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FRESH-WATER
BIOLOGY

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

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

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

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.

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

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

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

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

*
*

?
*

*
*

*
*
*

*
*
*
*

*
*
*

*
*
*
*
*

*
*
*
*

*
*

*
*
*

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

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

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

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.

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 !

6 i

4 ;

■9

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

.68

.91

•.S9

.08

.04

.42

. 10

■ 4

. 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

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

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

5
9
3

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

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.

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

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

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

Organisms abundant

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

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

Pressure 4 atmospheres, light re-
duced to f

128

Scanty filamentous algce

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

177

Lower limit of most shallow

water animals
Nostoc and diatoms

Light i; pressure 7 atmospheres

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

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

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

400

2,750

6,660

1,250

7,620

685

650

104,500

1,620

n. c.

17,350

200

7,620

400

85,160

2,350

Neu-
trality

260

2,220

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

1,145

11,760

1,190

1,050

o
o
o

390

20
o
o

25
750

,240
,110

100

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

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

Prairie Pond II

Pond I

Pond VII... .

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

100

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

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

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

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.

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

iJi

L-U

■

1-^

—

--.

4(i0

CAMBARUS

■ 1 1 -j^

:::

--4

—

"^^^^^^

:!7=

...

—

..J

60NI0BASIS

'I;;

\{'\\

'^p

--=

£r:-T-

Mz:

1 1 1 '1

HYDROPSYCHE

.---'

1 1 L'-'

—

ARGIA

-V

'r~.

=----

-:|^^^^H^H

-=^^--

- -^

-j

~~i

--,.

PERLA

'rll

Jz?--

-i-yz

IrZZ

-^-rflHH^HI^^^H

,--

•'

HEPT/IGENINA

zzTi

:-:-}

V:-~:

,=^7

— -

—

""}

PSEPHENUS

-Jf?

■:-!-:

33:

-34lHHlllill -

{

{STRONG current!
HARD BOTTOM |
MEDIUM LIGHT

UNDER STONES R^
ON STONES ESISI
STRONG LIGHT ^^

AMONG STONES f?^
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

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

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

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

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-

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.

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

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

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

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

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

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

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

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

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-

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.)

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.

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

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

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 (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 .

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?=

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.

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.

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^_ea rth de coctions, 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 calle anodules .

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»i i iimninm ii i i. .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

(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

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

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.

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

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.)

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.)

[9 (12) End view of cells triangular or quadrangular, seldom oval.

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 {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

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)

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.

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

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

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.)

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

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

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.

\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.

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.)

(3)

(103)

(96)

(35)

(32)

(29)

(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

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.)

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 (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 (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 (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

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 ' <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.)

(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.
^^ n iimiiiii jM ^ ^ ^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 (43) Mouth usually open, pharynx often rod-like 37

37 (42)

38 (39)

Mouth subterminal.

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///'-^>-

'''//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-

^^-Tja abUL-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.)

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

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.

^ ^ ^^ .

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 (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.

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.

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.

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 (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. .

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.

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.

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.

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.

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

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\

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.

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.

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

[4 (26) Posterior disc terminal; suckers large.

Poly stoma Zeder 1800

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.)

(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

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 (56) Testes two, more or less deeply lobed.

Subfamily Cladorchiinae Fischoeder 1901

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.

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.)

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.

^■

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