LIFE OF INLAND WATERS

NEEDHAM AND LLOYD

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THE LIFE OF INLAND WATERS

if I » H 1 L

SEASONAL CHANGES ON

SPRING
FLOODS

SUMMER
SUNSHINE

The view is from West Hill,

THE RENWICK MARSH AT ITHACA

AUTUMN
FIRES

."

WINTER
FREEZING

3oking across the valley.

h i g

THE LIFE OF INLAND

WAT

An elementary text book of fresh-water biology
for American students

BY
JAMES G. NEEDHAM

Professor of Limnology in Cornell University
and

J. T. LLOYD

Instructor in Limnology in Cornell University

1916

THE COMSTOCK PUBLISHING COMPANY
ITHACA, NEW YORK

COPYRIGHT, 1915
COPYRIGHT, 1916

THE COMSTOCK PUBLISHING CO.

5

PRESS OF \V. F. HUMPHREY, GENEVA, N. Y.

PREFACE

IN THE following pages we have endeavored to present a
brief and untechnical account of fresh-water life, its forms,
its conditions, its fitnesses, its associations and its economic pos-
sibilities. This is a vast subject. No one can have detailed
first hand knowledge in any considerable part of it. Hence,
even for the elementary treatment here given, we have borrowed
freely the results of researches of others. We have selected out
of the vast array of material that modern limnological studies
have made available that which we deem most significant.

Our interests in water life are manifold. They are in part
economic interests, for the water furnishes us food. They are
in part aesthetic interests, for aquatic creatures are wonderful to
see, and graceful and often very beautiful. They are in part
educational interests, for in the water live the more primitive
forms of life, the ones that best reveal the course of organic evolu-
tion. They are in part sanitary interests; interests in pure
water to drink, and in control of water-borne diseases, and of
the aquatic organisms that disseminate diseases. They are
in part social interests, for clean shores are the chosen places for
water sports and for public and private recreation. They are
in part civic interests, for the cultivation of water products for
human food tends to increase our sustenance, and to diversify
our industries. Surely these things justify an earnest effort to
make some knowledge of water life available to any one who may
desire it.

The present text is mainly made up of the lectures of the senior
author. The illustrations, where not otherwise credited, are
mainly the work of the junior author. Yet we have worked
jointly on every page of the book. We are indebted for helpful
suggestions regarding the text to Professors E. M. Chamot, G. C.
Embody, A. H. Wright, and to Dr. W. A. Clemens. Miss Olive
Tut tie has given much help with the copied figures.

i o Preface

Since 1906, when a course in general limnology was first estab-
lished at Cornell University, we have been associated in develop-
ing an outline of study for general students and a program of
practical exercises. The text-book is presented herewith: the
practical exercises are reserved for further trial by our own classes;
they are still undergoing extensive annual revision.

The limitations of space have been keenly felt in even' chapter;
especially in the chapter on aquatic organisms. These are so
numerous and so varied that we have had to limit otir discussion
of them to groups of considerable size. These we have illustrated
in the main with photographs of those representatives most
commonly met with in the course of our own work. Important
groups are, in some cases, hardly more than mentioned; the stu-
dent will have to go to the reference books cited for further infor-
mation concerning them. The best single work to be consulted
in this connection is the American Fresh-water Biology edited by
Ward and Whipple and published by John Wiley and Sons.
Our bibliography, necessarily brief, includes chiefly American
papers. We have cited but a few comprehensive foreign works;
the reference lists in these will give the clue to all the others.

It is the ecologic side of the subject rather than the sys-
tematic or morphologic, that we have emphasized. Nowadays
there is being put forward a deal of new ecologic terminology
for which we have not discovered any good use; hence we have
omitted it.

Limnology in America today is in its infancy. The value of
its past achievements is just beginning to be appreciated. The
benefits to come from a more intensive study of water life are
just beginning to be disclosed. That there is widespread interest
is already manifest in the large number of biological stations at
which limnological work is being done. From these and other
kindred laboratories much good will come ; much new knowledge
of water life, and better application of that knowledge to human
welfare.

JAMES G. NEEDHAM.
J. T. LLOYD.

CHAPTER I
Introduction

The study of water life p. 14. Epoch-making events: the invention of the
microscope, p. 15. The publication of the Origin of Species, p. 17. The
discovery of Plancton, p. 18. Agencies for the promotion of the study
of Limnology, p. 20. Biological field stations, p. 23.

CHAPTER II
The Nature of Aquatic Environment

I. Properties and uses of water: transparency, etc., p. 26. Stratification,
p. 31. The content of natural waters, p. 40.

//. Water and land, p. 55.

CHAPTER III
Types of Aquatic Environment

I. Lakes and Ponds: Lakes temporary phenomena, p. 60. The Great
Lakes, p. 63. The Finger Lakes, p. 64. The lakes of the Yahara valley,
p. 66. Flood plain lakes, p. 67. Solution lakes, p. 68. Depth and
breadth, p. 71. High and low water, p. 74.

77. Streams: Gradient of stream beds, p. 77. Ice in streams, p. 80. Silt,
p. 84. Current, p. 85. High and low water, p. 87.

///. Marshes, swamps and bogs: Cat-tail marshes, p. 91. Okefenokee
Swamp, p. 93. Climbing bogs, p. 94. Muck and peat, p. 95. High
and low water, p. 96.

CHAPTER IV
Aquatic Organisms

I. Plants: The Algae, p. 101. Chlorophylless water plants, p. 139. The
mossworts, p. 146. The fernworts, p. 149. The seed plants, p. 151.

II. Animals. Protozoans, p. 159. The lower invertebrates, p. 163. Arthro-
pods, p. 183. Insects, p. 195. Vertebrates, p. 231.

12

Contents

CHAPTER V

Adjustment to Conditions of Aquatic Life

I. Individual Adjustment, \>. 242. i. To open water : Flotation, p. 243.
Swimming, p. 249.

2. Adjustment to shore life, p. 251. Avoidance of silt, p. 252. Bur-
rowing, p. 254. Shelter building, p. 257. Withstanding current, p. 258.

3. Adjustment of life cycle: Encystment, p. 261. Winter eggs, p. 266.

4. Readaptation to aquatic life: Plants, p. 270. Animals, p. 273.

//. Mutual Adjustment, p. 282. i. Insectivorous plants, p. 283.
2. The larval habits of river mussels, p. 286.

CHAPTER VI
Aquatic Societies

I. Limnetic Societies. i. Plancton, p. 294. Seasonal range, p. 302.
Plancton pulses, p. 305. Distribution in depth, p. 307.

2. Necton, p. 313.

II. Littoral Societies, i. Lenitic Societies, p. 315. Plants, p. 318. Ani-
mals, p. 324. Spatial relations of lenitic animals, p. 326. The life of
typical lenitic situations, p. 333. Of ponds, p. 334. Of marshes, p.
341. Of bogs, p. 348. Of stream beds, p. 356.

2. Lotic societies, p. 363. Plancton gathering forms, p. 364. Free
living foragers, p. 368. Shelter-building foragers, p. 371.

CHAPTER VII
Inland Water Culture
I. Aboriginal water culture, p. 377.

//. Water crops: Plants, p. 379. Animals, p. 382. Fish culture, p. 384.
The forage problem, p. 387. Staple forage crops, p. 389 The way
of economic progress, p. 399.

///. Water culture and civic improvement, -p. 401. Reclamation enterprises :
Waste wet lands, p. 402. Reservoirs, p. 403. Scenic improvement,
p. 404. Private water culture, p. 406. Swamp reservations, p. 408.

BIBLIOGRAPHY p. 413

List of initials and tail-pieces p. 420

Index p. 421

CHAPTER I

INTRODUCTION

INDIANS GATHERING WILD RICE, N. MINNESOTA

(HE home of primeval man was
by the waterside. The springs
quenched his thirst. The bays
afforded his most dependable
supply of animal food. Stream-
haunting, furb caring animals
furnished his clothing. The
rivers were his highways. Water

sports were a large part of his recreation; and the
glorious beauty of mirroring surfaces and green flower-
decked shores were the manna of his simple soul.

The circumstances of modern life have largely
removed mankind from the waterside, and common
needs have found other sources of supply; but the

13

j_j. Introduction

primeval instincts remain. And where the waters are
clean, and shores unspoiled, thither wTe still go for rest,
and refreshment. Where fishes leap and sweet water
lilies glisten, where bull frogs boom and swarms of
May-flies hover, there we find a life so different from
that of our usual surroundings that its contemplation
is full of interest. The school boy lies on the brink of a
pool, watching the caddisworms haul their lumbering
cases about on the bottom, and the planctologist plies
his nets, recording each season the wax and wane of
generations of aquatic organisms, and both are satisfied
observers.

The study of water life, which is today the special
province of the science of limnology*, had its beginning
in the remote unchronicled past. Limnology is a
modern name; but many limnological phenomena were
known of old. The congregating of fishes upon their
spawning beds, the emergence of swarms of May-flies
from the rivers, the cloudlike flight of midges over the
marshes, and even the "water bloom" spreading as a
filmy mantle of green over the still surface of the lake —
such things could not escape the notice of the most
casual observer. Two of the plagues of Egypt were
limnological phenomena; the plague of frogs, and the
plague of the rivers that were turned to blood.

Such phenomena have always excited great wonder-
ment. And, being little understood, they have given
rise to most remarkable superstitions, f Little real

*Limn os = shore, waterside, and logos — a treatise: hydrobiology.

fThe folk lore of all races abounds in strange interpretations of the simplest
limnological phenomena; bloody water, magic shrouds (stranded "blanket-
algae"), spirits dancing in waterfalls, the "will o' the wisp" (spontaneous com-
bustion of marsh gas), etc. Dr. Thistleton Dyer has summarized the folk lore
concerning the last mentioned in Pop.Sci. Monthly 19:67, 1881. In Keightly's
Fairy Mythology, p. 491 will be found a reference to the water and wood maids
called Rusalki. "They are of a beautiful form with long green hair: They
swing and balance themselves on the branches of trees, bathe in lakes and
rivers, play on the surface of the water, and wring their locks on the green
mead at the water's edge." On fairies and carp rings see Theodore Gill in
Smithsonian Miscellaneous Collections 48:203, 1905.

Limnology

knowledge of many of them was possible so long as the
most important things involved in them — often even
the causative organisms — could not be seen. Progress
awaited the discovery of the microscope.

The microscope opened a new world of life to human
eyes — "the world of the infinitely small things." It
revealed newT marvels of beauty everywhere. It dis-

FIG. i. Waterbloom (Eugleiia) on the surface film of the Renwick
lagoon at Ithaca. The clear streak is the wake of a boat just passed.

covered myriads of living things where none had been
suspected to exist, and it brought the elements of
organic structure and the beginning processes of
organic development first within the range of our
vision. And this is not all. Much that might have
been seen with the unaided eye was overlooked until
the use of the microscope taught the need of closer
looking. It would be hard to overestimate the stimu-
lating effect of the invention of this precious instrument
on all biological sciences.

1 6 Introduction

With such crude instruments as the early micro-
scopists could command they began to explore the world
over again. They looked into the minute structure of
everything — forms of crystals, structure of tissues,
scales of insects, hairs and fibers, and, above all else,
the micro-organisms of the water. These, living in a
transparent medium, needed only to be lifted in a drop
of water to be ready for observation. At once the early
microscopists became most ardent explorers of the
water. They found every ditch and stagnant pool
teeming with forms, new and wonderful and strange.
They often found each drop of water inhabited. They
gained a new conception of the world's fulness of life
and one of the greatest of them Roesel von Rosenhof,
expressed in the title of his book, "Insekten Behisti-
gung"* the pleasure they all felt in their work. It was
the joy of pioneering. Little wonder that during a
long period of exploration microscopy became an end
in itself. Who that has used a microscope has not been
fascinated on first acquaintance with the dainty ele-
gance and beauty of the desmids, the exquisite sculptur-
ing of diatom shells, the all-revealing transparency of
the daphnias, etc., and who has not thereby gained a
new appreciation of the ancient saying, Natura maxime
miranda in minimis.^

Among these pioneers there were great naturalists —
Swammerdam and Leeuwenhoek in Holland, the latter,
the maker of his own lenses; Malpighi and Redi in
Italy; Reaumer and Trembly in France; the above
mentioned, Roesel, a German, who was a painter of
miniatures; and many others. These have left us
faithful records of what they saw, in descriptions and
figures that in many biological fields are of more than
historical importance. These laid the foundations of

*Belustigung = delight.

t Nature is most wonderful in little things.

Important Events 17

our knowledge of water life. Chiefly as a result of their
labor there emerged out of this ancient "natural
philosophy" the segregated sciences of zoology and
botany. Our modern conceptions of biology came
later, being based on knowledge which only the per-
fected microscope could reveal.

A long period of pioneer exploration resulted in the
discovery of new forms of aquatic life in amazing
richness and variety. These had to be studied and
classified, segregated into groups and monographed,
and this great survey work occupied the talents of
many gifted botanists and zoologists through two
succeeding centuries — indeed it is not yet completed.
But about two centuries after the construction of the
first microscope, occurred an event of a very different
kind, that was destined to exert a profound influence
throughout the whole range of biology. This was the
publication of Darwin's Origin of Species. This book
furnished also a tool, but of another sort — a tool of the
mind. It set forth a theory of evolution, and offered
an explanation of a possible method by which evolution
might come to pass, and backed the explanation with
such abundant and convincing evidence that the
theory could no longer be ignored or scoffed out of
court. It had to be studied. The idea of evolution
carried with it a new conception of the life of the world.
If true it was vastly important. Where should the
evidence for proof or refutation be found? Naturally,
the simpler organisms, of possible ancestral character-
istics, were sought out and studied, and these live in the
water. Also the simpler developmental processes, with
all they offer of evidence; and these are found in the
water. Hence the study of water life, especially with
regard to structure and development, received a mighty
impetus from the publication of this epoch-making book.
The half century that has since elapsed has been one of
unparalleled activity in these fields.

1 8 Introduction

Almost simultaneously with the appearance of
Darwin's great work, there occurred another event
which did more perhaps than any other single thing to
bring about the recognition of the limnological part of
the field of biology as one worthy of a separate recogni-
tion and a name. This was the discovery of plancton
-that free-floating assemblage of organisms in great
water masses, that is self -sustaining and self -maintaining
and that is independent of the life of the land. Lilje-
borg and Sars found it, by drawing fine nets through
the waters of the Baltic. They found a whole fauna
and flora, mostly microscopic — a well adjusted society
of organisms, with its producing class of synthetic
plant forms and its consuming class of animals; and
among the animals, all the usual social groups, herbi-
vores and carnivores, parasites and scavengers. Later,
this assemblage of minute free-swimming organisms
was named plancton.* After its discovery the seas
could no longer be regarded as "barren wastes of
waters"; for they had been found teeming with life.
This discovery initiated a new line of biological explora-
tion, the survey of the life of the seas. It was simple
matter to draw a fine silk net through the open water
and collect everything contained therein. There are
no obstructions or hiding places, as there are every-
where on land; and the fine opportunity for quantita-
tive as well as qualitative determination of the life of
water areas was quickly grasped. The many expedi-
tions that have been sent out on the seas and lakes of
the world have resulted in our having more accurate
and detailed knowledge of the total life of certain of
these waters than we have, or are likely to be able soon
to acquire, of life on land.

Prominent among the investigators of fresh water life
in America during the nineteenth century were Louis

*Planktos = drifting, free floating.

Aquatic Life 19

Aggassiz, an inspiring teacher, and founder of the first
of our biological field stations; Dr. Joseph Leidy, an
excellent zoologist of Philadelphia, and Alfred C. Stokes
of Connecticut, whose Aquatic Microscopy is still a use-
ful handbook for beginners.

Our knowledge of aquatic life has been long accumu-
lating. Those who have contributed have been of very
diverse training and equipment and have employed
very different methods. Fishermen and whalers; col-
lectors and naturalists; zoologists and botanists, with
specialists in many groups; water analysts and sani-
tarians; navigators and surveyors; planktologists and
bacteriologists, and biologists of many names and sorts
and degrees ; all have had a share. For the water has
held something of interest for everyone.

Fishing is one of the most ancient of human occupa-
tions; and doubtless the beginning of this science was
made by simple fisher-folk. Not all fishing is, or ever
has been, the catching of fish. The observant fisherman
has ever wished to know more of the ways of nature, and
science takes its origin in the fulfillment of this desire.

The largest and the smallest of organisms live in the
water, and no one wras. ever equipped, or will ever be
equipped to study any considerable part of them.
Practical difficulties stand in the way. One may not
catch whales and water-fleas with the same tackle, nor
weigh them upon the same balance. Consider the dif-
ference in equipment, methods, area covered and num-
bers caught in a few typical kinds of aquatic collecting :

(i). Whaling involves the cooperative efforts of
many men possessed of a specially equipped vessel. A
single specimen is a good catch and leagues of ocean
may have to be traversed in making it.

(2). Fishing may be done by one person alone,
equipped with a hook and line. An acre of water affords
area enough and ten fishes may be called a good catch.

2O Introduction

(3). Collecting the commoner invertebrates, such as
water insects, crustaceans and snails involves ordinarily
the use of a hand net. A square rod of water is suffi-
cient area to ply it in; a satisfactory catch may be a
hundred specimens.

(4). For collecting entomostracans and the larger
plancton organisms towing nets of fine silk bolting-cloth
are commonly employed. Possibly a cubic meter of
water is strained and a good catch of a thousand speci-
mens may result.

(5). The microplancton organisms that slip through
the meshes of the finest nets are collected by means of
centrifuge and filter. A liter of water is often an ample
field for finding ten thousand specimens.

(6). Last and least are the water bacteria, which are
gathered by means of cultures. A single drop of water
will often furnish a good seeding for a culture plate
yielding hundreds of thousands of specimens.

Thus the field of operation varies from a wide sea to
a single drop of water and the weapons of chase from
a harpoon gun to a sterilized needle. Such divergencies
have from the beginning enforced specialization among
limnological workers, and different methods of studying
the problems of water life have grown up wide apart,
and, often, unfortunately, without mutual recognition.
The educational, the economic and the sanitary inter-
ests of the people in the water have been too often dealt
with as though they are wholly unrelated.

The agencies that in America furnish aid and support
to investigations in fresh water biology are in the main :

i. Universities which give courses of instruction
in limnology and other biological subjects, and some of
which maintain field stations or laboratories for investi-
gation of water problems. 2. National, state and
municipal boards and surveys, which more or less
constantly maintain researches that bear directly upon

Investigations 21

their own economic or sanitary problems. 3. Socie-
ties, academies, institutes, museums, etc., which
variously provide laboratory facilities or equip expedi-
tions or publish the results of investigations. 4.
Private individuals, who see the need of some special
investigation and devote their means to furthering it.
The Universities and private benefactors do most to
care for the researches in fundamental science. Fish
commissions and sanitary commissions support the
applied science. Governmental and incorporated insti-
tutions assist in various ways and divide the main work
of publishing the results of investigations.

It is pioneer limnological work that these various
agencies are doing; as yet it is all new and uncorre-
lated. It is all done at the instance of some newly
discovered and pressing need. America has quickly
passed from being a wilderness into a state of highly
artificial culture. In its centers of population great
changes of circumstances have come about and new
needs have suddenly arisen. First was felt the failure
of the food supply which natural waters furnished;
and this lack led to the beginning of those limnological
enterprises that are related to scientific fish culture.
Next the supply of pure water for drinking failed in our
great cities; knowledge of water-borne diseases came
to the fore: knowledge of the agency of certain
aquatic insects as carriers of dread diseases came in;
and suddenly there began all those limnological enter-
prises that are connected with sanitation. Lastly, the
failure of clean pleasure grounds by the water-side,
and of wholesome places of recreation for the whole
people through the wastefulness of our past methods of
exploitation, through stream and lake despoiling, has
led to those broader limnological studies that have to
do with the conservation of our natural resources.

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WATER

F ALL inorganic substances,
acting in their own proper
nature, and without assist-
ance or combination, water
is the most wonderful. If
we think of it as the source
of all the changefulness and
beauty which we have seen

in the clouds; then as the instrument by which the earth we have
contemplated was modelled into symmetry, and its crags chiseled into
grace; then as, in the form of snow, it robes the mountains it has
made, with that transcendent light which we could not have conceived
if we had not seen ; then as it exists in the foam of the torrent, in the
iris which spans it, in the morning mist which rises from it, in the
deep crystalline pools which mirror its hanging shore, in the broad
lake and glancing river, finally, in that which is to all human minds
the best emblem of unwearied, unconquerable power, the wild, various,
fantastic, tameless unity of the sea; what shall we compare to this
mighty, this universal element, for glory and for beauty? or how shall
we follow its eternal cheerfulness of feeling? It is like trying to paint
a soul." — RUSKIN.

CHAPTER II

THE NATURE CDF AQUATIC
ENVIRONMENT

PMOPEKTIES
AND USES

ATER, the one abundant
liquid on earth, is, when
pure, tasteless, odorless
and transparent. Wa-
ter is a solvent of a
great variety of sub-
stances, both solid and
gaseous. Not only does
it dissolve more sub-
stances than any other
liquid, but, what is more
important, it dissolves
those substances which
are most needed in solution for the maintenance of
life. Water is the greatest medium of exchange in the
world. It brings down the gases from the atmosphere;
it transfers ammonia from the air into the soil for
plant food; it leaches out the soluble constituents
of the soil; and it acts of itself as a chemical agent
in nutrition, and also in those changes of putrefaction
and decay that keep the world's available food supply
in circulation.

Water is nature's great agency for the applica-
tion of mechanical energy. It is by means of water

25

26 Nature of Aquatic Environment

that deltas are built and hills eroded. Water is the
chief factor in all those eternal operations of flood and
floe by which the surface of the continent is shaped.

Transparency. — Water has many properties that fit
it for being the abode of organic life. Second only in
importance to its power of carrying dissolved food
materials is its transparency. It admits the light of
the sun; and the primary source of energy for all
organic life is the radiant energy of the sun. Green
plants use this energy directly; animals get it in-
directly with their food. Green plants constitute
the producing class of organisms in water as on land.
Just in proportion as the sun's rays are excluded,
the process of plant assimilation (photosynthesis) is
impeded. When we wish to prevent the growth of
algae or other green plants in a reservoir or in a spring
we cover it to exclude the light. Thus we shut off
the power.

Pure water, although transparent, absorbs some of
the energy of the sun's rays passed through it, and
water containing dissolved and suspended matter
(such as are present in all natural water) impedes
their passage far more. From which it follows, that
the superficial layer of a body of water receives the
most light. Penetration into the deeper strata is
impeded according to the nature of the water content.
Dissolved matters tint the water more or less and give
it color. Every one knows that bog waters, for
example, are dark. They look like tea, even like very
strong tea, and like tea they owe their color to their
content of dissolved plant substances, steeped out of
the peaty plant remains of the bog.

Suspended matters in the water cause it to be turbid.
These may be either silt and refuse, washed in from
the land, or minute organisms that have grown up in

Transparency 27

the water and constitute its normal population. One
who has carefully watched almost any of our small
northern lakes through the year will have seen that
its waters are clearest in February and March, when
there is less organic life suspended in them than at
other seasons. But it is the suspended inorganic
matter that causes the most marked and sudden
changes in turbidity — the washings of clay and silt
from the hills into a stream; the stirring up of mud
from the bottom of a shallow lake with high winds.
The difference in clearness of a creek at flood and at
low water, or of a pond before and after a storm is often
very striking.

Such sudden changes of turbidity occur only in the
lesser bodies of water; there is not enough silt in the
world to make the oceans turbid.

The clearness of the water determines the depth
at which green plants can flourish in it. Hence it is
of great importance, and a number of methods have
been devised for measuring both color and turbidity.
A simple method that was first used for comparing the
clearness of the water at different times and places
and one that is, for many purposes, adequate, and one
that is still used more widely than any other,* consists
in the lowering of a white disc into the water and record-
ing the depth at which it disappears from view. The
standard disc is 20 cm. in diameterf; it is lowered
in a horizontal position during midday light. The
depth at which it entirely disappears from view is
noted. It is then slowly raised again and the depth
at which it reappears is noted. The mean of these
two measurements is taken as the depth of its visibility

*Method of Secchi: for other methods, see Whipple's Microscopy of Drink-
ing Water, Chap. V. Steuer's Planktonkunde, Chapter III.

tWhipple varied it with black quadrants, like a surveyor's level-rod target
and viewed it through a water telescope.

28 Nature of Aquatic Environment

beneath the surface. Such a disc has been found to
disappear at very different depths. Witness the fol-
lowing typical examples:

Pacific Ocean 59 meters

Mediterranean Sea 42 meters

Lake Tahoe 33 meters

Lake Geneva 21 meters

Cayuga Lake 5 meters

Pure Lake (Denmark), Mar 9 meters

Fure Lake (Denmark), Aug 5 meters

Pure Lake (Denmark), Dec 7 meters

Spoon River (111.) under ice 3.65 meters

Spoon River (111.) at flood 013 meters

It is certain that diffused light penetrates beyond the
depth at which Secchi's disc disappears. In Lake
Geneva, for example, where the limit of visibility is
2im. photographic paper sensitized with silver chloride
ceased to be affected by a 24-hour exposure at a depth
of about 100 meters or when sensitized with iodobromide
of silver, at a depth about twice as great. Below this
depth the darkness appears to be absolute. Indeed it
is deep darkness for the greater part of this depth, 90
meters being set down as the limit of "diffused light."
How far down the light is sufficient to be effective in
photosynthesis is not known, but studies of the distri-
bution in depth of fresh water algae have shown them
to be chiefly confined, even in clear lakes, to the upper-
most 20 meters of the water. Ward ('95) found 64
per cent, of the plancton of Lake Michigan in the upper-
most two meters of water, and Reighard ('94) found
similar conditions in Lake St. Clair. Since the inten-
sity of the light decreases rapidly with the increase in
depth it is evident that only those plants near the sur-
face of the water receive an amount of light comparable
with that which exposed land plants receive. Less than
this seems to be needed by most free swimming algae,

Transparency 29

since they are often found in greatest number in open
waters some five to fifteen meters below the surface.
Some algae are found at all depths, even in total dark-
ness on the bottom; notably diatoms, whose heavy
silicious shells cause them to sink in times of prolonged
calm, but these are probably inactive or dying individ-
uals. There are some animals, however, normally
dwelling in the depths of the water, living there upon

90

120

UQlMeters Deftfi.

FIG. 3. Diagram illustrating the penetration of light into the water of a lake;
also, its occlusion by inflowing silt and by growths of plants on the surface.

the organic products produced in the zone of photo-
synthesis above and bestowed upon them in a consider-
able measure by gravity. To the consideration of
these we will return in a later chapter.

The accompanying diagram graphically illustrates
the light relations in a lake. The deeper it is the greater
its mass of unlighted and, therefore, unproductive
water, and the larger it be, the less likely is its upper
stratum to be invaded by obscuring silt and water
weeds.

30 Nature of Aquatic Environment

Mobility — Water is the most mobile of substances,
yet it is not without internal friction. Like molasses,
it stiffens with cooling to a degree that affects the
flotation of micro-organisms and of particles suspended
in it. Its viscosity is twice as great at the freezing
point as at ordinary summer temperature (77°F.).

Buoyancy — Water is a denser medium than air; it
is 775 times heavier. Hence the buoyancy with which
it supports a body immersed in it is correspondingly
greater. The density of water is so nearly equal to
that of protoplasm, that all living bodies will float in
it with the aid of very gentle currents or of a very little
exertion in swimming. Flying is a feat that only a
few of the most specialized groups of animals have
mastered, but swimming is common to all the groups.

Press are- -This greater density, however, involves
greater pressure. The pressure is directly proportional
to the depth, and is equal to the weight of the super-
posed column of water. Hence, with increasing depth
the pressure soon becomes enormous, and wholly insup-
portable by bodies such as our own. Sponge fishers
and pearl divers, thoroughly accustomed to diving,
descending naked from a boat are able to work at depths
up to 20 meters. Professional divers, encased in a
modern diving dress are able to work at depths several
times as great; but such depths, when compared with
the depths of the great lakes and the oceans are com-
parative shoals.

Beyond these depths, however, even in the bottom
of the seas, animals live, adjusted to the great pressure,
which may be that of several hundred of atmospheres.
But these cannot endure the lower pressure of the
surface, and when brought suddenly to the surface they
burst. Fishes brought up from the bottom of the
deeper freshwater lakes, reach the surface greatly

Maximum Density 31

swollen, their scales standing out from the body, their
eyes bulging.

Maximum density — Water contracts on cooling, as do
•other substances, but not to the freezing point — only
to 4° centigrade (39.2° Fahrenheit). On this pecu-
liarity hang many important biological consequences.
Below 4° C. it begins to expand again, becoming lighter,
as shown in the accompanying table:

Temperature Weight in Ibs.

C° F° percu. ft. Density

35 95 62.060 .99418

21 70 62.303 .99802

10 50 62.408 -99975

4 39 62.425 i.ooooo

o 32 62.417 -99987

Hence, on the approach of freezing, the colder lighter
water accumulates at the surface, and the water at the
point of maximum density settles to the bottom, and
the congealing process, so fatal to living tissues generally
is resticted to a thin top layer. Here at o° C. (32° F.)
the water freezes, expanding about one-twelfth in bulk
in the resulting ice and reducing its weight per cubic
foot to 57.5 pounds.

Stratification of the water — Water is a poor conductor
of heat. We recognize this when we apply heat to the
bottom of a vessel, and set up currents for its distribution
through the vessel. We depend on convection and not
on conduction. But natural bodies of water are heated
and cooled from the top, when they are in contact with
the atmosphere and where the sun's rays strike.
Hence, it is only those changes of temperature which
increase the density of the surface waters that can pro-
duce convection currents, causing them to descend, and
deeper waters to rise in their place. Minor changes
of this character, very noticeable in shallow water, occur

Nature of Aquatic Environment

every clear day with the going down of the sun, but
great changes, important enough to effect the tempera-
ture of all the waters of a deep lake, occur but twice a
year, and they follow the procession of the equinoxes.
There is a brief, often interrupted, period (in March
in the latitude of Ithaca) after the ice has gone out, while
the surface waters are being warmed to o°C. ; and
there is a longer period in autumn, while they are being
cooled to o°C. Between times, the deeper waters of

W/NTER

SUMMER

4

FIG. 4. Diagram illustrating summer and winter temperature conditions in

Cayuga Lake. The spacing of the horizontal lines represents

equal temperature intervals.

a lake are at rest, and they are regularly stratified
according to their density.

In deep freshwater lakes the bottom temperature
remains through the year constantly near the point of
maximum density, 4° C. This is due to gravity. The
heavier water settles, the lighter, rises to the top.
Were gravity alone involved the gradations of tempera-
ture from bottom to top would doubtless be perfectly
regular and uniform at like depths from shore to shore.
But springs of ground water and currents come in to

Lake Temperatures

33

disturb the horizontal uniformity, and winds may do
much to disturb the regularity of gradations toward the
surface. Water temperatures are primarily dependent
on those of the superincumbent air. The accompany-
ing diagram of comparative yearly air and water
temperatures in Hallstatter Lake (Austria) shows
graphically the diminishing influence of the former on
the latter with increasing depth.

I

10

'O -

>s-

o-
-6.

10'-

o-

10-
Cf-

o-

10-

J-
o-

6-
o

60

1OO

•s-

o-

O

FIG. 5. Diagram illustrating the relation of air and water temperatures at
varying depths of water in Hallstatter Lake (after Lorenz).

34

Nature of Aquatic Environment

FIG. 6. Diagram illustrating the distribution of temperature in Cayuga Lake

throughout the year.

The yearly cycle — The general relation between sur-
face and bottom temperatures for the year are graphi-
cally shown in the accompanying diagram, wherein the
two periods of thermal stratification, "direct'" in summer

"inverse'"

when the warmer waters are uppermost, and
in winter when the colder waters are uppermost, are
separated by two periods of complete circulation, when
all the waters of the lake are mixed at 4° C. The range
of temperatures from top to bottom is much greater in
the summer "stagnation period"; nevertheless there

The Yearly Cycle 35

is more real stagnation during the winter period; for,
after the formation of a protecting layer of ice, this
shuts out the disturbing influence of wind and sun and
all the waters are at rest. The surface temperature
bears no further relation to air temperature but remains
constantly at o° C.

After the melting of the ice in late winter the surface
waters begin to grow warmer; so, they grow heavier,
and tend to mingle with the underlying waters. When
all the water in the lake is approaching maximum
density strong winds heaping the waters upon a lee
shore, may put the entire body of the lake into complete
circulation. How long this circulation lasts will depend
on the weather. It will continue (with fluctuating
vigor) until the waters are warm enough so that their
thermal stratification and consequent resistance to
mixture are great enough to overcome the disturbing
influence of the wind. Thereafter, the surface may be
stirred by storms at any time, but the deeper waters of
the lake will have passed into their summer rest.

On the approach of autumn the cooling of surface
waters starts convection currents, which mix at first the
upper waters only, but which stir ever more deeply as
the temperature descends. When nearly 4°C., with
the aid of winds, the entire mass of water is again put
in circulation. The temperature is made uniform
throughout, and what is more important biologically,
the contents of the lake, in both dissolved and suspended
matters, are thoroughly mixed. Nothing is thereafter
needed other than a little further cooling of the surface
waters to bring about the inverse stratification of the
winter period.

Vernal and autumnal circulation periods differ in
this, that convection currents have a smaller share, and
winds may have a larger share in the former. For the
surface waters are quickly warmed from o° C. to 4° C.,

36 Nature of Aquatic Environment

and further warming induces no descending currents,
but instead tends toward greater stability. It some-
times happens that in shallow lakes there is little vernal
circulation. If the water be warmed at 4° C. at the
bottom before the ice is entirely gone, and if a period
of calm immediately follow, so that no mixing is done
by the wind, there may be no general spring circulation
whatever.

The shallower the lake, other things being equal, the
greater will be the departure of temperature conditions
from those just sketched, for the greater will be the
disturbing influence of the wind. In south temperate
lakes, temperature conditions are, of course, reversed
with the seasons. In tropical lakes whose surface
temperature remains always above 4° C., there can be
no complete circulation from thermal causes, and in-
verse stratification is impossible. In polar lakes, never
freed from ice, no direct stratification is possible.

It follows from the foregoing that gravity alone may
do something toward the warming of the waters in the
spring, and much toward the cooling of them in the fall.
By gravity they will be made to circulate until they
reach the point of maximum density, when going either
up or down the scale. Beyond this point, however,
gravity tends to stabilize them. The wind is responsi-
ble for the further warming of the waters in early sum-
mer, and the heat in excess of 4° C. has been called by
Birge and Juday "wind-distributed" heat. They esti-
mate that it may amount to 30,000 gram-calories per
square centimeter of surface in such lakes as those
of Central New York, and the following figures for
Cayuga Lake show its distribution by depth in August,
1911, in percentage remaining at successive ten-meter
intervals below the surface :

Below o 10 20 30 40 50 60 70 So 100 133 meters
% 100 50.2 16.7 7.1 3.7 2.4 1.8 1.2 .7 .3 remaining

Thermodine 37

These figures indicate the resistance to mixing that
gravity imposes, and show that the wind is not able to
overcome it below rather slight depths.

Vernal and autumnal periods of circulation have a
very great influence upon the distribution of both
organisms and their food materials in a lake; to the
consideration of this we will have occasion to return
later.

The thermocline — In the study of lake temperatures
at all depths, a curious and interesting peculiarity of
temperature interval has been commonly found per-
taining to the period of direct stratification (mid-
summer). The descent in temperature is not regular
from surface to bottom, but undergoes a sudden acceler-
ation during a space of a very few meters some distance
below the surface. The stratum of water in which
this sudden drop of temperature occurs is known as the
thermocline (German, Sprungschiclit]. It appears to
represent the lower limit of the intermittent summer
circulation due to winds. Above it the waters are more
or less constantly stirred, below it they lie still. This
interval is indicated by the shading on the right side of
figure 4. Birge has designated the area above the
thermocline as the epilimnion; the one below it as
hypolimnion.

Further study of the thermocline has shown that it is
not constant in position. It rises nearer to the surface
at the height of the midsummer season and descends a
few meters with the progress of the cooling of the
autumnal atmosphere. This may be seen in figure 7,
which is Birge and Juday's chart of temperatures of
Lake Mendota as followed by them through the season
of direct stratification and into the autumnal circula-
tion period in 1906. This chart shows most graphically
the growing divergence of surface and bottom tempera-
tures up to August, and their later approximation and

Nature of Aquatic Environment

final coalescence in October. Leaving aside the not
unusual erratic features of surface temperature (repre-
sented by the topmost contour line) it will be noticed
that there is a wider interval somewhere between 8 and
1 6 meters than any other interval either above or below
it. Sometimes it falls across two spaces and is rendered
less apparent in the charting by the selection of inter-
vals. It first appears clearly in June at the 10-12 meter
interval. It rises in July above the 10 meter level.

FIG. 7. Temperature of the water at different depths in Lake Mendota in
1906. The vertical spaces represent degrees Centigrade and the figures
attached to the curves indicate the depths in meters. (Birge and Juday).

In the middle of August it lies above the 8 meter level,
though it begins to descend later in the month. It
continues to descend through September, and is found
in early October between 16 and 18 meters. It dis-
appears with the beginning of the autumnal circulation.
The cause of this phenomenon is not known. Richter
has suggested that convection currents caused by the
nocturnal cooling of the surface water after hot summer
days may be the cause of it. If the surface waters were

Circulation 39

cooled some degrees they would descend, displacing the
layers underneath and setting up shallow currents
which would tend to equalize the temperature of all the
strata involved therein. And if the gradation of tem-
peratures downward were regular before this mixing,
the result of it would be a sudden descent at its lower
limit, after the mixing was done. This would account
for the upper boundary of the thermocline, but not for
its lower one. Perhaps an occasional deeper mixing,
extending to its lower boundary, and due possibly to
high winds, might bring together successional lower
levels of temperature of considerable intervals. Perhaps
the thermocline is but an accumulation of such sort of
thermal disturbance-records, ranged across the vertical
section of the lake, somewhat as wave-drift is ranged in
a shifting zone along the middle of a sloping beach.
At any rate, it appears certain that the thermocline
marks the lower limit of the chief disturbing influences
that act upon the surface of the lake. That it should
rise with the progress of summer is probably due to the
increasing stability of the lower waters, as differences
in temperature (and therefore in density) between upper
and lower strata are increased. Resistance to mixing
increases until the maximum temperature is reached,
and thereafter declines, as the influence of cooling and
of winds penetrates deeper and deeper.

In running water the mixing is more largely mechani-
cal, and vertical circulation due to varying densities is
less apparent. Yet the deeper parts of quiet streams
approximate closely to conditions found in shallow
lakes. Such thermal stratification as the current
permits is direct in summer and inverse in winter, and
there are the same intervening periods of thermal over-
turn when the common temperature approaches 4° C.
In summer and in winter there is less "stagnation" of
bottom waters owing to the current of the stream.

40 Nature of Aquatic Environment

The thermal conservatism of water — Water is slower
to respond to changes of temperature than is any other
known substance. Its specific heat is greater. The
heat it consumes in thawing (and liberates in freezing)
is greater. The amount of heat necessary to melt one
part of ice at o° C. without raising its temperature at all
would be sufficient to raise the temperature of the same
when melted more than 75 degrees. Furthermore, the
heat consumed in vaporization is still greater. The
amount required to vaporize one part of water at 100° C.
without raising its temperature would suffice to raise
534 parts of water from o° C. to i° C. ; and the amount
is still greater when vaporization occurs at a lower
temperature. Hence, the cooling effect of evaporation
on the surrounding atmosphere, which gives up its
heat to effect this change of state in the water; hence,
the equalizing effect upon climate of the presence of
large bodies of water; hence the extreme variance
between day and night temperatures in desert lands;
hence the delaying of winter so along after the autumnal,
and of summer so long after the vernal equinox.
Water is the great stabilizer of temperature.

The content of natural waters — Water is the common
solvent of all foodstuffs. These stuffs are, as every-
body knows, such simple mineral salts as are readily
leached out of the soil, and such gases as may be washed
down out of the atmosphere. And since green plants
are the producing class among organisms, all others
being dependent on their constructive activities, water
is fitted to be the home of life in proportion as it con-
tains the essentials of green plant foods, with fit condi-
tions of warmth, air and light.

Natural waters all contain more or less of the elemen-
tary foodstuffs necessary for life. Pure water (H2O)
is not found. All natural waters are mineralized
waters — even rain, as it falls, is such. And a compara-

Natural Waters 41

tively few soluble solids and gases furnish the still
smaller number of chemical elements that go to make
up the living substance. The amount of dissolved
solids varies greatly, being least in rainwater, and
greatest in dead seas, which, lacking outlet, accumulate
salts through continual evaporation. Here is a rough
statement of the dissolved solids in some typical waters :

In rain water 30— 40 parts per million

In drainage water off siliceous soils 50— So

In springs flowing from siliceous soils 60— 250

In drainage water off calcareous soils 1 40— 230
In springs flowing from calcareous

soils 300— 660

In rivers at large 120— 350

In the ocean 33000 — 37370

Thus the content is seen to vary with the nature of
the soils drained, calcareous holding a larger portion of
soluble solids than siliceous soils. It varies with
presence or absence of solvents. Drainage waters from
cultivated lands often contain more lime salts than do
springs flowing from calcareous soils that are deficient
in carbon dioxide. Spring waters are more highly
charged than other drainage waters, because of pro-
longed contact as ground water with the deeper soil
strata. And evaporation concentrates more or less
the content of all impounded waters.

All natural waters contain suspended solids in great
variety. These are least in amount in the well filtered
water of springs, and greatest in the water of turbu-
lent streams, flowing through fine soils. At the con-
fluence of the muddy Missouri and the clearer
Mississippi rivers the waters of the two great currents
may be seen flowing together but uncommingled for
miles.

The suspended solids are both organic and inorganic,
and the organic are both living and dead, the latter

42 Nature of Aquatic Environment

being plant and animal remains. From all these non-
living substances the water tends to free itself: The
lighter organic substances (that are not decomposed
and redissclved) are cast on shore ; the heavier mineral
substances settle to the bottom. The rate of settling
is dependent on the rate of movement of the water and
on the specific gravity and size of the particles. Fall
Creek at Ithaca gives a graphic illustration of the carry-
ing power of the current. In the last mile of its course,
included between the Cornell University Campus and
Cayuga Lake, it slows down gradually from a sheer
descent of 78 ft. at the beautiful Ithaca Fall to a scarcely
perceptible current at the mouth. It carries huge
blocks of stone over the fall and drops them at its foot.
It strews lesser blocks of stone along its bed for a quar-
ter of a mile to a point where the surface ceases to break
in riffles at low water. There it deposits gravel, and
farther along, beds and bars of sand, some of which
shift position with each flood rise, and consequent
acceleration. It spreads broad sheets of silt about its
mouth and its residual burden of finer silt and clay it
carries out into the lake. The lake acts as a settling
basin. Flood waters that flow in turbid, pass out
clear.

Whipple has given the following figures for rate of
settling as determined by size, specific gravity and form
being constant:

Velocity of particles falling through water
Diameter i. inch, falls 100. feet per minute.

. i if t( q " " "

!oi " " !is " "

.001 " " .0015 " "
.0001 " .000015 " "

Suspended mineral matters are, as a rule, highly
insoluble. Instead of promoting, they lessen the
productivity of the water by shutting out the light.

Gases from the Atmosphere 43

Suspended organic solids likewise contribute nothing
to the food supply as long as they remain undissolved.
But when they decay their substance is restored to
circulation. Only the dissolved substances that are
in the water are at once available for food. The soil
and the atmosphere are the great storehouses of these
materials, and the sources from which they were all
originally derived.

Gases from the atmosphere— -The important gases
derived from the atmosphere are two: carbon dioxide
(CO2) and oxygen (O). Nitrogen is present in the
atmosphere in great excess (N, 79% to O, nearly 21%,
and CO2, .03%), and nitrogen, is the most important
constituent of living substance, but in gaseous form,
free or dissolved, it is not available for food. The
capacity of water for absorbing these gases varies with
the temperature and the pressure, diminishing as
warmth increases (insomuch that by boiling they are
removed from it), and increasing directly as the pres-
sure increases. Pure water at a pressure of 760 mm. in
an atmosphere of pure gas, absorbs these three as
follows :

Oxygen CO2 Nitrogen

At o°C 41-14 1796.7 20.35

At 20°C 28.38 901.4 14.03

At double the pressure twice the quantity of the gas
would be dissolved. Natural waters are exposed not
to the pure gas but to the mixture of gases which make
up the atmosphere. In such a mixture the gases are
absorbed independently of each other, and in propor-
tion to their several pressures, which vary as their
several densities: the following table* shows, for

*Abridged from a table of values to tenths of a degree by Birge and Juday
in Bull. 22, Wise. Geol. & Nat. Hist. Survey, p. 20.

44 Nature of Aquatic Environment

example, the absorbing power of pure water at various
temperatures for oxygen from the normal atmosphere
at 760 mm. pressure:

Water at o°C 9.70 cc. per liter at i5°C 6.96 cc. per liter

" s°C 8.68cc. " " " 2o°C 6.28cc. " "

" io°C 7.7700. " " " 2S°C 5.7600. " "

The primary carbon supply for the whole organic
world is the carbon dioxide (CO2) of the atmosphere.
Chlorophyll-bearing plants are the gatherers of it.
They alone among the organisms are able to utilize the
energy of the sun's rays. The water existing as vapor
in the atmosphere is the chief agency for bringing these
gases down to earth for use. Standing water absorbs
them at its surface but slowly. Water vapor owing to
better exposure, absorbs them to full saturation, and
then descends as rain. In fresh water they are found in
less varying proportion, varying from none at all to con-
siderable degree of supersaturation. Birge and Juday
report a maximum occurrence of oxygen as observed in
the lakes of Wisconsin of 25.5 cc. per liter in Knight's
Lake on Aug. 26, 1909 at a depth of 4.5 meters. This
water when brought to the surface (with consequent
lowering of pressure by about half an atmosphere)
burst into lively effervescence, with the escape of a
considerable part of the excess oxygen into the air.
('n, p. 52). They report the midsummer occurrence
of free carbon dioxide in the bottom waters of several
lakes in amounts approaching 15 cc. per liter.

The reciprocal relations of C02 and 0 — Carbon dioxide
and oxygen play leading roles in organic metabolism,
albeit, antithetic roles. The process begins with the
cleavage of the carbon dioxide, and the building up of
its carbon into organic compounds; it ends with the
oxidation of effete carbonaceous stuffs and the reappear-
ance of CO o. Both are used over and over again.

Carbon Dioxide and Oxygen 45

Plants require CO2 and animals require oxygen in order
to live and both live through the continual exchange of
these staple commodities. This is the best known
phase in the cycle of food materials. The oxygen is
freed at the beginning of the synthesis of organic mat-
ter, only to be recombined with the carbon at the end
of its dissolution. And the well-being of the teeming
population of inland waters is more dependent on the
free circulation and ready exchange of the dissolved
supply of these two gases than on the getting of a new
supply from the air.

The stock of these gases held by the atmosphere is
inexhaustible, but that contained in the water often
runs low; for diffusion from the air is slow, while
consumption is sometimes very rapid. We often have
visible evidence of this. In the globe in our win-
dow holding a water plant, we can see when the sun
shines streams of minute bubbles of oxygen, arising
from the green leaves. Or, in a pond we can see
great masses of algae floated to the surface on a foam
of oxygen bubbles. We cannot see the disappearance
of the carbon dioxide but if we test the water we find
its acidity diminishing as the carbon dioxide is con-
sumed.

At times when there is abundant growth of algae near
the surface of a lake there occurs a most instructive
diurnal ebb and flow in the production of these two
gases. By day the wTell lighted layers of the water
become depleted of their supply of CO2 through the
photosynthetic activities of the algae, and become
supersaturated with the liberated oxygen. By night
the microscopic crustaceans and other plancton animals
rise from the lower darker strata to disport themselves
nearer the surface. These consume the oxygen and
restore to the water an abundance of carbon dioxide.
And thus when conditions are right and the numbers of

46 Nature of Aquatic Environment

plants and animals properly balanced there occur
regular diurnal fluctuations corresponding to their
respective periods of activity in these upper strata.

Photosynthesis is, however, restricted to the better
lighted upper strata of the water. The region of
greatest carbon consumption is from one to three meters
in depth in turbid waters, and of ten meters or more in
depth in clear lakes. Consumption of oxygen, however,
goes on at all depths, wherever animal respiration or
organic decomposition occurs. And decomposition
occurs most extensively at the bottom where the organic
remains tend to be accumulated by gravity. With a
complete circulation of the water these two gases may
continue to be used over and over again, as in the exam-
ple just cited. But, as we have seen, there is no circula-
tion of the deeper water during two considerable periods
of the year; and during these stagnation periods the
distribution of these gases in depth becomes correlated
in a wonderful way with the thermal stratification of
the water. This has been best illustrated by the work
of Birge and Juday in Wisconsin. Figure 8 is their
diagram illustrating the distribution of free oxygen in
Mendota Lake during the summer of 1906. It should
be studied in connection with figure 7, which illustrates
conditions of temperature. Then it will be seen that
the two periods of equal supply at all levels correspond
to vernal and autumnal circulation periods. The
season opens with the water nearly saturated (8 cc. of
oxygen per liter of water) throughout. With the warm-
ing of the waters the supply begins to decline, being
consumed in respiration and in decomposition. In the
upper six or seven meters the decline is not very exten-
sive, for at these depths the algae continually renew the
supply. But as the lower strata settle into their sum-
mer rest their oxygen content steadily disappears, and
is not renewed until the autumnal overturn. For three

Summer Stagnation

47

months there is no free oxygen at the bottom of the
lake, and during August there is not enough oxygen
below the ten meter level to keep a fish alive.

Correspondingly, the amount of free CO2 in the
deeper strata of the lake increases rather steadily until
the autumnal overturn. It is removed from circulation,
and in so far as it is out of the reach of effective light,
it is unavailable for plant food.

8 i-

\ .x v\v

r\ \ -f- ^^y r~%

' , \ / „ V7

i \ \ , t /\ A

FIG. 8. Dissolved oxygen at different depths in Lake Mendota in 1906. The
vertical spaces represent cubic centimeters of gas per liter of water and
the figures attached to the curves indicate the depths in meters. (Birge
and Juday.)

Other gases — A number of other gases are more or
less constantly present in the water. Nitrogen, as
above stated, being absorbed from the air, methane
(CH4), and other hydrocarbons, and hydrogen sulphide
(H2S), etc., being formed in certain processes of decom-

48 Nature of Aquatic Environment

position. Of these, methane or marsh gas, is perhaps
the most important. This is formed where organic
matter decays in absence of oxygen. In lakes such
conditions are found mainly on the bottom. In marshes
and stagnant shoal waters generally, where there is
much accumulation of organic matter on the bottom,
this gas is formed in abundance. It bubbles up through
the bottom ooze, or often buoys up rafts of agglutinated
bottom sediment.

Nitrogen— -The supply of nitrogen for aquatic organ-
isms is derived from soluble simple nitrates (KNO3,
NaNO3, etc.) Green plants feed on these, and build
proteins out of them. And when the plants die (or
when animals have eaten them) their dissolution yields
two sorts of products, ammonia and nitrates, that
become again available for plant food. Ammonia is
produced early in the process of decay and the nitrates
are its end products.

Bacteria play a large role in the decomposition of
proteins. At least four groups of bacteria successively
participate in their reduction. The first of these are
concerned with the liquefaction of the proteins, hydroly-
zing the albumins, etc., by successive stages to albu-
moses, peptones, etc., and finally to ammonia. A
second group of bacteria oxidizes the ammonia to
nitrites. A third group oxidizes the nitrites to
nitrates. A fourth group, common in drainage waters,
reduces nitrates to nitrites. Since these processes are
going on side by side, nitrogen is to be found in all
these states of combination when any natural water is
subjected to chemical analysis. The following table
shows some of the results of a large number (415) of
analyses of four typical bottomland bodies of water,
made for Kofoid's investigation of the plancton of the
Illinois River by Professor Palmer.

Nitrogen

49

The relative productiveness in open-water life of
these situations is shown in the last column of the table.

In parts
per million

Solids

Free
Ammonia

Organic
Nitrogen

Nitrites

Nitrates

Plancton
cms per
m3

Sus-
pended

Dis-
solved

Illinois River .

61.4

304.1

.860

1.03

.147

i-S9

I.9I

Spoon River .

274-3

167.1

•245

I.2Q

•°39

1. 01

•39

Quiver Lake .

2S.I

248.2

.165

.61

.023

.66

1.62

Thompson's L.

44.6

282.9

.422

I.OS

.048

.64

6.68

The difference between these four adjacent bodies of
water explains some of the peculiarities of the table.
The rivers hold more solids in suspension than do the
lakes, although these lakes are little more than basins
holding impounded river waters. Spoon River holds
the least amount of dissolved solids, and by far the
greatest amount of suspended solids. Since the latter
are not available for plant food, naturally this stream
is least productive of plancton. Illinois River drains a
vast and fertile region, and receives in its course the
sewage and other organic wastes of two large cities,
Chicago and Peoria, and of many smaller ones. Hence,
its high content of dissolved matter, the cities being
remote, so there has been time for extensive liquefac-
tion. Hence, also, its high content of ammonia, of
nitrites and of nitrates.

The two lakes are very unlike ; Quiver Lake is a mere
strip of shoal water, fed by a clear stream that flows in
through low sandy hills. It receives water from the
Illinois River only during high floods. Thompson's
Lake is a much larger body of water, fed directly from
the Illinois River through an open channel. Naturally,
it is much like the river in its dissolved solids, and in its
total organic nitrogen. That it falls far below the
river in nitrates and rises high above it in plancton
production may perhaps be due to the extensive con-

Nature of Aquatic Environment

sumption of nitrates by plancton algae. Nitrates, be-
cause they furnish nitrogen supply in the form at once
available for plant growths, are, in shallow waters at
least, an index of the fertility of the water. As on
land, so in the water, the supply of these may be
inadequate for maximum productiveness, and they may
be added with profit as fertilizer.

The carbonates — Lime and magnesia combine with
carbon dioxide, abstracting it from the water, forming

FIG. 9. Environs of the Biological Field Station of the Illinois State Labora-
tory of Natural History, the scene of important work by Kofoid and others

on the life of a great river.

solid carbonates (CaCO3 and MgCO3). These accumu-
late in quantities in the shells of molluscs, in the stems
of stoneworts, in the incrustations of certain pond
weeds, and of lime- secret ing algae. The remains of
such organisms accumulate as marl upon the bottom.
The carbonates (and other insoluble minerals) remain;
the other body compounds decay and are removed.
By such means in past geologic ages the materials for
the earth's vast deposits of limestone were accumu-

The Carbonates 51

lated. Calcareous soils contain considerable quantities
of these carbonates.

In pure water these simple carbonates are practically
insoluble; but when carbon dioxide is added to the
water, they are transformed into bicarbonates* and are
readily dissolved.! So the carbonates are leached out
of the soils and brought back into the water. So, the
solid limestone may be silently removed, or hollowed out
in great caverns by little underground streams. So
the Mammoth Cave in Kentucky, and others in Cuba,
in Missouri, in Indiana and elsewhere on the continent,
have been formed.

The water gathers up its carbon dioxide in part as it
descends through the atmosphere, and in larger part as
it percolates thro soil where decomposition is going on
and where oxidation products are added to it.

Carbon dioxide, thus exists in the water in three
conditions : ( I ) Fixed (and unavailable as plant food)
in the simple carbonates; (2) "half -bound" in the
bicarbonates; and (3) free. Water plants use first for
food, the free carbon dioxid, and then the "half bound"
that is in loose combination in the bicarbonates. As
this is used up the simple carbonates are released, and
the water becomes alkaline. § Birge and Juday have
several times found a great growth of the desmid
Staurastrum associated with alkalinity due to this
cause. In a maximum growth which occurred in
alkaline waters at a depth of three meters in Devil's
Lake, Wisconsin, on June I5th, 1907, these plants
numbered 176,000 per liter of water.

*CaCOs, for example, becoming Ca(HCO3)2, the added part of the formula
representing a molecule each of CO2 and H^O.

flf "hard" water whose hardness is due to the presence of these bicarbonates
be boiled, the CO2 is driven off and the simple carbonates are re-precipitated (as,
for example, on the sides and bottom of a tea kettle). This is "temporary
hardness." "Permanent hardness" is due to the presence of sulphates and
chlorides of lime and magnesia, which continue in solution after boiling.

§Phenolphthalein, being used as indicator of alkalinity.

52 Nature of Aquatic Environment

Waters that are rich in calcium salts, especially in
calcium carbonate, maintain, as a rule, a more abundant
life than do other waters. Especially favorable are
they to the growth of those organisms which use much
lime for the building of their hard parts, as molluscs,
stoneworts, etc. There are, however, individual pref-
erences in many of the larger groups. The crustaceans
for example, prefer, as a rule, calcium rich waters, but
one of them, the curious entomostracan, Holopedium
gibberum, (Fig. 10) is usually found in
calcium poor waters, in lakes in the
Rocky Mountains and in the Adiron-
dacks, in waters that flow off
archasan rocks or out of silic-
eous sands. The desmids
with few exceptions are more
abundant in calcium poor
waters. The elegant genus
micrasterias is at Ithaca espec- ^

ia11v abundant in thp neat FlG" I0- A gelatinous-coated mi-
laiiy aDUnaani peat- cr0crustacean, Holopedium gib-

Stained Calcium-pOOr waters berum, often found in waters

of sphagnum bogs. that are poor in calcium-

Other minerals in the water — The small quantities of
other mineral substances required for plant growth are
furnished mainly by a few sulphates, phosphates and
chlorids: sulphates of sodium, potassium, calcium
and magnesium; phosphates of iron, aluminum, cal-
cium and magnesium, and chlorids of sodium, potas-
sium, calcium and magnesium. Aluminum alone of
the elements composing the above named compounds,
is not always requisite for growth, although it is very
often present. Silica, likewise, is of wide distribution,
and occurs in the water in considerable amounts, and
is used by many organisms in the growth of their hard
parts. As the stoneworts use lime for their growth,
some 4% of the dry weight of Chara being CaO, so

Mineral Content

53

very

diatoms require silica to build their shells. When the
diatoms are dead their shells, relatively heavy though
extremely minute, slowly settle to the bottom, slowly
dissolving; and so, analyses of lake waters taken at
different depths usually show increase of silica toward
the bottom.

Iron, common salt,
sulphur, etc., often
occur locally in great
abundance, notably in
springs flowing from
special deposits, and
when they occur they
possess a fauna and
flora of marked pecu-
liarities and
limited extent.

An idea of the rela-
tive abundance of the
commoner mineral
substances in lake
waters may be had
from the following
figures that are con-
densed from Birge and

FIG ii A beautiful green desmid.Mzcra- Juday's report of 74
stenas that is common in bog waters. i

analyses.

MINERAL CONTENT OF WISCONSIN LAKES
Parts per million

F12O3 +

SiO2 A13O3 Ca Mg Na K CO3 HCO3

0.4 0.6 0.3 0.3 0.3

11.2 49.6 32.7 6.2 3.1

2.1 26.9 19.6 3.2 2.2

Minimum
Maximum
Average

o.S
33.0
11.7

o.o
12. o

2.1

4-9

91.7

SO4

o.o

18.7

9.8

Cl

i-S

10.0

3-9

This is the bill of fare from which green water plants
may choose. Forel aptly compared the waters of a

54 Nature of Aquatic Environment

lake to the blood of the animal body. As the cells of
the body take from the blood such of its content as is
suited to their need, so the plants and animals of the
water renew their substance out of the dissolved sub-
stances the water brings to them.

Organic substances dissolved in the water may so
affect both its density and its viscosity as to determine
both stratification and distribution of suspended solids.
This is a matter that has scarcely been noticed by
limnologists hitherto. Dr. J. U. Lloyd ('82) long ago
showed how by the addition of colloidal substances to a
vessel of water the whole contents of the vessel can be
broken into strata and these made to circulate, each at
its own level, independent of the other strata. Solids
in suspension can be made to float at the top of particu-
lar strata, according to density and surface tension.

Perhaps the "false bottom" observed in some north-
ern bog-bordered lakes is due to the dissolved colloids
of the stratum on which it floats. Holt ('08, p. 219)
describes the "false bottom" in Sumner Lake, Isle
Royal, as lying six to ten feet below the surface, many
feet above the true bottom ; as being so tenuous that a
pole could be thrust through it almost as readily as
through clear water; and as being composed of fine
disintegrated remains of leaves and other light organic
material. "In places there were great breaks in the
'false bottom,' doubtless due to the escape of gases
which had lifted this fine ooze-like material from a
greater depth: and through these breaks one could
look down several feet through the brownish colored
water. ' '

Perhaps the colloidal substances in solution are
such as harden upon the surface of dried peat, like a
water-proof glue, making it for a time afterward imper-
vious to water.

WATER AND
LAND

CEANS are the earth's
great storehouse of water.
They cover some eight-
elevenths of the surface
of the earth to an average
depth of about two miles.
They receive the off -flow
from all the continents
^^^^^^^^ and send it back by way

of the atmosphere.

The fresh waters of the earth descend in the first
instance out of the atmosphere. They rise in vapor
from the whole surface of the earth, but chiefly from
the ocean. Evaporation frees them from the ocean's
salts, these being non-volatile. They drift about with
the currents of the atmosphere, gathering its gases to
saturation, together with very small quantities of drift-
ing solids; they descend impartially upon water and
land, chiefly as rain, snow and hail.

They are not distributed uniformly over the face of
the continents for each continent has its humid regions
and its deserts. Rainfall in the United States varies
from 5 to 100 inches per annum. Two-thirds of it
falls on the eastern three-fifths of the country. For the
Eastern United States it averages about 48 inches, for
the Western United States about 12 inches ; the average
for the whole is about 30 inches. The total annual
precipitation is about 5,000,000,000 acre-feet.*

*An acre-foot is an acre of water i foot deep or 43,560 cubic feet of water.

55

56 Water and Land

It is commonly estimated that at least one-half of
this rainfall is evaporated, in part from soil and water
surfaces, but much more from growing vegetation; for
the transpiration of plants gives back immense quanti-
ties of water to the atmosphere. Hellriegel long ago
showed that a crop of corn requires 300 tons of water
per acre: of potatoes or clover, 400 tons per acre. At
the Iowa Agricultural Experiment Station it was shown
that an acre of pasturage requires 3,223 tons of water,
or 28 inches in depth (2^ acre-feet). Before the days
of tile drainage it was a not uncommon practice to
plant willow trees by the edges of swales, in order that
they might carry off the water through their leaves,
leaving the ground dry enough for summer cropping.
The rate of evaporation is accelerated also, by high
temperatures and strong winds.

The rain tends to wet the face of the ground every-
where. How long it will stay wet in any given place
will depend on topography and on the character of the
soil as well as on temperature and air currents. Show-
ers descending intermittently leave intervals for com-
plete run-off of water from the higher ground, with
opportunity for the gases of the atmosphere to enter
and do their work of corrosion. The dryer intervals,
therefore, are times of preparation of the materials
that will appear later in soil waters. Yet all soils in
humid regions retain sufficient moisture to support a
considerable algal flora. Periodical excesses of rainfall
are necessary also to maintain the reserve of ground
water in the soil. Suppose, for example, that the 35
inches of annual rainfall at Ithaca were uniformly
distributed. There would be less than one-tenth of an
inch of precipitation each day — an amount that would
be quickly and entirely evaporated, and the ground
would never be thoroughly wet and there would be no
ground water to replenish the streams. Storm waters

Soil and Stream-flow 57

tend to be gathered together in streams, and thus about
one- third of our rainfall runs away. In humid areas
small streams converge to form larger ones, and flow
onward to the seas. In arid regions they tend to
spread out in sheet floods, and to disappear in the sands.

In a state of nature little rain water runs over the
surface of the ground, apart from streams. It mainly
descends into the soil. How much the soil can hold
depends upon its composition. Dried soils have a
capacity for taking up and holding water about as fol-
lows: sharp sand 25%, loam 50%, clay 60%, garden
mould 90% and humus 1 80% of their dry weight. Water
descends most rapidly through sand and stands longest
upon the surface of pure clay. Thick vegetation with
abundant leaf fall, and humus in the soil tend to hinder
run-off of storm waters, and to prolong their passage
through the soil. Thus the excess of rainfall is gradually
fed into the streams by springs and seepage. Under
natural conditions streams are usually clear, and their
flow is fairly uniform.

Unwise clearing of the land and negligent cultivation
of the soil facilitate the run-off of the water before the
storm is well spent, promote excessive erosion and
render the streams turbid and their volume abnormally
fluctuating. Little water enters the soil and hence the
springs dry up, and the brooks, also, as the seepage of
ground water ceases. Two great evils immediately
befall the creatures that live in the streams and pools:
( i ) There is wholesale direct extermination of them with
the restriction of their habitat at low water. (2) There
occurs smothering of them under deposits of sediment
brought down in time of floods, with indirect injury to
organisms not smothered, due to the damage to their
foraging grounds.

The waters of normal streams are derived mainly
from seepage, maintained by the store of water accumu-

58 Water and Land

lated in the soil. This store of ground water amounts
according to recent estimates to some 25% of the bulk
of the first one hundred feet in soil depth. Thus it
equals a reservoir of water some 25 feet deep covering
the whole humid eastern United States. It is con-
tinuous over the entire country. Its fluctuations are
studied by means of measurements of wells, especially
by recording the depth of the so-called "water table."
On the maintenance of ground water stream-flow and
organic productiveness of the fields alike depend.

CHAPTER III

YPES OF AQUAT
ENVIRONMENT

o

I. LAKES AND
PONDS

UT of the atmosphere
comes our water supply
-the greatest of our
natural resources. It
falls on hill and dale,
and mostly descends

into the soil. The ex-
cess off-flowing from the

surface and outflowing from springs and seepage, forms
water masses of various sorts according to the topo-
graphy of the land surface. It forms lakes, streams or
marshes according as there occur basins, channels or
only plant accumulations influencing drainage.

The largest of the bodies of water thus formed are
the lakes. Our continent is richly supplied with them,
but they are of very unequal distribution. The lake
regions in America as elsewhere are regions of compara-
tively recent geological disturbance. Lakes thickly
dot the peninsula of Florida, the part of our continent
most recently lifted from the sea. Over the northern
recently glaciated part of the continent they are

59

60 Types of Aquatic Environment

innumerable, but in the great belts of corn and cotton,
and on the plains to the westward, they are few and
far between. They are abundant in the regions of more
recent volcanic disturbance in our western mountains,
but are practically absent from the geologically older
Appalachian hills. They lie in the depressions between
the recently uplifted lava blocks of southern Oregon.
They occur also in the craters of extinct volcanoes.
They are apt to be most picturesque when their setting
is in the midst of mountains. There are probably no
more beautiful lakes in the world than some of those in
the West, such as Lake Tahoe (altitude 6200 ft.) on the
California-Nevada boundary, and Lake Chelan in the
state of Washington*, to say nothing of the Coeur
d'Alene in Idaho and Lake Louise in British Columbia.
Eastward the famous lake regions that attract most
visitors are those of the mountains of New York and
New England, those of the woodlands of Michigan and
Wisconsin and those of the vast areas of rocks and water
in Canada.

Lakes are temporary phenomena from the geologists
point of view. No sooner are their basins formed than
the work of their destruction begins. Water is the
agent of it, gravity the force employed, and erosion
the chief method. Consequently, other things being
equal, the processes of destruction go on most rapidly
in regions of abundant rainfall. Inwash of silt from
surrounding slopes tends to fill up their basins. The
most extensive filling is about the mouths of inflowing
streams, where mud flats form, and extend in Deltas
out into the lake. These deltas are the exposed sum-
mits of great mounds of silt that spread out broadly
underneath the water on the lake floor. At the shore-
lines these deposits are loosened by the frosts of winter,

*Descriptions of these two lakes will be found in Russell' s Lakes of North
America.

Lakes Temporary Phenomena

61

pushed about by the ice floes of spring, and scattered
by every summer storm, but after every shift they set-
tle again at lower levels. Always they are advancing
and filling the lake basin. The filling may seem slow
and insignificant on the shore of one of the Great Lakes
but its progress is obvious in a mill pond, and the dif-
ference is only relative.

FIG. 12. An eroding bluff on the shore of Lake Michigan that is receding at
the rate of several feet each year. The broad shelving beach in the fore-
ground is sand, where the waves ordinarily play. Against the bare rising
boulder-strewn strip back of this, the waves beat in storms; at its summit
they gather the earth-slides from the bank above and carry them out into
the lake. The black strip at the rear of the sand is a line of insect drift,
deposited at the close of a midsummer storm by the turning of the wind on
shore.

On the other hand, lakes disappear with the cutting
down of the rim of their basins in outflow channels. The
Niagara river, for example, is cutting through the lime-

62

Types of Aquatic Environment

stone barrier that retains Lake Erie. At Niagara
Falls it is making progress at the rate of about five feet
a year. Since the glacial period it has cut back from
the shore of Lake Ontario a distance of some seventeen
miles, and if the process continues it will in time
empty Lake Erie.

FIG. 13. Evans' Lake, Michigan; a lake in process of being filled by encroach-
ment of plants. A line of swamp loose-strife (Decodon) leads the invading
shore vegetation. Further inwash of silt or lowering of outlet is precluded
by density of the surrounding heath. The plants control its fate.

Photo by E. McDonald.

When the glacier lay across the St. Lawrence valley,
before it had retreated to the northward, all the waters
of the great lakes region found their way to the ocean
through the Mohawk Valley and the Hudson. At that
time a similar process of cutting an outlet through a
limestone barrier was going on near the site of the
present village of James ville, New York, where on the

The Great Lakes

Clark Reservation one may see today a series of
abandoned cataracts, dry rock channels and plunge
basins. Green Lake at present occupies one of these
old plunge basins, its waters, perhaps a hundred feet
deep, are surrounded on all sides but one, by sheer
limestone cliffs nearly two hundred feet high.

When lakes become populated then the plants and
animals living in the water and about the shore line
contribute their remains to the final filling of the basin.
This is well shown in figure 13.

The Great Lakes con-
stitute the most magnifi-
cent system of reservoirs
of fresh water in the world ;
five vast inland seas,
whose shores have all the
sweep and majesty of the
ocean, no land being visi-
ble across them. All but
one (Erie) have the bot-
tom of their basins below
the sea level. Their area,
elevation and depth are
as follows:

FIG. 14. The larger lakes and rivers of

North America.

Area in Surface
sq. mi. alt. in ft.

Lake Ontario 7.240 247

" Erie 9-960 573

" Huron* 23.800 581

" Michigan 22.450 581

" Superior 31.200 602

*Including Georgian Bay.
t Approximate.

They are stated by Russell to contain enough water
to keep a Niagara full-flowing for a hundred years.

Depth in feet
meant maximum

738

2IO

730
870
I.OOS

300

70

250

325

475

64 Types of Aquatic Environment

The Finger Lakes of the Seneca basin in Central New
York constitute an unique series occupying one section
of the drainage area of Lake Ontario, with which they
communicate by the Seneca and Oswego rivers. They
occupy deep and narrow valleys in an upland plateau
of soft Devonian shales. Their shores are rocky and
increasingly precipitous near their southern ends. The
marks of glaciation are over all of them. Keuka, the
most picturesque of the series, occupies a forking valley
partially surrounding a magnificent ice-worn hill.
The others are all long and narrow and evenly contoured,
without islands (save for a single rocky islet near the
east Cayuga shore) or bays.

The basins of these lakes invade the high hills to the
southward, reaching almost to the head-waters of
the tributaries of the Susquehanna River. Here
there is found a wonderful diversity of aquatic situa-
tion. At the head of Cayuga Lake, for example,
beyond the deep water there is a mile of broad shelving
silt-covered lake bottom, ending in a barrier reef.
Then there is a broad flood plain, traversed by deep
slow meandering streams, and covered in part by
marshes. Then come the hills, intersected by narrow
post-glacial gorges, down which dash clear streams
in numerous beautiful waterfalls and rapids. Back
of the first rise of the hills the streams descend more
slowly, gliding along over pebbly beds in shining
riffles, or loitering in leaf -strewn woodland pools.
A few miles farther inland they find their sources in
alder-bordered brooks flowing from sphagnum bogs and
upland swales and springs.

Thus the waters that feed the Finger Lakes are
all derived from sources that yield little aquatic
life, and they run a short and rapid course among
the hills, with little time for increase by breeding:
hence they contribute little to the population of the

The Finger Lakes

6.5

Vi

lake. They bring in constantly, however, a supply
of food materials, dissolved from the soils of the
hills.

Bordering the Finger Lakes there 'are no extensive
marshes, save at the ends
of Cayuga, and the chief
irregularities of outline
are formed by the deltas
o f inflowing streams.
The two large central
lakes, Cayuga and Sen-
eca, have their basins
extending below the sea
level. Their sides are
bordered by two steeply -
rising, smoothly eroded
hills of uniform height,
between which they lie
extended like wide placid
rivers. The areas, eleva-
tions and depths of the
five are as follows:

FIG. i s.

The Finger Lakes of Central
New York.

A, Canandaigua; B, Keuka; C, Seneca; D,
Cayuga; E.Owasco; F, Skaneateles; G. Otisco;
H, the Seneca River; I, The arrow indicates the
location of the Cornell University Biological
Field Station at Ithaca. The stippled area at
the opposite end of Cayuga Lake marks the
location of the Montezuma Marshes.

Area

sq. mi.

Lake Skaneateles 13.9

Owasco 10.3

Cayuga 66.4

Seneca 67.7

" Keuka 18.1

Canandaigua 16.3

Surface
alt. in ft.

867
710
38i

444
709
686

Depth in feet
mean maximum

142

95
177
288

99
126

297

177
435
618

183
274

Birge and Juday found the transparency of four of
these lakes as measured by Secchi's disc in August, 1910,
to be as follows:

Canandaigua 12.0 ft. Seneca 27.0 ft.

Cayuga 16.6 ft. Skaneateles 33.5 ft.

66

Types of Aquatic Environment

The Lakes of the Yahara Valley in Southern Wisconsin
are of another type. They occupy broad, shallow basins
formed by the deposition of barriers of glacial drift

in the preglacial course of
the Yahara River. Their
outlet is through Rock
River into the Missis-
sippi. Their shores are
indented with numerous
bays, and bordered ex-
tensively by marshes.
The surrounding plain is
dotted with low rounded
hills, some of which rise
abruptly from the water,
making attractive shores.
The city of Madison is
the location of the Uni-
versity of Wisconsin,
which Professor Birge has
made the center of the
most extensive and care-
ful study of lakes yet
undertaken in America.
The area, elevation and
depth of these lakes is as
follows :

FIG. 1 6. The four-lake region of
Madison, Wisconsin.

LakeKegonsa
Wabesa

Monona .

Alendota

Area in Surface
sq. mi. alt. in ft.

842
844
845

Depth in feet
mean maximum

15

3
6

IS

849

IS
i5
27
40

36

75

85

Floodplain Lakes 67

Lakes resulting from Erosion — Although erosion tends
generally to destroy lakes by eliminating their basins,
here and there it tends to foster other lakes by making
basins for them. Such lakes, however, are shallow and
fluctuating. They are of two very different sorts,
floodplain lakes and solution lakes.

Floodplain Lakes and Ponds — Basins are formed in
the floodplains of rivers by the deposition of barriers
of eroded silt, in three different ways.

1 . By the deposition across the channel of some large
stream of the detritus from a heavily silt-laden tributary
stream. This blocks the larger stream as with a partial
dam, creating a lake that is obviously but a dilatation
of the larger stream. Such is Lake Pepin in the
Mississippi River, created by the barrier that is de-
posited by the Chippewa River at its mouth.

2. By the partial filling up of the abandoned chan-
nels of rivers where they meander through broad
alluvial bottom-lands. Phelps Lake partly shown in
the figure on page 50 is an example of a lake so formed ;
and all the other lakes of that figure are partly occluded
by similar deposits of river silt. Horseshoe bends are
common in slow streams, and frequently a river will cut
across a bend, shortening its course and opening a
new channel ; the filling up with silt of the ends of the
abandoned channel results in the formation of an "ox-
bow" lake; such lakes are common along the lower
course of the Mississippi, as one may see by consult-
ing any good atlas.

3. By the deposition in times of high floods of the
bulk of its load of detritus at the very end of its course,
where it spreads out in the form of a delta. Thus a
barrier is often formed on one or both sides, encircling a
broad shallow basin. Such is Lake Pontchartrain at
the left of the ever extending delta of the Mississippi.

68

Types of Aquatic Environment

Solution Lakes and Ponds — Of very different charac-
ter are the lakes whose basins are produced by the
dissolution of limestone strata and the descent of the
overlying soil in the form of a "sink." This is erosion,
not by mechanical means at first, but by solution. It

occurs where beds of soluble strata
lie above the permanent ground
water level, and are themselves
overlaid by clay. Rain water
falling through the air gathers
carbon dioxide and becomes a
solvent of limestone. Percolat-
ing downward through the soil it
passes through the permeable
carbonate, dissolving it and
carrying its substance in solution
to lower levels, of ten flowing out
in springs. As the limestone is
thus removed the superincum-
bent soil falls in, forming a sink
hole. The widening of the hole,
by further solution and slides
results in the formation of the
pond or lake, possibly, at the
beginning, as a mere pool.

Such a lake doubtless begins as a mere pool filling
a sink hole. Its area is gradually increased by the
settling of the bottom around the sink. Its configura-
tion is in part determined by the original topography
of the land surface, and in part by the course of the
streamflow underground: but its bed is unique among
lake bottoms in that all its broad shoals suddenly
terminate in one or more deep funnel-shaped outflow
depressions.

Lime sinks occur over considerable areas in the south-
ern states, and in those of the Ohio Valley, but perhaps

FIG. 17. Solution lakes of
Leon County, Florida,
(after Sellards).

The white spots in the lakes indi-
cate sinks

A. Lake lamonia; area at high
water 10 sq. mi.

B. Lake Jackson; area 7 sq. mi.

C. Lake Fafayette; area 3^
sq. mi.

D. Lake Miccosukee; are a y£ sq.
mi.; depth of north sink 28 ft.
Water escapes through this sink
at the estimated rate of 1000
gals, per minute.

O. Ocklocknee River; S, St.
Mark's River; T, Tallahassee.

Solution Lakes

69

QinK

the best development of lakes about them is in the
upland region of northern Florida. These lakes are
shallow basins having much of their borders ill-defined
and swampy. Perhaps the
most remarkable of them is
Lake Alachua near Gaines-
ville. At high water this
lake has an area of some
twenty-five square miles and
a depth (outside the sink) of
from two to fourteen feet.
At its lowest known stage it
is reduced to pools filling
the sinks. During its re-
corded history it has several
times alternated between
these conditions. It has
been for years a vast ex-
panse of water carrying
steamboat traffic, and it has
been for other years a broad
grassy plain, with no water
in sight. The widening or
the stoppage of the sinks
combined with excessive or
scanty rainfall have been
the causes of these remark-
able changes of level.

The sinks are more or
less funnel-shaped openings
leading down through the

FIG. 1 8. Lake Miccosukee, (after
Sellards), showing sinks; one in
lake bottom at north end, two in
outflowing stream, 2^2 miles dis-
tant. Arrows indicate normal
direction of stream flow, (reversed
south of sinks in flood time when
run-off is into St. Mark's River).

soil into the limestone.

Ditchlike channels often lead into them across the lake's
bottom. The accompanying diagram shows that they
are sometimes situated outside the lake's border, and
suggest that such lakes may originate through the
formation of sinks in the bed of a slow stream.

70 Types of Aquatic Environment

Such lakes, when their basins lie above the level of
the permanent water table, may sometimes be drained
by sinking wells through the soil of their beds. This
allows the escape of their waters into the underlying
limestone. Sometimes they drain themselves through
the widening of their underground water channels.
Always they are subject to great changes of level conse-
quent upon variation in rainfall.

Enough examples have now been cited to show how
great diversity there is among the fresh-water lakes of
North America. Among those we have mentioned are
the lakes that have received the most attention from
limnologists hitherto ; but hardly more than a beginning
has been made in the study of any of them. Icthyolo-
gists have collected fishes from most of the lakes of the
entire continent, and plancton collections have been
made from a number of the more typical : from Yellow-
stone Lake by Professor Forbes in 1890 and from many
other lakes, rivers and cave streams since that date.

Lakeside laboratories — On the lakes above mentioned
are located a number of biological field stations. That
at Cornell University is at the head of Cayuga Lake.
That of the Ohio State University is at Sandusky on
Lake Erie. The Canadian fresh-water station is at Go
Home Bay on Lake Huron. The biological laboratories
of the University of Wisconsin are located directly upon
the shore of Lake Mendota. Other lakeside stations
are as follows:

That of the University of Michigan is on Douglas
Lake in the northern end of the southern peninsula of
Michigan. This is an attractive sheet of water at an
altitude of 712 ft., covering an area of 5.13 square miles,
and having (as far as surveyed) a maximum depth of
89 feet and an average depth of 22 feet. Its transpar-
ency by Secchi's disc as measured in August is about
four meters.

Depth and Breadth 71

That of the University of Indiana is on Winona
Lake, a shallow hard water lake of irregular outline,
having an area of something less than a square mile,
an elevation of 810 feet, a maximum depth of 81 feet
and a transparency (Secchi's disc) varying with the
season between 7 and 15 feet.

That of the University of Iowa is on Okoboji Lake.

That of the University of North Dakota is on Devils
Lake, an alkaline upland lake (salinity i%) having an
area of 62^" square miles and a maximum depth of 25
feet. The salt-marsh ditch-grass (Ruppia maritima)
is the only seed plant growing in its waters.

That of the University of Montana is on Flathead
Lake, a cold mountain lake some thirty miles long by
ten miles broad having an elevation of 2916 ft. and a
maximum depth of 280 ft.

That of the University of Utah is on Silver Lake
(altitude 8728 ft.) some twenty miles from the Great
Salt Lake. Six small nearby mountain lakes all have
an altitude of more than 9000 feet.

Doubtless, with the growing interest in limnological
work, other lakeside stations will be added to this list.

Depth and Breadth — The depth of lakes is of more
biological significance than the form of their basins;
for, as we have seen in the preceding chapter, with
increase of depth goes increased pressure, diminished
light, and thermal stratification of the water. Living
conditions are therefore very different in shallow water
from what they are in the bottom of a deep lake, where
there is no light, and where the temperature remains
constant throughout the year. Absence of light pre-
vents the growth of chlorophyl-bearing organisms and
renders such waters relatively barren. The lighted top
layer of the water (zone of photosynthesis) is the pro-
ductive area. The other is a reservoir; tending to
stabilize conditions. Lakes may therefore be roughly

72 Types of Aquatic Environment

grouped in two classes: first, those that are shallow
enough for complete circulation of their water by wind
or otherwise at any time ; and second those deep enough
to maintain through a part of the summer season a
bottom reservoir of still water, undisturbed by waves or
currents, and stratified according to temperature and
consequent density. In these deeper lakes a thermo-
cline appears during midsummer. In the lakes of New
York its upper limit is usually reached at about thirty-
five feet and it has an average thickness of some fifteen
feet. Our lakes of the second class may therefore be
said to have a depth greater than fifty feet.

Lakes of this class may differ much among them-
selves according to the relative volume of this bottom
reservoir of quiet water, Lakes Otisco and Skaneateles
(see map on page 65) serve well for comparison in this
regard, since they are similar in form and situation and
occupy parallel basins but a few miles apart.

Max. % of vol.

Area in depth below Trans- Free COzt at Oxygenf at

Lake sq. mi. in ft. 50 ft. parency* surface bottom surface bottom

Otisco 2.64 66 7.0 9.2 —2.50 +3.80 6.72 o.oo

Skaneateles. 13.90 297 70.2 31.8 -1.25+1.00 6.75 7.89

*In feet, measured by Secchi's disc.

fin cc. per liter of water. Alkalinity by phenolthalein test is indicated
by the minus sign.

The figures given are from midsummer measure-
ments by Birge and Juday. At the time these observa-
tions were made both lakes were alkaline at the surface,
tho still charged with free carbon dioxide at the bottom.
Apparently, the greater the body of deep water the
greater the reserve of oxygen taken up at the time of
the spring circulation and held through the summer
season. Deep lakes are as a rule less productive of
plancton in summer, even in their surface waters,
because their supply of available carbon dioxide runs
low. It is consumed by algae and carried to the bottom

Currents 73

with them when they die, and thus removed from cir-
culation.

Increasing breadth of surface means increasing
exposure to winds with better aeration, especially
where waves break in foam and spray, and with the
development of superficial currents. Currents in lakes
are not controlled by wind alone, but are influenced as
well by contours of basins, by outflow, and by the
centrifugal pull due to the rotation of the earth on its
axis. In Lake Superior a current parallels the shore,
moving in a direction opposite to that of the hands of a
clock. Only in the largest lakes are tides perceptible,
but there are other fluctuations of level that are due to
inequalities of barometric pressure over the surface.
These are called seiches.

Broad lakes are well defined, for they build their
own barrier reefs across every low spot in the shores,
and round out their outlines. It is only shores that are
not swept by heavy waves that merge insensibly into
marshes. In winter in our latitude the margins of the
larger lakes become icebound, and the shoreline is
temporarily shifted into deeper water (compare summer
and winter conditions at the head of Cayuga lake as
shown in our frontispiece) .

Increasing breadth has little effect on the life of the
open water, and none, directly, on the inhabitants of
the depths; but it profoundly affects the life of the
shoals and the margins, where the waves beat, and the
loose sands scour and the ice floes grind. Such a beach
as that shown on page 61 is bare of vegetation only
because it is storm swept. The higher plants cannot
withstand the pounding of the waves and the grinding
of the ice on such a shore.

The shallower a lake is the better its waters are
exposed to light and air, and, other things being equal,
the richer its production of organic life.

74

Types of Aquatic Environment

High and low water — Since the source of this water is
in the clouds, all lakes fluctuate more or less with varia-
tion in rainfall. The great lakes drain an empire of
287,688 square miles, about a third of which is covered
by their waters. They constitute the greatest system
of fresh water reservoirs in the world, with an
unparalleled uniformity of level and regularity of
outflow. Yet their depth varies from month to month

ELEVATION
IN FEET
ABOVE
MEAN
SEA LEVEL
249 o

1896

1897

1898

1899

1900

1901

1902

19OJ

1904

190S

I90(i

190T

ELEVATION
INTOET
ABOVE
MEAN
SEA LEVEL

2490

OS
U
k.

ill

p>-g?
BJBg

£ z< z

£> a >

ia<p 5

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B < S 6
9. *<£

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B < P &
K Z<(5

ea >• <5 >•

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2480 =

~ 248 0

A

2410 ~

r ti'i70

I

5

7460 =

\

Z L

-J^

*^ ••

- 2460

iO

5

A

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d

£

74.50 =

\

} L

J 1

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TJ

= 24SO

f *

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r

2140 r

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5

K

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= 2,44-0

J

J

"Z43.O =

- 245 0

MONTHLY MEAN LEVEL OF LAKE ONTARIO AT OSWEGO.N Y

FIG. 19. Diagram of monthly water levels in Lake Ontario for twelve years;
from the Report of the International Waterways Commission for 1910.

and from year to year, as shown on the accompanying
diagram. From this condition of relative stability to
that of regular disappearance, as of the strand lakes of
the Southwest, there are all gradations. Topography
determines where a lake may occur, but climate has
much to do with its continuance. Lakes in arid regions
often do not overflow their basins. Continuous evapora-
tion under cloudless skies further aided by high winds,
quickly removes the excess of the floods that run into
them from surrounding mountains. The minerals dis-
solved in these waters are thus concentrated, and they
become alkaline or salt. We shall have little to say in

High and Low Water

75

this book about such lakes, or about their population,
but they constitute an interesting class. Life in their
waters must meet conditions physiologically so different
that few organisms can live in both fresh and salt water.
Large lakes in arid regions are continually salt;
permanent lakes of smaller volume are made temporarily
fresh or brackish by heavy inflowing floods; while

FIG. 20. Marl pond near Cortland, N. Y., at low water. The whiteness of the
bed surrounding the residual pool is due to deposited marl, largely derived
from decomposed snail shells. The marl is thinly overgrown with small
freely-blooming plants of Polygonum amphibium. Tall aquatics mark the
vernal shore line. (Photo by H. H. Knight).

strand lakes (called by the Spanish name playa lakes,
in the Southwest) run the whole gamut of water con-
tent, and vanish utterly between seasons of rain.

Complete withdrawal of the waters is of course fatal
to all aquatic organisms, save a few that have specialized
means of resistance to the drought. Partial withdrawal

Types of Aquatic Environment

by evaporation means concentration of solids in solu-
tion, and crowding of organisms, with limitation of
their food and shelter. The shoreward population of
all lakes is subject to a succession of such vicissitudes.
The term limnology is often used in a restricted sense
as applying only to the study of freshwater lakes.
This is due to the profound influence of the Swiss
Master, F. A. Forel, who is often called the "Father
of Limnology." He was the first to study lakes
intensively after modern methods. He made the
Swiss lakes the best known of any in the world.
His greatest work " Le Leman," a monograph on
Lake Geneva, is a masterpiece of limnological litera-
ture. It was he who first developed a comprehen-
sive plan for the study of the life of lakes and all
its environing conditions.

OURNEYING seaward,
the water that finds
no basins to retain it,
forms streams. Ac-
cording as these differ
in size we call them
rivers, creeks, brooks,
and rills. These dif-
fer as do lakes in the
dissolved contents of their waters, according to the
nature of the soils they drain. Streams differ most
from the lakes in that their waters are ever moving in
one direction, and ever carrying more or less of a load
of silt. From the geologist's point of view the work of
rivers is the transportation of the substance of the
uplands into the seas. It is an eternal levelling process.
It is well advanced toward completion in the broad
flood plains of the larger continental streams (see map
on page 63) ; but only well begun where brooks and
rills are invading the high hills, where the waters seek
outlets in all directions, and where every slope is
intersected with a maze of channels. The rapidity of
the grading work depends chiefly upon climate and rain-
fall, on topography and altitude and on the character
of the rocks and soil.

77

Types of Aquatic Environment

The rivers of America have been extensively studied
as to their hydrography, their navigability, their water-
power resources, and their liability to overflow with
consequent flood damage ; but it is the conditions they

FIG. 21. Streams of the upper Cayuga basin.

A . Taughannock Creek, with a waterfall 211 feet high near its mouth ;
B. Salmon Creek; C. Fall Creek with the Cornell University Biological Field
Station in the marsh at its mouth (views on this stream are shown in the initial
cuts on pages 24 and 82); D. Cascadilla Creek (view on page 5.s); E. Sixmile
Creek; F. Buttermilk Creek with Coys Glen opposite its mouth. (View on
page 7 7 ; of the Glen on page 25); G. Neguena Creek or the Inlet. The southern-
most of these streams rise in cold swamps, which drain southward also into
tributaries of the Susquehanna River.

Conditions in Streams

79

afford to their plant and animal inhabitants that
interest us here; and these have been little studied.
Most has been done on the Illinois River, at the floating
laboratory of the Illinois State Laboratory of Natural
History (see page 50). A more recently established
river laboratory, more limited in its scope (being
primarily concerned with the propagation of river
mussels) is that of the U. S. Fish Commission at Fair-
port, Iowa, on the Mis-
sissippi River.

In large streams, espec-
ially in their deeper and
more quiet portions, the
conditions of life are most
like those in lakes. In les-
ser streams life is subject
to far greater vicissitudes.
The accompanying figure
shows comparative sum-
mer and winter tempera-
tures in air and in water of
Fall Creek at Ithaca. This
creek (see the figtire on
page 24), being much
broken by waterfalls and
very shallow, shows hardly
any difference between sur-
face and bottom tempera- FIG
tures. The summer tem-
peratures of air and water
(fig. 22) are seen to main-
tain a sort of correspond-
ence, in spite of the thermal
conservatism of water, due to its greater specific heat.
This approximation is due to conditions in the creek
which make for rapid heating or cooling of the water.

10 IS 2O AS JO
JflNU fifty 1905

Diagram showing summer
and winter conditions in Fall Creek
at Ithaca, N. Y. Data on air
temperatures furnished by Dr. W.M.
Wilson of the U. S. Weather Bureau.
Data on water temperatures by Pro-
fessor E. M. Chamot.

So Types of Aquatic Environment

It flows in thin sheets over broad ledges of dark colored
rocks that are exposed to the sun, and it falls over pro-
jecting ledges in broad thin curtains, outspread in con-
tact with the air.

The curves for the two winter months, show less
concurrence, and it is strikingly apparent that during
that period when the creek was ice-bound (Dec. 15-
Jan. 31) the water temperature showed no relation to
air temperature, but remained constantly at or very
close to o°C. (32° F.).

Forbes and Richardson (13) have shown how great
may be the aerating effect of a single waterfall in such
a sewage polluted stream as the upper Illinois River.
"The fall over the Marseilles dam (710 feet long and 10
feet high) in the hot weather and low water period of
July and August, 1911, has the effect to increase the
dissolved oxygen, more than four and a half times, rais-
ing it from an average of .64 parts per million to 2.94
parts. On the other hand, with the cold weather, high
oxygen ratios, and higher water levels of February and
March, 1912, and the consequent reduced fall of
water at Marseilles, the oxygen increase was only 18
per cent. — from 7.35 parts per million above the dam
to 8.65 parts below * * * The beneficial effect is
greatest when it is most needed — when the pollution is
most concentrated and when decomposition processes
are most active."

Ice— -The physical conditions that in temperate
regions have most to do with the well- or ill-being of
organisms living in running water are those resulting
from the freezing. The hardships of winter may be
very severe, especially in shallow streams. One may
stand beside Fall Creek in early winter when the thin
ice cakes heaped with snow are first cast forth on the
stream, and see through the limpid water an abundant

Ice in Streams 81

life gathered upon the stone ledges, above which these
miniature floes are harmlessly drifting. There are
great black patches of Simulium larvae, contrasting
strongly with the whiteness of the snow. There are
beautiful green drapings of Cladophora and rich red-
purple fringes of Chantransia, and everywhere amber-
brown carpetings of diatoms, overspreading all the
bottom. But if one stand in the same spot in the
spring, after the heavy ice of winter has gone out, he
will see that the rocks have been swept clean and bare,
every living thing that the ice could reach having gone.

The grinding power of heavy ice, and its pushing
power when driven by waves or currents, are too well
known to need any comment. The effects may be seen
on any beach in spring, or by any large stream. But
there is in brooks and turbulent streams a cutting with
fine ice rubble that works through longer periods, and
adds the finishing touches of destructiveness. It is
driven by the water currents like sand in a blast, and it
cleans out the little crevices that the heavy ice could
not enter. This ice rubble is formed at the front of
water falls under such conditions as are shown in the
accompanying figure of Triphammer Falls at Ithaca.
The pool below the fall froze first. The winter increas-
ing cold, the spray began to freeze where it fell. It
formed icicles, large and small, wherever it could find a
support above. It built up grotesque columns on the
edge of the ice of the pool beneath. It grew inward
from the sides and began to overarch the stream face;
and then, with favoring intense cold of some days dura-
tion, it extended these lines of frozen spray across the
front of the fall in all directions, covering it as with a
beautiful veil of ice.

The conditions shown in the picture are perfect for
the rapid formation of ice rubble. From thousands of
points on the underside of this tesselated structure

82

Types of Aquatic Environment

minute icicles are forming and their tips are being broken
off by the oscillations of the current. These broken
tips constitute
the rubble.
They are some-
times remark-
ably uniform in
size— those form-
ing when this
picture was
taken were
about the size
of pea s — a n d
though small
they are the
tools with which
the current does
its winter clean-
ing. In the
ponds formed by
damming rapid
streams this rub-
ble accumulates
under the solid
ice.

"Anchor ice"
forms in the
beds of rapid
streams, and
adds another
peril to their in-
habitants. The
water, cooled „ .

, 1 /i r FIG. 23. The ice veil on Triphammer Falls, Cornell

DelOW trie ireez- University Campus. The fall is at the left, the

in0" point bv COn- Laboratory of Hydraulic Engineering at the right

*• . . .. ' . in the picture, the only open water seen is in the

tact With the air, foaming pool at the foot of the fall.

.

Anclior Ice

does not freeze in the current because of its motion,
but it does freeze on the bottom where the current
is sufficiently retarded to allow it. It congeals in
semi-solid or more or less flocculent masses which, when
attached to the stones of the bed, often buoy them up

FIG. 24. A brook in winter. Country Club woods, Ithaca, N. Y.

Photo by John T. Needham.

and cause them to be carried away. Thus the organ-
isms that dwell in the stream bed are deprived of their
shelter and exposed to new perils.

Below the frost -line, however, in streams where
dangers of mechanical injuries such as above men-
tioned are absent, milder moods prevail. In the bed
of a gentle meandering streamlet like that shown in the
accompanying figure, life doubtless runs on in winter

84 Types of Aquatic Environment

with, greater serenity than on land. Diatoms grow
and caddis-worms forage and community life is actively
maintained.

Silt — Part of the substance of the land is carried
seaward in solution. It is ordinarily dissolved at or
near the surface of the ground, but may be dissolved
from underlying strata, as in the region of the Mam-
moth Cave in Kentucky, where great streams run far
under ground. But the greater part is carried in
suspension. Materials thus carried vary in size from
the finest particles of clay to great trees dropped whole
into the stream by an undercutting flood. The lighter
solids float, and are apt to be heaped on shore by wave
and wind. The heavier are carried and rolled along,
more or less intermittently, hastened with floods and
slackened with low water, but ever reaching lower
levels. The rate of their settling in relation to size
and to velocity of stream has been discussed in the
preceding chapter.

Silt is most abundant at flood because of the greater
velocity of th"e water at such times. Kofoid ('03) has
studied the amount of silt carried by the Illinois River
at Havana. Observations at one of his stations
extending over an entire year show a minimum amount
of 140 cc. per cubic meter of river water; a maximum
of 4,284 cc., and an average for the year (28 samples)
of 1,572 cc. Silt in a stream affects its population in a
number of ways. It excludes light and so interferes
with the growth of green plants, and thus indirectly with
the food supply of animals. It interferes with the free
locomotion of the microscopic animals by becoming
entangled in their swimming appendages. It clogs the
respiratory apparatus of other animals. It falls in
deposits that smother and bury both plants and animals
living on the bottom. Thus the best foraging grounds
of some of our valuable fishes are ruined.

Current 85

Professor Forbes ('oo) has shown that the fine silt
from the earlier-glaciated and better weathered soils
of southern Illinois, has been a probable cause of
exclusion of a number of regional fishes from the streams
of that portion of the state.

It is heavier silt that takes the larger share in the
building of bars and embankments along the lower
reaches of a great stream, in raising natural levees to
hold impounded backwaters, and in blocking cut-off
channels to make lakes of them.

Current — Rate of streamflow being determined
largely by the gradient of the channel, is one of the
more constant features of rivers, but even this is sub-
ject to considerable fluctuation according to volume.
Kofoid states that water in the Illinois River travels
from Utica to the mouth (227 miles) in five days at
flood, but requires twenty-three days for the journey
at lowest water. The increase in speed and in turbu-
lence in flood time appears to have a deleterious effect
upon some of the population, many dead or moribund
individuals of free swimming entomostraca being
present in the waters at such times.

With the runoff after abundant rainfall a rapid rise
and acceleration occurs, to be followed by a much
slower decline. The stuffs in the water are diluted;
the plancton is scattered. A new load of silt is received
from the land; plant growths are destroyed and even
contours in the channel are shifted.

Current is promoted by increasing gradient of stream •
bed. It is diminished by obstructions, such as rocks or
plant growths, by sharp bends, etc. It is slightly
accelerated or retarded by wind according as the direc-
tion is up or down stream. Even where a stream
appears to be flowing steadily over an even bed between
smooth shores, careful measurements reveal slight and

2 3-9I

3 3-73

4 3-6o

5 3-32

6 3.04

7 2.89

8 2.81
10 2.73

12 2.64

14 2.46

15 2.17

16 1.73

86 Types of Aquatic Environment

inconstant fluctuations. The current is nowhere uni-
form from top to bottom or from bank to bank. In the
horizontal plane it is swiftest in midstream and is
retarded by the banks. In a vertical plane, it is swift-
est just beneath the surface and is retarded more and
more toward the bottom. The pull of the surface film
Depth Feet retards it a little and

in inches per sec. when ice forms on the

surface, friction against
the ice retards it far more
and throws the point of
maximum velocity down
near middepth of the
stream. A sample meas-
urement made by Mr.
Wilbert A. Clemens in
Cascadilla Creek at

Current and Depth in Cascadilla Ithaca in Open Water
Creek. Measured by W. A. Clemens, seventeen inches deep

gave rate of flow varying from a maximum of 3 . 9 1 feet per
second two inches below the surface down to i . 73 feet per
second one inch above the bottom, as shown in the col-
umns above. Below this, in the last inch of depth the
retardation was more rapid, but irregular. The current
slackens more slowly toward the surface and toward
the side margins of the stream.

Mr. Clemens, using a small Pitot-tube current meter,
made other measurements showing that in the places
where dwell the majority of the inhabitants of swift
streams there is much less current than one might ex-
pect. In the shelter of stones and other obstructions
there is slack: water. On sloping bare rock bottoms
under a swiftly gliding stream the current is often but
half that at the surface. On stones exposed to the
current a coating of slime and diatomaceous ooze
reduces the current 16 to 32 per cent.

High and Low Water

This accounts for the continual restocking of a stream
whose waters are swifter than the swimming of the
animals found in the open channels. In these more or
less shoreward places they breed and renew the supply.
Except in a stream whose waters run a long course sea-
ward, allowing an ample time for breeding, there is
little indigenous free-swimming population.

FIG. 25. Annually inundated bulrush-covered flood-plain at the mouth of Fall
Creek, Ithaca, N. Y., in 1908. Clear growth of Scirpus flmnatilis and a
drowned elm tree. The Cornell University Biological Field Station at
extreme right. West Hill in the distance.

High and Low Water — Inconstancy is a leading char-
acteristic of river environment, and this has its chief
cause in the bestowal of the rain. Streams fed mainly
by springs, lakes, and reservoirs are relatively constant;
but nearly all water courses are subject to overflow;
their channels are not large enough to carry flood
waters, so these overspread the adjacent bottomlands.
Every change of level modifies the environment by

88 Types of Aquatic Environment

connecting or cutting off back waters, by shifting cur-
rents, by disturbing the adjustment of the vegetation,
and by causing the migration of the larger animals. At
low water the Illinois River above Havana has a width
of some 500 feet; in flood times it spreads across the
valley floor in an unbroken sheet of water four miles
wide. Kofoid estimates that at time of high flood (18
feet above low-water datum) less than one-tenth as
much of this water is in the channel as lies beyond its
boundaries.

The rise of a river flood is often sudden ; the decline
is always much more gradual, for impounding barriers
and impeding vegetation tend to hold the water upon
the lowlands. The period of inundation markedly
affects the life of the land overflowed. Cycles of seasons
with short periods of annual submergence favor the
establishment of upland plants and trees. Cycles of
years of more abundant rainfall favor the growth of
swamp vegetation. Certain plants like the flood-plain
bulrush shown in the preceding figure seem to thrive
best under inconstancy of flood conditions.

MARSHE

AMPS AND BOG!

GREAT aquatic en-
vironment may be
maintained with
much less water than there is in a lake or a river if only
an area of low gradient, lacking proper basin or channel,
be furnished with a ground cover of plants suitable for
retaining the water on the soil. Enough water must be
retained to prevent the complete decay of the accumu-
lating plant remains. Then we will have, according to
circumstances, a marsh, a swamp or a bog.

There are no hard and fast distinctions between these
three; but in general we may speak of a marsh as
a meadow-like area overgrown with herbaceous aquatic
plants, such as cat-tail, rushes and sedges; of a swamp
as a wet area overgrown with trees ; and of a bog as such
an area overgrown with sphagnum or bog-moss, and
yielding under foot. The great Montezuma Marsh of
Central New York (shown in the initial above) is

89

90 Types of Aquatic Environment

typical of the first class ; the Dismal Swamp of eastern
Virginia, of the second; and over the northern lake
region of the continent there are innumerable examples
of the third. These types are rarely entirely isolated,
however, since both marsh and bog tend to be invaded
by tree growth at their margins. Such wet lands occupy
a superficial area larger by far than that covered by
lakes and rivers of every sort. They cover in all
probably more than a hundred million acres in the
United States; great swamp areas border the Gulf
of Mexico, the South Atlantic seaboard, and the lower
reaches of the Mississippi, and of its larger tributaries,
and partially overspread the lake regions of upper
Minnesota, Wisconsin, Michigan and Maine. In the
order of the areas of " swamp land" (officially so desig-
nated) within their borders the leading states are
Florida, Louisiana, Arkansas, Mississippi, Michigan,
Minnesota, Wisconsin and Maine.

Swamps naturally occupy the shoal areas along the
shores of lakes and seas. Marine swamps below mean
tide occur as shoals covered with pliant eel-grass.
Above mean tide they are meadow-like areas located
behind protecting barrier reefs, or they are mangrove
thickets that fringe the shore line, boldly confronting
the waves. With these we are not here concerned.
Fresh-water marshes likewise occupy the shoals border-
ing the larger lakes, where protected from the waves by
the bars that mark the shore line. In smaller lakes,
where not stopped by wave action, they slowly invade
the shoaler waters, advancing with the filling of the
basin, and themselves aiding in the filling process.

That erosion sometimes gives rise to lakes has
already been pointed out; much oftener it produces
marshes; for depositions of silt in the low reaches of
streams are much more likely to produce shoals than
deep water.

Cat -Tail Marshes

Cat-tail Marshes — In the region of great lakes every
open area of water up to ten feet in depth is likely to
be invaded by the cat -tail flag (Typha). The ready
dispersal of the seeds by winds scatters the species
everywhere, and no permanent wet spot on the remotest
hill-top is too small to have at least a few plants. Along

FIG. 26. An open-water area (Parker's Pond) in the Montezuma Marsh in
Central New York. Formerly it teemed with wild water fowl. It is sur-
rounded by miles of cat-tail flags (Typha) of the densest sort of growth.

the shores of the Great Lakes and in the broad shoals
bordering on the Seneca River there are meadow-like
expanses of Typha stretching away as far as the eye
can see. Many other plants are there also, as will be
noted in a subsequent chapter, but Typha is the
dominant plant, and the one that occupies the fore-
front of the advancing shore vegetation. It masses its
crowns and numberless interlaced roots at the surface

92

Types of Aquatic Environment

of the water in floating rafts, which steadily extend into
deeper water. The pond in the center of Montezuma
Marsh shown in the preceding figure is completely
surrounded by a rapidly advancing, half -float ing even-
fronted phalanx of cat-tail.

FIG. 27. "The Cove" at the Cornell University Biological Field Station, in
time of high water. Early summer. Two of the University buildings
appear on the hill in the distance.

Later conditions in such a marsh are those illustrated
by our frontispiece : regularly alternating spring floods,
summer luxuriance, autumn burning and winter freez-
ing. This goes on long after the work of the cat-tail,
the pioneer landbuilding, has been accomplished.
The excellent aquatic collecting ground shown in the
accompanying figure is kept open only by the annual
removal of the encroaching flag.

Okefenokee Swamp

93

The Okefenokee Swamp. In southern Georgia lies
this most interesting of American swamps. It is
formed behind a low barrier that lies in a N., N. E. —
S., S. W. direction across the broad sandy coastal plain,
intersecting the course of the southernmost rivers of

FIG. 28. A view of "Chase's Prairie" in the more open eastern portion of the
Okefenokee Swamp, taken from an elevation of fifty feet up a pine tree on
one of the incipient islets. The water is of uniform depth (about four or
five feet). This is one of the most remarkable landscapes in the world.

Photo by Mr. Francis Harper.

Georgia that drain into the Atlantic. Behind the bar-
rier the waters coming from the northward are retained
upon a low, nearly level plain, that is thinly overspread
with sand and underlaid with clay. They cover an
area some forty miles in diameter, hardly anywhere too
deep for growth of vascular plants. There is little dis-
coverable current except in the nascent channels of the

94 Types of Aquatic Environment

two outflowing streams, St. Mary's and Suwannee
Rivers. The waters are deeper over the eastern part of
the swamp, the side next the barrier; and here the
vegetation is mainly herbaceous plants, principally
submerged aquatics, with occasional broad meadow-
like areas overgrown with sedges. These are the so-
called "prairies." The western part of the swamp
(omitting from consideration the islands) is a true
swamp in appearance being covered with trees, prin-
cipally cypress. A few small strips of more open and
deeper water (attaining 25 feet) of unique beauty,
owing to their limpid brown waters and their setting
of Tillandsia-covered forest, are called lakes.

The whole swamp is in reality one vast bog. Its
waters are nearly everywhere filled with sphagnum.
Whatever appears above water to catch the eye of the
traveler, whether cypress and tupelo in the western part
or sedges and water lilies on the "prairie," everywhere
beneath and at the surface of the water there is sphag-
num; and it is doubtless to the waterholding capacity
of this moss that the relative constancy of this great
swamp on a gently inclined plain near the edge of the
tropics, is due.

Climbing bogs — In-so-far as swamps possess any basin
at all they approximate in character to shallow lakes;
but there are extensive bogs in northern latitudes that
are built entirely on sloping ground; often even on
convex slopes. These are the so-called "climbing
bogs." They belong to cool -temperate and humid
regions. They exist by the power of certain plants,
notably sphagnum, to hold water in masses, while
giving off very little by evaporation from the surface.
A climbing bog proceeds slowly to cover a slope by the
growth of the mass of living moss upward against
gravity, and in time what was a barren incline becomes
a deep spongy mass of water soaked vegetation.

Conditions in Swamps 95

Conditions of life — In the shoal vegetation-choked
waters of marshes there is little chance for the formation
of currents and little possibility of disturbance by wind.
Temperature conditions change rapidly, however, owing
to the heat absorbing and heat radiating power of the
black plant-residue. The diurnal range is very great,
water that is cool of a morning becomes repellantly hot
of a summer afternoon. Temperatures above 90° F.
are not then uncommon. Unpublished observations
made by Dr. A. A. Allen in shoal marsh ponds at the
Cornell Biological Field Station throughout the year
1909, show a lower temperature at the surface of the
water than in the bottom mud from December to April,
with reverse conditions for the remainder of the year.
The black mud absorbs and radiates heat rapidly.

Conditions peculiar to marshes, swamps and bogs are
those due to massed plant remains more or less per-
manently saturated with water. Water excludes the
air and hinders decay. Half disintegrated plant
fragments accumulate where they fall, and continue
for a longer or shorter time unchanged. According to
their state of decomposition they form peat or muck.

In peat the hard parts and cellular structure of the
plant are so well preserved that the component species
may be recognized on microscopic examination. To
the naked eye broken stems and leaves appear among
the finer fragments, the whole forming a springy or
spongy mass of a loose texture and brownish color.
The color deepens with age, being lightest immediately
under the green and living vegetation, and darkest in
the lower strata, where always less well preserved.

The water that covers beds of peat acquires a brown-
ish color and more or less astringent taste due to in-
fusions of plant-stuffs. Humous acids are present in
abundance and often solutions of iron sulphate and
other minerals.

96 Types of Aquatic Environment

Muck is formed by the more complete decay of such
water plants as compose peat. The process of decay is
furthered either by occasional exposure of the beds to
the air in spells of drought, or by the presence of lime
in the surrounding soil, correcting the acidity of the
water and lessening its efficiency as a preservative.
Muck is soft and oozy, paste-like in texture and black
in color. In the openings of marshes, like that shown
on page 89 are beds of muck so soft that he who ven-
tures to step on it may sink in it up to his neck. In
such a bed the slow decomposition that goes on in hot
weather in absence of oxygen produces gases that
gather in bubbles increasing in size until they are able
to rise and disrupt the surface.* So are formed marsh
gas (methane) which occasionally ignites spontaneously,
in mysterious flashes over the water — the well known
"Jack-o-lantern" or "WiU-o- the- wisp" or "Ignis
fatuus" -and hydrogen sulphide which befouls the sur-
rounding atmosphere.

The presence in marsh pools of these noxious gases,
of humous acids, and of bitter salts, and of the absence
of oxygen — except at the surface, limits their animal
population in the main to such creatures as breathe air
at the surface or have specialized means of meeting
these untoward conditions.

High and Low Water — Swamps being the shoalest of
waters are subject to the most extreme fluctuations.
That they retain through most dry seasons enougli
water for a permanent aquatic environment is largely
due to the water-retaining power of aquatic plants.
Notable among these is sphagnum, which holds en-
meshed in its leaves considerable quantities of water,
lifted above the surrounding water level. Aquatic seed

*See Penhallow, "A blazing beach" in Science, 22:794-6, 1905.

High and Low Water

97

plants, also, whose stems in life are occupied with
capacious air spaces, fill with water when dead and
fallen, and hold it by capillarity. So, they too, form
in partial decay a soft spongy water-soaked ground
cover.

Marshes develop often a wonderful density of popu-
lation, for they have at times every advantage of water,
warmth and light. The species are fewer, however,
than in the more varied environment of land. Com-
paratively few species are able to maintain themselves
permanently where the pressure for room is so great
when conditions for growth are favorable, and where
these conditions fail more or less completely every dry
season. Aquatic creatures that can endure the condi-

tions shown
must have
over the

in the accompanying figure
specialized means of tiding
period of drouth.

m m

£&

i • *, ,

FIG. 29. The bed of a marsh pool in a dry season, showing deep mud cracks,
and a thin growth of bur-marigold and club rush.

CHAPTER IV

AQUATIC CDEGANI

IS the testimony of all
biology that the water
was the original home of
life upon the earth.
Conditions of living are
simpler there than on
the land. Food tends
to be more uniformly dis-
tributed. The perils of
evaporation are absent.
Water is a denser medi-
um than air, and sup-
ports the body better, and there is, in the beginning,
less need of wood or bone or shell or other supporting
structures. Life began in the water, and the simpler
forms of both plants and animals are found there still.
But not all aquatic forms have remained simple.
For when they multiplied and spread and filled all the
waters of the earth the struggle for existence wrought
diversification and specialization among them, in water
as on land. The aquatic population is, therefore, a
mixture of forms structurally of high and low degree.
All the types of plant and animal organization are
represented in it. But they are fitted to conditions so
different from those under which terrestrial beings live
as to seem like another world of life.

99

IOO

A quatic Organisms

The population of the water includes besides the
original inhabitants — those tribes that have always
lived in the water — a mixture of forms descended from

ancestors that once lived on
land. The more primitive
groups are most persistently
aquatic. Comparatively few
members of those groups that
have become thoroughly fit-
ted for life on land have re-
turned to the water to live.

'ATER PLANTS

(VERY large group of plants
has its aquatic members.
The algae alone are predomi-
nantly aquatic. Most of them live wholly immersed;
some live in moist places, and a few in dry places,
having special fitnesses for avoiding evaporation. In
striking contrast with this, all the higher plants, the
seed plants, ferns, and mosses, center upon the land,
having few species in wet places and still fewer wholly
immersed. Their heritage of parts specially adapted
to life on land is of little value in the water. Rhi-
zoids as foraging organs, a thick epidermis with auto-
matic air pores, and strong supporting tissues are little
needed under water. These plants have all a shore-
ward distribution, and do not belong to the open water.
Only algae, molds and bacteria are found in all waters.

The Algae 101

THE ALGAE

It is a vast assemblage of plants that makes up this
group; and they are wonderfully diverse. Most of
them are of microscopic size, and few of even the larger
ones intrude upon our notice. Notwithstanding their
elegance of form, their beauty of coloration and their
great importance in the economy of water life, few of
them are well known. However, certain mass effects
produced by algae are more or less familiar. Massed
together in inconceivably vast numbers upon the sur-
face of still water, their microscopic hosts compose the
' 'water bloom. ' ' Floating free beneath the surface they
give to the water tints of emerald* of amberf or of
blood f. Matted masses of slender green filaments
compose the growths that float on oxygen bubbles to
the surface in the spring as "pond scums." Lesser
masses of delicately branched filaments fringe the
rocky ledges in the path of the cataract, or encircle sub-
merged sticks and piling in still waters. Mixtures of
various gelatinous algae coat the flat rocks in clear
streams, making them green and slippery; and a rich
amber-tinted layer of diatom ooze often overspreads the
stream bed in clear waters.

These are all mass effects. To know the plants com-
posing the masses one must seek them out and study
them with the microscope. Among all the hosts of
fresh water algae, only a few of the stoneworts (Char-
aceae) are in form and size comparable with the higher
plants.

Many algae are unicellular; more are loose aggre-
gates of cells functioning independently; a few are
well integrated bodies of mutually dependent cells.

*Volvox in autumn in waters over submerged meadows of water weed.

fDinobryon in spring in shallow ponds.

\Tricliodesmium erytlircBiim gives to the Red Sea the tint to which its
name is due. The little crustacean, Diaptomus, often gives a reddish tint to
woodland pools.

IO2 Aquatic Organisms

The cells sometimes form irregular masses, with more or
less gelatinous investiture. Often they form simple
threads or filaments, or flat rafts, or hollow spheres.
Algal filaments are sometimes simple, sometimes
branched; sometimes they are cylindric, sometimes
tapering ; sometimes they are attached and grow at the
free end only ; sometimes they grow throughout ; some-
times they are free, sometimes wholly enveloped in
transparent gelatinous envelopes. And the form of the
ends, the sculpturing and ornamentation of the walls and
the distribution of chlorophyll and other pigments are
various beyond all enumerating, and often beautiful
beyond description. We shall attempt no more, there-
fore, in these pages than a very brief account of a few
of the commoner forms, such as the general student of
fresh water life is sure to encounter; these we will
call by their common names, in so far as such names
are available.

The flagellates — We will begin with this group of
synthetic forms, most of which are of microscopic size
and many of which are exceedingly minute. That
some of them are considered to be animals (Mastigo-
phora) need not deter us from considering them all
together, suiting our method to our convenience. The
group overspreads the undetermined borderland be-
tween plant and animal kingdoms. Certain of its
members (Euglena) appear at times to live the life of a
green plant, feeding on mineral solutions and getting
energy from the sunlight; at other times, to feed on
organic substances and solids like animals. The more
common forms live as do the algae. All the members of
the group are characterized by the possession of one or
more living protoplasmic swimming appendages, called
flagella, whence the group name. Each flagellum is
long, slender and transparent, and often difficult of

Flagellates

103

observation, even when the jerky movements of the
attached cell give evidence of its presence and its
activity. It swings in front of the cell in long serpen-
tine curves, and draws the cell after it as a boy's arms
draw his body along in swimming.

Many flagellates are permanently unicellular ; others
remain associated after repeated divisions, forming
colonies of various forms, some of which will be shown in
accompanying figures.

Carteria- -This is a very minute flagellate of spherical
form and bright green in color (fig. 300). It differs
from other green flagellates in having four flagella : the
others have not more than two. It is widely distrib-
uted in inland waters, where it usually becomes more
abundant in autumn, and it appears to prefer slow
streams. Kofoid's notes concerning a maximum occur-
rence in the Illinois River are well worth quoting:

"The remarkable outbreak of Carteria in the autumn
of 1907 was associated with unusually low water, and

FIG. 30. Flagellates.

Carteria; b, Sph&rella; c, Euglena; d, Trachelomonas; e, Pandorina; f, Glenodinium;
g, Synura; h, and i, Dinobryon; a colony as it appears under low power of the microscope
and a single individual highly magnified ;j , Ceratium.

104 Aquatic Organisms

concentration of sewage, and decrease of current. The
water of the stream was of a livid greenish yellow tinge.
* * * The distribution of Carteria in the river was
remarkable. It formed great bands or streaks visible
near the surface, or masses which in form simulated
cloud effects. The distribution was plainly uneven,
giving a banded or mottled appearance to the stream.
The bands, 10 to 15 meters in width, ran with the
channel or current, and their position and form were
plainly influenced by these factors. No cause was
apparent for the mottled regions. This phenomenon
stands in somewhat sharp contrast with the usual
distribution of waterbloom upon the river, which is
generally composed largely of Euglena. This presents
a much more uniform distribution, and unlike Carteria,
is plainly visible only when it is accumulated as a super-
ficial scum or film. Carteria was present in such quan-
tity that its distribution was evident at lower levels so
far as the turbidity would permit it to be seen. It
afforded a striking instance of marked inequalities in
distribution."

Similar green flagellates of wide distribution are
Chlamydomonas and Sphaerella (fig. 306) commonly
found in rainwater pools.

Certain aggregates of such cells into colonies are very
beautiful and interesting. Small groups of such green
cells are held together in flat clusters in Gonium and
Platydorina, or in a hollow sphere, with radiating
flagella that beat harmoniously to produce a regular
rolling locomotion in Pandorina (fig. 30 e), Eudorina
and Volvox.

Volvox — The largest and best integrated of these
spherical colonies is Volvox (fig. 31). Each colony may
consist of many thousands of cells, forming a sphere
that is readily visible to the unaided eye. It rotates

Vofaox

105

constantly about one axis, and moves forward therefore
through the water in a perfectly definite manner.
Moreover, the "eye spots" or pigment flecks of the
individual cells are larger on the surface that goes fore-

FIG. 31. Volvox, showing young colonies in all stages of development.

most. Sex cells are fully differentiated from the
ordinary body cells. Nevertheless, new colonies are
ordinarily reproduced asexually. They develop from
single cells of the old colony which slip inward some-
what below the general level of the body cells, repeat-
edly divide, (the mass assuming spherical form),
differentiate a full complement of flagella, a pair to each
cell, and then escape to the outer world by rupturing
the gelatinous walls of the old colony. Many develop-

io6

Aquatic Organisms

ing colonies are shown within the walls of the old ones
in the figure.

Often, when a weed-carpeted pond shows a tint of
bright transparent green in autumn, a glass of the water,
dipped and held to the light, will be seen to be filled
with these rolling emerald spheres.

Euglena — Several species of this genus (fig. 30^) are
common inhabitants of slow streams and pools. They
are all most abundant in mid-summer, being apparently

attuned to high tempera-
tures. They are common
constituents of the water-
bloom that forms on the
surface of slow streams.
Figure I (p. 15) shows such
a situation, where they re-
cur every year in June. Cer-
tain of them are common in
pools at sewer outlets,
where bloodworms dwell in
the bottom mud. When
abundant in such places
they give to the water a
livid green color. Their
them important agents in

1

-

FIG. 32. A Dinobryon colony.

great abundance makes

converting the soluble stuffs of the water into food
for rotifers and other microscopic animals.

Dinobryon- -This minute, amber-tinted flagellate
forms colonies on so unique a plan (fig. 30/2) they are
not readily mistaken for anything else under the sun.
Each individual is enclosed in an ovoid conic case or
lorica, open at the front where two flagella protrude
(fig. 302') and many of them are united together in branch-
ing, a more or less tree-like colony. Since flagella

The Flagellates 107

always draw the body after them, these colonies swim
along with open ends forward, apparently in defiance
of all the laws of hydromechanics, rotating slowly on
the longitudinal axis of the colony as they go. Dino-
bryon is of an amber yellow tint, and often occurs in
such numbers as to lend the same tint to the water it
inhabits. It attains its maximum development at
low temperatures. In the cooler waters of our larger
lakes it is present in some numbers throughout the year,
though more abundant in winter. Kofoid reports it as
being "sharply limited to the period from November to
June" in Illinois River waters. Its sudden increase
there at times in the winter is well illustrated by the
pulse of 1899, when the numbers of individuals per
cubic meter of water in the Illinois River were on suc-
cessive dates as follows:

Jan. loth, 1,500

Feb. yth, 6,458,000

i4th, 22,641,440

followed by a decline, with rising of the river.

Dinobryon often develops abundantly under the ice.
Its optimum temperature appears to be near o° C. It
thus takes the place in the economy of the waters that
is filled during the summer by the smaller green
flagellates.

Synura (fig. 30^) is another winter flagellate, similar
in color and associated with Dinobryon, much larger
in size. Its cells are grouped in spherical colonies
united at the center of the sphere, and equipped on the
outer ends of each with a pair of flagella, which keep the
sphere in rolling locomotion. The colonies appear at
times of maximum development to be easily disrupted,
and single cells and small clusters of cells are often found
along with well formed colonies. Synura when abund-
ant often gives to reservoir waters an odor of cucumbers,.

loS

Aquatic Organisms

and a singularly persistent bad flavor, and under such
circumstances it becomes a pest in water supplies.

Glenodinium (fig. 3Qf), Peridinium, and Ceratium
(fig. 307) are three brownish shell-bearing flagellates of
wide distribution often locally abundant, especially in
spring and summer. These all have one of the two long
flagella laid in a transverse groove encircling the body,

the other flagellum free (fig. 33).
Glenodinium is the smallest,
Ceratium, much the largest.
Glenodinium has a smooth
shell, save for the grooves where
the flagella arise. Peridinium
has a brownish chitinous shell,
divided into finely reticulate
plates. Ceratium has a heavy
grayish shell prolonged into
several horns.

On several occasions in spring
we have seen the waters of the
Gym Pond on the Campus at
Lake Forest College as brown
as strong tea with a nearly pure
culture of Peridinium and con-
currently therewith we have
seen the transparent phantom-larvae of the midge
Corethra in the same pond all showing a conspicuous
brown line where the alimentary canal runs through
the body, this being packed full of Peridinia.

Trachelomonas (fig. 30 d) is a spherical flagellate hav-
ing a brownish shell with a short flask-like neck at one
side whence issues a single flagellum. This we have
found abundantly in pools that were rich in oak leaf
infusions.

FIG. 33. Ceratium (The trans-
verse groove shows plainly,
but neither flagellum shows
in the photograph.)

Diatoms

log

Diatoms — Diatoms are among the most abundant of
living things in all the waters of the earth. They occur
singly and free, or attached by gelatinous stalks, or

FIG. 34. Miscellaneous diatoms, mostly species of Navicula; the filaments
are blue-green algae, mostly Oscillator ia.

aggregated together in gelatinous tubes, or compactly
grouped in more or less coherent filaments. All are
of microscopic size. They are most easily recognized by
their possession of a box-like shell, composed of two
valves, with overlapping edges. These valves are
stiffened by silica which is deposited in their outer walls,
often in beautiful patterns. The opposed edges of the

no Aquatic Organisms

valves are connected by a membraneous portion of the
cell wall known as the girdle. A diatom may appear
very different viewed from the face of the valve, or from
the girdle (see fig. 35*2 and b, or j and k). They are
circular-like pill-boxes in one great group, and more or
less elongate and bilateral in the others.

Diatoms are rarely green in color. The chlorophyll
in them is suffused by a peculiar yellowish pigment
known as diatomin, and their masses present tints of
amber, of ochre, or of brown ; sometimes in masses they
appear almost black. The shells are colorless; and,
being composed of nearly pure silica, they are well
nigh indestructible. They are found abundantly in
guano, having passed successively through the stomachs
of marine invertebrates that have been eaten by fishes,
that have been eaten by the birds responsible for the
guano deposits, and having repeatedly resisted diges-
tion and all the weathering and other corroding effects
of time. They abound as fossils. Vast deposits of
them compose the diatomaceous earths. A well-known
bed at Richmond, Va., is thirty feet in thickness and of
vast extent. Certain more recently discovered beds
in the Rocky Mountains attain a depth of 300 feet.
Ehrenberg estimated that such a deposit at Biln in
Bohemia contained 40,000,000 diatom shells per cubic
inch.

Singly they are insignificant, but collectively they are
very important, by reason of their rapid rate of increase,
and their ability to grow in all waters and at all ordinary
temperatures. Among the primary food gatherers
of the water world there is no group of greater import-
ance.

In figure 35 we present more or less diagrammatically
a few of the commoner forms. The boat-shaped, freely
moving cells of Navicula (a, b, c] are found in every
pool. One can scarcely mount a tuft of algae, a leaf

Diatoms

in

of water moss or a drop of sediment from the bottom
without finding Naviculas in the mount. They are
more abundant shoreward than in the open waters of
the lake. The "white-cross diatom" Stanroneis (d), is a
kindred form, easily recognizable by the smooth cross-
band which replaces the middle nodule of Navicula.

FIG. 35. Diatoms.

a, valve view showing middle and end nodules, and b, girdle view of Naviaila. c, another
species of Navicula; d, Stauroneis; e, valve view and /, girdle view of Tabellaria; g,
Synedra; h, Gyrosigma; i, a gelatinous cord-like cluster of Encyonema showing girdle
view of nine individuals and valve view of three, j, valve view and k, girdle view of
Melosira; l,Stephanodiscus; m, Meridian colony, with a single detached individual shown
in valve view below; n, a small colony of Asteriondla; o, valve view, and p, girdle view
of Camplylodiscus; q, cluster of Cocconema. (Figures mostly after Wolle).

Tabellaria (e and /) is a thin flat-celled diatom that
forms ribbon-like bands, the cells being apposed, valve
to valve. Often the ribbons are broken into rectangu-
lar blocks of cells which hang together in zig-zag lines
by the corners of the rectangles. The single cell is long-
rectangular in girdle view (slightly swollen in the middle
and at each end, as shown at e, in valve view), and is
traversed by two or more intermediate septa. Tabel-
laria abounds in the cool waters of our deeper northern
lakes , at all seasons of the year. It is much less common
in streams.

112 Aquatic Organisms

The slender cells of the" needle diatoms," Synedra (g),
are common in nearly all waters and at all seasons.
They are perhaps most conspicuously abundant when
found, as often happens, covering the branches of some
tufted algae, such as Cladophora, in loose tufts and
fascicles, all attached by one end.

Gyrosigma (h) is nearly allied to Navicula but is
easily recognized by the gracefully curved outlines of its
more or less S-shaped shell. The sculpturing of this
shell (not shown in the figure) is so fine it has long been a
classic test-object for the resolving power of microscopic
lenses. Gyrosigma is a littoral associate of Navicula,
but of much less frequent occurrence.

Encyonema (i} is noteworthy for its habit of develop-
ing in long unbranched gelatinous tubes. Sometimes
these tubes trail from stones on the bottom in swift
streams. Sometimes they radiate like delicate filmy
hairs from the surfaces of submerged twigs in still
water. The tubes of midge larvae shown in figure oo
were encircled by long hyaline fringes of Encyonema
filaments, which constituted the chief forage of the
larvae in the tubes and which were regrown rapidly
after successive grazings. When old, the cells escape
from the gelatine and are found singly.

The group of diatoms having circular shells with
radially arranged sculpturing upon the valves is repre-
sented by Melosira (j and k) and Stephanodiscus (I) of
our figure. Melosira forms cylindric filaments, whose
constituent cells are more solidly coherent than in
other diatoms. Transverse division of the cells in-
creases the length of the filaments, but they break with
the movement of the water into short lengths of usually
about half a dozen cells. They are common in the
open water of lakes and streams, and are most abundant
at the higher temperatures of midsummer. Cyclotella
is a similar form that does not, as a rule, form filaments.

Diatoms

Its cells are very small, and easily overlooked, since
they largely escape the finest nets and are only to be

Car/WaSS,

%«*«*•

J?VV

..-

WL,

y*

^*S^ > < "* ' •

SSN8S ME

vj '

**t

*' -i •

-2-*J«-.. •

A^

56R»^y." *^*s %

tW$ -i. "

c6 -

FIG. 36. A nearly pure culture of Meridion, showing colonies of

various sizes.

gathered from the water by filtering. Often, however,
their abundance compensates for their size. Kofoid
found their average number in the waters of the Illinois

H4 Aquatic Organisms

River to be 36,558,462 per cubic meter of water, and he
considered them as one of the principal sources of food
supply of Entomostraca and other microscopic aquatic
animals. Stephanodiscus (I) is distinguished by the
long, hyaline filaments that radiate from the ends of the
box, and that serve to keep it in the water. A species
of Stephanodiscus having shorter and more numerous
filaments is common in the open waters of Cayuga Lake
in spring.

The cells of Meridian are wedge-shaped, and grouped
together side by side, they form a flat spiral ribbon of
very variable length, sometimes in one or more com-
plete turns, but oftener broken into small segments.
This form abounds in the brook beds about Ithaca,
covering them every winter with an amber -tinted or
brownish ooze, often of considerable thickness. It
appears to thrive best when the temperature of the
water is near o° C. Its richest growth is apparent after
the ice leaves the brooks in the spring. As a source of
winter food for the lesser brook-dwelling animals, it is
doubtless of great importance. A view of a magni-
fied bit of the ooze is shown in figure 36.

The colonies of Asterionella (?z) whose cells, adhering
at a single point, radiate like the spokes of a wheel, are
common in the open waters of all our lakes and large
streams. It is a common associate of Cyclotella, and of
Tabellaria and other band-forming species, and is often
more abundant than any of these. The open waters of
Lake Michigan and of Cayuga Lake are often yellowish
tinted because of its abundance in them. Late spring
and fall (especially the former) after the thermal over-
turn and complete circulation of the water are the
seasons of its maximum development. Asterionella
abounds in water reservoirs, where, at its maxima, it
sometimes causes trouble by imparting to the water an
aromatic or even a decidedly "fishy" odor and an
unpleasant taste.

Diatoms

Campylodiscus (o and p) is a saddle-shaped diatom of
rather local distribution. It is found abundantly in the
ooze overspreading the black muck bottom of shallow
streams at the outlet of bogs. In such places in the
upper reaches of the tributaries of Fall Creek near
Ithaca it is so abundant as to constitute a large part of
the food of a number of denizens of the bottom mud — •
notably of midge larvae, and of nymphs of the big
Mayfly, Hexagenia.

These are a few — a very few — of the more important
or more easily recognized diatoms. Many others will
be encountered anywhere, the littoral forms especially
being legion. Stalked forms like Cocconema (fig. 355 and
fig. 37) will be found attached to every solid support.
And minute close-clinging epiphytic diatoms, like
Cocconeis and Epithemia will be
found thickly besprinkling the
green branches of many sub-
merged aquatics. These adhere
closely by the flat surface of one
valve to the epidermis of aquatic
mosses.

In open lakes, also, there are
other forms of great importance,
such as Diatoma, Fragillaria, etc.,
growing in flat ribbons, as does
Tabellaria. It is much to be
regretted that there are, as yet,
no readily available popular
guides to the study of a group,
so important and so interesting.

Equipped with a plancton net and a good microscope,
the student would never lack for material or for prob-
lems of fascinating interest.

FIG. 37. A stalked colony
Cocconema.

n6

Aquatic Organisms

Desmids — This is a group of singularly beautiful
unicellular fresh-water algae. Desmids are, as a rule,
of a refreshing green color, and their symmetry of form
and delicacy of sculpturing are so beautiful that they
have always been in favor with microscopists. So

FIG. 38. A good slide-mount from a Closterium culture
as it appears under a pocket lens. Two species.

numerous are they that their treatment has of late been
relegated to special works. Here we can give only a
few words concerning them, with illustrations of some
of the commoner forms.

Desmids may be recognized by the presence of a clear
band across the middle of each cell, (often emphasized
by a corresponding median constriction) dividing it
symmetrically into two semicells. Superficially they
appear bicellular (especially in such forms as Cylindro-

Desmids

117

cystis, fig. 40 e), but there is a single nucleus, and it lies
in the midst of the transparent crossband. The larger
ones, such as Closterium (fig. 38) may be recognized with
the unaided eye, and may be seen clearly with a pocket
lens. Because it will grow per-
ennially in a culture jar in a
half -lighted window, Closterium
is a very well known labora-
tory type.

Division is transverse and sep-
arates between the semicells.
Its progress in Closterium is
shown in figure 39, in a series of
successive stages that were photo-
graphed between 10 p. M. and 3
A. M. Division normally occurs
only at night.

In a few genera (Gonatozygon,
(fig. 400) Desmidium, etc.) the
cells after division remain at-
tached, forming filaments.

Desmids are mainly free float-
ing and grow best in still waters.
They abound in northern lakes
and peat bogs. They prefer the
waters that run off archaean
rocks and few of them flourish
in waters rich in lime. A few
occur on mosses in the edges of
waterfalls, being attached to the
mosses by a somewhat tenacious gelatinous invest-
ment. One can usually obtain a fine variety of
desmids by squeezing wisps of such water plants
as Utricularia and Sphagnum, over the edge of a
dish, and examining the run-off. The largest genus of
the group and also one of the most widespread is

FIG. 39. Photomicrographs
of a Closterium dividing.
The lowermost figure is
one of the newly formed
daughter cells, not yet
fully shaped.

n8

Aquatic Organisms

g

FIG. 40. Desmids.

Filamentous Conjugates

119

m.

.•A; •„-

Cosmarium (fig. 40 5). The
most bizarre forms are found
in the genera Micrasterias (figs.
40 q and r) and Staurastrum.
These connect in form
through Euastrum (fig. 40 o)
Tetmemorus (fig. 40 n) Netrium
(fig. 40 d), etc., with the sim-
pler forms which have little
differentiation of the poles of
the cell; and these, especially
Spirotaenia (fig. 40 b) and Gon-
atozygon (fig. 40 a) connect
with the filamentous forms
next to be discussed.

The Filamentous Conjugates
• — This is the group of fila-
mentous algae most closely
allied with the desmids. It
includes three common genera
(fig. 41) — Spirogyra, Zygnema,

and Mougeotia. The first of these being one of
the most widely used of biological ' 'types" is known
to almost every laboratory student. Its long, green,
unbranched, slippery filaments are easily recognized
among all the other greenery of the water by their
beautiful spirally- wound bands of chlorophyl. The
other common genera have also distinctive chlorophyl
arrangement. Zygnema has a pair of more or less
star-shaped green masses in each cell, one on either side
of the central nucleus. In Mougeotia the chlorophyl

FIG. 41. Filamentous con-
jugates.

a, Spirogyra; b, flat view, and c,
edgewise view of the chlorophyl
plate in cells of Mougeotia; d,
Zygnema.

a, a little more than two cells g Docidium baculum

from a filament of Gonatozygon It Docidium undulatum

b Spirotcenia i Closterium pronum

c Mesotanium j Closterium rostratum

d Netrium k Closterium moniliferum

e Cylindrocystis I Closterium ehrenbergi

Penium nt Pleurotanium

n Tetmemorus

o Euastrum didelta

p Euastrum verrucosum

q Micrasterias oscitans

r Micrasterias americana; (for

a third species see page 53).
5 Cosmarium, face view, and

outline as seen from the side

I2O Aquatic Organisms

is in a median longitudinal plate, which can rotate in
the cell : it turns its thin edge upward to the sun, but
lies broadside exposed to weak light. Spirogyra is
the most abundant, especially in early spring where it
is found in the pools ere the ice has gone out. All, being
unattached (save as they become entangled with rooted
aquatics near shore), prefer quiet waters. Immense
accumulations of their tangled filaments often occur on
the shores of shallow lakes and ponds, and with the
advance of spring and subsidence of the water level,
these are left stranded upon the shores. They chiefly
compose the "blanket-moss" of the fishermen. They
settle upon and smother the shore vegetation, and in
their decay they sometimes give off bad odors. Some-
times they are heaped in windrows on shelving beaches,
and left to decay.

We most commonly see them floating at the surface
in clear, quiet, spring-fed waters in broad filmy masses
of yellowish green color, which in the sunlight fairly
teem with bubbles of liberated oxygen. These dense
masses of filaments furnish a home and shelter for a
number of small animals, notably Haliplid beetle larva?
and punkie larvae among insects; and entanglement
by them is a peril to the lives of others, notably certain
Mayfly larva? (Blasturus). The rather large filaments
afford a solid support for hosts of lesser sessile algae;
and their considerable accumulation of organic contents
is preyed upon by many parasites. Their role is an
important one in the economy of shoal waters, and its
importance is due not alone to their power of rapid
growth, but also to their staying qualities. They hold
their own in all sorts of temporary waters by develop-
ing protected reproductive cells known as zy 'go spores,
which are able to endure temporary drouth, or other
untoward conditions. Zygospores are formed by the
fusion of the contents of two similar cells (the process

Siphon Algae

121

o-t,.

is known as conjugation, whence the group name) and
the development of a protective wall about the result-
ing reproductive body. This rests for a time like a seed,
and on germinating, produces a new filament by the
ordinary process of cell division. These filamentous
forms share this reproductive process with the desmids,
and despite the differences in external aspect it is a
.strong bond of affinity between the two groups.

The siphon algcc — This
peculiar group of green
algas contains a few forms
of little economic con-
sequence but of great
botanical interest. The
plant body grows out in
long irregularly branch-
ing filaments which,
though containing many
nuclei, lack cross par-
titions. The filaments
thus resemble long open
tubes, whence the name
siphon algas. There are two common genera Vau-
cheria and Botrydium (fig. 42). Both are mud-lov-
ing, and are found partly out of the water about as
often as wholly immersed. Vaucheria develops long,
•crooked, extensively interlaced filaments which occur in
dense mats that have suggested the name "green felt."
These felted masses are found floating in ponds, or
lying on wet soil wherever there is light and a con-
stantly moist atmosphere (as, for example, in green-
houses, where commonly found on the soil in pots).
Botrydium is very different and much smaller. It has
an oval body with root -like branches growing out from
the lower end to penetrate the mud. It grows on the
bottom in shoal waters, and remains exposed on the

FIG. 42. Two siphon algas.

A, Botrydium; B, a small fruiting portion of a
filament of Vaucheria.; ov, ovary; sp, spermary.

122 Aquatic Organisms

mud after the water has receded, dotting the surface
thickly, as with greenish beads of dew.

The water net and its allies — The water net (Hydro-
dictyori} wherever found, is sure to attract attention by
its curious form. It is a cylindric sheet of lace-like
tissue, composed of slender green cells that meet at

FIG. 43. A rather irregular portion of a sheet of water net

(Hydrodictyon)

their ends, usually by threes, forming hexagonal meshes
like bobbinet (fig. 43). Such colonies may be as broad
as one's hand, or microscopic, or of any intermediate
size; for curiously enough, cell division and cell
growth are segregated in time. New colonies are
formed by repeated division of the contents of single

The Water Nets

123

cells of the old colonies. A new complete miniature
net is formed within a single cell; and after its escape
from the old cell wall, it grows, not by further division,
but by increase in size of its constituent cells.

Water net is rather local and sporadic in occurrence,
but it sometimes develops in quantities sufficient to fill
the waters of pools and small ponds.

FIG. 44. Pediastrum: Several species from the plancton of

Cayuga Lake.

Pediastrum is a closely related genus containing a
number of beautiful species, some of which are common
and widespread. The cells of a Pediastrum colony are
arranged in a roundish flat disc, and those of the outer-
most row are usually prolonged into radiating points.
Several species are shown in figure 44. In the open-

I24

Aquatic Organisms

meshed species the inner cells can be seen to meet by
threes about the openings, quite as in the water net;
but the cells are less elongate and the openings smaller.
Five of the seven specimens shown in the figure lack
these openings altogether.

New colonies are formed within single cells, as in
Hydrodictyon. In our figure certain specimens show
marginal cells containing developing colonies. One
shows an empty cell wall from whence a new colony has
escaped.

Other green algce —
We have now men-
tioned a few of the
more strongly
marked groups of the
green algae. There
are other forms, so
numerous we may
not even name them
here, many of which
are common and
widely dispersed.
We shall have space
to mention only a
few of the more im-
portant among them,
and we trust that

the accompanying figures will aid in their recognition.
Numerous and varied as they are, we will dismiss them
from further consideration under a few arbitrary form
types.

i. Simple filamentous forms. Of such sort are
Ulothrix, CEdogonium, Conferva, etc., (fig. 45). Ulo-
thrix is common in sunny rivulets and pools, especially
in early spring, where its slender filaments form masses

FIG. 45. Filamentous Green Algse.

a, Ulothrix; b, CEdogonium, showing characteristic
annulate appearance at upper end of cell; c,
Conferva (Tribonema); d, Draparnaldia. (After
West).

Other Green Algae

125

half floating in the water. The cells are short, often no
longer than wide, and each contains a single sheet of

FIG. 46. A spray of Cladophora, as it appears when
outspread in the water, slightly magnified.

chlorophyl, lining nearly all of its lateral wall. CEdogo-
nium is a form with stouter filaments composed of
much longer cells, within which the chlorophyl is dis-

126

Aquatic Organisms

posed in anastomosing bands. The thick cell walls,
some of which show a peculiar cross striation near one
end of the cell, are ready means of recognition of the
members of this great genus. The filaments are
attached when young, but break away and float freely
in masses in quiet waters when older; it is thus they
are usually seen. Conferva (Tribonema) abounds in
shallow pools, especially in spring time. Its filaments
are composed of elongate cells containing a number of

separate disc-like chlor-
ophyl bodies. The cell
wall is thicker toward
the ends of the cell, and
the filaments tend to
break across the middle,
forming pieces (halves of
two adjacent cells) which
appear distinctly H-
shaped in optic section.
This is a useful mark
for their recognition. It
will be observed that
these then are similar
in form and habits to
the filamentous conju-
gates discussed above,
but they have not the
peculiar form of chlor-

ophyl bodies characteristic of that group. (Eodgonium
is remarkable for its mode of reproduction.

2. Branching filamentous forms — Of such sort are a
number of tufted sessile algae of great importance:
Cladophora, which luxuriates in the dashing waterfall,
which clothes every wave-swept boulder and pier with
delicate fringes of green, which lays prostrate its pliant
sprays (fig. 46) before each on-rushing wave, and lifts

FIG. 47. Two species of Chastophora,
represented by several small hemi-
spherical colonies of C. pisiformis and
one large branching colony of
C. incrassata.

Other Green Algae 127

them again uninjured, after the force of the flood is
spent. And Chcstophora (fig. 47 ; also fig. 89 on p. 182) ;
which is always deeply buried under a transparent mass

FIG. 48. Chsetophora (either species) crushed and outspread
in its own gelatinous covering and magnified to show the
form of the filaments.

of gelatin; which form little hemispherical hillocks of
filaments in some species, and in one, extends outward
in long picturesque sprays, but which has in all much
the same form of plant body (fig. 48) — -a close-set branch-
ing filament, with the tips of some of the branches ending
in a long hyaline bristle-like point. Chaetophora grows
very abundantly in stagnant pools, and ponds in mid-

128

Aquatic Organisms

summer, adhering to every solid support that offers,
and it is an important part of the summer food of many
of the lesser herbivores in such waters.

Then we must not omit to mention two that, if less
important, are certainly no less interesting: Drapar-
naldia (fig. 45^) which lets its exceedingly delicate sprays
trail like tresses among the submerged stones in spring-

. , , ,;.'--,.

• 'VA, :•>

>

FIG. 49. Coleochate scutata. "Green doily."

fed rivulets ; and Coleochate (fig. 49) , which spreads its
flattened branches out in one plane, joined by their
edges, forming a disc, that is oftenest found attached to
the vertical stem of some reed or bulrush.

Miscellaneous lesser green alga — Among other green
algae, which are very numerous, we have space here for
a mere mention of a few of the forms most likely to be
met with, especially by one using a plancton net in open
waters. These will also illustrate something of the

Lesser Green Algae

129

remarkable diversity of form and of cell grouping among
the lesser green algae.

Botryococcus grows in free floating single or compound
clusters of little globose green cells, held together in a
scanty gelatinous investment. The clusters are suffi-
ciently grape-like to have suggested the scientific name.
They contain, when grown, usually 1 6 or 32 cells each.
They are found in the open waters of bog pools, lakes,

/>>?•!! :. ' 84 f .- -'

" V,-- . • .? (• , *t i
\- '? ,'. * ~ '.' #.

£•••» *

FIG. 50. Miscellaneous green algas (mostly after West).

a, Botryococcus; b, Cedastrum; c, Dictosphczrium; d, Kirchnerella;
e, Selenastrum; f, Ankisirodesmus falcatus; g, Ophiocytium; h,
Tetraspora; i, Crucigenia; j, Scenedesmus;, k, Rhicteriella; I,
Ankisirodesmus setigerus; m, Oocystis.

and streams, during the warmer part of the season,
being most abundant during the hot days of August.
When over-abundant the cells sometimes become filled
with a brick-red oil. They occur sparingly in water-
bloom.

Dictyosphcerum likewise grows in more or less spheri-
cal colonies of globose cells. The cells are connected
together by dichotomously branching threads and all
are enveloped in a thin spherical mass of mucus. The
colonies are free floating and are taken in the plancton of
ponds and lakes and often occur in the water-bloom.

130 Aquatic Organisms

Ccdastrum is another midsummer plancton alga that
forms spherical colonies of from 8 to 32 cells ; it has much
firmer and thicker cell walls, and the cells are often
angulate or polyhedral. New colonies are formed within
the walls of each of the cells of the parent colony, and
when well grown these escape by rupture or dissolution
of the old cell wall. Our figure shows merely the out-
line of the cell walls of a i6-celled colony, in a species
having angulate cells, between which are open inter-
spaces. Kofoid found Ccelastrum occurring in a maxi-
mum of 10,800,000 per cubic meter of water in the
Illinois River in August.

Crucigenia is an allied form having ovoid or globose
cells arranged in a flat plate held together by a thin
mucilaginous envelope. The cells are grouped in fours,
but 8, 16, 32, 64 or even more may, when undisturbed,
remain together in a single flat colony. During the
warmer part of the season, they are common constit-
uents of the fresh-water plancton, the maximum heat
of midsummer apparently being most favorable to their
development.

Scenedesmus is a very hardy, minute, green alga of
wide distribution. There is hardly any alga that
appears more commonly in jars of water left standing
about the laboratory. When the sides of the jar begin
to show a film of light yellowish -green, Scenedesmus
may be looked for. The cells are more or less spindle-
shaped, sharply pointed, or even bristle-tipped at the
ends. They are arranged side by side in loose flat rafts
of 2, 4 or 8 (oftenest, when not broken asunder, of 4)
cells. They are commcn in plancton generally, espec-
ially in the plancton of stagnant water and in that of
polluted streams, and although present at all seasons,
thev are far more abundant in mid and late summer.

Lesser Green Algae 131

Kirchnerella is a loose aggregate of a few blunt-
pointed U-shaped cells, enveloped in a thick spherical
mass of jelly. It is met with commonly in the plancton
of larger lakes. Selenastrum grows in nearly naked
clusters of more crescentic, more pointed cells which are
found amid shore vegetation. Ankistrodesmus is a
related, more slender, less crescentic form of more
extensive littoral distribution. The slenderest forms of
this genus are free floating, and some of them like .4.
setigcra (fig. 50 /) are met with only in the plancton.

Richtericlla is another plancton alga found in free
floating masses of a few loosely aggregated cells. The
cells are globose and each bears a few long bristles upon
its outer face. Kofoid found Richteriella attaining a
maximum of 36,000,000 per cubic meter of water in
September, while disappearing entirely at temperatures
below 60° F.

Ooeystis grows amid shore vegetation, or the lighter
species, in plancton in open water. The ellipsoid cells
exist singly, or a few are loosely associated together in a
clump of mucus. The cells possess a firm smooth wall
which commonly shows a nodular thickening at each
pole.

Ophiocytium is a curious form with spirally coiled
multinucleate cells. The bluntly rounded ends of the
cells are sometimes spine-tipped. These cells some-
times float free, sometimes are attached singly, some-
times in colonies. Kofoid found them of variable
occurrence in the Illinois River, where the maximum
number noted was 57,000,000 per cubic meter occur-
ring in September. The optimum temperature, as
attested by the numbers developing, appeared to be
about 60° F.

Tctraspora — We will conclude this list of miscellanies
with citing one that grows in thick convoluted strings

132 Aquatic Organisms

and loose ropy masses of gelatin of considerable size.
These masses are often large enough to be recognized
with the unaided eye as they lie outspread or hang down
upon trash on the shores of shoal and stagnant waters.
Within the gelatin are minute spherical bright green
cells, scattered or arranged in groups of fours.

BLUE-GREEN ALG^E (Cyanophycece or Myxophyce a: ) .
The "blue-greens" are mainly freshwater algas, of simple
forms. The cells exist singly, or embedded together in
loose gelatinous envelope or adhere in flat rafts or in
filaments. Their chlorophyl is rather uniformly dis-
tributed over the outer part of the cell (quite lacking the
restriction to specialized chloroplasts seen in the true
green-algae) and its color is much modified by the
presence of pigment (pkycocyanin) , which gives to the
cell usually a pronounced bluish-green, sometimes, a
reddish color.

Blue-green algae exist wherever there is even a little
transient moisture — on tree trunks, on the soil, in
lichens, etc. ; and in all fresh water they play an import-
ant role, for they are fitted to all sorts of aquatic
situations, and they are possessed of enormous reproduc-
tive capacity. Among the most abundant plants in the
water world are the Anabcenas (fig. 179), and other blue-
greens that multiply and fill the waters of our lakes in
midsummer, and break in "water-bloom" covering the
entire surface and drifting with high winds in windrows
on shore. Such forms by their decay often give to the
water of reservoirs disagreeable odors and bad flavors,
and so they are counted noxious to water supplies.

There are many common blue-greens, and here we
have space to mention but a few of the more common
forms. Two of the loosely colonial forms composed of
spherical cells held together in masses of mucus are
and Microcstis. Both these are often

Tetranspora

133

associated with Anabsena in the water-bloom. Ccelos-
phasrium is a spherical hollow colony of microscopic size.
It is a loose association of cells, any of which on separa-
tion is capable of dividing and producing a new colony.
Microcystis (fig. 51-4) is a mass of smaller cells, a very
loose colony that is at first more or less spherical but
later becomes irregularly lobed and branching. Such
old colonies are often large enough to be observed with
the naked eye. They are found most commonly in late

summer, being hot
weather forms. When
abundant these two are
often tossed by the
waves upon rocks along
the water's edge, and
from them the dirty blue-
green deposit that is
popularly known as
"green paint."

Among the members
of this group most com-
monly seen are the motile
blue-greens of the genus
Oscillatoria (fig. 5 1 G) .
These grow in dense, strongly colored tufts and patches
of exceedingly slender filaments attached to the bottoms
and sides of watering troughs, ditches and pools,
and on the beds of ponds however stagnant. They
thickly cover patches of the black mud bottom
and the formation of gases beneath them disrupts their
attachment and the broken flakes of bottom slime that
they hold together, rise to the surface and float there,
much to the hurt of the appearance of the water.

The filaments of Oscillatoria and of a few of its near
allies perform curious oscillating and gliding movements.
Detached filaments float freely in the open water, and

FIG. 51. Miscellaneous blue-green
algae (mostly after West).

A, Microcystis (Clathrocystis) ; B, C, D,
Tetrapedia; E, Spiriilina; F, Nostoc; G,
Oscillatoria; H, Rivularia.

134

Aquatic Organisms

during the warmer portion of the year, are among the
commoner constituents of the plancton.

There are a number of filamentous blue-greens that
are more permanently sessile, and whose colonies of
filaments assume more definite form. Rivularia is
typical of these. Rivularia grows in hemispherical
gelatinous lumps, attached to the leaves and stems of
submerged seed plants. In atitumn it often fairly
smothers the beds of hornwort (Ceratopliylluni) and
water fern (Marsilea) in rich shoals. Rivularia is

FIG. 52. Colonies of Rivularia on a disintegrating
Typha leaf.

browTnish in color, appearing dirty yellowish under the
microscope. Its tapering filaments are closely massed
together in the center of the rather solid gelatinous
lump. The differentiation of cells in the single filament
is shown in fig. 51 H. Such filaments are placed side
by side, their basal heterocysts close together, their tips
diverging. As the mass grows to a size larger than a pea
it becomes softer in consistency, more loosely attached
to its support and hollow. Strikingly different in form
and habits is the raftlike Merismopcedia (fig. 53). It
is a flat colony of shining blue-green cells that divide in
two planes at right angles to each other, with striking

Red and Brown Algae

135

regularity. These rafts of cells drift about freely in
open water, and are often taken in the plancton, though
rarely in great abundance. They settle betimes on the
leaves of the larger water plants, and may be discovered
with a pocket lens by searching the sediment shaken
therefrom.

FIG. 53. Merismopsedia.

RED and BROWN ALGJE (Rlwdopliycece andPh&ophycecB)
— These groups are almost exclusively marine. A few
scattering forms that grow in fresh water are shown in
figure 54. Lemaneo, is a torrent-inhabiting form that
grows in blackish green tufts of slender filaments,
attached to the rocks in deep clear mountain streams
where the force of the water is greatest. It is easily

136

Aquatic Organisms

recognizable by the swollen or nodulose appearance of
the ultimate (fruiting) branches. Chantransia is a
beautiful purplish-brown, extensively branching form
that is more widely distributed. It is common in clear
flowing streams . It much resembles Cladophora in man-
ner of growth but is at once distinguished by its color.

d

FIG. 54. Red and brown algse (after West).

a, Lemanea; b, Chantransia; c. Batrachospermum; d, Hydrurus.

Batrachospermnm is a freshwater form of wide distri-
bution, with a preference for spring brooks, though occur-
ring in any water that is not stagnant. It grows in
branching filaments often several inches long, enveloped
in a thick coat of soft transparent mucus. The color is
bluish or yellowish-green, dirty yellow or brownish.
Attached to some stick or stone in a rivulet its sprays, of
more than frond-like delicacy, float freely in the water.

Hydrurus grows in branched colonies embedded in a
tough mucilage, attached to rocks in cold mountain
streams. The colonies are often several inches long.
Their color is olive green. They have a plumose
appearance, and are of very graceful outline.

The Stoneworts

137

The stoneworts (Characece) .- -This group is well repre-
sented in freshwater by two common genera, well known
to every biological laboratory student, Char a and
Nitella. Both grow in protected shoals, and in the
borders of clear lakes at depths below the heavy beating
of the waves. Both are brittle and cannot withstand

FIG. 55. Nitella glomerulifera.

wave action. Both prefer the waters that flow off from
calcareous soils, and are oftenest found attached to a
stony bottom.

The stoneworts, are the most specialized of the fresh-
water algae: indeed, they are not ranked as algae by
some botanists. In form they have more likeness to
certain land plants than to any of the other algae.

138 Aquatic Organisms

They grow attached to the soil. They grow to consider-
able size, often a foot or more in length of stem. They
grow by apical buds, and they send out branches in
regular whorls, which branch and branch again, giving
the plant as a whole a bushy form. The perfect regu-
larity of the whorled branches and the brilliant colora-
tion of the little spermaries borne thereon, doubtless
have suggested the German name for them of "Cande-
labra plants."

The stone worts are so unique in structure and in repro-
ductive parts that they are easily distinguished from
other plants. The stems are made up of nodes and
internodes. The nodes are made up of short cells from
which the branches arise. The internodes are made up
of long cells (sometimes an inch or more long), the
central one of which reaches from one node to another.
In Nitella there is a single naked internodal cell com-
posing entirely that portion of the stem. In Chara this
axial cell is covered externally by a single layer of
slenderer cortical cells wound spirally about the central
one. A glance with a pocket lens will determine whether
there is a cortical layer covering the axial internodal
cell, and so will distinguish Chara from Nitella. Chara
is usually much more heavily incrusted with lime in our
commoner species, and in one very common one, Chara
fcetida, exhales a bad odor of sulphurous compounds.

The sex organs are borne at the bases of branchlets.
There is a single egg in each ovary, charged with a rich
store of food products, and covered by a spirally wound
cortical layer of protecting cells. These, when the egg
is fertilized form a hard shell which, like the coats of a
seed, resist unfavorable influences for a long time.
This fruit ripens and falls from the stem. It drifts
about over the bottom, and later it germinates.

At the apex of the ovary is a little crown of cells,
between which lies the passageway for the entrance of

Chlorophylless Plants 139

the sperm cell at the time of fertilization. This crown
is composed of five cells in Chara ; of ten cells in Nitella.
It is deciduous in Chara; it is persistent in Nitella.

The stoneworts, unlike many other algae, are wonder-
fully constant in their localities and distribution, and
regular in their season of fruiting. They cover the
same hard bottoms with the same sort of gray -green
meadows, year after year, and although little eaten by
aquatic animals, they contribute important shelter for
them, and they furnish admirable support for many
lesser epiphytes.

CHLOROPHYLLESS WATER PLANTS, BACTERIA

AND FUNGI

Nature's great agencies for the dissolution of dead
organic materials, in water as on land, are the plants
that lack chlorophyl. They mostly reproduce by
means of spores that are excessively minute and abund-
ant, and that are distributed by wind or water every-
where; consequently they are the most ubiquitous of
organisms. They consume oxygen and give off carbon
dioxide as do the animals, and having no means of
obtaining carbon from the air, must get it from car-
bonaceous organic products — usually from some carbo-
hydrate, like sugar, starch, or cellulose. Some of them
can utilize the nitrogen supply of the atmosphere but
most of them must get nitrogen also from the decompo-
sition products of pre-existing proteins. Many of them
produce active ferments, which expedite enormously the
dissolution of the bodies of dead plants and animals.
Some bacteria live without free oxygen.

It follows from the nature of their foods, that we find
these chlorophylless plants abounding where there is the
best supply of organic food stuffs. Stagnant pools
filled with organic remains, and sewers laden with the

140 Aquatic Organisms

city's waste. But there is no natural water free from
them. Let a dead fly fall upon the surface of a tumbler
of pond water and remain there for a day or two and it
becomes white with water mold, whose spores were
present in the water. Let any organic solution stand
exposed and quickly the evidence of rapid decomposition
appears in it. Even the dilute solutions contained in a
laboratory aquarium, holding no organic material other
than a few dead leaves will often times acquire a faint
purple or roseate hue as chromogenic bacteria multiply
in them.

Bacteria — A handful of hay in water will in a few
hours make an infusion, on the surface of which a film
of "bacterial jelly" will gather. If a bit of this "jelly"
be mounted for the microscope, the bacteria that secrete
it may be found immersed in it, and other bacteria
will be found adherent to it. All the common form-
types, bacillus, coccus and spirillum are likely to be seen
readily. Thus easy is it to encourage a rich growth of
water bacteria. Among the bacteria of the water are
numerous species that remain there constantly (often
called "natural water bacteria"), commingled at certain
times and places with other bacteria washed in from the
surface of the soil, or poured in with sewage. From the
last named source come the species injurious to human
health. These survive in the open water for but a short
time. The natural water bacteria are mainly beneficial ;
they assist in keeping the world's food supply in circula-
tion. Certain of them begin the work of altering the
complex organic substances. They attack the proteins
and produce from them ammonia and various ammonia-
cal compounds. Then other bacteria, the so-called
"nitrifying" bacteria attack the ammonia, changing it
to simpler compounds. Two kinds of bacteria succes-
sively participate in this: one kind oxidizes the

Bacteria 141

ammonia to nitrites; a second kind oxidizes the
nitrites to nitrates. By these successive operations the
stores of nitrogen that are gathered together within the
living bodies of plants and animals are again released
for further use. The simple nitrates are proper food
for the green alga?, with whose growth the cycle begins
again. And those bacteria which promote the pro-
cesses of putrefaction, are thus the world's chief agen-
cies for maintaining undiminished growth in perpetual
succession.

Bacteria are among the smallest of organisms. Little
of bodily structure is discoverable in them even with
high powers of the microscope, and consequently they
are studied almost entirely in specially prepared cul-
tures, made by methods that require the technical
training of the bacteriological laboratory for their
mastery. Any one can find bacteria in the wTater, but
only a trained specialist can tell what sort of bacteria
he has found; whether pathogenic species like the
typhoid bacillus, or the cholera spirillum; or whether
harmless species, normal to pure water.

The higher bacteria — Allied to those bacilli that grow
in filaments are some forms of larger growth, known as
Trichobacteria, whose filaments sometimes grow
attached in colonies, and in some are free and motile.
A few of those that are of interest and importance in
fresh-water will be briefly mentioned and illustrated
here.

Leptothrix* (Fig. 56^7 , b and c] grows in tufts of slender,
hairlike filaments composed of cylindric cells sur-
rounded by a thin gelatinous sheath. In reproduction
the cells are transformed directly into spores (gonidia )
which escape from the end of the sheath and, finding
favoring conditions, grow up into new filaments.

*Known also as Streptothrix and Chlamydothnx.

142

Aquatic Organisms

Crenothrix (Fig. 56 d, e and/) is a similar unbranched
sessile form which is distinguished by a widening of the
filaments toward the free end. This is caused by a
division of the cells in two or three planes within the
sheath of the filament, previous to spore formation.
Often by the germination of spores that have settled
upon the outside of the old sheaths and growth of new
filaments therefrom compound masses of appreciable

FIG. 56. Trichobacteria.

a, b, c, Leptothrix (Slreptolhrix, or Chlamydothrix) . a, a colony; 6, a single filament; c, spore
formation; d, e, /, Crenothrix; d, a single growing filament; e, a fruiting filament; /, a
compound colony; g, Cladothrlx, a branching filament; h, Beggiatoa, younger and older
filaments, the latter showing sulphur granules, and no septa between cells of the filament.

size are produced. In the sheaths of the filaments a
hydroxide of iron is deposited (for Crenothrix possesses
the power of oxidizing certain forms of iron) ; and with
continued growth the deposits sometimes become
sufficient to make trouble in city water supply systems
by stoppage of the pipes. In nature, also, certain
deposits of iron are due to this and allied forms properly
known as iron bacteria. Cladothrix (Fig. 56 g), is a
related form that exhibits a peculiar type of branching
in its slender cylindric filaments.

Water Molds

Beggiatoa (fig. 56 h) is the commonest of the so-called
sulfur bacteria. Its cylindric unbranched and unat-
tached filaments are motile, and rotate on the long axis
with swinging of the free ends. The boundaries be-
tween the short cylindric cells are often obscure,
especially when (as is often the case) the cells are filled
with highly refractive granules of sulfur. Considerable
deposits of sulfur, especially about springs, are due to
-the activities of this and allied forms.

Water molds — True fungi of a larger growth abound
in all fresh waters, feeding on almost every sort of
organic substance contained
therein. The commonest of
the water molds are the Sap-
rolegnias, that so quickly
overgrow any bit of dead
animal tissue which may
chance to fall upon the sur-
face of the water and float
there. If it be a fly, in a
day or two its body is sur-
rounded by a white fringe of
radiating fungus filaments,
outgrowing from the body.
The tips of many of these
filaments terminate in cylin-
dric sporangia, which when

FIG. 57. A common water mold,
Saprolegnia. (After Engler and

i escap-

mature, liberate from their ruptured tips innumerable
biciliated free-swimming swarm spores. These wander
in search of new floating carcases, or other suitable food.
Certain of these water molds attack living fishes,
entering their skin wherever there is a a slight abrasion
of the surface, and rapidly producing diseased condi-
tions. These are among the worst pests with which the
fish culturist has to contend. They attack also the

144 Aquatic Organisms

eggs of fishes during their incubation, as shown in a
figure in a later chapter.

Most water molds live upon other plants. Even the
Saprolegnias have their own lesser mold parasites.
Many living algas, even the lesser forms like desmids
and diatoms are subject to their attack. Fine cultures
of such algae are sometimes run through with an
epidemic of mould parasites and ruined.

THE HIGHER PLANTS

(Mossworts, Fernworts and Seed Plants)

In striking contrast with the algae, the higher plants
live mainly on land, and the aquatics among them
are restricted in distribution to shoal waters and to
the vicinity of shores. There is much in the bodily
organization of nearly all of
them that indicates ancestral
adaptation to life on land.
They have more of hard parts,
more of localized feeding
organs, more of epidermal
specialization, and more dif-
erentiation of parts in the
body, than life in the water
demands.

They occupy merely the
margins of the water. A few
highly specialized genera,
well equipped for with-
standing partial or complete
submergence occupy the
shoals and these are backed Fl?: 58- The marsh mallow,

. , , ! . , Hibiscus Alosclieutos.

on the shore line by a

mingled lot of semi-aquatics that are for the most part
but stray members of groups that abound on land.
Often they are single members of large groups and are
sufficiently distinguished from their fellows by a name
indicating the kind of wet place in which they grow.
Thus we know familiarly the floating riccia, the bog
mosses, the brook speedwell, the water fern and water
cress, the marsh bell flower and the marsh fern, the
swamp horsetail and the swamp iris, etc. All these

145

146 Aquatic Organisms

and many others are stragglers from large dry land
groups. That readaptation to aquatic life has occurred
many times independently is indicated by the fact that
the more truly aquatic families are small and highly
specialized, and are widely separated systematically.

Bryophytes — Both liverworts and mosses are found
in our inland waters, though the former are but spar-
ingly represented. Two simple Riccias, half an inch long
when grown, are the liverworts most commonly found.
One, Ricciafluitans, grows in loose clusters of flat slender
forking sprays that drift about so freely that fragments
are often taken in pond and river plancton. The larger
unbroken more or less spherical masses of sprays are found
rolling with the waves upon the shores of muddy ponds.
The other, Ricciocarpus natans, has larger and thicker
sprays of green and purple hue, that float singly upon the
surface, or gather in floating masses covering considerable
areas of quiet water. They are not uncommonly found in
springtime about the edges of muddy ponds. Under-
neath the flat plant body there is a dense brush of
flattened scales.

Water mosses are more important. The most
remarkable of these are the bog mosses (Sphagnum).
These cover large areas of the earth's surface, especially
in northern regions, where they chiefly compose the
thick soft carpet of vegetation that overspreads open
bogs and coniferous swamps. They are of a light grey-
green color, often red or pink at the tips. These
mosses do not grow submerged, but they hold immense
quantities of water in their reservoir cells, and are able
to absorb water readily from a moist atmosphere ; so
they are always wet. Supported on a framework of
entangled rootstocks of other higher plants, the bog
mosses extend out over the edges of ponds in floating
mats, which sink under one's weight beneath the water

Mossworts

147

level and rise again when the weight is removed. The
part of the mat which the sphagnum composes consists
of erect, closely-placed, unbranched stems, like those
shown in fig. 59, which grow ever upward at their tips,

FIG. 59. Bog-moss, Sphagnum.

and die at the lower ends, contributing their remains
to the formation of beds of peat.

The leaves of Sphagnum are composed of a single layer
of cells that are of two very different sorts. There are
numerous ordinary narrow chlorophyl-bearing cells, and,
lying between these, there are larger perforate reservoir
cells, for holding water.

148

Aquatic Organisms

The true water mosses of the genus Fontinalis are
fine aquatic bryophytes. These are easily recognized,
being very dark in color and very slender. They grow
in spring brooks and in clear streams, and are often seen
in great dark masses trailing their wiry stems where the
current rushes between great boulders or leaps into
foam-flecked pools in mountain brooks.

Another slender brook-inhabiting moss is Fissidens
julianum, which somewhat resembles Fontinalis, but
which is at once distinguished by the deeply channeled

bases of its leaves, which
enfold the stem. The
leaves are two ranked and
alternate along the very
slender flexuous stem, and
appear to be set with edges
toward it.

There are also a few
lesser water mosses allied
to the familiar trailing
hypnums, so common in
deep woods. They grow
on stones in the bed of
brooks. They cover the
face of the ledges over
which the water pours in
floods and trickles in times of drouth, as with a fine
feathery carpet of verdure that adds much to the beauty
of the little waterfalls. They give shelter in such places
to an interesting population of amphibious animals, as
will be noted in chapter VI, following. The leaves of the
hypnums are rather short and broad, and in color they
are often very dark — often almost black.*

FIG. 60. Water mosses.

a, Fontinalis; b, Fissidens julianum, with a
single detached leaf, more enlarged; c,
Rhvnchostegium rusciforme, with a single
detached leaf at the left. (After Grout.)

*Grout has given a few hints for the recognition of these "Water-loving
hypnums" in his Mosses with a Hand Lens, 2d edition, p. 128. New York,
1905-

Peter idophytes

149

There are also a few hypnums found intermixed with
sphagnum, on the surface of bogs, and as everyone
knows there are hosts of mosses in all moist places in
woods and by watersides.

FIG. 61. Two floating leaves of the "water shamrock," Marsilea, in the midst
of a surface layer of duck-meat (Spirodela polyrhiza). "Lemna" on fig. 62.

Pteridopliytes — Aquatic fernworts are few and of very
unusual types. There is at least one of them, how-
ever, that is locally dominant in our flora. Marsilea,
the so-called water shamrock or water fern, abounds on

150

Aquatic Organisms

the sunny shoals of muddy bayous about Ithaca and in
many places in New England. It covers the zone
between high and low water, creeping extensively over
the banks that are mostly exposed, and there forming
a most beautiful ground cover, while producing longer
leaf -stalks where submerged. These leaf -stalks carry
the beautiful four-parted leaf-blades to the surface
where they float gracefully. Fruiting bodies the size

.; .- V/1 «I&r"V. ^-^# «;;••. "-jf. ^ ~j^^'~&a*;3*--ti-vi-' . >t

*^^^S*J^?^i^n;

•^•\":.i^ ' *T£1^- >^A^"^^^^-.'-1 '

**&3*^:?\J^-

FIG. 62. Floating plants: The largest branching colonies are Azolla; the
smallest plants are Wolffia; those of intermediate size are Lemna minor.

Photo by Dr. Emmeline Moore.

of peas are produced in clusters on the creeping stems
above the water line, often in very great abundance.

Then there are two floating pteridophytes of much
interest. Salvinia, introduced from Europe, is found
locally along our northeastern coast, and in the waters
of our rich interior bottom lands the brilliant little
Azolla flourishes. Azolla floats in sheltered bogs
and back waters, intermingled with duckweeds. It is
reddish in color oftener than green and grows in minute
mosslike pinnately branched sprays, covered with

Aquatic Seed Plants 151

closely overlapping two-lobed leaves, and emits a few
rootlets from the tinder side which hang free in the
water. In the back waters about the Illinois Station at
Havana, Illinois, Azolla forms floating masses often
several feet in diameter, of bright red rosettes.

Shoreward there are numerous pteridophytes grow-
ing as rooted and emergent aquatics ; the almost grass-
like Isoetes, and the marsh horsetails and ferns, but
these latter differ little from their near relatives that
live on land.

Aquatic Seed Plants- -These are manifestly land
plants in origin. They have much stiffening in their
stems. They have a highly developed epidermal
system, often retaining stomates, although these can
be no longer of service for intake of air. They effect
fertilization by means of sperm nuclei and pollen tubes,
and not by free swimming sperm cells.

Seed plants crowd the shore line, but they rapidly
diminish in numbers in deepening water. They grow
thickest by the waterside because of the abundance of
air moisture and light there available. But too much
moisture excludes the air and fewer of them are able to
grow where the soil is always saturated. Still fewer
grow in standing water and only a very few can grow
wholly submerged. Moreover, it is only in protected
shoals that aquatic seed plants flourish. They cannot
withstand the beating of the waves on exposed shores.
Their bodies are too highly organized, with too great
differentiation of parts. Hence the vast expanses of
open waters are left in possession of the more simply
organized algae.

An examination of any local flora, such as that of
the Cayuga Lake Basin* will reveal at once how small a
part of the population is adapted for living in water.

*The following data are largely drawn from Dudley's Cayuga Flora, 1886.

152

Aquatic Organisms

In this area there are recorded as growing without
cultivation 1278 species. Of these 392 grow in the
water. However, fewer than forty species grow wholly
submerged, with ten or a dozen additional submerged
except for floating leaves. Hardly more than an eighth,

therefore, of the so-
called "aquatics" are
truly aquatic in mode
of life: the remaining
seven-eighths grow on
shores and in springs,
in swamps and bogs, in
ditches, pools, etc.,
where only their roots
are constantly wret.

The aquatic seed
plants are representa-
tive of a few small and
scattered families. In-
deed, the only genus
having any consider-
able number of truly
aquatic species is the
naiad genus Potamo-
geton. Other genera
of river- weeds, or true
pond weeds, are small,
scattered and highly
diversified. They bear
many earmarks of
the special situations

FIG. 63. The ruffled pond-weed;
mogeton crispus, one of the most
mental of fresh water plants.

Pota-

orna-

independent adaptation to

in the water which they severally occupy. In the
economy of nature the Potamogetons or river weeds
constitute the most important single group of sub-
merged seed plants. They are rooted to the bottom
in most shoal waters, and compose the greater part of

Aquatic Seed Plants 153

the larger water meadows within our flora. They have
alternate leaves and slender flexuous stems that are
often mcrusted with lime.

There are evergreen species among the Potamogetons,
and other species that die down in late summer. There
are broad leaved and narrow leaved species. There
are a few, like the familiar Potamogeton uatans whose
uppermost leaves float flat upon the surface, but
the more important members of the genus live wholly
submerged. Tho seed-plants, they mainly reproduce
vegetatively, by specialized reproductive buds that are
developed in the growing season, and are equipped with
stored starch and other food reserves, fitting them when
detached for rapid growth in new situations. These
reproductive parts are developed in some species as
tuberous thickenings of underground parts; in others
as burr-like clusters of thickened apical buds ; and in
still others they are mere thickenings of detachable
twigs.

The Potamogetons enter largely into the diet of wild
ducks and aquatic rodents and other lesser aquatic
herbivores. They are as important for forage in the
water as grasses are on land.

Other naiads are Nais (fig. 85) and Zannichellia.

Eel-grass (Vallisneria) is commonly mixed with the
pond weeds in lake borders and water meadows.
Eel-grass is apparently stemless and has long, flat,
flexuous, translucent, ribbonlike leaves, by which it
is easily recognized. The duckweeds (Lemnaceas, figs.
6 1 and 62) are peculiar free-floating forms in which the
plant body is a small flat thallus, that drifts about freely
on the surface in sheltered coves, mingled with such
liverworts as Ricciocarpus, with such fernworts as
Azolla, with seeds, eel-grass flowers, and other flotsam.
There are definite upper and lower surfaces to the thal-
lus with pendant roots beneath hanging free in the

154

Aquatic Organisms

water. Increase is by budding and outgrowth of new
lobes from pre-existing thalli. Flowering and seed
production are of rare occurrence.

The water lily
family includes
the more con-
spicuous of the
broad- leaved
aquatics, which
pre-empt the
rich bottom mud
with stout root
stocks, and
heavily shade
the water with
large shield-
shaped leaves,
either floating
upon the sur-
face, as in the
water shield and
water lilies or
lifted somewhat
above it, as in the
spatterdock and
the lotus. They
are long-lived
perennials, re-
quiring a rich
muck soil to root
in. These are
FIG. 64. Leaf-whorls. distinguished

A, and C, the hornwort (CeralophyUum) ; B, the water milfoil foT the beauty

(Myriophyllum). .4 is an old leaf, the upper half normally 1 r ~

covered with algae and silt; the lower half cleaned, save for a and iragranCC OI

closely adherent dwelling-tube of a midge larva in the fork at , .

the right. C, is a young partly expanded leaf whorl from the tiieiT
apical bud.

Aquatic Seed Plants 155

The bladderworts (Utricularia) comprise another
peculiar group. They are free-floating, submerged
plants with long, flexuous branching stems that are
thickly clothed with dissected leaves. Attached to the
leaves are the curious traps or "bladders" (discussed in
Chapt. VI) which have suggested the group name.
Being unattached they frequent the still waters of
sheltered bays and ponds where they form beautiful
feathery masses of green. They shoot up stalks above
the surface bearing curious bilabiate flowers.

FIG. 65. The water weed, Pliilotria (Anacharis or Elodea}, with
two young black-and-green-banded nymphs of the dragonfly A nax
on its stem, and a snail, Planorbis, on a leaf.

The hornwort (Ceratopliyllum^) is another non-rooting
water plant that grows wholly submerged and branch-
ing. It is coarser, however, and hardier than Utricu-
laria and much more widespread. Its leaves are stiff,
repeatedly forking, and spinous-tipped (fig. 64 A and C).

The water milfoils (Myriophyllum) are rooted aqua-
tics, superficially similar to the hornwort but dis-
tinguishable at a glance by the simple pinnate branch-
ing of the softer leaves (fig. 64.6).

Then there are a few very common aquatics that
form patches covering the beds of lesser ponds, bogs

156

Aquatic Organisms

and pools. The common water weed, Philotria, (fig. 65) ,
with its neat little leaves regularly arranged in whorls of
threes; and two water crowfoots, Ranunculus, (fig. 66),
white and yellow, with alternate finely dissected leaves ;
and the water purslane, Ludvigia palustris, with its
closely-crowded opposite ovate leaves.

These are the common plants of the waterbeds about
Ithaca. They are so few one may learn them quickly,

for so strongly marked
are they that a single
spray or often a single
leaf is adequate for
recognition.

Then there are three
small families so finely
adapted to withstand-
ing root submersion
that they dominate all
our permanent shoals
and marshes. These
are (i) the Typhaceas
including the cat-tails
,, and the bur-reeds,

.biG. 66. A leaf of the white water-crow- , . 1 - 1 '

foot, Ranunculus. which torm vast stretch-

es of nearly clear

growth, as discussed in the last chapter; (2) the Alis-
maceag, including arrow heads and water plantain, and
(3) the Pontederiaceas, represented by the beautiful blue
pickerel -weed. All these are shown in their native
haunts in the figures of chapter VI.

Another family of restricted aquatic habitat is the
Droseraceae, the sun-dews, which grow in the borders of
sphagnous upland bogs. They are minute purplish-
tinted plants whose leaves bear glandular hairs.

Few other families are represented in the water by
more than a small proportion of their species. Those

Aquatic Seed Plants

157

families are best represented whose members live
chiefly on low grounds and in moist soil. A few rushes
(Juncaceae) invade the water on wave-washed shores
at fore front of the standing aquatics. A few sedges

FIG. 67. Fruit clusters of four emergent aquatic seed
plants; arrow-arum (Peltandra), pickerel- weed (Pon-
tederia), burr-reed (Sparganium), and sweet flag
(Acorns).

(Carices) overrun flood-plains or fringe the borders of
ditches. A very few grasses preempt the beds of
shallow and impermanent pools. A few aroids, such
as arrow arum and the calla adorn the boggy shores.
A few heaths, such as, Cassandra and Andromeda over-
spread the surface of upland sphagnum bogs with dense

158

Aquatic Organisms

levels of shrubs, and numerous orchids occupy the sur-
face of the bog beneath and between the shrubs.
Willows and alders fringe all the streams, associated
there with a host of representatives of other families
crowding down to the waterside. A few of these on
account of their usefulness or their beauty, we shall
have occasion to consider in a subsequent chapter.

Such are the dominant aquatic seed plants in the
Cayuga Basin; and very similar are they over the
greater part of the earth. The semi-aquatic represen-
tatives of the larger families are few and differ little
from their terrestrial relatives: the truly aquatic
families are small and highly diversified.

ANIMALS

ANY of the lower groups of
animals are wholly aqua-
tic, never having de-
parted from their ances-
tral abode. Other groups
are in part adapted to
life on land. A few
others, after becoming fit
for terrestrial life, have
been readapted in part to
life in the water. Aqua-
tic insects and mammals,
especially, give evidence
of descent from terres-
trial ancestors. As with

plants, so with animals, it is the lower groups that
are predominantly aquatic. The simplest of animals
are the protozoans ; so with these we will begin.

Protozoans

159

Protozoans— One of the best known animals in the
world, one that is pedagogically exploited in every
biological laboratory, is the Amoeba (fig. 69^). Plastic,
ever changing in form and undifferentiated in parts,
this is the animal that is the standard of comparison
among things primitive. Its name
has become a household word, and an
every-day figure of speech. A little
living one-celled mass of naked pro-
toplasm, that creeps freely about
amid the ooze of the pond bottom,
and feeds on organic foods. It
grows just large enough to be recog-
nized by the naked eye when in most
favorable light, as when creeping up
the side of a culture jar: on the
pond bottom it is undiscoverable
and a microscope is essential to
study it.

Related to Amoeba are several
common shell-bearing forms of the
group of Sarcodina (Rhizopoda)
that often become locally abun-
dant. Difflugia (fig. 69^) forms a
flask-shaped shell composed of mi-
nute granules, that, magnified, look
like grains of sand stuck together
over the outside. The soft amoeba-like body protrudes
in pseudopodia from the mouth of the flask, when travel-
ing or foraging, or withdraws inside when disturbed.
Arcella (fig. 696) secretes a broadly domeshaped shell,
having a concave bottom, in the center of which is the
hole whence dangle the clumsy pseudopodia. One
species of Arcella, shown in the following figure, has
the margin of the shell strongly toothed. Both of
these genera, and other shell-bearing forms, secrete

pIG. 69.

Protozoans.
6- Arcella; c

i6o

A qua tic Orga nisms

FIG. 70. Arcella den fata.
Through the central opening
there is seen a diatom, re-
cently swallowed.

bubbles of gas within their
shells whereby they are caused
to float. Thus they are often
taken in the plancton net from
open water of the ponds and
streams.

Other protozoans that have
the body more or less cov-
ered with vibratile cilia (Cil-
iata), are very common in
freshwater, especially in ponds
and pools. Best known of
these is Paramecium, (fig.
7 1 a) another familiar biolog-
ical-laboratory "type" that

grows abundantly in plant infusions. It is found in

stagnant pools, swimming near the surface. There

are many species of Paramecium. Some of them and

some members of allied genera are characteristic of

polluted waters. Other allied genera are parasitic,

and live within the bodies of the

higher animals. Stentor is (as the

name signifies) a more or less

trumpet-shaped ciliate protozoan,

that may detach itself and swim

freely about, but that is ordi-
narily attached by its slender

base to some support. Its base

is in some species surrounded by

a soft gelatinous transparent

lorica, as shown in the figure.

Some species are of a greenish

color. Stentor and Paramecium,

tho unicellular, are quite large

enough to be seen (as moving

species) with the unaided eye.

Ciliate pro-
tozoans.

.4, Paramasciiim; n, nu-
cleus; v, v, vacuoies; /,
food-ball at the bottom of
the rudimentary esopha-
gus; C, Stentor; I, lorica.

Protozoans

161

Cothurnia (fig. 73c) is a curious double form that is
often found attached to the stems of water weeds. The
two cells of unequal height are surrounded by a thin
transparent lorica. For beauty of form and delicacy or
organization it would be hard to find anything surpas-
sing this little creature.

Vorticella and its allies are among the commonest
and most ubiquitous of protozoans. They are sessile
and stalked, with some portion or all of the base con-
tractile. Vorticella forms clusters of many separate
individuals, while Epistylis forms branching, tree-like
compound colonies (fig. 72). Oftentimes they com-
pletely clothe twigs and grass stems
lying in the water, as with a white
fringe. Often they cluster about the
appendages of crustaceans and insects,
or thickly clothe their shells. Some-
times they cling to floating algal fila-
ments in the water-bloom (see fig. 1 79
on p. 295).

Ophrydium forms colonies of a very
different sort. Numerous weak-stalked
individuals have their bases imbedded
in a roundish mass of gelatin. The
colonies lie scattered about over the
bottom of a lake or pond. They are
roundish, or often rather shapeless
masses varying in size from mere specks
up to the dimensions of a hen's egg. In the summer of
1906 the marl-strewn shoals of Walnut Lake in Michigan
were so thickly covered that a boat-load of the soft
greenish-white colonies could easily have been gathered
from a small area of the bottom.

Oilier forms of protozoa there are in endless variety.
We cannot even name the common ones here : but we
will mention two that are verv different from the fore-

FlG_ ?2 A colony Of

egg. probably the egg of

1 62

Aquatic Organisms

going in form, and habit. PodopJirya will of ten be encoun-
tered by searching the backs of aquatic insects or the
sides of submerged twigs, or other solid support, to which
it is attached. It is sessile, and reaches out its suctorial
pseudopodia in search of soft-bodied organisms that are
its prey.

Anthophysa is a curious sessile form that is common
in polluted waters. It forms very minute spherical
colonies that are attached to the transparent tip of a

C

FIG. 73. Three sessile protozoans.
A, Anthophysa; B, Podophrya; C, Cothurnia.

rather thick brownish stalk. The stalk increases in
length and diameter with age, occasionally forking when
the colony divides. It soon becomes much more con-
spicuous than the colonies it carries. It often persists
after the animals are dead and gone. After a vigorous
growth, the accumulated stalks sometimes cover every
solid support as with a soft flocculent brownish fringe.
Besides these and other free-living forms, there are
parasitic Protozoa whose spores get into the water.
Some of these are pathogenic; many of them have
changes of host ; all of them are biologically interesting;
but we have not space for their consideration here.
We must content ourselves with the above brief
mention of a few of the more common and interesting
free-living forms.

Aquatic Organisms 163

METAZOANS

Hydras are the only common fresh-water representa-
tives of the great group of Coelenterates, so abundant
in the seas; and of hydras there are but a few species.
Two of these, the common green and brown ones,
H. Tirdis and H. fnsca, are well enough known, being
among the staples of every biological laboratory.
Pedagogically it is a matter of great good fortune that
this little creature lives on, a common denizen of fresh-
water pools; for its two-layered sac-like body repre-
sents well the simplest existing type of metazoan
structure.

Hydras are ordinarily sessile, being attached by a
disc-like foot to some solid support or to the surface
film, from which they often hang suspended. But at
times of abundance (and under conditions that are not
at present well understood) they become detached and
drift about in the water. A hydra of a brick-red color
swarms about the outlet of Little Clear Pond at Saranac
Inn, N. Y., in early summer, and drifts down the out-
flowing stream, often in such abundance that the water
is tinged with red. The young trout in hatching ponds
through which this stream flows, neglect their regular
ration of ground liver, and feed exclusively upon the
hydras, so long as the abundance continues. The
hydras play fast-and-loose in the stream, attaching
themselves when they meet with some solid support,
and then loosening and drifting again.

Clear, sunlit pools are the favorite haunts of hydras,
and the early summer appears to be the time of their
maximum abundance. They attach themselves mainly
to submerged stems and leaves, and to the underside of
floating duckmeat. They feed upon lesser animals
which abound in the plancton, and, multiplying rapidly
by a simple vegetative process of budding with subse-

1 64

Aquatic Organisms

quent detachment, they become numerous when
plancton abounds. Kofoid ('08) found a maximum
number of 5335 hydras per cubic meter of water in
Quiver Lake during a vernal plancton pulse in 1897.

Fresh-water sponges grow abundantly in the margins
of lakes and pools and in clear, slow-flowing streams.
They are always sessile upon some solid support. In
sunlight they are green, in the shade they grow pale.
The species that branch out in slender finger-like pro-
cesses are most suggestive of plants in both form and

color, but even the slen-
derest sponge is more
massive than any plant
body; and when one
looks closely at the
surface he sees it rough-
ened all over with the
points of innumerable
spicules, and sees open
osteoles at the tips. By

FIG. 74. Three simple metazoans of these sigllS Sponges of

isolated structural types. ., .

A. a scruff back, Cheetonotus; B, Hydra, bearing a Whatever lOrm Or COlOr

reCOgnized.

The commonest sponges are low encrusting species
that grow outspread over the surfaces of logs and
timbers. When, in early summer, one overturns a
floating log that has been long undisturbed he may find
it dotted with young sponges, growing as little yellow.,
circular, fleshy discs, bristling with spicules, and each
with a large central osteole. Later they grow irregular
in outline, and thicker in mass. Toward the end of
their growing season they develop statoblasts or
gemmules (winter-buds) next to the substratum (see
fig. 164 on p. 264), and then they die and disintegrate.
So our fresh-water sponges are creatures of summer,
like daffodils.

Fresh-Water Sponges

165

All sponges are aquatic, and most of them are marine.
Only the fresh-water forms produce statoblasts, and
live as annuals.

In figure 74 we show two other simple metazoans
(unrelated to Hydra and of higher structural rank

FIG. 75. A semi-columnar sponge from the Fulton Chain of Lakes near Old
Forge, N. Y. Half natural size. Photo, kindly loaned by Dr. E. P. Felt
of the N. Y. State Museum.

than the sponges) that during the history of syste-
matic zoology, have been much bandied about among
the groups, seeking proper taxonomic associates.
Clicctonotus often appears on the side of an aquarium jar
gliding slowly over the surface of the glass as a minute
oblong white speck. It is an inhabitant of water con-
taining plant infusions, and an associate of Paramecium
which to the naked eye it somewhat resembles.

1 66

Aquatic Organisms

Macrobiotics may be met in the same way and place,
but less commonly. It may also be taken in plaiicton;
but its favorite habitat appears to be tangles of water-
plants, over whose stems it crawls clumsily with the aid

of its four pairs of stub-
by strong-clawed feet.
It also inhabits the
most temporary pools,
even rainspouts and
stove urns, and is able
to withstand dessi-
cation.

Chaetonotus is probably
most nearly related to
the Rotifers; Macro-
biotus, to the mites.

Bryozoans - The
Bryozoans or "moss
animals" (called also
Polyzoans) are colonial
forms that are very
common in fresh water.
They grow always in
sessile colonies, which
have a more or less
plant-like mode of
branching. Their fixity
in place, their spreading
branches and the
brownish color of the
test they secrete give
the commoner forms

an aspect enough like minute brown creeping water
mosses to have suggested the name. The individ-
ual animals (zooids) of a colony are minute, requir-
ing a pocket lens for their examination, but the colo-

I

FlG. 76. Bryozoan colonies, slightly en-
larged; a dense colony of Plumatella on
a grass-stem; a beginning colony on a
leaf (above) ; and a loosely grown colony
of FredericeUa.

Brvozoans

67

I

in
n

nies are often large and conspicuous. Two of the
commoner genera are shown in figure 76, natural
size. These may be found in every brook or pond,
growing in flat spreading colonies on leaves or pieces of
bark or stones. Often a flat board that has long been
floating on the water, if overturned, will show a com-
plete and beautiful tracery of entire colonies outspread
upon the surface. New zooids are produced by bud-
ding. The buds remain permanently attached, each
at the tip of a branch. With growth in length and the
formation of a tough brown-
ish cuticle over every por-
tion except the ends, the
skeleton of the colony devel-
ops. This skeleton is what
we see when we lift the leaf
from the water and look at
the colony — brown, branch-
ing tubes, with a hole in the
end of each branch. Noth-
ing that looks like an ani-

1 • • -11 r L-U -^ FIG. 77. Three zooids of the bryo-

mal is visible, for the zooids " zo^ PlumateUat magnified.
which are very sensitive and
very delicate have all with-
drawn into shelter. They
suddenly disappear on the slightest disturbance of the
water, and only slowly extend again.

If we put a leaf or stone bearing a small colony into a
glass of water and let it stand quietly for a time the
zooids will slowly extend themselves, each unfolding a
beautiful crown of tentacles. There are few more
beautiful sights to be witnessed through a lens than the
blossoming out of these delicate transparent, flower-
like, crowns of tentacles from the tips of the apparently
lifeless branches of a populous colony. They unfold
from each bud, like a whorl of slender petals and slowly

I, expanded; m, retracted; n, partly re-
tracted; t, anus; j, intestine; k, de-
veloping statoblast.

1 68

Aquatic Organisms

extend their tips outward in graceful curves. Then one
sees a mouth in the midst of the tentacles, and water-
currents set up by the lashing of the cilia which cover

FIG. 78. A colony of Pectinatella, one-half natural size. Note the
distribution of buds in close groups over the surface. The large
hole marks the location of the stick around which the colony grew.

them. A close examination with the microscope will
reveal in each zooid the usual system of animal organs.
The alimentary canal is U-shaped its two openings
being near together at the exposed end of the body.

Brvozoatis 169

Several Bryzoans secrete a gelatinous covering
instead of a solid tube, and the colonies become in-
vested in a soft transparent matrix. Pectinatdla
(fig. 78) is one of these. It grows in large, more or
less spherical colonies, often resembling a muskmelon
in size, shape and superficial appearance. It is a not
uncommon inhabitant of bayous and ditches and slow-
flowing streams. It grows in most perfect spherical
form when attached to a rather small twig. The
clustered zooids form grayish rosettes upon the surface
of the huge translucent sphere. Late in the season
when statoblasts appear the surface becomes thickly
besprinkled with brown. Still later, after the zooids
have died, and the statoblasts have been scattered the
supporting gelatin persists, blocks and segments of
it, derived from disintegrating colonies, now green from
an overgrowth of algae, are scattered about the shores.

There are but a few genera of fresh-water bryozoans
—some six or seven — and Pliimatella is much the com-
monest one. Plumatella and allied forms grow in water
pipes. They gather in enormous masses upon the sluice-
ways and weirs of water reservoirs. They sometimes
cover every solid support with massive colonies of inter-
laced and heaped-up branches. Thus they form an
incrusting layer thick enough to be removed from flat
surfaces with shovels. Its removal is demanded because
the bryozoans threaten the potability of the water sup-
ply. They do no harm while living and active, but
when with unfavorable conditions they begin to die,
their decomposing remains may befoul the water of an
entire reservoir.

Cristatella is a flat, rather leech-shaped form that is
often found on the under side of lily pads. It is re-
markable for the fact that the entire colony is capable
of a slow creeping locomotion.. The zooids act together
as one organism.

170

Aquatic Organisms

The free-living flatwonns abound in most shoal fresh
waters. Some live in shallow pools; others in lakes
and rivers, others in spring-fed brooks. They gather
on the under sides of stones, sticks and trash, and con-
ceal themselves amid vegetation, usually shunning
the light. They are often collected unnoticed, and
crawl at night from cover and lie outspread upon the

FIG. 79. Flatworms.

A, diagram of a planarian, showing food cavity; M, mouth at end of cylindric pharynx, directed
downward underneath the body; B, Dendroccelum; C, a chain of five individuals of Stenos-
totnum formed by automatic division of the body, (after Keller). Note the anterior position
of the mouth and the unbranched condition of the alimentary canal in this Rliabdocxle type.

sides of our aquaria. We may usually find the larger
species by lifting stones from a stream bed or a lake
shore, and searching the under side of them.

Flatworms are covered with vibratile cilia and travel
from place to place with a slow gliding motion. They
range in length from less than a millimeter to several
centimeters. The smaller among them are easily mis-

Flatworms 171

taken for large ciliate protozoans, if viewed only with
the unaided eye ; but under the microscope the alimen-
tary canal and other internal organs are at once
apparent. They are multicellular and have little like-
ness to any infusoria, save in the ciliated exterior.
Most members of the group are flattened, as the com-
mon name suggests, but a few are cylindric, or even
filiform. A few are inclined to depart from shelter and
to swim in the open water, especially at time of abund-
ance. Kofoid ('08) found them in the channel waters
of the Illinois River in average numbers above 100 per
cubic meter, with a maximum record of 19250 per cubic
meter.

The large flatworms resemble leeches somewhat in
form of body, but they have more of a head outlined
at the anterior end. They lack the segmentation of
body and the attachment discs of leeches, and their
mode of locomotion is so very different they are readily
distinguished. They do not travel by loopings of the
body as do leeches, but they glide along steadily, pro-
pelled by invisible cilia.

The most familiar flatworms are the planarians:
soft and innocuous-looking little carnivores, having
the mouth opening near the midventral surface of the
body, and the food-cavity spreading through the body
in three complexly ramifying branches. They are
often brightly colored, mottled white, or brick red, or
plumbeous, and they have a way of changing color with
every full meal; for the branched alimentary canal
fills, and the color of the food glows through the skin
in the more transparent species . The eggs of planarians
are often found in abundance on stones in streams in
late summer. They are inclosed in little brownish
capsules, of the size and appearance of mustard seeds,
and each capsule is raised on a short stalk from the
surface of the stone. Increase is also by automatic

172

Aquatic Organisms

transverse division of the body, the division plane lying
close behind the mouth. When a new head has been
shaped on the tail-piece, and a new tail on the head-
piece, and two capable organisms have been formed,
then they separate. In some of the simple (Rhab-
docoele) flatworms the body divides into more than two
parts simultaneously and thus chains of new individuals
arise (hg. 79 c).

Thread-worms or Nematodes, abound in all fresh
waters, where they inhabit the ooze of the bottom, or
thick masses of vegetation. They are minute, color-
less, unscgmented, smoothly-contoured cylindric worms
rarely more than a few millimeters long. The tail end
is usually sharply pointed. The mouth is terminal at
the front end of the body, and is surrounded by a few
short microscopic appendages. Within the mouth
cavity there are often little tooth-like appendages.
The alimentary canal is straight and cylindric and
imappendaged, and the food is semifluid organic sub-
stances.

FIG. 80. Diagram of a Nematode worm.

>K, mouth; n, nerve ring; e, alimentary canal; ov,
on, ovaries; u, anus. (After Jagerskiold) .

We can hardly collect any group of pond-dwellers
without also collecting nematodes. They may occupy
any crevice. They slip in between the wing- pads of
insect nymphs, and into the sheaths of plant stems.
When we disturb the trash in the bottom of our collect-
ing dish, we see them swim forth, with violent swings
and reversals of the pliant body. They may easily be
picked up with a pipette.

Bristlc-Bea ring Worms

173

Oligochetes — Associated with the nematodes in the
trash and ooze, there is a group of minute bristle-bear-
ing worms, the naiads (Family Naidse) , similar in slender-
ness and transparency of body, but very different on
close examination; for the body in Nais is segmented,
and each segment is armed with tufts of bristles of
variable length and form. There are many common
members of this family. Besides the graceful Nais
shown in our figure there is Chcetogaster, which creeps
on its dense bristle-clusters as on feet. There is
Stylaria with a long tongue-like
proboscis. There is Dero that lives
at the surface in a tube of some
floating plant stuffs, such as seeds
(fig. 82) or Lemna leaves, slipping
in and out or changing ends in
the tube with wonderful celerity;
and there are many others.

Dero bears usually two pairs of
short gill-lobes at the posterior end
of the body.

All these naiads reproduce habitually by automatic
division of the body, which when in process of develop-
ment, forms chains of incompletely formed individuals,
as in certain of the flatworms before described.

Another group of Oligochetes is represented by
Tubifex and its allies. These dwell in the bottom mud,
living in stationary tubes, which are in part burrows,
and in part chimneys extended above the surface.
The worms remain anchored in these and extend their
lithe bodies forth into the water. On disturbance they
vanish instantly, retreating into their tubes. They are
often red in color, and when thickly associated, as on
sludge in the bed of some polluted pool, they often
cover the bottom as with a carpet of a pale mottled
reddish color.

FIG. 81. Nais. (after
Leunis)

174

Aquatic Organisms

FIG. 82. Dero, in its case made of floating seeds.

Aquatic earthworms, more like the well-known
terrestrial species, burrow deeply into the mud of the
pond bottom.

Other worms occur in the water in great variety; we
have mentioned only a few of the commonest, and
those most frequently seen. There are many parasitic
worms that appear in the water for only a brief period
of their lives: hair-worms (Gordius, etc.), which are
freed from the bodies of insects and other animals in
which they have developed; these often appear in
watering troughs and were once widely believed to
have generated from horse-hairs fallen into the water.
There are larval stages (Cercaria) of Cestodes and
others, found living in the water for only a brief interval

of passage from one
host animal to ano-
ther. There are
smaller groups also
like the Nemertine
worms, sparingly
represented in fresh-
water ; for informa-
tion concerning
these the reader is
referred to the
larger textbooks of
zoology.

FIG. 83. Tubifex in the bottom mud.

Leeches 175

Leeches — The leeches constitute a small group whose
members are nearly all found in fresh -water. They
occur under stones and logs, in water- weeds or bottom
mud, or attached to larger animals. The body is
always depressed, and narrowed toward the ends, more
abruptly toward the posterior end where a strong sucker
is developed. The front end is more tapering and neck-
like, and very pliant. There is no distinct head, but
at the front is a sort of cerebral nerve ring and there are
rudimentary eyes in pairs, and surrounding the mouth
is a more or less well-developed anterior sucker. The
great pliancy of the muscular body, the presence of the
two terminal suckers, and the absence of legs or other
appendages determine the leech's mode of locomotion.
It ordinarily crawls about by a series of loopings like a
"measuring worm," using the suckers like legs for
attachment. The more elongate leeches swim readily
with gentle undulations of the ribbon-like body. The
shorter broader forms hold more constantly with the
rear sucker to some solid support, and when detached
tend to curl up ventrally like an armadillo.

Leeches range in size from little pale species half an
inch long when grown, to the huge blackish members
of the horse-leech group (Hcemopis] a foot or more in
length. Many of them are beautifully colored with
soft green and yellow tints. The much branched
alimentary canal, when filled with food, shows through
the skin of the more transparent species in a pattern
that is highly decorative.

Leeches eat mainly animal food. They are para-
sites on large animals or foragers on small animals or
scavengers on dead animals. Very commonly one finds
the parasites attached to the thinner portions of the
skins of turtles, frogs, fishes and craw-fishes. There is
no group in which the boundary between predatory and
parasitic habits is less distinct than in this one; many

176

Aquatic Organisms

leeches will make a feast of vertebrate blood, if occasion
offers, or in absence of this will swallow a few worms
instead.

The mouth of leeches is
adapted for sucking, in some
cases it is armed for making
punctures, as well: hence the
food is either more or less fluid
substances like blood or the
decomposing bodies of dead
animals, or else it consists of
the soft bodies of animals
small enough to be swallowed
whole.

The eggs of leeches are
cared for in various ways:
commonly one finds certain
of them in minute packets,
attached to stones. Others
(Hccmopis, etc.) are stored in
larger capsules and hidden
amid submerged trash. Oth-
ers are sheltered beneath the
body of the parent, and the
young are brooded there for
a time after hatching, as
shown in the accompanying
figure. Nachtrieb (12) states
that they are so carried "until
the young are able to move
about actively and find a host
for a meal of blood."

Leeches are doubtless fed upon by many carnivorous
animals. They are commonly reported to be taken
freely by the trout in Adirondack waters. In Bald Moun-
tain Pond they swim abundantly in the open water.

FIG. 84. A clepsine leech
(Placobdella rugosa], over-
turned and showing the
brood of young protected
beneath the body. (From
the senior author 'sCeneral
Biology) .

Rotifers

177

The Rotifers constitute a large group of minute
animals, most characteristic of fresh -water. They
abound in all sorts of situations, and present an extra-
ordinary variety of forms and habits. Their habits
vary from ranging the open lake to dwelling symbioti-
cally within the tissues of water plants ; from sojourning
in the cool waters of peren-
nial springs, to running a
swift course during the tem-
porary existence of the most
transient pools. They even
maintain themselves in rain-
spouts and stone urns, where
they become dessicated with
evaporation between times of
rain.

Rotifers are mainly micro-
scopic, but a few of the larger
forms are recognizable with
the unaided eye. Often they
become so abundant in pools
as to give to the water a tinge
of their own color. Grouped
together in colonies they be-
come rather conspicuous.
The spherical colonies of Cono-

chilus when attached to leaf-tips, as in the accom-
panying picture, present a bright and flower-like
appearance. Entire colonies often become detached,
and then they go bowling along through the ^ water,
in a most interesting fashion, the individuals jostling
each other as they stand on a common footing, and
all merrily waving their crowns of cilia in unison. ^ Often
a little roadside pool will be found teeming with the
little white rolling spheres, that are quite large enough
to be visible to the unaided eye.

FIG. 85. Three colonies of the
rotifer, Conochilus, attached
to the tips of leaves of the
pond-weed, Nais.

178

Aquatic Organisms

Melicerta is a large sessile rotifer that lives attached
to the stems of water-plants and when undisturbed
protrudes its head from the open end of the tube, and
unfolds an enormous four-lobed crown of waving cilia.
It is a beautiful creature. Our picture shows the cases
of a number of Melicertas, aggregated together in a

cluster, one case serving as a
support for the others.

The crown of cilia about the
anterior end of the body is the
most characteristic structure
possessed by rotifers. It is
often circular, and the waving
cilia give it an aspect of rota-
tion, whence the group name.
It is developed in an extra-
ordinary variety of ways as
one may see by consulting in
any book on rotifers the figures
of such as Stephanoceros, Flos-
cularia, Synchceta, Trochos-
phcera and Brachionus.

The cilia are used for driv-
ing food toward the mouth
that lies in their midst, and
for swimming. Most of the
forms are free-swimming, and
many alternately creep and
swim.

Brachionus (fig. 87) shows
well the parts commonly found in rotifers. The body
is inclosed in a lorica or shell that is toothed in front
and angled behind. From its rear protrudes a long
wrinkled muscular "foot," with two short "toes"
at its tip. This serves for creeping. The lobed
crown of cilia occupies the front. Behind the quad-

FIG. 86. Two clusters of rotifers
(Melicerta), the upper but
little magnified. Only the
cases (none of the animals)
appear in the photographs.

Rotifers

179

rangular black eyespot in the center of the body
appears the food communicating apparatus (mastax),
below which lie ovaries and alimentary canal. Any
or all the external parts may be wanting in certain

FIG. 87. A rotifer (Brachionus cntzii) in dorsal and ven-
tral views. (After France).

rotifers. The smaller and simpler forms superficially
resemble ciliate infusoria, but the complex organization
shown by the microscope will at once distinguish them.
Rotifers eat micro-organisms smaller than them-
selves. They reproduce by means of eggs, often
parthenogenetically. The males in all species are
smaller than the females and for some species males
are not known.

i So

Aquatic Organisms

Molluscs — A large part of the population of lake and
river beds, shores, and pools is made up of molluscs.

They cling, they
climb, they bur-
row, they float — -
they do every-
thing but swim in
the water. They
are predominantly
herbivorous, and
constitute a large
proportion of the
producing class
among aquatic
animals. Two great
groups of molluscs
are common in
fresh water, the
familiar groups of
mussels and snails.

Fresh-water mus-
sels (clams, or
bivalves) abound
in suitable places,
where they push
through the mud
or sand with their
muscular protrusi-
ble foot, and drag
the shell along in
a vertical position
leaving a channel-
like trail across the bottom. They feed on micro-organ-
isms.

The two commonest sorts of fresh-water mussels are
roughly distinguished by size and reproductive habits

FIG. 88. A living mussel, Aiwdonta, with foot
retracted and shell tightly closed. A copious
growth of algae covers the portion of the
shell that is exposed above the mud in loco-
motion: the remainder is buried in oblique
position with the foot projecting still more
deeply into the mud.

Molluscs 181

thus : Unios and their allies are large forms that have
pearly shells and that live mainly in large streams and
lake borders. They produce enormous numbers of
young, and use mostly the outer gill for a brood
chamber. They cast the young forth while still minute
as glochidia, to become attached to and temporarily
parasitic on fishes. The relations of these larval
glochidia with the fishes will be discussed in chapter V.
The lesser mussels (family Sphasridse) dwell in small
streams and pools and in the deeper waters of lakes.
Their shells are not pearly. They produce but a few
young at a time and carry these until of large size,
using the inner gill for a brood-pouch. The stouter
species, half an inch long when grown, burrow in stream-
beds like the unios. The slenderer species climb up
the stems of plants by means of their excessively mobile
adhesive and flexible foot. On this foot the dainty
white mussel glides like a snail or a flatworm, up or
down, wherever it chooses.

Snails are as a rule more in evidence than are mussels,
for they come out more in the open. They clamber
on plants and over every sort of solid support. They
hang suspended from the surface film, or descend there-
from on strings of secreted mucus. They traverse
the bottom ooze. We overturn a floating board and
find dozens of them clinging to it, and often we find
a filmy green mass of floating algae thickly dotted with
their black shells.

They eat mainly the soft tissues of plants, and micro-
organisms in the ooze covering plant stems. A ribbon-
like rasp (radula) within the mouth drawn back and
forth across the plant tissue scrapes it and comminutes
it for swallowing. Because snails wander constantly
and feed superficially without, as a rule, greatly altering
the form and appearance of the larger plants on which

I 82

Aquatic Organisms

they feed, their work is little noticed; yet they con-
sume vast quantities of green tissue and dead stems.
The commoner pond snails lay their eggs in oblong
gelatinous clumps that are outspread upon the surfaces
of leaves and other solid supports. Other snails are
viviparous.

The two principal groups of fresh-water snails may
roughly be distinguished as (i) operculate snails which
live mainly upon the bottom in larger bodies of water,
and have an operculum closing the aperture of their
shell when they retreat inside, and which breathe by

FIG. 89. Two pond snails (Limncea palustris) foraging
on a dead stem that is covered with a fine growth of
the alga, Chcetophora incrassata.

means of gills: (2) pulmonate snails, which most
abound in vegetation-filled shoals, breathe by means of
a simple lung (and come to the surface betimes, to refill
it with air) and have no operculum.

The snails we oftenest see are members of three
genera of the latter group: Limncea, shown in the
accompanying figure, having a shell with a right-hand
spiral and a slender point; Physa, having a shorter
spiral, twisted in the opposite way, and Planorbis,
shown in fig. 65 on p. 155, having a shell coiled in a flat
spiral. A ncylus is a related minute limpet-shaped snail,
having a widely open shell that is not coiled in a spiral.
Its flaring edges attach it closely to the smooth surfaces
of plant stems or of stones.

Crustaceans 1 83

ARTHROPODS

We come now to that great assemblage of animals
which bear a chitinous armor on the outside of the
body, and, as the name implies, are possessed of jointed
feet. This group is numerically dominant in the world
today on sea and land. It is roughly divisible into
three main parts; crustaceans, spiders and insects.
The crustaceans are the most primitive and the most
wide-spread in the water- world; so with them we will
begin.

The Crustaceans include a host of minute forms, such
as the water fleas and their allies, collectively known
as Entomostraca, and a number of groups of larger
forms, such as scuds, shrimps, prawns and crabs, col-
lectively known as the higher Crustacea or Malacos-
traca. A few of the latter (crabs, sow-bugs, etc.) live
in part on land, but all the groups are predominately
aquatic, and the Entomostraca are almost wholly so.

The Entomostraca are among the most important
animals in all fresh waters. They are perhaps the chief
means of turning the minute plant life of the waters into
food for the higher animals. They are themselves the
chief food of nearly all young fishes.

There are three groups of Entomostraca, so common
and so important in fresh water, that even in this brief
discussion we must distinguish them. They are:
Branchiopods, Ostracods and Copepods.

The Branchiopods, or gill-footed crustaceans, have
some portion of the thoracic feet expanded and lamelli-
form, and adapted to respiratory use. The feet are
moved with a rapid shuttle-like vibration which draws
the water along and renews the supply of oxygen. The
largest of the entomostraca are members of this group ;
they are very diverse in form.

184 Aquatic Organisms

The fairy shrimp, shown in the accompanying figure,
is one of the largest and showiest of Entomostraca. It
is an inch and a half long and has all of the tints of
the rainbow in its transparent body. It appears in
spring in rainwater pools and is notable for its rapid
growth and sudden disappearance. It runs its rapid
course while the pools are filled with water, and lays
its eggs and dies before the time of their drying up.
The eggs settle to the bottom and remain dormant,
awaiting the return of favorable season. The animal
swims gracefully on its back with two long rows of
broad, thin, fringed, undulating legs uppermost, and
its forked tail streaming out behind, and its rich colors

fairly shimmering in the
light.

Of very different appear-
ance is the related mussel-

FIC' FS' C'"m' shrimp (Estheria) , which has

its body and its long series
of appendages inclosed in a bivalve shell. Swimming
through the water, it looks like a minute clam a centi-
meter long, traveling in some unaccountable fashion;
for its legs are all hidden inside, and nothing but the
translucent brownish shell is visible. This shell is
singularly clam-like in its concentric lines of growth on
the. surface and its umbones at the top. This, in
America, is mainly Western and Southern in its distri-
bution, as is also Apus, which has a single dorsal shell
or carapace, widely open below and shaped like a horse-
shoe crab.

These large and aberrant Branchiopods are all very
local in distribution and of sporadic occurrence. As
the seasons fluctuate, so do they. But they are so
unique in form and appearance that when they occur
they will hardly escape the notice of the careful observer
of water life.

Water- Fleas 185

Water-fleas— -The most common of the Branchiopods
are the water-fleas (order Cladocera) such as are shown
in outline in figure 91. These are smaller, more trans-
parent forms, having the body, but not the head, in-
closed in a bivalve shell. The shell is thin, and finely
reticulate or striated or sculptured, and often armed
with conspicuous spines. The post-abdomen is thin and
flat, armed with stout claws at its tip and fringed with
teeth on its rear margin, and it is moved in and out
between the valves of the shell like a knife blade in its
handle. The pulsating heart, the circulating blood, the
contracting muscles, and the vibrating gill-feet all show
through the shell most
clearly under a microscope.
Hence these forms are very
interesting for laboratory
study, requiring no prepara-
tion other than mounting
on a slide.

Some water-fleas, like
Simocephalus, shown in fig-
ures 91 and 92 swim freely FlG gi Water.fleas

On their backS, in Which a. Daphne; &, Chydorus; c, Simocephalus;
• , • •, • 1 d, Bosmina. Note the "proboscis."

position gravity may aid

them in getting food into their mouths. When the
swimming antennae are developed to great size, as in
Daphne (fig. 91 a), the strokes are slow and progress is
made through the water in a series of jumps. When
the antennas are shorter, as in Chydorus (fig. 91^), their
strokes are more rapidly repeated, and progression
steadier.

The Cladocerans are abundant plancton organisms
throughout the summer season. They forage at a little
depth by day, and rise nearer to the surface by night.

The food of water-fleas is mainly the lesser green
algas and diatoms. They are among the most important

186

A quatic Organisms

herbivores of the open water. They are themselves
important food for fishes.

The importance of water fleas in the economy of
water is largely due to their very rapid rate of reproduc-
tion. During the summer season broods of eggs suc-

FIG. 92. A water-flea (Simocephalus vetulus) in its ordinary
swimming position. Note the striated shell, and the ali-
mentary canal, blackish where packed with food-residue in
the abdomen.

cessively appear in the chamber enclosed by the shell
on the back of the animal (see figure 93) at intervals
of only a few days. The young develop rapidly and
are themselves soon producing eggs. In Daphne pulex,
for example, it has been calculated that the possible

Ostracods 1 87

progeny of a single female might reach the astounding
number of 13,000,000,000 in sixty days.

The Ostracods are minute crustaceans, averaging
perhaps a millimeter in length, having the head, body
and appendages all inclosed in a bivalve shell. The shell
is heavier and less transparent than that of the water
fleas . It is often sculptured, or marked in broad patterns

FIG. 93. One of our largest water-fleas, Eurycenis lamellatns,
twenty times natural size. Note the eggs in the brood chamber
on the back. Note also the short beak and the broad post-
abdomen (shaped somewhat like a butcher's cleaver) by which
this water-flea is readily recognized.

with darker and lighter colors. The inclosed appenda-
ges are few and short, hardly more than their tips show-
ing when in active locomotion. There are never more
than two pairs of thoracic legs. The identification of
ostracods is difficult, since, excepting in the case of
strongly marked forms, a dissection of the animal from
its shell is first required.

188

Aquatic Organisms

FIG. 94. An Ostracod (Cypris
virens), lateral and dorsal views,
(after Sharpe.)

Some Ostracods are free-
swimming (species of Cypris,
etc.) and some (Notodromas)
haunt the surface in sum-
mer; but most are creeping
forms that live among
water plants or that burrow
in the bottom ooze. In pools where such food as alga?
and decaying plants abound Ostracods frequently
swarm, and appear as a multitude of moving specks
when we look down into the still water.

Relicit pools in a dry summer are likely to be found
full of them. Both sexes are constantly present in
most species of Ostracods, but a few species are repre-
sented by females only, and reproduce by means cf
unfertilized eggs.

The Copepods are the perennial entomostraca of open
water. Summer and winter they are present. Three
of the commonest genera are shown in figure 95, toge-
ther with a nauplius — the larval form in which the
members of this group hatch from the egg. Nothing is
more familiar in laboratory aquaria than the little

white Cyclops (fig. 96, swim-
ming with a jerky motion,
the female carrying two
large sacs of eggs.

A more or less pear-shaped
body tapering to a bifurcate
tail at the rear, a single
median eye and a pair of
large swimming antennae at
FIG. 95. Common copepods the front, and four pairs of

e, Cyclops; /, Diaptomus; g, Canthocamp- fhnrarMn QW1 m TT1 i n Cf
tus; h, a nauplius (larva) of Cyclops. UlOrdCU, bWl [Ig

Figures e and / show females bearing egg Vvo-n^atTi r>Tl nrar>tp>ri'7P>
sacs, while the detached antenna at the UtSHtJd.111, Lrlldl d,V* LCli/iC

right shows the form of that appendage mfvm'hm-Q nf
in the male. IlieillUtUb Ul

Copepods

189

The species of Diaptomus are remarkable for having
usually very long antennae and often a very lively red
color. Sometimes they tinge the water with red, when
present in large numbers.

Copepods feed upon animals planet on and algae,
especially diatoms. They are themselves important
food for fishes, especially for young fishes.

The higher Crustacea,
(Malacostraca) are rep-
resented in our fresh
waters by four distinct
groups, all of which
agree in having the
body composed of
twenty segments that
are variously fused
together on the dorsal
side, each, except the
last, bearing (at least
during development) a
pair of appendages.
Of these segments five
belong to the head,
eight to the thorax and
the remainder to the
abdomen. Mysis (fig.
97) is the sole represen-
tative of the most primitive of these groups, the order
Mysidacea. Its thoracic appendages are all biramous
and undifferentiated ; and still serve their primal
swimming function. Mysis lives in the open waters of
our larger lakes, in their cooler depths. It is a delicate
transparent creature half an inch long.

The Scuds (order Amphipoda) are flattened laterally,
and the body is arched. The thoracic legs are adapted

FIG. 96. A female Cyclops, with eggs.

190 Aquatic Organisms

for climbing, and the abdominal appendages for swim-
ming and for jumping. The body is smooth and pale;
often greenish in color. The scuds are quick and active.
They dart about amid green water-weeds, usually
keeping well to shelter, and they swim freely and
rapidly when disturbed. In figure 98 are shown
three species that are common in the eastern United
States.

The scuds are herbivores, and they abound among
green, water plants everywhere. They are of much
importance as food for fishes. They are hardy, and
capable of maintaining themselves under stress of

FIG. 97. My sis stenolepis, (After Paulmier).

competition. They carry their young in a
pectoral broodpouch until well developed ; and
altho they are not so prolific as are many
other aquatic herbivores, yet they have possibilities
of very considerable increase, as is shown by the fol-
lowing figures for Gammarus fasciatus, taken from
Embody 's studies of 1912:

Reproductive season at Ithaca, Apr. iSth to Nov. 3d,
includes 199 days.

Average number of eggs laid at a time 22. Egg lay-
ing repeated on an average of 1 1 days.

Age of the youngest egg-laying female 39 days : num-
ber of her eggs, 6.

Possible progeny of a single pair 24221 annually.

A sell/us is the commonest representative of the order
Isopoda; broad, dorsally-flattened crustaceans of some-

Decapoda 191

what larger size, that live sprawling in the mud of the
bottom in trashy pools. Their long legs and hairy
bodies are thickly covered with silt. Two pairs of
thoracic legs are adapted for grasping and five pairs for
walking, and the appendages of the middle abdominal
segments are modified to serve for respiration. Asellus
feeds on water-cress and on other soft plants, living and
dead, are found in the bottom ooze. It reproduces
rapidly, and, in spite of cannibal habits when young,

FIG. 98. Three common Amphipods.

A, Gammarus fasciatus; B, Eucrangonyx graalis; C, Hyalella knickerbockeri.
(Photo, by G. E. Embody).

often becomes exceedingly abundant. An adult female
of Asellus communis produces about sixty eggs at a
time and carries them in a broodpouch underneath her
broad thorax during their incubation. There is a new
brood about every five or six weeks during the early
summer season.

Both this order and the preceding have blind
representatives that live in unlighted cave waters, and
pale half -colored species that live in wells.

The crawfishes are the commonest inland representa-
tives of the order Decapoda. These have the thoracic

192 Aquatic Organisms

segments consolidated on the dorsal side to form a hard
carapace, and have but five pairs of walking legs (as
the group name indicates) , the foremost of these bear-
ing large nipper-feet. This group contains the largest
Crustacea, including all the edible forms, such as crabs,
lobsters, shrimps, and prawns, most of which are marine.
Southward in the United States there are fresh-water
prawns (Palcemonetes} of some importance as fish food.

The eggs of crawfishes are carried during incubation,
attached to the swimmerets of the abdomen, and the
young are of the form of the adult when hatched. They
cling for a time after hatching to the hairs of the swim-
merets by means of their little nipper-feet, and are
carried about by the mother crawfish.

Crawfishes are mainly carnivorous,
their food being smaller animals,
dead or alive, and decomposing flesh.
In captivity they are readily fed on
scraps of meat. Southward, an omni-
vorous species is a great depredator
in newly planted fields of corn and
cotton. Hankinson ('08) reports

that the crawfishes "form a very FIG- 99- Aseii«s

.. - 1 • r r j r tiCUS> (X2> after Sars)

important it not the cmei tood 01

black bass, rock bass, and perch" in Walnut Laker

Michigan.

Spiders and Mites are nearly all terrestrial. Of the
true spiders there are but a few that frequent the water.
Such an one is shown in the initial cut on page 158.
This spider is conspicuous enough, running on the
surface of the water, or descending beneath, enveloped
in a film of air that shines like silver ; but neither this
nor any other true spider is of so great importance in
the economy of the water as are many other animals
that are far less conspicuous. In habits these do not
differ materially from their terrestrial relatives.

Spiders and Mites

193

Of mites there is one rather small family (Hydrach-
nidae) of aquatic habits. These water-mites are minute,
mostly rotund (sometimes bizarre) forms with unseg-
mented bodies, and four pairs of long, slender, radiating
legs. One large species (about the size of a small pea)
is so abundant in pools and is so brilliant red in color
that it is encountered by every collector. Others, tho

\

FIG. 100. An overturned female crawfish (Cambarus bartoni), showing
the eggs attached to the swimmerets (four thoracic legs broken off).

smaller, are likewise brilliant with hues of orange,
green, yellow, brown and blue, often in striking patterns.
Water-mites, even when too small to be distinguished
easily by their form from ostracods or other minute
Crustacea are easily distinguished by their manner of
locomotion. They swim steadily, in one position;
not in the jerky manner of the entomostraca. The
strokes of their eight hair-fringed swimming feet come

194

A g ltd tic Orga n isms

in such rapid succession that the body is moved
smoothly forward. A few water-mites that dwell in the
open water of lakes are transparent, like other
members of open- water plancton.

Water-mites are nearly all parasitic : they puncture
the skin and suck the blood of larger aquatic animals.
Certain of them are common on the gills of mussels:
others on the intersegment al membranes of insects.

FIG. 101. Water mites of the genus Limnochares

Nothing is more common than to find clusters of red
mites hanging conspicuously at the sutures of back-
swimmers and other water insects.

Many mites lay their minute eggs on the surface of
the leaves of water plants. Their young on hatching
have but three pairs of legs.

Aquatic Insects 195

INSECTS

This is the group of animals that is numerically
dominant on the earth today. There are more known
species of insects than of all other animal groups put
together. The species that gather at the water-side
give evidence, too, of most extraordinary abundance of
individuals. Who can estimate the number of midges
in the swarms that hover like clouds over a marsh, or
the number of mayflies represented by a windrow of
cast skins fringing the shore line of a great lake? The
world is full of them. Like other land animals they are
especially abundant about the shore line, where condi-
tions of water, warmth, air and light, favor organic
productiveness .

Nine orders of insects (as orders are now generally
recognized) are found commonly in the water. These
are the Plecoptera or stoneflies; the Ephemerida or
mayflies; the Odonata or dragonflies and damselflies;
the Hemiptera or water bugs; the Neuroptera or net-
winged insects; the Trichoptera or caddis-flies; the
Lepidoptera or moths ; the Coleoptera or beetles ; and
the Diptera or true flies. These, together with the
Thysanura or springtails, which hop about upon the
surface of the water in pools, and the Hymenoptera,
of which a few members are minute egg-parasites and
which, when adult, swim with their wings, represent
the entire range of hexapod structure and metamor-
phosis. Yet the six-footed insects as a class are pre-
dominantly terrestrial. It is only a few of the smaller
orders, such as the stoneflies and the mayflies, that
are wholly aquatic. Of the very large orders of moths,
beetles and true flies only a few are aquatic.

Aquatic insects are mainly so in their immature
stages; the adults are terrestrial or aerial. Only a few
adult bugs and beetles are commonly found in the

196

A qu a tic Orga n isms

water. Other insects are there as nymphs or larvse;
and, owing to the great change of form that is undergone

FIG. 102. The green darner dragonfly, A naxjunius; adult and nymph
skin from which it has just recentty emerged. Save for the displaced
wing cases the skin preserves well the form of the immature stage.

Photo by H. II. Knight

at their final transformation, they are very unlike the
adults in appearance. How very unlike the brilliant

Aquatic Insects

197

adult dragonfly, that dashes about in the air on shim-
mering wings, is the sluggish silt-covered nymph, that
sprawls in the mud on the pond bottom! How unlike

the fluttering fragile caddis-fly is the
caddis-worm in its lumbering case!

As with terrestrial insects, so with
those that are aquatic, there are
many degrees of difference between
young and adult, and there are two
main types of metamorphosis, long
familiarly known as complete and
incomplete. With complete meta-
morphosis a quiescent pupal stage is
entered upon at the close of the
active larval life, and the form of
the body is greatly altered during
transformation. Adults and young
are very unlike. Caddis -worms, for
example, the larvae of caddis-flies, are
so unlike caddis-flies in every exter-
nal feature, that no one who has not
studied them would think of their
identity.

The caddis-fly shown in the accom-
panying figure is one that is very
common about marshes, where its
larva dwells in temporary ponds and
pools. Often in early summer, the
bottom will be found thickly strewn
with larvas in their lumbering cases.
Then they suddenly disappear.
They drag their cases into the shelter
of sedge clumps bordering the pools,
and transform to pupae inside them. A fortnight later
they transform to adult caddis-flies, and appear as
shown in figure 103, pretty soft brown insects marked
with straw-yellow in a neat pattern. The larva is
of the form shown in figure 104, a stocky worm-like

FIG. 103. Caddis-fly.
(Limnophilus sp.)

198

Aquatic Organisms

FIG. 104. Caddis-worms: larvae of Halesus guttifcr.

creature, half soft and pale
where constantly protected by
the walls of the case in which
it lives, and half dark colored
and strongly chit ini zed where
exposed at the ends. There
are stout claws at the rear
for clutching the wall of the
case; there are soft pale fila-
mentous gills arranged along
the side of the abdomen, and
there are three spacing tuber-
cles upon the first segment
of the abdomen for insuring
that a fresh supply of water
shall be admitted to the case
to flow over the gills. The
legs are directed forward, for

FIG. 105. The larval case of
Limnophilus, attached end-
wise to a submerged flag leaf,
in position of transformation.

Caddis-fly

199

FIG. 106. End view of pupal case of Limno-
philus showing silken barrier; enlarged.

readier egress from
the case ; they reach
forth from the front
end, clutching any
solid support.

The larva of Lim-
nophilus lives in the
case shown in figure
105. This is a dwel-
ling composed of flat
plant fragments
placed edgewise and
attached to the out-
side of a thin silken
tube.

^ The larva, living

in this tube, clam-
bers about over the vegetation, jerkily dragging its
cumbrous case along, foraging here and there where
softened plant tissues offer, and when disturbed, quickly
retreating inside. It frequently makes
additions to the front of its case, and
casts off fragments from the rear; so
it increases the diameter to accom-
modate its own growth.

When fully grown and ready for
transformation the larva partially closes
the ends, spins across them net-like
barriers of silk to keep out intruders
while admitting a fresh water supply.
Then it molts its last larval skin
and transforms into a pupa, of the
form shown in the accompanying figure,
having large compound eyes, long anten-
nae, broad external wing-cases and
copious external gills.

FIG. 107. Pup;
Limnophilus.

of

200

Aquatic Organisms

Then ensues a quiescent period of a fortnight or more
during which great changes of form, both external and
internal, take place. The stuffs that the larva accumu-
lated and built into its body during its days of foraging,
and that now lie inert in the soft white body of the pupa
are being rapidly made over into the form in which
they will shortly appear in the body of the dainty aerial
caddis-fly. However, the pupa is not wholly inactive.
By gentle undulations of its body it keeps the water
flowing about its gills; and when, at the approach of
final transformation, its new muscles
have grown strong enough, it is siezed
with a sudden fit of activity. It
breaks through the barred door of
the case, pushes out, swims away,
and then walks on the surface of the
water, seeking some emergent plant
stem, up which to climb to a suitable
place for its final transformation.
There the caddis-fly emerges, at first
limp and pale, but soon becoming
daintily tinted with yellow and brown,
full-fledged and capable of meeting the
exigencies of life in a new and wholly
different environment.

It is a marvelous change of form
and habits that insects undergo in
metamorphosis — especially in com-
plete metamorphosis. Such trans-
formations as occur in other groups are hardly com-
parable with it. The change from a tadpole to a frog,
or from a nauplius to an adult copepod, is slight by
comparison; for there is no cessation of activity, and no
considerable part of the body is even temporarily put
out of use. But in all the higher insects an extra-
ordinary reversal of development occurs at the close of

FIG. 1 08. Pupal skins
of Limnophilus, left
at final molting at-
tached to a reed
above the surface of
the water.

Lymph and Larva

2OI

active larval life. The larval tissues and organs disin-
tegrate, and return to a sort of embryonic condition,
to be rebuilt in new form in the adult insect.

With incomplete metamorphosis development is
more direct, there is no pupal stage, and the form of the
body is less altered during transformation. Metamor-
phosis is incomplete in the stoneflies, the mayflies, the

dragonflies and dam-
selflies and in the
water bugs. The im-
mature stage we shall
speak of as a nymph.
All nymphs agree in
having the wings de-
veloped externally
upon the sides of the
thorax. Metamor-
phosis is complete in
all the other orders
above mentioned.

FIG. 109. Water boatmen (Conxa), two „, .

adults and a nymph of the same species. Ineir immature

stage we shall call

a larva. All larvas agree in having the wings devel-
oped internally: they are invisible from the outside
until the pupal stage is assumed. It should be
noted in passing that "complete" and "incomplete"
as applied to metamorphosis are purely relative terms.
There is in the insect series a progressive divergence
in form between immature and adult stages, and the
pupal stage comes in to bridge the widening gap
between.

There is less change of form in the water bugs than
in any other group of aquatic insects. The nymph of
the water boatman (fig. 109) differs chiefly from the
adult in the undeveloped condition of its wings and
reproductive organs.

2O2 Aquatic Organisms

The groups of aquatic insects that, are most com-
pletely given over to aquatic "habits are the more
generalized orders that were long included in the single
Linnaean order Neuroptera (stoneflies, mayflies, dragon-
flies, caddis-flies, etc. )* Our knowledge of the immature
stages of aquatic insects was begun by the early micro-
scopists to whom reference has already been made in
these pages: Swammerdam, Rcesel, Reaumur, and
their contemporaries, f They delighted to observe
and describe the developmental stages of aquatic
insects, and did so with rare fidelity. After the days
of these pioneers, for a long time little attention was
paid to the immature stages, and descriptions of these
and accounts of their habits are still widely scattered!.

It is during their immature stages that most insects,
both aquatic and terrestrial ones, are of economic im-
portance. It is then they mainly feed and grow. It
is then they are mainly fed upon. The adults of many
groups eat nothing at all : their chief concern is with
mating and egg-laying. Hence the study of the im-
mature stages is worthy of the increased attention
it is receiving in our own time. It will be a very long
time before the life histories and habits of all our
aquatic insects are made known, and there is abundant
opportunity for even the amateur and isolated student
of nature to make additions to our knowledge by work
in this field.

*Under this name (we still call them Neuropteroids) the American forms
were first described and catalogued by Dr. H. A. Hagen in his classic "Synopsis
of the Neuroptera of North America." (Washington, 1861). Bugs, beetles,
moths and flies have received corresponding treatment in systematic synopses
of their respective orders, only the adult forms being considered.

fMuch of the best of the work of these pioneers has been gathered from
their ancient ponderous and rather inaccessible tomes, and translated by
Professor L. C. Miall, and reprinted in convenient form in his "Natural History
of Aquatic Insects" (London, 1895).

JThe completest available accounts of the life histories and habits of North
American aquatic insects have been published by the senior author and his
collaborators in the Bulletins 47, 68, 86 and 124 of the New York State Museum.

Stoneflies

203

The stoueflics (order Plecoptera) are all aquatic.
The}7 live in rapid streams, and on the wave-washed
rocky shores of lakes. They are among the most
generalized of winged insects. The adults are flat-
bodied inconspicuous creatures of secretive habits.

Little is seen of
them by day,
and less b y
night, except
when some bril-
liant light by the
waterside at-
tracts them to
flutter around it .
The colors are
obscure, being
predomin a n 1 1 y
black, brown or
gray; but the
diurnally- active
foliage inhabit-
ing chloroperlas
are pale green.
They take wing
awkwardly and
fly rather slowly,
and may often
be caught in the
unaided hand.

^^^ ^^^^ They are readily

picked up with

the fingers when at rest. The wings (sometimes
aborted) are folded flat upon the back. They are
rather irregularly traversed with heavy veins. The
tarsi are three- jointed. This, together with the flat-
tened head, bare skin, and long forwardly-directed

FIG. no. An adult stonefly, Perla immarginata.

204

A qiiatic Or&a n is ins

antennae, will be sufficient for recognition Jof members
of this group.

Stonefly nymphs are elongate and flattened, and very
similar to the adults in form of body. They possess
always a pair of tails at the end of the body. Most of
them have filamentous gills
underneath the body, tho a
few that live in well aerated
waters are lacking these.
The colors of the nymphs
are often livelier than those
of the adults, they being
adorned with bright greens
and yellows in ornate pat-
terns.

The nymphs are mainly
carnivorous. They feed
upon mayfly nymphs and
midge larvae and many
other small animals occur-
ring in their haunts.

One finds these nymphs
by lifting stones from water
where it runs swiftly, and
quickly inverting them.
The nymphs cling closely
to the under side of the
stones, lying flat with legs
otitspread, and holding on
by means of stout paired

claws that are like grappling hooks. Their legs are
flattened and laid down against the stone in such a
way that they offer little resistance to the passing
current. Stonefly nymphs are always found associated
with flat-bodied Mayfly nymphs of similar form, and
with greenish net- spinning caddis- worms.

FIG. in. The nymph of a stone-
fly, Perla immarginata.

(Photo by Lucy Wright Smith.)

Mayflies

205

The mayflies (order Ephemerida) are all aquatic.
live in all fresh waters, being adapted to the
greatest diversity of situations.
The adults are fragile insects, hav-
ing long fore legs that are habit-
ually stretched far forward, and
two or three long tails that are
extended from the tip of the body
backward. The wings are corru-
gated and fan like, but not folded,
and are held vertically in repose.
The hind wings are small and incon-
spicuous. The antennas are minute
and setaceous. The head is con-
tracted below and the mouth parts
are rudimentary. Thus, many
characters serve to distinguish the
mayflies from other insects and
make their group one of the easiest
to recognize.

Mayflies are peculiar also, in
their metamorphosis. They
undergo a moult after the assump-
tion of the adult form. They
transform usually at the surface
of the water, and, leaving the
cast-off nymphal skin floating, fly
away to the trees. Body and wings
are then clothed in a thin pellicle
of dull grayish and usually pilose
skin, which is retained during a
short period of quiescence. During
FIG. 112. An adult may- this period (which lasts but a few
fly sipMonums aitem'a- minutes in Camis and its allies,

tus,

but which in the larger forms lasts
one or two days) they are known as subimagos or

206

Aquatic Organisms

duns. Then this outer skin is shed, and thev come

•/

forth with smooth and shining surfaces and brighter
colors, as imagos, fully adult, and ready for their
mating flight. Lacking mouth parts and feeding not
at all, they then live but a few hours.

There are few phenomena
of the insect world more strik-
ing than the mating flight of
mayflies. The adult males fly
in companies, each species
maneuvering according to its
habit, and the females come
out to meet them in the air.
Certain large species that are
concerted in their season of
appearance gather in vast
swarms about the shores of all
our larger bodies of fresh water
at their appointed time. By
day we seen them sitting
motionless on every solid sup-
port, often bending the stream-
side willows with their weight ;
and when twilight falls we see
all that have passed their final
molt swarming in untold num-
bers over the surface of the
water along shore.

The nymphs of mayflies are all recognizable by the
gills upon the back of the abdomen. These are
arranged in pairs at the sides of some or all of the first
seven segments. The body terminates occasionally in
two but usually in three long tails. The mouth parts
are furnished with many specialties for raking diatoms
and for rasping decayed stems. Mayfly nymphs are
among the most important herbivores in all fresh waters.

FIG. 113. The nymph of the
mayfly, Siphlonurus alternates.

(Photo by Anna Haven Morgan.)

Dragon flies

207

The dragon flies and datnselflics (order Odonata) are
all aquatic. The adults are carnivorous insects that go
hawking about over the surfaces of ponds and meadows,
capturing and eating a great variety of lesser insects.
The larger dragonflies eat the smaller ones.

FIG 114. An adult damselfly, IscJiniira verticalis, perching on the stem of a
low galingale, Cy perns diandrus.

The form of body in the dragonflies is peculiar and
distinctive. The head, which is nearly overspread by
the huge eyes, is loosely poised on the apex of a narrow
prothorax. The remainder of the thorax is enlarged and
the wings are shifted backward upon it, and the legs
forward, adapting them for perching on vertical stems.

208 Aquatic Organisms

The abdomen is long and slender. On the ventral side
of its second and third segments, far removed from the
openings of the sperm ducts, there is developed in the
male a remarkable copulatory apparatus, that has no
counterpart in any other insects. The venation of the
wings, also, is peculiar, nothing like it being found in
any other order.

The dragonflies hold their wings horizontally in
repose. The damselflies are slender forms that hold
their wings vertically (or, in Lestes, obliquely outward)
in repose. Fore and hind wings are similar in form in
the damselflies; dissimilar, in the dragonflies.

FIG. 115. A nymph of the damsel-
fly, Ischnura verticalis.

The nymphs of the entire order are recognizable by
the possession of an enormous grasping labium, hinged
beneath the head. This is armed with raptorial hooks
and spines, and may be extended forward to a distance
several times the length of the head. It is thrust out
and withdrawn with a speed that the eye cannot follow.
It is a very formidable weapon for the capturing of
living prey. It is altogether unique among the many
modifications of insect mouth parts.

Damselfly nymphs are distinguished by the posses-
sion of three flat lanceolate gill-plates that are carried
like tails at the end of the abdomen. The edges of
these plates are set vertically, and they are swung from
side to side with a sculling motion to aid the nymphs in

swimming.

Dragonfly Nymphs 209

Dragonfly nymphs have their gills developed upon
the inner walls of a rectal respiratory chamber, and not
visible externally. Hence, the abdomen is much wider
than in the damselflies. Water drawn slowly into the
gill chamber through an anal orifice, that is guarded by
elaborate strainers, may be suddenly expelled by the
strong contraction of the abdominal muscles. Thus
this breathing apparatus, also, is used to aid in locomo-
tion. The body is driven forwrard by the expulsion of
the water backward.

Damselfly nymphs live for the most part clambering
about among submerged plants in still waters; a few

FIG. 1 1 6. The burrowing nymph of a Gomphine dragonfly,
with an elongate terminal segment for reaching up
through the bottom mud to the water.

cling to plants in the edges of the current, and a very
few cling to rocks in flowing water. Dragonfly nymphs
are more diversified in their habits. Many of them
also clamber among plants, but more of them sprawl
in the mud of the bottom, where they lie in ambush to
await their prey. One considerable group (the Gom-
phines) is finely adapted for burrowing in the silt and
sand of the bottom.

All are very voracious, eating living prey in great
variety. All appear to prefer the largest game they
are able to overpower. Mam^ species are arrant canni-
bals, eating their own kind even when not starved to it.
As a group they are among the most important carni-
vores in shoal fresh waters.

2IO

A qua tic Organisms

The true bugs (order Hemiptera) are mainly terres-
trial, and have undergone on land their greatest differ-
entiation. The aquatic ones are usually found in still
waters and in the shelter of submerged vegetation.
Tho comparatively few in species, they are important
members of the predatory population of ponds and

FIG. 117. A giant water bug (Benacus griseus)
clinging to a vertical surface under water,
natural size.

pools. They are often present in great numbers, if
not in great variety. The giant water bugs (fig. 117)
are among the largest of aquatic insects. These are
widely known from their habit of flying to arc lights,
falling beneath them, and floundering about in the dust
of village streets.

Water Bugs

211

The eggs of the giant water-bugs are attached to
vertical sterns of reeds just above the surface of the
water. They are among the largest of insect eggs.
Those of Benacus (fig. 118) are curiously striped. The
eggs of a smaller, related water-bug, ZaithaorBelostoma,
are attached by the female to the broad back of the

FIG. 118. Eggs of Benacus, enlarged; the lower-
most are in process of hatching.

male, and are carried by him during their incubation.
The nymphs of this family, on escaping from the egg
suddenly unroll and expand their flat bodies, and attain
at once proportions that would seem impossible on
looking at the egg (fig. 119).

Most finely adapted to life in the water are the water
boatmen (fig. 109 cm p. 201) and the back-swimmers,

212

Aquatic Organisms

which swim with great agility and are able to remain for
a considerable time beneath the surface of the water.
The eggs of these are attached beneath the water to any

solid support. Most
grotesque in form
are the water- scor-
pions (Nepidas) , that
breathe through a
long caudal respira-
tory tube. The
eggs of these are in-
serted into soft plant
tissues, with a pair
of long processes on
the end of each egg
left protruding.

At the shore-line
we find the creep-
ing water-bugs

Fie, 1 19. A new-hatched Benacus, and amOng matted roots

a detached egg. in the edge of the

water, with shore
bugs and toad bugs just out on land.

Nymphs and adults alike are distinguished from the
members of all other orders by the possession of a
jointed puncturing and sucking proboscis beneath the
head, directed backward between the fore legs.

Nymphs and adults are found in the water together
and are alike carnivorous. Being similar in form they
are readily recognized as the same animal in different
developmental stages.

The net -winged iti sects (Neuroptera) are mainly
terrestrial or arboreal. Two families only have aquatic
representatives, the Sialididas and the Hemerobiidas,
and these are so different, they are better considered
separately.

Dobsons

213

i. SialididcB— -These are the dobsons, the fish flies
and the orl flies. The largest is Corydalis, the common
dobson (fig. 120), whose larva is the well known "hell-
grammite", that is widely
used as bait
lives under
rapids. It is a

It

for bass,
stones in
''crawler"

of forbidding appearance,
two or three inches long
when grown, having a
stout, greenish black body,
sprawling, hairy legs, and
paired fleshy lateral pro-
cesses at the sides of the
abdomen. There is a
minute tuft of soft white
gills under the base of each
lateral process. There is
a pair of stout fleshy pro-
legs at the end of the ab-
domen, each one armed
with a pair of grappling
hooks. The larvae of the
fish-flies ( Chauliodes] are
similar in form . but smaller
and lack the gill tufts under

the lateral filaments. The larva of the orl-fly differs
conspicuously in having no prolegs or hooks at the end
of the body, but instead, a long tapering slender
tail. Fish-fly larvae are most commonly found clinging
to submerged logs and timbers. Orl-fly larvae burrow
in the sandy beds of pools in streams and in lake shores.
All appear to be carnivorous, but little is known of
the feeding habits of either larvae or adults. Tho large
and conspicuous insects they are rather secretive and
are rarely abundant, and they have been little observed.

FIG. 1 20. An adult female dob-
son, Corydalis cornuta, natural
size.

214

Aquatic Organisms

FIG. 121. Insect larvae.

2. HemcrobiidcE — Of this large family of lace-wings
but two small genera (in our fauna) of spongilla flies,
Climacia and Sisyra, have aquatic larvae. The adults
are delicate little insects that are so secretive in habits

and so infrequently
seen that they are
rare in collections.
Their larvae are com-
monly found in the
cavities of fresh water
sponges. They feed
upon the fluids in the
body of the sponge.
They are distin-
guished by the posses-
sion of long slender
piercing mouthparts,

diving-beetle larva (Coptolomus interrogalns) , longer tliail the head

jr Helen Williamson Lyman); b, a hellgrammite, o

(Ctarydalts cornuta, after Lintner); c, an orl-fly an(J thorax together,

larva (Siahs infumala, after Maude H. Anthony). «=> •

and by paired ab-
dominal respiratory filaments, that are angled at the
base and bent underneath the abdomen. These larvae
are minute in size (6 mm. long when grown) and are
quite unique among aquatic insect larvae in form of
mouthparts and in manner of life.

The caddis-flies (order Trichoptera) are all aquatic,
save for a few species that live in mosses. They con-
stitute the largest single group of predominantly aquatic
insects. They abound in all fresh waters.

The adults are hairy moth -like insects that fly to
lights at night, and that sit close by day, with their long
antennae extended forward (see fig. 1 03 on p. 197). They
are not showy insects, yet many of them are very dainty
and delicately colored. They are short-lived as adults,
and, like the mayflies, many species swarm at the shore
line on summer evenings in innumerable companies.

a, a.
after

Caddis-flies

215

The larvae of the caddis-flies mostly live in portable
cases, which they drag about with them as they crawl
or climb ; but a few having cases
of lighter construction, swim
freely about in them. Such is
Tricenodes, whose spirally wound
case made from bits of slender
stems is shown in the accompany-
ing figure.

The cases are wonderful in
their diversity of form of materials
and of construction. They are
usually cylindric tubes, open at
both ends, but they may be
sharply quadrangular or trian-
gular in cross section, and the
tube may be curved or even coiled
into a close spiral*.

Almost any solid materials that
may be available in the water in
pieces of suitable size may be used in their case build-
ing: sticks, pebbles, sand-grains and shells are the

staple materials. Sticks may be
placed parallel and lengthwise,
either irregularly, or in a con-
tinuous spiral. They may be
placed crosswise with ends over-
The case of the free- lapping like the elements of a
larvae of Trias- stick chimney, making thick
walls and rather cumbrous cases.
However built, the case is always lined with the secre-
tion from the silk glands of the larva. This substance
is indeed the basis of all case construction. The larva

FIG. 122. The larva of a
spongilla fly, Sisyra (after
Maude H. Anthony).

FIG. 123.

swimming
nodes.

*As in Helicopsyche, (see fig. 221, on page 370) whose case of finely textured
sand grains was originally described as a new species of snail shell.

2l6

Aquatic Organisms

builds by adding pieces one by one at the end of the
tube, bedding each one in this secretion, which hardens
on contact with the water and holds fast. Small snails

and mussel shells are
sometimes added to the
exterior with striking
ornamental effect, and
sometimes these are
added while the protes-
ting molluscs are yet
living in them.

Some of the micro-
caddis-flies (family Hy-
droptilidae) fashion
"parchment" cases of
the silk secretion alone.
These are brownish in
color and translucent.
They are usually com-
pressed in form and
are carried about on
edge. Agraylea decor-
ates the parchment
with filaments of Spiro-
gyra, arranged concentrically over the sides in a single
external layer.

Some caddis-worms build no portable cases at all, but
merely barricade themselves in the crevices between
stones, attaching pebbles by means of their silk secre-
tion, and thus building themselves a walled chamber
which they line with silk. In this they live, and out of
the door of the chamber they extend themselves half
their length in foraging. Other caddisworms construct
fixed tubes among the stones, and at the end of the tube
that opens facing the current they spin fine-meshed
funnel-shaped nets of silk. These are open up stream,

FIG. 124. Cylindric sand cases of
one of the Leptoceridae, (en-
larged) .

Caddis-worms

217

and into them the current washes organisms suitable
for food. The caddis-worm lies with ready jaws in wait
at the bottom of the funnel, and cheerfully takes what
heaven bestows, seizing any bit of food that may chance
to fall into its net. These net-spinners belong to the
family Hydropsychidae.
When minute animals
abound in the current the
caddis-worms appear to
eat them by preference:
at other times, they eat
diatoms and other alga?
and plant fragments .
The order as a whole tends
to be herbivorous and
many members of it are
strictly so; but most of
them will at least vary
their diet with small may-
fly and midge larva? and
entomostracans , when
these are to be had.

Caddis -worms are more or less caterpillar-like, but
lack paired fleshy prolegs beneath the body, save for a
single strongly-hooked pair at the posterior end. The
thoracic legs are longer and stronger and better devel-
oped than in caterpillars, and they are closely applicable
to the sides of the body, as befits slipping in and out
of their cases. The front third of the body is strongly
chitinized and often brightly pigmented; the
remainder, that is constantly covered by the case, is
thin skinned and pale. Most caddis -worms bear fila-
mentous gills along the sides of the abdomen, but some
that dwell in streams are gill-less and others have gills
In great compound clusters or tufts.

FIG. 125. The larva of Rhyucophila
fuscula in its barricade of stones,
exposed by lifting off a large top
stone.

21 8 Aquatic Organisms

Caddis-fly pupa? are likewise aquatic (and this is
characteristic of no other order of insects) , and like the
larvae, they often bear filamentous gills along the sides
of the abdomen. They are equipped with huge mandi-
bles that are supposed to be of use in cutting a way out
through the silk just before transformation. The
mandibles are shed at this time. The adult caddis-flies
are destitute of jaws and are not known to feed; so
they are probably short-lived.

FIG. 126. Eggs of Triasnodes.

The eggs of caddis-flies usually are laid in clumps of
gelatine. Sometimes they are arranged in a flat spiral,
as in Triaenodes, shown in the accompanying figure:
sometimes they are suspended from twigs in a ring-like
loop, as in Phryganea. Oftener they form an irregular
clump. They are usually of a bright greenish color,
but those of the net spinning Hy dropsy ches, laid on
submerged stones in close patches with little gelatine,
are tinged with a brick-red color.

The moths (order Lepidoptera) are nearly all terres-
trial. Out of this great order of insects only a few
members of one small family (Pyralidae) have entered
the water to live. These live as larvae for the most part
upon plants like water lilies and pond wreeds that are
not wholly submerged. Hydrocampa, removed from

Moths

219

its case of two leaf fragments, looks like any related land
caterpillar, with its small brown head, its strongly

FIG. 127. Two larval cases of the moth
Hydrocampa, each made of two pieces
of Marsilea leaf. Upper smaller case
unopened, larva inside; lower case opened
to show the larva, its cover below.

chitinized prothorax and the series of fleshy prolegs
underneath the abdomen. By these same characters
any other aquatic caterpillar may be distinguished from
the members of other orders. Paraponyx makes no

22O

Aquatic Organisms

case, differs strikingly in being covered with an
abundance of forking filamentous gills which sur-
round the body as with a whitish fringe. It feeds, often
in some numbers, on the under side of leaves of the white
water-lily, or about the sheathing leaf bases of the
broad-leaved pond weeds (Potamogeton).

Elophila fulicalis lives on the exposed surfaces of
stones in running streams, dwelling under a silt-covered
canopy of thin-spun silk, about the edges of which it
forages for algas growing on the stones. Its body is

FIG. 128. Larva of Elophila

depressed, and its gills are unbranched and in a
double row along each side. It spins a dome-shaped
cover having perforate margins under which to pass
the pupal period. It emerges, to fly in companies of
dainty little moths by the streamside.

All these aquatic caterpillars like their relatives on
land, are herbivorous. They are all small species;
they are of wide distribution and are often locally
abundant.

The beetles (order Coleoptera] are mainly terrestrial,
there being but half a dozen of the eighty-odd families
of our fauna that are commonly found in the water.
Both adults and larvae are aquatic, but, unlike the bugs,
the beetles undergo extensive metamorphosis, and

Beetles

221

larvae and adults are of very different appearance.
Beetle larvae most resemble certain neuropteroids of the
family Sialididae in appearance, and there is no single
character that will distinguish all of them (see fig. 121 on
p. 214). Only a few beetle larvae (Gyrinids, and a few
Hydrophilids like Berosus) possess paired lateral fila-
ments on the sides of the abdomen such as are charac-
teristic of all the Sialididae.
Aquatic beetle larvae are
much like the larvae of the
ground beetles (Carabidae)
in general appearance, hav-
ing well developed legs and
antennae and stout rapacious
jaws.

Best known of water
beetles are doubtless the
" whirl -i -gigs" (Gyrinidae),
which being social in their
habits and given to gyrating
in conspicuous companies on
the surface of still waters,
could hardly escape the
notice of the most casual ob-
server. Their larvae, how-
ever, are less familiar. They

are pale whitish or yellowish translucent elongate crea-
tures, with very long and slender paired lateral ab-
dominal filaments along the sides of the abdomen.
They live amid the bottom trash where they feed upon
the body fluids of blood worms and other small
animal prey. Living often in broad expanses of shoal
water where there are no banks upon which to crawl
out for pupation, they construct a blackish cocoon
on the side of some vertical stem just above the surface
of the water and undergo transformation there. The

FIG. 129. A diving beetle,
Dytiscus, slightly enlarged.

222

Aquatic Organisms

eggs are often laid on the under side of floating leaves

of pond weeds.

The diving beetles (Dytiscidse and
Hydrophilidse) are by far the most num-
erous and important of the aquatic
beetles. These swarm in every pond
and pool, and are among the most
important carnivores of all such waters.
They range in size from the big brown
Dytiscus (fig. 1 29) down to little fellows
a millimeter long. Their prevailing
colors are brown or black, but many of
FIG. 130. One of the lesser forms are prettily flecked and

the lesser diving
beetles, Hydro-
par us, seven
times natural
size.

streaked with
yellow (fig. 130).
The eggs of the
Dytiscus and of
other members
of its family are
inserted singly
into punctures in
the tissues of
living plants (fig.
131). Those of
the Hydrophilids
are for the most
part inclosed in
whitish silken
cocoons attached
to plants near the
surface of the
water.

FIG. 131. Eggs of the diving beetle,
Dytiscus, in submerged leafstalks, nearly
ready for hatching: the larva shows
through the shell. (From Matheson)

Beetles

223

The Haliplids are a small family of minute beetles,
having larvae of unique form and habits. These larva?

FIG. 132. Larvae of the beetle, Peltodytes,
in mixed algal filaments, twice natural
size; below, a single larva more highly
magnified. (From Matheson).

live among the tangled filaments of the coarser green
algae, especially Spirogyra, and they feed upon the
contents of the cells that compose the filaments, sucking

224 Aquatic Organisms

the contents of the cells, one by one. They are very
inert-looking, stick-like, creatures and easily pass
unobserved. Of our two common genera one (Pelto-
dytes) is shown in figure 132. The body is covered
over with very long stiff jointed bristle-like processes,
giving it a burr-like appearance. The larva of the
other genus (Haliplus) is more stick-like, has merely
sharp tubercles upon the back, and has the body ter-
minating in a long slender tail.

The Riffle beetles (Parnidse and Amphizoidse) prefer
flowing water. They do not swim, but clamber over
the surfaces of logs and stones. They are mostly small
beetles of sprawling form, having stout legs that
terminate in curved grappling claws. There is great
variety of form among their larvae, the better adapted
ones that live in swift waters showing a marked ten-
dency to assume a limpet-like contour. This cul-
minates in the larva of Psephenus, commonly known as
the "water penny." This larva was mistaken for a
limpet by its original describer. It is very much
flattened and broadened and nearly circular in outline,
and the flaring lateral margins encircling and inclosing
the body fit down all round to the surface of the stone
on which it rests (see fig. 160 on page 260). Under-
neath its body are tufts of fine filamentous gills, inter-
segment ally arranged.

The flies (order Dipt era) are a vast group of insects.
Among them are many families wrhose larvae are wholly
or in part aquatic. The changes of form undergone
during metamorphosis are at a maximum in this group :
the larvae are very different indeed from the adults.

Dipterous larvae are very diversified in form and
details of structure. The entire lack of thoracic legs
will distinguish them from all other aquatic larvae.
They agree in little else than this, and the general

Flies

225

tendency toward the reduction of the size of the head
and of the appendages. Many of them are gill-less and
many more possess but a single cluster of four tapering
retractile anal gill filaments.

FIG. 133. An adult midge, Tanypus carneus,
male.

By far the most important of the aquatic Diptera in
the economy of nature are the midges (Chironomidae).
These abound in all fresh waters. The larvae are
cyliridric and elongate, with distinct free head, and body
mostly hairless save for caudal tufts of setae. They are
distinguished from other fly larvae by the possession of a
double fleshy proleg underneath the prothorax, and a
pair of prolegs at the rear end of the body, all armed
with numerous minute grappling hooks. Many of
them are of a bright red color, and are hence called
"blood worms.'

226

Aquatic Organisms

Midge larvae live mainly in tubes which they fashion
out of bits of sediment held together by means of the
secretion of their own silk glands. These tubes are
built up out of the mud in the pond bottom as shown in
the accompanying figure, or constructed in the crevices

FIG. 134. Tubes of midge larvae in the bed of a pool.

between leaves, or attached to stems or stones or any
solid support. They are never portable cases. They
are generally rather soft and flocculent. The pupal
stage is usually passed within the same tubes and the
pupa is equipped with respiratory horns or tufts of
various sorts for getting its air supply. The pupa (see
fig. 171 on p. 280) is active and its body is constantly
undulating, as in the caddisflies.

The eggs of the midges are laid in gelatinous strings
in clumps and are usually deposited at the surface of
the water. Figure 135 shows the appearance of a bit
of such an egg-mass. This one measured bushels in

Flies

quantity, and doubtless was laid by thousands of
midges. Figure 136 shows a little bit of it — a portion
of a few egg strings — magnified so as to show the form
and arrangement of the individual eggs. Such great
egg masses are not uncommon, and they foreshadow the
coming of larva? in the water in almost unbelievable
abundance.

FIG. 135. A little bit of an egg mass of the midge,
Chirononins, hung on water weeds (Philotria).

Midge larva? are among the greatest producers of
animal food. They are preyed upon extensively, and
by all sorts of aquatic carnivores.

Three families of blood-sucking Diptera have aquatic
larvae; the mosquitos (Culicidas), the horseflies
(Tabanidae) and the black flies (Simuliidae) . Mosquito

228 Aquatic Organisms

larvae are the well known "wrigglers" that live in rain
water barrels and in temporary pools. They are
readily distinguished from other Dipterous larvae by
their swollen thoracic segments and their tail fin. The
pupae are free swimming and hang suspended at the
surface with a pair of large respiratory horns or trum-
pets in contact with the surface when at rest.

FIG. 136. A few of the component egg-strings, magnified.

The larvas of the horseflies are burrowers in the mud
of the bottom. They are cylindric in form, tapering
to both ends, headless, appendageless, hairless, and
have the translucent and very mobile body ringed with
segment ally arranged tubercles. They are carnivorous,
and feed upon the body fluids of snails and aquatic
worms and other animals. The white spiny pupae are

Flies 229

formed in the mud of the shore. The tiny black eggs
(fig. 138) are laid in close patches on the vertical stems
or leaves of emergent aquatic plants.

Black fly larvae live in rapid streams, attached in
companies to the surfaces of rocks or timbers over
which the swiftest water pours. They are blackish,
and often conspicuous at a distance by reason of their
numbers. They have cylindric bodies that are swollen
toward the posterior end, which is attached to the
supporting surface by a sucking disc. Underneath the
mouth is a single median proleg, and on the front of the
head convenient to the mouth, there is a pair of "fans,"
whose function is to strain forage organisms out of the
passing current. The full grown larva spins a basket-
like cocoon on the vertical face of the rock or timber,
and in this passes its pupal stage. The eggs are laid
in irregular masses at the edge of the current where the
water runs swiftest.

In like situations we meet less frequently the net-
winged midges (Blepharoceridae), whose scalloped flat
and somewhat limpet-shaped larvae are at once recogniz-
able by the possession of a midventral row of suckers
for holding on to the rock in the bed of the rushing
waters. The naked pupa is found in the same situation
and is attached by one strongly flattened side to the
supporting surface.

These five above-mentioned families are the ones
most given over to aquatic habits. Then there are
several large families a few of whose members are
aquatic: Leptidae, whose larvae live among the rocks
in rapid streams, hanging on and creeping by means of
a series of large paired and bifid prolegs; Syrphidae,
whose larvae are known as "rat -tailed maggots" since
their body ends in a long flexuous respiratory tube,
which is projected to the surface for air when the larva
lives in dirty pools ; Craneflies (Tipulidae) see fig. 215 on

230

Aquatic Organisms

FIG. 138. The eggs
of a horsefly on
an emergent bur-
reed leaf.

FIG. 137. The larva of a horsefly, Chrysops.

P- 359) whose cylindric tough-
skinned larvae have their heads
retracted within the prothorax,
and bear on the end of the abdo-
men a respiratory disc perforate
by two big spiracles and sur-
rounded by fleshy radiating fila-
ments ; minute moth-flies — Psycho-
didae, (see fig. 214 on p. 359)
whose slender larvae live amid
the trash in both brooks and
swales. Swaleflies ( Sciomyzidae)
whose headless and appendage-
less larvae hang suspended by
their posterior end from the sur-
face in still water; and others
less common.

It is a vast array of forms this
order comprises, this mighty group
of two-winged flies, that is still so
imperfectly known; and some of
the most highly diversified of its
larvae are among the commoner
aquatic ones.

There is little need that we should give any extended
account of the groups of back-boned animals — fishes,
amphibians, reptiles, birds and mammals. In water as
on land they are the largest of animals, and are all
familiar. The water- dwellers among them, excepting
the fishes and a very few others, are air-breath-
ing forms that are mainly descended from a terrestrial
ancestry. They haunt the water-side and enter the
shoals to forage or to escape enemies, but they cannot
remain submerged, for they have need of air to breathe.

The fishes have remained strictly aquatic. They
dominate the open waters of the larger lakes and streams.
They have multiplied and differentiated and become
adapted to every sort of situation where there is water
of depth and permanence sufficient for their mainten-
ance. They outnumber in species every other verte-
brate group.

Within the water the worst enemies of fishes are
other fishes; for the group is mainly carnivorous, and
big fishes are given to eating little ones. Hence, tho
all can swim, few of them do swim in the open waters,.
and these only when well grown. Those that so expose
themselves must be fleet enough to escape enemies, or
powerful enough to fight them. Little fishes and the
greater number of mature fishes keep more or less
closely to the shelter of shores and vegetation. The
accompanying diagram, based on Hankinson's (08)
studies at Walnut Lake, Michigan, represents the
distribution of fishes in a rather simple case. The
thirty-one species here present range in adult size
from the pike which attains a length above three feet,
to the least darter which reaches a length of scarcely an
inch and a half. One species only, the whitefish,

231

232

Aquatic Organisms

dwells habitually in the deep waters of the lake. One
other species, the common sucker, is a regular inhabit-
ant of water between fifteen and forty feet in depth.
The pike, ranges the upper waters at will pursuing his
prey over both depths and shoals; but he appears to
prefer to lie at rest among the water-weeds where his

- ' '**/*• * &• ~ f^'^e-fJ: ~--S* .

FIG. 139. Ale-wives (Clupea pseudoharengus) on the beach of Cayuga Lake,
after the close of the spawning season. A single large sucker lies in the
foreground.

great mottled back becomes invisible among the lights
and shadows.

The pondweed zone on the sloping bottom between
five and twenty-five feet in depth is the haunt of most
of the remaining species, including all the minnows, cat-
fishes, sunfishes, and the perches. The last named
wander betimes more freely into the deep water; all of

Distribution of FisJies

233

these forage in the shoals, especially at night. The
catfishes are more strictly bottom feeders, and these
feed mainly at night. A few species keep to the close
shelter of thick vegetation at the water's edge, and one
species, the least darter, prefers to lie over mottled
marl-strewn bottoms at depth between fifteen and
twenty feet.

So it appears that some two-thirds of the species
have their center of abundance in the pondweed zone:
here, doubtless they best find food and escape enemies.

FT

20
40
60

80

100

J^\,—- 'pondweted zone

n>^ —

a, whitefish, i species.

c, pike, i species.

e, sucker, i species.

n, perch and wall-eye, 2 species.

o, bass, sunfish, minnow, etc.,

19 species.

r, catfishes, 2 species.
5, mudminnow, etc., 3 species.
x, least darter, i species.

FIG. 140. Diagram illustrating the habit-
ual distribution of the thirty-one species
of fishes in Walnut Lake, Michigan.
Data from Hankinson.

Only a few of the stronger and swifter species venture
much into the deeper water: the weaklings and the
little fishes frequent the weed-covered shoals.

The eggs of fishes are cared for in a great variety of
ways. Their number is proportionate to the amount of
nurture they receive. No species scatters its eggs
throughout the whole of its range, but each species
selects a spot more or less circumscribed in which to lay
its young. Carp enter the shoals and scatter their eggs
promiscuously over the submerged vegetation and the
bottom mud with much tumult and splashing. A
single female may lay upwards of 400,000 eggs a season.

234

Aquatic Organisms

Doubtless many of these eggs are smothered in mud and
many others are eaten before hatching. Suckers seek
out gravelly shoals, preferably in the beds of streams, at
spawning time. Dangers are fewer here and a single
female may lay 50,000 eggs. Yellow perch attach their
eggs in strings of gelatin trailed over the surface of
submerged water plants. The number per fish is still

FIG. 141. A splash on the surface made by a carp in spawning.

ftvrther reduced to some 20,000 eggs. Sunfishes make
a sort of nest. They excavate for it by brushing away
the mud with a sweeping movement of the pectoral fins.
Thus they uncover the roots of aquatic plants over a
circular area having a diameter equal to the length of
the fish. On these roots the female lays her eggs, and
the male guards them until they are hatched. With
this additional care the number is further reduced to
some 5000 eggs. Sticklebacks actually build a nest, by

Food of Fishes 235

gathering and fastening together bits of vegetation.
It is built in the tops of the weeds — not on the pond
bottom. The nest is roughly spherical, with a hole
through the middle of it from side to side. Within the
dilated center of the passageway the female lays her
eggs: the male stands guard over the nest. After the
hatching of the eggs he still guards the young. It is
said that when the young too early leave the nest, he
catches them in his mouth and puts them back. The
stickleback lays only about 250 eggs.

Thus in their extraordinary range of fecundity the
fishes illustrate the wonderful balance in nature. For
every species the number of young is sufficient to
meet the losses to which the species is exposed.

The food of fresh-water fishes covers a very wide
range of organic products ; but the group as a whole is
predaceous. A few, like the goldfishes and golden
shiners, are mainly herbivorous and live on algae and
other soft plant stuffs. Others like carp and gizzard-
shad live mainly on the organic stuffs they get by
devouring the bottom ooze. Many, either from choice
or from necessity, have a mixed diet of plant and animal
foods. But the carnivorous habit is most widespread
among them. In inland waters they are the greatest
consumers of animal foods.

Such fishes as the pike which, when grown, lives
wholly upon a diet of other fishes, are equipped with an
abundance of sharp raptorial teeth. The sheepshead
has flattened molar-like teeth strong enough for crushing
shells and adapting it to a diet of molluscs. Other
fishes, even large ones like the shovel-nosed sturgeon,
have close-set gill-rakers. These retain for food
the plancton organisms of the water that is strained
through the gills. The young of all fishes are plancton
feeders.

236

Aquatic Organisms

The Amphibians are the smallest of the five great
groups of vertebrates. They are represented in our
fauna mainly by frogs and salamanders. A few of the
more primitive salamanders (Urodela), such asNecturus,
breathe throughout life by means of gills, and are
strictly aquatic. A few are terrestrial, but most are
truly amphibious. They develop as aquatic larvse
(tadpoles), having gills for breathing and a fish-like
circulation: they transform to air-breathing, more or
less terrestrial adult forms; and they return to the
water to lay their eggs in the primeval environment.

FIG. 142. A leopard frog. Rana pipietis.

The period of larval life varies from less than two
months in the toad to more than two years in the bull-
frog.

The eggs of amphibians are, for the most part, de-
posited in shallow water, often in masses in copious
gelatinous envelopes (see fig. 201 on p. 342). In some
cases the egg masses are large and conspicuous and well
known. Examples are the long egg-strings of the toad
that lie trailing across the weeds and the bottom; or
the half-floating masses of innumerable eggs laid by the
larger frogs. The eggs of the smaller frogs are less
often seen, those of the peeper being attached singly
to plant stems. Dr. A. H. Wright (14) has shown that
the eggs of all our species of frogs are distinguishable
by size, color, gelatinous envelopes and character of
cluster.

Amphibians

237

a B CD

G H

Adult amphibians are carnivorous. They all eat
lesser animals in great variety. Frogs and toads have
a projectile and adhesive tongue which is of great service
in capturing flying insects; but they eat, also, many
other less active morsels of flesh that they find on the
ground or in the water.
The food of some of the
lesser stream-inhabiting
salamanders, such as
Spelerpes, is mainly in-
sects, while that of the
vermilion-spotted newt
is mainly molluscs.

The amphibia are a
group of very great bio-
logical interest. They
represent a relatively
simple type of vertebrate
structure. Their devel-
opment can be followed
with ease and it is illumi-
nating and suggestive of
the early evolutionary history of the higher verte-
brates. They illustrate in their own free-living forms
the transition from aquatic to terrestrial life. And they
show in the different amphibian types many grades of
metamorphosis. The transformation is more extensive

FIG. 143. Diagram of individual eggs
from the egg mass of the toad and
seven species of frog occurring at
Ithaca. Eggs solid black; gelati-
nous envelopes white. (After
Wright).

A, Toad, eggs in double gelatinous tubes, form-
ing strings, the inner tube divided by cross
partitions; B, pickerel frog; C, peeper (no
outer envelope) ; D, green frog (inner en-
velope ellipitical) ; E, tree frog (outer en-
velope ragged) ; F, bull frog (no inner
envelope); G, leopard frog; H, wood frog.
All twice natural size.

FIG. 144. The spotted salamander, Ambystoma tigrinum.

238 Aquatic Organisms

in frogs than in any other vertebrates, involving
profound changes in internal organs and in manner of
life.

The reptiles are mainly terrestrial. Southward there
are alligators in the water, but in our latitude there are

FIG. 145. The common snapping turtle.

only a few turtles and water snakes. These make their
nests on land. They hide their eggs in the sand or in
the midst of marshland rubbish, where the sun's
warmth incubates them.

These also are carnivorous.

Water Birds

239

The water birds, tho more numerous than the two
preceding groups, are but a handful of this great class
of vertebrates.

The principal kinds of birds that frequent the water
are water-fowl — ducks, geese and swans; the shore
birds — plover, snipe and rails; the gulls, the herons
and the divers. Some of these that, like the loon, are

FIG. 146. Wild geese foraging in a marsh in Dakota.

superably fitted for swimming and diving, feed mainly
on fishes. Most water birds consume a great variety of
lesser animals. The ducks and rails differ much in diet
according to species. Thus the Sora rail eats mainly
seeds of marsh plants, while the allied Virginia rail in
the same locality eats miscellaneous animal food to the
extent of more than 50 per cent, of its diet.

Only the wTaterfowl that are prized as game birds are
extensively herbivorous. They eat impartially the
vegetable products of the land and of the water. The

240

Aquatic Organisms

wild ducks and geese eat great quantities of duckmeat
(Lemna) and succulent submerged aquatics. Canvas-
backs fatten on the wild celery (Vallisneria). In
Cayuga Lake in winter they gorge themselves with the
starch-filled winter buds of the pondweed, Potamogeton

FIG. 147. Floating nest of pied-billed grebe (Podilymbus podiceps) in
a cat-tail marsh, surrounded by water.

pusillus. They also dive and pluck up from the bottom
mud the reproductive tubers of the pond weed, Potamoge-
ton pectinatus (see fig. 228 on p. 381).

Water birds, having attained the freedom of the air,
are wide ranging beyond all other animals. They come
and go in annual migrations. They settle here and

Aquatic Mammals 241

there, and commit local and intermittent depredations.
The water birds nest mainly on land, and in their
nesting and brooding habits they differ little from their
terrestrial relatives.

The aquatic nianuuah of inland waters fall mainly in
two groups, the carnivores and the rodents. Here
again, the carnivores that are more expert swimmers
and divers, such as fisher, martin, otter and mink are
all fish-eating animals. They have become fitted to

FIG. 148. A muskrat, Fiber zibethicus.

utilize the chief animal product of the water. Of these
four the mink alone has withstood the "march of
progress," and retains its former wide distribution.

Of rodents there are two fur-bearers of much import-
ance, the beaver, now driven to the far frontier, and the
muskrat. The muskrat has become under modern
agricultural conditions the most important aquatic mam-
mal remaining. By reason of its rapid rate of repro-
duction, its ability to find a living in any cat-tail marsh,
big or little, and its hardiness, it has been able to main-
tain its place.

CHAPTER V

ADJUSTMENT TO CONDITIONS
OF AQUATIC LIFE

INDIVIDUAL
ADJUSTMENT

O infinitely varied are
the fitnesses of aqua-
tic organisms for the
conditions they have
to meet that we can
only select out of a
worldf ul of examples a
few of the more wide-
spread and significant.
We shall have space
here for discussing

only such adaptations to life in the water as are common
to large groups of organisms, and represent general
modes of adjustment. First we will consider some of
the ways in which the species is fitted to the aquatic
conditions under which it lives, and then we will take
note of some mutual adjustments between different
species.

The first of living things to appear upon the earth
were doubtless simple organisms that were far from

242

Flotation 243

being so small as the smallest now existing, or so large
as the largest. They grew and multiplied. They
differentiated into plants and animals, into large and
small, into free-swimming and sedentary. Some be-
took themselves to the free life of the open waters and
others to more settled habitations on shores. The
open-water forms were nomads, forever adrift in the
waves: the shoreward forms might find shelter and a
quiet resting place.

LIFE IN OPEN WATER

In the open water there are certain great advantages
that lie in minuteness and in buoyancy. These quali-
ties determine the ability of organisms to float freely
about in the more productive upper strata of water.
To descend into the depths is to perish for want of
light. So the members of many groups are adapted for
floating and drifting about near the surface. These
constitute the plancton.

On the other hand, large size has its advantages when
coupled with good ability for swimming and food
gathering. In the rough world's strife the battle is
usually to the strong. It is the larger, wide-ranging,
free-swimming organisms that dominate the life of the
open water. These constitute the necton.

Plancton and necton will be discussed in the next
chapter as ecological groups, but in this place we may
take note of the two very different sorts of fitness, that
they have severally developed for life in the open water,
the plancton organisms being fitted for flotation, and
the necton for swimming.

Flotation — All living substance is somewhat heavier
than water (i. e. has a specific gravity greater than i)
and therefore tends to sink to the bottom. The veloc-

244 Adjustment to Conditions of Aquatic Life

ity in sinking is determined by several factors, one of
which is external and the others are internal:

The external factor is the varying viscosity of the
water.

The internal factors are specific gravity, form and
size.

We have mentioned (p. 30) that the viscosity of the
water is twice as great at the freezing point as at
ordinary summer temperatures; which means, of course,
that the water itself would offer much greater resistance
to the sinking of a body immersed in it. We are here
concerned with the internal factors.

Lessening of Specific gravity— -The bodies of organisms
are not composed of living substance alone, but con-
tain besides, inclusions and metabolic products of
various sorts, which oftentimes alter their specific
gravity. The shells and bone and other hard parts of
animals are usually heavier than protoplasm; the fats
and gelatinous products and gases are lighter. We
know that the fats of vertebrates, if isolated and thrown
upon the water, will float; and that a fat man, in order
to maintain himself above the water, needs put forth
less effort than a lean one. There are probably many
products of the living body that are retained within
or about it and that lessen its specific gravity, but the
commonest and most important of these seem to fall
into three groups:

1. Fats and oils, which are stored assimilation
products. These are very easily seen in such plancton
organisms as Cyclops (see fig. 96 on p. 189) where they
show through the transparent shell as shining yellowish
oil droplets. Most plancton algae store their reserve
food products as oils rather than as starches.

2. Gases, which are by-products of assimilation, and
are distributed in bubbles scattered through the tissue

Flotation 245

where produced, or accumulate in special containers.
These greatly reduce the specific gravity of the body,
enabling even heavy shelled forms (see p. 159) to float.

3. Gelatinous and mucilaginous products of the body
which usually form external envelopes (see fig. 10 on
p. 52) but which may appear as watery swellings of the
tissues. Their occurrence as envelopes is very common
with plants and with the eggs of aquatic animals ; they
may serve also for protection and defense, and for
regulating osmotic pressure, but by reason of their low
specific gravity they also serve for flotation.

Improvment of form — We have already called atten-
tion (p. 42) to the fact that size has much to do with the
rate of sinking in still water. This is because the
resistance of the water comes from surface friction and
the smaller the body the greater the ratio of its
surface to its mass. Given a body small enough, its
mere minuteness will keep it long afloat. But in
bodies of larger size relative increase in surface is
brought about in various ways:

1 . By extension of the cell in slender prolongations
(see fig. 50, j, k, 1, on p. 129).

2 . By the aggregation of cells into expanded colonies :

a. Discoid colonies, as in Pediastrum (fig. 44 on
p. 123).

b. Filaments, as in Oscillatoria (fig. 34 on p. 109).

c. Flat ribbons of innumerable slender cells placed
side by side, as in many lake diatoms (Fragil-
laria, Tabelaria, Diatoma).

d. Radiate colonies as in Asterionella (fig. 35 n on
p. in).

e. Spherical colonies as in Volvox (fig. 31, p. 105:
see also a b c of. fig. 50 on p. 129), wherein the
cells are peripheral and widely separated the

246 Adjustment to Conditions of Aquatic Life

interstices and the interior being filled with
gelatinous substances of low specific gravity.
/. Dendritic colonies, as in Dinobryon (fig. 32 on
p. 106).

3. In the Metazoa, by the expansion of the external
armor and appendages into bristles, spines and fringes.
Thus in the rotifer Notholcalongispina (fig. 149),
a habitant of the open water of lakes, there is a
great prolongation of the angles of the lorica,
before and behind; and in the Copepods (fig. 95,
p. 1 88) there is an extensive development of
bristles upon antennas and caudal appendages.
Expansions of the body, if mere expansions,
serve only to keep the body passively afloat ; but
many of them have acquired mobility, becom-
ing locomotor organs. Cilia and flagella are the
simplest of these, and are common to plants and
animals. Almost all the appendages of the
higher animals, antenna?, legs, tails, etc., are
here and there adapted for swimming. A body
whose specific gravity is but little greater than
that of the water may be sustained by a mini-
mum use of swimming apparatus. The lesser
Uoog- flagellate and ciliate forms, both plant and
spined animal, maintain their place by continuous lash-
rotifer. ^ng Q£ ^e wa^er jf we watch a few waterfleas

in a breaker of clear water we shall see that their swim-
ming also, is unceasing. Each one swims a few strokes
of the long antennae upward, and then settles with
bristles all outspread, descending slowly, as resistance
yields, to its former level. This it repeats again and
again. It may turn to right or to left, rise a little
higher or sink a little lower betimes, but it keeps in
the main to its proper level. Its swimming powers
are to an important degree supplemental to its inade-

Flotation

247

quate powers of flotation. The strokes of its swim-
ming antennas are, like the beating of our own hearts,
intermittent but unceasing, and when these fail it falls
to its grave on the lake bottom.

Flotation devices usually impede free swimming,
especially do such expansions of the body as greatly
increase surface contact with the water. It is in the
resting stages of animals, therefore, that we find the
best development of floats: such, for example, as the
overwintering statoblasts of the Bryo-
zoan, Pectinatella, shown in the accom-
panying figure. Here an encysted mass
of living but inactive cells is sur-
rounded by a buoyant, air-filled an-
nular cushion, as with a life preserver,
and floats freely upon the surface of
the water, and is driven about by the
waves.

Too great buoyancy is, however, as
much a peril to the active micro-organ-
isms of the water as too little. Contact
with the air at the surface brings to soft
protoplasmic bodies, the peril of evap-
oration. Entanglement in the surface
film is virtual imprisonment to certain
of the water-fleas, as we shall see in
the next chapter. It is desirable that
they should live not on but near the
surface. A specific gravity about that
of water would seem to be the optimum
for organisms that drift passively about : a little greater
than that of water for those that sustain themselves in
part by swimming.

Terrestrial creatures like ourselves, who live on the
bottom in a sea of air with solid ground beneath our
feet, have at first some difficulty in realizing the nicety

FIG. 150. The over-
wintering stage
of the bryozoan,
Pectinatella ; a
stato blast or
gemmule. The
central portion
contains the liv-
ing cells. The
dark ring of min-
ute air-filled cells
is the float. The
peripheral an-
chor-like pro-
cesses are attach-
ment hooks for
securing distribu-
tion bv animals.

248 Adjustment to Conditions of Aquatic Life

of the adjustment that keeps a whole population in the
water afloat near to, but not at the surface. This comes
out most clearly, perhaps, in those minor changes of
form that accompany seasonal changes in temperature
of the water. In summer when the viscosity of the
water grows less (and when in consequence its resist-

a

b

PIG. 151. Summer and winter forms of plancton animals : sum-
mer above, winter below, a, the flagellate Ceratium; b, the
rotifer Asplanchna; c, d, e, water- fleas; c and d, Daphne;
e, Bosmina. (After Wesenberg-Lund).

ance to sinking is diminished) the surface of many
plancton organisms is increased to correspond. The
slender diatoms grow longer and slenderer, the spines
on certain loricate rotifers grow longer. Bristles and
hairs extend and plumes and fringes grow denser. Even
the form of the body is altered to increase surface-
contact with the water. A few examples are shown in

Swimming

249

the accompanying figures. These changes when fol-
lowed thro the year show a rather distinct correspon-
dence to the seasonal changes in viscosity of the water.

FIG. 152. Seasonal form changes of the water-flea, Bosmina coregoni. The
fractional figures above indicate date: those below indicate corresponding
temperatures in °C. (After Wesenberg-Lund.)

Swimming — For rapid locomotion through the water
there are numberless devices for propulsion, but there
is only one thoroly successful form of body; and that

is the so-called "stream-line form" (fig.
153). It is the form of body of a fish:
an elongate tapering form, narrowed
toward either end, but sloping more
gently to the rear. It is also the form
of body of a bird encased in its feathers.
It is probably the form of body best
adapted for traversing any fluid medium
with a minimum expenditure of energy.
The accompanying diagram explains its
efficiency. The white arrow indicates
direction of movement. The gray lines
indicate the displacement and replace-
ment of the water. The black arrows
indicate the direction in which the
forces act. At the front the force of
the body is exerted against the water;
at the rear the force of the water is exerted against the
body. The water, being perfectly mobile, returns

FIG. 153. Stream-
line form. For
explanation
text.

see

250 Adjustment to Conditions of Aquatic Life

after displacement; and much of the force expended
in pushing it aside at the front is regained by the
return-push of the water against the sloping rearward
portion of the body.

The advantage of stream-line form is equally great
whether a body be moving through still water, or
whether it be standing against moving water. A
mackerel swimming in the sea is benefited no more than
is a darter holding its stationary position on the stream
bed. To this we shall have occasion to return when
discussing the rapid-water societies.

Apparatus for propulsion is endlessly varied in the
different animal groups. Plants have developed hardly
any sort of swimming apparatus beyond cilia and
flagella. These also serve the needs of many of the
lower animals — the protozoa, the flat worms, the roti-
fers, trochophores and other larvae, sperm cells generally,
etc. But more widely ranging animals of larger size
have developed better swimming apparatus, either with
or without appendages. Snakes swim by means of
horizontal undulating or sculling movements of the
body, and so also do many of the common minute
Oligochaete worms. Horseleeches swim in much the
same manner, save that the undulations of the body are
in the vertical plane. Midge larva? ("bloodworms")
swim with figure-of-8-shaped loopings of the body that
are quite characteristic. Mosquito larvae are
"wrigglers," and so also are many fly and beetle larvas,
tho each kind wriggles after its own fashion. Dragon-
fly nymphs swim by sudden ejection of water from the
rectal respiratory chamber.

All of these swim without the aid of movable appen-
dages ; but the larger animals swim by means of special
swimming organs, fringed and flattened in form and
having an oar-like function. These may be fins, or

Life on the Bottom 251

legs, or antennae, or gill plates, in infinite variety of
length, form, position and design.

Great is the diversity in aspect and in action of the
animals that swim. Yet it is perfectly clear, even on a
casual inspection, that the best swimmers of them all are
those that combine proper form of body — stream-line
form — with caudal propulsion by means of a strong
tail-fin.

LIFE ON THE BOTTOM

Shoreward, the earth beneath the waters gives
aquatic organisms an opportunity to find a resting place,
a temporary shelter, or a permanent home. Flotation
devices and ability at swimming may yet be of advan-
tage to the more free-ranging forms; but the existence
of possible shelter and of solid support makes for a line
of adaptations of an entirely different sort. Here dwell
the aquatic organisms that have acquired heavy armor
for defense; heavy shells, as in the mussels; heavy
carapaces as in the crustaceans ; heavy chitinous armor
as in the insects ; or heavy incrustations of lime as in the
stone worts.

The condition of the bottom varies from soft ooze in
still water to bare rocks on wave washed shores. The
differences are very great, and they entail significant
differences in the structure of corresponding plant and
animal associations. These have been little studied
hitherto, but a few of the more obvious adaptations to
bottom conditions may be pointed out in passing.

First we will note some adaptations for avoidance of
smothering in silt on soft bottoms ; then some adapta-
tions for finding shelter by burrowing in sandy bottoms
and by building artificial defenses: then some adapta-
tions for withstanding the wash of the current on hard
bottoms.

252 Adjustment to Conditions of Aquatic Life

Avoidance of silt — Gills are essentially thin- walled
expansions of the body, that provide increased surface
for contact with the water, and thus promote that
exchange of gases which we call respiration. Gills
usually develop on the outside of the body; for it is

only in contact with the water
that they can serve their func-
tion. Inmost animals that live
in clear waters they are freely
exposed upon the outside; but
in animals that live on soft
muddy bottoms they are with-
drawn into protected chambers
(or, rather, sheltered by the
outgrowth of surrounding parts)
and fresh water is passed to
them thro strainers. Thus the
gills of a crawfish occupy capa-
cious gill chambers at the sides
of the thorax, and water is
admitted to them thro a set
of marginal strainers. The gills
of fresh-water mussels are located
at the rear of the foot within the
inclosure of valves and mantle,
and water is passed to and from
them thro the siphons. The gills
of dragonfly nymphs are located
on the inner walls of a rectal

respiratory chamber, and water to cover them is slowly
drawn in thro a complicated strainer that guards the
anal aperture, and then suddenly expelled thro the
same opening, the valves swinging freely outward.

There is probably no better illustration of parallel
adaptation for silt avoidance than that furnished by the

\

FIG. 154. The abdomen of
Asellus, inverted, showing
gill packets.

Avoidance of Silt

253

crustacean, Asellus, and the nymph of the mayfly,
Caenis. Both live in muddy bottoms where there is
much fine silt. Both possess paired plate-like gills.
In Asellus they are developed underneath the abdomen ;
in Caenis upon the back. In Asellus they are double;
in Caenis, simple. In
Asellus they a're blood
gills; in Caenis, tracheal
gills. In both they are
developed externally in
series, a pair correspond-
ing to a body segment.
In both they are soft and
white and very delicate.
But in both an anterior
pair has been developed
to form a pair of enlarged
opercula or gill covers.
These are concave pos-
teriorly and overlie and
protect the true gills.
The gills have been ap-
proximated more closely,
so that they are the more
readily covered over ; and
they have developed in-
terlacing fringes of radi- FIG. 155. The nymph of the mayfly

ating marginal hairs, Csenis' showins dorsal gin packets.

which act as strainers,

when the covers are raised to open the respiratory

chamber.

Such are the mechanical means whereby suffocation
in the mud is avoided. It must not be overlooked that
there is a physiological adaptation to the same end. A
number of soft bodied thin-skinned animals have an
unusual amount of haemoglobin in the blood plasma—

254 Adjustment to Conditions of Aquatic Life

enough, indeed, to give them a bright red color. This
substance has a great capacity for gathering up oxygen
where the supply is scanty, and of yielding it over
to the tissues as needed. True worms that burrow in
deep mud, and Tubifex (see fig. 83 on p. 174) that bur-
rows less deeply and the larger bright red tube making
larvae of midges known as "blood worms" (see fig. 236
on p. 393) are examples. Since these forms live in the
softest bottoms, where the supply of oxygen is poorest,
where few other forms are able to endure the conditions,
their way of getting on must be of considerable efficiency.

II

Burrowing— -The ground beneath the water offers
protection to any creature that can enter it ; protection
from observation to a bottom sprawler, that lies littered
over with fallen silt; protection from attack about in
proportion to its hardness, to anything that can bur-
row.

Animals differ much in their burrowing habits and in
the depth to which they penetrate the bottom. Many
mussels and snails burrow very shallowly, push-
ing their way along beneath the surface, the soft foot
covered, the hard shell-armored back exposed. The
nymphs of Gomphine dragonflies (fig. 116 on p. 209)
burrow along beneath the bottom with only the tip
of the abdomen exposed at the surface of the mud.
Other insect larvae descend more deeply into burrows
which remain open to the water above : while horsefly
larvae and certain worms descend deeply into soft mud.

The two principal methods by which animals open
passageways thro the bottom are (i) by digging, and
(2) by squeezing thro. Digging is the method most
familiar to us, it being commonly used by terrestrial
animals. Squeezing thro is the commonest method of
aquatic burrowers.

Bun-owing

255

FIG. 156. A nymph of a burrowing mayfly, Ephemera. (Prom Annals
Entom. Soc. of America: drawing by Anna H. Morgan).

The digging of burrows requires special tools for mov-
ing the earth aside. These, as with land animals, are
usually flattened and shovel-like fore legs. The other
legs are closely appressed to the body to accommodate
them to the narrow burrow. The hind legs are directed
backward. The head is usually flattened and more or
less wedge-shaped, and often specially adapted for
lifting up the soil preparatory to advancing thro it
(see fig. 116 on p. 209).

One of the best exponents of the burrowing habit is
the nymph of the may-
fly, Hexagenia, whose
innumerable tunnels
penetrate the beds of
all our larger lakes and
rivers. It is an un-
gainly creature when
exposed in open water;
but when given a bed
of sand to dig in, it
shows its fitness. Be-
sides having feet that are admirably fitted for
scooping the earth aside, it has a pair of enormous

Fu.. 157. The front of a burrowing may-
fly nymph, Hexagenia, much enlarged,
showing the pointed head, the great
mandibular tusks and the flattened
fore legs.

256 Adjustment to Conditions of Aquatic Life

mandibular tusks projecting forward from beneath
the head. It thrusts forward its approximated blade-
like fore feet, and with them scrapes the sand
aside, making a hole. Then it thrusts its tusks into
the bottom of the hole and lifts the earth forward and
upward. Then, moving forward into the opening
thus begun, and repeating these operations, it quickly
descends from view.

Squeezing thro the bottom is the method of progress
most available to soft-bodied animals. Those lacking
hard parts such as shovels and tusks with which to dig
make progress by pushing a slender front into a narrow
opening, and then distending and, by blood pressure
enlarging the passageway. The horsefly larva shown in
figure 137 on page 230 (discussed on page 227) is a good
example. The body is somewhat spindle-shaped, taper-
ing both ways, and adapted for traveling forward or
backward. It is exceedingly changeable in proportions
being adjustable in length, breadth and thickness.
Indeed, the whole interior is a moving mass of soft
organs, any one of which may be seen thro the trans-
parent skin, slipping backward or forward inside for a
distance of several segments. The body wall is lined
with strong muscles inside, and outside it bears rings
of stout tubercles, which may be drawn in for passing,
or set out rigidly to hold against the walls of the burrow.
The extraordinary adjustability of both exterior and
interior is the key to its efficiency. When such a larva
wishes to push forward in the soil, it distends and sets
its tubercles in the rear* to hold against the walls, and
drives the pointed head forward full length into the mud ;
then it compresses the rear portion, forcing the blood

*Certain cranefly larvae (such as Pedicia albivitta and Eriocera spitwsa) that
live in beds of gravel have one segment near the end of the body expansible to
almost balloon-like proportions, forming a veritable pushing-ring in the rear.

Shelter Building 257

forward to distend the body there, thus widening the
burrow. And if anyone would see how such a larva gets
through a narrow space when the walls cannot be
pushed farther apart, let him wet his hand and close the
larva in its palm ; the larva will quickly slip out between
the ringers of the tightly closed hand; and when half
way out it will present a strikingly dumb-bell-shaped
outline. Here, again, we see the advantage of its
almost fluid interior.

This adjustability of body, is of course, not peculiar to
soft bodied insect larvae ; it is seen in leeches and slugs
and many worms.

The mussel's mode of burrowing is not essentially
different from that above described. The slender
hollow foot is pushed forward into the sand, and then
distended by blood forced into it from the rear. When
sufficiently distended to hold securely by pressure
against the sand, a strong pull drags the heavy shell
forward.

Ill

Shelter building — Some animals produce adhesive
secretions that harden on contact with the water.
Thus, these are able to bind loose objects together into
shelters more suitable for their residence than any that
nature furnishes ready made. The habit of shelter
building has sprung up in many groups; in such
protozoans as Difflugia (see fig. 69 c on p. 39) ; in such
worms as Dero (see fig. 82 on p. 174); in such rotifers
as Melicerta (see fig. 86 on p. 178) ; in such caterpillars
as Hydrocampa (see fig. 127 on p. 219); in nearly all
midges, as Chironomus (see figure 134 on p. 226) and
Tanytarsus (see fig. 134 on p. 226); and especially in
the caddis- worms, all of which construct shelters of some
sort and most of which build portable cases. The
extraordinary prevalence in all fresh waters of such forms

258 Adjustment to Conditions of Aquatic Life

as the larvae of midges and caddis-flies would indicate
that the habit has been biologically profitable.

According to Betten the habit probably began with
the gathering and fastening together of fragments for a
fixed shelter, and the portable, artifically constructed,
silk lined tubes of the higher caddis-worms are a more
recent evolution.

IV

Withstanding the wash of moving waters — Where
waters rush swiftly, mud and sand and all loose shelters

FIG. 158. Stone from a brook bed, bearing tubes of midge
larvae and portable cases of two species of caddis-worms.
The more numerous spindle-shaped cases are those of
the micro-caddisworms of the genus Hydroptila. For
more distinct midge tubes see figs. 134 and 223.

are swept away. Only hard bare surfaces remain, and
the creature that finds there a place of residence must
build its own shelter, or must possess more than ordin-
ary advantages for maintaining its place. The gifts of
the gods to those that live in such places are chiefly
these three:

i. Ability to construct flood-proof shelters. Such
are the fixed cases of the caddis-worms and midge larvae
(fig. 158) to which we shall give further consideration in
the next chapter.

Withstanding the Wash of Moving Waters 259

2. Special organs for hanging on to water- swept
surfaces. Such organs are the huge grappling claws of
the nymphs of the larger stoneflies (see fig. in on p.
204) and of the riffle beetles: also powerful adhesive
suckers, such as those of the larvae of the net-winged

midges.

3 . Form of body that
diminishes resistance to
flow of the water. This
we have already seen is
stream-line form. In
our discussion of swim-
ming we pointed out
that the form of body
that offers least resist-
ance to the progress of
the body through the
water will also offer least
resistance to the flow of
water past the body. So
we find the animals that
stand still in running
water are of stream-line
form ; darters and other
fishes of the rapids;
mayflies, such as Siph-
lurus and Chirotenetes ;
even such odd forms as the larvae of Simulium, which
hangs by a single sucker suspended head downwards in
the stream. Indeed, the case of Simulium is especially
significant, for with the reversal of the position of the
body the greater widening of the body is shifted from
the anterior to the posterior end, and stream-line form
is preserved. Such forms as these live in the open,
remain for the most part quietly in one position and
wait for the current to bring their food to them.

FIG. 159. The larva of the net-
winged midge, Blepharocera, dorsal
and ventral views.

260 Adjustment to Conditions of Aquatic Life

FIG. 1 60. Limpet-shaped
animals. At right the larva
of the Parnid beetle, Pse-
pherms, known as the
"water-penny." At left,
the snail, Ancylus.

There are other more numerous forms living in rapid

water that cling closer to the solid surfaces, move about

upon and forage freely on these surfaces, and the

adaptations of these are related to the surfaces as much

as to the open stream. These
have to meet and withstand the
water also, but only on one side;
and the form is half of that of
our diagram (fig. 153). It is that
figure divided in the median
vertical plane, with the flat side
then applied to the supporting
surface, and flattened out a bit at
the edges. This is not fish form,
but it is the form of a limpet.
This is the form taken on by a

majority of the animals living in rapid waters. When

the legs are larger they fall outside of the figure, as in

the mayfly shown on page 367, and

are flattened and laid down close

against the surface so as to present only

their thin edges to the water. When

the legs are small, as in the water-

penny, (fig. 1 60) they are covered in

underneath. Sometimes there are no

legs, as in the flatworms, and in the

snail, Ancylus.

Here, surely, we have the impress

of environment. Many living beings

of different structural types are mould-

ed to a common form to meet a com-

mon need; and even the non-living

shelters built by other animals are

fashioned to the same form . The case

of the micro-caddisworm, Ithytrichia

,, ,„ ^ N ...... i 1

confusa (fig. 161 ) is also limpet-shaped ;

FlG

1- ,T.he larva

of the caddis- worm,

ithytnchia confusa.

Adjustment of the Life Cycle

261

so also is the pupal shelter of the caterpillar of Elophila
fulicalis; hardly less so is the portable case of the larva
of the caddis-fly, Leptocerus ancylus or of Molanna
angustata.

ADJUSTMENT OF THE LIFE CYCLE

Life runs on serenely in the depths of the seas where,
as we have noted in Chapter II, there is no change of
season; but in shoal and impermanent waters it meets
with great vicissitudes. Winter's freezing and summer's
drouth, exhaustion of food and exclusion of light and of
air, impose hard conditions here. Yet in these shoals
is found perhaps the world's greatest density of popula-

FIG. 162. The flattened and limpet-shaped cases of Ithytrichia
confusa, as they appear attached to the surface of a sub-
merged stone.

262 Adjustment to Conditions of Aquatic Life

tion. Here competition for food and standing room is
most severe. And here are made some of the most
remarkable shifts for maintaining ua place in the sun."

Encystment — The shifts which we are here to consider
are those made in avoidance of the struggle — shifts
which have to do with the tiding over of unfavorable
seasons by withdrawal from activity. This means
encystment or encasement of some sort or in some
degree. The living substance secretes about itself
some sort of a protective layer, and, enclosed within it,
ceases from all its ordinary functions.

This is the most familiar to us in the reproductive
bodies of plants and animals; in the zygospores of
Spirogyra and desmids and other conjugates; in the
fruiting bodies of the stoneworts; in the seeds of the
higher plants; and in the over- wintering eggs of many
animals. Most remarkable perhaps is the brief seasonal
activity of forms that inhabit temporary pools. Such
Branchipods as Chirocephalus (see fig. 90 on p. 184)
Estheria and Apus, appear in early spring in pools
formed from melting snow. They run a brief course of
a few weeks of activity, lay their eggs and disappear to
be seen no more until the snows melt again. Their
eggs being resistant to both drying and freezing, are
able to await the return of favorable conditions for
growth. The eggs of Estheria have been placed in
water and hatched after being kept dry for nine years.

But it is not alone reproductive bodies that thus tide
over unfavorable periods. The flatworm, Planaria
velata, divides itself into pieces which encyst in a layer
of slime and thus await the return of conditions favor-
able for growth. The copepod, Cyclops bicuspidatus,
according to Birge and Juday (09) spends the summer
in a sort of cocoon composed of mud and other bottom
materials rather firmly cemented together about its

Encystment

263

body. It forms this cocoon about the latter end of
May. It reposes quietly upon the bottom during the
entire summer — thro a longer period, indeed, than
that of absence of oxygen from the water. Hatch-
ing and resumption of activity begin in September and
continue into October. Marsh (09) suggests that
with us this species "may be considered preeminently a

FIG. 163. Hibernacula of the common bladderwort.

winter form." It is active in summer only in cold
mountain lakes.

The over- wintering buds (hibernacula) of some aqua-
tic seed plants are among the simplest of these devices.
Those of the common bladderwort are shown in figure
163. At the approach of cold weather the bladderwort
ceases to unfold new leaves, but develops at the tip of
each branch a dense bud composed of close-laid incom-
pletely developed leaves. This is the hibernaculurru
It is really an abbreviated and undeveloped branch.

264 Adjustment to Conditions of Aquatic Life

Unlike other parts of the plant, its specific gravity is
greater than that of water. It is enveloped only by a
thin gelatinous covering. With its development the
functional activity of the old plant ceases; the leaves
lose chlorophyl; their bladders fall away; the tissues

FIG. 164. The remains of a fresh- water sponge that has
grown upon a spray of water-weed. The numerous
rounded seed-like bodies embedded in the disintegrating
tissue are statoblasts. See text.

disintegrate; and finally the hibernacula fall to the
bottom to pass the winter at rest. When the water
begins to be warmer in spring, the buds resume growth,
the axis lengthens, the leaves expand, air spaces
develop and gases fill them, buoying the young shoots
up into better light, and the activities of another season
are begun.

Whiter Eggs 265

Statoblasts — Perhaps the most specialized of over-
wintering bodies are those of the Bryozoans and fresh-
water sponges, known as statoblasts. These are little
masses of living cells invested with a tough and hard
and highly resistent outer coat. They are formed
within the flesh of the parent animal (as indicated for
Bryozoan in fig. 77 on p. 167), and are liberated at its
dissolution (as indicated for a sponge in the accompany-
ing figure). They alone survive the winter. As noted
earlier in this chapter, their chitinous coats are often
expanded with air cavities to form efficient floats:
sometimes in Bryozoan statoblasts there is added to
this a series of hooks for securing distribution by ani-
mals (see fig. 150 on p. 247). Often in autumn at the
Cornell Biological Field Station collecting nets become
clogged with these hooked statoblasts.

In the fresh-water sponges the walls of the statoblast
are stiffened with delicate and beautiful siliceous
spicules, and there is at one side a pore through which
the living cells find exit at the proper season. Since
marine sponges lack statoblasts, and some fresh -water
species do not have them, it is probable that they are
an adaptation of the life cycle to conditions imposed
by shoal and impermanent waters.

Winter Eggs — Another seasonal modification of the
life cycle is seen in the Rotifers and water-fleas. Here
there are produced two kinds of eggs; summer eggs
that develop quickly and winter eggs that hibernate.
The summer eggs for a long period produce females
only. They develop without fertilization. In both
these groups males are of very infrequent occurrence.
They appear at the end of the season. The last of the
line of parthenogenetic females produce eggs from which
hatch both males and females and the last crop of eggs
is fertilized. These are the over- wintering eggs.

266 Adjustment to Conditions of Aquatic Life

The accompanying figures illustrate both kinds of
eggs in the water-flea, Ceriodaphnia, an inhabitant of
bottomland ponds. Figure 165 shows a female with
the summer eggs in the brood chamber on her back.
These thin-shelled eggs are greenish in color. They
hatch where they are and the young Ceriodaphnias live

FIG. 165. Ceriodaphnia, with summer eggs.

within the brood-chamber until they have absorbed all
the yolk stored within the egg and have become very
active. Then they escape between the valves of the
shell at the rear.

Winter eggs in this species are produced singly.
Figure 166 shows one in the brood chamber of another
female. It is inclosed in a chitinized protective cover-

Winter Eggs 267

ing, which, because of its saddle-shaped outline, is called
an ephippium. This egg is liberated unhatched by the
molting of the female, as shown in figure 167. It
remains in its ephippium over winter, protected from
freezing, from drouth and from mechanical injury,

FIG. 1 66. Ceriodaphnia bearing an ephippium containing the
single winter egg.

and buoyed up just enough to prevent deep sub-
mergence in the mud of the bottom. With the return
of warmer weather it may hatch and start a new
line of parthenogenetic female Ceriodaphnias.

Thus, it is that many organisms are removed from our
waters during a considerable part of the winter season.

268 Adjustment to Conditions of Aquatic Life

The water-fleas and many 'Of our rotifers are hibernating
as winter eggs. The bryozoans and sponges are hiber-
nating as statoblasts. Doubtless many of the simpler
organisms whose ways are still unknown to us have their

FIG. 167. Ceriodaphnia, molted skin and liberated ephippium
of the same individual shown in the preceding figure. This
photograph was taken only a few minutes after the other.
The female after molting immediately swam away.

own times and seasons and modes of passing a season of
rest. It is doubtless due, also, to the ease and safety
with which they may be transported when in such
condition that they all have a wide distribution over the
face of the earth. In range, they are cosmopolitan.

Readaptation to Life in the Water 269

Readaptations to life in the water — The more primitive
groups of aquatic organisms have, doubtless, always
been aquatic; but the aquatic members of several of
the higher groups give evidence of terrestrial ancestry.
Among the reasons for believing them to have devel-
oped from forms that once lived on land is the possession
of characters that could have developed only under
terrestrial conditions, such as the stomates for intake of
air in the aquatic vascular plants, the lungs of aquatic
mammals, and the tracheae and spiracles of aquatic
insects. Furthermore, they are but a few members
(relatively speaking) of large groups that remain
predominantly terrestrial in habits, and there are among
them many diverse forms, fitted for aquatic life in very
different ways, and showing many signs of independent
adaptation.

I

The vascular plants are restricted in their distribution
to shores and to shoal waters. They are fitted for
growth in fixed position and they possess a high degree
of internal organization with a development of vessels
and supporting structures that cannot withstand the
beating of heavy waves. As compared with the land
plants of the same groups, these are their chief structural
characteristics :

1. In root: — reduced development. With submer-
gence there is less need of roots for food-gathering, since
absorption may take place over the entire surface.
Roots of aquatic plants serve mainly as anchors; in a
few floating plants as balancers; sometime they are
entirely absent.

2. In stems: — many characteristics, chief of which
are the following:

a. Reduction of water-carrying tubes, for the ob-
vious reason that water is everywhere available.

270 Adjustment to Conditions of Aquatic Life

b. Reduction of wood vessels and of wood fibers
and other mechanical tissues. In the denser
medium of the water these are not needed, as
they are in the air, to support the body. Pliancy,
not rigidity, is required in the water.

c. Enlargement of air spaces. This is prevalent
and most striking. One may grasp a handful
of any aquatic stems beneath the water and
squeeze a cloud of bubbles out of them.

d. Concentration of vessels near the center of
the stem where they are least liable to injury
by bending.

e. A general tendency toward slenderness and
pliancy in manner of growth, brought about
usually by elongation of the internodes.

3. In leaves: — many adaptive characters; among
them these:

a. Thinness of epidermis, with absence of cuticle
and of ordinary epidermal hairs. This favors
absorption through the general surfaces.

b. Reduction of stomates, which can no longer
serve for intake of air.

c. Development of chlorophyl in the epidermis,
which, losing the characters which fit it for
control of evaporation, takes on an assimilatory
function.

d. Isolateral development, i. e., lack of differ-
entiation between the two surfaces.

e. Absence of petioles.

/. Alteration of leaf form with two general tend-
encies manifest: Those growing in the most
stagnant waters become much dissected (blad-
derworts, milfoils, hornworts, crowfoots, etc.).

Those growing in the more open and turbu-
lent waters become long, ribbonlike, and very
flexible (eelgrass, etc.).

Readaptations to Life in the Water 271

4. In general: — the following characteristics:

a. The production of abundance of mucilage,
which, forming a coating over the surface, may
be of use to the plants in various ways :

1. For flotation, when the mucilage is of low
specific gravity.

2. For defense against animals to which the
mucilage is inedible or repugnant.

3. For lubrication: a very important need;
for, when crossed plant stems are tossed by
waves, the mucilage reduces their mutual
friction and prevents breaking.

4. For preventing evaporation on chance ex-
posure to the air.

5. For regulating osmotic pressure, and aiding
in the physical processes of metabolism.

b . Development of vegetative reproductive bodies :

1. Hibernaculea, such as those of the bladder-
wort (fig. 162).

2. Tubers such as those of the sago pondweed
(see fig. 228), the arrow-head, etc.

3. Burs, such as terminate the leafy shoots of
the ruffled pondweed (see fig. 63).

4. Offsets and runners, such as are common
among land plants.

5. Detachable branches and stem segments,
that freely produce adventitious roots and
establish new plants.

c. Diminished seed production. This is correlated

with the preceding. Some aquatics such as
duckweeds and hornworts are rarely known to
produce seeds; others ripen seeds, but rarely
develop plants from them. Their increase is
by means of the vegetative propagative struct-
ures above mentioned, and they hold their
place in the world by continuous occupation
of it.

272 Adjustment to Conditions of Aquatic Life

II

The mammals that live in the water are two small
orders of whales, Cetacea and Sirenia, and a few
scattering representatives of half a dozen other orders.
Tho few in number they represent almost the entire
range of mammalian structure. They vary in their
degree of fitness for water life from the shore-haunting
water-vole, that has not even webbing between its toes,
to the ocean going whales, of distinctly fish-like form,
that are entirely seaworthy. It is a fine series of
adaptations they present.

For all land-animals, returned to the water to live,
there are two principal problems, (i) the problem of
getting air and (2) the problem of locomotion in the
denser medium. Warm-blooded animals have also
the problem of maintaining the heat of the body in
contact with the water. To begin with the point last
named, aquatic mammals have solved the problem of
heat insulation by developing a copious layer of fat and
oils underneath the skin. This development culminates
in the extraordinary accumulation of blubber in arctic
whales.

No aquatic mammals have developed gills. They all
breathe by means of lungs as did their terrestrial ances-
tors. All must come to the surface for air. Their
respiratory adaptations are slight, consisting in the
shifting of the nostrils to a more dorsal position and
providing them with closable flaps or valves, to prevent
ingress of the water during submergence.

It is with reference to aquatic locomotion that
mammals show the most striking adaptations. About
in proportion to their fitness for life in the water they
approximate to the fish-like contour of body that we
have already discussed (page 249) as stream-like form.
Solidity and compactness of the anterior portion of the

Aquatic Adaptations of Insects 273

body are brought about by consolidation of the neck
vertebrae and shortening of the cranium. Smoothness
of contour, (and therefore diminished resistance to
passage through the water) is promoted by (i) the loss
of hair; (2) the loss of the external ears; (3) the
shortening and deflection of the basal joints of the legs;
(4) elongation of the rear portion of the body. Caudal
propulsion is attained in the whales by the huge
dorsally flattened tail; in the seals (whose ancestors
were perhaps tailless) by the backwardly directed hind

legs.

Compared with these marine mammals those of our
fresh waters show very moderate departures from
terrestrial form. The beaver has broadly webbed hind
feet for swimming. The muskrat has a laterally
flattened tail. The mink, the otter and the fisher, with
their elongate bodies and paddle-like legs, are best
fitted for life in the water, and spend much time in it.
But all fresh-water mammals make nests and rear their
young on land.

Ill

The insects that live in the water have adaptations for
swimming that parallel those of mammals, just noted;
but some other adaptations grow out of the different
nature of their respiratory system, and, more grow out
of the difference in their life cycle. The free-living
larval stage of insects offers opportunity for independ-
ent adaptation in that stage. Adult insects of but two
orders, Coleoptera and Hemiptera, are commonly
found in the water. These, as compared with their
terrestrial relatives, exhibit many of the same adapta-
tions already noted in mammals ; ( I ) approximation to
stream-line form, with (2) consolidation of the forward
parts of the body for greater rigidity; (3) lowering of
the eyes and smoothing of all contours; (4) loss of hair

274 Adjustment to Conditions of Aquatic Life

and sculpturing, and (5) shortening of basal segments of
swimming legs, with lengthening of their oar-like tips,
flattening and flexing of them into the horizontal plane,
and limiting their range of motion to horizontal strokes
in line with the axis of gravity of the body. Caudal
propulsion does not occur with adult insects; none of
them has a flexible tail. Oar-like hind feet are the
organs of propulsion. The best swimmers among them
are a few of the larger beetles: Cy bister, which swims
like a frog with synchronous strokes of its powerful
hind legs, and Hydrophilus, with equally good swimming
legs, which, like the whale, has developed a keel for
keeping its body to rights.

Adult insects, like the mammals, lack gills, and rise
to the surface of the water for air; but they take the
air not through single pairs of nostrils, but a number of
pairs of spiracles, and they receive it, not into lungs,
but into tracheal tubes that ramify throughout the
body. The spiracles are located at the sides of the
thorax and abdomen, in general a pair to each seg-
ment.

In diving beetles the more important of these are
the ones located on the abdomen beneath the wings.
Access to these is between the wing tips. The beetles
when taking air hang at the surface head downward.
The horny, highly arched, fore wings are fitted closely
to the body to inclose a capacious air chamber. They
are opened a little at their tips for taking in a fresh air
supply at the surface. Then they are closed, and the
beetle, swimming down below, carries a store of air with
him.

In other beetles there are different methods of gather-
ing and carrying the air. The little yellow-necked
beetles of the family Haliplida?, gather the air with the
fringed hind feet, pass it forward underneath the huge
ventral plates which, in these beetles cover the bases

Aquatic Adaptations of Insects

275

of the hind legs, and thence it goes through a transverse
groove-like passage (fig. 168) to a chamber underneath
the wing bases, where there are two enlarged spiracles
on each side. The beetles of the family Hydrophilidas
have their ventral surface covered with a layer of fine
water-repellant pubescence, to which the air readily
adheres. Thus the air is carried exposed upon the
surface, where it shines like a breastplate of silver.

In the waterbugs, the air is usually carried on the
back under the wings, but the inverted back-swimmers
conduct air to their spiracles through longitudinal

FIG. 168. Diagram of the air-taking apparatus of the beetle,
Haliplus. The arrow indicates the transverse groove that
leads to the air chamber. (From Matheson).

grooves that are covered by water-repellant hairs, and
that extend forward from the tip of the abdomen upon
the ventral side. The water walking-stick, Ranatra,
and some of its allies have developed a long respiratory
tube out of a pair of approximated grooved caudal
stylets. This long tail-like tube reaches the surface
while the bug stays down below, breathing like a man
in a diving bell.

The immature stages of aquatic insects are far more
completely adapted to life in the water than are the
adults. Some members of nearly all the orders, and all

276 Adjustment to Conditions of Aquatic Life

the members of a few of the smaller orders live and grow
up in the water. These facts have been noted, group
by group, in Chapter IV. Here we may explain that
the reason for this probably lies in the greater plasticity
of the immature stages. All are thin-skinned on hatch-
ing from the egg, and a supply of oxygen may be taken
from the water by direct absorption thro the general
surface of the body. With growth gills develop; but
these have no relation to the structure or life of the
adult and are lost at the final transformation.

FIG. 169. Adult aquatic insects: a, the
back swimmer (Notonecta) ; b, the water-
boatman (Corixa); c, a diving beetle
(Dytiscus); d, a giant water-bug (Benacus).

Here again we find all degrees of adaptation. The
larvae of the long-horned leaf beetles (Donacia, etc.)
that live wholly submerged have solved the problem of
getting air by attaching themselves to plants and per-
forating the walls of their internal air spaces, thus
tapping an adequate and dependable air supply that is
rich in oxygen. This method is followed also by the
larvae of several flies and at least one mosquito. There
are many aquatic larvae that breathe air at the surface
as do adult bugs and beetles. Some of these, such as
the swaleflies and craneflies, (fig. 215) differ little from
their terrestrial relatives. Others like the mosquito
are specialized for swimming and breathe thro respira-
tory trumpets. A few like the rat-tailed maggot

Aquatic Adaptations of Insect Larva 277

parallel the method of Ranatra mentioned above in
that they have developed a long respiratory tube,
capable of reaching the surface of the water while they
remain far below.

FIG. 170. Tracheal gill of the mayfly nymph, Heptagenia, show-
ing loops of tracheoles toward the tip.

Of those that breathe the air that is dissolved in the
water a few lack gills even when grown to full size ; but
these for the most part live in well aerated waters, and
possess a copious development of tracheae in the thinner
portions of their integument. Such are the pale
nymphs of the stonefly, Chloroperla, that live in the

278 Adjustment to Conditions of Aquatic Life

rapids of streams and the slender larvae of the punkie
Ceratopogon, that live where algae abound.

The gills of insect larvae are of two principal sorts:
blood-gills and tracheal gills. Blood-gills are cyliridric
outgrowths of the integument into which the blood
flows. Exchange of gases is between the blood
inside the gills and the water outside. Such gills
are most commonly appended to the rear end of the
alimentary canal, a tuft of four retractile anal gills
being common to many dipterous larvae. Bloodworms
have also two pairs developed upon the outside wall of
the penultimate segment of the body (see fig. 236 on
p. 393). Such gills are most like those of vertebrates.

Tracheal gills are more common among insect larvae.
These are similar outgrowths of the skin, traversed by
fine tracheal air-tubes. In these the exchange of gases
is between the water and the air contained within the
tubes, and distribution of it is thro the complex system
of tracheae that ramify throughout the body. The
tracheae where they enter such a gill usually split up
into long fine multitudinous tracheoles that form
recurrent loops, rejoining the tracheal branches (fig.
170).

Tracheal gills differ remarkably in form, position and
arrangement. In form they are usually either slender
cylindric filaments, or small flat plates. Filamentous
gills are more common, only this sort occurring on stone-
fly nymphs (fig. in on p. 204), and on caddis-worms.
Lamellif orm or pi ate -like gills occur on the back of may-
flies (fig. 113), and on the tail of damselflies (fig. 115).
Either kind may grow singly or in clusters. Filament-
ous gills are often branched. In the stonefly, Taeniop-
teryx, they are unbranched but composed of three some-
what telescopic segments. Both filamentous and
lamelliform gills occur on many mayflies.

Aquatic Adaptations of Insect Larvce 279

There is another form of tracheal gills, sometimes
called "tube gills" developed upon the thorax of many

dipterous pupae. Whatever their form
they are merely hollow bare chitinous
prolongations from the mouth of the
prothoracic spiracle. They are ex-
panded "respiratory trumpets" in
mosquito pupae, branching horns in
black-fly pupae, and fine brushes of
silvery luster in bloodworm pupae.
No pupae, save those of the caddis-
flies, have tracheal gills of the ordin-
ary sort.

Gills are developed rarely on the
head, more often on the thorax, and
very frequently on the abdomen.
They grow about the base of the maxil-
lae in a few stonefly and mayfly
nymphs, about the bases of the legs
in most stonefly nymphs and almost
anywhere about the sides or end of
the abdomen in all the groups. They
are ventral in the spongilla flies, dorsal
in the mayflies, lateral in the orl-fly
and beetle larvae, caudal in the damsel-
flies, anal in most dipterous larvae,
and they cover the inner walls of a
rectal respiratory chamber in dragon-
flies. Such extraordinary diversity in
structures that are so clearly adaptive
is perhaps the strongest evidence of
the independent adaptation of many
insect larvae to aquatic life.

Propulsion by means of fringed swimming legs
occurs in a few insect larvae, such as the caddis-worm,
Triaenodes, and the ' 'water- tiger" Dytiscus. The gill

FIG. 171. Tube-gills
of Dipterous pupae :
a, of a mosquito,
Culex ; b, of a black-
fly, Simulium ; c,
of a midge, Chiro-
nomus. (a and b
detached).

280 Adjustment to Conditions of Aquatic Life

plates of many mayflies and damselflies are provided
with muscles, and these are used for swimming.
Caudal propulsion is also the rule in these same groups.
Among beetle and fly larvae locomotion is mainly
effected by wrigglings of the body, that are highly
individualized but only moderately efficient, if judged
by speed.

It is worthy of note that the completest adaptations
to conditions of aquatic life do not occur in those groups
of insects that are aquatic in both adult and larval
stages. Beetle larvae and water-bug nymphs take air
at the surface, and in structure differ but little from
their terrestrial relatives. Fine developments of tra-
cheal gills occur in the nymphs of mayflies and stone-
flies, and in caddis worms; internal gill chambers, in the
dragonfly nymphs; attachment apparatus for with-
standing currents, in some dipterous larvae ; the utmost
adaptability to all sorts of freshwater situations occurs
in the midges; and in adult life these insects are all
aerial.

What then is the explanation of the dominance of
this remarkable insect group in the world to-day — a
dominance as noteworthy in all shoal freshwaters as it
is on land? What advantages has this group over
other groups? There is no single thing; but there are
two things that, taken together, may give the key to
the explanation. These are:

1. Metamorphosis, the changes of form usually per-
mitting an entire change of habitat and of habits
between larval and adult life. The breaking up of the
life cycle into distinct periods of growth and reproduc-
tion permits development where food abounds.

2. The power of flight in the adult stage permits easy
getting about for finding scattered sources of food supply
and for laying eggs.

Aquatic Adaptations of Insect Larvae 281

In quickly growing animals no larger than insects
these matters are very important ; for even a small and
transient food supply may serve for the nurture of a
brood of larvae. And if the food supply be exhausted
in one place, or if other conditions fail there, the adults
may fly elsewhere to lay their eggs. The facts of
dominance would seem to justify this explanation, since
those groups that most abound in the world to-day are
in general the ones in which metamorphosis is most
complete and in which the power of flight is best
developed.

II. MUTUAL
ADJUSTMENT

A.RIOUS phenomena of
association between non-
competing species are
manifest alike in terres-
trial and aquatic socie-'
ties. The occurrence of
producers and consumers
is universal. Carnivores
eat herbivores, and para-
sites and scavengers fol-
low both in every natural
society. Symbiosis is as
well illustrated in green hydra and green ciliates as in
the lichens. The mutually beneficial association be-
tween fungus and the roots of green plants is as well
seen in the bog as in the forest. The larger organisms
everywhere give shelter to the smaller, and many ex-
amples, such as that of the alga, Nostoc, that dwells in
the thallus of Azolla, or the rotifer Notommata paras ita
that lives in the hollow internal cavity of Volvox, occur
in the water world.

We shall content ourselves here with a very brief
account of two associations, one of which has to da
mainly with a mode of getting a living, the other with
providing for posterity. The first will be insectivorous
plants; the second the relations between fishes and
fresh -water mussels.

282

Insectivorous Plants

283

I

Insectivorous plants- -The plants that capture insects
and other animals for food are a few bog plants such as
sundew and pitcher-plant, and a number of submerged
bladderworts. These
have turned tables on
the animal world. Liv-
ing where nitrogenous
plant-foods of the or-
dinary sorts are scanty,
they have evolved ways
of availing themselves
of the rich stores of pro-
teins found in the bodies
of animals. The sun-
dew seems to digest its
prey like a carnivore;
the bladderwort ab-
sorbs the dissolved sub-
stance like a scavenger.
Charles Darwin studied
these plants fifty years
ago, and his account
('75) is still the best
we have.

The sundew, Dro-
sera, captures insects
by means of an adhesive
secretion from the tips
of large glandular hairs
that cover the upper surface of its leaves (fig. 172).
The leaves are few in number and spatulate in form, and
are laid down in a ros3tte about the base of a stem,
flat upon the mud or upon the bed of mosses in the
midst of which Drosera usually grows. They are red
in color, and crowned and fringed with these purple

FIG. 172. A leaf of sundew with a
captured caddis-fly. The glandular
hairs are bent downward, their tips
in contact with the body of the
insect. Other erect hairs show
globules of secretion enveloping their
tips.

284 Adjustment to Conditions of Aquatic Life

hairs, each with a pearly drop of secretion at its tip
sparkling in the light, like dew, they are very attractive
to look upon. The insect that makes the mistake of
settling upon one of these leaves is held fast by the tips
of the hairs it touches : the more it struggles the more
hairs it touches, and the more firmly it is held. Ere it
ceases its struggles all the hairs within reach of it
begin to bend over toward it and to apply their tips to
the surface of its body. Thus it becomes enveloped
with a host of glands, which then pour out a digestive
secretion upon it to dissolve its tissues. When digested
its substance is absorbed into the tissue of the leaf.

The pitcher-plant, Sarracenia, captures insects in a
different way. Its leaves are aquatic pitfalls. They
rise usually from the surface of the sphagnum in a bog
(see fig. 207 on p. 350) on stout bases from a deep seated
root stalk. They are veritable pitchers, swollen in the
middle, narrowed at the neck and with flaring lips.
The rains fill them. Insects fall into them and are
unable to get out again ; for all around the inner walls
in the region of the neck there grows a dense barrier of
long sharp spines with points directed downward.
This prevents climbing out. The insects are drowned,
and their decomposed remains are absorbed by the
plant as food.

It is mainly aerial insects that are destroyed, flies,
moths, beetles, etc. ; and we should not omit to note in
passing that there are other insects, habituated to life
in the water of the pitchers, and that normally develop
there. Such are the larvas of the mosquito, Aedes
smithi, and of a few flies and moths.

The bladderworts (Utricularia) are submerged plants
that float just beneath the surface. On their bright
green, finely dissected leaves are innumerable minute
traps (not bladders or floats as the name of the plant
implies) having the appearance shown in the accom-

Insectivorous Plants

285

panying figure. These capture small aquatic animals,
such as insect larvae, crustaceans, mites, worms, etc.

The mec-
hanism of
the trap is
shown dia-
grammati-
cally in
figure 174.
First of all
there is a
circle of
r a d i a t -
ing hairs
about the
entrance,
set diagon-
ally out-
ward, like
the leaders
of a fisher-
man's fyke
net, and
well adapt-
ed to turn
the free-
swimming
water - flea
to ward the

FIG. 173. A
spray of|the
common
bladder wort,
Utricularia.

proper point of ingress. Then there is a trans-
parent elastic valve stopping the entrance, hinged by

286 Adjustment to Conditions of Aquatic Life

one side so that it will readily push inward, but holding
tightly against the rim when pressed outward. This

is the most important
single feature of the trap.
It makes possible getting
in easily and impossible
getting out at all. Dar-
win speaks of a Daphnia
which inserted an anten-
nae into the slit, and was
held fast during a whole
day, being unable to with-
draw it. On the outer
face of the valve near its
margin is a row of glan-
dular hairs. These have
roundly swollen terminal
secreting cells. They may
be alluring in function, tho
this has not been proven.
Directed backward across
the center of the valve are
four stiff bristles, that
may be useful for keeping

FIG. 174. Diagram of the mechanism OUt of the passageway ani-

of a trap of one of the common blad- mals tOO big to paSS

derworts. A, The trap from the 1 1 . -, • -, ,

ventral side, showing the outspread through it SUCh as might

leader hairs converging to the entrance, blockade the entrance.
1. leaders, r. rim, v, valve. B, A „ ... .. -,
median section of the same r, rim; v, bmall animals wnen en-
valve; w, x, y, 2 epidermal hairs; trapped Swim about f Or a
w. from the inner side of the rim ;.%",., , . • • -, <
from the free edge of the valve; y, long time inside, but in

from the base of the valve; z, from the end they die and are

the general inner surface of the trap. ., 1 TVT

decomposed. New traps

are of a bright translucent greenish color ; old ones are
blackish from the animal remains they contain. The
inner surface of the trap is almost completely covered

The Larva Habits of Fresh-water Mussels 287

with branched hairs. These are erect forked hairs ad-
jacent to the rim, and flat-topped four-rayed hairs over
the remainder of the wall space. These hairs project
into the dissolved fluids, as do roots into the nutriet
solutions in the soil, and their function is doubtless the
absorption of food.

II

The larval habits of fresh-water mussels— -The early life
of our commonest fresh-water mussels is filled with

c

FIG. 175. Small minnows bearing larval
mussels (glochidia) on their fins.

shifts for a living that illustrate in a remarkable way
the interdependence of organisms. The adult mussels
burrow shallowly through the mud, sand and gravel of
the bottom (as noted on page 108) or lie in the shelter of
stones. Their eggs are very numerous, and hatch into
minute and very helpless larva?. For them the vicissi-
tudes of life on the bottom are very great. The chief
peril is perhaps that of being buried alive and smoth-
ered in the mud. In avoidance of this and as means

288 Adjustment to Conditions of Aquatic Life

of livelihood during early development the young
of mussels have mostly taken on parasitic habits.
They attach themselves to the fins and gills of fishes
(fig. 1 75) . There they
feed and grow for a
season, and there they
undergo a metamor-
phosis to the adult
form. Then they fall
to the pond bottom
and thereafter lead
independent lives.

The eggs of the river-
mussels are passed in- FIG. 176. A gravid mussel (Symphynota
to the WatertubeS Of complanata) with left valve of shell and

mantle removed, showing brood pouch
the gills where they (modified gill) at B. (After Lefevre and

are incubated for a Curtls->

time. Packed into these passageways in enormous
numbers they distend them like cushions, filling them
out in various parts of one or both gills according to
the species, but mostly filling the outer gill. When
one picks up a gravid mussel from the river bed the
difference between the thin normal gill and the gill that
is serving as a brood chamber (fig. 176) is very marked.

Glochidia — In the case of a very few river mussels
(Anodonta imbecillis, etc.) development to the adult
form occurs within the brood chamber; but in most
river mussels the eggs develop there into a larval form
that is known as a glochidium. This is already a bivalve
(fig. 177) possessing but a single adductor muscle for
closing the valves and lacking the well developed system
of nutritive organs of the adult. It is very sensitive
to contact on the ventral surface. In this condition
it is cast forth from the brood chamber.

Glochidia 289

If now the soft filament of a fish's gill, or the pro-
jecting ray of a fin by any chance comes in contact with
this sensitive surface the glochidium will close upon it
almost with a snap; and if the fish be the right kind
for the fostering of this particular mollusc, it will
remain attached. It is indeed interesting to see how
manifestly ready for this reaction are these larvae. If a
ripe brood chamber of Anodonta (fig. 88 on p. 180) be
emptied into a watch glass of water, the glochidia
scattered over the bottom will lie gaping widely and
will snap their toothed valves together betimes, whether
touched or not. And they will tightly clasp a hair
drawn across them.

Doubtless gills become infected when water contain-
ing the glochidia is drawn in through the mouth and
passed out over them. Fins by their lashing cause
in the water swirling currents that bring the glochidia
up against their soft rays and thin edges.

Glochidia vary considerably in form and size, in so
much that with careful work species of mussels can
usually be recognized by the glochidia alone. Thus it
is possible on finding them attached to fishes, to name
the species by which the fishes are infected.

In size glochidia range usually between .5 and .05
millimeter in greatest diameter. Some are more or
less triangular in lateral outline and these have usually
a pair of opposed teeth at the ventral angle of the valves.
Others are ax-head shaped and have either two teeth or
none at all on the ventral angles. But the forms that
have the ventral margin broadly rounded and toothless
are more numerous. Whether toothed or not they are
able to cling securely when attached in proper place to
a proper host.

The part taken by the fish in the association is truly
remarkable. The fish is not a mere passive agent of
mussel distribution. Its tissues repond to the stimulus

290 Adjustment to Conditions of Aquatic Life

FIG. 177. Glochidia and their development,
into larval mussels, a, b, c, d, stages in the
encystment of glochidia of the mussel, Ano-
donta, on the fin of a carp; e and /, young
mussels (Lampsilis) a week after liberation from
the fish; g, glochidium of the mussel, Lampsilis.
before attachment. (After Lefevre and Curtis).

h, glochidium of the wash-board mussel, Quadriila
heros, greatly enlarged and stained to show the
larval thread (I 1} and sensory hair cells (s h c)
The clear band is the single adductor muscle.

i, a gill filament of a channel cat-fish bearing
an encysted glochidium of the warty-back mussel:
the cyst is set off by incisions of the filament.
The darker areas on the edges of the valves indi-
cate new growth of mussel shell. (After Howard.)

j. Encysted young of Plagiola donaciformis, showing
great growth of adult shell, beyond the margin
of glochidial shell — much greater growth than
occurs in most species during encystment. (After
Surber.)

of the glochidia in a
way that parallels the
response of a plant to
the stimulus of a gall
insect. As a plant
develops a gall by new
growth of tissue about
the attacking insect,
and shuts it in and
both shelters and feeds
it, so the fish develops
a cyst about the glo-
chidium and protects
and feeds it. The tis-
sues injured by the
valves of the glochi-
dium produce new
cells by proliferation.
They rise up about the
larva and shut it in
(fig. 177). They sup-
ply food to it until the
metamorphosis is com-
plete, and then, when
it is a complete mussel
in form, equipped with
a foot for burrowing
and with a good sys-
tem of nutritive or-
gans, they break away
from it and allowT it
to fall to the bottom.
Since this period lasts
for some weeks, or
even in a few cases,
months, the fishes by

Glochidia 291

wandering from place to place aid the distribution of
the mussels, but they do much more than this.

It is to be noted, furthermore, that this relation is a
close one between particular species, just as it is be-
tween plants and gall insects. Each attacking species
has its own particular host. Recent careful studies
made by Dr. A. D. Howard and others at the Fairport
Biological Laboratory have shown such relations as
the following:

Species of Mussels Host Species

1. Yellow Sand Shell (Lampsilis anodontoides) on the gars

2. Lake Mucket (Lampsilis luteolus) on the basses and perches

3. Butterfly Shell (Plagiola securis) on the sheepshead

4. Warty Back (Quadrula pustulosa) on the channel catfish

5. Nigger-head (Quadrula ebeneus) on the blue herring

6. Missouri Nigger-head (Obovaria ellipsis) on the sturgeons

7. Salamander mussel (Hemilastena ambigua) on Necturus

Some of these mussels infect one species of fish ; some,
the fishes of one family or genus ; a few have a still wider
range of host species, these last being visually the
species having the larger and stronger glochidia with the
best development of clasping hooks on the valve tips.
A very special case is that of Hemilastena, a mussel
that lives under flat stones and projecting rock ledges
in the stream bed. Living in the haunts of the mud-
puppy, Necturus, and out of the way of the fishes, it
infects the gills of this salamander with its glochidia.

The glochidia will grow only on their proper hosts.
They will take hold on almost any fish that touches
them in a manner to call forth their snapping reaction,
but they will subsequently fall off from all but their
proper hosts, without undergoing development.

Whether it be the mussel that reacts only to a certain
kind of fish substance, or the fish that reacts to form a
cyst only for a certain glochidial stimulus is not
known. The relation appears onesided, and beneficial
only to the parasitic mussel; yet moderate infesta-

292 Adjustment to Conditions of Aquatic Life

tion appears to do little harm to the fishes. The
cysts are soon grown, emptied and sloughed off, leaving
no scar. And a few fishes, such as the sheepshead
which is host for many mussels, appear to reap an
indirect return, in that their food consists mainly of
these same mussels when well grown.

It may be noted in passing that one little European
fish, the bitterling, has turned tables on the mussels.
It possesses a long ovipositor by means of which it
inserts its own eggs into the gill cavity of a mussel,
where they are incubated.

CHAPTER VI

OCIETIE

LIMNETIC
SOCIETIES

IREAT bodies of water
furnish opportunity for
all the different lines
of adaptation discussed
in the preceding chap-
ter. The sun shines
full upon them in all its
life-giving power. The
rivers carry into them
the dissolved food sub-
stances from the land.
Wind and waves and
convection currents dis-
tribute these substances throughout their waters.
Both the energy and the food needed for the main-
tenance of life are everywhere present. Here are
expanses of open water for such organisms as can float
or swim. Here are shores for such as must find shelter
and resting places; shores bare and rocky; shores low
and sandy ; shores sheltered and muddy, with bordering
marshes and with inflowing streams. The character
of the population in any place is determined primarily
by the fitness of the organisms for the conditions they
have to meet in it.

293

294 Aquatic Societies

For every species the possible range is determined
by climate; the possible habitat, by distribution of
water and land; the actual habitat, by the presence of
available food and shelter, and by competitors and
enemies.

Our classification of aquatic societies finds its basis
in physiographic conditions. We recognize two princi-
pal ecological categories of aquatic organisms:

I . Limnetic Societies, fitted for life in the open water,
and able to get along in comparative independence of
the shores.

II. Littoral Societies, of shoreward and inland dis-
tribution.

FIG. 178. Diagram illustrating the distribution of
aquatic societies, in a section extending from an
upland marsh to deep water. The littoral region
is shaded.

The life of the open water of lakes includes very small
and very large organisms, with a noteworthy scarcity
of forms of intermediate size. It is rather sharply
differentiated into plancton and necton; into small and
large; into free-floating and free-swimming forms.
These have been mentioned in Chapter V, where their
main lines of adaptation were pointed out. It remains
to indicate something of the composition and relations
of these ecological groups.

PhinctOH

295

PLANCTON

If one draw a net of fine silk bolting-cloth through
the clear water of the open lake, where no life is visible,
he will soon find that the net is straining something out

FIG. 179. "Water bloom" from the surface of Cayuga
Lake. The curving filaments are algse of the genus
Anabasna. The stalked animalcules attached to the
filaments are Vorticellas. The irregular bodies of
small flagellate cells, massed together in soft gelatine,
are Uroglenas.

of the water. If he shake down the contents and lift
the net from the water he will see covering its bottom a
film of stuff of a pale yellowish green or grayish or brown-
ish color, having a more or less fishy smell, and a
gelatinous consistency. If he drop a spoonful of this
freshly gathered stuff into a glass of clear water and

296 Aquatic Societies

hold it toward the light, he will see it diffuse through
the water, imparting a dilution of its own color; and in
the midst of the flocculence, he will see numbers of
minute animals swimming actively about. Little can
be seen in this way, however. But if he will examine a
drop of the stuff from the net bottom under the micro-
scope, almost a new world of life will then stand
revealed.

It is a world of little things ; most of them too small
to be seen unless magnified; most of them so trans-
parent that they escape the unaided eye. Here are both
plants and animals; producers and consumers; plants
with chlorophyl, and plants that lack it; also, parasites
and scavengers. And it is all adrift in the open waters
of the lake.

Tho plancton-organisms are so transparent and
individually so small, they sometimes accumulate in
masses upon the surface of the water and thus become
conspicuous as "water bloom." A number of the
filamentous blue-green algae, such as Anabaena, fig. 179,
and a few flagellates, accumulate on the surface during
periods of calm, hot weather. Anabsena rises in August
in Cayuga Lake, and Euglena rises in June in the back-
waters adjacent to the Lake (see fig. i, on page 15).

The plants of the plancton are mainly algae. Bacteria
and parasitic fungi are ever present, though of little
quantitative importance. They are, of course, import-
ant to the sanitarian. Of the higher plants there are
none fitted for life in the open water; but such of their
products as spores and pollen grains occur adventi-
tiously in the plancton. It is the simply organized
algae that are best able to meet the conditions of open-
water life. These constitute the producing class.
These build up living substance from the raw materials
offered by the inorganic world, and on these the life of

Phuictou

297

all the animals of both the plancton and the necton,
depends.

These are diatoms, blue-green and true-green algae,
and chlorophyl-bearing flagellates. Concerning the
limnetic habits of the last named group, we have spoken
briefly in Chapter IV (pp. 102-108). Being equipped
with flagella, they are nearly all free-swimming.
Most important among them are Ceratium, Dinobryon
and Peridinium.

Most numerous in individuals of all the plancton
algae, and most constant in their occurrence throughout
the year, are the diatoms (see fig. 35 on p. 1 1 1). Wher-
ever and whenever we haul a plancton net in the open
waters of river, lake or pond, we are pretty sure to get
diatoms in the following forms of aggregation:

i. Flat ribbons composed of the thin cells of Dia-
toma, Fragillaria, and Tabelaria.

2. Cylindric filaments composed of
the drum-shaped bodies of Melosira and
Cyclotella.

3. Radiating colonies of Asterionella.

4. Slender single cells of Synedra.
And we may get less common forms

showing such diverse structures for flota-
tion as those of Stephanodiscus (fig. 35 1}
and Rhizosolenia (fig. 180); or we may
get such predominantly shore ward forms
as Navicula and Meridion.

The blue-green algae of the plancton
are very numerous and diverse, but the
more common limnetic forms are these :
i . Filamentous forms having :

(a) Stiff, smoothly-contoured fila-
ments; Oscillatoria (see fig. 34
on p. 109) and Lyngbya, etc.

Sinuous nodose filaments, Ana-
basna (fig. 179), Aphanizomenon,
etc.

FIG. 180.

a, Rhizosolenia;

b, Attheya.

298

Aquatic Societies

FIG. 181. Rotifers.

Plancton 299

(c) Tapering filaments that are immersed in more
or less spherical masses of gelatine, their points
radiating outward; Gloiotrichia, Rivularia (see
Fig. 51, on p. 133, and 52),_etc.
2. Non-filamentous forms having:

(a) Cells immersed in a mass of gelatine, Micro-
cystis (including Polycystis and Clathrocystis,
see fig. 51 on p. 133), Ccelosphserium, Chrooco-
ccus, etc,

b) Cells arranged in a thin flat plate. Tetra-
pedia (fig. 51), Merismopsedia (see fig. 53 on p.
135)- etc.

Representatives of all these groups, except the one
last named, become at times excessively abundant in
lakes and ponds, and many of them appear on the
surface as "water bloom."

Of the green algae there are a few not very common
but very striking forms of rather large size found in the
plancton. Such are Pediastrum (see fig. 44 on p. 123)
and the desmid, Staurastum. There are many minute
green algae of the utmost diversity in form and arrange-
ment of cells. Most of those that are shown in figure
50 on page 129 occur in the plancton; Botyrococcus is
the most conspicuous of these. A few filamentous
green forms such as Conferva (see fig. 45 on p. 124) and
the Conjugates (fig. 41 on p. 119), occur there adventi-
tiously, their centers of development being on shores.

The animals of the plancton are mainly protozoans,
rotifers and crustaceans. The protozoans of the open

FIG. 181.

i, Philodina. 2, 3, Rotifer. 4, Adineta. 5, Floscularia. 6, Stephanoceros. 7,Apsilus.
8, Melicerta. 9, Conochilus. 10, Ramate jaws, u, Malleo-ramate jaws. 12, Micro-
codon. 13, Asplanchna. 14, 15, Synchaeta. 16, Triarthra. 17, Hydatina. 18, Poly-
arthra. 19, Diglena. 20, Diurella, 21, Rattulus. 22, Dinocharis. 23, 24, Salpina.
25, Euchlanis. 26, Monostyla. 27, Colurus. 28, 29, Pterodina. 30, Brachionus.
31, Malleate jaws. 32, Noteus. 33, 34, Notholca. 35, 36, Anuraea. 37, Ploesoma.
38, Gastropus. 39. Porcipate jaws. 40, Anapus. 42, Pedalion.

From Genera of Plancton Organisms of the Cayuga Lake Basin, by
O. A. Johannsen and the junior author.

300

A quatic Societ ies

water are few. If we leave aside the chlorophyl-
bearing flagellates already mentioned (often considered
to be protozoa) the commoner forms among them are
such other flagellates as Mallomonas (see fig. 185 on
page 309), such sessile forms as Vorticella (fig. 179)

FIG. 182. Plancton Cladocerans from Cayuga Lake. The
larger, Acroperus liar pee; the smaller, Chydorus sp.

and such shell-bearing forms as Arcella and Difflugia
(see fig. 69 on p. 159).

The rotifers of the planet on are many. The most
strictly limnetic of these are little loricate forms such
as Anuraea and Notholca, two or three species of each
genus. When one looks at his catch through a micro-
scope nothing is commoner than to see these little thin-

Plauctou 301

shelled animals tumbling indecorously about. Some-
times almost every female will be carrying a single large
egg. Several larger limnetic rotifers, such as Triarthra,
Polyarthra and Pedalion, bear conspicuous appendages
by which they may be easily recognized. The softer-
bodied Synchaeta will be recognized by the pair of ear-
like prominences at the front. Other common limnetic
forms are shown at 2 (Rotifer neptunius), 21 and 25 of
figure 181.

The Crustacea of fresh-water plancton are its largest
organisms. They are its greatest consumers of vege-
table products. They are themselves its greatest con-
tribution to the food of fishes. Most of them are
herbivorous, a few eat a mixed diet of algae and of the
smaller animals. The large and powerful Leptodora is
strictly carnivorous. The following are the more
truly limnetic forms :

I. Cladocerans; species of

Daphne (fig. 234) Diaphanosoma

Chydorus Ceriodaphnia (fig. 165)

Bosmina (fig. 91 ) Polyphemus

Sida Bythotrephes

Acroperus (fig. 182) Leptodora. (fig. 186)

II. Cope pods; species of

Cyclops Epischura

Diaptomus Limnocalanus

Canthocamptus ( see figures 95 and 96)

Of plancton animals other than those of the groups
above discussed, there are no limnetic forms of any
great importance. There is one crustacean of the
Malacostracan group, My sis relicta, that occurs in the
deeper waters of the great lakes. There is one trans-
parent water-mite, A fax crassipes, with unusually long

302

Aquatic Societies

and well fringed swimming legs, that may fairly be
counted limnetic. There is only one limnetic insect.
It is the larva of Corethra — a very transparent, free
swimming larva, having within its body two pairs of
air sacs that are doubtless regulators of its specific
gravity.

FIG. 183. The larva of the midge, Corethra. (After Weismann.)

Seasonal Range. There is no period of absence of
organisms from the open water, yet the amount of life
produced there varies, as it does on land, with season
and temperature. In winter there are more organisms
in a resting condition, and among those that continue
active, there is little reproduction and much retardation
of development. Life runs more slowly in the winter.
Diatoms are the most abundant of the algae at that
season.

There is least plancton in the waters toward the end
of winter — February and early March in our latitude.
The returning sun quickens the over-wintering forms,
according to their habits, into renewed activity, and
up to the optimum degree of warmth, hastens reproduc-
tion and development. With the overturn of the
waters in early spring comes a great rise in the produc-
tion of diatoms, these reaching their maximum often-
times in April. This is followed by a brisk develop-
ment of diatom-eating rotifers and Crustacea. Usually
the entomostraca attain their maximum for the year in
May. This rise is accompanied by a marked decline
in numbers of diatoms and other algae, due, doubtless,
to consumption overtaking production. The warmth

Seasonal Range 303

of summer brings on the remaining algae, first the greens
and then the blue-greens, in regular seasonal succession.
It brings with them a wave of the flagellate Ceratium,
which, being much less eaten by animals than they,
often gains a great ascendency, just as the browsing of
grass in a pasture favors the growth of the weeds that
are left untouched. Green algas reach their maximum
development in early summer, and blue-greens, in mid
or late summer, when the weather is hottest.

With the cooling of the waters in autumn, reproduc-
tion of summer forms ceases and their numbers decline.
The fall overturning and mixing of the waters usually
brings on another wave of diatom production, followed
by the long and gradual winter decline. This is often
accompanied, as in the spring, by abundance of Dino-
bryon. The flagellate Synura (see fig. 30 on p. 103) is
rather unusual in that its maximum development occurs
often in winter under the ice.

The coming and going of the plancton organisms
has been compared to the succession of flowers on a
woodland slope ; but the comparison is not a good one ;
for these wild flowers hold their places by continuously
occupying them to the exclusion of newcomers. The
planctonts come and go. They are rather to be
likened to the succession of crops of annual weeds in a
tilled field; crops that have to re-establish themselves
every season. They may seed down the soil ere they
quit it, but they may not re-occupy it without a strug-
gle. And as the weeds constitute an unstable and
shifting population, subject to many fluctuations, so
also do the plancton organisms. They come and go;
and while on their going we know that when they come
again, another season, they will probably present col-
lectively a like aspect, yet the species will be in different
proportions.

304 Aquatic Societies

There are probably many factors determining this
annual distribution ; but chief among them would seem
to be these three :

1. Chance seeding or stocking of the waters.
Each species must be in the waters, else it cannot
develop there; and for every species, there are many
vicissitudes (such as famine, suffocation, and parasitic
diseases) determining the seeding for the next crop.

2. Temperature. Many plants and animals, as we
have seen, habitually leave the open waters when they
grow cooler in the autumn, and reappear in them when
they are sufficiently warmed in the spring. They pro-
vide in various ways (encystment, etc.) for tiding over
the intervening period. Some of them appear to be
attuned to definite range of temperature. Thus the
Cladoceran, Diaphanosoma, as reported by Birge for
Lake Mendota, has its active period when the tempera-
ture is about 20° C. (68° F.). For this and for many
other entomostraca reproduction is checked in autumn
by falling temperature while food is yet abundant.

3. Available Food. Given proper physical condi-
tions, the next requisite for livelihood is proper food.
For the welfare of animal planctonts it is not enough
that algae be present in the water ; they must be edible
algas. The water has its weed species, as well as its
good herbs. Gloiotrichia would appear to be a weed,
for Birge reports that no crustacean regularly eats it,
and it is probably too large for any of the smaller ani-
mals. Birge says also ( '96 p. 353) , ' ' I have seen Daphnias
persistently rejecting Clathrocystis, while greedily
collecting and devouring Aphanizomenon." Yet
Strodtmann ('98) reports Chydorns spJi<?ricus as feeding
extensively on Clathrocystis, even to such extent that

Plancton Pulses 305

its abundance in the plancton is directly related to the
abundance of that alga. Each animal may have its
food preference. The filaments of Lyngbya are too
large for the small and immature crustaceans to handle.
Ceratium has too hard a shell; it appears to be eaten
only by the rather omnivorous adult Cyclops. For
animal planctonts in general Anabaena and its allies
and the diatoms and small flagellates appear to be the
favorite food.

Obviously, the amount of food available to any
species is in part determined by the numbers of other
species present and eating the same things.

Plancton pulses- -The organisms of the plancton
come in waves of development. Now one and now
another appears to be the dominant species. In most
groups there are a number of forms that are competitors
for place and food. The diatoms Asterionella,
Fragillaria and Tabelaria may fill the upper waters of
a lake together or in succession. A species of Diap-
tomus may dominate the waters this May, and
species of Cyclops may appear in its stead next May.
Yet while species fluctuate, the representation of the
groups to which they belong remains fairly con-
stant.

These sudden waves of plancton production are
made possible, as every one knows, by the brief life
cycle of the planctonts, and by their rapid rate of
increase. If a flagellate cell, for example, divide no
of tener than every three days, one cell may have more
than a thousand descendants, within a month. The
rotifer, Hydatina is said to have a length of life of some
thirteen days, but during most of this time it is rapidly
producing eggs, and the female is mature and ready to
begin egg laying in 69 hours from hatching. Some of
the larger animals live much longer and grow more

306 Aquatic Societies

slowly, but even such large forms as Daphne have an
extraordinary rate of increase, as we have already
indicated on pages 186 and 187. The rises in produc-
tion grow out of:

1. Proper conditions of temperature, light, etc.

2. Abundant food

3. Rapid increase

Declines follow upon failure of any of these, and
upon the attack of enemies. So swift are the changes
during the growing season that those who systematically
engage in the study of a lake's population take planctoii
samples at intervals of not more than fourteen days,
and preferably, at intervals of seven days.

Local Abundance — Plancton organisms tend to be
uniformly distributed in a horizontal direction. Al-
though many of them can swim, their swimming, as
we have noted in the preceding chapter, is directed far
more toward maintenance of level, than toward change
of location. There are, however, for many plancton
organisms, well authenticated cases of irregular hori-
zontal distribution, one of which, for Carteria, we
quoted on pages 103 and 104. Alongside that record
for a little flagellate, let us place Birge's ('96) record for
the water-flea, Daphne pulicaria, in Mendota Lake.

'The Daphnias occurred in patches of irregular extent
and shape, perhaps 10 by 50 meters, and these patches
extended in a long belt parallel to the shore. The
surface waters were crowded by the Daphnias, and
great numbers of perch were feeding on them. The
swarm was watched for more than an hour. The water
could be seen disturbed by the perch along the shore
as far as the eye could reach. On this

occasion the number was shown to be 1,170,000 per
cubic meter of water in the densest part of the swarm."

Distribution in Depth 307

Shoreward Range — Few plancton organisms are
strictly limited to life in open water. Most of them
occur also among the shore vegetation in ponds and
bays and shoals. They are very small and swim but
feebly, and there is room enough for their activities in
any pool. They mostly belong in the warm upper
strata of the lake, and similar conditions of environ-
ment prevail in any pond. It is the deep waters of the
lake that maintain uniform conditions of low and
stable temperature, and scanty light; and it is the
organisms of the deeper strata that do not appear in the
shoals.

Hence, though the aquatic seed-plants pushing out
on a lake shore are stopped suddenly at given depth,
as with an iron barrier, the more simple and primitive
algae of the plancton range freely into all sorts of suit-
able shoreward haunts. We shall meet with them
there, commingled with numberless other forms that
have not mastered the conditions of the open water.
In each kind of situation (pond, river or marsh has each
its plancton) we shall find a different assemblage of
species. In all of them we shall find the planctonts are
less transparent; in none of them will there be quite
such uniformity, from place to place, as is found in the
population of the open waters of the lake.

Distribution in Depth. Since plancton organisms
tend to be uniformly distributed in a horizontal plane
one may ply his nets at any point on a lake with the
expectation of obtaining a fair sample ; but not so with
depth, except at times when the waters are in complete
circulation. A net drawn at the surface would make
a very different catch from one drawn at a depth of
fifty feet. Certain species found in abundance in the
one would not be represented in the other. The
organisms of the lakes tend to be horizontally stratified.

308

A quatic Societies

Each species has its own level ; its own preferred habi-
tat, where it finds optimum conditions of pressure, air,
temperature and light. Fig. 184 is a diagram of the
midsummer distribution in depth of seven important
synthetic planctonts of Cayuga Lake.

B

c

D

Ft.
o

IO
20
30
40

50
60
70
80
90
IOO

Ft.
o

10
20
30
40

SO

60

70

So

90

too

FIG. 184. Diagram illustrating midsummer distribution of
seven important synthetic organisms in the first one hundred
feet of depth of Cayuga Lake. A, Ceratium; B, Dinobryon;
C, Mallomonas; D, Anabasna; E, Microcystis (Clathrocystis) ;
F, Asterionella; G, Fragillaiia.

(Based in part on Juday— 15)

Light is the principal factor determining distribution
in depth. This we have touched upon in Chapter II,
under the subject of "Transparency." It is only in the
upper strata of lakes, within the reach of effective light,
that green plants can grow. Animals must likewise
remain where they can find their food; whence it
results that the bulk of the plancton in a lake lives in its

Distribution in Depth

309

uppermost part, the thickness of this productive
strattim varying directly with the transparency of the
water.

It is not at the surface, however, but usually a little
below it — a depth of a meter, more or less — at which
the greatest mass of the plancton is found. Full sun-
light is perhaps too strong; for average planctonts a
dilution of it is preferred. Free-swimming planctonts
such as rotifers and entomostraca move
freely upward or downward with changes
of intensity of light. Anyone who has seen
Daphnes in a sunlit pool congregating in
the shadow of a water-lily pad will under-
stand this. These animals rise nearer to
the surface when the sun goes under a
cloud, and sink again when the cloud
passes. The extent of their regular diur-
nal migrations appears to be directly relat-
ed to the transparency of the water.

Temperature also is an important factor
determining vertical distribution. Forms
requiring the higher temperatures are
summer planctonts that live at or near
the surface. Others that are attuned to lower tem-
peratures may find a congenial summer home at a
greater depth. Thus the flagellate Mallomonas (fig.
185) in Cayuga Lake is rarely encountered in summer
in the uppermost fifty feet of water, though it is com-
mon enough at depths between 50 and 100 feet, where
the temperature remains low and constant. The
average range of Daphne pulicaria is said to be deeper
than that of other Daphnias.

The gases of the water have much to do with the
distribution of animal planctonts, especially below the
thermocline, where the absence of oxygen from some
lakes during the summer stagnation period excludes

FIG. 185. Mal-
1 o m o n a s
ploessi.

(After Kent.)

3io Aquatic Societies

practically all entomostraca. Certain hardy species of
Cyclops and Chydorus appear to be least sensitive to
stagnation conditions. The insect Corethra, (fig. 183)
is remarkable for its ability to live in the depths, where
practically no free oxygen remains.

Age appears to be another factor in vertical distribu-
tion. On the basis of his studies of the Entomostraca
of Lake Mendota, Birge ('96) has formulated for them
a general law of distribution, to the effect that (i)
broods of young appear first in the upper waters of the
lake (quite near the surface) ; (2) increase of population
results in extension downward, and the mass becomes
most uniformly distributed at its maximum develop-
ment; (3) with decline of production there is relative
increase of numbers in the lower waters.

Perhaps this shifting downward merely corresponds
to the wane of vigor and progressive cessation of swim-
ming activities with advancing age.

In the case of many plants spore development or
encystment may follow upon a seasonal wave of produc-
tion, with a resulting change in vertical distribution.
Filamentous blue-green algae develop spores. The
ordinary vegetative filaments are buoyed up in part by
vacuoles within the cells, that lessen their specific
gravity; but spores lack these. Hence the spore-bear-
ing filaments settle slowly to the bottom, and may be
found in numbers in the lower waters ere they have
reached their winter resting place. Dinobryon main-
tains itself at the surface in part by means of the lash-
ings of its rlagella, but when its cells encyst, the flagella
stop, and the fragmenting colonies slowly settle. Thus,
both internal and external conditions have much to do
with vertical distribution. In general it may be said
that during their period of highest vegetative activity
all plants are necessarily confined to surface waters;
that most animals are closely associated with them,

Distribution in Depth

,n

.

but that the constant fall of organic material toward
the bottom makes it possible for some animals to dwell
in the depths, if they can endure the low temperature
and the other conditions found there. There are some
animal planctonts, such as species of Cyclops and
Diaptomus, that range the water (oxygen being pre-
sent) from top to bottom. There are many that are
confined during periods of activity to the warmer
region above the thermocline. There are a few like
Leptodora that seem to prefer intermediate depths,
and there are a few
(Heterocope, Limno-
calanus, My sis, etc.)
that dwell in the cold
water below the ther-
mocline.

Collectively, this
extraordinary assem-
blage of organisms
that we know as
plancton recalls in
miniature the life of
the fields. It has, in its teeming ranks of minute
chlorophyl-bearing flagellates, diatoms and other algasr
a quick-growing, ever-present food supply that, like
the grasses and low herbage on the hills, is the mainstay
and dependence of its animal population. It has in
some of its larger algas the counterparts of the trees
that support more special foragers, are less completely
devoured, and that, through death and decomposition,
return directly to the water a much larger proportion
of their substance. It has in its smaller herbivorous
rotifers and entomostraca, the counterpart of the hordes
of rodents that infest the fields. It has in its large,
plant-eating Cladocerans, such as Daphne, the equiva-
lent of the herds of hoofed animals of the plains; and

FIG. 1 86. Leptodora.

312 Aquatic Societies

it has at least one great carnivore, that, like the tiger,
ranges the fields, selecting only the larger beasts for
slaughter. This is Leptodora (fig. 1 86) . It is of phan-
tom-like transparency, and though large enough to be
conspicuous, only the pigment in its eye and the color
of the food it has devoured are readily seen. It ranges
the water with slow flappings of its great, wing-like
antennae. It can overtake and overpower such forms
as Cyclops and Daphne and it eats them by squeezing
out and sucking out the soft parts of the body, rejecting
the hard shell. Leptodora, in a small way, functions
in this society as do the fishes of the necton.

The total population of plancton in any lake is very
considerable. Kofoid ('03) reported the maximum
plancton production found by himself in Flag Lake near
Havana, 111., as 667 cubic centimeters per square meter
of surface: found by Ward ('95) in Lake Michigan,
176, do.; found by Juday ('97) in the shoal water of
Turkey Lake in Indiana, 1439 do. Kofoid estimated
the total run-off of plancton from the Illinois River as
above 67,000 cubic meters per year — this the produc-
tion of the river, over and above what is consumed
by the organisms dwelling in it.

If we imagine the organisms of a lake to be pro-
jected downward in a layer on the bottom, this thick
layer would probably represent a quantity of life equal
to that produced by an average equal area of dry land.

The Necton

THE NECTON

The large free swimming animals of the fresh waters
are all fishes. Indeed, as we have already noted (p.
233), but a few of the fishes range through the open
waters. Such are the white-fish, the ale-wife and the
ciscos, — all plancton feeders, — and a few more
piratical species, like the lake trout and the muskel-
longes that feed mainly on smaller fishes.

Necton, it will thus be seen, is not a natural society.
It contains no producing class. It is sustained by the
plancton and by the products of the shores.

These fishes all have a splendid development of
stream-line form. They all swim superbly. And
according as they feed on plancton or on other fishes
they are equipped with plancton strainers or with
raptorial teeth. Excellent plancton strainers are those
of the lake fishes. They are composed of the close-set
gill-rakers on the front of the gill arches, and they
strain the water passing through. This mesh is adapt-
ed for straining the larger animal planctonts while let-
ting the lesser chlorophyl-bearing forms slip thro.
Thus the fishes reap the crop of animals that is matur-
ed, without destroying the sources for a crop to come.

LITTORAL
SOCIETIES

NDER the sheltering
influence of shores the
vascular plants may
grow. Animals elude
the eyes of their ene-
mies, not by becom-
ing transparent, but
by taking on colors and forms in resemblance to their
environment. They escape capture, not alone by fleet-
ness, but also by development of defensive armor, by
shelter-building and by burrowing.

Large and small and all intermediate sizes occur
together along shore, and those that appear betimes in
open water make shifts innumerable for place and
food and shelter for their young.

There are many factors affecting the grouping of
littoral organisms into natural associations, most of
them as yet but little studied ; but the most important
single factor is doubtless the water itself. The density
of this medium and the consequent momentum of its
masses when in motion so profoundly affect the form
and habits of organisms that they may be roughly
divided into two primary groups for which are sug-
gested the following names:

Leu i tic Societies

315

I. Lenitic* or still-water societies.

II. Lotic] or rapid-water societies, living in waves or
currents.

LENITIC
SOCIETIES

OKED together, less by
any common character
of their own than by
the lack of lotic charac-
teristics, we include
under this group name
those associations of
littoral organisms that dwell in the more quiet places
and show no special adaptations for withstanding the
wash of waves or currents. Wherever we draw the
line between lenitic and lotic regions, there will be
organisms to transgress it, for hydrographic conditions
intergrade. We have already seen how many organ-
isms transgress the boundary between limnetic and
littoral regions. Just as in that case we found a fairly
satisfactory boundary where the increasing depth of still
water is such as to preclude the growth of the higher
plants, so here the boundary between lenitic and lotic
regions may be placed where the movement of the
water is sufficient to preclude the growth of these same
plants.

* Leu is = calm, placid.
jLotus = washed.

31 6 Aquatic Societies

The reason why lenitic societies include practically
the entire population of vascular plants has already
been stated (p. 145): the plants have a complexity of
organization that cannot withstand the stress of
rapidly moving waters. They fringe all shoals, how-
ever, and they fill the more sheltered places with growths
of extraordinary density. In such places they pro-
foundly affect the conditions of life for other organisms :
the supplies of food and light and air, and the oppor-
tunities for shelter.

Streams and still waters, inhabited by lenitic societies,
may be divided roughly into three categories :

1. Those that are permanent.

2. Those that dry up occasionally.

3. Those that are only occasionally supplied with
water.

These so completely intergrade, and so vary with
years of abundance or scarcity of rainfall, that
there is no good means of distinguishing between them.
Perhaps for the humid Eastern States and for bodies of
still water the words pond and pool and puddle convey
a sense of their relative permanence. The population
of the pond is, like that of the lake, to a large extent
perennially active. It will be discussed in succeeding
pages. That of the pool is composed of those forms
that are adjusted to drouth: forms that can forefend
themselves against the withdrawal of the water by
migration, by encystment, by dessication, or by bur-
rowing, or by sending roots down into the moisture of
the bed. Some of these will be mentioned in the dis-
cussion of the population of the marshes. The puddles
have a scanty population of forms that multiply rapidly
and have a brief life cycle. The synthetic forms
among them are mainly small flagellates and protococ-

Lenitic Societies

317

FIG. 187. Lick Biook near Ithaca in spring. Its bed runs
dry later in the season. (Photo by R. Matheson.)

Aquatic Societies

coid green algae. The herbivores are such short-lived
crustaceans as Chirocephalus (see fig. 90 on p. 184) and
Apus, which have long-keeping, drouth -resisting eggs;
such rotifers as Philodina, remarkable for its capacity for
resumption of activity after dessication ; such insects as
mosquitoes. The carnivores are such adult water-bugs
and beetles as may chance to fly into them.

Whether a population shall be able to maintain itself
depends on the continuance of favorable conditions, at
least through the period of activity of its members.
In these pages we shall give attention only to the life
of relatively permanent waters.

Plants- -The shoreward distribution of plants in
natural associations is determined mainly by two
hydrographic factors: (i) movement and (2) depth of
the water. It is directly related to exposure to waves
and to currents. Everyone knows the difference in
appearance between plants growing immersed in a quiet

FIG. ib8. The forefront of the Canoga marshes, where partly sheltered
from the waves of Cayuga Lake, clumps of the lake bulrush lead the
advance of the shore vegetation.

Lenitic Plants 319

pool and those growing on a wave- washed shore. The
former appear as if robed in filmy mantles of green, full-
fledged with leaves, and luxuriant. The latter appear
as if stripped for action, unbranched, slender and bare.
At one extreme are the finely-branched free-floating
bladderworts (see fig. 173 on p. 285) at the other are
such firmly rooted, slender, naked, pliant-topped forms
as the lake bulrush (figure 188) and eel-grass. These
latter anchor their bodies firmly and closely to the soil,
and send up into the moving waters overhead only soft
and pliant vegetative parts, that offer the least possible
resistance to the movement of the water, and that, if
broken, are easily replaced. The long cylindric shoots
of the bulrush have their vessels lodged in the axis and
surrounded with a remarkable padding of air cushions.
They are not easily injured. The flat ribbon-like
leaves of eel-grass are marvels of adjustability to waves.

Between these two extremes are all gradations of
form and of fitness. Of the pool-inhabiting type are
the water crow-foot, the water milfoil, the water horn-
wort; of the opposite type are the long-leaved pond-
weeds and the pipeworts. Intermediate are the broader-
leaved pondweeds and Philotria.

These sometimes are found in running streams, but
they usually grow in the beds in dense mutually sup-
porting masses that deflect the current. If one place a
current meter among their tops he will find little move-
ment of the water there.

There is another place of security from waves, for
such plants as can endure the conditions there. It is
on the lake's bed, below the level of surface disturbance.
The stoneworts (see fig. 55 on p. 137) are branched and
brittle forms, very ill adapted to wave exposure, and
most of them live in pools, but a few have found this
place of security beneath the waves. There are
extensive beds of Chara on the bottom of our great

320

Aquatic Societies

FIG. 189. Shore-line vegetation.

Shore Plants 321

lakes, at a depth of 25 feet more or less, and within the
range of effective light. Associated with these, but
usually on the shoreward side, are beds of pondweeds.
Often there are bare wave-swept shores behind these
beds with no sign of aquatic vegetation that one can
see from the shore.

Depth of water determines the adjustment of aquatic
seed plants in three principal categories:

1. Emergent aquatics. These occupy the shallow
water, standing erect in it with their tops in the air,
and are most like land plants. They are by far the
most numerous in species.

2. Surface aquatics. These grow in deeper water,
at the front of (and oftentimes commingling with) the
preceding. The larger ones, such as the water lilies
are rooted in the mud of the bottom, and bear great
leaves that float upon the surface. The smaller ones
such as the duckweeds (see figs. 61 and 62, p. 149) are
free-floating.

3. Submerged aquatics. These form the outermost
belt or zone of herbage. They are most truly aquatic
in habits. Except for such forms as dwell in quiet
waters, they are rooted to the bottom. Depth varies
considerably within this zone. It extends from the
outer limits of the preceding (hardly more than five

FIG. 189.

A. Branches of four submerged water plants: (i) Philotria, (2) Cerato-
phyllum, (3) Ranunculus, (4) Nais.

B. Emergent aquatics, including a clump of arrow arum; two of the
pendulous club-shaped fruit-clusters are seen at (5) dipping into the water.

C. Zonal arrangement of the plants of the shore-line. The background
zone is cat-tail flag (Typha). Next comes a zone of pickerel-weed (Ponte-
deria) in full flower. Next, a zone of water lilies and such other aquatics
with floating leaves as are shown in D and E. In the foreground is a zone of
submerged plants — a mixture of such forms as are shown in .4 above.

D. A closer view: Lemna, free-floating and Marsilia with four parted
floating leaves, and Ranunculus, in tufted sprays, submerged.

E. The floating leaves and emergent flower spikes of a pond weed,
Potamogeton. (Photo by L. S. Hawkins.)

322 Aquatic Societies

feet at most) to the limits of effective light. Within
such a range of depth conditions of movement, pressure,
warmth and light find also a considerable range; hence,
the forms differ at the inner and outer margins of the
zone. Its forefront is usually formed by Chara as
stated above, and pondweeds follow Chara, with a
number of other forms usually commingled, in the
shallower part.

These groups are not free from intergradation since
some forms like the spatterdock (fig. 195 on p. 335) are
in part emergent, and some of the pondweeds have a
few floating leaves. But they are nevertheless con-
venient, and they represent real ecological differences.

Distribution of these plants in depth results in their
zonal arrangement about the shore line. When all
are present they are arranged in the order indicated.
It is an inviolable order ; for the emergent forms cut off
the light from those that cannot rise above the surface,
and the latter overshadow those that are submerged.
The zones may vary in width and in their component
species, but when all are present and crowded for room
they can occur only in this order. The two accompany-
ing figures illustrate zonal arrangement ; figure iSgC, on
a low and marshy shore; figure 190, on a more elevated
shore, backed by a terrestrial flora.

The alg(R of littoral societies are those of the plancton
(practically all of which drift into the shoals) plus
numberless additional non-limnetic forms, many of
which are sessile. As with the vascular plants, algae
that are fragile (see fig. 198 on p. 338) and the larger
that float free (Spirogyra, etc.) develop mainly in pools
and quiet waters, while those having great pliancy of
body (Cladophora, see fig. 46 on p. 125) and protective
covering (slime-coat diatoms, etc.) are more exposed to
moving waters.

Zonal Arrangement of Plants

323

FIG. 190. Zonal arrangement of plants. At the front is a zone of Marsilea
extending down into the water. Next is a zone of bur-reed, with the
spiny seed-heads showing near the center of the picture. Back of this
is a zone of tall composites. The flower clusters of the joe-pye-weed
show above the bur-reed tops. In the background is a zone of trees.

324

Aquatic Societies

The animal population of the shores is likewise dis-
tributed largely in relation to water movement, or to
conditions resulting therefrom. There is a zonal
arrangement of animal life along shores that is only a
little less definite than that of plants. It is much less
obvious, for plants are fixed in position and come out
more into the open and into view. Nevertheless, even
the most free-roving animals, the fishes, as we have
already seen (p. 233), keep in the main to certain shore-
ward limits.

Distribution in relation
to depth and to character
of bottom comes out
clearly in Headlee's stud-
ies of the mussels of Win-
ona Lake. In that lake
the play of the waves on
shore yields a clean beach
line of sand and gravel,
and sifts the finer mater-
ials into deeper water.
The succession is gravel
FIG. 191. Diagram of distribution of and sand marlv sand

mussels in Winona Lake, Indiana. ', •* . . '

sandy marl, coarse white
marl, marly mud and very
soft black mud. The last
named, beginning at a

depth of some 20 feet,

covers a very large central portion of the lake bottom.
Mussels cannot live in it for they sink too deeply
and the fine sediment clogs their gills. Hence the
mussels are restricted to the strip along shore. With-
in this strip they are arranged according to hard-
ness of bottom and exposure to waves. The accom-
panying diagram illustrates the distribution of four of
the common species. The two Anodontas, having

A, outline of lake with the mussel zone
stippled and marked out by two ten-foot
contours.

B, shows the relation of four of the common-
est species to depth and character of bottom :

1. Anodonta edentula. 3. Unio rubigniosa.

2. Anodonta grandis. 4. Lamfsilisluteoltis.

Phuicton Animals 325

lighter shells less prone to sink, live in the deeper zone
of mixed marl and mud, and so are able to forage farther
out on the bottom. On account of their thinner shells
they are excluded from residence near the shore line,
where the waves would crush them. The heavier
shelled Unio requires a more solid bottom for its sup-
port, and is uninjured by the beating of heavy waves.
Hence, its shoreward distribution. Lampsilis, however,
is a more freely ranging form, having a rather light shell.
It overspreads the range of all the others, coming in the
less exposed places rather close to shore.

Plancton animals- -The animals of the shoreward
plancton are less transparent than those of the lake.
They are also far more numerous. They show more
color. The color is often related to situation. In
small ponds and marshes they are darker as a rule than
in large ponds. They include forms of very diverse
habits among which are the following:

1 . Forms that swim freely and continuously in the
more open places. These only are common to both
littoral and limnetic regions.

2. Forms that are free swimming, but that rest
betimes on plants; Cladocerans with adherent "neck
organs" ; Copepods with hooked antennae, etc.

3. Forms that can and that do swim betimes, but
that more habitually creep on plants; many ostracods,
copepods and rotifers.

4. Forms that live on or burrow in the slime that
covers stems or other solid supports, and that swim
but poorly and but rarely in the open water; Leeches
and oligochete worms, rhizopods and midge larvae.

5. Sessile forms that cannot swim, but that become
detached and drift about passively in the open water,
at certain seasons; hydras, statoblasts of fresh-water
sponges and of bryozoans, resting eggs of rotifers and of
cladocerans, etc.

326 Aquatic Societies

Few of these can thrive in the waters of the limnetic
region of a lake ; but there is at least one member of the
first group that takes advantage of an abundant supply
of food in lake waters, migrates out, and develops
enormously, overshadowing in numbers sometimes the
truly limnetic forms. It is Chydorus sph&ricus. It is
rather a littoral than a limnetic species, yet it often
abounds in the open lakes, following a rich development
there of blue-green algae suitable for its food.

SPATIAL RELATIONS

A large part of the animal life of the littoral region is
disposed in relation to upper and lower surfaces of the
water. This grouping by levels is due to gravity.
Where the air rests upon the water, making available
an unlimited supply of oxygen, there at the surface are
aggregated forms that require free air for breathing.
Where the water rests upon the solid earth, there at the
bottom are the forms that hide or burrow in the ground.

Plants and animals differ most markedly here. Light
is the prime requisite and source of energy for chloro-
phyl-bearing plants. It is not light but oxygen that
holds many animals at the surface of the water; and
it is indifference to light that allows many other animals
to dwell in the obscurity of the bottom.

Life on the bottom has a number of advantages among
which are the following :

1. Shelter is available.

2. Energy is saved when a resting place is found, and
continuous swimming is unnecessary.

3. Gravity brings food down from above.

4. Hiding from enemies is easier in absence of strong
light.

It has also its perils chief among which are :—

1 . Failure of oxygen | either of which may result

2. Excess of silt in suffocation.

Spatial Relations 327

In the last chapter we have discussed the more
important lines of specialization that have fitted the
members of the bottom population to meet or to
profit by these conditions. Under the subject "pond
societies," further specific illustrations will be cited.

Life at the surface is less tranquil than on the bottom.
There are two kinds of animals that can maintain them-
selves there, (i) Those having bodies (together with
the air they hold about them) lighter than the wrater;
which rise to the surface like a cork and have to swim
in order to go down below. These are mainly adult
insects whose problem of getting air we have discussed
in the preceding chapter.

(2) Those having bodies heavier than the water,
which maintain themselves at the surface by some sort
of hold on the surface film. If free-swimming, they
have to swim up to the surface and break through the
film before they can use it for support. Certain insect
larvae, water-fleas, rotifers, ciliates, etc., are of this
habit. Creeping forms must first climb up some
emergent stem, break through and then glide away sus-
pended underneath the film. Pond-snails and hydras
are of this sort. In an aquarium one may see either,
hanging suspended, and dimpling the surface where the
foot is attached by the downward pull on the film.

The relations of certain water-fleas to the surface film
are particularly interesting. For many of these, such
for example as Bosmina, this is a constant source of
peril. If in swimming a Bosmina accidentally breaks
through this film it falls over on its side and is held there
helpless lying on the surface unable to swim away.
Unless some disturbance dash it again beneath the
water, its only chance for release seems to lie in
moulting its skin and slipping out of it into the
water. Usually when a catch of surface plancton from

328 Aquatic Societies

Cayuga is placed in a beaker, the Bosminas begin
to break through one by one, and soon are gathered in a
little floating company in the center.

Scapholeberis (fig. 192), however, appears to be
especially fitted to take advantage of the surface film.
It is able to maintain a proper position at the surface:
it possesses specialized bristles for breaking the film and
laying hold upon it ; its ventral (uppermost) margin
is straightened and extended posteriorly in a long
spine; as much contact may be had as is needed.
Suspended beneath the surface, where algas from below
and pollen from the air accumulate, Scapholeberis

FIG. 192. Scapholeberis mucronata,
suspended beneath the surface film.
(After Scourfield.)

TOWS placidly about, foraging ; or it is borne along by the
towing of air currents acting on the surface water — a
sort of submarine sailing.

Scapholeberis is unique among wrater-fleas in this
habit. There is also an Ostracod, Notodromas, of
similar habit ; and it is worthy of note that both these
creatures have blackish markings on the ventral edges
of the valves and are pale dorsally. As in the sloths
which climb inverted in trees, the usual coloration of the
body is reversed with reversal of position.

Then there are some little creatures that take advan-
tage of the tenacity of the surface film to cover them-
selves with it as with a veil. Copepods, ostracods,
rotifers and what not, climb up the surface of emergent
stems, pushing a film of water ahead until they are well
above the general surface level, where they rest and

Sp a Ha I Re I a tio ns

329

feed, and find more oxygen. The larva of Dixa is one
of the most interesting of these. It will float in the
surface film, but not for long, if any support be at hand.
Touching a leaf it immediately bends double, and
pushes forward by alternate thrusts at both ends, until
it has lifted a film of water to a satisfactory level.

On the surface are deposited the eggs of many insects
having aquatic larvae, but these eggs are heavier than

water, and unless anchored to
some solid support or buoyed
up with floats (as are such eggs
as those of Culex and Core-
thra) nearly all of them settle
to the bottom. There are,
however, a few midges whose
egg-clusters float freely. A
brief account of the egg-lay-
ing of one of them, Chironomus
merid'ionalis, will illustrate
several points of dependence
on the surface tension.

The female midge, when
ready to lay her eggs, rests
for a time on some vertical
stem by the water side in the
attitude illustrated in figure
194. She extrudes her eggs
which hang suspended at the
She then flies over the water
carrying them securely in a rounded clump of gelatin.
After a long preparatory flight, consisting of coursing
back and forth in nearly horizontal lines at shoul-
der height above the surface of the water — a per-
formance that lasts often twenty minutes — she
settles down on the surface and rests there with
outspread feet. The usefulness of her elongate tarsi is

FIG. 193.

Dixa

Larva of

midge, inverted, to show: a,
caudal lobe; b, creeping
bristles; c, prolegs. The
arrow indicates the direction
of locomotion, middle fore-
most, both ends trailing.

tip of the abdomen.

330

Aquatic Societies

here apparent. They rest like long out-riggers radiately
arranged upon the surface, easily supporting her weight
while she liberates the egg mass and lets it down into
the water. At the top of the egg clump appears a cir-
cular transparent disc from which the egg mass depends.
This disc catches upon the surface film, tho pulled
down into it in a little rounded pit-like depression

by the weight of the eggs. Slowly
the eggs descend pulling out the gelatin
attaching them to the disc into a slender
thread that thus becomes stretched to
a length of several inches. The female
flies away to the shore and leaves them
so. Then they drift about like floating
mines, transported by breezes and cur-
rents. This little disc of gelatin dimp-
ling the surface film is indeed a frail

A

B

D

FIG. 194. The egg-laying of Chironomus meridionalis.

A, The female at rest extruding the egg-mass.

B, The female resting on the surface film, letting the egg mass down into the water.

C and D, The egg mass liberated and hanging suspended from the surface film by a delicate
gelatinous cord attached to a small disc-like float.

bark for their transportation. When driven by waves
and currents, they break their slender moorings and
settle to the bottom, or adhere to floating stems
against which they are tossed.

There is another phenomenon of the water surface so
curious and interesting it merits passing mention here.
There is a black wasp Priocnemis flavicornis, occasion-
ally seen on Fall Creek at the Cornell Biological Field

Spatial Relations 331

Station, that combines flying with water transportation.
Beavers swim with boughs for their dam, and water-
striders run across the surface carrying their booty, but
here is a wasp that flies above the surface towing a load
too heavy to be carried. The freight is the body of a
huge black spider several times as large as the body of
the wasp. It is captured by the wasp in a waterside
hunting expedition, paralyzed by a sting adroitly
placed, and is to be used for provisioning her nest.
It could scarcely be dragged across the ground, clothed
as that is with the dense vegetation of the water-
side; but the placid stream is an open highway. Out
onto the surface the wasp drags the huge limp black
carcass of the spider and, mounting into the air with her
engines going and her wings steadily buzzing, she sails
away across the water, trailing the spider and leaving
a wake that is a miniature of that of a passing steamer.
She sails a direct and unerring course to the vicinity of
her burrow in the bank and brings her cargo ashore
at some nearby landing. She hauls it upon the bank
and then runs to her hole to see that all is ready.
Then she drags the spider up the bank and into her
burrow, having saved much time and energy by making
use of the open waterway.

Intermediate between surface and bottom the life of
the water that is not included in either of the two strata
we have just been discussing, but that has continuous
free range of the open water, is still considerable. It
corresponds in part to the planet on of the open waters,
as we have sesn. It corresponds in part, also, to the
necton; and, as in the open water, so also in the shoals,
the larger and more important free-swimming animals
are fishes. Its spatial relations are complicated by the
habit some air-breathing forms (especially insects)
have of ranging downward freely thro the depths;

332 Aquatic Societies

also by the way in which forms like Chironomus, that
ordinarily remain in hiding in the bottom, come out
betimes in the open and take a swim. But there yet
remain at least two classes of organisms that belong
neither to the top nor to the bottom, nor yet to the
free-swimming population. These are forms that are
able to sustain themselves above the mud by taking
advantage of plant stems or other solid supports. These
get their oxygen from the water. They are:

1. Climbing forms, that hold on by means of claws,
as do the scuds and some dragonfly, damselfly and may-
fly larvae, or by a broad adhesive foot as do certain
minute mussels. Many members of this group find
temporary shelter between the leaves and scales of
plants.

2. Sessile forms that remain more or less per-
manently attached, like sponges, bryozoans, hydras,
etc.

Many members of both these groups construct for
themselves shelters. Chironomus, for example, while
usually living in such tubes as are shown in figure 134
on page 226, is able to creep about freely upon the
stem. Cothurnia (fig. 73) and Stentor, and many
sessile rotifers build themselves shelters.

Such support may be found on the bottom itself
where that is hard ; but the bottom is soft where most
seed-plants grow. Furthermore, to ascend and remain
above the level of the hordes of voracious bottom
dwellers must be a means of safety. It is clear, there-
fore, that plants rising from the bottom and branching
extensively must add enormously to the biological rich-
ness of the shoals, by the support and shelter they
afford to such animals as these.

Size — As on land a weed patch is a miniature jungle,
having a population of little insects roughly correspond-

Life in Some Typical Lenitic Situations 333

ing in social functions to the larger beasts of the forest,
so in the water there are large and small, assembled in
parallel associations. The larger, as a rule, inhabit the
more open places. Paddle -fish and sturgeons and gars
belong to the rivers; the qualitative demands of their
appetites exclude them from living in the brooks. There
is not a living there for them. Little fishes belong to
the brooks and to the shoals. In our diagram on page
233 we have already shown how in a small lake shore-
ward distribution of the fishes corresponds roughly with
their size, the largest ranging farthest out, and the
smallest sticking most closely to shelter. The senior
author has shown (07) a parallel to this in the distribu-
tion of diving beetles in an angle of the shore of a weedy
pond. Here the most venturesome beetle was Dytiscus
(see fig. 129 on p. 221). It was taken at the front of
the cat-tails in about three feet of water. The associa-
ted species were disposed closely, tho not strictly in
accordance with their size, between that outer fringe
and the shore, Acilius, Coptotomus, Laccophillus,
Hydroporus, (see fig. 130) Ccelambus and Bidessus
following in succession, the last named (a mere molecule
of a beetle, having but 2t;W the weight of Dytiscus)
being found only among the trash at the very shore line.

LIFE IN SOME TYPICAL LENITIC SITUATIONS

The association of organisms in natural societies is
controlled by conditions; but conditions intergrade.
Lakes, ponds, rivers, marshes all merge insensibly,
each into any of the others; and their inhabitants
commingle on their boundaries. Yet these names stand
for certain general average conditions that we meet
and recognize, and with which certain organisms are
regularly associated. It will be worth while for us to
note the main characteristics of the life of several of the
more typical of such situations.

334

Aquatic Societies

Pond societies— -The kind of associations we now come
to discuss are typically represented in ponds, but they
occur also in any bodies of standing fresh water, that
are not too deep for growth of bottom herbage, nor too
exposed to wind and wave for the growth of emergent

FIG. 195. Where marsh and pond meet. The head of "the cove" at the Cor-
nell Biological Field Station. Beds of spatterdock backed by acres of cat-
tail flag. Neguena valley in the distance.

aquatics along shore. The same forms will be found
in ponds, lagoons, bayous, sheltered bays and basin-
like expansions of streams. The bordering aquatics
will tend to be arranged in zones, as discussed in the
preceding pages, according to the closeness of their
crowding.

i. The shoreward zone of emergent aquatics will
include, in our latitude, species of cat-tail (Typha), of

Pond Societies

335

bur-reed (Sparganium) , of bulrush (Scirpus), of spike-
rush (Eleocharis) , of water plantain (Alisma) , of arrow-
head (Sagittaria) , and arrow-arum (Peltandra, of pick-
erel-weed (Pontederia) , of manna grass (Glyceria), etc.

2. The intermediate zone of surface aquatics will
include such as:

(a). These rooted aquatics with floating leaves:
white water-lily (Castalia), spatterdock (Nymphasa),
water shield (Brasenia), pondweed (Potomogeton) , etc.

FIG. 196. A spray of the sago pondweed, Potamogeton, coated with
slime-coat diatoms, its leaf tips bearing dwelling tubes of midge
larvse (Chironomus).

336 Aquatic Societies

(b). These free-floating aquatics; species of duck-
weed (Lemna, Spirodela), water fernworts (Azolla,
Salvinia), liverworts (Riccia), etc.

3. An outer zone of submerged plants will include
such forms as pondweeds (Potamogeton), hornwort
(Ceratophyllum) , crow-foot (Ranunculus), naiad
(Najas), eel-grass (Zostera), stonewort (Chara), etc.

These grow lustily and produce great quantities of
aquatic stuff which serves in part while living, but prob-
ably in a larger part when dead, for food of the animal
population, and the ultimate residue of which slowly
fills up the pond. These plants contribute largely to
the richness and variety of the life in the pond, by
offering solid support to hosts of sessile organisms, both
plants and animals. Their stems are generally quite
encased with sessile and slime-coat algae, rotifers,
bryozoans, sponges, egg masses of snails and insects
and dwelling tubes of midges (fig. 196). Especially do
floating leaves seem to attract a great many insects to
lay their eggs on the under surface. This is doubtless
a shaded and cleanly place, so elevated as to be favor-
able for the distribution of the young on hatching.

The algce of ponds are various beyond all enumerating.
It is they, rather than the more conspicuous seed-plants,
that furnish the basic supply of fresh food for the animal
population. Small as they are individually, their rapid
rate of increase permits mass accumulation which
often become evident enough. Such are:

( i ) . The masses of filamentous algae, (Spirogyra and
its allies; Ulothrix, Conferva, etc.) collectively called
"blanket algae" that lie half-floating in the water, or are
buoyed to the surface by accumulated oxygen bubbles.

(2). The beautiful fringes of branching sessile algae
(Chaetophora, fig. 198, Cladophora, etc.) that envelop
every submerged stern as with a drapery of green.

Pond Animals

337

(3). The lumps of brownish gelatin inclosing com-
pound colonies (Rivularia, see fig. 52 on p. 134, etc.),
that are likely to cover the same stems later in the
season, and that sometimes seem to smother the green
vegetation.

(4). The spherical lumps of greenish gelatin that lie
sprinkled about over the bottom — rather hard lumps
inclosing compact masses of fila-
ments of Nostoc, etc.

(5). The accumulated free-
swimming forms that are not
seen as discrete masses, but that
tint the water. Volvox tints it
a bright green; Dinobryon, yel-
lowish; Trachelomonas, brown-
ish; Ceratium, grayish, etc.

Such differences as these in
superficial aspect, coming, as
many of them do, with the regu-
larity of the seasons, suggest to
one who has studied them the
principal component of the
masses ; but one must see them
with the microscope for certain
determination .

The animals of the pond that breathe free air are a few
amphibians (frogs and salamanders), a few snails
(pulmonates) and many insects. The insects fall into
four categories according to their more habitual posi-
tions while taking air:

(i). Those that run or jump upon the surface.
Here belong the water-striders and their allies — long
legged insects equipped with fringed and water-repel-
lent feet that take hold on the surface film, but do not
break through it. Here belong many little Diptera that
rest down upon the surface between periods of flying.

FIG. 197. Diagram of a lily-
pad, inverted, showing
characteristic location and
arrangement of some
attached egg clusters.

a, Physa; 6, Planorbis; c, Trias-
nodes; d, Donacia; e, Hydro-
campa; /, Enallagma (inserted
into punctures) ; g, Notonecta
(laid singly) ; /;, Gyrinus.

338

Aquatic Societies

Here belong the hosts of minute spring-tails that gather
in the edges in sheltered places, often in such numbers
as to blacken the surface as with deposits of soot.
Minute as these are they are readily recognized by
their habits of making relatively enormous leaps from
place to place.

,^(2). Those that lie prone upon the surface. Best
known of these because everywhere conspicuous on still

FIG. 198. Two fallen stems enveloped with a rich growth
of the alga, Chcetophora incrassata.

waters, are the whirl-i-gig beetles. Less common and
irm.ch less conspicuous are the pupae of the soldier- flies
(Stratiomyia, etc.) and the larvae of the Dixa midges.

(3). Those that hang as if suspended at the surface,
with only that part of the body that has to do with
intake of air breaking through the surface film. Here
belong by far the larger number of aquatic insects.
Here are the bugs and the adult beetles, alertly poised,

Pond Animals

339

with oar-like hind legs swung forward, ready, so that a
stroke will carry them down below in case of approach
of danger. Here hang the wrigglers — larvae and pupae
of mosquitoes. Here belong the more passive larvae of
many beetles and flies and the pupae of swale-flies and
certain crane-flies.

(4). Those that rest down below, equipped with a
long respiratory tube for reaching up to the surface for

FIG. 199. Diagram of distribution of pond life. The right side
illustrates the zonal distribution of the higher plants, i, shore
zone; 2, standing emergent aquatics; j?, aquatics with floating
leaves; 4, submerged aquatics, 5, floating aquatics; 6, free swim-
ming algas of the open water.

The left side represents the principal features of the distribution of
animals, r, s, t, u, forms that breathe air; v, w, x, y, and z, forms
that get their oxygen from the water.

(From the Senior Author's General Biology)

air. Such are Ranatra, and the rat -tailed maggots of
syrphus -flies.

The animals of the pond that are more strictly aquatic
in respiratory habits (being able to take their oxygen
supply from the water itself) are so numerous that we
shall be able to mention only a few of the larger and
more characteristic forms. First there are the inhabi-
tants of the bottom. These fall into two principal cate-
gories, the free-living and the shelter-building forms.
The free-living forms may be grouped as follows:

340

Aquatic Societies

(i). Bottom sprawlers that lie exposed, or only
covered over with adherent silt. These are character-
ized by a marked resemblance to their environment.
Such crustaceans as the crawfish and Asellus, such
insects as Ephemerella, Casnis and other mayfly nymphs

Libellula, Didymops,
Celithemis (fig. 200)
and other dragonfly
nymphs, and certain
snails and flatworms
belong here.

(2). Bo torn dw 1-
lers that descend more
or less deeply into the
mud or sand, by the
various means already
discussed in the pre-
ceding chapter.
Among the shallow
burrowers are many
shell-bearing molluscs,
both mussels and
snails; a few mayfly
and dragonfly nym-
phs. Descending
more deeply in muddy
beds are some true worms and horsefly larvae.

The shelter-building forms of the bottom may be
grouped as:

(i). Forms making portable shelters. These are
mainly caddis-worms that construct cases of pieces of
wood or grains of sand.

(2). Forms making fixed shelters These are
such caddis- worms as Polycentropus, such worms as
Tubifex (see fig. 83 on p. 174) and such midges as
Chironomus (see fig. 134 on p. 220).

FIG. 200. A bottom spra \\ier: nymph of
of the dragonfly, Celithemis eponina.

Marsh Societies 341

It is some of these animals of the pond bottom that
give to the littoral region its great extension out under
the open waters of the lakes. It is only a few members
of the population that are able to endure conditions in
the depths far out from shores. These are such as:

Small mussels of genus Pisidium.

Mayfly nymphs of the genus Hexagenia.

Midge larvae of the genus Chironomus.

Caddis- worms in the cylindric cases of sand, not yet
certainly identified, etc.

The larger animals of the pond that belong neither
to surface nor bottom and that correspond to neither
plancton nor necton of the open water may be grouped
as:

(ij. Climbing forms (most of which can swim on
occasion) , such as the scuds (Amphipods) , the nymphs
of dragonflies such as Anax, of damselflies such as Lestes
and Ischnura, of mayflies such as Callibaetis, larvae of
caddisflies such as Phryganea and of moths such as
Paraponyx, mussels such as Calyculina, and many
leeches, entomostracans and rotifers.

(2). Sessile forms such as hydras, sponges, bryzoans
and rotifers.

II

Marsh Societies. — We come now to consider the
associations of organisms in waters that are not too deep
for the growth of standing aquatics. Shoalness of
water and instability of temperature and other physical
conditions at once exclude from residence in the marsh
the plants and animals of more strictly limnetic habits ;
but it is doubtless the presence of dense emergent plant
growth that most affects the entire population. This
gives shelter to a considerable number of the higher
vertebrates, and these rather than the fishes are the
large consumers of marsh products. The muskrat

342

Aquatic Societies

breeds here and builds his nest of rushes. He prefers,
to be sure, the edge of a marsh opening, where in deep
water he may find crawfishes and molluscs, with which
to vary his ordinary diet of succulent shoots and tubers.

FIG. 201. The eggs of the spotted salamander, Ambystoma tigrinum.

(Photo by A. A. Allen.)

Deep in the marsh dwell water birds, such as grebes,
rails, coots, terns, bitterns, and in the north, ducks'and
geese as well. Such non-aquatic birds as the long-billed
marsh- wren and the red -winged blackbird use the top
of the marsh cover as a place to build their nests and

Marsh Plants

343

use also the eaves of marsh plants for building materials.
Several turtles and water snakes are permanent resi-
dents as are also a few of the frogs. Most of the frogs
visit the marsh
pools at spawn-
ing time, making
the air resound
with their nup-
tial melodies.
The spotted sal-
amander is the
earliest amphi-
bian to spawn
there. Though
the adult is but
a transient, its
larvae remain in
the marsh pools
through the sea-
son.

The plants are
the same kinds
found in the
marginal zone of
the pond border,
but here they of-
ten cover large
areas in a nearly
pure stand. In
our latitude in the more permanent waters, the
dominant species usually are cat-tail, phragmites,
bur-reed and the soft-stemmed bulrushes; in the
shoals that dry up each year they are sweet flag,
sedges, manna grass and the hard-stemmed bul-
rushes. Such plants as these have strong inter-
laced roots and runners that form the basis of the marsh

FIG. 202 Tear- thumb.

344

A quatic Societies

cover, and that support a considerable variety of more
scattering species. One of the most widespread of
these secondary forms is the beautiful marsh fern,
whose black rootstocks over-run the tussocks of the
sedges, shooting up numberless fronds. Scattering
semi-aquatic representatives of familiar garden groups
are the marsh bellwort (Campanula aparinoides}, the
marsh St. John's wort (Hypericum virgiuiciim) and the
marsh skull-cap (Scittellaria galericulata] : these are
dwarfish forms, however, that nestle about the bases of
the taller clumps. With them are straggling prickly
forms, such as the marsh bedstraw (Galium palustre),
the white grass (Leersia) and the tear-thumb (Polygo-
num sagittatum, fig. 202). Strong growing forms that
penetrate the marsh cover with stout almost vine-like
stems are the marsh five-finger (PoteutiUa fxilnstris) the

FIG. 203. A marshy pool with flowers of the white water crow-foot rising
from the surface.

Marsh Animals 345

joint weed (Polygonum} and the buck-bean (Menyan-
thes trifoliata). True climbers also, are present in the
marsh although usually only on its borders; such are
the climbing nightshade bittersweet (Solamim dulca-
mara} and the beautiful fragrant-flowered climbing
hemp-weed (Mikania scandens). Here and there one
may see a protruding top of swamp dock (Rumex
vcrtic Hiatus), a water hemlock (Cicuta bulbifera) or a
swamp milkweed (Asdepias incarnata}.

Every opening in the marsh contains forms that are
more characteristic of ponds and ditches, such as arrow-
heads and water plantain. And even the little trash
filled pools often contain their submerged aquatics.
Such a one is shown in the figure 203, a shallow pool
filled with fallen leaves, its surface suddenly sprinkled
over with little star-like flowers when the white water-
crowfoot shoots up its blossoms.

Algae often fill these pools; sometimes minute free-
swimming forms that tint their waters, but more often
"blanket algae," whose densely felted mats may smother
the larger submerged aquatics.

The animal life of the marsh is also a mixture of pond
forms and of forms that belong to the more permanent
waters. The fishes are bullheads and top minnows and
others that can endure foul waters, scanty oxygen and
rapid fluctuations of temperature. Of crustaceans,
ostracods and scuds are most abundant. Of molluscs,
Pisidium and Planorbis are much in evidence, and other
snails are common. Insects abound. Some are aqua-
tic and some live on the plants. Of all Odonata, Lestes
(fig. 204) is perhaps the most characteristic marsh inhabi-
tant ; of mayflies, Blasturus and Caenis ; stoneflies, there
are none. Of caddis-flies there are many, but Limno-
ph-ilus indivisus is perhaps the most characteristic marsh
species. It is not known to inhabit any waters except

346

Aquatic Societies

1

those that dry up in summer. The commonest beetles
are small members of the families Hydrophilidae,
Dytiscidae and Haliplidae. The most characteristic of

the bugs is the slen-
der little marsh -
treader, Limno-
bates. Swale-flies,
mosquitos, crane-
flies and ubiqui-
tous midges abun-
dantly represent
the aquatic Dip-
tera.

There are, of
course, man}' in-
sects dependent
upon particular
plants. Such are
the tineid moth,
L'nn na cea ph ragmi-
tella, that burrows
when a larva in
the Typha fruit
spike, and the wee-
vil, Sphenophorus,
that burrows in the
Typha crown ; the
leaf-beetle, Dona-
da enter gi n at a,
whose larva feeds
on the submerged roots of the bur-reed, etc. Here are
also a number of characteristic spiders, such as the
diving spider, Dolomedes.

Doubtless the lower groups of animals possess species
that are addicted to dwelling in marshes, and fitted to
the peculiar conditions such places impose, but these

FIG. 204. A damselfly. Lestes uncatus.

Marsh Societies

347

have been little studied. There is hardly any situation
where the fauna is so imperfectly known.

As compared with the land, fauna and flora of
marshes are characterized by a small number of species,
and enormous numbers of individuals. In other words,

FIG. 205. "Tree-swallow pond": a once famous collecting ground in the
R en wick_ marshes at Ithaca. Photo taken in spring after the burning and
the freezing and the floods, but before the growth of the season.

the population is one of small variety but of great den-
sity. Such forms as are fitted to maintain themselves
where floods and fire alternately run riot find in the rich
soil and abundant light and moisture opportunity for a
great development. Fire sweeps the surface clear of
trees, which would overtop and overshadow' the
herbage and would create swamp conditions. The
ground layer of water-soaked trash prevents the burn-

348 Aquatic Societies

ing of the root stocks; it also prevents deep freezing
after the fires have run. Plants that are capable of
renewing their vegetative shoots from parts below the
level of the burning, are the ones that year after year,
maintain their place in the sun.

Ill

Bog Societies. Bogs belong to moist climates and to
places where water is held continuously in an amount
sufficient to greatly retard the complete decay of plant
remains. Acids accumulate; especially, humous acids.
The soil becomes poor in nutriment, especially in
available nitrogen. Plants can absorb little water,
at least at low temperature; and the typical bog
situation is therefore said to be "physiologically dry."
With such conditions there go some striking differences
in flora and fauna. The plants are "oxylophytes" like
sphagnum and cranberry, i. e., plants that can grow in
more or less acid media, and that have many of the
superficial characteristics of desert plants; such as
vestiture of hairs or scales or coatings of wax, thickened
cuticle, leaves so formed or so closed together as to
limit or retard transpiration. The kinds of plants are
fewer; the individuals crowd prodigiously. They are
eaten by animals less than in any other situation.
Their remains, partly decomposed, are added to the soil
in the form of deposits of peat. The animal population
is correspondingly reduced and scanty.

Sphagnum. The most characteristic single organism
in such a situation is the bog-moss, Sphagnum (fig. 206;
see also fig. 59 on p. 147). This grows in cushion-like
masses of soft erect unbranched stems, that are in-
dividually too weak and flaccid to stand alone, but that
collectively make up the largest part of the bog cover.
The masses are loose and easily penetrated by the roots

Sphagnum

349

and runners of other stronger plants. It is the inter-
penetration of these that binds the bog cover together,
making it resilient under foot.

The leaves of Sphagnum are interspersed with cells
that are mere water reservoirs having porous walls.
Some of these leaves are deflexed against the stem and
make excellent capillary
conduits for water upward
or downward. Whether the
abundant supply be in the
air above or in the soil be-
low, these make provision
for the equitable distribu-
tion of it. Wherefore, these
masses of sphagnum become
water reservoirs, holding
their supply often against
gravity, and bathing the
roots of all the cover plants
that rise above the surface
of the bog.

Sphagnum belongs to the
shore, and it is quite incap-
able of advancing into the
water unassisted. But with
the help of stronger more straggling plants whose roots
and branches penetrate and interlace in its masses in
mutual support, it is able to extend as a floating border
out over the surface of still water in small lakes and
ponds. These floating edges may be depressed by the
weight of a man until they are under water, but they
are tough and elastic, and rise again unharmed when
the weight is removed. Long, strong, pliant-stemmed
heaths and slender sedges are the plants commonly
associated with sphagnum in the making of this floating
border. In the bog cover equally close is its association
with the common edible cranberry.

FIG. 206. Bog moss, Sphagnum ;

a the tip of a spray; b, a few cells from
a leaf; x, long interlaced lines of slen-
der sinuous chlorophyl-bearing cells, and
y, large empty water reservoir cells hav-
ing pores in their walls for admission of
water and annular cuticularisations
for support.

350

Aquatic Societies

Some habitual associates of sphagnum are shown in
figure 207. In such a place as the foreground of this
picture, if one slice the bog cover with a hay-knife, he

^$^%&w&&nysi

Si^B^SS^i^kJfe-aSI

FIG. 207. A bit of bog cover. (McLean, N. Y.). From the central clump
of pitcher-plant leaves rises one long-stalked flower. The surrounding bog
moss is Sphagnum. A few slender stems of cranberry trail over the moss.
The taller shrubs are mainly heaths such as Cassandra and Andromeda.

(Photo by H. H. Knight.)

may easily lift up the slices; for they are composed of
living material to a depth of only about a foot. Below
is peat; at first light colored and composed of identifi-
able plant remains, but, deeper, becoming darker and
more completely disintegrated. The slices cut from

Bog Plants

the surface have sphagnum for their filling, but they are
tough and pliant, like strips of felt, owing to the close
interlacing of roots and stems of the other plants of the
bog cover.

A I any delightful herbs grow on the surface of the bog.
The pitcher-plant shown in our figure is one, and the

sundew (see fig. 172 on p.
283) is another carnivor-
ous species. These, as we
have seen in the preceding
chapter, have their own
way of getting nitrogen when
the available supply is small.
Orchids of several genera
(Habenaria, etc.) and moc-
casin flowers (fig. 208) there
bear beautiful flowers. Cot-
ton grass (Eriophorum) is
showy enough with its white
tufts held aloft when in
fruit, and a beaked rush
( Rynchospora) is its natural
associate. In places where
the surface rises in little
hummocks, there are apt to
be patches of the xerophytic
moss, Polytrichium, associ-
ated with charming little

^ colonies of wintergreen and

goldthread. At the rear

of the heath shown in our figure stand huckleberries and
bog brambles and masses of tall bog ferns while thickets
of alder and dogwood crowd farther back.

Where sphagnum borders on open water, there often
lies in front of it the usual zone of aquatics with floating
leaves, as shown in the accompanying picture, and in

FIG. 208. A charming bog plant,
the moccasin flower. Cypri-
pedium reginae).

352

Aquatic Societies

still deeper water there are apt to be beds of Chara and
of pondweeds. These and the molluscs associated
with them, leave their calcined remains deposited on
the pond bottom as a stratum of marl. Thus the

FIG. 209. Mud pond, near McLean, X. Y. This is a bog pond, surrounded
in part at least by floating sphagnum. The outlet (to left in the picture) is
bordered by tussock sedges, backed up by extensive alder thickets.

(Photo by John T. Needham.)

filling of a bog pond is in time accomplished by the
deposition of a layer of marl over its bottom, and a
much thicker mass of peat over the marl. Successive
stages in the filling process are graphically shown in
Dachnowski's diagram, copied on the next page.

Peat formation and filling of beds goes on, of course, in
ponds where there is no sphagnum; goes on wherever

Peat and Marl

353

the conditions for incomplete decay of plants prevail;
and from the foregoing it will be seen that peat is not
likely to be composed of the remains of sphagnum
alone. The forefront of advancing shore vegetation is
led by a number of plants of very different character.

Bf Bs Bm 5 M

MF

Bf Bs Bm S M O-W

FIG. 210. Dachnowski's diagram illustrating three stages in the filling
of a pond with deposits of peat and marl. Peat is stippled; marl,
cross-lined.

OW, open water; M, marginal succession; S, shore succession; B, bog succession,
including bog meadow (Bm), bog shrub (Bs), and bog forest (Bf); MF, mesophytic
forest.

354

Aquatic Societies

The accompanying diagram
shows five modes of progress into
deeper water of pioneer land-
building plants.

a is the method of the spike-
rush on gently sloping shore. It
is the method by which number-
less shore plants extend their hold-
ings,— subterranean off-shoots.

b is the method of the tussock
sedges (see also fig. 209) which on
the loose mud in shallow waters
build up solid clumps. Many of
these, less than a foot in diameter,
are yet of such firmness that they
will sustain the weight of a man.
Every one knows such clumps,
from having used them (as step-
ping stones are used) in crossing
a swale. New offsets lie hard
against the old ones, roots descend
in close contact, and fibrous root-
lets interlace below in extraordin-
ary density.

c is the method of the swamp
loosestrife, Decodon, a method of
advancing by long single strides.
The tips of the long over-arching
shoots dip into the water, and
then develop roots and buds and
a copious envelope of aerating tis-
sue. If these new roots succeed

FIG. 211. Diagram illustrating the method of
advance into deeper waters of typical land-
building plants.

a, Spike rush; b, tussock sedge; c, swamp loose-
strife; d, cat-tail flag; e, Sphagnum and heaths.

La nd-b n ilding PI a ;/ ts

in taking a good hold on the bottom, then other shoots
spring from this new center and repeat the process.

d is the method of the cat-tail flag. It consists in
developing an abundance of interlaced fibrous roots,
and then simply floating on them. Much mutual sup-
port is required by plants that grow so tall ; and any
great advance of a few clumps beyond the general front
may result in disaster from overturn by winds.

e is a method of mutual support between species of
very different sorts. It is that of the sphagnum and
heaths just discussed. Greater progress over deep
water is made by this method than by any of the others.

A photograph of the first named is reproduced as
figure 212.

FIG. 212. A bit
of running
root- stock of
a spike rush.
E I e o c h a ris
pa I u s tr is ,
showing its
method of ad-
vance over the
pond bottom.
Bra nching
subterran can
off-shoots ex-
tend down a
sloping shore
u n t i 1 t h e y
reach a depth
of water in
which the}-
cannot func-
t io n eff ec-
tively.

Aquatic Societies

IV

The population of stream beds — If we distinguish
between lenitic and lotic societies by presence or
absence of growths of vascular plants, then the greater
part of stream beds shelter lenitic societies. The
greater part has not a current of sufficient swiftness to
prevent the growth of such plants. And indeed it is
only in restricted portions of any stream that we
find the animals specially adapted to meet conditions
imposed by currents.

Where the stream bed forms a basin, there the condi-
tions of life, for the larger organisms at least, approxi-
mate those of a lake. Hence we find in those places
in large streams where the water is deep and still, there
occur many forms like those in lakes. The sturgeon
belongs in both, and so do the big mussels and the
operculate snails, the big burrowing mayflies, the big
tube dwelling midge larvae, etc. The basins of creeks
offer conditions like those in ponds; the basins of
brooks, conditions like those of pools. And the largest
species are restricted to such of the larger basins as can
afford them adequate pasturage and suitable places for
rearing their young. To be sure, in all those basins,
the water is constantly passing on down stream and
the plancton of the basin, while in part developing there,
is in a large part constantly lost below and constantly
renewed from above. Kofoid (08) states that "The
plancton of the Illinois River is the result of the
mingling of small contributions by tributary streams,
largely of littoral organisms and the quickly growing
algse and flagellates, and of the rich and varied plancton
of tributary backwaters, present in an unusual degree
in the Illinois because of its slightly developed flood-
plain, and from which it is never entirely cut off, even
at lowest water. * * * * To these elements is added
such further development of the contributed or indigen-

The Population of Stream Beds 357

ous organisms as time permits, or the special conditions
of nutrition and sewage contamination facilitate.
Though continually discharging, the stream maintains
the continuous supply of plancton, largely by virtue of
the reservoir backwaters — the great seedbeds from
which the plancton-poor but well fertilized contribu-
tions of tributary streams are continuously sown with
organisms whose further development produces in the
Illinois River a plancton unsurpassed in abundance."

Doubtless, in every stream the plancton supply is
constantly renewed from sheltered and well populated
basins, which serve as propagating beds. And, indeed,
on every solid support diatoms are growing, and the
excess of their increase is constantly being released
into the passing current. In the swiftly flowing,
plancton-poor streams about Ithaca there is not tirns
for much increase of free planctonts by breeding. The
waters run so swift a course they can only carry into
the lake such forms as they have swept from their
channels in their rapid descent.

While there has been much study of the life of the
open water of rivers there has hitherto been little
study of their beds. Where the beds are sandy with
flow of water over them we know the life differs from
that of muddy basins. The heavier-shelled mussels and
snails are on the sand ; and the commoner insects there
are the burrowing nymphs of mayflies and Gomphine
dragon-flies, and the caddis- worms that live in portable
tubes of sand.

The beds of the smallest streams are easy of access,
and a few observations are available to indicate that
their study will bring to light some interesting ecological
relations. A few very restricted situations will be cited
in illustration.

358

Aqua tic Societies

Moss patches — On
the rocky beds of

large brooks that run
low but do not en-
tirely run dry, there
are frequent patches
of the close-growing
moss, Hydrohyp-
num. These patches
frequently cover the
vertical face of a
waterfall (fig. 213).
The little water that
remains in dry season
trickles through the
layer of moss, and
in times of flood the
speedier torrent
jumps over it. Under
the flattened frond-
like green sprays
there is compara-
tively quiet water
at all times; and in
this situation there
lives a peculiar as-
semblage of insects
that differ utterly
from the lotic forms

dwelling in the same streams (to be discussed in a later
part of this chapter), tho often dwelling within a few
feet of them. They lack all the usual adaptations for
meeting the wash of currents. They are (with occa-
sional intermixture of a few larva3 of small midges
and of Simulium) the following:

FIG. 213. A moss-bed covering the face of a
rock ledge (in flood time, a waterfall) in
the bed of Williams Brook at Ithaca,
N. Y. The water seen on the rock above
trickles down through this moss. Here is
a restricted and peculiar animal poptila-
tion.

Moss Inhabitants

359

1. The slender larvae of soldier-flies (Euparhyphus
brevicorms). Each bears a pair of ventral hooks that
may serve for attachment.

2. The greenish larva? of the cranefly (Dicrano-
uiyia simulans).

3. The warty-backed larvae of the Parnid beetle
(Elmis qiiadrinotatus] .

4. Larvae and pupae of a little black Anthomyid fly
(Limnophom sp.?).

a be d e f g

FIG. 214. Insect larvae from a moss patch such as is shown in the
preceding figure. a, Psychoda; b, Elmis; c, d, e, Euparhyphus, c,
being lateral, d, dorsal and e, ventral views, c and e show the huge
ventral hooks on the penultimate segment ; / and g, cases of an un-
known caddis- worm, /, composed mainly of sand; g, mainly of moss.

360

Aquatic Societies

5. The slender larvae of a moth fly (Psychoda alter -
nata], its body covered with deflexed spines.

6. The larvae of an unknown caddis-fly whose cases
are composed sometimes of stones, sometimes of moss

fragments.

Leaf-drifts — In the beds of wood-
land brooks, there are barriers of
fallen leaves, piled by the current
upon the bare, obtruding roots of
trees. These leaf -drifts have a
population of their own, the most
characteristic member of which
about Ithaca is the huge larva
shown in figure 215. This is the
larva of the giant cranefly, Tipula
abdominalis. Associated with this
larva in these water-soaked masses
of leaves, are the nymphs of such
stoneflies as Nemoura and of such
mayflies as Baetis and Leptophle-
bia, a few beetles and often many
scuds (Gammarus). In the mud
behind the leaf -drifts, there are
often earthworms, washed down
from fields above.

In the clear pools in upland
streams that flow through swampy
woods, when the bottom is strewn
with forest litter intermixed with brownish silt, there
dwell a number of forms that certainly belong to the leni-
tic rather than to the lotic societies. Such are the caddis-
worms of figure 216. With these are associated small
mussels of the genus Sphaerium, squat dragonfly
nymphs of the genus Cordulegaster, and climbing
nymphs of the genus Boyeria, water-skaters on the

FIG. 215. Two larvag of
the giant cranefly, Tip-
ula abdominalis, an in-
habitant of leaf-drifts in
woodland brooks.
Natural size

Leaf-drifts

361

surface and burrowing mayflies in the beds, and a con-
siderable variety of the lesser midges on every possible
support.

FlG. 216. A bit of the bed of a pool in a woodland stream, show-
ing among the forest litter the wooden cases of the larva of the
caddis-fly, Halesus guttifer. (See also fig. 104 on p. 198). Pro-
tective resemblance. There are 14 cases in the picture.

LOTIC
OOETIES

CCORDING to the
grouping outlined on
page 315, we designate
by this name those as-
semblages of organisms
that are fitted for life
in rapidly moving water
-that are washed by
currents, as the name
signifies. Whether the
water flow steadily in
one direction as in
streams, or back and

forth with frequent shifts of direction as on wave-
washed shores, the organisms present in it will be much
the same sorts. The plants will be mainly such algae
as Cladophora, and slime-coat diatoms: the animals
will be mainly net-spinning caddis-worms and a variety
of more or less limpet-shaped invertebrates.

The animals of lotic societies are mainly small inver-
tebrates. There are fishes, indeed, like the darters that
live in the beds of rapid streams. These lie on the
bottom where the current slackens, lightly poised on
their large pectoral fins, or rest in the lee of stones,
darting from one shelter to another. It is only a few

363

364 Aquatic Societies

lesser animals, of highly adapted form and habits, that
are able to dwell constantly in the rush of waters.

These lesser animals may be roughly divided into two
categories according to the sources of their principal
food supply:

1 . Plancton gathering forms, that are equipped with
an apparatus for straining minute organisms out of the
open current.

2. Ordinary forms that gather home-grown food
about their dwelling places.

i. Plancton Gatherers. --These are they that live
mainly on imported food, which by means of nets or
baskets or strainers they gather out of the passing
current. These are the most typical of lotic organisms,
for they must needs live on the exposed surfaces that
are washed by the current. They dwell on the bare
rock ledge, over which the water glides swiftly, or on the
top of the boulders in the stream bed, or on the exposed
side of the wave-washed pier. They are few in kinds,
and very diverse in form, and show many signs of
independent adaptation to life in such situations.
Among them are four that occur abundantly in the
Ithaca fauna. These four and their mode of attach-
ment and of plancton gathering are illustrated in the
accompanying diagram. The fly larva, Simulium,
adheres by a caudal sucker, gathers plancton by means
of a pair of fans placed beside its mouth, while its body
dangles head downward in the stream. The larva of
the caddis-fly, Hydropsyche, lives in a tube and con-
structs a net of silk that strains organisms out of the
water running through it. The caddis-worm, Brachy-
centrus, attaches the front end of its case firmly to the
top of a boulder in the stream bed, and then spreads its
bristle-fringed middle and hind feet widely to gather in
any organisms that may be adrift in the passing water.

Plancton Gatherers

365

The nymph of the "Howdy" Mayfly, Chirotenetes, fixes
itself firmly with the stout claws of its middle and hind
feet clutching a support, and extends its long fore feet
with their paired fringes of long hair outspread like a
basket to receive what booty the current may bring.
These four are so different they are better considered
a little further separately.

The larva of Simulium (the black-fly, or buffalo gnat)
perhaps the most wide-spread and characteristic animal

FIG. 217. Plancton-gathering insects
of the rapids. The arrow indicates
direction of steam-flow.

of running water, is unique in form and in habits. It
hangs on by means of a powerful sucker that is located
near the caudal end of its soft and pliant bag-shaped
body. But it may also attach itself to the stones by a
silken thread spun from its mouth: and if it then
loosens its sucker, it will dangle at the end of the thread,
head upstream. By means of these two attachments,
it may travel from place to place without being washed
away, but in the swiftest water, it can make only short
moves side wise. It travels by loopings of its body, like
a leech. So it shifts its location with changes of water
level, always seeking the most exposed ledges which a
thin sheet of water pours over. There it gathers in
companies, so closely placed side by side as to form
great black patches on the stones.

366 Aquatic Societies

There is little movement from place to place. The
larvas hang at full stretch, their pliant bodies swaying
with little oscillations of the current, their fans out-
spread, straining what the passing stream affords.
Each of these fans is composed of several dozen slender
rays, each one of which is toothed along one margin
like a comb of microscopic fineness, and all have a
parallel curvature like the fingers of an old-fashioned
reaper's cradle. They are efficient strainers.

When grown the larva spins its half cornucopia-
shaped straw-yellow cocoon on the vertical face of a
ledge where the water will fall across its upturned open
end, then transforms to a pupa inside. The pupa bears
on the prothorax a pair of long, conspicuous, many
branched respiratory horns, or "tube gills" (see fig. 171
on p. 280).

The eggs are laid at the edge of the swifty flowing
water on any solid support, on the narrow strip that is
kept wet, and, by oscillations of the current, occasionally
submerged.

Hydropsyche, the seine making caddis-worm, lives in
sheltering tubes of silk, spun from its own silk glands,
fixed in position on the surface of a stone (oftenest in
some crevice) , and covered on the outside with attached
sticks or broken fragments of leaves or stones. Always
one end of the tube is exposed to the current, and at
this end, the larva reaches out to forage. Here it con-
structs its net of crosswoven threads of fine silk. The
net is a more or less funnel-shaped extension of silk from
the front of the dwelling- tube. The opening is directed
upstream, so that the current keeps it fully distended.
The semi-circular front margin is held in place by
means of extra staylines of silk. The mesh is rather
open on the sides, but on the bottom there is usually a
small feeding surface that is much more closely woven.

Plancton Gatherers 367

The larva lies in its tube in readiness to seize anything
the current may throw down upon its feeding surface
or entangle in the sides of its net. The whole net is so
delicate that it collapses on removal from the water.
To see it in action, it is best examined through a
"water-glass."*

Brachycentrus, the "Cubist" caddis-worm, is re-
stricted in habitat to spring-fed streams flowing
through upland bogs. It constructs a beautiful case
that is square in cross- section. Each side is covered
with a single row of sticks (bits of leaf stalks, grass
stems, etc.) placed crosswise. The larva fastens its
case by a stout silken attachment to the top of some
current-swept boulder and then rests with legs out-
spread as indicated in figure 217 in a receptive atti-
tude, waiting for whatever organic materials the current
may bring within its grasp.

The Nymph of Chirotenetes , the ' ' Howdy' ' Mayfly, lives
on the rock ledge or where the water sweeps among the
stones. Its body is of the stream-line form discussed
in the last chapter — the form best adapted to diminish-
ing resistance to the passage of water, as well when at
rest as when swimming. The nymph sits firmly on its
middle and hind feet. Holding its front feet forward, it
allows the current to spread out their strainer-like
fringes of long hairs. These retain whatever food is
swept against them, and the mouth of the nymph is
conveniently near at hand. It uses its feet for stand-
ing but moves from place to place by means of swift
strokes of its finely developed tail fin, supplemented by
synchronous backward strokes of its strong tracheal gill
covers. It has almost the agility and swiftness of a
minnow.

*A "water-glass" is any vessel having opaque sides and a glass bottom, of
convenient size for use. An ordinary galvanized water pail with its bottom
replaced by a circular glass plate set nearly flush, is excellent.

368 Aquatic Societies

2. Ordinary Foragers .—These are the members of
lotic societies that lack such specialized means of
gathering food from the passing current, and that forage
by more ordinary methods. They live for the most
part on the sides of stones and underneath them, and
not on their upper surfaces. These also live where the
water runs swiftly, and, for the most part, out of the
reach of those fishes that invade the rapids. There are
two principal categories among them: a. Free-living
forms that are more or less flattened or limpet-shaped.
b. Shelter-building forms, that are in shape of body
more like the ordinary members of their respective
groups.

a

The limpet-shaped forms are members of several
orders of insects, worms and snails. Their flattened
form and appressed edges are doubtless adaptations to
life in currents. They adhere closely, and are on
account of their form, less likely to be washed away;
the current presses them against the substratum.

Not the most limpet-like but yet the best adapted
for hanging on to bare stones in torrents is the curious
larva of the net-veined midge, Blepharocera (see fig. 159
on p. 259) , an inhabitant only of clear and rapid streams.
The depressed body of this curious little animal is
equipped with a row of half a dozen ventral suckers,
each of which is capable of powerful and independent
attachment to the stone. So important have these
suckers become that the major divisions of the body
conform to them and not to the original body segments.
On these suckers, used as feet, the larva walks over the
stones under the swiftest water, foraging in safety where
no enemy may follow.

Most limpet-like in form of all is the larva of the
Parnid beetle, Psephenus, commonly known as the

Ordinary Foragers

369

"water-penny" (see fig. 160 on p. 260). It is nearly
circular and very flat with flaring margins that fit down
closely to the stone. It adheres closely and is easiest
picked up by first slipping the edge of a knife under it.
Viewed from above, it has little likeness to an ordinary
beetle larvae, but removed from the stone and over-
turned, one sees under the shell a free head, a thorax
with three short legs, an
abdomen and some minute
soft white segmentally
arranged tracheal gills on
each side.

Other insect larvae that
have taken on a more or
less limpet-like form, are
the nymphs of certain May-
flies and of many stoneflies
(fig. in on p. 204). The
body is strongly depressed.
The lateral margins of the
head and thorax are ex-
tended to rest down on the
supporting surface. The
legs are broadened and are
laid down flat so as to
offer less resistance to the
currents, and stout grap-
pling claws are developed
upon all the feet. Such is
Heptagenia whose nymphs
abound in every riffle and
on every rocky shore.
One may hardly lift a stone from swift water and
invert and examine it without seeing them run with
sidelong gait across its surface, outspread flat, and
when at rest appearing as if engraven on the stone.

FIG. 218. The nymph of a may-
fly (Heptagenia) from the
rapids, showing depressed form
of the body and legs.

(Photo by Anna H. Morgan.)

370 Aquatic Societies

The head is so flat and flaring that the eyes appear
dorsal in position instead of lateral as in pond-dwelling
Mayfly nymphs.

A more remarkable form is the torrent -inhabit ing
nymph of Rithrogena whose gills are involved in
the flattening process. They also are flattened and
extended laterally and rest against the stone. But,

FIG. 219. The nymph of an unknown mayfly from mountain
torrents, showing oval ventral attachment-disc formed be-
neath the body.

most remarkable of all, the anterior pair is deflected
forward and the posterior pair, backward, to meet on
the median line beneath the body, and both are
enlarged and margined; By the close overlapping
of all the gills of the entire series there is formed a large
oval attachment-disc of singularly limpet-like form.

A similar flat attachment-disc is formed on the
ventral side of the mayfly nymph shown in figure 219,

Shelter-building Forms 371

but on a wholly different plan. The gills are not
involved in the disc, but instead the body itself is
flattened and shaped to an oval form underneath, and
fringed with close set hairs.

There is in the mayflies a rather close correlation
between the degree of flattening of the body and the
rate of flow of the water inhabited. It is well illus-
trated by the allies of Heptagenia; also by those of
Ephemerella, among which occur swift -water forms.
Epeorus, Iron and Rithrogena form an adaptive series.
Among the Parnid beetles, Elmis (fig. 2i4b), Dryops
and Psephenus (fig. 160) form a parallel series.

There are snails that dwell in the rapids. The most
limpet-shaped of these is Ancylus (fig. 160 on page 260)
whose widely open and flaring shell has in it only a
suggestion of a spiral. Certain other snails (such as
Goniobasis livescens) are of the ordinary form and are
able to maintain themselves on the stones by means of
a very stout muscular closely-adherent foot. Simi-
larly, a number of flat worms, that
adhere closely are found creeping
in the rapids.

Shelter -building foragers are num-
erous in individuals but few in
kinds. One tube-dweller, Hy-
dropsy che, is a plancton gatherer
and has been already discussed.
There are other shelter building
caddis -worms living among stones
in running water. Ryacophila FIG. 220. Two pupal
builds at close of larval life a barri- cases of the caddis-fly

i r .. , .. ~ Ryacophila, removed

cade or stones as shown in the fig. from the stones.
125 on page 217, and shuts itself in
and spins about itself a brownish parchment-like cocoon
of the form shown in the accompanying figure. Heli-
copsyche constructs a spirally coiled case that is

372

Aquatic Societies

strikingly like a snail shell, and fastens it down closely
in the shallow crevices of stones on exposed surfaces.

FIG. 221. The spirally coiled cases of the
caddis-worm, Helicopsyche.

A number of other caddis-worms build portable cases
of sand and stones. Those of Gcera (fig. 222) are
heavily ballasted by means of stones attached at the
sides with silk. These lie down flat against the bottom

and doubtless serve the
double purpose of de-
flecting the current and
preventing the case from
being washed away.

The tubes of the mid-
ges are here made of less
soft and flocculent ma-
terials than in still
waters. Tanytarsus
makes an especially
tough case of a pale
brownish color, like dried
grass. It is of tapering
form, and easily recog-
nized by the three stay
lines that run out from
the open forward end.
A small greenish yellow
larva with rather long

FIG. 222. Stone-ballasted cases of
caddis-worms of the genus Goera.

Limpet-shaped Shelters

373

antennas lives within, and protrudes its pliant length
in foraging on the algal herbage that grows about its
front door. And
there are many
other lesser
midges whose
larvae dwell in
silt-covered
tubes on rocks
in the rapids.
Often they oc-
cur so commonly
as to almost
cover the surface.

Shelters also limpet-shaped — It should be noted in
passing that this flattened form, which is characteristic
of so many members of lotic society, is characteristic
not only of the living animals but also of their shelters.
The tarpaulin-like web of the moth Elophila fulicalis
is flat, and the pupal shelter is quite limpet-
shaped. The case of Leptocerus ancylus is widely
cornucopia-shaped, its mouth fitted to the stone. The
coiled case of Helicopsyche is a very broad spiral, closely

FIG. 223. Larval cases of the midge, Tanytarsus,
attached to a stone in running water.

FIG. 224. The maxilla of a mayfly, Ameletus ludens,
showing diatom rake.

374

Aquatic Societies

attached in the hollows of stones and crevices of rock
ledges. The case of the caddis-worm, Ithytrichia, (fig.
162 on p. 262) is broadly depressed.

Thus the impress of environment is seen not only
in the form of a living animal but also in that of the
non-living shelter that it builds. In this there is a
parallel of form in the secreted shell on the back of the
snail, Ancylus, and manufactured shell on the back of
the caddis-worm, Helicopsyche. One would have to
search widely to find better examples of the effects of
environment in molding to a common form these
representatives of many groups of very diverse
structural types. Two of them, at least, were suffi-
ciently like lotic mollusca to have deceived their
original describers. Psephenus was first described as a
limpet and Helicopsyche as a snail.

Foraging habits- -The food of the herbivores in lotic
societies is algae. There are none of the higher plants

present, save a few
mosses of rather local
distribution . It is not
surprising therefore
that the food gather-
ing apparatus of these
forms should present
special adaptative pe-
culiarities. The
mouth-parts of may-
flies and of midges
show much develop-
ment of diatom rakes
and scrapers. For
scraping backward

FIG. 225. The sheltering tubes of
midge larvae. Photographed under
running water on the rocky bed of a
stream.

the labrum is often

used. In the net-spinning caddis-worms it is bordered
on either side by a stiff brush of bristles, and in midge

Foraging Habits

375

larvae there is developed both before and behind its
border a considerable array of combs and rakers. In
use the head is thrust forward, and these are dragged
backward across the surface that supports the growth
of diatoms and other algae.

The principal carnivores of the rapids are the nymphs
of stoneflies (see fig. 1 1 1 on p. 204) and a few small
vertebrates. Among the latter are the insect-eating
brook salamander Spelerpes, and a number of small
fishes, such as darters, dace and minnows.

CHAPTER VII

INLAND WATER CULTURE

WATER (CULT!

ARDLY any native
species found by the
white man in America
had done so much to
alter and improve its
environment as had the
American beaver. Cer-
tainly the red man had
done less. Thousands
of acres of fertile valley
land now tilled by Amer-
ican plowmen was
levelled up behind
beaver dams. These followed one another in close
succession in the valley of many a woodland stream.
The wash from the hills settled in their basins. As
they were filled, dams were built higher, and thus the
rich soil grew deeper.

The beaver was a builder of ponds. His only method
was by damming gentle streams. He cut down trees
with his great chisel-like teeth, trees often six, eight, or
ten inches in diameter. He cut off their boughs and

377

378

Inland Water Culture

drew them to the place where a dam was to be con-
structed. He piled them as a framework for a dam,
weighted them in position with stones, filled the inter-
stices with trash and leafage and covered the water
side over completely with mud, making it impervious.
And when the water had risen behind it he built him a
dome-shaped house on the edge of the pond thus
created, having passageways opening beneath the
water, and he plastered it over with mud. When
marsh plants grew about the edges of the lands he had
thus inundated, he cut channels through them for easy
passage to his favorite feeding grounds. His staple
food was the bark of aspens and birches that grew
thickly near at hand, but this he varied with succulent
shoots and tubers of aquatics. These nature planted
for him, as soon as he had prepared his water-garden.
This was aboriginal water culture.

•f

•

I'/:-: . i :

FIG. 226. An aboriginal water-garden. A beaver dam and pond. (From Morgan.)

CROPS

ERTILITY dwells at the
water side, where the
essential conditions for
g r o w t h — m o i s t u r e ,
warmth, air and light-
abound. There Nature's
crops are never failing.
They are abundant crops
compared with which the
herbage of the uplands
appear thin and scatter-
ing . If they are not our
crops, that is not Nature's
fault but our own. We
have given all our toil and care to the cultivation of the
products of the land, and have left the waters to pro-
duce what they might, often in the face of neglect and
injury.

Time was when the waters furnished to man the most
dependable part of his livelihood — fish and oysters and
edible roots and excellent furs. That was before the
days of agriculture. Primitive man, while gathering
his fruit and roots and grains from the wild, saw the
supply failing and planted a garden to increase his
sustenance. Had he by like means endeavored to
supplement his stores of water products, we might now
have had a water culture, comparable with agriculture.
A number of native water plants furnished food to
the red men in America. One of these, the wild rice

379

38o

Inland Water Culture

FIG. 227. A flower-cluster of wild rice, fertile
above, staminate below. Little brown syrphus
flies of the genus Platypeza cling to the stam-
inate blossoms.

(fig. 227), is ob-
tainable in our
own markets in
very limited
quantity and at
fancy prices : it
grows as a wild
plant still. The
Indian ate both
the nut-like seeds
and the stocks of
the wild lotus ;
also the tubers of
the arrowhead ,
the stocks of the
arrow- arum, the
enormous rhizo-
mes of the spat-
terdock, the suc-
culent shoots of
the cat- tail, and
other rather
coarse and watery
wild plant pro-
ducts, that we
esteem better
food for muskrats
than for men.
The starch-filled
tubers of the sago
pondweed (fig.
228) are choice
food for water-
fowl, and if ob-
tainable in suffi-
cient quantity
would probably

Water Crops

be prized by men, for when cooked they are both pleas-
ing in appearance and very palatable.

A number of rushes of different sorts were in aborigi-
nal times used for coarse weaving of mats, etc.; and
one of these, the narrow-leaved cat-tail, we have of late
begun to use in new ways; in paper making and in

FIG. 228. Tubers of the sago pondweed.
Potamogeton pectinatus.

cooperage. The initial cut on the preceding page shows
a field of cat-tail carefully cut and shocked for use in the
calking of barrels that are to hold watery liquids. The
leaves are placed singly between the staves of the
barrels, where they swell when wet, packing the joints
tightly.

It may be that none of these plants will ever be cul-
tivated. Some are abundant enough for present needs

382

Inland Water Culture

without it. Wild rice is but another cereal grain, tho
an excellent one. We already have garden roots in
great variety of sorts that we prize more highly than
we do these wild aquatics. The white water lily will
be cultivated in the future for its beautiful flowers
rather than for its edible tubers.

FIG. 229. The white water lily, Castalia odorata.

The animal products of the water are more important.
Aquatic molluscs, crustaceans, and vertebrates have
ever furnished staple foods. Tho fresh water molluscs
are no longer eaten, immense accumulations of their
shells along some of our inland waterways bear silent
testimony to the extent to which they were once con-
sumed by the aborigines. Their shells also served
other primeval uses, as cups and as scrapers. In our
own day a new and important use has been found for
them in the manufacture of pearl buttons and orna-

Fish

383

ments. They make the best of buttons, neat and dura-
ble and beautiful, a great improvement over the buttons
of wood and metal formerly in use. The annual
product of pearl buttons from this source is now worth
many millions of dollars. It is all derived from wild

FIG. 230. Valve of a mussel shell, with "blanks" cut from it,
in process of manufacture into pearl buttons.

mussels; the method in use is exploitation, not hus-
bandry.

Fish- -The great staple food product of the water is
fish. In our day frogs are used but locally and fresh
water crustaceans and other animals, hardly at all;
but fishes are used everywhere. They have been a
staple food from the beginning of human history, and
probably will be to the end. Hence it is that inland

384 Inland Water Culture

water culture means to a large extent the raising of
fishes.

Fish culture* in America is in a very backward state
as compared with animal husbandry in other lines.
This is manifest in many ways; among them, the
following :

1. There is lack of improved cultural varieties.
Our fishes are wild fishes. Save for a few races of gold
fishes — all fancier's fishes — and some not very desirable
varieties of carp, hardly any improvements have as
yet been made by selection and careful breeding.

2. There is lack of knowledge of the best kinds of
forage for fishes and of how it may be provided for their
use. This is half of the problem of raising any animal.

3. There is lack of any practical system of manage-
ment, that provides for the breeding and feeding and
rearing of stock, generation after generation, under
control.

In what, then, does the fish culture of the present
consist? Mainly in this one thing, the care of the
young. This includes the gathering and hatching of
fish eggs and the rearing of the young fishes thro their
earlier stages on artificial food in hatcheries. By this
means the enormous losses that occur under natural
conditions in early life are avoided, and vast numbers
of fry and fingerlings are grown to a size suitable for
planting in natural waters. Thus far the methods are
well worked out. Thus far our fish culture is bril-
liantly successful. But this is really only the first step.
How these little fishes when turned loose in pond and
stream shall find for themselves the means of a liveli-
hood is the unsolved part of the problem. Planted
here they seem to thrive; there, they fail. Every

*The substance of the following pages covering this subject was published
by the senior author in the Indianapolis News in 1909, and again in the Farmers
Magazine in 1912.

Fish Culture 385

planting in a new place is more or less an experiment.
Sheep culture would be in a state quite comparable
with the fish culture of to-day, if after rearing lambs
on the bottle they were turned loose in an unexplored
forest to shift for themselves.

The hatcheries are raising fry and not fishes. This is,
of course, what they were commissioned to do, the
underlying idea being merely that of putting back into
the lakes and streams a copious supply of young fishes
to occupy the place of the adult fishes taken out. But
experience has shown that the mere planting of fry
soon reaches its effective limit, after which the planting
of more fry is sheer waste. The conditions in the wild
are not such as yield much advantage from this intensive
propagation of the voting. Oftentimes the fry planted
in the trout streams about Ithaca may be found shortly
afterward in the stomachs of the few adult trout that
live in the same streams. Feeding fishes on the young
of their own kind is not good husbandry.

The planting of fry and of fingerlings is effective
where conditions permit of their growth. The removal
of enemies is a supplemental measure of great value
where practicable. The care of natural feeding grounds
to prevent their destruction is very important, but
usually impossible, for want of enlightened public
opinion. Protecting of breeding fishes when on their
spawning grounds — the time when they are most
easily discovered and destroyed — is also very import-
ant. And the bringing back into habitable places of
young fishes stranded in the side pools of bottomland
streams, where they would perish with the evaporation
of the water, is rescue work of a good sort. All these
things are done in the interests of public fishing at the
present day. They are such measures as are taken to
preserve wild game in a forest or livestock on an open
range. They have to do rather with hunting than with
husbandry.

386 Inland Water Culture

The day is coming — is already at hand — when he
who wants fishes fresh from the water will have to
raise them. Public waters are "fished-out." In spite
of closed seasons, and frequent plantings of hatchery-
reared fry, they continue to be "fished-out." With the
growth of our population they are going to be always
' ' fished-out ;" and there is no hope for the future of any
fishing that shall be worth while except in waters that
are privately controlled.

This does not mean that there will be no fishing in
the future. It only means that fish raising is going
the way wild pig raising has gone.

When game began to fail — venison, wild turkeys, etc.,
the pioneer began to raise pigs. At first he gave them
little attention, except at killing time, and furnished
them no food. He raised them about as we raise
fishes now. He turned them loose in the woods to
forage for themselves as we now plant fish fry in the
streams. They ranged the whole area where their
food grew.

Nowadays, thousands of hogs are raised where one
was raised then, but they do not run the range; they
are kept in small lots, and the broad areas are devoted
to raising forage for them. The present day method
of obtaining our meat supply is very unromantic as
compared with chasing a razorback hog with a shot-
gun through the woods at the end of the acorn season,
but it is the inevitable way of progress in animal hus-
bandry.

Raising animals and their forage together is not good
husbandry. It is exceedingly wasteful and unproduc-
tive; yet that is the way we still raise fish in America.
We ought to be doing better than this. It is idle to
plant more fish in the water until we can supply more
stuff for them to eat. And we cannot expect more
forage to grow unless we provide suitable conditions.

The Forage Problem 387

When we raise other stock-feed we find a few perfectly
definite things to be done:

1 . We clear a field and prepare it.

2. We fence it to keep out enemies and undesirable
competitors.

3. We plant it with selected seed; and after a
period of growth,

4. We use the crop at the time of its maximum
value.

All these things we shall have to do if we ever have
a real fish culture. The first two of these things are
usually cared for in the construction of fish-ponds ; the
other two are generally neglected.

The forage problem is less simple than is the raising
of pigs on clover, for at least two reasons:

1. Plant foods are not eaten directly by the more
valuable fishes, and often there are a number of turns-
over of the food stuffs before the fishes are reached.
For example, diatoms and other synthetic planet on
organisms are eaten by water-fleas and midge larvae,
that are in turn eaten by little fishes, that are eaten by
big fishes. There must be at least two turns-over —
one kind each of plant and animal forage — since the
desirable food-fishes are carnivorous.

2. There may be one or more changes of diet during
development. Thus the pike when newly hatched eats
such water-fleas as Simocephalus, (see fig. 92 on p. 186)
picking them one by one with automatic regularly-
timed snappings of its jaws. When grown a little
larger it eats midge larvae, mayfly nymphs and other
small insects. Still later, it eats large insects and
mixes small fishes in its diet; and as it attains full
stature it restricts its diet to frogs and larger fishes.
When grown it takes hardly anything smaller than a
golden shiner.

388 Inland Water Culture

Studies of the food of the common sunfish, Eupomotis
gibbosus,\yy the senior author ('08) have shown that in
Old Forge Pond, when one inch in length the food is
predominantly entomostraca and very small midge
larvae. When two inches in length, it is entomostraca
and midge larvae of larger size, together with small may-
fly nymphs (Caenis) and minute snails. When three
inches in length, it is grown midge larvae, mayfly nymphs
and caddis- worms. At this size apparently the diet of

FIG. 231. The common sunfish. Eupomotis gibbosus.
(Photo by George C. Embody)

entomostraca and small midge larvae is outgo wn, and
the fishes are seeking bigger game.

At three inches in length, this fish is itself the
favorite food of adult bullheads.

Except ing for a few fishes that range the open waters,
such as white-fish and lake herring, and that continue
to feed largely on plancton, there is at least one neces-
sary shift of diet accompanying growth; that from
plancton to the food of the adult. In an earlier chapter
(see p. 235) we have briefly indicated the principal
changes of diet then occurring.

Staple Foods

389

The food relations of aquatic organisms are exceed-
ingly complex. They change with age and season and
situation. The eater and the thing eaten often
exchange roles. Yet there are some fairly constant
food dependencies between the major groups of
organisms. These have been set forth by that veteran
student of the forage problem, Prof. S. A. Forbes, in the
table copied herewith (fig. 233), and this table indi-
cates (what detailed food studies at large abundantly
confirm) that fishes eat almost every living thing that
the water offers.

FIG. 232. The nymph of the dragonfly, Anax
junius, devouring a small sunfish.

The young of all fishes eat plancton. This sounds
like one point of general agreement, until we reflect
on the variety of organisms of which plancton is com-
posed. Which of these are best for use in fish culture
we scarcely know at all. Fortunately, they are of
nearly universal distribution in shoal fresh waters,
where the young of fishes are found.

Staple foods — While a list of all foods, eaten by all
fishes would include practically every thing that is
found in the water, yet when careful food studies are
made there are a number of organisms so constantly
recurring that they stand out as of prime importance.
A few aquatic herbivores are found as commonly and

390

Inland Water Culture

as regularly in the stomachs of wild food fishes, as grass
would be found in the stomachs of wild cattle. And
just as stock feeding has made progress with the isola-
tion and study and increase of the grasses, so fish cul-
ture would be advanced by study and cultivation of
the staples of wild fish food.

PRINCIPAL

FOOD RELATIONS

or
AQUATIC ORGANISMS
(ILLINOIS)

BACTE: fliA

ALGAE

HIGHER PLANTS

PROTOZOA

5

c
<t

1

WORMS

CRAWFISHES

IN sec TS

MOLLUSK.S

FISHES

1

1

TURTLE s

SfflfENTS

<a

1

TERRESTRIAL WAS res

X

X

X

X

X

X

X

X

X

X

X

X

BACTCRIA

X

X

X

X

X

X

X

ALGAL

X

X

X

X

X

X

X

X

Hi CHER PLANTS

X

X

X

X

X

PROTOZOA

X

X

X

X

X

X

ROTIFERS

X

X

X

X

ENTOMOSTRACA

X

X

X

X

X

X

X

WORMS

X

X

X

X

CftA w FISHES

X

X

X

X

X

/NSfCTt

X

X

X

X

X

X

X

MOLLUSCS

X

X

X

X

X

F/SH e s

X

X

X

X

X

X

X

X

X

X

FROGS

X

X

X

X

X

X

TURTLES

X

X

SERPENTS

X

BIROS

X

X

FIG. 233. Forbes' (14) table of food (at left) and feeding
organisms (above).

Our best fishes are carnivores, and the animals they
eat are chiefly a few hardy, prolific, and widely dis-
tributed herbivores, such as water-fleas, scuds, midge
larvae, mayfly nymphs and other fishes. These feed,
of course, on plants; but we hardly know as yet what
plants are of most value to them. They thrive where
herbage abounds ; and yet we know that abundance of

Water- Fleas

herbage may not necessarily mean good crops; for
weeds may be much more conspicuous in a pasture than
the close-cropped grasses that yield the forage there.
Certain species of pondweeds have been shown by
Miss Moore ('15) to be often used as green food, and
Birge (' 1 1 ) has given many notes on the food preferences
of herbivorous plancton Crustacea.

The above mentioned staples invite much attention
but we shall have space for noticing but a few represen-
tatives of the groups to which they severally belong.

f tract

x

Abdominal processes

Abdominal sftoe

Brood- chamber
Heart

A bdominal claws

Posf- abdomen

Leys '

FIG. 234. Daphne (after Dodds).

Water- fleas — As a typical representative of this great
group of herbivores, we may speak of Daphne (fig. 234).
Its manner of life and its enormous reproductive
capacity have already been briefly mentioned (pp. 186-7
and 306). It is a very valuable animal in water culture
on account of its ability to turn the great growths of
colonial diatoms and algas into excellent food for fishes.
Little is known, as yet, unfortunately, about the condi-
tions that make for its growth. Plancton studies of

3Q2 Inland Water Culture

water-fleas have consisted in the main of the counting
of individuals in random catches; and, as Haeckel ('90)
long ago pointed out, this has about as much economic
value as the counting of straws would have in an oat
field.

The extraordinary growths of certain plancton algae
(Anabsena, Aphanizomenon, etc.) that often give
trouble in water-supply reservoirs, might be made into
fish food through the agency of daphnias, if we only
had learned how to manage our water crops.

FIG. 235. Gammarus fasciatus (after Paulmier).

Water-fleas are of very great value as food for young
fishes, they form also a considerable part of the food
of such larger fishes as are equipped with gill strainers
for gathering them out of the water. They are, of
course, largely absent from the water during the winter
season. Their value as forage organisms lies in their
good quality and their extraordinary reproductive
capacity.

The scuds- -This group of herbivores is typified by
Gammarus (fig. 235) a hardy, wide-ranging habitant of
the water weeds. It swims well, yet prefers to occupy
the sheltering crevices of dense leafage. It can leap

The Scuds 393

and dodge like a rabbit. It feeds on a great variety of
both living and dead herbage. It is itself a favorite
food for most fishes.*

The scuds are easily managed in pond culture. They
are not remarkably prolific. As already mentioned on
page 190, the possible progency of a single pair in one
year is somewhat less than 25,000. But they carry
their young in a pectoral brood pouch until well equipped
for life.

The chief merits of the scuds as forage organisms
(in addition to desirability as food) lie in their hardi-
ness, their ability to find a living and to take care of
their own young until well started in life, their constant
succession of overlapping broods thro the season and
their permanent residence in the water.

There are other herbivorous crustaceans of some-
what similar habits, among which the fresh- water
prawn, Palaemonetes, is probably useful as fish forage.

Midge larvcE — Larvae of midges of the genus Chirono-
mus popularly known as "blood-worms" (fig. 236) are

FIG. 236. A "blood-worm."

of prime importance as fish food. Small ones are eaten
almost as universally as are plancton entomostraca,
and the large ones continue to be eaten whenever
obtainable by fishes as large as adult trout and white-

*Its value has long been recognized by fishermen; on account of its abund-
ance in an excellent trout stream at Caledonia, N. Y., it has been locally known
as the "Caledonia shrimp."

394 Inland Water Culture

fish. In a most extensive examination of the contents
of fish stomachs Forbes ('88) found them "of remarkable
importance, making in fact nearly one- tenth of the
food of all the fishes studied." Ferguson fed some red-
bellied minnows (Chrosomus erythrogaster) for 22 days
all the midge larvae (Chronomus viridicollis) they would
eat and nothing else. The grown minnows ate on an
average twenty-five blood-worms per day; the half-
grown ones, eleven. The senior author ('03) found that
25 brook trout taken at random from one of the best
natural ponds of the New York State Fish and Game
Commission at Saranac Inn, N. Y., had in their
stomachs more than 100 blood-worms each.

Midge larvae are among the most ubiquitous of
freshwater organisms. They feed mainly upon dia-
toms, and other simple organisms found in water or
growing sessile on or round about their homes; the
larger ones eat also the disintegrating tissues of the
higher plants. They dwell among all sorts of aquatic
plants, spreading their thin filmy tubes in every crevice
or along the stems. Little is seen of them there on
casual observation. They are like the rodents of the
fields, hidden in their runways. But one cannot place
a handful of any water weed in a dish of water without
soon seeing some dislodged midge larvae swimming
about the edges with characteristic figure-of-8-shaped
loopings of the body.

They dwell on the bottom (see fig. 134 on p. 226).
Indeed, as already noted, they may dwell far out on the
bottom under the deep water of great lakes. Here in
deep darkness and heavy pressure they dwell in enor-
mous numbers feeding upon the rich spoils of the plancton
rained down on them by gravity from above. They
often fill the soft bed with their silt- covered flocculent
tubes.

Midge Larvae 395

These tubes, like the ones on the stems, open to the
surface at both ends. The larva, within, holding on to
the silken lining of the walls with its claws, swings its
body in vigorous undulations, driving a current of
water thro the tube. This serves for respiration. It
also serves to drive diatoms and other food organisms
into net -like barriers spun across the exit; these bar-
riers are repaired or renewed after every catch. Food
is thus carried into the shelter of the case. But food
is also gathered from exposed surfaces whenever it can
be reached from open ends of the tube. It is gathered
by scraping the sessile diatoms and algae from stems.
For such work the mouth of the larva is equipped with
elaborate rakes and scrapers.

The larva of Chironomus is relatively simple. It
appears much less complex in organization than are
many of its insect competitors. It has a cylindric
worm-like pale and naked body with a bifid proleg
underneath at the front and a pair of prolegs behind,
caudal tufts of bristles, and a few simple gills. The
prolegs are armed with hooks and on them it creeps
somewhat like a looping caterpillar. From its mouth
it spins the fluid silk, and spreads it ere it hardens with
the front proleg. All in all, it is a shy and defenseless
and secretive creature, without any special gift of
locomotion.

This apparent weakling has been able to possess
itself of the entire littoral region of the earth, perhaps
by reason of the following characteristics :

1. Ability to live on foodstuffs that have a very
general distribution.

2. Ability to build its own shelter.

3. Consequent adaptability to variety of conditions.

4. Great reproductive capacity.

5. Brief life cycle.

396

Inland Water Culture

Chironomus lays several hundred eggs, and in the
warm season a generation may completely develop in
five or six weeks; so the very considerable increase of
one brood may be rapidly repeated in geometric ratio.

The limitations to its use as a forage organism in fish
ponds lie in its complicated life history. It quits the
water at the end of the pupal stage. It flies away,
mates in the air, and returns to the water to lay its eggs.
During its aerial life it is not easily managed.

Mayfly nymphs constitute one of the most important
groups of aquatic herbivores. We single out Callibastis
for illustration of another staple fish food. It is an
active nymph that swims from place to place by means

TV- - T J^y ,. V"T^- r*i-_ r-TTTt,Tl) j / • ' -. I . J \ i

FIG. 237. The nymph of Callibsetis: Drawing by Anna H. Morgan.

(From Annals Ent. Soc. America)

CallibcBtis 397

of quick strokes of its tail and gills, and that clambers
freely about over shore vegetation. It is an artful
dodger; and it is protectively colored. It feeds on a
great variety of vegetable substances living and dead,
and hence finds abundant food in every weedy pond.
It is eaten by every carnivore in the pond that can
catch it ; and doubtless it has many enemies that exceed
it in swiftness and many others that lie in ambush and
capture it by stealth. Hence, tho nearly always
present, it rarely appears very abundantly in old
ponds.

The life cycle of Callibaetis is run in less than six
weeks. A single female may lay 1000 eggs. If all
these were to develop and reproduce, the increase from
a single pair during one summer season would be some-
thing like this:

ist brood 1,000 (half females)

2d brood 500,000.

3d brood 250,000,000.

4th brood 125,000,000,000.

These alluring possibilities of increase in an organism
that is choice fish food once led the senior author into a
series of experiments that extended through two years
and that met with uniform failure because the breeding
of the mayflies could not be controlled. The rearing
was easily managed but even with the largest measure
of freedom that could be provided, the adults would
not mate and lay eggs in captivity. The problem of
their successful artificial propagation is still unsolved.
However, there has never been a new pond opened at
the Cornell University Biological field station, that has
not received the eggs of wild females of Callibsetis, and
that has not raised a good crop of the nymphs ere
their slower-breeding carnivorous enemies developed.

398 Inland Water Culture

Mayflies, like Callibaetis and the little Casnis, that
have a number of broods each season with overlap of
generations, are suited for use in forage propagation
because at all times of the year nymphs of good size are
present in the water. On the other hand, such forms
as Blasturus cupidus, which flies in May, and Siphlurus
alternatus which flies in June, are absent from the water
at the close of their breeding season or are represented
there only by eggs and very minute nymphs.

Best known of the mayflies that fishes eat are the
nymphs of the big burrowing Hexagenias from lake
and river beds. Food examinations have abundantly
shown their importance. However, they develop
slowly, requiring at least two years to reach maturity.

The Hexagenia nymphs are natural associates of
bloodworms on the lake bottom. They, and the blood-
worms with them, and the entomostraca swimming
above them are the mainstay and dependence of the
lake's fish population.

Other herbivorous insects of promise as forage organ-
isms are caddis- worms and aquatic caterpillars. Other
invertebrates are a number of pond snails. But the
animals above discussed we regard as most important.

Forage fishes— -The largest single item in the bill-of-
fare of fishes generally is other smaller fishes. Herbi-

FIG. 238. The golden shiner.
(Photo by George C. Embody)

The Way of Economic Progress 399

vorous fishes, non- competitors for food, may therefore
be used to furnish a principal crop of animal forage.
For this use carp are objectionable because they grow
too fast and soon become too large to be swallowed by
the other fishes. They eat the eggs of bass, and root
up the bottom and tend to exterminate their own
vegetable forage. Minnows are also objectionable
because they eat the eggs of other fishes. But very
valuable for such use are the golden shiner, (fig. 238)
and the gizzard shad, (Dorosoma cepedianum), of our
great rivers. Even the goldfish is an excellent agent
for turning masses of blanket algae and other soft fresh
vegetable foods into excellent forage for larger fishes.

The way of economic progress— -The future of fish
culture lies in further scientific studies to be made
along the lines that have proven of value in the
raising of land animals. More knowledge is what is
needed :

1. Intimate detailed knowledge of the fishes them-
selves is needed; knowledge of their natural history,
their requirements of food and of protection for
their young; their enemies, internal and external;
their natural races and possibilities of improvement by
breeding. Only such knowledge can furnish a
basis for developing methods of control.

2. Equally detailed knowledge is needed of the
economic species that furnish forage or that menace
the welfare of the cultivated species; knowledge of all
the more important ones, from the forage fishes, crusta-
ceans, insects, snails, etc., even down to the diatoms.
The product must be followed to its principal sources
and the cultural relations that all these organisms bear
to each other must be better understood. The enemies
of every stage of fish life must be studied (fig. 239).

4oo

Inland Water Culture

3. More knowledge
is needed of the water
bodies themselves;
knowledge of their
physical, chemical and
hydrographic c o n d i -
tions, their purity, con-
tamination, and all
other conditions that
affect the welfare, that
promote or hinder the
normal growth and ac-
tivities of the useful
organisms contained in
them. We must know
these things in order
to know how to make
and keep the waters productive.

Knowledge is being accumulated in all these lines
in a slow and desultory way, thro the voluntary
activity of many diverse and widely scattered agencies.
Fish culture has not yet had the benefit of that
efficient agency of economic progress that has brought
such rapid improvement in animal husbandry — the
experiment station. A fish cultural experiment station
is what is now urgently needed : an institution equipped
for water culture, and charged with the duty of carrying
out a well planned line of experiments bearing on its
economic problems. This is needed to supplement the
hatcheries and to bring their work to fruition.

FIG. 239. Eggs of the pike, Esox
lucius, overgrown with two species of
fungus.

WATER CULTURE AND
IMPROVEMENT

HE three chief interests
of the public in water
culture lie (i) in mak-
ing the waters produc-
tive; (2) in keeping the
waters clean and (3) in
preserving the beauty
of the waterside. Hap-
pily, these are con-
cordant, and not con-
flicting interests.
Another interest of everybody is in pure water to
drink. For city-dwellers, public water supplies must
be kept uncontaminated — a matter of ever increasing
difficulty as our population grows. This vast subject
falls without our present scope: its literature may be
found by following up a few references (Whipple, et. a/.)
given in the bibliography at the close of this volume.
There are two very large reclamation enterprises,
with which water culture should have much to do in the
future :

1. The reclamation of waste wet lands, and

2. The utilization of water reservoirs.

A few words maybe said here concerning each of these.

401

4O2 Inland Water Culture

AYHAT SHALL BE DONE WITH THE MARSHES?

There are millions of acres of waste wet lands in
America, that are producing little or nothing of value.
That this land will yet be made to contribute much
more largely to human sustenance, there can be no
doubt: for,

1 . It is the richest of all the land, in foodstuffs that
make for soil fertility. It contains organic remains
accumulated for ages, together with the wash from
surrounding slopes.

2. It is generally the best located of all the land
with respect to transportation facilities. Inland
marshes almost everywhere are traversed by railways,
their levels having invited the attention of the route-
locating engineer; many marshes border on navigable
waterways.

3. It is the last of the land available for occupation,
and with our population quadrupling every century,
the pressure for room is becoming ever more intense.

While it is inevitable that most of this land will yet
be used for production of human food, it is by no means
certain how this may best be done. Drainage is the
one method hitherto tried, but drainage has its serious
limitations :

1. Much of the wet land cannot be profitably
drained.

2. Its value as a water reservoir is largely destroyed
by drainage.

There is another plan for making marshes productive
that has not yet been tried on any adequate scale — a
plan that involves water culture as well as agriculture.
The marshes — now neither wet nor dry — cannot be
used as they are; but if by a shifting of some of their
topsoil they be made in part into permanently dry,
and in part into deeper reservoirs of water, they might

The Wastage of Reservoir Sites 403

then be cultivated in their entirety. The dry part
would be available for ordinary agricultural use and
crops can be grown by methods already well worked
out. The permanent water could be made to produce
fish and fish forage and other water crops. The
advantages of this plan over drainage would appear
to be the following:

1. Increased productiveness.

2. Permanent water storage.

3. Diversifying of crops: it wrould not be merely
adding more of crops already extensively cultivated.

4. Diversifying the industries of the people.

5. Completer utilization of the wet areas.

THE WASTAGE OF RESERVOIR SITES

There is another service that water culture may
render to great public works. It may make water
reservoirs productive. The various measures now
being widely considered for the development of our
water resources should be co-operative rather than con-
flicting. The making of reservoirs for holding the
surplus rainfall near the headwaters of streams, allow-
ing it to flow as needed, should result in three distinct
and permanent civic benefits:

1 . Permanent water power.

2. Continuous navigation.

3. Increased production of food.

One of the things that has stood in the way of the
development of reservoirs has been the necessity for
condemnation of valuable agricultural lands needed
for the reservoir site. Such lands when covered with
water are, of course, removed from agricultural use.
But they might yet be used for water culture, and
indeed the value of the resulting crops might thereby
be increased.

404 Inland Water Culture

Some special development of the water bed would,
of course, be needed to fit them for an intensive water
culture. The one great open basin of water, now full
and now reduced, that is the usual thing in reservoirs,
would hardly suffice. But with no extraordinary
increase of cost the greater part of the bottom, espec-
ially in shoal water, might be divided into fish ponds,
so constructed as to be under control. By deepening
these considerably and using the excavated earth for
building strips of dry land between them, the holding
capacity of the reservoir might be increased. It would
be increased by just so much as the volume of earth
taken from below and placed above the high water
level. Then as much water as under the present plan
could be drawn off for power or navigation, and the
residue in the pond bottom would suffice for main-
tenance of the fishes therein.

On this plan, in a reservoir of 100 acres having 90
acres of shoal water on which fish ponds could be
developed, 50 acres could be permanently devoted to
fish raising, and at least half or much more to agricul-
tural crops, without interfering with its efficiency for
water storage and regulation of stream-flow. This
would be much better than having it all lie fallow to the
end of time. It would transform a water waste into a
water garden. Incidentally, it would cure also the
unsightliness of a vast area of exposed and reeking mud
during the season of low water.

The beauty of the shore-Hue — Another public interest
with which water culture must ever be identified is that
of preserving the beauty of the landscape. As nature
has given of her bounty to the waterside, so also she has
lavished her beauty there.

What flowers adorn the shore-line! The fragrant
water lily, the stately lotus, the queenly iris, the bril-

The Beaut v of the Shore Li tie

405

liant hibiscus, the soft blue pickerel -weed, the sweet
forget-me-not ! What foliage in pondweed and water

FIG. 240. The common wild forget-me-not.

shamrock, in arrowhead and arrow-arum, in water-
shield and spatterdock! What exquisite submerged
meadows the pondweeds, bladderworts and the mil-
foils make! How inviting are the shores where these

406 Inland Water Culture

abound, how unattractive, those from which these have
been removed.

The landscape belongs to all. Its condition affects
the public weal. It is good to dwell in a place where
the environment breeds contentment ; where peace and
plenty and satisfaction grow out of the right use of
nature's resources; where wise measures are taken to
preserve the bounteous gifts of nature and to leave them
unimpaired for the use and benefit of coming genera-
tions.

Much of the scenic beauty of every land lies in its
shore lines; and it should be a part of public policy to
keep unimpaired as far as possible the attractiveness of
all public waters. Streams differ far less from one
another in their own intrinsic characters than in the
way they have been used by the hand of man. They
differ less by topography and latitude ; far more by the
cleanness of their waters, by the trees that crowrn their
headlands, and by the flower-decked water-meadows
that fill their bays and shoals. The famous distant
lakes and streams that attract so many people far from
home every summer are not more beautiful or restful
than many homeland waters once were, or might
again be, were but a little public care exercised to keep
their waters clean and the beautv of their shores and

mS

bordering vegetation unspoiled.

Private water culture — Great as are the benefits to be
hoped for in public works, those to be derived from the
application of a rational water culture to private
grounds are probably in the aggregate far greater. On
thousands of farms there are waterside waste lands,
lying bare and abused, that might be reclaimed to use-
fulness and beauty through intelligent water culture.

The making of a pond on the home farm is good work
for the slack season; and once properly constructed it

Private Water Culture

407

is permanent, and will with a minimum of attention
yield returns out of all proportion to its cost. It will
yield fresh fish for the table. It will yield healthful
sports for the boys and girls who should be kept at
home; angling, and swimming in the summer and
skating in the winter. It will yield beauty; the beauty
of a mirroring surface, reflecting trees and hills and

FIG. 241. A beautiful cover for a mud bank. The water-shamrock, Marsilea,
in front, then arrowheads, then sedges.

sky and passing cloud: the beauty of the aquatics
planted on the shore line: the beauty of the water
animals, of flashing dragonfly and gyrating beetles, and
leaping fishes. It will add to the joy of living.

The accompanying diagram is intended as a sugges-
tion for the development of a tract of upland waste wet
land into a water garden. Its noteworthy features are
found in the provision for growing forage under con-
trol, and, in so far as need be, apart from the animals

408

Inland Water Culture

B

f o /? A c £~ P 0 ND\ r\

FIG. 242. Diagram illustrating the conditions for fish production on an 80
acre tract of wet upland, traversed by a trout stream. A , in a wild state.
B, equipped for intensive fish raising.

Area devoted to fish, in A, one acre more or less; in B, one acre of inclosed ponds.

Devoted to fish forage, in A the same acre of open stream; in B, forty acres of ponds,

planted and under control.
Devoted to land crops, in A none, — it is all too wet and sour; in B, all the made land

between the ponds.

that are to eat it. This is a suggestion for the applica-
tion of the principles discussed in the earlier pages of
this chapter. There is, of course, nothing original
about it: it is what has made modern animal hus-
bandry possible. It has not been applied to fish cul-
ture, however, and we are not able to give any figures of
production because it has not been tried out in a practi-
cal way even on such a scale as is here shown.

Swamp Reservations — Now, having presented a plan
for complete utilization of the marshes, we hasten to
add that we believe it would be a great misfortune if

Swamp Reservations

409

all the marshes were to be "improved." Some of them
are already serving their best use as refuges and breed-
ing grounds of wild water fowl. In all of them there is
a whole wonderful fauna and flora that we could ill
afford to lose. That these would be lost under an

*'

-

^at

-^

&-• ' "'%

' *-v.rf
-st.
«»-7>

ft*J -- | ;

--9 *Srfp ^>"

-^

Z3% ^

FIG. 243. Wall painting
from an ancient Egyptian
tomb showing the plan of a
house with a water-garden.
(After Brinton).

intensive water culture is highly probable (see fig. 244),
for our own cultivated crops are in the main successful
about in proportion as we eliminate the wild to make
room for them.

Since the wet land is almost the last of the unoccupied
land remaining near to the centers of human habitation,
and since it is the dwelling place of the largest remnant
of native wild life, we should not be taking measures for

4io

Inland Water Culture

FIG. 244. A pond at Lake Forest, 111., containing islands covered bybutton-

For effects of grazing, corn-

making it over to cultural uses without at the same time
providing reservations where the wild species may be
preserved for future generations. Each of these wild
species is the end product of the evolution of the ages.
When once lost it is gone forever: it can never be
restored. We are not wise enough, nor farsighted
enough to know whether the qualities lost with it would
ever be of use to our posterity. We are now only at
the beginning of knowledge of our plant and animal
resources.

But quite apart from any possible economic values
that these creatures of the wild may possess, they have
other values for us that we should not ignore. Ere

Swamp Reservations

411

bush and divided by a pasture fence,
pare the extreme ends.

The left hand end is closely pastured.

their destruction is complete, public reservations
should be made to preserve the best located of the
marshes for educational uses. As we have need of
fields and stock-pens because we must be fed, so also
we have need of this wild life because we must be
educated. It was with our forefathers in their early
struggles to establish themselves in the New World:
it conditioned their activities, lending them succor or
making them trouble. In its absence it will be
harder to comprehend their work. The youth of the
future has a right to know what the native life of his
native land was like. It will help to educate
him.

412 Inland Water Culture

Exploitation is reaping where one has not sown.
Mere exploitation is but robbing the earth of her
treasures. Usually it enriches only the robber, and him
but indifferently. Getting something for nothing usually
does not pay. It tends to rob posterity.

Exploitation is the method of a bygone barbarous
age — an age when men, emerging from savagery,
acquire dominion over earth's creatures ere attaining
to a sense of responsibility for their welfare.

Conservation is the method of the future. It means
greater dominion and completer use, but it also means
restraint and regard for the needs of future generations.
We are urging that in the use of our aquatic resources,
the wasteful methods of exploitation be abandoned;
and in two directions:

1. We urge that water areas, adequate to our
future needs for study and experiment, be set apart
as reservations and forever kept free from the
depredations of the exploiter, and of the engineer.

2. We urge that in those areas which are to be made
to contribute to human sustenance, the wasteful,
destructive and irresponsible practices of the hunter be
abandoned for the more fruitful and fore -looking
methods of the husbandman.

BIBLIOGRAPHY

(.B) at end of a citation indicates a comprehensive bibliography.

Adams, Chas. C., and others. 1909. An ecological survey of Isle Royale,

Lake .Superior, pp. 468. Rept. Biol. Surv. Mich. (B)
Adams, Chas. C. 1913. Guide to the study of animal ecology. New York.

pp. 183. (B)
Aldrich, J. M. 1912. The biology of some western species of the Dipterous

genus Ephydra. Jour. N. Y. Ent. Soc. 20:77-99. 3 pis.
Aldrich, J. M. 1913. Collecting notes for the Great Basin and adjoining

territory. (Dipt.) Ent. News. 24:214-221. (B)
Alexander," C. P. and Lloyd, J. T. 1914. The biology of the N. A. craneflies

(Tipulidae, Diptera) I. The genus Eriocera Macquart. Pomona Jour, of

Entomology and Zoology. 6:12-34. 3 pis.
Alexander, C. P. 1914. Biology of N. A. craneflies. (Tipulidae, Diptera).

II. Liogma nodicornis Osten Sacken. Ibid. 6:105-118.

1915. III. The genus Ula Haliday. Ibid. 7:1-8.

1915. IV. The tribe Hexatomini. Ibid. 7:142-158.
Allen, A. A. 1914. The red-winged blackbird: a study in the ecology of a

cat-tail marsh. Proc. Linnaean Soc. New York. 43-128. 22 pis. (B)
Allen, T. F. 1888-94. The Characeas of America. New York.
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Much additional limnological work has appeared in the Transactions of the
American Microscopical Society; Transactions of the Wisconsin Academy
Sciences; American Naturalist; Botanical Gazette; Bulletin Illinois State
Laboratory of Natural History; Annales de Biologie Lacustre; annales de
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Zoologisches Jahrbucher, and other current biological journals.

The seven general limnological works that we regard as most useful arc: —
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Eyferth, 1909; Lampert, 1910, and Steuer, 1910.

~^Mr *»-<&

LIST OF INITIALS AND TAIL-PIECES

Page 24 Primrose Falls, Fall Creek. Cornell University Campus.

Page 25 Coy's Glen near Ithaca : upper falls.

Page 59 Lake Temagami, Ontario, Canada.

Page 76 A "carry" between lakes.

Page 77 Buttermilk Creek near Ithaca.

Page 89 Pond in the Montezuma Marshes, Central New York.

Page 99 Six Mile Creek near Ithaca.

Page 100 A spray of Buttonbush.

Page 158 Water Shamrock and Water Spider.

Page 242 Pool at foot of Primrose Falls, Fall Creek.

Page 281 Maligne Lake, British Columbia. (Photo by J. C. Bradley.)

Page 282 Coy's Glen at the mouth.

Page 293 Gorge of Six Mil Cereek near Ithaca.

Page 314 Williams Brook, near the Cornell U. Biol. Field Station.

Page 315 The Staircase Falls, Coy's Glen.

Page 375 Sunfish swimming. Photo hy Dr. R. W. Shufeldt. From
the Nature-Study Review.

Page 377 Duck Creek, near Cincinnati, Ohio.

Page 379 Shocked Cat-tail Flags on the Montezuma Marsh.

Page 401 Lowermost fall of Buttermilk Creek near Ithaca.

420

ERRATA

PAGE

19 line 4, for Connecticut read New Jersey.

33 line 2, for effect read affect : line 4, for procession read precession .

97 last line, for club rush read spike rush.

103 at end after Ceratium add, (figure reversed in copying).

127 line 4, for form read forms.

133 head line, for Tetranspora read Blue-green Algae.

177 line 14, for dessicated read desiccated.

188 line 12, for Relicit read Relict.

201 heading, for Lymph read Nymph.

226 line 12, for p. 280 read p. 279.

230 line 1, for p. 359 read p. 360.

245 line 18, for keep it long afloat read insure that it will float.

257 line 31, for fig. 134 on p. 226 read 6g. 223 on p. 373.

259 line 27, for Siphlurus read Siphloniirus.

268 line 5, for season read period.

271 line 18, for Hibernaculea read Hibernacula.

309 line 28, for fifty read twenty, line 29, for 50 and 100 read 30
and 40.

342 in legend to fig. 201 for tigrinum read punctatum.

343 line 1, for eaves read leaves.

398 line 6, for Siphlurus read Siphlonurus.

420 add in proper order this line:

Page 292. A Bed of Pickerel Weed.

294 fig. 178 with legend reprinted below:

----LENITIC-,

L/TTORAL

LIMNETIC

PLKNC70N

AND
A/£CTON

FIG. 178. Diagram illustrating the distribution of
aquatic societies, in a section extending from an
upland marsh to deep water. The littoral region
is shaded.

PAGE

aborigines ................... 3^2

acids, humous .......... 95. 96, 348

Acilius ................... 333

Acorus ...................... 157

Acroperus harpae .......... 300, 301

adaptations ........... 260, 274, 277

Adineta ..................... 299

adjustment ............... 248, 261

adjustments, individual ....... 242

mutual ....... 242, 282

adjustability to waves ......... 319

aeration ..................... 73

Agassiz, Louis ................ 19

Agraylea .................... 216

agriculture ................ 379, 4°2

agricultural crops ............. 404

air-breathing ................ 231

air-chambers .............. 275, 277

air-spaces ................. 265, 271

air-tubes .................... 279

albumins .................... 48

alder ................. 158, 351, 352

ale-wives ................. 232

algae, 26, 28, 29, 45, 46,

100, 101, 102

151

373

72,

110, 119, 137,
169, 1 80, 181,

220, 223, 295,
304, 307, 311,

144, 145,

183, 189, 217,
296, 301, 302,

322, 391, 345, 356, 362, 373,

390, 395

algae, "blanket" ....... 336, 345, 399

blue-green

109, 132, 297, 302, 326
filamentous blue-green 296, 310
brown .............. 135, 136

fresh water ............. 101

free-swimming ........ 28, 339

gelatinous ............. 101

green ....... 124, 129,299,302

filamentous green ....... 124

plancton ......... 50, 244, 392

protococcoid green ...... 318

lime-secreting .......... 50

marine ................ 135

of ponds ............... 335

red ................. 135, 136

sessile .......... 120, 126, 336

PAGE

algae, siphon 121

" slime-coat 335

tufted 112, 126

" unicellular 112, 126

Allen, Arthur A 95, 342

Alismaceae 156

Alisma 334

alligators 238

Ambystoma tigrinum 237, 342

ammonia 25, 48, 49, 140

Amoeba 159

amphibians. . . 148, 231, 236, 237, 337

Amphipoda 189, 191, 341

Amphizoidae 224

Anabaena 132, 133, 295, 296, 297,
305, 3«8, 392

Anacharis 155

Anapus 299

Anax 155,341,389

junius 196

Ancylus 182, 260, 370, 373

Andromeda 157, 350

angling 407

animalcules 295

animal forage 387, 399

animal husbandry 384, 400, 408

animals, hoofed 312

animals, limpet-shaped 260

animal life of marshes 345

animal population 324

animals, warm-blooded 273

Ankistrodesmus falcatus 129

" setigerus. . . 129, 131
Anodonta 180, 288, 290

edentula 324

" grandis 324

imbecillus 288

antennae 185, 189, 247, 251, 312

Anthomyid fly 359

Anthophysa 162

Anthony, Maude H 214, 215

Anuraea 299, 300, 303

Aphanizomenon 297, 304, 392

apical buds 154, 138

Appalachian hills 60

applied science 21

Apsilus 299

421

422

Index

PAGE

Apus 184,263,318

aquaria 165, 170

aquatic animals 180

bryophytes 148

carnivores 327

caterpillars. . . .219, 220, 398

" collecting 19

Diptera 346

" environment 25

" fernworts 149

herbivores 190, 396

insects 158, 195, 276

larvae 236

locomotion 273

" mammals. . 158, 241, 270, 273

microscopy 19

organisms 99, 389

" resources 412

rodents 153

" seed-plants 151, 307

societies 282, 293

aquatics, broad-leaved 154

emergent 151, 321, 334, 339,

341

floating 334, 339

rooted 334

submerged 94, 115, 321, 339

345

surface 321, 334

Arcella 159, 160, 299

armor 246

armor, chitinous 183, 251

aroids 157

arrow-heads . .272, 334, 345, 380, 405

Arthropods 183

arum, arrow. . .157,321,334,380,405

Asclepias incarnata 345

Asellus 190, 191, 192, 253, 340

aspens 378

Asplanchna 248, 299

Asterionella in, 114, 245, 297, 303,
305, 308

Atax crassipes 301

Azolla. .150,151,153,282,334

Bacillus 140

bacillus, typhoid 141

back-swimmers 211, 276

bacteria 20, 48, 100, 139, 141, 296,
390

chromogenic 140

iron 142

PAGE

bacteria nitrifying 140

sulfur 143

bacterial jelly 140

Baetis 360

balancers 370

Baltic 1 8

barometric pressure 73

barrier reefs 73

bars, building of 85

basins 59,65,67,71,356

bass 233,291,399

Batrachospermum 136

bayous 169, 334

bays 307

beach 73, 81

beaver 241, 274, 377, 378

beetles 195, 220, 275, 276, 277, 281,

3i», 346

beetles, adult 338

diving. . . .221, 222, 275, 276

gyrating 407

Parnid 260, 359, 367

riffle 224, 259

whirl-i-gig 221, 338

Beggiatoa 142, 143

Belostoma 211

Benacus 210, 211, 212, 276

Betten, Cornelius 258

bicarbonates 51

Bidessus 333

Biological Field .Stations, Ameri-
can 22, 23

Biological Field Station, Cornell

University, 65, 87, 95, 266, 330,

335, 397
Biological Lab., Fairport 23, 79, 291

birches 378

birds 231, 239, 249, 390

Birge, E. A., 36, 37, 38, 43, 44, 46, 47,
5i, 53, 65, 66, 72, 263,
304, 306, 310, 391

bitterling 292

bittern 342

bivalve 180, 185, 288

blackbird, red- winged 342

black-fly 227, 264

bladders 265, 284

bladderworts, 155, 264, 271, 272, 283,
284,285,286,319,405

blanket-moss 120

Blasturus 120, 345, 398

Blepharoceridae 228

Index

423

PAGE

Blepharocera 259, 367

bloodworms, 106, 250, 254, 279, 280,
3io, 394, 395, 398

blubber 273

bog cover 348, 349, 350, 351

bog-moss. .89, 145, 146, 147, 348, 349

bog-pond 352

bog-pools 129

bogs, 53, 89, 90, 94, 95, 115, 146, 149,

I52., i55,348. 35i

bogs, climbing 94

bogs, peat 117

bogs, sphagnum 52, 64, 157

bogs, upland 156

Bosmina . . 185, 248, 249, 301, 328, 329

Botryococcus 129, 299

Botrydium 121

bottom, false 54

bottom herbage 334

bottom-lands, alluvial 67

bottom, black muck 115

bottom mud, 95, 106, 133, 154,243,252
bottom ooze. . .48, 159, 181, 191, 235

bottom population 327

bottom slime 133

bottom sprawlers 254, 340

Boyeria 360

Brachionus 178, 179, 299

Brachycentrus 363, 364, 366

brambles 351

Branchiopods. . . 183, 184, 185, 263

Brasenia 334

Brinton, D. G 409

bristles 246, 248

brood-chamber 187, 267, 288

brood-pouch 190, 191, 393

Brook, Lick, Ithaca 317

Williams, Ithaca 358

brooks 77, 81, 167, 170, 333, 356

Bryophytes 146

Bryozoans, 166, 169, 247, 266, 269,

325, 332, 335, 341

buck-bean 345

buds, over-wintering 264

buffalo gnat 364

bugs 210, 277

bullheads 345, 388

bull-frogs 14, 236

bulrush 319, 334, 343

buoyancy, of organisms 243, 247

bur-reed 156, 157, 323, 334, 343, 346
burrowing. . . .251, 254, 257, 314, 316
burrows 254, 255

PAGE

burs 272

buttons, pearl 382, 383

Bythotrephes 301

Caddis-flies, 195, 197, 200, 214, 218,
258, 260, 280, 283, 341,
345, 36o, 361, 363, 370

Caddis-worms, 14, 84, 197, 198, 257,
258, 260, 262, 279, 280,

34°, 34i, 357, 359, 360,
362, 363, 365, 370, 371,
372, 373, 388, 398
Caems. . .205, 253, 340, 345, 388, 398

Calcium salts 52

Caledonia shrimp 393

calla 157

Callibaetis 341, 396, 397, 398

Calyculina 341

Cambarus bartoni 193

Campanula aparinoides 344

Campus, Cornell University .... 42

Campylodiscus in, 115

Canthocamptus 188, 301

canvas-backs 240

capillarity 97

Carabidae 221

carapace 184, 192, 251

carbonates 50, 51

carbon consumption 44

carbon dioxide 43, 44, 45, 50, 51, 72,

139

Carices 157

carnivores, 18, 171,209,222,241,282
283,312,318,374,390,397

carp 233, 234, 235, 384, 399

Carteria ,. . . . 103, 104, 306

Cassandra 157, 350

cases, cylindric, of sand 341

limpet-shaped 261

" portable 371

" stone-ballasted 371

Castalia odorata 334, 382

cataract 101

caterpillars 257

catfish 232. 233, 289, 291

cat-tail flag ... .91, 92, 156, 321, 333,
334,343,355,357-380,381

cat-tail, narrow-leaved 381

celery, wild 240

Celithemis 340

cells, aggregated 104, 131, 254

association of 133

" chlorophyl-bearing . . . . 147, 349

424

Index

PAGE

cells, cortical 138

division of ... 112, 117, 121, 122

flagellate 295, 305

internodal 138

multinucleate 131

rectangular blocks of 149

reproductive 12

reservoir 146, 147, 349

sex 105, 139, 151, 250

cellulose 139

cell wall 123

Ceratium 103, 1 08, 248, 296, 302, 305,

308,337
Ceratophyllum 134, 154, 155, 321, 334

Ceratopogon 279

Cercaria 174

Ceriodaphnia 267, 268, 269, 301

Cestodes 174

Cetacea 273

Chaetogaster 1 73

Chaetonotus 164, 165, 166

Chaetophora. . 126, 127, 182, 336, 338
chamber, respiratory . .250, 252, 253

Chamot, E. M 79

Channels 59, 77, 89

Chantransia 81, 136

Chaia 52, 137, 138, 139, 319, 322, 334,
352

Characeae 101, 137

Chauliodes 213

chemical analysis 48

Chirocephalus 184, 263, 318

Chironomidae 225

Chironomous 228, 257, 280, 329, 330,

332, 336,340, 34i, 393,

394, 395, 396

Chirotenetes 259, 364, 366

Chlamydomonas 104

Chlamydothrix 141, 142

Chloroperla 203, 278

chloropliyl no, 119, 125, 139, 265,
271, 296

Cholera spirillum 141

Chrosomus erythrogaster 394

Chrysops 230

Chydorus 185, 300, 301, 303, 305,
310,326

Cicuta bulbifera 345

cilia 160, 170, 246, 250

ciliates 246, 282, 327

circulation periods 35, 37, 46

Cladocera 185

Cladocerans 185, 300, 301, 303, 304,
312

PAGE

Cladophora 81, 112, 125, 126, 136,
322, 336, 362

Cladothrix 142

clams 1 80

Clathrocystis. . . .297, 304, 305, 308

Climacia 214

climate 294

Closterium 117,119

Clupea pseudoharengus 232

coastal plain 93

coats, chitinous 266

Cocconeis 115

Cocconema in, 115

Coccus 140

cocoon 213

Coelambus 333

Coelastrum 129, 130

Coelenterates 163

Coelosphaerium 132, 133, 297

Coleochaete 128

Coleoptera 195, 220, 279

colonies dendritic 246

discoid 245

expanded 245

radiate 245

spherical 104, 107, 245

Colurus 299

conjugation 121

Conjugates, filamentous. . . .119, 126

conjugates 263, 299

Conferva 124, 126, 299, 336

Conochilus 177, 249

conservation 21, 412

control, methods of 399

coots 342

Copepods 183, 188, 189, 200, 246,
263, 301, 303, 325, 328

Coptotomus 214, 335

Cordulegaster 360

Corethra 108, 301, 310, 329

Corixa 201, 276

Corydalis 213, 214

Cosmarium 119

Cothurnia 161, 162, 332

crabs 183, 192

crabs, horse-shoe 184

cranberry 348, 349, 350

craneflies.229, 277, 339, 346, 358, 360
crawfishes 175, 191, 192, 252, 340,

342, 390

creeks 77

Creek, Fall, Ithaca 330

Crenothrix 142

Cristatella 169

Index

425

PAGE

crops, diversifying of 403

crowfoots 156, 271

Crucigenia 129, 130

Crustacea 183, 189, 192, 193, 301 302

Crustaceans 20, 45, 52, 161, 183,

187, 251, 253, 285, 299,

304, 318, 340, 345, 382,

383, 399

Culex 280, 329

Culicidae 227

current 83, 85, 356

current meter 86, 319

currents, conduction 31

convection 31, 38, 292

descending 36

Curtis, W. T 290

cuticle 271

Cyanophyceae 132

Cybister 275

Cyclops 188, 189, 244, 263, 301, 303,
305, 310, 311, 312

Cyclotella 112, 114, 299

Cylindrocystis 1 16, 119

Cyperus diandrus 207

Cypripedium 351

Cypris 188

cyst 289, 290, 291, 292

Dace 374

Dachnowski's diagram 352

damselflies 195, 207, 279, 280, 281,

332, 341, 346

Daphne 185, 186, 248, 301, 306, 309,
312, 39i

Daphma 285, 292, 303, 304, 306

darters, least 231, 233

darters 250, 259, 362, 374

Darwin, Charles 17, 18, 283, 285

Decapoda 191

Decodon 354

decomposition 48

defense 251

deltas 60, 65

Delta of Mississippi 67

Dero 173, 174,257

desiccation 316,318

Desmidium 117

desmidssi 52, 53, 116, 117, 119,
121, 144, 263

Diaphanoscma 301, 304

Diaptomus 101, 188, 189, 301, 303,

305, 3ii

Diatoma 115, 245, 297

PAGE

diatomaceous earths no

diatomaceous ooze 86

diatoms 29, 53, 81, 84, 101, 109, no,
115, 144, 183, 189, 206, 217,
248, 297, 302, 303, 305, 311,
362, 387, 394, 395, 399

diatoms, colonial 391

epiphytic 115

needle 112

sessile 395

slime-coat 322, 336

"white-cross" in

diatom rakes 373

Dictyosphaerium 129

Dicranomyia 359

Didymops 340

Difflugia 159, 257, 299, 303

Diglena 299

Dinobryan 101, 106, 107, 246, 296,
303, 308, 310, 337

Dinocharis 299

Diptera 195, 224, 337

Diptera, aquatic 225

blood- sucking 227

discs, attachment 171

" respiratory 230

" sucking 228

dissolved colloids 54

distribution 266, 322, 339, 389

distribution, vertical 310, 324

ditches 133, 152, 169, 345

ditch-grass 71

Diurella 299

divers 239, 241

divers, pearl 30

Dixa 329

dobsons 213

Docidium 119

dogwood 351

Dolomedes 346

Donacia 337, 346

Dorosoma 399

dragonflies 195, 197, 207, 254, 280,
332, 340, 341, 356, 389 407

drainage 402

Draparnaldia 124, 128

Droseraceae 156

Drosera 283

drouth 97

Dryops 370

duckmeat 149, 161, 240

ducks 239, 240, 342

duckweeds. . .150, 153, 272, 321, 334

426

Index

PAGE

Dudley's Cayuga Flora 151

dwelling-tubes of midge larvae

N« 335, 336, 365

Dytiscidae 222, 346

Dytiscus 221, 222, 276, 280, 333

Ears, external 274

earthworms 310

economic progress 399

eel-grass 90, 153, 319, 334

egg-parasites 195

eggs, of amphibians 237

of Benacus 211

of crawfishes 192

drouth-resisting 318

of fishes 233

of leeches 176

of pike 400

of salamander 342

of snails 335

of Trisenodes 218

summer 266, 267

winter 266, 267, 268, 269

Ehrenberg no

Eleocharis 334

Elmis 359, 370

Elodea 155

Elophila 220, 260, 272

Embody, George C 191, 388

Enallagma 337

Engler 143

encasement 263

Encyonema 1 1 1 , 112

encystment 263, 289, 290, 304, 310,

3i6, 361

Entomostraca 85, 114, 183, 184, 188,
193, 302, 304, 309, 310,
312, 388, 390, 398
Entomostracans ... .20, 52, 217, 341

Epeorus 370

Ephemera 255

Ephemerella 340, 370

Ephemerida 195, 205

ephippium 268, 269

epidermis 271

epilimnion 37

epiphytes 139

Epischura 301

Epistylis 161

Epithemia 115

Eriocera 256

Eriophorum 351

erosion 57, 60, 68

PAGE

Estheria 184, 263

Esox lucius 400

Euastrum 119

Euchlanis 299

Eucrangonyx 191

Eudorina 104

Euglena. .15, 102, 103, 104, 106, 296

Euparhyphus 359

Eupomotis 388

Eurycerus 187

evaporation 40, 55, 56, 76, 99, 100,
247

evolution 17, 410

Experiment Stations for fish

culture 400

exploitation 21, 412

Fall Creek, Ithaca. . . .42, 79, 87, 115

Falls, Triphammer, Ithaca 81

fats 244, 273

fauna 18, 53

fecundity of fishes 235

Felt, E. P 165

females, parthenogenetic .... 266, 268

Ferguson, W. K 394

ferments 139

ferns 351

fern worts 145, 153

Fiber zibethicus 241

field stations 20

filaments, algal 102

filaments, spore-bearing 319

filter 20

filtering 113

fingerlings 384, 385

fins 250

' ' pectoral 234

fish's bill of fare 398

Fish Commission, United States 79
Fish and Game Commission,

New York State 344

fish culture 21, 384, 385, 387, 389,
390, 399, 400, 408

fish 290,379,383,403

fish eggs 384

fisher 241, 274

fishes 282, 362, 386, 387, 389, 390,

399, 404

fish-flies 213

fish food 183, 189, 190, 235, 294, 390,

391, 392, 393, 396, 397

fish forage 384, 386, 393, 403, 408

fish fry 384

Index

427

PAGE

fish fry, planting of 384, 385, 386

raising 385

fish, fresh for the table 407

fishponds 387, 396, 404

fish population 398

fish raising 404, 408

Fissidens julianum 148

flagella 102, 103, 104, 105, 106, 108,

246, 250, 310

flagellates 102, 103, 106, 107, 246,

248, 296, 302, 303, 305,

306, 309, 311, .316, 356

flagellates, chlorophyl-bearing . . 299

green 104

shell -bearing 108

spherical 108

winter 107

flatworms 170, 171, 172, 173, 250,
260, 263, 340, 370

floats 247, 266, 284

flocculence 295

flood 57, 67, 75, 87

flood conditions 88

flood-decline 88

flood plain 64, 77, 87, 356

flood plain of rivers 67

flood rise 88

flora 18, 53

Florida 59

Floscularia 178, 299

flotation 243, 245, 246, 247, 251, 272,
297

flotsam 153

foliage 405

food, abundance of 306

available 304

" dependencies 389

" dissolved 26

examinations 398

food-fishes 387, 390

food preferences 305, 391

" relations 389

foodstuffs 395, 402

food supply 21,25

Fontinalis 148

forage fishes 398 , 399

foragers 367

foragers, shelter-building 370

foraging grounds 57

foraging habits 373

forage organisms 396, 398

Forbes, Stephen A. 70, 80, 389, 390,
394

PAGE

Forel, F.A 53,76

forget-me-not 405

Fragillaria 115, 245, 297, 305, 308

Fredericella 166

freezing point 244

frog, bull 237

' green 237

' leopard 236, 237

" pickerel 237

1 tree 237

' wood 237

frogs 175, 236, 237, 343, 383, 387, 390

frost-line 83

fungi 139

fungi, parasitic 296

fungus 282, 400

fur-bearers 241

furs . . - - - 379

Galingale, low 207

Galium palustre 344

Gammarus 190, 191, 360, 392

gas, marsh 96

gases 25, 40, 41, 43, 44, 45, 46, 54, 55,
56, 244, 252, 265, 2'79, 309

gases, noxious 96

Gastropus 299

gars 291,333

geese 239, 240, 242

gelatin 127, 161, 169

gemmules 164, 247

gill arches 313

" cavity 292

" chambers 209, 252

" covers 253, 366

gill-plates 208, 251

gill-rakers 235, 313

gill-strainers 392

gills 182, 217, 233, 235, 236, 252, 273,
275, 279, 280, 288, 369, 370, 397

gills, anal 279

" blood 279

" filamentous 204, 224, 279

" mussel 181

" tracheal 278, 279, 368

" tube 280,368

glacial period 62

glaciation 64

glands 284

Glenodinium 103, 108

glochidia 181, 287, 288, 289, 290, 291

Gloiotrichia 297, 304

Glyceria 334

428

Index

PAGE

Goera 371

goldfish 384, 399

golden shiner 235, 387, 399

goldthread 351

Gomphines 209, 254, 357

Gonatozygon 117, 119

Goniobasis 370

gonidia 141

Gonium 104

Gordius 174

gorges, post-glacial 64

gradient of channel 85

gravel, deposits of 42

gravity, specific 243, 244, 246

grebes 342

grouping by levels 326

Grout, A. J 148

gulls 239

Gyrinidae 221

Gyrinus 337

Gyrosigma 112

Habenaria 351

habitat 294

Haeckel, E 392

haemoglobin 253

Haemopsis 175, 176

hairs 248, 274

hairs, glandular 283, 285

Halesus guttifer 198, 361

Haliplidae 223, 275, 346

Haliplus 277

hand-net 20

Hankinson, T. L 231, 233

Harper, Francis 93

hatcheries 384, 385, 400

Hawkins, L. S 321

Headlee, T. J 324

heaths 157, 351, 355, 357

Hehcopsyche 370, 372, 373

hellgrammite 214, 313

Hellriegel 56

Hemerobiidae 212, 214

Hemilastena 291

Hemiptera 195, 210, 274

hemp-weed, climbing 345

Heptagenia 278, 368, 370

herbivores 18, 128, 153, 180, 186, 282,
318,373,389,390,392

herring 291, 313

herons 239

Heterocope 311

Hexagenia 115, 255, 341, 398

PAGE

hibernacula 264, 265, 272

hibernating 269

Hibiscus 145, 405

Holopedium 52

hooks 247, 266

hornwort. 134, 154, 155, 271, 272, 334

horseflies 227, 254

horse-leeches 175, 250

host species 291

Howard, A. D 289, 291

huckleberries 351

humid regions 55, 56

humus 57

husbandry 385, 386, 412

Hyalella 191

H^datina 299, 305

Hydra 163, 164, 282, 325, 327. 332,

341

Hydrachnidae 193

Hydrocampa 218, 257, 337

Hydrodictyon 122. 124

hydrogen sulphide 47, 96

Hydrohypnum 358

hydromechanics 107

Hydrophilidae 222, 276, 346

Hydrophilids 221, 222

Hydrophilus 275

Hydroporus 222, 333

Hydroptilidae 216

Hydroptila 258

Hydropsychidae 217

Hydropsyche._.2i8, 363, 364, 365, 370

hydroxide of iron 142

Hydrurus 136

Hymenoptera 195

Hypericum virginicum 344

hypnums 148, 149

hypolimnion 37

Ice 35,36,80, Si, 120

ice, anchor 82, 83

ice, floes 61

ice in streams 8 1

ice rubble 81,82

Ignis fatuus 96

Illinois State Laboratory of Na-
tural History 50, 79

infusoria 171,179

inclusions 244

increase, rapidity of 306

incrustations of lime 251

Indianapolis News 384

Indians 13

Index

429

PAGE

insects 183, 251, 274, 357, 358, 367,

39», 399

insects, aquatic 338

gall 291

herbivorous 398

net-winged 195, 212

" plancton-gathering .... 364

internodes 138

inundation 88

iris 4°4

iron 53

iron sulphate 95

Isoetes 151

Isopoda 190

Ischnura verticalis 207, 208

Ithytrichia 260, 262, 372

Jack-o-lantern 96

Jagerskiold 1 72

Johannsen, O. A 299

jointweed 345

Jo-pye-weed 323

Juday, C. 36, 37, 38, 43, 44, 46, 47,

51,53, 72,263,308, 312
Juncaceae 157

Kent 309

Kirchnerella 129, 131

Knight, H. H 75, 196, 350

Kofoid C. A. 22, 48, 83, 85, 88, 103,

107, 113, 130, 131, I64,

171, 312, 356

Laccophilus 333

lace-wings 214

lagcons 334

Lake Alachua 69

" Canandaigua 65

" Cayuga 28, 32, 36, 42, 60, 64,
65, 73, 114, 123, 151,
218, 232, 240, 295, 296,
300, 308, 309

Lake Coeur d'Aleiie, Idaho 60

' Devil's, Wisconsin 51, 71

Erie 63

' Evans' Michigan 62

' Flag 312

Flathead 71

' Pure, Denmark 28

' Geneva 28, 76

Great Salt 71

Green 63

' Hallstatter, Austria 33

PAGE

Lake Huron 63

" Kegonsa 66

Keuka 64, 65

" Knight's 44

Louise, B.C 60

" Mendota 37, 38, 46, 47, 66, 304,
306,310

Miccbsukee 69

Michigan . .28, 61, 63, 114, 312
" Monona 66

Okoboji 71

" Ontario 63

" Otisco 65, 72

Owasco 65

" Pepin 67

Phelps 57

Pontchartrain 67

" Quiver 49, 164

" Seneca 65

Silver 71

" Skaneateles 65, 72

St. Clair 28

" Sumner, Isle Royal 54

" Superior 63,73

Tahoe 28,60

" Thompson's 49

" Turkey 312

" Wabesa 66

" Walnut 161,233,239

" Winona 71, 324

" Yellowstone 70

lakes .59, 60, 231, 232, 299, 307, 316,

333, 356, 406

alkaline or salt 74

crater 60

' ' currents in 73

" depth of 71

Lakes, Finger 64, 65

lakes, floodplain 67

" of Florida 69

" Fulton Chain of 165

Lakes, The Great 61, 63, 91, 301

lakes, playa 75

polar 36

solution 67, 68

strand 75

Swiss 76

of Wisconsin 66

of Yahara Valley 66

stagnation periods of . . . .34, 46
Lakeside Biological Laboratories

70, 71

Lampsilis 290, 291, 324, 325

430

Index

PAGE

larvae, of black flies 227, 364

of beetles 120, 250, 368

of caddis-flies 215

of craneflies 256

dipterous 224, 227, 288

of fish-flies 213

of horseflies. . . .227, 230, 340

of mayflies 120, 332

of midges 226, 227, 250, 258,
325, 338, 341, 356,
373, 387, 388, 389,
. 390, 393, 394, 397

of mosquitoes 227, 250

" of orl flies 213

" of punkies 120

of spongilla flies 215

leaf -beetle 346

leaf-drift 360

leech, clepsine 176

leeches, 171, 175, 176, 257, 325, 341.

364

Leersia 344

Leeuwenhoek 16

Lefevre, G 290

Leidy, Joseph 19

Lemanea 135, 136

Lemnaceae 135

Lemna 150, 173, 240, 321, 334

Lepidoptera 195, 218

Leptidae, aquatic 229

Leptoceridae 216

Leptocerus 216, 260, 372

Leptodora 301, 311, 312

Leptophlebia 360

Leptothrix 141, 142

Lestes 341,345,346

Leunis 173

Libellula 340

lichens 132, 282

life cycle 260, 261, 274, 316, 397

life, on the bottom 326

" at the surface 327

" in open water 243

light 306, 307, 308

light relations 29

Liljeborg 18

Lime 50

limestone 50

Limnaga 182

Limnacea 346

Limnephilus 197, 198, 199, 200

Limnobates 346

Limnocalanus 301, 311

PAGE

Limnochares 194

limnological phenomena 14

Limnophilus 345

Limnophora 359

limpet 260

Lintner, A. J 214

liverworts 146, 153, 334

lobsters 192

locomotion 273, 281

locomotion, rolling 104, 107

locn 239

Lorenz 33

lorica 106, 161, 178

loricate forms 299

lotus 380, 404

Lloyd, J. U 54

lubrication 272

Ludvigia palustris 156

lungs 275,276

Lyman, Helen Williamson 214

Lyngbya. .297, 305

Mackeral 250

Macrobiotus 164, 166

Magazine, Farmers' 384

maggot, rat-tailed 229, 277, 339

magnesia 50

Malacostraca 183, 189, 301

Mallomonas 299, 308, 309

Malpighi 16

mammals 231, 273. 274

Mammoth Cave, Kentucky .... 5 1 ,84

manna grass 334, 343

mantle 252

marl 5°, 75- 352

marsh bedstraw 344

bellwort 344

fern 145,344

five-finger . 344

gas 48

horsetails 151

mallow 145

" Montezuma 65, 87, 91, 92

ponds 95

Renwick, Ithaca 347

skull-cap 344

St. John's wort 344

marsh-treader 346

marsh-wren 342

marshes 14, 48, 59, 64, 65, 66,
73, 89, 90, 95, 97, 263,
307, 3i6, 333, 345, 346, 402,
411

Index

431

PAGE

marshes, Canoga 318

cat-tail 91, 240, 241

fresh-water 90

utilization of 408

Marsilea 134, 149, 321, 323, 334. 407

marten 241

Mastigophora 102

Matheson, Robert. 222, 223, 277, 317

mating nights 206

matter, dissolved 26

matter, suspended 26, 42

mayflies 14, 115, 195, 205, 253, 255,
259, 260, 280, 281, 345, 356,
357, 36o, 361, 368, 370, 372,

373, 398

mayfly, burrowing 255

mayfly, howdy 364, 366

McDonald, E 62

McLean, New York 350, 352

Mediterranean Sea 28

Melicerta 178, 257, 299

Melosira 111,112, 297, 303

Menyanthes trif oliata 34 5

Meridion in, 113, 114, 297

Merismopaedia 134, 135, 299

Mesotaenium 119

metabolism 44, 272

metamorphosis 195, 197, 200, 201,

205, 220, 237, 287,

290

Metazoa 246

metazoans 163, 164, 165

methane 47, 48, 96

Micrasterias 52, 53, 119

microplancton 20

microscope 15, 101, 115, 327

Microcystis. . . 132, 133, 297, 303, 308

midge, net- winged 228, 259, 267

midges 14, 225, 254, 257, 258, 358,
36i, 371, 373

migrations 240, 316

Mikania scandens 345

milfoils 271, 405

mink 241, 274

minnow, red-bellied 294

minnows 232, 233, 287, 345, 366, 374,

394, 399

mites. . 192, 285

moccasin flower 351

mold parasites 144

molds 100

mollusca, lotic 373

molluscs 50, 52, 180, 216, 235, 288,
342, 345, 352, 382, 390

PAGE

molluscs, shell-bearing ......... 340

Monostyla .................. 299

Moore, Emmeline ......... 150, 391

Morgan, Anna H ........... 206, 253

mosquitoes 227, 280, 284, 318, 339,

346
moss, brook- inhabiting ........ 148

moss patches ................. 358

moss, xerophytic .............. 351

mosses ................... 146, 149

mossworts .................. 145

moth-flies ................. 230, 360

moth, tineid .................. 346

moths ............ 195, 218, 284, 341

Mougeotia .................. 119

Mountains, Rocky ............ no

mucilage .................... 272

muck .................. 95, 96, 154

mucus ................ 129, 131, 181

mud banks ................... 407

mud pond ................... 352

mud puppy .................. 291

muscles .................. 256, 281

muskellunge ................. 313

muskrat .......... 241, 274, 341, 380

mussel, salamander ........... 291

mussel shells ................. 216

mussel, wash-board ........... 289

mussel, warty-back ........... 289

mussels 180, 181, 194, 240, 2=51, 252,

254, 257, 286, 287, 288, 289,

290, 291, 292, 324, 332, 341,

356, 357, 36o, 383

mussels, eggs of ............... 287

mussels, fresh- water. . . . 180, 282, 286

Myriophyllum ............ 154, 155

Mysidacea .................. 189

Mysis ............ 189, 190, 301, 311

Myxophyceae ............... 132

Nachtrieb, H. F ............ 176

Naidae ..................... 173

naiads ................ 152, 1/3,334

Nais ........... 153, 173, 177, 321

Najas ....................... 334

nauplius .................. 188, 200

Navicula ......... 109, no, 112, 299

navigation .................. 403

necton2i3, 243, 294, 296, 313, 331,

Necturus ................. 236, 291

Needham, John T ........... 83, 352

Nemoura .................... 360

Nematodes ............... 172, 173

432

Index

PAGE

Nepidae .................... 212

Netrium .................... 119

nets, of silk bolting-cloth ...... 18, 20

Neuroptera ........... 195, 202, 212

newt, vermilion-spotted ........ 237

New York State Museum ...... 165

nigger-heads ................. 291

nightshade bittersweet ......... 345

Nitella ............... 137, 138, 139

nitrates ............. 48, 49, 50, 141

nitrites ................. 48, 49, 141

Nitrogen 43, 47, 48, 50, 139, 141, 348,

nodes ...................... 138

Nostoc ............... 133,282,337

nostrils ..................... 273

Noteus ..................... 299

Notholca ......... 246, 299, 300, 303

Notodromas .............. 188, 328

Notommata parasita .......... 282

Notonecta ................ 276, 337

nucleus ................... 117, 121

Nymphasa ................... 334

nymph ................... 201, 204

nymph, damselfly ............. 208

dragonfly . . 250, 252, 340, 360
Hexagenia ........... 398

mayfly 278, 340, 341, 369,

387, 388, 390, 396
stonefly ........... 204, 279

Obovaria ellipsis .............. 291

Odonata .............. 195, 207, 345

CEdogonium .......... 124, 125, 126

offsets ...................... 272

oils ......................... 273

Oligochaete ............... 173, 250

Oocystis .................. 129, 131

ooze" ..................... 173, 251

opercula .................... 253

operculum ................... 182

Ophiocytium .............. 129, 131

Ophrydium .................. 161

orchids ................... 158, 351

organs, locomotor ............. 246

organisms, chlorophyl-bearing 71
littoral ..... 314, 315, 356

lotic .............. 263

orl flies .................. 213, 280

Oscillatoria ....... 109, 133, 245, 297

osmotic pressure .......... 245, 272

osteole ...................... 164

Ostracods. 183, 188, 193, 225, 328, 345

PAGE

otter 241, 274

overflow 87

oxydation 44, 5 1

oxygen 43, 44, 45, 47, 48, 72,

101, 120, 139, 183, 254, 263,

277, 309, 3«t 326, 329, 332,
339, 345

oxygen, consumption of 44

dissolved 80

excess 44

free 310

oxylophytes 348

oysters 379

Pacific Ocean 28

paddle-fish 333

Palaemonetes 192, 393

Palmer 48

Pandorina 103, 104

Paper making 381

Paramecium 160, 165

Paraponyx 219, 341

parasites 18, 120, 175, 282, 296

Parnidae 224

Parnids 370

Paulmier 392

peat 95, 96, 147, 348, 350, 352

Pectinatella 168, 169, 247

Pedalion 299, 300

Pediastrum 123, 245, 299, 303

Pedicia albivitta 256

peeper 236, 237

Peltandra 157, 334

Peltodytes 223, 224

Penium 119

peptones 48

perch 232, 233, 291, 306

perch, yellow 234

Peridinium 108, 296

Perla 203, 204

petioles 271

Phaeophyceae 135

Philotria" 155, 156, 228, 319, 321

Philodina 299, 318

photomicrographs 117

photosnythesis . .26, 28, 29, 45, 46, 71

Phragmites 343

Phryganea 34 1

Physa 182, 337

pickerel-weed. 156, 157, 321, 334, 405

pike 231, 232, 233, 235, 387

pipewort 319

Pisidium 341, 345

Index

433

PAGE

pitcher-plant 283, 284, 350, 351

Pitot-tube current meter 86

Placobdella 176

Plagiola 289, 291

Plagues of Egypt 14

Planaria 263

planarians 170, 171

plancton 18, 20, 28, 45, 48, 49,
70, 72, 85, 123, 129, 130,
131, 134, 135, 161, 164, 166,
185, 189, 194, 235, 243, 294
295, 296, 299, 300, 301, 302,
303, 313, 322, 341, 356, 357,
387, 388, 389, 391, 394

plancton animals 299, 301, 325

Crustacea 391

entomostraca 393

feeders 235

gatherers 263, 270

local abundance 306

net 115, 160

of open waters 331

organisms 248, 296

pulses 305

shoreward range 307

of surface 327

plancton strainers 313

planctonts, summer 309

synthetic 308

Planorbis. . ." 155, 182, 337, 345

plant assimilation 26

plant infusions 160, 165

plants, chlorophyl-bearing ... 44, 326

floating 150

insectivorous 282, 283

submerged 155, 334

transpiration of 56

vascular. . .270, 316, 322, 356

Platydorina 104

Platypeza 380

pleasure grounds 21

Plecoptera 195, 203

Pleurotaenium 119

pliancy 271

Ploesoma 299

plover 239

Plumatella 166, 167, 169

plumes 248

plunge basins 63

Podilymbus 240

Podophrya 1 62

pollen grains 296

pollen tubes 151

PAGE

Polyarthra 299, 300

Polycystis 297

Polycentropus 340

Polygonum 75, 344, 345

Polyphemus 301

Polytrichium 351

Polyzoans 166

pond culture 393

pond-dwellers 172

pond at Lake Forest, 111 410

pond, making of a 406

Pond, Old Forge 388

Pond, Parker's 91

pond-scums 101

pond-snails 327

pondweed, ruffled 152, 272

sago 326, 380, 387

pondweeds 152, 153, 240, 272, 319,

321, 334, 352, 391,

405

pondweed zone 232, 233

ponds 59, 121, 155, 167, 299, 307, 316,

333, 345, 356, 397

ponds, hatching 163

inclosed 408

Pontederiaceae 156

Pontederia 157, 321, 334

pools 14, 57, 64, 81, 133, 156, 163,

164, 184, 210, 307, 316, 319, 322,

35.6

pools, impermanent 157

polluted 173

" rainwater 184

stagnant 127, 139, 160

temporary 177, 227, 263

Potamogeton 152, 153, 220, 240, 321,

334, 336, 387

Potentilla 344

prawn, freshwater 393

prawns 183, 192

Precession of the Equinoxes .... 32

precipitation 55

Priocnemis 330

production, decline of 310

products, animal 382

gelatinous 244, 245

metabolic 244

mucilaginous 245

prolongations 245

propagation 385, 398

propagation, artificial 397

propulsion 249, 250

propulsion, caudal 279

434

Index

PAGE

Protection of breeding fishes .... 385

proteins 48, 139, 148

proteins, liquefaction of 48

protoplasm 30, 244

Protozoa 250, 390

Protozoa, parasitic 162

protozoans 158, 159, 160, 161, 257,
299

protozoans, ciliate 171

sessile 162

Psephenus 224, 260, 267, 370, 373

pseudopodia 159, 162

Psorophora 284

Psychoda 359, 360

Psychodidae 230

Pteridophytes 149, 150, 151

Pterodina 299

pubescence 276

puddles 316

pulmonates 337

punkies 279

pupa of Limnophilus 199

pupae of blackfly 280

dipterous 280

Pyralidae 218

Quadrula 289, 291

Radula 181

rail, Sora 239

" Virginia 239

rails 224, 342

rain 44

rainfall 55, 56, 57, 69, 74, 77, 88, 316

rainfall, excess of 56

surplus 403

variation in 70

rainspouts 166, 177

rainwater 41, 57, 68

Rana pipiens 236

Ranatra 276, 278, 339

Ranunculus 156, 321, 334

rapids 64

rate of streamflow 85

Rattulus 299

readaptations 270

Reaumur 16, 202

Redi 16

regions, arid 57, 75

limnetic 315, 325, 326

littoral 315, 325, 326, 341,

395
Reighard, J 28

PAGE

relations, cultural 399

spatial 326,331

Renwick, Ithaca 15

reptiles 231, 238

resemblance, protective 361

Reservation, Clark 63

reservations, public 411

reservoirs 403, 404

reservoirs site 403

respiration 252

Rhabdoccele 170, 172

Rhichteriella 129, 131

Rhizopoda 159

rhizopods 325

Rhizosolenia 297

Rhodophyceae 135

Rhynchostegium 148

Riccia 145, 146, 334

Ricciocarpus 153

rice, wild 13, 379, 380, 382

riffles 64

rills 77

Rithrogena 369, 370

River, Chippewa 67

Illinois 48, 49, 79, 80, 83,
85, 103, 107, 131, 171,

312, 356, 357

River, Mississippi 41, 67, 79

Missouri 41

Niagara 61

Seneca 65, 91

Spoon 28, 49

St. Mary's 69

St. Mark's 69

Susquehanna 64

" Smvannee 94

rivenveeds 152

Rivularia 133, 134, 297, 337

rocks, archaean 52

rock ledges 363

rodents 241, 312

Roesel 16, 202

rotifers 106, 166, 177, 178, 179, 246,
248, 250, 257, 266, 269, 282,
298, 299, 300, 302, 305, 309,
312, 318, 325, 327, 328, 341,

39«

rotifers, loricate 248

resting eggs of 325

sessile 332

Rumex 345

runners 272

Ruppia maritima 7 l

Index

435

PAGE

rush, beaked 351

club 334

spike 354,359

rushes.... ..89,157,381

Ryacophila 370

Rynchospora 351

Sagittaria 334

salamander, spotted 237

salamanders. .236, 237, 291, 337, 379

Salpina 299

salts, mineral 40

Salvinia 150, 334

sanitation 21

Saprolegnia 143, 144

Saranac Inn 163

Sarcodina 1 59

Sarracenia 284

Sars 18

saturation 44, 55

Scapholeberis 328

scavengers 18, 175, 282, 283, 296

Scenedesmus 129, 130

Sciomyzidae 230

Scirpus 87, 334

scuds 183, 189, 190, 332, 341, 345,
360, 390, 392, 393

Scutellaria 344

seals 244

Secchi'sdisc 27, 28, 65, 71

secretions 257

sedges 89, 94, 157, 343, 344, 407

sedges, tussock 352, 354, 357

seed plants 145

seed production 272

seeds 203

seepage 57,59

Selenastrum 129, 131

Sellards 69

serpents 390

sewage 140

sewage contamination 357

sewers 159

sheepshead 235, 291, 292

shelter-building 257, 314, 340

shelters. .258, 260, 294, 326, 372, 395

shell, butterfly 291

yellow sand 291

shells 244

shoals 30, 73, 90, 91, 145, 156, 231, 232,

307,331,333,343
shore lines 404, 406, 407

shore vegetation 91, 131

PAGE

shovels 256

shrimps 183, 184, 192

Sialididae 212, 213, 221

Sialis 214

Sida 301

Silica 52, 53, 109, no

silt 26, 27, 29, 42, 67, 77, 84,
85, 191, 251, 252, 254

silt, adherent 340

depositions of 90

excess of 326

" inwash of 60

Simocephalus 185, 186, 387

Simuliidae 227

Simulium 81, 259, 280, 358, 363, 364

sinks 68, 69

Siphlonurus (= Siphlurus) 205, 206,

259, 398

siphons 252

Sirenia 273

Sisyra 214, 215

sludge 173

sluiceways 169

Smith, Lucy Wright 204

snails 180, 181, 216, 227, 254, 260.

337, 340, 345, 357, 37«, 373
388, 398, 399

snails, limpet-shaped 182

operculate 182, 356

pulmonate 182

viviparous 182

snakes 250

snipes 239

societies, aquatic 294, 296

bog 348

lenitic. . .315, 316, 356, 360

limnetic 293, 294

littoral 294, 314,322

lotic 315, 356, 360, 362, 367,

372,373

soils, calcareous 41, 51, 137

siliceous 41

Solanum dulcamara 245

soldier-flies 338, 359

solids, dissolved 41, 49

suspended 41, 43, 54

solidity 274

solutions 68, 84, 95

sow-bugs 193

Sparganium 157, 334

spatterdock . . . 154, 322, 334, 380, 405

spawning grounds 385

spawning time 234, 343

436

Index

PAGE

Spelerpes 237, 374

spermaries 138

sperm nuclei 151

Sphaerella 103, 104

Sphaeriidae 181

sphagnum 89, 94, 117, 146, 147, 149,
284,348,349,350,351,352,

353, 355, 359

Sphenophorus 346

spicules 164, 266

spiders 183, 192, 346

spiracles 270, 275, 276

Spirillum 140

Spirodela 149, 334

Spirogyra 1 19, 120, 216, 223, 263, 322

336

Spirotasnia 119

Spirulina 133

sponge fishers 30

sponges. 165, 266, 269, 332, 335, 341
sponges, fresh-water 164, 265, 266,

325

sponges, marine 266

spongilla flies 214,280

sporangia 143

spore development 310

spores 140, 142, 296

springs 53, 57, 59, 64, 84, 152

springtails 195, 338

stagnation 35, 39

starches 244

statoblasts 164, 165, 169, 247, 265,
266, 269, 325

Staurastrum 51, 119, 299

Stauroneis in

Stenostomum 170

Stentor 160, 332

Stephanoceros 178, 299

Stephanodiscus . . . . in, 112, 114,297

Steuer 27

Sticklebacks 234, 235

Stokes, Alfred C 19

stomates 151, 270, 271

stoneflies 195, 203, 259, 278, 280, 345,

360, 368, 374

stoneworts 50, 52, 101, 137, 138, 139,
251,263,319,334

strainers 252, 253, 365

strata, soluble 68

stratification, horizontal 307

thermal 31, 34, 35, 39,

46,54,71
Stratiomyia 338

PAGE

stream-line form 249, 250, 251, 259,
273, 274, 313, 366

streams 59, 77, 141, 231, 319, 406

streams, pollution of 80, 130

Streptothrix 142

Strodtmann 305

sturgeon, shovel-nosed 235

sturgeon 291, 333, 356

Stylaria 173

suckers 232, 233, 234, 259

sulfur 53

sundew 156, 283, 351

sunfish 232, 233, 234, 388

Surber 289

surface film 181, 327, 328, 337

swale-flies 230, 277, 329, 346

swales 56, 64

Swammerdam 16, 202

Swamp, Dismal 90

Okefenokee 93

swamps, coniferous 152

marine 90

sweet flag 157,343

swimmerets 192

symbiosis 282

Symphynota 287

Synchaeta 178, 299, 300, 303

Synedra in, 112, 297

Synura 103, 107, 303

Syrphidae 229

syrphus flies 339, 380

Tabelaria m, 114, 115,245,297,303,

305

Tabanidae 227

tadpoles 236

tailfin 251

Tanypus 225

Tany tarsus 257, 371, 372

tardigrade 164

tear-thumb 343, 344

teeth, raptorial 235, 313

temperature 25, 37, 244, 248, 304,

306, 307, 308
temperature, at different depths

32, 34, 35, 36, 38

changes of 40

conditions of. .32, 36, 46

fluctuations of 345

levels of 39

optimum 131

range of 33, 34

yearly cycle of 34

Index

437

PAGE

tentacles 176

terns 342

Tetmemorus 119

Tetrapedia 130, 299

Tetraspora 129, 131

thallus 153

thermocline 37, 39, 72, 309, 311

thoracic appendages . . . .183, 188, 189

Thysanura 195

Tipulidae 297

Tipula 360

tides 73

toads 236, 237

Tseniopteryx 279

topography 74

trachea 275

tracheae 270, 278, 279

Trachelomonas 103, 108

tracheoles 278, 279

transpiration 348

Trembly 16

Tria;nodes 215, 218, 280, 337

Triarthra 299, 300

Tribonema 124, 126

Trichobacteria 141, 142

Trichodesmium 101

Trichoptera 195, 214

trochophores 250

Trochosphaera 178

trout 163, 176, 313, 385, 393, 394

trumpets, respirator}^ 277, 280

tubercles 256

tube-dwellers 370

tubes 121, 226, 240, 278, 372

tubers 272, 380, 382

Tubifex 173, 174, 254, 340

turtles 175, 238, 343, 390

tusks, mandibular 255, 256

Typhaceae 156

Typha 91,321,334,346

Ulothrix 124, 336

Unio 181,323, 324

L'rodela 236

Uroglena 295

Utricularia 117, 155, 284, 285

Vacuoles 310

Vallisneria 153, 240

valves 109, 252, 273, 288

vapor 55

vaporization 40

Vaucheria . 121

PAGE

vegetable forage 399

vegetative propagation 272

ventral suckers 367

vertebrates 239, 374, 382

Volvox. .101, 104, 105, 245, 282, 337
Vorticella 161, 295, 299

Ward, H. B 28, 312

waste wet lands 401, 402, 407

water-boatman 201, 211, 276

water-birds 239, 240

water-bloom 14, 15, 101, 104, 106,
129, 132, 133, 161, 295,
296, 299

water-borne diseases 21

water-bugs 195, 210, 276, 318

water-content 26

water-cress 145

water crops 392, 403

water crowfoot 156, 319, 344

water culture 377, 378, 379, 391, 400
401, 402, 403, 404, 406,
409

waterfalls 64, 80, 81, 117, 358

water-fern 134, 145, 149, 334

water-fleas 19, 185, 186, 246, 247, 248,
249, 266, 267, 269, 285, 306,
327,328,387,390,391,392

waterfowl 91, 239, 380. 409

water-garden 378,404, 407, 409

water-glass 409

water hemlock 345

water hornwort 319

water-lily 154, 334, 382, 404

water-meadows 153, 406

water milfoil 154, 155, 319

water-mites 193, 194, 301

water mold 140, 143, 144

water mosses 146, 148

water-net 122, 123

water-penny 224, 260, 368

water-plantain 324, 345

water plants 100

water power 403

water purslane 156

water reservoirs. . .169, 349, 401, 402

water-scorpion 212

water- shamrock 149, 405, 407

water shield 154, 334, 405

water-skaters 360

water snakes 238, 343

water-striders 237

water table 58, 70

438

Index

PAGE

water-tiger 280

water-vole 273

water walking-stick 276

water weeds. . .156, 161, 190,232,392

water, buoyancy of 30

density of .30, 31, 36, 54, 314

depth of 29, 307, 321

for drinking 21

fertility of 56

force of 135

' ' freezing of 31,80

ground 30, 56

hardness of 51

high and low 74, 96

mineral content of 52, 53

" mobility of 30

population of 100

run-off 56, 57, 85, 117

running 39

as a solvent 25, 40

stagnant 130

" standing 44

storage of 403

surface tension of 54

thermal conservation of 40, 79
transparency of . . . 26, 308, 309

turbidity of 27

underground channels of . 70
viscosity of 30, 54, 244, 248,
249

wastage of 403, 404

waters, alkaline 51

cave 191

drainage 48

flood 42

PAGE

waters, mineralized 40

polluted 162

public 386, 406

Weismann 301

wells 191

Wesenberg-Lund 248

whales 19, 274, 275

Whipple, G. C 27, 42, 401

whitefish 231, 233, 313, 388, 393

wiers 169

Will-o'-the wisp 96

willows I s8

Wilson, W. M 79

winds 27, 33, 35, 85

Wolffia 150

Wolle in

worms 254, 257, 285, 367, 390

worms, cylindric 172

hair 174

Nematode 172

Nemertine 174

oligochete 325

parasitic 174

thread 172

true 340

wrigglers 227, 250, 339

Wright, A. H 236, 237

Zaitha 211

Zannichellia 153

zooids 166, 169

Zostera 334

Zygnema 119

zygospores 120, 263