Kansas.

Fig. 1040. Limnetis brevifrons. A, head of male. X 8.
of shell. X 3. (After Packard.)

B, shape

THE FAIRY SHRIMPS (PHYLLOPODA)

673

60 (53) First and second post-cephalic limbs prehensile in the male; carapace
distinctly bivalve, enclosing head, with concentric growth
lines around a more or less prominent umbo.

Family Limnadhdai: .61

61(66) With pediculated dorsal organ on front of head 6i

62 (63) Shell broad oval, much flattened, subtriangular, with about 18 lines
of growth; fiagella of second antenna 12- to is-segmente<l;

18 to 22 pairs of limbs " I^hmuuiia.

Only one species Limmidia iinuriccjna Morse iH-js.

This species was described from specimens colIccte<l
at Lynn, Massachusetts.

Another possible species, Limnadia coriofea lialdc-
man, was collected at Cincinnati and in ditches ahing
the Susquehanna river, but it has not been sufTuiently
described so that its relati(jnships can be determine*!.
See Packard (1883, pp. .51.5, ,} 14).

Fig. 1041. Limnadia americana. Side view.
(After Packard.)

X \.

63 (62) Shell narrow-ovate, rather prominent behind the umboncs with 4 to

5 lines of growth; fiagella of second antennae q- to lo-seg-
mented; 18 pairs of limbs Eulimnadia . . 64

64 (65) Shell narrow-ovate, with 4 lines of growth; telson with 12 pairs of
• ^ "* dorsal spinules not including the terminal spine.

Eulimnadia agassizii Packard 1S74.

This small crustacean has only been o})ser\-e<l on
Penikese Island, Massachusetts. The fi^'ure shows
the large dorsal organ projecting above the eye. The
valves of the carapace are whitish and ver\- trans-
parent. Their shape is regularly oval.

Fig. 1042.

Eulimtuidia agassizii. Side view. X a.
(Alter Packard.)

65 (64) Shell narrower than that of Eulimnadia agassizii, with 5 lines 01 growth ;
telson with 16 fine teeth above.

Eulimnadia tcxana Packard 1S7.'.

The valves of the carapace are whitish and
rounded oval in shape.

This species has l)een collectetl in Kansas,
Nebraska, and Texas. It is s;iid to be com-
mon in the last locality in early spring. The
figure shows only the shape of the shell.

Fig. 104,?. Eulimruuiia trxan^t. Shape of shell,
side view. X 7. (.After P.-tckard.)

66 (61) Shell oval, more or less globose, with 18 to 22 lines of growth, amber
colored; no pediculated dors;il-organ on front of head;
fiagella of second antennae 11- to 17-segmented; 24 to 28
pairs of limbs Estluria . . 67

674 FRESH-WATER BIOLOGY

67 (70) Umbones one-sixth length of shell from anterior end 68

68 (69) Shell large (16 mm. long), flat; umbones small; flagella of second

antenna 13- and 15-segmented.

Estheria californica Packard 1874.

Thus far this species has been collected at two
localities in Cahfornia. The small size of the umbones
is remarkable. Length of shell, i6 mm.; height,
10 mm ; breadth, 4 mm.

Fig. 1044. Estheria californica. Shell, side view. X 3-
(After Packard.)

69 (68) Like Estheria californica but umbones more prominent and dorsal
edge of shell sloping down to posterior end.

Estheria newcomhii Baird 1866,

Possibly the same as the last species but as Packard's and
Baird's figures appear to differ somewhat the two are separated.
It is found only in California.

Fig. 1045. Estheria newcombii. Shell, side view. X 2. (After Eaird.)

70(67) Umbones more than one-sixth length of shell from anterior end. . 71

71 (72) Shell long and narrow; umbones small, one-fifth length of shell from
anterior end; telson armed with small fine teeth; hands of
male short and thick; flagella of second antenna 15- and
14-segmented. . . . Estheria compleximanus Packard 1877.

Packard reported this species from two localities in
Kansas and more recently Richard discovered it in a
collection from Lower California. Length of shell,
II mm.; height, 5.5 mm.

Fig. 1046. Estheria compleximanus. Shell, side view.
X 3. (After Packard.)

72 (71) Shell more or less swollen or globose; umbones prominent.

73

73 (74) Shell globose, wider than high; umbones prominent and oblique

one-fourth length of shell from anterior end, Hues of growth

not sharply marked Esfheria digiieti Richard 1895.

Described from Lower California.

74 (73) Lines of growth well marked; shell not wider than high 75

75(78) Flagellaof second antennae 15- and 14-segmented 76

76 (77) Shell globose with 24 lines of growth; umbones large and prominent,
two-fifths length of shell from anterior end.

Estheria helfragei Packard 187 1.

This fine species was described by Packard from specimens collected
in the month of April at Waco, Texas.
Fig. 1047. Estheria helfragei. Shell, side view. X 4- (After Packard.)

THE FAIRY SHRIMPS (PHYLLOPODA)

675

77 (76) Shell globose with 13 lines of growth; umbones prominent, one-
third length of shell from anterior end.

Est her ia sclosa Pearse igi3.

This species resembles Eslheria bclfraRci in many resiK-cts hut is ca-sily
distmguished by the smaller number of lines of growth and the length of
the dorsal setae at the anterior edge of the telson. Collected in eastern
Nebraska from small pools.

Fig. 1048. Estheria setosa. Shell, side view. X .?.

78(75) Flagella of second antenna 17- and 16-scgmented 79

79 (80) Shell swollen; umbones rather prominent, one-fourth length of shell

from anterior end; dorsal margin short, sudtleniy sloping at
posterior end; telson with larger teeth interpolated l)etwecn
the smaller ones Estheria mexieana Claus 1 860.

A species of very wide range extending from Lake Winnipeg
through Kansas, Nebraska, Kentucky, Ohio, and New Miticn
into Mexico. It is rather variable in its structure.

Fig. 1049, Eslheria mexieana. Shell, side view. X4. (.After i';iik:ir'l

80 (79) Shell somewhat globose; umbones more prominent than in Estheria

mexieana, slightly nearer the anterior end than in Estheria
heljragei Estheria morsei Packard 1S71.

South Dakota, Nebraska. Fig. 1049 shows the general structure of this species.

IMPORTANT PAPERS ON FRESH-WATER PHYLLOPODA

Calman, W. T. 1909. Crustacea. Lankester's Treatise on Zoolog>', Pt.

VII, Fasc. 3: 29-55. London and New York.
Daday, E. 1910, Monographic systematique des Phyllopodes Anostraces.

Ann. Sci. Natur., (9) 11: 91-492, 84 figs.
Hay, 0. P., and W. P. 1889. A contribution to the knowledge of the Genus

Branchipus. Amer. Natur., 23: 91-95.
Packard, A. S. 1883. A Monograph of the Phyllopod Crustacea of North

America, with Remarks on the Order Phyllocarida. 12 Ann. Rept. U. S.

Geol. Surv.: 295-590, 39 pis., i Map.
Pearse, A. S. 1913. Notes on Phyllopod Crustacea. 14 R^'pt. Michigan

Acad. Sci.: 191-197, 3 pis.
Shantz, H. L. 1905. Notes on North American Species of Branchinecla and

their Habits. Biol. Bull., 9: 249-264; pis. 10-12.

CHAPTER XXII
THE WATER FLEAS (CLADOCERA)

By EDWARD A. BIRGE

Dean, University of Wisconsin

When men began to study nature by the aid of the microscope
in the seventeenth century the ''insects" were among the first ob-
jects to be examined. In 1669, the Dutch physician, Swammerdam,
described in his history of insects the " pulex aquaticus arborescens^'
— the water-flea with branching arms. This was one of the
Cladocera, still called Daphnia pulex, the commonest species in
shallow pools. These creatures he described and figured, giving an
account of their structure and habits and speaking of their sudden
appearance in enormous numbers, and their equally sudden dis-
appearance. So the Cladocera made their debut into science along
with the microscope.

For nearly a century Httle was added to the knowledge of the
group. In 1755, the German, Schaeffer, gave the first really good
account of their structure. In 1785, 0. F. Mueller, the Danish
naturalist, issued the first general systematic work upon Entomo-
straca. This described many of the species as we now know them
and gave a firm scientific basis for further knowledge of the Clado-
cera. In the rapid advance of science during the latter half of the
nineteenth century the systematic work of the group was substan-
tially done, the Norwegian, G. 0. Sars, having contributed more
than any other one man. This work showed that the Cladocera
constitute the largest group of fresh-water Crustacea in number of
species; the most diversified in size, in structure, and in habits.

During the opening years of the present century the scientific
study of fresh-water life has advanced rapidly and the biology of
the Cladocera is receiving much attention. The conditions of
variation and the nature of the variants are examined, as well as
the conditions of sexual reproduction, the centers of origin and
dispersal of species, and other similar matters.

The Cladocera are particularly well suited for study by those
persons who are interested in observing animals with the micro-

676

THE WATER FLEAS (CLADOCERA)

677

-m^^

-- BO

scope and who cannot command the resources of a university labo-
ratory. They are easily collected and preserved and the species
may be readily identified, since little or no microscopic dissection
is needed to make out the specific characters. Many of the Clado-
cera are so transparent that the internal or^^ans can be studied in
detail when the animal is viewed from the side under the microscope.
Many of the forms can
readily be kept alive in
small aquaria, and their
habits observed. There
is still a great amount of
work to be done in this
country in finding out
the local geographical
distribution of the spe-
cies and the variation of
the variable forms.
- The suborder is di-
vided into two sections so
different that few state-
ments can be made of
them in common. The
first, and by far the larger
section, the Calypto-
mera, have a large, bi-
valve shell, which covers the body and legs. The second section, the
Gymnomera, includes two species in our fresh waters. These retain
the shell only as a brood sac; the body and legs being free. In the
account which follows, the Calyptomera are kept in mind. The
animals belonging to this group range in size from about 0.2 mm.
to 3.0 mm., or even more. All have a distinct head, and a body
covered by a fold of the skin, which extends backward and down-
ward from the dorsal side of the head and constitutes a bivalve
shell. The junction of head and body is sometimes marked by a
depression, the cervical sinus or notch (Figs. 105 1. lOT.v logi).'

1 The figures referred to are designed to give the specific characters raih.r than
the anatomy, which is shown only incidentally.

Fig. ioso. Daplinia Umgispina. A', ;intcnnulc; A", antenna:
AP, abdominal processes; .4.S', abdominal setae; B, brain with
optic ganglion and ocellus; BC, brood case with (Icvclopin^ ova;
E,eye, with three eye muscles of left side; //. heart with venous
opening on side and exit in front; HC. hepatic cecum; /, intes-
tine; L, legs; MJ, mandible; O. ovary; PA. jxist alxlomen with
anal spines and terminal claw; R, rostrum or Ix-al;; .SG. >hcll
gland. (After Sars.)

678 FRESH-WATER BIOLOGY

In the head is the large compound eye (Fig. 1050). This has nu-
merous or few lenses (Figs. 1059, 1076, 1169), and is capable of being
rotated by three muscles on each side. It is a most conspicuous
organ, by its size, its dark pigment, and its constant motion during
Hfe. In the head are also the brain, the optic gangUon, with its
numerous nerves to the eye, the ocellus, or pigment spot, the an-
tennary muscles, and the anterior part of the digestive tract. The
head bears two pairs of appendages: (i) The antennules (Figs. 105 1,
1079, 1114, 1152), which carry sense-rods, the olfactory setae, usually
placed at the end, and have also ordinarily one or more lateral sense
hairs; (2) the antennae, the main organs of locomotion, large swim-
ming appendages, with a stout basal joint bearing two branches or
rami, which, in turn, carry long plumose setae. The number of the
antennary setae may be expressed by a formula which shows the
number of the setae on each joint of each branch of the antenna;
the numbers for the dorsal branch occupying the place of the
numerator of a fraction. The formula thus constructed reads

Daphnia (Fig. 1050), ^^^~^ • that for Sida (Fig. 105 1), 5^^^.

The antennae are moved by powerful muscles, which may occupy
a great part of the interior of the head (Fig. 1050) . On the size of the
antennae, the length and number of the setae, and on the size of the
muscles operating them, depends the type of locomotion. Latona
(Fig. 1052) leaps suddenly from point to point by single powerful
strokes of its broad antennae. The smaller Daphnidae (Fig. 1079)
hop, rather than leap, by more numerous and less vigorous strokes.
The heavier forms of this family (Fig. 1075), with smaller anten-
nae, have a rotating, unsteady motion, produced by rapid strokes.
Drepanothrix (Fig. 1104), whose antennae bear saber-like setae,
scrambles and pushes itself about, and the mud-haiuntmg Ilyocry plus
(Fig. 1 1 10) crawls and pulls itself about among the weeds, rather
than swims. The members of the large family of the Chydoridae
have small antennae and move them very rapidly; while their
progress varies from a rapid whirling-motion, as in Chydorus (Fig.
1 1 50), to a slower wavering and tottering progress, as in Acroperus
(Fig. 1 1 21). In the Macro thricidae and Chydoridae the post-

THE WATER FLEAS (CLADOCERA) 679

abdomen is often an efficient aid to locomotion. It ma\- [)u.sh tlu-
animal along, as in Ilyocryptus (Fig. mo) and Camptoccrcus (Fig.
1119). In Dunhevedia (Fig. 1134) it is peculiarly ciTectivc. broad
and stout, covered with numerous small spines and setae, and by ii.s
aid the animal may execute sudden and vigorous jumj)s.

The head also bears the mouth parts: (i) The mandibles (Figs.
1050, 1068, 1099, and others); stout, strongly chitinizcd organs.
made in one piece and without a palpus. Their op|)osing faces are
toothed and ridged and they grind the food very perfectly. (2) The
maxillae, a pair of very minute organs, lying concealed on the ven-
tral surface of the body, just behind the mandibles. Each is a
small, pointed structure, bearing several curved setae. They work
like a pair of hands to push the food between the mandibles. (3)
The labrum, an unpaired structure, attached to the rear of the
head and closing the mouth from below. In many of the Mac-
rothricidae and Chydoridae this structure bears a keel or projection
which is of systematic value (Figs. 1051, 1060, 1106, 1135).

The axis of the head may continue that of the body {extended, Fig.
1 100), or it may be bent downward {depressed, Fig. 1087). That
part in front of the eye is known as the vertex. There is usually a
sort of beak in front of, or between, the antennules, which is known
as the rostrum, whose size and shape have systematic value. There
is commonly a ridge above the insertion of the antenna, which helps
to stiffen the side of the head and to support the pull of the antcn-
nary muscles. This is the fornix, whose shape and extent may form
an important systematic character (Figs. 1063, 1083).

The shell, though called bivalve, is really in one piece, bent along
the back, but never showing a division or joint at this i)lace. It
has very different forms, as seen from the side, nearly square, oval,
or round. It may be marked in the most various fashions. It
may bear hairs, or spines, along the ventral edge. There may be
a single spine on the dorsal side, prolonging the junction of the
valves, as in Daphnia, or each valve may have one or more spines
at the lower posterior part, the infero-posteal angle (Fig. 1076).
This angle in the Chydoridae may be acute or rounded, smooth or
toothed, and its characters are of systematic value. The shell is
always a duplicature of the skin. Its inner wall is far more

68o FRESH-WATER BIOLOGY

delicate than the outer, and between the walls the blood circulates
and the inner surface serves as a respiratory organ.

Just back of the head, on the dorsal side, lies the heart, an oval
or elongated sac (Figs. 1050, 105 1, 1089), whose rapid pulsations are
easily seen in the living animal. It receives the colorless or yellow
blood by one opening on each side and expels it in front. There are
no blood vessels, but the circulation passes along definite courses
through a complex series of passages all over the body. The
movements of the blood corpuscles may be readily seen in trans-
parent Cladocera.

Respiration is not served by any single organ. The legs and
the inside of the valves are the main surfaces for the exchange of
gases.

In the anterior part of the valves lies an organ whose structure
is not readily made out. This is the shell gland (Figs. 1050, 105 1,
1056), a flattened glandular tube in several loops, which probably
serves the function of a kidney.

The body lies free within the valves and is divided into the main
portion, bearing the feet, which is not plainly segmented, and a
single unjointed portion, the post-abdomen. Through it runs the
intestine, and along the sides of the body lie the simple reproduc-
tive organs. To the ventral side are attached the feet, ordinarily
five pairs, sometimes six. These are mainly leaf-like structures,
each with several parts, bearing numerous hairs and long setae (Figs.
1050, 1 142). Their structure is too complex to describe here. In
the first two famihes all the feet are similar and foliaceous. Their
use is to create a current of water through the valves, bringing
in oxygen for respiration and particles of food. The latter consists
chiefly of algae, though nothing edible is rejected that the current
brings in. The food particles collect below the body between the
bases of the feet and are fed forward into the mouth. The maxillae
push them between the jaws as the labrum opens, the mandibles
grind them up, and they pass on into the esophagus. Cladocera
are normally eating all of the time.

In the Daphnidae and remaining famiHes the feet differ in struc-
ture ; the first pairs being more or less prehensile and having other
functions besides the main one of drawing in water. These animals

THE WATER ELEAS (CLADOCER.A) 68 1

live chiefly among the weeds, and the hooks and spines of the first
foot aid them in cUnging to plants and also may help to pull off
attached algae, etc., for food.

In the more transparent species the digestive tract may be seen
throughout its full extent. The narrow csopha«,^us ( Figs. ^050, 105 1 ,
1096) widens suddenly into the stomach, wliich lies in the head and
whose posterior end passes insensibly into the intestine. Attached
to the stomach in many species are two sacs, often long and curwd
(Figs. 1050, 1053, 1060, 1064, iico). These arc the hepatic ccta.
which no doubt function as a digestive gland, l^he stomach and
intestine have a muscular wall and a lining of dark-colored, glandu-
lar cells. The cavity is ordinarily filled with food. The intestine
has a direct course in the first four families. In the Macrothricidae
it is sometimes direct (Fig. 1106), and sometimes convoluted (Figs.
1 100, 1 103). In the Chydoridae it is always convoluted and there
is often a cecimi attached to the ventral side near the [)osterior end
(Figs. 1 1 21, 1 141). The terminal part of the intestine, the rectum,
is always transparent and the muscles which open and c lose it can
easily be seen. The anus Hes either at or near the vnd of the post-
abdomen, as is usually the case in the first live families, or in the
Chydoridae and in some forms of the other families (Figs. 1089.
1091, 1 100, 11C9), on the dorsal side.

The post-abdomen is ordinarily jointed to the body and is bent
forward; hence its dorsal side may come to be the lower one. On
the dorsal side it bears two sensory hairs, often very long (Fig. logo),
the abdominal setae. At the end of the post-abdomen are two ter-
minal claws, which, in turn, may have spines at their base, the basal
spines (Figs. 1123, 1144), or, when numerous, the {K-ctcn (Fig.
1066), and the concave side may also have a row of very fine spinules
(denticulate). The post-abdomen almost always has more or fewer
spines, or teeth, the anal spines. In the (liNcioridae there are fre-
quently two rows on each side behind the anus, the marginal and
lateral denticles (Fig. 1147). These spines and teeth may have the
most diverse shape and structure (squamae, fascicles, etc.). and fur
nish important systematic characters. Their main use seems to Ik»
to comb the legs and keep them clean and free from foreign matters
and from parasites which might other^vise readily attach them.selves.

682 FRESH-WATER BIOLOGY

Little study has been given to the senses of the Cladocera, except
that of sight. As special organs of touch there are the abdominal
setae, which are sometimes very long (Fig. 1090) ; sensory hairs on the
basal joint of the antenna near the body (Fig. 1075), or near the apex
(Figs. 1051, 1053, 1089) ; the lateral sense hair of the antennule (Figs.
1089, 1 1 17, 1 1 54); the flagellum on the antennule of the Sididae
(Figs. 105 1- 1 05 7), which is often fringed with fine hairs; and the
frontal sense hair of Bosmma (Fig. 1096). Any of the innumerable
hairs and setae may also serve this sense, though not specially modi-
fied for that purpose. There is no auditory organ. Whether the
olfactory setae really give sensations of smell and taste is doubtful,
although the structure of the sense rods is such that they may well
serve a chemical sense. They lie at the entrance of the valves in
the current of water which is coming in under the impulses of the
feet, and may take cognizance of the particles of food, etc., which
come along with the water. The Cladocera are certainly able to
discriminate between different kinds of particles brought in by the
legs, eating some and rejecting others. They have decided tastes
in the matter of diet, preferring some forms of algae to others. In
general, the diatoms are eaten in preference to the blue-green algae.
In the selection of food, the Cladocera are aided also by sensations
which arise in the mouth, since they may reject particles which
have been brought into the mouth and partially chewed.

The eye is obviously the visual organ. It is sensitive to light and
can no doubt distinguish objects by the shadows which they pro-
duce, although its lenses are by no means numerous enough, or
perfect enough, to give sensations of form. The constant motions
of the eye are for the purpose of moving the lenses so that they will
cover the entire field of vision, and the animal no doubt directs its
movements by sensations which it receives through the eye. The
Cladocera respond differently to light of different intensities and
various colors. Most of them react positively to a weak light and
negatively to a strong one. There is, however, much difference in
this respect. Drepanothrix, for example, is vigorously repelled by
the light of a lamp, which will attract all the other Cladocera in
the vessel with it. Newly hatched Cladocera are attracted by Hght
which will repel older forms. On a bright, calm day a few inches

THE WATER FLEAS (CLADOCERA) 683

of water at the surface of a lake may be deserted by the Clado-
cera. A Httle deeper may be found young forms, and still dcciK-r,
perhaps one or two meters below the surface, the aduh animals.
The temperature of the water also has much influence on the reac-
tion to hght. In cold water Cladocera are attrac ted by a light
which will repel them at higher temperatures. The linmetic forms
oi Daphnia pulex ordinsinly remain durin<r the daytime in the cool
water immediately beneath the thermocline. though they may rise
into the warm water during the night. In the winter, when the lake
is skimmed with ice, the same animals may be seen in the bright
sunshine immediately below the ice. Practically ail of the (Madocera
react negatively to the blue rays of the spectrum, are nearly un-
influenced by the rays at the red end, and iind the yellow ra}s the
most attractive.

The ocellus is rarely absent (Diaphanosoma. Daplnda rctrocuna,
longiremis) ; sometimes rudimentary (many forms of D<iplmia)\
sometimes larger than the eye {Leydigia, Dadaya); and rarely the
sole organ sensitive to Hght {Monospilus). It is not known in what
respects its function differs from that of the e)'e.

This imperfect sketch shows how complex the structure of the
Cladocera is, — wonderfully complex, when their small size is con-
sidered. The smallest of them are hardly more than one one-
hundredth of an inch in length. Yet these have ten complicattxl
legs, besides the numerous other structures named and many which
have not been mentioned. Probably no other animals of so small
size have so complex a structure, yet they must sulTer the disgrace
of being eaten by Stentor and so being among the few Metazoa
which are swallowed whole by one-celled animals.

The reproduction of the Cladocera is noteworthy. During the
open season the females produce eggs which develoj) without being
fertihzed. These may number only two, the usual number in the
Chydoridae, or, in the larger Daphnidae, there may be more than
twenty. These eggs are deposited in the cavity bounded by the
dorsal part of the valves and the upper side of the body - the
brood case. Here they develop and hatch in a form quite like
that of the parent and are well grown before they are set free.
Hence there are no free-living larval forms of Cladocera. such as

684 FRFSH-WATER BIOLOGY

are so abundant in the Copepoda. The young are nourished in the
brood-cavity, not only by the yolk of the egg, but also by a secretion
from the dorsal wall of the sac. The brood case may be closed
behind by extensions of the body — ^the abdominal processes —
which have some systematic importance. This parthenogenesis
goes on regularly through the favorable season for growth, closing
when the pools begin to dry or other unfavorable conditions arise.
Several successive broods of females are ordinarily produced in this
way, although in Moina, which lives in temporary pools, the second
generation may be sexual. Sooner or later true females and males
are hatched from the eggs. These females produce one or two eggs,
large and opaque, with abundant yolk and thick shell, and which
must be fertilized by the male before developing. These eggs pass
into the brood sac, whose walls have usually acquired a peculiar
structure. In the Chydorinae (Fig. 1159) they are merely thick-
ened and darkened. In the Daphnidae (Figs. 1073, io79> i093)>
a semi-elliptical portion of the dorsal region of each valve becomes
greatly altered to form the ephippium, so called from its resem-
blance to a saddle. In the Chydorinae the sexual egg is deposited
in the brood sac and the whole shell is then molted ; the egg remain-
ing enclosed in it. Where the ephippium is developed, this separates
during the molt from the rest of the shell and closes about the one
or two eggs deposited in it. In either case the eggs lie over to the
next favorable season before they develop.

This process of sexual reproduction occurs at different times in
various species. Like the blossoming of flowers, it cannot always
be directly correlated with any definite conditions of food or tem-
perature. In those species which live in the open waters of lakes,
sexual reproduction is often greatly reduced or wholly absent and
the species is carried on from year to year by asexual generations.
In many species the males are very rarely seen and in none are they
abundant.

The males are smaller than the females and usually of similar form.
They are distinguished by larger antennules; the post-abdomen is
usually somewhat modified (Fig. 1144); the first foot is frequently
armed with a stout hook which serves to clasp the females. In Moina
this function is performed by the very large antennules (Fig. 1092).

THE WATER FLEAS (CLADOCERA) 685

Little is known regarding the length of life of the individual
Cladocera. It doubtless varies from a few weeks to several moDihs
Limnetic forms probably have a longer life than the littoral, as the
food supply and other conditions of life are more constant. Individ-
uals from the broods of Daphnia longispina {liyalina) which arc born
late in October and in November may sur\'ive through the winter
and produce one or more broods of young in the spring. The last
survivors die in June, weakened by old age and attacked by par-
asitic fungi. This is probably about the maximum length uf
life.

The Cladocera are found in all sorts of fresh waters. Lakes and
ponds contain a much larger number of forms than do rivers..
The shallow, weedy backwaters of a lake whose level is fairly
permanent harbor a greater variety of species than does any other
kind of locality. Here are found almost all of the Chydoridae and
Macrothricidae, as well as most of the representatives of the other
families. In such localities are found the best conditions for the
life of these animals: warmth, shelter from enemies, and abundant
food. It must not be supposed, however, that each square rod of
such waters harbors a like population. On the contrar}-. anyone
who collects frequently in one lake will come to know certain places
as especially favorable to these creatures, which are }> resent iri^
greater number and variety than in places apparentl\- (juite simi-
lar and closely adjacent. While by far the greater number of
species belong to the littoral region, living among the weeds and
feeding on algae and similar organisms, a few species live near the
bottom. Several species are commonly found in or near the mud,
although not specially adapted to a life in the mud; such are
Alona quadrangularis and Drepanothrix. The genera Ilyocryptus and
Monospilus live regularly on the bottom; their structure is adjusted
to a life in the mud and their shells are often overgrown by algae.
These forms may and do swim, but more often scramble about on
the bottom, pulling with their antennae and pushing with the post-
abdomen. In both forms the old shell is not cast oil in molting,
the new and larger shell appearing beneath it (Figs. 1 1 10. nf)S).

The species of Moma are found most commonly in mudd\- pools,
such as those in brick-yards, though not conlined to such waters.

'\

686 FRESH-WATER BIOLOGY

With them are frequently associated members of the Daphnia
pulex group. These last are also found in temporary pools of clear
and weedy water, and, less frequently, in lakes. Daphnia magna
in Europe is found in waters which are slightly brackish and very
possibly does not disdain slightly alkaline waters in this country.

The limnetic region of the inland lakes has a cladoceran popula-
tion, large in number of individuals but not rich in species. Chy-
dorus sphaericus is almost the only Chydorid which is ever abun-
dant here, though any species may be present as an accidental
visitor. The regularly limnetic species belong chiefly to the genera
Bosmina, Diaphanosoma, Daphnia, and Holopedium. These forms
are transparent — an obviously protective character. Chydorus
is an exception and the size of this species is so small that trans-
parency mxay be unnecessary. Apart from transparency and a
general lightness of build, the limnetic forms have generally no
peculiar characters. Holopedium forms a marked exception to
this statement, as its globular gelatinous case is wholly unique in
the group and indeed in the Crustacea.

Certain forms are intermediate in character between the limnetic
and the Httoral forms. Such is Ophryoxus gracilis (Fig. iioo),
which paddles about in the open waters between weeds, and such
also is Sida crystallina (Fig. 105 1). Both of these forms are trans-
parent, but they are never present in large numbers in the open
water, nor are they likely to be found far out from the weedy
margin.

In southern waters, where are found masses of floating plants
such as the water hyacinth, the distinction between the littora
and Umnetic species quite disappears.

The Gymnomera differ widely in structure and habits from the
Calyptomera. The section includes two species in our fresh
waters: Polyphemus pediculus (Fig. 1169), and Leptodora kindtii
(Fig. 1 1 70). In both forms the shell is reduced to an egg case and
the feet are free, jointed, and provided with stout spines and hairs.
In Leptodora the body is long and jointed, while in Polyphemus it
is very short. Both animals are predacious, feeding on protozoa,
rotifers, and minute Crustacea. Polyphemus lives chiefly in marshes
and in the weedy margins of ponds and lakes, but may also be

THE WATER FLEAS (CLADOCERA) 687

found in the limnetic region and in Ihc Orcat Lakes. Uptodora
is always limnetic in its habits. It is ahnost perfectly transi)arcnt;
the dark eye and yellow stomach alone bein<r visible when the animal
is viewed by transmitted light. It is by far the lar^'cst of the
Cladocera, reaching a length of 18 mm. Its winter eggs hatch as
nauplii and this is the only species of Cladoccra in which thi->
characteristic crustacean larva appears.

The Cladocera have great economic value. Together \sith the
Copepoda they constitute the chief agency for converting the
smaller algae of fresh water into a form edible by the carnivorous
aquatic animals. They are the prey of insect larvae, which are in
turn an important item in the bill of fare of the larger fishes. Clado-
cera are themselves of great value as food for young fishes and there
is a period in the life of almost every fish when it feeds exclusively
on Entomostraca. Even the larger fishes do not disdain these
animals. The great spoonbill {Polyodon) fills its stomach with
Bosminae, or other tiny inhabitants of the water from which it
strains its food.

The geographical distribution of Cladocera ofTcrs little of interest
that can be stated in a brief sketch, chiefly because the species are
so widely distributed. Some species, like Chydorus sphacricus, are
cosmopolitan. A majority of the species found in this country are
found also in Europe. Where a species is peculiar to this region
it is often but slightly different from the European form. The
student of Cladocera should presume that any species is probably
intercontinental, though it may prove to be more restricted in its
range. The study of our forms has not gone far enough to enable
us to speak of the local distribution of each species within the
general area which it covers, but it is known that the rare s|x?cit^
are very irregularly distributed. On the whole, the fauna of the
various regions of the country is strikingly similar. Init with some
forms peculiar to each region. The southern states contain numer-
ous species which are common to them and to South America.
but are not found in the northern states.

The student of Cladocera will fmd the cone net (p. 68) the l>est
agent for collecting the Httoral forms. The catc h should be put
into a cup, which should be filled with water, and the debris allowed

688 FRESH-WATER BIOLOGY

to settle before pouring off the water and the Crustacea through the
funnel. As little as possible of the weed and debris should be in-
cluded in the catch, since it is a wearisome task to search for the
various species in a catch which contains great masses of weed with
but few Crustacea. It is well to retain a part of the weed in a
separate bottle, so that species which go to the bottom may not
be overlooked. It is also well to cover the cup with one's hat, or
otherwise, while the debris is settling so that species which fly from
the light may not go into the weed at the bottom. Numerous hauls
of the net should be made and concentrated so as to give abundant
material. Considerable experience with collections sent me by
students of Cladocera has shown me that the chief faults of the
collector are including too much debris in the[^catch and taking
too few hauls of the dredge.

The best preservative I have found to be strong, 95 per cent,
alcohol. This keeps the shape of the species as well as or better
than anything else. Certain soft-bodied forms with strong muscles
may be distorted by any fluid which kills and hardens quickly.
Such are Pseudosida, Latona, and Latonopsis, and, to a less degree,
Moina and Diaphanosoma. For these also we have nothing better
for field use than alcohol. If their forms are to be well preserved
they should be killed individually by some poison like osmic acid,
or chloral hydrate, and then hardened gradually, according to regu-
lar microscopic methods. Formalin distorts many species.

I have found no better mounting fluid than pure glycerine. I
place the animal with a small drop of glycerine in the center of the
slide and support the cover glass by three bits of paper thick enough
to permit the cover to press slightly on the specimen. The cover
glass is put on carefully so that the glycerine occupies its center
only. A bit of soft paraffin (melting point about 50° C.) is placed at
the edge of the cover glass, and, on warming the sHde, the paraf-
fin melts and runs in, sealing the mount. The cover may after-
wards be cemented down by any microscopic cement, and this
should be done if the preparation is to be kept; but for purposes
of study it is well not to do so, since an advantage of the method is
the ease with which the specimen can be unmounted for study or
dissection.

THE WATER FLEAS (CLADOCERA) 68q

KEY TO NORTH AMERICAN FRESH-WA ri-R CLADOCERA

1 (248) Body and feet covered by a bivalve shell. Feel in Kencral f.iiiaccou^

not plainly jointed. . . . Section A. Calyptomera

2 (21) Six pairs of feet, all similar, except the last, and all foliaccous.

Tribe L Ctenopoda

3 (18) Shell of ordinary type. Antenna biramous in female, rami llaiim..,,

the dorsal with numerous setae, both lateral and terminal.

Family Sididak Baird 4

Head large; cervical sinus present. Antennules large, movable, .\nlcnn.ic with terminal
setae only on ventral ramus. Eye large, with numerous lenses; ocellus small or a? ■ ' • ..
tine simple, usually with more or less distinct median cecum or cnlargt-mcnt at
rarely with 2 hepatic ceca. Heart elongated. Male usually with charactcri-! '

the flagellum united with the base into one structure, long, taix-ring. with a row of hue ^pmulcs
toward apex; usually with grasping organ on first foot and copulatory organs on ixfet -abdomen.

4 (5) Dorsal ramus of antenna 3-jointed, rostrum present.

Sida Straus 1820.

Head with large gland on dorsal side; pointed rostrum; no fomices. .\ntennulcs of 9
attached to side of rostrum, short, truncate, with short llagellum. Ventral ramus of antennae
2-jointed. Antennules of $ very long; no copulatory organ; first fcxjt with hook.

Only one American species. . . Sida crystallina {0. V. 'SiiiUcr) i-j^s.

■y^'
^f^-

A **^^^*tit^<ii£ii:j

I MM. I '

Fig. 105 1. Sida crystallina. (Unless otherwise indicated all figures were dniwn i-sjiccLUl) for this

chapter.)
Color yellowish-hyaline, sometimes with brilliant blue SF>ots. Ungth. 9. 3.0-4.0 mm
$ , 1.5-2.0 mm.
Common in lakes and ponds among weeds.

5 (4) Dorsal ramus of antenna 2-jointed.

6 (9) With lateral expansion on basal joint of dorsad ramus of antenna.

Liitofhi Straus 1S20 . . 7

Large, tongue-shaped projection on ventral side of head, 't^ventral surface coi^ca^. Vcnilral
ramus of antennae 3-Jointed. Long setae on posterior marpn of valves. h>c dorsal, far Irum
optic ganglion. $ with copulatory organ; no hook on lirbt toot.

690

FRESH-WATER BIOLOGY

7 (8) Antennary expansion very large; no hepatic ceca.

Latona setifera (O. F. Miiller) 1785.

Antennules of both sexes alike, bent, with large, hairy flagellum set on at angle, looking like

continuation of base. Color yellow; not transparent; old 9 often with briUiant colors in

late autumn. Length, 9 , 2.0-3.0 mm. ; ^ , ca. i .5 mm. Widely distributed, but never abundant,

among weeds in ponds and lakes.

'//nm-

MM. I.

Fig. 1052. Latona setifera.

8 (7) Antennary expansion small; hepatic ceca present.

Latona parviremis Birge 1910.

Antennule of 9 with basal part and long slender flagellum, like Latonopsis; of ^ very long,
like other Sididae. Color yellow. Length, 9' to 2.5 mm.; $ , 0.8 mm. Northern Wisconsin,
Michigan, Maine; in weedy waters of lake .

Fig. 1053. Latona parviremis.

9 (6) Without lateral expansion of antenna. . .

10

10(13) No spines on post-abdomen. . Diaphanosoma Yi'^chei i^s^ . . 11
No rostrum, fornix, or ocellus. Antennule small, truncated; olfactory setae terminal, with
slender flagellimi. Dorsal ramus of antennae 2-jointed; ventral 3-jointed. Claws with 3 basal
spines. $ with long antennule; copulatory organ; hook on first ''oot.

THE WATER FLEAS (CLADOCKRA)

691

II (12) Reflexed antenna not reaching posterior margin of valves.

„,„„,,:. Diaplianosoma brachyurum (Lieven) 1848.

Eye pigment large; eye filliuK end of head. Color yd-
lowish-transparent. Length. V . oS-o.g mm.; ^.ca. 04
mm. Common in marshes ami wec<ly margins of Ukr^
Very probably the next s|K'cics is merely a limnetic van

ety of this.

Fig. 1054. Diaphanosoma bra(hyurum.

O.I MM. i

12 (11) Antenna when reflexed reaches or exceeds posterior margin of valves.

Diaphanosoma Icuchtcnbcrgianum I-'i.scher

1850.

J^-^

^ (f^m^^^-

Eye not filling end of head, pigment small.
Color hyaline. Length. V , o.<>-i.i mm.; ^ . to
0.8 mm. Common in open waters of lakes

Fig. 1055. Diaphanosoma Uucklrnbergu

13 (10) Spines on post-abdomen U

14 (17) Eye dorsal, far from insertion of antennule and optic ganglion. No

rostrum Latonopsis Sars i^^i^ . . 15

No tongue-shaped process on ventral side of head, or antennary expansion. Otherwise much
like Latona parviremis. Posterior margin of valves with ver>- long setae (often lost). 6 with
long antennule, copulatory organ, and hook on first foot.

15 (16) Shell gland drawn out into very long posterior loop.

Latonopsis occidental is Hirge kSqi.

Post-abdomen with about 9 small anal spines. Color yellowirJi-trans-
parent. Length, ? , to i .8 mm. ; ^ , ca. o.O mm. New Lngbnd lo Colorado
and Texas; in weedy pools and lakes.

^^^^^.IbK^ , yV^

O^ MM

^ 1 ' \V ' , Figs 1056, 1057 . h. LaUmopns pctidtntHu
\ / , (Sec alio Fig 1057 J

i

692

FRESH-WATER BIOLOGY

16 (15) Shell gland of ordinary form. . . Latonopsis fasciculata Daday 1905.
Post-abdomen with projections on dorsal (posterior) margin and 12-14 clusters of 2-3 lancet-
shaped anal spines. Color yellowish. Length, 9- to 2.0 mm.; ^ , to i.o mm. Louisiana,
Texas; in weedy pools and lakes.

W

I

Fig. 1057. a, Latonopsis fasciculata;
b, Latonopsis occidentalis.

Fig. 1058. a, Latonopsis fasciculata; b, Pseudosida bidentata.

17 (14) Eye ventral or in middle of head. Rostrum present.

Pseudosida Herri ck 1884.
Only one American species. . . Pseudosida bidentata Herrick 1884.

General form like Sida but head more depressed and dorsum more arched. Rostrum present;
no fornix or cervical glands. Antennules attached as in Sida, long basal part with olfactory
setae on side, and long flexible fiagellum. Dorsal ramus of antennae with 2, ventral with 3,
joints; setae very unequal in length. Post-abdomen with about 14 clusters of spinules; claws
with 2 large 'basal spines and a very small spine proximal to them.

$ with antennule of standard form; copulatory organs. Complex grasping apparatus on
first foot.

Color yellowish, semi-transparent. Length, 9 . to 1.8 or 2.0 mm.; ^ , 0.9 mm. Southern
states, in pools and lakes.

0.5 MM. I

Figs. 1059, 1058, b. P. bidentata. (After Foster. ) (.See also Fig. 1058.)

THE WATER FLEAS (CLADOCERA)

693

18(3) Enclosed in gelatinous mantle. Antcnn;
with 3 terminal setae. . .

simple in fi-malc, cylimlrical,
lamily HoU)1'kuu>ak Sars.

fvl

Animal enclosed in a large, globular, transparent, (k-licatc hut U>uk\\. Kfblinou> lav oum
ventrally and forming 2 valves. Body much compressed, shell of lu-ati and lx..i\ s. , , i' I,,
high, as seen from side, leaving uncovered the mouth parts, the ends of the I. •
part of body. Antennule small, fixed; with 5-0 olfactory seta.- and lateral s-
flagellum. Antennae in 9 long; basal joint curved, annulated; the single tatuvi.', j i.,,.,
antennae of $ biramous. Post-abdomen large,
fleshy, not bent forward; with rather long,
curved anal spines and clusters of very fine
spinules; abdominal setae long, set on single,
long, conical projection. Claws large, curved,
denticulate, not set ofT from body by distinct
joint. Eye small, with numerous len.ses; ocellus
small. Intestine simple with 2 hepatic ceca.
Branchial sac on second to fifth feet. Color
transparent. Swims on its back.

Sole genus with characters of family.
Holopedimn Z3.dd3.ch. iSss ■ 19

19 (20) Ventral margins of valves
with fine spines.
Holopedium gibberum Zaddach 1855.

Post-abdomen elongated (ca. one-third
length of body) and tapering; anal spines
numerous, up to 20. Claws with i
basal spine. Length, 9. 1-5-2.2 mm.;
$ , 0.5-0.6 mm.

This remarkable and beautiful species
is not uncommon in open water in
northern lakes; has been found in the
Great Lakes, and in many inland waters,
both lakes and smaller bodies of water.

Figs. 1060, 1061, a. Holopedium gibberum
(gelatinous case not shown). (See also
Fig. 1061.)

0.5 MM

20 (19) Ventral margin of valves smooth.

Holopedium anuizoniium Stinpi-Im looj-

Post-ahdomcQ sh«>rt. I)lunt («.a
one-fourth of IkkIv in It-nKthl, i»ilh
7-S anal spines, the row continued
forward by .% 4 verv •-'" ■
Claws without has.1I
inal setae ver>' loni; a
unknown. Ix-ngth. V ' >-
Charles, L»»uiMana.

Fio. ic/ii. a UMptJimm
b IlolofuJium aHMiomU

>ulr*.

i
i-ike

694

FRESH-WATER BIOLOGY

21 (2) Five or six pairs of feet. First and second pairs more or less prehen-
sile, others foliaceous. . . . Tribe IT Anomopoda . . 22

Antennules attached to ventral side of head, not covered by for-
nices 23

22 (117)

23 (76, 83)

Antennules of female usually small, sometimes rudimentary; if
large, never inserted at anterior end of ventral surface of
head. Dorsal ramus of antenna 4-jointed, ventral ramus
3-jointed. Intestine simple with 2 hepatic ceca.

Family Daphnidae Straus . . 24

Five pairs of feet, the first two prehensile and without branchial lamella; the fifth with large

recurved seta, extending around branchial sac. Antennules in general small or rudimentary,

and when large not at the anterior extremity of the head. Antennae long, not strong, cyUndrical,

setae °~^^~^ . Post-abdomen distinctly set off from body, usually more or less compressed,

always with anal spines. Abdominal setae not borne on distinct projection or papilla. Claws
sometimes pectinate; always denticulate, unless worn by use; never with basal spine. Intes-
tine not convoluted, with 2 hepatic ceca. Eye large; ocellus usually small, sometimes want-
ing. Summer eggs ordinarily numerous; typical ephippium formed, containing i or 2 eggs.
$ usually with hook on first foot.

24 (48) Rostrum present 25

25 (39) No cervical sinus. Valves with polygonal, usually rhomboidal, mark-

ing, and with a posterior spine. Crest on dorsal side of head.
Daphnia O. F. Miiller 1785 . . 26

Form oval or elliptical, except as modified by crest of head (helmet) in some species. Body
always compressed, often greatly so. Valves reticulated; dorsal and ventral margins roundmg
over toward each other and provided with spinules along posterior part. Rostrum well-marked
in 9 and pointed. Antennules small or rudimentary, not movable, placed behind rostrum.
Abdominal processes 3-4, all ordinarily developed; the anterior especially long, tongue-shaped
and bent forward. Ephippium with 2 eggs. Summer eggs often very numerous.

Head of $ without rostrum; antennules large, movable, ordinarily with long, stout, anterior
seta or flagellum; first foot with hook and long flagellum.

26 (34)

27 (30)

28 (29)

Claws with pecten 27

Heavy, thick-bodied forms. Fornix and secondary fornix (Fig. 1063)
well developed. Distal pecten with more than 1 2 teeth. . 28

Antennules large for genus; post-abdomen with deeply sinuate
\ margin Daphnia magna Straus 1820.

Form rounded or oval, body thick and heavy, not transparent.
Post-abdomen long, with deep indentation behind anus, breaking
through row of anal spines. These are about 1 2 in proximal and
8-10 in distal set. Claws with two pectens of numerous teeth.
Ephippium characteristic; dorsal margin of valves separates with
it both behind and before; 2 eggs, placed obliquely. Summer
eggs numerous. Length, 9 , ^0 5.0 mm.; $ , 2.0 mm. or more. The
largest of the family. Maine, Colorado, Nebraska, N. Dakota,
California.

Fig. 1062. Daphnia magna, post-abdomen.

THE WATER FLEAS (CLADOCERA)

6<>>

29 (28) Rostrum and antcnnules pulcx-Ukc; p.^st-abdomen tapered not
^^^^^^^ Ddpliniu psitUirea iH:iird)\hso.

General form hke D. macui hut smaller an.l more tmn*.
parent. 1 ost-alxlonun taiK-riiiK. not sinuate, with aU.ut 10
anal teeth anc many Justtrs <.f sh..rt. line hair>. Claws »,ih
two pectens the <iistal having ahout 15 teeth. Unicth. 9 to
2.8 mm. besides spme of 0.8 mm.; ^ , to 1.8 mm. NcbraJt*.
m pools. ^^

Fig. 1063. Daphnia psittacca. note small <*ci.i,.i... , ,.,i,u»
lx;hin(l |jrimary.

0.5 MM

30 (27) Secondary fornix rudimentary or very small. Tcx-th (.f distal (k-, t.n

rarely exceeding 10, usually fewer :

31 (32, 33) Ocellus present; head not hclmeted.

Daplinia pulcx (de Gecr) 1778.

I MM. 1

B<Kly stout and

• vn; r.-ually not
.:: ;■..:...! An-
i.:.;.it - \in.- small.
the apc.x apiK.arinK a.s lupiliar «»n |k»-
terior surface of rostrum iVist ab-
domen without sinus; anus at end;
anal spines iJ-17. Summer ejacs
numerous; ephippium with two cfocs
plattd nearly vertically

Color red to yellow-brown, vcr>' variable.
Length, 9. to 2.5 mm. In pt>ols and bkcs in
all regions; numerous varieties.

Fig. 1064. Daphnia puUx.

D. pulex includes a preat number of
varieties, many of which havr l>em de-
scribed as distinct sjx-iies I' '■ nl
will be safe in assijcnins to / :. .c.
heavy-bodied forms with I- as.
In many cases the identitn.ainjn oi the
variety is more imix)rtant than that of the
species, but the varieties have n«>t l>ccn
worked out for this country. A few may
be noted:

Figs. 1065.1066.

Daphnia puUx. post-abdoiDCO

ami claw.

Var. pulicaria Forbes. A semi-trans-
parent limnetic form. vcr>- close to pmUx^
but more sli>;htly built. Lon>: Hiinc.

Common in lakes.

V'ar. dathratii Forbes. Only i; anal
spines. IVcten with j-4 larpe tcrlh.
Yellowstone.

\ar. mitttirhaha derrick "^'"^ ' ' ■'-
over heart in adult 9 ^ '^'f'
and younK'- Minnes.t.T nv.
Var. ohtusii Kurz
absent. 9-10 anal spines. Rostrum long and pointed. Mainr. W im-mm

Var. curvirostris Eylmann. Rostrum very long and
valves. Nebraska, California.

ontinutd l).uk\\

696 FRESH-WATER BIOLOGY

32(31,33) Ocellus present; head helmeted. . Daphnia arcuata Forbes iSg 3.

Very transparent. Vertex rounded, rostrum extending^ back-
ward and applied to margin of valves. Slender spine projecting
from middle of valves. Anal spines about 10-12; claws with
distal pecten of some 6 teeth. Length of 9 to 2 mm., besides
spine of about 0.5 mm. Wyoming, Wisconsin; in open waters of
lakes.

This species forms a transition to the retrocurva forms.

0.1 MM. t— -

33 (31, 32) Ocellus absent;

Fig. 1067. Daphnia arcuala.

head helmeted. . Daphnia retrocurva Forbes 1SS2.

Body much compressed, pellucid. Eye small, with
numerous projecting lenses and Uttle pigment; no ocellus.
Spine ordinarily above middle of valves, directed upward.
Crest very variable, often enormous. Claws with two
pectens, the distal of 7-9 teeth. Anal spines 7-12. Sum-
mer eggs ordinarily 2; sometimes as many as 6. Length,
9, to 2.0 mm., besides spine, which may reach 0.5 mm.

Widely distributed
in limnetic region of
lakes. Shape of head
extremely variable;
all forms from var.
breiiceps B i r g e ,
where the crest is
hardly visible, to the
exLieme of extension shown by retro-
curia proper. This species replaces
in the United States the European D.
cucullata, which is related to D. longi-
spina, much as this form is to D. pulex.
D. retrocurva never has the extremely
acuminate form of head whichcucullata
sometimes shows.
Very probably study will show that all the pulex forms (31, 32, 33) must be united into one
polymorphic species.

34 (26) Claws without pecten 35

35 (38) Ocellus present, though small.

Daphnia longispina (O. F. Miiller) 1785 . . 36
Spine long; claws without pecten. Male without long papilla on posterior part of body.
This species is so variable that almost no characters can be given for it. It is less robust than
the pulex forms, ordinarily fairly transparent; often hyaline. This part of the species divides
at once into 2 sections or subspecies, each with numerous varieties which have never been
thoroughly studied in the United States.

t).5 MM

Fig. 1068. Daphnia retrocurva.

f>^

Fig. 1069. Daphnia longispina. (See also Fig. 1050, p. 677.)

THE WATER FLEAS (CLADOCERA)

36 (37) Head not helmeted; eye close to margin. . Daplmii longispina profn-r

There are numerous varieties of D. lon^ispina pr()iH.T; <lciR-n<linK on i.rot».>rtion of v .1
The head may be large or small, its ventral marKin struiKht, com ave. or • onvcx Th.- ■
have a large pigment with few lenses embedded in it, or it may be small.r with nutn.
jecting lenses.

Found in all regions of the United States.

37 (36) Head helmeted and eye therefore removed from margin. lsu;illy

more dehcate and transparent than 36.

Daphnia longispimi var. hyalina Leydig 1H60.
D. longispina var. hyalina varies conspicuously and greatly in the form and sizt- of the irr»t
and of the ventral and dorsal margins of the head, which may be concave, convex, or slraixhl
with any form of crest. The crest may be small and rounded (var. hyalina lypica). cxtcmlcil
into a broad semi-elliptical form (form mendotac); more or les.s triangular, with an acute |Mjint
in front (form galeata); which may be extended into a short spine. .\n indehnitc numljcr ol
other forms are present, some of which have been studied and describe<l. but not namc«l by
Entemann. The form of the crest in specimens from any one lake is fairly uniform 'ihouxh
2 varieties may be present), changing with the season, being larger in summer than in s|>rinic.
Adjacent lakes may vary greatly. Deep water forms usually have ^mailer (rests than ihine
from the shallow surface water. All varieties found in open water of lakes, in all parts ol ihe
coimtry.

Figs. 1070, 107
38 (35) Ocellus absent

Daphnia longispina var. hyalina. A and B. form typica.
D, form galeata.

0.2 MM .

C. furni mcndolac.

head helmeted.

Daphnia loni^ispiiia var. lougircmis Sars 1S61.
Valves broadly oval; spine long and slender. Head small and rounde<I with crest, .\ntcnnac
very long, reaching well toward posterior margin of valves when rellexed. Lenut h. 9 • t" • ^ '"'p-
This is the only representative of the European cuculUita groui) as yet sc-cn in this count r>-. No
doubt other forms will be discovered. Indiana; Wisconsin, in deep water of lakes in soulhcro
part of state; in surface waters in northern part.

Fig. 1072. Daphnia loniircmis.

698

FRESH-WATER BIOLOGY

39 (25) Cervical sinus present. No crest 40

40 (45) Valves transversely striated. Post-abdomen broad, with indenta-

tion in which anus opens.

Siniocephalus Schoedler 1858 . , 41

Body large and heavy; shell thick. Head and rostrum small. Valves large, somewhat
quadrate, with rounded angles and sometimes a posterior spine; marked with oblique striae,
anastomosing irregularly and with cross-connections. Two abdominal processes developed,
placed far apart. Post-abdomen large, broad, truncate, posterior end emarginate and bear-
ing the anal spines. Claws rather straight, always denticulate, sometimes pectinate. Summer
eggs numerous; ephippium large, triangular, with one egg. Antennules of ^ like 9 but with
2 lateral sense-hairs. First foot without flagellum and with small hook. Poor swimmer; swims
often on its back. Color yellow to yellow brown.

41 (44) Vertex rounded, smooth. No posterior spine on valves 42

42 (43) Ocellus elongated. Vertex rounded over. Claws denticulate.

Simocephalus vetulus (O. F. Miiller) 1776.

Ocellus large, elongated, rarely rhom-
boidal. No spine on valves, though
there may be a blunt posterior angle.
Post-abdomen very broad, deeply
emarginate; anal spines about ten, de-
creasing from the claws; the larger
bent and ciliate at the base. Claws
long, slender, little curved, denticulate
only. Length, 9 > to 3.0 mm.; ^ , ca.
i.o mm.

Not very abundant, but found every-
where in weedy water.

Fig. 1073 •

0.1 MM

Simocephalus vetulus, with
ephippium.

43 (42) Ocellus rhomboidal or round. Vertex with obtuse or rounded angle.
Claws pectinate. . . Simocephalus exspinosus (Koch) 1841.

Valves much as in vetulus, but striae do not
anastomose so freely. Post-abdomen slightly
narrower toward apex; anal spines up to 12,
evenly curved, not bent; claws with pecten of
8-12 teeth and denticulate. Color and gen-
eral appearance much as preceding species.
Length, 9.t03.omm.; ^, to 1.3 mm.

Not common; reported from Massachu-
setts, Wisconsin, and the southern states.

Fig. 1074. Simocephalus exspinosus.

THE WATER FLEAS (CLADOCERA)

699

44(41) Vertex angulated spinous. Blunt, rounded posterior spine on
valves in old individuals. Ocellus rhomlx)idal or tri'inRuiar
rarely elongated. . . Simocephulus scrnUaius (KiKh} iSjii'

Anal spines 8-12, the larser l)cnt and ciliatr. (laws wnf, „„c
denticles. Color yellow or brownish. I^cnKth. 9 , 3.8- j o mm
$ , to 0.8 mm.

Common everywhere amonp weeds; the most abundant m>c-
cies. Very variable in outline of head.

Fig. 1075. Simoctphalus icrruUtuu

0.1 MM.

45 (40) Valves obscurely reticulated and with some striar. Posterior an<i

ventral margins straight, the latter extended into a \yo\i\\ or

spine Scapholcbcris Schocdlcr 1S58 . . 46

Body not compressed; shape more or less quadrate. Cervical sinus deep. F'omicrs and
rostrum well developed. Head small, depressed. Valves almost rectan^'ular. the infcro-
posteal angle of each produced into a longer or shorter spine; ventral margin with short, fmc
setae. Claws denticulate, not pectinate. One abdominal projection devclopc*!. .\ntcnnulc«
small, about alike in both sexes, borne behind the rostrum. .Summer eggs numerous; one
ephippial egg. $ much like 9 J hook on first foot.

46 (47) Color usually dark, often nearly black.

Scapholeberis mucronata (O. Y. MuUer) 1785.

Valves arched dorsally in old
specimens; fK)sti-rior and ven-
tral margins straight; at their
junction a spine often sh«jrt,
but often very long; in v«r.
armata Merrick as long as ven-
tral margin of valve, .\nten-
nules very small. almo!it im-
movable, set iK'hintI l>eak.
Post -abdomen short and broad.
rounded at i)i)sterior end; $-ii
anal teeth. U-ngth. 9 . 0.8-1 .0
mm.; $ . ca. 0.5 mm.

The form with frontal spine
has never In-cn foun<l in the
United .*>tates. Common ever)'-
where in pools and lakes in
weedy water, or swimming on
Fig. 1076. Scapholeberis mucronata. its back near or at the surface.

47 (46) Color whitish or greenish; transparent or opaque, not black.

Scaphohbcris iiuritii (Fischer) 1840.

Head larger than in mucrouata, rostrum long, lying ag.tinst
margin of valves, .\ntennules l)ehind rostrum, conical, large, and
movable; sense-hair about middle. Valves with blunt pn.jr. tion
at infero-posteal angle, ob.scurely striate and n-ticulate m (rxrtit.
and with small elevations elsewhere. U-ngth. 9 . ca 1 o mm ;

Not^ common; in weedy ix)ols and margins of lakes. Northern
states.

Fig. 1077. ScaphoUbcris aurito.

0.1 MM.

700 FRESH-WATER BIOLOGY

48 (24) No rostrum. Cervical sinus present. . . .

49

49 (65) Head small and depressed. Antennules small. Valves oval or
round. No post-anal extension of post-abdomen.

Ceriodaphnia Dana 1853 . . 50

General form rounded or oval; size small, rarely exceeding i mm. Vertex a rounded or angu-
lar projection, usually nearly filled by eye. Valves oval or round to subquadrate, usually
ending in a sharp dorsal angle or short spine. Antennules not very freely movable. One
abdominal process ordinarily developed. Post-abdomen of various forms, large. Ephippium
triangular, with one egg placed longitudinally. Antennules of ^ with long, stout seta, modi-
fication of flagellum; first foot with hook and long flagellum. Free swimming; motion
saltatory.

50 (51) Head with a short spine or horn.

Ceriodaphnia rigaudi Richard 1894.

Valves reticulated. Head produced in front of antennules into a
short, conical, sharp-pointed, hornlike process. Two abdominal proc-
esses. Post-abdomen with 5-6 anal spines. Claws smooth or den-
ticulate. Antennules rather slender; lateral sense-hair somewhat
distal to middle. Length of 9> 0.4-0.5 mm.; d (South American),
0.38 mm.

Pools; Louisiana, Texas.

The form with horn on vertex also is found in South America,
mingled with typical C. rigaudi. Probably both forms should be in-
cluded in C. cornuta Sars.

Fig. 1078. Ceriodaphnia rigaudi.

51 (50) Head without horn 52

52 (53) Claws pectinate Ceriodaphnia reticulata (Jurine) 1820.

Head obtusely, or not at all, angu-
lated in front of antennules. Valves
reticulated, ending in spine or angle.
Antennules small, with sense-hair near
apex. Anal spines 7-10. Claws with
pecten of 6-10 teeth and denticulate.
Color variable, shades of red and yel-
low. Length of 9. 0.6-1.4 mm.; of
$ , 0.4-0.8 mm.

Common, widely distributed.

Fig. 1079.

Ceriodaphnia reticulata, with
ephippium.

53 (52) Claws not pectinate 54

THE WATER FLEAS (CLADOCFRA)

701

54 (55) Head and valves strongly reticulated and covered with jk.
short spinules Ccriodaphnia ncuuthin.i R,,

General shape rotund with well-developed spine. Head much dc-prrssc*!, n.' .„

front of antennules or at vertex. Antennules short and thick with sc'iisc--hair'nr {.

abdomen narrow, much like quadrannula, with 7-0 anal spines. Claws dcnticulau . ..,,, ict

in the proximal two-fifths of the claw obviou.sly longer than ihc remainder. CoJor whjtith-
transparent to very dark. Length, 9. to i.o mm., $ unknown.

Manitoba, in weedy slough.

.p-¥

Fig. 1080. Ceriodaphnia acanthina. FiG. 1081. Details of vilve. much enlwiceil.

(54) Valves not spinulated 56

(57, 62) Post-abdomen abruptly cut into near apex, serrate alwvc,
spines below Ceriodaphnia mcgalops *><.v^ i>f>!

Head angulated before antennules; valves striatwl. Anten-
nules with sense-hair near apex. Post-alxlomcn J)n»a<i. with
an angle near apex, cut into below angle, limly x-rralr al«)ve
and with 7-9 slender anal spines be-low. (Maws not pectinate.
Length. 9. io-i-5 mm.; $ , 0.6-0.8 mm.

Widely distributed but not common.

Fig. 1082. Ceriodaphnia ttugalcps.

57 (56, 62)

58 (59)

Post-abdomen not cut into; of ordinary form.

;8

Fornices projecting into spinous processes. F^yc small.

Ceriodaphnia lamslris Birgc 1803

Head angulati^l in front <»f an-
tennule; vertex with t'inc spinulc*.
lornices very briKid. tri;ini:uUr;
with spines at tip. Valxt-^ with
stout, short pi»sterit»r sj>inc. Munr-
times divide*!, but ">i .IK «ith
^-4 s|)inules. Pt»st ..' ' •

Quadrjiigult}. ' U! 'f

yellow. trans|xircnl. i.<n(.'tn. V.
o.S-o.(; mm.

Wisconsin, Michigan; limnetic
in lakes.

Fig. 1083. CmodapkmU iauilni

702

FRESH-WATER BIOLOGY

59 (58) Fornices of ordinary form; eye large 60

60 (61) Head inflated in front of antennules. Small form not exceeding
0.7 mm Ceriodaphnia pulchella Sars 1862.

Form of ordinary type. Head rounded in front; inflated m
region behind eye, angulated in front of antennules Valves retic-
ulated but not plainly so. Post-abdomen not sinuate above anal
spines, which number 7-10. Length, ? , 0.4-0.7 mm.; cf, 05 mm.

Found among weeds and limnetic in lakes and in pools; reported
from all regions. Forms agreeing perfectly with this description
may be found, as also qiiadrangula forms, but other varieties occur
which are difficult to assign to either species, but which so closely
agree with them as to render it impossible to make a new species
Fig. 1084 Ceriodaphnia for them.

pulchella.

61 (60) Head angulated but not inflated in front of antennules. Length to

i.o mm. . . Ceriodaphnia qiiadrangula (O. F. Miiller) 1785.

General form like reticulata. Valves reticulated, often not plainly marked. Antennules
with lateral sense-hair near apex. Post-abdomen narrowing toward apex, often, but not always,
sinuate above anal spines; these number 7-9. Claws large, denticulate. $ antennules with
long flagellum, hook-Uke at tip. Color transparent to pinkish opaque. Length, V , to i.o
mm ; ^ , to 0.6 mm.

Common in all regions; found both among
weeds and limnetic. C scitida Herrick seems
to be a large variety of this species, 0.1 MM.

Figs. 1085, 1086. Ceriodaphnia quadrangula.

62 (56, 57) Post-abdomen very broad, obliquely truncate 63

63 (64) Vertex evenly rounded, without spines. Antennules moderate.

Ceriodaphnia laticaudata P. E. Miiller 1867.

General form round. Valves ventricose
below. Post-abdomen large, dilated near
middle, obHquely truncated and bearing
8-1 1 spines on lower margin. Claws long,
denticulate. Color transparent or opaque,
through red and red-brown to nearly black.
Length, 9 . to 1.0 mm., but not seen larger
than 0.7 mm. in United States; Z . to 0.7
mm.

Wisconsin and Minnesota to Florida, Lou-
isiana, and Texas.

This species is C. consors Birge.

Fig. 1087. Ceriodaphnia laticaudata.

aiMNT.

THE WATER ELEAS (CL ADOCKRa)

703

64 (63) Vertex angulated, with spines. Antennulcs long.

Ccriodaplinia rotunda Sars 1867.

General form much like prccedinR. Head anslcl at vcrtr.
with spmes Antennulcs lon^ and slender. I'ost al-i.- • ^
samewhat enlarged, hut not s(j much as in latuaudata t
toward apex, ohiKiuely truncate, with 7 o slender an.i
Color yellowish or brown, not transfiarent. IxrnKth ', • ,
i.o mm.; $ , to 0.6 mm. • ♦ •

Rare, Wisconsin. Both this species and the precetJinx live
among weeds.

Fig. 1088. Ceriodaphnia mlutula. (After Lilljcburjt )

65 (49) Head large and usually extended. Antennulcs larRc and fri-idy

movable. Post-abdomen with posl-anal extension. . 66

66 (67) Body compressed. Valves elliptical, crested dor.siiilv. C()mi)l»;ii-ly

covering body. Ocellus present. Fornix and atxlominal
process well developed. . . . Mohwdaplmia Herrick 18S7.
Cervical sinus present; no cervical gland. Valves tumid in posfero-dorsiil rrpion; crcsJed:
minute spines on ventral margin; sharp angle, not spine, at junction of durvil an.| venirai
margins; marked with oblique striae, usually invisible in preserved siH.-cimcn^ .\ntennulc»
attached on ventral surface of head, sense-hair about middle: olfactory set.ic small. One larjje
abdominal process, broad, concave in front, somewhat saddle-shajXHl, forming a transition to
the condition in Moina. Post-abdomen as in Moiua, with slender j)ost-anal projection l>earinx
about 10 finely ciliate spines and a much longer distal spine with 2 unequal pronKs. the biJrmi
(Fig. 1094). Claws denticulate. Summer eggs numerous. Male (.South .\merica) much like
Moina, with large curved antennules.

Only one certain species. . Moinodaphnia madcdyii (King) 1853.

Color yellowish, transparmt.
Length. 9. ^^- 'o ^^■

Louisiana. In weedy pcx>l«
and lakes.

Ilerrick's M. alabamrnsis is re
ported as larger (1.68 mm ) ami
may possibly be a different *pe
cies. Herrick had only Kinx's
very imperfect tles^ription for
comparist)n with hi-; form, .ind
his own description ' . 1-

ingly imiK-rfect. " >(

M . mdiUayii from I v 1

form identical wiiii ihai irom

0.1 MM. • ■ >- ' ' ' " -^ ^^"^ ^^'•^^"^

Fig. io8g. .\foimhiaphmj madtiyii.

67 (66) Body thick and heavy. Valves somewhat rhomlH)idal. not wholly
covering body. Fornix small. Ocellus absent. AMominal
process represented by horse-shoe shaped told.

Moina Haird 1S50 . . 68

Cervical sinus present. Valves thin, obscurely reticulated or striate<l; no ix.sterior Vi^nt.
Head large, thick, rounded in front; sometimes with (lee|) depres.sion alH)ve eye; no r. .strum.
Antennules long, spindle-shaped, freely movable; lateral sense-hair al)«)ut muldle .No regular
abdominal projection, but in old 9 a horse-shoe shaFx-d ridge which closes the briHMl-<aviiy.
Post-abdomen extended into conical post-anal part, bearing cihatol si.ines ami Indent i uw»
small; abdominal setae very long. Summer eggs numerous; ephippium oval, with i or 3 c«*.
Antennule of $ very long and stout, modified into clasping organ; denticulate, witti Miiaii
recurved hooks at apex. First foot with hook. .... , -n, ^ ^ t,

The species of Moina ordinarily inhabit muddy pools and similar placw. ITiey arc sclt-
bodied, weak creatures; liable to be much distorte.l by preserving llui.ls. I he spcoc* arc mucn
alike and often hard to distinguish unless $ and ephippial 9 arc present.

704

FRESH-WATER BIOLOGY

68 (69) Post-anal spines fewer than

Animal small, about 0.5 mm. long.

Moina micrura Kurz 1874.

Small, transparent; head relatively very
large; deep cervical sinus; supra-ocular de-
pression small or absent. Terminal portion
of post-abdomen small with 4-6 spines and a
much longer bident. Claws pectinate. Male
unknown. Length, 9 > 0.5-0.6 mm.

Illinois, Arkansas, Louisiana.

Fig. 1090. Moina micrura.

69 (68) Post-anal spines 8 or more. Animal larger, about i .0 mm. or more. . 70

70 (75) Supra-ocular depression present; claws pectinate; no fiagelliun on

first foot of male 71

71 (72) Two ephippial eggs; antennules of male with sense seta in middle.

Moina hrachiata (Jurine) 1820.

Body stout, heavy; greenish, not transparent. Head ordinarily much depressed, so that
vertex often lies almost on level of ventral margin of valves. Deep supra-ocular depression.
Valves faintly reticulated. Post-anal spines 7-1 1 besides bident; claws pectinate. Anten-
nules of $ with 4 hooks; first foot without flagellum. Length, 9 , to 1.5 mm.; ^ unknown in
United States. ,. ., , t 1

Wisconsin, Nebraska, Missouri; no doubt widely distributed. In pools.

0.2 MM. L

Fig. 1091. Moina hrachiata

72 (71) One ephippial egg.

73

THE WATER FLEAS (CLADOCERA)

73 (74)

Valves smooth;
middle:

ephippium reticulated around edges, smooth in
antennules of male with sense sc-ta near middle.

Moina rcctirostris (Loydig) i860.

Colorless, or with bluish cast. Head extended or liitic depressed- .!,.<. . .r. ;. .1 1

ocular depressions. Post-abdomen with long ' '

projection and 10-15 post-anal spines and C
bident. Claws pectinate. Antennules of $ '
with 5-6 hooks at apex. Length, V, 1.0-2.0 />

Widely distrih- ' N^
muddy

0.4-0.6 to i.o mm.

uted;

pools,

Fig. 1092. Male antennule. A, Moina rcctirostris. B, M. affinis
C, M. macrocopa.

0.1 MM. s—^
09^ Ephippium A \fmma
H.U jfimi,. ( . i/
{A an<lt .iflcT ISI\)9-

74 (73) Valves striate; ephippium reticulated all over; antennules of male
with sense seta near base. . . . Moitui affinis Birgc iSq\.

005 MM L

!7S3

Much like .\f . rcctirostris, from which the
young 9 ^re hardly distin>:uish;ihlf .\ntm-
nules of $ broad, frin^ri-d with lint- hair> »jo
inner margin; 4-0 h(H)ks at end. Ix-n^th. 9t
0.8-1.0 mm.; ^.o.s-o.Omm.

Wisconsin to Louisiana.

M. rcctirostris, affinis. and briukiiitii ha\*e
been often confused in faunal list.«i.

Fig. 1094. Moina affinis, apex «>f pml-abdomen.

75(70) No supra-ocular depression; claws not pectinate; antennules of male
with sense seta in middle or l)eK)\v; hrsl foot of male
with long flagellum. . Moifui ynacroiopii Straus i8.'o.

Not very transparent; yellowish or grernish. J! ' -• ■ r.\.
Terminal part of post-abdomen long, with 10- 1: <-*

bident. Two ephippial eggs. ^ with eK»ngatitl h. ^»

on antennule. Length, 9, to 1.8 mm:^ . o.s-<).f> mm.

Pools, Wisconsin, Nebra.ska, Colorado. N. Dakota: doubtlcM
widely distributed. , ,, a n . it

This species is M. paraJoxa Wcismann anil .1/. fl<igciUi<i liu-

dendorf.

Fig. loys Moina macro<.vpi.

0.2 MM.

7o6

FRESH-WATER BIOLOGY

76 (23, 83) Six pairs of feet. Antennules of female large, fixed. Intestine
simple; no ceca Family Bosminidae Sars . . 77

Body short and high often oval or round. Valves cover body and abdomen. Antennules
of 9 long, immovably fixed to head. No abdominal process or ocellus. Intestine without
convolutions or ceca. Animals small, rarely exceeding 0.5 mm.

77 (82) Antennules of female approximately parallel to each other, curving
backward, fixed to head; olfactory setae on side, usually
near base Bosmina Baird 1845 . . 78

Animal usually hyaline: valves thin; infero-posteal angle with spine — the miicro. Antennules
of 9 immovably fixed to head; olfactory setae on side, with small triangular plate above them;
distal position of antennules looks segmented. Antennae with 3- and4-jointed ramus. Post-
abdomen somewhat quadrate; anus terminal: spin.es small and inconspicuous; claws set on a
cylindrical process. ^ smaller than 9 > with short, blunt rostrum; large free antennules; hook
and long flagellum on first foot.

Little work has been done in this country on this very diflacult genus; but it is certain there
are not so many species nor so great an amount of variation here as in Europe.

78 (79)

Claws with two series of spinules.

Bosmina longirostris (O. F. Miiller) 1785.

Two series of spinules on
^ — :^--^— ^-.^ claws, the basal increasing

in length distally, contin-
ued by very fine denticles
to tip of claw. Frontal
sense-hair about midway
\ between eye and junction
of antennules. Antennules
:% moderate or short (var.
; . j| brevicornis) ; sometimes re-
% curved at apex (var. cor-
I nula). Transparent or
^^^ clear yellowish. Length, 9 -
■^^ 0.3-0.5 mm.; ^, 0.25-0.4
mm.

Very common and very
variable. In open water
of lakes, in weedy mar-
gins, in pools and marshes.

^

:;,^

X

<

0.1 MM. 4

Fig. 1096. Bosmina longirostris, typical specimen; p, post-abdomen more highly magnified.
Rostrum; a, var. cornuta: b, var. brevicornis.

79 (78) Claws with basal series of spinules only 80

THE WATER FLEAS U J..\l )( ki:r.\)

80 (8i) Mucro shorter than claws and process bearing I hem.

Bosmina uhlusiroslris Sars 1861.

Frontal sense-hair near junction of antennules. Antcnnuks shorter than Icnclh of v«lv«
bhell reticulated or smooth. Length, y, 0.3-0.5 mm.

In pools and lakes; not rare; very variabie.

U.

ft ^1

0.1 MM. ,

Figs. 1097, 1097, a. Bosmina obtusiroslris.

81 (80) Mucro longer than claws and process.

Bosmina loni^ispittii Ix*ydig i860.

Frontal scnsc-hair nt-ar juik tion of anttnnulc*.
Mucro and antennuks long. Shi-il >triatn!. marL*
especially plain un head. Tran.sjKircnt. lx-nx(h,
9 , ca. 0.4 mm.

Rare, in lakes.

Fig. 1098. Bosmirui I'ttct ptna.

Sole American species.

82 (77) Antennules united at base, and diverging at ape.\; numerous long
olfactory setae on their ventral side.

Bostfiiuopsis Richard 1895.

Bosminopsis deitcrsi Richard 18Q5.

In K'lniTd! muih like Bos-
mina. Has.ii jurt of anlm-
niili-s uniloi v^ith . n. h .thrr
and ht-atl to • fxiC

rostrum; diN> ''y

mar a|x"X. wi: r.. .-UC-

pling. olfai-tor>- srtac. Anten-
na with ^joint«-«! rnmi IN»*I-
alMl«)nun tai-* 'at

tiaws; I l.i: '*r

I laws and x '^^i'

luitc sninulfs .ni{iii»ir t>> it.
$ with larpi- mov.ihlc an-
tinnulcs; sh.>r* -><"•- Mrrt
fiH)t with hi> ' "tu

IxiiK'th. 9. *•' 'i'

o.JS nim.

Lake Charlcsand CalcMktt
^- . , River, La.

Fig. 1099. Bosminopsis Jcilcrsi.

7o8

FRESH-WATER BIOLOGY

83 (23, 76) Antennules of female long, freely movable, usually inserted at

anterior end of ventral surface of head. Rami of antennae
3- and 4-jointed. Intestine simple or convoluted. Hepatic
ceca usuaDy wanting. Five or six pairs of feet.

Family Maceothricidae Norman and Brady . . 84

Abdominal process usually absent; rarely present {Ilyocryptus). Feet 5 or 6 pai'rs the
first two prehensile; the last, if present, rudimentary. Post-abdomen marked off from body,
usually large, often bilobed; anus terminal or lateral. Labrura usually with keel or marked
projection. Valves often crested. Fornices well developed. . . , ,

The members of this family are so various in form that it is hard to find many common
character"^- yet the general appearance is always characteristic. The size and position of the
antennules will show the membership of every genus except Ilyocryptus; and there is no trouble
in recognizing that genus as belonging to the family.

84 (95) Intestine convoluted 85

85 (86) Valves with spine at supero-posteal angle.

Small hepatic ceca.

Ophryoxus Sars 1861.

Sole species Ophryoxus gracilis Sars 1861.

General form elongated, some-
what daphnid. Antennules long,
slender, fringed with numerous
hairs behind, lateral sense-hair
near base; olfactory setae vmequal.
Antennae long, weak. Six pairs of
feet. Post-abdomen long, taper-
ing at apex, anus dorsal, post-anal
portion large with numerous short,
blunt, cihated spines, the proximal
mere elevations bearing fine spi-
nules. Claws straight, with (usu-
ally) two stout basal spines. In-
testine with convolution in middle
of body; 2 small hepatic ceca.
Antennules of $ longer than 9 I
sense-hairs longer. Vasa deferen-
tia open on ventral (anterior) side
of post-abdomen about middle.
Strong hook on first foot. Color transparent, last foot often purple in old 9 • Length, 9 . to
2.0 mm.; ^,1.0 mm. , r i_i jji-

Widely distributed in lakes among weeds. Swims with constant but rather feeble paddhng
motion. Spine longer in young than adult.

86 (85) No such spine 87

0.1 MM. w._4

Fig. 1 100. Ophryoxus gracilis.

87 (92) Hepatic ceca present.

88 (89) Antennary setae 9 , ; ^ , 1 valves narrowed behmd and

• 0-0-3 1-1-3

prolonged into short tube. . Parophryoxus Doolittle 1909.
Sole species Parophryoxus tubulatus Doolittle 1909.

Form elongated oval; narrow crest on head and valves. Head rounded, rostrum well
marked; cervical sinus present. Valves thin, transparent; unmarked or faintly reticulated;
prolonged behind into a sort of tube, best seen from above; ventral margin with moderate
setae. Post-abdomen elongated, triangular; post-anal part long and slender, narrowed toward
apex somewhat as in Ophryoxus; bearing a few very small spines. Claws long, rather straight;
with 2 basal spines. Antennules cylindrical, slender; with basal sense-hair and three conspicu-
ously long olfactory setae. Antennae long, slender; basal joint annulated; setae not conspicu-
ously dissimilar. Feet, 6 pairs; the last rudimentary. Eye moderate, with few lenses; ocellus

THE WATER FLEAS (CLAUUC ERA)

lare;e, some distance from apex of rostrum. Intestine convolultfj wiili vtn.i,! lup,'
$ with hook on first foot; vas deferens opens near claws Length, ^ . \u 13 mm f«.lor

transparent-yellowish.

Maine. New Hampshire; among weeds in lakes. The diflcrtntc in unlinnary setae o( i and
9 holds for all specimens hitherto seen.

Q.2 MM.

Fig. iioi. Parophryoxus liibulatus. (,.\flcr lJ(.K)lililc.;

0-0-1-3

Strchloccrus Sars 1862

QO

(88) Setae "^ ^ ^ ^^ ; animal small, spherical.

Body round-oval, not compressed or crested. Labrum with larse, serrate, acute proco*.

Antennules large, flat, bent, or rather twisted, broadened in distal jxirf: with l.itrml vnsc-

hair near base, several hairs on posterior face, rows of fine hairs, and su! ■ • t.ir.

Post-abdomen bilobed; the pre-anal part compressed, semi-circular: ; icd,

with fine spines or hairs. Claws small, curved, with several equal mii. , u.n-

cave edge. Five pairs of feet. Intestine convoluted, with small hepatic tcva. ^ ^Lurupean,
of 5. serricaudatus) small, triangular, much like 9 ; tirst foot without hook.

90 (91) Dorsal margin of valves smooth.

Strchloccrus scrriaiudalus (Eischcr) 1849.

0.1 MM. ' Pre-anal part of po5t abtJo-

nun with serrate margin and
bearing rows of fine haira.
Anterior margin of anlennule
somewhat tiM»the<l ('ol«»r
whitish ojaquc to yellowish.
LitiKth, 9. «^'i 05 nim : $,
la. 0:5 mm.

Rare but widely distributol
in wetily yiooU .md mnrrin^ ol
lakes. Kep..: New

England. \Vi> -ka,

Louisiana l : >r-

nia.

91 (90) Valves reticulated, the edges of
ridges, which give
0.05 MMa

Fir.. iio->.

rfaiiu.

the reticulations making scalc-Ukc

the dorsal margin a scrrale apjH-arancc.

Strchloccrus pygnuuus Sars ux)i.

Pre-anal part of post -abdomen not serrate, with 4-5 ro^j
of fine hairs. Color grayish white, uixi.jue. to nearly Mac*
in enhinnial 9 . Z unknown. , / .i„

Len''th 9 o.2^.-'S mm. The smallest member of the

familv^and one of the smallest of the group -— '"

weedy pools, with 5. icrruaudaiui.

1-lG. lioj. atreUvccrui p>

yio

FRESH-WATER BIOLOGY

92 (87) No hepatic ceca; setae — ^— ^ 93

93 (94) Convolution of intestine in middle of body. Valves crested, with

strong tooth on crest Drepanothrix Sars 1861.

Sole species Drepanothrix dentata (Euren) 1861.

Valves reticulated; dorsal margin arched, crested, with conspicuous, short, backward-
pointing tooth about middle. Antennules broad, flat, twisted, though not so much as in
Streblocerus; post-abdomen compressed but not extended into a thin edge; almost quadrate
as seen from side. Margin with 2 rows of small spines, about 20, and with several rows of hairs
besides scattered groups; apex truncate, emarginate, with anus in depression. Claws short,
broad, crescentic, smooth, or denticulate; 5 pairs of feet. $ much like young 9 ; hook on first
foot; post-abdomen without spines; vasa deferentia open in front of claws. Color whitish to
yellowish; opaque or transparent. Length, 9> ca. 0.7 mm.; ^, ca. 0.4 mm. Not commonly
collected though widely distributed and probably not very rare in shallow waters of lakes, on
bottom or among weeds. Maine, Michigan, Wisconsin, Minnesota, Colorado.

0.1 MM. . I

Fig. 1 104. Drepanothrix dentata.

94 (93) Convolution of intestine in hind part of body and in post-abdomen.

No dorsal tooth Acantholeheris Lilljeborg 1853.

Sole species Acantholeheris curvirostris {0. F.MiiUer) 1776.

Form in general angu-
lar-oval, not compressed,
without crest. Posterior
margin of valves rounded
over into ventral, both
fringed with long, close-
set, plumose setae. La-
brum with long, slender,
conical process. Anten-
nules large, flat, somewhat
curved, expanded toward
apex. Post -abdomen large,
moderately broad, not
compressed or divided,
hairy, with 20 or more
small dorsal spines in each
row; anus terminal. Claws
short, stout, broad, curved,
denticulate, and with 2
small basal spines set side
by side. Six pairs of feet Intestine without ceca, convoluted, the loops lying in great part in
post-abdomen, $ resembling young 9 . antennules with 2 proximal sense-hairs; first foot
with small, inconspicuous hook, post-abdomen emarginate dorsally, vasa deferentia open
behind claws. Color yellow, not transparent. Length, 9 , to 1.8 mm.; $ , 0.5-0.7 mm.

In pools and margins of lakes among weeds, reported especially frequent in Sphagnum bogs.
Maine, Wisconsin, Louisiana; probably in all regions of the United States.

95 (84) Intestine simple 96

0.5-MM. »

Fig. 1105. Acantholeheris curvirostris.

THE WATER FLEAS (CLADOCERA)
96 (99) Hepatic ceca present; post-abdomen bilobed-

0-0-1-3
1-1-3

antennary scUi-

97 (98) Post-abdomen very large, with few spines. . Grimaldina Richard ,89.
^^^^ ^P^'^^^ GrimaUina hn.zzai Richard i8g..

Fig. 1 106. Grimaldina brazzai.

Body comprcs.scd. somewhat /mad-
ran^ular. with all m.i': ' Uc*

slightly convex. I'om .,„.

mous. much (omprcsv ; .^\.

elliptical in form; the pre aiul i-^rtioo
nivKJed |jy a notch into two jartv ol
which the anterior is the smallrr"- a
lonK spine in the notch which maris
junction of anal and pre anal (wrt* on
anal part two lateral rows of Miulj.
slender spines. aU)ut 7 in anterior.'
and 5 in rxjslerior row. Claws wnaJI
denticulate, with i .small hasal spine!
Ephippium roundtnl (j u a d r a n r u I a r:
CRR-chamhers rcniform with concave
sides toward each other. ^ (.South
America) small, like immature 9; an-
tennuleswith 2 ba.sal sense hairs; small
hook on first foot. Color rcrfdish-
brown. Length, 9 to og mm ; ^J .
0.5 mm. Louisiana; weedy prwb of
dear water.

98 (97) Post-abdomen moderate; numerous small spines on prc-anal part.

clusters of hairs on anal part. . . Whissicsid Daday iqov

Sole American species Wlassicsia kinistimnsis Ww^i.- \gio

Form ovaJ, not com-
pressed. Valves crrsled;
with spines on ventral mar-
gin; market! by vcr>- deli-
cate transverse striae which
anastomose, forminj: hne
vertical meslies Olfactory
setae subeijual. Two
rounde<| projct lions at base
of labrum on ventral sur-
face t>f heati. I^brum with
strong tonical projection
l^ointin^' backwanl and a
second f^rojcition just in
front of small terminal
lolx.'. I'ost aUlomcn with
line spines and hair> .\b-
dominal set .le ver>- lon^. not
set on projection Claws
with V e r >' small basal
spines live jwiirs of feet;
branchial sacs on all le«r&>

$ with large antennule; small keel on labrum; hook on first foot. Color yellow. Ixnicih,

9, 0.8 mm.; ^,0.4 mm. Marsh at Kinistino. Manitoba.

Fig. 1107. Wlassicsia kinistinemis.

99 (96) No hepatic ceca; post -abdomen various.

712

FRESH-WATER BIOLOGY

TOO (107, 116)

loi (102)

Antennary setae

0-0-0-s

1-1-3
Wide crest on dorsal margin of valves. Antennules at apex of
head. Post-abdomen bilobed, of moderate size.

Bunops Birge 1893.
Sole American species Bunops serricaudata (Daday) 1888.

General form rounded, much compressed;
high keel on dorsal side. Front of head flat,
somewhat kite-shaped, with boss or umbo
over eye. Strong triangular keel on la-
brum. Valves faintly reticulated, produced
behind into rounded projection; ventral
margin gaping in front, inflexed behind,
fringed with rather long straggUng hairs or
weak setae. Antennules with basal sense-
hair and two pairs of sense setae near apex;
olfactory setae somewhat unequal. Post-ab-
domen much like Strcblocerus; bilobed, pre-
anal portion flattened, semi-circular, with 7-8
notches or teeth on the dorsal margin and
3-4 rows of fine hairs; anal portion with fine
hairs and 3-4 spines. Color transparent,
tinged with yellow. ^ unknown. Length of
9 to i.o mm. Maine, Wisconsin; very local
in distribution, but not rare when present.

Fig. 1 108.

o \ MM. «

Bunops serricaudata.

102 (loi) Vertex of head forming sharp angle in front of insertion of anten-

nules. Dorsal crest of valves absent or small. Post-abdo-
men very large, with numerous long spines.

Ilyocryptus Sars 1861 . . 103
' General form oval-triangular, the head forming the apex of the triangle, while the enorm.ously
dilated ventral and posterior edges of the valves round into each other; these have long, close-
set fixed setae, usually branched and fringed. Antennules long, free y movable, 2-jomted,
basal joint very small, attached to ventral side of head behind vertex; olfactory setae unequal.
Antennae short, powerful; basal joint annulated nearly to apex; with long sense setae; motor
setae not plumose, smooth, or with sparse hairs. Abdommal process long, tongue-shaped,
hairy Post-abdomen large, broad, compressed; anus on side or near apex; many spines on
dorsal margin; numerous, long, curved, lateral spines and setae; fine spmulesnear base of
claws. Claws long, straight, denticulate, and with 2 slender basal spines. Intestine simple, no
ceca, but enlarged near rectum. Six pairs of feet. ^ with larger antennules than 9 , bearing
2 sense-hairs; no hook on first foot. ,. , ,. ^, ^- _i

In most species the old shells are not cast off in molting but overlie the youngest in several
layers The species live in mud, creep about among weeds, though they can and do swim;
are often greatly loaded with mud and vegetable growths, neariy concealing structure.

103 (106) Anus opening on dorsal margin of post-abdomen; molting imper-

fect 104

104 (105) Eight or more pre-anal spines; antennary setae short. _^

Ilyocryptus sordidus (Lieven) 1848.
Post-abdomen emarginate

0.1 MM

Ilyocryptus sordidus.

Fig. 1 1 09
Not very common but widely distributed in weeds on muddy bottoms

where anus opens; 8-14 pre-
anal marginal spines; lateral
post-anal spines about 8-10;
marginal row of nvimerous
smaller spines. Ocellus
nearer base of antennule than
eye. Six to eight summer
eggs.

Color red, but often so
loaded with debris as to be
opaque. Length, 9» ca. i.o
mm., $ , 0.42 mm.

THE WATER FLEAS (CLADOCKRA) 7,^

105 (104) Five to seven prc-anal spines; anlennary setae ordinarily ver>' long.

Ilyocryptus spin if cr Il'errick 1884.

:^'W

Anus (.|K>ns in (lrpre\>ion oo
florsal margin of p(>%( al4<iontm;
<; 7 pre anal spinps; 4 8 |)i>s( aiul
lateral spines in ..:■ - - \n

tt-nnary st-tar us»i.
timi's cqualint' Ir • , ^

in s<inu- sjxi : rt.

apparently \>< .-ht

til tt-n siimrii' : _ ip.

Ilium fiitrnvil ami r^)

$ unknown Cot ■.tl-

(iish. Length. 9. •

This siK-rics is / ir»;

/. halyi Uraiiy. N • .'.n;

Maine to Lake Suixriur an«! (.ulj
of Mexico l'rol»alily in .ill rriouns
of United States.

FiC. 1 1 10. IlyocrypiHi ipinifn.

106 (103) Anus at end of post-abdomen; molting complete.

Ilyocryplus cicNlifrons SaTS i86i.

0.1 MM

Fig. nil. Ilyocryptus acutifrons.

Post-abdomen not emar^i: '8

small spines near claws, shor' iw;

about () lonp, curved, lateral ; f 8

marginal spines corresponding lo pre auaJ^ of
other species; the proximal two dirrttoJ for-
ward; from distal spine of this st-t a <(cric» of
vcr>' small marginals to anus, .\ntcnnulc club-
shaped, hairy. Ocellus nearer eye than inser-
tion of antennules. ("laws as in /. JorJiJui
Three to four summer eggs. S unknown
Color reddish or yellowish. I.trik'th. 9 f^-
0.7 mm.

Rhode Island, Colorado

107 (100, 116) Antennary setae

0-0-1-3
1-1-3

basal seta of 3-jointed ramus slout

and stiff iU(/(-r(j///r/.v Haird 1843

108

Shape oval or rotund, somewhat compressed, with dorsal crest. Hca.l large, onlinarily noC
depressed; vertex evenly or abruptly rounded; rostrum short. \^'"!^^'' ."^•■»'^'" "f.^; '^
ordinarily with long, stout, movable spines, which project in sc-yeral «i'rfvttons^ „" ^^TT
large; lateral sense hair near base. Antennae large; the proxmial sc-ta of ., jo.n cjl n»mu. onj.
stiff, and spinous; the others sparsely plumose or partly spmous. Hvc i;'"7; \"< " •;;*''•
dominal process. Post-abdomen large; often bilobed. ( laws small. InteMme s„npl. .>.. . .xa
$ with large antennules; hook on first foot.

108 (115) Dorsal margin of head evenly roundeil.

109 (114) Head extended; rostrum far from m
enlarged near distal end.

irgin of valves, .\nlcnnulc5
110

714

FRESH-WATER BIOLOGY

no (hi) Post-abdomen not bilobed. . M acrothrix laticornis (Junne) 1S20.

Fig.

t2. Macrothrix laticornis.

Form round-ovate. Valves crested,
the dorsal edge serrate with fine teeth.
Head evenly rounded. Labrum with
large triangular process. Antennule
broader distally; a setiferous projec-
tion on posterior margin near apex;
anterior margin with several fine in-
cisions and clusters or rows of hairs;
olfactory setae conspicuously unequal.
Post-abdomen with numerous fine
spines and hairs; anus terminal.
Claws small. Color grayish white or
yellowish. Length, 9. 0-5-o-7 mm.;
$ , 0.3-0.4 mm.

Widely distributed; found in all
parts of the country but nowhere very
abundant.

Ill (iio) Post-abdomen bilobed ■. 112

112 (113) Conspicuous fold or folds of shell of head at cervical sinus.

Macrothrix montana Birge 1904.

Form ovoid. Head large; dorsal margin evenly rounded;
the shell extended into collar-like folds in front of cervical
sinus. Antennules stout, large, enlarged near apex, about 6
anterior cross-rows of hairs, and 3-4 stouter posterior setae;
olfactory setae unequal. Post-abdomen bilobed. Claws hardly
larger than spines. Color transparent, in preserved speci-
mens. $ unknown. Length, 9 . ca. 0.55 mm.

Colorado.

Fig. 1 1 13. Macrothrix montana.

113 (112) No such folds. Macrothrix hirsuticornis Norman and Brady 1867.

Form broadly ovate, not very different from M. laticornis.
Antennules broad, flat, bent, varying in form but always enlarged
distally; with 6-8 rows of stiff hairs on anterior side; sometimes
stout setae on posterior side; olfactory setae unequal. Post-abdo-
men large, broad, bilobed; pre-anal part not flattened nor with
projection for abdominal setae; numerous small spines and hairs
on both anal and pre-anal parts. $ unknown. Length, 9 . o-55
mm.

New England, Colorado.

Fig. 1 1 14. Macrothrix hirsuticornis.

THE WATER FLEAS (CLADOCERA)

Antcn-

114(109) Head much depressed; rostrum close to margin of valves,
nules slender, not enlarged near distal end.

Macrotltrix borysthcnica Malilc 1890

Dorsal marKin of heafi evenly roun<ic*l o\<r int.. »V...f •
valves without sinus. Front of lu-a<l rem r -.^

trum is very close to valves. Antennule^ . xl

tered tine hairs; olfactory setae small. e<jual ; . .wjcn

elongated, bilobed; with numerous fjne spinulcn an<l hain
on both lobes. Claws .small. Kye m«»<lcratc; o<rllu» at
rostrum. Color transparent Length. 9. '" « « mm.

Albuquerque, New Mexico (Herrick;

Fig.

Macrothrix horystheniiii. (.\fter Matile.)

115 (108) Dorsal margin of head curved abruptly in front of eye. .Antennuk-s
slender Macrothrix rosea (Jurinc) i8io.

Form broadly ovate. Valves reticulated, crested, not serrate. Head large; its (lorsal mar-
gin rounding over abruptly into anterior margin. Antennulcs long, slender, not enlarRnl near
apex; lateral sense-hair near base on small elevation; olfactor\' setae une(|ual. ro>t-aU)iimm
extended into blunt process, on which abdominal setae are borne; pre-anal jurt >*-mi clli(»tical.
with numerous spinules along convex edge and many fine hairs: anal jKirt with st- veral sfnall
spines. Claws small, smooth. Summer eggs numerous; ephippium well <level()|)e<l. with ; ciar»-
Antennules of $ long, curved. Post-abdomen terminating in long, lleshy pri>jtvti<>n oq
which the vasa deferentia open. Hook of first foot serrate at tip Color tran>i»rrnl to
yellowish or sometimes a ruddy tinge. Length, 9. ca. 0.7 mm.; $, 0.4 mm. Common
everywhere in marshy pools and margins of lakes.

M. tenuicornis Kurz is a variety of this species All ^ $ found in .\merica a^rcc with M.
elegans Sars.

0.1 MM I

Fig. 1 1 16. Macrothrix rosea.

7i6

FRESH-WATER BIOLOGY

ii6 (loo, 107) Antennary setae ; all similar and plumose.

^ 1-1-3

Lathonura Lilljeborg 1853.

Sole species Lathonura rectirostris (0. F. Mliller) 1785.

General form long-oval, not com-
pressed. Valves unmarked; the
ventral margin with short, close-set,
smooth, lancet-shaped, or spatulate
spines. Antennules straight, with
sense-hair near base; 2 pairs of sense
setae in distal half. Post-abdomen
very small, extended behind into a
long conical process, which bears the
very long abdominal setae; covered
with fine spines and setae. Claws
small, smooth, or denticulate. Sum-
mer eggs, 2 to 10; I ephippial egg.
$ like young 9 . with larger anten-
nules; 2 lateral sense-hairs, the addi-
tional one — the distal — the larger;
olfactory setae longer. First foot
with hook. Vas deferens opens at
claws. Color transparent to clear
yellow or greenish. Length, 9 > to
i.o mm.; $ , ca. 0.5 mm.

Widely distributed in weedy mar-
gins of lakes but nowhere common.

Fig. 1 1 17. Lathonura rectirostris.

117 (22) Fornices extended so as to cover antennules in whole or in part, and
uniting with the rostrum into a beak, projecting ventrally in
front of antennules. . Family Chydoridae Stebbing . . 118

0-1-3

Antennae small, rami 3- jointed; setae =^ or ^ . Labrum with large keel. Five or six

0-0-3 0-0-3 J . . ,

pairs of feet. No true abdominal process or ephippium. Post-abdomen compressed, jointed to
body. Intestine convoluted. Ocellus always present. $ with hook on first foot; large anten-
nule; short rostrum.

118 (119) Anus terminal. 2 hepatic ceca. Summer and ephippial eggs
numerous Subfamily Eurycercinae Kurz.

Sole genus Eurycercus Baird 1843.

THE WATER FLEAS (CLADOCKR

\)

»7

Only one American species.

Euryccrcus lanidlatus (U. V. Muilcr; 1-81

Body stout, heavy. i'oM alxlomm vit>- Urir«.
flattened, general form (|ua<lraiiK'ular; aruis t«-nnin*l.
in depression; (l<)rs.il niarK'in. with \.r\ : .:;i.r<>u»
— over 100 — saw like ti-fth. C'lav. • m*

projection, with 2 basal spines and <: Sit

pairs of feet. Inte.stine with hejxaii. . • . .1 .... 1 ii^j-
volution. $ Uke yoiuiK 9 ; h.x.k on tir>t fcit; v%%
deferens opens at base of tlaw on ventral (anterior)
side. Color yeliowish-hrown. oia(iue. Ix-nKth, 9.
to 3.0 mm. or more; ^ . to 1.4 mm. '1'he Luxcst
member of the family. Found ever>-where; in ijcr-
manent pools or margins of lakes among weeds.

Fig. 1 1 18. Eurycercus lameUdJiu. Poa-.M^iumrn.

119 (118) Anus on dorsal side of post-abdomen, whose post-anal portion l)cars
denticles. No hepatic ceca. Two siminiiT eggs; one
ephippial egg. $ with strong hook on first fixjt.

Subfamily Chydorin.\e . . 120

120(247) Eye present i.'«

121 (246) Eye and ocellus of ordinary size; antennulcs do not [)rojccl Ix^yond

rostrum, though olfactory setae may 122

122 (171) Posterior margin of valves not greatly less than ma.ximum height, i:^

No species of Pleuroxus belong in this section, though s«)me individuals of lys and iw m.»y
seem to do so.

123 (135) Body compressed; claws with secondary tooth in middle.

124(129,132) Crested; post-abdomen narrow,' with marginal and Liicral

denticles '^S

1 Terms denoting relative size are to be unclcrstcHHJ with reference to llic s*-clit)n in
which they occur.

7i8

FRESH-WATER BIOLOGY

125(128) Crest on head and valves. . Camptocercus Baird i&A3 • • 126
Form oval- greatly compressed, with crest on head and back. Valves with angles rounded;
small teeth at infero-po steal angle; longitudinally striated. Post-abdomen very long, slender,
with numerous marginal denticles and lateral squamae. Claws long,_ straight, with i basal
spine; a series of small denticles, terminating in a larger one about the middle of claw; extremely
fine teeth thence to apex. Five pairs of feet.

126 (127) Post-abdomen with 15-17 marginal denticles.

Camptocercus rectirostris Schoedler 1862.

Head extended or de-
pressed. ^ without
denticles on post-abdo-
men. Color yellow-
transparent. Length,
9 , to i.o mm.

Common everywhere
among weeds in mar-
gins of lakes, etc. Most
of the specimens from
the United States are of
the variety biserratus.

Fig. 1119. Camptocercus
0.1 MM. h ' rectirostris.

127 (126) Post-abdomen with 20-30 marginal denticles.

Camptocercus macrurus (O. F. Miiller) 1785.
Much Uke the preceding. Very rare, but reported from most regions in the United States.
Undoubtedly the preceding species has been mistaken for this by some observers.

128 (125) Crest on valves only. . Kurzia Dybowski and Grochowski 1894.

This genus is Alonopsis (part) of older authors; Pseudalona Sars.
Sole American species Kurzia latissima (Kurz) 1874.

General form subquadrate;
greatly compressed; but with only
slight crest on back, none on head.
Head small, the rostrum reaching
not much below middle of valves,
though longer than antennules.
Post-abdomen long, slender;
lower angle usually produced into
a lobe; 10-12 marginal denticles.
Claws of Camptocercus type. J
like 9 ; rostrum shorter; post-
abdomen with small denticles; vas
deferens opens on ventral (upper)
side; strong hook on first foot.
Color yellowish, transparent.
Length, 9> o-6 mni.; $ , 0.4 mm.

Found in all regions among
weeds in pools or lakes.

Fig. II 20. Kurzia latissima.

129 (124, 132) Crest on head and valves; post-abdomen broad, without
marginal denticles. . . . Acroperus Baird 1843 . . 130
Body thin, compressed; crest on head and back. Valves subquadrate, obliquely striated;
infero-posteal angle rounded or acute, usually with teeth. Post-abdomen large compressed;
without marginal denticles but with lateral row of squamae. Claws long, straight, with i basal
spine and secondary denticles, much as in Camptocercus. Intestine with large intestinal cecum.
Eye larger than ocellus. Color yellow-transparent.

THE WATER FLEAS (CLADOCI-RA) jic,

130(131) Dorsal margin much arched Irn'/>rra5 /wrp.;, Baird 1H35

Eye anfl ocellus m-ar niarKin ko»-
trum acute. Kleven lo twelve fcruufn o(
fine spinules on {tost-alMlomen. l^m^h.
9. to o.S mm.; ^ . to 00 mm

Common ever>where. amoni; »c*t|»,
ill relatively oinrn water; not in muddy

IKJOIS.

u;. 1 121. Acrop<rui hjrpct.

0.1 MM.

131 (130) Dorsal and ventral margins nearly straight.

Acropcriis angiistiitus Sars 1863.

Crest larger than in A . harpar; eye and
ocellus removed from margin and rostrum
obtuse. Length, 9. to o.g mm; ^. 0.6
mm.

Common in similar situations to prctc*!-
ing species. Transition forms l)etwem these
species may be found and ver>" prolxibly
they should be united.

Fig. 1 1 22. Acroprrui jnKuiliiJui

0.1 MM. I «

r32 (124, 129) No crest 133

^33 (134) Valves not tumid; post-abdomen broad.

Alonopsis Sars 1S62

/T'i

tii^

General form resembling Acroprrus but less com-
pressed and without crest. Keel of InSnim m^w'^mtr
or small, almost triangular. Vahi - I

but striae often inconspicuous. 1
broad; with well-develoix^i mar,: \

pairs of feet, the last very small. S **'ii' "*"*'
characters. Color yellow.

Fig 1123. a, Alonopsis flonfala: h. AUfmoptii

(MU'T n.v.littic

0.1 MM.

J 0.1 MM.

133^^(133^) 15-17 marginal denticles [hmo psis chn^ata Surs i^i.

Minute tooth at infero-posteal angle of valves. Post-abdomen with lateral f.^. i. I- Im.Mh.
9 , ca. 0.8 mm.
1336(133^0 About II marginal denticles. . Alonopsis aurcohi IhKAiiiki.i:.

No lateral fascicles or infero-posteal tooth. Ix-ngth, 9 ^■'^- '/^ TI^.^MinT*""" ^^
species in margins of lakes and ponds among weeds. Rare; rei)ortcd only from Maine

720

FRESH-WATER BIOLOGY

134 (133) Valves tumid in anterior part; post-abdomen narrow.

Euryalona Sars 1901.
Sole American species Euryalona occidentalis Sars 1901.

Euryalona occidentalis Sars.

General form resem-
bling Kurzia, but less
compressed; no crest.
Valves gaping in front,
tumid in infero-ante-
rior region; marked
obscurely with concen-
tric lines; dorsal mar-
gin arched. Keel of
labrum angled behind
but not prolonged.
Post-abdomen very
long, slender, lobed at
apex; with about 20
marginal and very fine
lateral denticles.
Claws straight, armed
about as in Campto-
Z with strong hook; vas deferens opens on
Color dark brown-yellow. Length, 9 . to

cercus. Five pairs of feet; hook on first foot of 9 •
upper (ventral) side of post-abdomen about middle,
i.o mm.; '$ 0.7 mm- . , , , , ,

Florida, Louisiana, Texas; not uncommon m weedy pools and lakes.

135 (123) Body not greatly compressed; claws with i basal spine, or rarely

none 13^

For all species with two spines on terminal claw, see 171 Q.

136 (168) Rostrum not greatly exceeding antennnles i37

137 (167) Rostrum pointed 138

138 (150) Infero-posteal angle rounded, without teeth 139

139 (144, 147) Post-abdomen with marginal and lateral denticles.

140

140(143) Post-abdomen relatively long and narrow; marginal . denticles
numerous, longer distally. Basal spine stout and long.

Oxyurella Dybowski and Grochowski 1894 . . 141

In general like Alona. Post-abdomen long, slender; with marginal and lateral denticles,
the former numerous and ending in a group of large denticles at angle of post-abdomen. Termi-
nal claw straight, with one large basal spine, attached some way distal to base of claw. Color
yellow or yellow-brown. This genus is the same as Odontalona Birge.

141 (142) 12-15 marginal denticles.

Oxyurella tenuicaudis (Sars) 1862.

Marginal denticles very small near anus;
the distal 4-5 much larger; the penulti-
mate largest. Length, 9, ca. 0.5 mm.;
$ , 0.4 mm.

Widely distributed but not abundant
anywhere. New England and Wisconsin
to Gulf of Mexico. This species is Alona
tenuicaudis Sars.

Fig. 1 1 25. Oxyurella tenuicaudis. Apex of
post-abdomen. (See also Fig. 1129, b.)

THE WATER FLEAS (CLADOCERA)

721

(141)

About 16 marginal denticles.

Oxyurclla longUaudis (Birgc) igio.

Between Alona and f .' '
Valves with conccntrii :
marginal dentiiles. lar^ •
nullimate much larger, an.:
larKer still and serrate on

Basal spine stout, attai lutl aL....; .,.,, .

way from base- of daw. ^ unknown
Length, 9 . 0.5-0.6 mm.

Rather rare amon^ wec<ls. Lake CliArlcs.
La.

Fig. 1 1 26. OxyurtlU Umtuaitdn.

143 (140) Post-abdomen not noticeably narrow; distal denticles not conspicu-

ously larger. Basal spine small. Alomj{miJsis\H:ck-s) . . 151
Take up the key at the number indicated where the genus is discussed a^ a unit.

144 (139, 147) Post-abdomen with marginal denticles only. ... ; ;

145(146) Post-abdomen large, denticles very small. Alondladiaphdr.i
Turn to the key at the number indicated where the species named is discu.sscd.

146 (145) Post-abdomen of moderate size; denticles of usual size.

Alona guttuUi
Turn to the key at the number indicated where the species named is discussed.

147 (139, 144) Post-abdomen with numerous clusters of large spines.

Lcydigia Kurz 1874
General shape oval, much compressed but not crested. Head small, extendcl; V-' •'
labrum rhomboidal with angles blunt or rounded. Post-abdomen very large, com; •
semi-elliptical in form; post-anal part much expanded, with numerous clusters of
spines in distal clusters very long. Claws long and slender. Kye smaller than wcIIun (J
with blunt rostrum; process on upper (ventral) side of post-abdomen on which vas deferens
opens; post-abdomen with spines. Color yellow.

148 (149) Valves without markings. Leydigia quadrangular is (Lcydig) i860.
Keel of labrum with minute setae. Claws with basal spine. Length. 9 • to 0.9 mm ; '

0.7 mm.

In all regions of the country; not common; found singly among weeds.

149 (148) Valves striated longitudinally.

Leydigia acanthoccrcoidcs (Fischer) 1854.

Keel of labrum with long cilia. Claws without basal spine. Length. 9 1 to 10 dmu. or more;

d (European), 0.7 mm.
Rare: Louisiana.

I^O

148

0.2 MM.

Fig. 1 1 2 7 Leydigia acatUkocercoides.

722

FRESH-WATER BIOLOGY

150 (138) Infero-posteal angle rounded, with small tooth or teeth.

151

151(166) Valves with longitudinal striae. . . . yl/awa Baird 1850 . . 152
General form subquadrate; compressed, not crested. Valve with supero-posteal angle
rounded or well marked; infero-posteal angle rounded, almost always without teeth. Fornices
broad; rostrum short and blunt, little exceeding the apex of the antennules. Antennules
short, thick; olfactory setae equal. Keel of labrum large, ordinarily rounded; the posterior
angle not acuminate. Feet, 5 pairs, rarely 6; the 6th, if present, rudimentary. Post-abdomen
broad, compressed, with various armature. Claws with i basal spine and denticulate. Color
yellow in some shade, varying from light to dark, with shade of brown in large species. All
species littoral.

152 (153) Infero-posteal angle with 1-3 small teeth.

Alona monacantha Sars 1901.

In general form and appearance not unlike A .
intermedia. Valves distinctly striated; infero-
posteal angle rounded and with 1-3 small teeth.
Post-abdomen with g-io denticles; claws with
very long basal spine. Keel of labrum angled
behind. Length, 9 > o-35~0-4 nirn.

This species may be confused with Alonella
karua (232). The length of the basal spine on
terminal claw offers a ready distinction.

Louisiana; in weedy pools.

Fig. 1 1 28. Alona monacantha.

0.1 MM

153 (152) Infero-posteal angle unarmed i54

154 (155) Post-abdomen long, narrow; distal marginal denticles very long.

See Oxyurella . . 140

155 (154) Post-abdomen not notably long 156

156 (157) Post-abdomen with marginal denticles only.

Alona guttata Sars 1862.

Form much hke A. costata, but usually smaller and dorsal margin less arched. Valves
smooth, striate, or tuberculate (var. tuberciilata Kurz). Post-abdomen short, broad, shghtly
tapering toward apex; truncate, angled, with longest marginal denticles at angle; denticles
8-10, pointed, small; no squamae. Claws with small basal spine. Post-abdomen of d without
spines; vas deferens opens behind claws, without any projection. Length, ?, ca. 0.4 mm.;
^ , 0.3-0.35 mm. See Fig. 11 29, d.

Not uncommon everywhere.

Fig. 1 1 29. a, Alona quadrangularis; b, Oxyurella ienuicaudis; c, Alona costata; d, Alona guttata; e, Alona
rectangula; f, Alona rectangula var. pulchra; g, Alona intermedia.
These figures are not drawn to the same scale.

THE WATER FLEAS (CLADOCERA)

157 (156) With marginal and lateral denticles

158 (161) Size large; 14 or more marginal (kninK:-.

159 (160) Cluster of fine spinules at base of claw.

723

^■S\^<.

■•^^.-,'r^'C-^-J

0.1 MM.

Mouii ajjinis (U-ydig) i860.

Greatest hi-i^ht usually near ti.i.lflr
valves. \'alvcs IcmKituMinally •
ticulatod, often not plainly miir.
with rhomboidal keel; its torn. •
lated, sometimes n)un(lc<J. i
large, not widened behind ant;
serrate marginal dentitl«-s an' I
of small S(iuamaf. Claws Ion,
with long ba.sal spine and 45 ;

r;

mentary. Length, 9. t" « o mm.; ^ . to 0.7
mm.

The largest species of the gcnuA; very abun-
dant in all regions, in maririn of jinnd* and
lakes, among weeds.

Fig 1130. Alotui r-,nf

160 (159) No spinules at base of claws.

Alona quddrangularis {O. V . Miiilcr) 1785.

Greatest height usually posterior to middle of valves. Valves usually plainly striated.
sometimes conspicuously so, with a reticulated area in infero-anterior region (var. /<-/>iJu Hirifr).
Labrum with large keel of variable form; often quadrate or with rounder! angles. Post aWo-
men large, flattened, dorsal margin dilated; with 15-18 serrate marginal denticles and row o(
lateral squamae. Claws large, with long basal spine; no spinules on inside of basal ^%T^e.
Length, 9. to 0.9 mm.; <? , to 0.6 mm. See Fig. 1129, a. In similar KKalitii's to prrcnlinjc
species; also on bottom of open water.

161(158) Size moderate or small. Fewer than 14 denticles.

This section of the genus needs much additional study. There are s|K'iics .md numerous
varieties beside those listed.

162 (163) Lateral fascicles or squamae do not extend beyond dorsal marpin
of post-abdomen ^loun costatu Sars iSO:.

Evenly arched or greatest height behind middle; posterior margin ranvcx. Valve* «ri*ted
or smooth. Post-abdomen short, broad; with straight dorsiil (lower) manan tapenng toward
apex; with about 12 subequal denticles and a row of fine squamae. rost-alMl.>mcn of J taper-
ing; no marginal denticles; very fme squamae; vas deferens ojK-ns at
extending out ventral to (above) claws; claws without basal spme. I
more; ^ , 0.4 mm. See Fig. 11 29, c.

Found everywhere and very abundant.

163(162) Lateral fascicles long, extending beyond dorsal ma r^nn. if*;

164 (165) Post-abdomen not broadened toward ape.\.

AloHii rcctiin'^-M.i :

Body evenly arched; general form like A. guttata. Valves striate*!, rrtin.l.ntcl.
rarely tuberculate; ventral margin usually somewhat a'"vex 1' ■;
enlarged toward apex, angle rounded; with 8-0 marginal ( enticles or
as many fascicles, the distal long enough to project beyond margin *'' i
without cecum, enlarged at junction of intestine and rectum. s*.incwh.ti a-s .»
Length, 9, 0.35 to 0.42 mm. See Fig. 1129, c. /. x ; t. . ii..ii:rK

Common everywhere. Most specimens found belong to var. puUHra nciuai.

\\itx of pfucrsa
ngth. 9.05 nim or

' '-ly

it

■ uc

724

FRESH-WATER BIOLOGY

165 (164) Post-abdomen broader toward apex. Alona intermedia Sars 1862.

Body evenly arched but not very high. Post-abdomen
. long, broad, enlarged toward apex, with rounded angle; the

^ ^^ 8-9 marginal denticles rather small and thick; the lateral

denticles or fascicles much more conspicuous, consisting of
bundles of fine setae. The distal seta in each bundle is the
largest and the size of setae increases toward apex of post-
abdomen. The distal bundles {project beyond margin of
post-abdomen. Length, 9- ca. 0.4 mm. See Fig. 11 29, g.
Rare; specimens closely agreeing with Lilljeborg's descrip-
O I MM I tion and figures found in Wisconsin. Possibly not Sars' inter-

' media, as his figure of that species resembles some varieties

Fig. 1 13 1. Alona intermedia. of Lilljeborg's rectangula.

166(151) With oblique striae Alonella karua . . 232

Turn to the key at the number indicated where the species named is discussed.

167 (137) Rostrum broad, semicircular Graptoleberis Sars 1863.

Sole species Graptoleberis testudinaria (Fischer) 1848.

__^^^^>.jytu.-anm.<uB tim,,^,^,^^ Posterior margin with 2 strong teeth at

^^^ ^ ' ^^.7^-^^^**^%^ infero-posteal angle; valves and head with

y'"^ "~ <*" '^ ^^^Ssv conspicuous reticulation. Head large;

j^ " j::^ \^bv fornix very broad, forming a semicircular

M^, . , - •■ '^^^ rostrum, covering antennules and extend-

y^' ' " • " ^ ^"-"^-^ ^^^ down as far as ventral margin of

£/^ . ,^«=^j, "^4 valves. Post-abdomen bent at the sharp

ff^^ K ■^-»s?^?l'^^-^W \ pre-anal angle; tapered toward claws, so

/'Q^^^j-'^ '~ :.^ ' jz^~ ^ that form is nearly triangular; marginal

^^^'^ y *^ ^ V^ spines small; lateral fascicles minute, some-

^ V^Ll , -^ ^ ^ JJ,^'-^ times wanting. Claws small, with i mi-

TS^\r\™\^\tHWN\rTn^\^^^'^ ^n ^"^^ ^^s^' SP'^^' sometimes wanting (var.

\WM\ ,m\i#W \\ \^\^^\^ ^^ N.-^ ^-^^^^.^ Bjrgg). ^ ^j^i^ iQj^g^ gignder post-

0.1 MM- - \ ii abdomen, without spines; vas deferens

Fig. 1 132. Graptoleberis testudinaria. opens on ventral side; claws very minute;

hook of first foot slender.
Color gray to yellow-white; sometimes opaque. Length, 9- o-5-o.7 mm.; J, 0.5 mm. or
less.

Common among weeds or on bottom of pools and margin of lakes.

168 (136) Rostrum considerably exceeding antennules 169

169 (170) Post-abdomen with marginal denticles only. Alonella. . 240, 241
Turn to the key at the nimibers indicated where two species are discussed.

170 (169) Two to four marginal denticles; long series of lateral denticles.

Rostrum very long, recurved. . . Rhynchotalona Norman 1903.
Sole species Rhynchotalona falcata (Sslts) 1861.

General form of body like Alona. Ros-

^ ^ trum very long, slender, and recurved

under the head. Post-abdomen stout,

thick, bent at anus, truncate at apex;

with about four rather stout marginal

tf#7 -/ -" iV ^\ denticles near apex, and a lateral series,

^-^^'^' '^ - *\ continued nearly to anus, of very fine

spinules in an unbroken row. Intestine
with cecum. $ (European) with long
rostrum, bilobed at apex; post-abdomen
tapering and armed with hairs only; ordi-
nary hook on first foot. Color yellow or
0.1 MM. - greenish. Length, 9 , 0.5 nmi.; ^ ,0.4 mm.

F1G.1133. Rhynchotalona falcata. Maine, Michigan.

THE WATER FLEAS (CLADOCKRA)

171 (122) Posterior margin of valves considerably Kss llian maximum height.

All species of Pleuroxus belong here; also AloncUa excisa an<l <-.ri\'M<j.

172 (204) Body elongated, form not spherii al.

173 (174, 175) Lower part of posterior margin excised or crenulalwl.

AloncUa excisa, A. cxigwi • ; ; . .

Turn to the key at the numbers indicated where two species are discusv ;

174 (173, 175) Posterior margin with numerous teeth along whole length.

Pleuroxus procurvatus, P. trutUiitus iK,s. i,ji

Turn to the key at the numbers indicated where two sik-cIcs are disrusM<i

175 (173, 174) Teeth (if any) only at infero-jHjslcal angle. \-h

176 (179) Infero-posteal angle well marked, ordinarily with trcth 177

177(178) Rostrum long /7<'//r<u;o- most s{K'nes 186

Take up the key at the number indicated where the genus is discussed as a unit.

178 (177) Rostrum short UoticUa dctUiifra . .

Take up the key at the number indicated where the genus is discussed a.s a unit.
N.B. If the rostrum is broad, semi-circular at vnd, see 167.

179 (176) Infero-posteal angle rounded 180

180 (185) With well-marked tooth or teeth 181

181 (182) Rostrum long, recurved Pleuroxus striatus .

Turn to the key at the number indicated where the species named is di.scusse<i.

182(181) Rostrum short D u )i /lanl la Kiuf; iS-~,^ ..-,

General shape rounded. Valves tumid, gaping below; obscurely reticulatc<!; infcn>-i»i»Mc«l
angle rounded, with i or 2 teeth on ventral margin in front of angle. I'ost-aiH!. tm n l-cnt
abruptly behind anus; post-anal part thick, somewhat foot-shajx'd as strn from d

(lower) margin lying parallel to ventral margin of valves; with many fine dcnti'
Claws short, curved, with i basal spine. $ with usual characters; ixjst-alxionuu >-i.
as 9 > with fine hairs only.

183 (184) Form short and high, as dorsal margin is much arched.

Dunhrccdi,! srHi'cr,: (Hirire) 1S77.

^ ^ V"; ' ^ X,^ Keel of labrum pro(iuce<i into a stmicwhat tm .

^^.^ I ' ' ^ • ^ v^^ form, its ventral margin sm(H)th. Color yellow. 1

^: \ 9, to 0.5 mm.; /, ca. o..^f) mm.

\ New England and Wisconsin to Colorado, l^

; " " ^ Jl, and Texas. Not common; among wcttls. I'crhap

. , , cal with D. crassa King.

■''^■<- . ^

aiMMf. . . f-

726

FRESH-WATER BIOLOGY

^■--^^i

184 (183) Form more elongated, as dorsal margin is little arched.

Dunhevedia serrata Daday 1898.

,'^ ^._ „ ^ Usually 2 teeth at infero-posteal

angle, a very small posterior and a
larger anterior one. Keel of labrum
serrate in anterior part, smooth be-
hind; about 10-12 serrations, pointing
backward. ^ unknown. Color yel-
low. Length, 9 . ca. 0.7 mm.

Louisiana, Texas; in pools and lakes
among weeds; not abundant.

Fig. 1 135. Dunhevedia serrata. a, labrum;
h, post -abdomen.

0.1 MM.

185 (180)

Infero-posteal angle without teeth, or tooth very small; rostrum long
or short 186

186 (203) Claws with 2 basal spines.

Pleuroxus Baird 1843

187

Rostrum long and pointed, rarely bent forward. Dorsal margin much arched; posterior
margin short, usually less than one-half height, rarely toothed along entire length; infero-
posteal angle rarely rounded, usually sharp and toothed. Keel of labrum large, usually tongue-
shaped; posterior angle prolonged. Post-abdomen with marginal denticles only, cf smaller
than 9 » with usual characters; post-abdomen varies in different species.

Three types of form are distinguishable in the genus: (i) relatively long and low species:
striatus type (P. striatus, hastaius, hamulatus); (2) short, high-arched forms: denticulatus
type (P. denticulatus, aduncus, trigonellus, truncatus); (3) the second form with rostrum bent
forward: {P. procurvatus, uncinatus). All species littoral.

187 (190) Rostrum bent up in front 188

(189) Rostrum bent sharply into hook; teeth along whole posterior
margin of valves Pleuroxus procurvatus Birge 1878.

General form and markings like P. denticulatus. Posterior
margin of valves with 7-8 teeth along the whole length.
Post-abdomen like P. denticulatus but slightly more broad-
ened behind anus, d unknown. Color yellowish, transpar-
ent or opaque. Length, 9 > ca. 0.5 mm.

Northern states, common in weedy waters.

Fig. 113b. Pleuroxus procurvatus.

0.2 MM. 1.

189 (188)

Rostrum merely curved forward; teeth at infero-posteal angle only.

Pleuroxus uncinatus Baird 1850.

Infero-posteal angle with 2-4 rather long, curved teeth,
sometimes branched. Rostrum long, acute, bent forward.
Post-abdomen like P. trigonellus, broad, somewhat tapered
toward apex; about 13 good-sized marginal denticles. Color
dirty gray, or with green or yellow tinge. Length, 9,
0.7-0.9 mm.; ^ (European), 0.56 mm.

Nebraska (Fordyce). The species is very close to P.
trigonellus, separated by procurved rostrum and large teeth
at infero-posteal angle.

t>4MM.

Fig. ii37« Pleuroxus uncinatus. European specimens.

THE WATER FLEAS (CLADOCKKA)

190 (187) Rostrum not bent forward.

191 (192) Numerous teeth along whole posterior margin.

Plcuroxiis /run,. It 1,^ <(

I-. Mullcr

Posterior marKiii unn inm ,
set teeth; valves striate! tli.
nearly longitudinal, tlie .,t)i,
men much like /'. tri>-ondius. >l,»{htiy'u- ■
apex, an^le mu.Klecl; 12-14 marginal . Ic..'-

Nebraska (Fordyce).

Fig. 1 138. PUuroxus Irunai

I F^urnj

icati ^I«xlm«■n

192 (191) Teeth at infero-posteal angle only

193 (196) Post-abdomen long, slender, convex on ventral (upiK-r; side. 194

194 (195) Supero-posteal angle sharp but not projecting- infcro-posteaJ
angle a sharp point J'laaoxus /iaslatt4s S^irs 1862.

Infero-posteal anple a sharp point, with a vcn- snuill
tooth; valves reticulated, longitudinal marks oftrn m.,rr
distinct, givmg appearance of striation. if.
denticles. Color yellow, transjKirent ur
black unless ephippial. Length, 9. ca. o.f. :
0.45 mm.

Rather rare; New England. Wisconsin. NcbnuJtA,
Caufornia.

Fig. 1139. PUuroxus Auj/o/mj.

0.1 MM

195 (194) Supero-posteal angle overhanging; infero-po.^^teal angle rounded,
with small tooth in front of it.

Plcuroxiis striiitHS SchtK-dler iS6j.

General shape much likr T ' . •

but never .so high archol as :
Valves obviously striatal. I'.
long, slender, with 20. or nmrt-. iiutrKiiiul
denticles. Color dark. rsjKHially oiU(jvie
on dorsal side, often nearly bUik. Length.
9. ca. o.S mm.; '. ca. of* mm.

In all (Kirts of Cnitctl States; commoa
among weetls.

This sjK'cies is /'. gradJis Hutlcndorf;
P. unidctts Birge.

aiMM

Fig, 1 1 40. Plfur>fXMs j/no/ni.

728

FRESH-WATER BIOLOGY

196 (193) Post-abdomen of moderate length; ventral (upper) margin straight,

or nearly so; greatest width behind anus 197

197 (200) Angle of post-abdomen sharp, with cluster of spines at apex. . 198

198 (199) Teeth at infero-posteal angle of valves; no hook on first foot
of female Pleuroxus denticulatus Birge 1877.

Infero-posteal angle with small tooth-
like spines. Post-abdomen moderately
long, straight, very little narrowed toward
apex; length of post-anal part 1.5 times,
or more, that of anal emargination; apex
truncate; with cluster of fine, straight
denticles at apex and 8-12 anterior to
these. Color greenish or yellowish, usu-
ally transparent. Length, 9 > 0.5-0.6
mm.; $ , 0.36 mm.

Common everywhere in weedy water.

Fig. 1141. Pleuroxus denticulatus.

199 (198) Infero-posteal angle rounded; first foot of female with stout hook.

Pleuroxus hamulatus Birge 1910.

Infero-p>osteal angle rounded, without teeth; valves reticulated; also marked by very fine

striae, which run nearly longitudinally.

Rostrum long, recurved. Keel of labrum small,
rounded, prolonged. Post-abdomen much
like P. denticulatus, but with apex more
rounded and denticles not so crowded there.
Denticles about 12-14. ^unknown. Color
horn-yellow, often dark on dorsal side like P.
striatus. Length, 9 . ca. 0.6 mm.

New England and southern states; prob-
ably a coastal form; not reported from north
central region. Common in pools and
weedy waters.

Pleuroxus hamulatus.
b, post-abdomen.

first foot;

1 143. Pleuroxus hamulatus.

200 (197) Angle of post-abdomen rounded 201

THE WATER FLEAS (CLADOCERA) 729

201 (202) Series of marginal denticles longer than anal emargination- post-
abdomen of male broadened in middle of posl-amd tiari
with crescentic dorsal margin.

Pleuroxiis trigoncllus (O. F. MuUcr) 17S5

Form of P. dentUulatui tvi>r Infrro-
postcal anRlc with 2 or \ .small trrth. ..ftm
minute, sometimes wantiriK I'mt aUlo-
mcn much as /'. drntuulatut; but i\ui^\
mar^'in slightly convex. I.roadcr Jx-hind
anus; ai^x rounde*!; 14-16 marKifwd licn-
tides, longer toward apex, hut not <liv
tinctly clustered there. ^ fxrt aMnmm
is characteristic; hroadene*! '
into a semi-elliptical plate, t
set hairs, no spines; jrreatly ;
ward aiK'X. forming' a slender prolan.
Color yellowish, transparent; j*.-:
men often dark. Lcn^h. 9 . o <> "im .
$ , 0.4 mm.

Not common; Maine, \Vi.vx)n<un, Ne-
braska; doubtless widely dislribute<l.

Fig. 1 144. PUuroxus lrif(meUus

Pa8t-»l«.J<>m«j:

202 (201) Row of marginal denticles about equals anal emargination; male
post-abdomen not crescentic.

Pleuroxus admicus (Jurinc) iSio.

9 very closely resembling P. triionrUut.
but differing as follows: valves striatc<l; in-
fero-posteal angle usually without teeth. iN^st-
abdomen shorter, the length of post -anal p*rl
hardly e.xceeding anal emargination; dors*!
margin slightly arched, with 0 u manorul
denticles; ape.\ rounde<i. <J i>ost-alxlomen
very diflerent from P. tri^ontUns: narrower
than 9. tajx'red toward claws; no dorul en-
largement or apical prolongation. Color born-
yellow, sometimes t)|)a(iue. Length. 9. ca.
0.6 mm.; ^ , ca. 0.45 mm.

Colorado, California. Among weeds or in
pools.

Fig. 11.(5. Plfuroxus aJumiiu.

0.1 MM.

203 (186) Claws with i basal spine [lonilln (most six-cics) . . 230

Take up the key at the number indicated where one sul)genus is discus.seii as a irniL

204(172) Body spherical or broadly ellipsoidal 205

205 (208) Well marked or small spine at infero-posteal angle 206

206(207) Valves conspicuously striated • Monelhi mimi . . ^4-'

Turn to the key at the number indicated where the species is discussed.

207 (206) Valves reticulated or not plainly marked. ChyJorus barnyUi

Chydorus hyhruius . . 2 it, 337
Turn to the key at the numbers indicated where the two species arc discussed.

730

FRESH-WATER BIOLOGY

208 (205) No spine at infero-posteal angle 209

209 (210) Valves with conspicuous projection on antero-ventral margin.

Anchistropus Sars 1862.
Sole American species Anchistropus minor Birge 1893.

Form globular. Ventral region tumid anteriorly
and ventral margin of valves bent sharply away from
each other about one-third way from front and the
valve folded out into a hollow groove and tooth,
which contains the strong hook of the first foot.
Head large, bulging over eye, the fornices broad and
forming a sort of flap-like rostrum, which can be
closely pressed to the valves. Post-abdomen broad
at base, pre-anal angle overhanging; rapidly narrow-
ing toward apex, which is prolonged into a lobe; a
few marginal spines. Claws with long, slender basal
spine, denticulate or smooth. First foot of 9 with
strong hook, toothed on concave side, which lies in
groove formed by folding of valves.

In A. minor, groove for hook of first foot near
anterior part of valves; hook not large. Color brown-
yellow. ^ unknown. Length, 9 > ca. 0.35 mm.

Maine, Michigan, Wisconsin, Louisiana.

Fig. 1 146. Anchistropus minor.

210(209) No such projection 211

211 (229) Post-abdomen ordinarily short with prominent pre-anal angle.

Chydoriis l^tdiCh. i^^2> ■ ■ 212
Shape spherical or ovate. Posterior angles little marked; infero-posteal angle usually un-
armed. Antennules short and thick. Rostrum long and acute. Post-abdomen usually short,
broad, rarely long and narrow (C. globosus); apex rounded; with marginal denticles only or
(C. globosus) with very fine lateral fascicles. Claws with 2 basal spines, the proximal often very
minute, rarely absent. ^ with short rostrum, thick antennule, hook on first foot, post-abdomen
often very narrow.

212 (213) Post-abdomen, long, narrow,

Pleuroxus-\ik.t.

Chydorus globosus Baird 1850.

Almost spherical; valves smooth or reticulated, sometimes
striated in front. Post-abdomen with small pre-anal angle;
numerous marginal denticles and very fine lateral fascicles.
Claws with 2 basal spines, the distal very long and slender.
Color bright yellow to dark brown, usually with dark spot in
center of valve. Length, 9 - to 0.8 mm.; $ , 0.6 mm.

Everywhere; in lakes and ponds, among weeds, but never
present in very large numbers.

C. globosus might well be type of a separate genus. The other
species fall into 3 groups: (i) The sphaericus group or Chydorus
proper (C. sphaericus, gibbus, piger, lalus, ovalis); (2) The
faviformis group, similar to (i) but with greatly developed cutic-
ular structures (C. faviformis, bicornutus); (3) The barroisi
group, with toothed labrum; denticles of post-abdomen shortest
in middle of row (C. barroisi, hybridus, poppei).

Fig. 1147. Chydorus globosus.

73J

THE WATER FLEAS (CLADOCERA)

213 (212) Post-abdomen short, broad; prc-anal an^lt- markc<I.

214 (215, 216) Shell covered with deep polygonal cx-Ils.

C/iyilorus fitviformis Birgc i8<;3

Mmh like spharrifus in form and nizt X
unknown. ('(.lor yi-llow to lixht bruwnith.

Lt-nKth, 9. 0.5 -0.0 mm.

New Kn^'land, Wistunsin, Mkhiican. Ijuuiti-

ana; nut common.

Fig. ii4,S. Chy<L,rus /arifa

cjukl tixU

0.1 MM.

215 (214, 216)

Shell with deep polygonal ceils and ciiticular ridges.

Clixdorus hiiornulus Doolilllc

')Oi.

0.1 MM.

Like faviformis in havinp «lcfp pulygonal
cuticular cells; but (listinRuishf*! l»y the dr-
velopment of an extraonlinary ami fnmjJcJl
system of thin cuticular ridges, whiih cxtcixl
far beyond the ordinary cell>. .\ lon^j honi
extends laterally from the mi«ldlc dorsal rcKtun
of each valve, from which radiate v>mc of ihc
ridges. $ unknown. Color yellow. Ixni^h.
9. to 0.7 mm.

Maine, New Hampshire, and New Jersey.

I'IG. 1149. Chydorns buornutmi. (..Mler I>oQl*llr

216 (214, 215) Shell of ordinary type -''

217(225) Ventral edge of keel of labrum smooth -»S

218 (219) Antero-dorsal surface of valves and head flattened.

Clivilorus i^ihhiis Ldljeborg livS

iVSo.

The cur\e of the flor«il surface somewhat ilat tend.
both in front and behin.l. making a M.rt of hump in
center of dorsal margin. X'alvi-s reticulatcl. \lr»d
small; rostrum projects from valves m chara.len^tK
wiv I'ost-abdomen with S 10 mannnal denUtic*.

way

Color yellowish to brown. I^-n>'th. 9 • o -S '"'"•
Lake Superior. WisconMM. Michigan; rare
This species is C ruguiosui lorl)e».

Fig. 1150. Lkydorus cit^m.

732

219 (2i8)

FRESH-WATER BIOLOGY

Dorsal surface not flattened; form usually spherical or broadly
ovate 220

220 (223, 224) Small forms not exceeding 0.5 mm., usually less. ... 221

221 (222) Fornices gradually narrowing into rostrum. All olfactory setae on

end of antennule. Chydorus sphaericus (0. F. MiUler) 1785.

Spherical or broadly elliptical. Shell usually reticulated,
sometimes smooth (var. nitidus Schoedler), sometimes
punctate (var. punctatus Hellich), or with elevations (var.
coelatus Schoedler). Post-abdomen with 8-9 marginal
denticles. Claws small; proximal basal spine very minute.
$ with post-abdomen much emarginate. Color light
yellow to dark brown. Length, ^,0.5-0.5 mm.; $,
0.2 mm. Small limnetic forms constitute var. minor
Lilljeborg.

The commonest of all Cladocera; found all over the
world.

Fig. 1 151. Chydorus sphaericus.

222 (221) Fornices abruptly narrowed into rostrum. Two olfactory setae

on side of antennule Chydorus piger Sars 1862.

General form much like C. sphaericus. Ventral margin of valves densely ciliated; valves
ordinarily marked by oblique striae, sometimes smooth. Fornices abruptly narrowed at rostrum.
Antennule with usual lateral sense seta and two olfactory setae on side. Post-abdomen with
8-g rather long marginal denticles. Claws with 2 basal spines, the proximal one minute. Z
post-abdomen narrow, but not excavated. Color light to dark yellow. Length, 9 » ca* o-4
mm. Rare; reported only from Maine.

/

0.1 MM

Fig. 1152. Chydorus piger.

223 (220, 224)

Entire specimen and lower side of rostrum with antennules.

Larger forms, to 0.8 mm. Antennules short and thick with
all olfactory setae terminal. . . . Chydorus latus Sars 1862.

Much like sphaericus, but larger. Mandible attached
some way back of junction of head and valve. Denti-
cles of post-abdomen 10-12. Claws sometimes with
only I basal spine. Color dark yellow-brown. Length,
9 , to 0.7-0.8 mm.

Rare; Canada, near Lake Erie.

Fig. II 53. Chydorus latus.

0.1 MM,

THE WATER FLEAS (CLADOC'KR A'l

224 (220, 223) About 0.5 mm. Antcnnule with one oli.ui..r% .. la j.r,,\:-: .,1
to cluster at end Chydorus aialu Kilrz xs-^^.

0.2 MM. *

Fig. 1 154. Chydorus ovalis. Entire specimen and
antennule.

Form roun»l <.r Port-

alMlomt-n with r. ij-i$

mar^'inal ricnticlr ' 'hiKawl

si)in(-^. the proximal mmutc. ('f>k)r

yellow. transjKirent I-rnKth. 9. to
0.0 mm.; ' <Kuro|K-ani, 05 mm.

Rare; Nebraska.

225 (217) Ventral edge of keel of labrum with one or more teeth.

::6

226 (227, 228) With several teeth; short spine at infcro-postcal angle of valves.

Chydorus barroisi (^Richard) iS<>4.

Form and size much like spkarruus. thoujch
ventral margin is lexs curved. Keel o( la-
brum acuminate behind: serrate, with (our or
more teeth. ro>t-alxlomen with well dcvd-
oped pre anal an«le; ia-12 marfrinal drnticlo.
shortest in middle of row. ( olor bruwnyd-
low. LenK'th, 9 . ca- ° 4 nim.

Rare; Lake Charles. Ix)uisiana.

Fig. II ss. Ckydorui tnirraul.

0.1 MM

227 (226, 228) With one tooth; infero-postcal spine present.

' ^ ' Chydorus hvhndus Daday

1005.

Similar to barroisi but with only one tcxuh on keel o( Ubrum.
Rare; Wisconsin. .Micliican. Ixmisiana, FcxaA.

Fic. 1 156. ChyJortu h)i>nJtu.

734

FRESH-WATER BIOLOGY

228 (226, 227) With one tooth on labrum; no spine on valves.

Chydorus poppei Richard 1897.

Like hyhridus but without spine at infero-posteal
angle. Tooth on labrum sometimes small or obso-
lescent.

Louisiana, California; rare.

Very probably the last two species should be
listed as varieties of barroisi. These species were
first placed in Pleuroxus, but have no verj^ close
afl&nity with either Pleuroxus or Chydorus; might
well be made a separate genus.

Fig. 1157. Chydorus poppet.

aiMM.

229 (211)

Post-abdomen large, pre-anal angle ordinarily not prominent.

Alonella Sars 1862 . .

230

This genus consists of a heterogeneous assemblage of forms; not assignable elsewhere and not
easily separable. There are 3 sections which might well constitute separate genera:

(i) y4/o?je//a proper. Rostrum long, slender, recurved; usually conspicuously so; post-
abdomen with marginal denticles only; claws with i basal spine. A.rostrata, dadayi,
nana. (2) Paralonella. Rostrum short, hardly exceeding antennules; post-abdomen with
very small marginal denticles, with or without lateral fascicles; claws with i basal spine.
A. karua, dentifera, diaphana, glohiilosa. (3) Pleuroxalonella. Rostrum moderate; post-
abdomen with marginal denticles only; claws with 2 basal spines. Pleuroxus-likt. A.
excisa, exigua.

230 (235) Rostrum short; post-abdomen with marginal and lateral denticles.

231

231 (234) Valves with infero-posteal angle toothed. . 232

232 (233) About 3 fine teeth; valves striated. . Alonella karua (King) 1853.

General shape like Alona and easily
taken for a member of that genus._ (See
152.) Valves with oblique striae; infero-
posteal angle with 1-4 minute teeth.
Post-abdomen broad, expanded behind
anus; apex rovmded; with about 8 minute
marginal denticles and as many lateral
fascicles, much larger. Claws with i
small basal spine. Color yellow, trans-
parent. Length, 9, 0.45 mm; $ (South
America), 0.23 mm.

Louisiana, Texas, Arkansas; not rare,
in pools and lakes.

Fig. 1158. Alonella karua.

0.i MM.

THE WATKR FLEAS (CEAOOCI.R \) 73.

233 (232) One to three rather strong teeth, valves reticulated.

Aloiulla dtntifcra Sars icxji.

/A

m<o:^

^fr^

0.1 MM.

ft^^'

v^^

Back liiKh arched; iiifcr<>-iK>sl»-aI .in^Ic a. uf.- «iih
1-5 fairly strong tL-clh. Rostn;' • ,^

ventral margin of valves. ]■ ,.

broad, somewhat exixindwl Im,.,.. '.\

rounded; with alx^ut 12 minute mar,
and as many very minute lateral f.i *,

with I very lon^ l)as;d spine. Color y. Iluw l.ru*n
Length. 5 ta. o..} mm.; ^ , o <s mm.

Louisiana and Te.xas; not rare in \*»A% and UJic^

Fig. iisy. Alonella Jcnti/cra, with developing cpbippium.

234(231) No infero-posteal teeth; form rotund

O.I MM, i

Uomild glohulosa Daday 1898.

Small; shafK- oval rotund; head
reachinK alx)ut to miil.il.- ..f >. .Kr^.
Valves striate<l; all ni \

and without teeth. I n

long, narrow; hr<)a<!. »;

about \2 minute m.i- .^

and as many slen<Ier ! ■ •>.

Keel of labrum with -- noulic*.
Color yellow-brown. Lcn^h. 9.
0.30-0.4 mm.

Lake Charles, Louisiana,
weeds.

This species is .! . sctUpta San.

Fig. 1 1 60. AlontUa (lobmlos*.

235 (230) Post-abdomen with marginal denticles only ^36

236 (237) Denticles minute; post-abdomen large, bent behind anus; no in-
fero-posteal tooth on valves. Alouiila diiiphaiia (King) 1S53.

0.1 MM

Head short, n>strum not rracb-
ing more than two thinls distance
toward ventral mrirdn. Wilvc*
striated. M)nii • to

reticulation. . ^:

infero-ix).steal i-

out teeth. I

slightly enlar^' h

numerous very inuuitc ir,.ii,.iiAJ
denticles anil no other !*jnnri.
Claws long: i ba5al sjMnc. lycnitth.
S . 0.5 mm.; S < o 4 rom. Ci>lor
yellow, transjwrcnt.

I^uisiana, Texas; in pooU and
lakes; rare.

Fic. 1 161. Aloneila dui^ksm*.

736 FRESH-WATER BIOLOGY

237 (236) Denticles of ordinary size; infero-posteal tooth present. . . 238

238 (243) Claws with one basal spine 239

239 (242) Rostrum long, recurved 240

240 (241) Shape elongated oval; valves striated

0.1 MM

Fig. 1 162. Alonella rostrata.

Alonella rostrata (Koch) 1841.

General form not unlike a Pletiroxus of the striatus
type. Valves striated or reticulated; infero-posteal
angle rounded and with minute tooth, sometimes ab-
sent. Rostrum long, slender, recurved. Post-ab-
domen moderately long, somewhat tapering toward
apex; angle rounded; 9-12 small marginal denticles.
Claws with i minute basal spine. Color yellow or
brown, usually rather dark. Length, 9' ca. 0.5 mm.;
$ , ca. 0.4 mm.

Rather rare; reported from New England, Michi-
gan, Wisconsin, Minnesota; probably to be found in
all regions.

This species is Pleuroxus acutirostris Birge.

241 (240) Shape short oval;

0.1 MM.

valves strongly reticulated.

Alonella dadayi Birge 1910.

Shape oval-rotund. Valves strongly reticulated
all over; infero-posteal angle rounded, with sev-
eral minute teeth. Rostrum long, pointed, re-
curved. Keel of labrum acuminate behind and
its margin with i projection. Post-abdomen
short, wide; pre-anal angle strongly marked, as
in Chydorus; with numerous small denticles; apex
rounded. Claws with i basal spine. Color
yellow to brown, often opaque. Length, 9i
0.25-0.3 mm.; $ (South America), 0.2 mm.

Louisiana, Texas; not rare in weedy pools.

This species is Leptorhynchus dentifer Daday,
whose specific name has to be changed on remov-
ing to Alonella, as Sars' species A. dentifera pre-
occupies the name.

Fig. II 63. Alonella dadayi.

242 (239) Rostrum short or moderate; shape globose; valves conspicuously
striated Alonella nana (Baird) 1850.

Very minute; Chydorus-like. Valves coarsely and con-
spicuously striated; minute tooth in infero-posteal region.
Rostrum varies, usually rather long, recurved, consider-
ably exceeding antennules. Post-abdomen short; pre-
anal angle strongly projecting; apex rounded; about 6
marginal denticles. Claws with i small spine. Color
brownish, usually opaque. Length, 9» 0.2-0.28 mm.;
$ , 0.25 mm.

New England, Wisconsin, Minnesota; rare. The small-
est member of the family.

Fig. 1164. Alonella nana.

OJ MM.

THE WATER FLEAS (CLADOCERA)

737

243 (238) Claws with 2 basal spines; posterior mar^'in of valves excised near
infero-posteal angle

244

244 (245) Post-abdomen fairly long; angled at apex; valves reticulated and
with fine striae Honclla excisa (VischLT) iSs.\.

1165

Alonella excisa. Entire specimen and details of
markings of valve.

Cicncral apixrarancc Pl/^u-
rorM5 like. Rostrum moder-
ate to lon^, never as pro-
lonsed as in A. ro strata nor
recur\e<l; longer in southern
forms. Infero-i>ostcal angle
marked, sf>metimes iinxiuce*!
into a fxjint; i)osterior mar-
gin al)ove it excisctl. si>mc-
times crenulatefl. Post ab-
domen long, narrow, not nju'-
rowing much toward apci;
apex angled; with al)out if-
10 small marginal denticles.
Color yellow to bnjwn.
Length. 9, to 0.5 mm.; ^,
0.28 mm.

Not uncommon in all lo-
calities; in weedy pools and
lakes.

245 (244) Post-abdomen short;

rounded at apex; valves without fine striae.
Alonella exigua (Lilljeborg; 1853.

Much like preceding sr>ecies but smaller. About 6-8 small
marginal denticles. Color yellow, not ver>- transparent.
Length, 9.0-3Smm.; ^, 0.28mm.

Maine, Wisconsin, Michigan; rare.

Fig. 1 166. Alonella exigua.

0.1 MM.

■*4

246 (121) Eye and ocellus very large; antennules project far beyond rostrum.

Dadaya Sars 1001.
Sole species Dadaya nidcrops {D^i.\:iy) iSq8,

Form rounded-oval; not a)mpresseti. Head
small, much dcpres,se<l; tumid alxjve eye; ros-
trum short and broad, .\ntennules long, mtxl-
erately stout, projecting far U-yond rostnim.
Post-abdomen of nKnlerate si/^, comprrw>l.
somewhat broadeni>d l>ehind anu.s slightly
narrowing toward ajx-x; angle roundcti; al>out
14-18 marginal denticles. Claws small, one
small basal spine. Kye very large, with few
lenses; ocellus nearly as large, crowtiixl d»»wn
into rostrum. X unknown. Color dark
brown. Length. 9 . '■i*- 0-< f""^-

A single siK-cimen of this s|»edes was found
in a collection from a wectly ikx)I at Smilb-
ville, Texas.

Fig. 1167. Dadaya m^ropi.

738

FRESH-WATER BIOLOGY

247 (120) No eye; ocellus only Monospilus Sars 1861.

Sole species Monospilus dispar Sars 1861.

Form oval or round. Shell not cast in molting, as in
Ilyocryptus. Valves nearly round with fine setae along
ventral edge. Head very small, depressed, movable.
Keel of labrum with about 4 scallops on ventral edge.
Post-abdomen broad, short, with about 5-7 marginal
denticles and numerous clusters of fine hairs. Eye lack-
ing; ocellus large. Antennules short, not reaching apex
of rostrum. $ with hook on first foot; post-abdomen
tapering, triangular, somewhat resembling that of Grap-
toleberis. Color brown-yellow. Length, J , ca. 0.5 mm.;
$ , ca. 0.4 mm.

New England, Wisconsin, Minnesota; rare.

Fig. 1 168. Monospilus dispar.

0.1 MM.

248 (i) Body and feet not covered by shell. Feet subcylindrical or flattened,
jointed, prehensile. . . . Section B. Gymnomera . . 249
No fomices. Rami of antennae 3- to 4-jointed. Feet, 4 to 6 pairs, jointed, prehensile.

249 (250) Four pairs of feet, stout, compressed, with claw-like spines and
branchial appendages.

Tribe I. Onychopoda.
Sole family Polyphemidae Baird.

Body very short. Shell converted into large globular brood-sac. Caudal process long,
slender, with 2 long caudal stylets or setae. Rami of antennae with 3 and 4 joints. Eye very
large; no ocellus. Labrum large. Two small hepatic ceca.

One genus Po/y/>/zeww5 0. F. Mtiller 1785.

Sole species Polyphemus pediculus (Linne) 1761.

Brood-sac globular, with
20-25 young in full grown
specimens. Antennules
very small, on ventral sur-
face of head. Head large,
filled in front by huge
movable eye. Antennae
with 7 setae on each ramus.
Feet stout, with strong
claws, and branchial ap-
pendage; fourth pair, very
small. Length, 9 > meas-
ured to back of brood-sac,
to 1.5 mm.; J , 0.8 mm.

Common in northern
United States in lakes,
pools, and marshes.

Fig. 1 169 . Polyphemus pedic-
ulus.

THE WATER FLEAS (CLADOCERA)

739

250 (249) Six pairs of feet, cylindrical, first pair vcrv long; without branc hial

appendages '. Tribe II. Haplopoda.

Sole family Lkptudoridai: LilljcU>rg.

Head elongated slender; eye filling anterior end. Body 4-Jointc<l. the first ivart l>carir.K
the 6 feet and dorsal brood-sac; the 3-jointed abdomen ends in 2 .short stylets or claws \u\vn
nules small, freely movable. Antennae with very large i)asal joint; rami 4-jointe<l with numer-
ous setae. Mandibles long, slender, pointed, with 3 spines near ai)ex. Ksojihajcus very Ume
stomach in last abdominal segment. 9 with very long antennules. The young from winter
eggs hatch as a naupHus.

Sole genus with characters of family Lcptodora Lilljcborg.

Sole species Lcplodora kindlii (Vockt') 1H44.

This beautiful, transparent creature is the largest of the Cladocera. the 9 reaching a length
of 18 mm. Rapacious, though its weak mandibles prevent it from being formid.iMr t., the
harder shelled entomostraca; nocturnal in coming to the surface.

Limnetic in Great Lakes and small lakes in northern United States; not rare.

Fig. 1 1 70. Leptodora kindlii.

IMPORTANT REFERENCES ON NORTH AMERICAN CLADOCERA.
BiRGE, E. A. 1891. Notes on Cladocera II. List of Cladocera from >Li.li-
son, Wis. Trans. Wis. Acad., 8: 379-398; i pi.
1893. Notes on Cladocera III. Descriptions of new and rare s|>ccic.s.

Trans. Wis. Acad., 9: 275-317; i pi-
1910. Notes on Cladocera IV. Descriptions of New and Rare Spec us
Chiefly Southern. Trans. Wis. Acad., 16: 10 18- 1066; 5 pi.
Herrick, C. L. 1895. Synopsis of the Entomostraca oi Minnesota. Second
Report of State Zoologist; 337 pp., 81 pi.
Contaia« much information and many figures, original and from various sourct-;; hut the
material is not very carefully or critically handled.

740 FRESH-WATER BIOLOGY

Keilhack, L. 1910. Phyllopoda. In Brauer's Siisswasserfauna Deutsch-

lands, pt. 10; 112 pp., 265 text figs.

An admirable account of the Cladocera of Germany, most of which are found in this country
also. It should be the first book procured by any one who can read German.

LiLLjEBORG, W. 1900. Cladocera Sueciae. Upsala. 701 pp., 87 pi.

Latin keys and diagnoses; otherwise German. Indispensable for a critical study of the
group.

Richard, J. 1894. Revision des Cladoceres. Part I. Sididae. Ann. Sci.
Nat., Zool., (7) 18: 279-389, 2 pi.
1896. Part II. Daphnidae. Ann. Sci. Nat., Zool. (8) 2: 187-363; 6 pi.
Invaluable for the families which they cover.

Sars, G. O. 1901. Contributions to the Knowledge of the Freshwater Ento-
mostraca of South America. Part I. Cladocera. Arch. Math. Nat.
Kristiana, Bd. 23, no. 3, 102 pp., 12 pi.
Necessary for the study of southern cladocera, but not needed for the northern states.

Note. — All illustrations for this chapter have been drawn especially for it, and all are made from the
actual specimens, except in a few cases, which are indicated.

CHAPTER XXIII
COPEPODA

By C. DWIGHT MARSH

United States Department of Agriculture

Of all animals encountered in fresh water, perhaps none are
more likely to arouse interest than the Copepoda. Wliilc many of
them are large enough to be seen and watched with the naked
eye, yet they are so small that a microscope is needed to get a
clear understanding of their form and structure. In company with
the Cladocera, they are almost universally distributed, and can be
collected in nearly any body of water. Unlike the Cladocera,
which show many erratic and bizarre species, the Copepoda are
graceful and symmetrical in their forms, with a beauty of structure
that is very attractive to the amateur student. Some are wonder-
fully transparent, while others are strikingl}' and in some cases
gorgeously colored.

Copepoda have been studied ever since the microscope was first
used. It is said that the first mention of these animals was made
by Stephen Blankaart in 1688. 0. F. IMuller in 1785 is credited
with having given the first scientific description of this group.
In 1820 Jurine published his famous ''Histoire des monocles qui se
trouve aux environs de Geneve." Some of the species which he
described are still recognized as valid, largely, however. b\- the
courtesy of succeeding writers; for Jurine made his distinctions on
insufficient grounds like color, and it is only through his figures
that one can conjecture what species he had in hand. No really
serious study of this group was made until the middle of the nine-
teenth century, when the publication of Baird's "Natural IIistor>-
of the British Entomostraca " in 1850 and the various papers ol
Claus a few years later were the beginning of exact work on these
forms. The work of Claus was of first importance. In Sorih
America articles were published recrardin- some forms in the early
part of the century, but nothing recognizable appeared until S. A.

74t

742

FRESH-WATER BIOLOGY

Forbes commenced his series of papers. Although these papers
were not extensive, they were exact and carefully worked out, and
to Forbes may be given the credit of laying the foundation for all
subsequent work in this country.

Though attractive in form, the Copepoda are complex in their
structure, and accurate classification can only be attained by care-
ful and laborious dissection, so that study of the order has been
neglected.

With the exception of the Harpacticidae, all the free-swimming
Copepoda are characterized by a distinct division of the body into
cephalothorax and abdomen, the former being composed of five or
six segments and the latter of from three to five. The appendages
are as follows, commencing with the front of the animal:

Frontalorgan

Upper Zip^TJ-^""^'
Mandible F
Lower Lip'jtzL',

First pair of antennae.

Second pair of antennae.

Mandibles.

First maxillae.

Second maxillae.

Maxillipedes.

First pair of swimming feet.

Second pair of swimming feet.

Third pair of swimming feet.

Fourth pair of swimming feet.

Fifth feet.

Furcal rami.

Fig. II 71. Diagrammatic figure of a female
Copepod. (After Giesbrecht and Schmeil.)

Terminal Setae
Inner orJ)ortal Setae

COPEPODA

All of these appendages are built on the same i)lan, which is
typically represented in the swimming feet of Cyclops (Fig. 1221).
Each foot consists of two basal segments, and attached to the outer
or distal of these are two branches or rami, each of three segments.
The outer ramus is known as the exopodite and the inner as the
endopodite. This typical plan may be very much modified but.
in most cases the fundamental structure can be recognized.

Of these appendages, the first antennae are ver\- characteristic.
They are so modified that one of the rami has entirely disappeared,
and the one remaining is made up of a considerable number of
segments, varying from six to twenty-five. In the same species
the number of segments in the antennae is ordinarih' invariable.
In some of the species of Cyclops the antennae are very short, in
others they may exceed the length of the cephalothora.x, while in
the other genera they may equal or exceed the length of the whole
body. The segments of the antennae are armed with hairs which
are definite in number and location. They have also sensory
structures arranged in definite places on the segments. The club-
shaped sensory appendage of the twelfth antenna 1 segment of
some of the species of Cyclops is one of the important means of
identification. Some of the species of Cyclops ha\e circlets or
crowns of spines on certain antennal segments which give them a
pecuUarly ornate appearance. In some of the species of Cyclops
there is a thin hyaline lamella extending longitudinall\- along cer-
tain of the segments, being especially marked on the last two. This
is particularly noticeable in Cyclops Juscus (Fig. 1223).

In the Cyclopidae the antennae are s^Tumetrical and, in the male,
are modified to form grasping organs. In the C\'ntropagidae it is
only the right antenna of the male that is so modilietl.

In many of the species of Diaptomus the antepenultimate seg-
ment of the right antenna of the male has a distinctive form.
This may be a hyaline lamella extending the length of the segment,
or it may be an extension of one side of the segment in a prt)cess
which varies from a blunt projection to a hook or, in some cases,
a long, slender digitiform extension. The armature of this segment
is constant and is one of the important characteristics used in
distinguishing species.

744

FRESH-WATER BIOLOGY

The fifth feet in Cyclops are very rudimentary structures.

In Diaptomus the fifth feet take on interesting forms. In the
female they are symmetrical, but not so well developed as the
preceding swimming feet. But in the male, the right fifth foot
differs from the left, and is modified so as to make a grasping
organ. The figures in the synoptical key show the form of these
appendages. The modifications are constant in a given species,
so that the fifth feet in this genus furnish the most important
means of specific identification.

In Epischura the fifth feet are modified more profoundly, and
this modification is accompanied by a pecuHar development of the
segments of the abdomen, which also serves as a grasping organ.

Fig. 1172. Nauplius of Cyc/o/)^. The
fourth pair of appendages are repre-
sented by two setae. (After Glaus.)

Fig. 1173. Second Stage of Cydo/'^, in
which are seen four pairs of appen-
dages. (After Claus.)

In their growth from the egg up, the Copepoda pass through a
compHcated series of forms. On issuing from the egg the young
animal is a flat, oval creature, without any division of the body
into cephalothorax and abdomen, and with only three pairs of
appendages, the first three of the mature animal, namely, the first
and second antennae and the mandibles. These are all used, in
this stage of the animal, as swimming organs. This is known as
the nauplius stage (Fig. 11 72). A series of molts follows. In the

COPEPODA -^-

second stage (Fig. 1173) a fourth pair of appendages is added,
which later are known as the maxillae. In a later stage three more
pairs of appendages are added, — the maxillipcdcs, and ihc first two
pairs of swimming feet: this is known as the mclanauplius stage.
The following stage is the first Cyclops stage; in this there is a dis-
tinct division of the body into cephaluthurax and abdomen, and the
third and fourth swimming feet are present in a rudimentary form.
In this stage, too, the anterior appendages have develoiK-d into
forms more similar to those in the mature animal.

The process of development is thus accompanied by a continued
increase in the number of appendages beginning at the anterior
extremity, in the number of segments of the cephalothorax and
abdomen, and in the complexity of the appendages, until the mature
forms are reached.

Some of the parasitic forms do not pass through all these stages.
There are some that never acquire the third and fourth swimming
feet; in others, by a progress of regression, the first and second
feet may disappear. Some parasitic forms jump the whole scries
of nauplius stages and almost immediately after leaving the egg
appear in the first Cyclops stage.

Hardly any body of water is without its copepod inhabitants,
although running waters have a less abundant population than
lakes. Frequently standing pools swarm with the individuals of
one or a few species of this order. Temporary pools in the spring,
which are formed in the same place in successive years, will some-
times be almost literally filled with Copepoda, which are strictly
seasonal in their life habits; for, as the pools disappear, the cojw-
pods disappear, their eggs sink in the mud of the bottom, and
remain until the waters of the next season bring about favorable
conditions for their generation.

The lakes produce an exceedingly abundant coix-ix>d fauna,
which has an important practical interest, for the ultimate focMJ of
fish is composed almost entirely of these organisms; that is, the
small fish of our most abundant species feed entirely ujKin Knto-
mostraca, of which Copepoda form the greater part, and, in many
cases, the mature fish also feed entirely on these same minute
creatures.

746 FRESH-WATER BIOLOGY

Similar conditions prevail in the ocean, where Copepoda form an
essential part of the plankton, which there, too, is an important
element in the food, not only of fishes, but of some of the great
ocean mammals. Our fresh- water Copepoda are descendants of
salt-water forms, and the elucidation of the lines of descent forms
a most interesting problem, towards the solution of which very
little has been done.

The distribution of the Copepoda in our lakes is a matter of
great interest. Certain species are characteristic of distinct regions
of the lakes. For example, Cyclops bicuspidatus, Diaptomus sicilis,
Diaptomus minutus, and Diaptomus ashlandi are characteristic of
the limnetic regions of the Great Lakes. Cyclops prasinus is espe-
cially characteristic of limnetic regions, Cyclops albidus and Cyclops
fuscus are more commonly littoral, while Cyclops hicolor and Cyclops
phaleratiis are more usually found in pools. Others, especially at
certain seasons, may be found only in the deeper waters, or are
''abyssal" in habitat. This is true of Limnocalanus macrurus,
which is rarely found at the surface in the summer season, but
almost entirely in the region below the thermocHne. Generally
speaking, the Diaptomi in lakes are characteristic of the limnetic
regions, but it does not follow that all Diaptomi are limnetic; for
there are many species that confine themselves strictly to the
extremely shallow waters of pools, like Diaptomus sanguineus, which
occurs widely through the temperate regions in the temporary
pools of spring. It should not be inferred, however, that these
distinctions between littoral, limnetic, abyssal, etc., are absolute.
In many cases, species commonly Httoral may adapt themselves to
a limnetic habitat, or those commonly found in limnetic regions
may become littoral, and flourish in those regions, thus forming
part of what is sometimes known as the tycholimnetic or tycholittoral
fauna. Cyclops bicuspidatus, for example, while ordinarily limnetic,
may become a part of the littoral fauna. In other cases, species
like Diaptomus oregonensis and Diaptomus minutus may seem to live
equally well in deep or shallow waters. Deep lakes and shallow
lakes have their characteristic copepod faunas, but this distinction
does not always hold rigidly; for frequently the species show a
great deal of elasticity in adapting themselves to changed conditions.

COPEPODA y^y

There is a marked difference in form and structure fx-twcrn the
Copepoda Hving in the open water and those that are Hmnetic in
their habit. Those that Hve among the weeds alongshore, or in
pools, are relatively short and stout, and frequently deeply colored.
A good example of this is Cyclops akr, which has recei\-ed its name
because of its dark color. It is to be presumed that Cyclops viridis
also received its name from its color, for man\' of iliese shore forms
show a distinctly green coloration. These ccjjors. doubtless, are i)r(>-
tective, for, because of them, the animals are almost invisible when
stationary upon a background of bottom mud or of the stems of
aquatic plants.

The limnetic species have long and slender bodies, Limuoca-
lanus macrurus being an especially good type. Some species of
Cyclops live either as limnetic or as littoral inhabitants; in these
cases one finds the same differences in form, the littoral variety
being short and stout, and the limnetic long and slender. This is
especially well shown in the varieties of Cyclops viridis and Cyclops
serrulatus. The figures in the systematic discussion of these species
show these differences which are especially well marked in the f ureal
rami (Figs. 12 14, 12 15). The littoral species have short and stout
furcal rami, whereas in the limnetic species these structures are
long and slender. The limnetic species are ordinaril\- colorless,
their transparent bodies making beautiful objects for examination
under low magnifying powers; for much of the internal anatomy
of the animal can be observed, while the animal is still alive: the
movements of the alimentary canal can be followed, and the beat-
ings of the heart observed. This lack of color is doubtless an
adaptation to the environment, for in open waters colorless animals
are much less conspicuous.

Occasionally the Copepoda are of a marked red color. This is
sometimes due to oil globules, and is especiall}- marked in some of
the species appearing in the early spring, or li\ing in tlie cold
waters of lakes at great altitudes. In other cases, and this is
markedly true of some of the Diaptomi, the integument may l>e
deeply colored in reds, blues, and purples. Diaptomus sJwshonc, a
large species found in the mountain regions of the West, is an esjje-
cially good example of a liiglily colored copepod.

748 FRESH-WATER BIOLOGY

As already noted, certain species appear in temporary pools only
in the spring season. In those that occur in lakes, there is some-
times a pronounced seasonal distribution. For example, in Green
Lake, Wis., on which extended studies have been made, Diaptomus
sicilis is common in the winter, but rarely found in the summer,
while most forms, as would be expected from the favorable food
conditions, are more abundant in the summer months.

Excepting the few winter forms, the maximum numbers of any
species occur in the months from May to September or early
November. Sometimes there are two maxima, one in the spring
and one in the fall. Generally speaking, the maximum develop-
ment occurs when the waters reach their highest temperature, but
other factors may modify the time. Generally speaking, also, the
maximum development in numbers is somewhat later in deep
lakes than that in shallow lakes, corresponding to the general law
for the development of the total plankton.

The great controUing factor in the distribution of the Copepoda
is, without doubt, temperature. That Diaptomus sicilis should be
found in Green Lake only in the winter is a matter of temperature,
for it is found in the cold waters of the Great Lakes throughout the
summer. Limnocalanus macrurus, which, in small, deep lakes, is
found during the summer only below the thermocline, comes to
the surface in the winter months when the surface water is colder.
In Wisconsin, Cyclops bicuspidatus is a common limnetic species in
the deeper lakes, but is rarely found in the shallower lakes except
in the winter season. It is evident that it prefers the colder waters.
On the other hand, Epischura lacustris and Diaptomus oregonensis
are distinctly summer forms, disappearing, for the most part, in
the winter months.

Partial studies have been made which have disclosed some very
interesting facts in regard to the vertical distribution of Copepoda
in our lakes. In general it may be said that most of these forms
are confined to the upper waters, above the thermocline, some
having very distinct vertical migrations, caused by changing con-
ditions of light and temperature. It has long been known that
not only are the open waters of our lakes peopled with myriads
of these minute creatures, which can readily be collected by a tow-

COPEPODA y4Q

net dragged behind a boat, but that collections made in the night
were much more successful than those in the (la>tinie. It \v;ls at
first inferred from these collections that the animals shunned the
light, and sank beneath the surface during the day, to rise again
at night. Careful studies of the subject, however, show that the
migration of these am'mals is by no means so simple a matter as
had been thought, and that very complex forces arc at work con-
trolling their movements. While some of them are sensitive to
the influence of light, it appears that temperature is much the
stronger factor, and that, generally speaking, they mo\e up (jr down
as the result of changes of temperature rather than because they
seek or avoid the light. This, without doubt, exj)lains the fact
that Limnocalanus remains in the deeper waters in the summer
and gradually rises higher as the waters cool off in the fall. On
the other hand, Cyclops prasinus has a marked preference for
warmer waters. During the summer it is found in the upper
layers of water, but in the winter it is inchned to a\oid the imme-
diate surface and seek the deeper and warmer waters.

Epischura lacustris is a very interesting species in its vertical
distribution; for it is large and a strong swimmer, and changes
its location from hour to hour during the day. It likes warm
water, but dislikes the Hght, and its vertical migrations both daily
and seasonal are the resultant of these two forces, so Uiat its move-
ments sometimes seem quite erratic.

It is a curious fact that the Copepoda differ in the character of
the habitat they like best at different times of their lives. Most
of the larval forms are found close to the surface in the daytime,
while the maturer animals are found at a greater or less depth.

It seems probable that the movements of the nauplii and larvd
Copepoda are caused by comparatively slight changes of tempera-
ture, and that a somewhat elaborate determination of the changes
of temperature in the upper layers of water ma\' explain their
movements, which now seem rather strange.

Through the study of the geographical distribution one may
hope to get some knowledge of the evolution of the si>ecies and
genera of the Copepoda, and it is on this account that this phxse
of the study of any group of animals is especially interesting to

750 FRESH-WATER BIOLOGY

the zoologist. Many of the species of the Cyclopidae are almost
if not quite cosmopolitan in their distribution; for example, Cyclops
leuckarti not only occurs all over North America, but in Europe,
Asia, and Africa, and without any variations that are character-
istic of the different regions. It seems very remarkable that an
animal as delicately organized as Cyclops should not show the
effect of change of location in its structure. Most of the recog-
nized American species of Cyclops are identical with those found
in other continents; and it is even possible that, when the genus
is known more thoroughly than at present, many of the species
which are now considered peculiar to our continent may be found
to be either identical with foreign species or at most only varia-
tions of those forms. So our common species of LimnocalanuSj
L. macrurus, is identical with the European form. On the other
hand, not only the species but the genera of Osphranticum and
Epischura are peculiar to North America. The genera of the
Harpacticidae have never been thoroughly worked over, and, while
some of our species are undoubtedly European, it seems probable,
from what we now know, that many of them are peculiar to this
continent. Eurytemora is world-wide in its distribution.

Of the Diaptomi there are now recognized thirty-nine species
in North America, and all of these are peculiar to this continent.
Not only are they peculiar to the continent, but many are peculiar
to certain regions. In a broad way, they illustrate very forcibly
what has been said before, — that Copepoda are controlled in their
distribution by temperature conditions. This can well be illus-
trated by a brief discussion of the geographical distribution of the
more common species. Diaptomus minutus is found from Green-
land and Iceland south to the northern tier of states in the United
States, but does not occur south of 42° to 43° N. L. Diaptomus
sicilis is confined to the northern tier of states. Diaptomus sici-
loides is found in a band farther to the south, being limited roughly
to the region between the thirty-sixth and forty-third parallels.
These three species are closely related to each other in structure,
and presumably are of the same Hne of descent. It will be seen
that their distribution, taken in a broad way, is one of latitude.

A similar relation exists between Diaptomus oregonensis, Diapto-

COPEPODA -.,

mus mississippiensis, and Diaplomus paUidiis. Diaptomus orc^o-
nensis is the more northern species. It is found from (jnc sidc'.»l
the continent to the other, as far north as the Saskatchewan region,
and as far south as Ilhnois and Indiana. Diaptomus pallidus is a
Mississippi Valley species, having been found from Minnesota to
Louisiana, and as far west as Colorado. Diaptomus mississippiensis
is a strictly southern species, being confined, so far as known, to
the Gulf States. It is evident that this distribution again is con-
trolled by temperature conditions.

The group which centers around Diaptomus alhuqucrqucnsis is
confined to the south, the most southern species being limited to
the island of Cuba. The group centering about Diaptomus sit^fti-
cauda is confined to the mountain regions of the West, where a
number of rather closely related species have been developed.
Probably the greatest number of species is found in this mountain
region of the West, where the lakes are separated from each other,
and isolation has led to the development of new species. It will
thus be seen that the one great controlling factor in the distribu-
tion of the Diaptomi is temperature.

It may perhaps be assumed that most of our North .\mcrican
species are descended from the same ancestors as those of the
other continents; that as the result of the glacial period the norths
ern forms were forced far to the south; and that, on the retreat of
the ice, some followed after the ice, while others remained behind,
but changed their form as the result of the changed environment.
Thus the more primitive forms would be found tt) the north. In
the south we would find specialized forms due to the various fac-
tors which have come into play in the evolution of these animals.
It is a pecuHar fact that in this change of conditions the Cyclo-
pidae should have succeeded in adapting themselves without change
of structure, while the Diaptomi all suffered changes. The ditTer-
ence in the behavior of these two families is a matter that is not
at all understood, but it seems possible that the Cyclopidae have
more efficient means of distribution, so that the development of
new species from isolation would not be as probable as in the case
of the Diaptomi. As a matter of fact, very little is known of the
life histories of these animals.

752 FRJSH-WATER BIOLOGY

Mention has been made of the fact that new species may arise
because of isolation. But the question arises, how do the ancestors
of any form first reach a given body of water? By what means
are these animals distributed from one place to another? Certain
species occur in bodies of water from one side of the continent to
the other; in some cases the same forms are found even in widely
separated continents. How have they reached these places? Eggs
are formed which fall into the mud of the floor of the lakes and
pools and retain their \itality, sometimes from one season to
another, even if the bodies of water disappear and the mud becomes
dry. Many species have been seen for the first time by rearing
them from eggs found in dried mud. It is natural to infer from
this that anything that would move the mud would also move the
eggs of the animals. Dried mud, in the form of dust, may be
widely disseminated, and thus the eggs might be carried to very
distant places. Water birds, too, carry mud on their feet from
one body of water to another, and in this way may easily transport
the eggs of Copepoda and possibly the living animals. Inasmuch
as these birds sometimes make long flights, it is clear that the
species of Copepoda may be planted in places far apart. There is
no doubt that in both these ways the distribution of the Copepoda
has been effected, but these are not the principal ways. It seems
evident, for many reasons, that they go from one place to another
mainly by direct water carriage. For example, Diaptomus sici-
loides has been found in only one lake in Wisconsin. If it were
readily carried by birds, one would expect to find it in other bodies
of water which seem to have the same kind of an environment.
On the other hand, in Lake St. Clair, although it is a very shallow
body of water, occur the Copepoda that are characteristic of the
deeper waters of the Great Lakes. In this case there seems to be
no doubt that these deep-lake forms have been carried into an en-
vironment where one would not expect to find them. It is notice-
able that in connecting bodies of water we find the same forms of
Copepoda. Irrigating ditches and ponds are almost entirely with-
out Copepoda. They are pecuHarly unprofitable collecting places
although the environment would seem to be favorable for the propa-
gation of these forms. For some reason, it is evident that the

COPEPODA

animals are not planted there. If the eggs of Copci)oda were dis-
seminated to any extent with the dust by winds, conditions would
seem to be unusually favorable; for such [)()n(ls arc found in dry
regions subject to heavy winds. '' Dust storms " are very common,
and in them large quantities of dust are moved from one place to
another. Ducks, too, frequent these ponds in enormous numbers,
and are continually on the wing, moving from one place to another.
It would seem, then, that in the arid and semi-arid regions condi-
tions were as favorable as possible for these two methods of trans-
portation. Yet the fact remains that the ponds are frecjuently
almost entirely devoid of copepod life, and one must conclude
that these methods of dissemination are of minor importance. It
apparently follows from these facts that, when once a form has
reached a mountain lake, it may remain in undisturbed possession
for a long time, and thus, by the ordinary processes of evolution,
one may expect to find in mountain regions a great variety of
species. As a matter of fact, in parts of the country where water
communication is easy, as in the Mississippi Valley, there prevails
great uniformity in the species, while in the mountain regions of
the West one finds a greater variety of species.

The ordinary means of collecting other forms of small water
animals and plants will serve for the Copepoda. The Hirge net is
the most useful form of collecting apparatus. Inasmuch as Co-
pepoda are extremely common in open and clean waters, the wire-
netting cap of the Birge net (p. 68) can frequently be disjx'nsed
with, and the apparatus thus simplified. A conical net of fine mus-
lin with the opening stiffened by a wire ring will serve admirabl}- for
making collections. This can be dragged behind a boat. or. if
weighted, can be thrown from the shore to a distance of from thirty
to forty feet, care being taken, as it is drawn in, to collect as little
as possible of floating debris or of mud if it strikes the bottom near
shore. The material collected in the end of the net can, !)>• in-
verting the net, be washed into a wide-mouthed bottle or tumbler
or tin fruit can, and then transferred to the homeopathic vials in
which it is stored. An easy way to make this transfer is to pour
the condensed material on little squares or circles of line muslin.
two or three inches in diameter, and then place cloth and all in
the preservative fluid.

754

FRESH-WATER BIOLOGY

For preservative fluid either 5 per cent formol or 75 per cent
alcohol can be used. Alcohol preserves the animals in a little
better shape, as formol is apt to make them brittle. Dissection is
best performed in a drop of glycerin on a slide. The transfer
from alcohol to glycerin should be made gradually, through mix-
tures of alcohol and glycerin. The larger forms of Copepoda can
be dissected under lenses magnifying from five to fifteen diameters;
but, for the smaller individuals, powers as high as one hundred
diameters must be used, and the work is very tedious. The
dissected material is best mounted for examination in Farrant's
solution, and the cover must be ringed with a good cement, —
Brunswick black, for instance.

If one wishes to make a serious study of the animals, the struc-
tures to be separated and studied are the following: the antennae,
male and female; the abdomens, male and female; the fifth feet,
male and female. In addition, the general form of the cephalo-
thorax must be noted, and, in some cases, the structure of the other
appendages of the cephalothorax. The Copepoda are so widely
distributed and their forms are so characteristic of biological con-
ditions that it is very desirable that every student of water forms,
even if his work is only of an amateur character, should be able
to make a separation into genera, and, in most cases, make at least
a provisional specific determination. Fortunately, the generic dis-
tinctions of our American forms are very easily made, and it is not
difficult to recognize some of the more common species.

Especially confusing to the beginner is the large number of im-
mature forms. Many of the larval stages of the more highly de-
veloped species resemble closely the mature forms of the simpler
species, so that the tyro is apt to think that he has a large number
of species, when he may have only several stages of one. It is
safest for the beginner to make no attempt at identification except
in the cases of evidently mature forms, such as egg-bearing females.

The Copepoda are an order of Crustacea, belonging to the sub-
class Entomostraca. Tliis subclass cannot be easily defined, but
it is sufficient for our purposes to say that they are the most simply
organized Crustacea. The Copepoda may be defined as those En-
tomostraca which do not have a shell-Hke covering of the body

COPEPODA

(in distinction from many of the Phyllopoda). wn,, i..ur or iivc
two-branched swimming feet on the thorax and an abdomen with-
out appendages. The Copepoda are divided into two subor(ler>.
the Eucopepoda and the Branchiura.

The Eucopepoda do not have compound e>es, and the Lg^s
develop in one or two brood pouches or ovisacs attached to the
abdomen. The Branchiura have two compound eyes. The females
do not have ovisacs, but the eggs are kud on stones or other con-
venient hard surfaces. The body is flattened. The KucopejKida
may be considered in two divisions, — Gnathosloniata. and Para,sita
or Siphonostomata. The Gnathostomata inckide the free-swim-
ming Copepoda; they have appendages about the mouth adapted
to mastication and the full number of body segments. The Si-
phonostomata are parasitic; they have the appendages alxiut the
mouth adapted for piercing or sucking, and generally also a re-
duced number of body segments. The following table shows this
classification :

Branch: Arthropoda.

Class: Crustacea.

Subclass: Entomostraca.
Order: Copepoda.

Suborder: (a) Eucopepoda.
Group I. Gnathostomata.
Group 2. Siphonostomata.
Suborder: (b) Branchiura.

KEY TO NORTH AMERICAN FREE-SWIMMING COPEI*ODA
(GNATHOSTOMATA)

I (104) Cephalothorax and abdomen distinctly separatL-d

2 (76) Antennae long, commonly nearly or quite as Ioiir as the whole

animal, and composed of 23, 24, or 25 segments. Antennae
of male asymmetrical, the right genicuhite and miMJilied as
a grasping organ. The fifth feet are uiilikc in the two sexes,
and in the male the right and left fifth feet arc dissimiLir.
Family CENXROPAcroAi

3(8,73) Endopoditesof first swimming feet composed of one segment. . .\

4 (7) Endopodites of second, third, and fourth swimming feet compose<l

of one segment. Each furcal ramus armed with three
large setae. Abdomen of male asymmetrical, and armed
on right side with a peculiar grasi)ing arrangement.

Epischuru . 5

756 FRESH-WATER BIOLOGY

5 (6) Abdomen of female not distinctly flexed to the right. Terminal

setae of furcae equal.

Epischura nevadensis Lilljeborg 1889.

Found in the mountain lakes of the western United States.
Length of female, 2 mm.
Length of male, 1.7 mm.

Fig. 1 1 74. Abdomen oi male Epischura nevadensis. X 24. (Original.)

6 (5) Abdomen of female distinctly flexed to the right, the external

furcal setae much larger than the others.

Epischura lacustris Forbes 1882.

Common in the Great Lakes and other large bodies of water in
the central and eastern United States.

Length of female, 1.78 mm.
Length of male, 1.38 mm.

Fig. 1 1 75. Abdomen of male Epischura lacustris. X 49. (Original.)

7 (4) Endopodites of second, third, and fourth feet composed of two

segments. Furcal rami elongated.

Eurylemora affinis Poppe 1880.

Really a salt-water form, and commonly found in fresh water only when it is more or less
closely connected with the sea. Only one species is known in America in fresh waters and that
has been found in waters connected with the Gulf of Mexico and the Atlantic Ocean.

Length of female, 1.5 mm.

Length of male, 1.5 mm.

8 (3' 73) Endopodites of first swimming feet composed of two segments, of

third and fourth swimming feet composed of three segments.
Furcal rami short. Right fifth foot of male terminates in
a more or less sickle-shaped hook. . . . Diaptomus. . 9

9 (22) Antepenultimate segment of the male right antenna without dis-
tinct appendage 10

COPEPODA

/ ^/

lo (ii) Right and left fifth feet of male nearly equal in length, icrminal
hook of right foot symmetrical.

Diaptumiis orcgomnsis Lilljeborg iSS«;.

The most widily <listril)Utc-«I of all North Amer-
ican species, and the one most likely to In- collc<.1c<l
in the northern part of the I'nite*! Statt-% It is
found from one side of the continent to the other.
The most noticeable characteristic is the equal
length of the fifth feet of the male

Length of female, 1.5 mm.

Length of male. 1.4 mm.

Fig. 1176. Diapinmus orrgonemii.
X 193. B, fifth foot of female.

.4. fifth fcrt u( Rulr.
X 200. (Uni'injl.i

11 (10) Left fifth foot of male shorter than right 12

12 (15) Left fifth foot reaching beyond first segment of right exopodile. . ij

13 (14) Terminal hook of right exopodite uniangular, right endopotlilc

equal in length to first segment of e.xopodile.

Diaptomus rcigluirdi Marsh iSt}^.

This has been found in only four localities, — Intermcfliate
Lake and Crooked Lake in northern Michigan, a lake on Beaver
Island in Lake Michigan, and Sodus Bay, N. V

Length of female. 1.14 mm.

Length of male, 1.02 mm.

Fig. 1177. Fifth feet of male DiJ />/<'««« rrKAurrfi. X US- (Original.)

14 (13) Terminal hook biangular, right cndopodite large, longer than \n>\
segment of exopodite.

Diaptomus mississippicnsis Marsh i.S«>4-

The most common form of the .Southern .States; it is abundant all
through the states bordering on the (iulf.

Length of female, i.-' mm.
Length oi male, i.i mm.

Fig 1178 Fifth feet of male Diaptomm misustippumis. X US

(.Orits'inal.)

758 FRESH-WATER BIOLOGY

15 (12) Left fifth foot of male, reaching end of first segment of right exopo-

dite, or only slightly exceeding it 16

16 (17) Antepenultimate segment of right antenna of male produced at

distal end into a blunt point, first segment of right exopo-
dite of fifth foot with marked quadrangular hyaHne appen-
dage Diaptomus hirgei Marsh 1894.

Fig. 1 1 79. Diaptomus birgei,ma.\e. ^ , terminal segment of right antenna. X iQi*
5, fifth feet. X 109. (Original.)

Common in Indiana and has been found in Wisconsin and on Long Island.
Length of female, 1.3 mm. Length of male, 1.2 mm.

17 (16) Antepenultimate segment of right antenna of male not produced

into blunt point on distal end 18

18 (19) Inner process of the terminal segment of exopodite of left male

fifth foot falciform, no hyaline appendage of first segment of
right exopodite Diaptomus pallidus Herrick 1879,

Occurs in Mississippi Valley, as far west as the foothills of the Rocky
Moimtains, but is comparatively rare north of Iowa and Illinois.
Length of female, 1.2 mm.
Length of male, 1.04 mm.

Fig. 1 180. Fiith ieet oi male Diaptomus pallidus. X 190- (Original.)

19 (i8)

20 (21)

COPEPODA

759

Inner process of terminal segment of left exopcxlitc of male i.fth
foot digitiform, hyaline appendage on internal distal angle
of first segment of right exo{)odite ,0

Lateral spine of second segment of right exopodite nearly straight
no blunt spine on posterior surLice of this se-gmenl. '

Diaptomui tyrtlli Vo\^\n: iSMM.

Widely spread in the mountain lak.-s of the West.
Lenf^th of female. 1.2 mm.
Length of male, 1.15 mm.

Fig. 1181. Fifth feet of male Diapiomui tyrtlli X lya
(Original.;

21 (20) A second hyaline appendage on dorsal side of distal margin of tirst

segment of right exopodite, lateral spine of second segment
of right exopodite strongly curved, and a blunt spine on
posterior surface of this segment.

Diaptomus coloradoisis Marsh i()i i.

In the Rocky Mountains in Colorado D. tyrclli is repiacctl by thi.s cio?<-Iy
allied species which is, apparently, the characteristic species of the moun-
tain lakes of Colorado.

Length of female, 1.38 mm.

Length of male, 1.32 mm.

Fig. 1182. Vdlh ieetol male Diaptomus coloTodemis. X uo. (.Original.)

22 (9) Antepenultimate segment of male riglu antenna with lateral lamella

or terminal process ^

23 (26, 42) Antepenultimate segment of right antenna of male Nvith h.Nalino

lamella

760

FRESH-WATER BIOLOGY

24 (25) Hyaline lamella broad, extending beyond the end of the segment,
second basal segment of right exopodite of male fifth foot
armed on the posterior surface with small hook.

Diaptomus leplopus Forbes 1882.

Found generally distributed through the
Mississippi Valley, and extending into Canada.
The variety piscinae occurs in some of the
more northern collections and as far west as
Flathead Lake, Montana. This dififers from
typical leplopus mainly in the greater length
of the endopodites of the male fifth feet and
in the fact that in the female fifth feet the
third segment of the exopodite is indistinctly
separated and armed with two spines with a
third one present on the second segment.
This third spine is absent in leplopus.

Length of female, 1.5 to 1.89 mm.

Length of male, 1.4 to 1.83 mm.

Fig. 1 1 83. Diaptomus leplopus, male. A, ter-
minal segments of right antenna. X 185. B,
fifth feet. X 83. (Original.)

25 (24)

Hyaline lamella narrow, extending beyond the end of the segment
slightly, if at all; first basal segment of right fifth foot of
male armed with hook equal in length to first segment of
exopodite Diaptomus clavipes Schacht 1897.

Has been found in three locali-
ties, in West Okoboji Lake, Iowa,
near Lincoln, Nebraska, and at
Greeley, Colorado.

Length of female from 1.37
to 2.5 mm.

Fig. 1184. Diaptomus clavipes, male.
A, fifth feet. X 83. B, terminal
segments of right antenna. X 141.
(Original.)

26 (23, 42) Antepenultimate segment of right antenna of male bears a slender
straight process 27

COPEPODA

761

27(32,35) Process much shorter than penultimate segment ,8

28 (31) Right endopodite of male fifth foot ru(hmentary [ ] ,g

29 (30) Lateral spine of second segment of right cx.,p«,.liic of male fifih

foot terminal Diuplunnts lintnn; v>>r)>,.. ,s.. .

Founri in Yellow-
stone I'ark an«l ui
tin- vallo' of the
(iailalin River,

Mont.ui.i

OiaUommt

.-l.fiMhfr^

Flc..tiHy
Union i

..Irn.ilr . M f<
t' r:r, :, ;, ■ .r..r- ■
<>i r:.(.t .i;.;f nr ; •
nvalf X 2 30 (
fifth foot of female
X 35&- (Ohsiiul )

30 (29)

Lateral spine of second segment of right cxopodite of male fifth fool
near the proximal end. . Diaptomus trybomi Lilljclx>rg 1H89.

Fig. 1186. Diaptomus trybomi. ^, abdomen of female. X 70 '':/'f|^ ''^' ''^ Ti'-.K,^.','**^
C, terminal segments of right antenna of male. X 100. (After Dc Oucnie and Kichanl )

The antenna! process is dentate on the outer margin and the alxiomcn of the female awi
metrical. Has been found only in Oregon.

Length of female, 1.5 mm.
Length of male, 1.4 mm.

762 FRESH-WATER BIOLOGY

31 (28) Right endopodite of male fifth foot about equal in length to first
segment of exopodite. . . Diapiomus judayi Marsh 1907.

Fig. 1187. Diaptomus judayi. A, terminal segments of right antenna of male. X 290. B, fifth feet
of male. X i45- C, abdomen of female. X 165. (Original.)
Lateral spine of the second segment of the right exopodite is median, first segment of the
female abdomen has a process on the posterior margin on the right side. Has been found only
in the mountains of Colorado.

Length of female, 0.93 mm.
Length of male, 0.9 mm.

32 (27. 35) Process nearly or fully equals penultimate segment 33

33 (^34; Right endopodite of male fifth foot equals in length first segment

of exopodite, spines of first basal segments large.

Diaptomus tenuicaudatus Marsh 1907.

Found in Saskatchewan.
Length of male, 1.195 mm.

Fig. 1 188. Diaptomus tenuicaudatus, male. A , fifth feet.
X 145. B, terminal segments of right antenna.
X 194- (Original.)

COPEPODA

763

34 (33) Right endopodite of male fifth f(X)t exceeds length of first segment
of exopodite, spines of first bas^d scgnu-nts small.

Diaptumus siciiis Forbes i»8i.

Found in the GrcAt XaktK f»nnjt
the m<)st abundant form laJccn in
limnetic ( ollertions; found to M>mr
extent in other lake* in the vimc
KeneraJ ri^ion. It iv a% a rule,
confme*! to the larger and flcrtwr
lakes. It is fre«iuently founcl a\m>-
ciate<i with I) miniUus l»ut i» read-
ily distinKuishe<l by the sJefMlrr.
symmetrical, sitkleshaiirtl hcmk
terminating the cxofM^lite trf the
riRhl fifth f<K»t of the male; thi* it
not a characteristic, h«iwever, that
will distinguish it frc)m s{irc>cs
found in other Ifnalities.

Lenjjth of fem;iJe. 1 js mm
Length of male, i i <; nun

Fig. 1 189. Diaptomus siciiis, male. A, terminal segments of
right antenna. X 194. B. fifth feet. X i94- (Original.)

35 (27, 32) Process exceeds in length penultimate segment 36

36 (39) Large. Lateral spine of second segment of exopotlite of right fifth

foot of male terminal or nearly so 37

37 (38) Process of antepenultimate segment of right antenna of male only

slightly longer than penultimate segment, antennae equal in
length to cephalothorax.

Diaptomus slwshonc Forbes 1803.

Rocky Mountains. Not so wi<1«prr*d
or characteristic of the mountain lakes ai
D. Tyrelli Popix-, althou>:h this K>ant n|*^
cics is by no means uncommon, juul i* e>|^-
ciaily striking because commonly colortd •
brigiit red.

IxMigth of fem.ile. J 9 mm.

Length of male, i.5 mm.

Fig. 1190. Diaptomus Shoshone, ma\e. i4, fifth feet.
X 108. B, terminal segments of right antenna.
X 180. (Original.)

764

FRESH-WATER BIOLOGY

38 (37) Antennal process of male exceeds ultimate segment, antennae
reach furca Diaptomus wardi Pearse 1905.

Washington.

Length of female, 2.9 mm.

Length of male, 1.6 mm.

Fig. 1 191. Diaptomus wardi, male. A, fifth feet.
X 173- B, terminal segments of right antenna.
X 112. (After Pearse.)

39 (36) Small. Lateral spine of second segment of right exopodite of
male on proximal half of segment, antennae reach beyond
furca 40

40 (41) Lateral spine of second segment of right exopodite of male fifth
foot short, right endopodite rudimentary, endopodites of
female fifth feet rudimentary.

Diaptomus minutus Lilljeborg 1889.

Northern United States and north
to Greenland and Iceland. It is one
of the most easily recognized species
because of the broad, saber-like hook
on the right fifth foot of the male and
the rudimentary endopodites of the
fifth feet of both sexes. It is common
in the waters of the Great Lakes, but
that is as far south as one may expect
to find it.

Length of female, i to i.i mm.

Length of male, i mm.

Fig. 1192. Diaptomus minutus. v4, fifth foot
of male. X 154. B, fifth feet of female.
X 200. (Original.)

COPEPODA

76s

41 (40) Lateral spine of second segment of right cxopoditc of male fifth
foot long, right endopodite criuals in length first sfjcmcnl
ofexopodite Oiaptomus ashLnJt SUr^h iSi^s

Foun<l in the Grrat Lakrs and v>ro«
lakes immt-diatcly n »nnra r«l wjlh them
and west to thr Slate <»f WashinKton.

Length of frmale. o.<>7 mm.

Length ^.>i male, o.tiy mm.

Fig. 1 193. Dijptomus ashlandi, male. .4, fifth
feet. X 145- B, terminal segments of right
antenna. X 145- (Original.)

42 (23, 26) Antepenultimate segment of right antenna of male l)cars curved
process 43

43 (46) Process equals or exceeds in length penultimate segment.

44 (45) Process about equals in length last two segments, second hasal
segment of right fifth foot of male dilated on inner margin,
endopodites of fifth feet in both sexes indi.>itincily two-
segmented Diaptomus cisoii Lilljeborg iSS<j.

Has been found only in CAlifomi*
and Nebraska.

IxnKth of female. 4 nmi
Length of male, j.5 mm.

Fig. 1194. DiaMomus
X 38. B, terminal
X 133- (Original.)

eiseni, male,
segments of

A. fifth feet,
right antenna.

766 FRESH-WATER BIOLOGY

45 (44) Process slightly exceeds in length penultimate segment, second

basal segment of right fifth
foot of male not dilated on
inner margin, endopodite
of left fifth foot one-seg-
mented.

Diaptomus franciscanus
Lilljeborg 1889.

Found only near San Fran-
cisco.

Length of female, 2.3 mm.
Length of male, 2 mm.

Fig. 1 195- Diaptomus Jranciscanus, male A, terminal
segments of right antenna. X 20c. B, fifth feet.
X 200. (After De Guerne and Richard.)

46 (43) Process shorter than penultimate segment 47

47 (66) One or both terminal processes of last segment of left exopodite of

male fifth foot distinctly falciform 48

48 (56, 63) Right endopodite of fifth foot of male small, shorter than first

segment of exopodite 49

49 (53) Terminal segment of right exopodite of fifth foot of male elon-

gate 50

50 (51, 52) In fifth foot of male right endopodite rudimentary, left endopodite

two-segmented and spatulate in form.

Diaptomus spatulocrenatus Pearse 1906.

Found in New England.
Length of female, 1.52 mm.
Length of male, 1.3 1.

Fig. 1196. Fifth feet of male Diaptomus spatulocrenatus. X 84.
(After Pearse.)

COPEPODA

767

51 (50, 52) Terminal segment of right cxopoditc („ „nh i.K.t oi niaU iiiuch
broader at distal end. lateral spine nearly Icrminal and
straight, left endopoditc elongate.

Diaptomus lonipfJatus Marsh 1907.

Founr! in I^ui^tana.
lA-riKth «)f ft-malc. i 49 mm.
LtnKth of male, i j?s mm

Fig. 1 197, Diaptomus conipedatus, maXt. ^, fifth feet. X 126.
B, terminal segments of right antenna. X 193. (Original.)

52 (50, 51) Terminal hook of right exopodite of fifth foot of malt- falciform,
lateral spine at distal third of segment, sei'ond Iw.sal seg-
ment of right foot broad at distal end with i)rotiiis at
external distal angle.

Diaptomus sanguifuus Forbes 1876.

Mississippi Valley. Occur* in
spriiiK. in st;i>:nanl pooJv

Ix-ngth of fi-malc. 1.4 lu j 1; mm
Length of male, i to 2 ram.

Fig. 1198. Diaptomus sanguineus, yl, terminal seg-
ments of right antenna of male. X i93- ^. hlth
feet of same. X no. (Original.)

768 FRESH-WATER BIOLOGY

53 (49) Terminal segment of right exopodite of male fifth feet of usual

length, lateral spine terminal 54

54 (55)^ Inner surface of left endopodite of male fifth foot rugose, terminal

, , spines of endopodites

' ^ of female fifth feet very

long.

Diaptomus stagnalis
Forbes 1882.

A very large species
found in the Mississippi
Valley in the spring.
Length of female, 4 to

4.5 mm.

Length of male, 3.5 to

4 mm.

Fig. 1199. Diaptomus stagnalis. ^ , fifth foot of female. (After Forbes.)
B, fifth feet of male. (After Herrick. and Turner.)

55 (54) In male, segments of right fifth foot short and broad, terminal hook
long and strongly curved, lateral spine long and straight;
in female, dorsal process on fifth cephalothoracic segment,
endopodites of fifth feet short and one-segmented.

Diaptomus saltillinus Brewer 1898.

Found in Nebraska.

Length of female, 1.5 mm.

Length of male, 1.25 mm.

Fig. 1200. Diaptomus saltillinus. A. terminal segments of right antenna of male. X 193-
feet of same. X 126. C, fifth foot of female. X 19.3. D, dorsal process of same.
(Original.)

COPEPODA

769

56 (48, 63) Right endopodite of fifth foot of male distinctly longer than first

segment of exopodite. .

57

57 (60) Second segment of right exopodite of male- fifth foot has oblique

ridge on posterior surface \g

58 (59) First segment of right exopoch'te of maK- lifth f.K.t has transversa'
ridge on the posterior surface.

Diaptomus asymmt trims Marsh nx>7.

Fig. 1201. Diaptomus asymmetricus .
male. X 103. B, abdomen of
(Original.)

A, fifth feet of
female. X yy.

In the male fifth f(jol the lateral
spine of the terminal »cKinrnt i*
about one-half as lung as ihc seg-
ment; the first segment of the fcnuir
abdomen has a prominent swelling on
the right side. Found in Cul*a.

LenKth of female, i.jg mm.

Length of male, i.i6 mm.

59 (58) First segment of right exopodite of male fifth foot has two curved
processes on posterior surface.

Diaptomus J or sal is Marsh ujo;.

In the male fifth UnA the I '.•'-'■
spine of the terminal s*Tment •
or e.xceeds in len>:th the s«-Rnui.;
fifth cephalothoracic seRmrnt .: ;
female i.s armnl with t»-o .1 r .
proies.ses. Found in lA)uiMan.i .1:.
Florida and probably in other state
bordering on the (iulf of .Mcxiio.

Length of female. 1 . 1 i mm.

Length of male, i.oog mm.

; 1202. Diaptomus darsalis. .4. fifth feet ol m*l« X U*
B, |)rofile dorsjil surface of cephalothorax ol Icmalc .X v--*
((jnginal.)

770
6o (57)

FRESH-WATER BIOLOGY

Second segment of right exopodite of fifth foot of male does not
have oblique ridge on posterior surface 6i

6i (62) Lateral spine of terminal segment of right exopodite of male fifth
foot terminal, endopodites distinctly two-segmented.

Diaptomus bakeri Marsh 1907.

In the female fifth foot the exopodites are
distinctly three-segmented, the endopodites
distinctly two-segmented. Found in Cali-
fornia.

Length of female, 1.27 mm.

Length of male, 1.124 mm.

Fig, 1203. Diaptomus bakeri.
X no. B, fifth foot of female.

A, fifth feet of male.
X 193. (Original.)

62 (61) Lateral spine of terminal segment of right exopodite of male fifth
foot situated on distal third of segment, right endopodite
indistinctly two-segmented, left one-segmented.

Diaptomus washingtonensis Marsh 1907.

The first abdominal
segment of the female
has a digitiform process
on the right posterior
border. Found in
Washington.

Length of female,

1. 187 mm.

Length of male,

1. 137 mm.

Fig. 1204. Diaptomus washingtonensis. yl , fifth feet of male. X 126.
B, abdomen of female. X no. (Onginal.)

COPEPODA

71

63 (48, 56) Right endopodite of fifth foot of male equals or only slightly ex-
ceeds first segment of exopodite (,»

64 (65) Terminal segment of right exopodite of male fifth fool ha> uhh^uc
ridge on posterior surface, lateral si)ine exceeds .scRment in
length Diaplomus lilhuijutrifuiniis Uvrtick liiijt

The fifth ccphalothoraric soRmcnt i.i ir.r umjue
has a dorsal pnui-ss, and thi- «-nd«»p«>ditr* of the
fifth feet are commonly two M-Kmcntr<l. Ki.untl in
New Mexico and Colorado. As thr rvamr irvli-
Gates, this form was ori^nally <lt"x-ril>c«l l»y Her-
rick, from material coUectcil in All»u<iucr<iuc. N M.
It is found, however, from Colorado to thr City ol
Mexico, and seems to be a tyfiical fonn o< the
Southwest.

Length of female. 1.7'' mm.

Length of male, 1.58 mm.

Fig. 1205. Diaptomus albuquerquensis. ^.dor-
sal process of female. X 180. B, fifth feet of
male. X 49. (Original.)

65 (64)

Terminal segment of right exopodite of male fifth foot (loes not
have oblique ridge on posterior surface; lateral spine short,
about one-half length of segment.

Diaptomus novatncxicanus Merrick 1895.

Fig. 1206. Fifth feet of
male Diaptomus novamexi-
canus. (After Herrick and
Turner.)

F'ound in New Mexico.
Length of female, i.i t<

66 (47)

Terminal orocesses of left exopodite of fifth fcx-t of male digili-
^form^dght endopodite shorter than first segment of exopc.
dite

772 FRESH- WATER BIOLOGY

67 (70) ■ First segment of exopodite of male fifth foot without hyaline
appendage 68

68 (69) Right endopodite of male fifth foot triangular in form, first ab-
dominal segment of female has digitiform process on right
posterior border Diaptomus nudus Marsh 1904,

Found in lakes near Pikes Peak,
Colorado.

Length of female, 1.132 mm.
Length of male, 1.115 di°i-

Fig. 1207. Diaptomus nudus. A. fifth feet of
male. X 105. B, abdomen of female. X 105.
(Original.)

69 (68) In male fifth foot, second basal segment with hyaline appendage
on inner margin, first segment of right exopodite with trans-
verse ridge, second segment with obHque ridge and hyaline
process near the outer margin.

Diaptomus purpureus Marsh 1907.

Found in Cuba. This is a conspicuous species, both on account of
the large size and the purple color of the furcae, furcal setae, and distal
ends of the antennae.

Length of female, 2.56 mm.

Length of male, 2.24 mm.

Fig. 1208. Fifth feet of male Diaptomus purpureus. X 76. (Original.)

COPEPODA

773

70 (67) First segment of right exopoditc of male fifth foot has hx-alinc
appendage ,

71 (72)

Hyahne appendage of first segment of exojxxlite of male fi/lh fool
at mner distal angle, endopKxlite of right foot about equals
first segment of exopodite.

Diaptomus signimmia Lilljclxjrg iMH<).

Fig. i20g. Diaptomus signicauda. /I, abdomen
of female. X 118. B, fifth feet of male.
X 174- (Original.)

The first segment of ihc abdcimcn ol
the female ha.s a difo'tifurm pr««'-^» •■"
the ri^ht posterior border K'-
mountain regions of wrMrrn '
States. It reprf>tnt
that are f()un<l in tli'
of the western p;irl 1.;
The peculiar apjK-ml,;
ment of the fcmali-
the name to the s|k-. .t ^ ,.
teristic of the Kroup. lOli'
Rocky Mountains and far'
likely to contain this or all'

Length of female, o •,

Length of m.ilc our.

72 (71) Hyaline appendage of first segment of exopodite of male fifth fo»il
on inner distal half, cndoi)odite of right fifth fool much
shorter than first segment of exopodite.

Diaptomus siciloidcs Lilljcborg iHvS<>.

Found in the Mississippi Valley and west to C alifurnia. A» D '^'f*^
ensis is typical of the Northern States, so D. suMrs m.tv ♦>r ronMdrfr.1
as typical of a region a little farther to the south. It • -^

Long Island on the east to the Rocky Mountains on :
not the exclusive form, is more a|)t to hv seen th,in .r ^

along the Ohio River.

Length of female. i.cX) to i.2iS '"f"

Length of male, i.oi to i.ii.'S nam.

Fig. 1210. Fifth feet
of male Diaptomus
siciloides. X 122.
(Original.)

73 (3, 8) Endopodites of first swimming feet comiH.scd of three s,-pmrnt.

74

774 FRESH-WATER BIOLOGY

74 (75) Endopodites of all swimming feet composed of three segments,
antennae of 23 segments (according to Herrick 24), furca
short. Only one species.

OsphKanticum lahronectum Forbes 1882.

Found widely distributed in the United States, more frequently
in the Mississippi Valley but never in large numbers, so that it is
comparatively rare in collections.

Length of female, 1.7 mm.

Length of male, 1.36 mm.

Fig. 1211. Abdomen of female Osphranticum labronectum. X 51.
(Original.)

75 (74) Endopodites of all swimming feet composed of three segments,
antennae of 25 segments, furca long.

Limnocalanus macrurus Sars 1862.

Found only in deep lakes. It is especially interesting, as it is the only
species of the Centropagidae found in both Europe and America. It is
widely distributed in northern Europe and Asia and is found in salt water
as well as in fresh. It is considered a representative of the "fauna re-
licta," that is, it is a salt water form which has become adapted to the
environment of fresh water.

Length of female, 2.4 mm.

Length of male, 2.2 mm.

Fig, 1212. Abdomen oiicxmXe Limnocalanus macrurus. X 37. (Original.)

76 (2) Antennae short, never longer than cephalothorax, generally much

shorter, and composed of from six to seventeen segments;
antennae of male symmetrically geniculate; fifth feet rudi-
mentary, composed of from one to three segments.

Family Cyclopidae.

Only one genus Cyclops . . 77

COPEPODA

The main points to be noted in the specific determination of the Rcnus ut:
length and number of segments in the antenna of the female;
armature of the antennal segments, espcciallv oi the lermiiuU'scjfmcnlA;
form of the abdomen, especially the form and armature of the (ureal rami'
form and armature of the rudimentary- fifth feet;

structure of the second antennae, of the maxillii)e<les. and of the swimminic feet
These last structures are of less importance.

77 (98) Antennae composed of twelve or more segments.

78 (92, 93) Antennae composed of seventeen segments 71;

79 (80) Fifth feet composed of one segment armed with one sf)inc anci

two long setae Cyclops atcr Hcrrick i88i.

It is a large dark-colored species, rather rare, probably diMrihutc«l very
widely, and growing in shallow water. In spite of its 'wide dinnbutian.
however, it is a rare form.

Length of female, 1.77 to 2.88 mm.
Fig. 1213. Fifth foot of Cyclops atrr. X J'/). iOri<inAl .

80(79) Fifth feet composed of two segments. . ^I

81 (84, 89) Second segment of fifth feet armed with seta and short spine. 82

82 (83) Spine of second segment of fifth feet small and near i-nd of .v-g

ment; last three segments of female antenna without hya-
line membrane Cyclops viridis J urine i8io.

Fig. 1 2 14. Abdomen of fe-
male Cyclops viridis, var.
americanus. X 77> (Origi-
nal.)

Fig. 1 2 15. Abdomen of
female Cyclops viridis,
var. brevispinosus. X
66. (Original.)

Cyclop

(or

Fi/lh (oo« ol
tiridii. X ilS.

ruciiuil.

(1 laki-s.
mil)

A widely distributed species, being found both in jxxils anc
form and general appearance, so that it has receive<l a number of ditlerrnl
which are now reduced to varieties, since it has been ftuind that there arr intr
showing all the stages between the extremes. W he
colored, while its relatives living in the open waters ol

It varies k'riMtl\
litlerrnl

III

When living i'l l>«»*'b

It IS apt t.. i< 'ri4y
)f our lakes are lolorli-ss and llm«»^i tran»-
par^ent? lEspVcially"nodcVabIe"is"th^^ the form of the fur..d r.n.i .v. ^h. wn in

Figs. 1214 and 1215. The forms found in pools generally have com|Kirai: ■ A

furcal rami; on the other hand, the forms in deep waters have Ions an.. «•

Even in the Hmnetic forms there is wide variation. n typi. .U virulis tlu ;. .
the outer angle of the furcal ramus. This is replaced in the orm whuh Hrrr »•

spinosus by a short broad spine. This variety is a common limnetic form u. «

lakes; a form with the furca armed at its outer angle with a srta ''•j;' 'M»'; •"
from mridis in the structure of the swimming feet and ot the lilt 1 ic-rt.
common in shallow waters, and is the variety that is m.)st rt-quent y scrti ^^

United States. Wherever a collection is made one is likely to get some form oi i^.-w. *aa
generally it will be americanus.

Length of female, 1.25 to 1.5 mm.

FRESH-WATER BIOLOGY

Spine of second segment of fifth foot stout, located at about middle
of segment; last three segments of female antenna with
delicate pectinate hyaline membrane.

Cyclops strenuus Fischer 1851.

It is one of the most common forms on the continent of Europe, but has
been found in America in only one locality, — a pond in the Adirondacks. It
is probable, of course, that it will be found in other localities, but it is a curi-
ous fact that hitherto it has been found only in a single collection. In its
general form it closely resembles viridis.

Length of female, 1.35 mm.

Fig. 1217. Fifth foot of Cyclops strenuus. X 358. (Original.)

84 (81, 89) Second segment of fifth feet armed with two setae 85

85 (86) Second segment of fifth feet elongate, inner setae spine-like, much

shorter than outer. . . . Cyclops bicuspidatus Claus 1857.

Fig. 1218. Abdo-
men of Cyclops bi-
cuspidatus. X 76.
(Original.)

Fig. 1 2 19. Abdo-
men of Cyclops bi-
cuspidatus, var.
navus. X 62.
(Original.)

Fig. 1220. Fifth foot
of Cyclops bicuspi-
datus. X 227.
(Original.)

The furca of this species is very characteristic. It not only has a lateral seta at a little more
than one-half its length, but it has a httle depression armed with minute spines on its outer
margin at a little less than one-fourth of its length. These characteristics — the position of the
lateral seta, the lateral depression with the elongated furca — are presumptive evidence that a
species with seventeen segmented antennae is bicuspidatus. If, in addition, one can make out
the two terminal setae on the second segment of the fifth feet, he can be pretty certain of his
identification. Cyclops bicuspidatus is most commonly a limnetic species, and is the Cyclops
which may be considered as characteristic of the Great Lakes. While the form described and
figured is the common one, this species has varieties simila" to those noted for viridis, and we
sometimes find in pools a form agreeing in general structure with the typical forms, but with a
short furca. This modification was named navus by Herrick, and the name can be well retained
as a varietal distinction. Navus, however, is not so common in pools as the corresponding
variety of viridis. Fig. 12 18 shows the typical form of furca in bicuspidatus, and Fig. i2ig the
form in the variety navus.

Length of female, i.i mm.

86 (85) Second segment of fifth feet short, armed with two nearly equal
setae 87

COPEPODA

87 (88)

Setae of fifth feet very elongate, last anlennal scgmcnl armeti wiih
serrate hyaline plate; common.

Cyclops Icuckarti Cbus 1857.

This sixties \s < " ..,

of the furcic. N
segmented antrtu;
of short rami, with ilu l.iii :
about midway of its liiit'th I
the structure of thi- lift I • ■
be quite sure of the i-:
American species has il
tion of tenuis, ami, vi fa-
only one locality. Thi

in another place, is pc :

is almost world wide in its <
been found in all continents.
variations which are fouml in
are also world wide, so that
Fig. 1221. Cyclops leuckarli. A, abdomen seems to have no efle* t <jn lli.
of female. X 69. B, fifth foot of same. Length of female. 1 a li.n.

X 232. (Original.)

(87) Setae of fifth feet of moderate length, last antennal st-gmcnl with-
out hyaline plate Cyclops tniuis Mav>h iQio.

It has been found in .Arizona and in the Isthmus o( Panama.
Length of female, i.i mm.

Fig.

Fifth foot of Cvc/u/)5 /fwttii. X 2:1. (OrifinaL)

89 (81, 84) Second segment of fifth feet armed with three setae. . ■ o

00 (91) With sensory club on twelfth anlennal segment, hyaline plaU of
seventeenth antennal segment smooth or srrrale. oRg .sacs
standing out from abdomen. . Cyclops albidus Junnc 1820.

77^ FRESH-WATER BIOLOGY

91 (90) With sensory hair on twelfth antennal segment, hyaHne plate of
seventeenth antennal segment deeply notched, egg sacs
lying close to abdomen. . . . Cyclops fuscus Jurine 1S20.

Cyclops fuscus and C. albidus resemble each other very closely, and it is only .
by a careful examination that they can be distinguished. They are very com-
mon, especially in pond collections, Cyclops albidus being found much the more
frequently. They are much larger than C. leuckarti and the furcal armature dif-
fers in that the lateral seta is placed near the end of the ramus (Fig. 1223). The
form of the fifth feet and of the furcal rami will readily serve to show when we
have one of these two species, and in most cases it will prove to be Cyclops albidus.
Length of female, about 2 mm.

Fig, 1224. Antennal segments of female Cyclops fuscus. X i37- (Original.)

92 (78, 93) Antennae composed of sixteen segments, fifth feet of three seg-
ments Cyclops modestus Herrick 1883.

This species is comparatively rare altho it has been found in a con-
siderable number of places. It occurs as far east as Pennsylvania, as
far west as Wyoming, while its northern and southern limits are Wis-
coDBin and Alabama.

Length of female, 1.2 to 1.25 mm.

Fig. 1225. Cyclops modestus. A, abdomen of
female. X 179. B, fifth foot. X 448.
(Original.)

93 (78, 92) Antennae composed of twelve segments, fifth feet of one segment.

94

94 (97) Fifth feet armed with three setae, swimming feet composed of
three segments • 95

779

95 (96)

COPEPODA

Furcae of variable length, armtd cxitrnally with a njw -
spines; very common. . . Cyi lops srrruJutus I is^ht::

The loiiK twelve scxmcntctl antennae uui thr trt

rate marKine<l furral rami M-nc u> «lf- ' •'

species. The fiKure i»f ihi- alHlonjrn 'I
acteristic structure of the f ureal r.tn-
gocxl deal of variation in the :
When scrrulalus is limnetic in
rami are lonj,' and slen<ler; ihi^
variety clt'Kans Herritk. When il iivcs m i-
littoral waters, the furcal rami arc <ih<irt an ■
this form is known as varir'- ' ' "

abdomen l'if,'ure<l may he m;
latus, dedans hc'\i\^, mut.\\ lu

sfwndingly shorter. Found every wiicri: liic »u*U over.
Length of female, o.8 to 1.25 mna.

Fig. 1226. Cyclops serrulatus. A, abdo-
men of female. X 67. B, fifth foot of
same. X 213. (Original.)

96 (95) Furcae short, without lateral row of spines.

Cyclops prasinus Kischcr iH/x>.

It is a minute limnetic form. It resembles serruiaius in \is lonx twdvr-

segmented antennae, but its abdomen is ver>' different. The fun .-J

resemble leuckarti in the fact that the lateral seta is jjlace*! at a\>
way of the length, but the species is distinguishe<l at a glance, not ■
its smaller size, but by the fact that the antennae are comiiosc<l 0/ t^cl'.c
segments. Cyclops prasinus is widely distril)ulc>d. esixxially in ibc laxxrr
bodies of water. It is common in the Great Lakes.
Length of female, 0.48 mm.

Fig. 1227.

Abdomen of female Cyclops prasinus. X I37- (Ori«iaaL)

07 (04) Fifth feet armed with one seta, swimming feet of two scgmcnls.

Cyclops varUijfts SAn> \^ 3.

Cyclops varicans occurs in Panama and Guatemala, but there are no authentic rrcurU* ol it«
occurrence in the United States.

98 (77) Antenna composed of eleven segments or less 99

99 (102, 103) Antennae composed of eleven segments 100

100 (loi Rami of swimming feet composed of ^l^^'/^'P"^^^-"-, ., . . .

Cyclops pitiilcratus Koch i^js.

This stout dark-colored species is not uncommon in shallow Ukr» and

.inant S^is and is readily recogni.cHl by the character, pvcn m ihc key.

Length of female, i.i mm.

stagnant pools, and

Fig. 1228. Abdomen of female Cyclops pkaUratus. X 69. (l)ri«in*U

x^

780 FRESH-WATER BIOLOGY

loi (100) Rami of swimming feet composed of two segments.

Cyclops bicolor Sars 1863.

It is not common, but is occasionally seen. The only species with
which it is Hkely to be confused is phaleratus, and the difference in the
segmentation of the swimming feet makes the distinction easy, as the
rami have only two segments, while in phaleratus they have three. The
fifth foot consists of a single segment and bears one spine.
X Length of female, 0.5 mm.

\ Fig. 1229. Fifth foot of Cyclops bicolor. X 450- (Original.)

102 (99, 103) Antennae composed of eight segments.

Cyclops fimhriatus Fischer 1853.

Is the only species with antennae of eight segments, and, if found, can easily be recognized
by this characteristic if one is sure that he is examining mature forms.
Length of female, 0.7 to 0.84 mm.

103 (99, 102) Antennae composed of six segments.

Cyclops aequoreus Fischer i860.

Found only in brackish water. It has been found in
America in waters connected with the Gulf of Mexico,
and those connected with the Pacific Ocean in Panama.

Fig. 1230. Abdomen and fifth feet of female Cyclops aequoreus.
X 73- (Original.)

104 (i) Cephalo thorax and abdomen not distinctly separated, so that the

whole body is somewhat worm-like; antennae short, never
composed of more than eight segments.

Family Harpacticidae . . 105
All species of Harpacticidae are very minute. Only a few species have been described and
those very inadequately. Probably there are many undescribed species and other genera
than those mentioned.

105 (108) Antennae composed of six segments, endopodites of all swimming

feet composed of two segments, segments of endopodite of
fourth foot fused so as to appear as one, endopodite of first
foot slightly elongate; found in fresh and brackish waters,
in New Mexico Marshia . . 106

106 (107) Furca of female two and one-half times as long as broad, furca of male

four times as long as broad, median furcal setae fused at base.
Marshia albuquerquensis Herrick 1895.

107 (106) Furcae of female and male twice as long as broad, median furcal

setae not fused at base. . Marshia hrevicaudala Herrick 1895.

108 (105) Antennae composed of eight segments, endopodites of swimming

feet composed of two or three segments, endopodite of third
foot usually much longer than exopodite, endopodite of male
fifth foot always of three segments.

Canthocamptus . . 109

COPEPODA

109 (120) Anal plate without spines, or sjiines are simple-, i.e.. .lu n..i n.i%.-

two points

no

110(113) Sides of last abdominal segment Ikivc spine-like prolonRalioii
caudad

Ill (112) Spines of anal plate few in number, noi cAcccning iivt- or s.x.

Cantliocamptiis slaphylitwidfs iVar^t- I.X)^.

^Ifc

Fig. 1231. Anal plate and furta <>( i anthomrnpiw ;..
(Aftir I'l-arsc 1

112 (ill) Spines of anal plate numerous.

Cant/ii),(inif)ti(s st<ipliyliuus (Jurinc) i8ao.

Fig. 1232. Last segment and furcai-of maXc Cantkuamptui tUipkyitmmt
(After Schmcil.j

113 (no) Sides of last abdominal segment do not have spine-like i>rolonpntion

caudad ;

114 (115) Furca long and slender, nearly four times as long .i.s uidc.

Canthocamplus idahocnsis Marsh igoj.

Fig. 1233. Furcaeof female rdw/A"r<Jwi/)/Mi I /.Jf.<'t>i< X 1 .-a

115 (114) Furca short, its length not exceeding twice its width ... 116

116(119) Furca with two setae '"

117 (118) Anal plate with spines. . Canthocamptus illinoisnisis ForU

118(117) Anal plate without spines. . Canthocamptus hicmalis PcarM.- i .>05.

/

Fig 1-34. AmJ plate of female Tjn/AiVdw^tej Ai**»«/u. >< 144-
>^ ■ (After I'can*e.)

782 FRESH-WATER BIOLOGY

1 19 (116) Furca with three setae. . Canthocamptus northumhricus Brady 1880.
This is probably, next to minutus, the most widely distributed species in North America.

120 (109) Spines of anal plate bifid. . . Canthocamptus minutus Claus 1863.

This is the most common species and is found everywhere in the north-
em continents.

Fig. 1235. The last segment and furcae of male Canthocamptus minutus.
(After Schmeil.)

SlPHONOSTOMATA

The parasitic Copepoda pass all or a part of their lives as para-
sites upon fish and other animals. They are exceedingly numer-
ous in both salt and fresh water, and very interesting because of
the strange forms which many of them assume, — forms which
would appear to be in no way related to the structure of a copepod.
Many of them would be taken for worms. Some bore into the
tissues of their hosts, others dwell in the gills, and still others in
the nasal cavities. One species is very abundant on the sheeps-
head of the Central States.

The appendages are profoundly modified to adapt them to their
parasitic existence. The swimming feet are more or less rudimen-
tary. The appendages about the mouth are modified into sucking
or prehensile organs. The antennae are similarly modified. In
some the second antennae are armed at the end with hooks to
enable the animal to retain its hold on its host. In some that are
semiparasitic, the appendages from the opposite sides are joined
together in a sucker. Sometimes the segmentation of the body
disappears entirely. The appendages in some are reduced to mere
protuberances, or may be hke roots penetrating the body of the
host.

And yet all these forms are free-swimming in their early stages.
When hatched from the egg they have the typical nauphus form

COPEPODA ^g^

of the true copepods, and go through a process of degeneration
later. In some the male dies immediately after reaching the ( ychps
stage; in others, the male, while highly organized, is very small and
lives as a parasite on the body of the fenKilc.

The parasitic Copepoda are much more numerous in salt watt-r
than in fresh. In an ordinary examination of fresh-water collec-
tions one is not apt to find them, although the male of ErgasUus
is occasionally seen. An examination of almost any group of fish.
however, will show that they are not at all rare.

It is a most fascinating study to compare the structure of these
degenerate forms with the highly organized free-swimming species.
thus finding evidence of the true copepod structure in animals that
at first sight would seem to be far removed from the co|K'P<k1.s.
The structural relationships of these peculiar forms are only im-
perfectly understood, so that no satisfactory classification has been
made, and, pending more thorough knowledge, all are grou[x*d
together, in a somewhat unscientific way, under the term " Siphom^
stomata." Although it is well known that these forms are very
numerous in the fresh waters of America, the family of the K^.- .
silidae is the only one which has been studied from a systen. •;
standpoint. Almost total ignorance prevails in regarti to the spe-
cies of the other families. From the studies in other countries
something is known of these famihes, and it may be assumed that
representatives of all of them can be found in American waters.
For the sake of completeness of record these families, six in all.
will be characterized briefly.

1. Ergasilidae. These resemble very closel)' the free-swimming
copepods, the general form being much like that of the Cyclopidae.
The second antennae are armed at the ends with h(K>ks. On the
ventral side of the body of the male there are ordinarily i)alches
of pigment of a deep steel-blue color. The males are free-swimming
through the whole period of their lives. The synopsis of the
Ergasilidae is adapted from C. B. Wilson.

Ergasilus is the only genus of this family, and specimens arc not
unfrequently taken in hmnetic collections. The>- ha\e Ixrn found
in nearly all parts of the United States.

2. CcUigidae. The body is flat, the caudal part of the abdomen

784 FRESH-WATER BIOLOGY

much reduced. The antennae of the second pair are armed with
hooks at the ends, but they are much shorter than in the Ergasilidae.

3. Dichelestidae. The body is elongated, the thoracic segments
distinct, the abdomen rudimentary except for the elongated genital
segment. At least the last two pairs of swimming feet are rudi-
mentary. The maxillipedes are armed with hooks.

4. Lernaeidae. The body is worm-like and unsegmented, and
the abdomen rudimentary. Processes growing from the head serve
to attach the animal to the host. The four swimming feet are

either very small or entirely lacking. A represen-
tative of this family is found on the sheepsheads of
the Mississippi Valley.

5. Lernaeopodidae. The head is distinct, the rest
of the body sac-shaped, and generally unsegmented.
The second maxillipedes are very large, and, arch-
ing over the head, are joined together to form an
organ for attachment to the host. The swimming
feet are entirely lacking.

6. Chondracanthidae. The body is indistinctly
^fodalhni^m\lln, Segmented, and the abdomen rudimentary. The

Sou? and Qili^nS first two palrs of swimming feet are rudimentary,
lo^^' *^ ^^^ '' the others lacking. The second antennae bear

hooks. The male is small, distinctly segmented, and lives as a

parasite on the female.

KEY TO NORTH AMERICAN FRESH-WATER ERGASILIDAE

I (8) Head completely fused with first thoracic segment, with no indi-
cation of union; carapace elongate, much longer than wide,
and more than half entire length 2

2 (5) Anterior margin of carapace evenly rounded, first antennae hardly
reaching end of first segment of second pair _. 3

3 (4) Second antennae one-third entire length.

Ergasilus funduHKroyeT 1863.

Basal segment of second antennae much swollen and widened distally; second segment with
I large process on its outer border. Foimd on the gills of Fundulus ocellaris.

COPEPODA

78s

4(3)

Second antennae half the entire length.

Ergasilus la hni, j , K ( . . \ i r 1 * ^

The two basal segments without swellings or |.r.Kci««. (ound oo the
striped bass, Roccus linealus. •"««« w uic

Fig. 1237. Ergasilus liibracii. (After WiUjoj

Anterior margin of the carapace projcctinK stronRly at the center
in a rounded knob, first antennae much longerihan in 2. 6
Terminal claw of second antennae simple.

Ergasilus ccntrarchidiirum Urighl i88i.

Both rami of fourth feet threc-segmentc<l. Found on the (amilv
Centrarchidae, the redeye, Ambloplites rupestris. snvall-mouth hUtk

bass, Micropterus dolomieu, etc.

Fig. 1238. Ergasilus ccnirarcliidarum. (Aitcr NViLvm.)

7 (6) Terminal claw toothed on the inner margin.

Ergasilus an r ulcus Wilson igii.

Exopodites of fourth feet two-seKmonlnl. Found on the NucKtU.

Lepomis pallidus.

Fig. 1239. Eri^a^thi-. i>uruifu\. ^ \nrr »m

\\\cx v\ iivin.j

786

FRESH-WATER BIOLOGY

8 (i) Head fused with first thoracic segment, but fusion indicated by

distinct indentations on lateral margins; carapace half en-
tire length and violin-shaped 9

9 (10) Second antennae as long as carapace.

Ergasilus versicolor Wilson 191 1.

Found upon species of catfish.

Fig. 1240. Ergasilus versicolor. (After Wilson.)

10 (9) Second antennae only one-half length of carapace.

Ergasilus chautauquaensis Fellows 1887.

Suborder Branchiura

There is but one family in this suborder, — the Argulidae. They
are ectoparasites upon fish, and are commonly known as fish lice.
They have compound eyes, four or five pairs of swimming feet, and
the first maxillipedes are modified into a pair of sucking disks. In
connection with the mouth is a true stinging organ which pene-
trates the skin of the host. They are found most abundantly in
the branchial chamber of the host, but may attach themselves to
other parts of the body. It is a matter of interest in this connec-
tion, as has been noted by Wilson, that they attach themselves in
such a way as to place the long axis of the body parallel to that of
the host, so that they will be less Hkely to be brushed ofi in its move-
ments. To this end, too, the under side of the body of the Argulus
is armed with backward-pointing spines, which aid in keeping it
in place. Argulus is strictly dependent on the blood of its host
for food, but can and does frequently swim about freely. Inas-
much as the eggs are laid attached to stones and similar objects, it
must leave the host at the breeding season. They are not con-

COPEPODA

787

fined to a single species of fish for a host, hut seem ahlc to make
use of a great variety, and may even attach themselves to other
aquatic animals, Hke tadpoles. Some of them can live almovi
equally well in both salt and fresh water.

The following key to the species of Ar^uhis which Im-,
described from the fresh waters of America is adapted from \Vi
paper on the Argulidae.

KEY TO NORTH AMERICAN FRESII-WATKR Akc.l LII)\L

1 (4, 9) Carapace lobes overlap base of abdomen.

2 (3) Diameter of sucking disks 0.25 mm.

Arguliis catoslomi Dana and llirnclt

Spines on antennae rcduccH in number, small and mrak'.
abdomen small and orbicular; found on »u<k«T. Catoti^
mus commersoni, and chub sucker, Lrtmysam imtfUj »^

longus.

FiC. 1241. Argulus catoitomi- lAficr Wi

3 (2) Diameter of sucking disks 0.15 mm

Argulus amfricanus Wilson i<x>v

Spines on antennae large and strong, reenforced; abdomen large and broadly cordate. Found
on mudfish, Amia calva.

4 (i, 9) Carapace lobes just reach base of abdomen 5

5 (8) Carapace orbicular, wider than long 6

6 (7) Anal sinus narrow and slit-like. A rgulus versicolor Wilson i (X>3 . male.

7 (6) Anal sinus broadly triangular. . .Ir^w/wj macuhsus Wilson IQ03.
Anal papiUae lateral; bases of antennae widely scparate.l; found upon the mUKaUoOft,

Lucius masquinongy .

8(5) Carapace orbicular, longer than wide.

Argulus dppcwiv U'.>^U^ \\ \\'>^M\ x-.
Found upon a sucker.
9(1,4) Carapace lobes do not reach abdomen

10 (16) Swimming legs with flagclla

11 (13) Carapace orbicular, wider than long

10
1 1

788

FRESH-WATER BIOLOGY

Abdomen medium, oval, anal sinus short, slit-like, papillae sub-
terminal Argulus versicolor Wilson 1903, female.

Anal papillae subterminal; bases of antennae close to mid-
line of carapace; found on the common pickerel, Lucius
reticulata.

Fig. 1242. Argulus versicolor, itmaXe. (After Wilson .)

13 (11) Carapace elliptical, longer than wide 14

14 (15) Flagella on anterior swimming legs.

Argulus lepidostei Kellicott 1877.

Carapace elliptical, longer than wide, its lobes very short,
barely covering two pairs of legs; abdomen broad, triangu-
lar, cut to the center or beyond with acute lobes; found on
the gar pike, Lepidosteus osseus.

Fig. 1243. Argulus lepidostei^ (After Wilson.)

15 (14) Flagella on all four pairs of swimming legs.

Argulus ingens Wilson 19 12.

Male 16 mm., female 21 to 25 mm. long. By far the largest American species. From the
alligator gar, Lepidosteus tristoechus, in Moon Lake, Miss.

16(10) No flagella on swimming legs. . . Argulus stizostethi'K.t\\icotii^?>o.

Carapace eUiptical, longer than wide; abdomen elongate, cut to the center or beyond; the
lobes lanceolate-acuminate; found on the blue pike, Stizostedion canadense.

IMPORTANT PAPERS ON FRESH-WATER COPEPODA

Van Douwe, C, and Neresheimer, E. 1909. Copepoda. Die Siisswasser-
fauna Deutschlands. Heft 11.

Forbes, Ernest B. 1897. A Contribution to a Knowledge of North Ameri-
can Fresh-water Cyclopidae. Bull. 111. State Lab. Nat. Hist., 5: 27-82;
13 Pl-

COPEPOIJA -5;^

GiESBRECHT, W., and ScHMEiL, O. 1898. Cop.-ixJ. T f.ynuu. ■.,...

Tierreich, 6 Lief.
GUERNE, J. DE, ET RiCHARD, J. 1889. Revision <k s I .iianidc-s deau doucc.

Mem. Soc. Zool. France, ii: 53-181; 4 pi.
Herrick, C. L., and TuRxNer, C. H. 1895. Synoi)sis of ihc Kntomoblraca o(

Minnesota. Geol. and Nat. Hist. Survey Minn., Zool. Scri.- IT : ,.t.

81 pi.
Marsh, C. D. 1893. On the Cyclopidae and ('ahinidac of Cini r.u w i^tuUMn.

Trans. Wis. Acad., 9: 189-224; 5 pi.

1895. On the Cyclopidae and Calanidae of Lake St. Clair. Lake .Mu! .
and certain of the inland lakes of Michigan. Bull. Mi<h I-isK (
No. 5; 24 pp., 9 pi.

1897. The Limnetic Crustacea of Green Lake. Trans. Wis. .\i ad., 1 1 ; lOj
168; 10 pi.

1903. The Plankton of Lake Winnebago and Green Lake. Bull. Wis. Gcol

and Nat. Hist. Survey, 12: 1-94; 22 pi.
1907. A Revision of the North American Species of Diaptomus. Traiw

Wis. Acad., 15: 381-516; 15 pi.

1910. A Revision of the North American Species of Cyclops. Trans. Wis
Acad., 16: 1067-1135; 10 pi.

ScHACHT, F. W. 1897. The North American Sjui io ..t J):.:t>:, mu^. Bull
111. State Lab. Nat. Hist., 5: 97-207; 15 pi.

1898. The North American Centropagidae belonging lo me v.tiur.i c^
phranticum, Lmnocalanus, and Epischiira. Bull. 111. Stale Lab. Nat
Hist., 5: 225-269.

ScHMEiL, Otto. 1892. Deutschlands freilebcnde Siisswasscr-Cope[KHlcn. I
Cyclopidae; 192 pp., 8 pi.
1893. Deutschlands freilebende Slisswasser-Copepocien. II. IhaiMan lu.u
100 pp., 8 pi.

1896. Deutschlands freilebende Siisswasser-CopeiKxlen. III. Ccnlroi>agi
dae; 144 pp., 12 pi.

Wilson, C. B. 1903. North American Parasitic CopeixxLs of the Family
Argulidae. Proc. U. S. Nat. Mus., 25: 635-74-^ -^o pi.

191 1. North American parasitic Copepods Belonging to the Family Erga
silidae. Proc. U. S. Nat. Mus., 39: 263-400; 20 pi.

CHAPTER XXIV
THE OSTRACODA

By R. W. SHARPE

Instructor in Biology, Dewitt Clinton High School, New York City

An early author says of the Ostracoda, "these little creatures are
enclosed in a bivalve shell of lime and seem to be very lively in
their native element, being almost constantly in motion by the
action of their antennae, or walking upon plants and other solid
bodies floating in the water." Also "by opening and closing their
valves, they enjoy light and move at their will, sometimes burying
themselves in the mud, sometimes darting through the water, the
humid air of their sphere. If they meet with any unforeseen object,
they conceal themselves all at once in their shells and shut the
valves, so that force and address seek in vain to open them."

The Ostracoda are found abundantly in all kinds of fresh and
salt waters. They owe their name to the possession of a two-
valved limy shell, which is hinged dorsally, and encloses the entire
body. They are commonly more or less bean-shaped (Fig. 1244),
and seen from above (Fig. 1255 5) are usually oval or egg-shaped.
In many cases the shells overlap each other, or there may be a
ventral flange present. They average about i millimeter in length.

The body of these little creatures is not segmented, and is com-
pletely enclosed in its bivalved shell, which is hinged along the
dorsal margin by means of a hinge ligament, somewhat as with
the molluscan bivalves. These valves are kept closed by adductor
muscles, their points of attachment being indicated by a number
of lucid spots about the middle of each valve (Fig. 1255a).
These are called "muscle impressions" and may often be of sys-
tematic value. At the anterodorsal end of the body is a single
eye, although it may occasionally be double. Most commonly the
shells of the sexes are of the same size and shape, although second-
ary sexual characters may appear here. For instance, the males
of the genus Candona are larger and of a different shape (Fig.
1300), while in Cypris and Notodromas the females are the larger.

790

THE OSTRACODA ^

Baker, in 1753, is said to be the first author who sumcienlly de-
scribed any of these small forms so that the description could l>c
recognized as referring to a CypHs. In the work "Kmi)loyment
for the Microscope" an anonymous correspondent descriJxrs an
insect with a bivalve shell, somewhat resembling a fresh-water
mussel, and gives a figure of it lying on its back.

Linnaeus, in his "Systema Naturae," in 1748, mentions a
species under the name ''Monoculus concha pedala." For many
years the general term ''Monoculus" was in use fur all en-
tomostraca until finally, in 1776, 0. F. Mailer, in his "Zoologiae
Danicae Prodromus," first established the genus C>/>n5, as well
as a number of other genera of the cntomostraca.

In 1894 G. W. MiiUer published his masterly work on the Ostra-
coda of the Gulf of Naples. His descriptions and figures are most
carefully and accurately made, and in connection with his similar
work on the fresh-water Ostracoda of Germany, published in iqoo,
may well form the best published basis for future wurk. He de-
scribes about 125 species from the Gulf of Naples and some 65 for
Germany.

Structure. — It is not uncommon for the extremities and ventral
edges of the shell of Cypris to exhibit a number of suhparallel
canals (Fig. 1271) which radiate outwards, and arc called "pwre
canals." The same regions may be tubcrculate. the right valve
alone with tubercles as in the subgenus Cy/>r/;/()///5 (Fig. 1270). or
the left valve alone similarly tubcrculate as with the subgenus
Heterocypris. Various species of other groups may thus be simi-
larly marked. Occasionally the shell may show a series of longi-
tudinal markings, as Ilyodromus (Fig. 1250) or a network of
anastomosing and parallel lines, as Cypria exscidpta.

Exclusive of the abdominal appendages, called the furca. there
are seven pairs of appendages in the C\prididai-. These may be
enumerated as follows: first antenna, second antenna, mandible,
first maxilla, second maxilla, first leg, and second leg, naming one
of each pair (Fig. 1244).

The anterior lip or labrum (Fig. 12^^) f^rms a prominence pro-
jecting between the bases of the second antennae and anteriorly
covering the oral orifice. The posterior lip or labium (Fig. 1 .'45)

792

FRESH-WATER BIOLOGY

forms a thin membrane, reenf orced by a pair of very strong chitinous
rods, each expanded into a transverse plate armed at their extremi-
ties with a series of about seven strong teeth. Posteriorly the lip
joins a sternumlike vaulted plate, carinated along the middle, and
placed between the bases of the first pair of maxillae.

First antennae
\ Second an^enr,^e
\ \ Eye

Branchial Plate of Mandible
! Stomach

Food balls

Branchial setae
Intestine

Ovary

Second foot
'.. Furca

Dorsal seta

-Sub-terminal claw
Terminal claw
^^^ ^'•Terminal seta
First foot
Branchial plate of maxilla

natatory setae Labrum

Fig. 1244. General anatomy of Cypris virens Jurine. (After Vavra.)

The mandibles (Fig. 1245) are each composed of a chitinous elon-
gate body, and a well-developed pediform palp (Fig. 1 245 b^) . They
are located on either side of the body immediately behind the
base of the second antennae with its upper acuminate extremity
(Fig. 1245 ^2) articulated to the inner surface of the corresponding
valve just in front of the adductor muscle impressions, whereas
the lower incurved extremity is wedged in between the lips. The
greater part of the body (Fig. 1245 ^^) is hollowed to receive the
powerful adductor biting muscles. The cutting edge (Fig. 1245 b^)
is divided into several strong, bifurcate teeth. The palp (Fig.
1245 60 forms a thick, fleshy, somewhat pediform jointed stem,
curving downwards, and bears on its outer side a narrow plate, a
so-called branchial appendage (Fig. 1245 ^^) which is provided with
a number of plumose setae.

THE OSTRACODA

793

The first pair of maxillae (Fig. 1245 c) is formed of a thick, mus
cular, basal part, from the extremities of which four dij^iiifomi
processes originate. The larger of these prominences ( Fig. 1 ^45 c'l
is jointed and movable and must evidently be regarded a,s a palp
whereas the three remaining form the immediate continuation .)f
the basal part and are the true masticatory lobes. The first <jnc of
these is usually armed with two strong spines (Fig. 1 245 c^ and Fig.
1270 e) which may or may not be toothed, and are regarded as of
specific importance. To the outer side of the basal part a large

Fig. 1245. (a) Lower lip or labium; {b) Mandible with palp; (c) First maiilU with braachbl pUta;

{d) Second maxilla of female with palp {Cypris ifuonirtum).

semilunar lamella (Fig. 1245 c^) is attached, which is generally called
the branchial plate. This plate may be seen to move rhythmically
in the living animal, and is for the purpose of renewing the sup|)ly
of fresh oxygen-laden water within the shell ca\ it >•. It is dircctwl
obliquely upwards and exhibits along the posterior edge a scries of
dense and regular finely plumose setae, from 16 to 20 in numlx-r.

The second pair of maxillae (Fig. 1245^) consists of the same
principal parts as the first, though ditTerent in ai)pearance. Thr
basal part (Fig. 1245 d') is much smaller, not divided at the end. and
terminating in a single masticatory lobe. The branchial lamella
(Fig. 1245 d^) are usually semicircular and provided with a few plu-
mose setae, while the palps (Fig. 1245 (P and Fig. 1290 d- "-" -f

794 FRESH-WATER BIOLOGY

different shapes in the sexes. In the female they are conical
(Fig. 1245 a'^), while with the male (Fig. 1299 e) they are con-
verted in a peculiar manner into powerful prehensile organs which
serve for grasping the female during copulation. The palps of
the right and left sides in the male are different in size and shape
(Fig. 1246 e-f). The form of these palps is regarded as of specific
importance.

The two pairs of antennae are found in the head region, and in
most cases are provided with long natatory setae, which aid in
swimming (Fig. 1268^). The mandibles and first maxillae serve
as mouth parts. The fifth pair may be modified in some cases, as
in the Limnicythere, serving as legs — in most cases as maxillipeds
or second maxillae. The fifth pair is known as the first legs
(Fig. 1260 J), and the sixth pair is known as the second legs (Fig.
1285 d). The second legs are commonly not ambulatory, but are
bent backwards within the shell. They are often called the
*' cleaning feet" on account of their observed use in cleaning the
valves of any foreign matter. The mouth parts commonly carry
a number of setae which create a current of water between the
valves for respiratory purposes.

The general color of the surroundings seems to have some rela-
tionship to the general color of the forms present. For instance,
all those living in algae-rich habitats are notably green, as many
species of Cypris, while those creeping about on the bottom amongst
dead leaves and ooze, are commonly devoid of any especial pig-
ment, as are most species of Candona. The color of the various
forms varies from yellowish white to yellow, green, blue, and violet
to purple. The species of Candona are commonly of a pearly
to yellowish white, while Cypris, Cypridopsis, and Cypria — forms
that inhabit algae-rich regions — commonly show a greenish color.

The food canal begins with a mouth, which is bounded by upper
and lower lips. It is interesting here to observe that the marine
forms belonging to the genus Pyrocypris are provided with phos-
phorescent glands in the upper lip, which cause much of the
phosphorescence of the sea. From the mouth the food passes
through a short esophagus to a stomach, which is commonly
followed by a short constriction separating it from the short

THE OSTKACODA

Stomach-like intestine (Fig. 1244). The intestine opens at Uie
origin of the furcal appendages.

Propagation. — The male sexual organs are usually large, of
complex structure, and may consist uf a whorled sack or spiny
cylinder, the ejaculatory duct (Fig. iJ4()/;j, cunnecting with the
testes and vas deferens, which may lead to a more or less chilinous
plate or penis (Fig. 1246 a). The testes usually consist of glands
which are partly extended within the shell proper and the shell
membrane, and may show through the shell as three or four gran-
ular bands (Fig. 1271 &), as in Candona and Cypris. The arrange-
ment of these testes may constitute a good generic character, as
in Spirocypris (Fig. 1267), where the testes originate in the ante-
rior part of the shell in parts of circles or circles.

The ovaries may show through the shell in its posterodorsal
part, and are arranged somewhat as the testes (Fig. 1244). They
usually lead to a chitinous plate by a vaginal canal or oviduct,
which retains the semen and undeveloped eggs as with Cypris, and
commonly lie between the two lamellae of either valve, and extend
diagonally to the posterior extremity, where they curve up to form
a nearly semicircular band. Here the true germinal layer is found,
which forais the ovicells. These ovicells are poured from the
ovary into the body cavity, where they generally accumulate in
its posterior part on either side of the intestine. Here they
attam their full development and are fertilized, after which they
are laid.

The inner genital organs of the male are more complicated
(Fig. 1246). As the ovaries, they are situated between the lamellar
of the valves, and commonly consist of a number of narrow and
elongate bands on either side, which are generally to be found
filled with numerous fine, thread-like bodies (Fig. i246(/), the sper-
matozoa, which may occasionall}' be curled up in si)iral groups. In
addition there are present a number of large nuclear cells (Fig.
1246 g). These are the gemiinal < .lis. <.r >pennat»K-ysts. fnim
which the spermatozoa develop.

The efferent or ejaculatory apparatus (Fig. 124O/O conM>i-s ol
the spiny cylinder already mentioned. It seems to be comiK>sc<l of
an inner tube (Fig. 1246 c), supported by a complicated chitmouc

796

FRESH-WATER BIOLOGY

skeleton of whorled radiating spines. The efferent duct leads
to a tube, the vas deferens, which in turn leads to the penis
(Fig. 1246 a).

These forms may also be propagated from unfertilized eggs, i.e.,
by parthenogenesis. In such cases there may be a sexual genera-
tion followed by a number of such parthenogenetic generations.
Again, in some forms males have never been discovered, even
after as many as 18 years of continuous observation by very carer

Fig. 1246. Cyprinotus dentate ShsiTpe. (a) Penis, X 210; (b) Efferent or ejaculatory apparatus; (c) Cross-
section of same, X 293; (d) Part of a spermatozoon, X 525; (e) Right maxillary palp of male, X
158; 00 Left palp of same; (g) Extremity of testicular tube, showing spermatocysts, X 120; (h) Ma-
ture spermatocysts, X 120.

ful observers. Herpetocypris reptans is a good example. Thus
some authors distinguish four types of the method of propagation,
as follows:

1. Always sexual as in Notodromas monacha, Cyclocypris laevis,
Cypria ophthalmica.

2. Temporarily parthenogenetic, as in Candona Candida, Cypri-
do p sis vidua.

3. Locally parthenogenetic, as in Cypris incongruens.

4. Always parthenogenetic, as in Herpetocypris reptans.

THE OSTRACODA ~ -

The method of propagation has been much ust^l as a ;.-■
character, but much more must be known of its constancy t .
it can be finally accepted as at all reliahle. I'lu- form of the penis
and of the vaginal plate, however, may hot h be accepted its constant
characters.

The eggs are provided with small lim\- shells, and commonl\
develop in from 5 to 14 days. They are laid in characteristic
ways. For example, the eggs of Candona camlnhi are whitish.
and are laid singly, without being fastened together; those «>f
Cypris incongruens are orange red, while those of Cypridopsis
vidua are dark green. Both are laid in i)ackets on the leaves and
stems of water plants, especially the under sides of Lemna leaves.
The eggs of N otodromas monacha are first white and later yellowish.
They are oval-elongate, and are laid in rows, pole to jkiIc, on
the roots of Lemna. The eggs of Ilcrpetocypris reptans are spher-
ical and of a yellowish color, which deepens later — indeed, when
freshly laid, they may be almost white.

Bottom forms, such as Candona and Ilcrpetocypris, laboriously
contrive by creeping and cra^vling to reach Lemna and other sur-
face plants. They first reach the roots, and later the upin-r sur-
faces, where they appear to scrape a place with their antennae, and
then deposit and fasten their eggs with line threads. All this must
be quite an acrobatic feat for them, as they must balance them-
selves meantime. After finishing, they pemiit them.selves to fall
to the bottom. It is here worthy of remark that these biological
distinctions such as habitat, means of locomotion, food, means of
propagation, and egg laying, all have their value in si>ccific

distinctions.

Their eggs also have remarkable vitality. An instance is on
record of samples of dried mud being sent to England from Jeru-
salem and entomostraca being raised therefrom {Cypns and /).;/>/i-
nia) after a lapse of from 24 to 30 years. G. O. Sars. of Nonvay,
has reported raising them from dried mud sent him from Australia
and China. In fact, he has described many new species from
material sent to him in this way.

The eggs hatch into nauplii, which resen.ble the adult, although
varying much in the shape of the shell and internal structure.

798 FRESH-WATER BIOLOGY

They molt many times before reaching maturity. The change
that takes place is most complete. The shell falls off, and all the
internal parts are shed, even to the minutest hairs.

The nervous system is composed of a so-called brain or supra-
esophageal ganglion, and several other gangha and connecting
nerve structures. The most important branches lead to the eyes,
which are either double as in Notodromas (Fig. 1247), o^"; more
commonly, as a single median-dorsal pigment spot.

The most common sense organs other than the eyes are found
on the second antennae (Fig. 1290 t). These resemble a club and
hence are often called ^'sense clubs." Other sense organs appear
on the second antennae of the male, especially such fornis as
Candona, Cypria, and Notodromas (Fig. 1298 c).
Most Ostracoda are omnivorous. Decaying
vegetation and small animals form a large part
of their diet. Cypridopsis has been observed
forming skeleton leaves. Some will eat their
own kind, if opportunity offers. While in cap-
tivity most forms will eat from thin slices of
potato. Notodromas is an exception to most
others, as it has the curious habit of swimming
back down and clings to the surface film in an
Fig. 1247. Notodromas mo- endeavor to obtain food. Some forms may also

nacha (O. F. M.). (a) Lens; •'

(di^ForebiLin^^^'''''^'''^' attack Hviug or dying animals. Instances are
also on record of their having attacked Melicerta
ringens, a common fixed rotifer. Thus they act principally as
scavengers, as their greediness and oftentimes great numbers
would constitute them no inefficient agent in the work of purifying
standing waters.

The fresh-water Ostracoda entirely lack any such organ as a
heart. The respiratory process therefore takes place through the
entire upper surface of the body, and through the inner cell layers
of the shell. A number of respiratory plates are fastened to the
mouth parts, the motions of which keep up a continuous stream
of fresh oxygen-laden water pouring through between the valves.

It is self evident that favorable or unfavorable life conditions
exert a striking influence on the distribution of Ostracoda in iso-

THE OSTKAKJin

lated waters, although this fact has nul received the attention it
should. Even though in general they seem to be no more sc-nsiiivc
to their surroundings than the Cladocera or the Coi>epoda vet
there is no doubt that the amount <.f light, of i,ressure, of 4ru.
tions in temperature and composition of the water, the rate of
flow of the same, the nature of the bottom, and the presence or
absence of algae, etc., must certainly exert a real or intrinsic in-
fluence on the prosperous development of all these Kntomostraca,
Direct or intense hght certainly accelerates all their life i)rocesses,
as may be evidenced in the fact that all free and actively swim-
ming forms are quite likely to turn towards a source of light, or,
in other words, are positively heliotropic. Shady areas in i)ooU
are not nearly so likely to contain the free swimming forms such
as Cypris, Cypria, Cyclocypris, and Xoiodromas excei)t occasionally
or sporadically, while the lighter and sunnier areas of the same
body will contain them in abundance; in other words, the more
uniform the distribution of light, the more nearl\- uniform becomes
the distribution of any certain form. On the other hand, it seems
a general rule that the less able these forms are to swim, the greater
the certainty that they are confined to the deeper and darker
areas, in the ooze and slimy debris of the bottom. It also apjx-ars
that some species may be affected but little by depth, and there-
fore light and pressure; Cypridopsis vidua has been found in all
depths from i centimeter to full}' 300 meters.

Experience teaches that practically no forms are found in pure
spring water or in well water. Even so. we fmd practically none
in waters that have been polluted with (l\es. or by chemical
means, although many different degrees of power of resistance in
this regard may be found. Some species may be enclosed in the
smaller glass aquaria and live almost indefinitely without change
of water, even though the water becomes quite foul. For example,
Cypria opthalmica has been known to survive in such acjuaria long
after the larger forms have died. Cyclocypris I ircis will al.so live
many months in water that has not been freshened. Some few
forms have been known to exist in suljihur waters, others in hot
springs and even in sewer drains. Cypris inconi^rucns has been
found in a pond fed by the drainage from a barnyard manuic

8oo FRESH-WATER BIOLOGY

heap. This species really seems to be indifferent to any variation
in the pollution of the swampy water in which they normally live,
variations and situations that would be fatal to most other Ostra-
coda. These forms have also been found in more or less perma-
nent ponds fed in part from the drainage from cesspools and from
leaky sewers.

Many bodies of water of different degrees of swiftness are like-
wise determinative of different forms. Brooks and rivers are not
especially good habitats, as plant life there is not abundant, and
most free-swimming Ostracoda seemingly delight to hang to such
supports. However, most forms may be occasionally or adven-
titiously found in such waters, as well as in quieter waters. Nolo-
dramas is typically an inhabitant of pure, fresh pools, although it
is a good swimmer, and has the curious habit of trying to support
itself on the surface film.

Among those forms depending upon the Ostracoda in part for
food, one must certainly include the young of many fishes, and
even the adult Coregonus or whitefish has been found with
Candona in the stomachs. Some of the larger marine fishes seek
Ostracoda in the mud. Even aquatic birds may include them in
their bill of fare, as, for example, the shoveler or spoonbill duck
has been found with Ilyodromus and Cypria in its stomach.

Owing to the variations in habitat, and the vicissitudes to which
most fresh-water Ostracoda are subject, and because of the vari-
able and inconstant nature of their surroundings, it is almost im-
possible to work out their exact distribution. Cyclocypris laevisy
Cypria opthalmica, Cypria exsculpta, and Cypridopsis vidua seem
to be cosmopoHtes in temperate zones, and the most indifferently
distributed of any, as they are found in all pools, ponds, swamps,
lakes, and rivers of both mountainous and level areas. Their small
size permits them to be readily carried about, and their power of
adaptation and scavenger habits permit them to thrive in almost
any apparently adverse situation. Notodromas, as already stated,
appears only in pure standing waters, and mostly in immense
numbers. Less abundantly, but still very widely distributed,
may be found various species of Candona, Cypris fuscata, and Her-
petocypris reptans.

THE OSTRACODA g^j

The vertical distribution of these forms has not been fully worked
out. Various species of Candona, Ilyocypris, as well a,s CypridopUs
vidua and CyclocypHs laevis have been found at dei)ths of at least
300 meters, while a few have been rq.orted from depths of fuUy
2500 meters.

The constancy of color, form, and size of most of these- species 15
still an open question, and yet requires much careful work. He-
cause of differences in methods of measurin^^ and the chante that
undeveloped or sexually immature indixiduals become destTilx-tl,
it is certain that there exist many discrepancies as to published
descriptions, and therefore of reports on distribution.

Despite these discrepancies and uncertainties, it is likely that
local varieties exist in many quite restricted arcius, that in many
cases are so far divergent that one would be disi)osed to aM-riljc
them to different species. On this account, if for no other, it Ls
advisable to be very careful concerning the estal)lishment of new
species. In all cases the appendages should be very critically
examined, and if these show differences and the shells are const:int
in general markings and form, then only should a new sixties
be created. Of course, very exact and minute descriptions arc
indispensable.

The distribution of Ostracoda seems to be both actively and
passively brought about. The creeping forms may be said to be
actively distributed, while the free-swimming forms are passively
distributed. Those that creep must actively exert thems^-lves if
in deep water, often against the force of the stream, to prevent
themselves from being buried in the mud. Pa.ssively. the swim-
mers may be distributed by high water or by direct means of
transport. The amount of water is of more consecjuence than the
flow of water. Even though the amount of water is great, they
still can remain in the place of their temi>orary abode, while in
brooks or rivers they are carried away by the force of the current,
and may become lost. In rainy seasons, therefore, the natural
increase may be very scanty, while in drirr pcri.Mls many indi-
viduals of both sexes find one another, and the eggs deiH).sited always
have a sufficient opportunity of fmding necessary nu.i.turc- fur
development.

8o2 FRESH-WATER BIOLOGY

Migration from one region to another may be brought about by
swimming beetles such as Belostoma, Gyrina, etc. Cyclocypris has
been observed hanging to the legs of such beetles, even though the
beetles were actively using their legs. Birds may also be of great
importance as carriers of both the minute flora and fauna of a
region. The eggs of Ostracoda, and even the animals themselves,
may be carried about on the bills and feet of aquatic birds, and
even fishes may act as a means of transport from one region to
another.

The Ostracoda belong to the plankton. In common with certain
other organisms, such as Rhizopods, Diatoms, Hydra, etc., they
appear in the plankton under certain conditions of temperature
and food, and hence are said to belong to the adventitious plank-
tonts, in distinction to such forms as Cyclops, which are always
in the plankton, and therefore called continuous planktonts,
or those that appear periodically, as Daphnia and some Rotifer a,
when they are called periodic planktonts. For evident reasons the
creeping or burrowing forms rarely occur in ordinary plankton
catches.

According to their habitat and mode of locomotion, the ostracod
adventitious planktonts may be classified as follows :

A. Free swimming.

1. Limnetic, with surface habits, as Notodromas monacha.

2. Free swimming, below the surface, as Cypris laevis,

C. incongruens, C. vidua, etc.

B. Creeping or burrowing.

1. Creeping on water plants or ooze, as Herpetocypris rep-

tans.

2. Burrowing in the slime or ooze, as Candona Candida ^

and Limnicy there.

Little is surely known of the duration of life of special forms.
Some species are present the entire year. They live over the
winter, and are also found in different developmental stages under
the ice. It is an easy matter to collect mud under ice in midwinter,
place it in a small aquarium jar and set in a moderately warm
place, and very shortly find plenty of Cypris, Cypria, and Candona.

THE ()STk.\(()|)A

Notodromas appears purely as a suninuT form. It winlcre in
different ''egg stages," develops in Ai)ril or May. ami I n.

ber has entirely disappeared. Cypridopsis vidua and ■ .„-

coiigruens appear in early spring and last until late autumn I .,■
spring forms appear to have a much shorter lil\- history.

These forms may be collected in great variety and' abundance
by drawing a Birgc or cone net ihrou.^h submerged plants prt-st-nt
in ponds, slow streams, and lakes, and by stirring uj) the lx)ttom

ooze and slime, and drawing the weighted net to and fr • ■- '^ -

bottom.

In this manner not only the free-swininiing forms may be cap-
tured, such as Cypris, Cypridopsis, etc., but typically })ottom forms
such as Candona, Herpetocypris, etc., may also be include<l. By
emptying the mud and all other accumulations in a beaker of
water, and stirring well, it will usually result in many of the Ostra-
coda getting air caught between their vaives, thus causing them to
float on the surface, from which they may be readily removed
with a "medicine dropper" or pipette. The use of a small hand
lens is advisable in determining whether or not Ostracoda arc
surely present. In any case, the ''catch" may now be concen-
trated by carefully pouring oil the contents of the beaker from
the sediment in the bottom into a small dip net made of Swiss or
bolting cloth.

After washing out as much of the soluble or other matter as is
possible, the remainder may be emptied into a Syracuse watch
glass or other shallow vessel containing but a small (|uantity of
water. Thus the catch is condensed to such bulk as may now be
easily transferred to small vials of preser\ati\-e tluid such as 90
per cent alcohol, or a mixture of 80 per cent alcohol and glycerin
in about the proportion of 10 to i. However, killing had k-tler
be done in about 70 per cent alcohol, which should \yc gradually
increased in strength, as in this manner the shells are more
likely to remain open than when killed in alcohMl ..f :, hi-h.-r

percentage.

If a large quantity of living forms should be desired, the entire
catch of a locaHty may be poured into a si)ecial pint strainer jar
(Fig. 1248).

8o4 FRESH-WATER BIOLOGY

This may be made out of a common pint fruit jar, by inserting

a funnel through one side of the cover for pouring in the catch,

and so arranged that the excess water may run off through an

overflow tube, after passing through a cloth strainer

made of the same material as the dip net, and which

is distended and held in place by two narrow wire

loops soldered to the inner end of the overflow tube.

■ --___^' . The strainer cloth is made in the form of a bag nearly

^"D ^ as long as the depth of the jar, with its upper end held

" in contact with the inner end of the overflow tube by

a couple of rubber bands.

In many cases it is recommended that the collected
material be allowed to stand in a shallow vessel after
reaching the laboratory, when the creeping forms will

Fig. 1248. Diagram ^ ^' j T j ,.1,

of strainer jar; aDDcar ou the surfacc of the ooze and slime, and others

(i) Funnel intake; -^ -t^

(3) clotWraiSr'. ^111 collcct about the edges of the vessel, commonly on
the side nearest the source of Hght, or the opposite.

If it is thought desirable, small portions of the ooze and slime
may be examined under the low power of the compound micro-
scope. Even the creeping Cyprididae are easier to find than the
Cytheridae, such as Limnicythere, as they are more active and
readily gather about the edges of any shallow vessel.

No satisfactory work in identification can be accomplished in
most cases until the body with its appendages is removed from the
shell. It is not necessary to place the specimens in weak acid so
as to decalcify the shell, as a little practice with dissecting needles
and microscope will soon enable one to remove the parts from the
shell without destroying them.

After a preliminary examination, place the specimen in a small
drop of Farrant's medium or in glycerin. The shell may now be
opened with a pair of No. 12 needles, which are mounted in handles,
or by the flexible probing needles used by dentists. Free the body
from the shell entire, if possible, and afterwards separate the ap-
pendages, beginning with the antennae and taking them in order to
the furca at the posterior extremity. This is not an especially
difficult process, excepting possibly the maxillae, which are com-
monly very small and securely joined in place, so that even the

THE OSTRA( ODA Ro^

finest needle is scarcely efficient as a dissecting instrument. T -
of the above two mounting media bring out to view even the ..... l
hairs or ciliated structures. Alcohol or water are not advisable as
dissecting media and should be risked with few specimens. Fur-
thermore, Farrant's medium makes a very good permanent mount,
providing there is not too much on the slide. Kither medium
should be added to the slide in small drops, then spread out in a
thin layer before attempting to dissect therein. It is commonly
best to make a preliminary examination of the di«»scclion with a
f-inch objective, to see that the mount has been well prci)arcd
and arranged. If so, add a small additional amount of the me-
dium, cover with cover glass, and the mount is permanent, pro-
vided the work is neatly done, too much medium is not added, and
the mounts are kept stored in a horizontal position when not in use.

The valves should be preserved entire, if possible, and removed
to one side of the slide for further study. It is often (le^iral)le that
they be removed to a separate slide and mounted in b.d-.un, es-
pecially if the slides are to be permanent and subject to muth
handling.

Drawings as well as study of a side view should always Ik- made
from one of the valves, rather than from the entire sixi'imcn. as
otherwise a distorted view is likely to result.

The dorsal view is more difficult to get - indeed, it is often
advisable not to attempt it. Unless this view is obtained directly
above the specimen, it is worthless. Sometimes one valve alone
may be used by fastening it to a needle or similar object, and
then studying while covered with glycerin, or. it the valve> arc
dissimilar the entire animal may thus be mounted so that an
exact profile may possibly be obtained. It is indeed often i^^-
sible to get very good dorsal profdes from many six-cimens while
they are in alcohol and glycerin in a s>Tacusc watch ghuv«i.

The following characters have been retained as of most value
in the following key: presence and length of natatory sc-tae of
the second antennae, segmentation of the second antennae, form
and number of spines of the first n.axillary i>rocess. armature ol
the second leg, arrangement of the spennatic gland, and armature
and shape of the furca.

8o6

FRESH-WATER BIOLOGY

KEY TO NORTH AMERICAN FRESH-WATER OSTRACODA

1 (2) Second antenna two-branched; one branch rudimentary, immobile,

the other elongate, flexible, with long natatory setae (Myo-
docopa); or both branches well developed, movable, and
natatory (Cladocopa) ; or both branches flattened, similar
tofeetof the Copepoda(PLATYCOPA). . . Marine Tribes.

These groups are not represented in fresh water so far as known.

2 (i) Second antenna simple, subpediform, clawed at apex. Mostly fresh-

water forms Tribe Podocopa . . 3

3 (4) Three nearly similar pairs of legs. Furca rudimentary. Second an-

tenna with flagellum (Fig. 1251 (i^), and httle adapted for
swimming Family Cytheridae . . 5

4 (3) Two dissimilar pairs of legs. Furca commonly weU developed. Sec-

ond antenna without flagellum and commonly with natatory
setae 9

5 (6) Parasitic on gills of Crustacea. Terminal claws of legs with four large

teeth (Fig. 1249 a) Entocythere Marshall 1903.

Only one species of this genus known.

Entocythere cambaria Marshall 1903.

Length 0.60 mm. Males abundant. Shell thin, frag-
ile and transparent. First antenna six-segmented. Sec-
ond antenna four-segmented. Flagellum unsegmented.
Caudal rami short and thick. Parasitic on gills of cray-
fish {Camharus). Wisconsin. A most remarkable
form, in that Ostracoda rarely adopt parasitic habits.

Fig. 1249.

Entocythere cambaria. (a) End of third leg;

(b) Side view, X 50. (After Marshall.)

6 (5) Not parasitic. Crawlers or burrowers. Terminal claws of legs with

not more than two teeth, or plain (Fig. i26od).

Limnicy there Brady 1868 . . 7

7 (8) Shell decidedly reticulate, with two lateral furrows. Furca blunt,

about three times as long as wide (Fig. 1250 a).

Limnicy there reticulata Sharpe 1897.

Length 0.66 to 0.70 mm. and 0.25 mm. wide. Grayish
white. Shell conspicuously marked with a honeycomb-
like network of polygonal reticulations, and deep lateral
furrows (Fig. 1250 ft). Furca (Fig. 1250a) cylindrical,
thick and blunt, about three times as long as wide, with
two small setae. Posterior dorsal part of carapace tapers
to a point. Muddy bottom of ponds. Illinois, April.

Fig. 1250.

Limnicythert reticulata, (a) Furca; (6) Dorsal view;

(c) Side view, X 54-

THI-: OSTRACODA

807

8 (7) Shell faintly reticulate, with one lateral furrow. Furca tapering to a
seta Hke extremity (Fig. 1251 b).

Limnuythac illinoisensis Sharpc 1897

k:

scKnirnictl
alnxif wvrn

y
1.
ot iitali alliK-ti Miih

Itvth at tip Sandy J.
Illinois Kivrr. I^ayuiu. iuvi ix».t
shores. May.

"I

Kir. ij<i
Limmi(\lkrrf iiii»(ni#»itt

sal vir». <^ J .:. .

flagcilum. J
maJf

'«) t>

9 (10) Abdomen without furca. Second legs not backwanlly uirtM tc(i.

Family I)AK\visruD\i .
Darwinula stcvcnsoni Hraiiy and RolxTlson 1870.

Length 0.70 to 0.80 mm. Kicht shell <-■. <
left. Abdomen ending in a olindriial un;
(Fig. 1252a). Sandy or muddy Ixiito"-
improvisa Turner i8qs, is a synonym

Fig. ijsj.
Dardinula slnensoni. (a) Tip of abdomen. X 166.

10 (9) Abdomen with furca. Second legs backwardly bent.

Pamily C'yprididak .

11 (12) Furca rudimentary, with a long seta at tip (Fig. 1253)- •

12 (ii) Furca band-like, with claws and setae at tip (Fie i-^^j) .

13

Natatory setae of second antennae long, reaching .it kaM l.» iji>s
of terminal claws. Second foot beak-shajH-d at tip. willi a
terminal claw. . . . Subfamily Cvpkidopsin v J

14 (15) Shell broad from above, tumid. Second antenna five-s<-gnicntrtl

Only one species in North America. The "^f » ^/^^P^"}^" ."^
American ostracod. . . CypnchpstsvuiiuiO.V.Mu]}^

Length 0.60 to 0.70 mm., plump. Markc«l <lor«lK
ith three prominent dark han.is. \ cry comn»on. «

with three i)ror
are present.

Fig. 1253. CyprUcpsis tuitt*. Furca. X 1 So.

8o8

FRESH-WATER BIOLOGY

15 (14) Shell rather narrow from above, compressed (Fig. 1254 b). Second

antenna four-segmented Potamocypris Brady 1870.

Only one species in North America.

Potamocypris smaragdina (Vavra) 1891.

Length 0.65 mm. Shell grass green, nearly
crescent-shaped, and thickly covered with long,
closely appressed hairs. Pools and ditches, July,
August, and September. Eggs vermilion red.
Ponds and ditches, April, July, August. South
Chicago, Mexico.

Fig. 1254.

Potamocypris smaragdina. (a) Side view, X 4°;

(6) Dorsal view; (c) Furca, X 150.

16 (17) With two distinct eyes (Fig. 1255 h) 18

17(16) With eyes fused, ornone apparent (Fig. 1258 c) 22

18 (19) First maxillary process with six spines. Furca with three long setae

and no spines (Fig. 1255 c-^) 20

19 (18) First maxillary process with six spines. Furca with four long setae

and no spines (Fig. 1256 c) 21

20 Second antenna six-segmented in both sexes. Second leg terminat-

ing in three setae, one of which is reflexed.

Notodromas Lilljeborg 1853.
Only one species in North America.

Notodromas monacha (O. F. Muller) 1785.

Length 1.18 mm. "Hump-
backed"; brownish yellow.
Active swimmers, resembling
the Cladocera in many move-
ments. Occasionally hang to
surface film of water, back
down, as Cyprois. Permanent
fresh ponds with algae. North-
ern Indiana, spring and sum-

FiG. 1255.
Notodromas monacha. (a) Side
view of male, X 30; (b) Dorsal
view, X 30; (c) Maxillary spines,
X 100; (d) Furca of female, X
60; (e) End of second leg, X no.

THE OSTk.\( ODA

809

21

Second antenna five-segmented in l)oth si-xes. Second leg U-nnl-
nating in one claw and one rdU-xcd st-ta (I-jk. i.-yOb).

Only one species found ni Aorlh Anurici.

Cyprois tpuirf^inoia Strautt l8>|.

I^nKth 1. 5.1 ram., bmfilh avf

mm 1. . -I- - ' I ■ ' - ' -

vdl,
less

water. ^

moniuha 1

ments. Ma> .

lorn (leljris. d:

later dry up. S« >

sli^'htly curvr«l;

miinly loriK- .^1

caRO, III. (Jack:»jii l^t.,. A^il.

May, June.

Fig. I :<,»',
Cytrois martinala :
tcmalc, X i^;
X ?«;: (<•) hur
(<i) .Maiillary «,

22 (2.^) Natatory setae of the second antennae entirely lacking (Fig. i:c>S c).

Subfamily Ca.ndunlnak . . 91

23 (22) Natatory setae of the second antennae very evident, usually extend-

ing at least to tips of terminal claws (Figs, i :(*s e and
1290 c) 24

24 (25) Terminal segment of second leg with three long setae and no claws,

— one seta reflexed (Fig. 12 58 /)).

Ilyocypris Brady and Norman 1S89 . ^6

25 (24) Terminal segment of second leg with at least Dnc claw (Fig.

12686), — and usually beak-shaped iS

26 (27) Shell with many prominent tubercles, knobs, and furrows. Nata-

tory setae reaching to tips of terminal claws, or slighUy
beyond Ilyocypris gibba KAV\\y\*Mr \^-^^

Length 0.85 to 0.05 mm. Shell much tuhftoiUl*

anteriorly and posteriorly, and dct-idc<JK fv:rT..»rvl
anterodorsally. Two prominent tiil»cr.
of the eye siH.t. Poor swimmer* _ \
straight, its terminal k\.:
plain. Termiii.il M-ta

of torminaUlaw. Sw.i . .n , , . .

the spring months. In .omj^ay wiiii /. .'yjJ; ». usu-
ally. Colorado, March.

Ftc i:c7

Ilyocypris tihhc. <J^ Skk virw. X 4S:

(ft) Donil view, X 44.

8io

FRESH-WATER BIOLOGY

27 (26) Shell with weak tubercles, knobs, and furrows. Natatory setae
reaching scarcely to tips of terminal claws.

Ilyocypris hradyi Sars 1890.

Length about as /. gibha. Height
of female 0.45 to 0.5 mm., breadth
0.32 to 0.5 mm. Male slightly larger.
Scarcely free swimming, but creeps or
burrows. Shell weakly tuberculate
and not furrowed posterodorsally.
Habitat and occurrence as /. gihba.
Furca strong curved, and much broad-
ened at base. About ten times as long
as width in middle. Dorsal seta plu-
mose and bent near tip. Distal half
of dorsal part of furca ciliate. These
two species are quite variable, thus
causing much confusion in diagnosis.
Both species are also found in Britain
and Germany.

Fig. 1258.
Ilyocypris bradyi. (a) Furca, X 200; (b)
End of second leg, X 150; (c) Dorsal
view, X 45; (d) Side view, X 45-

28 (29) Natatory setae of the second antenna shortened, no swimmers.

Second leg with a beak-Hke end segment and a claw (Fig.
1268 b) Subfamily Herpetocypridinae . . 30

29 (28) Natatory setae of the second antenna long, reaching at least to tips

of terminal claws. Second leg as above.

Subfamily Cypridinae . . 42

30 (31)

Furca abnormal, with three claws, — the usual dorsal seta being
replaced by a claw. Shell faintly longitudinally striated
(Fig. 1259) Ilyodromus Sars 1894.

Only one species known in America.

Ilyodromus pectinatus Sharpe 1908.

Length 1. 10 to 1.18 mm. Shell with
reticulate patterns anteriorly and
posteriorly. Posterior edge of furca
decidedly pectinate. The only known
species of the genus with a pectinate
furca. In ponds and slowly flowing
streams, with Typha, Iris, Chara, etc.
South Carolina.

Fig. 1259-

Ilyodromus pectinatus. (o) Side view, X 45".

(6) Furca> X 140.

THE OSTRAC(JI)\

>! I

31 (30) Furca normal, with two spines and tw., Mia. , l-.^. , ,r. j /.

32 (33) Second segment of first leg with two seta, on unlcr.or „uirg,n ^t^.

1260 d). Three spmes on first maxillary pr.Kc-vs ^

C hhuuxdotltcca Sau&sure iS :

33 (32) Second segment of first leg with one seta <,„ anterior margin (KIk

12// 6). Two spmes on first maxillary pnKrt-is

Hcrpctocypris Hrady .md Norman i8h

34 (35) Shell plain, no special markings of any sort. Seen from above the

shell is decidedly wedge-shaped anteriorly (Fig. ,,fx)). '

Chlamydotltcca aitcka SauMurc 1858.

Lcnjs'th T,.\o mm . Im i.-- ■
breadth 1.80 mm. N< '
of the largest siktocs «.i
Natatory setae of th.
reach to tijw of tcrmin.i
known. Sirn from .:
rnuch more we<li,'«'-sh.i;.
C. mixicana. It al>-.

stri|x-s in the shell. Fu:

about 18 times as Iopk .1
faintly pectinate on the di .•
Texas, Mexico. Ditchi-i an«i j.. i<
tober.

Fig. ij6o.
Chlamydothfca aUtka. (d) Side ^-icw, X«$,
(b) Dorsal view; (c) Fuica. X IVK U) Fml

ICK, X US.

35 (34) Shell with semicontorted and radially arranged colored Iwinds.
Shell more tumid from above (Fig. 1 'f>! 1 -h

36 (37) Shell with at least six sinuous radiating dark-green baml.s on its
sides C/iliimydol/nrii htrruki Turner iSq^,

LenRth .vcx> i:
width 1.4 < mm. I
sinuous and radi.i
bands. Claws of J»f>;
smooth. Termiiul ila
as lonjr as entire I' 1'
h.df the dor<il i
twenty times as
canal basin. Ohi-i

Fir.. 1 161.

Chlamydotketa ktmtki. («) SiAt rifw. X tf;

(6) Donalvif*: •> K»r«» • too.

8l2

FRESH-WATER BIOLOGY

37 (36) Shell with but three such bands.

Chlamydotheca mexicana Sharpe 1903.

Length 2.75 mm., height
1.55 mm., width 1.60] mm.
No males yet found. Two
or three narrow greenish
bands irregularly arranged
on sides of shell. Furca
straight, about twenty-
three times as long as wide
and faintly toothed on
about one-half of dorsal
margin. Ponds; Septem-
ber. Durango, Mexico.

Fig. 1262.

Chlamydotheca mexicana.

(a) Side view, X 25;

{b) First leg, X 100;

(c) Furca, X 125.

38 (39) Length about four mm Herpeiocypris harhatus Forbes 1893.

Width 1.60 mm., height 2.00 mm. Shell
fairly full, but not plump. Large, hairy, yel-
lowish brown in alcohol, with reddish patches
on either side. One of the largest of the
fresh-water ostracoda. Valves equal. Furca
about twenty times as long as wide, slightly
sinuate. Yellowstone River, Wyoming. July,
August.

Herpetocypris barhatus.

Fig. 1263.
(a) Side view with shell removed; {b) Furca.

(After Forbes.)

39 (38) Length less than three mm 40

40 (41) Dorsal edge of furca with five combs of coarse teeth (Fig. 1264 h).

Herpetocypris reptans Baird 1850.

Length 2.00 mm. to 2.50mm., height
0.80 mm. Brownish yellow. Furca
about sixteen times as long as wide,
slightly curved; its dorsal edge armed
with jive combs of coarse teeth. Furca
claws coarsely toothed. Muddy bot-
toms, ponds; April to September.
California.

Fig. 1264.

Herpetocypris reptans. (a) Side view;

(6) Furca.

THE OSTRACODA
41 (40) Dorsal edge of furca plain (Fi^. 120; /,).

Ucrpctocypris trshulhuiria Cushnun 1908.

IxrnKth J. 10 mm

mm . v. -I'l. _ ..-

txtra

I'urta >

as wi.l,., ,I^ .u«, jj^^^ j.^^^^

NcwfoundUnd. Mmy.

llfTfffUHyfrrii !'
view; {h) I
ihowin* un^

42 (43) Natatory setae of second antenna reach i.. u\>> ,,t terminal i

slightly beyond. Second leg with a lu-ak like cn«l ^
andaclaw(Fig. i268 6,('). . Subfamily Cvi-kiui'. ,

43 (42) Natatory setae of the second antenna reach bevontl tips of u-rmw»al

claws by about one-halt their length. Second leg with
three terminal setae of ditTerent lengths, two of ihcm rc-
flexed, the other short and claw like (Fig. iiaoc, f\.
Subfamily Cvclck'YPKIdin ■'

44 (45) Testes, if present, originating in anterior part of shell m iurm of

concentric circles or half circles (Fig. 1266).

S piracy pr is SharjK* 1903 .

45 (44) Testes, if present, not originating in anterior part of shell in form of

concentric circles or half circles (Fig. 1271 />).

CyprisO.V. Mullrr 17-

46 (47) Shell not tuberculate, excessively hairy (Fig. uof) <;).

Spirocypris passiticu Sharpc 190;

I r n p» h I ^9 mm .

.ili,
tors
1 , .

i.iiUiCllj, ,Nc» JcXif;

FlC. IJM..

Spirocypris passaica. (a) Side view, X Jo; (6) I)or**I view, u) FufVA.

14

FRESH-WATER BIOLOGY

47 (46) Shell very tuberculate, sparsely hairy and unusually plump (Fig.
1267 c) S piracy pris tuberculata Shsiipe igoS.

Length 0.93 mm., height
0.53 mm., width 0.70 mm.
Purplish brown, with one or
two dorsal transverse lighter
bands. Right valve sHghtly
overlaps the left anteriorly.
Natatory setae extend but
slightly beyond the ter-
minal claws. Furca about
thirty-two times as long as
wide. Shallow, weedy, and
swampy ponds; spring.
Chicago and northern In-
^ diana.

Fig. 1267.
Spirocypris tuberculata. (a) Side view, X 43; {b) Furca; (c) Dorsal view.

48 (49) First leg four-segmented, third and fourth segments united
(Fig. 1268 c). . . Subgenus Eurycypris G. W. Miiller 1898.
Only one species in this subgenus.

Cypris {Eurycypris) puhera O. F. Miiller 1785.

Length 2.10 mm., height
1.25 mm., breadth 1.20 mm.
Greenish in color. A dark
patch at its highest and cen-
tral part as seen from the side.
Shell sparsely hairy. Anterior
and postero-ventral margins
with prominent external tuber-
cles. Two prominent tuber-
cles at postero-ventral part cf
shell. This character alone is
suflBcient to identify this species
of c>^pris. First leg four-seg-
mented. Furca nearly straight,
about twenty-four tinies as long
as wide. Ponds; April to June.
Oregon.

Fig. 1268.
Cypris {Eurycypris) pubera.

(a) Side view, X 10;

(b) End of second leg;

(c) First leg;

(d) Furca;

(e) Second antenna;

(/) Posteroventral part of shell.

49 (48) First leg plainly five-segmented (Fig. 1277 b), third and fourth seg-

ments not united 50

50 (51) Inner anterior edge of right shell thickly tuberculate (Fig. 1270 a).

Subgenus Cyprinotus Brady 1885 . . 52

THK OSTKACODA
SI (50) Inner anterior edge of right shell plai„ n.-jg. , _,^, ^y

5. (53) Dorsal seU of furca .ore than one.h.f ,..„„. of .Merlin.,, .,,,
53 (5.) Dorsal -a^of Jurca^not ™re than ,„..ha,f length of ,u.

>lcnnin.tl

54 (55) Left shell larger than the right, an.l its cIlu-
1270 h). " *"

'•> not lulxrculatcil-ig,
^6

55 (54) Left shell smaller than the right and with •. tmv.. f

along the inner margin iV^:^^^^:^:'^ "^^^^^'^^-'^ ^^^^^i«
Cypris (Cyprinotus)prll,uida Sh

56 (57) Right-shell margin tuberculate only at anterior and |>ostcn.vcnlral
margins. Shell about four-sevenths as high as Um^ (Kig.
1270 a). . Cypris {Cyprinotiis) inconfirucns Ramdohr 1S08.

Shell (IruM'ly iti^irntnl
transluicnt ycllowiikh m
.•^mcxtth. 1.^'npth t {o ?o •
Left valv.
airvitl, al
wide. .^1

In qutir
JiKobal

even in tcmix>rar>" ;

watering tmu^h^ f '
JVnnsylvania.

(<i)K
of:;

Spin« ol bnrt n
19a

■■*. X

8i6

FRESH-WATER BIOLOGY

57 (56) Right-shell margins unusally tuberculate, as in Fig. 12716. Shell

not more than one-half as high as long (Fig. 1271 a).

Cypris (Cyprinotus) dentata Sharpe 1910.
Shell brownish yellow
and translucent in alco-
hol. Length 1.35 to 1.60
mm., and height not more
than one-half as great.
Shell pointed posteriorly,
and anterior half of ven-
tral margin slightly sinu-
atein the male, but nearly
straight with the female.
Natatory setae reaching
well beyond the terminal
claws. Males common.
Furca gently curved,
about sixteen times as
long as wide. Spines of
first maxillary process
toothed. Temporary
ponds. Stamford, Ne-
braska.

Fig. 1 27 1.
Cypris (Cyprinoius) dentata.
{b) Right shell from within, X 30; (c) Furca, X 105.

58 (59) Dorsal seta of furca less than width of furca from subterminal claw

(Fig, 1272c). . Cypris {Cyprinotus) burlingtonensisTxirneT 1894.

(a) Left shell from within

Length 1.50 mm., height 0.70 mm., width 0.70 mm.
Yellowish brown with bluish black longitudinal
stripes on dorsum and sides. Hairy. Natatory setae
extend slightly beyond tips of terminal claws.
Maxillary spines toothed . Furca slender and straight,
about eighteen times as long as wide. Dorsal seta
close to subterminal claw. Shallow, temporary, grassy
pools. Ohio, Georgia, Delaware.

Fig. 1272.

Cypris (Cyprinotus) burlingtonensis. (a) Side view, X 16;

[b) Dorsal view; (c) Furca.

59 (58)

Dorsal seta of furca more
claw

than

width of furca from subterminal
60

60 (61) Shell with no markings, translucent. Right valve the larger.

Cypris {Cyprinotus) americanus Cushman 1905.
Length 1.50 mm., breadth 0.70 mm.,
height 0.80 mm. Colorless. _ Natatory
setae reach to tips of terminal claws.
Fourth segment of first leg with four
short extra spines. Terminal segment
of second leg constricted in the middle,
and with two longitudinal rows of
minute spines extending from the
constriction to the tip. Furca nearly
straight and about twenty tirnes as
long as wide. Ponds and ditches.
Nantucket, Mass.

Fig. 1273.
Cypris (Cyprinotus) americanus. (a) Side
view, X 30; (b) Dorsal view; (c) Furca,
X 150; (d) End of first leg showing
extra spines, X 150.

8,7

THE OSTRACODA

6i (60) Shell reticulated, thin, the spermarics showing through. I

Cypris {Cyprnwtus) crnid Tu:

0.6s mm., width o.sgt<.oy« mm N "'..•;...

lary spmcs smocuh. l-„urll, m-kuh-u-
extra short spines, l-urca i urvtnl .

ponds and canal basins. Ohio. ««i*« wrruy

Cypris (Cyprinotus) crena. (a) SidJ tiew. X 15; (*) Furca ol mtk.

62 (63) Furca normal, with two spines and two setae (Fig. W7S</)

Subgenus Cyprii

63 (62) Furca abnormal, the terminal seta missing (Fig. ii^c).

Paracypris .W-w Subgenus

H

66

64 (65) Both spines of first maxillary process smooth

65 (64) Both spines of first maxillary process toothed (Fig. i 270 r;.

66 (67) Shell bluish black, with two yellowish areas in region of eye spot

(Fig. 1275 a) Cypris {Cypris) virais ]\inx\i: \^20.

Length 1.70 to 2.00 mm., height 0.90 to i.oo mm. Shell coverctl with short ! ur> x'\\
left valve slightly overlapping the right. Ventral edge flanged antoriorlv N.f
reach to tips of terminal claws. Dark to yellowish green. Furca weakly s'shajir.

and from eighteen to twenty times as long as average width, and its dorsal mar^ ...-.w.

Very variable. Weedy ponds; April to July. Massachusetts. Mexico. Ohio. Wiscoosm.

Fig. 1275-
Cypris (Cypris) virens. (a) Side view. X i8; (6) Dorsal view; (c) Furca.

67 (66) Shell bright, deep green, smooth, with minute punctures.

Cypris {Cypris) iiUissinui C'haml)crs 1877.

,_ Length 0.80 mm., height 040 mm. I

^ two terminal claws nearly same Irn^'th i

ing snow, Mt. Libert. C'olora<lo. .\llit

Fig. ii76. Cypris (Cypris) aUistimt Kurca.

6S (69) Terminal three segments of first leg longer than two-lhirdi of il*

terminal claw (Fig. 1277/)) • • 1^

69 (68) Terminal three segments of first leg shorter than two-lhinls of lU

terminal claw 7'

FRESH-WATER BIOLOGY

70 (71) Shell thin, and dirty to ocherous yellow.

Cypris {Cypris) testudinaria Sharpe 1897.

Length 1.15 mm., height 0.75 mm.,
width 0.65 mm. Natatory setae just reach
tips of terminal claws. Terminal claw of
first leg one-sixth longer than the last three
segments. Terminal claw of second leg
one- third as long as terminal segment.
Furca slightly curved, its dorsal edge ser-
rate two-thirds its length, and sixteen to
eighteen times as long as wide. Dorsal
seta two-thirds as long as terminal one,
and width of ramus from subterminal claw.
Terminal seta fully one-half as long as the
terminal claw. Ejaculatory duct five times
as long as wide, with spines thickly set over
the entire surface (Fig. 1277c), instead of in
wreaths, as is common. Ponds in woods.
Illinois.

Fig. 1277-
Cypris {Cypris) testudinaria. (o) Furca; {b) First leg;
(c) Part of ejaculatory duct of male, and origin of
vas deferens.

71 (70) Shell dark green to chestnut brown with transverse lighter patches dor-
solaterally (Fig. 1278(1-6).

Cypris {Cypris) fuscata Jurine 1820.

Length 1. 30 mm., height 0.80 to 0.95 mm., width
0.80 to 0.8s mm. Right shell overlaps left.
Sparsely hairy. Terminal claws of first leg less
than one-third longer than the last three segments.
Furca weakly S-shaped to nearly straight, and
from eighteen to twenty times as long as wide.
Terminal seta of furca weak, not more than one-
third as long as terminal claw; dorsal seta less than
width of furca from subterminal claw and about
one-half as long as the terminal seta. Sexual.
Common everywhere in shallow, grassy ponds and
swamps; April to June.

Fig. 1278.
Cypris (Cypris) fuscata. (a) Variety major, dorsal view,
X 20; (b) Variety minor, dorsal view; (c) Side view
variety major; {d) Furca, X 125.

72 Shell dark green with two light patches in region of the eyes (Fig.
1279 a) Cypris {Cypris) reticulata Zsiddsich 1S44.

Length i.io to 1.30 mm., height 0.72 mm., width
0.65 mm. Shell usually reticulate or tesselated.
Somewhat superficially resembhng Cypris fuscata
major. Natatory setae reach slightly beyond the
terminal claws. Fiurca straight, weakly bent near the
end, and from ten to twelve times as long as wide, and
faintly toothed along the dorsal margin. Terminal
seta slender and of the same length as the dorsal one,
which is situated about width of furca from subter-
minal claw. Abundant in small, temporary grassy
pools. Illinois, Massachusetts, New York, New
Jersey.

Fig. 1279.
Cypris (Cypris) reticulata, (a) Dorsal view, X 275; (&) Furca, X 1323.

THE OSTRACODA

810

73 (74) Posterior margin of furca pectinate (Fig. i ,So c).

Cypris iPanicypris) pcrdegans Hcrrick 1887.
LonKth v^omm . hciKht i 7 j mm., width 1^

mm. Color «U-ar 1..1I. ..
patti'rn in r K-ar !
shell is acutely w,
the side the ujHm r
parallel, with a I
ventrally. TerM!;
two small claws and ..u«.
spine like. Weetly jxjnds

. ,„ Fk. ijRo.

Lyprts (Paracypris) ptftUtam. («) Sidt vk« X •;
{b) Dorsal view; (c) Funa.

11,.^ «.,.v. .

^\.* l>uf««i «r<«

74 (73) Posterior margin of furca plain (Fig. 12S1 r).

Cypris {Paracypris) grandis ChamlxTs 1S77.

Length .^60 mm., heijjht 2 '•
mm. I'rom ahove. shell r- .
Bluish white to iKile Kfirnish
Arkansas River, Colora<lo. .Miuudc dooo loct.
A doubtful form.

Fig. ij8i.
Cypris (Paracypris) gramdis. («) Sidr rim. X 4.
(b) Dorsal view; (c) Furca; id) MatilUry palpi

of male. (After Chantben.)

75 (76) Terminal segment of second leg small, with two short claws. .in<l a
long refiexed seta (Fig. 12S2 </). Second antenna of maic
with two sense organs on fourth segment.

Cyprid Zenker 1S5.J

76 (75) Terminal segment of second leg long and narrow, with short cbw.
and two long reflexed setae (Fig. ijdo 0. Second antenna
of male without sense organs on the fourth segment.

C^'c/ocypm Brady and Norman iSSi^ . . 8q

77 (78) Right-valve margin not crcnulate anteriorly. X'alves alvnjt the

same size (Fig. 1284(1-6). . . . Subgenus Cy/^rt.

78 (77) Right-valve margin crenulate anteriorly. N'alves of deciderlly differ-

ent sizes (Fig. 1287 a-b).

Subgenus Physocyprui Xavra iS;i

79 (80)

80 (79)

Terminal claws of second leg approximately equal (Fig. 1 2S: </)• >^ «
Terminal claws of second leg evidently unequal (Fig. 1 285 <0

820

FRESH-WATER BIOLOGY

8 1 (82) Terminal claws of furca not more than one-half as long as furca
(Fig. 1283 b) 83

82 (81) Terminal daws of furca three-fifths as long as furca or longer (Fig.
1282 c) Cypria [Cypria) dentifera Sharpe 1897.

Length 0.69 mm., height 0.38
mm., width 0.26 mm. Brownish
yellow, with dark brown markings
and reddish blotches. Right valve
overlaps left anteriorly. Left-
valve margins crenulate, anteriorly.
Natatory setae reach length of
antennae beyond tips of terminal
claws. Terminal short claws of
second leg approximately equal
and as long as the terminal seg-
ment. Furca stout, ten times as
long as wide, its subterminal claw
with a comb of remarkably long
teeth. Males common. Algae-
rich ponds. Illinois, Ohio, New
York, New Jersey.

(c) Side view of left' valve', X 30; (6) Dorsal view; (c) Furca; (i) End of
second leg.

Cypria {Cypria) dentifera.

83 (84) Shell covered with a close reticulum of longitudinally subparallel
Hnes (Fig. 1283 c). Abdomen without processes.

Cypria {Cypria) exsculpta Fischer 1855.

Length 0.60 to 0.75 mm., height
0.38 to 0.42 mm., width 0.25 to 0.28
mm. Shell thin, covered with anasto-
mosing subparallel lines. Color clear
chestnut brown. Common in streams
and p)onds everywhere. Also com-
mon in bottom tows in river chan-
nels, lake and river shores. Caudal
rami short, stout and much curved;
both terminal claws smooth; dorsal
setae situated slightly beyond middle
of ramus. Distribution world wide.
This species may be at once identi-
fied by means of the reticulum of
anastomosing subparallel lines on the
valves. These may be readily seen
with a two-thirds-inch objective.

Fig. 1283. ,. ^

Cypria (Cypria) exsculpta. (o) Dorsal view, X 45; (b) Furca; (c) Striations on shell; {d) Spiny cyUnder

of ejaculatory duct, in sack.

THE OSTRACODA

84 (83) Shell plain, with small i)uiicta. Abdomen with two ■
processes ^ypria {Cypria) opOuilmi<a ]

Lcnglh 0.56 to o.Oo mm ,
mm., widlho.jjloo. t'>mr;
ik'ar Ijrown, with •!.
riorlyan<liK)Sli-rii.rl\
Natatory sotac vcr\
terminal tiaws liy n.
of the antrnna. 1(.
lonK as widi-. Suri
river chanmis ami
l'cl)ruary to OitoUr

and ditches where there i:* Utile or i^ . fac-
tion. Georgia, Illinois MinnrtoU. thrf •■■

Yu.. ijs^,
Cypria (Cypria) opikalmica (4) «vWr rirw. X m.
(b) Dorsal view; (o Furci. X I5T|; (/) Fmit.
X 100.

85 (86) Shell clear to brownish yellow, with a few scattered punrla.

Cypria (Cypriu) obcsa Sharpc iSg;.

Length 0.78 mm., hcixht 0.48 mm , width

0.33 mm. Plump. Furi n ' ■ ' ■ - -,

times as long as wide, it

times width of ramus fron.

and as long as the terminal st t-i \\Ac% i.L_,-^^

mon. In tow of sandy bkc »horr, M*y

Illinois.

Fic. ia8s.
Cypria (Cypria) obesa. («) Doml vim

(6)Furca; (r) Maxillary palp* o( auk; Id) >*c.-*ti

leg.

86 (85) Shell white, smooth, and shining, with numerous almost confluent

puncta Cypria {Cypria) mons Chambers 1877.

e Length 0.70 mm. A douhtful form, not well described

\ X" ^ Colorado, Mt. Elbert. Altitude 1 1. 000 fert

) ( \ F.o. ..sr,

Ct V Jh Cypria [Cypria) mons. (j) Dorsal \-iew. u»>^..W %«•». X ift.

^ ^^ (.Alter Chambers

87 (88)

Left shell higher than right. Terminal short setae ..i >....iid leg
about twice as long as the terminal segment (l-ig. i.-S;).

Cypria [Physocypria) pustulosa Shar]xr 1807.

Length 0.51 mm., height o i'^ n.m *i*th
0.22 mm. Clear hrownisli witi'
Kxtremitics of shell hairy \
flange on left valve (Fig ' ""•
setae three times as lonf,-
tween the i)lace of their 1
terminal claws. Furca ;
length of terminal claw I '
situated alM)Ut middle of (
in river channels, surface *»d liotto*;
lakes, and lake and river »horr». ^
SeptemlH-r Illinois.

Tb; {b\ kight xalvt. U) Firn k«; U) Fare*.
(e) Second le«.

822

FRESH-WATER BIOLOGY

(87) Left shell same height as right, but longer. Terminal short setae of
second leg about as long as terminal segment.

Cypria (Physocypria) inequivalva Turner 1893.

~ Length 0.42 to 0.55 mm., height 0.35

to 0.38 mm., width 0.26 to 0.28 mm.
Shell with irregular cross-shaped spots
dorsoanteriorly and posteriorly. Furca
curved, slender, its dorsal seta rudimen-
tary or absent. Males common. Amongst
algae of shallow ponds. Ohio, Georgia.

Fig. 1288.
Cypria (Physocypria) inequivalva. (a) Side view, X 44; {b) Dorsal view; (c) Furca.

89 (90) Dorsal seta of furca rudimentary or absent (Fig. 1289 c).

Cydocypris laevis O. F. Miiller 1785.

Length 0.45 to 0.48 mm., width 0.24 to 0.28 mm.,
height 0.30 to 0.3s mm. Color lemon yellow to chestnut
red or horn brown. Plump, and left shell overlapping the
right anteriorly. Furca stout, nearly straight, six times
as long as wide. Terminal seta more than one-half length
of terminal claw. Common in weedy streams, ponds, and
swampy regions; April to November. Delaware, Indi-
ana, Illinois, New York, New Jersey.

Fig. 1289.

Cydocypris laevis. (a) Dorsal view, X 60: (b) Side view, X 451

(c) Furca.

90 (89) Dorsal seta of furca plainly well developed. Terminal claws of furca
strong, and much bent at tip (Fig. 1290 e).

Cydocypris forbesi Sharpe 1897.

Length 0.55 mm., width 0.36
mm., height 0.39 mm. A small
form. Plump and sepia brown in
alcohol. Natatory setae four times
length of terminal claws. Penulti-
mate segment of second antenna
with but one seta. Terminal seg-
ment of second leg three-eighths
as long as the preceding segment
(Fig. 1290/). Furca about eight
times as long as wide. Both ter-
minal claws strongly bent at tip,
nearly smooth. Right palp of sec-
ond maxilla of male larger than
the left one. Terminal seta about
as long as width of furca. Males
common. Ponds in woods; April.
lUinois.

Fig. 1290,
Cydocypris forbesi. (a) Side view, X
60; lb) Dorsal view; (c) Second
antenna; (d) Maxillary palps of
male; (e) Furca; (f) Second leg.

91

THE OSTRAC'ODA

Terminal segment of second leg with three unlik.
IS reflexed(Fig. I20I J). . Subfamily (

»23

92 (94) Shell reticulate, very tumid. Small, plump forms not ■

mm. long. Second antenna of l>oih sc-xes 1..

Pur(UanJon<i Harlwig

93

Shell profusely ornamented with p<.lygonaI areas an<i tubcrdr*
(lug. 1 291 a).

Paracandona citplcctdla Hradv and Norman 1880

Lcnpth 0.56 to o <;« mm , Kri-ht ^ .. ^- ^ ,^,
mm., width 0.^2 t. " .

larger. One ternii
fused to terminal
stout, si.x timesasIuiiKa, v-iiii
length of suhterminal tbw. I .
scarcely evident. .\o otlu-r (
cod shows the ornamentation
and tubercles. The siK-rifu i,
refers to the striking external ai;. ,i:ai.r -.•_.
low, swampy regions, in mud and drlm» o< ihr
bottom; spring months. .New ]trsty

Fig. ijqi.
Paracandona euplectella. (a) Side view. X y*. (*) iJor-
sal view; (c) I'urca; (</) Second lot; (#/ Ut

palp.

94 (92) Shell plain, at least not reticulate or excessively tubcrcuUtc or
tumid. Q5

95 (96) Furca abnormal, terminal seta absent (Fig. i2()2 b).

Typhlocypris \'ejdovsky 1882

97

96 (95) Furca normal, with 2 claws and 2 setae (Fig. ij«)4 h).

Camloiui Haird 1S50 . . oq

97 (98) Furca nearly straight. Dorsal-valvo margins evenly curved (Fig.
1292 a-b) Typhlocypris pcircci Turner 1895.

Length 0.70 t») 0.70 mm . -^ '*
mm., height o,, \ to OM v
tinged with yelK)W '^J <
compres-siil. Funa n^
twelve times as lorn:

claw more than twi>-il,..

one. i^exual. l'jaiuLit.>rv duit »'i
of chitinous spines. .^h.illow. *■
June. Georgia.

Fio. i.H»j.
Tvphhcyprii peirtei. (<i> Side v4n» o< (rm«W. X »K
l6) Furci o( idaI*. (< ) Prtm

824

FRESH-WATER BIOLOGY

98 (97) Furca decidedly gurved.
1293 a). . .

Dorsal-valve margins '' humped " (Fig.
TypJilocypris delawarensis Turner 1895.

Lengdi 0.95 mm., width 0.43 mm., height 0.54 mm. Color
greenish yellow with brown blotches. Maxillary spines plain.
Terminal claws of furca slender and plain. Furca slender and
much curved. Creeks; March. Delaware. (A doubtful form,
not well described.)

Fig. 1293.
Typhlocypris delawarensis. (a) Side view, X is; (b) Furca.

99 (100) Shorter seta of terminal segment of second leg outwardly flexed

(Fig. 1294(71) Candona reflexa Shsivpe iSgj.

Shell twice as long as high, cine-
reous. Second leg five-segmented,
its terminal segment as wide as long,
and about one-third as long as the
penultimate segment. Furca eight
times as long as wide and slightly
curved. Dorsal seta as long as sub-
terminal claw. This is the only
Candona known with the peculiar,
partly reflexed seta of the second
foot, and it may be a characteristic
of a young stage. Tows along lake
shores along the bottom; April to
November. lUinois.

Fig. 1294.
Candona reflexa. (a) Second leg;
{b) Furca; (c) First leg.

100 (99) Shorter seta of terminal segment of second leg not outwardly
flexed (Fig. 1296 h) loi

loi (102) Length of shell more than 1.50 mm

Candona crogmani Turner 1894.

Length 1.52 mm., height 0.76 mm., width 0.58 mm.
Shell thin, pellucid, inequivalve, greenish yellow. Max-
illary spines plain. Second leg indistinctly segmented.
Furca straight, ten times as long as average width, its
terminal claws pectinate. Dorsal seta one-third length
of furca from subterminal claw. Shallow, temporary
ponds; December. Georgia.

Candona crogmani.

Fig. 1295.
(a) Side view, X 15; (*) Dorsal view;
(c) Furca.

102(101) Length of shell not more than 1.50 mm 103

103 (104) Length of shell less than one mm io5

104 (103) Length of shell more than one mm 108

8^5

THE OSTRACODA

105 (106) Subterminal claw of furai clcci(._ ..

Candotui simpsoni Sharp<- iR<j7

l^'^Uy S-shapedfFig. ii^fid).

LenKth 0.7? mm
mm. \'ill<i\vi>li v.:
ri«lit. Ui)iHT aii.l
paralk'l. I-urca turvol
lon>,'as wide with the mi!
S-sliapi'd a marknl .
twice width of funa fr(Ji
two-thirds its U-nKth. 1
and river shores, and poiuli
Illinois.

^jXUi^ aiiMJ AuluUltt.

,, , . Fig. iju6.

Landona simpsoni. (a) Side view. X 47. '<>. ^«cum m;
(f) Second aoteniu: (rf) Kuroi.

106(105) Subterminal claw not S-shapcd (Fig. 1297 f) ,0-

107 Shell with dorsal and ventral margins nearly parallel (Fig. i2Q7tf).

Candona paralida (i. \V. MuUcr 1900.

X at

Length 0.78 to 0.S5 mm., height
width 0.35 to 0.42 mm. Height t
I to 18. Furca straight. alx)ut sf\.
wide, its terminal seta rudiment ar\
claws doubly pectinate with unusu.
seta about twice width of furca imn. M.i.trrminal
claw. Second leg five-scgmcntctl. Swampy poodt;
May. Colorado.

Fig. 1J97.
Candona paralMa. (a) Side view. X sik; (fc) Sccoad liK
(c) Furca; (d) Terminal daws of furca.

108(109) Furca plainly curved (Fig. 1301 /»)

109 (108) Furcanotplainly curved, approximately .straight (Fig. i^gSJi

no

(in) Both claws of furca plainly S-shaped (Fig. i2()S J).

Candona si^nwidcs Sharpc 1S07.

Length of
I .(\\ mm. Si ■
Furca long a;
times as w
Dorsiil s*'t.i .1
of furca froni
male not ki
shores; .Ma\

Catulona iic»^
mnlc. X :s

826

FRESH-WATER BIOLOGY

III (no)

Both claws of furca not S-shaped — gently curved (Fig. 1299 a).

Candona recticauda Sharpe 1897.
Male 1. 1 8 mm. long, 0.70
mm. wide. Shell curved with
scattered papillar elevations.
The spermatogonia show
through as four bands. Sec-
ond leg six-segmented. Furca
straight, about thirteen times
as long as wide, with a dorsal
sinus base of furca very broad.
Right maxillary palp of male
club-shaped (Fig. 1300(f). Bot-
tom of ponds; February. Illi-
nois.

Fig. 1299.
Candana recticauda. (a) Furca;
(b) Secondleg; (c) End of second
antenna; (d) Right maxillary
palp of male; (e) Left maxillary
palp of male.

112(113) Second leg six-segmented 114

113(112) Second leg less than six-segmented 116

114(115)

Shell with fine longitudinal striations when in glycerin. Max-
illary palps of male enormously thickened, their fingers fully
as thick as the stem (Fig. 1300 d).

Candona fabaef or mis Fischer 1854.

Length i.oo to 1.26 mm., height
0.47 to o-somm., width 0.49 to 0.5 1
mm. Shell yellowish transparent,
strongly compressed, the left valve
overlapping the right at both ex-
tremities, and also with dorsal
flanges. Furca ten times as long
as wide, straight. Abundant in
small pools in March, April, and
September. Georgia, Illinois.

Fig. 1300.
Candona fabaeformis. (a) Side view of
male, X 30; {b) Side view of female,
X 30; (c) Furca; (d) Right max-
illary palp of male, X 75-

115 (114) Shell without fine longitudinal striations. Maxillary palp of male
with finger about one-half as thick as stem (Fig. 1301 c).

Candona acuminata Fischer 1854.

Length 1.2c to 1.50 mm., height 0.60 mm., width
0.46 to 0.50 mm. Posterior extremity of shell sharply
pointed. Dorsally about as Candona fabaeformis, but
less compressed, and dorsal flanges weaker. Furca
eight times as long as wide, decidedly curved, and
much the broader at its base. River shores and
ponds with rich vegetation; April, May, and Septem-
ber. Texas.

Fig. 1301.

Candona acuminata, (a) Left shell of female, X 20;

(6) Furca; (c) Left maxillary palp of male.

THE OSTRACODA

Ii6 Shell decidedly arched dors:

(Fig. 1302 a). . . .

ly, much
Camlona

llu- highest in '
i\iniliiiii (). F. M

LcriKth i.o.:; to i.^o mm . hcJKht 0(0
four or indistinctly live s«•^;^u•ntc.| I
long as avcra«t' wi.lth. dri i. lolly <ur-.
mon. Shallow, tcmjiorary (jonds aiiM n
September. Massachusetts.

Candona Candida.

Fig. hoj.

(a) Side view of (enulr

(couUc, X 7$.

8,7

^a„» .4

REFERENCES ON NORTH AMKRICAX 1 KKsH \\ \ri.k
OSTRACODA

Brady and Norman. 1889. A Monograph ol the Marine and Frt-sh-Wairr

Ostracoda of the North Atlantic and North-western FurojK-. Sci. Trans.

Royal Dublin Soc, Ser. 2, 4 : 63-270.
Herrick, C. L. 1887. Contribution to the Fauna of the Culf of Mexico

and the South. Memoirs of Denison Sci. Ass'n, i : 1-56.
Marshall, W. S. 1903. Entocythcrc camhur'm. \ rarasilic rktr.icNl.

Trans. Wis. Acad, of Sci. Arts and Letters, 14 : 1 17-144.
MtJLLER, G. W. 1894. Die Ostracoden des Golfes von N\-aiK-l. M..n..Ki -'•

Fauna und Flora des Golfes von Neapel. Berlin.
1900. Deutschlands Siisswasser-Ostracoden. Zoologica. Hc-fl 30, 1 1
Sharps, R. W. 1897. Contributions to a Knowledge of the North A-

can Fresh-Water Ostracoda included in the Families Cylhcridac and

Cyprididae. Bull. 111. State Lab. of Nat. Hist., 4: 414-484.
1903. Report of the Fresh- Water Ostracoda of the United Slates National

Museum, including a Revision of the Subfamilies and (k-nera of the

Family Cyprididae. Proc. U. S. Nat. Mus.. j6: 960-1 001.
1908. A Further Report on the Ostracoda of the United States National

Museum. Proc. U. S. Nat. :Mus., 35 : 399-430-
1910. On some Ostracoda, mostly new, in the Collection of the Unitol

States National Museum. Proc. of the U. S. Nat. Mu.s.. 3-^: v<5-U«-
Turner, C. H. 1893. Additional Notes on the Cladocera and Ostracoda of

Cincinnati, Ohio. Bull. Sci. Lab. Denison Univ.. S. pi. i : 1-18.

1894. Notes on American Ostracoda, with Descriptions of nr-.v <— — ^
Bull. Sci. Lab. Denison Univ., 8, pt. 2, 13-26.

1895. Fresh-Water Ostracoda of the United States. Gi-ol. and Nat. Hi>l.
Survey of Minn., Zool. Ser., 2: 277-337-

Vavra,W. 1891. Monographic Ostracoden Hohmens. Arehiv. der n.ilun%-.
Landesforschung von Bohmen, Bd. \T1I. no. 3.

CHAPTER XXV
HIGHER CRUSTACEANS (MALACOSTRACA)

By a. E. ORTMANN

Curator of Invertebrate Zoology, Carnegie Museum, Pittsburgh.

To the higher Crustaceans (subclass Malacostraca) belong such
forms as the sow-bugs, scuds, shrimps, prawns, crayfishes or craw-
fishes, and crabs. These popular names are not sharply defined, but
it appears convenient to restrict the name sow-bugs to the Isopods,
that of the scuds to the Amphipods. For the Mysidacea, the term
opossum-shrimps has been introduced, while the names shrimps and
prawns belong to certain Decapods, and are ahnost synonyms: the
former is now used chiefly for the smaller forms, the latter for
the larger ones. Crayfishes and Crawfishes are the Decapods of the
genera Cambarus and Potamohius. Often for these also the name
crabs is used, but this is a misnomer, and it should be restricted to
marine forms of the type of the common edible blue crab.

The great majority of the Malacostraca belong to the sea,
occurring in all regions, near the shore as well as on the bottom
of the deep sea, and floating and swimming on the surface. But a
considerable number have entered the fresh water, and are found
in rivers, creeks, ponds, lakes, etc. A few forms are known,
which live parasitic upon other aquatic creatures.

They are omnivorous, feeding on vegetable and animal matter,
both Hving and dead, but dead and decaying matter is preferred
by most of them. Asellus (of the Isopods) distinctly prefers de-
caying vegetable matter, while Palaemonias (of the Decapods)
seems to be speciaHzed as a mud-eater: at any rate, the pecuHar
hair-tufts on the claws probably serve the same purpose as in the
alKed tropical forms, where it has been observed that they are
used in gathering mud, like a small brush.

Generally, the fresh-water Malacostraca are not very conspicu-
ous, some because they are rather small and easily escape detec-
tion, while others, which are larger, keep in hiding, under stones

828

fflGHER CRUSTACEANS (MALyoMK.U A g,^

and logs, in holes, or among vegetation. But they arc present
practically everywhere, and in most budies of water, even
ones, one or several forms may be expected to occur. C".
forms (burrowing crayfishes) do not Ii\f iu opcFi water, but burrow
in the ground, going down to the groimd-waicT; their presence i^
indicated by piles of mud, brought out of the holes.

Fresh-water Malacostraca are found, with exception of the An-
tarctic regions, practically all over the world, including the Arctic.
but naturally are most abundant in the tropics. A numU-r of
groups are distinctly characteristic of temperate climates, and al
least one group (genus Cambarus, crayfish) has reached its hiKhesl
development in North America. Here Malacostraca an- found
ever3rwhere, but chiefly in the interior basin with its >;rcat and
diversified river systems. They become rather scarce on the west-
ern plains and in the arid regions, but are not entirely nW
there. The various forms are adapted to dilTerent surroumi...,. .
some prefer large rivers, others creeks or jx)nds. or small |)ools.
springs, and even subterranean waters.

They belong to very difTerent groups of the subclas> .Ma!
traca. The latter has been divided, in the more recent sy>;
into ten orders, and of these four possess representatives in our
fresh waters: Isopoda, Amphipoda. Mysidacea. and Deca:
These differ very much in their outer features, in general - .
of body, size, color, and details of mori)hology, so that it is hard
to give a short general account of their characters.

The body may be only a few millimeters long. u|) to one or two
centimeters (Isopods, Amphipods), or it ma\- be somewhat longer
(Mysidacea and some Decapods), while in otlur cases (prawns and
crayfishes among the Decapods) it may reach the considerable
length of ten centimeters and over. In tlu- smaller forms, ihe
color is generally inconspicuous, whitish or gra>ish. often more or
less transparent. The larger forms have more distinct color*.
which may become quite brilliant in certain parts of the IkkIv: the
large claws of the genus PaJjcmon (prawns) are. in the male sex.
often red, blue or purple. The crayfishes are. in genenU. of j^tx-n-

ish or brownish olive tints, but as a nde adult mak^ an '-

vividly colored, and in some species the adult male assumc-s a

830

FRESH-WATER BIOLOGY

entirely different from the greenish female and young: lighter or
darker red. At least two species are remarkable for their striking
color in both sexes: one is red, the other is beautifully blue.

The morphological characters of the Malacostraca are the follow-
ing:

ant

perp

Fig. 1303. Diagram of a higher Crustacean. (After Caiman.)

The body is enclosed in a comparatively hard shell, which is
articulated, forming a number of successive segments or somites,
which have a very constant number. Each somite may be com-
pared to a ring, which, however, is not completely circular, but the
upper part, called tergum or tergite, is convex, while the lower,
sternum or sternite, is rather fiat. The two unite on each side,
the tergite projecting over the sternite, and this projecting part is
called the pleuron. All these parts (as well as the appendages)
consist of a hornlike substance, called chitin, very often reinforced
by a considerable amount of calcareous matter.

In the anterior part of the body we have a headpiece, to which are
added several more or less obscure somites that are chiefly indi-
cated by their appendages. As the foremost appendage we may
regard the eyes (e in Fig. 1303). These, however, may not be true
appendages. Then follow two pairs of feelers, called antennulae
(antl) and antennae (ant); one pair of mandibles (mand), and two
pairs (first and second) of maxillae (max) .

Behind these parts the segmented body begins, including fifteen
somites, which all (barring reductions) bear appendages, with the
exception of the last, the telson (/). According to the appendages,

HIGHER CRUSTACEANS (MALACOsI KACAi 831

the body is distinctly divided into two parts: the iinlerior, ihonuc
or trunk {th), comprising the first eight somites; the iKJstcn t.
abdomen {ahd), with the six following (to which the teiM>n is ad.l. 1 .

The appendages of the thorax are called thoracic limbs. Some
or all of the first three of them are in many cases s|Hiiali/.« .'
maxilHpeds (maxp), and in this case the following live are i.: ^
peraeopods (perp). The abdominal appendages are ailled plct>|xxls
(pip), but those of the last (sixth) pair are often difTerentialetl m a
peculiar way, so as to form with the telson a taudal fan. and in
this case the name uropods (urp) is used for them.

The detail-structure of the appendages of the dilTerent re;,aons
of the body is very different. The eyes (only doubtfully n gardtd
as appendages) may be entirely sessile, or may be elevated ujxin
short, subcyHndrical, more or less movable eye-stalks. The an-
tennulae have an articulated base, with one or two terminal, articu-
lated branches (flagella). The antennae have an articulated basal
part, with one terminal, articulated flagellum, and often the Ixisal
part has a lateral scalelike process: the antennal scale t)r scapho-
cerite.

The mandible consists of a more or less solid part, to which an
articulated palpus may be attached. The maxillae are of various
shapes, and are probably to be regarded as mcxlifietl antcri-r
thoracic appendages. They consist of an inner and an nuirr
branch (endopodite and exopodite), which, however, are often
augmented by certain parts belonging originall)- to the gill ap|>a-
ratus.

The most marked difference is between the thoracic and the ab-
dominal appendages. The fonner consist originally of a larger,
seven-jointed inner branch (endopodite), and a smaller, articu-
lated outer branch (exopodite), but the latter may be absent.
The seven joints of the endopodite are rather constant. allhouKh
some of them may become united, or others may be sulxlividetl.
They have received separate names, which are, from the proximal
to the distal end: coxa, basis, ischium, mems. caq^us. proixxlu*.
dactylus (or coxopodite, basipodite. etc.). In certam thoracic
limbs, the last two joints (propodus and dactylus) assume ■ '- m-
liar position, forming a chela (j^inchers, claws).

832 FRESH-WATER BIOLOGY

The typical pleopods consist of a simple basal part, with two sub-
equal, terminal, articulated branches. But in many cases differen-
tiations and reductions are observed, the most important being
that of the uropods, referred to above, and the transformation of
certain pleopods into copulatory organs in the male.

In certain forms (Mysidacea and Decapoda) the dorsal shell of
the most anterior part of the body (head) is produced backward,
and covers more or less the thoracic somites in the shape of a shield,
curved down over the sides, which is called the cephalo thorax or
carapace (car). Very often the carapace has a median anterior
projection, called the rostrum (r).

The branchial apparatus of the Isopods is formed by the pleo-
pods. In all other groups special appendages (gills) of the thoracic
somites assume this function; they may be attached to the sides
of the thorax, or to the basal parts of the thoracic limbs.

The genital openings of the male are always originally on the
coxopodite of the eighth trunk-leg (or fifth peraeopod), those of the
female on the sixth (or third peraeopod), but in certain cases either
one of these may shift to the sternite.

All Malacostraca of the fresh water have separate sexes, and
very often the males are distinguished by secondary sexual char-
acters (size, color, development of claws). Copulation, or rather
conjugation, seems to take place in all of them, although this has
been observed in detail only in very few forms: it is best known m I
the crayfishes.

Propagation is by eggs. In the smaller forms (Isopoda, Amphi-
poda, Mysidacea), very Httle is known about propagation and
development, and with regard to the North American forms of
these groups investigations are altogether lacking. But from what
is known of exotic, chiefly European, forms it is probable that in all
the eggs are carried by the female for a certain period, before the
young are set free. In the Isopods, the female develops during
the breeding season pecuHar lamellae at the base of some thoracic
legs (four pairs in Asellus), which serve to cover and to hold the eggs.
In the Amphipods and Mysidacea similar, but greatly variable, de-
vices are present. In the Decapods, no such apparatus is known,

HIGHER CRUSTACEANS (M ALACOSTRACA) 833

but here the eggs are attached to the- pk-oixxls and arc carried
under the abdomen of the mother till the youn^r ^ri- ready to hate h.

Within these brood-pouches the embryonal develupmenl lakc-s
place. After the young have reached a more ur less advanced
stage, they leave the egg, but alwa>'s remain a certain time in ihr
brood-room of the mother. In the Isoi)o(ls iAscllus) the ynuu^
leave the egg at a rather early stage, and they have yet to undergo
considerable changes; in the other groups the lar\-a hatches in a more
advanced stage, and the subsequent changes are slight. In none
of our fresh-water crustaceans are free swimming lar\'ae known, but
these might be present in the families Atyidae and Falaemonidae.
in which such have been observed in their allied marine forms.

Of the life history of the Isopods, Ampliipods, Mysidacea. and
most of the Decapods, practically nothing is known. However, in
the Decapod-genus Camharus (crayfishes) more complete informa-
tion is at hand.

After hatching, the young crayfishes remain for a short time
with the mother, but soon leave her, and grow in the beginning at
a rather rapid rate, each increase in size being connected with a
moulting of the shell. Later, they grow less rapidly, and, after the
first summer, we may distinguish, in general, a spring and an
autumn moult. The total length of Hfe seems to be .sevend years:
four, five, or even more. Sexual maturity may be reache<i within
the first year, at least in some species. Males and females attain
about the same size, but in most species (except the burrowing)
the male possesses much stronger chelae than the lemale.

A very pecuhar difference is found among the males, which at
first was believed to be dimorphism, but has now been recognized
as alternating conditions in the Hfe of the same individual. Malts
of the first form have been distinguished from males of the sc-cund
form; the former is the fully developed and se.xually potent form,
while the latter is an impotent form. Generally speaking the first
form is assumed by the male in autumn, and lasts through the
winter (copulating season), while the other is assumetl in >pring,
and lasts through the summer. Young male>. in their first summer,
are always of the second fonn. Tlie ditTennce between thcM- two
forms is seen in the sexual organs: in the .uales of the second form

834 FRESH-WATER BIOLOGY

these organs are softer, the horny tips are undeveloped, and the
copulatory hooks on the ischiopodites of the peraeopods are small.

According to the general rule, that the males assume the first
form in autumn, the copulating season falls in the autumn, and
copulation may be repeated in the winter months. The male
seizes the female and holds it, stemites against sternites, chiefly
by the aid of the hooks of the ischiopodites of the peraeopods.
The sperm is discharged and stored in the female's annulus ven-
tralis, a pocket on the thoracic sternum, which thus serves as
receptaculum seminis. Oviposition takes place later, generally in
spring.

This seasonal cycle, as described, is not observed in all species,
but there are some, in which the alternation of the two forms of
the male is irregular and not connected with the seasons, and
where copulation and oviposition are also irregular. It has been
found that regularity of the annual cycle is connected with a habi-
tat in water which is subject to regular and considerable seasonal
changes of temperature (species living in rivers and ponds), while
irregularity of the life-cycle is found among those which live pref-
erably in water with slight temperature changes and that at the
same time is rather cool (species of mountain streams and of cool
springs or groundwater).

The fresh-water Malacostraca depend entirely upon the presence
of water, and cannot leave the water as a rule. This holds good
for the Isopoda, Amphipoda, and Mysidacea, and also for the
Atyidae and Palaemonidae among the Decapoda. In the water, the
Isopods (except the parasitic forms) crawl around on the bottom,
under stones, or climb among water weeds, but do not move by
swimming. The Amphipods are very lively in their movements,
which consist chiefly of swimming, often lying upon the side. The
swimming is often done in jerks, by curving and stretching the
compressed body. They move also by climbing among water weeds,
but hardly ever by crawling. All Mysidacea are distinctly swim-
ming forms, and so are the Atyidae and Palaemonidae among the
Decapods, while the movements of the crayfishes are of various
kinds, but fall under two main heads: crawling and swimming.
The first is the general mode of locomotion. It is not very rapid

HIGHER CRUSTACEANS (MALACOSTRACA) 835

and may take place in all three directions: forward, backward,
and sideward. More rarely the crayfishes move by swimming, and
chiefly so when alarmed and trying to escape; this swimming is
always backward, and is effected by quickly repeated strokes of
the abdomen. This kind of locomotion, however, is kept up only
for short distances.

With regard to the habitat, not much detail is known in the iso-
pods and amphipods. They seem to prefer more quiet bodies of
water, small streams and springs, to the larger rivers. Some of
them are not very particular as to their habitat, and consequently
possess a very wide geographical distribution, while others are very
restricted, possibly on account of special habitat preferences. The
only Mysidacean found in North America (Mysis relicta) inhabits
the Great Lakes to a considerable depth (as do two species of the
Amphipod-genus Pontoporeia). The genus Palaemon oi the Deca-
pods is known only from our largest rivers (Mississippi and Ohio).

In the genus Camharus, very complex conditions are observed
and the different species differ considerably in their ecology. Al-
though they all need water for their existence, it is a general rule
that all crayfishes are able to leave the water temporarily, and
some may stay out of the water for a considerable time, and do so
habitually. Of course, in order to moisten their gills, they always
have to return to the water.

In the water, the crayfishes try to hide, either under rocks, logs,
water weeds, etc., or they construct artificial hiding places (holes
and burrows). The latter tendency is, as will be seen, especially
developed in certain ecological groups. In connection with this
tendency to hide probably is the fact that the crayfishes seem to be
more or less nocturnal.

With regard to their ecological preferences, different types have
been distinguished in the genus Camharus. These are the fol-
lowing :

I. Species living in quiet waters: slowly running, large rivers,
ponds, lakes. To this group belongs chiefly the subgenus Cam-
harus, and its distribution over the coastal plains and the interior
basin expresses this ecological habit, since here such conditions are
pre-eminently found. But certain species of the subgenus Faxonius

836 FRESH-WATER BIOLOGY

also prefer these surroundings. These species are content with
hiding under other objects, and make holes only incidentally.

2. Species living preferably in water with a rather strong current.

{a) Species of the larger rivers. The subgenus Faxonius is typi-
cal for this habitat, and the location of its center of distribution in
the central basin with its large rivers expresses this.

{h) Species Hving in small streams of the uplands. The repre-
sentatives of this habitat belong chiefly to the subgenus Bartonius,
and its distribution over the Appalachian Mountains and the Alle-
gheny and Cumberland Plateau clearly indicates this.

Of course, there are all transitions between habitats (a) and (b),
as many of the river species go well up into the head-waters, and
vice versa. Yet the original differentiation in the habitat of the
subgenera Faxonius and Bartonius is very evident. All these spe-
cies in running water are good burrowers, and they generally ex-
cavate holes under protecting stones, etc. In some of the species
from the mountain streams this faculty of burrowing is rather highly
developed, and leads us to the next ecological type.

3. Burrowmg species (''chimney builders ") . These species have
retired from the open water into the ground water, and one may
understand the origin of this peculiar habit by imagining that
forms in the small upland streams, with well-developed burrowing
faculties, were forced, in periods of draught, w^hen the streams in-
habited by them began to dry up, to dig down in the bed into the
gravel and mud, to reach the water. Or one may imagine, that
they ascended in the streams up to the sources, and went under
ground, where the water appears in the shape of springs. In a
number of species this tendency has been carried to an extreme, and
it is known that these Hve habitually under the surface of the
earth, in the ground-water, where they excavate more or less com-
plex systems of holes, burrows, or tunnels, which open upon the
surface in one or more openings. These burrows are built by the
crayfish, by using the chelae in digging (hence the similarity of the
chelae in both sexes), and the material removed, mud, clay, etc.,
is carried to the surface, where it is piled up around the mouth of
the burrow in irregular or regular piles, generally known by the
name of ''mud chimneys." These burrows and chiefly the mud

HIGHER CRUSTACEANS (MALACOSTRACA) 837

chimneys have attracted much attention, and the idea has been
advanced that the chimneys are constructed by the crayfish for a
certain definite (useful) purpose. But recent investigations seem to
point to the conclusion that the regular shape of the chimneys,
when present, is accidental, and the mud piles are nothing but the
natural product of the burrowing, disposed of in the most con-
venient way (around the mouth of the hole) . The burrows them-
selves are rather irregular, more or less complex, and consist of
simple tunnels, often branching, and one or more pockets, or widen-
ings of the tunnel. They go down into the ground from one to
several feet, but always deep enough as to contain ground-water, at
least at the bottom.

Burrowing species are found chiefly in the subgenus Bartonius,
and form a very well defined morphological group, and it is just
this group of this subgenus, which has spread out from the original
territory (the mountains), and has descended into the plains. On
the western and southwestern plains is found another group of
burrowers which belong to the subgenus Cambarus.

Another special ecological group should not be forgotten. These
are the cave species. With the exception of the Mysidacea, all
our fresh-water Malacostraca have developed certain forms which
are adapted to the life in subterranean waters, and live in caves,
springs, artesian wells, etc. This peculiar habitat has affected
their structure greatly, and the most important and interesting
feature is the loss of the eyes. Some of these forms are entirely
blind, having lost the visual elements of the eyes (cornea and pig-
ment), while in others the reduction is only partial.

Among the Isopods, the only North American fresh-water form,
belonging to the Cirolanidae, is a blind subterranean form (Giro-
lanides texensis, Fig. 1304). Of the Asellidae, some live in caves and
have suffered the loss of the eyes. This is especially true of the
genus Caecidotea, the species of which have been found in caves of
Virginia, Georgia, Tennessee, Kentucky, Indiana, Illinois, and in
subterranean waters in Texas. Mancasellus, which possesses eyes,
has often been found in caves or in streams issuing from caves ; it also
lives in the Great Lakes.

838 FRESH-WATER BIOLOGY

The fresh- water Amphipods are remarkable for the development of
eyeless cave forms; in fact, there is a strong tendency among them
toward underground life. Of the 20 species known, 10 or 11 seem
to be inhabitants of caves, wells, or springs. Not all of them have
the eyes reduced, but the species of the genQYSiCrangonyx,Stygonectes ,
and A pocrangonyx are actually bHnd, and there is a bHnd species
in each of the genera Eucrangonyx and Gammarus, while the other
species of these two genera show all transitional stages from well-
developed eyes to more or less reduced eyes. The correlation be-
tween subterranean hfe and reduction of the eyes is very evident in
this group.

The only species of the decapod-family Atyidae found in the
United States, Palaemonias ganteri (Fig. 131 1), is a bHnd cave-form,
and it was discovered only recently (1901) in the waters of Mam-
moth Cave in Kentucky. This form has eye-stalks, but the visual
elements of the eye are gone. This is an extremely interesting
form on account of its primitive structure as well as its geographical
relations. Most of the members of this family, which is strictly a
fresh-water group, are found in the tropical and subtropical regions
of both hemispheres, but a form very closely alHed to the American
is known from caves in Carniola, Austria.

In the family Palaemonidae is included Palaemonetes antrorum,
v/hich was discovered in an artesian well in Texas. Also this species
is provided with eye-stalks, but the eyes themselves are obliterated.

Within the genus Camharus of the family Potamobiidae, five
cave species are known. They are all blind, but the eye-stalks re-
main. These species belong to different' subgenera, and the best
known is the famous blind crayfish of Mammoth Cave in Ken-
tucky {Camharus pellucidus), which is also found in other caves
in Kentucky and in Indiana. It belongs to the subgenus Fax-
onius, and represents a rather ancient t^-pe, so that we are jus-
tified in regarding it as an old immigrant into the subterranean
waters. Three species (C. hamulatus, C. setosus, and C. ayersi)
belong to the subgenus Bartonius, representing a primitive section
of it. The first of these is found in Nickajack Cave in eastern
Tennessee, while the two others are from caves in the Ozark region
in Missouri. These three species also must be old immigrants into

HIGHER CRUSTACEANS (MALACOSTRACA) 839

the caves. The fifth of the blind species is C. acherontis, found in
caves in Florida. This belongs to the subgenus Cambarus, and is
a member of a rather highly advanced section of the subgenus
which is common on the coastal plain, and is to be regarded as a
more recent addition to the cave fauna.

The economic value of the fresh-water Malacostraca is very
different in the different groups. While the isopods, amphipods,
and Mysidacea are small, the decapods are larger, but also of these
the Atyidae and certain Palaemonidae attain only a • medium
size. These groups naturally have only an inferior value for man,
and are generally overlooked and neglected. Of the larger forms,
certain species of Palaemon (prawns, also called shrimps) , and the
crayfishes have attracted attention, and are used by man, pri-
marily as food. Although this is generally the case in Europe and
with a number of tropical forms, in North America they are not
very popular, and are only occasionally eaten; yet there is no
doubt that Potaniohius and Cambarus are to be regarded as part
of the natural food supply of this country. Other uses, for instance
as fish bait, should be mentioned incidentally.

On the other hand, some kind of damage or injury done to man
or man's work has also been noticed in so far as certain burrowing
species are Hable to damage dams or levees, or to interfere with
farming operations. The latter species are also reported to be
injurious to crops, chiefly to sprouting plants.

In the general economy of nature, all the higher crustaceans
perform a twofold task. First, on account of their general habit
of devouring masses of decaying vegetable and animal matter,
they are to be counted among the scavengers, and second, they
themselves serve as food for other animals. They are most impor-
tant as fish-food, and even the larger forms are eaten by the larger
fishes. In addition, a number of other creatures feed upon them
(amphibians, water snakes, birds, and certain mammals).

Collecting Malacostraca is comparatively easy: the chief thing
is to ascertain their whereabouts. This is done along the banks
of streams, ponds, or lakes by turning over stones or logs, by
investigating overhanging banks, or examining bunches of water

840 FRESH-WATER BIOLOGY

weeds. The smaller forms may be taken in num.bers by transfer-
ring water weeds, dead leaves or other rubbish found on the bottom
into tubs or dishes, and picking out the specimens with a pair of
pincers. The larger forms must be caught by hand, or with a
small dip-net (minnow netting). For many forms the seine is a
very successful implement.

In collecting the burrowing crayfishes special efforts are neces-
sary. It sometimes happens that the crayfish can be induced to
come to the mouth of its hole by destroying the entrance. But
generally -the collector should not hesitate to go after the crayfish
by digging it out Of course, a spade or shovel is most efficient,
although often too heavy to be carried along, but a strong garden-
ers' trowel is very convenient: the best tool is a so-called pioneers'
bayonet. With this the ground should be loosened around the
hole, and the dirt be taken out with the hands, care being taken
always to follow the direction of the hole. By digging deep enough
(i to 3 feet), finally the pocket will be reached, in which the cray-
fish fives, and then it may be taken out.

Preservation should always be in alcohol. Formalin should be
avoided, except in cases of necessity. Even then the specimens
should never be left in the formafin for a long time: it hardens
them too much, makes all the appendages brittle, and renders
them unfit for safe handling. The best results are obtained by
killing them in weak alcohol and transferring them into stronger
(2 to 3 changes), until they finally are in 75 to 80 per cent alcohol:
when so treated all appendages remain soft and flexible as in fife.

For scientific study no special work is required in the case of
the larger forms, and all systematic characters may be seen with
the bare eyes or by the use of a hand-lens. In the smaller forms
it is necessary to study the appendages separately. They should
be teased out under a dissecting microscope (using two pairs of
pincers) and mounted in the usual way upon microscopic sHdes.
Care should be taken that the appendages are taken out in the
proper order, so that they do not become mixed. For the micro-
scopic investigation a very low power is sufficient.

HIGHER CRUSTACEANS (MALACOSTRACA) 841

KEY TO NORTH AMERICAN FRESH-WATER MALACOSTRACA

1 (26) Without carapace, but first thoracic somite coalesced with the head.

Eyes (when present) sessile. Thoracic Hmbs without exopo-
dites, first pair modified as maxillipeds 2

2 (11) Body depressed. Pleopods biramous, uniform in shape, with excep-

tion of the uropods and the anterior pairs of the male.

Order Isopoda . . 3

3 (4) Uropods lateral, forming with the telson a tail-fan.

P^amily Cirolanidae.
Only one genus and one species in the United States.

Cirolanides texensis Benedict 1896.

This is a blind form, which has been found in an arte-
sian well in Texas. All other representatives of this
family are marine. Many of them are ectoparasites on
fishes.

Fig. 1304. Cirolanides texensis Benedict. X 4.
(After Richardson.)

4 (3) Uropods inserted at the posterior end of the telson, not forming a tail-

fan 5

5 (10) Pleopods covered by a thin opercular plate, the modified first pair.

Body symmetrical. Free living. Family Asellidae . . 6
This is a typical fresh- water family.

6 (7) Mandibles without a palp. Last six pairs of thoracic legs with dacty-

lus biunguiculate Mancaselliis Harger.

P'ive species, Hving in springs and caves, some in rivers and lakes. Eyes present in all, but
small.

7 (6) Mandibles with a three- jointed palp. Last six pairs of thoracic legs

with dactylus uniunguiculate 8

8 (9) Eyes present. Head narrower than the first thoracic segment. Telson

not longer than broad Asellus Geoffroy.

Seven species in rivers, creeks, ponds, ditches,
springs, lakes. Some (as Asellus communis Say)
widely distributed, others more local. Common in
ponds, ditches, etc., living among decaying vegeta-
ble matter.

Fig. 1305. Asellus communis Say. X 2. (After Smith.)

842

FRESH-WATER BIOLOGY

9 (8) Eyes wanting. Head not narrower than the first thoracic segment.

Telson much longer than broad. . . Caecidotea Packard.
Four species, in caves, springs issuing from caves, and artesian wells.

10 (5) Pleopods not covered by an opercular plate. Body of female pecu-

liarly deformed, unsymmetrical, that of the male more or
less normal and symmetrical. Parasitic upon higher crus-
taceans Family Bopyridae.

Only one genus in the North American fresh waters.

Probopyrus Giard and Bonnier.

Chiefly a marine group; the only genus
known from the fresh water of North
America, enters with its hosts, being found
parasitic upon the gills and in the gill cav-
ities of Decapods of the genera Palacmo-
netes and Palaemon. Three species are
known, and are found along the Atlantic
coast from New Hamsphire to Florida, and
in the Mississippi River in Louisiana.

Fig. 1306. Probopyrus pandalicola Packard. A,
Male; X 30. B, Female; X 3. (After Richard-
son.)

II (2) Body compressed. Pleopods divided into two sets, the first three
pairs with multiarticulate rami, the last two pairs generally
similar to the uropods, with unsegmented rami. No sexual
modification of pleopods in the male.

Order Amphipoda . . 12

12(25) Antennulae with secondary flagellum. Telson clef t or entire. . . 13

13 (14) Fifth peraeopods shorter than the preceding. Second maxillipeds
smaller than the first. Uropods with two nearly equal

rami Family Lysianassidae.

Only one fresh-water genus in North America. . Pontoporeia Kroyer.

This family is chiefly marine; two spe-
cies live in rather deep wafer of the lakes
Superior and Michigan. These species
are closely allied to certain European
fresh-water forms, and probably immi-
grated into the lakes at the close of the
glacial time.

Fig. 1307. Pontoporeia hoyi Smith. X 4.
(After Smith.)

14 (13) Fifth peraeopods longer than the preceding. Second maxillipeds

generally larger than the first. Uropods with two unequal
rami or without rami. . . . Family Gammaridae. . 15
A family represented both in the sea and in fresh water, and containing a great number of
forms.

15 (20) Telson cleft. Uropods biramous 16

16 (19) Inner ramus of uropods rudimentary. Telson cleft not more than

three-fourths the distance to the base 17

HIGHER CRUSTACEANS (MALACOSTRACA)

843

17 (18) Outer ramus of third uropods uniarticulate.

Eucrangonyx Stebbing.
Five species are known, living in ponds, springs, and wells. Eyes either well developed or
more or less rudimentary. One species is blind.

18 (17) Outer ramus of third uropods biarticulate Niphargus Hay.

A single species in caves in Tennessee, with the eyes wanting or very rudimentary.

19 (16) Inner ramus of uropods not rudimentary, one-half or three-fourths

as long as the ©uter. Telson cleft to the base or nearly so.

Gammarus Fabricius.

Six species, two of them {G. fascialus Say
and G. litmiaeus' Smith), rather abundant in
rivers, lakes, and smaller bodies of water.
The other species are more local. Eyes
present, but one species is a blind cave-
form of Cuba.

Fig. 1308. Gammarus litnnaeus Smith. X 2.
(After Smith.)

20 (15) Telson entire 21

21 (24) Third uropods with rami 22

22 (23) Third uropods uniramus. Telson short and broad. Crangonyx Bate.
Three species are known, all without eyes, living in caves and wells, and with very local

distribution (Kentucky, Indiana, Connecticut, Wisconsin).

23 (22) Third uropods biramous, inner ramus rudimentary, outer uniarticu-

late. Telson long Stygonectes Hay.

Only one blind species, foimd in an artesian well in Texas.

24 (21) Third uropods without rami. . Apocrangonyx Stebbing.

One species, blind, from a well in Illinois.

25(12) Antennulae without secondary flagellum. Telson entire. Third uro-
pods uniramous Family Orchestiidae.

This family is abundantly represented in the sea.

Only one genus and species in the fresh water of North America.

Hyalella knickerhockeri (Bate) 1862.

This species possesses a very wide
range, and is found in rivers, ponds and
lakes from Maine to Florida and Cali-
fornia (and extends southward into Cen-
tral America). This genus (Hyalella) is
remarkable for the fact that all its spe-
cies are found exclusively in fresh water
and are restricted to North and South
America.

Fig. 1309. Hyalella knickerhockeri Bate.
X 5- (After Smith.)

26 (i) With a carapace. Eyes upon movable eye-stalks. Thoracic limbs
with or without exopodites, one, two, or three of the ante-
rior pairs modified as maxiUipeds 27

844 FRESH-WATER BIOLOGY

27 (28) Carapace coalesced dorsally with not more than three of the thoracic
somites. Thoracic limbs with natatory exopodites, first
pair modified as maxillipeds. Pleopods more or less re-
duced and greatly different in the two sexes. Eggs carried
in a brood pouch at the base of the thoracic legs.

Order Mysidacea.

This order forms part of the old division Schizopoda. The Mysidacea live chiefly in salt
water. The system of this group needs a thorough revision, and no satisfactory division into
larger groups (families) has been published.

Only species in North America. . . . Mysis relicta Loven 1862.

Fig. 1310. Mysis relicta Loven. X 2. (After Smith.)

Very few Mysidacea are known from the fresh water, and the present is identical with a
species living in lakes in northern Europe (Ireland, Scandinavia, Russia). It is found, in
North America, under similar conditions, in the lakes Superior and Michigan, down to a
considerable depth (150 fathoms).

In Europe, this form has been much discussed, and, as the name indicates, was supposed to
point to a former connection between the sea and the lakes in which it hves. It was believed
that these lakes were cut off from the sea and became fresh-water lakes, but retained part of the
original marine fauna adapted to the fresh-water conditions: these animals were called "marine
rehcs," and Mysis relicta was taken for one of the most prominent examples of this kind. How-
ever, this theory has been greatly shaken recently, and, as far as it concerns the North American
stock of Mysis relicta, there is no reason to assume that it is a marine relic, but we are to regard
it as an immigrant into the Great Lakes in glacial times (as Lysianassa).

28 (27) Carapace coalesced dorsally with all of the thoracic somites. Tho-
racic Umbs rarely with exopodites, the first three pairs modi-
fied as maxillipeds. Pleopods not much reduced, and not
very different in the two sexes, except the anterior ones.
Eggs carried under the abdomen, attached to the pleopods.

Order Decapoda . . 29

29 (34) Body and rostrum compresssed. Pleura of second abdominal
somite overlapping those in front. First two pairs of perae-
opods chelate. Anterior pleopods of the. male not trans-
formed into copulating organs 30

HIGHER CRUSTACEANS (MALACOSTRACA)

845

30 (31) Chelae of peraeopods weak, subequal, fingers with terminal hair-
tufts Family Atyldae.

Only species in North America. . . Palaemonias ganleri Hay 1903.

A typical and char-
— ' ucteristic fresh-water
^roup, abundant in the
tropics, but certain
forms are found in tem-
pera te regions, and
their distribution is
quite pecuHar, they
being found at rather
isolated localities, re-
mote from each other.
This discontinuity is a
mark of antiquity of
the c^roup. One of
these isolated forms is
founu in North Amer-
ica, Palaemonias ganleri
The nearest place where related

Palaemonias ganleri Hay.

(After Hay.)

Hay, and is blind, Hving in Mammoth Cave in Kentucky
forms are found is in the West Indies.

31 (30) Chelae of peraeopods inequal, the second pair larger, often much
larger, than the first, and very strong. Fingers without
terminal hair- tufts. . . . Family Palaemonidae . . 32

A family abundant in the sea, but also of great importance in the fresh water. All transi-
tional stages between life in the sea and in fresh water are found here.

32 {T)^) Mandible without palpus. Second pair of peraeopods only slightly
larger than the first, both of them rather weak. Size of
body medium Palaemonetes Heller.

Contains a number of species
which Uve in salt and brackish
water. One of them (P. vulgaris
Say) is fovmd along our Atlan-
tic coast. Other species have
become true fresh- water forms:
Two have been described from
the United States: P. paludosa
Gibbes and P. exilipes Stimp-
son, both from CaroHna, but they
are supposed to be identical.

Fig

1312. Palaemonetes exilipes Stimpson. X i. (After Smith.)
This form has also been found in Florida, in the Illinois River, and in Lake Erie,

2>2> (32) Mandible with palpus. Second pair of peraeopods, in the male,
excessively developed, very long (often longer than the
whole body), with strong chelae. Size of body considerable.

Palacmon Fabricius.

This genus (sometimes, but erroneously, called Bithynis) is extremely abundant in the fresh
water of the tropics. Only one species is recorded from the United States: P. ohionis Smith,
which is found in the Mississippi and lower Ohio Rivers (up to Cannelton, Ind.). Little
more is known about this species than that it exists and that it is locally used as food. (Not
even a figure of it has been published.)

846

FRESH-WATER BIOLOGY

34 (29) Body subcylindrical in its anterior part, abdomen depressed. Ros-
trum depressed. Pleura of second abdominal segment not
overlapping those in front. First three pairs of peraeopods
chelate, the first pair much larger than the others.

Family Potamobiidae . . 35

An exclusive fresh-water family of old age, and the most important group of higher crusta-
ceans in the fresh waters of North America. Its general distribution includes Europe, north-
eastern Asia, North and Central America. In the United States two genera are found: one,
containing a' few species, is believed to be identical with the European genus (Potamobius); the
other (Cambarus) is restricted to America, and has very many species. The differences .of
these genera are found chiefly in the sexual apparatus. _ , , , ,

In the southern hemisphere, in Australia, New Zealand, South America, and Madagascar
this family is represented by an allied one, Parastacidae while in the tropical belt similar
forms are missing. This peculiar distribution has given origin to much speculation, and
chiefly the close affinity of the southern forms has been introduced as evidence for the former
connection of the southern continents. , , , , , r , • , • , j

Through Huxley's book (1880) this family has become a standard group for biological study.

35 (36) Male copulatory organs rather simple. Peraeopods of male without
hooks on the ischiopodite. Female without receptaculum
seminis. A pleurobranchia present on the last thoracic
somite Potamobius Leach.

This is the genus which includes the Euro-
pean crayfishes, frequently, but incorrectly,
called Astacus. It possesses five species in
North America, the range of which is on the
western Pacific slope, from California to
British Columbia. One species {P. gamheli
Girard), has crossed the continental divide
in the region of Yellowstone Park, and is
found on both sides in the drainages of the
upper Columbia River and of the upper
Missouri.

The European species (about' six) have
frequently been subjects of systematic, ana-
tomical, biological, and embryological
studies. The best known species is the
common crayfish of Central Europe, Pota-
mobim astacus (Linnaeus) .

Fig. 13 13. Potamobius trowbridgei Stimpson.
X i (After Hagen.)

A species found abundantly in the drain-
age of the lower Columbia River in Wash-
ington and Oregon, and of considerable
economic value.

HIGHER CRUSTACEANS (MALACOSTRACA)

847

36 (35) Male copula tory organs more or less complex. Some peraeopods of
the male with hooks on the ischiopodite. Female with
receptaculum seminis (annulus ventralis) upon the sternum
of the thorax. No pleurobranchiae present.

Cambarus Erichson . .37

./""N.

Restricted to North America east of the
Rocky Mountains, Mexico, Guatemala,
and Cuba. It contains between seventy
and eighty species, which fall into six sub-
genera, four of which are represented in
the United States.

The geographical distribution of the
species of Cambarus is very interesting,
and apt to furnish evidence for the geo-
logical changes of our river-systems. This
genus is also eminently fit for ecological
studies on account of the great diversity
of the habit-preferences of the single
species.

Besides the four subgenera treated here,
two others have been distinguished {Para-
cambarus and Procambarus), but they do
not possess representatives in the United
States.

Fig. 13 14. Cambary,sbartoni Yahricras.
X I. (After Paulmier.)

The most common species in the eastern
United States, found in small streams of
the Appalachian chain from Tennessee
and the Carolinas to Maine and New
Brunswick.

37 (44) Sexual organs of male with more than two tips 38

38 (43) Third, or third and fourth, peraeopods of the male with hooks on the

ischiopodite. Sexual organs of male blunt or truncated,
with one soft tip, and several short, horny teeth.

Subgenus Cambarus Ortmann . . 39

Distribution: Chiefly southern and southwestern in the United States.

39 (42) Male with hooks on third peraeopods 40

40 (41) Areola narrow. Chelae elongated.

Section of Cambarus simulans Faxon 1884.

The areola is the posterior, median dorsal part of the carapace, included between the lines which
bound the lateral (branchial) regions. The areola is " obliterated," when these lines come into contact.

Two species in the southwestern United States and Mexico.

41 (40) Areola obliterated in the middle. Chelae short and broad.

Section of Cambarus gracilis Bundy 1876.

Three species, burrowing forms, on the coastal plain from South Carolina to Texas, and
northwards over the prairie region to Wisconsin.

848

FRESH-WATER BIOLOGY

42 (39) Male with hooks on the third and fourth peraeopods. Chelae elon-
gated. . . . Section of Cambarus blandingi Harlan 1830.

About seventeen species, falling into four groups, distributed over the Atlantic
and Gulf coastal plain, and passing up the Mississippi valley into the interior basin.
C. blandingi (Harian) is the type species of this group and of the whole genus. Its
distribution covers practically all of the range of the section. The other species are
more local, and some of them are probably mere local races. The blind species,
C. acherontis Loennberg, from Florida, belongs here.

Species of lakes, ponds, or sluggish rivers, avoiding strong current.

Fig. 1315. Cambarus {Cambarus) blandingi Harlan. Copulatory organ of male. X 4-
(After Faxon.)

In other species, the horny tips of these organs are more or less different, and
furnish important specific characters.

43 (38) Second and third peraeopods of the male with hooks on the ischiopo-
dite. Sexual organs of male with one soft, and two horny,
elongated points Subgenus Camharellus Ortmann.

Only one species is found in the United States: C. shufeldti Faxon, from Louisi-
ana; a few more species are known from Mexico.

This species appears to be geographically isolated from its related forms (in
Mexico).

Fig.

1316. Cambarus (Cambarellus) Shufeldti Faxon.
(After Faxon.)

Copulatory organ of male. X 4.

44 (37) Sexual organs of male with two tips, one soft, the other horny.

45

45 (50) Sexual organs rather slender, the terminal tips more or less elongated,

straight or gently curved. Ischiopodite of third peraeopods
of male with hooks, rarely also that of fourth.

Subgenus Faxonius Ortmann . . 46

Distribution: Pre-eminently in the large rivers of the central basin (Mississippi and Ohio,
and their tributaries). Very few species have reached the Atlantic drainage system.

46 (47) Sexual organs of male with the tips free only for a short distance.

Hooks on third, or on third and fourth, peraeopods.

Section of Cambarus limosus Rafinesque 18 17.

Five species, of which C. limosus (Rafinesque) (very generally called C. affinis Say, which
name, however, is a synonym) is the best known: it is found on the /Atlantic side of the Alle-
ghenies in rivers, ponds, canals, from New York and Pennsylvania to Virginia. The allied
species are found at a great distance from this, in Kentucky, Indiana, and Missouri, and among
them is the blind cave-species C. pellucidus (Tellkampf).

47 (46) Sexual organs of male with the free tips longer. Hooks on third
peraeopods only ... 48

HIGHER CRUSTACEANS (MALACOSTRACA)

849

48 (49) Tips of sexual organs rather straight.

Section of Cambarus propinquus Girard 1852.

About ten species belong here, but some of them are mere local races. The
most important ones are C. propiiujuus Girard, and C. rusticus Girard, both found
in the larger and smaller rivers of the interior basin. The other forms also belong
to these river systems, but extend also into the lower Mississippi drainage, to the
Atlantic side in Georgia and South Carolina, and to the Great Lakes and the St.
Lawrence system.

Fig.

1317. Cambarus (Faxonius) rusticus Girard. Copulatory organ of male. X
(After Faxon.)

A species characteristic for the lower Ohio and its tributaries,
the copulatory organs are more or less different.

In other species

49 (48) Tips of sexual organs gently, but distinctly, curved.

Section of Cambarus virilis Hagen 1870.

Twelve species are known, but again some may be only local forms." C. virilis Hagen pos-
sesses a wide range in the rivers of the central basin from Arkansas and Kansas to Canada.
A very abundant species is C. immunis Hagen, which prefers stagnant, often temporary, pools
of the western prairies. The other species are found chiefly in the lower Mississippi drainage
in Mississippi, Arkansas, Kansas, Oklahoma.

50 (45) Sexual organs rather stout, terminal tips rather short, strongly re-
curved. Ischiopodite of third peraeopods of male with
hooks Subgenus Bartonius Ortmann . . 51

Distribution: Chiefly in and near the Appalachian Mountains, but some species on the
coastal plain and the western plateau.

51(52) Eyes rudimentary. Chelae subelongated. Carapace subcylindrical.
Section of Cambarus hamulatus Cope and Packard 1881.
Three cave species belong here (see p. 837). ,

52(51) Eyes present. Chelae subovate. Carapace more or less ovate. . 53

53 (54) Rostrum with marginal spines.

Section of Cambarus cxtraneus Hagen 1870.
Three species, rather local in Kentucky, Tennessee, Northern Alabama, and Northern
I Georgia.

Rostrum without marginal spines 55

Areola wide, or a little narrower.

Section of Cambarus bartoni Fabricius 1798.

About four species, distributed over the Appalachian Mountains, where they live
in mountain streams, descending more or less toward the lowlands. The best-
known form is C. ftar/owj (Fabricius) (Figs. 1314 and 13 18), which covers the whole
range of the section, and has developed a number of more or less well defined local
races.

Fig.

:3i8. Cambarus {Bartonius) bartoni Fabricius.
(After Hagen.)

Copulatory organ of male. X 4.

In this subgenus, the shape of this organ is rather uniform in all species, which
is in strong contrast to the variability seen in the other subgenera.

850 FRESH-WATER BIOLOGY

56 (55) Areola very narrow, linear, or entirely obliterated.

Section of Cambarus diogenes Girard 1852.
Five species, all burrowing forms and chimney builders. Some (the more primitive forms)
are found in the Appalachian Mountains and upon the Allegheny and Cumberland Plateau;
others have descended to the Atlantic coastal plain, and have spread over the interior basin,
and westward to the Rocky Mountains, so, for instance, C. diogenes Girard. Again other
species are local forms of the lowlands.

IMPORTANT PAPERS ON NORTH AMERICAN HIGHER
CRUSTACEA

Andrews, E. A. 1904. Breeding Habits of Crayfish. Amer. Nat., 38: 165-

206.
Embody, G. C. 1912. Distribution, Food and Reproductive Capacity of

Same Fresh-Water Amphipods. Int. Rev. ges. Hydrobiol., Biol. Suppl.

III. 27 pp.
Faxon, W. 1885. A Revision of the Astacidae. Mem. Mus. Comp. Zool.

Harvard, 10: 1-186.
Hagen, H. a. 1870. Monograph of the North American Astacidae. 111.

Cat. Mus. Comp. Zool. Harvard, No. 3; 109 pp.
Harris, J. A. 1903. An Ecological Catalogue of the Crayfishes belonging

to the Genus Cambarus. Kansas Univ. Science Bull., 2: 51-187.
Hay, W. p. 1896. The Crawfishes of the State of Indiana. Rep. Indiana

Geol. Surv., 20:475-506..
1899. Synopsis of North American Invertebrates. VI. The Astacidae

of North America. Amer. Nat., T)^: 957-966.
Huxley, T. J. 1880. The Crayfish. The International Scientific Series.

New York.
Kingsley, J. S. 1899. Synopsis of North American Invertebrates. III.

The Caridea of North America. Amer. Nat., 2,3'- 709-719-
Ortmann, a. E. 1905. The Mutual Affinities of the Species of the Genus

Cambarus, and their Dispersal over the United States. Proc. Amer.

Philos. Soc, 44: 91-136.
1906. The Crawfishes of the State of Pennsylvania. Mem. Carnegie,

Mus., 2:343-523.
Packard, A. S. 1886. The Cave Fauna of North America. Mem. Nat.

Acad. Sci., 4: 1-156. .
Pearse, a. S. 1910. The Crawfishes of Michigan. Mich. State Biol. Surv.,

i: 9-22.
Richardson, H. 1905. A Monograph on the Isopods of North America.

Bull. U. S. Nat. Mus., 54; 727 pp.
Smith, S. I. 1874. The Crustacea of the Fresh Waters of the United States.

Rep. U. S. Comm. Fish., 2: 637-665.
Steele, M. 1902. The Crayfish of Missouri. Bull. Univ. Cincinnati, No.

10; 54 pp., 6 pi.
Weckel, Ada L. 1907. The Fresh- water Amphipoda of North America.

Proc. U. S. Nat. Mus., 32: 25-58.

CHAPTER XXVI
THE WATER-MITES (HYDRACARINA)

By ROBERT H. WOLCOTT

Professor of Zoology in the University of Nebraska

Conspicuous among aquatic organisms on account of their
activity and the brilHance of their coloring are the water-mites,
forming the group Hydracarina. These attractive httle creatures
may be met with in water almost anywhere, but being carnivorous
and thus dependent on the presence of much animal life, and hav-
ing a life-time extending over a number of months, they are found
regularly and in abundance only in pools which are moderate in
depth, permanent in character, and which possess a considerable
plant growth. There in the vegetation of the bottom and the shore
they live, clambering about over the surface of the plants, swim-
ming across from one stem or leaf to another, and feeding on
Crustacea, insect larvae or other animals which they may be able
to overpower and capture. A few species are pelagic, spending
most of their time in the open water of the lake or pond, while
other forms, as Tyrrellia, are found wandering over the moss and
debris which accumulates along a swampy portion of the shore.
Feltria is a genus containing small forms that are found only in the
mountain streams of Europe; yet in general water-mites are not
abundant in flowing streams except in sheltered places where there
is a growth of vegetation which protects them from the rapid cur-
rent. Two genera are parasitic in fresh-water mussels, and the
larvae and pupae of others attach themselves to aquatic insects or
other animals. Most of them are fresh-water forms, but a very
few have been described which are marine and a few others have
accustomed themselves in certain localities to life in brackish water.

Hydrachnids are generally distributed over the world but seem
to reach the greatest abundance in the clear, cool waters of the
spring-fed lakes and pools, rich in plant hfe, which are so charac-
teristic of all temperate latitudes, and which dot our northern states

851

852 FRESH-WATER BIOLOGY

and Canada. An interesting occurrence was the finding of a spe-
cies of Leber tia, a genus usually found in alpine and more northern
waters, in a spring at Omaha, Nebraska, the only record of the
genus in a state where bodies of water of that character are almost
lacking. At present about seventy genera are known, containing
several hundred described species, the number of which is fast
increasing.

The water-mites are found at all seasons of the year, even
under the ice in winter. Certain ones, especially of the red mites,
are abundant in pools in early spring, but the greatest number of
species appear as adults during the latter part of the summer or in
the fall. They are small forms usually from i to 2 millimeters
long, rarely exceeding a length of 5 millimeters, but on the other
hand, in the adult condition, rarely measuring less than half a
millimeter.

The color varies greatly, but is most frequently either some shade
of red or green; the same species may at the same locaHty and at
the same time be both red and different shades of green or bluish
green. The color is partly due to pigment deposited in the epidermal
cells, but from above or beneath blackish, brownish or greenish
spots are seen, which vary in size and intensity and are due to the
stomach and its blind diverticula seen through other more superfi-
cial structures. A whitish, yellowish, or reddish Y-shaped dorsal
mark, or markings of various form seen on the dorsal, lateral, or
posterior surfaces, are due to the presence of excretory matter in
the so-called Malpighian vessels, and thus are very variable in
number and extent. Hence while color is a clue to identification
which may be of service to the experienced observer, it cannot be
reHed upon, and is of little or no value in the discrimination of
species.

As seen in the water the hydrachnids appear at first glance like
small water spiders, possessing, as they do, four pairs of legs and a
pair of palpi corresponding to the pedipalps of spiders. But they
can at once be referred to the mites when it is noted that there is
no trace of segmentation or of division of the body into regions.

The body is compact and usually more or less globular, eUip-
soidal, or ovoidal, though in some cases compressed dorso-ventrally

THE WATER-MITES (HYDRACARINA)

853

or laterally, and in the males of certain species of Arrhenurus pro-
longed posteriorly into a curious handle-like appendage. The form
is more definite in the higher forms than in those which seem most
primitive. The skin in some forms is soft and the surface smooth,
but more usually it is marked by fine striae like the hues on the
palm of the hand, and in the lower forms it is often granulated or
papilla ted. Other species possess chitinous plates, which may be
few and small or larger and more numerous, and may even com-
pletely enclose the body in a sort of armor. These chitinous plates
do not seem to mark either higher or lower types and occur in
different famiHes. Glands occur here and there on the surface, and
also hairs and bristles, which are frequently accompanied by small
pieces of chitin.

There is usually a pair of eyes, but each can be seen on close
examination to be double, and in some cases the two of each side
are separate. They are of only moderate size, but prominent,
owing to the presence of dark pigment. There may be also, in
some of the lower forms, a ^' fifth"
or median eye, in the median line
between the others.

The four pairs of legs are artic-
ulated to an equal number of
coxal plates, or epimera. These are
frequently more or less fused, may
even form a single large plate cover-
ing the whole ventral surface, and
may also extend up on the sides so
as nearly to enclose the body, as in
Frontipoda. Sometimes the body is
constricted above this plate, giving
to the animal in lateral view the
appearance of a broad-crowned cap
or fiat-based knob, the legs springing
from the upper side of the projecting
epimeral plate. The legs are each
composed of six segments, and vary greatly in length, in the
form of individual segments, and in the character of the spines,

Fig. 1319. Pionacercus leuckarti Piersig, a
European form, showing extreme modi-
fication of the last pair of legs in the
male. (Legs shown on one side only;
palpi not shown.) (Modified from
Piersig.)

854 FRESH-WATER BIOLOGY

bristles and hairs which they bear. They are usually terminated by
two movable claws, but there may be only one, or rarely the leg may
end in a spine or bristle. The more active and the pelagic forms
have longer legs with fewer and longer spines and bristles, the less
active shorter, stouter legs with more thickly set and shorter bristles.
In some cases a number of long hairs in a close-set row on the outer
segments of the leg seem to aid in swimming and so are called swim-
ming-hairs; while in other cases curiously modified leg segments
and spines characterize the male and serve as accessory organs in
pairing (Fig. 1319).

The genital opening is situated behind or between the epimera
and is usually flanked by plates which bear characteristic cup-like
or knob-like structures known as acetabula, the exact nature and
function of which is unknown. There may be in addition movable
flaps, which may or may not cover the acetabula, and in some cases
such flaps, by fusion with the genital plates, seem to have become
immovable.

Between the anterior epimera is a plate, which has been termed,
from its form, the maxillary shield, and which is the ventral side of
a chitinous box called the camerostom, which encloses the mouth-
parts. To this are articulated the five-jointed palpi; at its anterior
end is the mouth-opening, through which project the stiletto-like
or sabre-like mandibles; and on its dorsal surface are the two
stigmata, leading by air-tubes into two air-sacs placed above the
pharynx, from which a system of tracheal tubes runs through-
out the body. In the forms parasitic on the fresh-water mussels
these tubes are lacking. The maxillary shield is frequently pro-
longed posteriorly into a kind of ancoral process, and the anterior
ventral angle of the camerostom may be produced into a sort of
rostrum. All these structures together are termed the capitulum.

The sexes are separate, sexual dimorphism being a common phe-
nomenon, and all species lay eggs. These may, rarely, be laid free
in the water, but are more usually deposited singly or in mass,
surrounded by a gelatinous envelope, on water plants or other
submerged objects. The embryo undergoes considerable develop-
ment before escaping from the egg membranes at which time it
becomes an active six-legged larva (Fig. 1320). This larva after a

TPIE WATER-MITES ^HYDRACARINA) 855

short free existence becomes a parasite either on an aquatic insect
which remains habitually in the water or on one which leaves the
water and becomes aerial. Other species place the eggs singly in
the tissues of fresh water mussels, or in masses between the gills,

Fig. 1320. Various types of hydrachnid larvae (each figure showing the legs of one side onlv)
a, Uiplodontus; b, Hygrobates; c, Arrhenurus; d, Hydrachna. (Modified from Piersig.)

and still others in the substance of fresh-water sponges or in the
gelatinous matrix of a colonial protozoan. In these cases the larva
does not become free but remains in the body of the mollusk or
other animal in which the eggs were laid. During this parasitic

856

FRESH-WATER BIOLOGY

existence the larval appendages drop off and the animal takes on
the character of a pupa, which increases greatly in size, drawing
nourishment from its host, and beneath the skin of which new
appendages are gradually developed. From this quiescent pupa
emerges an active, eight-footed nymph (Fig. 132 1) possessing legs
and palpi frequently quite similar to those of the adult, but with
smaller epimera and with a genital field lacking the structures which

d e J

Fig. 13 2 1 . Figures showing the ventral surface of the body of the nymphs of several genera ot water-mites.
(Appendages are similar to those of the adult and not shov/n here; compare with figures of adults on
succeeding pages.) a, Arrhenurus; b, Limnesia; c, Sperchon; d, Hygr abates; e, Fiona; /, Lebertia.
(Modified from Piersig.)

distinguish the adult. During this nymph stage the mite is not
usually parasitic except in the case of the mussel parasites. How-
ever, Unionicola crassipes has been found by Soar, in all stages, in
the fresh-water sponge, and the author has taken the differ nt de-
velopmental stages of a species of Fiona in the gelatinous matrix
of a colonial protozoan. Another moult must occur before the
mite becomes adult, but this is passed through rapidly and in the
forms in which the nymph is free frequently occurs while the animal
is clinging to aquatic plants. This moult may or may not be ac-

THE WATER-MITES (HYDRACARINA) 857

companied by the loss of the nymphal appendages and the develop-
ment of a new set, and the skin may be cast all at once or in several
portions. Instances have been described in which the nymph was
produced directly from the egg in the egg-mass.

These water-mites, like most aquatic animals, spend much of
their time in active motion, swimming with comparative rapidity
through the open water or more slowly walking over the bottom or
cHmbing about on plants or other objects. At times they stop
and remain stationary, cHnging to whatever object they may rest
upon, but a touch from another animal sends them whirHng on
again with rapid leg movements. When prey is secured they stop
to suck the juices from the body of the victim, casting aside the
carcass when it has been drained. Aside from the sense of touch,
which seems quite acute, the senses are poorly developed, or at
least appear to be little used. They rarely feign death, but almost
invariably attempt to escape a threatened danger by rapid flight.
The less uniform rate of motion they exhibit is of aid in distin-
guishing them from other forms, especially ostracods, with which
they may be confused. The leg movement also aids in their dis-
crimination.

Attractive as the hydrachnids are to the student of fresh-water
life and to the biologist, they are of economic importance only as
they afford an element in the food of fishes. Examinations of the
contents of fish stomachs frequently show that they have been
eaten, and their abundance at times would seem to indicate that
under such circumstances they might make up no inconsiderable
portion of the food. But they seem to go to pieces very quickly
and so are rarely reported in any numbers in the results of exami-
nations of such stomach contents.

In collecting these little fellows one needs a net, a number of
wide-mouthed bottles or jars, a pipette, and, in case he is not to
examine his collections within a few hours, a bottle of formahn.

The most serviceable net is the ''cone" or ''Birge" net (see
page 68). The net may be used from boat or shore and the mate-
rial, after being run into a wide-mouthed bottle or jar, be pre-
served in toio at once by adding directly a little strong formalin
and shaking thoroughly, of it may be carried home in the fresh

858 FRESH-WATER BIOLOGY

state. Frequently mites may be collected along shore by the use of
the pipette, being picked up individually as they swim about
in sight.

The material, if preserved in formalin, may be put aside for future
examination. If not, it should be poured soon into a fiat dish,
from which the mites may be picked out by means of a pipette.
The dish should be looked over several times, as some tend to hide
in the debris at the bottom, and stirring after the material has once
settled often reveals hidden specimens.

Five per cent formalin, into which they may be put directly, is
likely to make them brittle, and the catch is better preserved in a
mixture of glycerine, 2 parts by volume; pure water, 3 parts by vol-
ume; 2 per cent acetic acid, 2 parts by volume; absolute alcohol,
I part by volume.

If the mites are to be kept alive for observation their cannibal-
istic instincts make it necessary that different genera be segregated
and kept in separate dishes, with a small amount of some water
plant and a few Crustacea or non-predatory insect larvae as food.
Crowding should be guarded against.

The activity of water-mites makes them difficult objects to study
alive, but by the cautious addition of water saturated with chloro-
form vapor they may be narcotized, and, after being examined, will
come out from under the influence of the chloroform apparently
uninjured. The author has subjected specimens to this treatment
on several successive occasions without evident harm.

In the study of specimens it is necessary to make use of slide
mounts. The mouth-parts may be dissected and mounted sepa-
rately upon sHdes, and the palpi and legs may also be removed and
mounted. If the specimens have been kept in a solution contain-
ing some glycerine an opening may be made in the body-wall
through which the contents of the body can be pressed out, and in
that way transparent mounts of the complete individual secured.
The thickness of the body makes it difficult to secure a transparent
mount from material preserved in alcohol or formalin mixtures,
but the specimens may be successfully softened in some cases by a
weak potash solution or else must be mounted as opaque objects.

In the identihcation of water-mites care must be used, as the

THE WATER-MITES (HYDRACARINA) 859

general resemblance between them is close. But the characters
also seem to be very constant and few species are subject to marked
variation. The accompanying synopsis will aid in placing speci-
mens in the proper genus. The statements as to the numbers of
species refer to North America only.

The legs and the corresponding epimera are designated by Roman
numerals, beginning with the most anterior, and the palpal and leg
segments are referred to by Arabic numerals, numbering from the
base outward. Thus, ep. Ill is the third epimeron, leg seg. IV 4,
the fourth segment of the fourth leg, and pal. seg. 5 the distal
segment of the palpus. In most illustrations are shown the ven-
tral surface, only the legs of one side, and the palpus, detached and
more highly magnified; these are the characters most important
and most readily observed.

The arrangement of genera and higher groups here used is the
same as adopted in a previous paper (Wolcott, 05). It is not in
all respects satisfactory, but such a difference of opinion exists
among students of the group in this regard that the author is not
willing to accept any other system since proposed without himself
working the whole matter over again.

KEY TO NORTH AMERICAN FRESH-WATER HYDRACARINA

1 (6) Lateral eyes of the two sides close together in the median line and

borne on a common eye-plate 2

2 (5) Pal. seg. 5 deeply set into 4, eye-plate long and narrow.

Family Limnocharidae . . 3
3(4) Without swimming-hairs Limnochares La,tTeil\e 17 g6.

A very large clumsy red mite with
soft body, variable in form but in
general rectangular, found in pools in
bogs and swamps. Length 3.5-4 mm.
One species, generally distributed and
common at times.

Fig. 1322. Limnochares aquaticus (Lin-
naeus). Ventral surface, female. X g-
Inner surface, right palpus. X 95. (Mod-
ified from Piersig.)

4 (3) With swimming-hairs Cyclothrix Wolcott 1905.

Also red, but oval and more constant in form and recognized at once by the swimming-hairs.
One species found also in ponds and lakes with boggy or swampy shores, and known from
several northern states. Somewhat smaller than preceding genus.

86o

FRESH-WATER BIOLOGY

5 (2) Pal. seg. 5 free, eye-plate broad, consisting of two lateral portions

connected by a transverse middle piece. Family Eylaidae.

One genus only £y/aw Latreille 1796.

A red mite with body circular in outline
and usually smooth; with palpi slender in
form and richly supplied with hairs and
spines, many of them feathered; hind legs
without swimming-hairs and allowed to
trail motionless behind in swimming.
Several species, very closely allied and gen-
erally distributed and often very abundant.
Varying in size from about 2 to 5 mm.

Fig. 1323. Eylais extendens (Miiller), a Euro-
pean species. Ventral surface of female. X 7-
Inner side of right palpus. X 69. Eye-plate.
X 59- (Modified from Piersig.)

6 (i) Lateral eyes of the two sides widely separated and in no case borne

on a common eye-plate 7

7 (i8) Distal extremity of pal. seg. 4 produced beyond the point of inser-

tion of seg. 5, the two segments together resembling a
pair of shears S

8 (9) Mandible one-segmented, the terminal portion straight and stiletto-

like Family Hydrachnidae.

One genus only Hydmchna La^treiHe ijg6.

Mites of some shade of red or
brown, and sometimes spotted
with black, with the body glob-
ular, soft, and usually papillated;
capitulum produced into a snout.
Species numerous, occurring in
swamps, lakes and ponds every-
where and usually common.
Varying from i to even 8 mm.
in length.

Fig. 1324. Hydrachna geographica
(Miiller), a European species, also
found in New England. The largest
described hydrachnid. Ventral sur-
face, female. X 4- Palpus. X i6.
(Modified from Piersig.)

9 (8) Mandible two-segmented, the terminal segment curved and claw-
like Family Hydryphantidae. . . lo

THE WATER-MITES (HYDRACARINA)

86i

lo (ii) Literal eyes of each side separate and not enclosed in a capsule.

Subfamily Diplodoxtinae.
One genus only Diplodontus Duges 1834.

A large, brownish-red mite with
body broad, soft, and surface papil-
lated; capitulum forming a snout;
palpi very small; legs slender, with
long swimming-hairs. One cosmo-
politan species, generally distributed
in this country and abundant. About
2 mm. long.

Fig. 1325. Diplodontus despiciens (MvX-
ler). Ventral surface, male. X i5- Outer
side, palpus. X 103. (Modified from
Piersig.)

II (10) Lateral eyes of each side fused and contained in a chitinous capsule.

Subfamily Hydryphantinae. . 12

12 (17) Without swimming-hairs 13

13 (14) Median eye present Thyas Koch 1837.

A genus of red mites of moderate size
with papillated surface often with chitinous
plates; with capitulum forming a snout; legs
with only short spines; a bottom and shore
form in swampy situations. Varying in sjze
from I to 2 or even 2.5 mm. Few species
known from the Northern States and Canada
and not common.

Fig. 1326. Thyasvenusta Koch, a European,
species. Ventral surface, female. X i6. Outer
side, left palpus. X 65. (Modified from Piersig.)

14 (13) Median eye not present

IS

862

FRESH-WATER BIOLOGY

:S (i6) Genital flaps present, acetabula 3, knob-like

Panisus Kcenike 1896.

Similar to the preceding in appearance; with chitinous
plates more or less developed, in our one described species
covering most of the dorsal surface. One species, P. cata-
phractus, described by Kcenike (1895) from Canada, about
1.2 mm. in length.

Fig. 1327. Panisus cataphra.:tus (Koenike). Epimeral area,
genital area and maxillary shield. X 43- Outer side, left palpus.
X 93- (After Koenike.)

i6 (15) No genital flaps; numerous stalked acetabula.

Sporadoporus Wolcott, 1905.

A red mite with body beset by small conical
papillae; capitulum produced into a slender snout.
One American species, not yet described, known so far
only from Yellowstone Park, a little under medium

Fig. 1328. Sporadoporus invaharis (Piersig), a European
form. Ventral surface, female. X 31- Palpus. X 123.
(Modified from Piersig.)

17(12) With swimming-hairs Hydryphantes Koch iS 37.

A brownish-red mite, with a median eye
surroimded by a large chitinous plate;
adapted to more open water. Species
several, and occurring frequently. A little
above medium size ranging from 1.2 mm.
to about 2.2 mm.

Fig. 1329. Eydryphantes ruber (de Geer), a
European species. Ventral surface, female.
X 17. Outerside.leftpalpus, of female. X42.
(Modified from Piersig.)

THE WATER-MITES iHYDRACARINA)

863

18 (7) Distal extremity of pal. seg. 4 slightly or not at all produced be-

yond the insertion of seg. 5, but the latter free, tapering, the

tip bearing small claws or teeth, or ending in a sharp point.

Family Hygrobatidae . . 19

19 (22) Pal. seg. 5 sharply pointed, claw-like, opposable to the projecting

distal flexor margin of seg. 4, forming a sort of pincer.
Body entirely covered by a porous sheet of chitin, divided by
a suture into a smaller dorsal portion and a larger ventral.
Legs with swimming hairs. Subfamily Arrhenurinae. . 20

20 (21) Genital area lying between epp. IV, the cleft flanked by large valves

each bearing 3 or 4 acetabula.

Krendowskija Piersig 1895.

A dark brown mite of medium size, broadly
oval in form; with the capitulum movable and
protrusible, and the camerostom developed into
a long rostrum, sabre-like and curved upward.
One American species. A', ovata Wolcott, occur-
ring rarely in Wisconsin and Michigan. Other
species are described from Venezuela and southern
Russia. Each is a little over i mm. in length.

Fig. 1330. Krendowskija ovata Wolcott. Epimeral
area and genital area, female. X 75- Inner side, left
palpus, female. X 250. Side view of female, showing
proboscis. X 60. (After Wolcott.)

(20) Genital area lying posterior to epp. I\s the cleft flanked by two
plates forming together an elliptical or circular area, beyond
which are laterally extended, wing-like plates with numer-
ous acetabula Arrhenurus Duges 1834.

cs,^

A B CD

Fig. 1331. Arrhenurus. A, A. forpicatus Neuman; dorsal surface of female. X 27. B, Palpus of
A. albator (MuUer), outer side, male. X 113. C, A. maculator (MuUer), dorsal surface, male. X 30.
D, A. globator (Miiller), dorsal surface, male. X 39- AH European species. (Modified from Piersig.)

The females of this genus are approximately oval in form and possess few characters by
which they may be distinguished, but the males are highly and variously modified in form and
possess complicated accessory sexual structures, including a copulatory organ, the petiole. Leg

864

FRESH-WATER BIOLOGY

seg IV 4 is also usually modified in the male by the possession of a peg-like projection and
characteristic hairs. The species vary considerably in size, from about 0.55 mm. to nearly
2 mm. One of the most abimdant and widely distributed genera, common m clear, shallow,
hard waters where plant Ufe is abundant, with about 200 species, all of various shades of bluish
or brownish green, or red. There are about 50 species described from North America.

22 (19) Pal. seg. 5 not opposable to 4, and bearing at the distal end small

more or less distinct teeth or claws 23

23 (44) Epimera in both male and female united and more or less fused

into a single epimeral plate 24

24 (39) Body more or less compressed dorso-ventrally and completely en-

closed in a chitinous covering usually divided into a smaller,
elHptical or oval, dorsal plate and a larger ventral plate.

Subfamily Aturinae. . . 25

25 (26) Four smaller plates, variously shaped, anteriorly, between the dorsal

and ventral T orrenticola Fkisig iSgy .

A rather small mite, 0.6 to 0.75 mm. long of oval form,
with the capitulum produced into a sort of snout; no
swimming-hairs. One American species, rarely found,
and apparently identical with the European Torrenti-
cola anomala (Koch).

Fig. 1332. Torreniicola anomala (Koch). Ventral surface,
female. X 27. Outer side, right palpus, female. X no.
(Modified from Piersig.)

26 (25) The two plates, dorsal and ventral, covering the whole surface . . 27

27 (30) Rostrum developed, prolonged and curved upward 28

28 (29) Genital area without flaps or valves, with numerous acetabula free

in the body surface Tanaognathus Wolcott 1900.

rmm^

A rather small mite, strongly compressed
dorso-ventrally, and with few swimming-
hairs. One species, T. spinipes Wolcott,
about 0.7 mm. long, known only by a few
specimens from Michigan.

Fig. 1333. Tanaognathus spinipes Wdicott. Epi-
meral field and genital area, male. X 42- Outer
side, right palpus, male. X iQS- (After Wolcott.)

THE WATER-MITES (HYDRACARINA)

865

29 (28) Genital cleft flanked by two large movable valves, and also ace-
tabula set free in the body surface. Koemkea Woicott 1900.

A beautiful mite of striking form,
being greatly compressed and actually
concave dorsally; with swimming-
hairs. Brightly and variously colored.
One widely-distributed species, K.
concava Woicott, adapting itself to
varied conditions, and often common.
Of small size measuring 0.6 to 0.7 mm.
in length.

Fig. 1334. Koemkea concava Woicott.
Epimeral field and genital area, male. X 65.
Inner side, palpus, male. X 278. Side view,
capitulum and rostrum female. X 277.
(After Woicott.)

30 (27)

31 (36)

32 (35)

33 (34)

Rostrum short 31

Suture between the dorsal and ventral plates continuous, completely

enclosing the dorsal plate, or open posteriorly 32

Acetabula lying near the genital cleft, no modification of leg IV in

the male.

33

Ep. IV quadrilateral in form Mideopsis Neuman 1880.

A mite of bright colors, with body almost circular
in outline, slightly concave dorsally; a short rostrum;
swimming-hairs; 3 acetabula on each side, outside of
which are narrow, sickle-shaped flaps. One species,
M. orbicularis (Miiller), common to Europe and
America and widely distributed in this country. Of
medium size averaging about i mm. in length.

Fig. 1335. Mideopsis orbicularis {M.\i\\er). Ventral sur-
face, female. X 23. Outer side, right palpus. X 123.
(Modified from Piersig.J

34 (33) Ep. IV triangular Xystonotus Woicott 1900.

Body elliptical; capitulum small and
camerostom slightly developed into a
rostrum; no swimming-hairs; 3 acetabula on
each side, flanked by movable flaps. The
genus containing a single species. A', asper
Woicott, known only from two female
specimens from Michigan. Of small size,
0.61 mm. long.

Fig. 1336. Xystonotus asper Woicott. Ven-
tral surface, female. X 43- Outer side right
palpus. X 195. (After Woicott.)

866

FRESH-WATER BIOLOGY

35 (32) Ace tabula arranged along the posterior margin of the body, in one
or more rows, running forward on either side nearly to the
point of insertion of leg IV, which leg is, in the male, modi-
fied Aturus Kramer 1875.

Very small mites, varying in length from 0.33 to
0.38 mm., with the posterior margin of the body
cleft; no swimming-hairs; leg IV of male with
segs. 4 to 6 strikingly moditied. One species,
Aturus mirahilis, is recorded from Canada by
Koenike. The genus is characteristic of rapidly
flowing streams.

Fig. 1337. Aturus scaber (Kramer), a European spe-
cies. Ventral surface of male. X 6i. Outer side of
palpus, female. X 150- (Modified from Piersig.)

36 (31) Suture open anteriorly, the two ends passing around on to the ven-
tral surface 37

37 (38) Genital area with 4 acetabula on each side . . Axonopsis Vitrsig i^g^.

A very small, brightly-colored mite
about 0.45 mm. in length, with a median
cleft in the posterior margin of the oval
body; the anterior epimera extended
beyond the capitulum; few swimming-
hairs. One North American species,
rare, in northern lakes, apparently the
same as the European A. complanata
(MuUer).

Fig. 1338. Axonopsis complanata (Miiller).
Ventral surface of female. X so. Outer
side, right palpus. X 123. (Modified from
Piersig.)

i

THE WATER-MITES (HYDRACARINA)
38 (37) Genital area with numerous acetabula on each side.

867
Albia Thon 1899.

A mite of medium size, averaging
about I mm. in lengtii, with elliptical,
strongly compressed body; swimming-
hairs present. One North American
species, rather rare, in lakes of northern
states, frequently pale greenish in color.
This is identical with the only Euro-
pean species, A. slationis Thon, or
very closely related.

Fig. 1339. Alhia stationis Thon. Ven-
tral surface, female. X 31. Outer side,
palpus, female. (After Thon.)

39 (24) Body highly arched, in some cases laterally compressed, with no such
dorsal and ventral plate. Subfamily Lebertunae. . 40

Legs with swimming-hairs except in certain species of Leberiia.

40 (41) Leg IV with claws at tip, epimera only partly fused.

Lebertia Neuman 1880.

Medium-sized mites, varjnng in length from
0.8 to 1.5 mm., with ovoidal body, the surface
of which is soft or hard, in some cases with
small flecks of chitin, usually striate, but rarely
papillate; capitulum developed more or less into
a short snout. A genus of frequent occurrence
in colder waters, represented by several closely
allied species which h;ive only been recently
recognized as distinct.

Fig. 1340. Lebertia tau-insignita (Lebert) . of various
authors, L. dubia Thon. This species was referred to
North America by Koenike in 1895. but he has re-
cently identified three species in the material he
studied, all of them hitherto undescribed. Ventral
surface of female. X 19. Outer side, palpus,
female. X 70. (Modified from Piersig.)

41 (40) Leg IV without claws at the tip, ending in a sharp point, epimera
completely fused 42

868

FRESH-WATER BIOLOGY

42 (43) Body laterally compressed, epimeral plate extending up on the lat-
eral surface, leaving only a dorsal median furrow.

Frontipoda Koenike 1891.

A mite of medium size, somewhat less than
I mm. long, looking curiously like a very flat
elliptical seed, emarginate at the hilum where
the legs are bunched together; usually of a
greenish color. One species, frequent in our
northern lakes and apparently identical with the
one generally distributed European species, F.
musculus (Miiller).

Fig. 1341. Frontipoda musculus (Miiller). Ventral
surface, female. X31. Outer side of palpus, female.
X 93- (Modified from Piersig.)

43 (42) Body not so decidedly compressed, epimeral plate not extending
upward on the lateral surface. . . . Oxus Kramer 1877.

A form of medium size, different species vary-
ing in length from 0.64 to 1.4 mm., with body
elongate in form; legs crowded toward the an-
terior end. Known in North America only from
Wisconsin, where the one species seems to be
rare. This is undescribed, but is similar to O.
ovalis (Muller) and O. strigatus (Miiller) the
common European forms.

Fig. 1342. Oi(:M5 OTa/i5 (Muller). Ventral surface,
female. X 30. Oxus strigatus (WnW^r). Outer side,
palpus female. X 90. (Modified from Piersig.)

44 (23) Epimera arranged in groups, in the female always clearly separate
from one another, in the male closer together but distinct,
only in rare cases in contact or tending in a slight degree to
fuse 45

45 (64) Epimera in four groups, in the male in some cases only a narrow
interval between them 46

THE WATER-MITES (HYDRACARINA)

869

46 (53) Genital area usually lying far forwards, at least between epp. IV,

and the epimeral groups often separated by a considerable
interval, no ancoral process on the maxillary shield.

Subfamily Sperchoninae . 47

47 (52) Genital acetabula borne on a plate, no flaps present 48

48 (49) Acetabula numerous Limnesiopsis Piersig 1897.

A large hydrachnid, about 2 mm. in length, with
the surface of the body beset with sharp points. One
species, L. anomala (Koenike), described from Canada,
and generally distributed in northern lakes but no-
where common.

Fig. IS43- Limnesiopsis anomala (KoGnike). Epimeral
field and genital area, male. X 25. Outer side, palpus,
njale. X 49. (After Koenike.)

49 (48) Acetabula few, large 50

50 (51) Leg IV with terminal claws, no swimming-hairs.

Tyrrellia Koenike

895-

Body almost circular, papillated
with one or two dorsal chitinous
plates; mouth-opening in the middle
of a disk-like surface at the anterior
end of the capitulum, resembling the
condition seen in the Hydryphantidac;
a sluggish, dark-brown mite of medium
size averaging 1.2 mm. in length,
known from Canada and found
abundantly some years since at
Reed's lake, near Grand Rapids,
Michigan, where it was picked up
singly with the pipette in the debris at
the margin of the water in close prox-
imity to a swampy portion of the lake
shore. V^ery rare in Birge net hauls
at the same place. Two species taken,
one apparently the same as T. circii-
laris Koenike, previously described.

Fig. 1344. Tyrrellia circularis Koenike.
Ventral surface, female. X 26. Inner side,
palpus, female. X 4Q- (Modified from
Koenike.)

870

FRESH-WATER BIOLOGY

51 (50) Leg IV ending in a point, a long hair a little back from the tip, swim-
ming-hairs present Limnesia Koch 1837.

A mite varying from small to large in size,
or from 0.5 to 2 mm. in length, with oval
body, surface striate, sometimes papillose,
and even developing a chitinous meshwork;
two eyes on each side separate. Handsome
mites with bright red spots, very active, and
among the most powerful and voracious of
all. Ten North American species; generally
distributed and found under very varied con-
ditions.

Fig. 1345. Limnesia kistrionica (Hermann),
the most widely distributed North American spe-
cies, also found throughout Europe. Ventral sur-
face, female. X 16. Outer side, palpus, female.
X 51- (Modified from Piersig.)

52 (47) Genital acetabula along the margin of the cleft, covered laterally
by flaps; without swimming-hairs. Sperchon Kramer 1877.

Body oval, rarely with small chitinous
plates, smooth, or papillate; capitulum very
movable. A genus found in northern and
mountain lakes and streams. Three species
recorded from Canada. Species small to
medium in size, in length 0.5 to 1.5 mm.

Fig. 1346. Sperchon glandulosus Koenike, a
species recorded both from Europe and Canada.
Ventral surface, female. X 24. Outer side of
palpus, female. X 94- (Modified from Piersig.)

53 (46) Genital area lying posterior to epp. IV, at most only its anterior
end lying between their emarginate posterior angles; an
ancoral process present. . . Subfamily Pioninae. . 54

THE WATER-MITES (HYDRACARINA)
54 (6i) Posterior margin of ep. IV rounded or transverse . .

871
55

55 (58) With swimming-hairs , 56

56 (57) Transverse diameter of ep. IV the greater, suture between epp.
Ill and IV complete; no prominent papillae on pal. seg. 4,
acetabula very numerous Neumania Lebert 1879.

Mites of small to medium size, varj-ing
in length from 0.5 to i .6 mm., with soft body,
tending more or less to develop chitinous
plates or beset with chitinous points, rarely
smooth: leg IV usually with feathered spines.
Brightly colored, red or bluish forms, active,
but not markedly voracious. Several North
American species, common, and widely dis-
tributed.

Fig. 1347. Neumania spinipes (Miiller), a
European species represented in this countrj'by a
closely allied form, \entral surface, male. X 40.
Outer side, palpus, male. X 70. (Modified from
Piersig.)

57 (56) Longitudinal diameter of ep. IV at least equal to the transverse
suture between epp. Ill and IV incomplete medially; pal.
seg. 4 usually with prominent papillae; 5 or 6 acetabula on
each side on one or two plates.

(Non-parasitic species) Unionicola}isi\dema.n 1842.

58 (55) Without swimming-hairs.

59

872

FRESH-WATER BIOLOGY

59 (60) Posterior margin of ep. IV rounded; genital area midway between
epp. IV and the posterior end of the body, genital plates
elongated transversely Najadicola Piersig 1897.

A large mite, i-S to 2.5 mm. long,
the gravid female often very large,
reaching a length of even 6 mm., living
in fresh-water mussels and laying eggs
in masses between the gills. Honey-
yellow in color, more or less distinctly
finely vermiculate with white lines.
One North American species, generally
distributed.

Fig. 1348. Najadicola ingens (Koenike) .
Epimeral field and genital area, male.
X 23. (.After Koenike.) Inner side, pal-
pus, male. X 80. (After Wolcott.)

60 (59) Posterior margin of ep. IV straight; genital area at the posterior
end of the body, genital plates not elongated transversely.
(Parasitic species) Unionicola Haldeman 1842.

Varjdng from small to large in size,
or from 0.4 to 1. 9 mm. in length. Some
are active, free-swimming mites with
long legs, with swimming-hairs, and
leg I frequently with movable, dagger-
like spines. Others are mussel para-
sites, with shorter legs and no
swimming-hairs, leg IV in some cases
being characteristically modified in
the male sex. In both types strong
spines adjacent to the genital opening
serve together as an ovipositor. Cer-
tain free-swimming forms are regularly
pelagic and very transparent; the para-
sitic forms are dull-colored. Species
numerousand widely distributed, many
of them very abundant, especially the
parasitic forms. The latter are usually
mussel parasites though one species
has been recorded from a South
American imivalve.

Fig. 1349. Unionicola crassipes (MiiUer),
a common and widely -distributed, free-
swimming species, common to North
America and Europe. Ventral surface,
female. X 22. Palpus.outer side, female.
X 63. (Modified from Piersig.)

61 (54) Posterior margin of ep. IV with a prominent acute angle.

62

THE WATER-MITES (HYDRACARINA)

873

62 (63) Medial margin of ep. IV reduced to merely a medial angle which
forms a common angle with the medio-posterior angle of
ep. Ill; leg segs. IV 5 and IV 6 of male modified.

Tiphys Koch 1837.

Rather small mites, in length from 0.54 to i mm.,
with swimming-hairs and the hind leg of the male
strikingly modified. Few North American species,
rare, in our northern lakes, as yet not studied.

Fig. 1350. Tiphys liUaceus (Miiller), the most common
European species. Ventral surface, female. X 28. Outer
side, nght palpus, female. X 123. (Modified from

Piersig.)

63 (62) Medial margin of ep. IV not reduced, and, owing to the angle on
the posterior margin, ep. IV more or less clearly five-sided.

Piona Koch 1837,

Oval or elliptical forms of
various sizes, from 0.45 to 3 mm.
long, often brightly colored, with
swimming-hairs, and with char-
acteristic modifications of leg
segs. Ill 6 and IV 4 in the male,
the latter serving to assist in
grasping the female in pairing,
the former to carry the semen
to the female genital opening.
Hardy, active mites, adapting
themselves to a great variety of
conditions. More than twenty
American species, generally dis-
tributed over the continent.

Fig. 1351. Fiona rufa (Koch), a
European species. Ventral surface,
female. X 22. Outer side, palpus,
female. X 77- (Modified from
Piersig.) Fiona constricla (Wol-
cott), an American form. Leg seg-
ment IV 4, male. X 107. (After
Wolcott.)

64 (45) Epimera in three groups, epp. I being fused together behind the

capitulum, the groups also often close together in the male.

Subfamily Hygrobatinae . . 65

874 FRESH-WATER BIOLOGY

65 (66) Leg segs. I 5 and I 6 modified Atractides Koch 1837.

Small to medium-sized mites, vary-
ing in length from 0.48 to 1.5 mm.
with surface soft and striate, or with
a flexible or hard porous covering;
swimming-hairs present. Species
few in this country, rare, in northern
lakes.

Fig . 1 3 5 2 . A trac tides s pint pes Koch , a
species common to Europe and America.
Ventral surface, female. X 25. Outer
side of left palpus, female. X 103.
(Modified from Piersig.)

66 (65) Leg segs. I 5 and I 6 normal Hygrobaies Koch 1837.

*^

Mites var>'ing in size from small
to even large, or 0.5 to 2.5 m_m.,
brightly colored in many cases, with-
out swimming-hairs, but active, and
certain species frequently, if not regu-
larly, pelagic. Several species of gen-
eral distribution in northern United
States and Canada.

Fig. 1353. Hygrobaies longipalpis
(Hermann), a species found in North
America, Europe and Western Asia.
Ventral surface, female. X 13 • Outer
side, palpus, female. X 125. (Modified
from Piersig.)

In collecting water-mites with the Birge net one will ahnost always findin
the collection specimens of another mite of small size, brown in color, with
short legs, with the body indistinctly separated into cephalothorax and ab-
domen and with a horny body-covering. This belongs to the horny mites or
Oribatidae, probably to the genus Notaspis, and is a vegetable feeder living on
aquatic plants beneath the surface of the water. It can not swim, and will
either cling to objects at the bottom of the dish or float on the surface.^ Sev-
eral species occur and are generally distributed. The species increase in size
and num.ber to the southward.

THE WATER-MITES (HYDRACARINA) 875

IMPORTANT PAPERS ON NORTH AMERICAN FRESH-
WATER MITES

KoENiKE, F. 1895. Nordamerikanische Hydrachniden. Abh. des Natur-
wiss. Ver. zu Bremen, 13: 167-226. Also separate Bremen, 1895.
1912. A Revision of my "Nordamerikanische Hydrachniden." Transl.
by E. M. Walker. Trans. Can. Inst., 1912: 281-296.

Marshall, Ruth. 1903. Ten Species of Arrenuri belonging to the Subgenus
Megalurus Thon. Trans. Wis. Acad. Sci., 14: 145-172.

1904. A New Arrenurus and Notes on Collections made in 1903. Trans.
Wis. Acad. Sci., 14: 520-526.

1908. The Arrhenuri of the United States. Trans. Amer. Micr. Soc, 28:

85-140.
1910. New Studies of the Arrhenuri. Trans. Amer. Micr. Soc, 29: 97-110.
PiERSiG, R. 1 901. Hydrachnidae. Das Tierreich. Lief. 13.
WoLCOTT, R. H. 1899. On the North American Species of the Genus
Atax (Fabr.) Bruz. Trans. Amer. Micr. Soc, 20: 193-259.

1900. New Genera and Species of North American Hydrachnidae. Trans.
Amer. Micr. Soc, 21: 177-200.

1901. Description of a New Genus of North American Water-mites, with
Observations on the Classification of the Group. Trans. Amer. Micr.
Soc, 22: 105-117.

1902. The North American Species of Curvipes. Trans. Amer. Micr. Soc,
23: 201-256.

1903. The North American Species of Limnesia. Trans. Amer. Micr. Soc,
24: 85-107.

1905. A Review of the Genera of the Water-mites. Trans. Amer. Micr.
Soc, 26: 161-243.

CHAPTER XXVII
AQUATIC INSECTS

By JAMES G. NEEDIL\M

Professor of Limnology, Cornell University

Insects are essentially terrestrial animals. Their organization
fits them for exposure to the air. On land they are numerically
dominant, and it is a comparatively small portion of the group
that is to be found in the water. But the lesser portion of a
group so large is in itself a host, including a very great variety of
forms.

That insects are primarily terrestrial and that they have been
secondarily adapted to aquatic hfe is evidenced in many ways.
Their complete armor of impervious chitin and their respiratory
apparatus, consisting of internal branching chitin-lined air tubes
(tracheae), opening to the outside for the intake of air through
spiracles, speak strongly against an' aquatic origin. It would be
hard to imagine an organization more unsuited to getting air when
in the water.

Furthermore, all adult insects, even those that hve constantly
in the water, have preserved the terrestrial mode of respiration:
they all breathe air directly, instead of breathing the air that is
dissolved in the water. They have merely acquired means of
carrying air from the surface down into the water with them for
use there. They are no more aquatic in their mode of respiration
than is a man in a diving bell. It is only the more plastic immature
stages that have acquired a strictly aquatic type of respiratory
apparatus.

Again, it is only isolated and rather small groups of insects that
inhabit the water. A few of the smaller orders, like the stone-
flies. Mayflies, dragonflies and caddisfiies are practically all aquatic
in their immature stages; but the larger orders are not so.

There is abundant evidence of the independent adaptation of
the various groups. Practically all the adult insects found in the

876

AQUATIC INSECTS 877

water are either bugs or beetles. Of those aquatic insects having
complete metamorphosis, the pupa is strictly aquatic in caddisflies
only. The adaptations of the immature stages have chiefly to do
with their respiratory apparatus, and this is most extraordinarily
diverse. This will be discussed later. Suffice it here to say that
gills of several sorts may be developed upon either the outer or
inner surfaces of the body, and those on the outside may be dorsal
or ventral, and may be developed upon the head or on any seg-
ment of the thorax or abdomen : thus they bear all the usual- signs
of independent and adaptive origin.

Finally, it is to be noted that insects have not invaded the water
very far. Nearly all of them have stopped at the shores or in shoal
water; .only a few have established homes for themselves in deep
water. Only the phantom larvae of Corethra have become free
swimming and are regular plankton constituents; possibly a few
others also, for a Umited distribution-period immediately follow-
ing their hatching from the eg'g. The press of life on land result-
ing from the evolution of the highly successful hexapod type of
organization, with great adaptabihty, brief life cycle and excellent
reproductive capacity, may have resulted in the crowding into the
water of those moisture-loving forms whose structures were best
adapted to meet the new conditions. The severity of the competi-
tion on land is most evident to the careful observer; every nook
and comer has its insect inhabitants and every scrap of nutritious
food is eagerly sought by a host of competitors. It is easy to
conceive that a great variety of forms already accustomed to living
by the water side, finding food more abundant in the water than
out of it, might, if adaptable, become modified for entering the
water for a greater or less depth and for remaining there a greater
or less time.

And, as a matter of fact, adaptation of the adults has proceeded
only a little way. Some adult insects, as certain caddisflies and
damselflies, enter the water only to lay their eggs, and they remain
enveloped by a layer of adherent air while beneath the surface.
Some Hve constantly in the water but maintain communication with
the surface by means of a long respiratory tube, as does Ranatra.
The most nearly aquatic of adult insects are the bugs and beetles that

878 FRESH-WATER BIOLOGY

have developed oar- like hind feet and have become good swimmers;
these enter the water to depths of several feet and spend most of
their time near the bottom in shoal waters, but they must come to
the surface at intervals for air which they carry down with them
beneath their wing covers or adherent to the pile of their bodies.
A few adult insects also have taken to walking or running on the
surface of the water, but these are naturally the most minute forms,
as springtails, or those of slenderer build, like little Diptera and
water striders; and of this last-mentioned group, some wander far
from shore, even upon the surface of the ocean. But there are
few adult insects to be found far from the shelter of vegetation,
and it remains true that the great press of insect Hfe is at the shore
line.

The case is only slightly different with insect larvae. Most of
these have remained near shore. As compared with the adults,
their smaller size, less chitinized skin and greater plasticity have
allowed much more complete adaptation to aquatic Hfe. There
are some larvae, like those of beetles and of many flies, that take
air at the surface as do the adult beetles, and there are a few others,
that, descending the stems, tap the air spaces of plants far beneath
the surface and get oxygen from that unusual source ; but there are
also very many that are capable of a truly aquatic respiration,
being able to utilize the air that is dissolved in the water. Most
of these larvae when newly hatched absorb the oxygen directly
through their skins; and a few of them, especially such as live in
well aerated water, acquire no better means than this during their
larval existence, but most of them develop gills of some sort.

These gills are delicate outgrowths of the thinnest integument of
the body. Two types of gills are usually distinguishable, blood
gills, and tracheal gills. The former are more Kke the gills of
other aquatic animals; the latter are pecuHar to insects. The
blood gills are simple outgrowths of the body wall into which the
blood flows. The interchange of gases which constitutes the
respiratory process takes place between the blood within the gill
and the water outside it by means of direct diffusion through the
thin membranous wall. Such gills are very commonly developed
in dipterous larvae as paired and retractile appendages of the pos-

AQUATIC INSECTS 879

terior end of the alimentary canal, but they also occur on other
parts of the body.

Since tracheae are the established channels of air distribution in
the bodies of insects, and nearly all insects are hatched from the
egg in possession of a number of them, it is natural that tracheal
gills should be more commonly developed in the larvae of the
group. A tracheal gill differs from a blood gill chiefly in that it is
traversed by minute capillary branches of tracheae, and the air
is taken up by and distributed through the tracheae. Tracheal
gills are usually developed apart from and quite independently of
the spiracles or breathing pores. They arise from the thin interseg-
mental membranes of the body. They may be developed upon
the internal walls of the rectum, forming a large and very perfect
gill chamber, as in the young of dragonfiies. More frequently, they
are developed on the outside of the body. They may be flat and
lamelliform, as in the three caudal gills of the damselfiies and in the
paired dorsal abdominal gills of Mayflies, or they may be filamen-
tous, simple, branched or tufted, as in most other forms. Another
sort of tracheal gill (the so-called ''tube gill") is developed directly
from the pro thoracic spiracles in certain diptera at the assumption
of the pupal stage, in the form of respiratory trumpets (mosquito
pupae), combs (black fly pupae), brushes (midge pupae), etc. With
the development of gills, insect larvae have become independent of
the surface. Many of them remain wholly submerged through-
out their entire larval life. A few of them have progressed
farther from shore and into deeper water. Corethra has been already
mentioned as a plankton organism. A few larvae of midges and
a few caddis worms are constant denizens of the bottom silt in our
deeper fresh-water lakes. This seems indeed considerable prog-
ress into a new and totally different environment, when one re-
members that they are tied by parentage to the shore.

It is to be noted in passing that only in the Coleoptera and
Hemiptera has the adaptation of adults and immature stages been
parallel. In the other groups the adults do not live in the water.
The possession by a few adult insects {Pteronarcys, etc., among
stoneflies, and Chirotonetes , etc., among Mayflies) of rudimentary
gills does not indicate, as was once thought, that this is the primitive

88o FRESH-WATER BIOLOGY

condition ; it indicates only that, in these relatively primitive forms,
structures developed to a considerable extent upon the immature
stages have, in the rapid and incomplete transformation these imder-
go, been carried over in rudimentary form into adult Hfe.

Among aquatic insects are many beautiful and interesting
forms. The keys and figures in the following pages should enable
anyone who has learned the parts of the body of a grasshopper,
or who has mastered such elementary knowledge of insect anatomy
as every textbook of zoology or of entomology affords, to identify
most of the insects he will find in the water. There are many gaps
in our knowledge of all the groups; even the adult insects are not
well known except in the showier groups, which have always been
more attractive to the collector; and so many immature forms are
still imknown, it has been found impracticable to attempt to give
keys even to the genera in two orders, Plecoptera and Trichoptera.
Limitations of space have compelled restriction to the larger
groups among the Diptera. In most of the groups having com-
plete metamorphosis, the characterizations of the immature stages
have been adapted from the accounts of European writers, very
Httle ha\dng as yet been done on them in America. Here is an
attractive field in which the amateur and the isolated student may
still find pioneer work to do.

It is the purpose of this chapter to assist the student toward
acquaintance with such insects as he may find in the water. The
limitations of space allow but brief notice of the natural history of
any of the groups and restrict the keys to dealing with famihes and
genera. The aim is to supplement the general works on entomology
and not to duplicate any part of them. Keys to the orders of
adult insects are available in a number of manuals and textbooks,
hence there is need here only to point out the readier recognition
marks of those orders which commonly occur in the water, and to
give a key to the immature stages.

Recognition Characters

There are but nine orders of insects commonly found in water
in any stage: Plecoptera, Odonata, Ephemerida, Hemiptera, Neu-
roptera, Trichoptera, Lepidoptera, Coleoptera and Diptera.

AQUATIC INSECTS 88 1

The Odonata are distinguished by the venation of the wings,
especially by the possession of a distinct nodus and stigma of the
type shown in Fig. 1388.

The Ephemerida are distinguished by the venation of the wings
(Fig. 1387), and by their proportions and their extensive corruga-
tion.

The Hemiptera are distinguished by the possession of a jointed,
sucking proboscis, directed backward beneath the head and
thorax.

The Trichoptera are distinguished by the hairy covering of
their wings, the absence of jaws and proboscis (palpi are pres-
ent) and by a type of venation of wings similar to that shown
in Fig. 139 1.

The Lepidoptera are distinguished by their covering of powdery
scales, and by the possession of a coiled sucking proboscis.

The Coleoptera are distinguished by the hardened fore wings
(elytra) meeting in a straight line down the middle of the back.

The Diptera are distinguished by the possession of a single pair
of wings, with very few cross- veins in them (Fig. 1378).

The other two orders, Plecoptera and Neuroptera, lack the above
combinations of characters and may be readily recognized by their
general likeness to figures pubHshed in the following paragraphs
devoted to them.

Besides these nine orders, there are three others, of slight impor-
tance in the Ufe of the water, that are dehberately ignored. These
are: ^

(i) The Thysanura, or springtaijs, common on the surface of
water, but not living in it. TEey will be readily recognizable, if
collected, by their very minute size, entire absence of wings, mouth
parts retracted within the head, and the forked spring beneath
the abdomen by means of which they jump freely.

(2) The Orthoptera, of which some of the grouse locusts (family
Tettigidae) , Hving by the water side, occasionally jump in and take
a swim.

(3) The Hymenoptera, of which a few minute egg parasites,
enter the water as adults to find the eggs of their aquatic victims,
and these swim with their wings {Polynema, etc.).

882 FRESH-WATER BIOLOGY

Stoneflies {Order Plecoptera)

The stoneflies constitute a small and primitive group of insects
of inconspicuous coloration and rather secretive habits. They are
found almost exclusively about rapidly flowing water. Every
spring brook will furnish a few of the smaller grayish or brownish
species, and every larger rocky stream is the home of some of the
larger forms. During the winter months the small black Capnias
appear, often in great abundance on the surface of the snow,
Capnia necydaloides appearing usually in December, and Capnia
pygmaea, in March. Several species of Taeniopteryx appear also in
March, and may often be seen on mild, sunshiny days by the
borders of creeks, slowly and laboriously flying along the banks on
warm afternoons. Species of Nemoura appear in April, emerging
from the waters of cold brooks, and making short flights from one
gray tree trunk to another. All through the summer the larger
species are emerging from rocky streams, but these are very se-
cretive in habits. They may be beaten from the bushes along the
stream side, but are oftenest seen in numbers about street lamps
and are easiest collected when attracted to lights. The green
stoneflies {Chloroperla, etc.) fly mainly in midsummer, and frequent
the fresh foliage, in the midst of which they are quite incon-
spicuous.

Rudimentary wings occur in a number of the genera, Capnia,
Taeniopteryx, Pteronarcella, Ferla, etc., and, of course, the wingless
species are to be found near the waters from which they emerge
on transformation — in fact, not farther therefrom than they are
able to run or climb. The males alone are wingless in most cases.
The eggs of the females are practically mature at transformation.
While there is dearth of observations as to the feeding habits
of the adults, it is certain that they will lap up water and other
fluid substances, and the small grayish species eat dead grass leaves
and other solid food. The mandibles of the larger forms are weak
and rudimentary. The adult life, therefore, is probably very brief.
Concerning the egg-laying habits also, there is dearth of actual
observation. Females of many species may be taken when carry-
ing egg masses extruded at the tip of the abdomen; but just

AQUATIC INSECTS

883

where these are deposited, and when and how, are matters not
yet established. One species of Capnia, an undetermined, late
appearing species that occurs in Lake Forest, 111. in May, is
viviparous.

The nymphs of stoneflies are much easier to fmd and to collect
than are the adults. By Hfting stones or other obstructions out
of the bed of rapid permanent streams, and quickly turning them
over to look on the under side, the nymphs may usually be seen
lying flat, outspread, with widely extended legs clutching the sur-
face. They are always associated
with Mayfly nymphs of similar ap-
pearance, but are easily distinguished
by the presence of two claws on the
tip of each foot, where the Mayfly
nymphs have but one, and by the
lack of gills upon the dorsal side
of the abdomen. The nymphs of
larger species, as Perla (Fig. 1354),
are not easily managed in ordinary
aquaria. They cannot live long in
still water, and soon after being
placed in it, they manifest their
discomfort, by a vigorous swa>ing
of the body up and down. This
motion brings their tufted gills into
water. Running water aquaria are

Fig. 1354. The nymph of a stonefly, Perla.

better contact with the
essential for their maintenance.

Their transformation may often be easily observed where it
occurs naturally out of doors. It always takes place near to the
edge of the water. Often rocks that project but a few inches above
the surface are favorite places of emergence, and the exposed sur-
faces of these may sometimes be found covered several layers deep
with the skins of the nymphs that have come from the bed of the
adjacent parts of the stream. Transformation usually occurs at
night, but early and late stragglers may often be found by morn-
ing or evening light. The change from nymph to adult is, for insects,
comparatively sHght : wings and accessory reproductive organs are

884

FRESH-WATER BIOLOGY

perfected, and regressive development of gills, external armor, and
feeding apparatus occurs, but the change of form and of proportions
of the body is slight.

The nymphs of stoneflies are, so far as known, carnivorous:
they feed on the nymphs of Mayflies, on the larvae of caddisflies

%.

Fig. 1355. Pkromrcys dorsaia, adult female. FiG. 1356. Pteronarcys dorsata, grown nymph.

and small diptera and perhaps on the young of other stoneflies.
They are themselves the food of the trout and of other fishes that
frequent swift waters. Hudson has demonstrated the importance
of stoneflies as fish food in the mountain streams of New Zealand.
Adults and nymphs are equally serviceable for bait in all our
mountain streams.

While no keys to the genera of the nymphs of stoneflies have yet
been published, if the adults are known, the nymphs may be
readily determined by comparison, for the wing venation is fully

AQUATIC INSECTS 885

developed in the wing pads of the nymph and is comparable in
close detail with that of the adult. It is only necessary to remove,
as with a sharp razor, the wing pads from a well-grown nymph,
young enough so that the wings will not be already crumpled
within their sheaths, mount, and examine with the microscope.
Since, however, it is easier to get nymphs than adults, and nymphs
only will often be available, the following hints may be of assistance
in their recognition. Pteronarcys (Figs. 1355 and 1356) alone has
gills upon the first two segments of the abdomen. Taenia pteryx alone
has three- join ted, telescopic gill filaments attached singly at the base
of^ the coxae. Peltoperla alone has conic-pointed gill filaments, in
a few small clusters, concealed under the flaring, overarched mar-
gins of the thoracic segments. Perla and its alUes have copious
tufts of fine gill filaments before and behind the bases of all legs.
Chloroperla and its allies, and Capnia and Leuctra altogether lack
gills.

Mayflies {Order Ephemerida)

The Mayflies constitute a small group of very fragile insects,
all of which are aquatic in their earlier stages. They abound in
all fresh waters, both swift and stagnant. Some of the larger May-
flies are very well known, indeed, from their habit of transforming
all at one time and appearing in great swarms along shores of lakes
(Fig. 1357) and banks of the larger streams. They fly to lights
at night, and sometimes, under the arc lamps in city streets, they
accumulate in such heaps as to require removal in wagons. Such
concerted appearance of the adults of a single species gives some
conception of the abundance of individuals that may five and grow
up together in a restricted area; but it is to be borne in mind that
there are scores of other species living in the same waters, the
adults of which are rarely seen in numbers, of which the individuals
are probably quite as numerous. When their period of trans-
formation is extended through the summer season and their
habits are not gregarious, but solitary and secretive, they may
entirely escape the notice of the casual observer.

Mayflies are famed for their ephemeral existence — for Kving as
adults but a day. They are peculiar among insects, in that they

886

FRESH-WATER BIOLOGY

moult their external chitinous skin once again after they transform
from the nymphal form to that of the adult. It is chiefly these
callow and immature adults (known to the books as suh-imagoSy
and to British fishermen as dims) that fly to lights. Emerging

Fig. 1357.

Mayflies fallen beneath an electric-light post on Lake Erie.
H. S. Jennings.)

(Photograph by Professor

from a rent in the back of the old nymph skin, they spread their
newly expanded wings and rise feebly into the air, and if a light
be near, they swarm to it; otherwise they settle upon any conven-
ient tree or building, and sit stiffly (Fig. 1358) with uplifted wings
until ready for their final moulting. This may occur within a few

AQUATIC INSECTS 887

minutes, as in Caenis, or it may be delayed twenty-four hours or
more, as in most of our larger species. Caenis probably lives but a
few hours after leaving the water; but the larger forms live through
two days, their transformation from the nymph occurs in one night,

Fig. 1358. A newly-emerged Mayfly, Eexagenia bilineala.

their final moult the next night, and their period of adult activity
and egg-laying and their death the next evening.

The adults are peculiar in the venation of their wings (Fig. 1387)
and in the extent of the longitudinal furrowing of the same, in
the lack of functional mouth parts and in the buoyant function
assumed by the aHmentary canal, which, being no longer used for
food, is filled with air. While highly speciaUzed in most respects,
one very generalized character has been retained in the group:
the openings of the oviducts of the female are paired and separate.

The males of most species indulge in graceful ante-nuptial
flights, that to the observer appear most delightful and exhilarating.
They assemble in little companies and dance up and down, alter-
nately rising and falhng, flying upward and falling down again on
outspread wings in long vertical lines. The crepuscular species
such as Ephemera and Hexagenia, that compose the well-known
swarms, fly out over the surface of the water, where the females
meet the males, and afterwards settle down upon the surface of the
water to liberate their eggs. Caenis swarms over the edge of the

888

FRESH-WATER BIOLOGY

water just as darkness falls. Some of the less nocturnal species,
as Leptophlebia and Choroterpes, swarm out in the sunlight in
sheltered places of late afternoons, or dance up and down among
the mixed shadows and sunlight beneath the
canopied crowns of tall stream-side forest trees.
The females of Baetis creep beneath stones at
the surface of the water and deposit their eggs in
single-layered patches just beneath the surface.
The adult hfe of Mayflies is truly ephemeral
and is concerned wholly with reproduction; and
the struggle for existence is transferred largely to
the immature stages. The nymphs are highly and
independently specialized. They are adapted
to all sorts of aquatic situations. A few, like
Hexagenia, Ephemera, and Polymitarcys (Fig.
1359), are burrowers beneath the bottom silt.
A few, like Caenis and Ephemerella, are of seden-
tary habits and live rather inactively on the ^^^- ^^X^-JrcvsX''^ °^
bottom, and on silt- covered stems. Many are
active cHmbers among green vegetation; such are Callihaetis and
Blasturiis; and some of these can swim and dart about by means of
synchronous strokes of tail and gills with the swiftness of a minnow.
The species of Leptophlebia love the beds of slow-flowing streams,
and all the flattened nymphs of the Heptageninae Hve in swiftly mov-
ing water, and manifest various degrees of adaptation to withstand-
ing the wash of strong currents. The form is depressed, and margins
of the head and body are thin and flaring, and can be appressed
closely to the stones to deflect the current. So diverse are the
nymphs in form that the genera may be distinguished among them
by a beginner more easily than among the adult Mayflies.

Mayfly nymphs feed largely on dead vegetable substances — the
decaying stems and leaves of aquatic plants. They are of first
importance in the food of fishes. But we are as yet largely in
ignorance of the conditions that make for their abundance.

The study of this group has been greatly neglected by entomol-
ogists and our Mayfly fauna is very insufficiently known. The
ecology of the immature stages is especially in need of investigation.

AQUATIC INSECTS • 889

Dragonflies and Damselflies {Order Odonata)

This is another isolated group of insects, larger in size and of
stronger build. All our representatives of the group are aquatic
in their earher stages, but there are a few Hawaiian damselflies
whose nymphs live out of the water, on moist soil under the leaves
of liliaceous plants. All members of the order are carnivorous in
all stages. They are indeed among the most important of carni-
vorous forms about the shores of all fresh waters.

The wings of the adults are strongly developed and have a
peculiar venation (Fig. 1388). The legs are not used for walking,
but only for perching; to facihtate perching on vertical stems,
they are set far forward and graduated in length, so that they hold
the body when at rest in a more or less horizontal position. This
facihtates quick stopping and starting again. Correspondingly
the wings are shifted far backward, and tilted upward at their
fore margins, and the side pieces of the thorax are askew.

The males are pecuHar also among the orders in having the
accessory organs of reproduction (copulatory apparatus) developed
upon the ventral side of the second abdominal segment, far re-
moved from the opening of the sperm ducts upon the ninth segment.
The eyes are very highly developed, and the antennae are minute
and setaceous. In this they resembl the preceding order Ephem-
erida, but the two groups as they exist to-day are highly differenti-
ated from each other, although more or less intermediate fossil
forms point to their common origin in the past.

Among the dragonflies are many superb flyers. The speed on
the wing of Traniea and Anax equals, and their agihty exceeds,
that of swallows. They all capture their prey in flight, and are
dependent on their wings for getting a living. But the habit of
flight is very different in different groups. Only a few of the
strongest forms roam the upper air at will. There is a host of
beautiful species, the skimmers or LibelluHdae (Fig. 1360), that
hovers over ponds in horizontal flight, the larger species on tireless
wings, keeping to the higher levels. The stronger flying Aeschnidae
course along streams on more or less regular beats: but the Gom-
phines are less constantly on the wing, flying usually in short

890 FRESH-WATER BIOLOGY

sallies from one resting place to another, and alighting oftener on
stones or other flat surfaces than on vertical stems.

The damselflies are not such good flyers. The common black-
wing Calopteryx (Fig. 136 1) may usually be seen fluttering gaily
about the borders of creeks, but most damselflies are Httle in

Fig. 1360. The Blue Pirate dragonfly, Pachydiplax longipennis. (Drawn by
Mrs. J. G. Needham.)

evidence, and confine their locomotion to flitting from stem to
stem amid the shelter of vegetation.

The dragonflies eat other insects in vast numbers and in great
variety. A large part of their food consists of small diptera: and
because many of these small diptera are noxious species, mos-
quitos, etc., an extended inquiry was once made as to the feasibiUty
of using dragonflies to remove these pests : it appeared that dragon-
flies are not at all discriminating in their feeding, and wiU as readily
eat useful as noxious species. Then, too, they eat other dragonflies,
apparently preferring forms that are only a little smaller than them-
selves. Hagenius, for example, eats Gomphus, and Gomphus eats
Mesothemis, and Mesothemis eats Lestes, and Lestes eats Argia,
and Argia eats Ischnura, and so on from the greatest even unto the
least of them.

Many dragonflies are eaten by birds and other animals at their
transformation, before they are able to fly and escape; and some
of those that are not very strong-flying are eaten habitually by
birds — the smaUer Libellulines by king-birds, and the smaller
damselflies by swallows. But it is doubtful whether anything that
flies is able to capture in flight one of the swiftest dragonflies.

AQUATIC INSECTS

891

There is much diversity of egg-laying habits in the order. All
the damselflies and many dragonflies, especially Aeschnidae, are
provided with an ovipositor, by means of which punctures are
made in the stems of aquatic plants, in logs, in wet mud, etc., for
the reception of the eggs. The eggs are placed singly in the punc-
tures, and usually just below the surface of the water; but a few
damselflies descend the stems to place them deeper, and some
species of testes place them habitually in the stems above the sur-
face. Here they are subject to the attack of egg parasites. The
females of those dragonflies that lack a well-developed ovipositor
drop their eggs upon the surface of the water while in flight (usually
descending to touch the surface, and thus to wash them free),
whereupon the eggs scatter and fall to the bottom; or, they settle
on some plant stem at the surface and hang them in gelatinous
masses about the stem. In certain of the Cordulinae these masses
are long gelatinous strings, containing many hundreds of eggs. It
is easy to get the eggs of most Libellulines for study. When a fe-
male is seen tipping the surface of the water with her abdomen
while in flight, if she be captured uninjured and held by the tips
of the fore wings (leaving the hind wings free) and dipped against
the surface of the water in a glass, in imitation of her own motion
while at large, she wifl usually liberate eggs in great abundance in
the water. These require about three weeks for hatching, and the
nymphs begin to eat each other early in life.

There are nymphs of Odonata in all sorts of fresh water. Those
of some of the larger active species clamber about freely among

Fig. 1361. Damselfly nymphs; a, Calopteryx; b, Lestes.

water weeds, and even chase their prey, creeping stealthily upon it
until within range. Most damselflies (Fig. 1361) clamber about

892 FRESH-WATER BIOLOGY

among green stems, where they are quite inconspicuous. But
nearly all dragonfly nymphs get their living by waiting in hiding
for the approach of their prey, and comparatively few of them roam
freely about in the water. Most of the LibelluKdae are bottom
sprawlers (Fig. 1362) ; most of the Gomphines are burrowers beneath

Fig. 1362. The sprawling nymph of Didytnops transversa.

the bottom silt, and the nymphs of Cordulegaster are expert
ambuscaders, scratching a hole in the sand of the bottom and
gettmg into it, kicking the sand up over their backs until covered
excepting the tips of the eyes and of the respiratory orifice at
the end of the abdomen, and lying in wait until some unsuspecting
little animal suitable for food wanders within reach.

The chief organ for capturing prey in the nymphs of all the
Odonata is the remarkably developed labium (Fig. 1389^), which
has become elongated, hinged in the middle and folded back under
the thorax. It has acquired a formidable array of grappUng hooks
and spines at its tip. It is often longer than the fore legs when
extended and possesses muscles capable of extending it with light-
ning-like speed. It is thrown forward and opened by a single
movement, and when it closes on its victim it is withdrawn again
instantly, dragging the struggling captive back under the jaws,
which then come into play.

The problem of getting air has been solved in two ways in the
nymphs of the two suborders of Odonata. In the damselflies

AQUATIC INSECTS

893

(Fig. 1363), there are developed three more or less leaf like gills upon
the tip of the abdomen, and these are traversed by fine tracheae,
and doubtless assist in getting air, although not entirely essential
to that end. In the larger dragonfly nymphs there is developed

Fig. 1363. The nymph of Ischnura verticalis.

within the abdomen a respiratory chamber made out of the hinder
portion of the modified alimentary canal. Through the action of
the abdominal muscles, the water is alternately drawn into this
and expelled again. This chamber is lined with multitudes of
tracheal gills, and abundantly supplied with tracheae, constitut-
ing the most perfect aquatic respiratory apparatus developed in
insects.

Transformation occurs in most Odonata very close above the sur-
face of the water. The larger species transform for the most part
at night: the damselflies, at any time. The period of half an hour
or more required for drying the wings before sustained flight is
possible is a time of great peril in the life of the dragonflies. It is
a time of opportunity, however, for the coflector of Hfe history
material.

Water Bugs {Order Hemiptera)

A small part of this great order is aquatic ; a number of families
are well adapted for hfe in the water; a few run over the surface
and a few others live habitually on the wet shores and forage in the
flotsam and drift of the waves. Adults and nymphs are of similar
habits and are generally sufficiently alike in structure for ready
identification, the metamorphosis being slight. All are distin-
guished from the members of other groups by the possession of a
jointed puncturing and sucking proboscis that is directed backward
beneath the head. The families are so diverse in structure that

894

FRESH-WATER BIOLOGY

here again is given evidence of independent adaptation to aquatic
life, and nowhere could be found more complete intergradation of
habits between terrestrial and shore-loving forms and those that
dwell in the water.

The shore bugs (Acanthiidae) and toad bugs (Pelogonidae) are
essentially terrestrial; the marsh treaders (Hydrometridae), water

Fig. 1364. A giant water bug, Benacus, clinging to a vertical surface under water.

striders, skaters, etc. (Veliidae and Gerridae), have passed out upon
the surface, a few of them having acquired the ability to dive and
swim. The Nepidae and Belostomatidae are fairly adapted forms
that do not depart far or long from the surface of the water, and
only the Corixidae and Notonectidae have acquired very highly
speciaHzed apparatus for swimming and for carrying down a copious
air supply.

There are no tracheal gills developed in this order. Nymphs
and adults alike must come to the surface for air. They are easily
collected by sweeping aquatic vegetation with a dip net. The
Corixidae stick more closely to the bottom than do other forms.

AQUATIC INSECTS

895

Transformation occurs in the water, and is only a little more
of a change than are the earlier nymphal moults. The adults of
many genera fly from one body of water to another, and a few of
the largest forms (Fig. 1364) have a habit so well known of flying
to electric lights at night that they have been denominated ''electric
light bugs." These immense bugs are among the most powerful
members of the order; the largest of the dragon fly nymphs are no
match for them; they will frequently attack and kill frogs, and
they have even been found preying on woodpeckers, presumably
encountered in flight. Their weapon of offense is the stout beak,

Fig. 1365. A water bug (at the left) and a backswimmer (at the right),
resting at the surface of an aquarium.

which is capable of making painful wounds. Even the smaller
forms of Notonecta (Fig. 1365) can puncture the fingers of the
collector if carelessly handled.

The eggs of the more strictly aquatic members of the family are
fairly well known. Those of Benacus (Fig. 1366) and Amorgius
are deposited on the vertical stems of Typha, etc., above the
surface of the water; these are among the largest of insect eggs.
Those of the Nepidae, Nepa and Ranatra, are distinguished by
long appendages at the micropylar end, and are inserted into the
soft tissues of plants — into rotten, water-soaked wood, or into

8g6 FRESH-WATER BIOLOGY

green herbs. Those of Notonecta are deposited singly on the sides
of plant stems under water, and those of Corixa are deposited in
similar places or stuck on to the back of crawfishes.

The surface-haunting forms are characteristically of scavenger
habits, eating the insects of all sorts that fall upon the surface of

Fio. 1366. The eggs of the giant water bug, Benacm, on the
base of a Typha stem.

the water; while the more strictly aquatic bugs are truly predatory
with the possible exception of the minute Plea, which is believed
not to be carnivorous at all. The highly specialized Corixidae are
able to remain wholly submerged for long periods. They clamber
about amid the debris of the pond bottom, and when they come to
the surface for air, they do not remain there, but quickly descend
again to the shelter of the bottom trash. Of all Hemiptera these
are the ones most commonly eaten by fishes.

AQUATIC INSECTS 8q7

DoBSONS, Fish Flies, Spongilla Flies {Order Neuroptera)

But two families of this great and heterogeneous order, as now
commonly restricted, are aquatic, and these in their larval stages
only. The larvae of all the members of the small family Sialididae
are free-ranging carnivorous, aquatic forms, and in the family
Hemerobiidae, there are a few genera whose larvae Hve in the
water. These two families are so very different in every respect
that they are better considered separately.

SiALiDiDAE. Here belong a few of the most primitive of insects
having complete metamorphosis: the orl flies, fish flies, dobsons,
etc. They are mostly of large size, and are provided with ample
wings, which, however, serve but rather poorly for flight. The
dobsons are among the largest of insects, and their larvae, known
to the fishermen as hellgrammites, are famous as bait for black bass.

They are found in swift streams beneath the stones, where they
cling securely by means of their stout legs, aided by a pair of stout-
clawed processes at the end of the body. They are provided at
the sides of the abdomen with paired lateral fleshy processes, and
at the base of each of these there is a large tuft of fine tracheal gills.
They are blackish, ugly- looking crawlers, of slow growth, requiring
apparently several years to develop. When grown they crawl
out on shore and seek a suitable place beneath a log or stone;
for the pupae are not aquatic. The adult female lays her eggs in
broad flat masses on stones or timbers above the edge of the water,
and covers them over with a chalky white incrustation. The
eggs are piled several layers deep and are very numerous. On
hatching the young fall into the water, and begin at once their
predatory existence. But one species of dobson is found in the
eastern United States, the common Corydalis cornuta L. The
fish flies iChaiiliodes) are insects of similar appearance and
habits, about half as large as the dobsons, ha\dng an expanse
of wing of about one and a half inches. Their larvae usually fre-
quent still water, where they clamber over and under logs. A
rotten log on shore furnishes the favorite place for the excavation
of a pupal chamber. The eggs are laid above the water in naked
patches of one or more layers on either dead wood or green leaves.

898

FRESH-WATER BIOLOGY

The orl flies (Sialis) are still smaller having an expanse of wing of
an inch or less. They are plain, blackish in color, and rather
secretive in habits. Sometimes they occur in such
numbers as to blacken the herbage about the pond
border. The larvae (Fig. 1367) live among the stones
and gravel in the bed of brooks, and in the borders
of ponds, and transform in the wet sand on shore.
They are readily distinguished from other larvae
by the long tail-like prolongation of the last seg-
ment of the body. The female lays her eggs (Fig.
1368) in broad, single layered, blackish patches on
some stick or timber above the surface of the
water. The lateral filaments of the abdomen in
Sialis are thin-skinned, and contain tracheae, and it
is possible that they serve as organs of respiration;
there are no additional clusters
of fine gills at their bases. Un-
like the foregoing, these larvae
descend into the bottom silt
and burrow through it, and their long ab-
dominal filaments are close laid on the back,
as are the gills of the burrowing Mayfly
nymphs.

There is a striking general similarity be-
tween the larvae of the Sialididae and those
of the more generaHzed carnivorous Coleoptera.

Hemerobiidae. Only two genera in this large family of attrac-
tive insects are aquatic in our fauna, Climacia and Sisyra (Fig. 1369).
These are small insects, half an inch or less in expanse of wing,

Fig. 1367. The larva
of the orl fly, Sialis
infumata.

Fig. 1368. The eggs of the
orl fly; from a photograph.

Fig. 1369. A spongilla fly, Sisyra.

the former yellow and brown in color, the latter, plain brown.
Nothing is known of the feeding habits of the adults. Their larvae

AQUATIC INSECTS

899

(Fig. 1370) feed upon fresh- water sponges, and live within the oste-
oles of the same, or in depressions on the exterior of the sponge mass.
They puncture the tissue of the sponge with their long decurved
sucking mouth parts. The paired appendages of the abdominal
segments are bent downward underneath the body, and curiously
angulated; they are moved back and forward with a rapid, inter-
mittent, shuttle-like vibration. In
the well-grown larvae, the stomach
has no posterior opening, and the
sponge substance taken up through
the slender proboscis appears to be
wholly absorbed. Correspondingly,
the posterior part of the aHmentary
canal and its appendages are put to
a new use. The malpighian tubules,
or nephridia, are metamorphosed in
large part into silk secreting organs,
the rectum into a silk reservoir, and
the terminal aperture into a spin-
neret. When grown the larva leaves
the water and climbs to some suitable
supporting surface, and spins with this
apparatus first a wide canopy over
itself, and then a closer fitting inside
cocoon. Climacia weaves the outer
covering in a beautiful hexagonal
mesh; Sisyra makes both coverings
plain and close woven. Nothing is known of the feeding or egg-
laying habits of the adult, or of any other particulars except that
they are sparingly attracted to lights.

It should be mentioned, perhaps, in passing, that the immature
stages of another genus of Hemerobiidae, Polystoechotes, the genus
containing our largest representatives of the family, are as yet
unknown.

Fig. 1370. The larva of Sisyra.

900

FRESH-WATER BIOLOGY

The Caddisflies {Order Trichoptera)
The caddisflies constitute a large group of insects, nearly all of
which are aquatic in their immature stages. Among the adults
are many pretty species of soft colors and great elegance of form.
Having rudimentary mouth parts they are short-lived. They are
chiefly nocturnal in habits and fly to lights, often in great num-
bers. Some are diurnal and hover over water in long sustained
horizontal flight; others dance up and down in companies imder
the shelter of streamside trees. No insects are more common
about the wharf lights on the shores of our great lakes.

The larvae exliibit great diversity of structure and habits. Much
excellent work has been done on them in Europe, but our American
forms are little known. The most familiar larvae are the well
known ''caddisworms" that construct portable cases (Fig. 13 71),

Fig. 1371. Caddisworm cases. (Drawn by Mrs. J. H. Comstock.)

in which to live, and carry them about on their backs. These
cases are made out of a great variety of materials: sticks, smaU
stones, sand grains, bits of sheU, of leaves or of bark; in short, almost
any solid material suitably small and available. In many species
the construction of the cases is so uniform in pattern and materials
that the larvae may be known by the houses which they drag
about. The larvae of the Phrygeaneidae construct cylindrical cases
made of bits of stems, grass, etc., placed lengthwise in a continu-

AQUATIC INSECTS

901

ous spiral band; the larva of Helico psyche builds out of sand grains
a spirally coiled case, shaped like a snail shell. The materials
of the case are always stuck together by means of the secretion of
the salivary glands. Usually the cases are cylindrical but sometimes
they are triangular, or square in cross-section. Usually the sticks
used are placed lengthwise, but sometimes crosswise, as in stick
chimneys, to make the bulky and cumbersome dwellings of some
of the Limnophilidae. Sometimes, on the other hand, they are con-
structed so light and thin as to offer little hindrance to free loco-
motion, and a few larvae with well-developed swimming fringes on
their long oarlike feet swim freely
about. In the cases that are con-
structed by most larvae of the two
families Hydroptilidae (Fig. 1372)
and Rhyacophilidae, no extraneous
materials are used, but only the se-
cretion of the salivary glands; these
cases are therefore thin and parch-
ment-like. Most members of the
great family Hydropsychidae make
no portable cases at all, but only
runways in the crevices between the
stones in streams; these they line
with silken threads. Some of these
larvae, among which are the com-
monest members of the genus Hydro-
psyche, to be found in every swift

, 1 r 1 Ti Fig. 1372. Micro-trichoptera. On the

stream, Spm webs OI open mesn, like left, a lami; on the right, a pupa oi another

. r ^ smaller species, within its transparent case.

fishermen s semes, out from the up-
stream ends of their tubes or runways; clearly, this is for the
purpose of catching any little organisms set adrift in the stream.
These are mainly carnivorous larvae; many members of other
famines have a mixed diet of vegetable and animal food, but a
goodly number are characteristically herbivorous.

There are caddisfly larvae for all sorts of waters, and lor wet
situations, or mossy banks. A few species, accompanying the
"blood worms," have migrated far out on the bottoms of our larger

902 FRESH-WATER BIOLOGY

lakes into deep water. The gills of the caddisfly larvae are always
of the filamentous type, never lamelliform. They are wanting in
members of several families, and are variously disposed about the
body, singly or in clusters, in many others; their number, form,
and arrangement furnish group recognition characters. The more
typical caddisworms, having their gill filaments along the sides of
the abdomen completely inclosed within the case, keep water flow-
ing through by means of continual undulating motion of the abdo-
men; three tubercles at the base of the abdomen and a pair of
stout prolegs at its apex serve to keep the walls properly spaced
for the admission and the flow of the water. The case is always
large enough so the larva can entirely withdraw itself inside.
By this means it doubtless escapes from many enemies. But
some of the larger fishes, as, for example, brook trout, eat case
and all.

The pupa of caddisflies is peculiar in that it also is aquatic.
It is formed within the larval case or tube, the larva closing the
apertures with a perforate web of silk before its final moulting;
this web admits water for respiration, but keeps out enemies.
True tracheal gills, of the same type as those possessed by the larvae,
are present on the pupae of many caddisflies. All the pupae are
more or less active; some maintain constant undulating move-
ments of the abdomen to keep the water circulating, and at the
close of the pupal stage all work their way out of the larval case,
and swim to the surface of the water to undergo their final trans-
formation. In the case of species that inhabit swiit waters and
transform in the current, this takes place very quickly, the adult

emerging instantly on reaching the sur-
face and flying away at once. Although
the adults have jaws of the most rudi-
mentary sort, the mandibles of the pupa
are often large and conspicuous ; they are
supposed to be of use in cutting a way

Fig. 1373. An egg ring of PAryganea. OUt of the larVal CaSC.

The eggs of caddisflies are laid in
various ways and places. Some are dropped in the surface of
still pools while in flight, The females of some of the Hydro-

AQUATIC INSECTS 903

psychidae crawl beneath the water and spread their eggs in a
single layer over the lee side of stones in the gentler currents.
The big forms of Phryganea fasten their pretty green eggs in
a gelatinous ring (Fig. 1373) on the stem of some aquatic plant.

Aquatic Moths (Order Lepidoptera)

Of this great order of insects, only a few moths of the family
PyraHdae are aquatic. Many moths live as larvae on plants by the
waterside, and a few burrow in the tissues of submerged aquatic
plants, obtaining their air from the airspaces of the plant stems.
The aquatic caterpillars, like their terrestrial relatives, are distin-
guished from larvae of other orders by the possession of a brown
chitinous shield covering the prothoracic segment, by bristle-bear-
ing tubercles regularly disposed over the body and by fleshy grasp-
ing prolegs beneath the abdomen.

There are three types of aquatic larvae found commonly in our
fresh waters, two in ponds and one in rapid streams.

The larvae of Nymphula (Hydrocampa) are destitute of gills, and
greatly resemble pale terrestrial caterpillars. They live in flat
cases composed of two pieces cut out from green leaves of river-
weed or water-lily, and fastened together and lined with silk.
They live near the surface of the water. During the pupal stage
the cases are often found floating. The eggs are laid on or under
floating leaves.

The larvae of Paraponyx are provided with abundant branching
gills, which surround the body Hke a white fringe. These larvae live
in similar cases or between leaves in sheltering crevices that are
lined with silk.

The larvae of Elophila fulicalis, as recently described by Lloyd
from Ithaca, N. Y., live on the stones in rapid streams, protected
by an irregular shelter of thin-spun silk. They are in form strongly
depressed, and have unbranched gills arranged in two longitudinal
lateral rows. They feed mainly on such green algae as grow near
at hand. Each larva when grown fashions a broadly dome-shaped
pupal shelter or half-cocoon under some portion of the larval
shelter, with a row of marginal openings at either side to permit
free circulation of water and air through it.

904

FRESH-WATER BIOLOGY

Beetles {Order Coleoptera)

Of this great group of insects only a few families are wholly
aquatic, and a few others are partially so. The order as a whole is
predominantly terrestrial, and the aquatic families show unmistak-
able signs of having been developed from terrestrial ancestors.
All the adults and pupae are strictly terrestrial in their mode of
respiration, and nearly all the larvae likewise get their air supply
from above the surface of the water. The pupae of all are formed
either on land, or in direct communication with the air. The
families that are strictly aquatic are the Dytiscidae, HalipHdae,
Parnidae and Amphizoidae; those that show complete intergrada-
tion in habits are the Hydrophilidae and Dascyllidae. The Chrys-
omehdae are scarcely to be called aquatic at all in any proper
sense, although two of the subfamilies live on water plants.

There is such great diversity of habits and structure in water
beetles that the families may be best considered separately. We
begin with those that are least aquatic in habit.

Two small groups of leaf beetles of the great family ChrysomeHdae
feed upon water plants; the Galerucellinae, upon the floating leaves
of members of the water-Hly family. These dingy little beetles
lay their yellow eggs in small clusters on the upper surfaces of the
leaves, and the black-banded larvae, hatchmg therefrom, feed upon
the tissues, quite as their more famihar relatives feed upon land
plants. The other subfamily, the Donaciinae, or long-horned leaf-
beetles, is much more interesting. The larvae feed upon the roots
of aquatic plants, far beneath the surface of the water. They are
provided with a pair of spiracles near the end of the body and
these spiracles are armed with sharp corneous processes, capable
of being thrust into plant stems, of reaching the air spaces on the
inside, and of obtaining the air, rich in oxygen, contained therein.
Thus the larvae, while destitute of gills, and strictly air breathers,
get their air supply through the medium of the plants, while Hving
always beneath the water. The pupal stage likewise is passed
in the place where the larva lived on the roots, but the pupa is
inclosed in a water-tight cocoon, attached to the plant tissue and
containing air in free communication with that in the air spaces of

AQUATIC INSECTS 905

the plant. The adult beetles spend their lives among the leaves
of the plants, flying actively about when disturbed. They are of
shining, metaUic coloration, blue or green. Those that Uve on water
lilies deposit their eggs through holes eaten in the leaves, arranging
them in a curve around the opening on the under side. They are able
to place them thus through the possession of a long extensile
ovipositor.

The family Hydrophilidae is in part terrestrial and in part aquatic,
and the aquatic members show all degrees of adaptation to water
life. A few of the larger forms are expert swimmers, but many of
the smaller ones are fitted only for dabbling around in the mud at
the water's edge. The best-known member of the family is perhaps
the big black Hydrophilus, with finely fringed swimming legs and
with keeled sternum. It is attracted to electric lights in vast
numbers in the spring, where it falls beneath them and flounders
around in the dust of the street, giving a fine illustration of the use-
lessness of its specialization when in an unsuitable environment.
The larva of this beetle is commonly taken in ponds, not swimming,
but clinging to stems at the surface, its squat, hairy body not well
fitted for getting through the water, but with immense rapacious
jaws, very capable of seizing large Mayfly nymphs and adult Eu-
hranchipus when these swim within reach. Another hydrophilid
which often swarms into trap lanterns set over streams is Berosus,
whose aquatic larva is provided with lateral paired abdominal ap-
pendages somewhat like those of the neuropterous genus Sialis.

The eggs of Hydrophilus are laid in a white membranous capsule
attached to plant stems and leaves at the surface of the water.

The Amphizoidae and Parnidae are found as adult beetles clinging
to logs and stones in clear flowing streams. The former family
contains but a few far western species; the latter is widely dis-
tributed, and contains numerous genera and species. The name
''Riffle beetles" is applied to them to indicate the seat of their
greatest abundance. They are mostly of small size and their
coloration is usually inconspicuous, although some of them are
striped with red or yellow. The adults sun themselves on the
stones that protrude from the water, and fly readily from one rest-
ing place to another. Many of the larvae, especially the larger

9o6 FRESH-WATER BIOLOGY

ones, are strongly depressed in form, and have flaring lateral mar-
gins to the body segments that fit down closely against a stone,
limpet-like, to withstand the wash of the current; hence, these
are able to maintain a footing in the swiftest waters. The common
''water penny," the larva of Psephenus lecontei, illustrates the
extreme of flattening; this larva has developed abundant tracheal
gills from the thin membrane between the body segments, and these
are completely covered over by the projecting lateral margins of
the body segments. The adult female Psephenus crawls down on
the lee side of a stone and deposits her yellow eggs in broad one-
layered patches on its surface.

The Gyrinidae or whirligig beetles constitute a small group of
strictly aquatic forms, very peculiar in structure and habits. They
are well known to every one as shining black beetles of oval form,
that gather in companies upon the surface of brooks and ponds and
glide about in irregular curves with a speed which the eye can hardly
follow. When captured they exude a whitish repugnatorial fluid,
having a rather disagreeable odor. They hibernate as adult
beetles in the mud and in their season of activity they spend much
time beneath the water, in which they can dive and swim dextrously.
Their fore feet bear hooked claws with which they can cling to the
bottom when desiring to remain beneath the surface. They are at
once distinguishable from other water beetles by the unusual
brevity and peculiar formation of the hind legs, and by the
possession of divided eyes, there appearing to be one pair above
for vision of objects in air when the beetle lies on the surface, and
one below, presumably, for seeing things in the water.

The larva of the gyrinids is elongate and slender, and possesses
at the tip of the abdomen two pairs of backwardly directed grap-
pling hooks, and long slender paired filaments arranged segmen tally
along its sides somewhat like those of the Neuropterous genus
Sialis. Both larvae and adults are carnivorous. The larvae possess
long perforate sickle-shaped mandibles well adapted for punctur-
ing the skins of soft midge or other dipterous larvae, etc., and for
sucking out the fluid content of their bodies. The pupae of the
Gyrinidae are formed in thin cocoons attached to the side of verti-
cal plant stems above the water.

AQUATIC INSECTS 907

The little family of Haliplidae contains two genera of pretty little
beetles of brown color spotted with yellow, Ilaliplus and Peltody-
tes. These are easily distinguished from other beetles by the
sternal plates that broadly overlap the bases of the hind legs.
These beetles abound amid thick shore vegetation, and
their larvae adhere very closely to the trash, and are
most commonly found in floating mats of Spirogyra and
other filamentous algae. They are among the most
inactive of creatures, and in coloration and in form
show a high degree of protective resemblance. They
are easier overlooked than discovered even by the
collector searching for them. The stick-like larva of
Haliplus is shown in Fig. 1374; Peltodytes is strikingly
different superficially, being covered all over its body
by very long jointed slender bristle-like processes. //^^
Matheson has recently shown that the larvae feed upon
filamentous algae, sucking out the contents of the cells, |^ ^^J^|
one by one, and that the eggs are deposited by the
adult beetles within the coarser algal filaments.

The dominant family of water beetles is the Dytiscidae,
commonly known as diving beetles. These abound in
all fresh-water ponds. All are aquatic in both larval
and adult stages, but all take air at the surface of the
water, with the exception of some of the smaller larvae
which seem to be able to absorb their oxygen from the
water without having developed any special apparatus
therefor. All are carnivorous, and in all the pupa is
formed on shore.

In fitness for swimming, the adult beetles differ
greatly. Some of the larger forms like Cyhister are
possessed of loner oar-Hke hind lesrs provided \vith close- larva of 'naii-

, . . plus. (Drawn

set swimmmg frmges, and the long regular synchronous W Miss Edna
strokes of the legs drive the body forward with great
ease and swiftness; whereas, some of the lesser and more general-
ized forms, like Bidessus, with scanty swimming fringes, and with
legs otherwise Kttle modified, either in structure or in movement,
from what is useful in walking, swim very poorly. These do more

9o8

FRESH-WATER BIOLOGY

climbing than swimming, and, consequently, they keep nearer to
shore and to the shelter of submerged trash. In an aquarium

beetles of the size of Coptotomus
and Laccophilus may be seen feed-
ing in groups on the bodies of
dragonfly nymphs and tadpoles much
larger than themselves, which they
have overpowered. Their own exceed-
ingly hard chitinous armor doubtless
protects them from being eaten by
the majority of aquatic carnivorous
% animals.

Egg-laying appears to have been
observed hitherto only in DytiscuSy
which deposits its eggs singly in
punctures made in the green stems
of aquatic plants.
The larvae are voracious creatures, armed with long sickle-
shaped mandibles, like those of the larvae of the families just men-
tioned, each mandible with so deep a groove on the inner side that
it amounts to a perforation opening at the tip and the base. The

Fig. 1375. A predaceous diving beetle,
Dyiiscus.

Fig. 1376. Side view of the head of the larva and pupa of the diving beetle, Eydroporus.
(Drawings by Mrs. Helen Williamson Lyman.)

basal aperture Hes just within the mouth- opening when the tips of
the mandible are brought together. Nearly all the larvae of this
group capture only living prey, but a few like Eydroporus (Fig.
1376) will eat pieces of animals that have been killed for them.

AQUATIC INSECTS 909

Many of the largest larvae are fiercely cannibalistic and will eat
their brethren even when other food offers.

Some of the larvae are provided with swimming fringes on the
legs, some have them on the tail, and many have them in both
places. Some, like the larvae of Acilius, are exceedingly lithe and
graceful creatures. Others (Fig. 1377) scarcely swim at all, but
creep about among the trash at the shore line.

Fig. 1377. The larva of Coptolomus inlerrogatus.

In the present state of our knowledge, it is not possible to give
keys that will determine genera of Dytiscid larvae, and the best
means of identifying native larvae is by comparison with the beau-
tiful figures of Schiodte, who long ago (1861) described the European
representatives of many of our genera.

The Two-winged Flies {Order Diptera)

Of this immense order a considerable portion has taken to a
more or less aquatic life. A majority of the families have some
members that develop in the water, but only a few of the smaller
families are wholly aquatic. Those best fitted for hfe in the water
show adaptations of the most diverse sorts, so that here again the
families are best considered separately.

Since nearly all the families of the Diptera have some aquatic
members, the determination of the adult flies must be left to the aid
of the keys in the entomological manuals that are everywhere avail-
able. Each of these families has a characteristic type of wing ven-
ation, and some aid may be had from comparison with the typical
wings shown in Fig. 1378.

It is quite impossible in the space at command to give keys
to the genera of Dipterous families, these being very numerous

gio

FRESH-WATER BIOLOGY

Fig. 1378. Typical wing venation in the aquatic families of the Diptera.

a, Psychoclidae Moth flies h, Tabanidae Horse-flies

b, Tipulidae Crane-flies , i, Stratiomyidae Soldier flies

c, Blephoceridae Net-winged midges

d, Dixidae

e, Culicidae

/, Chironomidae
g, Simuliidae

Dixa-midges
Mosquitoes
Midges
Black-flies

j, Leptidae Snipe-flies

k, Dolichopodidae Dolichopods

I, Fmpididae The empids

m, Syrphidae Syrphus flies

M, Muscidae (5, lat.)

in the Chironomidae, Tipulidae, etc., or even to enter into detailed
statements as to their habits. A few of the families are compara-
tively small and unimportant. The moth flies (Psychodidae) are
very minute, being among the smallest of flies, and live as larvae

AQUAT C INSECTS

911

in the scum and about the edges of all sorts of fresh water,
while their adults swarm in thickets about the shores of pools. The
Ptychopteridae inhabit swales, their larvae living in the rotting trash
at the edge of the water, and the adults fluttering about the tops
of the adjacent herbage. The dixa midges (Dixidae) inhabit spring
brooks and clear pools, and their larvae (Fig. 1379), with bodies
bent double, slide out upon the surfaces
of wet leaves and stones, or edge off into
the water and whirl about in short curves ;
the adults dance in companies above the
surface of the water. Some larvae of the
Rhyphidae Kkewise inhabit pools, and the
adults sometimes assemble and dance in
the shelter of forest trees at some dis-
tance from the water. The few known
aquatic members of the Leptidae live as
larvae in streams and cHng with the well-
developed claws of their stout muscular
abdominal prolegs to the surfaces of
stones; the adults flit about the shore,
displaying their unusually gaudy colors
and velvety textures. These are small and comparatively un-
important families.

Then there are a few large families of which but a small proportion
of the members are adapted to aquatic life. The crane-flies (Tipu-
lidae) are essentially terrestrial: most of them live in moist earth or
wet leaves. Some are strictly amphibious, like Epiphragjna (Figs.
1380 and 138 1). They possess as larvae the usual terminal spira-
cles for breathing air, but have these set upon a respiratory disc
that can be closed by folding together on the middle line, and they
have a bundle of four anal gills that may then be protruded for
use under water. There is a fine development of fringes about the
respiratory disc of other species, and these fringes spread out upon
the surface film, holding the spiracles up to the air, while the larvae
are moving about in the water below. A few only of the syrphus
flies (Syrphidae) are aquatic, but the larvae of certain of these, the
common ^'rat-tailed maggots" are most pecuhar and interest-

Fio. i,:!79. Larva (R) and pupa (5) of
the dixa-midge. (After Johannsen.)

912

FRESH-WATER BIOLOGY

ing. A very ordinary sort of white fleshy legless fly larva has
the supporting base of the terminal spiracles drawn out into a flexu-
ous slender tube, as long as or longer than the body. The larva
Kves in the mud in shoal water, and with this tube reaches up to
the surface for air. A good many aquatic forms are included among

Fig. 1380. The CTane-&y Epiphragma/ascipemus,
adult female.

Fig. 1381. Epiphragma: a,\a.Tva.; b,
end of larva from above; c, pupa.

the host of higher diptera that are here dismissed as Muscidae
in the broad sense, but the larvae of these (Fig. 1382) differ from
their terrestrial relatives by characters of less moment than those
just mentioned.

A few small families are most interesting for their fitness for
special places in the water, both larval and pupal stages being
passed in similar situations. The net-winged midges (Blepharo-

AQUATIC INSFXTS 913

ceridae) live in rapid streams, and are peculiar in the very strongly
depressed form of both larva and pupa, and in the row of ventral
sucking discs which the larva has developed for hanging fast.

The black-flies (Simuliidae) also live in running water. The
larvae adhere to stones and timbers by a single sucking disc at
the hinder end of the flask-shaped body, which thus hangs sway-
ing in the current with head downstream.
Above the mouth on the front of the head
there are two processes which bear the name
of '^fans." These are composed of a very
large number of scythe-shaped rays fringed
along the side. Set at an angle upon the
pedicel, like the fingers of a reaper's cradle
upon the handle, together these constitute -^

a net for retaining small organisms adrift ^Ton^disc I?Vs™k-fl '^trA'-a'
in the water, and for holding them up to ^'^p^'^o''-
the mouth. This is an aboriginal plankton apparatus. Simulium
larvae play in the rapids, spinning silken threads in the water, and
swinging on them from place to place. Occasionally the threads
thus spun in the troughs of fish hatcheries have been sufficiently
numerous to entangle and kill newly hatched trout. These threads
are spun from the salivary glands; a final use for the secretion of
these glands is the making of the open-meshed half-cornucopia-
shaped cocoon in which, attached to the sides of the rocks or tim-
bers, the pupal stage is passed; a branched prolongation of the
tracheal lining of the prothoracic spiracles constitutes the so-called
*'tube gills," by means of which the black-fly pupa is able to
get its air supply while wholly submerged.

The soldier flies (Stratiomyiidae) live as larvae on the surface of
still water. They float stiff and rigid and stick-like, with a circlet
of water-repellent bristles surrounding the terminal spiracles, keep-
ing open the way to the air. The pupa is formed within the
larval skin, without further outward indication of the change than
a slight angulation of the latter posteriorly. The adult soldier
flies hover familiarly about the arrow heads on shore at egg-
laying time, and at other times frequent flowers to feed on their
nectar.

914

FRESH-WATER BIOLOGY

There remain three large families of the diptera of very great im-
portance. Two of these, the Culicidae and the Tabanidae, are impor-
tant because of the damage they do, and the other, the Chironomidae,
because of the food it furnishes to fishes. The mosquitoes (Culi-
cidae), since the discovery of their importance to man as agents
for the dissemination of the germs of malarial and other fevers,
have suddenly become well known. A number of good books are
now available containing descriptions, figures, and detailed accounts
of the habits and Hfe histories of the economic species. Some of
the most interesting members of the family are not included in these
books among the pests, since the adults do not bite. Corethra^
whose phantom larvae are a part of the plankton, is one of these,
and Pelorempis, the large culicid inhabitant of cold springs is
another.

The biting adults of the large horse-flies (Tabanidae) are like-
wise serious pests of the domesticated animals. Their naked

Fig. 1383. The speckled midge, Tanypus carneus, male.

translucent larvae, tapering to either end and ringed with fleshy
tubercles, are carnivorous, and are found in the trash of the
bottom in all shoal fresh waters. But two genera, Tahanus and
Chrysops, are of much importance in our fauna.

The midges (Chironomidae, Fig. 1383) constitute undoubtedly

AQUATIC INSECTS

915

the largest single complex of aquatic Diptera. They are a host;
indeed, the typical genus Chironomus is a host in itself. Their
larvae (Fig. 1384), with no better apparatus than a few blood gills
at the end of the abdomen, and their pupae, with nothing better
than ''tube gills" protruded from the prothoracic spiracles, are

Fig. 1384. The larva of Chironomus. (After Johannsen.)

able to live in all waters, from springs to stagnant pools and from
rills to deep lake bottoms. They are chiefly herbivorous and are
of very great importance in furnishing the food of a multitude of
the larger animals, including fishes. The larvae construct for

Fig. 1385. Dwelling-tubes of midge larvae {Chironomus) from the lake bottom.
(Photograph by T. L, Hankinson.)

themselves some sort of shelter, fastening the materials their envi-
ronment offers together with the silk-like secretion of their salivary
glands; some in rapid streams build cases on the stones; others,
on the lake bottom, build soft flocculent tubes of silt (Fig. 1385).

9i6

FRESH-WATER BIOLOGY

These latter larvae are red in color and are known as ■' blood worms."
The color is due to haemoglobin in the blood plasma; the capacity
of this substance for oxygen gathering seems to enable these blood
worms to live in water that is poor in oxygen.

In the preceding pages the principal groups of aquatic insects
are briefly characterized, and typical forms are figured. Hints are
given for the recognition of the nymphs of Plecoptera on page 885,
and of the larvae of aquatic Lepidoptera on page 903 . In the fol-
lowing pages keys are given for determining the adults of Trichop-
tera and Hemiptera, and for both adults and immature stages of
the other orders. An understanding of the venation of the wings
is essential to the study of adult insects of most orders, and the
following figure (Fig. 1386) is given to illustrate the wing venation
and explain the terminology used.

Fig. 1386. The venation of the wings of a stonefly, Chloroperla. The designation of veins is given
here for all succeeding wing figures:

C, Costa M, Media

Sc, Subcosta Cm, Cubitus

R, Radius A, Anal veins.

The radius has a main stem (Ri) and a principal branch {Rs) on the posterior side.
Media is often twice forked, and Cubitus once forked; the recognizable branches are numbered from
front to rear: three anal veins are likewise recognized.

AQUATIC INSECTS 917

KEY TO THE ORDERS OF AQUATIC INSECT LARVAE

1 (8) Larvae with wings developing externally (called nymphs in this chapter)

and no quiescent pupal stage 2

2 (7) With biting mouth parts 3

3 (6) With long, lilamentous caudal setae; labium not longer than the head,

and not folded on itself like a hinge 4

4 (5) Gills mainly under the thorax; tarsal claws two; caudal setae two.

(Stoneflies; see page 883) . . . Plecoptera.

5 (4) Gills mainly on the sides of the abdomen; tarsal claws single; caudal

setae generally three. (Mayflies ; see page 921).. Ephemerida.

6 (3) Caudal setae represented by three broad, leaf-Uke respiratory plates

traversed by tracheae, or by small spinous appendages; labium
when extended much longer than the head; at rest, folded
like a hinge, extending between the bases of the fore legs.
(Dragonflies and damselflies; see page 928) . . Odonata.

7 (2) Mouth parts combined into a jointed beak, which is directed beneath

the head backward between the fore legs.

(Bugs; see page 933) . . . Hemiptera.

8 (i) Larvae proper, with wings developing internally, and invisible till the

assumption of a quiescent pupal stage 9

9 (18) With jointed thoracic legs 10

10 (11) With slender, decurved, piercing mouth parts, half as long as the

body; small larvae, Hving on fresh- water sponges.
Family Hemerobiidae (see page 934) of . . Neuroptera.

11 10) With biting mouth parts 12

12 (15) With a pair of prolegs on the last segment only (except in Sialis,

Fig. 1367, which has a single long median tail-like process at
the end of the abdomen) these directed backward, and
armed each with one or two strong hooks or claws. . . 13

13 (14) Abdominal segments each with a pair of long, lateral filaments.

Family Sialididae (see page 935) of . . Neuroptera.

14 (13) Abdominal segments without long, muscular, lateral filaments, often

with minute gill filaments cylindric larvae, generally living
in portable cases. (Caddisflies; see page 936). . Trichoptera.

15 (12) Prolegs, when present, on more than one abdominal segment; if

present on the last segment, then not armed with single or
double claws (except in gyrinid beetle larvae, which have
paired lateral abdominal filaments), often entirely want-
ing 16

16 (17) With five pairs of prolegs, and with no spiracles at the apex of the

abdomen. . . (Moths; see page 903) . . Lepidoptera.

17 (16) Generally without prolegs; never with five pairs of them; usually

with terminal spiracles; long, lateral filaments often present

on the abdominal segments.

(Beetles, adults; see p. 937 ; larvae; see p. 943) . Coleoptera.

18 (9) Without jointed thoracic legs; with abdominal prolegs, or entirely

legless (Flies, etc. ; see page 943) . . Diptera.

9l8 FRESH-WATER BIOLOGY

KEY TO NORTH AMERICAN MAYFLIES
Imagos

1 (13) The cubital and first anal veins strongly divergent at the base (Fig.

1387). Venation never greatly reduced 2

2 (3) The posterior fork of the median vein very deep, almost reaching the

wing base; two long simple intercalaries between the first
and second anal veins Campsurus.

3 (2) The posterior fork of the median vein (M3-M4) forked for not more than

three-fourths of its length 4

Fig. 1387. The wings of Ephemera. (Drawn by Dr. Anna H. Morgan.)

4 (5) Between the first and second anal veins is a bunch of three or four long

straight intercalaries, conjoined basally before their attach-
ment to the principal veins; the second anal vein nearly
straight and unbranched Polymitarcys.

5 (4; Between the first and second anal veins are only shorter, sinuate, and

sometimes forking intercalaries, attached directly to the
first anal; the second anal vein sinuate and often branched
(Fig. 1387) 6

6 (7) The posterior fork of the median vein forked two- thirds to three-fourths

its length; vein Cu2 not more strongly bent at base than
the first anal Euthyplocia.

7 (6) This fork of the median vein occupying not more than half its length;

vein Cu2 more strongly bent at base than is the first anal
(Fig. 1387) 8

8 (12) The third anal vein simple, but attached to the hind margin by a

number of cross veins; in the narrow posterior fork of the
median vein there are one or more cross veins before the origin
of the intercalary; male forceps four-jointed 9

9 (10, 11) Caudal setae three in both male and female; fore tarsus of female

imago three-fourths as long as the tibia. . . . Ephemera.

10 (9, 11) Caudal setae two in the male and three in the female; fore tarsus

of the female two-thirds as long as the tibia. . Pentagenia.

11 (9, 10) Caudal setae two in male and female; fore tarsus of female as long

as the tibia Hexagenia.

AQUATIC INSECTS

919

12 (8) The third anal vein with a simple terminal fork and unattached to the

hind margin, although a few isolated short intercalaries
lie between; in the wider posterior fork of the median vein
there is no cross vein before the origin of the intercalary;
male forceps three-jointed Potamanthiis.

13 (i) The cubital and first anal veins parallel at base (in a few forms with

reduced and scanty venation, appearing a little diverg-
ent) j^

14 (15) Hind tarsi with five freely movable segments; eyes of the male simple

and remote; venation never greatly reduced; intercalary
veins between the first and second anal veins unattached
basally and in two pairs, of which the pair nearer the hind
angle is the longer Heptagenia.

15 (14) Hind tarsi usually with but four freely movable segments, the basal

segment being more or less completely consolidated with the
tibia; eyes of the male enlarged, often approximated on the
dorsal side and divided into superior and lateral portions
with corneal facets of different size; venation various,
sometimes greatly reduced; intercalary veins between the
first and second anal never as above 16

16 (17) The three anal veins nearly parallel to the hind margin of the wing

and to each other, ending in the outer margin; in the hind
wing the branches of the radial vein are strongly unilateral
on the anterior side Bactisca.

17 (16) Anal veins strongly divergent distally, usually both the second and

the third ending in the hind margin; forks of the radial vein
in the hind wing more symmetrical 18

18 (39) The posterior division of the median vein with a normal posterior

fork; hind wings, when present, usually but Uttle longer
than broad and with a copious venation 19

19 (32) The intercalaries between the first and second anal veins variable,

but usually more or less independent, and not directly
dependent from the first anal; three well-developed caudal

setae (except in Blasturus, in our fauna) 20

20(31) Hind wings present 21

21 (28) Bisector of the posterior fork of the median vein and bisector of the

cubital fork unattached basally; between the latter and
vein Cu2 no intercalaries; vein Cu2 in the hind wing rarely
preserved; caudal setae generally much longer than the
body; penultimate segment of the male forceps shorter
than the antepenultimate 22

22 (27) In the hind wing the subcostal vein reaches nearly to the wing apex;

male forceps three-jointed 23

23 (26) Hind wing with a slight concavity at the middle of costal margin;

five to six longitudinal veins between Mi and Mo; vcinlets
numerous about the wing margins and cross veins numerous
in the hind wings 24

24 (25) Third anal vein of the hind wing wanting; caudal setae of about

equal length Leptophlehia,

920

FRESH-WATER BIOLOGY

25 (24) Third anal vein of the hind wing present, and often followed by one

or two additional intercalaries; median caudal seta dis-
tinctly shorter than the others Blasturus.

26 (23) Hind wing with an angular lobe projecting forward from the middle

of the costal margin; four longitudinal veins between Mi and
M2; wing margins free from veinlets, and few cross veins in
hind wing Habrophlebia.

27 (22) In the hind wing the subcostal vein terminates in the costa at hardly

more than half the length of the wing, just beyond the
obtuse angulation having a thickened margin; forceps of
male more or less distinctly four-jointed. . . Choroterpes.

28 (21) Bisectors of the posterior fork of the median vein and of the cubital

fork both tending to attach themselves to the posterior
branch of their respective forks; between the latter and vein
Cu2 are generally some short intercalaries (the cubital region
thus being better developed than in group 21); caudal setae
about as long as the body; penultimate segment of the male
forceps longer than the antepenultimate 29

29 (30) Veins Cu2 and ist A separate to base Ephemerella.

30 (29) Veins Cu2 and ist A fused toward the base Drunella.

31 (20) Hind wings absent Caenis.

32 (19) The intercalaries between the first and second anal veins represented

by a series of veinlets, often sinuous or forking, extending
directly from the first anal to the wing margin; costal
angulation of hind wing close to the base; but two well-
developed caudal setae, the median one being rudimentary
or wanting; basal joint of hind tarsi evident but not well
developed 33

33 (36) Median caudal seta a distinctly segmented rudiment (Fig. 1354); for-

ceps of male three- jointed; posterior prolongation of sternum
of ninth segment of abdomen of female bifid at tip. . . 34

34 (35) Basal segment of fore tarsus of male shortest; claws of each tarsus

unhke each to each; hind wing with the costal angulation
acute, and the posterior fork of the median vein occupying
two- thirds the length of that vein Colohurus.

35 (34) Basal segment of fore tarsus of the male longest; claws of each

tarsus alike; hind wing with the costal angulation obtuse,
and the posterior division of the median vein forked through
one-third its length Chirotonetes.

36 (33) Median caudal seta more rudimentary or wanting; forceps of the

male distinctly four-jointed; posterior prolongation of the
sternum of the ninth abdominal segment in the female entire
at tip 37

37 (38) Claws of each tarsus alike; caudal setae at least one-half longer than

the body Siphlurus.

38 (37) Claws of each tarsus unlike; caudal setae about as long as the body

in both sexes Ameletus.

39 (18) Posterior fork of the median vein apparently simple, M4 being de-

tached and appearing as an intercalary; hind wings when
present at least twice as long as wide, and provided with
but 1-3 longitudinal veins 40

AQUATIC INSECTS 921

40 (45) Hind wings present 41

41 (42) Fore wings with numerous costal cross veins before the bulla; hind

wings with a moderate number of cross veins . . Callibactis.

42 (41) Fore wings without costal cross veins before the bulla; hind wings

without cross veins or with but 1-3 of them 43

43 (44) Marginal intercalary veinlets in pairs; hind wings oblong, with a

short costal angulation Bactis.

44 (43) Marginal intercalary veinlets of the fore wing single; hind wings

linear, with a spur-like costal angulation . . Centroptilum.

45 (40) Hind wings absent Clocon.

Nymphs

1 (11) Mandibles with an external tusk-like ramus, visible from above; gills

on abdominal segments 1-7 (often rudimentary on i),
double, flattened, linear, the margins fringed with respira-
tory filaments 2

2 (9, 10) Mandibular tusks longer than the head (burrowing species) . . 3

3 (6) With no frontal prominence 4

4 (5) Legs increasing in length posteriorly; gills of the first abdominal seg-

ment simple; lab rum longer than wide; maxillary palpus
two-jointed Polymitarcys.

5 (4) Legs decreasing in length posteriorly; lab rum wider than long; maxil-

lary palpus three- jointed Euthyplocia.

6 (3) With a conspicuous frontal prominence 7

7 (8) Frontal prominence rounded Hexagenia.

8 (7) Frontal prominence bifid at tip Ephemera.

9 (2, 10) Mandibular tusks shorter than the head, inconspicuous, only their

tips visible from above Potamanthus.

10 (2, 9) Unknown Campsurus and Pentagenia.

11 (i) Mandibles without projecting tusk-like ramus; gills not as in i. 12
12(13) Eyes dorsal; body strongly depressed; tarsal claws with lateral teeth;

dwellers in rapid streams and on wave-beaten shores adapted
to clinging to flat surfaces of rocks, timbers, etc.

Heptagenia.

13 (12) Eyes lateral; claws smooth or toothed below 14

14 (15) Gills completely concealed under an enormously enlarged, four-

spined dorsal thoracic shield Baetisca.

15 (14) Gills exposed; thoracic dorsum normal 16

16 (31) Outer caudal setae fringed on both sides 17

17 (24) Gills on abdominal segments 1-7 double 18

18 (21) Gills filamentous 19

19 (20) Each a pair of simple filaments Leptophlchia.

20 (19) Each a pair of clusters of slenderer filaments. . . . Hahrophlchia.
21(18) Gills lamelliform, at least on the middle segments 22

22 (23) Lamellae of each gill similar Blast urns.

23 (22) Lamellae of each gill markedly dififering in form at tip. Choroterpes,

92:

FRESH-WATER BIOLOGY

24 (17) Gills absent from one or more of segments 1-7; one pair more or less

elytroid, covering those behind it 25

25 (28) Gills present on the seventh abdominal segment, elytroid on the third

or fourth segment; a pair of tubercles on the apical margin
of each segment beside the middorsal line 26

26 (27) Head smooth above Ephemerella.

27 (26) Head armed above with a pair of erect occipital tubercles. Drunella.

28 (25) Gills absent from the seventh abdominal segment, elytroid on the

second segment; no dorsal abdominal tubercles. ... 29

29 (30) Elytroid gill cover subquadrate Caenis.

30 (29) Elytroid gill cover subtriangular Tricorythus.

31 (16) Outer caudal setae fringed only on the inner side 32

32 (37) Posterolateral angles of the hinder abdominal segments prolonged

into thin, flat, sharp lateral spines 33

33 (34) Fore legs conspicuously fringed with long hairs; gill tufts present

upon the base of maxillae and front coxae and at bases of

lamellae on abdomen Chirotonetes.

Fore legs without conspicuous fringes; no maxillary or coxal gills;

no gill tufts at base of lamellae on abdomen 35

Gills double on the basal abdominal segments; end of maxilla fringed

with simple hairs Siphlurus.

Gill lamellae all single; end of maxilla fringed with pectinated hooks.

Ameletus.

Posterolateral angles of the hinder abdominal segments hardly more
than acute — not prolonged in thin flat lateral spines. . 38

Gill lamellae simple 39

Lamellae obtuse at apex; maxillary palpus rounded at the apex.

Baetis.

Lamellae acute at apex; end of maxillary palpus truncated.

Centroptilum.

Gill lamellae double, at least on some of the anterior abdominal
segments 42

Antennae shorter than the body; tracheae of gill lamellae pinnately
branched Callibaetis.

Antennae longer than the body; tracheae of gill lamellae palmately
branched Cloeon.

KEY TO NORTH AMERICAN DRAGONFLIES

Imagos

1 (21) Fore and hind wings similar, usually held verticaUy in repose (damsel-

flies) Suborder Zygoptera . . 2

2 (5) Quadrangle (Fig. 1388) of the wings divided by a number of cross veins;

antenodal cross veins numerous; pterostigma lacking a
special brace vein; wings rather broad 3

3 (4) Basal space (space before the arculus) in all wings free from cross veins.

Calopteryx.

34 (33)

35 (36)

36 (35)

37 (32)

38 (41)

39 (40)

40 (39)

41 (38)

42 (43)

43 (42)

AQUATIC INSECTS 923

4 (3) Basal space of all wings traversed by cross veins Hetacrina.

5 (2) Quadrangle without cross veins; antenodal cross veins but two in each

wing; pterostigma with a brace vein at its proximal end in
the space behind vein Ri; wings narrower 6

6 (9) Vein M3 arising (i.e., separating from vein M1+..) nearer the arculus

than the nodus 7

Fig. 1388. Wing venation in the Odonata: (a) a drs.gon?^y, Cordulef^aster. (b) a damselfly, Argia;
(c) the region of the stigma, st, with its brace vein, 2, ar, arculus; al, anal loop; br, bridge; n, nodus;
o, oblique vein; t, triangle; /', subtriangle; g, quadrangle; sq, subquadrangle; v, basal subcostal cross
veins; z, veins as in Fig. 1386.

7 (8) Vein M2 separating from vein Mi at a distance of several cells beyond

the subnodal cross vein Lcstes.

8 (7) Vein M2 separating from vein Mi close to the subnodal cross vein, less

than the distance of one cell beyond it. Archilestes.

9 (6) Vein M3 arising nearer the nodus than the arculus 10

10 (11) Spines on the tibiae very long, twice as long as the intervals between

them Irgia.

11 (10) Spines of the tibiae hardly longer than the intervals between them. 1 2

12 (16) No pale postocular spots on the top of the head; sexes similarly

colored 13

13 (14, 15) Colors of dorsum blue and black; yellow beneath the thorax.

Chromagrion.

14 (13, 15) Colors of dorsum red and black; stout species. . Amphiagrion.

15 (13, 14) Dorsum bronzy green; slender species. . . . Nehallennia.

16(12) With round or ovoid postocular spots on the head 17

17 (18) Sexes with a general similarity in color, the female often of a lighter
shade; the superior abdominal appendages of the male
not strongly directed downward and inward. . . Enallagma.

924

FRESH-WATER BIOLOGY

1 8 (17) Sexes strikingly unlike in color; a bifid process arising from the

apical margin of the loth abdominal segment in the male
and the superior abdominal appendages strongly directed
downward and inward 19

19 (20) Males chiefly green and black, with normal rhomboidal stigma;

females with the orange of the abdomen covering something
less than the three basal segments (becoming wholly densely
pruinose with age) Ischnura.

20 (19) Males yellow or orange, with ovoid stigma which does not reach the

costal vein; females with the four basal segments of the
abdomen yellow or orange Anomalagrion.

21 (i) Fore and hind wings dissimilar, the latter broader at the base

(dragonflies proper) Suborder Anisoptera . . 22

22 (49) Triangle (Fig. 1388) about equally distant from arculus in fore and

hind wing; stigma with a brace vein at its inner end (except
in Cordulegaster) 23

23 (24) Stigma unbraced Cordulegaster.

24 (23) Stigma braced at its inner end against an inclined cross vein in the

space below it (Fig. 1362) 25

25 (36) Eyes widely separated on the top of the head 26

26 (27) Basal subcostal cross vein (Fig. 1388, h) present; a linear or spatulate,

median, sternal process on the first abdominal segment;
legs very short, the hind femora hardly reaching the apex
of the first abdominal segment Progomphus.

27 (26) Basal subcostal cross vein usually wanting; no median sternal

process on the first abdominal segment; legs longer, the
hind femora reaching or surpassing the middle of the second
abdominal segment 28

28 (31) Hind wings with a distinct anal loop (Fig. 1388, a) consisting of several

cells 29

29 (30) Anal loop normally consisting of three cells; first and fifth antenodal

cross veins matched in position and hyper trophied; stigma
broad with both sides convex; triangles not traversed by
cross veins Ophiogomphus.

30 (29) Anal loop consisting normally of four cells; first and seventh antenodal

cross veins matched in position and hj^Dertrophied; stigma
long and narrow with parallel sides; each triangle divided
by a cross vein Hagenius.

31 (28) Hind wings with no distinct anal loop, or with one consisting of a

single cell 32

32 (33) Triangle of the fore wing one- third shorter than that of the hind

wing; generally a single cell between the bases of veins A2
and A3 Lanthus.

33 (32) Triangle of the fore wing less than one-fourth shorter than that of the

hind wing; generally, two or more cells between A2 and A3
at their origin 34

34 (35) Hind femora naked, or with numerous short spines. . . Gomphus.

35 (34) Hind femora with five to seven long, strong spines. . Dromo gomphus.

AQUATIC INSECTS 925

36 (25) Eyes approximated on the top of the head 37

37(42) The radial sector (/?5, Fig. 1388, a) simple 38

38 (39) But two cubi to-anal cross veins; vein M. undulate; supratriangle

without cross veins; but one cross vein under the stigma.

Gomphacschna.

39 (38) With three or more cubito-anal cross veins; vein Mo not undulate;

supratriangle divided by cross veins; several cross veins
under the stigma 40

40 (41) Basal space traversed by cross veins Boyeria.

41 (40) Basal space open Basiaeschm.

42(37) Radial sector bearing an apical fork. 43

43 (48) Sectors of the arculus (veins Mi_3 and M4) separating from the

arculus at or below its middle 4_j.

44 (47) The radial sector symmetrically forked: between it and the supple-

mentary vein below it, one or two rows of cells 45

45 (46) Face strongly produced above, the upper margin of the frons very

acute; the veins Mi and Mo parallel to the level of the stigma;
radial sector and the supplementary vein below it separated
by a single row of cells Nasiaeschna.

46 (45) Face vertical, not sharply angulate at upper edge of frons; veins

Ml and M2 approximated at the stigma; the radial sector
and the supplementary vein below it separated by two rows
of cells Epiacschna.

47 (44) The radial sector strongly deflected toward the stigma at the base of

its fork, unsymmetric; between it and the supplementary
vein below it, three to seven rows of cells. . . . Aeschna.

48 (43) Sectors of the arculus springing from above the middle of the arcu-

lus Anax.

49 (22) Triangle in the hind wing much nearer the arculus than in the fore

wing; stigma without brace vein 50

50 (53) The triangle of the hind wing placed considerably beyond the arcu-

lus; the anal loop well developed and hardly longer than

broad; more than two cubito-anal cross veins.

51 (52) Dorsal surface of the head with the occiput larger than the vertex;

subtriangle of the fore wings usually divided by a cross vein;
four to six cross veins in the space above the bridge (Fig. 13 88) .

Didymops. ■

52 (51) Dorsal surface of the head with the occiput much smaller than the

vertex; subtriangle of the fore wings generally open; two
or three cross veins in the space above the bridge.

Macromia.

53 (50) The triangle of the hind wing retracted to the level of the arculus,

or even passing it a little sometimes; the anal loop, greatly
elongated (except in Nannothcmis) and becoming foot-
shaped; one or two cubito-anal cross veins 54

926 FRESH-WATER BIOLOGY

54 (67) Sectors of the arculus (veins Mi-g and M4) distinctly separate at their

departure from the arculus; anal loop elongate, but not
distinctly foot-shaped, the toe part being Httle or not at all
developed; the last antenodal cross vein extending from the
costal to the radial veins (except in D. lintneri, in which
it generally extends only from the costal to the subcostal);
colors often metallic blue or green on thorax and abdomen. 55

55 (56) Veins M4 and Cui in the fore wing parallel or a little divergent apically,

the number of rows of cells between them increasing toward
the margin of the wing Neurocordulia.

56 (55) Veins M4 and Cui in the fore wing approximated toward the margin

of the wing 57

57 (58) With large brown spots on all wings at nodus and apex.

Epicordulia.

58 (57) No brown spots at nodus and apex 59

59 (60) Four (rarely five) antenodal cross veins in the hind wing.

Tetragoneuria.

60 (59) Usually more than five antenodal cross veins in the hind wing. . 61

61 (62) Stigma very narrowly diamond-shaped, with the ends of it meeting

the sides by an angle of 30° to 35° Helocordulia.

62 (61) Stigma broader, less pointed 63

63 (64) Triangle of fore wings open Dorocordulia.

64 (63) Triangle of fore wings divided by a cross vein 65

65 (66) Inferior appendage at end of male abdomen bifurcated. Cordulia.

66 (65) Inferior appendage simple Somatochlora.

67 (54) The sectors of the arculus in close apposition or completely fused for

a little way beyond the arculus; anal loop generally dis-
tinctly foot-shaped, with well-developed ''toe"; the last
antenodal cross vein often discontinuous at the subcostal
vein 68

68 (69) Triangle of the fore wings four-sided; anal loop poorly developed, not

foot-shaped Nannothemis.

69 (68) Triangle of the fore wing fully differentiated, three-sided; anal loop

well developed and foot-shaped 70

70 (71) Triangle of the fore wing with its front and inner sides meeting by an

angle of about 100°; the subtriangle without cross veins;
the vein which bisects the anal loop straight. . . Perithemis.

71 (70) Triangle of the fore wing with its front and inner sides meeting by an

angle of about 90°; subtriangle divided into three or more
cells; bisector of the anal loop sinuous 72

72 (89) Triangle of the fore wing not placed distinctly beyond the level of the

apex of the triangle in the hind wing; pterostigma with its
ends parallel or not distinctly divergent. 73

73 (84) The sectors of the arculus (veins Mi-g and M4) in the fore wing more

or less completely fused for a short distance beyond the
arculus; the triangle of the fore wing not greatly produced
posteriorly, and (except in Celithemis) normally containing
but a single cross vein, and followed by two or three rows
of cells 74

AQUATIC INSECTS 927

74 (79) Vein Cui of the hind wing departing from the triangle at the hind

angle 75

75 (76) Sectors of the arculus (veins Mi_3 and M4) contiguous, but incom-

pletely fused for a distance beyond the arculus; wings
generally conspicuously spotted with yellow or reddish brown.

Celithemis.

76 (75) Sectors of the arculus in the hind wing distinctly fused for a distance

beyond the arculus 77

77 (78) Stigma short and thick, about twice as long as wide; anal loop with

a big heel, there being generally four cells between the bi-
sector and the heel point; face pure white. . . Leucorhinia.

78 (77) Stigma more than three times as long as wide; anal loop generally

with but two cells between the bisector and the heel point.

Sympelrum.

79 (74) Vein Cui of the hind wing migrated a httle way up the outer side of

the triangle, separating itself at a distance from the hind
angle 80

80 (81) With a single cross vein under the stigma, and a long vacant space

before that cross vein Pachydiplax.

81 (80) With two cross veins under the stigma and the adjacent spaces more

normal 82

82 (83) With a single row of cells between veins M2 and Rg. . . Mesothemis.
^7, (82) With two rows of cells for a distance between veins M2 and R^.

Micralhyria.

84 (73) Sectors of the arculus in the fore wing contiguous, but not completely

fused beyond the point of their departure from the arculus;
radial sector distinctly undulate (except in Ladona) ; triangle
of the fore wing very much elongated posteriorly and narrow
and generally traversed by two or more parallel cross veins,
and followed by three to seven rows of cells 85

85 (86) Vein Mia arising under the proximal fourth of the stigma; fore wings

with the subtriangle consisting of three cells, and the tri-
angle followed by three rows of cells Ladona.

86 (85) Vein M^ arising under the middle of the stigma; fore wings with the

subtriangle consisting of four to eleven cells, and the triangle
usually followed by four to six rows of cells 87

87 (88) Male with no ventral hooks on the first abdominal segment; female

with the hind tibia a little longer than the hind femur; the
sexes alike in wing patterno Libcllula.

88 (87) Male with a pair of ventral hooks on the first abdominal segment;

female with the hind femur and tibia of equal length; wings
dissimilarly colored in the two sexes Plathcmis.

89 (72) Triangle of the fore wing placed beyond the level of the apex of the

triangle of the hind wing; stigma with its inner end per-
pendicular, its outer end very oblique to the bordering veins;
wings broad at base and pointed at apex 90

90 (91) Radial sector regularly curved; hind wings with a broad, basal colored

band Tramea.

91 (90) Radial sector distinctly undulate; hind wings not covered at base by

a broad colored band Pantala.

928 FRESH-WATER BIOLOGY

Nymphs

1 (22) Three large leaf like respiratory plates at the apex of the slender abdo-

men, and with the body tapering posteriorly from the head
(damselflies) Suborder Zygoptera . . 2

2 (5) Basal segment of the antenna very large, as long as the other six to-

gether; median lobe of the labium with a very deep cleft;
gills thick, the lateral ones triquetral 3

3 (4) Median cleft of labium very deep, extending far beneath the level of the

base of the lateral lobes Calopteryx.

4 (3) Median cleft of the labium extending only to the level of the base of

the lateral lobes Hetaerina.

5 (2) Basal segment of antenna not longer than succeeding single segments;

labium with a very shallow closed median cleft or no cleft
at all; gills thin, lamelliform 6

6 (9) Median lobe of labium with a short, closed, median cleft; lateral lobe

trifid'at end; movable hook bearing raptorial setae; giUs
showing transverse segmentation 7

7 (8) Lateral lobe of the labium terminating in three teeth, between the

middle and external of which is situated a truncated and
serrated lobe Lestes.

8 (7) Three teeth only, terminating the lateral lobe of the labium, no trun-

cated and serrated lobe between them. . . . Archilestes.

9 (6) Median lobe of labium entire; lateral lobe bifid at end; hook naked;

gills various 10

10 (11) Labium with no raptorial setae on the mentum within; gills broad,

thick, dark colored, oval or oblong in shape and obtuse at
apex Argia.

11 (10) Labium with mental setae; gills thinner, more pointed and nar-

rower 12

12(15) Hind angles of the head strongly angulate 13

13 (14) Gills widest beyond the middle; body slender; head half as long as

wide Chromagrion.

14 (13) Gills widest across the middle; body stouter; head nearly as long as

wide Amphiagrion.

15(12) Hind angles of the head rounded 16

16 (17) Labium with one mental seta (and a rudimentary second one) each

side; antennae six- join ted; lateral lobe of the labium with
the distal end above the end hook hardly denticulated.

Nehallennia.

17 (16) Labium with three to five mental setae each side (one may be smaller

than the others), and end of lateral lobe denticulated dis-
tinctly; antennae seven-jointed (with the possible exception
oi Enallagma antennatum) 18

18 (21) Gills more than half as long as the abdomen, lanceolate; third seg-

ment of antennae less than a third longer than the second . 1 9

19 (20) Labium with four to six lateral setae, generally with five, and with

three (rarely four) mental setae each side; gills often with
a definite color pattern Enallagma.

AQUATIC INSECTS

929

20 (19) Labium with five or six lateral setae, and with four mental setae each

side; gills generally with no distinct pattern. . . Ischnura.

21 (18) Gills less than half as long as the abdomen, narrower and with a long

tapering point; third segment of antenna more than a third

longer than the second Anomalagrion.

Without external respiratory plates, but with a respiratory chamber
inside the wide abdomen; body less slender, and not widest
across the head. (Dragonflies; proper.)

Suborder Anisoptera . . 23
Labium flat or nearly so (the edges of the lateral lobes slightly up-
turned in racAo/^/e^yjc), without raptorial setae 24

24 (35, 46) Labium with its median lobe entire; antennae four- jointed, the
fourth joint rudimentary; fore tarsi two-jointed: burrow-
ing nymphs 25

(i)

23 (47)

Fig. i38g. Recognition characters of dragonfly nymphs. A, inner aspect of the labium; m, mentum;
sm, submentum; ml, median lobe; U, lateral lobe; ms, mental setae; \ls, lateral setae; It, end hook. B, end
of the abdomen as seen from above: 7, 8, Q, 10, abdominal segments; d, dorsal hooks; t, lateral spines;
s, superior appendage; /, paired lateral appendages; c, inferior appendages (cerci).

25 (26) Middle legs more approximate at the base than are the fore legs;

fourth segment of the antenna slender, erect, about as long
as the third segment is wide; the tenth abdominal segment
about as long as the ninth Progomplius.

26 (25) Middle legs not more (usually less) approximate than the fore legs

at base; the fourth segment of the antenna a mere rudiment,
orbicular or discoid, much shorter than the third segment
is wide; the tenth abdominal segment much shorter than
the ninth 27

27 (28) Wing cases strongly divergent on the two sides; lateral lobe of

labium blunt at apex Ophiogomphiis.

28 (27) Wing cases laid closely parallel along the back; lateral lobe of labium

ending in a sharp, incurved hook 29

29 (30) Abdomen very thin and flat, circular in outHne as seen from above;

third segment of antenna flat and subcircular. . Hagcnius.

30 (29) Abdomen less depressed, ovate to lanceolate in outline, at least twice

as long as wide 31

31 (32) Third joint of antenna very flat, thin, and in outUne circular or

broadly oval Lanthus.

930 FRESH-WATER BIOLOGY

32 (31) Third joint of antenna elongate, linear, little flattened. . . . 33

33 (34) Dorsum of the ninth abdominal segrnent rounded, or with a low,

obtuse, median longitudinal ridge Gomphus.

34 {s3) Ninth abdominal segment with a sharp mid-dorsal ridge, ending in a

straight apical spine Dromogomphus.

35 (24, 46) Labium with a short median cleft; antennae seven-jointed,

setaceous; tarsi three-jointed; climbing nymphs, with eyes
at sides of head 36

36 (39) Hind angles of the head, viewed from above, sharply angulate. . 37

37 (38) Lateral lobe of labium squarely truncate on apex Boyeria.

38 (37) Lateral lobe of labium with taper-pointed apex. . . . Basiaeschna.

39 (36) Hind angles of the head obtusely rounded 40

40 (45) With lateral spines on abdominal segments 4-, 5-, or 6-9. . . 41

41 (44) With lateral spines on segments 4-, or 5-9 42

42 (43) With dorsal hooks on abdominal segments 7-9. . . Nasiaeschna.

43 (42) With no dorsal hooks on abdomen Epiaeschna.

44 (41) With lateral spines on abdominal segments 6-9 Aeschna.

45 (40) With lateral spines on abdominal segments 7-9 Anax.

46 (24, 35) Labium with a shallow median cleft; antennae seven-jointed;

short; squatting nymphs, with face vertical, and eyes on
anterolateral angles; depressed; hairy; tarsi three-jointed.

Tachopteryx.

47 (23) Labium mask-shaped or spoon-shaped, when closed, covering the

fa-ce up to the bases of the antennae, armed with raptorial
setae 4^

48 (49) The prominent median lobe of the labium cleft into two variously

formed teeth at apex Cordulegaster.

49 (48) The median lobe of the labium entire 50

50 (53) Head with a prominent pyramidal frontal horn; abdomen flat and

almost circular in outhne as seen from above; legs long,
giving a spiderhke aspect to these big nymphs; the tenth
abdominal segment well exposed, not telescoped in the apex
of the ninth segment; teeth on the lateral lobes of the labium
with deep incisions between them 51

51 (52) Head hardly as \\dde across the eyes as across the bulging hind angles;

lateral spines not incurved, those of the ninth abdominal
segment hardly surpassed by the tips of the appendages;
dorsum of the tenth abdominal segment with no trace of a
dorsal hook Didymops.

52 (51) Head widest across the eyes; spines of the ninth abdominal segment

shorter, not nearly reaching the level of the apices of the ap-
pendages; dorsum of the tenth segment with a very rudi-
mentary dorsal hook Macromia.

53 (50) Head without pyramidal frontal horn; abdomen less flattened, more

elongate; teeth on the lateral lobes of the labium much
wider than high 54

AQUATIC INSECTS 931

54 (65) Lateral appendages of the abdomen more than half as long as the

inferiors; hind femora longer than the head is wide; when
the lateral spines are long, then there is a full series of big,
cultriform dorsal hooks on the abdomen 55

55 (56) Lateral setae four or five; mentum about as long as wide.

Epicordulia.

56 (55) Lateral setae seven; mentum of labium longer than wide. . . 57

57 (62) Abdomen with large, laterally flattened, generally cultriform dorsal

hooks 58

58 (59) Lateral spines of the ninth segment longer than half the length of

that segment; dorsal hooks on segments 3-9, highest on 6,
cultriform, and sharp \ Tetragoneuria.

59 (58) Lateral spines of the ninth segment shorter than half of that segment;

dorsal hooks less developed 60

60 (61) Dorsal hooks on segments 4-9 laterally flattened, but not cultriform.

Somatochlora.

61 (60) Dorsal hooks on segments 6-9, longest on 8 and cultriform.

Helocordulia.

62 (57) Abdomen with no dorsal hooks, or with these rudimentary, not

flattened laterally or cultriform, but small obtuse or pointed
prominences 63

63 (64) Hind angles of the head rounded; lateral spines of the ninth abdominal

segment one-fifth as long as that segment. . . . CordiiUa.

64 (63) Hind angles of the head angulate superiorly; spines of the ninth

abdominal segment one-third as long as that segment.

Dorocordulia.

65 (54) Lateral abdominal appendages generally less than half the length of

the inferiors; hind femora generally as long as the head is
wide; often when the lateral spines of the abdomen are long
the dorsal hooks are wanting or reduced 66

66 (67) With large, cultriform dorsal hooks on abdominal segments 3-9; eyes

small and situated on the mid-lateral margin of the head and
directed laterally Per it hem is.

67 (66) With no dorsal hook on the ninth abdominal segment; eyes over-

spreading more or less the anterolateral margins of the
head . . 68

68 (85) Basal segment of the hind tarsus more than half as long as the second

segment; lateral appendages of the abdomen not more than
half as long as the inferiors (except in Libellula quadri-
maciilata) ; superior abdominal appendage regularly tapering
to a point 69

69 (70) Abdominal appendages strongly decurved; lateral spines wanting

or extremely rudimentary Mesothemis.

70 (69) Abdominal appendages straight or very slightly declined; lateral

spines evident on abdominal segments 8 and 9 71

71 (74) With no dorsal hooks at all 72

932 FRESH-WATER BIOLOGY

72 (73) Abdomen smooth, depressed; head twice as wide as long, with eyes

very prominent laterally; lateral spines large and straight;
superior appendage one-third shorter than the inferiors.

Pachydiplax.

73 (72) Abdomen hairy at the apex; lateral spines small and sharply in-

curved; superior appendage as long as the inferiors.

Nannothemis.

74 (71) Dorsal hooks present, at least on the middle abdominal segments. 75

75 (80) Abdomen ovate in outline, rather abruptly narrowed to the posterior

end; hind margin of the eyes behind the middle of the
head 76

76 (77) Lateral spines long and straight; abdomen not narrowed posteriorly

before the eighth segment Celithemis.

77 (76) Lateral spines shorter and more or less incurvate; the abdomen

more or less narrowed before the eighth segment. ... 78

78 (79) Dorsal hooks as long as the segments which bear them. Leucorhinia.

79 (78) Dorsal hooks shorter than the segments which bear them.

Sympetrum.

80 (75) Abdomen lanceolate in outline, slowly narrowed to the pointed

posterior end; eyes capping the prominent anterolateral
angles of the head, their hind margin generally before the
middle of the top of the head; body generally hairy. . 81

81 (82) The tenth abdominal segment with subcarinate lateral margins;

appendages very long; lateral setae 0-3 Ladona.

82 (81) The tenth abdominal segment shorter, cylindric; appendages shorter;

lateral setae 5-10 ^^

^^ (84) Head a little narrowed behind the eyes; front border of the median
lobe of the labium entire Libellula.

84 (83) Head not narrowed behind the eyes to the hind angles; front border

of the median labial lobe crenulate Plathemis.

85 (68) Basal segment of the hind tarsus half as long as the second segment;

lateral appendages of the abdomen at least three-fourths
as long as the inferiors; lateral setae 10 or more; superior
appendage of the abdomen suddenly contracted at its basal
third, the dorsal two-thirds forming a long slender point. 86

86 (87) Movable hook of labium long and slender, setiform; teeth much

broader than high; spines of the eighth segment one-half
longer than the ninth segment; superior abdominal append-
age shorter than the inferiors Tramea,

87 (86) Movable hook of the labium short, hardly longer than the teeth;

teeth higher than broad; spines of the eighth segment as
long as the ninth segment; superior appendage equaling
the inferiors Pantala.

AQUATIC INSECTS 933

KEY TO AQUATIC AND SEMI-AQUATIC HEMIPTERA

1 (8) Antennae longer than the head, free. Forms that walk on the water. 2

2 (5) Last segment of tarsi split, claws inserted before the apex. ... 3

3 (4) Beak four-jointed; intermediate and posterior legs extremely long and

slender; body widest back of the prothorax.

Family Gerridae.

4 (3) Beak three-jointed; none of the legs extremely long and slender; body

widest across the prothorax Family Veliidae.

5 (2) Last segment of tarsi entire, claws inserted at the apex 6

6 (7) Body linear; head as long as thorax; legs extremely long and slender;

beak not reaching anterior coxae. Family Hydrometridae.

7 (6) Body oval ; head shorter than thorax ; legs not extremely long and slender ;

beak reaching intermediate coxae. . Family Acanthiidae.

8(1) Antennae shorter than the head, nearly or quite concealed beneath the

margin of the head, or in a cavity beneath the eyes. . 9

9 (12) Ocelli two; anterior coxal cavities open behind; antennae four-jointed,

simple. (Live near the water) 10

10 (11) Fore legs slender, fitted for running; eyes triangular.

Family PELOGONroAE.

11 (10) Fore legs stout, fitted for grasping; eyes projecting, subglobose.

Family Nerthrddae.

12 (9) Ocelli none; anterior coxal cavities open or closed behind; antennae

three or four-jointed, simple or with some of the segments
produced into a lateral hook. (Live in the water) . . . 13

13 (32) Anterior coxal cavities closed behind; antennae four-jointed, simple

or hooked 14

14 (15) Antennae simple; no caudal appendages; fore legs fitted for grasping,

middle and hind legs for walking. . . Family Naucoridae.

15 (14) Second and third (sometimes fourth) joint of antennae produced into

lateral hooks; end of abdomen with a pair of caudal append-
ages; fore legs fitted for grasping, middle and hind legs for
walking or swimming 16

16 (29) Antennae four-jointed; caudal appendages short, strap-shaped, re-

tractile; middle and hind legs flattened, fitted for swimming;
tarsi two-jointed. . . . Family Belostomatidae . . 17

17 (18) Fore tarsus with two claws Hydrocirius.

18 (17) Fore tarsus with a single claw 19

19 (22) Mesothorax with a strong mid-ventral keel 20

20 (21) An internal tooth borne upon both joints two and three of the an-

tenna; all the ventral surface of the body hairy. Serphus.

21 (20) An internal tooth borne upon joints two, three and four of the

antennae; venter hairy only in the middle. . . . Abedus.
22(19) Mesothorax without mid-ventral keel; antennae four-jointed. . . 23

23 (26) Furrow of the membrane of the fore wing regularly curved; an acute

internal tooth on antennal segments two and three, the
fourth simple and pointed 24

24 (25) Membrane of the fore wing small; the reentrant angle seen at either

side of the front of the head when viewed from above is
wholly in the front Fedinocoris.

934 FRESH-WATER BIOLOGY

25 (24) Membrane large; reentrant angle bordered externally by the eye

itself {Zaitha of most of our literature) .... Belostoma.

26 (23) Furrow of wing membrane S-shaped; a recurved internal tooth

borne on antennal segments two, three and four. ... 27

27 (28) Front femora grooved internally for the reception of the tibia {Belos-

toma oi most oi our UtersLtuie) Amorgius.

28 (27) Front femora not grooved internally Benacus.

29 (16) Antennae three-jointed; caudal appendages long, j&hform, grooved;

middle and hind legs fitted for walking; tarsi one-jointed.

Family Nepidae . . 30

30 (31) Body oval; legs not extremely long and slender; prothorax much

broader than head; anterior femora but little longer than
tibiae Nepa.

31 (30) Body linear; legs extremely long and slender; prothorax but Uttle

broader than head; anterior femora more than twice as
long as tibiae Ranatra.

32 (13) Anterior coxal cavities open behind; antennae three or four-jointed,

without lateral hooks t,t,

33 (38) Head inserted in the prothorax; antennae four-jointed; beak three

or four-jointed, not retractile; anterior tarsi one or two-
jointed, of the usual form, with two claws.

Family NoTONEcrroAE . . 34

34 (37) Antennae inserted in cavity beneath eyes, second joint thickest;

hind legs flattened, ciliated, fitted for swimming; abdomen
keeled and hairy. (Size larger) 35

35 (36) Last joint of antenna less than half as long as the third, which is

fringed with capitate hairs. Hind tarsi without claws.
(Body stouter) Notonecta.

36 (35) Last joint of antenna fringed with capitate hairs, and many times

longer than the third, which is very small and inconspicuous.
Hind tarsi with claws. (Body more slender). . . Buenoa.

37 (34) Antennae inserted beneath the margin of the head, third joint longest

and thickest; hind legs like the middle legs, tarsi with
claws; abdomen not keeled or hairy. (Size smaller, not
over 3 mm. long) Plea.

38 {$^) Head overlapping the prothorax; antennae three or four- jointed;

beak short, unjointed, retractile; anterior tarsi one-seg-
mented, flattened, with a fringe of hairs on the edge, and
without claws Family Corixjdae.

KEY TO NORTH AMERICAN AQUATIC NEUROPTERA

Adults

1 (4) Veins of the wing disc all ending in a succession of symmetrical forks,

the terminal forks forming a distinct peripheral zone;
antennae moniliform. . . Family Hemerobiidae . . 2

2 (3) The median vein repeatedly forked; some of the branches of vein Cui

again forked. . Sisyra.

AQUATIC INSECTS

935

3 (2) The median vein but once forked; the branches of vein Cui all simple.

Climacia.

4 (i) Veins of the wing disc extending outward in straighter lines, forks

fewer and less symmetrical; antennae cyHndric serrate, or
pectinate Family SiALroiDAE . . 5

5 (6) Fourth segment of the tarsus bilobed; posterior branch of the radial

sector forked. No ocelh Sialis.

Fig. 1390. Fore wings of two neuropterous insects, Sialis (above) and Climacia (below), h, humeral
cross- vein; st, stigma; designations of principal veins as in Fig 1386.

6 (5) Fourth segment of the tarsus simple, cylindric; posterior branch of the

radial sector simple. Three oceUi 7

7 (8) Hind angles of the head rounded; the median vein two-branched;

antennae with segments enlarged distally. . , Chauliodes.

8 (7) Hind angles of. the head bearing a sharp angulation or tooth; median

vein three-branched; segments of the antennae cylindric.

Corydalis.

1(4)
2 {3)

3(2)

4(1)
5(6)

Larvae

Mouth parts adapted for piercing and sucking, prolonged to half the
length of the body; Hving on fresh-water sponges. ... 2

Setae on the dorsum of the thorax pedunculate (i.e., the setigerous
tubercles elevated considerably above the level of the integ-
ument); the outer covering of the pupal case spun by the
larva is of a beautiful hexagonal mesh Climacia,

Thoracic setae sessile; the outer covering of the pupal case is close woven.

Sisyra.

Mouth parts adapted for biting 5

The last abdominal segment produced in a long, median, laterally fringed
tail-hke process; a pair of lateral filaments on abdominal
segments 1-7 Sialis.

Q36 FRESH-WATER BIOLOGY

6 (5) Last abdominal segment bifurcated, the fleshy forks each bearing a

pair of hooks and a minute, external, lateral filament; con-
spicuous lateral filaments on abdominal segments 1-8. . 7

7 (8) Lateral filaments with no tuft of fine tracheal gills at their bases.

Chauliodes.

8 (7) Lateral filaments each with a tuft of fine tracheal gills at its base.

Corydalis.

KEY TO NORTH AMERICAN CADDISFLIES

1 (2) Micro-caddisflies; very small, mothlike, hairy, the fore wings bearing

numerous erect clavate hairs; the marginal fringe of the
wings longer than their greatest breadth; form of wings
narrowly lanceolate; antennae rather stout and not longer
than fore wings Family Hydroptilidae.

2 (i) Larger caddisflies, with broader wings; marginal fringes never as long

as the wings are broad; antennae usually longer than the fore
wings 3

3 (26) Maxillary palpus five-jointed 4

4 (19) Last joint of the maxillary palpus simple, and not longer than the

other joints 5

5 (10) Ocelli present 6

6 (9) Front tibiae with two or three spurs, middle tibiae with four spurs. 7

7 (8) The first two joints of the maxillary palpus short and thick, the third

joint much longer and thinner. . Family Rhyacophilidae.

8 (7) The second joint of the maxillary palpus much longer than the first.

Females Family Phryganeidae.

9 (6) Front ribiae with a single spur, or with none; middle tibiae with only two

or three spurs. Females. . . . Family Limnophilidae.

10 (5) OceUi wanting 1 1

11(12) A closed cell in the principal fork of the median vein in the fore wings.

Family Calamoceratidae.

12(11) No closed cell in the median fork 13

13(18) A closed cell in the first fork of the radial sector (i^a) 14

14(17) Both branches of the radial sector forked 15

15 (16) Veins Ri and R2 confluent apically or connected by an apical cross

vein in the fore wing. Females. . Family Odontoceridae.

16 (15) Veins Ri and R2 not connected apically.

Family Sericostomatidae.

17 (14) Only the anterior branch of the radial sector forked.

Family Leptoceridae.

18 (13) No closed cell in the first fork of the radial sector.

Family Molannidae.

19 (4) Last joint of the maxillary palpus usually much longer than the others,

twisted, and divided imperfectly into subsegments. . . 20

20 (21) Ocelli present Family Philopotamidae.

AQUATIC INSECTS 937

21 (20) Ocelli wanting '. 22

22 (23) Front tibia} with three spurs Family Polycentropidae.

23 (22) Spurs of the front tibiae fewer than three 24

24 (25) Anterior branch of the radial sector in the fore wing forked.

Family Hydropsychidae.

25 (24) Anterior branch of the radial sector simple.

Family Psychomyiidae.

2; CU2 -

> 'A ^^2 *
Fig. 1391. The wings of a caddisfly, Hydropsyche.

26 (3) Maxillary palpi with fewer than five joints 27

27 (28) Maxillary palpi with four joints; ocelli present. Males.

Family Phryganeidae.

28 (27) Maxillary palpi with two or three joints 29

29 (30) Maxillary palpi filiform with cylindric smooth joints; fore tibiae with

a single spur. Males Family Limnophilidae.

30 (29) Maxilary palpi hairy or scaly, appressed against and often covering

the face; fore tibiae with two spurs. Males.

Family Sericostomatidae.

KEY TO NORTH AMERICAN AQUATIC BEETLES
Adults

1 (2) Hind tarsi with the antepenultimate segment broadly bilobed, and

receiving the rudimentary penultimate segment (which is
closely fused with the base of the last segment) in its apical
notch Family Chrysomelidae.

2 (i) Hind tarsi with the last three segments free and similar in form. . . 3

3 (8) Hind legs shorter than the fore; eyes four, two above and two on the

under surface of the head. . . . Family Gyrinidae . . 4

4 (7) Last abdominal segment rounded posteriorly and smooth below. . . 5

5 (6) Wing of the metasternum {w, Fig. 1392) broadly triangular. . Dineiites.

6 (5) Wing of the metasternum narrow, elongate, widened only at its extreme

outer endo Gyrinm*

938 FRESH-WATER BIOLOGY

7 (4) Last abdominal segment elongate pyramidal, and furnished with a mid-

ventral line of hairs Gyretes.

8 (3) Hind legs longer than the fore; eyes

two 9

9 (14) Base of the hind legs covered by broad

overlapping coxal plates.

Famxily Haliplidae . . 10

10 (1,3) Coxal plates concealing only the three

basal segments of the abdomen ;
last segment of palpi shorter
than the preceding segment. 1 1

11 (12) Pronotum widest before the middle.

Brychius.

12 (11) Pronotum widest at the rear end.

Haliplus.

13 (10) Coxal plates conceaHng all but the last

of the ventral abdominal seg-
ments; last segment of palpi
longer than the preceding seg-
ment Peltodytes.

14(9) Base of the hind legs exposed . ... 15

15 (48) Antennae shorter than the palpi; legs

usually with swimming fringes.
Family Hydrophilidae . . 16

16 (23) Scutellum wanting or indistinct or very

small and scalelike. Posterior

femora subcylindrical and not

noticeably widened in the mid- pic.1392. Diagram of the ventral

die ; pro thorax narrowed behind, aspect of a diving beetle, Coptotomus

narrower than the elytra. The fX'i^,'c,^ii^1""li'\^°''S:i

species are small, elongate, middle legs; d, labial palpi; e, eye;

roughly sculptured, greyish or {.rthe'pSfoti^; 5;. 'epipt "'?!,"
nearly black, and usually tinged the wing cover (elytron); f, pros-

- - - ,11. 1 temal process; /', metasternal fork;

k, hind coxa with /, the inner lam-
ina; p, the coxal process and q, the
coxal notch; r, trochanter of the
hind leg; s, femur; /, tibia; u, hind
tarsus of five jcints; /, 2, j, 4, 5- <5,
ventral abdominal segments, 5/^ sf-,
sP, sterna of pro-, meso-, and meta-
thoi ax, respectively; u', wing of the
metasternum; m, episternum, and
n, epimeron of the successive thor-

with bronze and metalHc col
ors 17

17 (20) Scutellum indistinct, or apparently want-
ing; if at all evident it is
distinctly triangular and acute.
Species from 1-2 mm. long. 18

18 (iq) Pronotum without striae; maxillary palpi ,., .»_...... „. -..- -_-^^ ^ .

as long as the head and thorax ^ -^^^ S^rV'nd ViS

together, the ultimate segment the figure, and the coxal border IS the

longer than the penultimate; ^^S^^^\^^%,
elytra with more than ten rows end of the coxal line.
of punctures. . . . Hydraena.

19 (18) Pronotum bearing from one to five longitudinal striae or abbreviated

grooves; the maxillary palpi much shorter than the head
and thorax together, the ultimate segment shorter than the
penultimate; elytra with only ten rows of punctures.
*^ Octhehius.

part of the coxal process, p, that is
marked off laterally by the posterior

AQUATIC INSECTS 939

20 (17) Scutellum appearing as a very small but distinct scale, shaped like

the last joint of one's thumb; the ultimate segment of labial
palpus longer than the penultimate. Species from 3-6 mm.
long 21

21 (22) The pronotum bearing five longitudinal striae; labial palpi moderately-

large Helophorus.

22 (21) The pronotum coarsely punctured but without longitudinal striae;

labial palpi short Hydrochiis.

23 (16) Scutellum distinct, moderately large. Posterior femora flattened

and distinctly widened at their middle; prothorax not
narrowed posteriorly, as wide as the elytra at their base.
The species are small or large, of oval, elliptical or even
hemispherical form, with not very coarse sculpture, and
are commonly pitchy black, often more or less testaceous,
very occasionally with metallic tinges 24

24 (43) Metasternum not prolonged into a spine; tarsi not compressed.

The species of this group are all smaller than those of the
next, less than 9 mm. long 25

25 (26) Fifth ventral segment w^th a deep notch in the middle of its apical

border; middle and posterior tibiae and tarsi bearing a close-
set fringe of long silky setae; scutellum elongate, acute.

Berosus.

26 (25) Fifth ventral segment not notched; tibiae and tarsi not fimbri-

ate 27

27 (28) First two ventral segments concealed by whitish translucent plates,

one on each side, upon which are a number of long appressed
setae. The species are very convex, have a tendency to
partially roll up like a sow-bug, and are from 1-2 mm. in
length Chaetarthria.

28 (27) No such plates over the first ventral segments 29

29 (30) Posterior tibiae incurved, small at base and considerably enlarged at

their apex Laccobius.

30 (29) Posterior tibiae straight; little or not at all thickened at their apex. 31

31 (32) Abdomen with apparently eight ventral segments. The single

species is i^ mm. long; of a black color with pale legs.

Limnebius.

32 (31) Abdomen with five ventral segments, the tip of the sixth often

visible. . .' 33

S3 (40) Terminal segment of the maxillary palpus rarely as long as, usually
shorter than, the preceding segment 34

34 (35) Elytra deeply longitudinally striate; tarsi of the middle and pos-

terior legs with only four segments Helocombus.

35 (34) Elytra not striate 36

36 (39) Mesosternum with a feeble transverse carina or simple 37

37 (38) Mesosternum with a feeble transverse carina; tarsi of the middle

and posterior legs with four segments Cymbiodyta.

38 (37) Mesosternum simple; all tarsi with five segments, the first usually

triangular Helochares.

940 FRESH-WATER BIOLOGY

39 (36) Mesosternum with a longitudinal carina; all tarsi with five segments,

the first one small Philhydrus.

40 {32>) Terminal segment of maxillary palpi distinctly longer than the

penultimate 41

41 (42) Large species 6.5-8.5 mm.; the elytra distinctly striate or striato-

punctate Hydrohius.

42 (41) Small species 1.5-3.5 mm.; the elytra not striate but with confused

punctuation Creniphilus.

43 (24) Metasternum prolonged into an acute spine; tarsi compressed so as

to be oarlike. The color is always pitchy black, occasion-
ally with yellow margins. The size varies from 9 to 35
mm 44

44 (45) Metasternum produced into a short spine never projecting as far

as the posterior margin of the first ventral segment. Pro-
sternum acutely carinate but not grooved for the reception
of the mesosternal carina Hydrocharis.

45 (44) Metatarsal spine \try long and acute, extending always beyond the

posterior margin of the first ventral segment. Prosterniun
with a keel-shaped process which is deeply grooved for the
reception of mesosternal carina, thus locking pro- and meso-
thorax together 46

46 (47) Length about 10 mm. Terminal segment of maxillary palpi as long

as or longer than the preceding; the antepenultimate seg-
ment straight; claws simple Tropisternus.

47 (46) Length about 35 mm. Terminal segment of maxillary palpi much

shorter than the preceding; the antepenultimate segment
arcuate; claws toothed Hydrophilus.

48 (15) Antennae longer than the palpi (equahng them in a few riffie beetles).

49

49 (90) Hind coxae broadly flattened out and sohdly fused with the meta-

sternum 50

50 (51) Metasternum divided by a transverse suture which separates a short

sclerite before the base of the hind coxae.

Family Amphizoidae.

A single genus from western mountain streams. Amphizoa.

51(50) Metasternum not thus divided Family Dytiscidae . . 52

52 (61) Scutellum invisible 53

53 (54) Third and fourth segments of the fore and middle tarsi not greatly

different from the others; prosternal process acute posteriorly.

Laccophilus.

54 (53) Third segment of the fore and middle tarsi deeply bilobed, the fourth

segment rudimentary or wanting 55

55 (56) Base of thorax united to the elytra by a short impressed fine on each

side, continued without interruption across the border of
each; hind margin of the posterior coxae grown sohdly
coherent with the first ventral segment of the abdomen,
which is considerably enlarged; form elongate; very small.

Bidessus.

56 (55) Base of thorax and elytra without a continuous impressed line. . 57

AQUATIC INSECTS 941

57 (58) Hind margin of the posterior coxae grown solidly coherent with the

first segment of the abdomen, which is considerably enlarged;
form round and very convex; shining; small.

Desmopachria.

58 (57) Hind margin of the posterior coxae overlapping but not coherent

with the first segment of the abdomen, which is not espe-
cially enlarged. Form various, but never so round and
convex as Desmopachria, nor so small and elongate as
Bidessus 59

59 (60) Hind coxal processes each divided by a deep posterior notch, the

inner ramus appressed against the first abdominal segment.

Hydrovatus.

60 (59) Hind coxal process not so formed Hydroporus.

(In the broader sense, as used here this genus includes
Coelambus, Deronectes)

61 (52) Scutellum visible 62

62 (63) Clypeal suture entire Dytiscus.

63 (62) Clypeal suture incomplete. 64

64 (65) More than 30 mm. long; inferior spur of hind tibiae much dilated,

bifid, much broader than other spur Cyhister.

65 (64) Less than 20 mm. long; the two spurs of the hind tibiae of equal or

nearly equal breadth 66

66 (73) Distal margin of each segment of the hind tarsi beset with a trans-

verse row of minute appressed bristles; anterior tarsi of
male with dilated segments forming a round disc. . . 67

67 (68) Spurs of hind tibiae acute at tip; claws of hind tarsi unequal, the

inner one sometimes obsolete Uydaticus.

68 (67) Spurs of hind tibiae emarginate at tip; claws of hind tarsi equal or

nearly so 69

69 (70) Elytra closely punctate, usually f our-sulcate ; female. . . Acilius.

70(69) Elytra not punctate, partly aciculate in female 71

71 (72) Middle femora beset with elongate setae; female. . Thermonedes.
72(71) Middle femora beset with short and stout setae. . . . Graphoderes.

73 (66) Hind tarsi without such appressed bristles; anterior tarsi of female

with dilated segments forming an oval disc 74

74 (79) A linear group of minute setae present upon the postero-external angle

of the hind femora 75

75 (76) Claws of the hind tarsus unequal; the tarsal segments produced

posteriorly in overlapping lobes Ilyhiiis.

76 (75) Claws of the hind tarsus equal and segments simple 77

77 (78) Wing of the metasternum very narrow and deflexed around the

front border of the external lamina of the hind coxa.

Ilybiosoma.

78 (77) Wing of the metasternum wedge-shaped, less noticeably deflexed.

Agabiis.

79 (74) No such linear group of setae on the postero-external angle of the

hind femora ^^

80 (81, 82, 83) Surface of the elytra reticulate Scutopterus.

942 FRESH-WATER BIOLOGY

81 (80, 82, 83) Surface of the elytra transversely aciculate. . . Colymbetes.

82 (80, 81, 83) Surface of the elytra with eight to ten longitudinal striae.

Copelatus.
8s (80, 81, 82) Surface of the elytra otherwise sculptured or plain. . . 84

84 (85) Prosternum plainly longitudinally sulcate; species reddish brown.

Matus.

85 (84) Prosternum not sulcate 86

86 (87) Apical segment of each palpus distinctly emarginate. Coptotomus.

87 (86) Apical segments of palpi obtuse or truncate 88

88 (89) Claws of the hind tarsus equal Agabetes.

89 (88) Claws of the hind tarsus unequal Rhantus.

90 (49) Hind coxae free 91

91 (no) Claws large; the three basal ventral segments of the abdomen

fused together, obhterating the sutures.

Family Parnidae . . 92

92 (93) Ventral abdominal segments (see Fig. 1392) seven in number.

Psephenus.

93 (92) Ventral abdominal segments five in number 94

94 (103) Fore coxae transversely elongated 95

95 (102) Sternum of the prothorax prolonged forward beneath the head in a

flat rounded lobe; head retracted within the front of the
prothorax; the two basal segments of the antennae dis-
tinctly enlarged 96

96 (97) Body rounded in outKne Lutrochus.

97 (96) Body oblong, elongate 98

98 (99) Antennae approximate, the terminal segments pectinate. Pelonomus.

99 (98) Antennae distant at base 100

100 (loi) Antennae slender Throscinus.

101 (100) Antennae short and thick, the second joint triangularly dilated, the

close-set distal segments lamellate Dryops.

102 (95) Sternum of prothorax not greatly produced forward; head free;

antennae long and serrate (California) Lara.

103 (94) Fore coxae rounded 104

104 (109) Sternum of prothorax produced forward in a flat rounded lobe;

head retracted within the front of the prothorax. , . . 105

105 (108) Antennae eleven- jointed 106

106 (107) Fore tibiae pubescent internally Elmis.

107 (106) Fore tibiae bare internally Sienelmis.

108 (105) Antennae six-jointed Macronychus.

109 (104) Sternum of prothorax not produced forward; head free.

Ancyronyx.
no (91) Claws of moderate size; basal ventral segments free.

Family Dascyllidae.

AQUATIC INSECTS 943

Larvae

1 (4) Herbivorous larvae with short, broad inconspicuous mandibles.

Family Chkysomelidak . . 2

2 (3) Feeding exposed on the floating leaves of water lilies, etc.; elongate

brownish larvae of sluggish habits Galcrucella.

3 (2) Short arcuate grublike larvae, white and translucent, feeding on the

submerged roots of aquatic plants Donacia.

4 (i) Carnivorous larvae, with prominent mandibles 5

5 (12) Mandibles sickle-shaped without internal teeth, but with an internal

groove or perforation extending almost from base to apex. 6

6 (7) End of the abdomen with two pairs of strong claws, and the middle

segments bearing single pairs of long lateral filaments.

Family GYRI^fIDAE,

7 (6) No claws at end of abdomen 8

8 (11) Eyes in groups of five; one claw on each tarsus.

Family Haliplidae . . 9

9 (10) Body nearly smooth, ending in a long tail Haliplus.

10 (9) Body bearing numerous very long and conspicuous bristlelike fila-

ments; no tail Peltodytes.

11 (8) Eyes in groups of six; two claws on each tarsus.

Family Dytiscidae.

12(5) Mandibles toothed internally, at base or in the middle 13

13 (14) Tarsi with two claws Amphizoa.

14(13) A single claw on each tarsus 15

15 (16) Antennae as long as or longer than the thorax.

Family Dascyllidae.
16(15) Antennae shorter than the thorax 17

17 (18) Larvae depressed; end of the abdomen with short cerci; gills, when

present, ventral in position Family Parxid.a.e.

18 (17) Body little depressed; cerci wanting; gills rarely present (and then

lateral in position, Berosus). . . Family Hydrophilidae.

KEY TO NORTH AMERICAN AQUATIC DIPTEROUS LARVAE

1 (65) Head chitinous, free, or retracted within the front of the prothorax.

Pupa usually free; when concealed in the old larval skin,
that skin splits on emergence of the imago in a longitudioal
I- or T-shaped cleft. . . . Suborder Orthorrhapha . . 2

2 (58) Mandibles opposed to each other, or inclined obliquely downward

and opposed to a strongly chitinized labial border.

Nematocera . . 3

3 (4) Body strongly depressed, and with a row of six ventral suckers for

attachment to the rock bed of rapid streams.

Family Blepharoceridae

4 (3) Body cylindric, and usually lacking ventral suckers; when ventral

suckers are developed they are more than six 5

944 FRESH-WATER BIOLOGY

5 (6) Head imperfectly chitinized in the rear, and wholly retracted within

the pro thorax; posterior spiracles situate upon a respiratory
disc Family Tipulidae.

6 (5) Head fully developed and usually free 7

7 (35) No prolegs developed upon the prothorax 8

8 (11) Prolegs developed upon some of the anterior segments of the ab-

domen 9

Q (10) The body terminates in a very long and conspicuous respiratory tube.

Family Ptychopteridae.

10 (0) Without respiratory tube, body U-shaped in locomotion.

Family Ddodae.

11 (8) Body without prolegs 12

12 (31) Thorax thickened, the outUne of its constituent segments more or

less confluent; a fin of swimming hairs developed beneath
the end of the abdomen, and often a respiratory tube on
the dorsal side Family Culicidae . . 13

13 (26) The last abdominal segment with a single dorsal breathing tube,

through which may be seen a pair of large tracheae. . . 14

14 (15) Antennae fold back against head and.terminate in two or three claws.

Corethrella.

15 (14) Antennae usually only with a few small erect bristles and one or two

pointed processes, or pendent and raptorial 16

16 (23) With brush of hairs projecting forward from the mouth, vibratile. 17

17 (22) Antennae not pendent and raptorial 18

18 (19) No ventral brush or rudder on last abdominal segment beyond air

tube; small species, one of which is found in water in
pitcher plant Wyeo7nyia.

19 (18) Last segment with ventral brush 20

20 (21) Head with thick spines; with four blood gills; with stellate hairs on

the abdomen. Small species Uranotaenia.

21 (20) Head without stout spines in addition to the usual setae.

Culex (sens. lat.).

22 (17) Antennae pendent and raptorial : . . . . Mochlonyx.

23 (16) Mouth brush folded outward, raptorial, not vibratile 24

24 (25) A plate on the side of eighth abdominal segment. . . Megarhinus.

25 (24) A patch of small scales on the side of the eighth abdominal segment.

Psorophora.

26(13) Last segment without long breathing tube 27

27 (30) Last segment dorsally with a flat area in which may be seen two

spiracles 28

28 (29) Large species with the anal segment bladderlike. Mandibles strongly

developed Pelorempis.

29 (28) Species of medium size with anal segment cylindrical. . . Anopheles.

AQUATIC INSECTS 945

30 (27) Last segment usually with hooks, no spiracles apparent. Larva

transparent. Cordlira.

31 (12) Body cyhndric, or depressed fusiform 32

32 {2>2), 34) Body ending in two fleshy points Family Rhyphidal.

2>d> (32, 34) Body ending in a tapering segment tipped with a tuft or circlet

of hairs Ccratopo^oniuc of Chiroxomidae.

34 (32, 33) Body ending in a strongly chitinized terminal segment, usually

produced in chitinous respiratory tube. . . Psychodidae.

35 (7) Prothorax with one or two prolegs 36

36 (57) A pair of prolegs beneath the prothorax, and another pajr at the end

of the abdomen Family Chiroxomidae . . 37

37 (38) Abdomen with prominent rounded elevations or cushions, with rows

of teeth on the inferio-anterior angles of the segments.

Fsamathiomyia.

38 (37) Abdominal segments without cushions 39

39 (40) With retractile antennae, the latter often quite long, long sliltlike

legs, the caudal tufts of hair mounted on cylindrical processes.

Tuny pus.

40 (39) Not with all the above characters 41

41 (44) With the two caudal hair tufts mounted on cylindrical projections. 42

42 (43) With blood gills on venter of eleventh segment. . . Hydrohacniis.

43 (42) With blood gills only at end of twelfth segment. . . Metriocnemus.

44 (41) Caudal tufts on small rounded papillae 45

45 (48) Antennae elongate, at least one-half as long as and often as long as

or longer than the head 46

46 (47) Antenna with one or two sense organs at tip of second segment.

(Rendered visible in preserved material by soaking in
water) Tanytarsiis.

47 (46) Antenna at most with a seta at tip of second segment at side of the

third segment Corynoncura.

48 (45) Antennae short 49

49 (50) Larvae usually blood red; eleventh body segment with two pairs of

blood gills C//m);/ow«5 (in part).

50(49) Larvae greenish, yellowish, or whitish 51

51 (52) The maxilliary palpus usually noticeably longer than broad. Larva

in pools, pond water, or slow streams .... Chironomiis.

52 (51) Palpus about as long as broad 53

53 (54) Full-grown larva not over 6 mm. long, green or bluish-green in color.

Anterior abdominal segments of greater diameter than the
posterior ones. Mandibles often transversely wrinkled;
the anterior prolegs usually with pectinate setae.

Cricotopus, Ortliocladius.

54 (53) Full-grown larva over 6 mm. in length; mandible not transversely

wrinkled 55

55 (56) Labium with teeth all rounded Diamesa.

$6 (55) Labium with middle tooth broadly truncate Thalassomyia.

946 FRESH-WATER BIOLOGY

57 (36) A single median proleg on the prothorax and a terminal sucking disc

upon the abdomen, serving for attachment to stones in
rapid streams; abdomen broadened posteriorly.

Family Simuliidae.

58 (2) Mandibles decurved, parallel, their motion vertical, or nearly so.

Brachycera . . 59

59 (64) Posterior spiracles placed together within a terminal cleft. ... 60

60(63) Terminal cleft vertical; head retractile.

Family Tab ANIDAE . . 61

61 (62) Last antennal segment much longer than the one preceding; dorsal

areas striated like those of the abdomen. . . . Chrysops.

62 (61) Last antennal segment not longer, usually much shorter, than the one

preceding; dorsal areas smooth or striated, but those of the
thorax nearly or quite free from striae Tabanus.

63 (60) Terminal cleft transverse; head not retractile.

Family Stratiomyiidae.

64 (59) Posterior spiracles separate Family Leptidae.

65 (i) Head membranous, very imperfectly developed, often apparently

wanting. Pupa formed in the hardened and contracted
larval skin (puparium), which opens by a circular cap or lid.

Suborder Cyclorhapha.
This group includes many of the higher aquatic Diptera
(Syrphujae SciOMYzmAE, etc.) still too insufficiently known to
admit of the construction of a satisfactory key.

Note: Acknowledgment is hereby made of help generously given in the preparation of the
foregoing keys in parts as follows: in Hemiptera by Mr. C. R. Plunkett; m Coleoptera by
Dr. J. C. Bradley; in Diptera by Dr. O. A. Johannsen.

IMPORTANT REFERENCES ON NORTH AMERICAN
AQUATIC INSECTS.

CoMSTOCK, J. H. 1917. Manual for the Study of Insects. 14th Ed. Ithaca.

Kellogg, V. L. 1905. American Insects. New York.

FoLSOM, J. W. 19 13. Entomology, with Reference to its Biological and

Economic Aspects. 2d Ed. Philadelphia.
Howard, L. O. 1901. The Insect Book. New York.
Miall, L. C. 1903. Natural History of Aquatic Insects.

CHAPTER XXVIII
MOSS ANIMALCULES (BRYOZOA)

By CHARLES B. DAVENPORT

Director of the Station for Experimental Evolution, Cold Spring Harbor, Long Island, N.Y.

Prominent among the animals commonly discovered in fresh
water are the Bryozoa, or moss animalcules, also called Polyzoa.
They are forms of exceedingly dehcate and attractive appearance,
often so transparent that under favorable circumstances the entire
structure may be made out under the microscope. Almost all
species form colonies composed of many individual animals (zooids)
united together and the whole mass is not only easily visible but
often conspicuous, whereas the separate zooids are so minute that
they can ordinarily be detected only with a hand lens. These
colonies take the form of branching threads spread on the surface
of stones, sticks, submerged plants or other objects in the water.
Others produce a thick crust, while still others form soHd jelly-like
masses which in one species reach the size of the closed fist and not
infrequently surpass that (Fig. 1401). The bulk of this mass con-
sists of transparent or faintly tinged gelatinous material from
which the individual zooids project into the water as they also
do from the filamentous colonies previously mentioned. The
expanded "head" (lophophore) of the zooid with its crown of
tentacles is difficult to see since the animals are exceedingly timid
and respond to the slightest disturbance by retreating instantly
within their protective covers where
they remain even long after the water
has become quiet again. Continuous

study of the colony in a dish of fresh Fig. 1393. CristalcUa mucedo; colony,

. natural size. (After Allman.)

water is rewarded by the appearance of

the spreading disks or heads, until the surface of the colony blossoms

with abundant groups of delicate tentacles. (Fig. 1393.)

All are essentially sessile, but a few, like Cristatella and Pectina-
tella, have the capacity for a sHght movement of the colony on

947

948 FRESH-WATER BIOLOGY

the substratum. The nature of the colony formation is variable:
sometimes close, forming a corm of zooids fused into one mass, as in
Cristatella; sometimes loose, each zooid being distinct, as in Urnatella.
Each zooid has a structure not unlike that of a rotifer. It
secretes a resistant outer covering. This is calcareous in some of
the marine forms, but is generally chitinous or gelatinous in those
of fresh water. So prominent and variable is this cuticula (con-
stituting the "zooecium, " or "cell") that its form is frequently
used as a means of distinguishing species. The body wall is very
thin, having reh'nquished its protective function in favor of the
cuticula. It is separated from the viscera by a relatively enor-
mous body cavity. In the case of species whose zooids are fused
together the body cavities are confluent. The ahmentary tract is
relatively simple. It consists of a U-shaped tube whose only
glands are localized in the epithehum of its walls. The mouth
end of the tube is furm'shed with a corona of numerous ciliated
tentacles which create a vortex at the mouth. The mouth is, in
one order of fresh-water species (Phylactolaemata), provided with
an "epistome" or protecting flap. A long esophagus leads to the
capacious stomach and this to the flask-shaped rectum. The
anus lies near the mouth either outside or inside the corona of
tentacles. For protection, the tentacles can be retracted quickly
under the shelter of the body cuticula like the proboscis of certain
polychaetes. There are numerous long slender muscles effecting
the retraction. The nervous system is simple. A brain Hes between
esophagus and rectum and sends nerves to tentacles and ahmentary
tract. Circulation is effected by the general fluid of the body
cavity. Well defined excretory tubules seem to be missing if we
except the doubtful case of certain Phylactolaemata. In the
Gymnolaemata the viscera periodically degenerate into a brownish
mass, a new ahmentary tract regenerates, and the degenerated
mass passes through the wall of the gut and is expelled by the anus.
Eggs are formed on the body wall and, in Phylactolaemata, the
sperm on the mesentery ("funiculus"). In the marine species the
embryos early become free-swimming, but in Phylactolaemata they
develop in a sort of uterus until they are young colonies.^ These

1 The fresh-water form, Pectinatella magnifica, produces a small free swimming spherical larva which
settles to the bottom almost immediately and there by budding gives rise to a colony.

MOSS ANIMALCULES (BRYOZOA) 949

are then set free, and, after a time, settle and affix themselves.
Like other sessile forms, Bryozoa have gained a variety of methods
of reproduction. Ordinary sexual reproduction and budding have
been already mentioned. In some Phylactolaemata — Peciinatella
and Cristatella — the colonies occasionally undergo fission and
move apart, and the same process occurs regularly in Urnatella.
Statoblast formation, which occurs on the funiculus in Phylacto-
laemata, is mentioned below.

The fresh-water Bryozoa do not constitute a natural group of
animals, but have descended from ancestors belonging to widely
distinct families. There can be no question that these ancestors
were marine animals. Excepting the suborder Phylactolaemata,
all fresh- water Bryozoa belong to groups most of whose representa-
tives are marine. The fresh-water forms seem to have made their
way up estuaries and rivers to lakes and ponds. Here they acquired
the capacity of forming statoblasts or hibernacula, by virtue of
which the species was enabled, on the one hand, to survive the
winter and, on the other, to be carried by waterfowl and winds
over divides from one drainage basin to another. Thus the fresh-
water species have become nearly cosmopolitan. Plumatella
prince ps has been found in North and South America, through-
out Europe, in Molucca, Japan, and Australia — i.e., in all but one
of the great geographical divisions of the land areas of the globe.

The fresh-water Bryozoa live in all kinds of fresh waters and are
indeed among the most ubiquitous of aquatic animals. They are
found in stagnant pools and in rushing rivers, although particular
species favor special habitats. The different species of Pluma-
tella occur in varied habitats. Paludicella and Peciinatella favor
running water and Lophopus, Cristatella. and Plumatella polymorpha
favor quiet ponds. The fresh-water Bryozoa feed on microscopic
organisms which are caught in the vortex created by their ciUated
tentacles. Diatoms are especially conspicuous objects in their
alimentary tracts. Since diatoms require Hght for their construc-
tive metaboHsm, they are found chiefly in the upper strata of the
water, and consequently Bryozoa are usually not found at great
depths. However, in a mass of material dredged by Professor H.
B. Ward from the Middle Ground, Traverse Bay, Lake Michigan,

950 FRESH-WATER BIOLOGY

at a depth of 23 to 36 meters, Paludicella ehrenhergii and Frederi-
cella sultana were abundant. Although Cristatella is usually found
on the underside of floating Hly pads or in other situations near
the surface, I have obtained it from the still waters of Trinity
Lake, Westchester County, New York, at a depth of 2 to 3 meters.
Asper records dredging Fredericella sultana in certain Swiss lakes
at a depth of 50 to 80 meters. Little light penetrates to such a
depth, and we may conclude that hght is not at all directly neces-
sary for the development of fresh-water Bryozoa. Indeed, masses
of Paludicella are sometimes obtained from water pipes where they
flourish to an alarming extent.

The Bryozoa have become adapted to Hfe in ponds by forming
statoblasts at certain seasons of the year. The entire significance
of the statoblasts has not been determined. Typically, they winter
over and one may find the shores strewn with them in the early
spring. They hatch out in New England late in May or early in
June. So the statoblasts have come to be regarded as winter buds,
or adaptations to preserve the race from being killed ofT by freezing
of the water. They often begin to develop early in the summer,
and I have observed what has been seen by European observers,
that some statoblasts hatch in nature even in September. Also
Fr. Miiller has informed Kraepehn that the fresh-water Bryozoa
of Blumenbau, Brazil, which experience no winters, nevertheless
form statoblasts. It seems fair to conclude that there are other
functions performed by the statoblasts than resistance to winter.
For instance, they serve to maintain the species during drought,
or they aid in distribution by clinging to the waterfowl or resisting
the action of digestive fluids. The wide distribution of the species
of fresh-water Bryozoa indicates the value of the statoblast in the
process of dispersion. For a detailed account of the distribution
of the fresh-water species in the United States see Davenport (1904).

Preserving. — The chief difficulties in the way of preserving
fresh-water Bryozoa arise, first, from the rapid contraction of the
polypides into the corm, and, secondly, in the case of the gelatin-
ous forms, from the large amount of water in the body; for, if the
specific gravity of the killing or preserving medium is very differ-
ent from that of the water, distortion will occur.

MOSS ANIMALCULES (BRYOZOA)

951

To kill expanded it is necessary first to narcotize. Chloral
hydrate is used, added slowly in crystals until the polypides do not
react to touch. To preserve in the natural form, the animals may be
plunged directly into 4 per cent formaldehyde (formahn, 10 per cent).

The classification of fresh- water Bryozoa has been in a state of
great confusion owing to the great variability in the form of the
colony. The form of the colony depends very largely upon external
factors, such as food supply, form of substratum, and crowding.
The statoblast has a form that is quite independent of external
factors, and upon it, consequently, great stress is laid in systematic
work. The form of the statoblast is, however, not wholly uncor-
related with that of the stock, so the form of the stock is to be
considered. In the following classification that proposed by
Kraepelin has been adopted entire.

KEY TO NORTH AMERICAN FRESH-WATER BRYOZOA

I (2) Anus opening inside the tentacular corona; tentacles incapable of

complete retraction Subclass Endoprocta.

Only one species known in North America.

Urnatella gracilis Leidy 185 1.

Stock consisting of a basal plate, from which
there usually arise two segmented stems termi-
nating in the polypide. More rarely one or
more than two stems arise from the disk.
Habit, running water. From Schuylkill River,
Pa.; Scioto River, O.; Illinois River, 111.

Fig. 1394. Urnatella gracilis, (a) Colony from
Illinois River at Havana. X13. (After Daven-
port.) {b) Single polyp. (After Leidy.)

2 (i) Anus opening outside the tentacular corona, which is capable of being

retracted Subclass Ectoprocta . . 3

3 (6) Zooecia sharply separated from each other; no epistome.

Order Gymnolaemata . . 4

4 (5) Stock consists of stolons from which at intervals an erect cylindrical,
hyahne single zooid arises, having a terminal aperture.

Pottsiella erccta Potts 1884.

Lophophore circular, 20 (10 to 21) tentacles. Habitat,
photophil; on upper surface of stones in rapids; sometimes
penetrating incrusting sponges (Ephydatia leidyi). From
Tacony Creek, Montgomery Co., Pennsylvania.

Fig. 1395.

Pottsiella erecta. X 25. (From Kraepelin's figure of a
Pennsylvania specimen.)

952

FRESH-WATER BIOLOGY

5(4)

Stock composed of zooids that are sharply separated from one another
by partitions; sparsely, usually oppositely branched; with
a chitinous cuticula. The zooids are club-shaped and have
a lateral, quadrangular aperture near the larger, distal end.
..-y.J ,H.. Faludicella ehrenhergii van Beneden 1848.

Zooids about 2 mm. long; lateral buds partly repent,
partly erect; about 16 tentacles. Habitat, flowing streams;
occasionally in water pipes. From Massachusetts, Penn-
sylvania, Illinois, and Lake Michigan.

Fig. 1396. Paludicella ehrenbergii. (a) Colony, half natural size.
{b) Portion of same enlarged. X 5- (After Kraepelin.)

6 (3) Zooecia confluent; epistome present. . Order Phylactolacmata. . 7

7 (14, 15) Statoblasts without hooks, rounded at ends 8

8 (9) Stock branched in form of antlers; more rarely massed with recumbent
and elevated tubes; mostly brown or incrusted with algae
and grains of sand; rarely hyaline.

Fredericella sultana Blumenbach 1774.

Tubes cylindrical, the older ones mostly keeled.
Without complete dissepiments. Apertures terminal
at the broadened or bifid ends of tubes. Polypide
very long and slender; tentacles arranged in a nearly
circular corona. Few tentacles, not exceeding 24.
Statoblasts dark brown, bean-shaped or eUiptical,
without float, and with smooth upper surface.
Habitat on wood, stones and water plants in standing
and slowly flowing waters. From Maine to Penn-
sylvania, westward to Wisconsin and even Flathead
Lake, Montana. Common in the Great Lakes.

Fig. 1397. Fredericella sultana, (a) Portion of branch,
natural size, (b) Polyp magnified. (After Hyatt.) (c)
^vV;^ Statoblast. (After Kraepelin.)

9 (8) Colonies consist of cylindrical tubes, which are either branched or form
massive clumps or run over the substratum as hyahne,
lobed tubes Plumatella Lamarck. . 10

Partitions rudimentary or absent, cuticula brown to hyaline, often incrusted. Tentacular
corona markedly horseshoe-shaped, with 40 to 60 tentacles. Intertentacular membrane present.
Statoblasts without hooks; either free, elliptical, with broad float, or (in the horizontal tubes)
without float, of large size and irregular shape.

The commonest genus of our fresh-water Bryozoa. Has'been reported from all continents ex-
cept Africa. Lives in the most diverse habitats, in ponds or streams, usually not in the light.

10 (13) Colony with vertical as well as horizontal branches 11

MOSS ANIMALCULES (BRYOZOA)

953

II (12) Cuticula thick and brown, with a keel that broadens at aperture.

Free statoblasts elongated; proportions i : 1.53 to i : 2.8.

Plumatella princeps Kraepelin 1887.

Tubes openly branched, repent,
with short lateral branches, antler-
like Var. a, emarginata.

Colony robust, branched often ris-
ing from subtratum. Keel little de-
veloped. Statoblasts elongated.

Var. /3, friUicosa.

Vertical branches predominate,
forming an intertwined mass.

Var. 7, mucosa.

Vertical tubes fused into a mass
from which only the aperture rises
free. ..... Var. 5, spongiosa.

Fig. 1398. Plumatella princeps, var. a. (a) Portion
of colony, two-thirds natural size, {b) Branch much
magnified. (After Kraepelin.)

12 (11) Cuticula rarely browned or keeled. Free statoblasts nearly circular,
I : I to I : 1.5. . . Plumatella polymorpha Kraepelin 1887.

Tubes creeping with short vertical side
branches. Cuticula semi-transparent; but
variable; keel not evident.

Var. a, repcns { = P .-arcthusa Hyatt).

Tubes repent, branching or thickly inter-
twined, covering the substratum. Few or no
vertical branches. Cuticula lightly colored to
transparent Var. jS, opprcssa.

Tubes repent, with many elongated and
branched vertical rami. Cuticula semi-opaque,
no evident keel Var. 7, cacspitosa.

Tubes repent. Vertical branches close to-
gether, even fused, forming great solidncss.
Cuticula brown, aperture hyaline, slightly
elongated Var. b, Jiuigosa.

Fig. i?99. PlumaleUa polymorpha, vnr. a. (a) Young colony, two-
thirds natural size, (b) Branch much magni6ed. (c) Statoblast,
X 40. (After Kraepelin.)

954

FRESH-WATER BIOLOGY

13 (10) Horizontal branches only. Cuticula delicate, colorless, hyaline.

Elevated aperture-cone wrinkled and besprinkled with
white. Free statoblasts nearly circular.

Plumatella punctata Hancock 1850.
Stock repent and open,
forming long hyaline tubes
that give rise to only a few,
likewise repent, lateral
tubes. . . . Var. a, prostrata.
From Maine, Pennsylvania,
Illinois, and Lake Erie.

Stock repent, very thickly
branched, completely cover-
ing the substratum, which
seems enveloped in thick
layer of gelatinous vesicles.
Var. /3, densa.

Fig. 1400. Plumatella punctata,
var. a. (a) Colony two-thirds
natural size, (b) Branch much
magnified. (c) Statoblast.
X 40. (After Kraepelin.)

14 (7) Statoblasts large, elliptical, but at each end drawn out into a sharp apex ;

broad float, hooks absent. Lophopiis cristallinus Pallas 1766.
Colony shaped like a sack; erect, sometimes more or less lobed by indentations of margin,
looking then sometimes hke a glove. Outer cuticula layer delicate and hyaline, more incrusted
at base. Polypides scattered, a group of them rising from each lobe. Lophophores with about
60 tentacles. The colony may divide along the constrictions between the lobes. Habitat,
chiefly standing water, such as pools, or, rarely, slowly flowing water. Chiefly attached to
plant stems. From Schuylkill and Illinois rivers.

15 (7) Statoblasts with hooks 16

16 (17) Colonies hyahne, in the form of a rosette, lobed, with horizontal

tubes only Pectinatella Leidy . . 17

They secrete a great gelatinous base which is common to many colonies. Aperture slightly
elevated above common coenecium. Statoblasts large and circular to subrectangular, with
broad bent float and one marginal row of anchor-shaped hooks.

1 7 Pol)^ides scattered or in double row along each lobe , the gelatinous base often

10 to 20 centimeters thick. Pectinatella magnifica Leidy 1851.

Tentacles 60 to 84 in number. Statoblasts about i mm. in diameter, provided with 11 to 22

hooks from 0.15 to 0.25 mm. long. Habitat, submerged branches or twigs of trees, wooden

stakes, gates of dams, walls of reservoirs or stones in brooks. Shady situations, such as south

walls of reservoirs, or wood-covered streams. From Maine to Mississippi.

Fig. 1401. Pectinatella magnifica. (a) Young colony, natural size, (b) Section highly magnified, (c)
Statoblast, ventral view, (d) Statoblast in profile. X iS- (e) Colony on plant stem. X |. (After Kraepelin.)

MOSS ANIMALCULES (BRYOZOA)

955

i8 (i6) Colony unbranched, gelatinous, with a flat ''sole."

Cristatella mucedo Cuvier 1798.

External cuticula lacking, or developed merely as a thin gelatinous layer under the sole.
All polypides contract into a common cavity. Statoblast large, circular, with float and a cir-
clet of hooks on both sides. Young corm of circular form later elongated, worm-like, attaining
a length of 2 to 5 cm. in summer, to 28 cm. in autumn. Colonics often gregarious in a common
gelatinous substance. Eighty to ninety tentacles. Statoblasts with 10 to .54 dorsal hooks, 20
to so ventral hooks. Habitat, in standing or slow-flowing water, on submerged branches of
dead trees, under side of Hly-pads, and on other aquatic plants.

Statoblasts less than i mm. in diameter; hooks on dorsal side 10 to 22; on ventral side

20 to 37 Var. a, genuina ( = C. ophidea Hyatt 1868).

From Maine, Massachusetts, New York, Illinois, and Lake Erie.
Statoblasts over i mm.; hooks on dorsal side 20-34; on ventral side 38-5°-

Var. /3, idae ( = C. idac Leidy 1858; C. tacustris Potts 1884).
From Rhode Island and Pennsylvania.

f^W//.

Fig. 1402. Cristatella mucedo. (a) Colony much enlarged. (6) Statoblast ventral aspect, (c) Statoblast
in profile. X 25. (After Allman.)

IMPORTANT REFERENCES ON FRESH-WATER BRYOZOA

Allman, J. 1856. A Monograph of the Fresh-water Polyzoa. London.
Davenport, C. B. 1890. Cristatella: The Origin and Development of the

Individual in the Colony. Bull. Mus. Comp. Zool., Harvard College, 20:

101-152.
1891. Budding in Paludicella and other Bryozoa. Bull. Mus. Comp.

Zool., Harvard College, 22: 1-114.
1904. Report on the Fresh-water Bryozoa of the United States. Proc.

U. S. Nat. Mus., 27: 211-221.
Hyatt, A. 1866-68. Obvervations on Polyzoa, Suborder Phylactolacmata.

Communications Essex Institute, 4'. 167-228; 5: 97-112, 145-160, 193-

232.

956 FRESH-WATER BIOLOGY

Kraepelin, K. 1887. Die Deutschen Siisswasser-Bryozoen. Eine Mono-
graphic. I, Anatomisch-Systematischer Teil. Abhandl. Naturw. Verein,
Hamburg, 10: 1-168.

Landacre, F. 1901. Sponges and Bryozoa of Sandusky Bay. Ohio Nat.,
i: 96-7.

Leidy, J. 1883. Urnatella graciHs. Jour. Acad. Nat. Sci., Phila., 9: 5-16.

CHAPTER XXIX
THE MOLLUSCA

By BRYANT WALKER, Detroit, Mich.

For the purposes of this treatise and in order to differentiate the
group from the other great phyla of the animal kingdom repre-
sented in our fresh-water fauna, the Mollusca may be defined as
animals with a soft body encased in a hard shell, which may be
either in one piece (univalve) or in two pieces (bivalve). In the
univalve mollusca or Gastropoda, commonly called snails, the shell
may be coiled either obliquely or horizontally or may be a simple
uncoiled, conical, tent-shaped secretion on the back of the animal.
In this class, the animal possesses a distinct head, with a pair of
contractile tentacles, at the base of which are placed the eyes.
On the lower side of the head, between the tentacles, is the mouth,
which, on its inner, upper margin, is usually provided with a chi-
tinous jaw of from one to three pieces. In the lower part of the
mouth is the radula, a muscular ribbon covered with minute teeth.

The fresh-water Gastropoda are divided into two main groups or
subclasses according as they breathe the free air by means of a
lung or are provided with a gill for subaqueous respiration. As
the name implies, these animals progress by crawling on the ven-
tral surface of the body, which is modified to form a flat, muscular
disk called the foot.

The bivalve mollusca or Lamellibranchia, usually known as clams
or mussels, have the body protected by two symmetrical, opposing
valves, which are united above by an elastic tissue called the
ligament. They have no head and have, accordingly, been called
the Acephala. They have no tentacles, eyes, jaws, or radula.
The mouth is simply an orifice at the anterior end of the body, on
each side of which is a flap or palpus, which assists in guiding the
food to the mouth. The foot is an axe-shaped mass of muscular
tissue (hence the name of Pelecypoda often used for the class),
which may be extended from the anterior portion of the shell and,

957

958 FRESH-WATER BIOLOGY

by effecting a lodgment in the bottom, drag the animal slowly-
forward. The lamelHbranchs breathe by means of two gills sus-
pended on each side of the body, which are divided into a series of
water tubes by septa or lamellae, through which the water circu-
lates by means of cilia. The whole body is enclosed in a soft
mantle, which secretes the shell along its outer margins. Poste-
riorly the mantle has two openings, through the lower of which
the water enters the shell, passes forward, aerating the gills and
carrying food to the mouth, and then flows out through the upper
opening.

A more detailed account of the structure of the two classes rep-
resented in our fauna will be found under the head of classification.

The North American Fauna

As would naturally be expected from the vast extent of the ter-
ritory included in the United States and British America and the
great diversity both in the climatic and physical conditions prev-
alent in different portions of the continent, the fresh-water fauna
of North America is not only one of great abundance, both in
species and individuals, but also of great diversity in character; and
a very large proportion of the genera represented are pecuHar to
it. While but one of the eighteen famihes represented in our fauna
is peculiar to the continent, that one, the Pleuroceratidae, is extraor-
dinarily developed both in genera and species and, where found,
its members usually occur in great abundance.

On the other hand, of the eighty-six genera recognized at the
present time, no less than forty-nine, or five-ninths, are peculiar
to North America, while of the many hundred of described species,
it is safe to say that more than ninety per cent are not found else-
where. Indeed, barring the comparatively small number of cir-
cumpolar species in the north, and the somewhat larger represen-
tation of tropical or subtropical forms found on our southern borders,
practically the whole of our molluscan fauna may be said to be
distinctively North American.

The distribution of the various families, genera, and species
represented in our fauna varies greatly in the different sections of
the continent.

THE MOLLUSCA 959

Most of the families have representatives in all portions of the
country where suitable conditions of environment are to be found.
But there are some notable exceptions. Thus the Viviparidae,
which form one of the most conspicuous elements of the fauna of
the Eastern States, are not found west of the Mississippi Valley.
The AmpuUaridae, which replace the Viviparidae in the tropics, are
only found in Florida and Southern Georgia; while the great
family of the Pleuroceratidae, the one family peculiar to our fauna,
is not found west of the Mississippi Valley drainage, except for a
few isolated species that occur in the northern Pacific states.

Many of the genera have a general distribution in all parts of
the continent. That is, some representatives of such genera will
be found practically every place where suitable conditions obtain.
But it is to be borne in mind that comparatively few species have
a general distribution. Many of them have, so far as known, a
very limited habitat, while others range over a large extent of
territory. Many of the genera are likewise restricted to certain
portions of the continent and particularly to certain drainage
systems, while others are confined to a very limited area. The
Coosa River in Alabama, in this respect, has a most remarkable
fauna. No less than six genera and very many species are known
to occur only in it and its tributaries.

But while, in a general way, it is true that our fauna as a whole
is well known, and its distinctive characters recognized, yet the
sum total of our present knowledge, large as it may seem, is very
small and inadequate when compared with what we might and
would like to know about it.

But a very small portion of the continent has been collected over
with any sort of thoroughness, and there are undoubtedly very
many new types, both generic and specific, yet to be discovered.
While, of course, the mere description of new species is the least
important part of the work of the conchologist, yet the accurate
knowledge of all the species found within our borders is the basis
for the solution of the larger problems of distribution and evolution,
which are of great importance. The exact range of very few, if
any, even of our most common species is exactly known. It is
very desirable that lists of the species occurring in all the states

960 FRESH-WATER BIOLOGY

and counties of the country should be compiled. Such local Hsts,
when the specimens are correctly determined, are of great value
and interest and are always acceptable contributions to scientific
hterature.^

The life history and habits of the different species form a subject
of great interest, and as yet but httle is known about them. Then,
too, very little is known of the internal anatomy of our species,
much less, indeed, than of the land mollusca. In all these lines
of work and study there is a fruitful and unreaped field of investi-
gation, which cannot fail to yield both pleasure and profit to the
student who will undertake to study the common forms of mollus-
can fife, which are to be found so abundantly in all parts of our
country.

Collection and Preparation of Specimens

Nearly every permanent body of water has its mollusks, varying
according to its character. Some species are found only in rapidly
flowing water, and others only in ponds and still water. Ditches
and other stagnant waters are usually good collecting ground for
Pisidia and other small species. The low places in the woods,
which dry up in the summer time, have a number of species that
are not found elsewhere, and which bury themselves in the mud
when the water disappears. Sand banks in rivers and lakes are
favorite resorts of many of the smaller species. The under side
of the Hly pads should be scrutinized, while the Ancyli should be
looked for on stones and dead clam shells.

The distribution of the different species in all the states and
territories being of prime importance, the collector should always
bear in mind:

First, that a dead shell is better than none at all;

Second, that dead shells should not be taken, if five ones can
be had, and that careful search will usually discover them in the
immediate vicinity.

Third, that all the species are extremely variable in their abun-
dance from year to year, and so it is a safe rule, "when you're
getting, to get a plenty."

1 The writer will gladly aid students in the identification of their specimens without
charge. Address 45 Alfred St., Detroit, Mich.

THE MOLLUSCA 961

The apparatus for collecting is very simple.

It is necessary to have a dipper and, if possible, a small dredge.
The dipper is made from an ordinary tin one by removing the
bottom and substituting one of fine wire cloth. By removing the
end of the handle, the dipper can be slipped on the end of a cane
or pole when in use. This is useful not only for reaching the larger
specimens from the shore or boat, but especially for sifting the mud
and sand from the bottom, where a multitude of small species live,
which otherwise would not be found. It will be found more con-
venient to empty the contents of the dipper, when thoroughly
washed out, into a pail or small bag, and carry the whole mass
home before undertaking to pick out the shells. If attempted in
the field, many of the smaller and more desirable things are apt to
be overlooked. By spreading the mass out in the sun for a short
time, it will become dry and friable so that the shells can be easily
separated and picked out. An ordinary reading glass is very useful
for the detection of the more minute forms in sorting over such
material.

Many desirable species live in water too deep for the convenient
use of the dipper, and for these it is necessary to have a small
dredge. One with an aperture of 9 by 6 inches is as large as can
be used satisfactorily by a single person in a boat.

Several small bags and a number of wide-mouthed bottles and
small vials should be carried, so that the specimens from different
localities may be kept separate. Care must be taken to keep the
more fragile species separate from the heavier ones, otherwise they
are likely to be damaged in moving about. For the same reason
it is better to fill the bottles partially with water while in the field,
as the mollusks then attach themselves to the glass and are less
likely to be broken. It is not necessary to take alcohol into the
field.

Specimens to be kept for anatomical purposes may be preserved
in alcohol, which at first should be greatly diluted, not stronger
than 25 per cent; after a day or two the specimens should be re-
moved to 50 per cent alcohol, and later to the undiluted. Formal-
dehyde, 2 per cent dilution, is an admirable preservative for ma-
terial of this kind. It should not, however, be used when it is

962 FRESH-WATER BIOLOGY

desired to keep the shells as specimens, as it destroys those left in
it any length of time.

With the exception of the larger species of Planorbis, which are
more easily cleaned by boiling, it is practically immaterial whether
the fluviatile univalves are boiled, or put directly into diluted alco-
hol for a day or two. In either case there is no difficulty in ex-
tracting the animals. The curved points of the collecting forceps
are convenient for this purpose, and hooks of various sizes can be
made from safety pins. By tying these on small wooden handles
very effective instruments can be made. Small hooks or ''probes"
of various sizes fitting into an adjustable handle are most convenient
and can be obtained from any dealer in dental instruments. A
small, fine-pointed dental syringe is indispensable for this work.
When the animal is completely extracted, the interior of the shell
should be thoroughly washed out with the syringe. A small piece
of sponge on the end of a fine copper wire, which can be bent in any
direction, is very useful for removing the mucus, which is apt to
adhere to the interior. This should always be carefully attended
to; if not it will greatly disfigure the specimen when dried. The
exterior should then be thoroughly scrubbed with a soft tooth or
nail brush. When perfectly clean, inside and out, the water should
be carefully emptied out and the shell put aside in the air, but not
in the sun, to dry.

It is not desirable to attempt to clean the minute species by
removing the animal. They should be put directly into 25 per cent
alcohol for a day or two. If to be left longer in the alcohol, the
strength should be increased. Twenty-four hours, however, in the
alcohol is all that is necessary. Then they can be dried in the air
without leaving any offensive odor. Either before or after drying
they can be cleaned, if necessary, by putting them in a bottle of
water, with some fine, clean sand, and shaking them together until
all the dirt has been removed by the sand. Jn the operculate
species, it is desirable to retain the opercula of, at least, part of the
specimens. While it adds to the labor, it increases the value of
the specimen if it is always done. These are easily removed from
the animal and, after being cleaned, should be put inside the shell
and the aperture plugged with cotton. All the foreign matter both

THE MOLLUSCA 963

inside and outside of the shell should be removed by thorough
washing. All the water species are apt to be more or less incrusted
with deposits of lime or oxide of iron. These can be removed by
immersing them in oxalic acid. Care should be taken not to pro-
long the operation, or the texture of the shell may be injured.
Elbow grease is the most effective agent for making good specimens.
When that fails, use the acid. The Ancyli are always more or less
coated in this way, and can easily be cleaned by floating them for
a few minutes on the acid, upside down, and then gently brushing
them off with a soft brush while held on the tip of the finger.

The larger bivalves should be well washed and, if necessary,
scraped off with the knife as soon as taken, care being taken not
to injure the epidermis.

They can be boiled, if desired, when the shells will open and the
animals easily removed. But, as a rule, it is more convenient,
unless collected in large quantities, to cut the muscles, which hold
the valves together, with a thin-bladed knife and scrape the animal
out. Care should be taken not to break the edge of the fragile
species when inserting the knife. All traces of the animal matter
should be removed, and after a thorough washing the valves tied
together with a string until thoroughly dried. Never use colored
twine for this purpose, as it is apt to stain the shells. Any surface
incrustation can be removed either with oxalic or muriatic acid.
The latter is more convenient for the larger species, and can be
applied with a small brush. To avoid trouble, it is safer to wear
rubber gloves, if a large quantity of material is to be cleaned. Care
must be exercised in using the acid and the specimens frequently
washed, lest damage be done to the shell. The smaller bivalves,
the Sphaeria and Pisidia, are best treated by putting into diluted
alcohol for a day or two and then drying them. If left too long
the shells are apt to open, which interferes with the looks of the
specimens. The larger species of Sphaerium are better with the
animal removed. This can be done after boiling, or a few days
in alcohol. As these are usually too small to be easily tied together
to keep the valves from gaping, each specimen, while the hinge is
flexible, should be closely wrapped up in a small piece of tissue
paper until completely dry.

964 FRESH-WATER BIOLOGY

While it is not usually desirable to keep ''dead" shells for the
cabinet, occasionally it is necessary. In such cases, the color can
be in some measure restored by applying a solution of paraffin
and gasoline (a cubic inch of the former in half a pint of the latter).
*'Dead" Unionidae can be improved in appearance and the bril-
liancy of the nacre measurably restored by applying muriatic acid.

A good collection is characterized by two essentials:

First, the careful selection and preparation of the specimens
themselves;

Second, absolute accuracy in the matter of the localities from
which they came.

There is Httle excuse for having poor and ill-cleaned specimens.
There is none at all for failure to keep accurate records of the col-
lector's fieldwork. A drawer of any common species, without any
indication of whence they came, even if well cleaned, would be
absolutely without value. Such a drawer of any of our species
from fifty or one hundred different localities, definitely indicated,
would be a valuable contribution to the conchology of any state.
Specific names can be suppHed or corrected any time, but a mis-
taken or erroneous locality can never be corrected. The collector,
therefore, should be careful never to trust to memory for facts of
this kind. Both in collecting and cleaning, the specimens from
each locality should be kept carefully separated and labeled. Too
much importance cannot be given to this point. The study of the
geographical distribution of the mollusca is one of the most im-
portant branches of conchological work, and, to be of any value,
this must be based on absolutely accurate work on the part of the
collector.

The manner of casing and arranging the collection is largely one
of individual preference. A catalogue, however, is essential, and
it is better to begin systematically in this particular and thus avoid
the necessity of doing it all over again when the collection begins
to assume considerable size. There should be a serial catalogue
and a card catalogue. Each addition to the collection should be
numbered as soon as received and entered in the serial catalogue,
which should be a book ruled in as many columns as the collector
desires.

THE MOLLUSC A 965

The card catalogue is convenient in a small collection. It be-
comes absolutely necessary in a large one. The cards should be
of uniform size for convenience in handling. If it is desired to
have a card for every entry, they can be smaller than if it is desir-
able for economy of space to have as many entries as possible on
one card. In the latter case a convenient size is that of the ordinary
library card, which can be ruled to hold twenty entries. The name
of the species is written on the top, and the number of each entry
of that species and the locality are entered below. Such a card as
this enables the collector to see at a glance not only whether any
given species is represented in his collection, but also from what
localities, and saves a large amount of time which would otherwise
be spent in turning over the leaves of a serial catalogue. The
cards can be kept in drawers or boxes of proper size and can be
arranged alphabetically under the different genera and families.
Guide cards slightly higher than the ordinary card, indicating the
genera, can be inserted in their proper places.

In collections intended for pubUc exhibition, it is usually neces-
sary to have the specimens mounted on cards or blocks. But in
private collections such an arrangement is a mistake, not only
on account of the greater room required for the collection, but
particularly because it prevents the handling of the specimens for
purposes of study.

Specimens under an inch in diameter are most conveniently
kept in glass vials. These can be obtained from any wholesale
druggist. They should be without a neck and of standard sizes.
The length will depend upon the standard size of the tray adopted.
For my own collection I use three sizes, i, |, | inch in diameter.
As these vials are rather fragile, the pressure of the cork is apt to
break them. The cork should therefore be softened by rolling or
crushing. A pair of plumber's burner pliers is useful for this
purpose. The serial number should be put on the cork or on a
small piece of paper inside. Specimens too large for the vials
should have the number on the shell in ink. Then, if a drawer
happens to be overturned, the specimens can be sorted out again
without difl&culty.

When numbered, the vials and specimens should be placed in

966 FRESH-WATER BIOLOGY

trays. For these a standard size should be adopted, so that they
will conveniently fit into the drawers of the cabinet. In the
National Museum at Washington, the unit is i by 2 inches, and
the larger sizes are all multiples of that unit. In the Academy of
Natural Sciences at Philadelphia, the unit is ij by 3. There is
one advantage in the use of the larger unit where space is a serious
question. For the small species the vials may be used only ij
inches in length, and two vials can be put into one tray, thus dou-
bling the capacity of the drawer. The trays should be of the same
depth. One-half inch is sufficient for most of the univalve species.
For the larger species, such as the Unionidae, requiring trays of
good size, f inch is better. These trays can be had of any paper-
box manufacturer, or can be easily cut out of cardboard by the
collector, the corners being fastened together by strips of gummed
paper. The character of the cases for a collection is determined
by the means and incHnation of the collector. Any case of shallow
drawers will do. If, however, cases are to be made, they should
be made of a standard size with interchangeable drawers. Each
tray should have a neat label giving the serial number, the name,
and the locality of the specimens it contains. A box, bottom
side up, can be used for separating the genera and species in every
drawer. Small labels of convenient size for designating them can
be had, already gummed, at any bookseller's.

In packing shells, small specimens should not be mixed with
large ones, as they are apt to get lost; nor should fragile shells be
put in with stronger ones, as they are likely to be broken. The
minute specimens can be put into gelatin capsules, small vials,
quills, or paper tubes made by rolling writing paper around a lead
pencil, gumming down the edge and stopping the ends with cotton.
Do not mix shells from different locahties. Write the locality on
a label and wrap it up with each vial or package. Use plenty of
cotton in packing fragile shells. Pill boxes and match boxes are
convenient for packing purposes. Wrap up each vial or box sepa-
rately, then, if a smash does occur, there is a fair chance of saving
some of the specimens and no danger of mixing the contents of
different packages. Do not send paper boxes by mail. Pack in
a wooden box.

THE MOLLUSC A 967

For purposes of dissection either fresh or alcoholic specimens
may be used. Live specimens may be killed by plunging them
into boiling water for a few seconds. The animal can thus be
removed from the shell in the usual way, using great care not to
mutilate it with the hook; or the shell, if not too heavy, can be
carefully broken away with the forceps. Preserved specimens are
frequently difficult to extract from the shell, in which case the shell
must be removed either by breaking or, if too thick, by dissolving
it in muriatic acid.

^'Two pairs of fine scissors will be necessary, one pair with straight
points, the other with curved points; one or more fine scalpels, and
two pairs of fine forceps, one straight and the other curved. Dis-
secting needles are also necessary. These can be made by forcing
the heads of fine needles, by means of a pair of pliers, into the end
of a round stick of small diameter. The point of one of these
needles should be bent so as to form a hook, first heating the end
of the needle to a white heat."

*'In dissecting the animal, a circular china dish about 4 inches
in diameter and 2 in depth will be necessary; also a piece of sheet
cork as large as will lie at the bottom of the dish, fastened to a
thin sheet of lead with either string or rubber bands. It is best
to have the lead of the same size as the cork. This leaded cork
is to be placed in the bottom of the dish, and the dish filled with
alcohol. If the animal has once been placed in alcohol, all dissec-
tions should be made in alcohol, but freshly killed specimens may
be dissected in water, and many of the organs at this time present
a much more natural appearance than when acted on by alcohol.
Place the animal on the cork and fasten it down with small pins,
or better yet, with very fine, short needles inserted through the
margin of the foot. Then with a fine pair of scissors, commencing
at the head, cut through the integument along the center of the
back, taking care not to injure any of the organs below. The
integument is now to be removed from the dorsal part, turned
back and fastened to the cork, removing the needles from the
margin of the foot and putting them through the edges of the
integument. All the organs of the anterior part of the snail are

968 FRESH-WATER BIOLOGY

thus brought into view, and further dissection of the organs can
be inteUigently made."-^

The method of preparing the jaws and hngual membrane for
examination is as follows:

''On opening the head (of the snail) from above, one readily
notices at the extreme anterior part, close against the outer integu-
ment, a prominent, oval body. This is called the buccal mass. It
is easily cut away from the animal, and will be found to contain
both jaw and lingual membrane. These can be removed by fine
scissors or knives from the buccal mass in the larger species, but
in the smaller species, the method usually employed is putting
the whole buccal mass in a watch crystal, full of a strong solution
of caustic potash. Allowing it to remain for several hours, the
potash will destroy all of the buccal mass, and leave the jaw and
lingual membrane perfectly clean and ready for examination.
They must be well rinsed in clean water, in another watch crystal,
before examination. Another more expeditious process, is to place
the whole buccal mass in a test tube with the solution of potash,
and boil it for a few seconds over a spirit lamp. Pouring the con-
tents of the tube into a watch crystal, the lingual membrane at-
tached to the jaw will be readily seen by a pocket lens. If the
species be small, its whole body may be thrown into the solution.
Still more minute species, may be treated in this way; crush the
whole shell between the glass sHdes; wash the particles of broken
shell in a few drops of water, still keeping the body of the animal
on the slide; when clean, drop on it the caustic potash and boil it
by holding the sHde itself over the spirit lamp.

"For purpose of examination, the jaw and Ungual membrane
may be simply mounted in water and covered with thin glass. One
must be sure in spreading out the lingual membrane not to have
its upper side down, and it is well to cut it transversely in several

^ No detailed instructions for the dissection of the fresh-water moliusks have been
published in this country. For an admirable, fully illustrated paper on the dissection
of the land snail, which can be easily adapted for the use of the student, see Simpson,
Bull. N. Y. State Museum, viii, p. 241 (1901;. The same author has published an
excellent study, fully illustrated, of the anatomy of Anodonta, which should be in the
hands of every student. See Rep. N. Y., State Mus. of Nat. Hist., 35, p. 169.

THE MOLLUSCA

969

places, as the teeth are beautifully shown and often stand detached
on the edges of the cut.

''For preservation for future study, the glycerin preparations
sold by the opticians will be found useful, though they have the
great disadvantages of deKquescing in warm weather." ^

The radula may also be mounted in Canada balsam. In this
case it should be stained with carmine or chromic acid, as otherwise
the specimens will in time become transparent.

Measurement and Descriptive Terms

The length or height of a univalve shell is the distance from the
apex to the basal edge of the lip, measured along a line drawn
through the axis.

The greater diameter is the greatest width, including the lip,
measured on a line drawn at right angles to the axis.

The lesser diameter is measured on the same plane, but on a line
at right angles to the greater diameter.

Shells are dextral or sinistral, accordingly as the aperture is on
the right or left of the axis, when
held, apex uppermost, with the
aperture facing the observer.

In bivalve shells, the length is
the distance from the anterior
to the posterior extremity; the
height is the distance at right
angles between two parallel lines
so drawn as to touch the highest
dorsal and lowest basal points;
the width is the greatest diameter
measured in a line at right angles
to the basal line.

The remainder of the terms in
common use are sufficiently indi-
cated on the following diagrams. 7-9. Greatest diameter.

1 W. G. Binney, Man. Am. Land Shells, p. 44- For full insLruclions in regard to
the preparation ot the radulae of the minute species, see Beecher, Journal X Y. Micro-
scopical Society, 1888, p. 7.

.-5

Fig. 1403. Th

1. Apex.

2. Spire.

3. Operculum.

4. Lip.

6. Umbilicus.
8. Suture,
o. Columella.
-5. Height.

970

FRESH-WATER BIOLOGY

Fig. 1404. The shell of a bivalve.

1. Hinge.

2. Beak.

3. Pseudo-cardinals.

4. Scar of anterior retractor.

5. Scar of anterior adductor.

6. Scar of protractor pedis.

7. Pallial line.

8. Scar of posterior adductor.

9. Scar of posterior retractor.
10. Lateral teeth.

Classification

Of the several classes into which the subkingdom of the Mollusca
is divided, but two, the Gastropoda and Lamellibranchia, are
represented in the fresh-water fauna of North America. The for-
mer includes all the univalve species commonly called snails or
periwinkles, and the latter, all the bivalve forms usually known as
clams or mussels.

The class Gastropoda, as the name implies, are mollusks in which
the ventral portion of the body is developed into a fleshy, more
or less expanded, creeping disk, called the foot, by the muscular
contractions of which the animal progresses.

When fully expanded, the animal is seen to have a distinct head,
with a pair of tentacles, at the base of which are placed the eyes.
In the center of the head, below and between the tentacles, is the
mouth, in which, on the upper surface, are situated the jaws, from
one to three, and, on the lower side, the lingual ribbon or radula,

THE MOLLUSCA

971

the surface of which is covered with numerous rows of small chitin-
ous teeth.

The Gastropoda are either ovo viviparous or oviparous. The sexes
are separate in some groups (Dioecia) and united in the same indi-
vidual in others (Monoecia). All of the fresh- water gastropods are
provided with an external shell, which covers the animal completely
when retracted, and which is spiral, discoidal, or conical in shape.

Owing to the torsion of the body, caused by the spiral shape of the
shell, the animal of all the fresh-water gastropods, while externally
bilaterally symmetrical, is internally asymmetrical. There is but
one lung or one functional gill, as the case may be, and the termina-
tions of the digestive and genital systems, instead of being posterior
and central, corresponding to the mouth, are on the side near the
respiratory chamber.

The Gastropoda are further divided into subclasses, accordingly
as the torsion of the viscera has or has not been accompanied by a
similar twisting of the visceral nerve loop. In the Euthyneura,
the visceral nerve loop lies beneath the intestinal canal, and was
consequently not affected by the torsion to which that organ was
subjected, while in the Streptoneura, the visceral nerve loop lies
above the intestines and became involved in the twisting of the
viscera and was consequently made to assume the form of the figure
8. The aquatic Euthyneura, which comprise practically all our
air-breathing or pulmoniferous fluviatile mollusks, are included
in the order Pulmonata; while the Streptoneura comprise all the
gill-breathing or branchiferous species, which are furnished with
a pecuUar chitinous or calcareous structure attached to the upper
surface of the posterior extremity called the operculum, and which,
when the animal retires within the shell, completely closes the
aperture. Species thus provided are termed operculate. The
Pulmonata, on the other hand, have no operculum, and are there-
fore called inoperculate.

The Pulmonata are divided into two suborders: the Stylomma-
tophora, in which the eyes are borne on the extremities of retractile
tentacles, and which are all terrestrial species; and the Basom-
matophora, in which the eyes are placed at the base of contractile
tentacles, and which are aquatic or amphibious in habit.

972 FRESH- WATER BIOLOGY

The Basommatophora are subdivided ijito three superfamilies
based mainly on the general character of their habitat:

I. Terrestrial or semiamphibious, living in damp places or near
the margin of the sea, but not in the water, — Akteophila.

II. Aquatic, living in fresh water and usually coming occasionally
to the surface for air, — Limnophila.

III. Aquatic, living in salt or brackish water along the seashore
in the littoral zone, — Petrophila.

The Streptoneura are divided into two orders:

I. The Aspidobranchia, in which the nerve centers are not
closely concentrated, and the original bilateral symmetry has not
wholly disappeared, there being two auricles to the heart and two
kidneys.

II. The Pectinibranchia, in which all trace of bilateral symmetry
in the circulatory, respiratory, and execretory systems has disap-
peared and the nervous system is more concentrated.

The fresh-water aspidobranchs all belong to the suborder Rhipido-
glossa, in which the radula has very numerous marginal teeth
arranged like the sticks of a fan.

The Pectinibranchia are divided into two suborders, of which
only one, the Taenioglossa, in which the radula has but one lateral
and two marginal teeth on each side of the central tooth, is repre-
sented in our fluviatile fauna. The fresh-water Taenioglossae are
all included in the superfamily Platypoda, in which the foot is flat-
tened ventrally for creeping purposes.

The several superfamilies of the Euthyneura and Streptoneura
are subdivided into families, of which thirteen are represented in
the North American fauna.

The class Lamellibranchia, so called from the form of the gills,
comprises all the fresh-water bivalve shells commonly called clams
or mussels. The name Pelecypoda is frequently applied to
this class from the hatchet-like shape of the foot. The lameUi-
branchs are aquatic mollusks, without a distinct head and with
the mantle divided into two lobes, which secrete a bivalve shell
united by a ligament, which covers the entire animal. The lobes
of the mantle are united by one or two transverse muscles, which
are attached to the inner surface of the valves and by their con-

THE MOLLUSCA

973

traction close the shell. They are destitute of jaws or radula, and
the cephalic region is furnished only with a pair of labial palps on
each side. They feed by ciliary action and breathe by gills sus-
pended on each side of the body. The digestive system consists
of a stomach, a liver, and a more or less convoluted intestinal canal
with its oral and anal extremities at the opposite ends of the body.
The edges of the mantle lobes in the fresh-water forms are usually
united between exhalent and inhalent orifices, and in some famihes
the posterior margins are extended in one or two siphons. The
foot is ventral, usually compressed, hatchet-shaped, and adapted
for burrowing. The nervous system consists of three principal
groups of ganglia (cerebral, pedal, and visceral), united by nerves.
They are monoecious or dioecious.

The following diagram represents the classification of the fresh-
water Gastropoda as thus briefly outlined.

Class

GASTROPODA

Subclass

Streptoneura.

Order Pectinibranchia Aspidobranchia

Suborder Taenioglossa Rhipidoglossa

Superfamily Platypoda

Euthyneura.
Pulmonata.

I

Basommatophora.

Limnophila Petrophila Akteophila.

•*■ \

Viviparidae Neritidac Lymnaeidae Siphonariidae Auriculidae.

Ampullariidae Planorbidae Gadiniidae

Valvatidae Ancylidae

Assimeniidae Physidae

Amnicolidae

Pleuroceratidae

The Radula

As the radula of the gastropod mollusca is very important as a
basis for classification, the following series of t>^ical forms is given,
which should be used in connection with the key.

974

FRESH-WATER BIOLOGY

AURICULIDAE

^^^n^n^

Fig. 1. Carychium exiguum Say.

SiPHONARIIDAE

29 27 17 15 13 11

'*^

^

Fig. II. Siphonaria alternata Say.

Gadiniidae

Fig. III. Gadinia reticulata Say.

Lymnaeidae

(VWl^^'^

Fig. IV. Lymnaea stagnalis L.

Planorbidae

C 1-8 U

Fig. V. Planorbis irivolvis Say.

THE MOLLUSCA
Physidae

Fig. VI. Physa humerosa GId.

Ancylidae

Fig. VII. Gundlachia meekiana Stimp.

Ampullariidae

Fig. VIII. Ampullaria paludosa Say.

975

C

Fig. IX. Viviparus inlertextus Say.

Valvatidae

r\

Fig. X. Vdlvata tricarinata Say.

976

FRESH-WATER BIOLOGY

ASSIMENIIDAE

Fig. XI. Assimenia grayana Leach.

Amnicolidae

■^^H

o

«

Fig. XII. Amnicola, porata Say.

PLEUROCERAXroAE

Fig. XIII. Anculosa dissimilis Say.

Neritidae

Fig. XIV. Neritina reclivata Say.

The classification of the Lamellibranchia is based primarily on
the structure of the gill. Each gill consists of "a, hollow vascular
axis bearing on each face a row of more or less flattened filaments
which are nothing more than simple expansions of the axis." The
LamelHbranchia are divided into four orders, according as these
filaments are flat and non-reflected (Protobranchia) or parallel,
ventrally directed and reflected (Filibranchia), or are united at

THE MOLLUSCA 977

regular intervals by vascular junctions (Eulamellibranchia) , or are
entirely absent (Septibranchia).

All of the North American fresh-water lamellibranchs belong to
the order Eulamellibranchia. This order is divided into nine sub-
orders, of which only one is represented in our fauna. The suborder
Submytilacea consists of ''Eulamellibranchia, in which the mantle
is only slightly closed, generally there is only a single suture.
Siphons absent or very short. Gills smooth. Nearly always dimy-
arian (with two adductor muscles). Shell equivalve with an exter-
nal ligament."

The Submytilacea are divided into a large number of families
of which seven are represented in the North American fauna:

Margaritinidae Sphaeriidae

Unionidae Cyrenidae

Dreissensiidae Cyrenellidae
Rangiidae.

KEY TO NORTH AMERICAN FRESH- AND BRACKISH-WATER

MOLLUSCA.

1 (103) Animal with a distinct head, bearing, usually, contractile tentacles.

Shell univalve Class Gastropoda . . 2

2 (63, 100) Animal inoperculate, pulmoniferous. . Order Pulmonata . . 3

3 (17,22) Animal terrestrial or semiamphibious. Shell spiral, columella

plicate at the base; outer lip usually dentate or Urate.

Family Auriculidae . . 4

4 (9) Foot entire, not divided transversely. . Subfamily Auriculinae . . 5

5 (6, 7) Shell minute, pupaeform, outer lip thickened, reflected, or expanded.

Carychium M tiller.

A group of small species of general distribution from the Atlantic to the Pacific.
The only genus in the family found at a distance from the seashore. Found in
damp places under dead leaves, pieces of bark, etc. They are usually included
among the terrestrial species and are included here rather on account of their
systematic position than as belonging strictly to the fresh-water fauna. Example,
C. exiguum Say, (Fig. 1405; X 10), from the Eastern States.
Fig. 1405

1 Unless otherwise indicated, the figures are of natural size. In other cases, the
amount of enlargement or reduction is indicated. To obtain the actual size of any
species, divide the length of the figure in millimeters by the index.

978

FRESH-WATER BIOLOGY

6 (5, 7)

Fig. 1406.
7 (5, 6)

Shell oval; lip thickened but not reflected; smooth within; no callous
deposit Auricula Lamarck.

The typical Auriculae are not represented in our fauna. A single species, A .
pellucens Mke. (Fig. 1406), belonging to the subgenus Auriculastrum Fischer, is
found along the southern Florida coast and keys.

Shell oval; lip thickened, with a single strong ridge revolving longi-
tudinally into the aperture Tralia Gray . . 8

A single species, T. pusilla Gmel., (Fig. 1407; X itd), found along the Florida
coast and "easily recognized by its pure brown color, three plaits and the single
ridge on the inside of the impressed outer lip" (Dall.).

Fig. 1407.

8 Shell oblong-ovate; lip thickened by a ridge of callus, simple or denticulate,
within the edge; no lirae or longitudinal ridges.

Subgenus Phytia Gray.

This group has been usually knowTi as Alexia Gray, but that name is preoccupied
and inadmissible. A single species, T. mysotis Dr., (Fig. 1408; X 2|), locally intro-
duced from Europe on both the Atlantic and Pacific coasts. The west coast form
is usually known as Alexia setifer Cooper.

Fig. 1408.

9(4) Foot divided transversely by a sulcus. Subfamily Melampinae . . 10

10 (11, 16) Shell globose-conic; lip sharp, with a dentate or nodulous callus
within Pedipes Adanson.

Several species are found on the southern Floridan and Californian coasts
and are easily distinguished by their globular form and unusually large parietal
tooth. Example, P. unisulcatus Cpr., (Fig. 1409; X 22) from CaUfomia.

Shell ovate-conic, oblong, or subfusiform; outer lip sharp, usually
Urate within Melampus Montfort . . la

Four subgenera: 12, 13, 14, 15.

12 (13) Shell ovate-conoid; spire short; body-whorl very large, broadest
above and tapering to the base; lip Urate within.

Subgenus Melampus s.s.

The species of this group are abundantly found in the salt marshes and
brackish water of both the eastern and western coasts. The shape of the shell
and the apertural armature are eminently characteristic. Example, M.lineatus
Say, (Fig. 14 10; X i,). from the Atlantic coast.

Fio. 1410.

THE MOLLUSCA

979

13 (14) Shell ovate-oblong; spire produced, pointed; outer lip thickened,
sometimes with one denticle on the callus.

Subgenus Ovatella Bivona.

A single European s^Qcits, Melamptis bidenlata Mont., (Fig. 141 1; X 2 j), intro-
duced on the coast of New England. "The shell, except for its smoother epidermis
and obsolete parietal denticle, is almost exactly like the lighter-colored forms
of Tralia tnysotis, a fact which has led to much confusion " (Dall.)- In living
examples, this species is easily distinguished by the transversely divided foot.
Fig. 1411.

14 (15) Shell elongated, solid, rounded to a point at both ends; outer lip
Urate within Subgenus Dctracia Gray.

A single species, Melampus buUoides Mont., (Fig. 1412; X 2,), is found along
the Florida coast and keys.

Fig. 141 2.

15 (12) Shell small, thin, subfusiform; spire elevated; columella twisted to
form one strong, spiral ridge entering the volutions; outer
lip thin, sharp, without internal lirae, thickening or denticu-
lations Subgenus Sayella Dall.

Only two minute species are known, both of which occur on the Florida coast.
Example, Melampus hemphilli Dall. (Fig. 1413; X 5.)

Fig. 1413-

16 (10, 11) Shell small, sinistral, elongate; lip slightly thickened, smooth
within Blauneria Shuttleworth.

A single species, 5. heteroclita Mont., (Fig. 1414; X 3 i), occurs on the Florida
coast. It is easily distinguished by its sinistral shape.

Fig. 1414.

17 (3, 22) Animals marine or semi-amphibious, living on rocks where they are

immersed at high tide. Head without tentacles. ... 18

18 (21) Shell patelliform, with a subcentral apex. Animal with a jaw and

both lung and gill Family SiPHONARnDAE.

Only one genus Siphonaria Sowerby . . 19

19 (20) Shell solid, porcellanous; surface with more or less elevated ribs ex-
l^®k tending to the margin Subgenus Siphonaria s.s.

Two species only, found on the east coast of Florida, Example, 5. dter-
y<^ nata Say, (Fig. 1415)-

Fig. 1415.

q8o fresh-water biology

20 (19) Shell thin, horny, smooth, or with fine radiating lines, which do not

interrupt the margin Subgenus Liriola Dall.

Two species are represented on the west coast. Example, Siphonaria
peltoides Cpr., (Fig. 1416; X li).

Fig. 1416.

21 (18) Shell patelliform, obliquely conical. Animal with a lung only; no

gill; no jaw Family Gadiniidae.

Only one genus Gadinia Gray.

Two species occur on the southern California coast. Another, de-
scribed from Cuba, may be looked for on the Florida keys. Example,
G. reticulata Sby., (Fig. 1417-)
Fig. 1417.

22(3,17) Animal aquatic, inhabiting fresh water 23

Four families: 23, 32, 50, 53-

23 (32) Shell spiral, dextral; spire more or less elongated; tentacles flattened,

triangular Family Lymnaeidae.

Only one genus Lytnnaca Lamarck . . 24

Eight subgenera: 24, 25, 26, 27, 28, 29, 30,31.

24 (25) Shell large, thin; spire slender and acute; body-whorl large, inflated;
columella strongly twisted; axis pervious.

\]] Subgenus Lymnaea s.s.

V! it

The typical species, L. stagnalis L., is circumboreal, but the typical form is
not found in America. The common American form is known as L. stagnalis
oppressa Say, (Fig. 1418; Xf).

.-./ ji '

Fig. 1418.

25 (26) Shell large, solid, bulimiform; spire short; body-whorl large, inflated;

axis impervious Subgenus Bulimnaea Haldeman.

I ' ^ \ \<K The typical and only species, Lymnaea megasoma Say, (Fig. 1419; X i),

\ yy\\ inhabits the northern United States and Canada, west to Manitoba,
\\\^^^^^</ ' ^ Minnesota and Iowa.

Fig. 1419.

THE MOLLUSCA

98

26 (27) Shell thin; spire short, acute; body-whorl large, inflated; lip expanded.

Subgenus Radix Montfort.

The typical species, Lymnaea auricularia L. (Fig. 1420), is European,
but has been locally introduced in several of the Eastern States.

Fig. 1420.

27 (28) Shell thin; spire short; body-whorl large, elongated, not inflated; sur-
face sculptured with spiral incised lines.

Subgenus Pseudosiiccinea Baker.

The typical species, Lymnaea columella Say, (Fig. 142 1 ), has a general distribu-
tion throughout the eastern United States and Canada.

Fig. 1421.
28 (2q) Shell very long and slender; spire elongated, acute; body-whorl long
and narrow; columella smooth. Subgenus Acella Haldeman,

A single species, Lymnaea haldemani "Desh." W. G. Binn., (Fig. 1422), occurs
in the St. Lawrence drainage system and the upper part of the Mississippi River.

Fig. 1422.

29 (30) Shell varying from elongate to short ovate; outer lip (usually) some-
what thickened within; columella somewhat twisted and
phcate; surface with strong, spirally impressed hues.

Subgenus Stagnicola Leach.

The typical species, Lymnaea palustris Mull., (Fig. 1423), is a circum-
boreal and is usually the most common species in the Northern States and
Canada.

Fig. 1423.

30 (31) Shell as in Stagnicola, but with the surface longitudinally costate.

Subgenus Polyrhytis Meek.

The only recent species known, Lymnaea utahensis Call., (Fig. 1424)1 is from
Utah.

Fig. 1424.

982 FRESH-WATER BIOLOaY

31 (24) Shell small, turreted; spire somewhat elevated; spiral sculpture
wanting or subobsolete; columella not twisted; inner lip
usually reflected over the umbilicus.

/\\\Y] Subgenus Galba Schrank.

This group of small species has a wide range from the Atlantic to the Pacific.
The example, Lymnaea obrussa Say, (Fig. 1425; X 15), is a common species in the
Eastern States.

Fig. 1425.

32 (50) Shell discoidal, sinistral, or dextral, or spiral with a very low spire.

Animal sinistral; tentacles cylindrical.

Family Planorbidae . . 33

The dextral species of this family present the apparent anomaly of a sinistral animal with a
dextrally-coiled shell. Such shells are not true dextral shells, but represent the condition of
hypertrophy, so called, in which the spiral growth of the shell, instead of being from the apex
downward, as is usually the case, is, as it were, from the apex upward, the result being an appar-
ently dextral shell with a sinistral animal. Such shells are also called ultradextral. In the
formation of the key to the subdivisions of the family, the shells are treated with reference to
their apparent mode of spiral growth.

33 (47) Shell discoidal Subfamily Planorbinae . . 34

34 (46) Aperture edentate PlanorUs Miiller . . 35

Six subgenera: 35, 36, 39. 40, 41 > 42.

35 (36) Shell sinistral, large; whorls rounded above and below, gradually in-

creasing; aperture but slightly expanded; lip simple and
sharp Subgenus Planorbis s.s.

^ '^^^^Ajrr^ ^ single, characteristic species, P. glabratus Say, (Fig. 1426; X s), is

'V^e' Jh-' found in Florida.

Fig. 1426.

36 (39) Shell dextral or sinistral, few whorled; the whorls carinate above and

rapidly enlarging; base funicular; aperture suddenly ex-
panded and lip thickened.

Subgenus Helisoma Swainson . . 37

37 (38) Shell dextral, carina ted above and below; spire and base funicular.

Section Helisoma s.s.

The typical species, Planorbis antrosus Con., (Fig. 1427; X i^),hasa
general distribution east of the Rocky Mountains and rarely on the
Pacific coast.

Fig. 1427-

THE MOLLUSCA

983

38 (37) Shell sinistral; early whorls flattened and carinate above; base funic-
ular Section Pierosoma Dall.

This group includes nearly all the larger North American Planorbes
and is represented by numerous species found in all parts of the country.
Type, Flanorbis Irivolvis Say, (Fig. 1428).

Fig. 1428.

39 (40) Shell sinistral; aperture campanulate; Hp thickened.

Subgenus Planorhella Haldeman.

The typical form, Planorbis campanulatus Say, (Fig. 1429; X li), is of
common occurrence and wide distribution in eastern Canada and the
United States north of Tennessee.

Fig. 1429.

40 (41) Shell dextral, much depressed; upper surface convex, base flattened;
body-whorl carinate; lip simple.

Subgenus Tropidiscus Stein.

A single species, Planorbis cultratus Orb.. (Fig. 1430; X 2), of this (in
America) tropical group has been collected in Texas and Florida.

Fig. 1430.

41 (42) Shell small, dextral; periphery carinated; base convex; aperture
oblique ; lip simple Subgenus Hippuetis Agassiz.

A group of small species of general distribution through the Northern
States and Canada. All of our species belong to the section Menetus H.
& A. Adams, of which the type is Planorbis opercularis Gld., (Fig. 1431;
X 3), from Cahfornia.

Fig. 143 I.

42 (35) SheU smaU, depressed; body- whorl rounded or obtusely angulated;
lip simple Subgenus Gyraulus Agassiz . . 43

43 (44, 45) Surface spirally striate and hispid.

. . Section Gyraulus s.s.

A few, small species, not uncommon in the eastern Northern States
and Canada. The group is not represented on the Pacific coast. Ex-
ample, Planorbis hirsutus Gld., (Fig. 1432; X3)-

984 FRESH-WATER BIOLOGY

44 (43, 45) Surface smooth or finely striate Section Torquis Dall.

^■^^

This group of small species is o\ general distribution from the At-
.7i:*5^ /--^ lantic to the Pacific. Type, Planorbis parvus Say, (Fig. 1433; X 45)-

Fig. 1433-

45 (43, 44) Shell minute; surface costate. . . Section Armiger Hartmann.

A The typical species only, Planorbis crista L., (Fig. 1434; X 7), repre-

sents this group in our fauna and has been recorded from Maine to Illi-
nois and northward.

Fig. 1434-

46 (34) Aperture with one or more sets of laminae or teeth behind the margin.

Segmentina Fleming.

The typical Segmentinae are not represented in our fauna. All of the
American species belong to the subgenus Planorbula Haldeman. The type
5. armiger a Say, (Fig. 1435; X 2) is common in the northern Eastern States
and Canada.

Fig. 1435.

47 (33) Shell spiral, dextral, flattened above and convex below; body-whorl

very large Subfamily Pompholiginae . . 48

48 (49) Shell imperforate Pompholyx Lea.

'i| \ Two or three species only are known from California. Type, P. effusa

•)) Lea., (Fig. 1436; X 2i).

Fig. 1436.

49 (48) Shell deeply umbilicate Carinifex W. G. Binney.

A\' \\l// ) '^^^ typical species, C. newberryi Lea., (Fig. 1437)1 is. from Cali-

\V^ijjg; / fomia.

Fig. 1437.

50 (53) Shell spiral, sinistral. Animal sinistral; tentacles slender, cylindrical.

Family Physidae . . 51

THE MOLLUSCA

985

ei (52) Shell with body-whorl usually inflated. Inner edge of mantle digitate
or lobed, extending partly over the shell.

Physa Draparnaud.

T The species of this genus are very numerous and extremely variable, so that
many more species have been described than really exist. The Physae are found
in all parts of the country, but the majority of the species are inhabitants of the
Northern States and Canada. Example, P. gyrina Say, (Fig. 143^; X li).

Fig. 1438.

52 (51) Shell slender, elongated. Inner edge of mantle simple, not extending

over the shell Aplexa Fleming.

The typical species, .4. hypnorum L., (Fig. 1439; X li), is circumboreal and has a
'),l general distribution through the Northern States and Canada from the Atlantic

'\\W'.vy/ to the Pacific.

Fig. 1439.

53 (23) Shell patelliform or depressed, dextrally spiral, neritiform or planorbi-

form. Animal sinistral or dextral; tentacles short, blunt,

cylindrical Family Ancylidae . . 54

Five genera: 54, 59, 60, 61, 62.

54 (59) Shell patelliform, small, thin; apex posterior, slightly inclined to one

side Ancyliis Miiller . . 55

55 (58) Apex inclined to the right Subgenus Ancylus s.s . . 56

56 (57) Apex subacute, radially striate Section Ferrissia Walker.

Numerous species and of general distribution, usually found adhering to
stones, etc., in running water. Type, Ancylus rividaris Say, (Fig. 1440; X 3)-
Fic. 1440.

57 (56) Apex depressed, smooth. ........ Section Laevapex Walker.

The species of this group are usually found in quiet water and are. as
a rule, larger, thinner, and more depressed than the Ferrissias. Type,
Ancylus diaphanus Hald., (Fig. 1441; X 2J).
Fig. 1441.

58 (55) Apex inclined to the left Subgenus Acroloxus Beck.

Only one American species, Ancylus nutlallii Hald., (Fig. 144^; X 2),
from Oregon, has been referred to this group, but its anatomy is un-
known and its generic position is very doubtful.

Fig. 1442.

986 FRESH-WATER BIOLOGY

59 (60) Shell large, thick and solid; apex smooth.

La7ix Clessin.

This genus is restricted to the Pacific coast and is distinguished by
the large size and thick sohd shells. Type, L. newberryi Lea. (Fig.
1443)-

Fig. i44i

60 (61) Shell ancyliform, small, thin, with a septum across the apical portion

of the interior Gundlachia Pfeiffer.

f5.v^ This very remarkable and peculiar genus has 'a general but very local

K/Mllf distribution from the Atlantic to the Pacific. Example, G. meekiana
Stimp., (Fig. 1444; X 6), from the Eastern States.

FlG^ 1444-

61 (62) Shell small, spiral, dextral, neritoid, or crepidula-like, with a broad,
thin, columellar plate projecting across the end of the aper-
ture next to the spire Amphigyra Pilsbry.

Only a single species, A. alabamensis Pils., (Fig. 1445; X 10), from the
Coosa River, Alabama, is known.

FiC. 1445-

62 (54) Shell very minute, dextral, spiral, subdiscoidal; columellar margin
broadly dilated Neoplanorhis Pilsbry.

Four species of this genus have been recently described from the Coosa
River, Alabama, and are among the smallest mollusks known in our
faima. Type, N. tantillus Pils., (Fig. 1446; X 10).

Fig. 1446.

63 (2, 100) Animal operculate, branchiferous (except Assimenia). Radula

with seven rows of teeth.

Order Pectinibranchiata. . Suborder Taenioglossa . . 64
Six families: 64, 65, 66, 71, 72, 90.

64 (65) Shell small, spiral, dextral, conical; operculum spiral. Animal pul-
moniferous Family Assimeniidae.

Only a single genus Assimenia Leach.

The Assimenias live in brackish water in the upper part of the littoral zone.
Two species occur on the Florida keys and two on the coast of California. Ex-
ample, A. calif ornica Try on, (Fig. 1447; X 4).

Fig. 1447.

THE MOLLUSCA

987

65 (66) Shell large, globose-turbinate; umbilicate; operculum corneus, con-
centric. Animal with the respiratory chamber divided into
two parts, one being the lung and the other containing a gill.

Family Amplllakiidae.
Only a single genus A mpullar ia LamnTck.

The Ampullarias are the largest of our fresh-
water snails. Two or three species occur in
Georgia and Florida. Example, A. paludosa
Say, (Fig. 1448).

Fig. 1448.

66 (71) Shell of moderate size, dextral, turbinate, imperforate, or subperforate;
operculum corneus. Animal branchiferous.

Family Viviparidae . . 67
Four genera: 67, 68, 69, 70

67 (68) Shell rather thin; operculum concentric, inner margin simple. Animal
with foot of moderate size, not produced beyond the snout.
Teeth of the radula multicuspid. . . Vivipariis ^\ontioxi.

Several species are found in the Mississippi Valley and
from Ohio and Indiana south to the Gulf. They arc
usually to be distinguished from the Campelomae by the
thinner and more globose shells and convex whorls. Ex-
ample, V.intcrtextus Say, (Fig. 1449; X li).

Fig. 1449-

988

FRESH-WATER BIOLOGY

68 (69) Shell thick and solid; operculum concentric, inner edge simple. Animal
with the foot very large, much produced beyond the snout.
Teeth of the radula simple or only minutely crenulate.

Catnpeloma Rafinesque.

This genus is peculiar to North America and the several
species are usually very abxmdant, when found. Though norm-
ally dextral, sinistral examples are not uncommon. They range
from the Mississippi Valley east to the Atlantic and from the St.
Lawrence Valley south to the Gulf. Example, C. subsolida Anth.,
(Fig. 1450).

Fig. 1450.

69 (70) Shell turreted; operculum with a subspiral nucleus.

Lioplax Troschel.

This genus is also peculiar to this country. The several species are restricted
to the states east of the Mississippi and south of Ohio and New Jersey. Type,
L. subcarinata Say, (Fig. 1451)-

Fig. 145 1.

70 (67) Shell (typically) large, solid, imperforate; spire elevated; operculum
concentric, with the inner margin reflected, forming an ele-
vated, marginal fold Tulotoma Haldeman.

This genus is peculiar to North America and is restricted to the
Alabama River and its tributaries in Alabama. The two leading
species are remarkable for their heavy, nodulous, or tuberculated
shell. Type, T. magnifica Con., (Fig. 1452).

Fig. 1452.

71 (72) Shell small, spiral, dextral, turbinate, or subdiscoidal; aperture entire,

circular; operculum round, multispiral. No basal denticles

on the central tooth of the radula. . Family Valvatidae.

Only one genus Valvata Miiller.

The several species of this genus are usually found in great numbers and
are of general distribution. Example, V. tricarinata Say, (Fig. 1453 ; X 4).

Fig. 1453.

THE MOLLUSCA

989

72 (90) Shell small, spiral, dextral. Central tooth of the radula with one or

more basal denticles. . . . Family Amxicolidak . . 73
Five subfamilies: 73, 74, 82. 88, 89.

73 (74) Operculum calcareous, concentric Subfamily Bythininae.

Only one genus Bythinia Gray.

A sinRle European species, B. tentaculala L., (Fig. 1454; X 2), has been intro-
duced by commerce from the Hudson River, along the line of the Erie Canal,
and into the Great Lakes as far west as Chicago.

Fig. 1454-

74 (82) Operculum corneus, paucispiral. Shell thin; columella not thickened.

Foot simple Subfamily Amnicolinae . . 75

Six genera: 75, 77, 78, 79, 80, 81.

75 (76) Shell smooth, usually subglobose. Central tooth of the radula multi-

cuspid, with a tongue-shaped process projecting on the ante-
rior surface and beyond the base and with several basal
denticles Amnicola Gould and Haldeman . . 76

Very numerous both in species and individuals. In shell characters some of
the more elongate species approach Paludestrina, but as a rule the shell is more
globose, with a shorter spire. Type, A. limosa Say, (Fig. 1455; X 4)-

Radula more minute and the denticulations of the cusps of the teeth
finer and sharper Subgenus Cincinnatta Pilsbry.

This subdivision is based wholly on the character of the lingual teeth. The
shell characters are those of Amnicola. Type, Amnicola cmcinnatiensis Anth.,
(Fig. 1456; X2i).

Shell similar to Amnicola, but more slender and elongated. Central
tooth of the radula with but one basal denticle on each side
and without the tongue-shaped process.

Paludestrina Orbigny.

The species of this genus are numerous and range from the Atlantic to the Pa-
cific. Example, P. nickliniana Lea, (Fig. i457; X 6).

Shell elongated, turreted, longitudinally ribbed or pHcate.

Trvonia Stimpson.

Fig. 14s 5

76

Fig. 1456.

77 (78)

Fig. 1457-
78 (77)

The type and only species, T. ./a//,ra/. Stimp.. (Fig. 145S; X 2i), is found fossU
M W in southern California and living in Nevada.

Fig. 1458.

990

FRESH-WATER BIOLOGY

79 (80) Shell elongated, strongly carinated on the periphery.

Pyrgulopsis Call and Pilsbry.

^ . The typical species, P. nevadensis Stearns (Fig. 1459; X 3), is from Nevada. Others

AVa \.^J^ have been described from the Mississippi and Tennessee valleys.

80 (81) Shell ovate-conic; whorls shouldered and usually coronated with
spines Potamopyrgus Stimpson.

Two species from Florida and Texas, respectively, are represented in our
fauna. Typically spinose, all the species are dimorphic, having both an angu-
late, spinose form and a smooth, ecarinate one. Example, P. coronatus Pfr.
(Fig. 1460; X3l).

Fig. 1460.

81 (75) Shell subpyramidal, rather sohd, smooth; body- whorl subangulated
at the periphery. . . . Littoridina Eydoux and Souleyet.

A South American genus. A single species from Florida, L. monroensis,
Frfld. (Fig. 1461; X 7), has been doubtfully assigned to it.

Fig. 1461.

82 (88) Shell with a large body- whorl and short spire; columella usually

callously thickened; operculum corneus, subspiral. Foot
simple. Central tooth of the radula with several basal

denticles Subfamily Lythoglyphinae . . 83

Five genera: 83, 84, 85, 86, 87.

83 (84) Shell depressed-conic; base concave, widely and deeply umbilicated.

Cochliopa Stimpson-

A Central American genus, of which one species, C. riograndensis P. and
F. (Fig. 1462; X 6), has been found in Texas and another (doubtfully) in
California.

Fig. 1462.

84 (85) Shell minute, globose-turbinate, narrowly but deeply umbilicated;
columellar lip thin; operculurr corneus, paucispiral; nuclear
whorls large, slowly and regularly increasing.

Clappia Walker.

Only a single species, C. clappii Walker (Fig. 1463; X 6^), from the Coosa
River, Alabama, is known. It somewhat resembles Somatogyrus in shape,
but can be easily distinguished by its deep umbilicus and peculiar operculum.

Fig. 1463.

THE MOLLUSCA

991

85 (86) Shell obliquely ovate, thick, solid, imperforate; columella flattened
and calloused; lip sinuous, effuse, and projecting anteriorly.
Verge winged Fluminicola Stimpson.

A characteristic west coast genus. In shell characters, it is quite simi-
lar to Somatogyrus, but differs radically in anatomical details and is widely
separated in range. Type, F. nuttalliana Lea (Fig. 1464; X 2).

Fig. 1464.

86 (87) Shell usually thick and soHd, imperforate or narrowly perforate;
body-whorl large; columella callously thickened; spire usu-
ally short; aperture very obUquc, lip projecting above; oper-
culum subspiral, nuclear whorls small, rapidly increasing.

Somatogyrus Gill.

A group of small species found, mainly, south of the Ohio and east of the

Mississippi. The thickened columella is characteristic and enables the species

to be easily separated from the associated genera. Example, S. subglobosus

Say (Fig. 1465; X2).

87 (86) Shell not very thick, imperforate; body-whorl large; spire short;
peritreme continuous in the same plane; columella scarcely
thickened. Verge simple Gillia Stimpson.

This genus is restricted to the Atlantic coast states, ranging from New Jer-
sey to South Carolina. Type, G. altilis Lea (Fig. 1466; X 2).

Fig. 1466.

88 (89) Shell as in Amnicolinae, very small; operculum circular, multispiral.

Foot simple Subfamily Lyogyrinae.

Only one genus Lyogyrus Gill.

A peculiar genus of minute species restricted to the Atlantic coast states.
Easily distinguished by its operculum. Type, L. pupoideus Gld. (Fig. 1467; X6).

Fig. 1465.

Fig. 1467.

89 (88)

Shell elevated, turreted; operculum subspiral. Foot divided by a

transverse sulcus Subfamily Pom.atiopsinae.

Only one genus Pomatiopsis Tryon.

The species of this group are terrestrial or rather semiamphibious in habit,
being always found near but not in the water. The divided foot is very pe-
culiar. The animal, aided by its long snout, progresses by a series of steps.
Type, P. lapidaria Say (Fig. 1468; X 4)-

90 (72) Shell dextral, spiral, thick, soHd, globose, or elongated; operculum
corneus, subspiral. Animal without an external verge. Cen-
tral tooth of the radula without basal denticles.

Family Pleuroceratidae . . 91
Seven genera: 91, 92, 94, 95, 97. 98, 99-

992

FRESH-WATER BIOLOGY

91 (92) Shell large, fusiform; base of aperture prolonged in a long canal.

lo Lea.

This group of large, striking species is confined to the rivers of east-
ern Tennessee. They are found only in very rapidly running water.
Example, /. spinosa Lea (Fig. 1469).

Shell globose-conic; columella callously thickened above and below;
aperture shortly channeled below.

Lithasia Haledman . . 93

The Lithasiae form a very distinct group characterized by the colu-
mella thickened by deposits of callus above and below and the short canal
at its base. With the exception of three species, which extend as far
north as the Wabash River, Indiana, the group is restricted to Ken-
tucky, Tennessee, and Alabama. Type, L. geniculata Con. (Fig. 147c).

Fig. 1470.
93 Shell similar to Lithasia, but with the basal canal more produced.

Section Angitrema Haledman.

This group connects Lithasia with lo. Type, Lithasia armigera Say
(Fig. I 471).

Fig. 1471.
94 (95) Shell obovate, thick, solid; spire short; body-whorl large; columella
callously thickened above, incurved below and subtruncate.

Eurycaelon Lea.

This genus, when restricted to the species grouping about the t3TDe, is
confined to the rivers of the Tennessee drainage system. Type, E. anthonyi
Budd (Fig. 1472).

Fig. 1472.

THE MOLLUSCA

993

95 (97) Shell elongated, conic, or cerithiform; aperture subrhomboidal, pro-
longed into a short canal below; columella twisted, not
callously thickened. . . . Pleurocera Rafinesque . . 96

Exceedingly abundant and of great variety. Numerous species have
been described from the rivers of Kentucky, Tennessee, and Alabama. A
few species extend north to the Great Lakes and west to the Mississippi
Valley. The species vary greatly in contour, ranging from long, slender,
and rather thin to large, heavy, and broadly conic. Example, P. canalicu-
latum Say (Fig. 1473).

Fig. 1473.

96 Shell smooth; spire obtusely conical; body- whorl subcyUndrical ; aper-

ture subquadrate; columella thickened below, twisted and
drawn back, base subcanahculate; lip very sinuous.
Vv Section Strephobasis Lea.

A niunber of nominal species have been described from Tennessee and
northern Alabama. Type, Pleurocera plena Anth. (Fig. 1474).

Shell ovate-conic to elongate; smooth, plicate, striate, or tuberculate;
aperture subrhomboidal, subangular at the base, but not
canaliculate; columella simple, smooth. . . Gofiiobasis \^t^.

This genus comprises about three-fifths of all the species of the family
and is enormously developed in the rivers of Tennessee and Alabama. A
few species extend north to the St. Lawrence Valley and west to Texas and
the western tributaries of the Mississippi. A small group of species is also
found on the Pacific coast and is the only genus of the family represented in
that region. Example, G. virginica Gmel. (Fig. 1475), from the Atlantic
states.

Fig. 1474.
97 (98)

Fig. 1475-

98 (99) Shell conical or globose-ovate; aperture with a slit along the suture,
entire below Gyrotoma Shuttleworth.

This remarkable genus is confined to the Coosa River, Alabama, where
it is represented by a considerable number of described species. The
sutural sHt is characteristic and is either direct, narrow, and deep, or ob-
lique, short, and wide. Example, G. demissum Lea (Fig. 1476).

Fig. 1476

994

FRESH-WATER BIOLOGY

99 (91)

Shell thick, solid, subglobose, with a very short spire, or thinner and
conical; aperture oval or subcircular, entire below; columella
callously thickened. . Anculosa Say.

This group differs from all of the genera of the family by the entire aperture.
The heavy, subglobose species range from the Ohio River south into Alabama and
Georgia but are not found in the northern Atlantic States nor in the Mississippi
Valley. The thin, conical species are characteristic of the Atlantic drainage
from New York southward. Type, A. praerosa Say (Fig. 1477) •

Pig. 1477.

100 (2, 63) Radula with numerous rows of teeth, consisting of a central
tooth, 2-5 laterals, and numerous marginals arranged like the
sticks of a fan.

Order Aspidobranchia . . Suborder Rhipidoglossa.
Represented by a single family. . . Neritidae . . loi

loi (102)

Fig. 1478.

Shell globose, imperforate, very thick and solid; aperture semi-
ovate, columellar region expanded, flattened, and thick-
ened; operculum calcareous, edge with projecting processes
(apophyses), articulating with the columella.

Neritina Lamarck.

A few species of this characteristic tropical genus are found in the fresh and
brackish waters of Florida and the Gulf coast. Example, N. reclivata Say (Fig.
1478).

102 (loi) Shell small, thin, corneus; columella concavely flattened, calloused;
operculum corneus, paucispiral, without apophyses.

Lepyrium Dall.

This genus was created for a single small species, known only from the
Coosa and Cahawba rivers in Alabama and is peculiar in the character of
the operculum. Type, L. showalteri Lea (Fig. 1479; X35).

Fig. 1479.

103 (i) Anunal acephalous. Shell consisting of two opposing, symmetrical
valves united by a ligament. Class Lamellibranchia . . 104

Represented by a single order, Eulamellibranchia . . 104
Seven families: 105, 106, 166, 167, i73, i74; in two groups; 104, 165.

104 (165) Shell equivalve; interior nacreous; ligament external; hinge with

or without teeth, but never with true cardinal teeth; when

present, the modified anterior lateral teeth are known as

pseudocardinals and the posterior teeth as laterals. . . 105

Two families: 105, io6.

THE MOLLUSCA

995

105 (106) Shell elongated, laterally compressed; hinge with usually only
pscudocardinals; laterals, when present, very obscure. Gills
without water tubes and with scattered interlamellar con-
nections, which in certain places form irregular diagonal rows.

Family jMargaritanidae.
Only one genus Margaritana Schumacher.

The typical species, M .margaritiJera'L. (Fig. 1480; X?), is circumboreal, but in this country is
found only in the northern Atlantic and Pacific states, being unknown, with one possible excep-
tion, from the whole interior portion of the continent. Another species is found in the Ten-
nessee and Ohio drainage systems, and two more have been described from the Gulf drainage.

Fig. 1480.

106 (105) Shell subcircular, oval, subtriangular, or elongated ; hinge edentulous
or with pscudocardinals only or with both pscudocardinals
and laterals. Gills with water tubes and distinct, contin-
uous interlamellar septa, running parallel to the filaments.

Family Unionidae . . 107

107 (121, 140) Marsupium formed by all four gills or by the outer gills only;
edge of marsupium always sharp and not distending; water
tubes simple in the gravid female.

Subfamily Unioninae . . 108

Five genera: 108,

13, 114. 115, 117

108 (113) All four gills serving as marsupia. Shell alike in both sexes, tri-
angular, quadrate or rhomboidal, solid, inflated, beaks
usually prominent, sculptured with a few coarse, subparallel
ridges, which are inflated where they cross the posterior
ridge; posterior ridge ordinarily well developed; hinge com-
plete, with strong teeth; hinge plate wide; berjk cavities deep
and compressed Quadrula Rafinesque . . 109

Four sections: 109, no, in, 112.

996

FRESH-WATER BIOLOGY

109(110) Surface plicate Section Crenodonta SchXnteT.

The species of this group, characterized by the heavy, plicate sculpture of the valves, are
among the largest and heaviest of the American Unionidae. They are very abundant throughout
the Southern States from Georgia to Texas. Two species range north into the St. Lawrence
drainage, the headwaters of the Mississippi, and to Lake Winnipeg. Type, Quadrula plicata
Say (Fig. 1481; Xi).

Fig. 1481.

no (in) Surface pustulose, with a radial furrow above the posterior ridge,
usually painted with triangular spots or chevron-shaped
Unes Section Quadrula s.s.

The typical species, Q. cylindrica Say (Fig. 1482; X 5), ranges through the entire Ohio,
Cumberland, and Tennessee river systems and west to Arkansas. A few other, less elongated,
species are found in Tennessee and Alabama.

Fig. 1482.

THE MOLLUSCA

997

III (112) Surface pustulose; no radial furrow above the posterior ridge;
unicolored or rayed, never painted as in Quadnda s.s.

Section Theliderma Swainson.

This section comprises three well-marked groups: first, that of the typical species, Quadrula
lachrymosa Lea (Fig. 1483), having a quadrate or rhomboid shell with a wide, shallow radial
furrow in front of the posterior ridge; second, that of Q. piislulosa Lea, with a rounded, quad-
rate shell with no radial furrow; third, two small species from Georgia and Florida, rounded-
rhomboid in shape, without the furrow and with the surface covered with zigzag corrugations.
Most of the species are found only in the Southern States, but the first two groups have repre-
sentatives ranging north to Michigan and Minnesota.

Fig. 1483.

112(109) Surface smooth StciionFiisconaia Simpson.

While the majority of the species of this
section are found in the Southern States, it is
well represented as far north as Michigan and
the upper Mississippi. Type, Quadrula un-
data Bar. (Fig. 1484)-

Fig. 1484.

998

FRESH-WATER BIOLOGY

113 (114) All four gills serving as marsupia. Shell large, solid, rhomboid,
truncated posteriorly in the male, elongated, with a strong
posterior ridge, sexes dissimilar in shape, the posterior region
being rounded and subcompressed in the female; hinge com- ^|
plete; surface pustulose, except on the extended portion of
the female Tritigonia Agassiz.

The type, T. tuber culata Bar . (Fig. 1485; X i), is very common in the Mississippi drainage and
in the Southern States from Alabama to Texas.

Fig. 1485.

THE MOLLUSCA

999

114 (115) Outer gills only serving as marsupia. Shell rounded; beaks sculp-
tured with numerous line irregular corrugations; hinge com-
plete; nacre violet Rotundaria RatVncsque.

The type, R. luberculata Raf. (Fig. i486), ranges from southern Michigan through the Ohio
Tennessee, and Mississippi systems, south to Texas. Another species ranges from Kentucky
and Tennessee to Iowa.

Fig. i486.

115 (117)

Outer gills only serving as marsupia. Shell alike in both sexes;
triangular to rhomboid, usually with a prominent umbonal
region; beaks at or near the anterior end; beak cavities shal-
low; hinge complete; surface smooth, brown to yellow,
usually not very dark, frequently rayed.

Pleurobema Rafmesque . . 116

This is a large group, of which
more than seventy species are
known. With the exception of a
few species found in the Ohio and
Mississippi drainage, it is confined
to the streams of the Southeastern
States from Tennessee and Georgia
to the Mississippi. The shells of
this genus are easily distinguished
from the Quadrulac, which they
often resemble by the uniformly
shallow beak cavities. Type, P.
cldva Lam. (Fig. 1487).

Fig. 1487.

ICX)0

FRESH-WATER BIOLOGY

ii6 Shell large, irregularly oval, inflated; surface with a number of

large, scattered tubercles. . . Section Plethohasus Simpson.

This section contains only two species, inhabiting the Ohio and Tennessee drainage areas.
The type, Pleurobema aesophus Green (Fig. 1488; X i), extends west into Missouri and Minnesota.

Fig. 1488.

117 (108) Outer gills only serving as marsupia. Shell alike in both sexes;

ovate to elongate, rounded in front, pointed or biangulate
behind; beaks nearer to the middle than to the anterior end;
hinge complete; surface usually smooth, dark brown to black,
often indistinctly rayed Z^^;z/o Retzius . . 118

118 (119, 120) Shell elongated, rhomboid or oval, more or less biangulated

behind; surface smooth or feebly corrugated; beak sculpture
consisting of a few rather strong ridges, which are nearly
parallel to the growth lines or slightly double-looped.

Section Elliptio Rafinesque.

The typical section of this genus is restricted to the Old World. The section Elliptio is the
largest group of Unionidae represented in our fauna. More than ninety species are recognized.
The metropoHs of the genus is in the Southeastern States, but representatives are found in all
of the Eastern, Southern, and Central States. Type, Unio crassidens Lam. (Fig. 1489; X 5).

Fig. 1489.

THE MOLLUSCA lOOl

119 (118, 120) Shell spinose Section Canlhyria Swainson

The typical and only species,
Unio spinosus Lea (Fif,'. 141^0;
X 3 ), is confined to the Altamaha
River, (JeorKia, and is one of the
most remarkable Unios known.
In the extraordinary develop-
ment of the spines, it is unique.

Fig. 1490.

120 (ii8, 119) Shell smooth; beaks sculptured with concentric ridges.

Section Uniomcrus Conrad.

The typical species, Unio tclralasmus
Say (Fig. 1491; Xj), has a wide range
from Ohio south to Alabama and Texas.
A few other species are found in Georgia
and Florida.

Fig. 1491.

121 (107, 140) Marsupium formed by the entire outer gills, distending trans-

versely, when charged; water tubes in the gravid female
divided longitudinally into three tubes, of which only the
center one is used as an ovisac. Hinge rarely complete, the
laterals or both the pseudocardinals and laterals being often
entirely wanting; sexual differences in the shell very rarely

present Subfamily Anodontixae . . 122

Eleven genera: 122, 123, 124, 125, 126, 127, 128, 129, 130, 134, 139.

122 (123) Hinge with lateral teeth wanting and only rudimentary pseudo-

cardinals; beak sculpture consisting of a few strong, con-
centric ridges. Ovisac of each water tube subdivided into
a number of compartments running crosswise to the gill.

Strophitus Ratinesque.

Only a few species are known, most
of them coming from the Southeast-
ern States. The species figured, S.
cdcntulus Say (Fig. 1402; Xi), has a
wide range from New England to
North Carolina and west to Minne-
sota and Tennessee.

Fig. 1492.

I002

FRESH-WATER BIOLOGY

123 (124) Shell thin; hinge edentulous; beak sculpture consisting of several
more or less doubly-looped parallel ridges, often slightly nod-
ulous on the loops Anodonta Lamarck.

This genus is the only one of the North American Naiades that has a general distribution
from the Atlantic to the Pacific. Numerous species are recognized. They are easily distin-
guished by the edentulous hinge and double loop of the beak sculpture. Example, A . grandis
Say (Fig. 1493; X5).

Fig. 1493.

124 (125) Shell smooth, elongated, rather thin, inequilateral, compressed;
epidermis shining, often rayed; a single, imperfect pseudo-
cardinal in each valve and sometimes vestiges of laterals.

Lastena Rafinesque.

Only a single species is
known, L. lata Raf. (Fig.
1494; X 1), and is found in the
Ohio, Cumberland, and Ten-
nessee river systems.

Fig. 1494.

125 (126) Shell smooth, elongated, subtriangular, with usually a high, sharp
posterior ridge; hinge with a rudimentary pseudocardinal
and lateral in each valve Gonidea Conrad.

This genus, represented
by a single species, G. ati-
gw/a/a Lea (Fig. 1495; x|),
as usually found, is remark-
able for the sharp posterior
ridge and more or less
flattened posterior region.
It is a characteristic west
coast species and ranges
from central California
north to British Columbia,
and east to Idaho.

Fig. 1495.

THE MOLLUSCA

lOO

126 (127) Shell smooth, elliptical; hinge edentulous; beak sculpture consisting
of a few fine, concentric ridges. . . Anodontoides Simpson.

The type, A. ferussaciana
Lea (Fig. 1496; x 1), is of
general distribution in the St.
Lawrence, Ohio, and Mis-
sissippi drainage areas. The
concentric undulations of the
beaks are characteristic.

Fig 1496.

127 (128) Shell small, solid, thick in front, with two radial ridges extending
from the beaks to the biangulated posterior end. Pseudo-
cardinals solid; laterals wanting Pegias Simpson.

A single species, P.fahula Lea (Fig. 1497), from the Cum-
berland and Tennessee river systems, is the only one known.

Fig. 1497

128 (129) Shell large, inflated, subrhomboidal, with two radiating rows of
knobs; beak sculpture coarse, continuous with that of the
surface which consists of oblique folds and wrinkles; pseudo-
cardinals large; laterals short and blurred.

Arcidens Simpson.

The typical and only species, ^ . confragosa Say (Fig. 1498; X j). is common throughout the
Ohio and Mississippi drainage systems and southwest to Texas.

Fig. 1498.

I004

FRESH-WATER BIOLOGY

129 (130) Shell large, solid, inflated, subrotund; beak sculpture weak, not
continuous with the surface sculpture, which consists of
oblique folds; hinge strong and complete.

Arkansia Ortmann and Walker.

The t5T5e and only species known. A. wheeleri O. and W. (Fig. 1499; XI), has recently been
discovered in the Old River, Arkadelphia, Ark.

Fig. 1499.

130 (134) Shell eUiptic-rhomboid, compressed ; pseudocardinals well developed;
laterals more or less imperfect or subobsolete.

Symphynota Lea . . 131

131 (132, 133) Shell smooth, shining, rayed; teeth delicate; laterals moderately
developed Subgenus Symphynota s.s.

The type, S.compressa Lea (Fig. 1 500; X t), is one of the common species of the Northern States,
ranging from New York west to Nebraska and south to Arkansas. Several other species are
found in the Atlantic drainage from New York to South CaroUna and in eastern Tennessee and
northern Alabama.

Fig. 1500.

THE MOLLUSCA

lOO:

132 (131, 133) Shell subrhomboid, compressed, posterior slope corrugated;
lateral teeth subobsolete. Subgenus Lasmigona Rafinesque.

The type and only species, Symphynota costata Raf. (Fig, 1501; X i), is common in the St.
Lawrence and Mississippi drainage systems.

133 (131, 132) Shell large, ovate-rhomboid, subcompressed, smooth; hinge
very heavy; lateral teeth imperfectly developed.

Subgenus Pterosygna Rafinesque.

Only one species, Symphynota complanata Bar. (Fig. 1502; Xi), which has a wide range
from the Great Lakes and the upper Mississippi south into Alabama and Arkansas.

Fig. 1502

134 (139) Shell rhomboidal, inflated, with a wcll-dcvclopcd posterior ndge;
pseudocardinals well developed; laterals subobsolete or

wanting Alasmidonta Say . . 13 5

Four subgenera: 135, 136, 137, 138.

ioo6

FRESH-WATER BIOLOGY

135 (136)

Shell ovate-rhomboid, solid, inflated; beak sculpture very coarse
and heavy; pseudocardinals large, solid; laterals very im-
perfect or wanting Subgenus Alasmidonta s.s.

The type and only species, A. undulata
Say (Fig. 1503; X 1), is a characteristic shell
of the Atlantic states south to North Caro-
lina, but is not found west of central New
York.

Fig. 1503.

136 (137) Shell small, decidedly rhomboid; beak sculpture sUghtly corrugated;
teeth compressed Subgenus Pressodon Simpson.

The typical species, Alasmidonta calceola Lea (Fig. 1504),
has a wide distribution through the Northern States from the
Mississippi eastward. Several other species occur in the
Atlantic and Southeastern States. One species, A . collina
Con., is remarkable for having one or more small spines
near the center of each valve.

Fig. 1504.

137 (138) Shell elongated, rhomboid, inflated, posterior slope sHghtly corru-
gated; pseudocardinals imperfect; laterals wanting.

Subgenus Rugifera Simpson.

The type, Alasmidonta marginata Say (Fig. 1505), ranges from New York and South Caro-
lina west to the Mississippi Valley. Another species is found only in the Tennessee and Cum-
berland river systems.

Fig. 1505.

THE MOLLUSCA

1007

138 (135) Shell thin, triangular, greatly inllated, with a high, sharp posterior
ridge; pseudocardinals compressed, reflcxed; laterals want-
ing Subgenus Bidlclla Simpson.

This group is composed of two very peculiar species found only in South Carolina and Georgia.
Type, Alasmidonta arcula Lea (Fig. 1506; X S).

139 (122)

I'lG. 1506.

Shell small, thin, elongate-elliptical; beak sculpture consisting of
fine parallel ridges, looped up in the middle; a high, irregular,
compressed pseudocardinal in each valve; laterals nearly
or quite lacking Hemilastena Agassiz.

The type and only species, H. ambigna Say
(Fig. 1507), occurs in the Ohio river system,

1 the Ohio river system,
rangmg norm to i\Iichigan, west to Iowa,
south to Arkansas, and east to Tennessee.

Fig. 1507.

140 (107, 121) Marsupium formed from the outer gill alone and usually from
the posterior portion only; edge of marsupium, when charged,
distending and bulging out beyond the original edge of the
gill; water tubes simple in the gravid female. Hinge com-
plete; male and female shells usually quite different.

Subfamily Lampsilinae . . 141
Twelve genera: 141, 146, 151, 152, iS3. is6, i59. i6o, 161, 162, 163, 164.

ioo8

FRESH-WATER BIOLOGY

141 (146) Male and female shells different; female shell with a decided infla-
tion in the post-basal region, which is thinner than the rest
of the shell, of different texture, often toothed, and usually
radiately sculptured; hinge complete; marsupium occupying
the posterior part of the gill only.

Truncilla Rafinesque . . 142
Four subgenera: 142, 143, 144, i45-

142 (143) Male shell smooth, no radial groove in front of the posterior ridge.
Female with a high posterior ridge, posterior slope flattened.

Subgenus Truncilla s.s.

The type, T. triquetra Raf. (Fig. 1508), occurs from western New York to Nebraska and south
to Kansas and northern Alabama. Five other species are found in Tennessee and Alabama.

Fig. 1S08.

143 (144) Male shell with a wide, radiating, shallow depression in front of the
posterior ridge. Female with a small, rounded, well-defined
radial post-basal swelling. . . Subgenus Scalenaria Agassiz.

The type, Truncilla sulcata Lea (Fig. 1509), ranges from the Tennessee River north to
southern Michigan. Two other species occur in Tennessee and Georgia.

Fig. 1509.

THE MOLLUSCA

1009

144 (145) Male shell with a posterior and central radiating ridge with a
furrow between. Female with a greatly produced inflation
a little behind the center of the base.

Subgenus Dysnoynia Agassiz.

This is one of the most remarkable groups of the genus and is represented by three species
from the Ohio, Cumberland, and Tennessee rivers. Type, Truncitla Joliata Hild. (Fig. 15 10;
X h)'

Fig. 1510.

145 (142) Male shell with a wide, shallow, radiating depression in front of
the posterior ridge. Female with a rounded, fohaceous
swelling at the posterior base. . . Subgenus Pilea Simpson.

Eight species, found mostly in the Tennessee drainage, but ranging north to southern Michigan
and west to Arkansas. Type, Truncilla personata Lea (Fig. 151 1).

Fig. 151

146 (151) Male and female shell different. Shell ovate to elliptical, smooth;
hinge complete. Female shell more or less expanded in
the post-basal region, but the expansion docs not differ in
texture from the rest of the shell. Marsupium occupying
the posterior part of the outer gill.

Lampsilis Rafinesque . . 147

lOIO

FRESH-WATER BIOLOGY

147 (150) Beak sculpture consisting of coarse parallel' ridges, scarcely looped
or fine and doubly looped.

Subgenus Lampsilis s.s. . . 148

148 (149) Shell often very large, usually rather thin, inflated, shining, fre-
quently rayed. Beak sculpture consisting of coarse parallel
ridges, scarcely looped Section Lampsilis s.s.

This group includes some of the largest of the Unionidae. Found in all of the Eastern States
from New England to Georgia and west to Arkansas. Type, L. ovata Say (Fig. 1512; X I).

Fig. 1512.

THE MOLLUSC A

Toil

149 (148) Shell oval to oblong; beak sculpture consisting of fine, doubly
looped ridges Section Eurynia Rafinesque.

This group has many species and is of general distribution from Manitoba to Texas and
eastward. Type, Lampsilis recta Lam. (Fig. 151,^; X 2).

Fig. 1513.

150 (147) Shell small, inflated, oval to obovate; male usually more or less
pointed posteriorly; female truncated obliquely on the post-
base; beak sculpture consisting of rather strong concentric
ridges Subgenus CarimciiUna Simpson.

A well-marked group of small, dark-colored species easily distinguished by the pecuHar beak
sculpture. Most of the species are confined to the Southern States from Georgia to Texa.s, but
two or three range north to Illinois and southern Michigan. Type, Lampsilis tcxasensis Lea
(Fig. i5i4;Xl).

Fig. 15 14.

IOI2

FRESH-WATER BIOLOGY

151 (152) Male and female shells alike. Whole outer gill serving as marsu-
pium, its edge thrown into a number of folds. Shell elon-
gate-triangular, solid and thick; hinge complete; hinge plate
wide and flat Ptychohranchus Simpson.

The typical species, P.phaseolus Hild. (Fig. 1515; X I), is common, ranging from Michigan
south to Alabama and Louisiana. Five other species are known, four in Alabama and one in
Arkansas.

Fig. 1515.

152 (153) Male and female shells alike. Marsupium occupying nearly the
whole of the outer gill and, when fully developed, folded.
Shell solid, round- triangular; hinge complete; hinge plate
wide and flat; surface sculptured by irregular ridges and
humps, painted with undulating, radiating, broken hair-
Unes or maculations Dromus Simpson.

Only two species are known, both from the Tennessee and Cumberland river systems. Type,
D. dramas Lea (Fig. 1516; Xs).

Fig. 1516.

153 (156) Male and female shells different, the latter being slightly inflated
in the post-basal region. Shell short oval, rounded, or retuse.
Marsupium occupying the posterior portion of the outer
gills and projecting far below the rest of the branchiae,
dolabriform or kidney-shaped. ObovariaRa,^esq\ie . . 154

THE MOLLUSCA

1013

154 (155) Shell retrorse to short oval; beaks high and central.

Subgenus Obovaria s.s.

A small group of species mostly found in the Southern States from Alabama to Arkansas.
The type, O. retusa Lam. (Fig. 15 17), occurs in the Ohio, Tennessee, and Cumberland systems,
and another species ranges north to southern Michigan.

Fig. 1517.

155 (154) Shell elliptical; beaks anterior.

Subgenus Pseudoon Simpson.

Two species only. The tyY>e, Ohovaria ellipsis Lea (Fig. 1518; X i), ranges from the upper
Mississippi and lower Great Lakes south to Tennessee and Arkansas. The other is found from
Arkansas to Louisiana and east to Alabama.

^^..

^^

Fig. 1518.

156 (159) Male and female shells different, the latter being more or less
inflated in the post-basal region. Shell triangular ovate,
with a distinct, often sharp posterior ridge; hinge complete.
Marsupium kidney -shaped, occupying the posterior portion
of the outer gills, but not extending quite to the hinder end.

Plagiola Agassiz . . 157

I

idi4

FRESH-WATER BIOLOGY

157 (158) Hinge heavy and strong; hinge plate wide and flat.

Subgenus Plagiola s.s.

The type and only species, P. securis Lea (Fig. 1519; X h), occurs abundantly in the Ohio and
Mississippi systems and south to Alabama.

Fig. I sic

58 (157) Hinge delicate; hinge plate narrow.

Subgenus Amygdalonaias Crosse and Fischer.

A group of only three species character-
ized by the sharp posterior ridge and arrow-
shaped pattern of the epidermis. Two of
them occupy the Mississippi drainage, ex-
tending into southern Michigan and south to
Alabama and Texas. The third is pecuHar
to Texas. Example, Plagiola elegans Lea
(Fig. 1520; XI).

Fig. 1520.

159 (160) Male and female shells alike; oval-solid, inflated, with a row of

large knobs running from the beaks to the center of the

base; hinge complete. Marsupium consisting of a few dis-

^ tinctly marked ovisacs situated just behind the center of the

' outer gill and projecting far below the rest of the branchiae.

Obliquaria Rafinesque.

The typical and only species, 0. reflexa
Raf. (Fig. 152 1 ), ranges from Michigan
south to Alabama and Texas.

Fig. 1521.

THE MOLLUSCA

lOl

i6o (i6i) Male and female shells alike ; very thick and solid, inflated, rounded-
triangular; surface nodular, radiately wrinkled, or lachry-
nious; epidermis painted with delicate green mottling on a
light ground. Marsupium consisting of several long purple
ovisacs pendent from near the central base of the outer
gills and formed into a close coil with the ends turned inward.

Cy progenia Agassiz.

The typical species, C. irrorata Lea (Fig. 1522), is common in the Ohio, Cumberland, and
Tennessee river systems. One other species occurs in the states west of the Mississippi, from
Missouri to Oklahoma.

Fic. 1522.

161 (162) Male and female shells different, that of the latter being slightly
swollen behind the middle of the base. Shell rather small,
elongated, dorsal slope plicately or nodulously wrinkled;
hinge complete. Marsupium occupying the central portion
of the outer gill Mai ion id us Simpson.

A small group of species characterized by their elongate shape and plicate dorsal slope. It
is restricted to the waters of Tennessee, Alabama, Georgia, and Florida. Type, M. conradicus
Lea (Fig. 1523)-

Fig. 1523.

ioi6

FRESH-WATER BIOLOGY

162 (163) Male and female shells much alike, but the latter is usually some-
what inflated in the post-basal region. Shell large, ovate,
usually rather thin, but in some species quite solid, gaping
at the anterior edge and on the dorsal slope ; normally winged
on the dorsal slope, but the wing is often lost in the adult;
hinge complete. Marsupium occupying the posterior portion
of the outer gills. Glochidia celt-shaped, with two spines on
each valve and with gaping margins . . Pro/>/em Rafinesque.
This group is well characterized by the large, usually thin shell, which is more or less alate in

the dorsal region. It occurs throughout the St. Lawrence and Mississippi systems and extends

south to Texas and Alabama. Type, P. data Say (Fig. 1524; X i).

Fig. 1524.

THE MOLLUSCA

1017

163 (164) Male and female shells not greatly different, the latter being some-
what more inflated and expanded in the post-basal region.
Shell thin, rather compressed, and winged on the dorsal
slope; hinge complete, but the pseudocardinals are reduced
to mere tubercles often nearly wanting. Marsupium as
in Froptera. Glochidia semicircular, very small, without
spines Paraptera Ortmann.

This genus in shell characters is very like the preceding, but has been separated on account
of the great difference in the shape of the glochidia. The type, and only species yet known to
belong to it, P. gracilis Bar. (Fig. 1525; X |), has a wide range from the Great Lakes south to
Alabama and west to the Mississippi Valley.

164 (141) Male and female shells different, the latter being swollen in the
post-basal region. Marsupial characters unknown. Shell
short-elliptical, solid, much inflated; pseudocardinals divided
into irregularly radiating, granular laminae; hinge plate
reduced to a mere rounded line behind the pseudocardinals.

Glchuld Conrad.

The type and only species, G. rotundata Lam. (Fig. 1526; X h), ranges from Florida to eastern
Texas. Conchologically very distinct by reason of its peculiar hinge, little is known of its
anatomical characters and further information is greatly to be desired, especially in regard to
the gravid female.

iiJ'V

Fig. 1526.

ioi8

FRESH-WATER BIOLOGY

165 (104) Interior of shell non-nacreous or porcellanous, or the whole shell

of a prevailing prismatic substance 166

Five families: 166, 167, 168, 173, i74-

166 (167) Shell of a prevailing prismatic substance, mytiliform, very in-

equilateral; beaks compressed, terminal; Ugament subinter-
nal; anterior adductor and pedal protractor muscles inserted
on a septum in the beak. Byssiferous.

Family Dreissensiidae.
Only one genus Congeria Partsch.

Represented in our fauna by two species. Example, C.
leucophaeata Con. (Fig. 1527; X 2), found on the Atlantic
coast from Maryland to Florida.

Fig. 1527.

167 (168) Shell porcellanous, subtrigonal, thick, and solid; ligament external;
hinge with true cardinal teeth and with both anterior and
posterior laterals; pallial line with a distinct sinus.

Family Cyrenidae.
Only a single genus Cyrena Lamarck.

Represented in our fresh-water fauna by a single species, C.
carolinensis Bosc (Fig. 1528), found in streams and brackish water
near the coast from South Carolina to Texas.

Fig. 1528.

168 (173) Shell non-nacreous, usually small and thin; hinge with cardinal and

both anterior and posterior lateral teeth; no hinge plate;
pallial Hne simple. . . . Family Sphaeriidae . . 169
Four genera: 169, 170, 171, 172.

169 (170) Shell oval, equilateral; beaks nearly subcentral; nepeonic valves

not distinctly separated from the subsequent growth of the
shell; cardinal teeth two in each valve. . Sphaerium ^co^oM.

This group contains the largest species of the
family and is easily distinguished from Musculium by
the thicker, striate shell and noncalyculate beaks.
The species are numerous and of general distribution.
Example, S. simile Say (Fig. 1529; X if).

Fig. 1529.

THE MOLLUSCA

1019

170 (171) Shell thin and delicate, suborbicular to oblong; beaks prominent,
usually retaining the nepeonic valves; cardinal teeth minute^
often obsolete; anterior and posterior laterals present.

Miisciiliiim Link.

This group has a general distribution. The prominent beaks with
the distinctly marlved nepeonic shell are the distinctive feature, but in
some species these are lacking. The thin, rounded, polished shell is,
however, quite characteristic. Example, M. partumeium Say (Fig.
i5oo; X2).

Fig. 1530.

171 (172) Shell subrhomboidal, thin, moderately inflated, with the posterior
side longer; cardinal teeth feeble, only one in each valve.

Eiipera Bourguignat.

A tropical group, of which two or three species occur in Florida, Ala-
bama, and Texas. The rhomboidal shape is characteristic. The shells
appear to be mottled and are usually so described, but according to
Dr. W. H. Dall these "spots" are caused by a parasitic infusorian that
attacks the interior of the shell. Example, E. singleyi Pils. (Fig. 1531;

X3).
Fig. 1531.

172 (169) Shell small, rounded, oval, or obliquely cuneiform, inequilateral,
anterior side longer; beaks subterminal; cardinal teeth
double in each valve Pisidium C. Pfeiffer.

The Pisidia are of general distribution and a great number of species
have been described. They are easily distinguished from the allied
genera by the very inequilateral shell, the hinge being on the shorter
side. Example, P. virginicum Bgt. (Fig. 1532; X 2).

Fig. 1532.

173 (174) Shell rounded, inflated, thin; beaks forward; surface smooth or
slightly concentrically sculptured; cardinal teeth, two in
the right and one in the left valve; no lateral teeth.

Family Cyrenellid.\e.
Only one genus Cyrcnclla Deshayes.

Represented in our fauna by a single species, C. floridana Dall (Fig.
1533; X 1 5), from Florida. It is easily distinguished by the lack of lateral
teeth.

Fig. 1533.

I020 FRESH-WATER BIOLOGY

174 (166) Shell thick, oval, subtrigonal, ventricose, smooth; beaks prominent;
ligament inclosed in a pit and invisible externally; hinge
with cardinal and both anterior and posterior lateral teeth;

pallial line sinuous Family Rangiidae.

Only one genus Rangia Des Moulins.

The typical species, R. cuneata Gray (Fig. 1534;
X 12), is found in great abundance in the brackish
waters of the Gulf coast from Alabama to Mexico.

Fig. 1534.

IMPORTANT PAPERS ON FRESH-WATER MOLLUSCA.

Baker, F. C. 1898. The Mollusca of the Chicago Area. Part I, Pelecypoda.
1902. Part II, Gastropoda.

191 1. The Lymnaeidae of North and Middle America.

BiNNEY, W. G. 1865. Land and Fresh-water Shells of North America, Part

II. Smithsonian Misc. CoU., v. 7, No. 143, 172 pp. Part III, No. 144,

128 pp.
Haldeman, S. S. 1842. Monograph of the Fresh-water Univalve Mollusca

of the United States. Continued by G. W. Tyron, Jr., 1870.
Ortmann, a. E. 191 1. A Monograph of the Najades of Pennsylvania.

Mem. Carnegie Mus., 4 : 279-347.

191 2. Notes upon the FamiHes and Genera of the Najades. Ann. Car-
negie Mus., 8 : 222-364.

Prime, Temple. 1865. Monograph of American Corbiculidae. Smithsonian
Misc. Coll., V. 7, No. 145, 192 pp.

Simpson, C. T. 19 14. A Descriptive Catalogue of the Naiades or Pearly Fresh-
water Mussels. Printed by Bryant Walker, Detroit, Mich. 1540 pp.

Stimpson, William. 1865. Researches upon the Hydrobiinae and Allied
Forms. Smithsonian Misc. Coll., v. 7, No. 201, 64 pp.

Tryon, G. W., Jr. 1873. Land and Fresh-water Shells of North America.
Part IV, Strepomatidae. Smithsonian Misc. Coll., v. 16, No. 253, 435 pp.

CHAPTER XXX
THE AQUATIC VERTEBRATES

By C. H. EIGENMANN

Professor of Zoology in Indiatta University, and Curator of Fishes in the Carnegie Museum, Pittsburgh, Pa.

INTRODUCTORY

The chief object in the life of any animal is to leave another
like it in its place when it dies. To accomplish this object it must
find a range in which it may secure its food and itself escape be-
coming food; it must secure a mate and a home in which its young
may be reared to the point of self-dependence. The world con-
tains a great variety of animals adapted to all possible environ-
ments. Either the greatly diverse characters of these animals
have arisen to adapt them to their different ranges and homes, or
the greatly diverse environments have been selected because they
were adapted to the otherwise and elsewhere acquired characters
of different animals. Certainly when new water or land areas arise
the latter will be the origin of its adopted fauna.

The vast territory containing the majority of the innumerable
lakes and streams with whose fauna and flora we are concerned,
extending from the Arctic regions south to the region of the Ohio
River, was a few thousand years ago covered with a continuous
sheet of ice. The fauna and flora of this area are composed
of immigrants, of animals and plants that moved in as the ice
moved out and selected the places adapted to their requirements.
While no doubt many of them have become modified since their
advent into this area, there can be no doubt that their fundamental
adaptations were elsewhere acquired and that in their case it has
been a selection of environments to suit these adaptations.

Fresh waters may be and are used first, for ranges; second, for
homes; or third, for both purposes by various animals. One finds
animals which breed on land but are adapted to utilize fresh waters

I02 2 FRESH-WATER BIOLOGY

daily or seasonally for ranges; others that range on land but visit
the water during breeding seasons to make therein their homes and
to enable their young to grow up in it. Still other animals utiHze
fresh waters both as a range and a home, — rarely, or never, leave
it or even are incapable of leaving it. Roughly speaking, mam-
mals, birds, and reptiles, in so far as they are aquatic, belong to
the first of this ecological group. Batrachians belong to the sec-
ond, a few batrachians and all fishes to the third.

The first of these groups is composed of more or less perfect
readaptations of land animals to water. The second is composed
of originally aquatic animals as yet imperfectly adapted to the
land, while the members of the third group are, and at all times
have been, the aquatic animals par excellence. While the visitors
or inhabitants of fresh water may be sharply distinguished from
the non-aquatic, the relations and adaptations of aquatic animals
to the different regions of the water are very diverse.

Mammals

The aquatic mammals are but imperfectly adjusted to some
part of the aquatic habitat and confine themselves to shallow
water and the shore. None of them could five in an enclosed space
filled with water. The number of truly aquatic mammals is small.
Most mammals only visit the water to drink. Others, as the moose,
seek the water to browse on the marginal vegetation or to escape
enemies. Others less inclined to enter water secure part of their
food from it. The raccoon fishes along the margins of streams
for crayfishes. A dexterous tomcat, proverbially wary of wetting
his feet, one memorable night neatly cleaned out two aquaria, one
stocked with rare blind fishes and one with still rarer axolotls.
None of the above dive.

The mink secures most of its food on land but it catches both
fishes and muskrats in the water into which it does not hesitate
to dive to escape an enemy or to secure food.

The more distinctly aquatic mammals are the star-nosed mole,
the muskrat, the beaver, and the otter. All of these use the water
as a range, making their homes in very close proximity to the
water if not actually in it. Of these the otter is a carnivore, the

THE AQUATIC VERTEBRATES 1023

rest plant feeders, though sometimes eating animal food. They
have been so reduced in numbers, — in some places entirely exter-
minated, — that they have become almost a neghgible part of the
aquatic vertebrate fauna. Only the muskrat must be considered
as an ecological element in all eastern fresh waters.

The muskrat is abundant along most of the eastern streams and
lakes. It is a shallow-water animal and affects its environment in
a specific way. It builds lodges of sod and cat-tail stalks, twigs
and vegetable debris. It gathers Hly roots, on which it feeds, but
its most specific action is on various mussels. The muskrat lodge
is always surrounded by shells of dead bivalves, and at Winona
Lake it has been found by Headlee that the muskrat sets a bound-
ary to the shoreward migration of mussels as the soft bottom of
the pelagic area sets a hmit to their migration toward deep water.
The activities of the muskrat are more restricted in winter than in
summer, but they do not hibernate.

Beavers have disappeared from thickly-settled regions. They
are, in some of their habits, larger editions of the muskrat. They
build lodges not unhke those of the muskrat. They cut and
gather twigs and stems for food but the action for which beavers
are conspicuous, is the building of dams, and creating of ponds.
They thus add to the extent of the aquatic en\ironment.

The seal-Hke otter is no longer a part of the aquatic en\ironment
in well settled parts of America. They are the most aquatic of
the fresh-water mammals. As swimmers, they are more expert than
fishes, which they catch and eat. They also prey upon muskrats
and aquatic birds.

Of the star-nosed mole. Stone says: "The star-nosed mole is a
creature almost as well fitted for a partially aquatic life as the
otter and mink, and, as a matter of fact, does pass most of its time
about the water; pushing extensive tunnels through the black,
peaty soil of swamps and along the borders of httle brooks and
ponds. The soft, black loam is thrown up in frequent heaps a
foot, more or less, in diameter; the opening of the burrow being
under the bank, and as often beneath the water as above. The
tunnel itself must frequently be flooded to the great discomfort
of its inmates.

I024 FRESH-WATER BIOLOGY

''But the old ones show no fear of the water; I have frequently
seen them swimming both under water and on the surface, even
where the current was pretty strong, and have always observed
them to be perfectly confident and unfrightened at such times."

Birds

In cold and temperate regions birds are seasonal, robbing, \isi-
tors of the water. Only one-fourth to one-fifth of our entire bird
fauna is in any sense aquatic.^

The passerine birds are dominant now and of this group none
are strictly aquatic. One hundred and twenty-nine of the 215
species of birds of Monroe County, Indiana, are passerine. Of
these only the red-winged blackbird, the six species of swallows,
the water thrushes, and the long-billed marsh wren are, even re-
motely, related to the water. Taking all the birds that range in
or about the water — for none of them can be said to home in the
water — one finds a graduated series, from those more to those
less aquatic in their habits. More than this, birds show the most
complete series of adaptations to different aquatic zones.

The swallows must, by courtesy, be mentioned as forming the
first of this series of ecological groups. They are never found
upon or in the water, but skim over its surface, occasionally just
touching it in their search for food. Mosquitoes and other minute
aquatic insects are the attraction for them and they are, therefore,
very definitely related to the aquatic fauna. They remain in the
latitude of the Ohio River from early April to September.

A second ecological group is formed by the kingfisher, the terns,
gulls, and (for fresh waters rarely) the pelicans. The kingfisher,
from his perch over a stream, dives into the water beneath him for
fishes. He is largely a shore fisher. The terns, gulls, and pelicans
dive from an aerial poise into the pelagic region of the lake and
secure fishes near the surface. The terns and gulls also alight to
pick the refuse floating on the surface for they are scavengers as

^ Out of 99 birds observed during the summer about one of the northern Indiana
lakes, 19 are more or less related to the water. Out of 215 birds observed at all
seasons of the year about Bloomington, Indiana, 55 are related to the water.

THE AQUATIC VERTEBRATES 1025

well as robbers. The kingfisher is a poor swimmer, but the terns,
gulls, and pelicans rest gracefully on the surface. In the latitude
of the Ohio the kingfisher is found between early March and No-
vember, rarely even in December. The terns migrate to the
northern lakes in summer and the pelicans are but stray visitors.
The terns, gulls, and pelicans have certainly acquired the adapta-
tion to the water at the ocean.

The third ecological group is formed by the grebes and loons.
They are pelagic birds, swimmers par excellence, both upon the
surface and in the water. The term diving ought not to be ap-
plied to the performance of both kingfisher and loon.

The fourth ecological group is formed by the bottom-feeding
ducks, the mudhen, geese, and swans. They are littoral or abys-
mal forms securing their food in the mud at the bottom, largely
about the margins of ponds or lakes in water not too deep to pre-
vent them from reaching the bottom when "tipping." Many
of the ducks are good swimmers under water, and the bay and
sea ducks are said to reach the bottom at a depth of 100 to 150
feet.

The fifth ecological group is formed by the herons, cranes, and
bitterns. These range in much the same zone as most of the ducks,
but their food, for the most part, is different. They stalk cau-
tiously, without jerk or sudden motion, or stand in water of a
depth not too great for their long legs. Their spearlike bill im-
pales fish or frog.

The sixth and last of the ecological groups of aquatic forms con-
tains the rails and snipes. These are shore birds, wading in the
shallowest water or along the wet shores, frequently moving with
the advancing and retreating waves, picking the stranded animals
from the surface or probing for their prey in the soft beaches.

All of the groups except the first, the swallows, nest as near the
water as possible. Less strictly aquatic are the swamp black-
bird and long-tailed marsh wren which build their nests in cat tails;
Ukewise the song and marsh sparrows, so abundant along margins
of stream or pond. From the nature of the case the waters of
northern and temperate zones are a closed book to all the birds in
winter. Hence, birds are not perennial elements of the aquatic

I026 FRESH-WATER BIOLOGY

fauna. Birds derive their food from the water. The few that, as
carrion, serve as food for other aquatic animals or that may be
captured by fish, otter, or alligator are a negligible quantity.

Reptiles

Reptiles, like mammals, are shallow-water and littoral forms,
largely in summer. As with mammals, a gradual gradation is
found from species living exclusively on land, — Hke the turtles and
snakes of the Mojave desert or the land tortoise and green snakes
of the Mississippi valley, — through those which do not ordinarily go
into the water but will enter it without hesitation if circumstances
demand, — like the black snake and garter snake, — to such as the
water snakes, leather snakes, geographic turtle, painted turtle,
and snapping turtle that bask on the margins of lakes and streams
but take to the water for food or at the slightest sign of danger;
and lastly, to the alhgators, musk turtles, and soft-shelled turtles
which give the final gradation to adaptations for Ufe in water. Of
these, the soft-shelled turtle, which can utilize the oxygen dis-
solved in the water, has probably reached the highest adjustment
to aquatic existence. But no hard and fast line can be drawn.
The habits of different species overlap so neatly that one finds a
shading from reptiles with a purely aquatic range to those with an
entirely terrestrial range. All of them have their homes on land
in so far as they have homes at all. Some secure only a part,
others all of their food from the water. Of those that obtain it
from the water some feed on fishes (purely aquatic food) ; others
like the alligators, which catch water birds, utilize the water to
secure terrestrial visitors in part. Others may seek both sorts
of food. Snakes take to the margin of water in part for fishes,
in part for frogs, etc.

The water snakes give birth to living young. Since the young
may be liberated in the water these snakes, in one sense, are the
most aquaric of the reptiles. But since they cannot utilize the
oxygen in the water the soft-shelled turtles exceed them in adap-
tation to an aquatic existence in this respect. All the turtles, as
well as the alligators, are compelled to make their homes or nests on

THE AQUATIC VERTEBRATES 1027

land. The soft-shelled turtles usually lay their eggs in sandy beaches,
sometimes in harder banks near the water. The painted turtles
and snapping turtles dig holes more remote from the water's edge.
The musk turtles lay their eggs in muck, in decaying stumps or
logs, or accumulations of decaying weeds on the margins of lakes.

No one would seriously doubt that the mammalian and rep-
tilian faunas of fresh waters have both been derived from terres-
trial ancestors. The adjustment to water conditions consists largely
in an adaptation of the limbs and tail to swimming and diving.
Both are organs primarily used for land progression. Further
adaptations in reptiles, such as the utilization of the oxygen in
the water by the turtles, are much more rare, and found only in
extreme adaptations to an aquatic sojourn.

The paths of turtles may readily be seen among fields of Chara
in shallow water. A painted, geographic, or a musk turtle may
be seen basking in the sun on the surface, the neck curved up, the
nose out of water. If disturbed it dives into the Chara and soon
disappears in one of its innumerable paths. A curious commen-
salism is reported between the soft-shelled turtle and the black
bass. The bass is said to follow the turtle, which, nosing about
under rocks and in crannies scares out some of the crayfishes and
other denizens of such places. These are then easily captured by
the attending black bass. There is a peculiar correlation between
the disposition of turtles and the degree of their armature. The soft-
shelled turtle is the least protected by bony plates. Next in order
comes the snapping turtle, with only a cross-shaped, ventral plate,
most of the ventral surface being open to attack. This is followed
by the musk turtle, the painted and the geographic turtle, Bland-
ing's turtle and finally the box turtle. The highest degree of pro-
tection is found in the terrestrial box turtle, whose plastron is
hinged and can be closed in front and behind. Correlated with
the defective armature in the soft-shelled turtle we find the extreme
of pugnacity. A soft-shelled turtle will snap and bite on suspicion
from the time it is half way out of its shell. The disposition of
the snapping turtle, with exposed ventral surface, is proverbial.
The musk turtle will bite, as anyone who has collected their eggs
can testify. On the other hand, the well-protected painted, geo-

I028 FRESH-WATER BIOLOGY

graphic, and Blanding's turtles, and above all, the terrestrial and
perfectly-armored box turtle, are the gentlest of creatures which no
amount of provocation will induce to bite. Although the correla-
tion between armature and disposition is very striking there may
be no causal relation between the two. The character of the food
may be the cause of the disposition.

Batrachians

The batrachians, as a group, are aquatic to a much greater
degree than the mammals or reptiles. In North America they are
summer and especially spring members of the aquatic fauna.
Some of them, with all their ancestry, have been strictly aquatic.
They are autochthons, products of evolution in fresh water. Such
aquatic forms have gills and a tail throughout life. The Siren and
the mud puppy, of deadly repute, belong to this group and so does
the blind salamander of Texas. Whereas in the reptiles and the
mammals gradations from pure terrestrials to less or more aquatics
have been noted, in the batrachians one finds gradations from the
purely aquatic to the more or less terrestrial, and none have reached
the possibiKty of living in deserts in dry places. So many of the
batrachians lay their eggs in water that those that do not are
accounted remarkable. In a small pond near Indiana University,
which has been examined at all seasons of the year, it has been
found that a salamander, AmUy stoma jefersonianum, begins to lay
as soon as the ice disappears after December. Sometimes this
happens early in January or it may not until March. After the
spawning of jeffersonianum comes that of Amhly stoma punctatum.
Both deposit their eggs in jellylike clumps. Hyla pickeringii and
Acris gryllus spawn in the same pond between early March and late
May. During late spring and early summer the newt, Diemictylus
viridescens, spawns here. Very frequently this pond dries up in
summer, and then there is an opportunity to see how any of the
aquatic batrachians may become terrestrial. Late in summer Am-
blystoma opacum spawns in this pond. Usually the pond is dry at
the time, whereupon the salamander lays its eggs under leaves or
under a board, coiling itself about the eggs. The hatching of such

THE AQUATIC VERTEBRATES IO29

eggs may be delayed much beyond the normal time and will then
occur at once with the first rain. The young still require a pond
for their growth from hatching to the metamorphosis. Toads and
frogs have evidently become adapted to range on land without
losing their ancestral habit of making their home in water. Whether
their webbed toes and swimming legs are in their original condi-
tion, or whether they are readaptations to water may be left in
abeyance.

The batrachians play an important part in the economy of small
pools, a less important one in small streams, and are a negligible
quantity in waters of any size. To the rule that their abundance
is in inverse proportion to the size of the body of water, the perenni-
branchs form the only exception. In early spring nearly every
puddle contains hundreds or thousands of toad eggs and larvae.
The tadpoles act as scavengers for a short time and then pass out
of the life of the puddle. Every pond of greater permanence
serves the frogs as the puddles and ponds do the toad. Frog tad-
poles are scavengers and mud eaters, with elongate, aUmentary
canal. They remain in the water much longer than young toads
and when they become adult may pass out of the Ufe of the puddle
or pond as completely as the adult toad, or may remain more or
less closely identified with the birthplace. When the adult frogs
remain about the water, they bear a different relation to the
aquatic Kfe from the young. The ahmentary canal has become
shortened and the frog is an eater of live food, insects, and fishes.
In its turn the frog serves as food for fishes, snakes, and birds.

Fishes

The chief and perennial vertebrate elements of the aquatic fauna
are the fishes. They, with a few batrachians and possibly a turtle,
are the only members of the fauna that have both their home and
their range in the water. They alone of the vertebrates are so
adjusted to an aquatic existence that they could be hermetically
Bealed in a balanced aquarium.

There are fishes, big and little, thick and thin, long and short,
deep, and of Httle elevation, sharp-nosed and blunt-snouted, tooth-

I030

FRESH-WATER BIOLOGY

Fig. 1535. Red-Eye or Goggle-Eye, Ambloplites rupestris (Rafinesque). Actual size, 32
115 mm. and 183 mm. long respectively.

THE AQUATIC VERTEBRATES

1031

less and fanged, naked and scaled, barbelcd and not, noctun.al
and diurnal, bottom sitters and top skimmers, riffle inhabitants and
pool dwellers, mud-puddlers and mountaineers, round-bellied and
serrate-edged. They are adapted, in short, to all conditions of
possible Jish environment. The same gamut of size, shape, and

Fig. 1536. Long-Eared Sunfish, Lepomis megalolis (Rafinesque). Actual size, 90 mm. long.

habit is found in the fresh waters of South^ America and North
America though the twc continents have no fishes in common.
The members of different families have thus independently become
convergently and divergently adapted.

Fresh-water fishes do not form a group by themselves. \'arious

Fig. 1537. Little Pickerel, Lucius vermiculatus (Le Sueur). Actual size. 119 mm. lonp.

marine famiUes have contributed to the fauna. But the larger
per cent of the fresh-water fishes belong to the single superorder
Ostariophysi. Of the 600 fresh-water species of North America,
307, or over half, belong to this group.

1 032 FRESH-WATER BIOLOGY

The fresh- water fishes of North America, exclusive of Mexico,
are distributed among the following families, of which those of
undoubted recent marine origin are printed in italics.

Lamprey 1 8 Salmon 28 Sunfish ; 37

Paddlefish i Trout perch i Perch 72

Sturgeon 7 Blindfish 8 Bass 4

Garpike 3 Killifish 52 Drum i

Bowfin I Mud minnow 2 Surf fish i

Characini i Pike 5 Cichlid 2 2

Carp 230 Alaska Blackfish i Goby 6

Sucker 51 Eel i Sculpin 21

Catfish 25 Stickleback 7 Cod i

Mooneye 3 Silver side 2 Sole i

Herring 5 Pirate perch 2

Gizzard shad i Elassoma 2 .

Few localities, even among the most favored, contain more than
50 species of the 600 found in North America. The entire Missis-
sippi basin harbors about 200 species, the Great Lakes with their
tributaries, 152,^ the state of Indiana, 163. Eel River in Indiana
(85 miles long), with all of its tributary lakes and streams, harbors
76 species. White River of Arkansas, 84; the Maumee basin, 87.
Bean Blossom Creek, about 25 miles long, harbors 44 species in
less than two miles near its middle. Lake Ontario with all of its
tributaries is inhabited by 73 species; Lake Champlain and its
tributaries by 54; Lake Chautauqua with its tributaries by 31;
the Winnipeg System, Canada, by 44; the St. Lawrence River, by
63 and 8 marine. Winona Lake of Kosciusko County, Indiana,
exclusive of its tributaries, harbors 23 species, Turkey Lake with-
out its tributaries, 29 species. The outlet of Turkey Lake, for a
mile of its length, harbors an equal number.

There is a vast difference in the number of species found in
equal areas of streams and lakes. Other things equal a given
area of surface water or a given cubic quantity of water of a small
stream harbors more individuals and greater diversity of species
than the same area and bulk of either a large river or lake. The
places in America from which the greatest diversity of fish life has
been reported are :

1 These are fully described and many of them figured in Jordan and Evermann's
Fishes of North and Middle America, Bull. U. S. Fish Com., and also in Jordan's
" Guide to the Study of Fishes," Henry Holt and Co.

2 Immigrants from South America.

3 Of these 27 are peculiar to the Great Lakes basin.

THE AQUATIC VERTEBRATES 1033

Saline and Washita, ^ mile above Arkadelphia, Arkansas 47 '

Fort Smith and neighborhood 50

Bean Blossom Creek, Indiana 44

Cypress Creek, Alabama 42

Obeys River, Tennessee 39

Tuscaloosa, Alabama 32

Mammoth Spring, Arkansas 37

Washita, Arkansas 36

In contrast with these the following poor faunas arc recorded:

Connecticut River 18

Clear Lake, California 13

Klamath basin, California 15

The entire Yellowstone Park' 10

San Luis River, California 4

Kicking Horse River, Canada 2

Salt Lake basin 14

Sevier River, Utah ^ 7

Columbia River System 37

Colorado basin 33

Pennamaguan Lake, Washington County, Maine 10

Meddybemp Lake and Dennys River, Washington County, Maine 9

Western Grand Lake System, Washington County, Maine 14

St. Croix River basin, Washington County, Maine 8

Perkins Lake, Idaho 7

Alturas Lake, Idaho 4

San Diego County, California 4

Of these the Connecticut, Klamath, Yellowstone, San Luis, the
Maine lakes and streams, and Alturas Lake each have entirely
distinct faunas and the Columbia and Colorado have only a few
species each in common with the Salt Lake basin. It is quite evi-
dent from an inspection of these lists, that a general consideration
of the fresh-water fauna of North America applicable to all cases
is quite out of the question. There are a number of quite distinct
faunas. A few general observations may be supplemented with
an analysis of a few typical localities to get at the nature of the
fish fauna.

Jordan 2 summarizes a long experience of gathermg fishes in
many waters of North America as follows:

''Some of the conditions most favorable to the existence in any
stream of a large number of species of fishes are the following, the
most important of which is the one mentioned first: Connection
with a large hydrographic basin; a warm climate; clear water; a
moderate current; a bottom of gravel, preferably covered by a

1 Two localities are included in this and several in the total of 50 in the next.
> "A Guide to the Study of Fishes," p. 307.

I034 FRESH-WATER BIOLOGY

growth of weeds; little fluctuation during the year in the volume
of the stream or in the character of the water.

"Limestone streams usually yield more species than streams
flowing over sandstone, and either more than the streams of regions
having metamorphic rocks. Sandy bottoms usually are not favor-
able to fishes. In general, glacial drift makes a suitable river
bottom, but the higher temperature usual in regions beyond the
limits of the drift gives to certain southern streams conditions
still more favorable. These conditions are all well reahzed in the
Washita River in Arkansas, and in various tributaries of the Ten-
nessee, Cumberland, and Ohio; and in these, among American
streams, the greatest number of species has been recorded.

''The isolation and the low temperature of the rivers of New
England have given to them a very scanty fish fauna as compared
with the rivers of the South and West."

Agassiz says concerning New England: "In this isolated region of
North America, in this zoological island of New England, as we
may call it, we find neither Lepidosteus, nor Amia, nor Poliodon,
nor Amblodon, nor Grystes, nor Centrarchus, nor Pomoxis, nor
Ambloplites, nor C alliums, nor Carpiodes, nor Hyodon, nor indeed
any of the characteristic forms of North American fishes so com-
mon everywhere else, with the exception of two Pomotis, one
Boleosoma, and a few Catostomus.^''

Continuing, Jordan says:

"Of the six hundred species of fishes found in the rivers of the
United States, about two hundred have been recorded from the
basin of the Mississippi. From fifty to one hundred of these
species can be found in any one of the tributary streams of the
size, say, of the Housatonic River or the Charles. In the Connecti-
cut River there are but eighteen species permanently resident; and
the number found in the streams of Texas is not much larger.**

"The waters of the Great Basin are not rich in fishes, the species
now found being evidently an overflow from the Snake River when
in late glacial times it drained Lake Bonneville. This postglacial
lake once filled the present basin of the Great Salt Lake and Utah
Lake, its outlet flowing northwest from Ogden into Snake River.
The same fishes are now found in the upper Snake River and the

THE AQUATIC VERTEBRATES 1035

basins of Utah Lake and of Sevier Lake. In the same fashion
Lake Lahonton once occupied the basin of Nevada, the Humboldt
and Carson sinks, with Pyramid Lake. Its drainage fell also into
the Snake [Klamath?] River, and its former Umits are shown in
the present range of species. These have almost nothing in com-
mon with the group of species inhabiting the former drainage of
Lake Bonneville. Another postglacial body of water, Lake Idaho,
once united the lakes of southeastern Oregon. The fauna of Lake
Idaho, and of the lakes Malheur, Warner, Goose, etc., which have
replaced it, is also isolated and distinctive. The number of species
now known from this region of these ancient lakes is about 125.
This list is composed almost entirely of a few genera of suckers,
minnows, and trout. None of the catfishes, perch, darters, or
sunfishes, moon-eyes, pike, killifishes, and none of the ordinary
eastern types of minnows have passed the barrier of the Rocky
Mountains.

" West of the Sierra Nevada the fauna is still more scanty, only
about seventy species being enumerated. This fauna, except for
certain immigrants from the sea, is of the same general character
as that of the Great Basin, though most of the species are different.
. . . The rivers of Alaska contain but few species, bareh' a dozen
in all, most of these being found also in Siberia and Kamchatka.
In the scantiness of its faunal Hst, the Yukon agrees with the Mac-
kenzie River, and with Arctic rivers generally."

The fauna of the Great Lakes and of the Red River of the north
is essentially Hke that of the Mississippi Valley.

The Origin of the Fresh-water Fishes. — Many of the fresh-water
fishes of North America have been more remotely or more recently
derived from the sea. Some of them, as the eel, still come from
the sea during each generation, to find in fresh water their range;
others are but seasonal visitors, entering the fresh waters from the
ocean as the salamanders enter them from the land, to find homes.
These various anadromous fishes will be considered later.^ Still

1 The anaclromous habit may be of double origin. The various salmons, many of
whose relatives live in fresh water, may be fresh-water species contributed to the ocean.
The shad and striped perch, on the other hand, whose relatives live in the ocean, have
become anadromous through the general habit of many oceanic fishes to seek the shore
and shallow water as the breeding season approaches.

1036 FRESH-WATER BIOLOGY

others, with both range and home in fresh water, belong to present
marine families and have evidently comparatively recently become
members of the fresh-water fauna.

A notable example of a fish comparatively recently contributed
by the sea to fresh water is Hysterocarpus traski Gibbons. It is a
viviparous fish of the rivers of central California. All of its rela-
tives live in the Pacific Ocean from which it is an undoubted
immigrant.

The sea basses furnish several illustrative examples. The striped
bass, Roccus lineatus, is an oceanic fish entering rivers to spawn,
while its nearest relative, Roccus chrysops, the white bass, is con-
fined to the Great Lakes and upper Mississippi Valley. Closely
related to these are the yellow bass, Morone interrupta, of the lower
Mississippi Valley, and the white perch, Morone americana, in
salt and fresh water from Nova Scotia to South Carolina. The
ninety other American members of this family are all marine.

Various species of Rohalos (Centropomus) enter fresh water.

The Mugilidae have added various species to the fresh waters
south of the United States. The Atherinidae have contributed the
skipjack to our rivers and lakes, and south of us this marine family,
whose eggs are provided with threads, has contributed and is con-
tributing to the fresh waters all the way from Mexico to Patagonia.

Fig. 1538. Skipjack, Labidestes siculus (Cope). Actual size, 95 mm. long.

The sticklebacks and kilHfishes help to bridge the gap, if such
exists, between the fresh waters and the ocean. Even the pipe-
fishes and flounders have a tendency to colonize fresh waters, and
the flounders at least have succeeded in South America.

The Sciaenidae, a marine family, has contributed the thunder-
pumper or white perch to the Great Lakes and Mississippi Valley,
and several other species to the streams of South America. Some
of its marine species occasionally run up streams.

The large family of the Cottidae has added the miller's-thumb.

THE AQUATIC VERTEBRATKS 1037

Others of undoubted marine origin have entered fresh water at
such remote periods that they have set up distinct fresh-water
families, as the suntishes, the perches, and the CichHdac.

Finally, we have the dominant fresh-water groups of characins,
minnows, carps, suckers, and catfishes whose origin from the
sea is so remote that the orders and superorders embracing all of
these dominant members of the fresh-water fauna, with the excep-
tion of Arius and related genera, are peculiar to fresh water.

Fig. 1539. Miller's Thumb, Coitus ictalops (Rafinesque).

Dispersal of Fresh-water Fishes. — No fishes have been or are
bemg permanently contributed to the land. The eel is capable
of moving over short stretches of land, and Periophthalmus may
leave the water in search of food. In the South American fresh
waters a relative of the catfish is said to be able to move from
pond to pond, and in the Congo and in South American rivers
live fishes that temporarily fly over the water. But all these spe-
cies are adapted to the water and can live for longer periods only
in connection with it.

The two factors that more than others are responsible for the
abundance or paucity of the faunas are accessibility and tempera-
ture. The latter will be considered more at length later. Acces-
sibihty demands some attention now.

A locality is accessible to fishes if it is connected with an inhab-
ited locality by a permanent or seasonal waterway. There are
fishes that apparently defy tliis general rule and that skip or have

1038 FRESH-WATER BIOLOGY

skipped in a tantalizing way, from mountain stream to mountain
stream, appearing wherever conditions are favorable. Here, as
elsewhere, the mystery will probably dissolve when all the facts
are in. The catfishes and darters have not been able to cross to
the Pacific slope in the United States, but in Mexico they have
accompUshed this feat. A tilting of the land, or change in relative
rainfall, or some other reason has enabled some of the Pacific
slope streams to capture some of the former tributaries of the Rio
Grande. With the tributary went the darters, the catfishes, and
other fishes it contained. A freshet or a cave-stream may some-
times be responsible for an apparently mysterious distribution.
Salt water is sometimes a barrier to the migration of fresh-water
fishes. Jordan ^ says of the streams of San Luis Obispo County,
California, of which the San Luis Creek mentioned before is one:

'^The county of San Luis Obispo lies along the coast of Califor-
nia, midway between Monterey and Santa Barbara. It is com-
posed of two or three isolated valleys opening out to the sea, and
surrounded on all sides by high and barren mountains. These
mountains have served as a barrier, shutting off all access of fishes
to the streams of the region from the larger basins of the north and
east. The valleys of San Luis Obispo are traversed by clear,
swift, cold streams rising in mountain springs. In these streams
very few species of fishes are found, and these few, except in one
case (Agosia nubila), are species which have come into the fresh
waters by way of the sea. None of the characteristic types of
the San Joaquin and Sacramento valleys are found in San Luis
Obispo County. This is evidently not due to any character of the
waters, but simply to the fact that these fishes cannot reach San
Luis Obispo except by descent to the sea."

But there is also evidence that the ocean is not invariably a
barrier. To quote again from Jordan : ^

"The passage of species from stream to stream along the Atlantic
slope deserves a moment's notice. It is under present conditions
impossible for any mountain or upland fish, as the trout or the
miller's thumb, to cross from the Potomac River to the James, or

1 Bull. U. S. Fish Com. for 1894, p. 141.

' "Guide to the Study of Fishes," pp. 312 and 313.

THE AQUATIC VERTEBRATES IO39

from the Neuse to the Santee, by descending to the lower courses
of the rivers, and thence passing along either through the swamps
or by way of the sea. The lower courses of these streams, warm
and muddy, are uninhabitable by such fishes. Such transfers are,
however, possible farther north. From the rivers of Canada and
from many rivers of New England the trout does descend to the
sea and into the sea, and farther north the white fish does this also.
Thus these fishes readily pass from one river basin to another. As
this is the case now every^where in the north, it may have been the
case farther south in the time of the glacial cold. We may, I
think, imagine a condition of things in which the snow fields of
the Allegheny chain might have played some part in aiding the
diffusion of cold-loving fishes. A permanent snow field on the
Blue Ridge in western North CaroHna might render almost any
stream in the Carolinas suitable for trout, from its source to its
mouth. An increased volume of colder water might carry the
trout of the head streams of the Catawba and the Savannah as
far down as the sea. We can even imagine that the trout reached
these streams in the first place through such agencies, though of
this there is no positive evidence. For the presence of trout in
the upper Chattahoochee we must account in some other way ....

"With the lowland species of the southern rivers it is different.
Few of these are confined within narrow limits. The streams of
the whole South Atlantic and Gulf Coast flow into shallow bays,
mostly bounded by sand pits or sand bars which the rivers them-
selves have brought down. In these bays the waters are often
neither fresh nor salt; or, rather, they are alternately fresh and
salt, the former condition being that of the winter and spring.
Many species descend into these bays, thus finding every facility
for transfer from river to river. There is a continuous inland
passage in fresh or brackish waters, traversable b>' such fishes,
from Chesapeake Bay nearly to Cape Fear; and similar con-
ditions exist on the coasts of Louisiana, Texas, and much of
Florida."

Adaptations to the Main Object id I z/r. — Fishes either lay
eggs that are fertilized in the water, retain eggs that have been
internally fertilized to the time of hatching or in a few species give

I040 FRESH-WATER BIOLOGY

birth to living young which have been carried far beyond the
*' hatching " point.

A. Migration. As the spawning season approaches, fishes under-
take a general inigratory movement. The migration may be of
great or very Hmited extent. The movement is in general one of
going upstream to small brooks and shoreward to shallow water.
In some cases the migration may mean the movement for a few
feet only. Some minnows and darters move to a favorably-placed
rock or weed. The skipjack in our small lakes moves to the zone
of pickerel weeds near shore. The sunfishes, black bass, and many
others move shoreward to shallow water. Some minnows move to

Fig. 1540. bucKer, Catostonius commersoni i,Lacept;de). Acluul size, 232 mm. long.

riffles from neighboring pools. The upstream movement of suckers
is powerful in CaHfornia, and has become proverbial in IlUnois and
neighboring waters.

The limit in the extent of migratory movements upstream is
reached by the Pacific coast salmons. The quinnat salmon of the
Pacific coast is the king of the migrants. It enters the Columbia
River at the age of four years, in March and April. The entire
summer is taken up, without food, in ascending to its spawning
grounds. It spawns a thousand miles and more from the ocean,
or in Alaska two thousand miles from the sea, in shallow riffles of
small streams at the headwaters of the streams it ascends. Alturas
Lake, near one of its spawning places, has an elevation of 7,335
feet. After spawning the adult dies. It never succeeds in regaining
the ocean. The Atlantic slope salmon {Salmo salar) ascends from
the ocean to the headwaters of streams north of Cape Cod. The
relative of the salmons, the cisco of Tippecanoe Lake, in December
ascends its tributary streams to spawn. The marine lamprey as-
cends streams from the Atlantic Ocean. The landlocked lamprey
(Petromyzon marinus unicolor) of central New York migrates eight

THE AQUATIC VERTEBRATES 104I

to ten miles from Cayuga Lake up the streams to spawn. The
silver lamprey of the Mississippi Valley ascends small brooks in
the spring. On the Pacific slope the Pacific lamprey ascends
streams in large numbers. At La Grange, Idaho, I found very
many congregated below a milldam which they had not been able
to ascend. The sturgeons, for the most part living in the sea, also
ascend streams to spawn.

While many species of fishes have the habit of entering fresh
water when they approach ripeness, the eel alone, of the fishes of
the northern hemisphere, has the reverse habit of taking to salt
water when the reproductive period approaches. It has been well
known for many years that during winter and early spring the
young of the eel enter the mouths of streams in enormous numbers.
Redi records the entrance of young eels into the Arno in 1667, and
says that at Pisa three million pounds of young eels 30-120 mm.
were taken in five hours. They find their way for hundreds of
miles from the ocean. ''Young individuals three to five inches
long ascend rivers in incredible numbers, overcoming all obstacles,
ascending vertical walls or floodgates, entering every large and
swollen tributary, and making their way even over terra firma to
waters shut off from all communications with rivers."

The American eel, which is closely related to the European eel,
is found in afl fresh waters emptying from the Gulf of St. Lawrence
to Mexico. Eels have been seen in Colorado 1500 miles from the
Gulf of Mexico, at an elevation of 7200 feet. Only the females
ascend such distances, the males remaining near the coast. While
in fresh water they feed on everything eatable. When the>' ap-
proach their full size, in about four years, they descend the streams
to the ocean in autumn. They are lost sight of beyond a distance
of a mile from shore, but about six months after they have entered
the sea, eel eggs have been found floating on the surface. Hiey
are large eggs, with a very large peri\dtelline space, and vesicular
yolk. They hatch into larvae quite unlike eels. These become
gradually greatly modified, but not in the direction of becoming
eel-Hke. It is not until the larvae are about a year old that they
are metamorphosed into young eels which ascend streams such as
their parents have descended two years previously. Like all fishes,

I042 FRESH-WATER BIOLOGY

such as the lampreys and salmon, which make very elaborate
preparations to produce their young at a great distance from
their range, the eels never regain their range, and probably all
die after the first reproductive period. It is not improbable that
in some landlocked lakes eels mature and reproduce in fresh water,
but no eels with ripe eggs, nor eggs, nor larval eels, have been found
in fresh water.

Homes of Fishes. — Emphasis has been laid on the fact that
the ultimate fate of all fresh water is locomotion, and that usually
currents exist between fresh-water lakes and the ocean. All fresh-
water fishes are adapted to this condition and make provision to
anchor their eggs or give birth to living young. There is but one
fresh-water fish known to me that has pelagic eggs, the eel. It
has not become adapted to rear its yoimg in fresh water, but enters
the sea before the reproductive period. This suggests that the
adaptation of fresh-water fishes to resist currents did not arise
after they had entered the fresh water, but that such oceanic
candidates for fresh-water existence as had eggs adapted to resist
the currents gained a permanent lodgment; while, on the contrary,
none of those with pelagic eggs have been able to estabHsh perma-
nent homes in fresh waters. All anadromous and fresh- water
fishes either have eggs heavier than water which lodge in gravel, or
produce attachable eggs. Many marine fishes have pelagic eggs,
and none of these have become permanent residents in fresh water.
Others have adhesive eggs, that at the moment of being laid will
adhere to foreign substances; others have cohesive eggs that will
become attached to each other, but not to foreign substances. Of
the adhesive eggs some are simply sticky all over and others have
mushroom-shaped processes that have sticky heads (stickleback).
The eggs of still other fishes have filaments that coil about foreign
substances. All of these types are found in fresh waters. The
fundamental adaptation, that to flowing water, was acquired by
the ancestors of fresh-water fishes before they were able to leave
the ocean.

Along with this adaptation against currents, we have in the
fresh-water fishes elaborate brooding habits that in part, at least,
are an adaptation to another fresh- water condition, i.e., the settling

THE AQUATIC VERTEBRATES 1043

of sediment. A very brief survey of the nature of the eggs and
the brooding habits as far as known is instructive.

Amia, the sunfishes, and the black bass build their nests in
shallow water with little or no current. The nest is either pre-
pared in weed-covered patches or on the sand. Afnia prefers
weed-covered patches but is not exclusive in its selections. The
nest, prepared by the male with the snout and fins, consists simply
of an area from which the vegetation has largely been removed,
or it may be but a saucer-shaped pit in sand. The eggs of Amia
are adhesive and are attached to the sides and bottoms of the
nest. The male remains over or near the nest until the eggs hatch,

Fig. 1541. Large-mouthed Black Bass, Micropterus salmoides (Lacepede).

occasionally fanning away sediment, and always while near the nest
ready to drive out intruders. The male accompanies the school of
young until they reach a length of 100 mm.

The sunfishes and black bass build their nests preferably in gravel
or sand, but not to the entire exclusion of the locahties preferred
by Amia. Their eggs are quite small and also adhesive, and are
found at the sides or bottom of a nest.

The male of the small-mouthed black bass builds the nest.
There are no secondary sexual characters. " Each ^ male tests the
bottom in several places by rooting into it with his snout and fan-
ning away the overlying mud or sand with his tail. If he does not
find gravel after going down three or four inches, he seeks another
place. Having found a suitable place, he cleans the sand and mud
from the gravel by sweeping it with his tail. He then turns over
the stones with his snout and continues sweeping until the gravel
over a circular spot, some two feet in diameter, is clean. The sand
is swept toward the edge of the nest and there forms a few inches
^ From Lydell, Bull. U. S. Fish Com., 22: 39.

I044 FRESH-WATER BIOLOGY

high, leaving the center of the nest concave like a saucer. The
nest is usually located near a log or large rock so as to be shielded
from one side. If the bank is sheer and the water deep enough,
the nest may be built directly against the bank." . . .

After spawning the male drives the female away. "The male,
and the male only, now continues to guard the nest, fanning sedi-
ment from the eggs and repelling enemies. At 66° F. the eggs
hatch in five days and the young fishes swarm up from the bottom
in twelve to thirteen days from the day of hatching.

" Shortly after the young small-mouthed bass rise from the nest
they scatter out over a space four or five rods across — not in a
definite school with all the fish moving together, but as a loose
swarm, moving independently or in small groups. The fry may
be at the surface or on the bottom, in weeds or clear water, and are
attended by the male until they are i| inches long. The swarm
then gradually disperses and the young fry, which were previ-
ously black, take on the color of the old fish."

Other fishes having adhesive eggs attach them to the lower
surfaces of rocks and boards. Several of our darters have this
habit, as well as several minnows. The eggs of some species of
darters are attached to the upper surfaces of rocks. Other fishes
suspend their eggs from aquatic plants, with or without nest
building. The goldfish, which has adhesive eggs, attaches them
singly to aquatic plants, as the fish swims about. The skipjack
probably does the same, though in this species, as in the case of
its marine relatives, the egg is suppHed with long, thread-Kke fila-
ments. I have seen pairs of these fishes wind in and out near
the surface among water plants, and once saw a pair of gar pikes
late in June going through the same performance. The yellow
perch provides similarly for its eggs. They are laid in long strings
which are suspended from aquatic plants. The eggs of the stickle-
backs have mushroom-shaped processes that are adhesive.

The lampreys, salmon, trout, some suckers, and some minnows
have eggs which are heavier than water. These fishes deposit
their eggs among the gravel of swift-flowing water where Kttle
sediment falls. Some of our catfishes and the miller's-thumb
have cohesive, agglutinating eggs. These are laid under boards

THE AQUATIC VERTEBRATES 1045

or in other protected places and guarded by the male. The male
Noturus not infrequently proceeds to swallow the eggs he guards
when they are uncovered.

''Both^ parents of the yellow catfish are a pale yellow color,
the number of eggs deposited was estimated at two thousand.
The incubatory period was five days in a mean water temperature
of 77° F., the lowest temperature being 75 degrees and the highest
80 degrees.

''During the entire hatching period both parents were incessant
in their efforts to prevent the smothering of the eggs, to keep them
clean, and to guard against intruders. The eggs were kept con-
stantly agitated and aerated by a gentle fanning motion of the
lower fins, and foreign particles, either on the bottom of the nest
or floating near the eggs, were removed in the mouth or by the
fins. The most striking act in the care of the eggs was the sucking
of the egg masses into the mouth and the blowing of them out,
this being repeated several times with each cluster before another
lot was treated.

''The male was particularly active in watching for intruders,
and savagely attacked the hands of the attendant who brought
food; he also rushed at sticks or other objects introduced into the
aquarium. Practically the entire work of defence was assumed
by the male, although the female occasionally participated.

"During the time the fry were on the bottom the attentions of
the parents were unrelaxed, and, in fact, were increased, for the
tendency of the different lots to become scattered had to be cor-
rected, and the dense packing of the young in the corners seemed
to occasion much concern. The masses of fry were constantly
stirred, as the eggs had been, by a flirt of the fins, wliich often
sent dozens of them three or four inches upward, to fall back on
the pile.

"The very young fry were also taken into the mouths of the
parents and blown out, especially those which became separated
from the main lot and were found in the sand and sediment. The
old fish would take in a mouthful of fry and foreign particles,
retain them for a moment, and expel them with some force. After
^ From Smith & Harron, liull. U. S. Fish Com., 22: 151.

1046 FRESH-WATER BIOLOGY

the young began to swim and became scattered, the parents con-
tinued to suck them in and mouth them, and, as subsequently-
developed, did not always blow them out.

*'An interesting habit of the parents, more especially the male,
observed during the first few days after hatching, was the mixing and
stirring of the masses of young by means of the barbels. With the
chin on the bottom, the old fish approached the corners where the
fishes were banked, and with the barbels all directed forward and
flexed where they touched the bottom, thoroughly agitated the
mass of fry, bringing the deepest individuals to the surface. This
act was usually repeated several times in quick succession. The
care of the young may be said to have ceased when they began to
swim freely, although both parents continued to show solicitude
when the attendant approached the aquarium from the rear."

In contrast to the nest-building habits are the habits of those fishes
seeking a definite sort of locaHty where to deposit their eggs. The
dace (Semotilus), stone roller {Campostoma), and rainbow darter
{Ethesostoma caeruleum) select gravelly bottom on shallow riffles
above a pool. The habits of the darter have recently been made
the subject of exhaustive study by Miss Cora D. Reeves.^ These
fishes spawn when the temperature reaches about 60° F. The
males select holdings which they guard and from which they drive
rival males by a display of color and by blows delivered with head
and tail. The female buries herself partly in the gravel, the male
taking a position over her, other males crowding in. A few eggs
and milt are extruded at a time and the spawning act oft repeated.
The eggs are adhesive and stick to the gravel.

The adaptation to currents in fresh water thus consists in various
devices to anchor the eggs. The adaptation against sediment is
found in the guarding and fanning habit of the male, the deposit
of eggs to the lower surface of rocks or boards and on riffles, and
the suspension of eggs from water weeds. To these groups of
more or less adaptive habits we must add the peculiar brooding
habits of some catfishes, Cichlids, and the blind fishes, and Cyprin-
odonts. Some of the South American catfishes have the habit of
carrying their eggs in the mouth. Some of them, Aspredo, carry

1 Biol. Bull., 14J 35.

THE AQUATIC VKRTKKRATKS

104;

them attached to the ventral surface. Several African and South
American Cichlids carry the eggs and young in their mouths and
gill chambers. The so-called myth, that a given fish leads about
his brood and guards them in his mouth when danger approaches,
is not a myth for some of these species.

The blind fishes of North America carry their eg«,^s in I heir gill
chambers. In these fishes the oviduct has moved forward so that it

--^

Fig. 1542. Rainbow Barter, Etheosloma caeruleum Storer, $ .

opens just behind the isthmus. The young are carried for a month
or two until they have reached a length of 10 mm. In a group of
Cyprinodonts reaching as far as Indiana, but increasing in diver-
sity of species and numbers of individuals southward, the eggs are
retained by the female until the yolk is absorbed by the growing
young fish, and sometimes for a much longer period. In the

Fig.

Rainbow Darter, Etheosloma cacruleum Storer, 9 • Actual size, 50 mr

blind fishes of Cuba the young are about an inch in length at the
time of birth and in the Cahfornia surf-perch thc\- may be twice
as long.

Secondary Sexual Characters. — Such features consist in size,
disposition, color, or structure. Large differences in all of these
are found in the kilUfishes. In some of these species the male
is minute and provided with an anal fin modified into a lance-

1048 FRESH-WATER BIOLOGY

like blade. This is not an intromittent organ but is apparently
used as a momentary clasper as the male darts at the female with
the lance directed forward and upward, Kberating the spermatozoa
in spermatophores as the tip of the lance comes in contact with
the female. A single impregnation may furnish the female with
spermatozoa for several broods of young.

The male of Amia has a caudal ocellus. In Rivulus it is the
female that possesses the caudal ocellus.

The differences in disposition in the black bass, in which no
other secondary sexual differences exist, are mentioned elsewhere.

Fig. 1544. Blunt-Nosed Minnow, Pimephales notatus (Rafinesque), $ . Actual size, 73 mm. long.

The greatest display of secondary sexual colors is seen in the sun-
fishes and especially in the little darters and in Chrosomus whose
brilliant coloration is scarcely surpassed by that of the humming
birds. The greatest display of secondary sexual color takes place
just before the breeding season. It may be used as a sex recog-
nition mark, a battle flag, as in the rainbow darter, or as a lure to
the female.

In many males small excrescences appear on the sides, on the
fins, or on the head during the breeding season. The anal fin is
often provided with booklets in suckers. The male of Campostoma
becomes covered with tubercles. Pimephales develops short, warty
horns on the head and the horned dace (Semotilus atromaculatus)
large, long ones. Some of these are used as excitants for the fe-
male, others undoubtedly to enable the male to cling to the female
during the spawning act.

Physical Environment and Adaptations to it. With the excep-
tions noted, fishes are always found in water. The character of
the water, i.e., the per cent of salt and other chemicals in solution,
determines the three major ecological divisions of fishes: I, the
marine fishes; II, the brackish water fishes; and III. the inland,

THE AQUATIC VERTEBRATES 1 049

fresh- water fishes. The first two groups are beyond the scope of
this chapter.

The inland fishes, according to the physical character of the
environments selected by them, may be divided into the following
groups, in part suggested by Cope and Jordan.

1. Lowland fishes: the bowfin, pirate perch, large-mouthed black
bass, sunfishes, mud-minnow, and some catfishes.

2. Channel fishes, ranging from lowland to upland: the channel
catfish, the moon-eye, gar pike, buffalo fishes, and drum.

3. Upland fishes: many of the darters, shiners, and suckers, and
the small-mouthed black bass.

4. Mountain fishes: the brook trout, and many of the darters
and minnows.

5. Lake fishes, inhabiting only waters which are deep, clear,
and cold: the various species of whitefish and the Great Lake
trout.

6. Anadromous fishes, or those which run up from the sea to
spawn in the fresh water: the salmon, sturgeon, shad, and striped
bass.

7. Catadromous fishes, that descend to the ocean to spawn: the
eel.

8. Cave fishes, found exclusively in cave streams: the Ambly-
opsidae.

Many of the species are found in more than one of the areas
mentioned.

Liland waters vary greatly in the amount of the solids in solu-
tion or suspension. In the Great Salt Lake and the alkali lakes of
the west the amount of solids in solution is prohibitive to fish life.
In all other waters, however small, if accessible, fishes are found.
Even temporary ponds are colonized by catfishes and sunfishes if
they are at all accessible. Sediment is present in variable amounts
and some fishes, depending exclusively upon sight to detect their
prey, are found only in water free from sediment.

Under given conditions in moving water, the amount of o.xxgcn in
solution is tolerably constant. When a body of fresh water freezes
over, or after the summer thermocline is formed, the oxygen may
become reduced in quantity or disappear altogether in the deeper

I050 FRESH-WATER BIOLOGY

portions of a lake. Through the reduction in oxygen fishes may
be either killed in large numbers or compelled to emigrate. Fishes
being exclusive water animals are especially adapted to utilize the
oxygen in the water. The gills are the universally present res-
piratory organs but in special cases the fins and part of the ah-
mentary canal may be forced into service. In the gar-pike the
air-bladder serves as a lung, at least for the ehmination of CO2.
Various other fishes have cellular air-bladders connected with the
aUmentary canal that suggest respiration. Tower found that in
fishes dying of asphyxiation the ratio of CO2 to O in the air-
bladder increases.

During the breeding season when the gill chambers are full of
eggs much of the respiration of the blindfishes is probably forced
on the fins and general surface. In the surf -fish, to which the Sac-
ramento Hysterocarpus belongs, the young are born fully devel-
oped.^ In their earliest development in the oyary the general
surface of the larva must act as a respiratory organ, later the ali-
mentary canal functions as such. A continuous stream of ovarian
fluid passes in at the gill-opening and out at the anus at this time.
Finally the fins become hypertrophied into enormous sheets super-
abundantly suppKed with blood vessels. In the Cuban blindfishes,
in which the young reach a length of an inch at the time of birth,
vascular lobes are developed in the ovary, which the young take
into their mouths and to which they cling, possibly both for food
and oxygen. It is very probable that those fishes that are capable
of living out of water for a time carry on respiration through their
moist skin.

Temperature and Adjustment to it. — In nearly all fresh waters
of the temperate region there is a fluctuation in the water be-
tween 32° to 80° F. The extreme fluctuation is found only on
the surface of the water. In the bottom of lakes eighty feet deep,
the annual fluctuation ranges perhaps between 39° and 60° F.
Fishes can always escape the extreme fluctuations by seeking deeper
water. That they are adjusted to live through extreme cold is
shown by the fact that some species may be frozen in ice and re-

1 The life history of this species has not been traced, but that of some of its
marine relations has.

THE AQUATIC VERTEBRATES 1051

vive when thawed out. The adjustment in this respect probably
increases as one goes northward. Turner says of the Alaskan
Dallia: "When taken from the traps the fish are immediately put
into these baskets and taken to the village, where the baskets of
fish are placed on stages out of the way of dogs. The mass of fish
in each basket is frozen in a few minutes, and when required to
take them out they have to be chopped out with an axe or beaten
with a club to divide them into pieces of sufhcient size to feed the
dogs.

''The vitaUty of these fish is astonishing. They will remain in
those grass baskets for weeks, and when brought into the house
and thawed out they will be as lively as ever. The pieces which
are thrown to the ravenous dogs are eagerly swallowed, the ani-
mal heat of the dog's stomach thaws the fish out, whereupon its
movements cause the dog to vomit it up alive."

The lower temperature hmit is set to fish Kfe by the freezing
point of the medium, 32° F. for fresh water, below this for salt
water. The upper observed Hmit in ponds is somewhere near
100 degrees.^ If the water is suddenly raised to this point, fishes
survive but a few seconds. While the upper limit may be set by
the effect of the increased heat on the protoplasm, its effect may
be indirect and operate through the reduction in the amount of 0
held in suspension by the warm as compared with the cold water.
That fishes will attempt any temperature is evidenced by the
fact that they occasionally enter water in the National Park hot
enough to boil them.

The adaptabihty of fishes to different temperatures is well shown
by Rhinichthys dulcis wliich is found in the streams coming from
the warm springs at Banff in the Canadian National Park, and
also in the icy waters of Vermilion Creek at the same place. The
same individuals are adjustable within wide limits, and the same
species is sometimes found over a long north and south range.
Nevertheless, temperature has doubtless played an important
part in setting a northern Hmit to the migration of species, as
they followed the retreating ice of the glacial period. In North

1 Jordan and Richardson (Proc. U. S. Xat. Mus., 2>3> • 3i9-3-^0 record Lucania browni
from a hot spring with a temperature of 128° F.

I052 FRESH-WATER BIOLOGY

America a southward migration has probably not taken place since
that time.

Fishes of cold waters are primarily members of the families of
salmon and trout, whitefish, miller's- thumb, and blackfishes. The
check by cold has not been placed on any individual migration or
limits set to the adult. Rhinichthys dulcis and the many species
adapted to the great range of variation in the temperature in any
of our temperate lakes shows this. The temperature factor de-
termining distribution is set rather by the adaptation of the eggs
to warm or cold water. Our trout, salmon, and whitefishes breed
largely in winter when the temxperature is low. The rate of de-
velopment of their eggs, like that of all cold-water eggs, is slow.
The warm-water species are warm-water species not because their
individuals are incapable of entering cold water, for many of them
do, but because their eggs will not develop in anything but water
much warmer than that in which the eggs of cold-water species
develop. Their eggs are of rapid development. They are ad-
justed to fluctuations in temperature and they respond to such
fluctuations in temperature by hastening or slowing their rate of
development.^ The point of attack of temperatures is on the eggs
and young, not on the adult, and temperature controls distribu-
tion through its influence on the eggs.

In all cold waters of the United States accessible to them, trout,
salmon, and whitefish are found. Some of them, the brook trout,
Rocky mountain whitefish, Coulter's whitefish and salmon, are
adjusted to swift currents; others, the lake trout and many white
fishes, to the stagnant waters of lakes. Some of the latter are
littoral or abysmal or pelagic, depending on the nature of their
food. The elevation of a stream has probably primarily nothing
to do with the distribution of its inhabitants, but because elevated
waters are usually cold (and frequently swift) ah accessible moun-
tain waters are inhabited by cold-water species. The number of
species adjusted to cold waters is not as great and their afiinities

^ The cod eggs which hatch in thirty days at a temperature of from 0.0-2° C.
hatch in thirteen days in a temperature of 6-7.9°. Herring eggs which require forty
days at a temperature of 2-3.9° C hatch in eleven at a temperature of 10-11.9°; the
shad which hatches in eleven days at a temperature of 13.5° hatches in three to five
days in a temperature of from 20-23°.

I

THE AQUATIC VERTEBRATES IO53

are not as varied as those adjusted to the warmer, more accessible
waters of the central and southern lowlands. The latter are the
homes of the black bass, sunfishes, catfishes, gar pikes, and others.

So called warm-water species are capable of a wide range of
adjustment to differing climates. Wherever a north and south
river connects warmer with colder areas in which the species are
otherwise different, the easy route of migration induces some sj)ecies
to extend their range into otherwise shunned areas. The Missis-
sippi has induced a southward migration of several species beyond
their normal range, the Nile has extended the equatorial African
fauna to its mouth. But the most notable example is offered" by
the Madeira and Tapajos to Paraguay and La Plata waterway.
It extends from the equator south to a latitude equal to that of
Memphis. Nearly all of the fishes of Buenos Aires belong to Ama-
zonian genera or even species. Only one or two Amazonian genera
have succeeded in reaching the borders of the United States.
Fifty Amazonian genera have reached the La Plata basin that have
not succeeded in going an equal distance south on the Atlantic
coast where they did not have the facilities or inducement of a
continuous waterway.

Current and Adjustment to It. — The major adaptation of all
fresh-water fishes is to the locomotion of water. Most fishes
stand head upstream, a position that makes the respiratory move-
ment easiest in a current. Different fishes, and in some cases the
same fishes at different seasons of the year, are adjusted to the
entire range of variation in the intensity of the locomotion. Water-
falls only are not inhabited by fishes, but even these are ascended
or descended if not too high. Different species of the Salmonidae
give us examples of the entire range of adjustment to currents.
Some of them five only in the stagnant water of deep lakes. Others
live only in swift mountain brooks. The members of the genus
Coregonus usually live in the stagnant waters of lakes, but Core-
gonus coulteri is found in a mountain torrent, and the Tippecanoe
Cisco, which lives in the stagnant water of the lake during the
greater part of the year, runs up the tributaries in December.
Other whitefishes and trout have the same habit. Difi'crent fishes
are even adjusted to the differences in the same small stream in

I054

FRESH- WATER BIOLOGY

which quiet pools alternate with swift-flowing ripples. In the
Mississippi Valley the riffles are occupied by darters, in Cuba by
gobies, in South America by characins, and, although belonging
to widely different famiHes, they greatly resemble each other.

Light and Adjustments to It. — In the shallower parts of clear
water the fluctuations in hght from day to night are but little less
than in the air. Various fishes are variously adjusted to the

Fig. 1545. Hog Sucker, Calostomus nigricans Le Sueur. Actual size, 305 mm. long.

light. Some are nocturnal, remaining hidden during the day, as
the common catfish. Some combine stereotropism with their neg-
ative hehotropism, and take shelter in crevices and under rocks.
The Hght-shunning habit on the part of their ancestors doubtless
accounts for the cave-inhabiting blindfishes of to-day. Some
diurnal fishes habitually stay in the shade of some tree, or log, or
pier, while others are found in the open. There seems to be a
complete gradation between the bhndfishes, which always live in

Fig. 1546. Hog Sucker, Catostomus nigricans Le iiueur. Actual size, 81 mm. long.

total darkness, and those fishes, Hke some sunfishes, that five in
total hght, as far as this exists.

The eye is not the only Kght-perceiving organ of aquatic verte-
brates. The skin is sensitive to Hght in many cases. The blind-
fishes, whose eyes are not functional and may be entirely removed,
nevertheless appreciate the difference between light and dark.
The young after having their eyes removed are as sensitive to

THE AQUATIC VERTEBRATES 105 5

light as those with eyes, and the entire skin seems equally sensitive
to light. The sight of the nocturnal fishes is worse than that of
owls, and their eyes are but Uttle used. The sight of the posi-
tively heliotropic fishes, on the other hand, is good, their eyes are
large and they depend on their eyesight for food. They capture
living food and are frequently pelagic in habit. Small-mouthed
fishes depending on their eyes for food will not take food that is
at rest. Small fragments of meat falling through the water will
readily be seized but will not be picked up from the bottom. The
great variety of artificial flies and gyrating baits are man's adapta-
tions to the fact that some large-mouthed fishes also select their
food by sight.

Depth and the Bottom, and Adjustments to Them. — No system-
atic study of the bottoms of our lakes has been made and it is
hence unknown how extensive the abysmal fauna is. In fishes
ranging in deep water the adjustment is probably due not so much
to the depth itself, as to the things that go with depth. Pressure
increases one atmosphere with each thirty feet in depth, plants
disappear beyond a few feet, and with the plants necessarily disap-
pear all the animals (fish food for the most part), that are associ-
ated with the plants.

The character of the bottom is not a simple element like tem-
perature, Hght, or current. There is a graduation from mud to
gravel and rock and each of these may be weed-covered or bare.
But whether the bottom is mud, gravel or rock depends on cur-
rent. That certain species are found principally on one bottom or
another is certain, but that the adjustment is to the character of
the bottom and not to the current and food that go with it is
doubtful.

The Biological Environment and Adjustment to It. — Food is the
controlling factor in the local distribution of fishes within any
unit, as chemical composition and temperature are controlling
factors in the geographical distribution among the dift"erent
units. Food itself is dependent on other food and this ultimately
on depth, nature of bottom, current, and the other elements of the
physical environment. For the most part the food of the young is
essentially different from the food of the adult of the same species,

1056 FRESH-WATER BIOLOGY

and consists of the organisms composing the plankton, largely
Entomostraca. The members of a local fish fauna are distrib-
uted in the following ecological groups: pelagic, littoral (bottom
fishes, all predacious fishes), and nocturnal.

To these should be added abysmal fishes, but nothing is known
of these in America except that Triglopsis is found in deeper water
of the Great Lakes.

Pelagic, abysmal, littoral, and nocturnal forms are such as find
their food in those regions or times. Their adaptations are but
secondary adjustments to the region in which their food is found.
Everything eatable is food for some fishes though few have such
omnivorous tastes as to take the entire bill of fare. The skipjack
{Lapidestes) is a surface ranger and occupies as definite a position
under the surface of the pelagic area of our lakes as the swallows
do over it. Insects and all other minute terrestrial organic mat-
ters reaching the surface of the water find a lodgment in their
stomachs. Frequently the fish darts out of the water as the
swallow dips into it to secure its food. Its food is not confined to
terrestrial strays, but it also takes Entomostraca and Chironomus
larvae. Zygonectes and Fundulus also range near the surface but
nearer the shores. In the mountain lakes in which the skipjack
is not found, the half-grown whitefish (Coregonus williamsoni) occu-
pies the same ecological niche. In Lake Tahoe on June evenings
individuals nine inches long rise to gnats blown into the lake, and
they can then be caught with a minute hook baited with a fly.

In the American tropics a killifish with half its eyes adapted to
seeing in air and the other half adapted to seeing in water also
ranges on the surface. Larger objects reaching the surface of the
water are secured by black bass, trout, and other fishes that range
and poise in deeper water and ''rise" to their prey near the sur-
face as the kingfisher dives for his. All fishes that rise to arti-
ficial bait, grasshoppers, etc., belong to this group. Some trout
rise more readily to a mouse but for esthetic reasons this cannot be
recommended for bait.

Another series of pelagic fishes is formed by the plankton feeders.
There are several sorts of these. The young of most fishes, the
sunfishes and minnows and some whitefishes, see their minute

THE AQUATIC VERTEBRATES IO57

prey and deliberately pick it from the water. Such are pro\'ided
with teeth either in their mouths or in their gullets. AniAher
series probably including the spoonbill catfish take in large quanti-
ties of water and strain the plankton from it. They have weak
teeth or none and specially-adapted gill rakers for straining the
water.

The various darters, a pecuHar American product, are all lit-
toral. They rest on their pectorals on the bottom, in shallow
water. With head erect and eyes protruding they are ready for
anything that moves within their range of \ision. They are found
among weeds and gravel, chiefly in flowing water so shallow that

Fig. 1547. Johnny Darter, Boleosotna nigrum Rafinesque. Actual size, 55 mm. long.

the surface is rippled. Associated with them, or in places similar
to these, in favorable locahties, are miller's-thumbs. The pirate
perch and trout perch should probably also be placed here.

Other bottom fishes with sucker mouth and elongate alimentary
canal are found over mud bottoms. These include Campostoma,
suckers, carp, and sturgeon in North America. In tropical America
their place is taken by peculiar armored relatives of the catfishes,
the Loricariidae. Lastly, the large, predacious fishes treat the
smaller fishes as they in their turn treat the plankton. Here be-
long the muscalonge, the pickerels, salmon trout, and the basses.
Our nocturnal catfishes and the ubiquitous eel are omnivorous.
They take what they can. Everything that tastes or moves and
is within reach is food for the nocturnal catfish. Some blindfishes
planted in a pool had a way of disappearing that was mysterious,
until the pool was drained and the sardonic catfish, lurking under a
rock and found in possession of the last bhndfish partly digested,
solved the mystery.

Fishes are adapted to their food in structure as well as habit.

1058 FRESH-WATER BIOLOGY

The dentition varies from none at. all to the crushing apparatus of
the white perch, the cutting incisors of some of the killifishes and
the raspHke patches of the teeth of the muscalonge. The mouth
varies in position, shape, and size according to the food, from the
ventrally-placed sucker mouth to the upward-pointing mouth of
Zygonectes; from the small mouth of the cisco to the capacious maw
of the muscalonge. The gill-rakers vary from none to the com-
pHcated strainers of the spoonbill catfish. The aHmentary canal
also varies with the food from the short canal of the flesh eaters
to the convoluted tube many times as long as the fish in the mud
eaters. That fishes are a very adaptable group is shown by the
fact that in South America a single family, the characins, have
the widest range of adaptation in the alimentary canal to different
food. Forbes has pointed out that the minnows of North America
are adjusted to a great variety of food. He distinguishes four
groups: (i) Intestine two to nine times as long as the fish, pharyn-
geal teeth not hooked, with grinding surface. (2) Intestine one to one
and two-thirds times as long as the fish, pharyngeal teeth hooked,
with grinding surface. (3) Intestine somewhat shorter than the fish,
teeth hooked, with grinding surface. (4) Intestine usually shorter
than the head and body, teeth hooked, without grinding surface.
Concerning the relation of these structures Forbes says:
*'It is consequently from a comparison of the ratios of these
groups that we shall derive the most interesting facts relating to
the correspondence of food and structure. The most conspicuous
result is the great preponderance of mud in the intestines of the
fishes of the first group, characterized by an extraordinarily elon-
gate intestine, and by pharyngeal teeth destitute of hooks and pro-
vided with a broad grinding surface. Here, as already noted,
mud, sand, and gravel amount to about three-fourths of the mat-
ter ingested, while in the third and fourth groups only trivial and
accidental quantities occurred. In the second group, on the other
hand, with intestines intermediate in length, mud was still abundant,
but much less so than in the first, averaging less than half the
whole. If we exclude this indigestible matter, however, we shall
find the first group still further distinguished by the predominance
of vegetation as compared with animal matter, the latter being

THE AQUATIC VERTEBRATKS 1059

only about one-third the former, while in groups three and four,
on the other hand, vegetation amounts to about one-third the
animal food. The groups last mentioned, distinguished from each
other as they are only by the presence of a masticatory surface
on the pharyngeal teeth in the first, and its absence in the second,
differ scarcely at all in their general food characters, and this
structural feature seems therefore to be of little significance. In
both the animal ratio amounts to seventy-five per cent, and vege-
tation stands in each at twenty-five; while insects are respectively
fifty and sixty-one."

Recently Putter has maintained that fishes absorb food in solu-
tion in the water. He found that a goldfish lived for forty-one
days in tap water which contained no organized food and the
oxygen consumed substantially accounted for the loss in weight.
When organic substances were dissolved in the tap water, the goldfish
survived for seventy-eight days, and the oxygen consumed greatly
exceeded the amount that would account for the loss in weight.

Food according to its nature may be detected by sight, perception
of vibrations, touch, smell, or taste.

Food is detected by sight in most fishes. Many fishes will
seize an object that is in motion without discrimination as to
what it is provided it is the right size. If it is suitable for food
that fact is discovered by touch or taste, or both, in the mouth
and the object is swallowed. If it is not fit for food it is rejected.
It is evident that in such cases sight only locates the moving
object, other senses distinguish its nature.

Neither friend nor foe of the fishes discloses his presence by
sound, but frequently does so by vibrations of lower frequency.
It is extremely doubtful whether any sound produced over water
is heard by fishes in the water. The sounds of the air are scarcely
capable of passing the surface of the water to an extent to be per-
ceived by an ear under water as highly developed as that of man.
The ears of fishes are much more simple than those of man. The
ability on the part of fishes to hear at all has been disputed, but
Parker ^ has recently made experiments that show conclusively
that fishes hear sounds produced under water.

1 Bull. U. S. Fish Com., 22 : 45-64.

Io6o FRESH-WATER BIOLOGY

In over half of our fresh-water fishes the air bladder is connected
by a chain of ossicles with the ear. In some of them the air
bladder comes in contact with the skin in an area just behind the
head. The intercostal muscles are not developed at this place and
a form of tympanum is thus produced. It has been suggested that
this Weberian apparatus, as it is called, is in reahty an auditory
organ ; that it is a static apparatus controlling the rising and sink-
ing of the fish in water; that it is a manometer acquainting the
fish with the degree of pressure that is exerted by the gases in the
air bladder against its walls; that it is a barometer acquainting
the fish with the variations in the atmospheric pressure; that it is
a sound producer. Judged by its structure alone, in some forms
the air bladder is divided into two small lateral parts connected
with the ossicles, the rest of the air bladder having disappeared, it
seems more than probable that it is an organ for the perception of
sound.

Vibrations of lower frequency than those producing sound, such
as may be produced by waves or bodies falling into the water, are
perceived by the lateral line organs of fishes. The lateral fine
organs of the head of the blindfishes are greatly exaggerated and
their ability to perceive vibrations enables these fishes to secure
Hving prey with precision. The lateral line organs of the head
take the place of the eyes of pelagic fishes in detecting food. Fer-
nandus Payne succeeded in getting an Amhlyopsis to respond to
the water dripping into its aquarium. It would rise to the point
where the drop of water struck and would try to seize it by snap-
ping at it. Perception of vibrations by the lateral line organs of
the head enabled it to locate the point of impact of the water.
Touch, taste, or smell could have nothing to do with it. These
fishes may touch recently-crushed amphipods on which they feed
without paying any attention to them unless a stray leg is still
moving. They will readily take meat attached to a string held in
the hand to give it motion.

Many fishes are conscious of the presence of food by perceiving
it either through the sense of smell, touch, or taste. Parker has
demonstrated that the catfish can detect minced earthworms by
its sense of smell. The elaborate experiments of Herrick with

THE AQUATIC VERTEBRATES lo6l

codfishes have shown that their sense of smell gives them but
vague information, while the senses of touch and taste, whose organs
are found over the entire body, enable the catfish to detect and
secure any food coming in contact with any part of the body. In
contrast to the bhndfishes (Amblyopsis) of the Ohio Valley caves,
the Point Loma blindfish secures its food through touch and taste.
A hungry Point Loma blindfish with a stroke of the fins brings
the mouth in position for operations as soon as any portion of its
skin, especially of the head, comes in contact with food.

Fish Enemies. — The enemies of fishes are the mink, otter, an
occasional raccoon and cat among the mammals; the kingfisher,
herons, ducks, loons, and terns among birds; an occasional bull-
frog and possibly Necturus among batrachians; several snakes,
and many fishes, spawn eaters, fry catchers, lampreys, and adult-
eating, predacious fishes.

The otter as a fish enemy has been practically eliminated. 71ie
occasional fish caught by the mink and raccoon will form but a
small annual total. In fact, by the changes incident to advancing
civilization, all but the aquatic enemies of the fishes have been
reduced to a point where their depredations can have but little
selective value.

Fishes evidently could avoid terns and kingfishers by living below
the few inches penetrated by these divers. But the advantages of
food near the surface evidently outweigh the danger of being
caught, as long as a sudden dive or a dart forward will enable the
fish to escape.

Herons and ducks are avoided by selecting water too deep for
these enemies. Color and swiftness are probably other adapta-
tions to the same enemies. The darter sits with outspread pec-
torals on the bottom of a stream or lake within easy reach of a
heron. A sudden motion of the powerful pectorals and he sits as
composedly somewhere else. The dart-like motion which gives the
darter its name is an adaptation to secure food and avoid enemies.
Swiftness, inconspicuousness, or ability to enter retreats are the
means of defense against the loon and his ilk. Howe\or, none
of the devices are always efficient.

The greatest enemy of fishes is the spawn stealer. At Lake

lo62 FRESH-WATER BIOLOGY

Tahoe the dead trout eggs from the hatchery were daily thrown
into the lake. Wliile no fish might be in evidence a handful
of trout eggs was sure to bring a bullhead {Cottus heldingi) from
under every rock. The same thing happened when the young
trout fry were planted in the brooks. The adaptations of the
black bass, sunfish, and Amia against depredations in their nests
have already been given. No doubt many young fishes are eaten
by minnows and sunfishes. A half-starved sunfish captured in a
cave began to pick out the larval bhndfishes in his pail, with neat-
ness and dispatch, as soon as there was light enough for it to see
them. The herding or schooling of their young by many fishes, as
an adaptation against enemies, has been described before. Against
their predacious neighbors strength, agility, endurance, and color
are the adjustments. The dispersal of a school and the leap out
of the water, reaching its maximum in the fhght of the flying fish,
are all adaptations to escape specific attacks. Aside from these
general adaptations in the habit, structural adaptations against
fish-eating enemies are also found.

The stickleback has divergent, erectile spines that can be locked
when erected. This arrangement is altruistic rather than egoistic.
While it does not prevent a duck or other animal from eating an
occasional stickleback the duck is not Ukely to be tempted by a
second stickleback. More effective weapons are the erectile dorsal
and pectoral spines of the catfishes. In the stone cats the spine
is surrounded by glandular tissue producing poison. The spine in
entering an opponent pierces the gland and carries some of the
poison into the wound.

Color must be looked upon as an adjustment to light in the
presence of enemies. The amount of color on the surface of a
fish is proportionate to the intensity of the light in the environment.
The arrangement of the color is conditioned by the surroundings.
Its presence is an adaptation to the physical environment and its
arrangement is an adaptation to the biological environment. All
animals living for generations in caves become bleached and finally
lose all pigment. Nocturnal fishes are in large measure black.
Bottom fishes, like the darters, hog sucker, miller's-thumb, are
mottled and crossbarred. Weed-inhabiting species are barred (yel-

I

THE AQUATIC VERTEBRATES T065

low perch), striped (black bass), or mottled (pickerels, sunfishes,
etc.). Large size and strength are the best adaptations against
existing fish enemies. Small size and insignificance are advan-
tageous for other reasons. Between these, alertness, with power
of quick movement, and protective color are the most efi'icient
means of escaping enemies.

But all of these adaptations are not always sufiicient. The
most insidious of the fish enemies is the lami)rey. So perfect is
its means of attachment to its prey, that such a hard-scaled and
vigorous fish as Amia calva can rarely prevent the attachment
and adhesion, although the most violent efforts be^made. If a
lamprey is attached to a stone of moderate size, the stone is fre-
quently brought out with the fish if the animal is jerked up sud-
denly. In letting go its hold all that is necessary is to fill the disc
with water from the respiratory bronchus, whereupon suction
ceases and the animal is free. In feeding, the sharp teeth pressed
against the skin of the animal to which it is attached naturally
call the blood to the place. This hyperaemia is caused even more
by the suction. At the same time the piston-Uke tongue with its
powerful muscles and the saw-Hke teeth soon rasp a hole through
the skin. The blood is then sucked from the fish and swallowed.
The whole operation is something Hke the extraction of blood by a
leech. The lamprey may remain upon a fish so long as the latter
supplies sufficient nutriment. Sometimes the fish becomes ex-
ceedingly pale and weak so that it floats near the surface. In
such a case, the fishermen know immediately that there is a lam-
prey attached to the fish, and, with a dip net, usually have no great
trouble in catching both. The birds of prey also make this their
opportunity and frequently carry oft" the floating fish, the lamprey
sometimes remaining attached until it has been carried a consid-
erable distance into the air.

That the injury to the food fishes is very great may be inferred
from the fact that sometimes out of fifteen catfish caught on a set
line in one night, ten to twelve have great raw sores where lampreys
have attacked them. In the spring, too, when the suckers {Catosto-
mus) run up to spawn, very many of them carry a lamprey, and
naturally by the great drain of blood it causes, the fish must be

1064 FRESH-WATER BIOLOGY

weakened, so that obstacles on the way to the spawning ground
are less Uable to be surmounted than if the fish were in full vigor.
In South America small catfishes Uve in the gills of larger catfishes.

Origin of Adapted Faunas. — It has been shown that the major
adaptations of fresh-water fishes were acquired by their ancestors
before they were ehgible to a fresh-water existence.

The origin and modification of the cave fauna gives us a con-
crete example of the change of location, resulting from predestined
adaptation and of subsequent minor adaptations. Caves are at the
present time being colonized by the immigration of salamanders of
the genus Sprier pes and other animals that have become adapted
to a cave existence through their habit of living in the dark under
rocks, bark, and other similar places. The adaptation to the con-
ditions of cave existence in this case determines the change of
location when the opportunity arises.

That minor adaptations will occur in these after they have
become exclusively cave forms, is shown by the structure of the
permanent cave salamanders of Missouri and Texas. These have
in large measure lost their color and have degenerate eyes.

A somewhat more complex example is furnished by the history of
the Horse Cave River. At Horse Cave, Kentucky, a wide valley
extends north and south. Tributary valleys come from the east and
west. The hills bordering these valleys are limestone capped with
sandstone. The north and south valley was formed by the Horse
Cave River that originally flowed over sandstone like that capping
the bordering hills. No doubt it had a fauna as varied as that of
any surface stream. The stream cut first through the sandstone,
then through the limestone. When it had reached the easily dis-
solving limestone of the Kentucky caves and Green River had cut
some distance below the surface. of this, some part of its water,
later more and more, found its way to the Green River by under-
ground channels. To-day not a sign is seen on the surface of the
streams that are responsible for the valley about Horse Cave. At
least one of them rushes through lofty chambers one hundred
eighty-five feet beneath the streets of Horse Cave City. With
this change in the environment, with the disappearance of Horse

THE AQUATIC VERTEBRATES 1065

Cave River from the surface, its inliabitants had to migrate.
They moved in two directions to adapted environments. The
shore fishes and channel fishes moved out to the Green River
where their descendants five to the present day. The negatively
heliotropic, nocturnal, or stereotropic fishes moved into the holes
dissolved in the bottom of the river. Hieir descendants live, at
the present time, in the stream below or within the valle\-. They
are colorless and all but eyeless, and have, no doubt, acc^uired this
exaggerated adaptation to their present abode since their immi-
gration. But the major adaptation to the cave existence they
possessed before the formation of the caves, and it was responsible
for their migration to their present habitat.

As was pointed out in the opening paragraphs, the fauna of the
glaciated region of North America has similarly been derived by
immigration from the south and possibly the ocean and Siberia to
the north and west. The Great Lake Basin has but twenty-seven
of its one hundred fifty-two species peculiar to itself; five are but
varieties of more southern species and the remaining twenty-one
more than represent the extent to which its fauna has become
adapted in this area for some of them (eight Salmonidae and eight
Cottidae) are cold-water species that may have been crowded out of
the region south of the basin by the encroaching heat after the
passing of the glacial epoch.

The selective migration to adapted locations must be added to
the factors contributing to the origin of adapted faunas. This
factor, ''change of location," is as important to the origin of
adapted faunas as the ''change of function" to the origin of
adaptive structures. Innumerable minor adaptations to heat,
sediment, light, food, and to the peculiar coml)inations found in
each selected locality have no doubt arisen in such localities.

io66 FRESH-WATER BIOLOGY

IMPORTANT WORKS ON AQUATIC VERTEBRATES

General
Cambridge Natural History, edit, by S. F. Harmer and A. E. Shipley.
Volumes: vn, Fishes; vni, Amphibia; v, Reptilia; rx, Birds; x, Mam-
mals. London.
ScHARFF, R. F. 191 2. Distribution and Origin of Life in America. New
York.
Bulletin of the U. S. Bureau of Fisheries; Washington, D. C.

(Contains many articles on Fishes, Birds, and Reptiles.)

Mammals
Ingersoll, Ernest. 1907. The Life of Animals. The Mammals. New

York.
Seton, E. T. 1909. Life Histories of Northern Animals. 2 vols. New York.
Stone, Witmer, and Cram. 1902. American Animals. New York.

Birds
Chapman, F. M. 191 2. Birds of Eastern North America. New York.
CouES, Elliott. 1903. Key to North American Birds. Boston.
RiDGWAY, Robert. Birds of North and Middle America. Bulletin U. S. Nat.

Mus., No. 50. Part I, 1901; Part II, 1902; Part III, 1904; Part IV,

1907; Part V, 1911.

Reptiles
Cope, E. D. 1898. Crocodilians, Lizards, and Snakes of North America.

Ann. Rep. Smithsonian Inst., pp. 153-1270.
DiTMARS, R. L. 1907. Reptile Book. New York.

Amphibia

C0PE,E. D. 1889. The Batrachia of North America. Bull. U. S. Nat. Mus.,

34: 1-525-
DiCKERSON, Mary C. 1906. Frog Book. New York.

Fishes
Jordan, D. S. 1905. Guide to the Study of Fishes. New York.
Jordan, D. S., and Evermann, B. W. i 896-1 900. The Fishes of North and
Middle America. Bull. U. S. Nat. Mus., No. 47. 4 Parts.
1902. American Food and Game Fishes. New York.

A number of admirable state lists have been published on Mammals, Birds, and Fishes. Nominally
confined to a single state, they are useful over a much wider territory.

CHAPTER XXXI
TECHNICAL AND SANITARY PROBLEMS

By GEORGE C. WHIPPLE

Professor of Sanitary Engineering, Harvard University

There are several very practical problems of fresh-water biology
which deserve consideration, and which will be treated briefly in
this chapter. They relate chiefly to some of the smallest organisms
found in fresh water, — the bacteria and the plankton. There are
other problems, to be sure, which have to do with larger organisms,
but most of these have been referred to in the various chapters
which have gone before.

First and foremost is the problem of disease transmission. Patho-
genic bacteria are not normally present in natural fresh waters,
but rivers and lakes in inhabited regions are subject to pollution
with the excrement of animals and human beings and such excre-
mentitious substances are liable to contain the germs of disease.
The adoption of the water carriage system of sewerage about the
middle of the nineteenth century greatly increased these chances
of fresh-water contamination. Water which contains excrementi-
tious matter or bacteria of fecal origin may be said to be con-
taminated; if bacteria are actually present the water is said to be
infected. The most noteworthy diseases which are water-borne
are typhoid fever, Asiatic cholera, and dysentery, but there are
other water-borne diseases, for contaminated water may contain the
spores of other bacteria, molds, and the ova of parasitic worms.
Fresh water also may serve as a medium within which mosquito
larvae grow and from which mosquitoes emerge. Special kinds of
mosquitoes play an important part in the transmission of yellow
fever and certain other diseases. Then there may be indirect as
well as direct relations between man and the microorganisms found
in water.

Microscopic organisms form the basis of the food supply of
fishes and thus indirectly contribute to human sustenance. Oysters

1067

I068 FRESH-WATER BIOLOGY

feed chiefly upon diatoms. The smaller Crustacea feed upon
bacteria and minute algae and protozoa, and are, in turn, devoured
by larger organisms.

In the public water supplies the appearance of algae and proto-
zoa in large numbers is the occasion of complaint by the water
consumers, for these organisms make the water unsightly and ill
smelling. They also clog filters and increase the cost of water
purification.

Water as a Conveyor of Disease Germs. There are few if any
bacteria pathogenic to human beings which are naturally found in
fresh waters. Trouble comes only when waters become infected
with pathogenic bacteria derived from other human beings or from
animals. Such bacteria do not thrive and multiply in natural
waters so far as is now known but are merely mechanically trans-
ported by water. Furthermore, instead of multiplying in water
pathogenic bacteria tend to decrease in numbers after the time of
infection. This is an important practical matter as it greatly
affects the safety of all pubUc water suppHes. For example, a
rapidly flowing stream may convey infection for long distances in
a short time, while, on the other hand, a lake or pubHc reservoir
may store the water for so long a time that there is opportunity for
dangerous bacteria to die.

The longevity of pathogenic bacteria in water depends upon
many things among which may be included the original character
of the bacteria themselves, the temperature of the water, the oppor-
tunities for sedimentation and destruction by other organisms, the
effect of sunlight, etc. Using general figures it may be said that
under average conditions about 70 per cent of typhoid fever bac-
teria will disappear the first week, 90 per cent during the first two
weeks, and 99 per cent during six weeks. They will live longer
in cold water than in warm water. That is why most of the
water-borne typhoid fever epidemics have occurred during the cold
months of the year. The spirillum of Asiatic cholera is known to
behave in a similar manner but less is known in regard to the rate
at which it dies. There is some reason to believe that it has a
shorter life in water than the typhoid fever bacillus. There is
a group of bacteria presumably of intestinal origin which give

TECHNICAL AND SANITARY PROBLEMS 1069

rise to dysentery and various diarrhoeal disturbances. Presumably
these bacteria behave in the same manner as the typhoid fever
bacillus.

The routine methods of bacteriology at the present time do not
permit of a trustworthy determination of the above-mentioned
pathogenic bacteria. It is true that in some instances such have
been isolated from water but the process is a difficult one and nega-
tive results are of Httle value. This being the case, modern sani-
tarians do not attempt to determine the safety of water by searching
for these pathogenic organisms. Instead they make tests to
determine the presence and abundance of an organism which is
commonly found in the intestines of man and warm blooded animals
generally known as bacillus coH. This test can be made with a
fair degree of reliability and it is much used.

B. Coli as an Index of Contamination. Unpolluted ground waters
contain practically no B. coli but in proportion as waters are subject
to contamination with excremental substances the numbers of B.
coK increase. All surface waters are likely to contain these germs,
but in unpolluted sources, such as uninhabited woodland areas, the
numbers are very small indeed. Even the broad waters of the
Great Lakes contain B. coh in small numbers though very often
they are absent from the quantities usually used in the test. Rivers
which drain farm lands contain B. coli in larger numbers; streams
and fresh waters which receive sewage contain them in still larger
numbers. B. coli, therefore, may be fairly regarded as a valuable
index of fecal contamination. This is so far true that the U. S.
government has established bacteriological standards for drinking
water served by interstate carriers which includes a permissible
Hmit for the number of B. coli. As stated by the U. S. Public
Health Service, waters in which B. coli are absent from two out
of five portions of 10 cc. may be used, but waters in which B. coli
is found in three or more out of live 10 cc. portions would be con-
demned. The dividing Hne apparently comes at a figure which is
about 150 B. coli per liter of water. The whole subject of B. coli
in water, the methods of its determination, and the interpretation
of its results is one which is now going through a series of evolu-
tionary changes. The reader is therefore referred to current

I070 FRESH-WATER BIOLOGY

scientific bacteriological literature and especially to the papers
which appear in the American Journal of PubHc Health.

Numbers of Bacteria in Water. There are two general methods
used for determining the numbers of bacteria in water. By the
first method nutrient gelatine is used as the culture medium and
the period of incubation is 48 hours at 20° C. According to the
second the media is nutrient agar and the period of incubation is
24 hours at 37° C. Both of these methods are useful but the gela-
tine method has been used more than the other. Neither method
gives absolute results; the figures are relative in both cases.

The numbers of bacteria as determined by the gelatine count
vary all the way from less than 100 in relatively clean waters to
many thousands in waters which are dirty and polluted. For
drinking purposes it is generally considered that the number of
bacteria determined by this method should be less than 100 per cc.
The numbers of bacteria in streams vary greatly according to the
rainfall. Very heavy rains wash the surface of the ground and
increase the numbers of bacteria in the drainage water. The sew-
age of cities contains anywhere from a few hundred thousand to
several milhon bacteria per cc. These bacteria are of many sorts,
but most of them are saprophytic in character and in water which
contains organic matter, even in small amounts, they are likely to
multiply enormously in the course of a day or two. Hence bac-
terial counts mean nothing unless the samples are examined im-
mediately after collection. They also mean Httle unless the
bacteriologist has a knowledge of the character of the waters.

Removal of Bacteria from Water. The best method of removing
bacteria from, water is the process of filtration. There are two
general methods in use at the present time, slow sand filtration and
mechanical filtration. In the former process the water is filtered
slowly downward through a bed of sand at such a rate that the water
above the sand descends ten to twenty feet in the course of a day.
By sedimentation within the pores of the sand bed and by the
adhesion of the bacteria to the sand grains at or just below the
surface of the filter the bacteria are removed from the water. The
process is partly physical, partly biological. The method is capable
of removing upwards of 99 per cent of bacteria from moderately

TECHNICAL AND SANITARY PROBLEMS 107 1

polluted waters and experience has shown that the waters are
thereby rendered entirely safe for drinking.

By the mechanical system of filtration the water is first coagu-
lated by the use of chemicals and then filtered rapidly through a
small bed of relatively coarse sand at rates which are 20 and 40
times as great as in the case of slow sand filtration. This process is
likewise effective in the removal of bacteria. The choice of the
two systems depends upon the amount of turbidity and color of the
water and upon its hardness and upon various local conditions of
an engineering character.

After water has been filtered it must be stored in the dark; other-
wise algae and other microscopic organisms are likely to develop and
become troublesome.

Bacteria in water may be killed by the use of liquid chlorine,
bleaching powder, ozone, and similar substances. These are poison-
ing processes. The quantities of chemicals used are so small that
they may be used with entire safety but it is necessary that the
chemicals be thoroughly and quickly mixed with water in order to
assure efficient sterilization. These processes are especially valuable
in cases of emergency and are not to be regarded as substitutes
for filtration. Swimming pools should be disinfected regularly in
order to prevent the transfer of pathogenic bacteria from person to
person.

Sewage may be treated in various ways to remo\e bacteria and
other objectionable substances. The processes used arc screening,
sedimentation, chemical precipitation, intermittent sand filtration,
contact beds, trickling filters, and disinfection. There are many
biological problems involved in these processes and especially in
intermittent sand filters and trickUng filters. Bacteria play an
important part in the disintegration and ultimate absorption of
putrescible organic matter while in trickling filters worms and
various larvae assist in the process.

Tastes and Odors in Water Supplies. Water supplies derived
from surface sources and stored in reservoirs frequently develop
tastes and odors that are very unpleasant. These are largel>- due
to the growth of algae and other microscopic organisms. The matter
is one of very considerable importance to waterworks superintend-

I072 FRESH-WATER BIOLOGY

ents, and much attention has been given to the study of these
growths during recent years. This study has resulted in success-
ful measures for destroying the organisms by the use of chemicals
and for removing the organisms and the odors produced by them
by aeration and filtration. Very Httle success, however, has been
achieved in preventing the organisms from growing.

Chemically pure water is free from taste and odor. Water con-
taining certain substances, as for example sugar or salt, may have
a decided taste but no odor. On the other hand water may con-
tain substances, hke vanilla, that have a strong odor but no taste.
The two senses, though distinct, are closely related to each other.
Most of the bad tastes observed in drinking waters are due to
organisms that produce odors rather than tastes.

Most surface waters contain some organic matter and have a
vegetable or earthy odor. When decomposing organic matter is
present the odors may be foul and disagreeable. These odors may
be classified in three general groups: — (i) those caused by organic
matter other than living organisms; (2) those caused by the de-
composition of organic matter; and (3) those caused by living
organisms.

Observation of Odor. The odor of cold water is best observed by
shaking a partly filled bottle of the water and immediately remov-
ing the stopper and applying the nose. The odor of hot water is ob-
tained by heating a portion of it in a tall beaker covered with a watch
glass to a point just short of boiling. When sufficiently cooled
the cover is slipped aside and the observation quickly made. The
intensity of odors is commonly indicated by numbers as follows: —
o, no odor; i, a very faint odor that would not be ordinarily de-
tected by a person drinking the water; 2, a faint odor that might
be detected by the consumer but that would not attract any spe-
cial attention; 3, a distinct odor that would be readily detected;

4, a decided odor, strong enough to make the water unpalatable^

5, a very strong odor that would make the water unfit for use.
The character of the odor is usually indicated by a letter which
stands for a descriptive adjective. For purposes of record the two
are combined. Thus 3f indicates a distinct fishy odor; 2v, a faint
vegetable odor; 4m, a decided moldy odor. Heating usually

TECHNICAL AND SANITARY PRUBLKMS 1073

intensifies an odor. In water analysis it is common to report the
odor of both hot and cold water.

Cause of Odors. The odors are caused by aromatic oils that are
produced during the growth of the microscopic organisms. After
disintegration the oily substances are scattered through the water.
In many instances the oils are characteristic of the organisms and
the presence of organisms in water can sometimes be determined
merely by the odor. They cannot always be thus recognized,
however, for the quality of an odor changes with its intensity. Cer-
tain organisms present in small numbers im[)art to the water an
odor that might be termed aromatic, Ijut when the same.(jrganisms
are present in larger numbers the odor might be more properly de-
scribed as fishy. The amount of oily matter required to produce a
noticeable odor is very small. The oily substance that gives
Synura its odor is recognizable when diluted to the extent of one
part in twenty-five million parts of water. This is not surpris-
ing, however, as the oil of peppermint can be recognized in a
dilution of one part in fifty million parts of water. The odors
of organisms are intensified by heating, by mechanical agitation,
by a change in the density of the water, by pressure, and by any
other cause that tends to rupture the cell walls and liberate the oil
globules.

The following table gives the natural odor of a number t)f the
common microscopic organisms. For convenience the\- ma\' be
grouped around three general terms, aromatic, grass)-, and lishy.
The aromatic odors are due chiefly to diatoms, one of the strongest
being that produced by Asterionella. Some of the green algae
produce sweetish, grassy odors, and this is even more true of the
blue-green algae. Ambacna produce an odor that varies greatly
according to its dilution, and various epithets have been applied to
it. The fishy odors are the most disagreeable of any obser\e(l in
drinking water, and that produced by Uroi^lemi is perliaps the worst.
The water that contains this organism in large numbers may ha\-e
an odor resembling that of cod liver oil. The odor of Synum is
almost as bad and even more common. When organisms decay
moldy or musty odors may be produced. Hut these odors of de-
composition are less characteristic than the odors of growth. Some

1074

FRESH-WATER BIOLOGY

of the blue-green algae have odors suggestive of the pig pen, doubt-
less because of their high nitrogen content.

Group

Organism

Natural Odor

Aromatic

DiATOMACEAE

Odor

Asterionella

Aromatic — geranium — fishy

Cyclotella

Faintly aromatic

Diatoma

Faintly aromatic

Meridion

Aromatic

Tabellaria

Aromatic.

Protozoa

Cryptomonas

Candied violets

MaUomonas

Aromatic — violets — fishy

Grassy

Cyanophyceae

Odor

Anabaena

Grassy and moldy — green-corn — nas-
turtiums, etc.

Rivularia

Grassy and moldy

Clathrocystis

Sweet, grassy

Coelosphaerium

Sweet, grassy

Aphanizomenon

Grassy

Fishy

Chlorophyceae

Odor

Volvox

Fishy

Eudorina

Faintly fishy

Pandorina

Faintly fishy

Dictyosphaerium

Faintly fishy

Protozoa

Uroglena

Fishy and oily

Synura

Ripe cucumbers — bitter and spicy taste

Dinobryon

Fishy, Hke rockweed

-

Bursaria

Irish moss — salt marsh — fishy

Peridinium

Fishy, like clam-shells

Glenodinium

Fishy

Prevention of Growths of Algae. Various means have been used
to prevent the growth of algae in reservoirs and standpipes. Some
of these, such as the exclusion of sunlight, are successful but most
of them afford only a partial remedy.

Soil Stripping of Reserooir Sites. The removal of the vegetation
and top-soil from the ground that forms the floor of a reservoir
tends to reduce the amount of the organic and mineral matter
available for the food supply of the organisms and thus tends to
diminish their number. In a number of instances, notably the
reservoirs that supply the city of Boston, the soil has been carefully
removed from the reservoir sites before the reservoirs were filled.
This has tended to reduce the growths of algae during the first few

TECHNICAL AND SANITARY PROBLKMS 1075

years after construction, but it has been found t at the effect of
this "soil stripping" is not always permanently successful and that
in the course of a few years heavy growths of organisms have s(jme-
times occurred. Where the reservoir sites are not thus cleaned
growths of algae are likely to be heavy during the first few \'ears
after construction, diminishing, however, withtime. The benefits
from soil stripping occur chiefly during the first few years after con-
struction. Whether or not there is economy in removing the soil
from the bottom of the reservoir depends upon local conditions.
Often it is advisable. In some cases it will be found cheaper not
to strip the reservoir bottom but to apply the money that would
be thus expended towards a filter plant.

Swamp Drainage. The presence of swamps on a catchment area
tends to foster the growth of algae and similar organisms. If these
are located above a reservoir they may seed the reservoir and thus
increase the number of organisms likely to be found there. The
quality of the water may be improved in some instances by draining
the swamps, thus diminishing the chances of the reservoir becoming
seeded and decreasing the amount of organic food supply in the
water. When reservoirs are constructed it not infrequently happens
that pools are left with no outlet. Organisms may develop rapidly
in such pools and be washed into the reservoir after a rain. So far
as possible reservoirs should be self-draining.

Elimination of Shallow Flowage. In the construction of reservoirs
efforts should be made to reduce the area over which the water
stands with a depth of less than ten feet. For in these areas of
shallow flowage aquatic plants are hkely to become seated and may
serve as a nidus for various organisms that ultimately become
scattered through the reservoir and give trouble. Cases occur
where it is wise to strip the soil from the areas of shallow flow-
age without attempting to strip the soil from the entire reservoir
bottom.

Prevention of Pollution. Like other plants the algae in water
grow best when fertilized. Nitrogen, potash, phosphates, and sim-
ilar substances stimulate their growth. Polluted waters are. there-
fore, more likely to develop objectional growths of algae than the
same waters unpolluted. The ehmination of pollution from a

1076 FRESH-WATER BIOLOGY

catchment area is desirable not only for sanitary reasons but also
for lessening the growths of algae.

Aeration. One of the elements of food supply required by algae
is carbonic acid, which is present to some extent in all surface
waters but is likely to be especially abundant in swampy and pol-
luted waters, and wherever organic matter is undergoing decay.
The stagnant water at the bottom of a reservoir, for example, usu-
ally contains large amounts of carbonic acid. The amounts of
carbonic acid may be considerably in excess of saturation, so that
when the water is exposed to the air the gas escapes. Thus the
process of aeration tends to reduce the likelihood of the occurrence
of heavy growths of algae. Aeration also tends to reduce the odors
of the water as the exposure of the water to the air gives opportunity
for the escape or volatilization of the essential oils. Sometimes
natural conditions of aeration exist and are very beneficial, when
water flows rapidly over the rocky bed of a stream.

Chemical Treatment. With our present knowledge little can be
done in the way of treating the water chemically to prevent the
growth of algae. It is possible that the appKcation of lime to reduce
the free carbonic acid in the water would be of some benefit but
this has never been practically used. Chemical treatment has been
successful in destroying organisms as referred to below.

Exclusion of Light. The exclusion of Hght from a reservoir is
an effective remedy in preventing the growth of algae. This can-
not be done in large reservoirs but in small reservoirs and in stand-
pipes it has proved very successful. In cases where ground water
that contained large amounts of plant food has been exposed in
open reservoirs algae growths have been very troublesome, and it
has been found that covering the reservoir or standpipe in which
the water is stored completely prevents the trouble. It has
become an axiom, therefore, among waterworks men that ground
waters should not be stored in the light.

Methods of Killing Algae. Various methods have been suggested
for killing algae in reservoirs, such as copper sulphate, bleaching
powder, ozone, and creosote. Of these copper sulphate has proved
to be by far the most effective. Quantities as small as one part in
one million by weight, and sometimes even smaller quantities, have

TECHNICAL AND SANTTAin' PROHMCMS 1077

been found sufficient to destroy the algae. The amount require<i
depends upon the kind of organisms present, and the amount and
character of the other organic matter. Copper sulphate is applied
to a reservoir by putting crystals of the salt in a gunnysack, or coarse
bag, and dragging it around the reservoir after a boat, letting it
dissolve in the water as it will. Preferably this should be done
while the wind is blowing, and when the water is in a state of some
agitation, so as to obtain a rapid dissemination of the solution
through the water of the reservoir. Unless care is exercised in this
regard there is danger that fish may be killed, and in any case there
is always danger that some fish may be killed. The method, there-
fore, is one that should not be used by one whose experience and
judgment is insufficient.

The copper sulphate treatment is not always entirely successful.
Sometimes after one kind of an organism has been destroyed by
its use some other organism will appear and be more troublesome
than the first. A single treatment of a reservoir with copper sul-
phate therefore does not always suffice, and when a second dose is
required it is usually necessary to use larger quantities than the
first time.

Purification of Water Containing Algae. Water that contains algae
may be purified by filtration, though the ordinar\' processes may
require some modification, depending upon the number and char-
acter of the organisms present. One of the essential elements of
successful filtration is that the water shall always contain a sufficient
quantity of oxygen throughout the process. Aeration, therefore,
may be necessary before or after filtration or both. It may be
accomplished by spraying the water into the air so that it falls in
drops, or by exposing it in thin films as it passes over a weir with a
considerable fall through the air. Generally speaking an exposure
from one to two seconds is necessary and sufficient.

As an illustration of successful purification of a water heavily
laden with algae maybe mentioned the old Ludlow supply of Spring-
field, Massachusetts, which during the summer contained very
heavy growths of Anahaena. The method employed was inter-
mittent sand filtration, similar to that commonly used for the treat-
ment of sewage. The water was first aerated and allowed to spread

1078

FRESH-WATER BIOLOGY

over the sand filter, which was built without cover as it was used
only during warm weather. After rapid percolation through the
sand it was collected in well ventilated under-drains. After the
water had passed through the sand the beds were allowed to stand
exposed to the air so that they themselves became well aerated.
This method almost completely did away with the obnoxious odors
that had previously existed in the water supply of the city. In this
instance the part played by aeration was very important as experi-
ments had shown that the water could not have been filtered satis-
factorily by the ordinary processes of slow sand filtration.

Mechanical filtration is also sometimes employed for the treat-
ment of algae laden water. Used in connection with aeration this
method may prove reasonably satisfactory, but special care must be
given to maintaining conditions of aeration throughout the process.
Sand filters are capable of satisfactorily removing the algae and
their accompanying tastes and odors if the growths are not too
heavy.

The presence of algae in water tends to clog both sand filters and
mechanical filters to an unusual extent and increases the loss of
head, and, therefore, shortens the period of service and in general
increases the cost of filtration. Where water is stored before
filtration, or where it passes through settHng basins copper sul-
phate is sometimes used as an auxihary process antecedent to
filtration.

Self -Purification of Streams. Various microscopic organisms
play an important part in the self -purification of streams. It has
long been known that rivers polluted by sewage and other waste
substances regain their purity to a considerable extent during their
subsequent flow. Various influences combine to bring about this
result, such as the natural death of pathogenic bacteria in an un-
favorable environment, the effect of sunHght, sedimentation of
suspended matter, oxidation of organic matter brought about with
the assistance of bacteria, and, what is of interest here, by the effect
of microscopic organisms. The cycle of changes by which nitroge-
nous matter is broken down by bacterial action and by which the
bacteria are destroyed by protozoa and other larger organisms,
the protozoa being devoured by rotifers and Crustacea, and these in

TECHNICAL AND SANITARY PROBLEMS 1079

turn being devoured by fish, is a biological phenomenon of great
practical importance. In this way natural streams succeed in
cleansing themselves so that waters once foul become clear and
attractive in appearance.

An excellent illustration of these biological changes is the Genesee
river below the city of Rochester. This river now receives practi-
cally all of the sewage of the city at a point about six miles dislant
from Lake Ontario. Below this point the river receives few acces-
sions. Studies made during the summer of 191 2 showed that the
effect of the discharge of the sewage into the river was to increase
the number of bacteria and reduce the number of green algae. Im-
mediately below the sewer there was a further increase in bacteria
and a reduction of the dissolved oxygen in the water. A mile or
two down stream the bacteria began to decrease and protozoa in-
creased. At the mouth of the river the rotifers disappeared but
Crustacea were found in abundance in the lake water around the
river mouth. Beyond one-quarter of a mile from the river mouth,
however, the Crustacea also showed a noticeable decrease. The
chemical changes that accompanied these biological conditions were
equally interesting. Below the entrance of the sewage the dissolved
oxygen in the water almost disappeared but later increased. As the
dissolved oxygen decreased the carbonic acid in the water increased.
At the river mouth there was an under run of the lake water back
into the river due to the lower temperature of the water in the
lake.

Algae also assist in self purification of streams and lakes by liber-
ating dissolved oxygen. Sometimes the growth of algae is so rapid
and the quantity of oxygen produced is so large that supersatu ra-
tion occurs. This commonly takes place in lakes in the region of
the thermocHne, as Birge and Juday have well shown. How great
a factor this oxygen production may be is probabl}' not yet realized
by sanitarians to its full extent.

Microscopic organisms in streams are also useful in removing
the effects of pollution by manufacturing wastes. On the other
hand some kinds of trade wastes are of such a character that they
tend to destroy microscopic life; such are acid (^r strongly alkaline
wastes, and wastes containing arsenic, copper, and other poisonous

lo8o FRESH-WATER BIOLOGY

substances. Even the wastes containing inert suspended matter
may interfere with microscopic Hfe along the shores by smothering
the tiny vegetable and animal cells. Oily wastes, such as the
wastes from gas works, may produce films upon the surface of a
stream; they then interfere with the absorption of oxygen by the
water from the air and thus exert a prejudicial influence on the
natural agencies of purification. It is for these reasons that the
discharge of trade wastes into streams is a matter that is seriously
in need of regulation. The wastes from manufacturing estabhsh-
ments are often more objectionable even than domestic sewage.
Perhaps the worst conditions arise when streams are polluted both
with domestic sewage and with trade wastes.

Identification of the Source of Water. Another practical applica-
tion of the microscopical examination of water is that of determin-
ing the origin of certain waters. One of the studies made in con-
nection with the celebrated Chicago drainage canal case was a
series of microscopical examinations of water from Lake Michigan
down the Ilhnois and Mississippi rivers to St. Louis. It was found
that certain varieties of organisms were present in the water of
Lake Michigan that could not be found in any of the tributary
streams, and the argument was made that as these same organisms
were found in the water supply of St. Louis taken from the Missis-
sippi river they must have been derived from Lake Michigan,
showing that some of the water supplied to St. Louis came from Lake
Michigan through the Chicago drainage canal and the rivers men-
tioned.

The studies made at Rochester in 191 2 showed that the water
near the surface of Lake Ontario contained various microscopic
organisms that could be readily identified but that these were absent
from the lower strata. Serial studies made at the shore of the lake
sometimes showed the presence of these organisms but at certain
times they were absent. The inference was that on these days the
water at the shore was that which had been drawn shoreward from
the deep strata. This finding corroborated the temperature obser-
vations and the wind records, and proved that the effect of a strong
off-shore wind was to blow the surface water away from the shore
and draw in the cold deep water from the lake.

TECHNICAL AND SANITARY PROBLEMS io8t

Ground waters normally do not contain microscopic organisms,
and when these are found in ground waters a natural inference is
that a ground water has been contaminated with surface water.
Thus the microscopical examination of ground water is sometimes
useful in determining questions of pollution.

Organisms in Pipes of Water Systems. When surface water
which contains algae and other microscopic organisms is allowed lo
flow through pipes, as in the distribution systems of public water
supplies, it frequently happens that the pipes become more or less
choked with what is popularly called pipe-moss. Sometimes this
pipe-moss acquires a thickness of several inches and forms a mat
upon the inside of the pipes which materially reduces their carrying
capacity. The organisms which give trouble of this character
are chiefly the Polyzoa, Plumatella, Pahidicelhu and PectinaUlla,
Fresh-water sponges are also found in pipes and masonry aqueducts.
Snails, worms, and various Crustacea may be found associated with
these moss growths. Dr. Thresh of London has described the
occurrence of fresh-water mussels in a thirty-six inch pipe which
attained such a growth that the bore was reduced to nine inches.

It is evident that the pipe dwelling organisms depend upon the
plankton for their food supply. The above-mentioned growtlis
do not occur in pipes which carry water which has been filtered or
ground water, which contains no microscopic organisms.

There is another organism sometimes found in ground waters
which contain salts of iron and magnesia, namely Crefwthrix.
There are three distinct varieties of this organism. One of these
deposits manganese in its gelatinous sheath, another deposits iron,
while the other deposits alumina. All of them grow best in waters
somewhat deficient in dissolved oxygen. Crcnothrix grows on
the walls of the pipes in tufts of filaments. The filaments become
attached and are found in the water discharged from the faucets.
The iron which impregnates the gelatinous sheaths that surround the
cells causes trouble in laundries. Clothes washed in such water
acquire rusty stains difficult to remove. Crcnothrix is sometimes
found associated with the pipe-moss above mentioned.

Pipe-moss may be removed from a distribution system of a water
supply by flushing, but the best practice is to pre\ent the growth?

lo82 FRESH-WATER BIOLOGY

from forming by using filtered water instead of water laden with
plankton.

Plankton and Fish Life. The occurrence of plankton in natural
waters has a definite and direct bearing upon the occurrence of
fish fife. Algae and protozoa and such organisms play an important
part in the cycle of changes which extend from the decomposition
of organic matter by bacteria to the food supply of man. This
cycle may be followed through the several elements of organic
matter, namely, nitrogen, carbon, sulphur, and phosphorus. The
proteid products of metaboHsm are consumed by bacteria; bacteria
are eaten by protozoa and the nitrate formed by bacterial action in
the presence of oxygen is utiHzed as food by algae; algae and proto-
zoa are consumed by rotifers and Crustacea and these latter form
the basis of the food of many fish. Some fish are provided with
special mechanisms for straining the plankton from the water, a
notable instance of this being the menhaden, a salt-water fish
which swims with its mouth open. The water enters through the
mouth and passes out through the gills, while the organisms that
are thus removed are carried to the stomach. The late Professor
Peck showed by experiments at Woods Hole that the abundance
and size of the menhaden are closely related to the abundance of
plankton. Similarly oysters have been shown to be dependent
upon the occurrence of diatoms in the waters which flow over the
oyster beds. Experiments made by the writer in the Great South
Bay, Long Island, showed that the best oyster beds were located
near mud flats where diatom hfe abounded.

Intimately connected with the occurrence of the plankton and
the bacteria associated with decomposition of organic matter is
the presence or absence of dissolved oxygen and carbonic acid in
the water of lakes at different depths, and fluctuations in the occur-
rence of these gases profoundly affect fish Hfe. If the amount of
organic matter at the bottom of a lake or pond is large the water
below the thermocHne may lose most of its oxygen during periods
of stagnation. It is impossible for fish to five under such conditions,
so that lakes and ponds which undergo stagnation are not Hkely to
contain such fish as naturally seek the colder water found only at
great depths during the summer. Thus it is seen that plankton

TECHNICAL AND SANITARY PROBLEMS 1083

studies and determinations of the amount of oxygen and carbonic
acid in stagnation may be a valuable guide to a fish commission in
determining the advisability of stocking certain lakes with certain
fish. The study of limnology is a matter of great practical impor-
tance to the human race.

INDEX

All technical terms and all scientific names are included, but only major references to
each are given. Important cross references are grouped together after other entries under a
given term. All figures refer to text pages.

Specific names are printed in italics and follow in alphabetic order the name of the genus
to which the species belong; the generic name is printed in italics only when it occurs exclu-
sively in a binomial combination and no reference is made to the genus alone.

Abedus, 933

Abothrium, 431; crassum, 431

Acanthiidae, 933

Acanthocephala, 16, 365, 416, 506-510, 542-
551; key, 545-551; lemnisci, 543, life
history, 544, proboscis, 542, p.- sheath,
543, references, 552; see Gordiacea; Nema-
toda (Parasitic); Parasitic Roundworms

Acanthocephalus, 547; ranae, 547

Acanthochasmidae, 391

Acanthochasmus coronarium, 391

Acanthocirrus, 445

Acanthocystis, 236; chaetophora, 236

Acantholeberis, 710; curvirostris, 710

Acella, 981

Ace tabula, 425

Achnanthaceae, 130

Achnanthes, 130; exilis, 130

Achromadora, 490; minima, 490

Acilius, 941

Acineta, 300; fluviatilis, 300

Acinetactis, 244; mirabilis, 244

Acmostomum crenulatum, 361, 364

Acoleidae, 447

Acoleus, 447; armatus, 447

Acrobeles, 495

Acrodactyla, 396

Acrolichanus, 396; lintoni, 396, petdosa, 396

Acroloxus, 98s

Acroperus, 718, angustatus, 719, harpae, 719

Actinastrum, 159; hantzschii, 159

Actinobdella, 655; annectens, 655, inequian-
nulata, 655

Actinobolus, 271; radians, 271

Actinolaimus, 485; radiatus, 485

Actinolophus, 234; minutus, 234

Actinomonas, 243; vernalis, 243

Actinophrys, 234; sol, 217, 234

Actinopoda, 234

Actinosphaerium, 234; eichhornii, 213, 234

Acuaria, 526; ardeae, 527, triaenucha, 526

Acuariinae, 526

Acyclus, 611; inquietus, 611

Adaptations of aquatic animals, 1022

Adineta, 619; vaga, 619

Aeolosoma, 638; hcmprichi, 638, Unebrarum,
638

Aeolosomatidae, 638

Aerobes, obligatory; sec Bacteria

Aeronemum, 164; polymorphum, 164

Aeschna (imago), 925, (nymph), 930

Agabetes (adult), 942

Agabus (adult), 941

Agamodistomum, 411; apodis, 411

Agamodistomum stage of Cercaria rubra, 420

Agamomermis, 520

Agamonema, 520; capsiilaria, 521, pap'd-
ligerum, 521, piscium, 521

Age series of ponds, 49

Akinete, 118

Alaimus, 499; simplex, 499

Alasmidonta, 1005; areola, 1007, caJceola,
1006, marginala, 1006, undiilata, ioo<i

Alasmidonta s. s., 1006

Albertia, 589; intrusor, 5S9

Albia, 867; stationis, S67

Alexia, 978; selifer, 978 ,

Algae, 13; methods of killing. 1076, preven-
tion of growths, 1074, purification of water
containing, 1077; see .\lgae, Blue-Cirecn;
Algae, Fresh-Water, excl. of Bluc-(irecn

Algae, Blue-Green (Cyanophyceae). Frcsh-
Water, 100-114; color, 102, cyanophycin
granules, 102, heterocysts, 103. key, 104-
114, phycocyanin, 102, 117, references, 114,
thermal springs, life of, loi, vacuoles. 103,
"water-bloom," 114; see .Mgae; .Mgac.
Fresh-Water, excl. of Blue-Green

Algae, Fresh-Water, excl. of BIue-Grccn. 115-
177; abundance, 121, akinete, 118. an-
theridium, iiy, antherozoid, 119. aplano-
spores, 118, centric forms, 12^, i hromato-
phores, 116. cultures, 123, and mediums of,
124, diatomin. 117, disc-shaped chroma-
tophores, 116. filamentous, 121. forms, 115,
gametes, 119, key, 125-177. life history, 122,
occurrence, 122, oogonium, 119. o»isporc,
119, palmella condition, 115, phycocyanin,

108 =

io86

INDEX

117, phycoerythrin, 117, phycophaein, 117,
pyrenoid, 116, references, 177, reproduc-
tion, physiology of, 120, zoosporangium,
119, zoospores, 118; see Algae; Algae, Blue-
Green; Bacillariaceae; Chlorophyceae; Pha-
eophyceae; Rhodophyceae

AUassostoma, 387; magnum, 387, parvun, 387

AUocreadiidae, 394

AUocreadiinae, 394

Allocreadium, 395; commune, 395, lobatum,

395
AUoeocoela, 354
Alona, 722; affinis, 723, costata, 723, guttata,

721, 722, intermedia, 724, monacantha, 722,

quadrangularis, 723, rectangula, 723, tenui-

caudis, 720
Alonella, 724, 734; dadayi, 736, dentifera, 735,

diaphana, 721, 735, exigua, 737, excisa, 737,

globulosa, 735, karua, 724, 734, nana, 736,

rostrata, 736, sculpta, 735
Alonopsis, 719; aureola, 719, elongata, 719
Amabilia, 448; lamelligera, 448
Amabiliidae, 448
Ambly plana cockerelli, 360
Ambloplitis rupestris, 1030
Ameletus (imago), 920, (nymph), 922
Ammonia in natural waters, 39
Amnicola, 989; cincinnatiensis, 989, limosa,

989
AmnicoUdae, 989
Amnicolinae, 989
Amoeba, 219; guttula, 220, /jmax, 220, />ro-

/eM5, 219, radiosa, 220, striata, 220, rerri^-

co^a, 220
Amoebea, 219
Amoebidae, 219

Amoeboid protozoa; see Sarcodina
Amoebotaenia, 445; cuneata, 445
Amorgius, 934

Amphiagrion (imago), 923, (nymph), 928
Amphibia, see Batrachia
Amphibious plants, see Plants, amphibious
Amphids. 466

Amphig3''ra, 986; alahamensis, 986
Amphileptus, 275; gutta, 275, meleagris, 294
Amphilina, 430

Amphimonas, 250; glohosa, 250
Amphipoda, 829, 842; see Malacostraca
Amphiprora, 130
Amphiproraceae, 130
Amphisia, 288

Amphistoma grande, 386, subtriquetrum, 386
Amphistomata, 385
Amphistome cercariae, 413
Amphitrema, 232; flavum, 232, wrightianum,

232
Amphizoa (adult), 940, (larva), 943
Amphizoidae, 940
Amphora, 128; ovalis, 128
AmpuUaria, 987; paludosa, 987

AmpuUariidae, 987

Amygdalonaias, 1014

Anabaena, no; circinalis, 110, jios-aquae, no

Anaerobes, facultative and obligatory; see
Bacteria

Anaerobic respiration, 38

Anapodidae, 570, 601; jee Rotatoria

Anapus, 601; ovalis, 601

Anarthra, 591; aptera, 591

Anax, 925, 930

Anchistropus, 730; minor, 730

Anculosa, 994, praerosa, 994

Ancyhdae, 985

Ancylostoma duodenale, 513, 521

Ancylus, 985; diaphanus, 985, mittallii, 985,
rivularis, 985

Ancylus s. s., 985

Ancyracanthus cystidicola, 527

Ancyrocephalus, 375

Ancyronyx, 942

Angiostoma, 521; nigrovenosum, 521

Angiostomidae, 521

Angitrema, 992

Anguillulidae, 521

Animal communities; see Communities, ani-
mal

Animalcules, moss; see Bryozoa
wheel; see Rotatoria

Animals, aquatic, food relations of, 53, 54

Anisonema, 257; acinus, 257

Anistoptera, 924, 929

Ankistrodesmus, 155

Annelida; see Hirudinea

Anodonta, 1002; grandis, 1002

Anodontinae, looi

Anodontoides, 1003; ferussaciana, 1003

Anomalagrion (imago), 924, (nymph), 929

Anomopoda (adult), 694

Anomotaenia, 446; constricta, 446

Anonchus, 502; monhystera, 502

Anopheles, 944

Anoplocephalidae, 444

Anortha gracilis, 334

Anostraca, 666

Antheridium, 119

Antherozoid, 119

Anthophysa, 248; vegetans, 248

Anuraea, 601; brevispina, 601, cochlearis, 601

Anuraeidae, 571, 601

Aorchis, 385; extensus, 385

Aphanizomenon, in; jlos-aquae, in

Aphai.ocapsa, 106; grevillei, 106

Aphanochaete, 169

Aphanolaimus, 498; spiriferus, 498

Aphanothece, 104; microscopica, 104

Aphelenchus, 483; microlaimus, 483

Aphrothoracida, 234

Apiocystis, 147; brauniana, 147

Aplanospore, 118

Aplexa, 985; hypnorum, 985

INDEX

1087

!\plop^5urf 43; filum, 443

A.pocra(ocj Cr^' S43

Apodina,J 30

Apparatu\^ and Methods, 61 ; references, 88, 8<.)

Apsilidae, v 1 1

Apsilus, 61 r^" bucinedax, 611

Aptogonum, 137; bailcyi, 137

Apus, 671; aeq/alis, 663, 671, longicaudalus,

672, lucasanus, 672, ncivbcrryi, 671
Aquatic animals, birds, earthworms, etc.;
5ee Animals, BiiHs, Earthworms, etc.,
aquatic
Arachnida, 17
Arcella, 221; dentata, 222, dlscoidcs, 222,

vulgaris, 222
Arcellidae, 220
Archer inia boltoni, 144
Archigetes, 430

Archilestes (imago), 923, (nymph), 928
Arcidens, 1003; conjragosa, 1003
Argia (imago), 923, (nymph), 928
Argulidae, 786-788; key, 787, 788; see Copc-

poda; Siphonostomata
Argulus, 787; amcricanus, 787, appendiculo-
sus, 787, catostomi, 787, ingens, 788, lepldo-
stei, 788, maculosus, 787, stizostethi, 788,
versicolor, 787, 788
xArhythmorhynchus, 550; brevis, 550, pumili-
rostris, 551, irichocephalus, 550, uncinalus,
5 50
Arkansia, 1004; wheeleri, 1004
Armiger, 984
Arrhenurinae, 863
Arrhenurus, 863; albator, S6s,forpicatus, 863,

globator, 863, macidator, 863
Arlemia salina, 668
Arthrodesmus, 141; convergens, 141
Arthropoda, 17
Arthrospira, 108; jenneri, 108
Ascaridae, 531

Ascaris, 531; ardeae, 532, cylindrica, 531,
entomelas, 531, hclicina, 532, lanceolata, 531,
longa, 531, lumbricoides, 512, microcephala,
532, mucronata, 532, nigrovenosa, 531,
/^ewj/a, 531, serpentulus, 532, sulcata, 531.
tenuicollis, 531
Ascaroidea, 531
Ascoglena, 252

Ascomorpha, 607; ecaudis, 607
Asellidae, 841

Asellus, 841; communis, 841
Aspidisca, 291; costata, 291
Aspidobranchia, 994
Aspidocotylea, 379
Aspidogaster, 380; conchicola, 380
Aspidogastridae, 379
Asplanchna, 607; herrickii, 582, 607, priodouUi,

607
Asplanchnidae, 571, 607
Asplanchnina, 607

.Asphmchnopus, 607; myrnuUo, »>o7

Assimeiiia, yS6; californica, 986

.\ssimcniidae, yH6

Association, cocfliticnt of, 54

Assulina, 230; minor, 230, 5fmiMWMm, 230

.\stacus, 846

Astasia, 254; tricliophora, 254

.\stasidae, 253

.Vstcrionclla, 133; Kracillima, 133

Asteromeycnia, 311; plumosa, 312, r<kfi^-

spiiulala, 31 2
.\symphyl()dora, larva of, 423
Atractidcs, 874; spinipes, 874
.\tractonema, 254: lorluosa, 254
Atrochus, 611; tcntaculalus, 611
Alurinae, 864

\lurus, 866; mirabilis, 866, scaber, 866
Alyidae, 845

.\ul.)phorus, 639; furcalus, 639, ruj^wj, 639
Auricula, 978; pelluccns, 978
Auriculidae, 977
Auriculinae, 977

Auridistomum, 397; clielydrae, 397
Auxospores, 125

Awerinzewia, 227; cycloslomala, 227
Axonopsis, 866; complanata, 866
Azygia, 392; /mcm, 392, sebago, 371, trreticolU,

392
Azygiidae, 392

Bacillariaceae (diatoms), 125-134; key, 125-
134; 5ee Algae, Fresh-Water, excl. of BIuc-
Green

Bacteria, 13, 90-99; aerobes, obligatory, 93,
anaerobes, facultative and obligatory, 93,
94, bacillus coli as index of contamination,
1069, classification, 90, forms, 91, metachro-
matic granules, 92, microorganism, 94,
movement, 92, number, 94, in natural
waters, 96, 1070, references, 99, spores, 92,
structure, 91

Baetis (imago), 921, (nymph), 922

Baetisca (imago), 919. (nymph), 921

Baileya, 176

Balla'dina, 28S

Bangia, 177; atro- purpurea, 177

Bartonius, 849

Basiacschna (imago). 925. (nymph). 930

Bastiana, 497; cxilis, 497

Bathymermis. 505

Batrachia (Amphibia). iojS. 1029: refer-
ences. 1066; stf W-rtebrala, a<iuatic

Batrachospcrmum, 176: grabussonirmf, 176

Bdellodrilus. 644; iUuminatus. 644. ihj/u-
bitis, 644. philadclphicus, 644, puhhcrrimus,
644

Bdelloida. 576, 619

Beetles, acjuatic; sec Colcoptcra; Insccta

Belostoma. 934

Beloslomatidae, 933

io88

INDEX

f

Benacus, 894, 934; eggs, 896

Berosus, 939

Bicosoeca, 245; lepteca, 245

Bidens beckii, 182

Bidessus (adult), 940

Bikoecidae, 245

Binuclearia, 163; tetrana, 163

Biology, Fresh- Water, 9; climate vs., 9, dis-
persal, 13, diversity, 12, fauna relicta, 10, in-
vestigators, II, journals on, 20, man the
modifying agent, 11, origin, 10, references
(general), 18-20, seasonal succession, 10,
stations, 12, stratification of organisms, 10,
types, 13, uniformity, 13, variety, 11; see
References for specific references

Biomyxa, 232; vagans, 232

Bipalidae, 360

Birds, aquatic, 1024-1026; references, 1066;
see Vertebrata

Bithynis, 845

Black-flies, aquatic; see Insecta; Simuliidae

Bladder-worms, 427

Blasturus (imago). 920, (nymph), 921

Blauneria, 979; heterodita, 979

Blepharisma, 283; lateritia, 283

Blepharoceridae, 943

Blue-Green Algae; see .\lgae, Blue-Green

Boleosoma nigrum, 1057

Bolting cloth, specimens in, 7; see Plankton

Bopyridae, 842

Bosmina, 706; longirostris , 706, longispina,
707, obtiisirostris, 707

Bosminidae, 706

Bosminopsis, 707; deitersi, 707

Bothria, 425

Bothriocephalus, 431; latus, 432, 433

Bothriomonus, 433; sturionis, 433

Bothromesostoma, 351; personatum, 351

Bothrostoma, 281

Botrydiopsis, 156; eriensis, 156

Botrydium, 172; granulatum, 172

Botryococcus, 149; hraunii, 149

Bottle, water-, 80

Bottom materials, 24; collecting, 70, differen-
tiation, 25, distribution of life, 35, muck, 26,
terriginous, 26, 45

Boyeria (imago), 925, (nymph), 930

Brachionidae, 605

Brachionus, 605; angular is, 605, bakeri, 579,
mollis, 605, pala, 605, punctatus, 605, quad-
ratus, 605

Brachycera (larva), 946

Brachycoeliinae, 400

Brachycoelium hospitale, 400

Branchinecta, 667; coloradensis, 667, lin-
dahli, 668, packardi, 667, paludosa, 662, 667

Branchinectidae, 667

Branchinella, 670; gissleri, 668, 670

Branchiobdella, 644; americana, 644, tetro-
donta, 644

Branchionidae, 570 i

Branch! ura, 786-788; see Argulidae; jpepoda

Brasenia, 193; peltata, 188 o

Brebissonia, 128

Brychius, 938

Bryozoa (moss animalcules), 17, 947-956;
appearance, 947, habitat, 951, key, 951-955,
methods of study, 950, occurrence, 949,
polyzoa, 947, references, 955, 956, stato-
blast, 950

BucephaUdae, 379

Bucephalus, 379; polymorphus, 412, pusillus,

379
Buenoa, 934

Bugs, aquaac (water) ; see Hemiptera
Bulbochaete, 167; mirabilis, 167
Bulimnaea, 980
Bullella, 1007

BuUinula, 225; indica, 225
Bumilleria, 164; sicula, 164
Bunodera, 388, 396, 398; luciopercae, 396
Bunoderuiae, 396
Bunops, 712; serricaudata, 712
Bursa, 476, 514
Bursaria, 285; truncatella, 285
Bythinia, 989; tentaculata, 989
Bythininae, 989

"Cabbage-snake," 534

Cabomba, 182

Caecidotea, 842

Caecincola, 391, 4CX3; parvulus, 400

Caenis (imago), 920, (nymph), 922

Caenomorpha, 285; medusula, 285

Caddisflies (Trichoptera) ; see Insecta; Tri-
choptera

Calamoceratidae, 936

Calceolus, 277; cypripediiim, 277

Caligidae, 783; see Copepoda

Callibaetis (imago), 921, (nymph), 922

Callidina, 619; angusticollis , 619

CalocyUndrus, 138

Calopteryx (imago), 922, (nymph), 891, 928

Calothrix, 113; thermalis, 113

Calyptomera, 689

Calyptorhynchia, 352, 361

Calyptotricha, 282; inhaesa, 282

Camallanidae, 528

Camallanus, 528; ancylodirus, 5x2, 529,
lacustris, 517. S18, oxycephalus, 529, trispi-
nosus, 529

Cambarellus, 848; shiifeldti, 848

Cambarincola macrodonia, 644

Cambarus, 847; affi,7iis, 848, bartoni, 847, 849,
blandingi, 848, diogenes, 850, extrdneus, 849,
gracilis, 847, hamidaius, 849, immunis, 849,
limosus, 848, pellucidus, 848, propinquus,
849, rusiicus, 849, simulans, 847, virilis, 849

Campascus, 229; cornutus, 229

Campeloma, 988; subsolida, 988

INDEX

1089

Camj/iSurus (imago), 91 8, (nymph), 921

Campipcercus, 718; macrurus, 718, rccliros-
tris, 7\8

Campylc\iiscus, 130; cribrosiis, 130

Candona, v823; acuminata, 826, Candida, 827,
crogmani, 824, Jabacformis, 826, parallcla,
825, recticai:da, 826, reflexa, 824, sigmoides,
825, Simpson!, 825

Candoninae, 809, 823

Canthocamptus, 7 So; hiemalis, 781, idaho-
cnsis, 781, illinoisensis, 781, minutus, 782,
northumbricus, 782, staphylinoides, 781,
staphylinus, 781

Canthyria, looi

Capillaria, 535; ransomia, 535

Carbon dioxide in water, 39; ^ee Water

Carchesium, 294; polypinum, 294

Carinifex, 984 ; newberryi, 984

Carteria, 144, 265; obliisa, 144

Carterius, 313; latitenta, 314, lenospcrma, 315,
tubisperma, 314

Carunculina, loii

Carychium, 977; exiguum, 977

Caryophyllaeidae, 430

Caryophyllaeus, 430

Castrada hofmanni, 351

Catatropis, 383; filaynentis, 383

Catenula, 334; lemnae, 334

Catenulidae, 334, 361

Cathypna, 595; /zow, 595

Calostomus commersoni, 1040; nigricans, 1054

Celithemis (imago), 926, 927, (nymph), 932

Centrifuge, 84

Centropagidae, 755

Centroptilum (imago), 921, (nymph), 922

Centropyxis, 222; acideata, 222

Centrorhynchidae, 549

Centrorhynchus, 549; spinosus, 549

Centrovarium, 401; lobotes, 401

Cephalobus, 495; sub-elongatus , 495

Cephalogonimus, 402; americanus, 402,
vesicaudus, 402

Cephalosiphon, 617; limnias, 617

Cephalothamnium, 247; caespitosiim, 247

Ceratium, 270; hirundinella, 270

Ceratodrilus thysanosomus, 644

Ceratoneis, 130, 134; crcM5, 134

Ceratophyllum, 178, 180, 182; demersum, 193

Ceratopogoniae of Chironomidae, 945

Cercaria, 371, 372, 411; as plankton organ-
ism, 372; agilis, 415. anchoroidcs, 422,
ascoidea (Gymnocephala), 415, biflcxa, 420,
bilineata, 411, brevicaeca, 417, cary/, 416,
clausii, 414, crenata, 417, dendritica, 418,
diaphana, 418, diaslropha, 414, doulhilti,
422, fasciolae hepaticae, 415. fiabeUiJormis
(tetracotyle form), 424. glandulosa, 418,
gorgonocephala, 373, 414. gracillima, 423.
hemilophura, 419, hyalocauda, 413, inhab-
ilis, 413, isocotylea, 417, konadcnsis, 412,

Uptacantha, 416, lurania (Cilcnmercaria^,
413, macrocerca, 421, tnrgalura. 416, mirro-
pharynx, 418, minuta, 415, mirabUis, 422,
pdlucida, 412, platyura, 419, polyadena, 418,
piychocfieilus, 424, racemosa, 419, rrflexa,

415, 421, rubra, 420, Agamodistomum stage
of, 420, tardigrada (RhopalcKcrca), 421,
trigonura, 419, trisolrnala, 420, trixohis, 421,
tubtristoma, 423, urbanrnsis, 412, -urightii,
422; 5fe Ccrcariac; Ccrcariucum; Para-
sitic Flatworms; Trcmatoda

Cercariae, amphistumt, 413, cotylocercous,
419, cystocercous, 421, distomc, 414. echi-
nostome, 420, furcoccrcous, 422, gastcros-
tomous, 412, gymnoccphalous, 415, holo-
stome, 423, leptoccrcac, 415, megalurous,

416, microcercous, 419, microcwtylac. 416,
monostome, 412, ornatae, 419, polya-
denous, 416, prostomatous, 412, rhahdcxoe-
lous, 412, rhopalocercous, 421, sctiferous,
423, stylet, 416; 5fc Cercaria; Cercariaeum;
Parasitic Flatworms; Trematoda

Cercariaeum, 423; Itelicis, 423, ra/fanj, 423;
j^e Cercaria; Cercariae; Parasitic Flat-
worms; Trematoda

Cercobodo, 244

Cercomonadidae, 244

Cercomonas, 244; longicaudata, 244

Cercorchis, 394

Ceriodaphnia, 700; acanthina, 701, cornuta,
700, consors, 702, lacustris, 701, laticaudala,
702, megalops, 701, pidchflla, 702, quad-
rangula, 702, reticulata, 700, rigaudi, 7cx>,
rotunda, 703, scilula, 702

Cestoda, Fresh- Water, 15, 365. 369. 424-453:
acetabula, 425, bladder-worms (cysticcrci).
427, bothria, 425, ciliated larva. 427,
cysticerci, 427, key, 429-451. life history,
427, onchosphere, 427. pleroccrcoid, 427,
proglottids, 424, references, 452, 453.
reproductive organs, 426, rostellum, 424,
scolex, 424, s. str., 430, strobila, 424, struc-
ture, 424; see Parasitic Flatworms; Para-
sitic Worms

Cestodaria, 369, 429: ^^^ Cestoda

Cestodes, monozootic. 429

Chaenia, 272; teres, 272

Chaetarthria, 939

Chaetogaster, 638; diaphanus, 638. limnaei,
638

Chaetomorpha, 165

Chaetonotidac, 626

Chactonotus, 626; acanthodfs, 627, acan-
thophorus, 629, brevispinosus, 627, enormis,
630, formostis, 627. larus, 627. longispi-
nosus, 628, maximus, 621, 623. 626. oftonu-
rius, 628. jim/7/5, 626, spinifcr, 629, 5A«««-
losus, 629

Chaetopeltis, 171

Chaetophora, lOS; pisiformis, 16S

logo

INDEX

Chaetophoraceae, i68

Chaetophoreae, i68

Chaetopoda (earthworms), aquatic, i6, 632-

645; see Oligochaeta
Chaetosphaeridium, 170; pringsheimii, 170
Chaeturina, 630; capricomia, 630
Chalarothoraca, 235
Chamaesiphonaceae, 107
Chamaesiphon, 107; incrustans, 107
Chantransia, 176; chalybea, 176
Chara, 174; coronata, 174, fragilis, 174
Characeae, 172
Characetum, 196
Characiopsis, 158
Characium, 158; longipes, 158
Charales, 172
Chareae, 174

Chauliodes (adult), 935, (larva), 936
Cheiracanlhiis horridiis, 53°, socialis, 530
Chilodon, 276; cucidlulus, 276
Chilodonopsis, 276; crenula, 276
Chilomonas, 261; Paramecium, 261
Chirocephalidae, 668
Chironomidae, 914, 945; Ceratopogoniae of,

945
Chironomus (lar\'a), 945, in part, 945
Chirotonetes (imago), 920, (nymph), 922
Chlamydomonas, 143, i44. 265; ohioensis, 144

pulvisculus, 265
Chlamydophora, 234
Chlamydotheca, 811; azteka, 811, herricki,

811, mexicana, 812
Chlorangium, 147, 266; sientorinum, 266

stentorum, 147
Chlorella, 153
Chlorellaceae, 153
Chlorobotrys, 151; regular is, 151
Chlorochytrium, 157; lemnae, 157
Choanoflagellata, 257
Choanotaenia, 446; infundibulum, 446, po-

rosa, 447
Chodatella, 155

Chondracanthidae, 784; see Copepoda
Chordata, 18
Chordodes, 537, 538; morgani, 538, occiden-

talis, 538
Choroterpes (imago), 920, (nymph), 921
Chlorococcum, 156; infusionum, 156
Chloroflagellida, 264
Chlorogonium, 143; euchlorum, 143
Chloropeltis, 252; hispidiila, 252
Chlorophyceae, 117, 134; key, 134-174; sec

Algae, Fresh-Water, excl. of Blue-Green
Chlorosphaera, 158; lacustris, 158
Chlorosphaeraceae, 158
Chlorotylium, 166; caiaraclarum-, 166
Chromadora, 490; minor, 490
Chromagrion (imago), 923, (nymph), 928
Chromatophores of algae, 116
Chromulina, 260

Chronogaster, 493; gracilis, 493
Chroococcaceae, 104
Chroococcus, 106; giganteus, 106
Chroolepideae, 170
Chrysoflagellida, 259
ChrysomeUdae (adult), 937, (larva), 943
Chrysops (larva), 946
Chrysopyxis, 263; urceolata, 263
Chydoridae, 716
Chydorinae, 717

Chydorus, 730; barroisi, 733, hicornutus, 731,
faviformis, 731, gibbiis, 731, globosus, 730,
hybridus, 733-. latus, 732, ovalis, 733, piger,
732, poppei, 734, rugulosus, 731, sphaericus,
732
Cilia, 238, 239; see Infusoria
Ciliata, 271

Cilia te protozoa; see Infusoria
Cincinnatia, 989

Cinetochilum, 283; margaritaceum, 283
Circulation of water in lakes, 27; epilimnion,
28, hypolimnion, 28, 38, thermocline, 28, 38,
waves and their action, 28
Cirolanidae, 841
Cirolanides texensis, 841

Cladocera (Water Fleas), Fresh-Water, 676-
740; digestive tract, 681, distribution, 687,
key, 689-739, method of study, 688, oc-
currence, 685, references, 739-740, repro-
duction, 683, shell, 679, structure, 677;
see Crustacea
Cladocopa, 806
Cladomonas, 261
Cladophora, 166; glomeraia, 166
Cladophoraceae, 165
Cladorchiniinae, 3S6
Clappia, 990; clappia, 990
Clathrocystis, 106; aeruginosa, 106
Clathrulina, 236; elegans, 236
Climacia (adult), 935, (larva), 935
Climacostomum, 285
Climate and fresh-water life, 9
Clinostomum, 408; marginatum, 408
Clock pump, 80

Cloeon (imago), 921, (nymph), 922
Clonorchis sinensis, 393->
Closterium, 137; moniliferum var. concavum,

137
Clostonema, 255; socialis, 255
Coccogoneae, 104
Coccomonas, 266
CocconeiJaceae, 129
Cocconeis, 129; pediculus, 129
Cocconema, 129; lanceolatutn, 129
Cochleare, 597; turbo, 597
Cochliopa, 990; riograndensis, 990
Cochhopodium, 221; bilimbosum, 221
Codonocladium, 259; umbellattim, 259
Codonoeca, 245; inclinata, 245
Codosiga, 259; botrytis, 259

INDEX

109 1

Coela:rf . *ceae, 158

Coelastrum, 159; sphaericum, 159

Coelenttrata, 15, 301, 316; see Hydrozoa

Coelhelm"nthes, 16; see Annelida

Coelosphav rium, 105; kutzingianum, 105,
106

Colacium, 25. : steinii, 251

Coleochaetacea,% 171

Coleochaete, 171, scutla, 171

Coleoptera (beetles), 904-909; key, 917,
adults, 937-942, larvae, 943. whirligig
beetles, 906; see Ini.'^cta

Coleps, 271; hirtus, 271

Collecting, methods of; see Methods of Col-
lecting

Collodictyon, 250

Collyriclidae, 383

CoUyriclum, 383; colei, 384

Coloburus, 920

Colorus, 597; grallator, 597

Colpidium, 278; striatum, 278

Colpoda, 278; campyla, 278

Coluridae, 568, 59s

Colurus, 597; grallator, 597

Colymbetes, 942

Communities, animal, 51; adaptations, 1022,
associations, 57, balance, 54, classification,
55, consocies, 56, creek, 58, formations, 57,
lake, 58, mores 56, rapids, 52, river, 58,
strata, 56, stream, 57

Conchostraca, 672

Conditions of Existence; see Existence, Con-
ditions of

Condylostoma, 284; patens, 284

Cone dredge, 68

Confervales, 160

Congeria, 1018; leucophaeata, 1018

Conjugales, 134

Conjugation in Infusoria, 242, in Mastigo-
phora, 242, in Sarcodina, 217

Conochiloides, 617, natans, 617

Conochilus, 617; unicornis, 617

Contamination, bacillus coli as index of, 1069

Contracoecum, 533; adunca, 533* spiculi-
gerum, 533

Copelatus (adult), 942

Copepoda, Fresh- Water, 741-789; develop-
ment, 745, distribution, 741, 746, vertical,
749, keys, 755-782, 784-786, 787-788, meth-
ods of study, 753, 754. occurrence, 745. ref-
erences, 788-789, structure, 742, vertical
distribution, 749; 5<?e Argulidae; Crustacea;
Ergasilidae; Gnathostomata; Siphonosto-
mata

Copeus, 591; pachyurus, 556, 565. S9i

Coptotomus (adult), 942; interrogates (adult),
938, (larva), 909

Corallobothrium, 439

Cordulegaster (imago), 924, (nymph), 930

Cordulia (imago), 926, (nymph), 931

Cordylophora, 319, 320, 321; colony, 318; la-
CHstris, 321; see Hydrozoa

Corethra (larva), 945

Corethrella (larva), 944

Corixidae, 934

Corona, 554

Corycia, 221; flava, 221

Corydalis (adult), 935, (larva), 936

Corynoneura (larva), 945

Corynosoma, 549

Corythion, 232; dubium, 232

Coscinodiscaceae, 126

Coscinodiscus, 126; apiculatus, 12G

Cosmarium, 138, 140; bolrylis, 140

Cosmocladium, 150; saxonicum, 140

Cothurnia, 297, plcctostyla, 297

Cottus ictalops, 1037

Cotylaapis, 380; cokcri, 380, insignis, 380

Cotylocercous cercariae, 419

Cotylogaster, 381; occidentalis, 381

Crabs, 828; see Malacostraca

Crangonyx, 843

Craspedacusta, 318, 322; kawaii, 322, sowerbyi,
322; see Hydrozoa

Crawfishes, 828; see Malacostraca

Crayfishes, 828; see Malacostraca

Creniphilus (adult), 940

Crenodonta, 996

Crepidostomum, 395; cornutum, 395

Cricotopus (larva), 945

Cristatella idae, 955, lacustris, 955. mucedo,
947, 955, ophidea, 955

Crucigenia, 159; apiculata, 159

Crustacea, 17; jrr CUidocera; Copepoda; Ma-
lacostraca; Ostracoda; Phyllopoda

Crustacea, Higher; see Malacostraca

Cryptodifflugia, 22S; oviformis, 228

Cryptoglena, 253; pigra, 253

Cryptogoniminae, 397

Cryptogonimus, 381, 391. 398; chyli, 39S

Cryptomonas, 261; ovata, 261

Cr>'ptonchus, 492; nudus, 492

Ctedoctema. 282; acanthocrypta, 282

Ctenopoda, 689

Cucullanidae, 529

CucuUanus, 528, 530; cliicllarius. 530. clegans,

517
Cucurbitella. 225; mcspUiformis, 225
Culex (larva), 944
Culicidae (larva), 944
Currents in water, influence of, 28
Cyanophyceac; sec Algae, Blue-Green
Cyanophycin granules, 102
Cyathocephalinac. 433
Cyathocephalus, 433: truncatus, 433
Cyathocotyle, 409
Cyathomonas, 260; truncala, 260
Cybister (adult), 941
Cyclanura, 253; orbiculata, 253
Cycle of matter, 207

1092

INDEX

Cyclidium, 282; glaucoma, 282

Cyclocoelidae, 382

Cyclocoelum, 382; mutabile, 382

Cyclocypridinae, 813

Cyclocypris, 819; forbesi, 822, laevis, 822

Cyclonexis, 263; annularis, 263

Cyclophyllidea, 439

Cyclopidae, 774

Cyclops, 774; nauplius of, 744, second stage
of, 744; aequoreus, 780, albidus, 777, attr,
775, bicolor, 780, bicuspidaius, 776, fim-
briatus, 780, Juscus, 778, leuckarti, 777,
modestus, 778, phaleratus, 779, prasinus,
779, serrulatus, 779, strenuus, 776, tenuis,
TJT, varicans, 779, liridis, 775

Cyclorchida, 444

Cyclorhapha (larva), 946

Cyclotella, 126; compta, 126

Cyclothrix, 859

Cyclustera, 445; capilo, 445

Cylinders, plankton, 73

Cylindrocapsa, 165; involuta, 165

Cylindrocapsaceae, 165

Cylindrocystis, 137; diplospora, 137

Cylindrospermum, iii; stagnqle, iii

Cylindrotaenia, 450; americana, 450

Cymatopleura, 131; apiculata, 131

Cymbella, 129; cuspidata, 129

Cymbellaceae, 128

Cymbiodyta (adult), 939

Cyphoderia, 229; ampulla, 229, var. /»a/>i/-
/a/a, 229

Cypria, 819; dentifera (Cypria), 820, exsculpta
(Cypria), 820, inequivalva (Physocypria),
822, mons (Cypria), 821, obesa (Cypris),
821, opthalmica (Cypria), 821, pustiilosa
(Physocypria), 821

Cyprididae, 807
Cypridinae, 810, 813
Cypridopsinae, 807
Cypridopsis, 807; vidua, 807
Cyprinotus, 814; americanus (Cypris), 816,
burlingtonensis (Cypris), 816, crena (Cy-
pris), 817, dentata, 796, (Cypris), 816,
incongruens (Cypris), 815, pellucida (Cy-
pris), 815
Cypris, 813, 817; altissima (Cypris), 817,
americanus (Cyprinotus), 816, burling-
tonensis (Cyprinotus), 816, crena (Cyprino-
tus), 817, dentata (Cyprinotus), 816, Juscata
(Cypris), 818, grandis (Paracypris) , 819,
incongruens (Cyprinotus), 815, pellucida
(Cyprinotus), 815, perelegans (Paracypris),
c^i9, pubera (Eurycypris), 814, reticulata
(Cypris), 818, testudinaria (Cypris), 818,
virens, 792, (Cypris), 817
Cy^jrogenia, 1015; irrorata, 1015
Cyprois, 809; marginata, 809
Cyrena, 1018; carolinensis, 1018
Cyrcnella, 1019; floridana, 1019

Cyrenellidae, 1019

Cyrenidae, 1018

Cyrtolophosis, 282; mucicola, 282

Cyrtonia, 599; tuba, 599

Cysticerci, 427

Cysticercoid, 451

Cysticercus, 451; fasciolaris, 447

Cystidicola, 527; farionis, 527, serrata, 527,

stigmatura, 527
Cystocercous cercariae, 421
Cytheridae, 806
Cytholaimus, 489; truncatus, 489

Dacnitis, 528, 52P

Dacnitoides, 530; cotylophora, 530

Dactylococcus, 155; infusionum, 155

Dactylothece, 150; braunii, 150

Dadaya, 737; macrops, 737

Dallasia, 279; frontata, 279

Dalyellia, 340; armigera, 346, articulata, 345,
bilineata, 361, 363, blodgetti, 343, dodgei, 342,
eastmani, 342, fairchildi, 343, inermis, 341,
marginatum, 361, 363, mohicana, 345, rheesi,
341, 343, 344, rochesteriana, 341, rossi, 345,
347, sillimani, 347, viridis, 346

Dalyellidae, 340, 361

Damselflies (Odonata), aquatic; nymphs,
891; see Insecta; Odonata

Daphnia, 694; arcuata, 696, cucullata, 696,
longispina, 677, 696, 697, var. hyalina, 697,
var. longiremis, 697, magna, 694, psittacea,

695, pulex, 695, var. clathrata, 695, var. cur-
virostris, 695, var. minnehaha, 695, var.
obtusa, 69s, var. pulicaria, 695, retrocurva,

696, var. breviceps, 696
Daphnidae, 694

Darwinulidae, 807; stevensoni, 807
Dascyllidae, 942; (larva), 943
Dasydytes, 630; saltitans, 630
Dasydytidae, 630
Dasymetra, 406; conferta, 406
Davainea, 441; anatina, 441
Davaineidae, 441

Debarya, 142; glyptosperma, 142
Decapoda, 829, 844; see Malacostraca
Dendrocoelum, 354, 361, 364; lacteum, 354,

364, sp., 364
Dendrocometes, 298; paradoxus, 298
Dendromonas, 247; virgaria, 247
Dendrosoma, 298; radians, 298
Denticula, 132; inflata, 132
Derepyxis, 264; amorpha, 264
Dero, 640; limosa, 640, obtusa, 640, perrieri,

640
Deropristis, 391; hispida, 392
Derostoma elongatum, 361, 363
Derostomum, 348
Desmarella irregularis, 259
Desmidiaceae, 134
Desmidium, 136; schwartzii, 136

INDEX

1093

Desmonema, 112; wrangelii, 112

Desmopachria (adult), 941

Desmothoraca, 236

Detracia, 979

Dexiotricha, 280; plagia, 280

Diamesa (larva), 945

Diaphanosoma, 690; hrachyurum, 691,
leuchtcnbergianum, 691

Diaptomus, 756; alberqiicrquensis, 771, asli-
landi, 765, asymmetricHS, 769, bakrri, 770,
birgei, 758, clavipes, 760, coloradensis, 759,
conipedatus, 767, dorsalis, 769, ciseni, 765,
Jranciscanus, 766, judayi, 762, Icplopiis,
760, lintoni, 761, minutus, 764, mississip-
piensis, 757, novamexicanus, 771, nudiis,
772, oregonensis, 757, pallidus, 758, />z/r-
Pureus, 772, reighardi, 757, saltillintis, 768,
sanguineus, 767, shoshone, 763, sicilis, 763,
siciloides, 773, signicauda, 773, spalulo-
crenatus, 766, stagnalis, 768, tcnuicaicdatus,
762, trybomi, 761, tyrelli, 759, wardi, 764,
washingtonensis, 770

Diaschiza, 593; hoodii, 593

Diatoma, 131; elongatum, 131

Diatomaceae, 131

Diatoms (Bacillariaceae) ; 5e(? Algae, Fresh-
Water, excl. of Blue-Green; Bacillaria-
ceae

[Dibothrium] cordiceps, 432

Dichelestidae, 784; 5ce Copepoda

Dichothrix, 113; interrupta, 113

Dicrocoeliidae, 407

Dicrocoelium, 407; dendriticum, 408

Dictyocystis, 148

Dictyosphaerium, 149; pulchellum, 149

Dictyosphaeropsis, 150; pdatina, 150

Didinium, 272; nasutiim, 272

Didymops (imago), 925, (nymph), 930; //«/-
?jerf, 926, transversa, 892

Differentiator, 508, 509

Difflugia 224; acuminata, 225, corona, 224,
constricta, 224, /efte^, 224, lobostoma, 224,
pyriformis, 225, urceolala, 224

Digenea, 379

Diglena, 589; forcipata, 589, rostrata, 589

Digononta, 619

Dilepididae, 444

Dilepis, 444; transfuga, 444, unilateral is, 444

Dileptus, 275; gii'a^, 275

Dimorophococcus, 148; lunatus, 148

Dina, 659; anoculata, 659, fervida, 660, wf-
crostoma, 659, />an'a, 659

Dinamoeba, 219; mirabilis, 219

Dineutes (adult), 937

Dinobryon, 264; sertularia, 264

Dinocharidae, 569, 597

Dinocharis, 597; pocillum, 597

Dinoflagellida, 269

Dinomonas, 248; wrax, 248

Dinops, 607

Dioctophyme, 523; renale, 523

Dioctophymidae, 523

Dioicocestus, 448; paronai, 448

Diorchis, 443; afuminata, 443, americana, 443

Diphyllolxjlhriidae, 431

Diphyllolxjthriinac, 432

Diphyllolwthrium, 432; latum. 432

Diplax, 593; videns, 593

Diplobothrium, 378; armatum, 378

Diplocardia, 643

Diplochlamys, 220; fragilis, 220, timida, 221

Diplodiscus, 387; tempcraltis, 3S7, 413

I)ipl()discinacr3S7

Diplodontinac, 86 1

Diplodontus, 861; drspiciens, 861

Diplogaster, 488; y?r/or, 488

Diplogonoporus, 433; grandis, 433, 434

Diplois, 593; daviesiae, 593

Diplophallus, 448; polymorphus, 448

Diplophrys, 233: archeri, 2,\},

Diploposthc, 446; larvis, 447

Diplostomulum, 411, 424; cuticola, 411, ro/-

w»5, 411
Dip nets, 67

Diplera (two-winged flies), aquatic, 909-916,
9i7i 943~946; black-flies (Simuliidae),
913, key, 917, 943-946, larvae, 917, midges
(Chironomidac), 914, wing venation, 910,
916; 5cr Chironomidae, Insecta, Simuliidae
Dipylidiidae, 440
Discodrilidae, 644

Disease germs, water as conveyor of, 1068,
transmission of, 1068

Dispersal of fresh-water life (biology), 13

Dispharagus, 526, ardeae, 527

Distemma, 589; seligcrum, 589

Distigma, 254; proteus, 254

Disloma dendriticum, 408. hflieis, 423, lancr-
olatum, 40S, oricola, 408. polyorchis, 397,
vagans, 423, var labile, 406; see Dislomum

Distomata, 388

Distome cercariae, 414

Dislomum aspersum, 391, centra ppcndictdalum,
411, flexum, 391, auriculatum, 396, dupli-
catum, 421, nodulosum, 396; see Disloma

Distribution of life, 35

Distyla, 593; inermis, 593. ohioensis, 593

Diurella, 595; stdcata, 595, /icrrt, 562, 595

Diversity of fresh-water life (biology), 12

Dixidae (larvae), 944

Dobson flies (Sialididac) ; j^-r Insecta, Ncuro-
tera, Sialididae

Docidium, 139; hactdum, 139

Dolichodorus, 484; heterocephaliis, 484

Donacia (larva), 943

Dormancy, 43

Dorocordulia (imago), 926, (nymph), 931

Dor>laimus, 485; fecundus. 485, labyrin-
thostomus, 485

Dosilia, 311; palmfri, 311, pluttwsa, 311

I094

INDEX

Dracunculidae, 523

Dragonflies (Odonata), aquatic; see Insecta

and Odonata
Drainage of swamps, 1075
Draparnaldia, 169; plumosa, 169
Dredge, cone, 68, pyramid, 71, triangle, 71
Dreissensiidae, 1018
Drepanidotaenia, 442; fasciata, 451, lanceo-

lata, 442
Drepanothrix, 710; dentata, 710
Dromogomphus (imago), 924, (nymph), 930
Dromus, 1012; dromus, 1012
Drunella (imago), 920, (nymph), 922
Dryops (adult), 942
Dunhevedia, 725; crassa, 725, serraia, 726,

se tiger a, 725
Dwarf plankton, 6; see Plankton
Dysnomia, 1009

Dytiscidae (adults), 940, (larvae), 943
Dytiscus (adult), 908, 941

Earthworms (Chaetopoda), aquatic; see

Chaetopoda and Oligochaeta
Echinochasminae, 391
Echinocotyle, 442; rosseteri, 442
Echinodermata, 15
Echinopharyphium, 391
Echinorhynchus, 547; gigas, 542, salvelini, 548,

thecatus, 548
Echinostoma, 391; spinulosum, 391
Echinostome cercariae, 420
Echinostomidae, 390
Eclipidrilus, 643; asymmetricus, 64s, frigidus,

643, palustris, 643
Ectoprocta, 951
Eiseniella (Helodrilus), 643; tetraedus (Helo-

drilus), 643, forma pupa (Helodrilus), 643
Elakatothrix, 152; viridis, 152
Elliptio, icxx>
Elmis (adult), 942
Elodea, 191, 192
Elvirea, 248; cionae, 248
Emea rubra, 457, 458
Enallagma (imago), 923, (nymph), 928;

antennatum (nymph), 928
Enchelys, 273; pupa, 273
Enchytraeidae, 642
Enchytraeus, 642
Encyonema, 129; auerwddii, 129
Endoprocta, 951
Endosphaera, 157; biennis, 157
Enteromorpha, 161; intestinalis, 161
Entocythere, 806; cambaria, 806
Entosiphon, 257; sidcatus, 257
Eosphora, 591; digitata, 591
Ephemera (imago), 918, (nymph), 921
Ephemerella (imago), 920, (nymph), 922
Ephemerida (mayflies), aquatic, 885-888,

917,918-922; keys: 917; imagos, 918-921;

nymphs, 921-922; see Insecta

Ephydatia, 307, 309, 314; crateriformis, 311,

everetti, 311, fluvaitilis, 309, japonica, 310,

leidyi, 951, millsii, 309, miilleri, 309, 310.

robusta, 310, subdivisa, 309, subtilis, 310
Epiaeschna (imago), 925, (nymph), 930
Epicordulia (imago), 926, (nymph), 931
Epilimnion, 28
Epiphragma fascipennis, 912
Epipyxis, 263; ulricidus, 263
Epischura, 755; lacustris, 756, nevadensis, 756
Epision, 449
Epistome, 948

Epistylis, 295; flavicans, 295
Epithemia, 134; turgida, 134
Epithemiaceae, 133
Eremosphaera, 153; viridis, 153
Eretmia, 603; trithrix, 603
ErgasiUdae, 783-786; key, 784-876; see

Copepoda and Siphonostomata
Ergasilus, 783; caeruleus, 785, centrarchida-

rum, 785, chautauquaensis, 786, funduli,

784, labracis, 785, versicolor, 786
Eschaneustyla, 288; brachyiona, 288
Estheria, 673; belfragei, 674, calif ornica, 674,

compleximanus, 674, digueti, 674, mexicana,

675, morsei, 664, 675, newcombii, 674, selosa,

675
Etheostoma caeruleum, 1047
Ethmolaimus, 491; americanus, 491
Euastrum, 140; elegans, 140
Eubranchipus, 668; bundyi, 670, dadayi, 669,

gelidus, 669, holmani, 668, 670, ornatiis, 669,

serratus, 670, vernalis, 668
Euchlanidae, 568, 593
Euchlanis, 595; macrura, 595
Eucrangonyx, 843

Eudorina, 146, 267; elegans, 146, 267
Euglena, 251; spirogyra, 251, viridis, 251
Euglenida, 251
Euglenidae, 251
Euglypha, 230; alveolaia, 231, brachiata, 231,

ciliata, 231, compressa, 231, cristata, 230,

mucronata, 230
Euglyphidae, 228
Euichthydina, 624
Eulamelhbranchia, 994

Eulimnadia, 673; agassizii, 673, texana, 673
Eumermis, 505
Eunotia, 134; pectinalis, 134
Eupera, 1019; singleyi, 1019
Euplotes, 291; charon, 291, patella, 291
Euryalona, 720; occidentalis, 720
Eurycaelon, 992; anthonyi, 992
Eurycercinae, 716
Eurycercus, 716; lamellatus, 717
Eurycypris, 814; pubera (Cypris), 814
Eurynia, ion

Eurytemora, 750; affinis, 756
Eustrongylus papillosus, 523
Euthyplocia (imago), 918, (nymph), 921

INDEX

1095

Eutreptia, 252; viriois, 252

Excentrosphaera, i:^; viridis, 153

Existence, conditior -of, 21-60; bottom mate-
rials, 24, different -tion in bottom material,
25, distrib'ition of life, 35, in lakes, 23, in
Lake Michigan, 35, dormancy, 43, mutk
bottons, 26, references, 60, terriginous bot-
toms, 26

Eylaidae, 860

Eylais, 860; extendens, 860

Fairy shrimps; see Phyllopoda

Fasciola, 389; hepalica, 389

Fasciolidae, 389

Fasciolinae, 389

Fascioloides, 389; magna, 389

Fasciolopsis, 389

Fauna relicta, 10

Faxonius, 848

Ferrissia, 985

Filaria, 524; amphiutnae, 524, ardeariim, 524,
cingula, 525, cistudinis, 524, hcliciniis (Pcle-
citus), 524, nilida, 524, physalura, 525,
solitaria, 521, 524, stigmatura, 527, triae-
nucha, 526, wymani, 524

Filariidae, 524

Filarioidea, 523

Filaroides, 522; mustelarum, 522

Filicollis, 548, 551; analis, S49, botulus, 549, 551

Fimbraria, 449; plicata, 449

Fimbriariidae, 449

Fishes, Fresh-Water, 1029-1065; adapt-
ations, 1039, adjustment to biological en-
vironment, 1055, to current, 1053, to light,
1054, to temperature, 1050, dispersal, 1037,
enemies of, 106 1, homes, 1042, migration,
1040, nests, 1043, number, 1033, origin,
1032, 103s, of adapted faunas, 1064,
plankton and fish life, 1082, references,
1066, secondary sexual characters, 1047; see
Vertebrata

Fish-flies (Sialididae); see Insecta, Neurop-
tera, Sialididae

Fish life, plankton and, 1082

Flagella, 238

Flagellate protozoa; see Mastigophora

Flatworms (Platyhelminthes), 15; free-liv-
ing; see Nemertina and Turbellaria; para-
sitic; see Parasitic Flatworms

Fleas, aquatic; see Cladocera

Flexiphyllum, 274; elongatiim, 274

Flies; black; see Insecta and Simuliidae;
damsel, dragon; see Insecta and Odonata;
fish; see Insecta and Neuroptera; two-
winged; see Diptera and Insecta
Florideae, 175
Floscularia, 609; campanulata, 561. 609, cdcn-

tata, 609, proboscidea, 609, iiniloba, 609
Floscularida, 572, 609
Flosculariidae, 572, 609

Flowing waters, 2

Fluctuations in numl>ers of organisms, 54

Flukes; see Trcmatoda

Fluminicola, 991; nutlalliana, 991

Food relations of aquatic animals, 53, 54

Foraminifcra, 2^2

Fordycc pump, 79

Fragilaria, 132; crototicnsis, 132

Fragilariaceae, 132

Franceia, 155

Frederkella sultana, 952 «

Free-living flatworms; sec Ncmcrlcans and
Turbellaria

Free-living nematodes; see Ncmatoda, free-
living

Free-living Roundworms; sec Nematoda, free-
living

Fresh-water algae, biology, life, etc.; see Al-
gae, Biology, Life, etc.. Fresh-water

Frontipoda, 868; musculus, 868

Frontonia, 280; Iciicas, 280

Funiculus, 948

Furcocercous cercariae, 422

Furcularia, 589; forficula, 589. longisela, 589

Fusconaia, 997

Fyke nets, 63

Gadinia, 980; reticulata, 9S0

Gadiniidae, 980

Galba, 982

Galerucclla (larva), 943

Gametes, 1 19

Gammaridae, 842

Gammarus, 843; limnaeus, 843

Gases, dissolved in water, 36, distribution, 37.
solubility, 37

Gasterostomata, 379

Gasterostomous cercariae, 412

Gasterostomum, 379

Gastropoda, 970, 977: •^«*<' Mollusca

Gastropodidac, 570, 603

Gastropus, 603 ; hyptopus, 603, siylifer, 599, (>o.\

Gastrostyla, 289; steinii, 289

Gastrotricha, fresh-water, 16, 621-631: dis-
tribution, 624, excretory organs, 623. key,
624-630, locomotion, 622, references, 631,
structure, 621

Geminella. 163

Genicularia, 135; spirolarnia, 135

Geoplana nigrofusca, 360, slolli, 360

Geoplanidae. 360

Gerda, 292; sigmoiJes, 292

Gerridae, 933

Gigantorhynchus hirudinaceus, 542

("lillia, 991: dltilis, 991

Gill nets, 64

Glass, water. 87

Glaucoma, 280; sdntUlans, 2S0

Glebula, 1017; rotundata, 1017

Glenocercaria, 413

1096

INDEX

Glenodinium, 270; pulvisculus, 270

Gloeocapsa, 106; polydermatica, 106

Gloeocystis, 150; vesiculosus, 150

Gloeotaenium, 152; loilelsbergerianum, 152

Gloeothece, 104; confluens, 104

Gloeotrichia, 114; pisum, 114

Glossiphonia, 651; complanata, 652, fusca,
652, heterodita, 652, nepheloidea, 651,
stagnalis, 651

Glossiphonidae, 651

Glypthelmiiis, 404; quieta, 404

Gnathobdellae, 656

Gnathostoma, 530; horridum, 530, sociale, 530

Gnathostomata, 755-782; key, 755-782; see
Copepoda

Gnathostomidae, 530

Golenkinia, 154; radiata, 154

Gomphaeschna (imago), 925

Gomphonema, 129; acuminatum, 129

Gomphonemaceae, 129

Gomphosphaeria, 105; aponina, 105

Gomphus (imago), 924, (nymph), 930

Gonatonema, 143; ventricosum, 143

Gonatozygon, 135; raljsii, 135

Gonidea, 1002; angulata, 1002

Gordiacea, 16, 365, 506-510, 535-542; devel-
opment, 536, key, 537-542, references, 551,
552; see Acanthocephala, Nematoda (Para-
sitic), Parasitic Roundworms

Gordius, 539; alascensis, 539, densareolatus,
540, 541, leidyi, 541, lineatus, 540, 541,
longareolatus, 540, plaiycephalus, 541, 542,
puerilis, 538, villoti, 540, 541

Gorgodera, 399; minima, 399

Gorgoderidae, 398

Gorgoderina, 399; attenuata, 399

Gorgoderinae, 398, 421

Goniobasis, 993; virginica, 993

Gonium, 145, 266; pectorale, 145, 266, so-
ciale, 266

Graphoderes (adult), 941

Grapple, 68

Graptoleberis, 724; testudinaria, 724

Grimaldina, 711; brazzai, 711

Gromia, 233; fluviatilis, 233, terricola, 233

Gryporhynchus, 445,451; cheilancristrotus, 445

Gundlachia, 986; meekiana, 986

Gymnamoebida, 219

Gymnocephala, 415

Gymnocephalous cercariae, 415

Gymnodinium, 270; fuscum, 270

Gymnolaemata, 951

Gymnomera, 738

Gymnostomina, 271

Gymnozyga, 135; brebissonii, 135

Gyratricidae, 353

Gyratrix hermaphroditus, 353

Gyraulus, 983; s. s., 983

Gyretes (adult), 938

Gyrinidae (adults), 937, (larvae), 943

Gyrinus (adult), 937
Gyrocoelia, 447
Gyrodactylidae, 374
Gyrodactylus, 374
Gyrotoma, 993; demissum, 993

Habrophlebia (irdago), 920, (nymph), 921
Haemopis, 657; grandis, 658, lateralis, 658,

marmoratis, 658, plumbeus, 658
Haemotococcus, 266
Hagenius (imago), 924, (nymph), 929
Hair snakes; see Gordiacea
Hairworms; sec Gordiacea
Halipegus, 408; occidualis, 408
Hallplidae (adults), 938, (larvae), 943
HaUplus (adult), 938, (larva), 907, 943
Halteria, 286; grandinella, 286
Hapalosiphon, 113; hibernicus, 113
Haplobothriinae, 432
Haplobothrium, 432; globuliforme, 432
Haplonema, 526; immutatum, 526
Haplopoda, 739
Haplotaxidae, 642
Haplotaxis emis sarins, 642
Harpacticidae, 780
Harringia, 607; eupoda, 607
Hassallius, 392
Hasstilesia, 409; tricolor, 409
Hastatella, 292; radians, 292
Hedruris, 528; androphora, 528, siredonis, 528
Heleopera, 227; picta, 227, rosea, 227
Heliozoa 213, 234
Helisoma, 982; s. s., 982
Helminthes, 365; see Parasitic Worms
Helochares (adult), 939
Helocombus (adult), 939
Helocordulia (imago), 926, (nymph), 931
Helodrilus (Eiseniella), 643; tetraedrus, 643,

forma pupa, 643
Helophorus (adult), 939
Hemerobiidae (dobson and fish flies), 898-

899; (adults), 934; 5ee Insecta and Neurop-

tera
Hemiciplostyla, 287
Hemidium, 269

Hemilastena, 1007; ambigua, 1007
Hemiptera (water bugs), aquatic and semi-
aquatic, 893-896, 917, 933-934; key, 917,

933-934; see Insecta
Hemistomidae, 409
Hemistomum, 410; (l$irva), 424; craterum,

410, denticulatum, 411
Hemiurus, 392

Heptagenia (imago), 919, (nymph), 921
Herpetocypridinae, 810
Herpetocypris, 811; barbatus, 812, reptans,

812, testudinaria, 813
Heronimidae, 384
Heronimus, 384; chelydrae, 384
Eerpohdella punctata, 659^

INDEX

1097

Herpobdellidae, 659

Herposteiron, 169; confervicola, 169

Hetaerina (imago), 923, (nymph), 928

Heterakidae, 532

Heter anther a graminea, 191

Heterocheilidae, 533

Heterocysts, 103

Heteromastigida, 248

Heteromastigidae, 246

Heteromeyenia, 312, 314; argyrosperma, 313,
re pens, 313, ryderi, 312

Heteromita, 249; ovata, 249

Heteronema, 256; acus, 256

Heterophrys, 235; myriopoda, 235

Helerostomum echinatiim, 411

Heterotricha, 283

Hexagenia (imago), 918, (nymph), 921; bi-
lineata, 887

Hexamita, 250; inflata, 250

Hexotricha, 277; globosa, 277

Hibernacula, 192, 949

Hippuetis, 983

Hirmidium, 259; inane, 259

Hirudinea (leeches), Fresh-water, 16, 646-660;
key, 651-660, methods of study, 651, ne-
phridia, 648, occurrence, 649, references,
660, reproduction, 647, 650

Hirudinidae, 656

Hiriido medicinalis, 657

Histrio, 290; erethisticus, 290

Histriobalantidium, 281

Holopedidae, 693

Holopedium, 693; amazonicum, 693, gib-
berum, 693

Holophrya, 272

Holosticha, 288; vernalis, 288

Holostomata, 409

Holostome cercariae, 423

Holostomum, 410; niiidum, 410

Holotricha, 271

Hormidium, 162; nitenz, 172

Hormospora, 163; mutabilis, 163

Homostyla, 287; elliptica, 287

Hormogoneae, 107

Hormotila, 148; mucigena, 148

Host, intermediate, 371, primary, 372, second-
ary, 372

Ilyalella knickerbockeri, 843
I Hyalodiscus, 219; riibicundus, 219

' Ilyalolampe fenestrata, 235

Hyalosphenia, 223; cuneata, 223, elegans, 223,
papilio, 223

Hyalotheca, 135; dissiliens, 135

Hydaticus (adult), 941

Hydatina, 599; senta, 599

Hydatinidae, 569, 599

Hydatinina, 599

Hydra, 316-322; development, 317, habitat,
318, key, 320-322, methods, 319, structure,
316; corala, 321, fusca, 321, grisea, 320,

oligaclis, 320, 321, pallida, 321, polypus, 321,

viridis, 320, viridissima, 320, vulgaris, 320;

see Hydrozoa
Hydracarina (water-mites). Fresh-water, 17,

851-875; development, 855, key, 859-874,

methods of study, 857, occurrence, 851,

references, 875, structure, 852
Hydrachna, 860; gcographica, 860
Hydrachnidae, 860
Hydracna, 938
Hydrobaenus (larva), 945
Jlydrobius (adult), 940
Hydrocampa, 903
Hydrocharis (adult), 940
Hydrochus (adult), 939
Hydrocirius, 933

Hydrocoleum, 109; homocotrichum, 109
Hydrodictyaceae, 160
Hydrodictyon, 160; rrticulaium, 160
Hydrogen sulphide in streams, 39
Hydrography, i ; see Limnology, Oceanology,

Rheology
Hydromermis, 505
Hydrometridae, 933
Hydrophilidae (adult), 938, (larva), 943
Hydrophilus, 940
Hydro porus (larva), 941, (larva and pupa),

908
Hydropsychidae, 937
Hydroptilidae, 936
Hydrosphere, i
Hydrovatus (adult), 941
Hydrozoa, Fresh-water, 316-322; key, 320-

322, medusae, 318, references, 322; see

Hydra
Hydryphantes, 862; ruber, 862
Hydryphantidae, S60
Hydryphantinae, 861
Hygrobates, 874; longipalpis, 874
Hygrobatidae, 863
Hygrobatinae, 873
Hymenolepididae, 441
Hymenolepis, 442; compressa, 442, fusus, 442,

megalops, 442
Hymenostoma, 281
Hypolimnion, 28, 38
Hypotricha, 286
Hysterophora, 3^,:?,, 361
Hysterothylacium, 534; brachyurum, 534
Ilystrichis papillosus, 52s

Ichthydiidae, 624

Ichthydium, 624; podura, 624, sulcatum,

625
Ichthyobdellidae, 655
Ichthyonema, 523; cylindraccum, 524
Idiogencs, 441
Ileoncma, 271; dispar, 271
Ilybiosoma (adult), 941
Ilybius (adult), 941

logS

INDEX

Ilyocryptus, 712; acutifrons, 7i3» halyi, 713.
longiremis, 713, sordidiis, 712, spinifer, 713

Ilyocypris, 809; bradyi, 810, gi6io, 809

Ilyodrilus, 641

Ilyodromus, 810; pedinatus, 810

Incrustation on aquatic plants, 185; car-
bonate of lime, 187, gelatinous covering,

187

Ineffigiata, 149

Infusoria (Ciliate Protozoa), Fresh- water, 14,
238-243, 271-300; cilia, 238, 239, ciliate
protozoa, 238, conjugation, 242, key,
271-300, methods of study, 242, physiolog-
ical processes, 241, references, 300, repro-
duction, 241, structure,. 239; see Protozoa

Insecta, aquatic, 17, 876-946; adaptation to
water, 876, of larvae to aquatic life, 878
keys, 917-946; of adults, 934-935. 937-942
of imagos, 918-921, 922-927; of larvae,
917, 935-936, 943-946; of nymphs, 921-922,
928-932; recognition of characters, 880
references, 946, wing venation, 916; see
Coleoptera, Diptera, Ephemerida, Hemip-
tera, Lepidoptera, Neuroptera, Odonata,
Plecoptera, Trichoptera

Intermediate host; see Host

Investigators in Fresh- Water Biology, 1 1

lo, 992; spinosa, 992

Iota, 482; octangulare, 482

Ironus, 486; americanns, 486

Ischnura (imago), 924, (nymph), 929; verti-
calis, 893

Isopoda, 829, 841; see Malacostraca

Jaws (trophi) of rotatoria, 559
Jensenia, 348; pinguis, 348
Journals on Fresh- Water Biology, 20

Kerona, 287; pediculus, 287

Keys to Fresh- Water Biology; Algae, Blue-
Green (Cyanophyceae), 104-114, Algae,
excl. of Blue-Green, 125-177, Acanthoceph-
ala, 545-551, Animalcules, 587-619, 951-
955, Argulidae, 787-788, Bacillariaceae,
125-134, Bryozoa, 951-955, Chlorophyceae,
134-174, Cestoda, 429-451, Cladocera, 689-
739, Copepoda, 755-782, 784-786, 787-788,
Coleoptera, 937-943, Diptera, 943-946,
Ephemerida, 918-922, Ergasihdae, 784-786,
Gastrotricha, 624-630, Gnathostomata,
755-782, Gordiacea, 537-542, Hemiptera,
933-934, Hirudinea, 651-660, Hydra, 320-
322, Hydracarina, 859-874, Hydrozoa,
320-322, Infusoria, 271-300, Insecta, 917-
946, Mollusca, 977-1020, Malacostraca,
841-850, Mastigophora, 243-270, Nema-
toda, Free-Living, 482-505, Nematoda,
Parasitic, 520-535, Neuroptera, 934-936,
Odonata, 922-932, Oligochaeta, 638-644,
Ostracoda, 806-827, Phaeophyceae, 174-

175, Porifera, 306-315, Protozoa, 219-236,
243-300, Phyllopoda, 666-675, Rhodo-
phyceae, 175-177, Rotatoria, 587-619,
Sarcodina, 219-236, Trichoptera, 936-937.
Trematoda, 374-424, Turbellaria, 333-364

Kirchneriella, 151; obesa, 152

Koenikea, 865; concava, 865

Krendowskija, 863; ovata, 863

Kurzia, 718; latissima, 718

Labidestes siculus, 1036
Laccohius (adult), 939
Laccophilus (adult), 940
Lacinularia, 617; socialis, 561, 575, 617
Lacrymaria, 274; olor, 274
Ladona (imago), 927, (nymph), 932
Laevapex, 985

Lagenophrys, 297; vaginocola, 297
Lagerheimia, 154; genevensis, 154
Lakes, 2, 4, 5; age series, 49, circulation of
water in, 27, conditions of existence in, 23,
in Lake Michigan, 35, epilimnion, 28, hypo-
limnion, 28, 38, thermocUne, 28, 38, waves
and their action, 28
Lamellibranchia, 970, 994; see Mollusca

Lamprothamnus, 174

LampsiUnae, 1007

Lampsilis, 1009; ovata, loio, recta, loii,
texasensis, loii; s. s., loio

Land planarians; see Turbellaria

Lanthus (imago), 924, (nymph), 929

Lanx, 986; newberryi, 986

Lara (adult), 942

Lasmigona, 1005

Lastena, 1002; lata, 1002

Lateriporus, 444

Lathonura, 716; rectirostris, 716

Latona, 689 ; parviremis, 690, setifera, 690

Latonopsis, 691; fasciculata, 692; occiden-
talis, 691

Lebertia, 867; dubia, 867, tau-insignita, 867

Lebertiinae, 867

Lechriorchis, 407; elongatus, 407, primus, 407

Lecithophora, 340, 361

Lecquereusia, 222; epistomium, 223, modesta,
222, spiralis, 223

Leeches; see Hurudinea

Lemanea, 175; lorulosa, 175

Lembadion, 281: bullinum, 281

Lemna, 178; minor, 192

Lemnisci, 543

Lepidoderma, 625; concinnum, 626, rhom-
boides, 625, squamatum, 625

Lepidoptera (moths), 903, 917; see Insecta

Lepidurus, 671; bilobatus, 671, couesii, 671,
glacialis, 671, lemmoni, 671

Lepocinclis, 253

Lepodermatidae, 402

Lepomis megalotis, 103 1

Leptidae (larvae), 946

INDEX

1099

Leptoceridae, 936

Leptodora, 739; kindtii, 739

Leptodoridae, 739

Leptomonas, 246

Leptophlebia (imago), 919, (nymph), 921

Leptorhynchus dentifer, 736

Leptozosma, 135; catenulata, 135

Lepyrium, 994; showalteri, 994

Lcrnacidae, 7 84; see Copepoda

Lernaeopodidae, 784; see Copepoda

Lestes (imago), 923, (nymph), 891, 928

Leuceruthrus, 392, 407; micro ptcri, 392

Leucochloridium, 409, 423

Leucophrys, 278; patula, 278

Leucorhinia (imago), 927, (nymph), 932

Leydigia, 721; acanthocercoides, 721, quadran-
gular is, 721

Libellula (imago), 927, (nymph), 931, 932

Lieberkiihnia, 233; wageneri, 233

Life, distribution of, 35; see Existence, con-
ditions of

Life, Fresh-water; see Biology, Fresh-water

Light, intensity of, 32, penetration in water of,
29, 30, vs. migration, 31

Ligula, 431

Ligulinae, 431

Limnadia, 673; americana, 673, coriacea,

673
Limnadiidae, 673
Limnebius (adult), 939
Limnesia, 87c; histrionica, 870
Limnesiopsis, 869; anomala, 869
Limnetic region, 4
Limnetidae, 672
Limnetis, 672; brevifrons, 672, gouldii, 672,

gracilicornis, 672, mucronatiis, 762
Limnias, 615; ceratophylli, 615
Limnicy there, 806; illinoisensis , 807, reticu-
lata, 806
Limtiocalanus macrurus, 774
Limnochares, 859; aquaticus, 859
Limnocharidae, 859
Limnocnida, 322; indica, 322, rhodesia, 322,

tanganyicae, 322; see Hydrozoa
Limnodrilus, 641; claparedianiis, 641, gracilis

641
Limnology, i; lakes, 2, 4, 5, limnetic region,

4, Httoral region, 4, ponds, 2, pools, 3,

shore zone, 3
Limnomermis, 505
LimnophiUdae, 936, 937
Limnoplankton, 6; see Plankton
Lionotopsis, 275; anser, 275
Lionotus, 276; wrzesniowskii, 276
Lioplax, 988; subcarinala, 988
Liporhynchia, 340, 361
Liriola, 980
Lissoflagellata, 243

Lithasia, 992; armigera, 992, geniculata, 992
Littoral region, 4

Liltoridina, 990; monroensis, 990

L<jp)h()phure, 947

LophopHs cristiiilinus, 954

Loricalina, 591

Loxocephalus, 2H0; granulosus, 280

Ixjxodes, 274; rostrum, 274

Loxogcncs, 400; arcanum, 400

L()xoi)h>lium, 27s; rostralum, 275

Lucius vcrmiculatus, 103 1

Luml)rii illiis, i'y\2; ruiUus, 642

Lun\l)riiulidac, 642

Lumbriculus, ^42; inconstans, 642

Lutrochus (adult), 942

Lycastoides alticola, 632

Lychnothamnus, 174

Lymnaca, 980; auricularia, 981. columella.
gSi, haldcmani, 981, megasoma, 980, obrussa,
982, palustris, 981, stagnalis, 980, utahensis
981, s. s., 980

Lymnaeidae, 980

Lyngbya, 108; major, 108

Lyngbyeae, 107

Lyogyrinac, 991

Lyogyrus, 99 1 ; pupoidt us, c)gi

Lysianassidae, 842

Lythoglyphinae, 990

Macrobdella, 65(1; decora, 656, seslertia. 656

Macromia (imago), 925, (nymph), 930

Macronychus (adult), 942

Macrostominae, 338

Macrostomum, 33S; appendiculatum, 338,
hystrix, 338, scnsitivum, 339

Macrothricidac, 708

Macrothrix, 713; horysthrnica, 715, eUgans,
715, hirsuticontis, 714, laticornis, 714, mon-
tana, 714, rosea, 715, ttnuicornis, 715

Malacostraca (Higher Crustacea), 828-850;
cave species, 837, development. 832, habi-
tat, 83s, key, 841-850. mcthtxi of study,
840, occurrence, 828, references. 850, struc-
ture, 830; see Crustacea

Mallomonas, 260

Mammals, a(iuatir, 1022-1024: references,
io6'>; srr \\Ttcl)rata

Man the modifying agent in fresh-water life,
1 1

Manayunkia speciosa, 632

Mancasellus. 841

Margaritana, 995; margaritiiera, 995

Margarilanidae, 995

Marionina jorlnsac, 642

Marl and marl lakes, aquatic plants factors
in ft)rmation of. 207

Marshia. 7S0; aibuqurrqurnsis, 780, brevkau-
data, 780

Mastax. 55S. 560

Mastigamoeba. 243: lotigi/ilum, 3a\

Mastigophora (Flagellate Trotuzoa). Fresh-
water, 14, 238-270, 300: conjugation, 342,

IIOO

INDEX

flagella, 238, key, 243-270, methods of
study, 242, pseudopodia, 238, physiologi-
cal processes, 241, references, 300. repro-
duction, 241, structure, 238; see Protozoa
Mastogloia, 128; smithii, 128
Matter, cycle of, 207
Matus (adult), 942

Mayflies, aquatic; see Ephemerida; Insecta
Mazocraes, 375
Meadow, aquatic, 197
Medionidus, 1015; conradicus, 1015
Mediorhynchus, 549
Medusae of Hydrozoa, 318
Megadistomvun, 392

Megalotrocha, 617; alboflavicans, 611, 617
Megalurous cercariae, 416
Megarhinus (larva), 944
Melampinae, 978
Melampus, 978; hidentata, 979, bulloides, 979.

hemphilli, 979, Uneatus, 978; s. s., 978
Melicerta, 615; ringens, 57s, 615
Mehcertida, 574, 611
Melicertidae, 615
Melosira, 126; varians, 126
Melosiraceae, 126
Menoidium, 255; pellucidum, 255
Meridion, 132; constrictum, 132
Meridionaceae, 132
Merismopedia, 105; elegans, 105
Mermis, 505

Mermithidae, 503, 510, 534
Meromyaria, 515
Mesenchytraeus, 642
Mesocarpeae, 142
Mesocestoides, 440
Mesocestoididae, 440
Mesodinium, 272; pvlex, 272
Mesomermis, 503; virginiana, 503
Mesostoma, 352; ehrenbergii, 352, patter soni,

361, 362, vividatum, 350, viviparum, 350
Mesostomatini, 351

Mesotaenium, 138; endlicherianum, 138
Mesothemis (imago), 927, (nymph), 931
MetaboUsm, temperature vs., 33
Metanema, 257
Metastrongylinae, 522

Methods of Collecting, 61-85; bottom, 70, by
pyramid dredge, 71, by runner net, 70, by
triangle dredge, 71; fish, 61, by fyke net,
63, by gill net, 64, by net, 61-66, by seine,
61, by trammel, 62, by trap, 65, by turtle
net, 66; invertebrates, in littoral vegetation,
67, by Birge net, 68. by cone dredge, 68, by
dip net, 67, by grapple, 68, by plankton
pump, 70; in open water, quaUtative, 72,
by plankton cyUnders, 73, by townet, 72;
in open water, quantitative. 74. by clock
pvunp, 80, by closable plankton net, 77,
78, by plankton pump, 78, by quantita-
tive plankton net, 74, by thresher tank-

pump, 80, by water-bottle, 80; references,
88-89; special methods, 85
Methods of Photographing, 86-88; under-
water, 86, by screen, 86, through water
glass, 87; references, 88-89
Metopidia, 597; ehrenbergii, 597
Metopus, 284; sigmoides, 284
Metorchis, 393; complexus, 393
Metriocnemus (larva), 945
Meyeninae, 308

Micrasterias, 140; papillifera, 140
Micrathyria (imago). 927
Microcercous cercariae, 419
Microchlamys, 221; patella, 221
Microcodides, 609; robustus, 609
Microcodon, 609; claviis, 609
Microcoleus, 109; delicatulus, 109
Microcotylae, cercariae, 416
Microcotyle, 375
Microcotylidae, 375
Microcystis, 105

Microdina, 619; paradoxa, 577, 619
Microdinidae, 619
Microdonidae, 609
Microgromia, 233; socialis, 233
Microhydra, 318, 319, 322; ryderi, 322; see

Hydrozoa
Microlaimus, 491; fluviatilis, 491
Microorganism, anaerobic, 94
Microphalhnae, 401
Microphallus, 401; opaciis, 370, 401
Microspora, 164; amaena, 164
Microstomidae, 337
Microstominae, 337
Microstomum, 337; caudatum, 338, lineare,

337, philadelphicum, 361, variable, 361
Microthamnion, 170; kiitzingianum, 170
Microthorax, 283; sulcatus, 283
Micro-trichoptera, 901
Mideopsis, 865; orbicularis, 865
Midges; see Chironomidae; Insecta
Migrations, daily depth, 32, light vs., 31
Mimodistomum, 392
Miracidium, 371

Mischococcus, 148; confervicola, 148
Mochlonyx (larva), 944

Moina, 703; affi,nis, 70S, brachiata,^ 704,
flagellata, 705, macrocopa, 705, micrura,
704, paradoxa, 705, rectirostris, 705
Moinodaphnia, 703; alabamensis, 703, in<ic-

leayii, 703
Molannidae, 936

MoUusca, Fresh and Brackish-water, 18, 957-
1020; classification, 970, collection and
preparation of specimens, 960, distribution,
959, jaws and lingual membrane, 968, key,
977-1020, measurement and descriptive
terms, 969, radula, 973, references, 1020;
see Gastropoda; Lamellibranchia
Monadida, 243

INDEX

I lOI

Monas, 246; fluida, 246

Monhystera, soo; seniiens, 500

Monocilia, 164

Monogenea, 374

Monogononta, 587

Mononchus, 486; major, 486

Monopisthocotylea, 374

Monopylephorus, 641

Monopylidium, 446

Monosiga, 258; ovata, 258

Monospilus, 738; dispar, 738

Monostoma, 382; affi,ne, 382, amitiri, 382,

aspersum, 2,^2, f aba, 384, incommodum, 382,

molle, 397, mutabile, 382, ornatum, 382,

spatulatum, 382
Monostomata, 382
Monostome cercariae, 412
Monostomum, 382
Monostroma, 161; bullosum, 161
Monostyla, 595; lunaris, 595
Monozooic cestodes, 429
Moss animalcules; see Animalcules; Bry-

ozoa
Moths, aquatic; see Insecta; Lepidoptera
Mougeotia, 138, 143
Musculium, 1019; partumeium, 1019
Mycoideaceae, 171
Myosyringata, 522
Myriophyllum spicatum, 182
Mysidacea, 829; see Malacostraca
Mysidacea, 844
Mysis relicta, 844
Myxonema, 168; hibricum, 168
Myxophyceae; see Algae, Blue-Green

Naias flexilis, 191, major, 193

Naididae, 638

Naidium, 640; osborni, 640

Nais, 639; communis, 639, elingiiis, 639

Najadicola, 872; ingens, 872

Nannoplankton, 6, 7, 84; centrifuge, 84,

Sedgewick-Rafter sand filter, 83, study, 84,

(quantitative), 83; ^ec Plankton
Nannothemis (imago), 926, (nymph), 932
Nasiaeschna (imago), 925, (nymph), 930
Nassula, 276; ornata, 276
Natural waters, bacteria in, 96
Naucoridae, 933
Nauplius of Cyclops, 744
Navicula, 128; rhynchocephala, 128
Naviculaceae, 127
Nebela, 226; collaris, 226, dentisioma, 227,

flabellum, 226, lageniformis, 226
Necator americanus, 512, 521
Nehallennia (imago), 923, (nymph), 928
Nelumbo, 181
Nemathelminthes (roundworms), 15, So<'s

see Acanthocephala; Gordiacea; Nema-

toda
Nematocera (larva), 943

Nrinattxla (frce-livinR and parasitic round-
worms), 1- rrsh-Wulcr i*',, j^s; ice Nana-
ti)da, Itli- Livins: \emal(Kla. Parasitic

Nemaloda, 1-rec LivinK. 4 5t« So.s: amphid*.
466, bursa, 47r», tulicula, 46.}. development,
464, digestive system, 467, di.stribution, 46a,
esophagus, 468, excretory orjcan (ntulle),
470, formula, 481, habitatn, 459, kc>-, 482-
505, locomotion, 470. methods of »tudy,
478, numlKT, 4r)0, occurrence, 460, refer-
ences, 505, rctictte, 470, roundworms. 459,
sexual organs, 471, spicula, 475, structure,
461, 462, threadworms, 459; see NemA-
loda

Ncmatoda, Parasitic, 506-510; 510-SJS;
bursa, 514, development, 516, csophaini&.
513. key, 520-535, life histor>-. 517. 519,
movement, 511, oral apparatus, 513, refer-
ences, 551-552, reproductive system, 516.
structure, 511, tail, 514. threadworms 511;
^ff Acanthocephala; Gordiacea; Nematoda

Nematoideum integumenti lumbruuli limosi,
521

Nematomorpha, 510

Nematotaenia, 450; dispar, 450

Nematotaeniidae, 449

Nemertina (Xemerteans), Fresh- Water, 15,
454~458; development, 457, habitats. 454.
occurrence, 457, references, 458, struc-
ture, 455

Neoechinorhynchidae, 545

Neoechinorhynchus, 545; cylindrattu. 546.
emydis, 546, gradlisentis, 545, ttntUui, 546

Neomermis, 503

Neoplanorbis, 986; tantiUus, 986

Nepa, 934

Nephdopsis obscura, 659

Ncphrocytium, 152; agardhianum, 152

Nepidae, 934

Nereis limnicola, 63.'

Neritidae, 994

Xeritina. 994; redivata, 994

Nerthriidac, 933

Net plankton, 6

Netrium, 138: latnrlhsum, 138

Nets, 61; Birge. 68. care of. 66, closahlc
plaiUtton, 77. dip, 67. errors of plankton, 78,
fyke, 63, gill, 64, cjuantitative plankton. 74.
runner, 70. tow, 72, trammel, 63, turtle. 66

Neumania. 871; spinipes, S71

Neurocordulia (imago), 926

Xeuroj^tera (dobson. fish and sponirilU flies),
Fresh-Water, 8tj7-89y: keys, (adults). 934*
935, (lar\ae), 917. 935-9J6; see Ilcracn>-
biidae; Insocta; Sialididac

Xiphargus, 843

Nitella. 173

Xitelleae, l^^

Nitzschia, 130: linearis, 13c, sturionis, 374

NiLzschiaceae, ijo

II02

INDEX

Nodularia, iii

Nostoc, no; commune, no

Nostoceae, no

Nostochopsis, 113; lobata, 113

Notaspis, 874

Noteus, 605; quadricornis, 605

Notholca, 603; longispina, 603

Notocotylidae, 382

Notocotylus, 383; quinqueserialis, 383

Notodromas, 808; monacha, 798, 808

Notommata, 591; aurita, 591, torulosia, 591,

truncata, 556, 591
Notommatida, 587
Notommatidae, 587
Notommatina, 587
Notonecta, 934
Notonectidae, 934
Notops, 601; brachionus, 601, davulatns, 601,

pelagicus, 601
Notopsidae, 569, 599
Notosolenus, 257; orbicularis, 257
Notostraca, 671
Nuclearia, 233; simplex, 233
Nudocotyle novicia, 383
Nuphar, 193
Nupharetum, 196
Nylandera, 171; tentaculata, 171
Nymphula, 903

Obliquaria, 1014; reflexa, 1014

Obovaria, 1012; ellipsis, 1013, retusa, 1013;
s. s., 1013

Oceanology, i ; pelagic region, 4

Ochromonas, 260

Octhebius (adult), 938

Octobothrium sagiltatiim, 375

Octocotylidae, 375

Octotrocha, 615; speciosa, 615

Odonata (damselflies, dragonflies), Fresh-
Water, 889-893, 917, 922-932; damselfly
nymphs, 89 1 , keys, 917; dragonflies (images) ,
922-927, (nymphs), 928-932; see Insecta

Odontalona, 720

Odontidium, 132; mutabile, 132, tabellaria, 132

Odontoceridae, 936

Odors, cause of, 1073, observation of, 1072

Oecistes, 615; brevis, 615

Oedogoniaceae, 167

Oedogonium, 167; crenulato-costatum, 167

Oikomonas, 244; steinii, 244

Oligobdella biannulala, 654

OHgochaeta (earthworms), Fresh-Water, 633-
64s; biology, 63s, excretory organs, 633,
key, 638-644, locomotion, 636, methods of
study, 636, occurrence, 632, references,
645, reproduction, 634, structure, 633; see
Chaetopoda

Oligorchis, 441

Olisthanella, 349; caeca, S49

OHsthanellini, 349

Oncholaimellus, 487; heterurus, 487

Oncholaimus, 487, punclatus, 487

Onchosphere, 427

Onychodromopsis flexilis, 289

Onychodromus, 289; grandis, 289

Onychonema, 136; laeve, 136

Onychopoda, 738

Oocardium, 141; stratum, 141

Oocystis, 151; solilaria, 151

Oogonium, 119

Oospore, 119

Open-water collecting; see Methods of Collect-
ing

Opercularia, 295; plicatilis, 295

Ophidonais, 639; serpentina, 639

Ophiocytium, 157; cochleare, 157

Ophiogomphus (imago), 924, (nymph), 929

Ophiotaenia, 438; filaroides, 425, 438, grandis,
439, lonnbergii, 438, perspicua, 439

Ophridinopsis, 296

Ophrydium, 296; eichhornii, 296

Ophryocotyle, 441; Proteus, 441

Ophryoglena, 278; atra, 278

Ophryoxus, 708; gracilis, 708

Opisthodon, 276

Opisthorchiidae, 393

Opisthorchis, 393; pseudofelineus, 393

Opisthotricha, 289

Opistomum, 340

Organisms, water; effect of pressure, 34, en-
vironment, 9, fluctuations, 54

Orchestiidae, 843

Oribatidae, 874

Ornatae, cercariae, 419

Orthocladius (larva), 945

Orthorrhapha (larva), 943

Orthosira, 126; orichalcea, 126

Oscillatoria, 108; limosa, 108, prolifica, 108

Oscillatoriceae, 107

Osphranticum labronectum, 774

Ostracoda, 790-827; development, 797, dis-
tribution, 801, genital organs, 795, key,
806-827, methods of study, 803, occur-
rence, 799, references, 827, structure, 791;
see Crustacea

Ovatella, 979

Oxus, 868; ovalis, 868, strigatus, 868

Oxytricha, 289; pellionella, 289

Oxyurella, 720, 722; longicaudis, 721, tenui-

caudis, 720
Oxyuridae, 533
Oxyuris dubia, 533

Pachydiplax (imago), 927, (nymph), 932;

longipennis, 890
Palaemon, 845; ohionis, 845
Palaemonetes, 845; exilipes, 845, paludosa,

84s, vulgaris, 845
Palaemonias ganteri, 845
Palaemonidae, 845

INDEX

1 103

Palmella, 150

Palmella condition, 115

Palmellaceae, 147

Palmellococcus, 153

Palmodactylon, 148

Palmodictyon, 149; viridis, 149

Paludestrina, 989; nickliniana, 989

Paludicella ehrenbergii, 952

Paludicola, 354

Pamphagus, 228; hyaliniis, 228, mutabilis, 228

Pandorina, 145, 267; niorum, 145, 267

Panisus, 862, cataphraclus, 862

Pantala (imago), 927, (nymph), 932

Paracandona, 823; euplectella, 823

Paracypris, 817; grandis (Cypris), 819, perele-
gans (Cypris), 819

Paragonimus, 390; kellicotii, 390, westcr-
manli, 390

Paragordius, 539; varius, 539, embryo of, 536

Paralonella, 734

Paramermis, 505

Paramoecium, 281; caudatum, 281

Paramphistoma cervis, 413

Paramphistomidae, 385

Paramphistominae, 385

Paranais, 639; liloralis, 639

Paraponyx, 903

Paraptera, 1017; gracilis, 1017

Parasitic Copepoda, 782-788; see Argulidae;
Copepoda; Ergasilidae; Siphonostomata

Parasitic Flatworms, 365-453; adaptability,
366, external, 367, methods of study, 368,
number, 365, period of free existence, 366;
see Cestoda; Parasitic Worms; Trematoda

Parasitic Roundworms, 506-552; differen-
tiator, 508, references, 551, technic, 507;
5ee Acanthocephala; Gordiacea; Nematoda,
Parasitic; Parasitic Worms

Parasitic Worms, 365-369, 452; adaptations,
365, external, 367, methods of study, 368,
period of free existence, 366, references,
452; see Acanthocephala; Cestoda; Gordi-
acea; Nematoda, Parasitic; Parasitic Flat-
worms; Parasitic Roundworms; Trema-
toda

Parmulina, 221; cyalhus, 221

Parnidae (adults). 942, (larvae), 943

Parophryoxus, 708; tubulatus, 708

Pectinatella, 954; magnifica, 948, 954

Pectinibranchiata, 986

Pedalion, 613; niirum, 613

Pedalionidae, 613

Pedetes, 613; sallator, 613

Pediastrum, 160; boryanum, 160

Pedipes, 978; unisidcatus, 97S

Pedinocoris, 933

Pegias, 1003; fabula, 1003;

Pegosomum, 391

Pelagic region, 4

Peleciius helicinus, 524

Pelogonidae, 933

Pelomyxa, 219; caroliiunsis, 219, paiustris,

219
Pelonomus (adult), 942
IV'lurempis (larva), 944
Peltodytes (adult), 938, (larva), 943
I'cnium, 138; cucurbitinum, 138
I'entagcnia (imago), 918, (nymph), 921
I'cranema, 255; irichophonim, 255
Peranemidac, 255
i'eridinium, 270; tabtilatum, 270
I'erispira, 273; strephosoma, 273
I'erithcmis (imago), 926, (nymjih), 931
Peritricha, 291
Perla, 883

Petalomonas, 256; plcurosigma, 25t'i
Phacus, 253; longicaudus, 253, plmronectes,

253
Phaenocora, 348; agassizi, 348
Phaeophyceae, 174-175; key, 174-175; see

Algae, Fresh-Water, excl. of Blue-Green
Phagocata, 359; gracilis, 359
Phalansterium, 25S; digitatum, 258
Phanerogams, aquatic, 198
Phascolodon, 277
Phialonema cyclostomum, 256
Philhydrus (adult), 940

Philobdella, 657; fioridana, 657, gracile, 657
Philodina, 619; brycci, sn, 619, roseola, 619
Philodinidae, 619
Philopotamidae, 936
Phormidium, 108; subfuscum, 108
Photographing, Methods of, 86-88; see

Methods of Photographing
Photography, under-water, 86; see Methods

of Photographing
Photokinesis, 328
Phragmitetum, 196

Phreoryctes {Ilaploiaxis emissarius), 642
Phryganea, 902
I'hryganeidae, 936, 937
I'hryganella, 227; hcmisphacrica, 228, nidtdus,

22^

Phycochromophyceae; see .\lgae, Blue-Gn-en

Phycoerythrin, 117

Phycophacin, 117

Phylactolaemata, 952

Phyllodistomum, 399; dmcriidnum, 399, fo-
lium, 414, 421

Phyllomitus, 248; amylophagtis, 248

Phyllopoda (fairy shrimps), 661-675; col-
lecting, 666, development, 664. key, 666-
675, occurrence. 661. 665. references. 675,
structure, 662; see Crustacea

Phyllosiphon, 172: afisari, 172

Physa, 985; i?,vri;ia. 985

Physaloptera, 526; constricta, 526, conUirta,
526

Physidae. 984

Physiography, 22

1 104

INDEX

I

Physocypria, 819; inequivalva (Cypria), 822,
puslulosa (Cypria), 821

Physomonas, 247; elongata, 247

Phytia, 978

Phytoflagellata, 259

Phytomastigida, 249

Phytomastigophora, 259

Pierosoma, 983

Pilea, 1009

Pimephales notatus, 1048

Pinnularia, 127; viridis, 127

Piona, 873; constricla, 873, rn}a^ 873

Pionacercus leuckarti, 853

Pioninae, 870

Pipette, piston, 82

Piscicola punctata, 655

Pisidium, 1019; virginicum, 1019

Piston pipette, 82

Pithophora, 166; kewensis, 166

Placobdella, 652; hollensis, 654, montifera,
652, parasitica, 653, pedicidata, 653, pha-
lera, 654, picta, 653, rugosa, 654; s. str., 653

Placocephalus kewense, 360

Placocista, 231; spinosa, 231

Plagiola, 1013; elegans, 1014, securis, 1014;
s. s., 1014

Plagioporus, 394; serotinus, 394

Plagiopyxis, 225; callida, 226, labiata, 226

Plagiorchiidae, 402

Plagiorchiinae, 403

Plagiorchis, 404, proximiis, 404

Plagiostoma (?) planum, 361, 364

Planaria, 355; agilis, 357, doroiocephala, 357,
foremanii, 355, fuliginosus, 359, gonoceph-
ala, 356, liguhris, 355, maculata, 356, wor-
gani, 358, simplex, 358, simplissima, 355,
truncata, 358, unionicola, 358, w/a/a, 358

Planarians; 5ee Turbellaria

Planariidae, 354

Planktology, 6

Plankton, 4, 6, character of organism, 7,
dwarf, 6, fish life and, 1082, Umnoplank-
ton, 6, nannoplankton, 6, 7, quantitative
study, 81, by piston pipette, 82, quantity,
47, 48, Sedgewick-Rafter cell, 82, size, 7,
specimens shown in bolting cloth, 7; see
Nannoplankton

Plankton pump, 70, 78; cylinders, 73,
quantitative plankton net, 74, quanti-
tative closable plankton net, 77

Planktonema, 163, 164; laulerbornii, 164

Planorbella, 983

Planorbidae, 982

Planorbinae, 982

Planorbis, 982; antrosus, 982, campanulalus,

983, crista, 984, cultratus, 983, glahratus,
982, hirsutus, 983, opercularis, 983, parvus,

984, trivolvis, 983; s. s., 982
Planorbula, 984

Plant societies, succession of, 197

Plants, amphibious, 183; succession of so-
cieties, 197

Plants, aquatic, 179, 180; distribution, 194,
factors in formation of marl and marl lakes,
207, floating, 178, groups, 197, growing in
soil, 202, 203, hibernacula (winter buds),
192, incrustation, mineral, 185, carbonate
of lime, 186, gelatinous, 187, leaves, 180,
submerged, 182, phanerogams, 198, refer-
ences, 209, reproduction, by runners, 189,
by pollination under water, 189, stomata on
submerged leaves, 184, submerged leaves,
182, succession of societies, 197, zones, 196;
see Vegetation, Larger (Higher)

Plants, water; see Plants, aquatic

Plathemis (imago), 927, (nymph), 932

Platoum, 228; parvum, 228

Platycola, 297; decumhens, 297

Platycopa, 806

Platydorina, 145, 268; caiidata, 145, 268

Platyhelminthes (Flatworms); see Cestoda;
Flatworms; Nemertina; Trematoda; Tur-
bellaria

Platytrichotus, 288; opislhoboliis, 288

Plea, 934

Plecoptera (stoneflies), 882-885, 917." nymphs,
883 ; see Insecta

Plectanocotyle, 375

Plectonema, in; wollei, in

Plectus, 492; tubifer, 492

Pleodorina, 146, 268; calif or nica, 268, illi-
noisensis, 146, 268

Pleorchis, 397; mollis, 397

Plerocercoid, 427, 451

Plethobasus, 1000

Pleurobema, 999; aesophus, 1000, claxa, 999

Pleurocera, 993; canaliculatum, 993, plena,

993

Pleuroceratidae, 991

Pleurococcaceae, 152

Pleurococcus, 152; vulgaris, 152

Pleurogenetinae, 400

Pleuromonas, 249; jaculans, 249

Pleuronema, 281; chrysalis, 281

Pleurosigma, 127; allenualum, 127

Pleurotaeniopsis, 13S; tiirgidus, 138

Pleurotaenium, 138, 139; nodulosum, 139

Pleurotricha, 289; lanceolata, 289

Pleurotrocha, 589; grandis, 589

Pleuroxalonella, 734

Pleuroxus, 726; acutirostris, 736, aduncus,
729, denticulaius, 728, gracilis, 727, hamu-
latus, 728, hastalus, 727, procurvatus, 726,
striatus, 725, 727, trigoncllus, 729, truncatus,
727, uncinatus, 726, iinidens, 727

Ploesoma, 603; hudsoni, 603, lenticulare, 603,
truncal urn-, 603

Ploesomidae, 570, ^03

Plumatella, 952; art'husa, 953, polymorpha.
953, princeps, 953, punctata, 954

INDEX

no:

Pncumatophilus, 406; lariabilis, 40G
Pneumobites, 403; breviplexus, 403, longi-

plexus, 403
Pneumonoeces, 403; coloradensis, 403
Podocopa, 806
Podophrya, 298; fixa, 298
Pollination under water, 189
Pollution, prevention of, 1075
Polyadenous cercariae, 416
Polyartemiella, 666; hanscni, 66(->,judayi, 667
Polyartemiidae, 666
Polyarthra, 591; platypicra, 591
Polycelis, 359; coronata, 359
Polycentropidae, 937
Polychaeta, 632
Polychaetus, 599; collinsii, 599
Polycotyle, 410; ornala, 410
Polycystididae, 353

Polycystis, 353; gaelti, 353, rooscvcili, 353
Polymitarcys (imago), 918, (nymph), 921;

alba, 888
Polymorphus, 548; minutus, 548
Polyopisthocotylea, 375
Polyphemidae, 738
Polyphemus, 738; pediculus, 738
Polyrhytis, 981

Polystoma, 376; inlcgerrimum, 376
Polystomidae, 375

Polystomoides, 376; coronatum, 376, hassalli,
376, megacotyle, 377, microcolyle, 377,
opaciim, 378, oblongum, 377, orbicidare, 377
Polytoma, 265; uvella, 265
Polyzoa; see Bryozoa
Pomatiopsinae, 991
Pomatiopsis, 991; lapidaria, 991
Pompholiginae, 984
Pompholyx, 611, 984; complanta, 611, ejfusa,

984
Pompholyxophrys, 235; punicea, 235
Pomphorhynchus, 551
Ponds, 2; age series, 49
Pontigulasia, 225; spcctabilis, 225
Pontoporeia, 842; hoyi, 842
Pools, 3

Porifera (sponges), Fresh-Water, 15, 301-315;
collecting, 304, development, 303, habits,
302, key, 306-315, methods of study, 305,
references, 315, structure, 301
Porphyridium, 106

Potamanthus (imago), 919, (nymph), 921
Potamobiidae, 846
Potamobius, 846; aslacus, 846, gambcli, 846,

troivbridgci, 846
Potamocypris, 808; smaragdina, 808
Potamogeton, 181; crispus, 189, 192, dcnsus,
185, heterophyllus, 183, 195, lucens, 193,
nutans, 182, pcctinatus, 182, 185, 191.
perfoliatus, 181, 191, 192, robbinsii, 191
Potamogetonetum, 196
Potamopyrgus, 990; coronalus, 990

Pottsiella creda, 951

Prasiola, 161; crispa, 161

Prawns, 828; see Malacostraca

Pressodon, 1006

Pressure in water, 34; cflecl ujxin organisms,
34

Primary host; sec Host, primar>'

I'rismatulaimus, 499; stenurus, 499

I'rislina, 640; Jlagellum, 640, iongiseta, var.
leidyi, 640

Proales, 589; sordida, 589, tigrida, 589,
werncckii, ^55, 589

Problems, Technical and Sanitary, 1067-
1083; algae, methods of killing, 1076, pre-
vention of growths of, 1074. purification of
water containing, 1077; bacteria, in water,
1070, bacillus coli as index of contami-
nation, 1069; disease, transmission of, 1067,
water as conveyor of germs, 1068; drainage
of swamps, 1075; odors, cause of, 1073,
observation of, 1072; organisms in pipes
of water systems, 1081; plankton and fish
life, 1082; prevention of pollution, 107s:
soil stripping of reservoir sites, 1074;
streams and self-purification, 107.S; water,
identification of source of, 1080, tastes and
odors in, 107 1

Probopyrus, 842; pandalicola, 842

Proboscis, 542; sheath, 543

Proglottids, 424

Progomphus (imago), 924, (nymph), 929

Proptera, 1016; alata, 1016

Prorhynchidae, 339

Prorhynchus, 339; applanatits, 340, stagnalis,

339
Prorodon, 274; ovum, 274
Prosthogoniminae, 402
Prosthogonimus, 402
Prostoma marginatum, 363
Prostomatous cercariae, 412
Prosostomata, 379

Protenes, 394; leptus, 394, angustus, 394
Protenteron, 401; diaphanum, 401
Proteocephalidae, 434
Proteocephalus, 434; ambloplitis, 436. exiguus,

437, macrocephaJus, 435, pcrplexus, 435,

pinguis, 437. Pusillus, 437. singularis, 435
Proteomyxa, 233

Proterosjwngia, 25S; hatckeli, 258
Protoclepsis occidcntalis, 654
Protococcaceae, 156
Protococcales, 1 43
Protosiphon, 156; botryoides, 156
Protozoa, 14, 210-300; see Infusoria; Masti-

gophora; Sarcodina
Psamathiomyia (lar\a), 945
Psephenus (adult), 942
Pseudalona, 718

PseudcKlirtlugia, 229; gradlis, 229
Pseudoccistcs, 617; rotifer, 617

iio6

INDEX

Pseudomermis, 505

Pseudoon, 1013

Pseudophyllidea, 430; larvae of, 450

Pseudo-pleurococcus, 153; vulgaris, 153

Pseudopodia, 238

Pseudosida, 692; bidentata, 692

Pseudosuccinea, 981

Pseudulvella americana, 171

Psilonemateae, 107

Psorophora (larva), 944

Psychodidae (larvae), 945

Psychomyiidae, 937

Pterodina, 611; casca, 611, patina, 611

Pterodinidae, 611

Pterodrilus, 644; alcicornus, 644, distichus,

644
Pteronarcys dorsata, 884
Pterosygna, 1005
Ptychobothriidae, 430
Ptychobranchus, 1012; phaseolus, 1012
Ptychopteridae (larvae), 944
Pulmonata, 977
Pump; plankton, 70, 78, clock, 80, Fordyce,

79, thresher-tank, 80
Purification of water containing algae, 1077
PyraUdae, 903
Pyramid dredge, 71
Pyrenoid, 116

Pyrgulopsis, 990; nevadensis, 990
Pyxicola, 297; carleri, 297
Pyxidicula, 222; cymbalum, 222
Pyxidium, 293; ramosum, 293

Quadrula, 995; cylindrica, 996, lachrymosa,

997, plicata, 996, pusttdosa, 997, undata, 997;

s. s., 996
Quadrulella, 226; symmetrica, 226
Qualitative methods of collecting, 72; see

Methods of Collecting
Quantitative plankton net, 74
Quantitative study; of nannoplankton, 83;

see Nannoplankton; of net plankton, 81;

see Plankton

Radiofilum, 163; flavescens, 163

Radiosphaera, 156

Radix, 981

Radula, 973

Ramosonema, 247; laxum, 247

Ranatra, 934

Rangia, 1020; cuneata, 1020

Rangiidae, 1020

Ranunculus aquatilis, 182, 183, 191. i93,

201
Raphidiophrys, 235; elegans, 235, viridis, 235
Rattenkonigcercarien, 414
RattuUdae, 568, 595
Rattulus, 595 ; cylindricus, 595. lalus, 595,

longiseta, 595
Redia, 371

References on Fresh-Water Biology, 18-20;
Acanthocephala, 551-552, Algae, Blue-
Green (Cyanophyceae), 114, Algae, excl. of
Blue-Green, 177, Amphibia (Batrachia),
1066, Animalcules, 620, 955-956, Appa-
ratus and Methods, 88-89, Bacteria, 99,
Batrachia (Amphibia), 1066, Birds, 1066,
Bryozoa, 955-956, Cestoda, 452-453,
Cladocera, 739-740, Copepoda, 788-789,
Crustacea, Higher (Malacostraca), 850,
Cyanophyceae (Algae, Blue-Green), 114,
Existence, Conditions of, 60, Fishes, 1066,
Gastrotricha, 631, Gordiacea, 551-552,
Hirudinea, 660, Hydra, 322, Hydracarina,
875, Hydrozoa, 322, Infusoria, 300, Insecta,
946, Malacostraca, 850, Mammals, 1066,
Mastigophora, 300, MoUusca, 1020, Nema-
toda, Free-Living, 505, Nematoda, Para-
sitic, 551-552, Nemertina (Nemerteans),
458, OUgochaeta, 645, Ostracoda, 827,
Parasitic Worms, 452, 551, Plants, Higher
(Larger), 209, Phyllopoda, 675, Porifera,
315, Protozoa, 236-237, 300, Reptiles, 1066,
Rotatoria, 620, Sarcodina, 236-237, Trema-
toda, 452-453, Turbellaria, 364, Vegetation,
Larger (Higher), 209, Vertebrata, 1066;
see Investigators in Fresh-Water Biology;
Journals on Fresh-Water Biology

Renette, 470

Renifer, 405; ellipticus, 405, elongatus, 407,
mcgasorchis, 407, variabilis, 406

Reniferinae, 405

Reproduction, physiology of, 120; see also
the specific subjects

Reptiles, Fresh-Water, 1026-1028; references
1066; see Vertebrata

Reservoir sites, soil stripping of, 1074, Pre-
vention of algae growths in, 1074

Rhabditis, 493; cylindrica, 493

Rhabdocoela, 333

Rhabdocoelida, 333, 361

Rhabdocoelous cercariae, 412

Rhabdolaimus, 494; minor, 494

Rhabdonema nigrovenosum, 521

Rhabdostyla, 293; vernalis, 293

Rhadinorhynchus, 550

Rhantus (adult), 942

Rheology, i; evolution of stream, 5

Rhinops, 599; vitrea, 565, 599

Rhipidendron, 262; splendidum, 262

Rhipidoglossa, 994

Rhizoclonium, 166; hieroglyphicum, 166

Rhizodrilus, 641; lacteus, 641

Rhizomastigidae, 243

Rhizopoda, 219

Rhizosolenia, 127; eriensis, 127

Rhizosoleniaceae, 127

Rhodophyceae, 175-177; key, i75-i77; see
Algae, Fresh- Water, excl. of Blue-Green

Rhoicosphenia, 129; curvata, 129

INDEX

1 107

Rhopalocerca tardigrada, 421

Rhopalocercous cercariae, 421

Rhyacophilidae, 936

Rhyncheta, 299

Rhynchobdellae, 651

Rhynchodemidae, 360

Rhynchodemus alrocyaneus, 360, sylvaticus, 360

Rhynchomesostoma, 349; rostralum, 349

Rhynchomonas, 246; nasida, 246

Rhynchoprobolus papiilosus, 361, 363

Rhynchoscolex, 337; simplex, 337, vcjdovski,
S37

Rhynchotalona, 724; falcaia, 724

Rhyphidae (larvae), 945

Rhythms of fresh-water organisms, 43; daily
depth migrations vs., 43

Rhyzota, 574

Richteriella, 154; botryoides, 154, globosa, 154

Rivularia, 114; minutula, 114

Rivulariaceae, 113

Rostellum, 424

Rotatoria (wheel animalcules), Fresh-Water,
16, 553-620; body, 554, corona, 554, 557,
the chief organ of locomotion, 562, cosmo-
poUtan characteristics, 578, development,
582, eggs, 580, excretory organs, 560, foot,
554, jaws (trophi), 558, 559. key, 587-619,
mastax, 558, 560, methods of study, 583,
minute males, 580, nervous system, 563,
Notommatidae as example, 555, occurrence,
554, references, 620, relationships, 586,
reproduction, 564, species (perennial), 581,
(summer), 581, (winter), 581, structure, 554,
579, trophi, 558, 559, variations of type
among Anapodidae, 570, Anuraedae, 571,
Asplanchnidae, 571, Bdelloida, 576, Branch-
ionidae, 570, Coluridae, 568, Dinocharidae,
569, Euchlanidae, 568, Floscularida, 572,
Flosculariidae, 572, Gastropodidae, 570,
Hydatinidae, 569, Melicertida, 574, Notom-
matidae, 566, Notopsidae, 569, Ploe-
somidae, 570, Rattulidae, 568, Rhizota,
574, Salpinidae, 567, Seisonacea, 577, 578,
Synchaetidae, 566

Rotifer, 619; citriniis, 619, nepiunius, 619

Rotifera; see Rotatoria

Rotundaria, 999; lubercidata, 999

Roundworms (Nemathelminthes), Fresh-
Water, 15; free-living; see Nematoda,
Free-Living; parasitic; ^ee Acanthoccph-
ala; Gordiacea; Nematoda, Parasitic;
Parasitic Roundworms; Parasitic Worms

Rugifera, 1006

Sagiltaria chinensis, 183, natans, 183
Salpina, 593; spinigera, 593
Salpingoeca, 258; convallaria, 258
Salpinidae, 567, 593

Sanitary Problems, Technical and. 1067-
1083; see Problems, Technical and Sanitary

Sajjrophilus, 279; agitans, 279

Sarcodina (amoeboid protozoa), 14, 210-237;
conjugation, 217, food, 212, 215, habitats,
211, key, 219-236, mclal)<)lism, 216, meth-
ods of study, 218, references, 236-237,
reproduction, 216, shells, 214, structure,
211; see Protozoa

Sayella, 979

Scalenaria, 1008

Scai)lit)leberis, Gyy; aurita, 699, mturonata, 699

Scaridium, 597; longuandutn, 597

Scencdesmus, 159; quddricauda, 159

Sciadium, 158; arbuscuia, 158

Siirpetum, 196

Schistocephalus, 432

Schislosomatidae, 409

Schistotaenia, 448; macrorhyncha, 448

Schizamphistominae, 387

Schizocanthum, 141; armalum, 141

Schizocerca, 605; dkersuornis, 605

Schizochlamys, 150; gelatinosa, 150

Schizomeris, 162; Icibleinii, 163

Schizonema, 128

Schizomycctes; sec Bacteria

Schizothrix, 109; rubella, 109

Schizophyceae; see Algae. Blue-Green

Schmardaella, 638; Jilijormis, 638

Scolex, 424

Scotinosphaera, 157; paradoxa, 157

Scuds, 828; sec Malacostraca

Scutopterus (adult), 941

Scyphidia, 292; j'romentellii, 292

Scytonema. 112; mirabile, 112

Scytonemaceac, 1 1 1

Seasonal succession of fresh-water life (biol-
ogy), 10

Seasonal temperature changes. 33

Secondary host; see Host, secondary

Sedgewick-Rafter cell, 82, sand filler, &i

Segmentina, 984; armigera, 984

Seines, 61

Seison anmdatus. 578

Seisonacea. 577, 578

Selenastrum. 159; gracile, 159

Sepedon. 913

Sericostomatidae, 936, 937

Serphus. 933

Setiferous cercariae. 423

Shore zone, 3

Shrimps, 828; sec Malacostraca

Shrimps. fair>-; see Crustacea; Phyllopoda

Sialididae (siMmgilla flics). S97-S9S; adults.
935; sec Insecta; Neuroptera

Sialis (adult). 935. (larva). 935; injunuita, 898

Sida, 689; cryslallina, 689

Sididae, 689

Simocephalus. 698; exspinoitu, 698. serru-
lalus, 699. irluJus, 698

Simuliidae (black-flics). 9x3; lar\'ac, 946; sef
Diptera; Insecta

iio8

INDEX

Siphlurus (imago), 920, (nymph), 922

Siphonales, 172

Siphonaria, 979; alternata, 979, peltoides, 980;

_ s. s., 979
Siphonariidae, 979
Siphonostomata (Parasitic Copepoda), 782-

788; structure, 783; see Argulidae; Cope-
poda; Ergasilidae
Sisyra (adult), 934, (larva), 899, 935
Slavina, 639; appendiculata, 639
Solenophrya, 299; per a, 299
Somatochlora (imago), 926, (nymph), 931
Somatogyrus, 991; subglobosus, 991
Sorastrum, 159; spinulosum, 159
Sow-bugs, 828; see Malacostraca
Sparganophilus, 643; benhami, 643, eiseni,

643, smithi, 643
Sparganum, 434; mansoni, 433, 434, pro-

liferum, 434, sebago, 434
Spathidium, 273; spathula, 273
Sperchon, 870; glandulosus, 870
Sperchoninae, 869

Sphaerella, 144; nivalis, 144, pluvialis, 144
Sphaeriidae, 1018
Sphaerium, 1018; simile, 1018
Sphaerocystis, 151; schraeteri, 151
Sphaerophrya, 299; magna, 299
Sphaeroplea, 165; annulina, 165
Sphaeropleaceae, 165
Sphaerostoma, 408
Sphaerozosma, 136; pulchriim var. inflatum,

136, verlebralum, 136
Sphenoderia, 229; dentata, 229, lenia, 230,

macrolepis, 230
Sphenomonas, 254; quadrangular is, 254
Sphyranura, 378; osleri, 378
Spicula, 475

Spilophora, 489; canadensis, 489
Spinitectus, 527; gracilis, 527
Spirocypris, 813; passaica, 813, tuberculala,

814
Spirogyra, 142; crassa, 142
Spiromonas, 249; angusta, 249
Spironoura, 533; affine, 533, gracile, 533
Spirostomum, 284; ambiguum, 184
Spirotaenia, 137; minuta, 137
Spirulina, 107; major, 107
Spiruridae, 525
Spirurinae, 525
Spiruroidea, 525
Spondylomorum, 144, 267; quarternarium,

144, 267
Spondylosium, 136; papillatum, 136
Sponges; see Porifera
Spongilla, 306, 311; aspinosa, 306, baileyi, 311,

Jragilis, 307, igloviformis, 307, lacustris,

306, novae-terrae, 307, paupercula, 306,

wagneri, 308
Spongilla-flies, 897; ^ec Hemerobiidae; In-

secta; Neuroptera

Spongomonas, 262; discus, 262

Sporadoporus, 862; invalvaris, 862

Spores of bacteria, 92; ^ee Bacteria

Sporocyst, 371

Sporozoa, 14

Stagnicola, 981

Stations, fresh- water biology, 12

Statoblast, 949

Staurastrum, 139; crenulatum, 139

Staurogenia, 160

Stauroneis, 128; anceps, 128

Stauroptera, 127

Stenelmis (adult), 942

Stenostomum, 334; agile, 336, coluber, 337,
grande, 336, leucops, 335, speciosum, 335,
ienuicauda, 336

Stentor, 285; coeruleus, 285, polymorphus, 285

Stephanoceros, 611; eichhornii, 611

Stephanodiscus, 127; niagareoe, 127

Stephanoprora, 391; gilberti, 391

Stephanops, 597; intermedins, 597

Stephanosphaera, 145, 266; pluvialis, 145,
266

Stichococcus, 152; bacillaris, 152

Stichorchis, 386, subtriquetrus, 386

Stichostemma asensoriatum, 457, rubrum, 455,
458

Stichotricha, 287; secunda, 287

Stigonema, 112; minutum, 112, ocellatum, 112

Stigonemaceae, 112

Stomata on submerged leaves, 184

Stoneflies; ^ee Insecta; Plecoptera

Stratification of aquatic organisms, 10

Stratiomyiidae (larvae), 946

Streams; bottom materials, 24, bottoms,
differentiation in, 25, current strength, 23,
evolution, 5, hydrogen sulphide, 39, rate
of flow, 27, self-purification, 1078, tem-
perature of water, 32

Streblocerus, 709; pygmaeus, 709, serricau-
datus, 709

Strephobasis, 993

Streptocephalidae, 670

Streptocephalus, 670; floridanus, 670, sealii,
670, texanus, 670

Strigea, 410; cornu, 410

Strobila, 424

Strombidium, 286; claparedii, 286

Strongyleae, 522

Strongylidae, 522

Strongylinae, 522

Strongyloidea, 522

Strongyloides stercoralis, 521

Strongylostoma, 350; gonocephalum, 350,
radiatum, 350

Strongylus, 522; auricularis, 523

Strophitus, looi; edentulus, looi

Stygonectes, 843

Stylaria, 639; fossularis, 639, lacustris, 635,
639

INDEX

IIOQ

Stylet cercariae, 416

Stylobryon, 245; petiolatum, 245

Stylohedra, 297

Stylonychia, 290; nolophora, 290

Styphlodora, 405; bascaniensis, 405

Submerged leaves, 182; stomata on, 184

Suctoria, 298

Surirella, 131

Surirellaceae, 130

Sutroa, 642; alpestris, 642, roslrala, 642

Sympetrum (imago), 927, (nymph), 932

Swamp, 3, 5, 59; drainage of, 1075

Symphynota, 1004; complanata, 1005, com-

pressa, 1004, coslata, 1005; s. s., 1004
Symploca, 109; liicifuga, 109
Synchaeta, 591; bdtica, 591, stylata, 591,

tremula, 591
Synchaetidae, 591; see Rotatoria
Synechococcus, 105; aeruginosus, 105
Synedra, 132; salina, 132
Synplecta pendula, 528
Synura, 262; uvella, 262

Tabanidae (larvae), 946

Tabanus (larva), 946

Tabellaria, 133; fenestrata, 133

Tabellariaceae, 133

Tachopteryx (nymph), 929, 930

Tachysoma, 290; parvistyla, 290

Taenia, 440, 447; crassicollis, 44'j,filum, 442,
pulchella, 450, scolopendra, 449

Taeniidae, 447

Taenioglossa, 986

Tanaognathus, 864; spinipes, 864

Tanaorhamphus, 547; lotigirostris, 547

Tank-pump, 80

Tanypus carneus, 914, (larva), 945

Tany tarsus (larva), 945

Tapeworms, 15; see Cestoda; Parasitic Flat-
worms; Parasitic Worms

Taphrocampa, 589; annulosa, 589

Tardigrada, 17

Tatria, 449; biremis, 449

Technical and Sanitary Problems, 1067-1083;
see Problems, Technical and Sanitary

Telmatodrilus, 641; mcgregori, 641, vejdovskyi,
641

Telorchinae, 393

Telorchis, 394; medius, 394

Temperature of water, 32; and metabolism,
33, in streams, 32, reaction of animals, 34,
seasonal changes, 33

Tentaculata, 17; see Bryozoa

Teratocephalus, 496; cornutus, 496

Terricola, 359

Terriginous bottom, 26, 45

Testacea, 220

Tetmemorus, 138; granulalus, 138

Tetrabothriidae, 440

Tetrabothrius, 440; macrocephalus, 440

retracoccus, 149

Tctrucotylc, 411; typica, 411

Tetracotyle form, 424

Tclracyclus, 133; lacustrii, 135

Tetradesmus, 160; wiscomiensis, 160

Tctruedron, 155; enormt, 155

Tetniguneuria (imago), 926, (nymph), 931

Tetramastix, 613; opolimsis, 613

Tetramitus, 251; lariabilis, 251

Tctra[X'dia, 105

Tctraphyllidc-a, 434

Tctraselmis, 2G4; limtiftis, 264

Tctraspora, 147; cxplanala, 147

Tetrasporaccac, 146

Tclrastnnma aquarium dulcium, 457; see
Nemcrtina

Tctrastrum, 160

Thalassomyia, 94s

Thallasironus, 486

Thamnoccphalus, 670; platyurus, 670

Thelaziidae, 527

Thermal springs, life of, 101

ThermocHne, 28

Theliderma, 997

Thermonectes (adult), 941

Thorea, 175; ramosissima, 175

Threadworms; sec Xt-maloda, Parasitic

Thresher tank-pump, 80

Throscinus (adult), 942

Thuricola, 296; valvata, 296

Thuricolopsis, 296

Thyas, 861; venusta, 861

Tintinnidium, 286; fluviatUis, 2S6

Tintinnus, 286

Tiphys, 873; liliaceus, 873

Tipulidae (larvae), 944 «

Tolypclla, 173; nidifua, 173

Tolypothrix, 112; lanata, 112

Torquis, 984

Torrenticola, 864; anomala, 864

Tow net, 72

Trachclius, 275; ovum, 275

TrdchelobdeUa I'ii-ida, 655

Trachelmonas, 252: hispUia, 252, hgrmUa,
252, voh'ocina, 232

Trachclophyllum, 273: tachyblaslum, 273

Tralia, 978; mysotis, 979, pusilla, 978

Tramca (imago). 927. (nymph). 93a

Trammel net, 62

Transmission, disease, 1067

Traps. 65

Trcmatoda (flukes), Fresh-Watcr. 15. 36s.
369-424, 452-453: ccrcaria. 37«. .^72. as
plankton organism, 372, dcprct- of infection,
373, development. 37 >. intormi-diatc host,
371, key, 374-424. miracidium. 37'. primary
host, 372, rcdia, 37 >. references. 45^-453.
sporocyst, 371, structure. 369. 370; see Para-
sitic piatworms; Parasitic Worms

Trentipohlia, 170; viaitwi, 170

mo

INDEX

Trentonia, 265; flagellata, 265
Trepomonas, 249; agilis, 249
Triaenophorinae, 433
Triaenophorus, 433
Triangle dredge, 71

Triarthra, 613; brachiaia, 613, longiseta, 613
Tribonema, 164; minor, 164
Trichinella spiralis, 534
Trichinellidae, 534
Trichocephaloides, 444
Trichoda, 279; pura, 279
Trichodina, 291; pediculus, 291
Trichogaster, 286
Trichomastix, 250
Trichophoreae, 113
Trichophrya, 299; sinuosa, 299
Trichoptera (caddisflies) , Fresh- Water, 900-
903, 917. 936-937; cases, 900, key, 936-937.
pupa, 902; see Insecta
Tricorythus (nymph), 922
Trichosotna contortum, 513
Trichostomina, 277
Trichostrongylidae, 522
Trichostrongylinae, 522
Trichostrongylus, 522; fiberius, 522
Trichosyringata, 534
Trichurinae, 534
Trichuris, 534; opaca, 534
Tricladida, 333, 354, 361

Trilobus, 501; longus, 501

Trinema, 231; camplanatum, 231, enchelys,
232, lineare, 232

Triophthaknus, 589; dorsualis, 589

Triphylus, 599; lacustris, 599

Triploceras, 139; gracile, 139

Tripyla, 498; lata, 498

Tristomidae, 374

Tritigonia, 998; tuberculata, 99S

Trochehninthes, 16

Trochiscia, 154; vestilus, 154

Trochosphaera, 613; solstitialis, 613

Trochosphaeridae, 613

Trochospongilla, 308; horrida, 308, leidyi, 308

Troglotrematidae, 390

Tropidiscus, 983

Tropidoscyphus, 254, 257

Tropistemus (adult), 940

Truncilla, 1008; foliata, 1009, personata, 1009,
sulcata, 1008, triquetra, 1008; s. s., 1008

Tryonia, 989; clathrata, 989

Trypanorhyncha, 434, 450

Tubefla, 313; pennsylvanica, 313

Tubifex, 642; miiltisetosus, 641, 642, tubifex,
641, 642

Tubificidae, 640

Tulotoma, 988; magnifica, 988

Tuomeya, 176; fluviatalis, 176

Turbellaria (free-living flatworms), Fresh-
Water, 15, 323-364; cultures, 331, digestive
apparatus, 325, habitat, 329, key, 333-364.

land planarians, 330, methods of study,
331, movement, 325, photokinesis, 328,
references, 364, reproduction, 326, respon-
siveness to stimuh, 328

Turbidity of fresh water, 29, 36

Turtle nets, 66

Two-winged flies; see Diptera; Insecta

Tylenchus, 483; devastatrix, 483, dipsaci, 483

Types of fresh-water hfe, 13

Typhlocypris, 823; delawarensis, 824, peircei,
823

Typhloplana, 350; viridata, 350

Typhloplanid from Canandaigua Lake, 361,
362; from Irondequoit, 361, 362

Typhloplanidae, 348, 361

Typhloplanini, 349

Tyrrellia, 869; circularis, 869

Ulothrix, 162; zonata, 162

Ulothrichaceae, 161

Ulvaceae, 160

Ulvella, 171; americana, 171

Under- water photography, 86; see Methods

of Photographing
Uniformity of fresh-water life (biology), 13
Unio, 1000; crassidens, 1000, spinosus, looi,

tetralasmus, looi, uniomerus, looi
Unionicola (non-parasitic species), 871
Unionicola (parasitic species), 872; crassipes,

872
Unionidae, 995
Unioninae, 995
Univalve, 957; see Mollusca
Uranotaenia (larva), 944
Urceolaria, 292

Urceolopsis, 256; sabulosa, 256
Urceolus, 256; cycloslomum, 256
Urnatella gracilis, 951
Umula, 299

Urocentnmi, 277; turbo, 277
Uroglena, 261; americana, 261
Uroleptus, 288; musculus, 288
Uronema, 279; marinum, 279
Urosoma, 290

Urostyla, 287; grandis, 287, trichogaster, 287
Urotricha, 273; farcta, 273
Utricularia, 188; infiata, 188, minor, 188

Vacuoles, 103

Vaginarieae, 109

•Vaginicola, 296; kptosoma, 296

VaUisneria, 181, 190; spiralis, 181, 185, 189,

190
Valvata, 988; tricarinata, 988
Valvatidae, 988
Vampyrella, 234; lateritia, 234
Vanheurckia, 128; rhomboides, 128
Variety of fresh-water life (biology), 11
Vaucheria, 172; re pens, 172
Vegetation, amount, 50

INDEX

IIII

Vegetation, Larger (Higher), Fresh-Water,

178-209; cycle of matter, 207, evolution,

198, references, 209, zones, 196; see Plants,

aquatic
Veliidae, 933
Venation, wing, 916; of stonctlics, 916; see

Insecta
Vertebrata, 1021-1066; adaptations, 1022,

references, 1066; see Amphibia (Batrachia);

Birds; Fishes; Mammals; Reptiles
Viviparidae, 987
Viviparus, 9S7; interlcxtus, 987
Volvocaceae, 143
Volvox, 146, 269; aureus, 2G9, globalor, 269,

perglobator, 269, spennatosphara, 269
Vortex, 340

Vortex (?) cavicolens, 361, 363
Vorticella, 293; campanula, 293

Wardius, 386; zibet hicus, 386

Water; acid or alkaline characteristics of, 40,
ammonia in, 39, bacteria found in natural,
96, number in, 96, 1070, biological con-
ditions in, 46, carbon dioxide in, 39,
chemical factors, 36, circulation, 27, irf
lakes, 27, conveyor of disease, 1068, current
strength in streams, 23, daily depth migra-
tions, 32, 43, density, 22, distribution of
gases, 37, of life, 35, expansion in freezing,

21, gases dissolved in, 36, general solvent,

22, identification of source of, 1080, index
of suitability, 46, influence of currents in,
28, odors in, 107 1, 1072, oxygen content,
37, penetration of light, 29, 30, physical
conditions of, 22, physical environment of
organisms in, 9, pressure in, 34, quantity
of life in, 46, of plankton in, 47, 48, reser-
voirs, purification of, 1074, 1076, 1077,
rhythms of organisms, 43, seasonal changes,
33, solubility of gases in, 37, tastes in, 107 1,
temperature, 32, in streams, 32, terriginous
bottom, 45, thermal properties, 21, tur-
bidity, 29, 36

Water Biology, Fresh-; sec Biology, Fresh-
Water
"Water-bloom," 100
Water bodies, physical features of, 8
Water bottle, 80

Water glass, 87

Water Life, Fresh-; see Biology, Fresh-Water
Water organisms, physical environment of, 9
Water plants and vegetation; srr IMants,

acjuatic; \'egetation, a(|uatic
Water supplier, tastes antl <Klors in, 1071
Water systems, organisms in piix-s of, loHi
Waters, flowing, 2
Waves and their action, 28
Wheel animalcules; see Rotatoria
Whirligig beetles, 906; see Coleoplcra; Insecta
Wilsonema, 495
Wing venation. 916
Winter buds (hibernacula), 192
Wlassicsia, 711; kinistinemis, 711
Wollea, no; saccala, no
Worms, earth; see Chactopoda; Oligochacta
Worms, free-living; see Nemaloda; Nemer-

tina (Nemerteans); Turbcllaria
Worms, parasitic; see Acanthcnephala; Ce»-

toda; Gordiacea; Nematoda, Parasitic;

Parasitic Worms; Trematoda
Wyeomyia (larva), 944

Xanthidium, 141; J'asciculaium, 141
Xiphidiocercariae, 416
Xystonotus, 865: as per, 865

Zannichellia, 189; repens, 185, palustris, 190

Zeugorchis, 407; aequatus, 407

Zoethamnium, 294; adatnsi, 294

Zone, shore, 3

Zones of vegetation, 196; characctum, 196,
nupharetum, 196, phragmitelum. 196,
potamogetonetum, 196, scirjx'tum. 196

Zoochlorella, 153

Zooccium, 948

Zoophytes, 301

Zoosporangium, 119

Zoospores, 1 18

Zostcra nana, 1S5

Zygnema, 142

Zygncmaceae, 141

Zygnemeae, 142

Zygocotyle, 388; ceratosa, 388

Zygocotylinae. 38S

Zygoptera (imago), 922, (nymph), 928

Zygospore, 119

I