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ANIMALS FOUND LIVING TOGETHER IN SHALLOW INLETS
FROM THE SEA, LONG ISLAND SOUND

A TEXTBOOK
IN GENERAL ZOOLOGY

BY

HENRY R. LINVILLE, Ph.D.

FORMERLY HEAD OF THE DEPARTMENT OF BIOLOGY, JAMAICA
HIGH SCHOOL, NEW YORK CITY

HENRY A. KELLY, Pd.D.

DIRECTOR OF THE DEPARTMENT OF BIOLOGY AND NATURE STUDY
ETHICAL CULTURE SCHOOL, FIELDSTON, NEW YORK CITY

AND

HARLEY J. VAN CLEAVE, Ph.D.

ASSOCIATE PROFESSOR OF ZOOLOGY, UNIVERSITY OF
ILLINOIS, URBANA, ILLINOIS

GINN AND COMPANY

BOSTON • NEW YORK • CHICAGO • LONDON
ATLANTA • DALLAS • COLUMBUS • SAN FRANCISCO

COPYRIGHT, 1929, BY HENRY R. LINVILLE, HENRY A. KELLY

AND HARLEY J. VAN CLEAVE

ALL RIGHTS RESERVED

PRINTED IN THE UNITED STATES OF AMERICA

629.1

(Tfje gtftengum jgregtf

GINN AND COMPANY • PRO-
PRIETORS • BOSTON • U.S.A.

PREFACE

This revision of Linville and Kelly's Textbook in General
Zoology is issued under the joint authorship of Henr^ R.
Linville, Henry A. Kelly, and Harley J. Van Cleave. The
work of revising the material of the original book and the
selecting and organizing of new material has been carried
out by the junior author, with the cooperation and approval
of the senior authors. It has been the policy throughout
the revision to retain those distinctive features of method
of presentation and organization which have received such
general commendation and approval from teachers of
biology throughout the country who are familiar with the
earlier edition.

The contents of this book have been selected and ar-
ranged as the basis for a full year's course in zoology for
students beginning the subject. In the revision of the
original edition an attempt has been made to give a dis-
tinct biological orientation of the subject. The possibility
of utilizing the text for the animal portion of a biological
course has been kept constantly before the authors. In a
course covering but a single semester or term, or in a bio-
logical course extending through the year, wide latitude of
choice is offered the teacher.

The treatment of the phyla is in a descending order from

the Arthropoda to the Protozoa, and in ascending order

from the fishes to man. After many years of experience

with classes of beginning students we believe that an order

of this nature is likely to yield the best results. We do not

deny that good results may be obtained by following what

iii

iv GENERAL ZOOLOGY

is sometimes called the ''order of evolution/' beginning
with the Protozoa. Although the chapters are interdepend-
ent, and biological principles are developed in large measure
in the consideration of groups where they find most ready
application, yet there is sufficient unity in the individual
chapters to make it possible for the teacher to diverge from
the sequence which we have employed.

Whatever the order followed, it is evident that recitations
on the chapters in the textbook should be held only after the
student has made his study in the laboratory. The textbook
in science has its greatest usefulness in connecting, extend-
ing, and illuminating the work of the laboratory. Labora-
tory work and field observations bring the student in touch
with actual things, and if the studies are properly conducted
they will aid in developing the power of independent judg-
ment. The untrained student cannot build up a conception
of the science of zoology from the more or less isolated
data of the laboratory and field ; in this fact lies the justi-
fication of a textbook in zoology.

The inductive method of presentation, in necessarily mod-
ified form, has been followed in the earlier chapters of the
book, as being the natural mode of approach to a new sub-
ject based upon laboratory work. After the study of the
grasshopper, for example, another animal which has easily
recognizable relationship to this form is considered. Not un-
til the selected representatives of the Orthoptera have been
described are the characters of the order mentioned. By that
time the student's mind is ready for the definition of Orthop-
tera. The conceptions of the larger groups of invertebrate
phyla and classes are developed in the same manner.

Against the possibility that direct, continuous, page se-
quence may be followed in a course covering only a part of
the text, some of the fundamental biological material has
been introduced relatively early. This explains the position

PREFACE v

of the chapters on Some of the Life Processes (Chapter XII),
on Living Matter : Protoplasm and the Cell (Chapter XIII),
and on Heredity and Evolution (Chapter XVII). For a
course planned to occupy less than a full year the authors
recommend the omission in their entirety or in part of the
chapters on The Dragon Flies (Odonata) and the May Flies
(Ephemerida) (Chapter III), The Spiders and Allies : Arach-
nida (Chapter XIV), Allies of the Acephala: Mollusca
(Chapter XIX), Allies of the Earthworms : Annelida (Chap-
ter XXII), and The Bath Sponge and Some Allies : Porifera
(Chapter XXVI). By deleting some of these chapters from
the invertebrate section, the teacher may gain time for the
consideration of some of the vertebrates.

Before entering upon the work of the current revision the
authors secured the cooperation of representative teachers
who have been using the textbook. More than a hundred
biology teachers responded with personal letters and inter-
views concerning the details of the proposed revision. This
list of our colleagues, who in innumerable ways have aided in
the course of the preparation of the revisipn, is too long for
detailed acknowledgment here. The detailed criticisms and
suggestions offered by Miss Helen Loomis of the Bowen
High School, Chicago, Illinois, and by Dr. W. H. D. Meier
of the State Normal School, Framingham, Massachusetts,
have been of great value in directing the course of the revi-
sion. Dr. T. H. Frison of the Illinois State Natural History
Survey has very generously aided in numerous details,
especially in the verification of entomological terms. Bernice
F. Van Cleave, by constant collaboration in selecting and
in rewriting material, has been in great measure responsible
for whatever merit the new material may possess. As an
experienced biology teacher in secondary schools her aid
in maintaining proper perspective and point of view has been
inestimable.

vi GENERAL ZOOLOGY

Although in the current revision there have been numer-
ous changes in and additions to the illustrations, the draw-
ings which have given such distinction to the original edition
have been for the most part retained. These were the work
of Mr. S. F. Denton, Mr. L. H. Joutel, and Mr. E. N.
Fischer. In numerous instances the key letters or numerals
standing at the ends of leader-lines have been replaced by
full names, thus obviating the necessity of referring to a
legend to secure the names. For the many courtesies which
have made possible the use of drawings and photographs,
acknowledgment is offered with the individual figures.

The extensive list of zoologists and specialists who aided
in the course of the preparation of the original edition will
be found in the detailed acknowledgment in the Preface of
that edition.

It is our hope that the quotations which introduce the
chapters will serve to suggest to the imagination of young
students the poetic side of animal life and of nature gener-
ally. For some of the most fitting quotations we are in-
debted to personal friends.

H. R. L.

H. A. K.

H. J. Van C.

CONTENTS

CHAPTER PAGE-

I. The Common Red-Legged Grasshopper 1

II. The Allies of the Red-Legged Grasshopper : Orthop-

tera 15

III. The Dragon Flies (Odonata) and the May Flies

(Ephemerida) 24

IV. The Cicadas, Plant Lice, and Scale Insects : Homoptera 30
V. The Bugs with Overlapping Wings : Hemiptera ... 39

VI. The Beetles : Coleoptera 43

VII. The Butterflies and Moths : Lepidoptera 54

VIII. The Flies : Diptera 69

IX. The Ants, Bees, and Wasps : Hymenoptera 77

X. The Insects : Hexapoda 95

XI. Classification and Distribution of Insects 107

XII. Some of the Life Processes 117

XIII. Living Matter : Protoplasm and the Cell 129

XIV. The Spiders and Allies : Arachnida 137

XV. The Crayfish 145

XVI. The Jointed-Foot Animals : Arthropoda 157

XVII. Heredity and Evolution 173

XVIII. The Clam and Other Bivalves : Acephala 189

XIX. Allies of the Acephala : Mollusca 207

XX. The Starfish and Some Allies : Echinoderma .... 221

XXI. An Earthworm 238

XXII. Allies of the Earthworms : Annelida 251

XXIII. Roundworms: Nemathelminthes 256

XXIV. The Planarians, Flukes, and Tapeworms: Plathel-

MINTHES (FLATWORMS) 261

XXV. The Fresh- Water Polyp and Some Allies: Ccelen-

terata , 267

vii

32009

viii GENERAL ZOOLOGY

CHAPTER PAGE

XXVI. The Bath Sponge and Some Allies : Porifera . . 283

XXVII. Amceba and Some Allies : Protozoa 288

XXVIII. The Past History of Invertebrates and the Be-
ginnings of the Vertebrates 299

XXIX. The Yellow Perch 311

XXX. The Allies of the Perch : Pisces 321

XXXI. The Green Frog 332

XXXII. The Allies of the Frog : Amphibia 344

XXXIII. The Pine Lizard and its Allies : Reptilia .... 351

XXXIV. The Domestic Pigeon 368

XXXV. The Allies of the Pigeon : Aves 377

XXXVI. The Gray Squirrel 403

XXXVII. The Allies of the Squirrel : Mammalia 412

XXXVIII. The Historical Development of Zoology .... 441

INDEX 453

GENERAL ZOOLOGY

CHAPTER I

THE COMMON RED-LEGGED GRASSHOPPER

Though I watch their rustling flight,
I can never guess aright
Where their lodging-places are ;
'Mid some daisy's golden star,
Or beneath a roofing leaf,
Or in fringes of a sheaf,
Tenanted as soon as bound.

Edith M. Thomas

Distribution. Grasshoppers, or locusts, are found almost
everywhere in the United States, — usually in fields, mead-
ows, and along roadsides. There are many different kinds of
grasshoppers, but the species which heads this chapter is one
of the most widely distributed. It is known to naturalists
as Melan'oplus l fe'mur-ru'brum. Its habitat (the locality
where it is naturally found) eomprises grassy areas in almost
every state except on the high Western plains, where its
place is taken by a species much resembling it, — the Rocky
Mountain grasshopper, or locust (Melanoplus spre'tus). The
lesser grasshopper (Melanoplus atla'nis), somewhat smaller
and darker in color, is also found in nearly every part of
the country. These and several other grasshoppers are about
three centimeters (a little over an inch) in length, and re-
semble each other so closely that the following description
will apply nearly as well to one as to another.

1 The first time a scientific name is used, an accent mark is placed after the
accented syllable as an aid in pronunciation.

1

2 GENERAL ZOOLOGY

Plan of External Structure. The entire body is covered
with a hard, horny substance called chitin. This gives pro-
tection to the internal organs. The body is divided into
three clearly marked regions : the head, the thorax, and the
abdomen (Fig. 2). Each region is further subdivided into a
series of rings called somites, which give flexibility to the
body in spite of the hard chitinous covering. These rings
are most clearly observed in the abdomen, which is made
up of ten easily counted somites. The three somites of the
thorax are less clearly distinguishable because they have
become slightly modified and shoved together. Though the
head seems to be but a single structure without division into
somites, it is fairly certain that six somites have been so
completely combined and fused to form the head that divi-
sions are no longer present. The external plan upon which
the grasshopper is built is thus seen to be a series of somites,
of which the anterior (front) somites bear jointed append-
ages modified for various uses.

The Head. The head of the grasshopper serves in taking
food and making the animal aware of its surroundings.
These functions are performed chiefly by appendages, or
paired outgrowths from the head. Certain of these append-
ages are purely sensory ; others aid in securing and devour-
ing food. The most conspicuous sensory appendages are the
pair of slender, jointed antennae, or feelers. In the grasshop-
per these are organs of touch and smell. Just behind the
antennae, on the sides of the head, is the pair of large
compound eyes. Each compound eye is covered with a
transparent layer of chitin which is divided into a large
number of six-sided divisions, each of which is called a
facet. Such an eye is said to be compound because each
facet has beneath it the necessary structures for sight.
Since the surface of a compound eye is convex, each facet
points in a different direction. It seems probable that each

THE COMMON RED-LEGGED GRASSHOPPER

Hypopharynx

unit of the eye does not make a complete image, but the
combined effect of all the units taken together produces a
mosaic pattern of whatever stands in range of the lenses.
In addition to the compound eyes, there are three ocelli
(Fig. 2), or simple eyes,
arranged, one almost Labrum

in the exact center of
the front of the head,
and one directly above
the base of each an-
tenna. Notwithstand-
ing these two kinds of
eyes, it is doubtful
whether the grasshop-
per is able to perceive
well the outlines of ob-
jects or to distinguish
much except light and
movement. The ocelli
probably do not per-
ceive objects at a
greater distance than
a few inches, nor the
compound eyes at a
greater distance than
a few feet.

The mouth of the
grasshopper is on the

ventral, or lower, surface of the head. It is surrounded by
a number of structures, together known as the mouth parts
(Fig. 1). These consist of a flap-like upper lip, or labrum ; a
lower lip, or labium ; a pair of maxillse ; a pair of mandibles ;
and a tongue, or hypopharynx. The maxilla? are located at
the sides of the mouth. Both they and the labium have

Maxillse

^^W0

Labium

Fig. 1. Mouth parts of red-legged grass-
-. hopper, (x 4)

4 GENERAL ZOOLOGY

short feeler-like organs called palpi. The hard mandibles
grind the food, which is held and passed in to them by the
other mouth parts.

The Thorax. The first somite of the thorax, called the
prothorax (Fig. 2), bears the first pair of legs. It is free
from the rest of the thorax. The dorsal surface (Lat. dor-
sum, " back ") is thickened and raised into a ridge, the sides
(lateral surfaces) are also thickened, and the whole forms
a protective shield or collar. The second somite, the meso-
thorax (Fig. 2), bears the second pair of legs; to the third,
or metathorax, the last pair of legs is attached. Each leg is
composed of a number of divisions, of which the principal
are the thick femur (Figs. 2, 3) and the spiny tibia (Fig. 3).
Each leg ends in a series of three small joints, forming the
tarsus, or foot, the last division of which bears two claws,
with a pad, the pulvillus, between them.

Of the two pairs of wings (Fig. 2), the first is attached to
the surface of the mesothorax, the second to the metathorax.
The anterior pair is somewhat hardened, forming protective
covers for the more delicate posterior wings, which are
folded like a fan beneath them. The latter only are used
in flight. The wings are simple extensions of the body wall,
and not jointed appendages like the legs. On the sides, just
beneath the posterior edge of the collar on the prothorax, is
a pair of breathing openings, or spiracles (not shown in the
figure). Two spiracles are placed just above the junction of
the second pair of legs (Fig. 2), and the abdomen bears eight
pairs along the sides.

The Abdomen. The first abdominal somite is much larger
than the others, though it does not form a complete ring,
owing to the space occupied by the cavities for the attach-
ment of the hind legs. Each side of this somite bears an
oval spot consisting of a thin skin stretched across a small
cavity and connected with a nerve, the whole forming an

Antenna--,

Compound eye .
Head

Anterior wing ^ 3

Posterior wing

Tympanum

Mandible
Labrum

. Palpus of maxilla

Labium
_ Labial palpus

. Femur of first leg
Prothorax

Mesothorax
Femur of second leg
Spiracle on mesothorax

Metathorax

Femur
of third leg

Spiracle on first somite
of abdomen

-Spiracle on second somite
of abdomen

"N. Abdomen

Fig. 2. External parts of male grasshopper, (x 4)

After Kingsley

6 GENERAL ZOOLOGY

ear, or tympanum (Fig. 2). The end of the abdomen in the
female is more tapering than in the male, and is furnished
with two pairs of blunt spines, which form an egg-laying
instrument, or ovipositor (Fig. 3).

The Digestive System. After this brief review of the main
features of the external anatomy, or structure, of the grass-
hopper, we turn our attention to the organs of the interior.
And first, owing to its size and the ease with which its parts
may be examined, we may consider the digestive system.
The function of the digestive system of an animal is to pre-
pare the food for use by the different organs of the body.
In the grasshopper the organs of digestion are the food tube,
or alimentary canal, and its accessory organs, the salivary
glands (Fig. 3) and gastric caeca (gastric, pertaining to the
stomach ; caeca, plural of caecum, a pouch or cavity open
only at one end).

The alimentary canal is a long tube extending through the
body and variously modified in the course of its extent. The
first division is the mouth, guarded on each side by the later-
ally moving mandibles. Between the mandibles, and arising
from the inner surface of the labium, is a short, brown,
tongue-like organ, the hypopharynx (Figs. 1, 3). At the
base of the hypopharynx opens the tube from the several
pairs of salivary glands. A portion of the slightly convex
surface of the inner side of the labrum is the epipharynx,
the seat of the sense of taste.

Beyond the mouth the alimentary canal continues as a
short, curved esophagus (Fig. 3), which leads to a large crop,
armed with rows of spine-like teeth. Posterior to the crop
is a very small gizzard, also furnished with spines, opening
directly into a large, thin- walled stomach (Fig. 3). At the
anterior end of the stomach are attached the six tubular
gastric caeca, closed at one end but opening into the stomach
at the other. Beyond the stomach the alimentary canal

THE COMMON RED-LEGGED GRASSHOPPER 7

continues as a slightly coiled tube, the intestine, and ends
posteriorly at the anal opening (Fig. 3).

The functions of these different parts are as follows. The
food, after being crushed by the mandibles and moistened by
the saliva, enters the crop, where it is subjected to the action
not only of the saliva but also of a fluid from the gastric
caeca. The "molasses" thrown out from the mouth as a de-
fensive fluid by the grasshopper, when handled, consists of
partially digested food from the crop, mixed with the diges-
tive fluids. When sufficiently dissolved and changed chemi-
cally, the food filters through the spines of the gizzard into
the stomach, where it is further acted upon by another
digestive fluid. The thin walls of the stomach allow the
prepared food to pass through and mingle with the blood
in the general body cavity. This process is called absorp-
tion. The anterior part of the intestine is thin-walled, and
absorption may take place there and also in the caeca. The
unused food material passes from the body by way of the
anal opening.

The Circulatory System. When the food has been acted
upon by the various digestive fluids, and so changed that it
may be used to supply the different organs with nourish-
ment, it is distributed over the body by the circulatory sys-
tem. At the same time certain waste matters are taken
away and carried to organs which remove them from the
body. In the case of man and many other animals, the cir-
culatory system is also the means by which oxygen is carried
to all the organs; but, as we shall see in a moment, this
work is otherwise provided for in the grasshopper. As soon
as the prepared food has been absorbed by the walls of the
stomach and intestine it mingles with the blood, which flows
through the body cavity in sinuses (spaces between the
various organs), though not in definite blood vessels. The
blood is propelled by a tubular, pulsating vessel, or heart

8 GENERAL ZOOLOGY

(Fig. 3), which extends through the abdomen just beneath
the dorsal surface. On account of its position in the body
it is often spoken of as the dorsal vessel. The heart is pro-
longed anteriorly into a tube leading to the head, and is
partially divided by valves into eight chambers, which per-
mit the movement of the blood only from the posterior to
the anterior end. When the blood has been passed out into
the general body cavity, it returns through a closed tube
(ventral sinus) between the muscle masses lying in the lower
(ventral) part of the body, and reenters the heart through
side openings.

The Respiratory System. The function of the respiratory
system is to provide for a constant supply of oxygen for all
the organs of the body and to remove waste material, chiefly
carbon dioxide. This is accomplished by a system of tubes,
called tracheae, communicating with the surface by the spir-
acles of the thorax and abdomen. The tracheae are con-
nected and form a network of tubes running to all parts of
the body, even out into the legs and wings. They are also
in connection with a system of large air sacs (Fig. 3) ex-
tending through the body. The tracheae are kept perma-
nently open by a spiral thickening of their chitinous lining,
so that air may enter freely at all times. Air is drawn into
and forced out of the tracheae by rhythmic contractions of
the body. A constant supply of oxygen is thus assured and
carbon dioxide is expelled. The completeness of the respir-
atory system in the grasshopper is in striking contrast to
the undeveloped character of the circulatory system.

The Excretory System. The union of the oxygen taken in
during respiration with the carbon in the body produces car-
bon dioxide, — a waste product. This leads us to consider
the organs which assist in the removal of materials which
have helped to build up the body substance and have be-
come so changed chemically that they are no longer useful.

Nerve leading to antenna -i
Esophagus — -\
Hypopharynx -

Labrum — r

Mandible

Subesophageal ganglion- -~^H

Salivary glands _ _/#-J

Antenna

Supraesophageal
ganglion

- Thoracic air sac
Gastric cseca

Gastric
cxca

Thorax

First abdominal
ganglion

Femur of third pair of legs

Malpighian tubes 1

^v-X- -^ - _ Abdominal

Oviduct

First joint-

of tarsus jn Cement

®pt/ gland - -

Ovipositor

Claw — ^

51 -Ami opening

% ^-Ovipositor

lOpening of oviduct

Fig. 3. Dissection of the common red-legged grasshopper (Melanoplus

femur-rubrum) . (x 4)

10 GENERAL ZOOLOGY

Such organs are termed organs of excretion. Besides carbon
dioxide, important excretory products are water and various
substances containing nitrogen, hence called nitrogenous
wastes. The two latter classes correspond to the material
removed by the kidneys of the higher animals.

Very little is known of the process of excretion in insects.
It has been generally believed that the carbon dioxide finds
its way to the surface through the tracheae. In some cases it
probably escapes through the skin. Water and the nitroge-
nous wastes are removed by malpighian tubes (Fig. 3), which
form so prominent an object when the body of the grass-
hopper is first opened. They ramify through the body cavity
and open into the alimentary canal at the junction of the
stomach and intestine, their contents passing to the outside
with the undigested food in the intestine. This undigested
food is not an excretion, using the word in the sense de-
fined above, since it has never formed a part of the body
substance. It has been suggested that as the chitinous
covering of insects is largely made up of carbon and nitro-
gen, the frequent casting of the skin (molting) may be an
act of excretion of considerable importance before the insect
reaches its adult state.

The Nervous System. All the processes just described,
even the flow of blood and the secretion (formation) of the
digestive fluids, are under the control of the nervous system.
Through its organs of sense the grasshopper is brought into
touch with the outside world ; by its control over the mus-
cles, movements are made. The nervous system of the
grasshopper consists of a series of connected nerve centers,
called ganglia (Fig. 3), from which nerves are given off to
the different parts of the body. There are two kinds of
nerves, sensory and motor ; the former carry messages from
the various sense organs to the ganglia ; the latter carry
impulses from the ganglia, which result in the contraction

THE COMMON RED~LEGGED GRASSHOPPER 11

of muscles and movements of the various organs, or of the
body as a whole.

The largest ganglion is in the head, and is generally called
the " brain," or, because of its position just above the esoph-
agus, the supraesophageal ganglion (Fig. 3). From this
ganglion pass the nerves which go to the eyes, antennae, and
labrum. Two cords encircling the esophagus pass to the
next ganglion, which, owing to its position just beneath the
esophagus, is called the subesophageal ganglion (Fig. 3).
This ganglion sends nerves to the mandibles and maxillae.
The supraesophageal and the subesophageal ganglia preside
over and coordinate the various general movements of the
grasshopper's body. It has been shown that an insect may
live for months with the anterior of these ganglia destroyed,
if the other is not injured. The insect will feed if food is
placed to its mouth, but it loses the power to go in search
of food. Of the other ganglia three are in the thorax and
five are in the abdomen, forming a median chain resting on
the ventral surface of the body cavity. These ganglia are
centers for the control of movements and respiration in the
somites to which they belong.

The Muscular System. All the muscles of the body are sup-
plied with microscopic nerves. The muscles are attached to
the hard covering of the body, and when stimulated by the
nervous system they contract, thus moving the part to
which they are attached. Though delicate in appearance the
muscles are in reality very strong, as may be understood
when the activity of the insect is 'considered.

The Reproductive System. As in most other animals, the
union of two dissimilar elements is necessary for the produc-
tion of a new grasshopper. These elements are the very
small, active sperm cells produced by the male, and the
much larger egg cells produced by the female. The repro-
ductive cells are produced in special organs called gonads.

12

GENERAL ZOOLOGY

On the union of these two cells the egg cell is said to be
fertilized, and the growth of a new individual is begun. Oc-
cupying a considerable part of the posterior portion of the
abdomen of the female are the ovaries (Fig. 3), two sets of
delicate tubular organs, in which the egg cells are developed.
These are connected with the surface by the egg tube, or
oviduct (Fig. 3). In the male the sperm cells are formed in
organs called spermaries, a tubular mass in the third,

Fig. 4. Rocky Mountain grasshopper laying eggs. (About natural size)

A, B, female laying eggs; C, diagram showing the arrangement of eggs in the
hole ; D, mass of eggs removed from hole and part of covering taken away ; E,

few eggs separated. (After Riley)

fourth, and fifth abdominal somites. After fertilization the
eggs are covered on the way down the egg tube by a sticky
substance poured out from the cement gland (Fig. 3). This
gland opens into an enlarged pouch, or bursa (Fig. 3), which
rests on and opens directly into the oviduct.

Development. The eggs of the red-legged grasshopper are
laid in the autumn in holes made by the ovipositor of the
female, in the ground of fields, pastures, and waysides.
They differ in no important respect from the eggs of the
Rocky Mountain grasshopper shown in Fig. 4. Each hole
contains from twenty to thirty-five eggs. A secretion from

THE COMMON RED-LEGGED GRASSHOPPER 13

the gland already mentioned
binds all the eggs in a single
hole into one mass, and
when the number is com-
pleted more fluid is poured
out, which hardens into a
firm covering. Here they
remain over the winter and
hatch out into young grass-
hoppers in the spring, quite
closely resembling the adult
except in absolute and rela-
tive size of parts and in the
absence of wings. They
grow rapidly, molting sev-
eral times during the sum-
mer, appearing each time a
little larger. While these
changes are going on the
young grasshopper is called
a, nymph (Fig. 5, A-E). The
last molt takes place late in
the summer. The nymph
climbs up some grass stem
or similar object. Tak-
ing firm hold, often
with its head pointing
downward, it remains
motionless for several
hours, till the skin
swells over the head
and thorax and finally
splits open along a me-

Fig. 5. Development of grasshopper
A X 6, B X 2, the others slightly enlarged l
1 From Packard's Text- Book of Entomology.

14 GENERAL ZOOLOGY

dian dorsal line. From this old skin the new head, thorax,
legs, wings, and abdomen are slowly withdrawn while the
new skin is still very soft. The body and all its appendages
expand and harden within half or three quarters of an
hour. It is now an adult insect, or imago, of full size and
with fully developed wings, which up to the last molt have
been of no use to the grasshopper.

Relation to Environment. Red-legged grasshoppers are
found in meadows, pastures, fields, and along roadsides,
though most abundant where the vegetation is succulent.
Specimens from low, damp ground are usually somewhat
darker in color than those from high, dry areas. Their food
consists of the leaves of grasses and other vegetation. The
strength of the mandibles and the complexity of the diges-
tive system fit them admirably for a life of constant forage.
Their color is, to a certain extent, protective, for they are
not easily seen among the dried grasses of the summer.

Grasshoppers have, when adult, three methods of pro-
gression, — walking, jumping, and flying. The many spines
pointing downward on the legs and the pulvilli between the
tarsal claws make climbing an easy matter.

The list of the grasshopper's enemies is long and formi-
dable, even if man is not considered. Small animals, such
as moles and birds, especially the crow and blackbird, feed
on the eggs and the young. Some species of wasps use the
nymphs to provision their nests, first stinging them to
render them helpless. They are also subject to a disease
caused by a fungous growth, and may often be found firmly
attached to some grass blade to which they have clung
before death. That they have been able to maintain them-
selves in such large numbers in spite of all their enemies,
marks them as successful competitors in the struggle for
existence.

CHAPTER II

THE ALLIES OF THE RED-LEGGED GRASSHOPPER:

ORTHOPTERA

The poetry of earth is never dead :

When all the birds are faint with the hot sun,

And hide in cooling trees, a voice will run

From hedge to hedge about the new-mown mead ;

That is the Grasshopper's — he takes the lead

In summer luxury, — he has never done

With his delights.

Keats

The Rocky Mountain Grasshopper. Though the common
red-legged grasshopper is widely distributed throughout the
United States, it has not attracted so much attention as the
Rocky Mountain grasshopper, for its effects on agriculture
have not been so marked. The latter has the remarkable
habit of migrating from its habitat on the dry plains east of
the Rocky Mountains, destroying in a few hours the labors
of the farmer for several months. Not only are growing crops
devoured, but every green thing is attacked, leaving the
country as bare as if a fire had swept over it. The grass-
hoppers show a tendency to become gregarious (having the
habit of associating in groups) from the beginning of their
life as nymphs, but their migrations are not generally begun
before they are at least half grown. These hordes proved
so destructive to the agricultural district of the Middle West
from 1873 to 1877 that a commission was appointed by the
government to study their habits and to report upon ways
and means for checking their devastations.

Control of Grasshoppers. Many machines have been con-
structed to capture the various kinds of grasshoppers when

15

16

GENERAL ZOOLOGY

they become abundant enough to threaten cultivated crops.
One of the commonest of these is called the hopperdozer.
As this is dragged across a field the grasshoppers start to
fly or jump but strike an upright wall and drop into a
trough filled with oil.

Since grasshoppers are chewing insects, one of the best
means of exterminating them is by use of sweetened poi-
soned bran, which they eat in preference to the vegetation.
In years when they are abundant many millions of dollars

worth of grain are saved
annually by poisoning and
by capturing the swarms
of grasshoppers invading
the fields.

Grasshoppers in History.
There are several species
of migratory grasshoppers
in the Old World whose
visitations in the past
have been destructive,
especially in Egypt, Palestine, Syria, Asia Minor, China,
Russia, France, and Germany. The prophet Joel has de-
scribed the onslaught of grasshoppers in the lines beginning

A day of darkness and of gloominess, a day of clouds and of
thick darkness, as the morning spread upon the mountains: a
great people and a strong; there hath not been ever the like,
neither shall be any more after it, even to the years of many
generations.1

It is easy to appreciate the fact that in thickly settled areas
famine and pestilence may follow the visitation of these in-
sects. Out of the twelve hundred or fifteen hundred species
of grasshoppers in the world, only about twelve have the
habit of migration to any great extent, and these are mostly

» Joel ii, 2.

Fig. 6. A meadow grasshopper

From the Illinois State Natural History
Survey

ALLIES OF THE RED-LEGGED GRASSHOPPER 17

species which live on large, elevated, open tracts of desert
or semidesert character, where the climate is dry and hot,
— for example, such regions as the steppes about the Cas-
pian Sea. Perhaps the determining factor in the migration
is excessive multiplication and the consequent need for new
feeding ground.

Grasshoppers have been and are used today as food in
various parts of the East. The records on the bricks of
Babylon and Nineveh show that they were known in early

Fig. 7. Katydid. (Natural size)1

times as food, and they are mentioned among the
clean meats in Leviticus xi, 22. They are in com-
mon use among the Arabs and the Bushmen ; our own Rocky
Mountain grasshopper has been eaten and pronounced quite
palatable.

Sounds. Many grasshoppers produce sounds by rubbing
the inner edge of the posterior femur against the outer edge
of the first pair of wings. Some grasshoppers produce a
noise in flight by the friction of the wings.

Long-Horned Grasshoppers. In contrast to the grasshopper
described in the last chapter there are others which have
very long antennae and are therefore called long-horned
grasshoppers (Figs. 6, 7). These have thread-like antenna?,
much longer than the body. Perhaps the most interesting

1 From Hunter's Studies in Insect Life.

18 GENERAL ZOOLOGY

are the katydids (Fig. 7), large green insects of arboreal
(tree-dwelling) habits, found in the eastern and central
United States. They afford an illustration of protective re-
semblance, — a term which is used to cover those cases in
which an animal possesses colors or shape which harmonize
with its environment (surroundings), or with some par-
ticular object in the environment, thus affording protection
against enemies. In the case of katydids the whole body
is green and the wings are thin and veined like a leaf. The
well-known note from which the name "katydid" is derived
is produced only by the male, and is made by rubbing the
base of one of the first pair of wings against the other
anterior wing. An auditory apparatus is found in both
sexes at the base of the front tibiae, not on the abdomen as
in the short-horned grasshoppers. The female has a long
sword-like ovipositor (Fig. 6) with which the eggs are thrust
in overlapping rows into the bark of twigs. The common
meadow grasshopper (Orchel'imum, Fig. 6) gives a good
idea of the appearance of a long-horned grasshopper.

Crickets. The crickets (Fig. 8, A) resemble the grass-
hoppers in the possession of long, slender antennae, but
differ from them in having the anterior wings overlapping,
instead of meeting in a ridge along the median line of the
back. They are widely distributed over the earth, and are,
as a rule, nocturnal in their habits. They feed mostly on
vegetable matter, though at times they destroy clothing.
Our native species live in the fields beneath sticks and
stones. The house cricket of Europe (Gryl'lus domes'ticus)
has spread into many parts of the United States. This is
the species famous in song and story. Its well-known chirp
is made only by the male. The principal vein on the ventral
surface of each anterior wing is thickened into a rasp-like
structure (Fig. 8, B) ; on another part is a hardened por-
tion called the scraper. The noise is produced by raising

ALLIES OF THE RED-LEGGED GRASSHOPPER 19

the anterior wings and rubbing the rasp of the right wing
against the scraper of the left. Fig. 8 shows one of the
species common in the eastern United States.

The mole crickets (Gryllotal'pa, Fig. 9) are burrowing in-
sects, which show interesting adaptations to subterranean

Position
of scraper

Rasp
Fig. 8. Cricket

-'Attachment
of wing

A, female (natural size) ; B, under surface of right wing of male, showing struc-
tures for producing sound

life. The fore legs are thickened and adapted to burrowing.
Roots are easily cut in two by means of a shear-like motion
of the joints of each front tarsus against the teeth of the
tibia of that leg. For this reason mole crickets, when numer-
ous, are sometimes
a serious pest. The
female mole cricket
watches over her eggs
and, when they are
hatched, feeds the
young till the first

molt. Mole crickets are found both in America and Europe.
Cockroaches. The cockroaches are cosmopolitan forms,
some of which infest our houses, where they feed on both ani-
mal and vegetable matter. They are dark-colored, flattened
insects, which depend upon their legs for escape, although

Fig. 9. Mole cricket. (Slightly enlarged)

20

GENERAL ZOOLOGY

most of them possess wings. The legs are adapted to running.
There is no development of strong jumping legs as in the
grasshopper and cricket. Their flattened bodies make it
easy for them to hide in crevices, whence they come out at
night to feed. They usually have a bad odor, and frequent

Fig. 10. Cockroaches. (Natural size)

all sorts of filthy places. The female carries her eggs about
with her in a large case till the young are nearly ready to
appear. Fig. 10 shows the German cockroach, or "Croton
bug" (Blatter la german'ica), with its egg case, and a larger
species, the so-called Oriental cockroach (Blat'ta orienta'lis),
though there is little evidence to show its original home.

Walking Sticks. The peculiar insects called walking sticks
are also related to the grasshoppers. Among them are some of
the most remarkable illustrations of protective resemblance
known in the animal kingdom. The common species in the

ALLIES OF THE RED-LEGGED GRASSHOPPER 21

eastern United States (Diapherom'era Jemora'ta) is shown
in Fig. 11. The body and legs are elongated to such an
extent that when at rest the resemblance to a twig is most
striking. The insect undergoes a seasonal change of color,
being brown when first hatched, turning green after feeding,
and changing to brown again as the season advances. This
walking stick is a voracious feeder on the leaves of trees.
One of the longest in-
sects now living is
a walking stick from
Africa, which has a
body about ten inches
long.

Closely related to
the walking sticks are
the peculiar East In-
dian insects known
as walking leaves. In
these insects the ante-
rior wings of the fe-
male are green and
veined like a leaf . The
people in the countries

where they are found believe that these insects are really
transformed leaves. The males are entirely different from
the females, having anterior wings which have no leaf-like
appearance.

Mantids. The mantids are remarkable for the develop-
ment of the fore legs, which are unusually large and strong
and armed with stout spines. The function of these legs is
to seize and hold living prey, which consists of other insects.
When the mantid is lying in wait the fore legs are held up
in the air, but when an insect comes within reach they
are extended with swiftness and precision. The eggs of the

Fig. 11. Walking stick. (About one half
natural size)

22

GENERAL ZOOLOGY

mantids are deposited in a mass of foam-like matter, which
the female discharges from the tip of the abdomen. This ma-
terial soon hardens and forms a protecting case for the eggs.

Fig. 12. Chinese mantid and egg mass, (x f )

The mantid shown with its egg case in Fig. 12 is a Chinese
species (Paratenode'ra sinen'sis), which has been introduced
in a number of places in the United States. The color is
brown and is to some extent protective. Since this incon-
spicuous coloration may render it easier for the insect to

ALLIES OF THE RED-LEGGED GRASSHOPPER 23

approach its prey or to escape notice while waiting for food,
it may be classed as an example of aggressive resemblance.
This term covers those cases where an animal, in resembling
its immediate environment, either in shape or color, or both,
is thought thereby to be assisted in attack on its prey.

Several species of mantids from India resemble different
flowers which are visited by insects, and seize upon such
unwary visitors as do not detect the imposition. In this
case the resemblance is to an object attractive to the prey,
and may be spoken of as alluring coloration.

Definition of Orthoptera (Gr. orthos, "straight"; pteron,
"wing"). All the insects mentioned in this chapter have the
mouth parts adapted to chewing, and most of them have
two pairs of wings. The posterior wings, when present, are
folded lengthwise like a fan beneath the hardened anterior
wings, and are thus protected from injury.

The newly hatched individual grows to the adult condi-
tion without any abrupt or conspicuous changes in form.
There is an evident increase in size each time the skin is
shed in the process of molting. The imagoes differ from the
nymphs chiefly in their larger size and the presence of
wings. This type of development in which the newly
hatched young gradually changes or transforms into the
adult is called incomplete metamorphosis. On account
of these common characteristics these insects are united
in a group, or order, called Orthop'tera, in allusion to the
longitudinal folding of the posterior pair of wings.

The chewing mouth parts with which the Orthoptera are
provided make them especially destructive to vegetation,
for they feed very largely on plants. Consequently many
members of the group are crop destroyers. Crickets and
cockroaches if given the opportunity become serious house-
hold pests. Many members of the order seem to have no
direct economic importance.

CHAPTER III

THE DRAGON FLIES (ODONATA) AND THE MAY FLIES

(EPHEMERIDA)

To-day I saw the dragon-fly
Come from the wells where he did lie.
An inner impulse rent the veil
Of his old husk : from head to tail
Came out clear plates of sapphire mail.
He dried his wings : like gauze they grew ;
Thro' crofts and pastures wet with dew
A living flash of light he flew.

Tennyson

Dragon Flies. The dragon flies (Libel'lula, Fig. 13) are
familiar insects found flying over the surface of still or run-
ning water. They feed on other insects, which they capture
on the wing. They are lovers of the sunshine, and are most
active in the brightest and hottest part of the day. The
larger kinds hawk freely over the surface of the water at
some distance above it, often far out from the shore, where
their range of vision is unobstructed.

It is not uncommon to find them coursing through the air
in fields and cities some distance from water. The smaller
and weaker kinds keep closer to the shore and the protec-
tion of vegetation. All are voracious feeders, destroying
large quantities of flies and mosquitoes. Many supersti-
tions have become associated with them in different parts
of the country; in the North, where they are popularly
called "devil's darning needles," it is believed that they sew
up the mouths and ears of children. In the South, where the
name "snake feeder" is generally used, they are thought to

bring dead snakes to life. It is, perhaps, needless to say that

24

'

Fig. 13. Dragon fly. (Natural size)
Nymph in water, nymph skin from which adult has emerged hanging to stem

26 GENERAL ZOOLOGY

they are not only harmless but are even highly beneficial.
The head is made up almost entirely of the great, staring,
compound eyes, which shine like fire as the dragon fly moves
about. The mouth has strong jaws, somewhat resembling
the powerful mandibles of the grasshoppers. The wings are
large, with many veins, and are moved by powerful muscles ;
but the legs are slender and small, as the dragon flies are
preeminently creatures of the air. The long and slender ab-
domen is used to balance the insect in its headlong flight.

The eggs, generally attached to water plants, hatch into
aquatic nymphs. The mouth parts of the nymphs are
unique in structure. The lower lip is enlarged and armed
with hooks at the extremity. This formidable organ is
hinged and folded, so that it can be extended to seize any
insect within reach. When not so engaged it covers the
entire face like a mask, giving a peculiar and comical aspect
to a front view. The nymphs breathe by means of tracheae,
which line the posterior portion of the alimentary canal.
When water is drawn into the canal, air is absorbed from
it by this system of air tubes, and water, deprived of its
free oxygen, is forced out again. When water is ejected
violently, the nymph darts forward. After successive molts
the nymph develops rudiments of wings and finally crawls
out of the water to some convenient support, when the skin
splits down the back (Fig. 13) and the dragon fly, with crum-
pled wings, slowly emerges. A short time elapses before the
body hardens and the wings expand, and then the imago
flies away to live its short adult life.

There are two quite distinct types of dragon flies, both
widely distributed over the world. The form represented in
Fig. 13 is of comparatively robust build. The eyes touch
each other along the median line of the head. The posterior
wings are broader at the base than the anterior pair, and
both pairs are held horizontally when the insect is at rest.

THE DRAGON FLIES AND THE MAY FLIES 27

To this type belong the best fliers of the group. The insects
which illustrate the other type, while they can easily enough
be recognized as dragon flies, are of more slender build. These
are commonly called damsel flies. Their eyes are widely sep-
arated on opposite sides of the head. The anterior and pos-
terior wings are alike in size and shape, and when not in
use are folded against the abdomen. The flight is less sus-
tained and more erratic than that of species of the first type.
Definition of Odonata (Gr. odous (odont-), " tooth"). The
dragon flies constitute the order Odona'ta, a word meaning
"toothed," perhaps in allusion to the teeth on the labium
of the nymphs. The Odonata are distinguished by the bit-
ing mouth parts and the four equal or nearly equal net-
veined wings. Though the nymphs do not closely resemble
the adults, there is no conspicuous change from one molt
to the next, except at the last molt. Then the fully formed
wings of the adult are liberated from the wing pads of the
nymph. Although the nymphs resemble the adults less
than in the case of grasshoppers the Odonata likewise have
incomplete metamorphosis.

The sun comes forth and many reptiles spawn ;
He sets and each ephemeral insect then
Is gathered into death without a dawn,
And the immortal stars awake again.

Shelley

May Flies. The May flies (Fig. 14), which stand in litera-
ture as the type of brief and purposeless existence, are deli-
cately constructed, pale insects, with usually four finely
veined wings and two or three long, white filaments project-
ing from the end of the abdomen. The eyes are compara-
tively large, but the mouth parts are so reduced that no
food can be taken during adult life, which in most species
lasts only a few hours. May flies appear in countless num-
bers in late spring or early summer, dance about in the air

28

GENERAL ZOOLOGY

at dusk in swarms so dense that the atmosphere seems one
mass of moving forms, and, after laying their eggs, perish
with the day, forming a great food supply for fishes and birds.

The eggs are laid in the water
and hatch into nymphs, which
do not at all resemble the adult
(Ephem'era, Fig. 14), but are
adapted to an aquatic existence
by the presence, along the sides of
the abdomen, of outgrowths of the
body wall penetrated by tracheae.
These outgrowths are called tra-
cheal gills. The delicate skin of
which the gills are formed permits
the passage of oxygen from
the surrounding water in-
ward, and allows the escape

Fig.„14. Nymph and imago of May fly. (Natural size)

of carbon dioxide. The young feed on small aquatic ani-
mals or on plants. After a year or more of this life beneath
the surface, during that time undergoing many molts, the
nymph develops rudimentary wings. From the nymph
issues a winged form which may be called a subimago.

THE DRAGON FLIES AND THE MAY FLIES 29

Within a very short time the skin is again cast, even to a
thin covering from the wings, and the true imago comes
forth. A molt in the winged state is known nowhere else
among insects. Though the reduced mouth parts make it
impossible for the adult May fly to take any food, the ali-
mentary canal is not useless. Air is taken in at the mouth,
and the capacious stomach acts as a balloon, being provided
with valves so that the air cannot escape.

Definition of Ephemerida (Gr. ephemeros, " lasting but a
day"). The May flies make up the order Ephemerida.
They may be distinguished from other insects by the two
pairs of lace-like wings, of which the hind pair is much the
smaller. Three or two fine, hair-like appendages extend from
the posterior end of the abdomen. The aquatic nymphs
have chewing mouth parts, but in the adults the mouth
parts are not functional. From the earliest nymph stages
to the imago there is a very clearly marked, though grad-
ual, change or incomplete metamorphosis.

CHAPTER IV

THE CICADAS, PLANT LICE, AND SCALE INSECTS:

HOMOPTERA

The shy cicada, whose noon-voice rings

So piercing shrill that it almost stings

The sense of hearing.

Elizabeth A. Kerr

Bugs. Though many people call any insect a bug, the
term "bug" is correctly applied to the insects belonging to
two orders, the Homop'tera and the Hemip'tera. These
orders comprise some of the most important insect competi-
tors of man. The insects of these two orders have long suck-
ing beaks in place of chewing mouth parts. They therefore
feed upon plant and animal juices instead of solid foods.

Cicadas. There are several species of cicadas in the United

States, of which the best known is the periodical cicada

(Tibi'cina septen'decim, Fig. 15). In the South this species

is usually called the thirteen-year locust, while in the North

it goes under the name of the seventeen-year locust. Many

of the cicadas which appear in the years between the cycles

of periodical cicadas belong to different species which in some

instances require not more than two years for their complete

development. The name harvest fly (Fig. 16) is frequently

applied to them. At the base of the abdomen of the male is

a "drum," or sound-producing organ, where a high-pitched

note is made by the rapid vibration of tightly stretched

membranes, somewhat in the way sound may be produced

by pushing up and down on the bottom of a tin pan. This

note, heard on hot summer days, has been celebrated as

the "song" of the cicada since the time of the Greeks.

30

CICADAS, PLANT LICE, AND SCALE INSECTS 31

The female of the periodical cicada lays her
eggs in slits, usually in the small terminal twigs
of trees. In a year in which these insects ap-
pear in large numbers the trees look as if a fire
had passed over them and scorched the ends
of all the twigs. The eggs hatch in about six
weeks, and the nymphs drop to the ground,
into which they dig. For a long period of time,'
thirteen years in the Southern states and seven-
teen years in the North, they lie in a cell,
feeding on the juices of the roots of trees.
Early in the summer of the thirteenth or
seventeenth year, they rise to the sur-
face, and, clinging to some convenient

support (Fig. 16, A),
cast their last nymph
skin (Fig. 16, B) to
come out as winged

Fig. 15. A study of the periodical cicada, (x J)

Female depositing eggs in stem of a plant, nymphal skin from which an

adult has emerged, and chimneys

32

GENERAL ZOOLOGY

creatures for their few weeks of adult life. In some cases,
when the nymphs reach the surface, they build peculiar
cones of clay (Fig. 15), several inches in height, over the
mouths of their burrows, entirely closing the top of the cone.
In the upper part of these they wait the period of their final
molt. The formation of these structures has been explained

Fig. 16. Harvest fly. (Natural size)
A, adult emerging from nymphal skin ; B, the cast skin ; C, adult 1

by some as due to the prevalence of long-continued wet
weather at the time of the emergence ; by others, as occa-
sioned by heating of the ground in certain localities by the
sun, thus bringing the nymphs to the surface before their
time. The cicadas have two pairs of transparent mem-
branous wings. When the wings are at rest they lie along
the sides and back of the body like a sloping roof.

Aphids. Everyone who has tried to keep plants indoors
must have noticed the small, green, oval insects known as

1 Reprinted by permission from Entomology, by J. W. Folsom, published by
P. Blakiston's Son & Co.

CICADAS, PLANT LICE, AND SCALE INSECTS 33

plant lice or aphids (Fig. 17). There are many species in-
festing different plants, upon the juices of which they feed.
Some attack the roots, but the greater number are found
upon the foliage. They are
generally not more than three
millimeters (about an eighth
of an inch) in length, with a
somewhat pear-shaped body,
and with or without wings.
In most species there is found
projecting from the back a
pair of slender tubes, which
secrete a sticky, waxen sub-
stance. This is probably pro-
tective in its nature.

One of the most interest-
ing aphids is the one living
on the roots of corn (Figs.
18, 19). This aphid {A' phis
maidi-rad'icis) has become a
domestic animal of one spe-
cies of ant. The cornfield
ant cares for the eggs of the
aphid in its nest through the
winter. In the spring when
the young aphids are hatched
the ants carry them through

Fig. 17. Aphids on grapevine.
(Slightly reduced)

Underground tunnels and Courtesy of the United States Depart-
. . ment of Agriculture

place them upon the roots

of weeds. This occurs before the corn is planted. As soon
as the corn is sprouted the ants transfer the aphids to the
corn roots. There they do much damage sucking the sap.
In return for their close attention the ants are paid by
securing the honey dew secreted by the aphids.

34

GENERAL ZOOLOGY

Very many of our cultivated plants and trees are
subject to damage by these insects. On the apple trees

Fig. 18. Aphid with wings. (Much enlarged)
From the Illinois State Natural History Survey

the woolly aphis (Erioso'ma lanig'erum) may live either
on the roots beneath the ground or on the branches.

In some species the eggs undergo
full development within the body of
the mother. In such cases the young
are born alive and fully formed. Re-
production in such instances is very
rapid. The food plant becomes so
completely covered that there is
scarcely standing room. An aphid
colony in the summer may consist
almost entirely of wingless females
(Fig. 19) which have the power of
producing generation after generation
of living young without fertilization.

This form of reproduction is known as parthenogenesis. The
young so produced are females, and many of them are wing-

Fig. 19. Wingless aphid

From the Illinois State
Natural History Survey

CICADAS, PLANT LICE, AND SCALE INSECTS 35

less, though winged females (Fig. 18) are produced which
start colonies in other places, sometimes on a different food
plant. Both winged and wingless females are able to pro-
duce young parthenogenetically within from ten to twenty
days. This kind of reproduction goes on till the approach
of cold weather or the failure of the food supply, when
males are produced. After pairing, the female lays eggs
which last through the winter and hatch into females in the
spring. These start
new colonies as al-
ready described.

Scale Insects. In-
cluded among the
scale insects are
some of the great-
est enemies to the
horticulturist. Al-
most all kinds of
trees and shrubs are
subject to their at-
tack. Most of these
scale insects become so changed in form (Figs. 21, 22) that
they would scarcely be recognized as insects. Ordinarily
they become immovably attached to the surface of the
plant, from which they draw their nourishment by means
of a beak, or sucking tube, thrust permanently into the
bark. The back of the insect is covered by a crust-like
scale which completely conceals the body. Fixed here
permanently, the female produces her eggs or her young,
which are at first sheltered by the parent scale. Frequently
the male (Fig. 22, d) is distinguishable from the female by
its smaller size and because it develops in an entirely differ-
ent manner. In most instances the young wingless females
after hatching from the egg soon leave the parent scale.

Fig. 20. An adult male scale insect.
(Much enlarged)

From the Illinois State Natural History Survey

36

GENERAL ZOOLOGY

They settle down at once and form permanent shelters over
their backs. Although the male, after hatching, at first
resembles the female, it emerges (Fig. 20) from its scale
after a time as a free-living, two-winged insect.

The San Jose* scale
(Aspidio'tus perni-
cio'sus, Fig. 21) was
introduced from the
Orient into this coun-
try about 1886. Since
that time it has spread
over the entire United
States and is one of
the most serious men-
aces to orchards. Tens
of thousands of acres
of fruit trees have
been killed outright
by this scale alone.

Oyster-shell scale
(Lepidosa'phes ul'mi)
attacks many shrubs
and fruit and shade
trees. It reproduces
so rapidly that the
entire bark becomes
incrusted with the scales (Fig. 22, c), and the trees soon
die unless the scales are killed or removed.

There are hundreds of species of scale insects some of
which are limited to a single food plant, although others
flourish on a great variety. The cottony scales are especially
destructive of shade trees. Oranges and other citrus fruits
are attacked by several species, the scales of which are
frequently observable on the skins of the marketed fruits.

Fig. 21. San Jose scale on young twig

Photograph by the Illinois State Natural
History Survey

CICADAS, PLANT LICE, AND SCALE INSECTS 37

Early in the history of the invasion of these scale insect
pests it was thought possible either to exterminate them or
at least to check their spread over the country. This has
proved to be impossible. Orchard and shade trees in many

Fig. 22. Oyster-shell scale insect

a, female, from beneath, showing eggs protected by scale (X 24) ; b, female from
above (x 24) ; c, female scale on branch (natural size) ; d, male scale (x 12) ;
e, male scales on twig (natural size). (After Howard, Yearbook, United States

Department of Agriculture, 1894)

parts of the country are kept alive only by periodic spray-
ing to kill the scales. Since these are sucking insects, get-
ting their food directly from the sap of the plant, poisons
are not available against them. The sprays, to be effective,
must on contact kill the insects under the scales.

38 GENERAL ZOOLOGY

Man is indebted to some of these insects for a variety of
products of greater or less value. One of the scale insects
(Coc'cus cac'ti), found on the cactus in Mexico, is the source
of the red coloring matter, cochineal ; to another {Tachar'-
dia lac'ca), of India, we are indebted for shellac. The manna
mentioned in the Book of Exodus is probably the secretion
of a scale insect. It is a sweet substance used today by the
Arabs as food.

Definition of Homoptera (Gr. homo-, "like"; pteron,
"wing"). The insects belonging to the Homoptera have
mouth parts modified as a sucking beak. In most instances
(except in the case of scale insects) there are two pairs of
membranous wings arranged as a sloping roof over the back.
Since the nymphs develop directly into the adults, the
Homoptera have incomplete metamorphosis.

CHAPTER V

THE BUGS WITH OVERLAPPING WINGS: HEMIPTERA

And there's never a blade nor a leaf too mean

To be some happy creature's palace.

Lowell

The Squash Bug. The squash bug (An'asa tris'tis, Fig. 23),
a well-known enemy of squash and pumpkin vines, pos-
sesses a beak with which it sucks plant fluids. This bug
is a little over two centimeters
(nearly an inch) long, and brown-
ish black in color. The two pairs
of wings are unlike in structure.
The under wings are membranous
and delicate, and

X

the outer wings
are stiffened at
the base and
have membranous tips which
overlap on the back at the
posterior end. The squash
bug has the power, in common
with many other allied species,
of pouring out an evil-smelling
secretion from two openings near
the base of the middle pair of
legs, which probably renders it
obnoxious to some creatures
which might prey upon it. Ob-
servations on the food of birds of

39

V

\J%

Fig. 23. Squash bug and young.
(Natural size)

40

GENERAL ZOOLOGY

the eastern United States seem to show that, so far at least
as the birds are concerned, these repellent odors are not in
all cases entirely effective, since many species of plant
bugs are fed upon quite generally by various kinds of birds.

a,

Fig. 24. The chinch bug

adult insect ; b, egg ; c-f, stages in development of the nymph ; wheat plant
with eggs on lowermost leaf and with nymphs on stems. (After Forbes)

Chinch Bug. The chinch bug (Blis'sus leucop'terus, Fig. 24)
is one of the worst enemies of the grain growers of the Mis-
sissippi Valley. Agricultural authorities estimated that in
one year (1914) the chinch bug alone caused a loss of more

BUGS WITH OVERLAPPING WINGS

41

than six million dollars' worth of grain in only thirteen
counties in Illinois (see Fig. 62).

Water Bugs. In almost every pond and stream, not only
in the United States but almost anywhere on the earth, are
to be found oval gray and black insects, usually a little
over a centimeter long (about half an inch). These are
water boatmen (Corix'a, Fig. 25, B). They have a long beak.
With this they suck the
body fluids of other water
creatures. They are adapted
to rapid locomotion in the
water by means of the length-
ened and fringed middle and
hind legs. They breathe a
thin film of air, which is
caught in the fine hairs which
cover the body, making them
look as if incased in polished
metal. Slight movements of
the legs cause currents of
water to pass over this air
film, helping to purify it,

Fig. 25. Water bugs. (All slightly
enlarged)

and making frequent Visits ^back swimmer, ventral view; A' back
& ^ swimmer, dorsal view; B, water boatman

to the surface unnecessary.

When the boatman is at the surface, air is taken into a
cavity under the wings, where the spiracles are placed, so
that quite a supply is on hand at all times. While these
insects are thus adapted to water life, at the same time
they can fly ; and they often leave their native element, espe-
cially if it is in danger of becoming dry.

Another widely distributed group of insects resembling
the foregoing are the back swimmers (Notonec'ta, Fig. 25, A,
A'), which have the curious habit of swimming on their
backs, as their common and scientific names denote. A favor-

42

GENERAL ZOOLOGY

covers.

ite position of these insects is to float with the head down
and the tip of the abdomen protruding just enough to
admit the passage of air to chambers beneath the wing
The back swimmers can inflict a momentarily
painful wound with their sharp beaks.
The giant water bugs, or electric-light
bugs {Bena'cus, Fig. 26), are about the
largest living Hemiptera. They fly read-
ily from pond to pond and in transit are
fcfo frequently attracted to electric lights.
They become especially important in fish
hatcheries and ponds because they attack
and kill small fishes, though they also
prey upon aquatic insects.

Definition of Hemiptera (Gr. hemi-,
"half"; pteron, "wing"). Members of
this order agree in possessing a sucking
beak and in having incomplete meta-
morphosis. Practically all of them have
two pairs of wings. The under wings are delicate and mem-
branous, and the outer wings have their bases hardened as
a protection to the under wings. On hatching from the eggs
the young fairly closely resemble their parents except in size
and in lack of wings.

Fig. 26. Giant water
bug, or electric-light
bug. (Natural size)

CHAPTER VI

THE BEETLES: COLEOPTERA

Now fades the glimmering landscape on the sight,

And all the air a solemn stillness holds ;
Save where the beetle wheels his droning flight,

And drowsy tinklings lull the distant folds.

Gray, Elegy in a Country Churchyard

More than two thirds of all the known insects are beetles.
Obviously no large proportion of these can be included in
an introduction to Zoology. The following are a few of the
most important.

June Beetles or May Beetles. During the warm evenings
of summer there is no more conspicuous insect than the big,
blundering, brown beetles (Fig. 27) that swarm about street
lamps and batter against our window screens. The hard
outer wings, or elytra, fit so perfectly over the back that the
June beetle (Phylloph'aga) seems to be dressed in a complete
suit of armor. These elytra meet in a perfectly straight line
down the middle of the back. The wings actually used
in flying are delicate and membranous. They are so much
longer than the elytra that even when the wings are brought
into the resting position their tips may stick out untidily
from under the elytra until the beetle tucks the ends in
place by folding the tips back. Like the grasshopper's the
body of the beetle is divided into three regions : the head,
thorax, and abdomen. The wings cover the back and sides
of the abdomen so completely that the somites are visible
only from the ventral surface.

The antennae are peculiarly constructed. Instead of end-
ing in a single thread-like tip, which usually indicates only

43

44

GENERAL ZOOLOGY

an organ of touch, these antennae end in a series of flattened
leaf-like structures, serving not only as tactile organs but
as organs of smell.

The white grubs (Fig. 27) so common in fields and gardens
are the young, or larvse, of the June beetles. They feed on
roots, sometimes in lawns frequently killing the grass over

s

Fig. 27. Adult June beetle, larva, and pupa. (Natural size)

large patches. In truck gardens they do great damage. The
adults center their attack above ground, devouring the
leaves, particularly of trees. The grub, or larva, when fully
grown stops eating and forms a small chamber in the soil
(Fig. 27), where it lies inactive. During this resting period
the entire body of the grub becomes reorganized. From
this resting stage, or pupa, the adult beetle finally emerges.
The June beetles belong to that family of beetles known
as the scarabs. Certain beetles of this same family have
long attracted the attention of observers by their curious

THE BEETLES: COLEOPTERA

45

habit of forming and rolling about a pellet of manure for
food for themselves or their larvae. We have several species
of these beetles in the United States, but the best known of
the group is the sacred beetle of the Egyptians (Ateu'chus
sa'cer, Fig. 28), the Scarabseus of the ancients, figures of
which are found carved in stone on the monuments of an-
cient Egypt. These beetles played an important part in the
symbolism of the Egyptians, to whom they typified the

Fig. 28. The sacred scarab. (X 2)
A, beetle with ball of manure ; B, scarab carved in stone

world and the sun, — the former on account of their round
pellets, the latter on account of the projections on the head,
which were likened to the rays of the sun.

The Japanese Beetle. One of the best examples that we
have of the rapid spread of a newly introduced pest is that
of the Japanese beetle (Popil'lia japon'ica). Introduced
into this country about 1916, probably on the roots of an
imported plant, by 1924 it had spread over an area of more
than a thousand square miles. Like the June beetle the
adult feeds above ground upon the foliage of trees and
shrubs, and the grub attacks the vegetation beneath, feed-
ing upon the roots. It is a well-known fact that a destruc-
tive animal like the Japanese beetle produces much more

46

GENERAL ZOOLOGY

alarming damage in its adopted home, for all its hereditary
enemies are lacking. The federal government is spending huge
sums of money in an. attempt to find natural means of check-
ing the Japanese beetle before it invades the entire country.
Tiger Beetles. The tiger beetles (Cicinde'la, Fig. 29) are
usually metallic, shining, bright-colored species, about one

and a half centimeters in
length, with large heads and
prominent eyes. They are
found on sandy roads or
beaches, flying about while
the sun shines. Some of them are bright
red or green; some are brown or black,
with white markings ; and others are pro-
tectively colored, resembling the sand on
which they live. They run swiftly, and
when disturbed take flight, only to alight
at a short distance, often facing about so
that they can better watch the pursuer.

The larvae are misshapen, dirty-white
grubs, living in holes which they dig in
sandy places. Two hooks on the dorsal
surface enable them to climb up and down
in their holes, which are sometimes thirty
centimeters or more deep, and prevent their being dragged
out when they have hold of their prey. Here, with the earth-
colored head even with the surface, they lie in wait, seizing
any passing insect with their strong jaws.

Water Beetles. The whirligig beetles (Dineu'tus, Fig. 30)
are familiar oval insects found in groups circling about on
the surface of still water. They can see both below and
above the surface of the water, as the two eyes are divided
into four, and the parts separated so that watch can be kept
for danger from either direction. The whirligigs are pro-

FlG. 29. Tiger

beetle and larva.

(Natural size)

THE BEETLES: COLEOPTERA

47

tected by a strong-smelling milky secretion which probably
renders them distasteful to fishes. They are able to dive to
escape danger, carrying down with them a small supply of air.
Beneath the surface of such ponds and pools as the whirli-
gig beetles frequent are to be found different species of div-
ing beetles (Dytis'cus, Fig. 31), which have adaptations
similar to those mentioned among the aquatic Hemiptera.
Thus in some the spiracles, which in land insects are along
the sides of the abdomen, are here placed beneath the edge

Fig. 30. Whirligig beetles. (Natural size)

of the wing covers on the back, and the space beneath the
wing covers is used as an air reservoir, which is replenished
with pure air by rising to the surface. In other species a
thin coating of air is carried on the under side of the abdo-
men. This supply is obtained by pushing the head above
water and capturing a bubble of air with the antennae, which
are quickly folded beneath the head, carrying the impris-
oned bubble to the under surface of the body.

Scavenger Beetles. A useful part in the economy of na-
ture is played by the scavenger beetles (Necroph'orus, Fig.
32), large, black, red-spotted insects, which dig beneath the
carcasses of small animals, thus burying them beneath the
surface. The female then lays her eggs in the decaying ma-
terial, upon which the larvae feed until ready to transform.

48

GENERAL ZOOLOGY

This exertion removes the carcass from the field of opera-
tions of other creatures which might feed upon it, if it were
left exposed, and thus destroy the eggs, or larvae. As these
beetles are protected by a fetid odor, their striking markings
are usually spoken of as an example of warning coloration,

iiiy

i

Fig. 31. Diving beetle. (Slightly enlarged)

a term applied to those appearances in animals which are
thought to be useful in notifying enemies of the presence of
something disagreeable or dangerous.

Lady Beetles. The common and well-known insects vari-
ously called lady beetles, ladybugs, or ladybirds (An'atis,
Fig. 33), are hemispherical in shape and generally reddish or
yellowish in color, with black spots. Both the imagoes and
larvae of most species feed upon scale insects, plant lice, and

THE BEETLES: COLEOPTERA

49

Fig. 32. Scavenger beetle. (Slightly
enlarged)

other insects injurious to vegetation ; hence they are to

be reckoned among the insects useful to the farmer.

The lady beetles are
protected by a yellow,
odorous fluid formed in
the blood. When the
insect is seized the fluid
oozes out from the ends
of the femora. The
bright colors of these
insects are usually cited
as an example of warn-
ing coloration.

Click Beetles. The
click beetles are a well-
known group, generally brown in color and of elongate form.

The species are able to leap into the air when placed on

their backs. The mechanism which

makes this possible consists of a

spine projecting backward on the

ventral surface of the prothorax,

and a corresponding cavity on the

ventral surface of the mesothorax.

The larvae are called wireworms and

live in decaying wood or attack the

roots of vegetables.

Fireflies. The flashing lights of

the fireflies (Photi'nus) on the first

warm evenings announce the com-
ing of summer. One would scarcely

accept these soft-bodied insects

(Fig. 34) as beetles were it not for

the way in which the outer wings meet down the middle

of the back in a straight line in true beetle fashion.

Fig. 33. Lady beetle. (x2)

50

GENERAL ZOOLOGY

Fireflies are, for the most part, nocturnal in their habits,
clinging to the underside of leaves during the day. They
are protected from the insect-eating birds by a strong odor
which renders them distasteful. The luminous spots are

on various abdominal
somites, generally the
last. Fireflies appear in
greatest numbers in the
latitude of the Middle
Atlantic states for a
week or more in the
month of June. Many
attempts have been
made to account for the
light produced by the
fireflies. The light-giv-
ing organ seems to con-
sist of fat cells inclosed
in a network of fine
tracheae. Though the
production of light is
the result of oxidation,
practically no heat is
liberated. Thus it is
interesting to note that
the efficiency of this
apparatus as a light-
producing organ is close
to 100 per cent. In such artificial illumination as a gas
jet, for example, only about 2 per cent of the radiant
energy consists of light rays. The function of the light of
the fireflies is not understood.

The Colorado Potato Beetle. The Colorado potato beetle
(Leptinotar'sa decim-linea'ta) is well known to every farmer

Fig. 34. Firefly. (Slightly enlarged)

THE BEETLES: COLEOPTERA 51

boy. It is particularly harmful because both the larvae
(Fig. 35, b) and adults (Fig. 35, d) feed upon the leaves
of the potato plants. Originally it was confined to the
Rocky Mountain region, where it fed on the wild relatives
of the potato. In about 1855 it commenced feeding on the
potato plant. It spread so rapidly that in about fifteen

Fig. 35. Stages in the life of the Colorado potato beetle

a, eggs on leaf ; b, larvae ; c, pupa from soil ; d, adult ; e, one wing ; /, a leg ;
a-d, natural size ; e, f, enlarged. (Redrawn from Riley)

years it appeared on the Atlantic coast and has become a
pest throughout the country wherever potatoes are grown.
The Cotton Boll Weevil. The cotton boll weevil (An-
thon'omus gran'dis) is one of the small snout beetles, the
larva of which lives in the buds of the plant, destroying the
fibers so that the infected boll produces no cotton. The boll
weevil is not a native of the United States, but came in
over the Mexican boundary about 1890. It has spread
widely over the cotton-growing states. In 1923 it destroyed
more than one half of the entire cotton crop.

52

GENERAL ZOOLOGY

Buffalo Beetles. Households are
frequently bothered by hairy, black
or brown larvae (Fig. 36, a) which vo-
raciously devour clothing, carpets,
upholstering, furs, and almost any-
thing of animal origin. These are the
larvae of the buffalo beetles (Anthre'-
nus, Fig.36). The work of these larvae
is often taken for that of moths. It
is difficult to keep collections of bird
and mammal skins and dried insect
collections because of these destroy-
ers. There are several genera (seepage
107 for definition of genus), all of
which belong to the one family called
dermestids or "skindevourers."
Wood-Boring Beetles. Beetles known as the long-horned
and the flat-headed beetles or buprestids do great damage

Fig. 36. One of the der-
mestids. (Enlarged)

a, larva ; b, adult beetle.

(Courtesy of the Illinois

State Natural History

Survey)

Fig. 37. The work of borers in wood. (Reduced)

a, long-horned borer and its tunnels ; b, tunnel of another species of long-horned

borer ; c, flat-headed borer and its tunnels ; d, bark ; e, sap wood ; /, heartwood.

(Courtesy of the United States Department of Agriculture)

THE BEETLES: COLEOPTERA 53

to trees. The larvae dig tunnels and burrows in the bark
and wood, frequently causing the death of trees and greatly
injuring the wood for use as lumber (Fig. 37).

Definition of Coleoptera (Gr. koleos, "sheath"; pteron,
"wing"). The insects which we have considered in this
chapter agree in possessing biting mouth parts and hardened
sheaths to cover the posterior wings. The wing covers, or
elytra, meet in a straight line down the middle of the back.
These insects are termed beetles or Coleop'tera. The Cole-
optera undergo complete metamorphosis, — the life history
comprising the egg, an active larva or grub, a resting pupal
stage, and the winged adult.

CHAPTER VII

THE BUTTERFLIES AND MOTHS: LEPIDOPTERA

And what's a butterfly? At best
He's but a caterpillar drest.

John Gay

The Monarch Butterfly. One of the commonest and best
known of our butterflies is the monarch, or milkweed, but-
terfly (Dan'aus ar chip' 'pus ; see illustration facing page 58).
It is a tawny-colored species expanding about ten centi-
meters (four inches). The wings have black veins, and the
margins are black with white spots. The colors are due to
the presence of tiny scales, which cover the surface regularly
and overlap like the shingles on a roof. Besides serving for
the display of the colors, the scales also strengthen the
wings. The scales are in origin modified hairs, like those
which cover the rest of the body. The same mouth parts
that were described for the grasshopper are present here
also. They have become elongated and modified to form a
tube which is coiled beneath the head when the butterfly is
not feeding. This proboscis is formed from the lengthening
and union of the maxillae. The mandibles are so small as to
be hardly visible. The anterior legs are so much reduced in
size that they cannot be used for walking, and the butterfly is
therefore practically four-legged . This is not true of all butter-
flies, for in many of them the front legs are well developed.

Practically all the butterflies living in the northern part

of the United States spend the winter as inactive adults

or as larvae or pupae. But the monarch butterfly is not

present in the North in any stage during the winter. It

54

Fig. 38. Stages in pupation of the milkweed caterpillar.1 (Slightly reduced)

1 Reprinted by permission from Entomology, by J. W. Folsom, published by
P. Blakiston's Son & Co.

56 GENERAL ZOOLOGY

passes the winter in the South, like our migratory birds,
and with approaching warm weather the different individ-
uals slowly work their way northward, the females laying
eggs in different places in the course of the journey. The
eggs are pale green and are deposited singly on the leaves
of the different species of milkweed. In about four days
the eggs hatch into caterpillars (Fig. 38), which imme-
diately proceed to devour the eggshells. For the rest of
their larval existence the caterpillars are voracious feeders
on the leaves of the milkweed. They grow for two or three
weeks, molting several times as they increase in size, till
they are conspicuous objects, nearly five centimeters (two
inches) long, prominently banded with yellow and black
(Fig. 38). When through feeding, each larva spins a pad
of silk on some convenient support and, molting once more,
appears in a mummy-like pupal condition (Fig. 38), at-
tached by hooks at its extremity to the pad of silk spun by
the larva. In the inactive pupal stage the milkweed butter-
fly is bright green with golden spots. To this, and to some
of the other naked pupae of butterflies, the name chrysalis
is given. The insect remains in the pupal stage for ten or
twelve days, when the skin splits (Fig. 39) and the butter-
fly comes out with crumpled wings, which soon expand and
harden.

The monarch butterfly possesses remarkable powers of
flight. Mr. Scudder, in his Guide to Butterflies, states that
it has been seen at sea five hundred miles from land, and
that it has within thirty years spread over nearly all the
islands of the Pacific, and even to Australia and Java.

It is asserted that these butterflies, although so brilliantly
colored and conspicuous, are not fed upon generally by
birds and other animals which might use them for food,
owing to their possessing a strong odor which renders them
distasteful. If this is the case, the distinctive coloration

Fig. 39. Emergence of the milkweed butterfly from its chrysalis.1

(Slightly reduced)

1 Reprinted by permission from Entomology, by J. W. Folsom, published by
P. Blakiston's Son & Co.

58 GENERAL ZOOLOGY

may be an advantage rather than otherwise, making it
easy for any animal to distinguish them from edible species.
The brilliant colors are usually cited as an illustration of
warning coloration.

The Viceroy Butterfly. Another butterfly of an entirely dif-
ferent genus (see page 107) and without any offensive odor,
— the viceroy (Basilar' chia archip'pus ; see illustration fac-
ing this page) , — closely resembles the monarch. The viceroy
belongs to a group of butterflies whose general body colora-
tion is blue and white, but instead of the livery of its rela-
tives it wears that of the monarch. It offers the best-known
illustration in North America of what is called protective
mimicrij, a term applied to those cases in the animal king-
dom in which a group of animals without disagreeable
qualities resembles, to a greater or less extent, animals pro-
vided with special means of defense. Protective mimicry
will be seen to differ from warning coloration in that the
latter is believed to protect an animal by marking it as a
source of real danger or unpleasantness ; the former is be-
lieved to protect by suggesting characters which have no
existence in fact. This explanation of the color of the
viceroy has been called in question, and observations are
wanting to show that the birds of the eastern United States
feed generally upon butterflies. Many cases of protective
mimicry are known among the butterflies of Africa and
South America. By the use of the term it is not meant, of
course, that there is anything conscious in the mimicry.

Swallowtail Butterflies. The magnificent insects called
swallowtail butterflies, widely distributed over the world,
have received their common name on account of the shape
of the hind wings. They often exhibit, within the limits of a
single species, great variation in color, size, and even in
the shape of the wings. The variation in form, size, and
color between individuals of the same species is spoken of as

MIMICRY

The monarch butterfly, the viceroy, and a close relative of the viceroy. The

lowermost figure shows typical coloration of the members of the genus to which

the viceroy belongs. (Courtesy of Boston Society of Natural History)

THE BUTTERFLIES AND MOTHS

59

dimorphism (Gr. di-, "two" ; morphe, "form") if the varia-
tions show two well-marked types ; and as polymorphism (Gr.
poly, "many") if there are several different variations. In
many species the males differ greatly from the females;
this is called sexual dimor-
phism. Many examples are
known in which broods of
the same butterfly appear
at two different seasons.
These broods often differ
widely in size and color
markings. This is known
as seasonal dimorphism. In
some cases seasonal dimor-
phism and polymorphism
are associated with changes
of temperature. The zebra
swallowtail {Iphicli'des
marcel'lus), which is ex-
tensively distributed in the
eastern United States,
has three different forms :
the early-spring form, the
late-spring form, and the
summer form. The spring
forms appear from pupae
which have lived through the winter. From the eggs
which the spring forms lay the summer form is developed.
Cabbage Butterflies. Very familiar to all is the white or
slightly yellowish butterfly seen so commonly flitting over
the gardens from early spring until late in the fall. This
is the common cabbage butterfly (Pi'eris ra'pse), so called

1 Reprinted by permission from Applied Entomology, by H. T. Fernald, pub-
lished by the McGraw-Hill Book Company, Inc.

Mil'

%

Fig. 40. Cabbage butterfly

a, adult ; b, eggs, side and end views (much
enlarged) ; c, larva ; d, chrysalis l

60 GENERAL ZOOLOGY

because its larvae (Fig. 40, c) live on the cabbage plant. The
tips of its anterior wings (Fig. 40, a) are grayish. The male
has one spot of gray on each of the anterior wings, the
female two. There is also a gray spot on the anterior margin
of the posterior wings of both sexes. There are several
variations of this species ; one form has both sexes entirely
white. This butterfly is another insect pest which has come
to us from a foreign country, and which has been most
prosperous in its adopted home. It first appeared in the
region of Quebec about the time of the Civil War. Within
twenty-five years it spread from the Atlantic to the Pacific,
and from northern Canada to the Gulf of Mexico. In the
far north it has two broods and in the south many broods
each year. By appearing earlier in the season and having
more than one brood a year it has driven out of our gardens
the native cabbage butterflies. These are rarely found now
except living on the wild relatives of the cabbage.

The larva of the cabbage butterfly is the familiar green
cabbage worm, which eats its way well into the head of
cabbage. The native cabbage butterflies (Pi'eris na'pi)
which this imported form has so largely replaced were much
less destructive, as their larvae feed only on the outer
cabbage leaves.

One of the better-known native species is called the
checkered white {Pi'eris protod'ice), so named because of the
beautiful, checkered dark and white pattern on the wings
of the female. The wings of the male are spotted.

Economic Importance of Butterflies. In contrast with the
moths, which are to be discussed later, the butterflies are
practically wanting in destructive . habits. The cabbage
butterfly is the only one of really great economic impor-
tance. It seems especially fitting that these creatures, which
add so much of beauty to man's surroundings, should not
be his enemies.

THE BUTTERFLIES AND MOTHS

61

Skippers. The skippers (Epargy'reus tit'yrus, Fig. 41) are,
like the butterflies, diurnal insects and are found in fields
and along woodsides, where they dart about in a most er-
ratic manner. They are closely allied to the butterflies. The
butterflies (Fig. 40, and illustration facing page 58) have club-

SaM« ]''~

tennae, while
in the skip-
pers the an-
tennae, though enlarged at the end,
are generally recurved, forming a
hook. The skippers have stouter
bodies than the butterflies, and
most of them hold the wings up-
right after the fashion of the but-
terflies ; but some hold only the
anterior wings in this position.
The larvae (Fig. 41) usually live in
a folded leaf, or in a nest of leaves,
and pass the pupal stage in a thin
cocoon of silk spun by the cater-
pillars before changing. In this
latter respect, too, the skippers differ from the butterflies,
since the latter (as shown in Figs. 38, 39) have a naked
pupal stage.

Commercial Silkworm Moths. Allied to both butterflies
and skippers is the great group of moths, — stout-bodied
insects, the antennae of which are usually feather-like or
thread-like (Figs. 42, 43). Moths have the habit of holding
the wings horizontally when at rest. They are nocturnal or

Fig. 41. Metamorphosis of
skipper. (Natural size)

62 GENERAL ZOOLOGY

diurnal in their habits, though by far the larger number fly
by night. Most of them spin some kind of cocoon in which
they pass the pupal stage.

We shall first consider the silkworm moths. Of these the
best known, as it is economically the most important, is
the Chinese silkworm moth (Bom'byx mo'ri). Cultivated in
China from very early times, the Chinese jealously guarded
the secrets of the manufacture of silk. As the story goes, in
the middle of the sixth century two monks brought the
eggs to Constantinople by stealth, concealed in a hollow
bamboo cane. The cultivation of the silkworm then spread
rapidly to those parts of Europe suited to its culture. From
1609 to the present day various efforts have been made to
introduce silk culture into the United States, the plan of
bounties and rewards to stimulate its growth having been
tried by the rulers in colonial days, and by several states
since the war of 1861-1865. These artificial means have
so far not met with great success. In China the caterpillar
thrives best on the leaves of the white mulberry, but it has
been found to do well on the Osage orange.

The silk glands extend through the body of the caterpil-
lar and open into the mouth. Toward the time of pupation
they increase in size and produce about four thousand yards
of material, which, on being exposed to the air, hardens and
becomes the silk of commerce. As there are two sets of these
glands, each silk filament is really double. Within this co-
coon of silk the larva casts its caterpillar skin and becomes
a pupa. In silk culture the cocoons are placed in an oven to
kill the pupae, and the silk is softened by being placed in
warm water. Then, by means of a twig moved about among
the cocoons, loose ends of several of them are caught, united
into one thread, and wound on a reel, which is placed at a
distance from the hot water so that the silk may dry. This
is the raw silk of commerce.

THE BUTTERFLIES AND MOTHS 63

Giant Silkworm Moths. We have several large moths in
the United States, expanding from ten to fifteen centimeters
(four to six inches), whose larvae spin silken cocoons, some
of which have been utilized to a limited extent by man.
They are magnificent insects, with broad wings beautifully
colored, and with large feather-like antennae. The antennae
of the male are much larger than those of the female. Even
in crowded cities the gorgeous brown and red cecropia is
not uncommon, while the polyphemus, luna, and promethea
are species of especial delight to those who love the beauti-
ful. The larvae feed on the leaves of forest and fruit trees
and are more or less armed with a variety of colored spines
and tubercles. The caterpillars, like other larvae which feed
upon plant food, are remarkable for the amount of food
which they consume and the great increase in size in early
life. The caterpillar of the American silkworm moth
(Te'lea polyphe' mus) , which weighs on hatching one twen-
tieth of a grain, increases to ten times its weight within ten
days, and to over four thousand times its weight in fifty
days. By this time it has consumed over one hundred oak
leaves, weighing almost three quarters of a pound, and
drunk nearly one half an ounce of water. The larvae of these
moths spin conspicuous brown cocoons, which can easily
be collected in the winter from the branches and leaves of
trees to which they are attached. In the spring the imagoes
escape from one end of the cocoons by cutting the silk with
a pair of stout spines, one on each side of the thorax, at the
base of the anterior wings.

Underwings. A very striking group of moths is the under-
wings {Catoc'ala), which have the anterior wings in sober
tints of brown or gray, but the posterior wings black with
broad markings of red or yellow. When at rest the pos-
terior wings are covered, and the moth tends to be protec-
tively colored; but when in flight the broad, contrasting

64 GENERAL ZOOLOGY

colors are conspicuous. It is usual
to account for the coloration of the

anterior wings by the prin-
ciple of protective resem-
blance.

Hawk Moths. The hawk
moths or sphinx moths (Fig.
42) are easily recognized
by the stout conical body,
long coiled proboscis, nar-
row pointed wings, and the
slender antennae. They are
dressed, for the most part,
in quiet olive and brown
tints and fly chiefly at twi-
light. Their larva? are large
naked caterpillars, often
with a curved horn near the
posterior extremity. The

/

FIG. 42. A sphinx moth. (Slightly
less than natural size)

Adult, larva, and pupa

THE BUTTERFLIES AND MOTHS

65

tobacco worm and tomato worm are the larvae of a well-
known species, Protopar'ce sex'ta (Fig. 42), found on tomato,

'iVx

s^

z/ ; ;\

7 1
//l

> 'i

V \ Y

potato, and tobacco plants. The pupa?
are remarkable for the long coiled pro-
boscis case.

Tussock Moths. The tussock moths,
though few in number of species and
inconspicuous in the adult stage, are
comparatively well known from their
conspicuous larvae, which are clothed
with white or brightly colored tufts of
hair. The white-marked tussock moth
(Hemerocam'pa leucostig'ma, Fig. 43) is
the commonest species in the eastern
United States. Long brushes of black
hairs are borne anteriorly and posteri-
orly, and four .dense clusters of white
hairs stand up prominently from just
behind the head. The females are wing-
less and look more like white grubs than
moths. When they emerge from the co-
coons the eggs are laid close by, often

on the cocoons. Fig. 43 shows the female in the act of

laying eggs in such a situation.

Fig. 43. Metamor-
phosis of tussock
moth. (Natural size)

66

GENERAL ZOOLOGY

The Gypsy Moth. The dangers of introducing destructive
insects from another country are well shown in the case of
the gypsy moth {Porthet'ria dis'par). About 1868 an ento-
mologist in Massachusetts set free some specimens of this
moth. His act has caused the direct expenditure of millions

of dollars and the loss of
many forest and shade
trees. Though the fe-
male rarely flies the spe-
cies has become widely
distributed throughout
the New England states.
The larvae when abun-
dant completely strip
all the leaves from the
trees.

The Codling Moth.
There are several insect
larvae which live in ap-
ples, all of which are
commonly called apple
worms. The most im-
portant one of these is
the larva of the codling
moth (Carpocap'sa pomo-
nel'la). It has become
so widely spread and so abundant in this country that mar-
ketable apples can be produced only by following a care-
fully timed program of spraying. The larvae are killed by
eating the poison when they attempt to eat their way into
the young apples. The adult moths (Fig. 44, /, g) become
mature about the time that apples are in bloom. The eggs
are laid upon the blossoms. As soon as the larvae (Fig. 44, e)
are hatched they begin to eat their way into the blossom

Fig. 44. Stages in the life of the cod-
ling moth. (Natural size)

a, tunnel of larva in apple ; b, point where
larva entered the apple ; d, pupa ; e, fully-
grown larva; /and g, adult moths; h, head
end of larva ; i, pupa in cocoon. (After the
Illinois State Natural History Survey)

THE BUTTERFLIES AND MOTHS

67

end (Fig. 44, b) of the young apples. If a poison spray has
been applied at the proper time the young larva gets a dose
of poison with its first and last meal and the apple escapes
being classed as a wormy cull.

Clothes Moths. Some of the small brownish "moth mil-
lers " so commonly seen flying in houses are the adults of
the clothes moth (Fig. 45), often so destructive of clothing,
carpets, and upholstered furniture. The adult moth lays its
eggs on woolen mate-
rial. When the eggs
hatch, the larvae pro-
ceed to eat the cloth.
There are three species
of clothes moths, each
belonging to a differ-
ent genus.

The Corn Borer. The
European corn borer
is the larva of a moth
which causes great
damage by boring into

the stalks of corn. This species (Pyraus'ta nubial'is) was
very recently introduced into this country, but it is making
alarming progress in its invasion of the corn belt. Individ-
ual states and the federal government have appropriated
very large sums of money for the study of this insect, but
so far there seems to be small hope.of checking its spread.

An insect which feeds on the surface of a plant may be
attacked directly by poison food or by deadly sprays. But
when an insect does its damage inside of the tissues of a
plant there is little chance of reaching it.

Measuring Worms. The measuring worms (Fig. 46) are
the larvae of a group of medium-sized moths. When some
of these larvae are at rest, it is difficult to believe them to

Fig. 45. A clothes moth. (Enlarged)

Adult, larva in case, and larva. (Courtesy of the
United States Department of Agriculture)

68

GENERAL ZOOLOGY

Fig.

When
moths

be caterpillars. Most of them
have three pairs of legs less
than other caterpillars, so that
a looping gait is the result,
whence the name "measuring
worms." They have the habit,
when disturbed, of dropping to
the ground on a silken thread,
which they spin as they fall.
Definition of Lepidoptera ( Gr .
lepis (lepidos), "scale"; pte-
ron, "wing"). The butterflies,
skippers, and moths, collec-
tively, are spoken of as Lepi-
dop'tera. The Lepidoptera
have four large wings covered
with scales, sucking mouth
parts, and undergo a complete
metamorphosis. The larvae,
called caterpillars, with few
exceptions, feed upon the
leaves of plants.

The butterflies and skippers
are active by day, and the
moths fly at night or in the
twilight. Most moths have
stout bodies and feather-
like antennae. Skippers have
antennae usually ending in an
enlarged hook-like tip. But-
terflies have enlarged knobs
at the tips of the antennae,
at rest, butterflies usually hold their wings erect, and
more commonly fold them against the body.

46. Measuring worms.
(Natural size)

CHAPTER VIII

THE FLIES: DIPTERA

. . . like small gnats and flies as thick as mist
On evening marshes.

Shelley

House Flies. The common house fly (Mus'ca domes'tica,
Fig. 47) is a cosmopolitan insect. The eyes are very large,
occupying the whole side of the head; the antennae are
short and composed of only three joints, the third bearing a
bristle. The mouth parts are formed for sucking and lap-
ping. They consist of a short tongue-like proboscis, with
large oval flaps, or lobes, on each side. These flaps are ex-
tensile and are roughened like a file on the inner surface,
thus permitting of their use as a scraper, by means of which
the insect can lap up sweets or other food. The proboscis
is made up of the united maxillae. The thorax bears but one
pair of wings, though the rudiments of others, called bal-
ancers or halteres, can be seen in the form of two little
round objects, borne on slender stalks. These balancers
also act as organs of hearing. Two broad scales are found
on the sides of the thorax, just behind the wings. The
legs are fitted for running. The pulvilli are large and bear
tubular hairs, which secrete a sticky fluid, by means of
which the fly can walk on smooth surfaces, even when up-
side down.

The eggs, over one hundred in number, are laid usually

in horse manure or garbage. They hatch within a day into

smooth, white, almost transparent, conical, footless larvae,

called maggots. The rudimentary mouth parts consist only of

69 *

70 '

GENERAL ZOOLOGY

■f TfJM ^

a few small hooks. The larvae feed for about a week, growing
rapidly and molting twice within that time, and then pass
into an inactive pupal stage within the larval skin. In a
week more the perfect insect appears by making a circu-
lar hole in one end of the pupal case by means of a large
bladder-like bulb, which swells out on the forehead and is

later withdrawn in-
to the head. Thus
within about two
weeks the life his-
tory is completed.
As the imagoes soon
lay eggs, there may
be several genera-
tions in the course of
the summer. With
the approach of cold
weather most of the
flies die, although
some hibernate in
sheltered places.
Someone has made
the calculation that if all the offspring of a single pair of
flies starting to reproduce in April were to live, by August
there would be from this one original pair enough to cover
the entire earth with a layer of flies forty-seven feet deep.
The house fly has always been considered a nuisance
about the house; but a more serious charge is laid at its
door, — that of transporting on the pulvilli and proboscis
the germs of typhoid fever. With the knowledge of its
favorite breeding place it should be possible, by insisting
on cleanliness in stables, by the daily collection of manure
and garbage and their proper disposal, to mitigate greatly,
if not entirely destroy, this menace to health.

Fig. 47. Metamorphosis of housefly. (Enlarged;

THE FLIES: DIPTERA 71

Flesh Flies. Equally well known are the blowfly (Calliph'-
ora vomito'ria) and the bluebottle (Lucil'ia cse'sar), which
deposit their eggs on fresh and decaying meat. These flies
hatch within a day, and the larvae greedily devour the de-
caying material, not hesitating, when that task is finished,
to devour each other.

The history of South Africa has been very largely con-
trolled by the biting flies known as the tsetse flies of the
genus Glossi'na. There are several species of these flies.
By their bite they infect man and domestic animals with
minute disease-producing protozoa known as trypanosomes.
African sleeping sickness, one of the most deadly human
diseases known, is produced by the bite of the tsetse fly. In
large parts of South Africa practically all horses and cows
are killed off by a disease known as nagana. Like human
sleeping sickness this also is produced by trypanosomes,
carried by the tsetse flies. The native game animals have
recently been found to harbor the protozoa without suffer-
ing any apparent ill effects.

Botflies. The botflies are parasites in the larval stage;
that is, they live in the bodies of other animals. There are
nearly one hundred species known, infesting various ani-
mals, living either under the skin, in the nostrils, or in the
stomach. The botfly of the horse (Gastroph'ilus e'qui,
Fig. 48) attaches its eggs singly by means of a sticky sub-
stance to the hairs of the legs, where the larva is pretty sure
to be swallowed when the animal licks or bites its legs to
remove the irritation. The larva then attaches itself to the
lining of the stomach by means of hooks which encircle its
mouth, and for nearly a year feeds on the substance of the
stomach wall. The pupal stage is passed in the earth, which
is reached through the alimentary canal. A few of these
parasites do no particular harm, but a large number may
cause death.

72

GENERAL ZOOLOGY

The sheep botfly {(Es'trus o'vis) in a similar manner at-
tacks the nostrils of sheep. The appearance of one of these
flies in a flock of sheep is sufficient to throw them into a
state of panic; they run about with their noses between
their legs, or try to bury them in dust, to escape their tor-
mentor. The female of this botfly does not lay her eggs as
do most other insects, but retains them within her body till

Fig. 48. Metamorphosis of horse botfly

A, egg on hair of horse (natural size) ; B, egg on hair of horse (enlarged) ;
C, young larva (enlarged) ; D, young larva (much enlarged) ; E, spines ; F, full-
grown larva (twice natural size) ; G, female (natural size). (After Osborn, Bulletin
No. 5, N. S., United States Department of Agriculture, Division of Entomology)

they hatch, and then deposits the living young, — that is
to say, in her method of reproduction she is viviparous.
Fruit Flies. The minute flies (Drosoph'ila) so often seen
about over-ripe fruit are commonly called fruit flies, pomace
flies, or vinegar gnats. Much that we now know of the laws
of heredity has come from the study of these minute flies.
They are easily reared and reproduce so rapidly that they are
favorite objects for laboratory study of the manner in which
characteristics are passed from one generation to another.

THE FLIES: DIPTERA

73

Hover Flies. Often a collector captures an insect flying
about flowers which has the characteristic manner and yel-
low and black colors of a wasp, but which has only two
wings. It is one of the hover flies, many of which afford
illustrations of protective mimicry. Some species of Eris'-
talis (Fig. 57) mimic
the male honeybee
and are therefore
named drone flies ;
others belonging to
Volucel'la (Fig. 57)
mimic bumblebees.
The larvae of some
feed chiefly upon
aphids and are there-
fore beneficial to the
farmer; yet others
inhabit pools of stag-
nant water or decay-
ing wood.

Mosquitoes. The
mosquitoes comprise Fig. 49. Development of mosquito. (Enlarged)
a group Widely dis- A, egg mass; B, larva; C, pupa. (After Howard,

tributed over the
tropical and temper-
ate regions of both hemispheres. In nearly all the species
observed the mouth parts of the females only are fitted
for piercing the skin of animals. The males, if they feed at
all, probably suck the fluids of plants ; in fact, both sexes
in the past history of the race were probably, and are
still, to some extent, plant feeders.

A common mosquito of the Mississippi Valley and the
East is Cu'lex pip'iens. The female lays her eggs (Fig. 49)
in irregular masses containing over two hundred eggs, on

Bulletin No. 25, N.S., United States Department
of Agriculture, Division of Entomology)

74 GENERAL ZOOLOGY

the surface of the water early in the morning. Within a day
they hatch, and the larvae are the familiar, active creatures
known as "wrigglers." The next to the last somite bears
a long respiratory tube through which the larva breathes
air when at the surface ; the last somite is provided with
four flaps (tracheal gills) which act as organs of respiration
when the larva is beneath the surface. In addition to these
methods of obtaining air, the skin is capable of absorbing
oxygen, and a network of tracheae lines the posterior part

of the alimentary
canal, so that oxy-
gen may be obtained
from the water taken
in at the anal open-

Anopheles Culex .

jTinr The 1j3t*v?p fppd
Fig. 50. Resting positions of mosquitoes. s*

(Slightly enlarged) on small particles of

After Grassi decaying matter in

the water, thus be-
ing useful as scavengers. After several molts and a life of
about a week, if the weather is warm they then pass into
the pupal stage, breathing by means of two air tubes aris-
ing from the thorax. In about two days the pupal skin
splits down the back and the imago works itself out of its
old skin, dries its wings, and flies away. Cold weather
retards these changes considerably.

Great interest attaches to the mosquitoes by reason
of the fact that malaria and yellow fever are both wholly de-
pendent upon mosquitoes for transmission from one per-
son to another. Malaria is carried by mosquitoes belonging
to the genus Anoph'eles, the females of which may be distin-
guished from the females of Culex by the greater length of
the palpi. Anopheles shows a tendency, especially on hori-
zontal surfaces, to alight with the hind end of the body
raised at a considerable angle to the surface ; Culex holds

THE FLIES: DIPTERA

75

the body parallel to the surface. In Anopheles the body and
beak are in the same plane no matter what the position
is; Culex is humpbacked, with the beak pointing down-
ward. These various distinctions are well shown in Fig.
50. The males of both genera can be distinguished from
the females by their larger and more feathery antennae.

Fig. 51. Crane fly. (Enlarged)

From the Illinois State Natural
History Survey

Fig. 52. The Hessian fly

a, adult; b, wheat plant suffering from

attack of the fly ; c, larva. The small lines

to the right of a and c indicate natural

length. (After Berlese) l

Many localities can be practically rid of these pests by
the drainage of the swamps or ponds in which they breed ;
by the use of kerosene or other oils on the surface of such
waters; or by the introduction of fish that feed on the
larvae.

Minnows, goldfishes, sunfishes, and sticklebacks are all
mosquito destroyers. It must be remembered that the insect
will breed successfully in any transient pool of water, or in

1 Reprinted by permission from Applied Entomology, by H. T. Fernald, pub-
lished by the McGraw-Hill Book Company, Inc.

76 GENERAL ZOOLOGY

any receptacle where water is left standing long enough for
the eggs to develop into mature mosquitoes.

Crane Flies. The crane flies (Fig. 51) look so much like
mosquitoes that many people mistake them for an extremely
large race of bloodthirsty mosquitoes. In fact, they are un-
able to bite.

The Hessian Fly. The Hessian fly (Phytoph'aga destruc'tor)
is a small gnat-like fly (Fig. 52) which appeared in this
country soon after the Revolution. It is thought that it
was brought over from Europe in straw transported by the
Hessian soldiers. The young (Fig. 52, c) develop in the
stems of wheat, rye, and barley. Here they do so much
damage that it is estimated that more than 10 per cent of
the wheat crop is destroyed by this fly in an ordinary year.

Definition of Diptera (Gr. dipteros, "two- winged")* The
insects collectively called flies agree in the possession of two
wings, the place of the posterior pair being taken by the
halteres, or balancers, which may therefore be considered
reduced wings. Although a few other insects have but a
single pair of wings, the flies alone possess halteres. The
flies belong to the order Dip'tera. The Diptera have the
mouth parts fitted for sucking or piercing. They undergo
complete metamorphosis. The larvae are commonly known
as maggots.

CHAPTER IX

THE ANTS, BEES, AND WASPS: HYMEN OPTERA

For so work the honey-bees,
Creatures that by a rule in nature teach
The art of order to a peopled kingdom.

Shakespeare, King Henry V

Social Wasps. The common brown wasps {Polis'tes, Fig.
53) are interesting on account of their communal life in
nests of paper made from wood pulp. The mouth parts are
fitted both for biting hard substances and also for lapping
the fluids of plants. The mandibles are much the same as in
such biting insects as the grasshoppers; the maxilla? are
elongate, sharp-pointed, lance-like organs, and the labium
is a flexible, tongue-like structure covered with hairs, to
which sweets adhere. There are four membranous, transpar-
ent wings, with few veins. The female is provided with a
formidable sting, — an important means of defense, — which
is in origin a modified ovipositor.

Early in the spring a female Polistes, which has wintered
in a crevice, begins the construction of a nest in some suit-
able place, either on the under side of a roof, especially in
deserted houses or barns, or on the. ground beneath a stone.
If there are fences or barns in the region, she will very likely
obtain a supply of wood from them ; if not, from stumps
and dead trees. After being chewed by her and moistened
by a secretion from her mouth, this material is fashioned
by the feet and mandibles into circular cells. These become
hexagonal as their number is added to and the pressure in-
creases. The whole is waterproofed by a glutinous secre-

77

78

GENERAL ZOOLOGY

tion, which is said to be increased in amount in those cells
which are most exposed to the weather. As soon as one cell
is finished the female lays an egg in it, and to her duty of
enlarging and strengthening the nest she soon has to add
the care of the footless, worm-like larvae, which hatch in a
few days. These are fed with both plant and animal food,
the former consisting of nectar which has been swallowed
and later regurgitated (that is, thrown back after being

Fig. 53. Paper-making wasp and nest. (Natural size)

swallowed) ; the latter, of caterpillar meat chopped fine by
the mandibles and worked into a jelly-like mass. In about
three weeks' time the first-born larvae spin a silken lining
and covering to the cell and pass into an inactive pupal
stage. Three weeks later the first imagoes appear, after
having cut a circular opening in the end of the cell.

These first imagoes differ somewhat from their mother
and are really imperfectly developed females, called neuters
or workers. They have the power, under certain conditions,
of laving eggs, but their eggs never produce true females.
Generally the workers attend strictly to the business of
caring for the young and repairing and enlarging the nest.
They assume care of the young at about the third day.

THE ANTS, BEES, AND WASPS 79

From the time the workers take up the tasks of the nest
the female is left free to devote all her energies to laying
eggs, and the nest is rapidly made larger by the workers.
Toward September males and females appear from the
cells, which up to this time have produced only workers.
The males die soon after mating. On the approach of cold
weather, the workers also die, and only females remain to
hibernate and begin a new nest the next spring.

Another type of nest, in which the horizontal layers are
inclosed in a thin envelope, is made by the somewhat
larger and stouter-bodied wasps (Ves'pa, Fig. 57) commonly
known as hornets. These wasps are generally conspicuously
marked with yellow, and their nests may be a foot and a half
in diameter.

The social wasps are the original paper-makers of the
world. The first suggestion as to the manufacture of paper
by man may have come from watching the work of these
insects, though the necessary steps may well have been
taken without such suggestion, as the use of the leaves of
palms and the bark of several trees is still common in China
and India. It is interesting to note that though the wasps
were the original inventors of paper, they have, in some
cases, learned to take advantage of man's present greater
facilities for its manufacture, thus saving themselves the
trouble of preparing the raw materials.

Solitary Wasps. Those wasps which are solitary in habit
make nests in various situations and of different materials
and store them with food, generally insects and spiders.
These they often sting so as to paralyze but not to kill them.
Each species has its own method of providing food, and
each keeps pretty closely to the same material for nest-
building. Thus the common mud dauber (Scel'iphron,
Fig. 54), seen flying about on sunny days over the muddy
edges of puddles and pools, builds its nests of clay and pro-

80

GENERAL ZOOLOGY

visions them with spiders. Each cell is filled with paralyzed
spiders ; on top, one egg is laid and the cell is sealed. When
the larva hatches, it finds the requisite amount of food to

Fig. 54. Mud dauber and nest. (Natural size)

carry it to the pupal stage. These wasps are distinguished
by the long pedicel, or stalk, joining the thorax to the
abdomen.

The digger wasps of the West, which belong to the genus
Sphex (Fig. 55), make holes a little over a centimeter (about
half an inch) in diameter and two or three centimeters deep,

THE ANTS, BEES, AND WASPS

81

in the hard, sun-baked earth, often choosing a place be-
neath the protection of the leaf of some plant. These holes
they provision with caterpillars, which they sting in several
places till they are paralyzed. In the process of provisioning
the nest some species close the opening with a pellet of
earth or with small stones, which they remove when they

Fig. 55. Digger wasp using pebble. (Enlarged)1

return with a new caterpillar. Dr. and Mrs. Peckham, who
have studied these insects very carefully, say that this is,
however, not an invariable habit, some individuals leaving
the nest open while searching for more caterpillars. These
authors have this to say of the habits of one of these insects :

Just here must be told the story of one little wasp whose in-
dividuality stands out in our minds more distinctly than that of
any of the others. We remember her as the most fastidious and
perfect little worker of the whole season, so nice was she in her
adaptation of means to ends, so busy and contented in her labor

1 From Peckham's Solitary Wasps.

82

GENERAL ZOOLOGY

of love, and so pretty in her pride over her completed work. In
filling up her nest she put her head down into it and bit away the
loose earth from the sides, letting it fall to the bottom of the bur-
row, and then, after a quantity had ac-
cumulated, jammed it down with her
head. Earth was then brought from the
outside and pressed in, and then more
was bitten from the sides. When, at last,
the filling was level with the ground, she
brought a quantity of fine grains of dirt
to the spot, and, picking up a small
pebble in her mandibles, used it as a
hammer in pounding them down with
rapid strokes, thus making this spot as
hard and firm as the surrounding sur-
face. Before we could recover from our
astonishment at this performance she
dropped her stone and was bringing
more earth. We then threw ourselves
down on the ground, that not a motion
might be lost, and in a moment we saw
her pick up the pebble and again pound
the earth into place with it, hammering
now here and now there, until all was
level. Once more the whole process was
repeated, and then the little creature,
all unconscious of the commotion that she had aroused in our
minds, unconscious, indeed, of our very existence, and intent
only on doing her work and doing it well, gave one final com-
prehensive glance around and flew away.

A common North American species of solitary wasp is
called the potter wasp (Eu'menes frater'na, Fig. 56). It
builds a pretty little jug-shaped nest of clay or mud, which
it attaches to vegetation and provisions with caterpillars.
The young, when full-grown, escapes through a hole which
it cuts in the side of the nest, as shown in the lower of the
two nests drawn in Fig. 56.

Fig. 56. Potter wasp and
nests. (Natural size)

THE ANTS, BEES, AND WASPS 83

The Honeybee. The life history of the honeybee (A'pis
mellifica, Fig. 57) has been quite well understood for a long
time. This insect offers a most interesting illustration of a
society all the members of which act together for the good of
the community. In their community, specialization of work
has been developed to a remarkable extent. The honeybee,
originally a native of the Eastern Hemisphere, possibly from
the region along the eastern shore of the Mediterranean Sea,
has been domesticated from very early times for the sake of
its two important products, honey and wax. Escaped swarms
in this country have become the wild honeybees, which nest
in hollow trees. In early summer a bee community in good
condition may contain from twenty-five to thirty-five thou-
sand workers, several hundred males, called drones, but only
one female, called the queen bee. The queen bee may be
distinguished from the workers and drones by her larger
size. The drones are stouter than the workers and have no
sting.

Upon the workers devolves most of the labor in connec-
tion with the life of the community. They secrete the wax
and fashion it into the cells of which the home is composed.
They bring water to the hive. They collect nectar from
flowers and later regurgitate it and ripen it into honey ; they
bring pollen to mix with nectar to make "beebread ; " they
gather propolis, a gummy substance from bud scales of
certain trees, especially the poplar, for filling crevices and
covering foreign objects which are too big to be removed
from the nest. When the young are hatched the workers act
as nurses and housekeepers for the community, feeding the
young and keeping the hive free from all substances which
might decay. In warm weather some of them may be seen
at the entrance and along the passageway, keeping the air in
motion with their wings, thus setting up a current which pro-
vides air and helps ripen the honey by evaporating the water

84 GENERAL ZOOLOGY

in it. Finally, as everyone knows, they are the defenders of
the hive, and by their great numbers and formidable stings
they constitute a bodyguard of no mean pretensions.

The name "queen bee" is misleading, if it suggests any
control or management of the affairs of the hive. She is care-
fully guarded by the workers, but that is on account of her
importance to them as the only fertile female in the com-
munity, though they can, as we shall see, produce other
queens from eggs which were destined for workers, if neces-
sity arises. As far as having any power to rule is concerned,
she is, in reality, ruled by the workers. It is her function
to lay the eggs from which all the other members develop.
Those eggs destined to become workers are laid in cells of
ordinary size ; those which are to become males are placed
in slightly larger cells; and those which are to become
queens, though differing in no way at first from those which
produce workers, are placed in special "royal" cells, much
larger and of an irregular shape. They are, of course, few
in number compared with the others.

When the eggs hatch, all the larvae are fed for several
days on a jelly-like substance consisting of regurgitated
food mixed with a secretion from glands in the heads of the
workers and poured out from their mouths. After this the
workers and males receive beebread, a mixture of pollen
and honey, while the young queens are continued on their
diet of elaborated material, "royal jelly," furnished by the
workers. When for any reason a hive loses its queen, the
workers proceed to break down the walls between three adja-
cent cells containing worker larvae, kill two of the occupants,
and bring the third to maturity as a queen by use of royal
jelly. The first eggs laid in the spring produce workers ; the
males are produced from unfertilized eggs laid by the queen.
When the larva is full grown no more food is supplied to it,
and the cell is sealed with a waxen cover. Within this prison

THE ANTS, BEES, AND WASPS 85

the larva spins a cocoon and changes to a pupa. Within
three weeks from the laying of the egg the worker bee cuts
a hole in the covering of its cell and emerges. A queen is
produced in somewhat less time ; a drone requires slightly
longer.

In late spring or early summer, as the colony has increased
in size, the time approaches for one of the new queens to
appear from the pupal stage. A peculiar noise may be heard,
made probably by the wings of the imprisoned queen. Part
of the ordinary work of the hive is neglected, and the old
queen rushes forth with a large number of the community,
generally alighting in a palpitating mass on some neighbor-
ing tree or other support. This is the "swarming" of the
bees. If provided with a new hive, they will generally settle
down quietly in their new home. Bees are particular as to
the state of the weather at the time of swarming, appear-
ing only when the sky is clear. The workers carry a store
of honey in their crops, as if prepared for a long trip, which
in a state of nature may often have occurred before the bees
could find a hollow tree or a crevice among rocks suitable for
a home. The swarming serves the purpose of lessening the
chances of a total extinction of the species, by increasing the
number of communities.

Meanwhile the new queen appears in the old hive, and
after a flight in the air with the drones, during which ferti-
lization occurs, she settles down to her duty of egg-laying.
This flight and the swarming are the only occasions upon
which the queen leaves the hive. The number of swarms
thus given off varies with the size of the original community
and seems to depend somewhat on climatic conditions. It is
not uncommon to have three swarms in a season. When the
community is to send out no more swarms, the queen is per-
mitted to sting the other young queens to death. If by any
chance two queens meet, a conflict begins at once, and the

86 GENERAL ZOOLOGY

usual result is the death of one of them. This is often spoken
of as due to the jealousy of the queens, but it may have a
meaning in connection with the necessity the community is
under of sending out swarms to maintain a separate exist-
ence. The sting of the queen is used only in these battles
and in slaying the young queens. At the end of the swarm-
ing season the workers set upon the drones and kill them,
casting their dead bodies out of the hive. The queens live
for several years, depositing two or three thousand eggs a
day during a part of the season. The workers live, as a rule,
less than two months.

The wax of which the cells of the comb are composed is
secreted in the form of thin plates in 'wax pockets" be-
neath some of the abdominal somites. While preparing this,
full-fed workers cling motionless to the cells in the upper
part of the hive, and in about twenty-four hours the wax
appears. This is removed by other workers and is used in
construction. Honey is made for food for the young and
for winter consumption of the colony. The pollen of flowers
is brought to the hive in "pollen baskets," clear spaces sur-
rounded by hairs on the outer side of the hind tibiae. The
basal joints of the hind tarsi are much enlarged and are used
as brushes to gather the pollen.

Bumblebees and Guest Bees. The bumblebees (Bom'bus,
Fig. 57) are social bees, having homes in fields, in deserted
mouse nests, and similar places. The nest is begun early in
the spring by a female which has wintered, and, as with the
social wasps, the burdens of the home are turned over to the
young workers when they emerge. Late in the season other
females and males appear, but there is no swarming as with
the honeybee. On the approach of cold weather the workers
and males die. The honey made is strong-smelling, but much
sought after by boys in the country, perhaps as much for the
danger connected with its capture as for the sake of the

THE ANTS, BEES, AND WASPS

87

honey itself. Boys in the West rob the bees by placing a
gallon jug partially filled with water in the vicinity of the
nest and thoroughly arousing the members of the commu-
nity. The boys make good their escape to a safe distance, and
the bees, perceiving the jug, fly to its open mouth, which

Mimicked forms, — insects with means of defense
The honeybee A wasp A bumblebee

(Apis mellifica) (Vespa occidentalis) (Bombus Howardii)

Mimicking forms, — insects without means of defense
A fly A beetle A fly

(Eristalis tenax) (Clytus marginicollis) (Volucella evecta)

Fig. 57. Mimicked and mimicking insects. (Natural size)

From photographs >

echoes the buzzing of their wings. Some bees fly into the
mouth of the jug, thus adding to the noise and attracting
others. It is said that with two disturbances of the nest the
worker bees can all be captured.

The red clover, of such great value as a hay crop, de°
pends almost altogether upon bumblebees for fertilizing the
flowers. The funnel-shaped flowers are too deep to allow

1 From Hunter's Studies in Insect Life.

88

GENERAL ZOOLOGY

the tongue of the honeybees to reach the nectar at the
bottom. But the bumblebees reach the bottom of the cup
and in so doing carry pollen from one flower to another.
The early blossoms of the clover come out in the spring
before many bumblebees are on the wing. These rarely

-j»

Fig. 58. Leaf-cutter
bee and nest. (Nat-
ural size)

produce seeds. A
farmer usually de-
pends on his sec-
ond cutting of the
clover for seeds,
because the second
crop is in blossom
after the bumble-
bees become ac-
tive.
There are several bees called guest bees (Psith'yrus), which
live in the nest of the bumblebees, apparently on good terms
with them, though they do not, so far as known, perform
any useful function. Their eggs are laid with the eggs of
the bumblebees, and the larvae feed on the food which the
bumblebees provide for their own young. Some of the guest
bees resemble their hosts quite closely ; others are different
in appearance, so that it cannot be said in all cases that the
bumblebees are deceived by the resemblance. One effect of
the dependence of the guest bees on their hosts is seen in

THE ANTS, BEES, AND WASPS 89

the absence from the hind legs of the former of the pollen-
collecting and pollen-carrying organs. It has been observed
that the bumblebees sometimes resent the introduction of
one of the guest bees into their nest, though they may later
become accustomed to it and make no further trouble.

Solitary Bees. There are solitary bees, just as there are
solitary wasps. Their habits are very diverse ; some make
nests of mud or dig tunnels in the ground ; some are car-
penters, boring into wood ; and others are leaf cutters,
taking circular pieces out of leaves, which they use to line
their nests. Fig. 58 represents the work of one species, the
leaf-cutter bee (Megachi'le latima'nus), which makes long
tunnels in wood or in the ground. The eggs are laid singly
on a paste of nectar and pollen, which is placed carefully
in a leaf-lined cell and covered with a circular lid. Several
such cells are generally to be found in one nest.

Ants. Ants have long been considered models of indus-
try. In many respects some of the features of their life
history are the most remarkable of anything in the insect
world. So specialized have the members of the community
become in some cases that there are not only males and
females, but large and small workers (workers major and
minor), and soldiers for the defense of the colony. Ants
build nests in the ground, piling up the material taken out
for their burrows in the characteristic ant hills; or they
make tunnels in wood. Some inhabit the interior of thorns
or the hollow stems of grasses ; others live on certain trees,
from which they obtain all their, food, forming a kind of
bodyguard which defends the tree from the attacks of
various enemies. The food of ants is both animal and
vegetable, the former consisting of other insects, the latter
of plant fluids. They are also extremely fond of the sweet
substance called honeydew, furnished by the aphids and
some few other insects.

90

GENERAL ZOOLOGY

The eggs are, of course, extremely minute, and hatch
into footless larvae (Fig. 59, D), which resemble those of
the bees and wasps. The workers (Fig. 59, A) take great
care of the young, feeding them and moving them about

D

<*-**

Fig. 59. The cornfield ant. (Much enlarged)

A, worker; B, winged male; C, wingless female; D, larva; E, pupa.
Forbes, Illinois State Natural History Survey)

(From

in response to changes in temperature and amount of mois-
ture. Among ants generally, the workers feed not only the
young but even give up food to each other, when this is
demanded by a stroke of the antennae. The pupal stage
(Fig. 59, E) is generally passed in silken cocoons. These

THE ANTS, BEES, AND WASPS 91

are the so-called "ant eggs," which are the objects of much
solicitude when a nest is exposed. The imagoes are unable
to escape from the pupal case without the help of the workers.
The males and females are at first winged (Fig. 59, B) and
take flight in great numbers into the air on some warm day
in spring. At this time fertilization occurs. On their return
the males soon die, and the females, stripping off their wings
(Fig. 59, C), become the mothers of colonies. The females
can be distinguished from the workers by their larger size
and the presence of well-developed ocelli.

Many other insects, especially beetles, live habitually in
the nests of ants, and, in some cases at least, seem to per-
form some useful function, — acting as scavengers, for
instance. These cases, like that of the bumblebees and guest
bees, may be cited as illustrations of commensalism (Lat.
com (=cum), "together"; mensa, "table"), an association
of one species of animal with another for support or advan-
tage, but not as a parasite.

An illustration of cooperation between two different spe-
cies of animals is shown in certain ants and aphids. As
mentioned in Chapter IV the cornfield ant (La'sius, Fig. 59)
collects eggs and young of a species of aphid and guards them
throughout the winter in burrows, thereby providing a con-
stant supply of honeydew. Some ants build a shelter of wood
pulp or mud over colonies of aphids, which are crowded
on a branch, from which they derive their nourishment.
These aphids are often spoken of as the cows of the ants.
In these cases the relation between the ants and aphids is
clearly of a more intimate character than the association
of the bumblebees and guest bees ; and the advantages
are mutual, for while the ants secure a constant supply
of food, the aphids receive care and a certain amount of
protection against their enemies. This association is spoken
of as symbiosis (Gr. syn, "together" ; bios, "life").

92 GENERAL ZOOLOGY

Several species, including the little black ant and the
minute red ants, become household pests.

The honey ant of Texas (Myrmecocys'tus mel'liger) has
one set of workers peculiarly modified to act as storage
vessels for sweets. The abdomens of these are distended
with a store of grape sugar, till they are as large as a cur-
rant. These workers cling to the roof of the nest, and in
times of famine can be drawn upon for food by the other
workers.

The agricultural ant {Pogonomyr'mex barba'tus) clears
large spaces, often several feet in diameter, cutting down
all vegetation growing thereon, and rears a grain-bearing
grass, storing its seeds in underground chambers. Several
kinds of ants have the habit of attacking other kinds and
carrying off their pupae. In one (Formi'ca sanguin'ea), a
small reddish species, the habit has become firmly fixed, and
periodical raids are made upon a larger black species, which
are afterwards raised in the nests of their captors. One ant
of a slave-making tendency (Polyer'gus rufes'cens), found
in Europe, has carried the habit so far that it has lost the
power of feeding and taking care of itself, depending entirely
on the exertions of its servants. The wars of ants have been
known for a long time, and many accounts are extant of the
fierceness of the struggle between opposing armies.

Gallflies and Ichneumon Flies. The gallflies form many
of the swellings on plants, known as galls. A common gall-
fly of the oak (Amphib' olips) is shown in Fig. 60. The gall
is caused by the female laying an egg in the leaf tissue,
which swells up when the larva hatches. The young feed
on the material of the gall until they are ready to go into
the pupal stage. Many of these galls harbor also guest gall-
flies, living with the others as commensals.

Closely allied to the gallflies are the ichneumon flies. One
species deposits its eggs in the burrows of a wood-boring

THE ANTS, BEES, AND WASPS 93

larva by means of its long ovipositor, and the ichneumon
larva on hatching moves along in its burrow until it finds
its host, when it fastens itself to it and destroys it by sucking
its blood. Many of the ichneumon flies are true parasites
in the larval stage, the eggs being deposited on the skin

c\;

<N -W

»

Fig. 60. Gallfly. (Natural size)

or in the body of the caterpillars, upon the fluids of which
the ichneumon larva feeds. The pupal stage is generally
passed within the body of its victim.

Sawflies. The sawflies have the base of the abdomen as
broad as the thorax. The ovipositor of the female con-
sists of a pair of saws, which are used to make slits in the
leaves and stems of plants, in which she deposits her eggs.
Fig. 61 shows the American sawfly (Cim'bex america'na),
our largest species. The larva looks like the caterpillar of a
butterfly or moth, but has more legs. It has the curious
habit of coiling the posterior end of its body about a branch,
as shown in the illustration. It forms a brown cocoon, in
which the winter is passed in the ground.

Larva? of the currant sawfly (Pteronid'ea ri'besi) fre-

94

GENERAL ZOOLOGY

quently become so very abundant that they destroy all the
leaves of currant and gooseberry bushes in the early spring.
Definition of Hymenoptera (Gr. hymen, "membrane";
pteron, "wing"). The insects which we have been consider-
ing in this chapter all agree in possessing mouth parts

Fig. 61. Metamorphosis of sawfly. (Natural size)

adapted both to biting and lapping, and four membranous
wings with few veins. The order is called Hymenop'tera. A
structural peculiarity is the union of the first abdominal
somite to the thorax. Consequently what appears to be the
division between the thorax and the abdomen really comes
after the first abdominal somite. The Hymenoptera undergo
complete metamorphosis.

CHAPTER X

THE INSECTS: HEXAPODA

Though numberless these insect tribes of air,
Though numberless each tribe and species fair,
Who wing the moon, and brighten in the blaze,
Innumerous as the sands which bend the seas ;
These have their organs, arts, and arms, and tools,
And functions exercised by various rules.

H. Brooke, Universal Beauty

Hexapoda (Gr. hex, "six"; pons (pod-), "foot"). The
previous chapters have been devoted to entomology, that
branch of zoology which treats of insects. The insects be-
long to the class Hexap'oda, the most numerous of all classes
of animals, comprising four fifths of the animal kingdom. In-
sects are built externally upon the plan of a series of somites,
grouped in three regions and with jointed appendages on
two of them, — the head and thorax. Except in very few
cases, where this number is reduced, the imagoes have six
legs. Hexapods are found in every variety of situation,
though they are, as a whole, adapted to life on the land and
in the air. A system of tracheae is universally present in the
imagoes, though the young of some species have gills for
breathing in the water. These gills are usually supplied with
tracheae, but in some species blood gills are found.

The hard, chitinous covering (exoskeleton) necessitates
frequent molts to provide for increase in size. Among many
of the lower orders of insects the young gradually grow into
the adult form without any change more sudden or conspic-
uous than the appearance of the functional wings at the last

molt. This type of gradual change to the adult form, or

95

96 GENERAL ZOOLOGY

incomplete metamorphosis, is illustrated by the grasshopper
(Fig. 5) and the squash bug (Fig. 23). Throughout their
development the young, or nymphs, are active and with few
exceptions pass through no inactive resting period.

The most marked change of form is seen in the higher
insects, the Coleoptera (Fig. 35), Lepidoptera (Figs. 38, 39),
Diptera (Fig. 47), and Hymenoptera (Fig. 59). In all of these
the egg hatches into a worm-like larva totally unlike the
adult. After several molts and great increase in size the
larva stops feeding and becomes inactive. This resting
stage, which is usually very different in appearance from
the larva, is called the pupa. From this pupa the adult, or
imago, finally emerges. This cycle of stages, passing from
egg through larva and pupa to the adult, is called complete
metamorphosis.

Along with the changes in body form in insects having
complete metamorphosis there are even more striking
changes going on inside the body. The internal organs of
the larva rarely become the organs of the imago. The tis-
sues of the larva become reconstructed to form the organs
of the adult. This process of reconstruction is carried on very
largely by the white blood cells, or phagocytes, which destroy
the larval organs and aid in building up the new organs for
the adult. In the fly maggot the wings and legs do not
become evident until the adult emerges from the pupa.
But even in the larva they begin to develop as small buds,
or "imaginal disks," inside the body.

Insect Behavior. Insects are provided with a nervous sys-
tem and sense organs that enable them to be affected by
conditions that exist outside their own bodies. These sense
organs are of various kinds, and for some of them we
have no idea as to the functions they may perform. The
other sense organs more or less closely resemble those found
in the human body, and we therefore assume that they serve

THE INSECTS: HEXAPODA 97

the insect in much the same way that similar organs serve
man. Experiments prove conclusively that insects feel,
see, hear, taste, smell, and we know that they are able to
recognize differences in temperature. But the remarkable
thing is that many insects have additional sense organs
which we are entirely unable to interpret because we have
nothing like them in our own bodies. In studying other
animals we are limited by our understanding of our own
senses, and find it hard to appreciate the fact that what we
see with our eyes and hear with our ears may not be exactly
the same as effects produced on the nervous system of
another animal. As human beings we view our own actions
in the light of intelligence. When we attempt to explain the
actions of other people or of other animals, it is only with
difficulty that we can interpret on the basis of what we
actually observe. When a man is lost in the woods at night
he walks toward any light, reasoning that he may find help.
But this does not make it safe to assume that a moth flies
toward a light because of any intelligent motive. In fact
the movement of the moth in this instance is involuntary.

Most of the actions of insects are purely reflex, involving
none of the higher types of mental activity known as intelli-
gence. When a stimulus acts upon an insect and causes the
body to take a definite position there is no choice of action
on the part of the insect. The response under these condi-
tions is called a tropism. Tropisms are purely mechanical
or involuntary responses to a stimulus, not involving intelli-
gent choice of action.

It is difficult to draw the line between these automatic
reflexes and the acts which are spoken of as instinctive. An
instinctive act is one which an individual performs without
ever having been taught. When a wasp paralyzes spiders
and places them in her nest to serve as food for her unborn
young there is small possibility that she has any prevision

98 GENERAL ZOOLOGY

or intelligent knowledge of the young not yet born, much
less any precise understanding of their needs. Yet the wasp
gathers the spiders without being taught to do so. Similarly
when the butterfly selects a certain kind of plant on which
to lay the eggs her act is not intelligent but probably a
combination of instincts and reflexes.

Among the higher insects, especially among the social
Hymenoptera such as the wasps and ants, many observa-
tions have been made upon actions that are interpreted as
involving intelligence. In many of these the enthusiasm of
the observer has run away with his judgment. There is an
impression that ants behave with a high degree of intelli-
gence, yet when anyone studies them carefully he finds
that in many instances they perform their tasks in a purely
reflex, mechanical way and show no ability to modify their
actions when conditions are changed for them. One observer
noticed that a wasp going diligently about the feeding of
young, bit pieces from a larva and persisted in trying to get
them into the mouth of the dead larva from which they were
cut. It is really doubtful if even the Hymenoptera have any
power of abstract reasoning. The actions of most insects
thus seem to be chiefly the lower types of behavior though
intelligence may play some part.

Man versus Insects. Professor S. A. Forbes of the Univer-
sity of Illinois has aptly expressed the struggle between
insects and man:

We commonly think of ourselves as the lords and conquerors of
nature, but insects had thoroughly mastered the world and taken
full possession of it long before man began the attempt. They had,
consequently, all the advantage of a possession of the field when
the contest began, and they have disputed every step of our in-
vasion of their original domain so persistently and so successfully
that we can even yet scarcely flatter ourselves that we have gained
any very important advantage over them.

THE INSECTS: HEXAPODA 99

Economic Importance of Insects. According to the report
of the Secretary of Agriculture for 1925, about 30 per cent
of our entire population now live on farms. The gross in-
come from' farm products in 1925 was over twelve billions
of dollars. When it is considered that our crops are attacked
not by one but often by many different insects, and that,
according to the estimate of one of the state entomologists
of New York, there is no crop cultivated which infesting
insects do not diminish by at least one tenth, it is plain that
the economic relations of insects to agriculture are ex-
tremely important. Nearly every order has its injurious
forms. Thus the Orthoptera has its locusts ; the Hemiptera,
its plant bugs ; the Homoptera, its aphids ; the Coleoptera,
its wireworms and beetles ; the Diptera, various flies ; and
almost the whole army of the larvae of the Lepidoptera feed
on plants.

Control of Crop Pests. In the preceding chapters frequent
mention has been made of insects injurious to native and
cultivated vegetation. Regardless of whether the damage
is by adult or immature insects it assumes one or the other
of two forms, depending upon the type of mouth parts pos-
sessed by the attacking insect. Chewing insects devour the
tissues of the plants, and sucking insects rob them of their
sap, so that the plants wilt and become weakened or die
(Fig. 62). In either case the old proverb of "an ounce of pre-
vention is worth a pound of cure," holds true. The United
States Department of Agriculture, state departments of agri-
culture and individual entomologists have long studied the
various insect pests of importance to agriculture and have
worked out many methods of control and prevention of
injury. For destruction of chewing insects, poison sprays
and powders are applied to the plants to be protected. The
insects die upon eating these poisons. Such treatment is
wholly ineffective for sucking insects. They are controlled

100

GENERAL ZOOLOGY

by what are called contact insecticides, — substances which
kill when they touch the body. Oil emulsions, nicotine com-
pounds, insect powders, corrosive materials such as certain
combinations of lime and sulphur, are used in the war
against sucking insects. As an indirect protection of crops
many preventive measures have been developed. These
are based upon a knowledge of life history and of habits
other than feeding habits. Fall plowing kills many insects

fc&:

'-*MP>i

&PA>^-- — bar

f^-lr.-

Fig. 62. A cornfield in which a band of road oil was placed as a barrier
after the field had been attacked on one side by chinch bugs

In the part of the field to the left of the line every plant was destroyed. (After

Illinois State Natural History Survey)

which would live through the winter if the ground in which
the larvae or pupae are living were not disturbed. Rotation
of crops is a big factor in insect control, for a field constantly
planted with the same crop becomes a breeding place for
the insect enemies of that crop. Some of the very worst
crop destroyers, such as the chinch bug (Figs. 24 and 62)
and the Hessian fly (Fig. 52), are held in check by keeping
fields free from old straw and vegetation in which these in-
sects seek shelter for the winter.

If it were not for civil war among the insects man would
have little chance to compete with them. Lady beetles

THE INSECTS: HEXAPODA 101

(Fig. 33) feed upon scale insects and plant lice. Several
entire families of Hymenoptera live as parasites on other
insects and kill many harmful species. Diseases are not
limited to the higher animals. Bacteria and fungi attack
and kill some of man's worst insect enemies.

Insects of the Household. Attention has been called to
the unsanitary habits of cockroaches living in houses.
Clothes moths, buffalo beetles, and crickets as destroyers
of articles of cloth and other organic material (for ex-
ample, fur and feathers) have been discussed in earlier chap-
ters. These are but the beginnings of the invasion which
insects carry against man into his household. The larvae
of beetles and of Lepidoptera attack and destroy or render
unusable his stored food materials. Cereals become in-
fested with webworms, the larva? of minute moths. Beans
and nuts are destroyed by larvae of weevils belonging to the
Coleoptera. Blowflies lay their eggs on meat that is ex-
posed to their attack, and the developing maggots feed
thereon. Dr. Britton, state entomologist of Connecticut,
in 1917, estimated that it costs the American people two
hundred million dollars a year to feed insect pests of stored
foods alone. These are but a few of the aggressors against
man in his private domain, the home.

Some insects are even more bold and, if unsanitary con-
ditions permit, will attack man himself. Body and head
lice and bedbugs feed upon the human body if conditions
favorable for them are permitted to exist. In some locali-
ties fleas become so abundant as to make life miserable by
their bites. Unless houses are kept screened, flies and
mosquitoes render man at least uncomfortable and, as ex-
plained in the next section, even endanger his life.

Insects and Disease. Malaria is sometimes said to have
been one of the big obstacles to the economic progress of the
human race. Sir Ronald Ross, the Englishman who proved

102 GENERAL ZOOLOGY

that the bite of the mosquito is the only means of spreading
malaria, estimated that in India alone more than a million
persons die annually of this disease. But the outright deaths
are but a small part of the ravages of malaria. Dr. L. 0.
Howard of the United States Department of Agriculture
estimates that this disease in the United States alone is
responsible for a financial loss of not less than one hun-
dred million dollars each year. Yet malaria is doomed if
mosquitoes are exterminated.

Yellow fever, which until the opening of the twentieth
century was one of the most dreaded diseases in this coun-
try, depended entirely upon the bite of the mosquito (Aedes)
for transmission. Dr. Reed with his coworkers, Carroll,
Lazear, and Agramonte, working in Cuba, discovered the
relations of mosquitoes to yellow fever. Dr. Reed, Dr. Car-
roll, and Dr. Lazear gave their lives directly or indirectly in
one of the most unselfish personal sacrifices in the interest
of mankind. The knowledge growing out of their experi-
ments has saved millions of lives, and today yellow fever
(Fig. 63) is entirely wiped out of the United States.

The importance of understanding the relation of insects
to disease is now well acknowledged. Yellow fever had com-
pletely disappeared from the United States because of suc-
cessful campaigns against the mosquitoes transmitting the
disease before anyone knew what organism the mosquito
is responsible for carrying. Professor Noguchi, a Japanese
scientist working in this country, showed in 1918 that yellow
fever is due to an organism called Leptospira.

In both malaria and yellow fever the disease germs un-
dergo a necessary part of their development in the body of
the mosquito transmitting them from one person to another.

Typhoid fever and dysentery are two diseases which the
house fly is responsible for spreading. The germs of both
these diseases are very abundant in the intestinal wastes

THE INSECTS: HEXAPODA

103

passed from the bodies of infected persons. Where fecal
matter is not properly disposed of, flies, because of their
filthy habits, get disease germs on their feet and bodies.

Fig. 63. Maps showing the effects of control measures against yellow fever
Yellow fever areas shown in black. (Courtesy of the International Health Board)

Then, when they alight upon food material it becomes
contaminated with germs, and anyone eating it is liable
to contract the disease.

During the World War there was a great increase in our
knowledge of the relations of insects to disease. Lice are re-
sponsible for transmitting typhus fever and also trench
fever, both of which were so prevalent during the war.

104

GENERAL ZOOLOGY

Stamen

Pist

Bubonic plague, or the "Black Death," which swept Eu-
rope and Asia during the Middle Ages, killing millions of
people, is another insect-borne disease. Rat fleas inoculate
the germs into the human body by their bite. One reason
why this disease spreads so rapidly is the fact that the
germs which produce the plague live in rats and are thus

carried by ships to all
parts of the world.

Relations between
Insects and Flowers.
In order to make seed,
the flowering plants
must have the pollen
furnished by the sta-
mens (Fig. 64) carried
to the pistil of the
same kind of plant.
The pollen is neces-
sary to the fertiliza-
tion of the ovule,
which later grows into
the seed. Continuous
pollination of a plant
by pollen which it furnishes from its own stamens has been
found to be detrimental to the vigor of the seeds. We find in
nature many devices to insure fertilization by pollen from an-
other plant of the same kind, — that is, by cross-pollination.
Some plants have the stamens and pistils so placed in the
flower that no pollen can fall from one to the other ; some
ripen their stamens and pistils at different times. Many
have the stamens and pistils on separate plants, and a great
number, though the stamens and pistils are close together,
are wholly or partially sterile to their own pollen and "set"
their seeds only if the pistils receive pollen from the sta-

Fig. 64. Diagram of pear flower

Courtesy of the United States Department
of Agriculture

THE INSECTS: HEXAPODA

105

mens of another plant of the same species. This is the case
with many of the fruit trees.

The wind carries pollen for some plants which have their
stamens and pistils more or less exposed, but a great number
of plants, especially those with the most beautiful flowers,
depend on insects to bring about pollination. So far has
this dependence gone that, in many cases, plants have be-
come unable to pollinate themselves. It is now clear that
the color, scent, nec-
tar, and form of flow-
ers, in many cases,
have been developed
in connection with
insect visitors. The in-
sects most concerned
in the pollination of
flowers are flies, butter-
flies, wasps, and bees.

Some insects visit
flowers for the sake of
the nectar. Pollination
results from the insect

brushing itself against the pollen-bearing organs and subse-
quently rubbing this pollen on to the pistil in a neighboring
flower in the search for nectar. But the case of the yucca moth
(Tegetic'ula, Fig. 65) is somewhat different. The yucca moth
is a white moth a little over a centimeter (about half an inch)
long, which lives in the flower of the yucca, or Spanish bayo-
net, a familiar plant of the dry southwestern plains. During
the day the female remains quiet, but at dusk (in the breed-
ing season) she begins laying her eggs within the pistil of
the flowers, among the ovules, which, when the flower is fer-
tilized, are to grow into seeds. Upon these seeds the larva
will feed. If this were all, there would be no peculiarity

Fig. 65. Yucca moth. (Natural size)
After Riley

106 GENERAL ZOOLOGY

deserving of mention ; but the female goes a step further
and makes sure of a supply of seeds for the larva by col-
lecting pollen from the stamens and thrusting it into the
pistil. The advantage to the larva is obvious, since its
supply of food is rendered certain ; the advantage to the
plant probably lies in the fact that not all the seeds thus
provided are eaten by the larva before reaching maturity.
This association may be cited as an illustration of symbiosis.
As mentioned under the topic of bumblebees, these bees
are very largely responsible for pollenizing the red clover.
The honeybee is an important partner of the apple, pear,
blackberry, and raspberry, aiding them by insuring polli-
nation. In the milkweed flowers the pollen is borne in
V-shaped packets. As a wasp or a bee visits a flower to get
the nectar, the pollen masses become attached to its feet
and are carried away by the visitor. The structure of the
milkweed flower is such that when the insect visits another
flower the packages of pollen attached to its feet slip into
grooves which bring them into contact with the pistils, thus
insuring fertilization of the flower. The pollen masses in
some instances become so firmly attached that the insect
is held prisoner. The early cultivation of Smyrna figs in
this country was unsuccessful. It finally became known
that small wasps essential for pollinizing the flowers were
lacking. When these insects were introduced into Califor-
nia, the fig industry became established.

CHAPTER XI

CLASSIFICATION AND DISTRIBUTION OF INSECTS

The mute insect, fix't upon the plant

On whose soft leaves it hangs, and from whose cup

Drains imperceptibly its nourishment,

Endear'd my wanderings.

Wordsworth

Nomenclature and Classification of Insects. In order to
write intelligently about animals, it is necessary that nat-
uralists should have some uniform system of naming, or
nomenclature, since the common names of animals vary
not only in the different countries and languages but even
in different parts of the same country. It will be noticed
that each insect, when first spoken of in these chapters, is
accompanied by a scientific name printed in italics. Thus
the Rocky Mountain grasshopper is Melanoplus spretus;
the common red-legged grasshopper, Melanoplus femur-
rubrum ; the lesser grasshopper, Melanoplus atlanis. These
different kinds or species of grasshoppers differ in size,
color, and habitat, and they each receive a different specific
name, as spretus, femur-rubrum, and atla?iis. They agree
in other characteristics, such as the general structure, size,
and proportion of their parts, and they are therefore placed
in the same group, or genus, -^- Melanoplus. The word
"genus" is thus seen to be a term of wider application
than the word "species." A genus may include one or
several species. The generic and specific names make up
the complete scientific name of an animal. The names are
always taken from the Latin or Greek, or are Latinized in
form, so that they are understood by all scientific men.

107

108 GENERAL ZOOLOGY

They often refer to some striking characteristic of the ani-
mal; thus, Melanoplus means "black armor," in allusion
to the dark-colored exoskeleton. Sometimes the reference
is to the locality where the animal is found, as atlanis, re-
ferring to the Atlantic states ; sometimes the name is given
in honor of some student of animals, as Darwin'ii, named
after the naturalist, Charles Darwin. The scientific name
first given to an animal, if accompanied by a description,
is the name it must bear, and the species is known under
that name wherever found. This system of nomenclature
was introduced by Linnaeus.

The words "species," "genus," and the other terms
applied to groups of animals are man's invention, for his
convenience in scientific description. Individuals which re-
semble each other in a large number of characters — and
especially if the individuals are able to interbreed — are
usually said to belong to the same species. The test of inter-
breeding, while of almost universal application, is not in-
variably a means of distinguishing the species, since in some
cases two different species can produce offspring (called
hybrids), though the latter are usually not fertile, — that is,
they are not themselves capable of producing young.

Often within the limits of a single species there are groups
of individuals which vary from the others in one or more
characters. Especially is this true of those species with a
wide range, living under diverse conditions. In such cases
the different forms which the species assumes are termed
varieties, and a varietal name is sometimes added to the
generic and specific names. We have already referred to
the seasonal variations of the swallowtail butterfly.

The different genera are arranged in groups, or classified,
according to their resemblances and differences. A number
of genera which show similar structural characteristics of
more general character than those used to constitute a genus,

CLASSIFICATION AND DISTRIBUTION 109

make up a family. Thus the grasshoppers of the genus
Melanoplus and those of all the other genera having short
antennae combined with certain other characters in common,
are placed in the family Locus'tidae. The katydid and other
green grasshoppers, with many meadow species, belong to
an entirely different family. The crickets (Gryl'lidae) and
the cockroaches (Blat'tidae) are allied to both of the grass-
hopper families. By common consent family names end in
-idae. Families are united to form orders, and orders in turn
make up classes. The largest and most important of the
orders which make up the class Hexapoda have already
been discussed. As we shall see later, the classes are united
to form phyla (sing., phylum), the primary divisions of the
animal kingdom.

The Simplest Insects. In the study of insects we began
with the grasshopper because it is large enough to study
easily. There are two orders of insects which are even
simpler in structure than the grasshoppers and therefore
are said to be "lower" than the Orthoptera. These are the
Thysanu'ra, or fish moths, and the Collem'bola, or spring-
tails. The insects of both these orders lack wings altogether.
In their development these lowest insects have no metamor-
phosis, for the young immediately upon leaving the eggs
are almost exactly like their parents. Because of their sim-
ple structure many people believe that these are much like
the insects which first appeared upon the earth in some past
geological time.

Thysanura. Glue is frequently eaten off the bindings of
books, and wall paper is often loosened from the walls, by a
minute, wingless, silvery insect, the fish moth, or silverfish
{Lepis'ma sacchari'na, Fig. 66). In spite of their small size
and retiring habits, they may cause great damage to libra-
ries and in households because of their appetite for paste,
starch, and such substances.

110

GENERAL ZOOLOGY

Collembola, or Springtails. These wingless insects, still
smaller than the Thysanura, are of very little importance.
They occur on the surface of water and under leaves and
stones. At times they become so abundant on snow that
they are called snow fleas. They make surprisingly quick

jumps by extending a spring-like
tail, which at rest lies underneath
the body. Until they jump into
the air they might readily be mis-
taken for minute particles of soot
or dirt.

Isoptera, or Termites. Often
in old logs, stumps, or under
stones swarms of small white in-
sects resembling ants are seen
(Fig. 67). They hollow out gal-
leries in wood and soil similar to
those made by ants. Although
these insects are often called white
ants, they are not ants and are
not closely related to them. They
belong to an order known as the
Isop'tera, which is but slightly
higher than the Orthoptera. Like
ants, hundreds or even thousands
of individuals live together, forming a society. There are
several classes of individuals. Wingless, white, thick- waisted
insects are the workers. They gather food, build the nests,
and care for the young. The soldiers are wingless, like the
workers, but have very large heads and powerful jaws for
the defense of the colony. The kings and queens, or fathers
and mothers, have wings. On reaching maturity they fly
away in pairs. After this flight they shed their wings. The
queen lays eggs which the workers care for.

Fig. 66. Fish moth. (Enlarged)
After Marlatt

CLASSIFICATION AND DISTRIBUTION

111

The termites are especially abundant in the tropics.
Some species build large mounds, twelve feet or more in
height. Their food is chiefly wood, and they often destroy
buildings and furniture. Jamestown, the capital of St.
Helena, was largely destroyed by termites and had to be
rebuilt on that account. Though less numerous in the north-
ern United States,
houses are some-
times greatly dam-
aged by them.

Degrees of Spe-
cialization. The lack
of special adapta-
tions or modifica-
tions of the various
organs marks the
ancestral insects as
generalized forms, as
distinguished from
their more or less
specialized descend-
ants of today, in
which the organs
have become modi-
fied to perform different functions. Thus the greatly de-
veloped hind legs of the grasshoppers are a specialization
in structure, fitting the insect to progress by leaps as well
as by walking.

Very different degrees of specialization often exist in the
organs of the same species ; thus the digestive system of the
grasshopper is quite complex, while the separate prothorax
is a generalized character, which shows the grasshopper to
be allied in this respect more closely to the primitive type
than are insects like the wasps, for example, where the three

Fig. 67. Termites or white ants.
(Much enlarged)

A, female ; B, male. (From United States Depart-
ment of Agriculture, Bulletin No. 1^72)

112 GENERAL ZOOLOGY

divisions of the thorax are grouped in one mass. Within the
limits of every order there are different degrees of specializa-
tion, and there are cases in every order where loss or decline
of parts (called degeneration) has been brought about through
various causes. Among the May flies the mouth parts of
the imago have become degenerate in connection with the
short adult life, which lasts only long enough for mating
and the laying of eggs for a new generation. In some scale
insects the female becomes degenerate in connection with
the quiescent life beneath a protecting scale. She loses eyes,
antennae, and legs, becoming very little more than a bag
capable of feeding and reproducing. Parasitism also brings
about degeneration.

From the study of the forms in which different organs ap-
pear in the orders of insects (that is, from the study of mor-
phology, the science of form), the naturalist is able to say
which kinds of insects have, on the whole, become most spe-
cialized in structure, and which have, on the whole, varied
least from the primitive generalized type. While all zoolo-
gists agree that the Thysanura and Collembola are the low-
est orders of insects, there are many differences of opinion
on the arrangement of the other orders. In an introduction
to zoology it is not necessary to consider some of the orders
which contain only very unusual or uncommon insects.

Generalized Insects. The generalized, or lower, orders
which have been taken up in this book are the Thysanura,
Collembola, Ephemerida, Odonata, Orthoptera, Isoptera,
Homoptera, and Hemiptera. The insects of all these orders
agree in having incomplete metamorphosis or no metamor-
phosis at all.

Specialized Insects. The insects which have complete met-
amorphosis are generally recognized as the more highly
developed. The Coleoptera, Lepidoptera, Diptera, and Hy-
menoptera are specialized, or higher, orders.

CLASSIFICATION AND DISTRIBUTION 113

Fossil Insects. We have but a very imperfect picture of
the insect life of the past. The remains of any animal of a
past time are called a fossil. Contrary to general belief, a
fossil is not necessarily an animal which has turned to stone,
for many fossils are not petrified. However, most of the
records of insects from past ages are preserved for us in the
rocks of which the crust of the earth is built up. The agen-
cies whereby fossils have been preserved are commonly as
follows: Wherever areas of land are uplifted, the atmos-
pheric agencies of wind and water begin their work of wear-
ing them down again. The worn materials, in the form of
clay, sand, or mud, as may be seen today after a rain, find
their way in rivulets to lower ground, or into a river which
deposits them still lower, finally even to the bottom of the
sea. When there, or in a temporary resting place in some
lake or pond, the material forms a bed into which the re-
mains of animals may drop. Under favorable conditions
their hard parts are preserved in perfect form. The sub-
stance in them may be replaced by minerals, and the entire
mass consolidated into rock by heat and the pressure of
other materials upon it. Even footprints may be made in
the soft mud at the edge of ponds, and indelibly preserved
in the rocks of later times.

The geologist has worked out in detail the order in which
the rock material of the world has been laid down. By study-
ing the fossil remains of living things the zoologist can pic-
ture something of the life of each of the great epochs in the
earth's history, though, owing to the conditions of preserva-
tion, by far the greater part of the record has been lost. It is
as though we should try to get a connected idea of the his-
tory of the United States from a book from which had been
torn the whole of the early voyages, much of the colonial
period, and many pages from the story of the Revolution,
the Civil War, and later history. Unfortunately the geo-

114 GENERAL ZOOLOGY

logical record is especially incomplete with regard to the
insects, so that it does not give us much help in this par-
ticular problem.

Most fossil-bearing rocks are formed on the floor of the
oceans. Since insects very rarely live in salt water, it is not
surprising that fossil remains of these animals are relatively
rare. Coal is a form of fossilized plants of a past age. Some
of the best specimens of fossil insects are found in the coal
deposits. Especially around the Baltic Sea, another inter-
esting type of fossil insects has been discovered. These are
the perfectly natural-looking specimens entombed in fossil
amber.

Of the remains of winged insects which have so far been
discovered, the earliest are those belonging to the orders
Orthoptera, Hemiptera, Ephemerida, and Odonata.

Distribution of Insects. Insects occur in every part of the
earth which man has explored. Even in the Arctic and
Antarctic regions insects are not wanting. Although many
species are very widely distributed, being cosmopolitan (dis-
tributed over practically the whole earth), many others are
of very limited range. No one has been able to offer a satis-
factory explanation of why the monarch butterfly and many
species of beetles have spread over so much of the earth's
surface and some other species are found in only a limited
locality of but a few miles in extent.

Any condition which tends to limit the distribution of a
species to a restricted area is called a barrier. To land
animals such a barrier may be a mountain range, a desert,
or a large body of water. To a desert-inhabiting species it
might be a forest. To aquatic animals, waterfalls or rapids
are often insurmountable. Temperature conditions are
very definite in their effects on the distribution of animal
life. Food supply is another important factor. The ocean is
a barrier to nearly all land species.

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The animal life of any region is known as its fauna.
Though insects are widely distributed over the earth, a
study of the different species shows that there are more or
less well-marked areas, each of which possesses its charac-
teristic species. Though much overlapping occurs, as might
be expected in the case of animals which can fly freely from
place to place, yet on the whole it is possible to separate
fairly well-marked regions, the climatic and other bound-
aries of which have prevented any great intercommunica-
tion, thus producing peculiar forms of life in each region or
realm. Six realms are very commonly recognized (Fig. 68).
These do not exactly agree with the geographical divisions
into continents. The animal life of the Americas is fairly
distinct from that of the rest of the earth. Here two realms
are recognized, the Nearctic and the Neotropical. The
boundaries of the six realms are as follows :

1. The Nearctic realm includes all Greenland and North
America south nearly to the tropic of Cancer.

2. All Central and South America and the coastal region
of Mexico comprise the Neotropical realm.

3. All Europe, Africa north of the tropic of Cancer, and
Asia south to an irregular line close to thirty degrees north
latitude is called the Palaearctic realm.

4. The Ethiopian realm is that part of Africa south of the
Sahara Desert, Madagascar, and the southern tip of Arabia.

5. The Oriental realm includes the tropical regions of
Asia, namely, India, Ceylon, and South China.

6. The Australian realm is one of the most distinctive
because the animal life is so different from that of the
neighboring regions. This includes the continent of Aus-
tralia, New Zealand, and many of the surrounding islands.

The student who has recently studied physical geography
may be able to see some relationship between the divisions
of these regions and climatic conditions.

CHAPTER XII

SOME OF THE LIFE PROCESSES

You may bring up a dog on the food of a man, and yet you cannot make a
man of him. — John Burroughs

Organ Systems. When we first began to study the insects
there was little reason to make comparisons between them
and our own bodies. But now that we have finished the
study of this group let us begin to make some comparisons
between what we have learned about insects and what we
previously knew about our own bodies. In spite of the dif-
ferences in form, we call many of the parts by the same
names in the two bodies, chiefly because they perform
somewhat similar or identical functions. The leg of a grass-
hopper with its many joints, its skeleton on the surface and
muscles inside the skeleton, is very different from the human
leg, yet both of them serve for locomotion. Similarly, in
the grasshopper we found organs of digestion and circula-
tion, a respiratory system, an excretory system, and a re-
productive system, all of which in functions correspond to
parts of our own bodies.

Likenesses of Living Things. In spite of difference in struc-
ture there are a few things which all living animals do, no
matter how complicated or how simple they may be. They
have the power of taking lifeless food material and making
it over into part of their living bodies. As a result of the
energy which they derive from this food they live and
respond to outside forces which act upon them. Finally,

they have the ability to grow and produce other individuals

117

118 GENERAL ZOOLOGY

of their own kind. Regardless of how they are constructed
or how and under what circumstances they live, there is a
striking similarity in the processes of changing food ma-
terial into the living substance (protoplasm) of their bodies
and the use of this food for producing energy. Because of
these likenesses, and because we are most interested in, and
familiar with, human structure, we are going first to review
this process in our own bodies. Later, as we study each
animal, we may note in what ways it is different from, and
similar to, man.

Digestion Defined. Food is taken into the body either as
a solid or a liquid. The entire process of digestion consists
in changing all the foods to a liquid state which is able to
pass through the wall of the digestive tract. In terms of the
chemist and physiologist foods may be classed as water,
salts, proteins, carbohydrates, and fats. Water and the
various salts used as food are capable of being used with-
out change. The other food substances must be changed
before they are available for use.

Enzymes. The digestive system produces fluids which act
upon the different food substances. The name enzyme is
applied to the materials in the digestive fluids which bring
about digestion.

The peculiar quality of an enzyme is to cause a chemical
change in another substance without itself losing any of its
own properties. Thus, trypsin, the enzyme which acts on
proteins, can do so and still remain trypsin. Similarly, the
enzyme ptyalin acts upon starch, and steapsin upon fats.

Why Food is Changed. Let us consider for a moment why
it is necessary for an animal to secrete elaborate chemical
mixtures like digestive fluids. If we were to examine the
alimentary canal, we should find that there are no openings
leading from the canal to the body cavity which might per-
mit food to pass directly to different organs. The wall of the

SOME OF THE LIFE PROCESSES 119

canal is thin, but it is made of small bodies, or cells, which
are packed closely together. Water will pass through this
membrane easily, but certain other substances, although
in a liquid state, will not pass through so readily. Those
solutions which pass through an animal membrane readily
are called crystalloids; for example, solutions of salt or
sugar. Liquids which do not pass readily through an ani-
mal membrane are known as colloids ; for example, solu-
tions of meat juice or starch. The action of the digestive
fluid is a double one : it changes the state of the solid food
physically, by rendering it liquid ; it changes the state of
organic foods (both solid and liquid) chemically, giving at
the same time to each of the altered food substances a new
physical property, namely, that of being able to pass through
the intestine wall.

For illustration, we may suppose that a piece of potato
which contains a great deal of starch is taken as food. In
the mouth and intestine the starch is changed physically by
being made liquid or partially so, and it is changed chemi-
cally into a sugar compound by the action of the enzyme
ptyalin, which is present in the saliva. In the latter state,
what was once starch passes readily through the wall of the
intestine. A protein substance like meat juice cannot pass,
except in a slight degree, through the intestine until it has
been changed chemically. This is done in the intestine by
the enzyme trypsin, which is produced from the secretions
of the pancreas. The changed substance is called a peptone.
The enzyme steapsin, also produced by the pancreas, sepa-
rates the fats into compounds known as glycerin and fatty
acid. The fatty acids combine chemically with the alkali
in the digestive tract, resulting in compounds similar to
soap ; the process is therefore called saponification. When
the proteins are changed to peptones, the starch to sugar,
and the fats to glycerin and soaps, then these organic foods

120 GENERAL ZOOLOGY

are ready to pass with any inorganic foods — as, for ex-
ample, salt and water — through the wall of the intestine.
The enzymes just discussed are very important and it is
only by their activity that many foods are changed in the
digestive processes. A considerable number of other enzymes
and materials produced by the liver and by glands in the
walls of the stomach and intestine aid in digestion.

Absorption. Digested food passes through the intestine
wall and mixes with the body fluids, in accordance with a
principle known in physics as osmosis. It is well known
that a crystalloid, like salt or sugar, if placed in a vessel of
water, will soon diffuse through the water. In doing so it
exerts a certain amount of pressure. This is called osmotic
pressure. If a permeable membrane be interposed between
a solution of crystalloids and one of colloids, both sub-
stances will exert some osmotic pressure, but by far the
greater amount is exerted by the crystalloid, because of its
greater facility in diffusing through water.

Applying the principle of osmosis to absorption in the in-
testine, we have crystalloids in the cavity of the intestine,
a permeable though not porous membrane (the intestine
wall), and colloids in the blood and body-cavity fluid. The
digested food diffuses through the intestine wall because of
the pressure it exerts in seeking to mix with more water.
Food on passing to the blood is changed by the cells of the
intestine wall from the crystalloid condition to a colloid,
and is henceforth incapable of passing back through the
membrane.

Assimilation. The food is transported by the blood in the
blood vessels or in the body cavity to tissues, where some of
it is transformed into protoplasm. Just how this is done no
one has been able to discover, but it is known that the trans-
forming process, which is called assimilation, takes place
in all tissues that are alive, — for example, muscles and

SOME OF THE LIFE PROCESSES 121

nerves. We know that the building up of new protoplasm
takes place in growth, when new cells are formed, and that it
is also made necessary on account of the slow and impercep-
tible destruction of the protoplasm in oxidation (see below).

It will be helpful at this point to know that of all the food
taken into the circulatory system of an animal but very
little, except during growth, is actually made into proto-
plasm. The carbohydrates and the fats that are absorbed,
and those that are- made from proteins by the protoplasm,
together with some unassimilated proteins, are destroyed
after they have been stored temporarily in the various tis-
sues of the body, especially in the muscle cells or in the liver.

Respiration. So far we have traced the food through those
changes leading to its assimilation by the living animal.
Protoplasm and the food materials stored within it are
chemical substances which unite rather readily with oxygen.
In spite of the fact that oxygen destroys the substance of
which protoplasm is composed, there are few animals which
are able to exist without oxygen. Oxygen is necessary to
life because the union of oxygen with protoplasm and stored
food material sets free the energy which is used by the
animal in its movements and other life activities. The
stored food material and the living protoplasm are broken
down, not as wanton destruction but as the only means
whereby the animal obtains its energy.

When oxygen combines with the material of a living
organism, the process is called respiration. Special organs
of respiration are found in most of the higher animals.
Thus in man the lungs, in fish the gills, and in insects the
tracheae are organs adapted to supplying the body with
oxygen and to giving off* certain types of wastes. The es-
sential characteristic of a breathing organ is a thin, moist
membrane, with thin-walled capillary blood vessels on one
side and air on the other. In man these conditions permit

122 GENERAL ZOOLOGY

oxygen to pass through the tissue of the lungs into the blood-
filled capillaries and permit wastes to escape from the blood.

In the circulating blood there is a red-colored substance
called haemoglobin. Oxygen combines chemically with this,
and the compound goes with the blood until it reaches
tissue cells which have some food stored in them ; then the
oxygen combines with the food, which may be carbohydrate,
fat, or protein. The chemical union of oxygen with other
elements is of the greatest importance in the life of any
plant or animal. A simple example of the result of the
chemical union of oxygen with another element may be ob-
served in the burning of coal. It is well known that coal
is composed chiefly of carbon. When a quantity of coal is
heated it begins to unite with oxygen from the air. During
this process four phenomena may be observed : first, the
quantity of oxygen in the room is reduced ; second, the
quantity of coal is reduced ; third, an invisible gas is
formed ; and fourth, heat and light are given off.

When oxygen unites chemically with carbon two kinds of
gas may be formed, either carbon monoxide or carbon di-
oxide, or both. The union of a solid element with a gaseous
one to form a gaseous compound accounts for the fact that
so great a mass of coal disappears in burning, leaving only
the mineral ash behind. We call the union of oxygen with
another substance oxidation.

Forms of Energy. It is important to observe that as oxi-
dation takes place heat and light, which are called forms of
energy, are given off. Energy — that is, the power to do
work — can be transformed from one form to another ; for
example, the heat derived by oxidizing coal may be trans-
formed into mechanical energy like that of an engine, and
the mechanical energy may be changed into electricity, and
the electricity into mechanical energy again, or into heat
and light. We may regard the energy which is suddenly

SOME OF THE LIFE PROCESSES 123

released upon the oxidation of the carbon in the coal as
having been stored there by the sun millions of years ago,
when the coal was the growing tissue of a tree. We may
borrow from physics two other terms which will help us in
getting the notion of the states in which energy may exist.
Energy at rest — as, for example, chemical affinity (that
is, the readiness of the carbon to combine with oxygen) —
is called potential energy ; energy in action, as heat, light,
electricity, and motion, is called kinetic energy. As we have
already seen, potential energy may become kinetic energy,
and kinetic energy may become potential energy.

Carbohydrates, and especially fats, are capable of com-
bining with a relatively large amount of oxygen because of
the small proportion of that element in those compounds
and the large proportion of carbon. Carbohydrates, chiefly
glycogen, one of the many kinds of sugar in nature, are fre-
quently made from proteins by the protoplasm in the cells
and are stored in the liver cells of the higher animals, to be
later transported to their muscle cells and stored in them
until needed. In animals that have no liver, as an earth-
worm, the glycogen is stored in the cells of the lining of the
body cavity and in the muscles. Fats, made either from
carbohydrates or from protein food by the protoplasm, or
stored directly in cells from the fatty acids absorbed through
the intestine, are reserve material and are capable of sup-
plying energy when there is need of it.

When carbohydrates and fats are oxidized the resulting
compounds are carbon dioxide and water, as these foods
contain only carbon, hydrogen, and oxygen. Proteins are
far more complex. All proteins contain at least carbon,
hydrogen, nitrogen, oxygen, sulphur, and usually, in addi-
tion, phosphorus. When they are oxidized many different
compounds result. The best known of these are uric acid,
carbon dioxide, and water. All these compounds are wastes.

124 GENERAL ZOOLOGY

Carbon dioxide, whether derived from carbohydrates, fats,
or proteins, makes its way by the blood to the lungs, and
there passes through the moist membrane and is exhaled.
The carbon dioxide which is given off through the respira-
tory organs is produced within the living protoplasm.
Lungs, gills, or other respiratory surfaces are regions where
the blood supply from all parts of the body is able to get
rid of its carbon dioxide. Between the entrance of the oxy-
gen into the body and the discharge of carbon dioxide, the
essential part of respiration takes place. This is the actual
union of oxygen with stored food material within the proto-
plasm or with the protoplasm itself.

Metabolism. In the foregoing paragraphs we have shown
how food material through the process of digestion and
assimilation becomes made over into the substance of a
living animal. The term anabolism covers all these changes
from the time the food enters the body until it has become
a part of the living animal either as living protoplasm or
as stored food material. All the constructive or building-up
activities of the animal body, namely, growth, repair, and
storage, are the products of anabolism.

Living bodies are constantly changing. One of the most
characteristic changes is the destruction of protoplasm and
stored material to furnish the energy characteristic of living
things. These destructive changes make up the process
called katabolism. Respiration and the getting rid of other
waste materials which have been part of the living animal
(excretion, see page 125) are the chief manifestations of
katabolism.

All the physiological and chemical changes which occur
between the time when food is taken into the body and when
it is used or broken down to liberate energy are collectively
called metabolism. Metabolism is thus the sum of all the
changes involved in anabolism plus those of katabolism.

SOME OF THE LIFE PROCESSES 125

Excretion. The last of the stages of metabolism is excre-
tion. Excretory material is only that waste which has been
formed by the breaking down of the living protoplasm and
the food material stored in it. The carbon dioxide and
water removed from the body in the process of respiration
are excretory products. In addition various nitrogen com-
pounds, of which urea and uric acid are the most familiar,
are produced by the processes of katabolism. These wastes,
dissolved in water, are collected by the blood and carried
to the kidneys. Here they are separated from the blood
and passed from the body as urine.

Other Wastes. The undigested food and the indigestible
substances that pass through the length of the intestine
are not excretory products, — a fact that has already been
stated in the chapter on the grasshopper. These wastes
are called feces, or fecal matter.

Vitamins. Until recently it was very generally thought
that growth and health depended only upon sufficient quan-
tities of food. It was discovered, however, that ample food
under certain conditions may produce diseases. Sailors
living on canned and dried foods became ill of a skin disease
called scurvy, which disappeared when fresh fruits and
vegetables were given to them. Similarly, Orientals eating
practically no food but polished rice became subject to a
disease called beriberi. The disease disappeared when they
ate unpolished rice, containing part of the outer coating.
Some of the nutritional diseases and their cures were dis-
covered before anyone knew a scientific explanation of their
causes. It is now known that these diseases are due to the
lack of certain substances called vitamins. The vitamins are
substances which must be present in the food if the animal
is to be perfectly nourished (Fig. 69). If entirely deprived
of vitamins for a long time, experimental animals die. No
one knows exactly what vitamins are. They occur in most

126

GENERAL ZOOLOGY

fresh vegetables and fruits, the outer coating of grains,
many fats, yeast, liver, milk, and eggs.

So far the vitamins have usually been named as vitamins
A, B, C, D, and E. It is probable that others beyond these
five may be discovered. Vitamin A is a growth-promoting
vitamin. Animals fed on a diet lacking nothing but this
vitamin fail to grow normally and develop diseased eyes

Fig. 69. These guinea pigs were from the same litter

The smaller one shows the effects of a diet deficient in vitamins. (Courtesy of
Dr. Percy R. Howe, Forsyth Dental Infirmary)

and bones and have a decidedly unnourished appearance.
This vitamin is found most abundantly in milk, eggs, but-
ter, and cod-liver oil.

Vitamin B is also growth-promoting. It occurs in seeds,
in yeast and egg yolks, and to a smaller extent in meat, milk,
and certain vegetables and fruits. Its complete lack in the
diet produces inflammation of the nerves, which may result
in paralysis and death.

Vitamin C occurs abundantly in citrus fruits, tomatoes,
and some other fresh fruits and vegetables. Milk, lean meat,
and some dried vegetables contain vitamin C in smaller
amounts. Lack of this vitamin produces the skin disease
called scurvy.

Vitamin D is especially abundant in cod-liver oil. Lack
of this vitamin leads to poor bone formation and a disease
called rickets.

SOME OF THE LIFE PROCESSES 127

Vitamin E is one of the most recently discovered of the
vitamins. Its lack in food has serious effects on the repro-
ductive system. Animals deprived of it are either sterile
or unable to produce young strong enough to live. Lettuce,
cereals, meat, and egg yolks are the principal sources of this
vitamin.

Methods of Reproduction. Every kind of animal has the
ability of producing individuals of the same species. Only
living things are capable of reproducing. Among animals
there are several different ways in which reproduction may
take place. Some of the simpler forms of life, which will be
discussed later, undergo a separation of the entire body
into two or more parts, each of which grows into a complete
animal. This simple and direct method of increasing num-
bers is called asexual reproduction. Most animals have a
much more complicated means of reproducing. In these,
special organs are set apart chiefly for the purpose of pro-
ducing young. These are the reproductive organs, such as
were described for the grasshopper. They consist of the
gonads, which produce the eggs and the sperm, besides
ducts and various other organs and structures used in the
reproductive process. Through sexual reproduction the
young is produced only after the egg and sperm have united
in the act of fertilization. The story of the creation of a
new individual from the fertilized egg is a long one. By
gradual and orderly changes, following a definite plan, the
simple, fertilized egg takes on the appearance of a living
creature. Some of these changes, which with others com-
prise the science of embryology, will be discussed in the
chapter on living matter and the cell (Chapter XIII).

Glands of Internal Secretions. Within recent years much
has been learned about the glands which have no ducts but
empty their secretions directly into the blood. These are
called the endocrine glands or glands of internal secretion.

128 GENERAL ZOOLOGY

Some of them are so small that no one has thought them im-
portant until recently. Yet several are so important that
death is sure to follow their removal. The thyroid and para-
thyroid are located in the neck region of man and of many
other vertebrates. A lack of iodine in the food causes the
thyroid to swell in a disease called goiter. Years ago many
operations for the removal of the thyroid in cases of goiter
proved fatal. This was because other small glands of ex-
treme importance were removed accidentally in taking out
the thyroid. These are the parathyroids.

The hypophysis lies on the ventral side of the brain just
above the roof of the mouth. This minute gland regulates
growth. Giants are overgrown because of too active a
hypophysis. At the upper end of each kidney there is a
small gland called the suprarenal. Among other functions
this gland controls blood pressure and in critical situations
produces secretions that stimulate the body to unusual
action. Within the reproductive organs, or gonads, there are
important cells which have no part in forming germ cells.
These so-called interstitial cells regulate the development of
secondary sexual characters, such as the spurs of the rooster
or the beard of man.

These few instances of functions give but an introduction
to the understanding of these ductless glands. Though
their functions are not fully understood, we do know that
growth and development and the functioning of many organs
are largely controlled by these glands. Even the character
and personality of an individual are greatly influenced by
them.

CHAPTER XIII

LIVING MATTER: PROTOPLASM AND THE CELL

But marvel! Lump to egg doth grow,
Puffs itself up and cracks in two.

Goethe, Faust

Protoplasm. Every living thing, whether it be a plant or
an animal, is made up of a material called protoplasm. This
living material is not a simple substance but is a mixture of
various chemical compounds occuring in fairly definite pro-
portions. Proteins, fats, sugars, starches, and various salts
and minerals are dissolved and mixed as fine particles and
droplets in water to comprise the chief bulk of the living
protoplasm. These are the same kinds of materials that are
used as food. However, the protoplasm is not built up di-
rectly from food taken into the body. All foods must first
be changed to a liquid state, and some must be changed
chemically by the process of digestion. Then this liquid
food material may be assimilated and become a part of
the living animal. The exact composition of the protoplasm
is never the same at any two instants, for it is one of the
characteristics of living beings that material is constantly
being destroyed and its place being taken by new substances
supplied as food.

The Cell and its Structure. All but the very simplest mi-
croscopic animals and plants have their protoplasm divided
into myriads of small units, each of which is called a cell
(Fig. 70). The cell is thus the microscopic unit of structure
of the animal body. The material is not uniformly distrib-
uted within the cell. There is a central body, usually

129

130

GENERAL ZOOLOGY

Centrosome

Chromatin

Vacuole

Nucleus

Cytoplasm

rounded in shape, which is called the nucleus (Fig. 70).
The more fluid protoplasm around it is called cytoplasm.
The single unit of protoplasm, the cell, has the power of
carrying on all the activities of the living animal, but when
many cells are united the various functions of living animals
are distributed among them.

Tissues. In all animals, except the very simplest micro-
scopic forms, the cells in different parts of the body are

specialized for carry-
ing on certain kinds
of work for the whole
body. Thus there is
a division of labor;
some cells, for exam-
ple, do the moving for
all the body and are
termed muscle cells.
When these cells of
similar function are
grouped together they
are made up of what
is known as a tissue.
The muscle tissue,
with which all are familiar in the form of a piece of lean
beefsteak, is composed of countless numbers of muscle cells.
The organs which have been discussed in the preceding chap-
ters as the conspicuous structures within the body are made
up of various tissues. In these tissues the cytoplasm of the
individual cells becomes modified in form and structure for
carrying on limited functions.

Function of the Nucleus. The nucleus seems to control the
activity of the cell. Within the nucleus there is a substance
that is very important because it has the power of passing
from one generation to the next those features and condi-

•%

Stored
material

Fig. 70. Diagram of an animal cell.
(Greatly magnified)

LIVING MATTER

131

tions which are hereditary. This nuclear material is called
chromatin (Figs. 70, 71).

Reproduction of the Cell. There is only one way in which
new cells are formed, and that is by a process called cell
division. The usual method of division of a nucleus is by
a very complicated procedure called mitosis. By an intri-
cate series of stages the chromatin of the nucleus becomes

, Centrosome
.Chromatin,

Chromosomes'

E " F ^ A " G

Fig. 71. Diagrams showing a cell undergoing mitosis and division

absolutely equally divided into two parts, and from each of
these a new nucleus is formed. The important steps in
this mitosis, or nuclear division, are outlined below.

Division of the Nucleus. The scattered granules of chro-
matin within a nucleus that is about ready to start division,
join to form a continuous thread (Fig. 71, B). The thread
later breaks up into small masses known as chromosomes
(Fig. 71, C). While this has been going on, a small body,
the centrosome, in the cytoplasm just outside the nucleus
becomes active and forms a structure known as the spindle
(Fig. 71, C). While the spindle is being formed the wall
surrounding the nucleus breaks down and disappears. The
chromosomes, which are thereby set free in the cytoplasm,

132 GENERAL ZOOLOGY

become attached to some of the fibers making up the spindle.
For a very short time the chromosomes are arranged mid-
way (Fig. 71, D) between the two ends of the spindle.
While in this position each of the chromosomes splits
lengthwise into two exactly equal parts. Immediately after
the splitting of the chromosomes the halves of the chromo-
somes begin to move away from each other toward the
poles of the spindle (Fig. 71, E). When the chromosomes
become grouped around the two poles of the spindle they
begin to lose their individual forms (Fig. 71, F). A mem-
brane starts to form around each group of chromosomes.
When these two membranes are completed there are two
nuclei within the cytoplasm of the original cell (Fig. 71, G).

Division of the Cell. This condition is only temporary, for
ordinarily mitosis is followed by a division of the cytoplasm.
The mass of the cytoplasm begins to constrict about its
middle (Fig. 71, F). As this constriction deepens, the origi-
nal mass of cytoplasm is pinched into two pieces, each of
which surrounds a nucleus (Fig. 71, G). By this means two
new cells take the place of the one cell with which the
description started. Each of the two new cells contains but
half the material from the mother cell. But it is one of
the characteristics of living protoplasm that it can take
material furnished to it as food and build up more proto-
plasm in the process termed growth. By growth the two
small cells increase in size until they are as large as the
mother cell which produced them.

Numbers of Chromosomes. As mentioned in an earlier
paragraph the chromatin material is very important in the
nucleus. It seems that the whole elaborate process of mito-
sis has as its chief aim the exact division of this material.
When the chromatin forms into chromosomes there is al-
ways a fixed number of chromosomes typical for each species
of animal. In some animals there are only two, while others

LIVING MATTER 133

have different numbers, which sometimes reach more than a
hundred in every cell. Each cell in the body tissues of a man
contains forty-eight chromosomes.

Protoplasm and Life. Though protoplasm is made up of
well-known substances it can be produced only by proto-
plasm. Many scientists have tried to mix materials to-
gether to produce protoplasm. Although they can produce
something which looks like protoplasm, no experiment has
ever produced living protoplasm ; in fact, it is very doubt-
ful if living protoplasm can ever be formed artificially.

Mitosis during Sexual Reproduction. In the chapter deal-
ing with life processes mention was made of the fact that
reproduction is usually through specialized products called
germ cells. In the formation of the young from the germ
cells we find one of the most conspicuous instances of cell
division. The changes which lead up to the multiplication
of cells in the embryo will be described here.

Germ Cells. Germ cells produced by females are rela-
tively large cells containing stored yolk to be used as
food material by the developing young (Fig. 72, A). The
cells produced by the males are very small cells (Fig. 72, B,
sperm cell), capable of locomotion, called spermatozoa or
sperm. Neither of these minute bodies in any measure re-
sembles the animal which produced it. Yet after a long
series of steps, or stages, an egg and a sperm unite and finally
form an individual like the animals which produced them.

Maturation and Fertilization. The act whereby an egg and
a sperm are united to start the formation of a new individual
is called fertilization (Fig. 72, B-D). Before this act can
take place both egg and sperm must have gone through a
period of preparation, which is called maturation. During
maturation the most important changes take place in the
nuclei of the germ cells. It will be remembered (p. 131)
that the nucleus contains a substance called chromatin, and

134 GENERAL ZOOLOGY

that this chromatin is the substance by which hereditary
characters are passed from one generation to the next. After
maturation each germ cell has but one half the amount of
chromatin which it possessed before maturation started.
This reduction of the chromatin prepares the germ cells for
fertilization. In consequence, when a mature egg and ma-
ture sperm join in fertilization each brings but one half its
original amount of chromatin. The fertilized egg therefore
contains the usual or normal supply of chromatin, one half of
which was in the mature egg before fertilization and the other
half was added by the sperm (Fig. 72, E). At the end of fer-
tilization the sperm and egg have completely joined to form
a single cell having a single nucleus. It is from this single
cell, the fertilized egg, that the new individual has its origin.

Cleavage. By mitosis the nucleus of the fertilized egg
divides to form two nuclei and from the one cell two com-
plete cells are produced (Fig. 73, B), but they remain
attached to one another. This multiplication of cells from
the fertilized egg is called cleavage. After two cells have
been formed, each undergoes mitosis and cleavage, so that
from two cells four are produced (Fig. 73, C). This cleavage
process continues in^all the higher animals until the original
fertilized egg has formed a large number of cells.

Blastula. Even as early as the eight-cell stage in the em-
bryo, or developing young, the cells in many species arrange
themselves in such a manner as to have a small cavity in the
interior of the group. Such a stage where the cleavage cells
are arranged as a single layer of cells surrounding a cavity
is called a blastula (Fig. 73, E).

Gastrula. In later development one region of the blastula
wall begins to push inward just as a hollow rubber ball may
be indented (Fig. 73, F). As this ingrown region deepens
the cells which were in a single layer during the blastula
stage become recognizable as an outer-surface covering, or

Mature egg

nucleus

First and second polar cells
Sperm nucleus
First cleavage
spindle

Fig. 72. Maturation and fertilization in the egg of a worm, Nereis

After Wilson

136

GENERAL ZOOLOGY

ectoderm, and a layer lining the inturned region, called the
endoderm. This stage, when the embryo consists of two
layers of cells, is called a gastrula.

Later Development. Between the ectoderm and endoderm
a third layer, or group, of cells forms (Fig. 73, G). These
are called the mesoderm. From these three layers of cells
the fully formed animal grows. The cells which differed

Blastula /fr~ '^^^>Gastrvla/^'

"^xX~

- -Ectoderm

..cavity

-ff- Vv cavity 'f?

Hi S LA
1 /\\}~*~l X, ' U4

^--Mesoderm

3 n * q H

1 c

f -Endoderm

Fig. 73. Cleavage of the egg and early development of the starfish.

(Enlarged diagrams)

A, egg before development starts ; B, two cells resulting from the division of
the fertilized egg ; C, four-cell stage ; D, eight-cell stage ; E, section through
the blastula stage ; F, section through gastrula stage ; G, a later gastrula, show-
ing how mesoderm is formed

little from one another except in size become specialized
for various work. This specialization began with the forma-
tion of the gastrula, for the cells of the endoderm form a
sac, which in some animals serves as a stomach, or later
develops into a digestive system. From the outer layer, or
ectoderm, the skin and the nervous system develop. The
lining of the alimentary canal comes from the endoderm.
The most of the rest of the body is formed from mesoderm.
This includes the muscles, excretory system, circulatory
system, and reproductive organs.

CHAPTER XIV

THE SPIDERS AND ALLIES: ARACHNIDA

A noiseless, patient spider,

I marked where, on a little promontory, it stood isolated ;

Marked how, to explore the vacant, vast surrounding,

It launched forth filament, filament, filament out of itself ;

Ever unreaching them — ever tirelessly speeding them.

Walt Whitman

Spiders. Spiders have several of the anterior somites
joined into a single mass, the head-thorax, or cephalothorax
(Fig. 74), followed by the abdomen. The cephalothorax
bears six pairs of appendages, — two pairs of the nature
of jaws and four pairs of walking legs. The chelicerse, the
first pair of jaws, are appendages composed of two seg-
ments, of which the terminal segment is sharp pointed and
hollow, for the passage of a poisonous secretion from a gland
placed partly in the head and partly in the basal segment.
The second pair of jaws, or pedipalps, bear jointed feelers,
used for handling food. On the front of the head are eight
simple eyes ; compound eyes and antennae are wanting.

Two little slits on the under side of the abdomen open into
the breathing organs, or lung books, which consist of a pair of
sacs containing a number of thin plates, like the leaves of
a book. Between the two slits are the external openings
of the reproductive organs. At the end of the body are three
pairs of spinnerets, consisting of a number of little tubes
leading from glands in the abdomen, which secrete a viscous
fluid that hardens into silk on exposure to the air. Two
tracheae (Fig. 74), which give off branches to different parts
of the abdomen, open just in front of the spinnerets.

137

138

GENERAL ZOOLOGY

Many spiders build circular webs of silk, in which they
capture insects to suck their blood. A common species of
garden spider (Miran'da auran'tia) is shown in Fig. 75.
The spider first spins a line across the space where the web
is to be and then attaches near its center other threads,

which it carries to dif-
ferent points, making
the radiating founda-
tion lines of the web.
These lines are all dry
and inelastic. Concen-
tric spiral lines of an
adhesive nature are
then added, the hind
legs being used to place
the threads. An oval
cover of silk is spun in
the center. Beneath
this, or in a folded leaf
at the side, the spider
lurks in watch for its
prey. A zigzag band of
white silk crossing the
center is usually added
to strengthen the web.
When an insect is cap-
tured the spider rushes out, and if there is any danger of
the escape of the prey it is deftly wound with more silk
till its struggles have ceased. If it proves to be a wasp or
other dangerous captive, or if it is too big to be safely man-
aged, it is often assisted to escape by the spider's cutting
the web, which is then repaired for another victim.

Like the click beetles and many others of the Coleoptera,
this spider when alarmed has the habit of dropping to the

Palpus

Chelicera

,Cephalothorax

Breathing organ

Openings to
{reproductive organs

|- Abdomen
I - - - Fourth leg
y ■ Trachese
-Spinnerets (3 pairs)

Fig. 74. External anatomy of a spider,
Epeira vulgaris. (Enlarged)

After Emerton

THE SPIDERS AND ALLIES

139

• "- ; ••

Fig. 75. Garden spider and web. (Reduced) v

ground as if dead. It spins a thread of silk as it drops ;
when the danger is over, it is able by this means to return
to the web.

The eggs of the garden spider are laid in the autumn in a
sac of silk (Fig. 76), which may contain from five hundred
to two thousand eggs. These eggs hatch early in the winter,
and the young live in the case through the cold weather.

140

GENERAL ZOOLOGY

By spring a comparatively small number of spiders emerge;
for they are cannibals and the survivors have lived only
because they had brothers and sisters to eat, no other food
having been provided for them. By successive molts, with-
out marked metamorphosis, they reach their adult size.

The dark-colored, hairy spiders (Lyco'sa) found under
sticks and stones are called wolf spiders. They usually build

tubular tunnels in the ground, which
they line with silk. These do not make
a web to capture their prey, but spring
upon it as they run about in search of
food. The females may often be seen
dragging after them the large gray ball
which contains, at first, their eggs, and
afterwards the young. After a certain
time the young leave the silken case,
and for some time longer run about over
the body of the mother.

These spiders are often called tarantu-
las, but that name should be restricted
to the large hairy spiders of the warm
parts of the world. The true tarantulas
(Fig. 77) can be distinguished from all
other spiders by the fact that the ter-
minal segment of the chelicerse works vertically instead of
horizontally. Tarantulas are universally dreaded in the
countries where they grow to be of large size, and they are
believed to be very poisonous. The ability of any spider
to pierce the human skin depends, of course, on its size and
the strength of its jaws ; the effect produced by the bite
depends not only on the amount of poison injected into the
wound but also on the age and mental and physical condi-
tion of the person bitten. Though many stories of death
by tarantula bites have been told, most of them are clearly

Fig. 76. Egg case of
garden spider. (Nat-
ural size)

After Wilder

THE SPIDERS AND ALLIES

141

Fig. 77. A tarantula

untrue. Whatusuallyhap-
pens is that persons bitten
by them suffer only tem-
porary pain and swelling,
something like that which
follows the sting of a bee.
Among the most inter-
esting of the tarantula
family are the trapdoor
spiders of the Western and
Southern states, and of
southern Europe. They
build burrows, which they
line with silk, and provide
with a lid lined with silk,
attached by one edge to

the mouth of the burrow. A European species builds a nest

with a side tube (Fig. 78), into which it can retreat in time

of danger, closing a door at the entrance

of this tube.

Harvestmen. The long-legged harvest-
men, or daddy-long-legs (Liobu'num,

Fig. 79), are allied to the spiders. They

can be recognized by the eight extremely

long legs, which are thus developed as

organs of touch, as well as for walking.

They are familiar creatures, found in

damp and shady places. They feed on

small insects, especially aphids.

Mites and Ticks. The mites and ticks

are related to the harvestmen and to

spiders. They show less segmentation

of the body than the preceding groups

(Fig. 80). They are small, oval, eight-

■o-

Fig. 78. Burrow of

a trapdoor spider,

showing side tube

After Emerton

142

GENERAL ZOOLOGY

legged forms. The mouth parts are more or less united
to form a beak for sucking blood. They live as parasites.

Fig. 79. Harvestman. (Natural size)

Ticks in Relation to Disease. Almost everyone who spends
any time in the woods has had the experience of finding a
small brown creature firmly attached to his skin, rapidly

A B

Fig. 80. Cattle tick. (Enlarged)

A, male tick ; B, female filled with blood from host. (From the United States

Department of Agriculture)

gorging itself with blood. This is the common wood tick.
The species found in the eastern part of the United States
is practically harmless. A closely related species (Derma-
cen'tor venus'tus) in the northwest of our country carries

THE SPIDERS AND ALLIES

143

an organism which produces a very serious human disease
called Rocky Mountain spotted fever. In the Bitterroot
valley of Montana more than 75 per cent of the cases end
in death. Texas fever, a disease of cattle in the southern
part of the United States, is due to a parasite also carried
by the bite of a tick (Margar'opus annula'tus, Fig. 80).
The disease carried by this tick has resulted in cattle losses
in the Southern states amounting to millions of dollars.

Fig. 81. Itch mites burrowing in the skin of man. (Enlarged)

Mites as Parasites. There are many species of these mi-
nute, almost microscopic animals. Some of them are para-
sites of man. The harvest mites, or chiggers, are common in
woodland pastures in midsummer. Young harvest mites
have the habit of burrowing into the skin of man, where
they set up intense irritation and severe itching. The pecul-
iar part of it is that these mites which attack man commit
suicide by doing so. Only the ones which become attached
as parasites on the bodies of insects reach maturity. The
itch mites (Fig. 81) are another type of almost microscopic
creatures which burrow beneath the skin and lay their eggs
in these burrows. One species (Sarcop'tes scab'iei) produces

1 Reprinted by permission from Ha ndbook of Medical Entomology, by W. A. Riley
and 0. A. Johannsen, published by The Comstock Publishing Co.

144

GENERAL ZOOLOGY

a skin disease of man commonly called "the itch." Other
species attack various mammals. Mange, a common skin
disease of dogs, is produced by mites burrowing in the skin.
Scorpions. The scorpions have the body plainly seg-
mented. In the common scorpion {Bu'thus, Fig. 82), found

under sticks in our Southern
states, the pedipalps are greatly
elongated, making a formidable-
looking pair of claws. The ab-
domen is provided with a sting
at its extremity. This is not
operated like the sting of a bee
or wasp but is a lance-like organ
which is thrust into the enemy
by the whip-like motion of the
whole tail. The whip scorpion
(Thelyph' 'onus) , also found in
similar situations in the South,
is another formidable-looking
creature, with immensely de-
veloped pedipalps. These are
used to pull open decaying
wood in search of small insects,
which form its food. Its appearance accounts for the
dread it inspires, but there is no evidence to show that
it is harmful to man.

Definition of Arachnida. The name "Arach'nida" is ap-
plied to the spiders, scorpions, mites, and ticks, all of which
are segmented animals with jointed appendages but lack-
ing antennae. There are normally four pairs of legs, though
the young stages commonly have but three pairs. The lack
of antenna? and the greater number of legs are the two
most conspicuous points of difference between the Arach-
nida and Hexapoda.

g§g

gjp*-

tE&

jW'wi

~-

/Wjj^:

9

d

s^r tg

^k^»^

mzdr

Fig. 82. Photograph of scorpion

American Museum of Natural
History

CHAPTER XV

THE CRAYFISH

All night the crawfish deepens out her wells,

As shows the clay that freshly curbs them round.

J. P. Irvine, Summer Drought

Habitat and Distribution. Crayfishes, also called craw-
fishes, are found in bodies of fresh water on every continent
except Africa, and on many of the large islands. All the
crayfishes of the United States east of the Rocky Moun-
tains belong to the single genus Cam'barus. On the Pacific
coast the crayfishes are slightly different. All of them be-
long to the genus As'tacus. An eastern American species
(Cam'barus limo'sus) is used as an example in this chapter.
In structure all members of the genus Cambarus are so
nearly identical that for a general laboratory study any
species available is entirely satisfactory.

External Plan of Structure. The body, except for the ven-
tral surface of the abdomen, is covered with a thick wall,
formed, like the covering of insects, from the hardening of a
secretion of the outer layer of the skin. Unlike the insects,
this protecting sheath is filled with carbonate of lime. The
body is divided into a cephalothorax and abdomen (Fig. 83),
as in the arachnids. There are no indications on the dorsal
surface of separate somites in the cephalothorax, but on the
ventral surface transverse grooves and paired appendages
indicate a division into thirteen somites. The abdomen
(Fig. 83) plainly consists of seven somites, of which the
first six bear jointed appendages. The external plan upon

which the crayfish is formed is similar to that of the insects

145

146 GENERAL ZOOLOGY

and arachnids ; that is, a series of somites placed one after
the other, with all appendages jointed.

The Cephalothorax. The shell covering the dorsal and lat-
eral surfaces of the anterior region of the body is distinct
from the hard parts elsewhere on the body, and is termed the
carapace. At the anterior dorsal end of the carapace there
is a prominent beak, or rostrum, beneath which, on either
side, extends an eye, borne on a stalk. Study of the living
crayfish enables one to see how well the rostrum and the
squame, mentioned below, protect the stalked movable
eye. The eye is compound ; the manner in which the image
is formed is practically the same as in the insects. Cray-
fishes have no simple eyes.

The cephalothorax bears at its anterior end six slender,
many-jointed feelers, the short ones called antennules (Fig.
83), the long ones, antennse. The four antennules are really
the four branches of a single pair of appendages coming
from a short stem which is attached to the body. On the
upper surface of one of the segments of this stem is a small
hole surrounded by a number of bristles. The hole opens
into a cavity which contains several small grains of sand
placed there by the crayfish itself after every molt (the
process of molting is explained in Chapter XVI). This
organ, with its nerve connections, constitutes the "ear" of
the crayfish (Fig. 83), the chief function of which is to help
the animal to balance itself during locomotion. The techni-
cal name otocyst is given to it. The antennae are the inner
branches of a pair of double-branched appendages. The
outer branch of each is short, flat, and triangular, and lies
just below the eyes, where it serves a protective function. It
is called the squame. On the lower, or basal, segment of the
stem of this pair of appendages is a small, hard, round swell-
ing, or papilla (Fig. 84, II, 1), on which is the opening from the
"kidney," or green gland, shown in broken outline in Fig. 83.

- Opening of green gland
Antennule

E ~ -Antenna

Sixth abdominal appendage

Mandible -i

Third maxilliped I-*

Subesophageal ganglion %

Posterior portion of stomach
First thoracic ganglion

First walking leg

Right digestive gland

Ventral thoracic-abdominal artery-
Sternal artery

Right sperm duct Ipk

Opening of sperm duct ^V

First abdominal appendage - -"^~^15&|^^^

Second abdominal

appendage '

Third abdominal appendage

— Rostrum

(^.Position of "ear"
--Eye

Supraesophageal
ganglion

- - Gastrolith

Anterior portion
of stomach

-Sto7tiach

"teeth"

Cephalothorax

- -Anterior
median artery

-Ostium

Heart
Pericardium
Right spermary

Dorsal
abdominal artery

Intestine

I {Abdominal muscle

Abdomen

-Anus

Fig. 83. Dissection of crayfish. (Slightly enlarged)

148 GENERAL ZOOLOGY

About the mouth are six pairs of appendages. The first,
the hard mandibles (Fig. 83), are adapted to crushing into
smaller bits the food seized by the large claws. Each mandi-
ble bears a short palpus (Fig. 84, III, 2). Next in the series
are the first and second maxillse (Fig. 84, IV, V) and the first,
second, and third maxillipeds (Fig. 84, VI, VII, VIII). The
maxillipeds help to hold the food in place at the mouth ; the
maxillae also assist in this, and probably, with the wall of
the mouth cavity, are the seat of the sense of taste. The
second pair of maxillae also act as " gill-bailers' ' (Fig. 84,
V, 3-4; Fig. 85), which, by their motion, help to maintain
a current of water in the gill chamber, thus providing oxygen
for respiration. The separation between head and thorax is
understood to come between the second maxillae and the
first maxillipeds, thus making five pairs of appendages in
the head region.

After the maxillipeds the next thoracic appendages are
the large claws, or chelipeds (Fig. 83), composed of seven
segments, of which the last two from the body, or distal two,
are modified to form a nipper, with which the animal cap-
tures and holds even rapidly swimming fishes. The remain-
ing thoracic appendages are the four pairs of walking legs
(Fig. 83; Fig. 84, XI, XII), also composed of seven seg-
ments, the first two pairs with nippers at their ends, and
the last two pairs without nippers. The three pairs of
maxillipeds, the one pair of chelipeds, and the four pairs
of walking legs constitute the eight pairs of appendages of
the thorax.

The Abdomen. There are six pairs of appendages on the
abdomen. The first abdominal appendages of the female are
small, single, and thread-like; in the male (Fig. 83) they
are long and rigid, differing considerably from all the others
except the second pair. The second abdominal appendage
in the female is like the third. The third, fourth, and fifth

4 XI

XII

XVI

XIX

Fig. 84. Appendages of the crayfish (Cambarus), from the left side.

(Natural size)

1, protopodite; 2, endopodite ; 3, exopodite; h, epipodite with gill filaments;
5, gill with gill filaments. (I, II, III, etc., stand for the number of the somite in

the animal's body)

150 GENERAL ZOOLOGY

pairs, called swimmerets, are alike in both sexes. The pair
of appendages of the sixth somite are made up of broad,
flat branches jointed to a short, thick stem. With the last
somite, called the telson (which is without appendages), they
form a strong tail fin. By being doubled underneath it is
capable of striking hard blows against the water and forcing
the crayfish suddenly backward. A basal stem with two
branches is seen in all the abdominal appendages except in
the first pair of the female.

Homology. A stem and two branches are apparent in
several appendages. This is important enough to deserve
further discussion. The simplest condition of the branched
appendage is seen in the third, fourth, and fifth abdomi-
nal appendages (Fig. 84, XVI). If the branches are spread
slightly, the form resembles the capital letter Y. If we
take a swimmeret as a model, the stem, which is termed
the protopodite (Fig. 84, XVI, 1), is seen to be made up of a
short basal segment, the coxopodite, and a long segment, the
basipodite. Of the two branches, the one nearer the median
line of the body is the endopodite (Fig. 84, XVI, 2) ; the
outer is the exopodite (Fig. 84, XVI, 3). Wherever in the
series of appendages we find a stem and two branches,
the protopodite corresponds to the protopodite of all the
other appendages of the series, — and so with the endo-
podites and the exopodites.

All the remaining appendages of the crayfish are con-
structed on the same general plan as the swimmerets ; but
the original plan, in being modified for different functions,
has frequently become obscured. Thus in the walking legs
we have no evidence of a two-branched condition. In the
very early stages of development the young crayfish before
hatching has legs that bear two branches, but one of these
disappears entirely before the young is hatched. In the case
of the lobster the young animal (Fig. 86) still has the two-

THE CRAYFISH

151

branched legs after hatching and only later in development
loses one branch. The remaining appendages are too com-
plicated to be studied here in detail ; but the early stages
in the embryo show that all of them, whatever their adult
structure, begin their existence as two-branched appendages
similar to the swimmerets.

When two or more organs or structures are constructed
upon the same plan and develop in the young in the same

Gill-bailer

on second maxilla-.

First maxilliped -)

Second maxilliped —?
with first gill

f^^Last gill

•Sixth gill

Fig. 85. Gill chamber and gills of crayfish. (Slightly enlarged)

way, they are said to be homologous. Since all the append-
ages of the crayfish are of the two-branched type, they fur-
nish a good example of homology.

The Digestive System. The mouth (Fig. 83) of the cray-
fish is located between the two mandibles. Reference to
Fig. 83 will give an idea of the length of the esophagus and
the position and relative size of the stomach. The latter has
two more or less clearly marked regions, — the anterior, en-
larged region and the posterior, funnel-shaped space. As the
food passes into the anterior portion the unbroken bits are
caught between the grinding surfaces of three hard processes
extending from the stomach wall. These three "teeth" —
one in the median dorsal line and two at the sides — to-
gether constitute the "gastric mill." Muscles attached to
them and to the inner surface of the carapace, by contract-

152 GENERAL ZOOLOGY

ing, perform the operation of grinding. The posterior part
of the stomach is filled with slender filaments which extend
from the wall out into the cavity. These filaments prevent
the unbroken particles of food from passing through into
the intestine, allowing only the thoroughly ground-up food
to do so. Absorption does not occur in either division of the
stomach but in the intestine, which extends straight from
the stomach to the ventral surface of the telson. A pair of
digestive glands lie one on either side of the stomach and in-
testine. They open by tubes into the posterior division of
the stomach and have the combined functions of digesting
food and absorbing some of the products of digestion.

The Circulatory, Respiratory, and Excretory Systems. The
heart is a muscular organ lying beneath the dorsal body
wall posterior to the stomach. The blood finds its way into
the heart through three pairs of openings furnished with
valves to prevent the escape of blood. When the heart con-
tracts the blood flows both forward and backward at the
same time through the tubes called arteries. Five arteries
pass forward to the organs in the front part of the body
while two are directed backward to supply blood for the
posterior region. These arteries branch into many smaller
vessels with open ends. From the open ends the blood
flows into spaces called sinuses surrounding the internal
organs. of the body. All the sinuses connect with a still
larger, median cavity, the ventral sinus, lying along the
ventral wall of the thorax and abdomen. Branches from
the median ventral sinus extend out into the gills. The
blood is carried back to the base of the gills by another set
of channels parallel to the set entering the gills. Finally
the blood reaches the pericardial sinus, in which the heart
lies. The delicate plume-like gills (Fig. 85) are attached
to or near the basal joints of the thoracic appendages. On
each side of the body they extend dorsally into partially

THE CRAYFISH 153

closed chambers bounded by the body wall on the inside and
the carapace on the outside. Since the crayfish frequently
journeys from pond to pond in dry seasons, the gills are
thus protected from sudden drying. Water is drawn into
and is forced out of this gill cavity by the gill-bailers on the
second maxillae (Fig. 84, V, 3-4; Fig. 85). The blood flow-
ing into the gills from the ventral sinus gives up its carbon
dioxide waste and receives oxygen from the water.

The green glands are prominent organs (Fig. 83) in the
ventral region of the body cavity in the head. A large artery
carries blood to them, and nitrogenous waste matter is
separated by them from the blood and is discharged from
the opening on the basal segment of each antenna.

The Nervous System. The central nervous system of the
crayfish is much like that described for the grasshopper. A
double cord extends the length of the body. On this cord
there are seven enlargements, or ganglia, in the cephalo-
thorax and six in the abdomen. The "brain," or supraeso-
phageal ganglion, is a large mass of nerve tissue (Fig. 83)..
Pairs of nerves may be traced from the brain to the eyes,
the antennae, and the antennules. Two slender cords, simi-
lar to those described for the grasshopper, extend from the
brain, encircle the esophagus, and join the subesophageal
ganglion posterior to the mouth. This ganglion sends off
the nerves to some of the head somites and to some of the
thoracic somites. There are five other ganglia in the thorax
joined to each other (Fig. 83) and to the six ganglia in the
abdomen by the double nerve cord which is a continuation
of the cords that encircle the esophagus.

The Muscular System. The muscles of the abdomen are
arranged in a very complicated fashion and are capable of
powerful action. The compact muscle bundles of the ab-
domen, or "tail," of the crayfish and also of the shrimp are
the chief parts used by man as food. In all parts of the body

154 GENERAL ZOOLOGY

the muscle bundles are attached to the inner surface of the
exoskeleton. This is just the opposite of the relations of
muscles to skeleton in our own bodies.

The Reproductive System. The three-lobed organ which
produces the germ cells lies just beneath the heart. In the
male this is a spermary, or testis, while in the female it
is called an ovary. In both sexes a pair of ducts lead from
the reproductive organ (or gonad) to a pair of openings on
the bases of certain walking legs. These sperm ducts of the
male open on the basal segment of either fourth walking
leg. In the female the oviducts lead to similar openings on
the second walking legs.

Development. Cambarus limosus lays its eggs in the spring.
Most species of crayfishes lay their eggs then. The princi-
pal burrowing species, Cambarus diog'enes, lays its eggs in
April and they hatch in May, while a river species, Cambarus
immu'nis, lays its eggs in the fall and they hatch in the fol-
lowing spring. When the egg-laying season arrives the male
deposits spermatozoa in a shallow cup called the annulus on
the ventral surface of the female between the fourth pair
of legs. The mass of spermatozoa stays in the annulus till
the female lays her eggs. It is not certain how long the
spermatozoa lie there before the eggs are laid. However,
when the eggs are discharged from the oviducts they pass
back over the mass of spermatozoa. Fertilization is accom-
plished when a spermatozoon enters an egg. The fertilized
eggs are fastened to the swimmerets by a glutinous sub-
stance. There the embryos develop, and the young, when
they hatch, remain clinging to the female's swimmerets by
their chelipeds. The young crayfishes are not set free until
they are able to care for themselves.

Relation to Environment. Crayfishes live in a great variety
of places. They are fresh-water animals. As a rule they
crawl on the bottom of rivers, brooks, and ponds, conceal-

THE CRAYFISH 155

ing themselves in crevices or under protecting pieces of
rock or submerged logs. Several species make burrows in
the soft earth of meadows. The most widely distributed of
these is Cambarus diogenes. Species which live in ponds
that are likely to dry up in the summer, and also a few that
live in rivers, leave the water in summer and burrow into
the earth until they come to water. At the bottom of their
burrows, sometimes three feet from the surface, they dig
out a flask-shaped enlargement and stay in it or near it
till the next spring. The chimneys made at the top of the
"wells " referred to in the quotation at the beginning of the
chapter are made by the burrowing crayfish merely as an
incident in getting rid of the mud brought from below.
Sometimes crayfishes stop up their burrows completely. In
that case they probably remain in a dormant condition
without food till spring returns. In the bed of a pond or
river where jutting stones abound crayfishes rest with the
abdomen doubled beneath them and the head toward the
open. Boys often lure them from their hiding places with
a piece of meat tied to the end of a weighted string. The
animal invariably seizes the meat in a cheliped and usually
can be drawn to the surface before it has time to " think'3
the matter over and let go.

The distribution of crayfishes is directly related to their
power of adapting themselves to conditions of considerable
variability. If a certain definite degree of temperature or
of clearness of water were required, they would be restricted
to a very limited area, and, indeed, it would be difficult for
them to maintain themselves at all.

A striking example of adaptation to an unusual environ-
ment is found in the cave-dwelling crayfish, Cambarus pel-
lu'cidus. Professor Eigenmann, Dr. 0. P. Hay, and others
have explored the caves of Indiana and Kentucky for
the purpose of studying the animals of their subterranean

156 GENERAL ZOOLOGY

rivers. The blind crayfish has small and abortive eyes, but
its sense of touch is developed to a marvelous degree of
delicacy. Dr. Hay says that although the crayfishes may
be resting quietly on the bottom of a rivulet, it is impossible
to capture them with a net. They feel the jar in the water
and dart backward with great accuracy to a protecting rock.
In general appearance the blind crayfish differs from others
chiefly in having an exoskeleton which is so clear that one
may see the animal's stomach as a blue mass within, and
in being provided with antennae longer than the body.

Crayfishes are eaten by fish large enough to swallow
them, and they in turn catch small fish with great facility,
and also insect larvae, snails, tadpoles, and even frogs.
They have been known to prey upon each other, and also
to eat both dead and living plant and animal food. They
seem to be omnivorous.

In America crayfishes seem to be used as food chiefly by
the French portion of our population. Possibly the rapid
depletion of the lobster fisheries may cause people generally
to turn to the lobster's nearest edible relative. In France
the crayfish industry is quite extensive, there being many
farms on which crayfishes are raised for the market.

CHAPTER XVI

THE JOINTED-FOOT ANIMALS: ARTHROPODA

The Shelly Crawlers each returning year

Cast off their shells and new-made Armour wear.

Oppian, Halieutica

The Allies of the Crayfish : Crustacea

The Lobster. Except for the considerable difference in
size, and the slight differences in the shape of the body,
the number of gills, and the structure of abdominal append-
ages, the description of the adult crayfish would serve for
an account of the structure of our common species of Ameri-
can lobster, Hom'arus america'nus. The lobster is found in
greatest numbers along the coast of Maine and of the Ca-
nadian maritime provinces. Toward the south the number
gradually decreases to the Delaware breakwater, beyond
which they are very rare. In their days of greatest abun-
dance they grew to be about sixty centimeters (two feet) in
length, weighing twenty-five pounds, but with the increase
in the activity of the lobster-fishing industry they are now
rarely to be found weighing over two pounds.

The lobster lives on the bottom. It is protectively col-
ored, but it does not depend wholly upon that condition
for escaping the notice of its enemies. In shallow waters
lobsters are known to conceal themselves beneath masses
of brown seaweed in pits and holes, and also to find safe
retreat beneath jutting ledges of rock, where they rest with
the abdomen doubled beneath, ready to dart out and seize
passing prey in their claws. We have no way of knowing
the exact habits of the animal when at its greatest depth

157

158 GENERAL ZOOLOGY

(a hundred fathoms), but since its enemies are probably
quite as persistent there as in the shallow water, every
means of defense is likely to be employed to the utmost.

The lobster is capable of swimming with great rapidity
by suddenly doubling its flexible, muscular abdomen be-
neath and shooting backward through the water. This
form of locomotion does not appear to be depended on
except to enable it to escape from impending danger. Its
usual mode of progression is by walking on the tips of
the last four pairs of legs, the chelipeds being extended
anteriorly, apparently to expose as little of its bulk to the
water as possible. Experiments indicate that lobsters do
not travel great distances. Hence if all the lobsters in a
certain bay and vicinity are caught, the chances are against
that region recovering its lost supply. Laws have been
passed by the individual states to regulate the lobster fish-
eries. The chief attempts at avoiding extermination have
been the prohibition of the sale of lobsters under a certain
length and the protection of females carrying eggs. Hatch-
eries have also been established for rearing the young to the
stage where they leave the surface of the water and begin
to live on the floor of the ocean. All these attempts have
been only partially successful and have not really solved
the problem of materially increasing the numbers.

Molting in the lobster, as in some other animals with a
hard exoskeleton, is an extremely important and critical
event. The number of molts an individual lobster may have
depends, in a great measure, upon the abundance of its
food. Males molt more frequently than females; hence
the largest lobsters are always males. Very young lobsters
molt more frequently than those of the size we find in the
market. During the process of molting it sometimes hap-
pens that an appendage is broken off. In the ordinary
course of its life, also, the lobster may lose a claw or an

THE JOINTED-FOOT ANIMALS

159

antenna. It is regenerated in two or three molts after the
accident. The crayfish and many other animals have the
same power.

The female lobster lays her eggs usually during the sum-
mer months. The eggs remain attached to the swimmerets
until the next spring, when the embryos hatch. The larval
lobster (Fig. 86) immediately floats
to the surface, and for several weeks
swims about there. Its length at first
is about eight millimeters (one third
of an inch). In general appearance it
slightly resembles the adult lobster.
The large thoracic appendages are not
leg-like but are two-branched, and the
abdomen has no appendages. After
the sixth molt the lobster is about
two thirds of an inch long. The outer
branches of the legs have disappeared
and the young lobster has gained ab-
dominal appendages. It is now nearly
like the adult in all respects. At
about this time the young leaves the
surface, goes to the bottom, and makes
its way to well-protected places near
the shore.

The commercial value of the lobster is very great. As an
article of human food it is fast becoming a luxury. Lobsters
rank next to codfish in importance in the New England
fisheries. In 1924 close to ten million pounds were marketed
with a value of over three million dollars. Most of the lob-
sters for market are caught in traps commonly called lobster
pots. Bait is placed inside the trap, and when the lobster
crawls through a small opening in the funnel-shaped en-
trance it is unable to discover the exit.

Fig. 86. First larval stage
of American lobster. (x7)

After Herrick

160 GENERAL ZOOLOGY

The Common Prawn. The prawn (Palsemone'tes vulgaris,
frontispiece), is found abundantly among seaweeds near
shore in sea water and also in brackish and almost fresh
water. It is a good example of a pelagic, or surface-inhabit-
ing, animal of considerable size, which is so nearly transpar-
ent that it may be overlooked unless it moves. The prawn,
or, as it is frequently called, the shrimp, is about two inches
long and resembles in general form the lobster or the cray-
fish. The body is, however, more compressed (flattened from
side to side) and more strongly arched from head to tail.
The carapace is thin but tough and leathery, and covered
with many reddish-brown dots. It is so transparent that
the stomach and intestine can be seen clearly while the an-
imal is at rest.

The Edible Shrimp. A close relative of the prawn is the
shrimp (Cran'gon vulga'ris), the tail of which is very much
sought as food. This species is very widely distributed, for
it lives in shallow water on both the Atlantic and Pacific
coasts of North America, and the same species occurs in

Europe.

Crabs. The species represented in Fig. 87 (Pagu'rus
pollica'ris) is called the hermit crab, probably because it
lives in a " house* ' by itself. The house consists of the shell
of a dead snail, which may have been washed to the beach,
or may have rested on the bottom of the bay. The hermit
crab in its early life is pelagic, but at a certain stage of its
development it sinks to the bottom, finds a snail shell, and
backs into it ; from that time on, the general shape of the
body and the special modification of certain organs are de-
termined by the form of the snail shell. The abdomen is
soft, and all the abdominal appendages except the terminal
ones are misshapen and useless. The terminal appendages
extend laterally like flanges, and prevent the body from
being drawn forcibly from the snail shell by an enemy.

THE JOINTED-FOOT ANIMALS

161

The chelipeds are abnormally developed and, besides being
of use in capturing prey, serve the important function of
closing the aperture of the shell in times of danger.

Hermit crabs live in great abundance along gravelly
beaches, where they are useful scavengers of dead animals
in the water. In spite of the heavy houses which they carry,
they move about with surprising facility. As suggested by
one observer, they are wary, cunning, belligerent, and

Fig. 87. Blue crab and hermit crab, (x J)

cowardly, making great pretense of fighting, but on the first
show of force by an opponent withdrawing into their shells.
A small, shore species more frequently seen never becomes
as large as Pagurus pollicaris, which is a deep-water species.
All the species, however, when the individuals are young,
choose small shells ; as they grow older and larger after each
molt, the unused space in the shell becomes less and less.
Naturalists have observed the action of hermit crabs that
have become too large for the shell. The animal searches
about for a suitable larger shell, and when it finds one
withdraws its body from the old shell and extends it into
the new.

162 GENERAL ZOOLOGY

The spider crab (Libin'ia emargina'ta, frontispiece) stalks
slowly over the sea bottom in shallow and deep water where
rocks and fixed plants and animals abound. It can neither
run nor swim, an inference which might be drawn from the
slender, stilt-like appearance of its legs. Having no means
of aggressive defense, it relies almost wholly on the fact that
its color is very much like its surroundings. The cephalo-
thorax is covered with coarse, hair-like, flexible spines, and
the general color is dull gray. Frequently we find on the
back small seaweeds, hydroids (p. 271), sea anemones
(p. 275), and even rock barnacles (p. 166), growing as they
would on rock. This protective resemblance appears to be
very successful from the point of view of the spider crab,
for it is in some regions more abundant than any other
kind of crab. In some parts of Long Island Sound the
spider crabs are so numerous that they get into the lobster
pots set by fishermen and crowd them so that no induce-
ment remains for the lobsters to enter, much to the disgust
of the fishermen. Along the Atlantic coast this species
grows to have chelipeds which extend over one foot from
tip to tip. The giant Japanese spider crab has chelipeds
which extend over fifteen feet from tip to tip, and has a
body correspondingly large.

The edible crab, more frequently called by naturalists the
blue crab (Callinec'tes sap'idus, Fig. 87), is characterized by
having sharp lateral spines of large size, and by the last pair
of thoracic appendages being flattened and adapted to
swimming. The chelipeds are strong and fitted for cutting ;
the succeeding three pairs of appendages have no nippers,
but come to a point.

As is well known, the blue crab is caught in large num-
bers along the Atlantic and Gulf coasts for the markets in
the cities. The industry is of considerable value commer-
cially, and for that reason very general attention has been

THE JOINTED-FOOT ANIMALS

163

given to the distribution and habits of this crab. It is caught
most easily soon after the molting, which takes place in early
summer, and is then called a soft-shell crab ; at this time
also the species is considered most valuable as food.

The blue crab is not confined to the salt water, for it is
found frequently in rivers some distance from bays. Wher-
ever they are, they devour much
of the organic waste that flows

V [x

.. .f-^Stry- -V'-;. *;\v*

:M-j-m

■ . :.-KJi. ■.M'*>^a':./.r.-tifcy»^^..a^£Stifc Tfiifi- •

XL

^, ■»- '-* S-r* -■'$■'' /T

%>.../-.> ■■*&~j «i§u -,;

r

-■■■■: ,«

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\ ,-.x • -S* >&3i .>

i-v '».'■».

Fig. 88. Fiddler crabs. (Slightly reduced)

down to the sea. They
are therefore impor-
tant as scavengers.

The most noticeable
thing in the structure
of the fiddler crab

(U'ca pugila'tor, Fig. 88) is the presence in the males of a
large cheliped. Sometimes it is the right one that is larger,
and sometimes the left one ; the females have their chelipeds
small and of equal size. The name "fiddler" is supposed to
have been derived from the fancied resemblance of the large
cheliped to a fiddle, and of the small one to a bow.

The Sow Bug. The sow bug, and a related species called
the pill bug because of its habit of rolling up into a ball, are
found under stones, boards, logs, and in other dark, moist

164

GENERAL ZOOLOGY

places. The flattened condition of the body reminds one of
the cockroach, which shows the same adjustment of the

form of the body to the necessities of life.

The species represented (Fig. 89) belongs

to the genus Onis'cus.

The body has twenty somites, as have the

crayfish and all the forms described so far in

this chapter. A pair of short, jointed anten-
nae and a pair

of compound

eyes without

stalks, that

is, sessile eyes

(Lat. sedere,

"sit"), are
the most noticeable organs of
the head. They have a sec-
ond pair of antennae, which
are rudimentary. The mouth
parts are small and adapted to
feeding on plant food. The
breathing organs are
y gills, protected by

Fig. 89. Sow bug.

(x3)

\

y

>v:.

• "

*f '10^

-ST*"

flat, plate-like struc-

FiG. 90. Caprella. (x 2)

tures on the under surface of the abdomen. The female
bears a brood pouch on the under surface of the body,
in which the eggs are carried and the young develop.

THE JOINTED-FOOT ANIMALS

165

Fig. 91. Daphnia, a water flea.
(Much enlarged)

After Forbes

Caprella. Probably one of the strangest-looking free forms
to be found in the sea is the little, brown Caprel'la geomet'rica

(Fig. 90). It lives among
seaweeds, on which it can
be discerned with diffi-
culty.

Water Fleas. Water fleas
(Daph'nia) have the body
inclosedinashell(Fig.91).
The feathery antennas are
used for swimming. The many different species of water fleas
are among the most abundant animals in lakes and rivers.
Many kinds of fishes feed upon these minute crustaceans.
The eggs and young are carried inside the
shell at the back of the body.

Cyclops. Any fresh-water pond will af-
ford millions of specimens of the genus
Cy' clops (Fig. 92), and the sea contains
species of the same genus in such num-
bers that they with allied genera form
a large part of the food of many fishes,
and even some species of whales find in
them an abundant food supply. Their
powers of reproduction are so enormous
that it has been estimated that the de-
scendants of one Cyclops may number,
in one year, 4,500,000,000 individuals.
Though microscopic in detailed structure,
on close observation it is easy to see them
darting spasmodically through the water
in aquariums. A single compound eye in the middle of the
head gives them their name, in reference to the race of
mythical giants of Sicily. Two pairs of antennas, used in
locomotion, extend from the front of the head. The legs are

Fig. 92. Cyclops.
(Much enlarged)

After Claus

166 GENERAL ZOOLOGY

two-branched appendages, also used in swimming. One pair
of antennae and the legs are not shown in the figure. Two
long appendages extend from the end of the abdomen. The
body consists of fifteen somites, five in each of the three
regions, head, thorax, and abdomen. The female, in the
summer season, carries about with her two large brood sacs
of eggs, which extend diagonally out behind.

Parasitic Crustacea. A large number of different forms re-
sembling Cyclops in many respects have adopted a parasitic
life. They occur on various hosts, but the greater number
of them are found on fishes. They live on every part of the
body. Some live in the alimentary canal, or in the gill
region, feeding only on the food of the host ; some tempo-
rarily seek their host for the body fluids, while others are
permanent parasites external or internal. In general these
forms are spoken of as "fish lice." To the extent that they
are dependent on a host, the normal, external structure tends
to be modified out of all resemblance to the type represented
by Cyclops. The somites lose their distinctness, and the
form of the body is altered by protuberances of various
kinds. The mouth parts become adapted as holding and
sucking organs. As the external organs degenerate, the tend-
ency of certain internal organs is also to become rudimen-
tary. Some of these parasitic organisms are so degenerate
in form and structure that they have lost all appearance of
being animals at all. In many cases it is the female only
which is parasitic, the males leading a free life and showing
the normal structure of their race.

Barnacles. Despite the great apparent difference between
the fixed, shell-bearing barnacles and the free-swimming
crabs and other forms discussed in this chapter, naturalists
have shown that they are in reality closely allied both in
development and in structure. In some places barnacles
literally incrust the coast-rock between tide lines with hard,

THE JOINTED-FOOT ANIMALS

167

sharp-edged shells, composed of carbonate of lime. One
species lives on the backs of whales. The shell is usually a
little over a centimeter high, and narrower at the top than
at the base. Related species grow to be at least four centi-
meters high. At the top of the rock barnacle are two hard,
movable valves, meeting in a median line, which, on open-
ing, expose long, feather-like processes. These feathery
processes are the feet. The animal lies on its dorsal surface
within a several-valved shell,
and by rapid movement of the
feet creates currents of water
which bring to the mouth mi-
croscopic animals and plants
as food. When the feet are not
scooping in food the valves are
closed, forming a most effective
armor for the parts beneath.
Though the barnacle in its
adult condition, as just de-
scribed, has nothing to fear,
in early life it swims free at

the surface of the water in the midst of millions of the
young of crabs and other animals. There it is subject to
the attacks of animals which might devour it, and many
young barnacles are undoubtedly destroyed. At this time
it would not be recognized as a barnacle by those who have
seen only the adult form. It has an unsegmented body, a
long upper lip, single median eye, as in Cyclops, and three
pairs of jointed legs. This larval form is called a nauplius
and resembles Fig. 93. The barnacle nauplius stage under-
goes further complicated changes before it attaches itself
by the head to some solid object, as a rock, pile, or ship
bottom, when the swimming appendages are absorbed and
the shell and feathery foot processes are developed.

Fig. 93. Nauplius stage of A Hernia.
(Much enlarged)

After Joly

168

GENERAL ZOOLOGY

Trilobites. Some of the most abundant of the forms in
the earlier periods of life on the earth were the tri'lobites

(Pha'cops cauda' tus, Fig. 94), which are
an extinct type of the Crustacea. They
are named trilobite from the apparent
division of the body longitudinally into
three parts. The length of the body
varied from a fraction of one inch to two
feet. They are thought to have lived in
shallow water along shores, and through
a long period of the earth's history must
have been a most characteristic feature
of the fauna of the world. Of the many
species of trilobites not one remains liv-
ing at the present day.

Definition of Crustacea (Lat. crusta,
"shell"). The crayfish and the species
mentioned thus far in this chapter belong
to the class Crusta'cea. They are constructed on the plan
of a series of body divisions (somites) seldom exceeding
twenty in number. The somites
are usually bilaterally symmetri-
cal (uniform in structure on either
side the median line). Typically
each somite has a pair of branched,
jointed appendages. Two pairs of
antennae are present. The exo-
skeleton contains chitin and car-
bonate of lime. Crustacea are
essentially aquatic in their habits
and, with the exception of the
lowest forms, breathe through

gills. Nine tenths of the class are said to live in the ocean,
some in fresh water, and relatively few species on land.

Fig. 94. Trilobite

Taken from a report
of the Geological Sur-
vey, United Kingdom

Fig. 95. Zoea stage of crab.
(Much enlarged)

After Emerton

THE JOINTED-FOOT ANIMALS 169

As in the insects, the hard exoskeleton necessitates fre-
quent molts to provide for growth, and also, as in that class,
growth is sometimes accompanied by marked metamorpho-
sis after hatching. Many of the Crustacea have direct
development from a rather simple larval stage (Fig. 93).
However, the lobsters (Fig. 86) and the crabs (Fig. 95) un-
dergo a more complicated development, in which the indi-
vidual passes through several different larval forms before
reaching the adult condition. In the crayfish the develop-
ment is similar to that of the lobster with the exception
that the various larval stages are passed before the egg is
hatched. Thus in the crayfish the young does not leave
the egg until it has passed through these stages and closely
resembles the adult.

Animals related to Crustacea and to Hex apod a

There are several groups of animals which in some
respects resemble the crustaceans and the insects. But
these differ so much from their nearest relatives in certain
characteristics that they are now considered as belonging to
several independent classes. A number of these forms are
inconspicuous and have value for the advanced student
only. The familiar forms commonly known as the centipeds
and the millipeds are the only members of these groups that
will be discussed here.

Centipeds. The common centiped {Litho'bius, Fig. 96),
found under the bark of trees, is an elongate, flattened ani-
mal, with long antennae, many somites, and a pair of legs
on every somite. There is a poison gland in the base of the
first pair of legs, which is used to kill earthworms and in-
sects, upon which Lithobius feeds. The house centiped (Scu-
tig'era) feeds largely on flies, cockroaches, and other insects.

Centipeds are widely distributed over the world. In the
tropics they grow to be over thirty centimeters (one foot)

170

GENERAL ZOOLOGY

long. Some species are poisonous, even to man, and death
has been known to result from their bite. They are active
creatures and feed on living animals. The number of so-
mites varies from about nine to over two hundred. A pair
of legs is attached to each somite. The following lines were

Fig. 96. Centiped (below) and milliped (above). (Reduced)

written by Sir E. Ray Lankester, of England, after an
attempt to study the order in which the legs were moved :

A centipede was happy — quite

Until a toad in fun

Said, ''Pray, which leg moves after which?"

This raised her doubts to such a pitch,

She lay exhausted in the ditch,

Not knowing how to run.

Millipeds. Other elongate forms called millipeds (Spirob'-
olus, Fig. 96) may be distinguished from the centipeds by
the more cylindrical body. Millipeds also possess a greater

THE JOINTED-FOOT ANIMALS 171

number of legs than centipeds, each somite, with the excep-
tion of several coming directly after the head, bearing two
pairs of legs. They live in damp places and feed on living
or decaying vegetable matter ; they are entirely harmless.
Many have the power of coiling themselves up when dis-
turbed. The larvae, when first hatched, have few somites,
and but three pairs of legs.

Definition of Arthropoda. The animals described so far in
this book belong to the phylum (see page 109) Arthrop'oda
(Gr. arthron, "joint"; pous (pod-), "foot").

The body of an arthropod is made up of bilaterally sym-
metrical somites arranged in a linear series. There is always
a head composed of from four to six fused or united somites.
The somites of the remainder of the body are grouped into
one region, the trunk (centipeds and millipeds) ; or into two
regions, thorax and abdomen (Hexapoda, some Crustacea).
The head is sometimes fused with the thorax, the abdomen
being a distinct region (Arachnida, some Crustacea). Ap-
pendages, wherever present, are jointed. Except in the mil-
lipeds they occur as a single pair on each somite. The
somites and appendages are covered with a chitinous exo-
skeleton ; in some members of the phylum the exoskeleton
is very hard and filled with carbonate of lime.

The digestive tract extends nearly straight through the
body from the anterior end to the posterior end. The blood,
which is usually colorless, is carried through the body in a
partially complete system of vessels with a tubular, or
heart-like, pumping organ in the dorsal region of the body
cavity.

Respiration takes place through gills (Crustacea), lung-
like sacs (Arachnida), or through an internal network of
tabes (tracheae) opening in two lateral series on the exte-
rior of the body (centipeds, millipeds, insects, and some
arachnids).

172 GENERAL ZOOLOGY

The nervous system generally consists of a "brain,"
dorsal to the gullet, two connectives passing one on either
side of the gullet and uniting below to form a ganglion,
from which a double nerve cord extends along the ventral
body wall to the posterior end. Sense organs characteristic
of the phylum are jointed antennae, and simple and com-
pound eyes.

From the foregoing statements we come to recognize a
few features as distinctive for all arthropods. These dis-
tinguishing characteristics are a segmented body covered
with a chitinous exoskeleton and with jointed appendages
arranged in pairs.

CHAPTER XVII

HEREDITY AND EVOLUTION

A fire-mist and a planet,

A crystal and a cell,

A jelly-fish and a saurian,

And caves where the cave-men dwell,

Then, a sense of law and beauty,

And a face turned from the clod ;

Some call it Evolution,

And others call it God.

Cakruth

Although every species of animal tends to produce young
resembling itself, no two individuals even of the same species
are ever precisely alike. That the young of each species
tend to resemble their parents, we say is due to heredity;
that they never exactly resemble them, we say is due to
variation.

Variations. As a rule, the differences between animals of
the same species are slight. However, an occasional indi-
vidual different from any of its kin in certain respects may
make its appearance. This difference may be conspicuous,
such as a change in color, or very inconspicuous and affect-
ing only some small organ or structure of the body. The
abrupt appearance of individuals showing differences from
their relatives is spoken of as mutation, and the individual
is called a mutant or a sport.

Artificial Selection. Animal breeders have known for a
long time that many of the ordinary differences and the
mutations which occur in their flocks and herds are passed
from one generation to the next. In fact, they have used
both these kinds of variations in producing more desirable

173

174 GENERAL ZOOLOGY

types of live stock. From each generation the stockman
selects his best cattle or his best pigs as breeding stock. By
best he means those which come the nearest to his idea of
what a perfect animal should be. Thus if he is raising cat-
tle chiefly for meat, he selects the largest animals. On the
other hand, if he is interested in producing milk, he chooses
those animals which yield the most or the best milk, with
little regard for the size or form, which concerned the meat
producer. His choice of breeding stock is called artificial
selection. In this manner, beginning back before the dawn
of history, man has gradually improved his domestic ani-
mals. In consciously selecting desirable traits for his breed-
ing stock he has at the same time eliminated many
undesirable characteristics from his flocks and herds, for
desirable as well as undesirable traits are passed on from
generation to generation by heredity.

New races and breeds of domestic animals (Fig. 97)
differing in many respects from each other are being pro-
duced continuously. Some of these have existed for a long
time, others have been produced within the past few years.
A Percheron horse and a thoroughbred saddle horse are
extremely different in appearance. But we know that man
by his own choice has produced these and many other breeds
of domestic animals by selecting from stocks that were
originally alike. Most of the many breeds or races of do-
mestic animals breed true. This means that two individuals
of the same breed produce young like themselves except for
that degree of ordinary variation which marks all individ-
uals. Occasionally sports, or mutants, utterly different
from their relatives in certain respects make their appear-
ance in breeds of domestic animals. Some of these muta-
tions are hereditary and are utilized to change the character
of a breed. Hornlessness in cattle is a condition that has
existed for a long time in some breeds, and in other breeds

Fig. 97. A few of the many varieties of cultivated pigeons
These varieties, and others, have been developed from the same stock or ancestry.
1 silver runt ; 2, muffed tumbler ; 3, dragoon ; 4, homer ; 5, saddle fantai ;
6, white maltese ; 7, English red trumpeter ; 8, white pouter ; 9, English owl ;

10, white fantail. (After Gruenberg)

176 GENERAL ZOOLOGY

mutants of the hornless condition have arisen from pure
stock within recent times.

From the foregoing paragraphs we see that the inherent
tendency to vary, whether slightly or conspicuously, has fur-
nished the material with which man has worked to produce
his various breeds of domestic animals. By selection man
has obtained forms so widely different from each other that
if they occurred in nature we should not hesitate to call them
distinct species. Yet we know enough of their histories to
know that one breed of horses or of cattle has been devel-
oped from another. This gives us the idea that animal
forms are plastic and may change, producing new breeds
or varieties. Heredity operates on those characters wherein
the individual differs from others of its kind just as well as
on those characters which are borne by all members of the
race or breed. By the method of artificial selection man
makes the two contrasting forces of heredity and variation
work together to produce new races of animals.

Menders Law of Heredity. Man has long sought for a
means of explaining how heredity operates. Since the open-
ing of the twentieth century much progress has been made
toward an understanding of laws, or principles, governing
heredity. Studies have been made on many different kinds
of animals representing most of the important "groups of
the animal kingdom. Out of these experiments there have
come definite laws, by means of which it is possible to pre-
dict with reasonable certainty what kind of offspring will
be produced by two individuals. Although many other laws
and principles are involved in the study of heredity, the
real explanations started with the work of Gregor Mendel.
He was an Austrian monk who experimented with garden
peas, and in 1865 he communicated his discoveries to the
Society of Naturalists at Briinn. These have since been
described as "the greatest discovery in biology since Dar-

HEREDITY AND EVOLUTION 177

win." Mendel's work received little attention at first, but
a full generation later a Dutch scientist, de Vries, redis-
covered the work of Mendel. In 1900 Mendel's work be-
came generally known to the scientific world. Since that
date the study of heredity has been the most actively pur-
sued of all the branches of biology. There have been an
extremely great number of studies in which it has been
shown that heredity of given characters follows the prin-
ciples laid down by Mendel. In studying the operation of
heredity it has been discovered that some of the conditions
which we ordinarily think of as simple are really due to
several different causes. This has led to the use of the term
unit character to distinguish those traits or characters which
pass as indivisible units from one generation to its offspring.
According to Mendel's principles, when mating occurs be-
tween two animals of the same species (Fig. 98) differing in
but one of the many unit characters, the offspring will often
show not a condition intermediate between the two parents
but the character which appeared in only one of the parents.
Thus the offspring of one white and one black guinea pig
will be not gray but black, in color agreeing with one of the
parents, not intermediate between them. A character from
one parent which impresses itself in the offspring to the ex-
clusion of the contrasting character from the other parent is
said to be dominant. In contrast, the character which is not
seen in the offspring of the first generation (or Ft) is said to
be recessive. If experiments were not carried further than
one generation it might seem that the recessive character
is entirely lost. But when the experiment is carried further,
new facts are brought out. When the black guinea pigs,
whose parents were one black and the other white, reach
maturity and are bred together their offspring will be some
of them black and some of them white. The proportions
of the black and the white individuals in this second gen-

178 GENERAL ZOOLOGY

eration follow definite laws. Of course, in a single litter the
numbers may be different, but if large numbers of individ-
uals are considered the second generation of young (called
F2 for convenience) from the black and white grandparents
will be in the ratio of three blacks to one white. If white
individuals of this second generation are bred together they
produce nothing but white young even though the grand-
parents were coal black. If the black guinea pigs of the
second, or Fg} generation are bred together we find that
though they all look the same there are two different kinds

X Cf^j) Pen cuts 0dP X <X^3
F

F9

r

x

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F I ' 1 I 1 1 1 I ' 1

Fig. 98. A diagram showing how hair color is inherited in guinea pigs

of the black individuals. One out of three of the black
animals of the Fg generation can produce nothing but black
offspring, and two thirds of the black individuals of the F2
generation, when bred together, may produce either white
or black young. Those individuals of the F2 generation
which are capable of passing only their own color to their
offspring are said to be homozygous. In contrast, those
which may have offspring either like themselves or showing
the recessive character are called heterozygous.

Since each individual has its origin as a pair of germ cells
which unite to form a fertilized egg, we must go back to the
germ cells to seek an explanation of how heredity operates.
It is very generally agreed that the chromatin within the
nuclei of the germ cells is the material concerned in matters

HEREDITY AND EVOLUTION 179

of heredity. This chromatin does not contain black hair or
anything resembling the other characters which it passes
on from parent to child. It is simply material which causes
development to go in a certain manner. The chromatin is
said to be a determiner of characters though in itself it
does not possess the characters.

It will be recalled that when cells divide by mitosis, the
chromatin becomes arranged in minute bodies called chro-
mosomes (Figs. 71, 72). The ability to determine a great
number of hereditary characters must be present in each
chromosome. For instance, in the fruit fly (Drosoph'ila) more
than four hundred different hereditary characters have been
studied. Yet this fly has but four chromosomes in each germ
cell. This gives some idea of how very numerous and how
extremely small each mass of chromatin for determining a
single character must be. The name gene is applied to that
particle of chromatin which determines a single hereditary
characteristic. No one has ever seen a gene. From the way
chromosomes behave in heredity, it is necessary to assume
that these minute units exist in the chromosomes, though
they are probably so small that even the best microscopes
could not reveal them in the chromosomes.

In the ordinary cells of the body (except the germ cells)
the chromosomes are recognizable as two sets. This may be
understood if we remember that each cell of the body is
formed by mitosis of the fertilized egg. Therefore each cell
has the same number of chromosomes as were present in the
fertilized egg. Two sets of chromosomes were united to form
the fertilized egg. One of these was present in the egg before
fertilization and the other was contributed by the sperm cell
when it joined with the egg at fertilization. If both parents
are alike with regard to a given character, both germ cells
carry the same kind of a gene and the offspring will be homo-
zygous. In the case of hair color mentioned above, if one

180 GENERAL ZOOLOGY

parent carries the gene for black and the other for white the
offspring will be black because black is dominant, but the
offspring will be a heterozygous black. This means that
when the heterozygous individual comes to produce germ
cells, half of them will contain the gene for black and the
other half the gene for white.

In a human being there are many characters which are
hereditary. Some of these are physical characters and are
fairly easily recognized and studied. It seems probable
that many other characters, such as mental traits, are like-
wise passed from generation to generation, but these are not
so easily studied and measured. Brown eyes in man are
dominant over blue eyes. Not every person who has brown
eyes carries only the gene for brown, for many persons are of
mixed inheritance or are heterozygous as to eye color.

When we consider the behavior of more than a single pair
of characters, the problems of heredity become more com-
plex. With the exception of a few instances each pair of
characters acts absolutely independently of all other char-
acters in heredity. In addition to the hair color of guinea
pigs discussed above, the hair of these animals may be either
short or long. Experiments show that short hair is dominant
over long hair. Each of these two coat conditions occurs in
both the black and the white individuals. If a black guinea
pig with short hair is crossed with one having long, white
hair, all the young will be black and all will have short hair,
for both these traits are dominant. When members of this
F\ generation are bred together, four different kinds of
individuals may be produced, two of which are entirely
new combinations of the characters of the grandparents.
The four different combinations are as follows : (1) animals
with black, short hair like one grandparent; (2) animals
with white, long hair like the other grandparent ; (3) black
animals with long hair ; (4) white animals with short hair.

HEREDITY AND EVOLUTION 181

The last two types represent combinations of characters
which did not exist in either the parents or the grandparents
and which are different from conditions in any of their an-
cestors. In the offspring two characters which were origi-
nally associated in the ancestors may become separated and
act entirely independently of each other. In breeding to-
gether members of the Fi generation there is just the same
chance for black to become associated with long hair as for
it to remain with its original associate, short.

Many new varieties of plants and animals have been
produced by new recombinations of characters like the ex-
ample just cited. It was chiefly by methods of this sort
that Burbank produced his many varieties of fruits and
vegetables.

In the foregoing pages we have seen how new combina-
tions of characters are readily explainable on the basis of
definite laws of heredity. Further, we have observed the
readiness with which man at his own pleasure creates new
types of plants and animals by selection and by crossing
individuals showing either slight or pronounced desirable
variations. The question now arises as to the relation which
exists between the differences among animals produced
under man's direction and observation and the differences
among animals in nature.

Fossil Animals. Students of fossil life of past ages (paleon-
tologists) tell us that there are but few species of animals
living today which are the same as those existing in the
distant past of the earth's history. The early layers of the
crust of the earth contain no remains of what we today
speak of as the higher animals, or vertebrates (fishes, rep-
tiles, birds, and mammals). Furthermore, these various
forms of vertebrates did not all appear at once. There was
a time when fishes were the highest type of animal living on
the earth. In later fossil deposits remains of amphibians,

182 GENERAL ZOOLOGY

reptiles, and birds are found, indicating that these forms
came into existence later than the fishes. Finally, mammals,
the highest creatures of the animal kingdom, made their ap-
pearance, as shown by the fact that their fossil remains are
found in late deposits but not in early ones. It has been
well stated that the history of life on the earth has been
written in tablets of stone. These give us an accurate,
though incomplete, record of the fact that through the ages
life upon the earth has been incessantly changing. Species
of one age are different from, yet show undeniable relation-
ship to, those of the age before. Age upon age has witnessed
a gradual increase in the complexity of the animal popula-
tion. The oldest fossil rocks contain nothing but the simplest
types of animals. The most recent contain all the highest
in addition to the lower forms. At intervals between these
extremes we can point with certainty to the age when each
group of animals first made its appearance. Evidently
throughout the past history of the earth some factors have
been at work, causing one species, or group, to give rise to
different forms. There has been progress in this procession
from the simpler to the more complex types of body. This
progress is what is ordinarily called evolution. Evolution is
a principle that seems to operate throughout the entire uni-
verse. All that the idea of evolution necessarily means is
this progressive change, the evidences of which are all about
us. When we go beyond this observable fact of a changing
universe into the question of what has brought about the
changes, we have entered another field. All scientists at the
present time agree that evolution is a fact. Few agree in
their attempts to explain how evolution operates.

Natural Selection. Charles Darwin worked out a theory
to explain how evolution operates. This theory has been
so much discussed and criticized that the average person
thinks that Darwin's theory of natural selection embodies

HEREDITY AND EVOLUTION 183

the entire idea of evolution. In fact, natural selection is
but one of many theories by which evolution is explained.

In introducing the discussion of natural selection Darwin
makes use of the principle of artificial selection among
domesticated animals. According to Darwin, something
similar to this artificial selection by man goes on in nature,
producing the different species of animals as we know them
today. Stated briefly, Darwin's theory of natural selection
rests on a series of arguments as follows: (1) there is a
tendency for each species of animal to produce more in-
dividuals than can survive, because of lack of food, shel-
ter, or other natural limits to numbers (overpopulation) ;
(2) this overproduction leads to a conflict or contest be-
tween all individuals of the same species (struggle for exist-
ence) ; (3) in this contest all individuals having a handicap,
or weakness, of any sort would be at a disadvantage in the
struggle and would be the first to be starved or killed
(elimination of the unfit) ; (4) thus only the best individ-
uals, those having some superior trait of cunning, speed,
strength, or the like, would live (survival of the fittest).
According to this argument only the superior individuals of
each generation would live and have opportunity to produce
young. The very same advantages which permitted the
parents to triumph over their less well-fitted brothers would
be passed on to the next generation by heredity. Thus new
traits, no matter how small, if they gave the owner ad-
vantages over his neighbors, would become emphasized.
According to this belief Nature in a metaphorical sense
chooses those individuals best suited to improve the race in
a manner highly comparable to the part played by man in
selecting his breeding stock from among his flocks of domes-
tic animals.

In order to understand the principle of natural selection
we must consider for a moment the struggle for existence.

184 GENERAL ZOOLOGY

This term is used by Darwin in "a large and metaphorical
sense, including dependence of one being on another, and
including (which is more important) not only the life of the
individual but also success in leaving progeny." The strug-
gle results from the tendency of living things to increase
more rapidly than the means of subsistence. Professor
Jordan of Stanford University says :

If the eggs of a common house fly should develop, and each of
its progeny should find the food and temperature it needed, with
no loss and no destruction, the people of a city in which this might
happen could not get away soon enough to escape suffocation
from a plague of flies.

Professor Thomson of Edinburgh, Scotland, gives this illus-
tration :

A female aphis, often producing one offspring per hour for days
together, might in a season be the ancestor of a progeny of atomies
which would weigh down five hundred millions of stout men.

A rapid increase would be noted on the part of any animal,
were the various checks to its multiplication removed.
The struggle for life goes on between different individuals
of the same species, as in a swarm of grasshoppers; be-
tween individuals of different species, as grasshoppers and
insect-eating birds ; and between living organisms and the
conditions of existence, such as temperature, winds, moist-
ure, and food supply.

The caddis flies are, in their immature stage, aquatic lar-
vae which build protective cases composed of grains of sand,
or bits of straw, or leaves (Fig. 99). These cases afford con-
cealment and protection to the young. Applying the prin-
ciple of natural selection here, we may say that those
caddis flies which varied in the direction of protective cases
have survived, and those which did not have been devoured
or otherwise destroyed ; hence a race of case-building cad-

HEREDITY AND EVOLUTION

185

dis flies is in existence today. Natural selection results in
"the survival of the fittest" for the particular environment,
and the principle is used to explain the degeneration due to

parasitism, as well as the development of
increased complexity in animal structure.
Zoologists of the generation following
Darwin attempted to explain all evolu-
tion as the result of natural selection.
With the discovery of instances where
natural selection obviously could not
explain the course of evolution many at
once declared the whole idea of natural
selection worthless. The more we learn
of nature the more does it appear that
the operations of the universe are in
accord with general plans or laws. But
there is neither necessity nor reason to

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wUm

Fig. 99. Caddis flies. (Enlarged)

186

GENERAL ZOOLOGY

believe that but a single method produces a given result.
It seems entirely probable that natural selection has played
an important part in organic evolution. It is at the same
time true that natural selection cannot explain all the changes
that have taken place in the various types of animals.

Sexual Selection. The principle of sexual selection, also
formulated by Darwin, is an extension of the principle of
selection to account for the secondary sexual characters
which exist in many animals. In most insects, where there
is sexual dimorphism, the male, though usually smaller, is

Fig. 100. Stag beetles (male left, female right). (Natural size)

more brightly colored ; it is armed or ornamented with
spines, which the female does not possess, or it has special
sound-producing organs. In the common stag beetle (Lu-
ca'nus, Fig. 100) the mandibles of the male are of larger
size than those of the female. Among the birds, in those
cases where the sexes are differently colored, the males are
usually more brilliant; they often have spurs, wattles,
crests, or plumes, while the females are without these struc-
tures, or have them in less degree. It is only the male birds,
too, which possess the gift of song. Among the fur-bearers
special characteristics, such as horns, antlers, and tusks,
often occur. These various secondary sexual differences are
ascribed by Darwin to sexual selection, which "depends,
not on a struggle for existence in relation to other organic

HEREDITY AND EVOLUTION 187

beings or to external conditions, but on a struggle between
the individuals of one sex, generally the males, for the pos-
session of the other sex. The result is not death to the un-
successful competitor, but few or no offspring. Sexual
selection is, therefore, less rigorous than natural selection.
Generally the most vigorous males, those which are best
fitted for their place in nature, will leave most progeny.
But in many cases victory depends not so much on general
vigor as on having special weapons confined to the male sex.
A hornless stag or spurless cock would have a poor chance
of leaving numerous offspring." The greater brilliancy of
many males is accounted for by ascribing it to the choice
by the females, through countless generations, of the most
brilliantly colored and attractive males. The song of male
birds is accounted for in a similar manner.

The Inheritance of Acquired Characters. Though Darwin
considered that species have arisen largely through the ac-
tion of natural selection on favorable variations, he ad-
mitted also other factors in evolution on which some
naturalists today lay great stress. It is a truism of our
everyday life that the use of an organ sooner or later affects
its structure. Thus the brawny arm of the blacksmith may
be directly attributed to the kind of work he does. Among
the insects we may instance the enlarged fore legs of the mole
cricket and mantid, the enlarged hind legs of the grass-
hopper, and the absence of eyes in certain cave-inhabiting
insects. With this principle are associated the names of
Erasmus Darwin, grandfather of Charles Darwin, and the
French naturalist Lamarck.

The chief difficulty in the application of the principle of
the inheritance of acquired characters as a factor in evolu-
tion lies in the fact that we have little or no evidence that
the characters acquired by use or disuse during the life
of an individual are transmitted to its descendants. Many

188 GENERAL ZOOLOGY

unsuccessful experiments have been performed in the at-
tempt to furnish this direct evidence.

The Mutation Theory. It will be remembered that Dar-
win laid stress upon indefinite, or fluctuating, variations as
furnishing the material for selection. The mutation theory
stands in sharp contrast with the selection theory in em-
phasizing the hereditary transmission of definite variations.
With the mutation theory is associated the name of Hugo de
Vries, a Dutch botanist of Amsterdam, Holland. He was
led to express the principle from his studies of the variations
in a species of evening primrose introduced from America
and found growing in waste places near Amsterdam.

According to this principle new species have been pro-
duced by sudden and perfectly definite changes (mutations)
in the organism, though it is not necessary to assume that
these changes are always great. The theory makes no
attempt to account for the presence of mutations, but when
they occur it is a striking fact that the characters tend to be
handed on to the descendants. Many of de Vries's conclu-
sions regarding the mutations which he observed in prim-
roses are today explained as due to impure stock giving rise
to new combinations according to Mendel's principles. How-
ever, he formulated a principle which has become the basis of
one of the most active fields in the investigation of heredity.

Experimental Study of Evolution. The study of heredity
that is being carried on so actively in the research labora-
tories of all civilized countries is really the study of some
aspects of evolution. New kinds of plants and of animals
are being continually produced by artificial selection which
essentially is very similar to the principle of natural selec-
tion expounded by Darwin. New mutations are being ob-
served regularly in the laboratory experiments in genetics.
It is becoming more and more obvious that Nature is not
restricted to a single method of producing new forms of life.

CHAPTER XVIII

THE CLAM AND OTHER BIVALVES: ACEPHALA

And I then engaged myself, with the other merchants, in a pearl fishery in
which I employed many divers on my own account.

Sindbad the Sailor, in the Arabian Nights

The Long-Neck Clam

Habitat and Distribution. The animal which is described
first in this chapter is commonly known as the long-neck
clam or the soft-shell clam. It is more accurately designated
by its scientific name, My' a arena 'ria (Fig. 101). As the
specific name implies, the animal lives in the sand. It is
found in great abundance along our Atlantic coast, even as
far north as the Arctic regions.

External Structure. The shell of the clam has the same
general use as the carapace of the crayfish. In both ani-
mals these hard, external parts protect the organs within
from injury and also afford surface for the attachment of
muscles. The clam's shell, however, is never molted. It
grows continuously from the time it begins existence at the
little rounded prominence called the umbo (pi., umbones),
or beak (Fig. 101).

Anyone who examines a dry shell of this kind can tell
which is the youngest portion of the shell. Probably he will
observe at the same time the little spoon-shaped piece ex-
tending horizontally inward from one of the valves of the
shell. This projection is always on the left valve. It meets
a brown, rubber-like pad beneath the umbo of the right
valve, and is joined with it. As long as the two valves hold

together at this point, the pad, which is called the hinge

189

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THE CLAM AND OTHER BIVALVES

191

ligament, has a tendency to separate the valves at an acute
angle. In life two thick, short muscles extend across from
valve to valve and resist the spreading action of the hinge
ligament.

The Mantle and the Mantle Cavity. When the valves are
shut they inclose a considerable space besides the body
proper. Fig. 101 represents the most important organs as

A B

Fig. 102. Mechanism for opening and closing mussel shell

A, valves of mussel closed ; B, valves of mussel open ; 1,2, hinge ligament ; 2a, ad-
ductor muscle contracted ; 2b, adductor muscle relaxed ; 3, outer layer of shell ;
-4, middle layer of shell ; 5, inner (mother-of-pearl) layer l

they might lie in the hollow of the right valve. Fitting
close to the inner surface of the valves is the mantle (Fig.
101). Except at the edge, where the mantle folds (halves)
unite, the mantle is quite thin ;" its chief use is to secrete
the calcareous substance of which the shell is composed.
The shell is deposited in three layers (Fig. 102, 3, 4, 5),
— the outer layer called the periostracum, the middle layer
called the prismatic layer, and the inner layer called the
nacreous (or pearly) layer. After the shell is formed at the

1 From Lang's Lehrbuch.

192 GENERAL ZOOLOGY

edge, the thin part of the mantle folds continues to deposit
the nacreous layer, which is sometimes called mother-of-
pearl.

The mantle folds inclose a mantle cavity. An opening at
the anterior end of the mantle cavity allows the foot (Fig.
101), the single locomotor organ, to be extended to the out-
side. At the posterior end of the mantle cavity is situated
the double- tubed siphon (Fig. 101). Only the lower tube of
the siphon is connected directly with the mantle cavity.
This siphon enables Mya to lie buried, anterior end down,
in the mud and sand, still maintaining communication with
the food-laden and air-laden water above. In large speci-
mens of this clam the siphon is over twenty-five centimeters
(ten inches) long.

The Digestive System. The ventral opening of the siphon
(Fig. 101) is surrounded by many short tentacles which
guard the passage. An ingoing current is created in the
water by cilia on the gills. Ordinarily only microscopic
food passes through this incurrent opening of the siphon.
In the mantle cavity the particles of food are carried for-
ward over the gills and along the mantle till they come
within range of the waving palps, or mouth appendages.

The mouth opening is situated between the four palps,
and is very small. It has no organs of any kind for seizing
or chewing food ; none are needed. The food once swal-
lowed passes through the short esophagus to the stomach.
Surrounding the stomach is the large, paired digestive gland,
which secretes the digestive fluid. Situated in the end of the
stomach, and in the anterior end of the intestine, we find,
in Mya arenaria, and in many species related to it, an organ
called the crystalline style. In Mya this structure is three
or four inches long. It is soft and clear, like thick, color-
less jelly, and lies in a long, thin-walled sac opening into
the stomach. The style produces substances of use in the

THE CLAM AND OTHER BIVALVES 193

processes of digestion and also aids in keeping the food well
mixed in the stomach.

The intestine coils and twists in many planes from the
posterior end of the stomach to the point where it penetrates
the heart. The penetration of the heart by the intestine is
of common occurrence in the class to which Mya belongs,
but it occurs in no other class of animals. The part of the
alimentary canal from the heart to the anus is called the
rectum. The rectum is inclosed in a large, spindle-shaped
organ of unassigned name and unknown function.

The Circulatory, Respiratory, and Excretory Systems. When
the food is absorbed by the wall of the intestine it passes
into small blood spaces filled with colorless blood. The
blood with the contained food then passes into the open ends
of small blood vessels. These blood vessels lead (in cer-
tain near relatives of Mya which have been studied more
fully) to a large blood space below the pericardium, the sac
which incloses the heart. From the blood space (not shown
in the figure) blood passes by vessels to the nephridia (kid-
neys). The nephridia in Mya arenaria lie one on either side
near the heart. The anterior end of the left nephridium is
indicated in Fig. 101. The rest of the organ could not be
shown in the drawing.

The nephridia are spongy, brownish organs of great com-
plexity. Each nephridium of the clam opens at one end
into the pericardium. The other end of each nephridium
opens into the mantle cavity just posterior to the digestive
gland.

The blood vessels in the nephridia divide into capillaries.
The nitrogenous waste of the body (uric acid) passes into the
nephridial tube and is carried out into the mantle cavity.
The small blood vessels convey the partially purified blood
into a vessel that runs along the line of attachment of the
gills.

194 GENERAL ZOOLOGY

There are four of these gills and they hang like double
curtains along the right and left sides of the body (Fig. 101).
Oxygen, dissolved in the water, passes through the incurrent
tube of the siphon into the mantle cavity and over the gills.
The gills are thin and soft, and are thus adapted for the
ready passage of oxygen to the blood vessels inside.

In the blood the oxygen combines with hsemocyanin, a
substance analogous to haemoglobin (see page 122). At the
same time the waste carbon dioxide in the blood is given
off to the water in the mantle cavity. The mantle folds, as
well as the gills, take part in respiration. It is possible for
them to do so because of their rich supply of blood vessels.

Returning from the gills and the mantle, the blood, freed
of carbon dioxide, is carried to the right (Fig. 101) and left
auricles of the heart. These thin-walled, sac-like reservoirs
force the blood into the ventricle of the heart. The heart
contracts and forces the blood both forward and backward
through arteries. The anterior artery lies above the intes-
tine, and the posterior artery lies below the rectum. Both
arteries branch into smaller arteries in all parts of the body.
The blood flows from the open ends of the smallest arter-
ies into blood spaces, from which it is once more collected
and carried to the purifying organs in the manner already
described.

The Siphon. Besides the rows of cilia which carry food
from the region of the incurrent tube to the mouth, there
are rows of cilia on the body and along the mid-ventral line
of the mantle, and it is known that these cilia wave toward
the incurrent tube. Food that has been rejected, or waste
that has accumulated, may be carried by the out-waving
cilia to the base of the incurrent tube. By muscular con-
traction of the siphon at its base these substances may be
expelled through the tube. The excurrent tube of the si-
phon, however, is the customary path of exit for substances

THE CLAM AND OTHER BIVALVES 195

that are not used by the organism. All the undigested sub-
stances that pass through the intestine must leave the ani-
mal by the dorsal tube. In addition, it is likely that wastes
from the nephridia, and from the gills and mantle, may
pass from the mantle cavity through a slit-like opening
(Fig. 101) at the base of the gills, and be carried out with
the unused materials.

The Nervous System. In contrast with the nervous sys-
tem of the arthropods with its long series of ganglia dis-
tributed through the length of the body, this system in the
mollusks consists of but three pairs of large ganglia. Lying
on the right and left sides of the esophagus, just posterior
to the mouth, is a pair of cerebropleural ganglia. They are
joined by a cerebral commissure running over the esophagus.
As the name of the ganglia implies, there are two ganglia
joined in each nerve mass. One pair controls the "head'
region ; the other pair controls the sides of the body close
by. The cerebropleural ganglia are joined to the pedal
(foot) ganglion by two connectives, one on either side. The
pedal ganglion controls the movements of the foot. The
visceral ganglion is joined to the cerebropleural ganglia by a
pair of cerebrovisceral connectives. The visceral ganglion
controls the organs in the posterior region of the body.

The Reproductive System. The pair of large gonads, which
in male clams contain spermatozoa and in the females the
eggs, lies in the midst of the coils of the intestine. Each
gland has a short, slender tube, with an external opening
(not shown) near the opening of the nephridium, just be-
low the attachment of the gills.

Development. The very early history of the young Mya
arenaria is incompletely known. We know, however, that
after a short period of development and growth young long-
neck clams swim about on the surface of the water. Soon
after the appearance of their shell they sink to the bottom.

196

GENERAL ZOOLOGY

If they are fortunate enough to fall near the shore line,
they anchor themselves to a seaweed, or to a pebble, by a
tough, gelatinous thread (Fig. 103, 3) which is secreted
by a gland at the base of the foot (Fig. 103, 1). This thread
is called the byssus. In certain mussels found in the sea the
byssus is a permanent and very complicated organ of the

adult, but in Mya are-
naria it disappears when
the clam is about five
millimeters (one fifth of
an inch) long. At that
time the animal burrows into the
mud and sand, where it usually re-
mains permanently.

Relation to Environment. The adult
Mya arenaria lives in soft mud and
sand between high-tide line and a
few feet beyond low-tide line. The
reason the clam lives in that situa-
tion is because food is most abun-
dant there. Lying almost helpless
in its mold of mud, the long-neck
clam is rendered in a measure in-
dependent of conditions outside, as long as the currents of
water carry the bountiful supplies of food over its burrow.
Although the clam is not so highly esteemed as an article
of human food as its relative the oyster, it is nevertheless
of great value.

The American Oyster

Habitat and Distribution. The American oyster {Os'trea
virgin'ica, Fig. 104) is found in shallow to deep water
along the Atlantic coast from the Gulf of Mexico to Mas-
sachusetts Bay. As the artist has shown in the picture, the

Fig. 103. Young long-neck
clam

1, foot; 2, siphon; 3, byssus

thread; U, pebbles. (After

J. L. Kellogg)

THE CLAM AND OTHER BIVALVES

197

animal lies attached to the bottom, frequently to another
oyster shell. Although many oysters may live thus fastened
to each other, there is no organic connection between them.
They sometimes form clumps so large and heavy that the
basal ones sink into the mud and die. The valves of the
living ones extend outward at any angle. When oysters
are not crowded in the "bed," the usual method of liv-
ing is the one shown in the illustration. There the valves

Fig. 104. Group of living oysters. (Reduced)

extend horizontally, and we can distinguish an upper and a
lower valve. The lower valve is always much larger and
deeper than the upper one. The lower one is the left valve.
Comparison with the Clam. The internal organs of Ostrea
virginica and Mya arenaria are very much alike. The
large, dark-brown digestive gland, the coiled intestine, the
three-chambered heart, and the reproductive glands have a
common plan in the two species. A noticeable difference is
the entire absence of a foot in the oyster. Applying the
principle of adaptation, we can readily explain the absence
of that organ. There are two adductor muscles in the clam,
in the oyster only one.

198

GENERAL ZOOLOGY

Development. In the months of May to September, in
the latitude of Baltimore, the male and female oysters send
out into the water their spermatozoa and their eggs. A
female oyster may yield in one season at least sixteen mil-
lion and probably as many as sixty million eggs. The num-
ber of male cells is great beyond all powers of expression.
Of course we should expect that in spite of the countless
spermatozoa, many eggs would never be fertilized at all,

on account of their being carried
away by unfavorable currents.
Eggs that are not carried away
fall to the bottom naturally.
Those eggs which are fertilized
swim to the surface as larvae
after a few hours' development.
There surface fish may, as Pro-
fessor William K. Brooks once
suggested, "gulp down in a few
seconds oysters equal in number
to the population of Baltimore. "
Within one to six days after
fertilization the oyster "fry"
(swimming larvae, Fig. 105) sink to the bottom again and
affix themselves to whatever solid object they happen to
touch. At this time they are about three tenths of a mil-
limeter (one eightieth of an inch) long. For a few weeks
after beginning their stationary life they are liable to be
crunched to death by voracious crabs, — among others, the
blue crab (Fig. 87).

Economic Importance. The largest and most important
"oyster farms" along our coast are in Chesapeake Bay.
There and elsewhere the beds have been surveyed and leased
under laws of the states. So vast is the oyster-fishing indus-
try in this country that more than fourteen millions of dol-

Fig. 105. Oyster larva.
(Much enlarged)

1, mouth; 2, stomach; 3, anus;

U, shell; 5, adductor muscle; 6,

circle of cilia. (After Moebius)

THE CLAM AND OTHER BIVALVES 199

lars are yielded annually by the oysters and their products.
On the coasts of Holland, Belgium, and France far greater
care is taken of their species (Ostrea ed'ulis) than we take
of ours ; but the natural conditions here are superior to the
natural conditions there.

Oysters when subjected to sewage contamination may
become carriers of typhoid fever. When grown and mar-
keted under sanitary conditions they are not only harmless
but a very wholesome food.

Relation to Environment. According to the pioneer in-
vestigations of Professor Brooks and others, oysters are to
be found most abundantly in the quiet, semi-stagnant water
of shallow inlets. Into such inlets slowly flowing creeks
enter, giving to the water of the inlet a brackish quality.
When food consisting of microscopic plants and animals is
carried to the oyster by the natural currents in the water, it
may enter at any point between the separate folds of the
mantle. Cilia on the inner surface of the mantle folds, and
on the four gills, sweep the minute organisms forward to the
mouth, which lies near the hinge. The four palps aid in the
process. In brackish water the most important food organ-
ism of the oyster multiplies in vast, invisible hordes. These
organisms are plants called diatoms. Diatoms live in the
soft mud at the bottom and are carried bj^ the water cur-
rents within range of the cilia in the oyster's mantle folds.

In times of storm the home of the oysters' food may be-
come a source of great danger to them. Once covered with
mud or with shifting sand, the life of a bed of oysters is at an
end. At the mouths of rapidly flowing rivers no oysters
are to be found, chiefly because the silt (fine sediment) and
the debris of decaying plants are unfavorable to the growth
of the animal.

Aside from the physical agencies which are favorable or
unfavorable to oysters, there are many animals which come

200 GENERAL ZOOLOGY

into definite and usually unfavorable relations to them. Only-
one of these animals, so far as known, is anything but harm-
ful to the oyster. That one is a little crab, about thirteen
millimeters (half an inch) wide, which spends its life in the
mantle cavity of its messmate. The greatest enemy of the
adult oyster is the starfish (Fig. 124). There are various
boring snails, which make round holes through one of the
valves with their rasping tongues and draw out what they
need of the soft parts (compare Fig. 119). Another enemy
is the boring sponge, which, as it grows, makes holes in the
valves by a secretion which it produces. Like most other
animals, the oyster has its parasites. With all these facts
before us, the statement of Professor Moebius regarding
the European oyster, that each oyster when born has
1145000 °f a chance to survive and reach adult age,
seems well within reason.

The Scallop

Habitat and Distribution. Of all the shellfish that inhabit
the shallow waters of the Atlantic coast of our country,
none is more beautiful in color or in line than the common
scallop, Pec' ten irra'dians (Fig. 106). Scallops are abun-
dant among the eelgrass of shallow bays and inlets from
the Gulf of Mexico to Massachusetts Bay. Above the latter
region the waters are made colder by the arctic currents.
Pecten irradians and many other species of sea animals do
not live north of Cape Cod.

Relation to Environment. The very young scallop holds to
some fixed object after the manner of a young soft-shell clam
(Fig. 103). The adult scallop has no byssus, and only the
rudiment of a foot. The scallop in the foreground of the
picture is in what we might call the attitude of rest. It has
released its single adductor muscle, which, we may say in
passing, is the only part of the animal sold for food.

THE CLAM AND OTHER BIVALVES 201

In the act of swimming the valves open and close quickly,
by the alternate action of the hinge ligament and the large
adductor muscle. On closing, the valves catch a quantity of
water between the mantle folds. The water escapes under
pressure from within, through a round opening at either
end of the straight flange of the hinge. The resulting
action of these jets of water backward, against the body
of water outside, is to force the larger and broader end
of the animal forward. When the scallop ceases swimming,
it immediately falls to the bottom.

Shipworms. The shipworms are marine bi-
valve mollusks that have taken
to burrowing in wood. The
shell covers but part of the
long, wormlike body. Piles
and wharves and other wooden
structures on the water fronts
become honeycombed and are
completely undermined by the
burrows of these animals. They
cause great damage in many
|y regions along the coast.

a*

Fig. 106. Group of living scallops, (x J)

202

GENERAL ZOOLOGY

The Fresh- Water Mussel

Habitat and Distribution. In fresh waters generally, wher-
ever sufficient carbonate of lime is carried in solution, one
may find mussels living nearly covered in sand and mud.
The species represented in Fig. 107, Ellip'tio complana'tus,
is distributed in the rivers and brooks of the Atlantic states.

Fig. 107. Living fresh-water mussel, (x \)

Comparison with Other Forms. The valves of the mussel
are equal, like those of the clam and the scallop. The valves
of the fresh-water species are held together by a hinge lig-
ament, aided by two pearl-covered ridges running parallel
and fitting into grooves. The mantle folds are not united
as they are in the clam. The siphons are here merely open-
ings between the two mantle lobes, not a protruding tube
as in the clam. At two adjoining places in the posterior
region the rim of the mantle folds is fringed with short ten-
tacles. Dorsal and ventral openings, or siphons, are formed
by the meeting of opposite edges at the places where the

THE CLAM AND OTHER BIVALVES

203

tentacles occur. Water, bearing food and oxygen, is carried
in by the ventral siphon, and undigested substances are
carried out by the dorsal siphon.

The foot of the mussel is large and muscular. It enables
the animal to plow its way through mud or even through
heavy gravel. The gills and the palps are practically identi-
cal in structure in the mussel, the clam, the oyster, and the
scallop. With the exceptions just mentioned, the organs have
the same general plan of structure in the four animals named,
and the description given for
the clam applies to the three
other forms. There are two ad-
ductor muscles in the mussel.
The sexes are usually separate.

Development. All fresh-water
mussels, except the small finger-
nail shells, carry their young in
their gills. When fully formed,
the larvae escape from the brood
pouch of the female mussel. Fish
"nosing" along the river bed

touch the young mussel, which at that stage is called the
glochidium (Fig. 108). The shells of the glochidium clamp
together and become attached to the gills or fins of the fish.
Some species live only on gills and others on fins. For each
species of mussel the larvae will become attached to only
certain kinds of fishes. After attachment the tissues of the
fish grow around the glochidium, entirely surrounding it.
For several weeks the glochidium is transported on the fish.
During this time it may be carried into another river, even
by way of the sea. When the period of development within
the cyst on the fish is completed, the cyst, or covering,
breaks away. This liberates the young mussel, which now
ceases to be a parasite and begins an independent life. If

2 l

Fig. 108. Larva of mussel.
(Much enlarged)

1, shell; 2, adductor muscle;

3, larval hook ; 4, larval thread.

(After Balfour)

204 GENERAL ZOOLOGY

this happens in a favorable place, it burrows into the mud
and begins the life of its adult kin.

Economic Importance. The distribution of fresh-water
mussels has become a matter of considerable economic im-
portance, especially in the states of Iowa and Illinois.
Many factories have been established for the purpose of

Fig. 109. Mussel fisherman with boat equipped for capturing fresh-
water mussels

Photograph by F. M. Woodworth, courtesy of F. C. Baker

making pearl buttons from the valves. According to the
annual report of the United States Bureau of Fisheries, ap-
proximately twenty-six thousand tons of mussel shells with
a value of over one million dollars were taken (Fig. 109)
by fishermen in 1922. These shells furnished material for
over eight million dollars' worth of manufactured products,
such as buttons and pearl novelties.

So many mussels have been taken from the streams
(Fig. 109) in many regions that they have become practi-

THE CLAM AND OTHER BIVALVES

205

cally exterminated. The United States Bureau of Fisheries
has studied the problems of mussel propagation very care-
fully. In many of the streams commercial catching of mus-
sels is prohibited in the hope of natural restoration. Fishing
crews carry on rescue work to save fishes stranded in back-
water ponds and bayous after high water. Before the
rescued fishes are returned to the streams they are placed
in tanks containing liberal quantities of glochidia. By this
means each fish may carry
several hundred young mus-
sels back into the streams.

Pearls. True pearls of fine
quality have been found in
many species of mussels in all
parts of the Mississippi Val-
ley. In nature, pearls are
formed around some irritat-
ing object. Parasitic worms
and eggs of some of the small
mites infecting the mussels
are the most frequent bodies
around which pearls are

formed (Fig. 110). In reality, pearls are tombs incasing the
bodies of intruders. Even sand grains at times become the
nucleus around which certain kinds of pearls are formed.

Japanese scientists recently discovered methods of pro-
ducing "culture" pearls by inserting objects inside the man-
tle. When perfect spheres cut from shells are introduced
into the mantle, the culture pearls are almost perfect.

Relation to Environment. There are more than five hun-
dred varieties of fresh-water mussels in the United States.
Of these, some live only in muddy streams, and others are
limited to sandy or to rocky bottoms. In streams, shallow
waters, where riffles are formed, harbor the greatest number

Fig. 110. Section of mantle fold of
mussel showing how a pearl is formed

1, cells of mantle; 2, external epithe-
lium of mantle ; 3, internal (ciliated) ep-
ithelium ; If, position of shell ; 5, pearl ;
6, remains of parasite. (After Jameson)

206 GENERAL ZOOLOGY

of both species and individuals. Though they move about,
the majority of individuals spend most of their time with
the posterior end bearing the siphon directed upstream.
Thus the flow of water downstream brings a continuously
fresh supply of food to the animal. Fishermen (Fig. 109)
make use of this habit. They always drag their clam bars
downstream, so that the hooks may catch into the open
shells. Mussels cannot survive in water that is polluted
with sewage.

Definition of Acephala. The four animals described in this
chapter are representatives of a class called Aceph'ala.
Acephala means "without a head." They are called bi-
valves because the shell is in two pieces. Acephala are
usually bilaterally symmetrical animals with an external
skeleton composed of two nearly equal valves. They have
no internal skeleton. The body is without a head and is not
divided into somites. There are no jointed appendages.
The mantle folds surround the body proper and secrete the
shell substance. Locomotion is most frequently accom-
plished by a single muscular organ, the hatchet-shaped foot.
The valves are held together by a hinge ligament, aided
sometimes by ridge-like processes fitting into grooves. The
valves are closed by one, or two, adductor muscles.

Four palps surround the mouth and carry the food in-
ward. The esophagus is short. The stomach receives the se-
cretion from a pair of digestive glands. The intestine coils
several times and ends posteriorly. The circulatory system
is nearly complete. There are two auricles and one ventricle
in the heart. The pairs of glands of the reproductive system
in male and female individuals seem to differ only in micro-
scopic structure. In some species the sexes are separate. In
others the individuals are hermaphroditic ; that is, the male
and female sexual glands are present in the same animal.

CHAPTER XIX

ALLIES OF THE ACEPHALA: MOLLUSCA

The frugal snail, with forecast of repose,
Carries his house with him where'er he goes.

Charles Lamb

The Pond Snail. Any one of several genera and species
of snails that live in fresh water might be given the name
"pond snail" with equal accuracy. The one represented in
Fig. Ill (Phy'sa) is quite common not only in ponds but in
rivers as well.

Externally the most noticeable feature of the pond snail is
its thin, spiral shell. This structure is made of the same ma-
terial as the shell of bivalves. A large portion of the animal's
body fills the "mouth" of the shell and extends spirally
toward the top. Between the shell and the body wall lies
the mantle, which throughout life continues the growth of
the shell in the characteristic spiral direction.

When the snail is disturbed it draws the entire body into
the shell ; but when it is feeding, as shown in the picture,
one can see the long, muscular foot, broad in front and
pointed behind. The anterior region of the body is the head,
more or less sharply marked off from what lies behind. The
mouth opens beneath an extensile upper lip. In the mouth
is a short, muscular tongue, on which grows a long but
minute ribbon of rasp-like teeth. The pond snail uses this
rasping tongue to tear into bits the soft plant tissues on
which it feeds. A most interesting experience is to watch
a pond snail as it crawls slowly up the side of an aqua-
rium, feeding on the microscopic plants as it goes. At

207

208

GENERAL ZOOLOGY

Fig. 111. Group of living pond snails. (Natural size)

such times one can see the mouth open and the tongue
sweep back and forth, with tiny, rhythmic movements.
The two tentacles are organs of touch. The eyes lie one
in front of either tentacle at its base. On the right side, and
partly beneath the edge of the shell, is an aperture which
opens over a small hollow space in the body when the snail
comes to the surface. This space is the so-called "lung" of
the pond snail. The lung is adapted to using the oxygen of

ALLIES OF THE ACEPHALA

209

the atmosphere. Anyone who owns an aquarium contain-
ing snails may observe them crawling up the side of the
vessel on their way to the surface. When they arrive there
they remain for some time, opening and closing the lung to
admit the air. In aquariums which have a supply of water
plants growing in them, the pond snail does not appear to
go to the surface so often.
It is well known that
plants give off oxygen.
Some of this oxygen held
in the water may pass
through the snail's skin,
which is thin and soft.
The waste carbon dioxide
of the snail is discharged
into the water.

It is not uncommon to
see a pond snail crawling
upside down at the sur-
face of the water. The
explanation of this curi-
ous phenomenon is the
same as the explanation
of how they can get along
on any kind of a surface.
Just below the mouth is

the opening of a gland, which extends through the middle
of the foot near the lower surface. If we look closely at
the inverted snail, we can see the wall of this gland con-
tracting with a wave-like movement in the act of sending
the secreted mucus (slime) forward to be poured out at the
opening. The mucus spreads out a short distance on the
water, or blade of a water plant, or submerged object, and
forms a bed over which the animal moves.

Fig. 112. Mucus threads of pond snail
in water. (Reduced)

After Kew

210

GENERAL ZOOLOGY

When the foot is extended in locomotion, the pond snail
weighs less than an equal volume of water. If the animal
releases its hold on an object at the bottom, it floats to the
surface quickly. Conversely, if the animal releases its hold
on the surface of the water, it draws the entire body into
the shell and quickly falls to the bottom. In the second in-
stance the weight of the
snail's body is greater
than the weight of an
equal volume of water.

We find vertical threads
of mucus in snail aquaria
and in ponds (Fig. 112).
A snail on leaving the bot-
tom may pour out mucus
from its foot-gland in the
usual way. The mucus
fastened at the bottom
will be paid out in the
form of a thread as the
animal floats slowly up-
ward, held back by this
thread. When the snail gets to the surface the thread is
moored there in a patch of mucus. Each thread thus formed
becomes a permanent pathway, tending to increase in thick-
ness and in strength as the snail makes use of it.

In the spring and summer months the pond snail lays
eggs even in captivity. The gonad is hermaphroditic, hence
every individual is likely to deposit eggs. The eggs may be
found on the branches of water plants, or even on the per-
pendicular sides of a glass aquarium, imbedded in an ellip-
tical, clear, gelatinous mass from two millimeters to six
millimeters long. In each mass from five or six to twenty-
five eggs may be distinguished.

Fig. 113. Living land snail. (Slightly
reduced)

ALLIES OF THE ACEPHALA

211

The Land Snail. One of the commonest of the land snails
in America is the one shown in Fig. 113 (Polygy'ra). The
many species of the genus Polygyra live in moist, protected
places during the day and come out to feed at night. Fre-
quently they leave their
hiding-places in cloudy,
damp, but not in rainy,
weather.

) The organs to
be noted on the
exterior of this animal are
the same as in the pond snail. The
openings of all the internal organs
occur in the same position in both
animals. There are four tentacles
in this land snail, — an upper, long
pair bearing the eyes, and a lower, short pair, which are
the organs of touch. The edge of the mantle is thickened

to form a collar.

The Garden Slug. The particular species of garden slug
of which the habits are suggested in Fig. 114, is Li' max

Fig. 114. Garden slug feed
ing at night. (X \ )

212 GENERAL ZOOLOGY

max'imus. It is a native of Europe, not of America, and
since its introduction here has become a more unwelcome
guest in greenhouses than any other species of slug or snail.

In brief terms we may describe a slug as a snail with a
rudimentary shell. The elliptical plate of muscle on the dor-
sal surface of Limax is all that is left of the mantle. In the
process of degeneration, which we may well suppose has
occupied thousands of years, the mantle folded back over
the shell as the latter decreased in size. If we examine the
interior of the mantle, we find a thin, calcareous plate, which
is the rudimentary shell.

The ravages of Limax maximus are not serious if the
florist does not allow refuse to collect about his buildings.
Many adopt the method of scattering ashes or cinders about
the plants to be especially protected. A slug crawling into
such an obstruction is stimulated by the dryness of the
ashes, or the roughness of the cinders, to secrete mucus from
the glands that occur in the skin. This mucus is like that
which is secreted from its foot-gland while crawling. Owing
to the unusual amount of mucus given off at such times, the
animal dies from exhaustion, and from suffocation by the
drying of its skin.

Garden slugs that live out of doors burrow into the ground
and curl up when the coldest weather comes. Those in green-
houses remain active throughout the year.

Several other slugs, some of which are smaller and much
more widely distributed than Limax maximus, occur under
logs and damp leaves. At times these become numerous
enough to do considerable damage in gardens.

The Oyster Drill. A few minutes' walk along almost any
pebbly beach between Florida and the Gulf of St. Lawrence
would afford a collector the opportunity of observing the
subject of this description, the oyster drill (Urosal'pinx ci-
ne'rea, Fig. 119). In such a walk the artist discovered the

ALLIES OF THE ACEPHALA 213

unfortunate periwinkle at the left of the picture, with the
oyster drill of the foreground engaged in devouring the soft
parts of its victim through the hole made in the thick shell.
For the purposes of illustration the oyster drill was placed
on another periwinkle in the same position it occupied on
the first when discovered. In deep water the oyster drill
devotes itself to the business which gave it the name it bears.
There are several other species of snails, however, which
have the same habit of boring through the oyster's valves
and feeding on the soft parts.

The oyster drill, in common with all other species of snails
that have their habitat on the seashore, possesses a very
thick shell, adapted to the severe conditions of life there.
The sand and pebbles are constantly shifting under the
pressure of the waves, and only those snails that have thick
shells can endure the conditions.

The Periwinkle. The periwinkle, a littoral (shore) species
(Littori'na litto'rea, Fig. 119), is a native of Europe. Its pres-
ence here is accounted for by the supposition that specimens
were accidentally thrown in with the gravel used for ballast
on ocean-going vessels, and thrown out again when the ves-
sel reached its port in America. The first specimens noticed
in America by conchologists (students of shells) were re-
ported at Halifax, Nova Scotia, in 1857. Since that time
the periwinkle has been making its way down the coast. It
may now be found in southern waters. The new home in
America seems to be especially favorable for the periwinkle,
for on the rocky coast of New England there are so many
of them that on first impression there appears to be no other
species. This snail depends on plant food altogether.

On account of its great abundance the periwinkle is much
used as an article of human food in England and on the
Continent. It is one of the many species of snails and slugs
used as food, especially by the French people.

214

GENERAL ZOOLOGY

The Nudibranch. The strange-looking creature shown in
Fig. 115, Dendrono'tus arbor es'cens, is to be found on seaweeds
and under submerged rocks along the north Atlantic coast.
Tree-like processes grow on the upper part of the body.
These processes are to some extent used in respiration.
Since they are thin, oxygen can pass into the animal through
them, and the waste carbon dioxide can pass out. The group
of animals to which they belong is called Nudibranchia'ta,

in reference to the fact
that their gills are naked.
There is no indication of
a rudimentary shell.

Definition of Gasteropoda

(Gr. gaster, "stomach";

pous (pod-), "foot").

The class represented by

the nudibranch, the slug,

and the snails is given

the name Gasterop'oda.

The class name is only figuratively correct. The ventral

surface, not the stomach, is modified to form a locomotor

organ, the foot.

An important characteristic of the Gasteropoda is the un-
symmetrical arrangement of organs. With the exception
of the mouth and the opening of the mucus gland, all the
openings of the body are on the right side, even in cases like
the slug and nudibranch, where the general form of the
body is bilaterally symmetrical. When a shell occurs it is
composed of one piece, and the characteristic form is spiral.
A shell-forming organ, the mantle, is usually present.

The body of a gasteropod is not divided into somites, but
the head is slightly marked off from the rest of the animal, and
is provided with eyes and nonjointed tentacles. A tongue-
like organ bears a ribbon of minute teeth for tearing food.

Fig. 115. Photograph of living nudi-
branch. (Natural size)

ALLIES OF THE ACEPHALA

215

The Squid. In the waters of the Grand Bank of New-
foundland and southward to Massachusetts the members of
a species of squid, Ommas'trephes illecebro'sus (Fig. 116, A),
occur in great numbers. They capture small fish and are
themselves prey for cod and other large fish.

Fig. 116. Cephalopods. (Reduced)

A, a squid ; B, an octopus. (From Van Cleave, courtesy of McGraw-Hill

Book Company, Inc.)

The body of the squid is composed of a head and a slender,
conical portion, the former having a pair of large, movable
eyes (Fig. 116, A). Arising from the head region are ten
long, club-shaped arms, corresponding to the foot of the
Acephala and the Gasteropoda. Two of the arms are longer
than the other eight, but all are provided on part of the
inner surface with many sucking disks, adapted to holding
the prey. The mouth has two horny jaws, resembling in
appearance the bill of a parrot turned upside down. The
tongue is adapted to rasping.

216 GENERAL ZOOLOGY

The conical portion of the body is the mantle, highly
modified by the existence of strong, muscular bands. Part
of the space within the muscular mantle is occupied by the
internal organs inclosed in a body cavity. The remainder
of the space, the mantle cavity itself, connects with the
outside by a narrow opening, at either side of the neck,
and also by the siphon. A pair of feather-shaped gills, one
attached to either side of the body, lies in the mantle cavity.
Imbedded in the tissue of the mantle, on the side opposite
the surface shown in the figure, there is a long, pen-shaped
structure composed of chitinous material. This represents
the remains of the shell. The sexes are separate.

In locomotion the squid contracts and relaxes the circular
muscles of the mantle, alternately decreasing and increas-
ing the volume of the mantle cavity. During relaxation,
water enters the mantle cavity at the sides by the neck, a
valve in the siphon being closed ; in contraction the valves
at the side openings are closed and the water is discharged
through the siphon. The siphon may be directed forward
or backward at will. If it is bent in the direction of the
arms, as it commonly is, the squid during strong contraction
of the mantle darts backward "with the speed of an arrow,"
balanced and steered by the aid of the double mantle fin.

No more beautiful example of rapid color change can be
witnessed than the one going on constantly in the skin of
captive squids. From bluish white the color may change on
the instant to mottled red or brown. The change may be
sudden and complete, or the colors may fluctuate repeatedly
from one shade to another and shimmer over the surface
seemingly as rapidly as the controlling nerves can act.
Observers who have been fortunate enough to come upon a
'school" of squids in a harbor have been puzzled by the
sudden disappearance of the animals. In times of danger
the ability to change color to resemble the environment

ALLIES OF THE ACEPHALA 217

must be of considerable value to them in escaping the
notice of enemies, as well as useful in coming unseen into a
school of small fish.

Another and still more effective means of escaping from
the attack of a superior enemy is employed by the squid
when driven to its last resource. It has in its body cavity a
sac which secretes a black, inky fluid. A tube from the ink
sac passes to the siphon, and in the moment of need the sac
and the muscular mantle contract and force the black, con-
fusing fluid into the water. The squid then has a chance to
escape.

Along the coast of Newfoundland giant squids, belonging
to a genus different from the one here described, are occa-
sionally brought up from the deep sea and stranded on
the shore. These monsters have a body about twenty feet
long, and some of their arms measure more than thirty-five
feet.

The Octopus. A close relative of the squid is the much-
maligned octopus, or devilfish (Fig. 116, B). The body of
the devilfish is sac-like and has but eight arms. Although the
arms of these creatures may get to be several feet long, they
are not nearly so dangerous to man as their appearance
and stories about them might lead one to suppose.

The Chambered Nautilus. Almost the sole representative
of a once numerous race living in the depths of the sea, is
the chambered, or pearly, nautilus (Nau'tilus pompil'ius,
Fig. 117). This species now has a restricted distribution in
the vicinity of certain south Pacific islands, such as New
Guinea and the Philippines. The nautilus lives on the
bottom, usually in water from one hundred to seven hun-
dred meters deep (three hundred and twenty-five to
twenty-three hundred feet).

The shell of the nautilus is divided into compartments by
cross partitions. Each of these compartments represents a

218

GENERAL ZOOLOGY

space in which the animal lived at successive stages in its
growth. The chambers of the entire series are filled with
air and are connected by a slender tube called the siphun-
cle, borne in a thin- walled, calcareous tube (Fig. 117, 11).

Fig. 117. Nautilus. (Reduced)

1, mantle ; 2, dorsal fold of mantle ; 3, tentacles ; k, head-fold ; 5, eye ; 6, siphon ;
7, position of nidamental gland; 8, shell-muscle; 9, living chamber; 10, parti-
tions between chambers ; 11, siphuncle with tube. (After Ludwig) l

Oliver Wendell Holmes, in his poem "The Chambered
Nautilus," thus refers to the phenomena of its growth :

Year after year beheld the silent toil

That spread his lustrous coil ;

Still, as the spiral grew,
He left the past year's dwelling for the new,
Stole with soft step its shining archway through,

Built up its idle door,
Stretched in his last-found home, and knew the old no more.

Fossil Relatives of the Nautilus. Many millions of years
ago, in the early history of the earth, the most ancient of the
immediate ancestors of the nautilus lived. This form had
a straight shell and is called Orthoc'eras.

1 From Hertwig-Kingsley's Manual of Zoology.

ALLIES OF THE ACEPHALA

219

vtr

1

la--

;

'■r{'

From the study of fossils in later
layers of the earth's crust we know that
the group of nautiloids (nautilus-like
animals) grew to be of large size, and
their shells showed coiling more and
more to the close coil of the present-day
nautilus. All the hundreds of species of
nautiloids, except four species of the
nautilus, disappeared as living things
ages before man came into existence
upon the earth.

Definition of Cephalopoda (Gr. kephale,
"head"; pous (pod-), "foot"). Because
of their structural relationship, the
squid, octopus, nautilus, and the fossil
nautilus-like forms belong in a class to-
gether, the Cephalop'oda.

In this class the body has a distinct
head. No part shows indications of be-
ing divided into somites. The head has
two large eyes. The mouth is surrounded
by divisions of the primitive foot, called
arms or tentacles. These divisions of
the foot either have sucking disks for
holding on, or smooth surfaces which
perform the same function. In the
mouth there is a parrot-like beak and a
rasping tongue. A shell-forming mantle
either incloses the shell, as in the squid,
or lies beneath it, as in the nautilus and
in Orthoceras.

There are two gills in the mantle cavity in the squid, and
four in the nautilus. A siphon is present in all the exam-
ples described. The sexes are separate.

m

w

(I

Fig. 118. Fossil Or-
thoceras. (Reduced)

After Blake

220

GENERAL ZOOLOGY

Definition of Mollusca (Lat. molluscus, "soft"). The phy-
lum Mollus'ca includes five classes. For the purpose of ele-
mentary study the most important of these are the Acephala,
the Gasteropoda, and the Cephalopoda.

On the basis of the facts presented in this and the pre-
ceding chapter, we may formulate the following statement
concerning the phylum. Mollusca are soft-bodied animals
provided usually with a hard, calcareous, partly chitinous
shell, which in some forms occurs on the exterior, and in
others is partially or completely inclosed by a sheet of shell-
forming muscular tissue, the mantle. The body proper is
never divided into somites, and the appendages are never
jointed.

Fig. 119. Living oyster drill and periwinkle, (x §)

CHAPTER XX

THE STARFISH AND SOME ALLIES: ECHINODERMA

Let the mere star-fish in his vault

Crawl in a wash of weed, indeed,
Rose- jacy nth to the finger-tips.

Robert Browning

The Starfishes

Habitat and Distribution. The purple starfish (Aste'rias
vulga'ris, Fig. 120) is found most abundantly north of Cape
Cod in tide-pools on rocky shores, and in deep water near
the shore. It is only in the warmer season, however, that one
may witness a scene like that portrayed in the illustration.

In addition to the species here mentioned there are several
other species on the Atlantic coast. The Pacific coast is
also well supplied with starfishes, some of which are con-
siderably more than a foot in diameter. While most of the
starfishes have only five arms, as pictured in Fig. 120, some
have as many as twenty arms. When the winter storms
come on, starfishes and many other tide-pool animals that
are not fixed permanently migrate to the deeper water, in
order to be in more protected places.

External Structure. Up to this chapter we have been giv-
ing our attention to animals that have a perfect, or slightly
modified, bilateral symmetry. The starfish evidently has a
plan of structure for which we must find some other name.

Instead of organs and structures being paired on the two
sides of the body they are repeated around a central axis
like the spokes of a wheel. In a specimen we observe five
arms extending from a central region. The position of the

221

222 GENERAL ZOOLOGY

arms with reference to the central region, or disk, is practi-
cally the same as the position of radii in a circle. Hence we
say that the starfish is radially symmetrical. We find it
necessary also to change a few terms of location. In the
picture of the tide-pool study we are looking down upon the
aboral surface of the three starfishes. The opposite side has
the mouth at the center, and for that reason is called the
oral surface.

The aboral surface and part of the oral surface of Asterias
is thickly set with hard, limy spines that arise from small
plates of the same material just within the skin. Between
the spines there are many short, soft projections — the gills.
The spines of the oral surface are longer and more pointed
than those of the aboral surface. By examining the aboral
spines with a hand lens one can make out a circle of very mi-
nute structures surrounding the base. Each of these struc-
tures consists of a short stalk supporting two branches that
open and close like nippers. These short stalks with their
branches are called pedicellarise. The body surface is kept
clean by the pedicellarise, and small animals are prevented
from injuring the delicate gills by the protective action of
these same organs.

Along the middle of the oral surface of each arm there is a
groove which begins at the mouth and ends near the tip.
The roof of the groove is formed by two series of flat, cal-
careous plates, set together like the rafters of a frame house.
Between the plates four rows of slender, flexible tube feet
(Fig. 121, ab) extend to the outside. The groove is called the
ambulacral groove, because it protects the ambulacral organs
(Lat. ambulare, "walk"). A few of the ambulacral organs
(tube feet) near the tips of the arms are sense organs for
"smelling" food. The remainder are the organs of locomo-
tion. At the very end of each arm there is a small red eye,
protected by a circle of spines.

Fig. 120. Tide-pool study of starfishes, East Point, Nahant,

Massachusetts

224

GENERAL ZOOLOGY

One who has not observed a living starfish gets the idea
from preserved specimens that the body is rigid, and that
the plates of the skeleton make the arms inflexible. Such is
not the case, for the body of the living animal is very supple.
The Water- Vascular System. On the aboral surface at one
of the angles between the arms lies a small round disk usu-
ally of different color from
the surrounding parts (Fig.
121, ra; Fig. 122; Fig. 123).
This is the sieve plate, some-
times known by the name
madreporic body. The plate
is perforated with fine holes,
through which the sea water
passes to the stone canal (Fig.
121, s; Fig. 123). Near the
mouth the stone canal joins
the ring canal (Fig. 121, r;
Fig. 123), which in turn joins
five radial canals (Fig. 121, c ;
Fig. 123) that extend through
the middle of the roof of the
ambulacral groove. Many
short tubes branch off in pairs
from the radial canals and
join the tube feet. At the exposed end of a tube foot is a
sucking disk ; at the inner end is a bulb-shaped expansion,
the ampulla (Fig. 121, a; Fig. 122; Fig. 123). From the
sieve plate to the tube feet there is a continuous cavity, and
because of the fact that water passes through the entire set
of tubes it is called the water-vascular system.

This system of tubes provides the starfish with its means
of locomotion. The walls of the tube feet and ampulla? are

iFrom Hertwig-Kingsley's Manual of Zoology.

Fig. 121.

Water-vascular system
of starfish

a, ampullae ; ab, tube feet ; c, radial
canal ; m, sieve plate ; n, radial nerve ;
p, Polian vesicle ; r, ring canal, with
nerve ring beneath it ; s, stone canal ;
t, Tiedemann's vesicle l

THE STARFISH AND SOME ALLIES

225

muscular. There are valves in the branches of the radial
canals which lead to the tube feet. The entire system is
filled with water which enters through the sieve plate. It
is a well-known fact in physics that water is not readily
compressible. This means that when the tubes are filled

"

<

0 5* " J

Regenerating
ray-

Anus

Intestinal cseca-

Sieve plate

Pyloric cxcumj
cross section

-rvKtrFosition
^ -of eye

'Ambulacral
plates

-'—Ampulla

St Retractor muscle

of stomach
~~ Stomach pouch

jjg^— Reproductive gland

Tube of pyloric cseca

- %- Pyloric caecum

Tube foot---- -*>£ -r^yfy

Reproductive gland
cross section

mm

IB

Fig. 122. Dissection of a starfish ; aboral view. (Slightly reduced)

with water a contraction of the muscles in the ampullae
forces the water out into the tube feet. But since the tube
feet are already filled with water, their muscles have to re-
lax and permit the tubular part of the foot to stretch out
longer in order to make room for the water entering under
pressure from the ampullae. When a whole group of tube
feet are thus extended to full length, the disks on the ends
of the feet are pressed against some object and by suction
become attached.

226

GENERAL ZOOLOGY

The longitudinal muscle fibers in the tube feet then con-
tract and drive the contained water back to the ampullae.
When the scores of tube feet in the advancing arms of
a starfish contract they pull the body along and extend
again to renew their hold. The arms themselves, mean-
while, are turned up a little on the tips and remain in
a more or less set attitude. They may bend now and
then to pass an obstruction. When it is necessary the

Interradial pouch

of intestine
Sieve plate
Stone canal

1 g 1 v - •

Anus

Intestinal csecum

l

Cavity of pyloric csecum
Pyloric caecum

Calcareous plate j
Reproductive gland j
Nerve ring

^mm^^pulla I h*?** «**
| ! i | Stomach pouch Tuhe foot
Retractor muscle of stomach
Mouth ' i Radial nerve

Ring canal Stomach

Fig. 123. Dissection of a starfish in oral to aboral section.

(Slightly reduced)

animal becomes quite flexible. It can bend its arms and
central disk and pass through seemingly impossible holes.
Digestive System. In the animals that have been studied
previously, the digestive system has been a more or less
complicated tube running straight through the body, or
sometimes coiled. The digestive system in the starfish is
entirely different (Fig. 123). There is a circular mouth
which leads directly into a large stomach filling most of
the space within the disk. Two short pouches, or pockets,
extend from the stomach into each arm, thus giving more
space for digestion. From its aboral end the stomach
gives off five branches, one to each arm. Each of these

THE STARFISH AND SOME ALLIES

227

branches divides to form a pair of pyloric cseca. These are
glands which aid in digestion. The intestine, which leads
from the stomach to the aboral wall of the disk, is very
small. It is too small to carry the undigested waste from
the stomach and probably serves only to remove small quan-
tities of waste. Any solid waste particles must pass through
the mouth. A pair of small branched tubes, called the in-
testinal cseca, are attached to the intestine. Recent studies
indicate that these cseca
pulsate in the living star-
fish and probably serve as
respiratory organs. The
function of the pyloric
cseca is digestive ; they
secrete a fluid analo-
gous to the digestive
fluid of the earthworm
and the clam. The in-
testine ends at the anus
(Figs. 122, 123), which
lies near the center of
the aboral surface.

Aster ias feeds on oys-
ters, mussels, clams, and

snails. Many fanciful theories have been proposed in the
effort to explain how the starfish is able to get at the soft
parts of animals with thick, heavy shells. By referring to
Fig. 124 we can see the attitude of Asterias when it has
captured an oyster. While crawling along the bottom the
hungry starfish "smells" its prey by means of the tube feet
at the tip of the arms. It then moves in the direction of
the oyster or mussel and arches itself over the shell, touch-
ing the bottom all around with the tips of its arms. Next
it turns the shell about until the hinge ligament rests on

Fig. 124. Starfish devouring an oyster.
(Reduced) ■

Photograph by Dr. H. M. Smith ; courtesy
United States Bureau of Fisheries

228 GENERAL ZOOLOGY

the bottom and the free edges of the closed valves lie just
beneath the captor's mouth. Then the starfish takes a firm
hold on the bottom with the tube feet of the outer portion
of its arms and simultaneously applies the suckers of the
remaining tube feet to both valves of the mollusk.

Then the struggle begins. The mollusk has long before
closed its valves tightly by means of its strong adductor
muscles, and the only way the starfish can get at the soft
parts is to force the valves open. This it does by a long-
continued, steady pull on the surface of the valves, with
two sets of tube feet drawing in opposite directions. The
mollusk has great momentary strength, but it seems to be
as difficult for it to keep up the strain as it is for a man to
hold out his arm several minutes at a time. A single tube
foot of the starfish is very weak, and the combined strength
of all its tube feet measures less than the momentary
strength of an oyster. Yet, even with the exertion of much
less than its full strength, the starfish can open the valves
in from fifteen to thirty minutes.

As soon as the valves are open a few millimeters the star-
fish contracts certain muscles in its body cavity, which
bring the stomach down toward the oral surface and cause
it to pass through the mouth opening, turning inside out
on its way. The everted stomach is applied to the soft body
of the mollusk, and digestion and absorption begin imme-
diately. With slight variations this is the method which
starfishes employ in opening and digesting oysters, snails,
and other mollusks.

Starfishes are one of the most serious enemies of the
oyster industry. Oyster fishermen drag mop-like tangles
over the oyster beds. Starfishes become entangled in the
fibers and are then brought to the surface and destroyed.

The Circulatory, Respiratory, and Excretory Systems. The
circulatory system is too small to be indicated in drawings

THE STARFISH AND SOME ALLIES 229

on the scale of the dissection drawings. A very delicate
circular blood vessel lies just below the ring- canal of the
water- vascular system and sends a branch into each arm
below the radial canal. The body cavity is filled with a
fluid similar to the blood, which is colorless. The system of
blood vessels is not complete.

The body gets much of the oxygen it needs by way of the
water-vascular system. The remainder comes in through
the many short-branched gills, that cover the aboral sur-
face between the spines like the pile of a soft mat. The
gills are thin-walled tubes continuous with the body cavity
through openings between the plates of the skeleton. Thus
the fluid within the body cavity also fills the gills. In the
gill this body fluid gives up its carbon dioxide to the water
bathing the surface of the gills, while at the same time dis-
solved oxygen in the water passes through the delicate walls
of the gills into the body fluid. As mentioned on page 227,
the intestinal caeca also probably aid in respiration. Car-
bon dioxide passes out through the same organs which bring
in the oxygen.

The diagram shows nine bulb-like organs on the outer
margin of the ring canal. These are called the Polian vesicles
(Fig. 121, p). The small glandular bodies, Tiedemann's vesi-
cles (Fig. 121, t), which join the Polian vesicles are thought
to have the function of producing amcebocytes, described
on page 243. The cells on escaping into the body cavity
consume the waste substance of metabolism and make their
way through the body wall, perishing on the outside. Aste-
rias has no definite organs of excretion, like kidneys or
nephridia.

The Nervous System. If an observer takes a live starfish
and parts the tube feet in an arm so that the animal's skin is
exposed between the second and third of the four rows, he
may see the dead-white, radial nerve cord extending along

230 GENERAL ZOOLOGY

just beneath the skin (Fig. 123). Fig. 121 shows the posi-
tion of the nerve ring just beneath the ring canal. The
circular blood-vessel lies between the ring canal and the
nerve ring.

Reproduction and Development. The sexes of the star-
fishes are separate, but externally there is no difference be-
tween them. At the time the dissections were made for
the drawings, the sexual glands in the specimens were small
(Figs. 122, 123). As the first of June approaches, the ten
sexual glands increase in size until they occupy all the
available space in the body cavity of the arms. The ovaries
of the females, when they contain ripe eggs, are bright orange
in color ; the spermaries of the males are a light cream color.
From about the first to the middle of July, in the latitude of
Boston, the sexual cells are sent out into the water through
ten small holes on the aboral surface, two at each angle be-
tween the arms all around. The egg cells are fertilized by
the sperm cells in the water, and within a few hours the
young starfish in the blastula stage (see page 134) is swimming
about at the surface by the aid of cilia. The most striking
incident in the development of a starfish is the change that
takes place after about three weeks of life as a free-swim-
ming larva, when it settles toward the bottom and fastens
temporarily to a seaweed.

Until this time the body of the larva has been bilaterally
symmetrical, showing no evidence whatsoever of the radial
arrangement characteristic of the adult. On the posterior
region a star-shaped bud is formed, which becomes the
adult starfish. As the bud grows it draws into itself the
larva which gave rise to it. The starfish attains the stage of
sexual maturity within a year.

Regeneration. It is not unusual to find in a lot of star-
fishes dredged from the bottom many specimens that have
one or more arms shorter than the others (Fig. 122). This

THE STARFISH AND SOME ALLIES 231

means that some accident has befallen the irregular speci-
mens, and that new arms are being formed to take the place
of those that were lost. It has been found that a starfish
deprived of all its arms will, under favorable circumstances,
reform all five ; but one that has suffered an injury as exten-
sive as a cut through the entire disk probably never survives.
Serpent Stars and Basket Stars. The serpent stars and
brittle stars (Ophioder'ma) have slender arms which are
much more sharply marked off from the disk than are those
of the common starfish. They are much less abundant
than the common starfish, and being nocturnal in habits
are rarely about in the daylight. The tube feet play no
part in the locomotion of these animals, for the flexible
arms move very readily and, clasping around objects, move
the entire body much more rapidly than is possible to the
common starfish. The food is chiefly small organisms and
decaying organic matter. The basket star (Gorgonoceph'alus)
lives in the depths of the ocean, where the pressure of the
water is very great. The arms are very finely branched.

The Sea Lily

At the present day we find here and there in the compara-
tively warm, deep waters of the ocean, animals like that
shown in Fig. 125 (Pentacri'nus bla'kei). In past geological
eras the crinoids to which the sea lily belongs were very
widely distributed, and fossil remains are abundant in many
localities. Members of the genus Pentacrinus may be ob-
tained by dredging in the deep waters about Porto Rico,
and in the South Pacific and the Indian oceans.

The sea lily is a relative of the starfish and the basket
star. The central disk and the radial arrangement of the
arms make the resemblance striking. The sea lily is differ-
ent from the starfish and the basket star in having a long

232

GENERAL ZOOLOGY

i#

I

li

'i

I

iter

miim

stalk which grows from the center of the aboral surface and
sends root-like branches in among the rocks at the bottom.

The mouth and the arms lie on
the oral surface, which is upper-
most. A water- vascular system
is present, but it is of no service
in locomotion. Movement in
Pentacrinus is limited to the
arms. Food is brought to the
mouth by the wave-like action
of cilia on the inner edge of all
the arms.

Sea Urchins and Sand
Dollars

Sea urchins and sand dollars
have no arms. The entire ani-
mal (Fig. 126) is contained in a
hard shell which in the urchin is
roughly hemispherical, and in
the sand dollar is flat and disk-
shaped as the name indicates.
There is a large opening in the
shell on the oral surface for the
mouth, and fine double rows of
small openings for the tube feet.
The body is covered with mov-
able spines. The sea urchins live
chiefly on rocky ocean shores,
where they feed upon seaweed
and upon both living and dead
animals. The sand dollars bury
themselves in the sand and feed chiefly on the microscopic
plants and animals living in the sand and mud.

FA

Fig. 125. Sea lily
From Report of H. M. S. Challenger

THE STARFISH AND SOME ALLIES

233

Practically any tide pool along the north Atlantic coast
that affords specimens of starfishes will harbor several
sea urchins. The geographical distribution of the species
Strongylocentro'tus drobachien' sis (Fig. 126) is very wide.
It is found on the coast of Great Britain and Norway, along
the north Atlantic coast, and also on the north Pacific coast,
— in all these regions
from tidewater down
to several hundred
fathoms.

If deprived of its
spines a sea urchin
suggests, as Professor
W. F. Ganong has
aptly said, "an old-
fashioned door-knob,"
for it is flattened on
its oral surface and
curved above into a
rounded dome. From
the center of the dome
one may trace down-
ward twenty radiating rows of calcareous plates, fitting
against one another closely. Five pairs of these plates radi-
ating at equal angles have many fine holes for the tube feet ;
five other pairs of plates lie in the spaces between the regions
of tube feet. All over the aboral surface and over most of
the oral surface, the plates bear short, rounded knobs on
which the spines fit and form a ball-and-socket joint. On
each tube foot area at the point nearest the center of the
aboral surface lies an eye; and between every two eyes
there is an opening for the eggs or spermatozoa to emerge.
A sieve plate lies in one of the spaces between two eyes.
The mouth has five sharp teeth which meet together in a

Fig. 126. Photograph of a sea urchin.
(Slightly reduced)

234 GENERAL ZOOLOGY

point. The breathing organs are finely branched gills, located
on the oral surface around the mouth.

It feeds on both animal and plant substance. Small ani-
mals are captured by the tube feet. The tube feet may be
extended to a distance equal to half the diameter of the
body ; they affix by the sucking disk to some small creature
and draw it to the mouth. All food is then ground into bits
by the five sharp teeth before being swallowed.

A sea urchin, when taken from the water and placed in a
person's hand, causes a gentle tickling of the skin. This it
does with its movable spines. The spines may be of use as
levers in pushing the body along, but locomotion in a defi-
nite direction is accomplished by the tube feet on the oral
surface, aided by some of those on the aboral surface, all
extending and contracting much as in the starfish. The
uppermost tube feet are used as tentacles for feeling and it
may be for smelling also.

In certain parts of our eastern coast members of the
genus Strongylocentrotus live in cavities -in the rock which
are excavated by the animals themselves. A related species
living on the coast of California burrows a hole in the solid
rock deep enough to conceal itself entirely. No one knows
positively how the burrowing is done. Probably three fac-
tors take part to a varying degree, — gnawing by the teeth,
slow grinding by voluntary movement of the spines, and
incessant slight turnings of the whole body by the waves.

The Sea Cucumber

Sea cucumbers of various species are found in every
ocean. The species represented in Fig. 127 (Cucuma'ria
chronhjel'mi) is found in Puget Sound, Washington. It lives
on the bottom.

The animals are about four inches long. The body is cylin-

THE STARFISH AND SOME ALLIES

235

drical, but without calcareous plates that touch one another
and keep the form constant. The only trace of a skeleton
comparable to that of the sea urchin consists of scattered
bits of calcareous secretions of definite form beneath the

Fig. 127. Photograph of a living sea cucumber. (Natural size)

skin. Although the sea cucumber is radially symmetrical,
having the five double rows of tube feet along the cylinder,
we can speak of the anterior and posterior ends because the
animal lies flat.

The anterior region is the oral region. At the center we
observe the round mouth, about which are the ten branch-

236 GENERAL ZOOLOGY

ing tentacles. Internally there is a water- vascular system
with a ring canal and radial canals. In respiration water is
drawn into the intestine at the aboral end, and an exchange
of gases takes place through internal gills that join the
intestine.

The tentacles in the picture are not extended in the usual
radial direction. The reason is that when photographed the
animal was using its tentacles as well as its tube feet to
crawl along the bottom of a dish of sea water. When the
animal is at rest the tentacles are probably used to capture
small animals and to pass them to the mouth.

Relatives of Cucumaria have been known by observers
to disgorge the entire set of internal organs through the
mouth opening. In captivity they appear to do this when
placed in unfavorable situations. It is not so remarkable
that they should lose their internal organs, as it is that they
should regenerate them all again as perfect as ever. If sea
cucumbers throw out their internal organs in nature, it
would appear to be a very expensive process. Since they do
perform this action, in nature as well as in captivity, there
must be some reason for it. The only reason that suggests
itself is based on the fact that fish prey upon sea cucumbers.
The sea cucumber is a slow-moving animal, and once seen
by a roving fish the chances of escape under ordinary cir-
cumstances would be few indeed. If the prospective victim
when disturbed were to eject its internal organs into the
water, the fish, true to the instinct of its kind, would gobble
up the swiftly moving object, and probably go away
satisfied.

Sea cucumbers are prepared and used as food by the
Chinese, and it is reported that the Siwash Indians of the
northwest of the United States eat them, and sea urchins
also.

THE STARFISH AND SOME ALLIES 237

Definition of Echinoderma

Each of the five animals described in this chapter repre-
sents one of the five classes that make up the phylum
Echinoder'ma (Gr. echinos, "hedgehog"; derma, "skin").

The most important characteristics of the phylum are the
radial symmetry of the body; the occurrence of repeated
divisions or organs of the body to the number of five, or
in multiples of five ; the existence of a water- vascular sys-
tem ; and the presence of limy plates in the skin, arranged as
either a continuous shell or as scattered plates. No other
phylum has parts occurring in fives, and none other has a
water-vascular system.

CHAPTER XXI

AN EARTHWORM

I guess the pussy-willows now
Are creeping out on every bough

Along the brook ; and robins look
For early worms behind the plough.

Henry van Dyke, An Angler's Wish

Habitat and Distribution. The animal (Lumbri'cus terres'-
tris) which is the subject of this chapter is distributed
widely throughout the world. This and very many other
species live in the soil, where their burrows extend obliquely
downward, sometimes many feet. One rather common spe-
cies, Helodri'lus foz'tidus, marked by red and dark bands of
color, lives in manure heaps. When irritated it gives off an
offensive odor, whence its specific name. The species most
commonly used in laboratories is Lumbricus terrestris. It
is found in small, cylindrical burrows, which it makes in the
soil wherever it is not too dry or too sandy. In spite of the
usual habit of living in the earth, these animals can live
for many days in water. Representatives of the many
species and the few genera of earthworms are found in
practically all places from Arctic to Antarctic regions, in-
cluding isolated oceanic islands.

External Structure. In external structure the body of
an earthworm is very simple. The anterior end is slender
and pointed when extended in life, and the posterior region
is flattened above as well as below. The somites of the an-
terior region differ also from those in the posterior region in
being longer. There is no head, no thorax, and no abdomen.
There are no appendages except bristles, almost microscopic

238

AN EARTHWORM 239

in size, which occur in rows on the ventral surface of every
somite except a few at the anterior end. The openings of
the body are the mouth at the anterior end just beneath the
prostomium (lip), the anus at the posterior end, and various
openings on the ventral surface, which are connected with
internal organs to be described later. An earthworm has
no eyes, yet it knows of the existence of light, and shuns
intense light ; it has no ears, but it becomes aware of the
approach of an enemy by the jar communicated through
the soil. In a mature earthworm a thick band, consisting
of the thickened body wall, is visible at about one third the
length of the animal from the anterior end. This is called
the clitellum.

All the many species of earthworms agree very closely in
general structure and arrangement of the organs of the
body. However, the following discussion is of the single
species Lumbricus terrestris. Locations of the various organs
will not agree exactly for any other species. Besides the
more technical points of difference Lumbricus terrestris may
be recognized as the species that has the tail very much
flattened.

The internal anatomy of an earthworm seems, on refer-
ence to Fig. 128, to be very complicated, but each system
of organs has well-defined uses.

Digestion. The first division of the digestive system of the
earthworm is the mouth (Fig. 128), followed by the pharynx,
the latter having a very thick muscular wall. The pharynx
can be protruded slightly or retracted, and the cavity en-
larged by strands of muscle fibers which extend to the body
wall. Food, consisting of particles of leaves, animal tissues,
and even soil, is drawn into the pharynx by the sucking
action which takes place when the cavity of the pharynx is
enlarged. The food passes directly through the esophagus.
Before the ingested (swallowed) food reaches the crop the

240 GENERAL ZOOLOGY

secretion, and sometimes even hard particles from the
calciferous glands, mixes with it. This probably serves to
neutralize whatever acid may be present, and helps to
maintain the contents of the esophagus in an alkaline con-
dition. Thus the digestive fluid of the intestine, which is
alkaline in chemical nature, can act without interference.
The crop is a temporary reservoir for the food, and the
gizzard is the only place in the entire digestive system
adapted for dividing large particles of food into minute
pieces. Earthworms are known to swallow small, rough
pebbles, and even sharp pieces of glass, for the purpose of
using them in the gizzard to grind into bits other particles
which are swallowed as food. The strong muscles in the
wall of the gizzard, by contracting, grind the contents to-
gether, and every particle is worn smaller.

The process of digestion in an earthworm begins when,
on seizing food with its lip, the animal pours out a secretion
from glands in the pharynx. Digestion continues as the food
is being drawn into the pharynx, and while on its way
through the esophagus.

The digestive fluid of the earthworm resembles the diges-
tive fluid of the higher animals, in being capable of acting
on the three important classes of organic foods.

Circulation. Whenever an animal body is too large or com-
plicated for the food to reach all the cells directly, we find
a circulatory system developed. The circulatory system of
an earthworm is complete and rather complex. The dorsal
blood vessel extends the length of the animal, along the
middle, between the body wall and the alimentary canal.
The blood flows toward the anterior region in somewhat
regular "pulses," carried along by waves of muscular con-
traction in the wall of the blood vessel itself. Between the
pharynx and the crop are situated five pairs of "hearts."
These short tubes receive most of the blood that comes

Mouth a

Prostomium

First somite
--Second somite

Subesophageal ganglion

Subneural blood vessel %X

Internal end of nephridium- -1^-.^

Anterior seminal receptacle

Posterior seminal receptacle- -

Basal portion
of seminal vesicle -
External end of nephridium—^

Ventral blood vessel

Ovary r^fd

Oviduct

Body wall

Ventral nerve chain -It

— Supraesophageal ganglion
— Pharynx
- - Wall of pharynx

Retractor muscle of pharynx
- Beginning of esophagus

Seventh somite

First heart

Lateral blood vessel

--Septum

Anterior seminal
vesicle

- Calciferous gland

-Fifth heart

~rfr Parietal blood vessel
J- fr~ Dorsal blood vessel

"Posterior seminal
vesicle

- End of esophagus

- - Crop

- Gizzard

sr * Intestine

Fig. 128. Dissection of an earthworm, Lumbricus terrestris. (x4)
Lateral blood vessels and connections. (After Johnston)

242 GENERAL ZOOLOGY

forward, take up the waves of contraction sent along the
dorsal vessel, and force the blood into the ventral blood ves-
sel, which carries it posteriorly in a regular flow. Below the
ventral nerve chain is the subneural blood vessel, in which the
blood probably flows backward. The lateral blood vessel, with
its connections, is limited to the region anterior to the crop.
Capillaries (fine blood vessels joining larger ones) branch
in the wall of the intestine and connect in a very complicated
fashion with all the large vessels. Absorbed food passes into
the capillaries and is carried with the blood to the larger
blood vessels, to be transported to all parts of the body.
All about the intestine, in the hollow spaces of the somites,
there is a large quantity of body-cavity fluid, which is very
much like the blood in the vessels, except that it is colorless.
It is thought that much of the absorbed food mixes with
this fluid. The outcome is the same with food carried by
the regular circulatory system and with that taken up by
the body-cavity fluid. This food is carried by the blood and
body-cavity fluid to all parts of the body, where it is assim-
ilated by the tissues.

Respiration. The earthworm has neither gills, tracheae,
nor lungs; still it can breathe quite as perfectly as the
animals which possess one or another of those organs. The
outer skin of the earthworm is thin and moist, and just
beneath it are capillaries. While in its burrow, or even in
water, air comes in contact with the skin, and its most im-
portant element, oxygen, passes through and mixes with
the blood. At the same time the blood in the capillaries
gives up its carbon dioxide, which passes through the skin
into the air.

Excretion. Carbon dioxide is given off only from the skin ;
water probably in part from the skin ; uric acid and water
are discharged from pairs of small funnel-shaped tubes in
the lateral portions of the cavity of the somites. These

AN EARTHWORM 243

excretory organs are called nephridia. They correspond in
function to the kidneys of* the higher animals. Each ne-
phridium opens into the cavity immediately anterior to the
somite which contains the greater portion of the organ. The
external opening of a nephridium is on the ventral surface.

The funnel-shaped end of a nephridium is lined with cilia
(hair-like structures). The cilia beat inward and carry such
liquid waste products as collect in the body cavity into the
tube of the nephridium. Blood vessels, which break up into
capillaries in the wall of the nephridium, also carry a cer-
tain amount of waste. The excess water and the nitrogenous
waste in the blood are separated in these capillaries and go
down the tube, to be discharged at the external opening.
The body-cavity fluid is filled with small, free-moving
cells, called amcebocytes. These amcebocytes are similar to
the white corpuscles of our own blood. They have the
power of changing their form quickly by extending irregular
pointed processes from any part of the cell body. Owing to
this power they can inclose any small particle of solid matter.

Nerve Control. In the preceding paragraphs we have been
considering the stages of metabolism, without making any
reference to the fact that no activity of internal or external
organs could take place in the body of an earthworm if it
were not for the controlling influence of the nervous system.
Ingestion, digestion, absorption, circulation, respiration,
and excretion constitute a chain of processes, largely be-
cause the nervous system, acting through the system of
muscles, especially in the digestive and the circulatory sys-
tems, causes them to take place according to a definite plan.
In order to understand how the nervous system of an earth-
worm acts, it will be necessary first to have some knowledge
of the structure of its nervous tissue.

The general plan of the nervous system of an earthworm
is similar to that of the grasshopper and the crayfish, but

244

GENERAL ZOOLOGY

less specialization is evident than in either of the other
animals. The " brain" (supraesophageal ganglion, Fig. 128)
is a simple, very small, bilobed ganglion, joined by connec-
tives to a subesophageal ganglion ; from the latter a pair of
connectives extend along the ventral wall of the body cavity
to the posterior end, with a ganglion in every somite. The
brain and ventral nerve chain constitute the central nervous

Cuticle of skin - -
Sensory nerve ganglion

Sensory nerve fiber

Anterior branch of
sensory nerve fiber

===^ _'.'■"* Longitudinal muscle fibers

Motor nerve fiber

. - Posterior branch of sensory
nerve fiber

Ventral nerve cord
Motor nerve ganglion

Fig. 129. Arrangement of nerve fibers for reflex action in the earthworm

Reconstructed from drawings by Havet

system. In each somite three pairs of nerves run out to the
muscles of the body wall and the internal organs. The en-
tire set of nerves leaving the central nervous system con-
stitutes the peripheral (surface or outlying) nervous system.
If we were to trace one of the nerves outward from the
central nervous system as it penetrates the muscular tissue,
we should find that it divides into many very fine fibers.
Certain fibers can be traced to the end as their fine branches
become attached to a muscle fiber. The nerve fiber that is
united with a muscle fiber (Fig. 129) is a slender portion

AN EARTHWORM 245

of a nerve cell, the nucleus of which is in the central nervous
system. Nerve cells of this type are called motor nerve cells.
Mingled with them is another type of nerve cell, which has
its nucleus in a sense organ at or near the skin of the animal
and with the terminal portion of its principal fiber extend-
ing into the central nervous system. Cells of this type are
called sensory nerve cells.

Reflex Action. In case an object touches one of the fine
sensory hairs on the skin of an earthworm, a message, or
impulse, is sent along the sensory fiber to the ventral nerve
chain. There the impulse is transferred to the motor nerve
cells. When the impulse reaches the end of the motor fiber,
the muscle fiber to which it is attached contracts. When
many sensory nerve cells are stimulated in this way, many
motor cells will carry out the transferred impulse, the
muscles will contract, and the animal moves away. This
kind of nerve action is called reflex action because, in a
sense, the impulse is reflected back from the ventral
nerve chain.

Reproduction. Every earthworm contains both sper-
maries and ovaries. As explained on page 206, animals
which have the male and female glands in the same body
are called hermaphrodites. There are two pairs of sper-
maries in an earthworm, hidden in the three pairs of seminal
vesicles, indicated in Fig. 128. The single pair of ovaries is
very small. Although each earthworm produces sperma-
tozoa, or sperm, and eggs, the eggs of one individual are
always fertilized by the sperm of another.

Reproduction takes place chiefly in the spring. On warm
spring evenings the worms crawl from their burrows and
lie stretched out on the surface of the ground with the tail
still holding tight in the mouth of the burrow. While in
this position two individuals may become paired in the act
of copulation. The two worms have the ventral surfaces to-

246

GENERAL ZOOLOGY

gether for about one third of their length, with the "heads"
pointing in opposite directions. This position brings each
worm in a position such that the small openings which lead
into sperm-receiving sacs (seminal receptacles) are in con-
tact with the openings of the male reproductive organs of the
other individual. Each worm expels a quantity of its sperm
into the seminal receptacles of the other. In these recepta-
cles the sperm is retained until the eggs are ready to be laid.

n
m

A B C

Fig. 130. Egg capsule, egg, and spermatozoon, of earthworm

A, egg capsule; B, egg with nucleus; ov, eggs; C, spermatozoon: n, nucleus;

m, middle piece ; t, tail *

The presence of the thick band, the clitellum, referred to on
page 239, indicates that the individual is sexually mature.
The clitellum is provided with glands on its ventral surface.
Just preceding the time of egg-laying these glands secrete
a thick mucus which forms a band about the clitellum. The
band of mucus is then moved forward slowly. At the four-
teenth somite the eggs are caught up from the oviduct, which
forces them out, at the time the band, or capsule, passes.
Farther forward the sperm that has been stored in the semi-
nal receptacles is received into the capsule. At the anterior

1 From Sedgwick and Wilson's General Biology.

AN EARTHWORM 247

end the capsule begins to draw together at the ends, and
when this egg capsule (Fig. 130, A) has been pushed off it
is a short, spindle-shaped, tough-coated sac, about as large
as a grain of wheat. Inside the capsule each egg unites with
a sperm in the act of fertilization.

Egg capsules are found buried in the soil and under stones
and boards and other protected places. They are often mis-
taken for seeds of some plant, which accounts for their iden-
tity being unknown to most people.

Relation to Environment. We could find no animal better
than an earthworm to show how an organism may be adapted
to its environment. In the first place, the slender, rounded
body with its pointed anterior end is the best possible form
for movement through the soil, which is usually displaced
by muscular effort. The appendages, which in the earth-
worm's relatives are never hard enough to be used for dig-
ging, are here only minute bristles. The animal is thus not
impeded by useless organs. The smooth skin is thin, and
since it is kept moist it serves as a breathing surface.
Branched gills such as are developed on many relatives of
the earthworm that live in the sea, would in an earthworm
be not only superfluous but even much in the way.

It is a wonderful fact that the earthworm has no eyes and
still is able to distinguish light from darkness ; for, except in
the time of a rainstorm or in case of disease, it never leaves
its burrow in the daytime. Earthworms not only know the
direction from which light comes but they crawl away from
light of high intensity and crawl toward light of low inten-
sity. In nature earthworms come out at night in the warm
season, probably in response to the stimulus of a low in-
tensity of light, but also for the purpose of obtaining food.
They often leave the tail firmly anchored in the mouth of
the burrow by means of the projecting bristles. When dis-
turbed they spring back into the opening with incredible

248 GENERAL ZOOLOGY

speed. It is interesting to observe them with the help of a
pocket flash light on a warm rainy night in spring or early
summer.

When earthworms rest in the daytime, just below the
mouth of their burrows, they do so probably as the result
of at least four stimuli, — light, heat, fresh air, and mois-
ture. If certain of these stimuli were taken away, or even
changed in degree, the earthworm would undoubtedly move.

For example, if the moisture of the ground should become
lessened by continued dry weather, the animal would have
to forego the fresh air and retreat in order to prevent its skin
from drying, which would shut off respiration altogether. If
moisture becomes too great, as in a rainstorm, the burrows
are filled with water, and most of the oxygen in the narrow,
close quarters is driven out and the rest is soon used up.
The earthworm is then compelled, if it has been resting near
the surface, to leave its burrow and crawl about. This it
may do in protected places without serious results, since the
heat at such times cannot have its drying effect on the skin.
When the storm is over, those that are not caught up by
birds or trampled under foot by large animals can make
their way into the soil again.

A food supply is assured to them, for besides the leaves
which they drag into their burrows, they devour the soil
itself, taking it into their mouths as they burrow along.
Black soil called humus is made up of the usual soil min-
erals, mixed with a large amount of decaying vegetable
matter and some animal matter. Completely decayed or-
ganic matter is that which has returned to its original
inorganic, mineral state. The partially decayed organic
matter can still be used as tissue-building and energy-
producing food ; it is this which the earthworms get in
the soil they swallow.

AN EARTHWORM 249

It is one of the habits of earthworms to come to the sur-
face at night to void the indigestible contents of the intes-
tine. The coiled, worm-shaped " castings" are familiar to
anyone who has noticed the ground where the grass is thin,
even by the sides of much-used pavements in cities. The
soil in the castings is usually brought from depths varying
from a very few inches to as great a depth as five feet.
Observations made by Darwin extended over a period of
more than forty years. During that time he also collected
facts from all parts of the world and published a book en-
titled The Formation of Vegetable Mould through the Action
of Worms. His observations are extremely valuable to us
now, for they show how small agencies acting over wide
areas, through ages or even years of time, can yield tre-
mendous results.

If every active earthworm voids its castings at the sur-
face, fallen leaves, sticks, and other bits of organic objects
will in a short time be covered with a thin coating of earth
brought up from beneath. The acids present at all times in
the soil attack and disintegrate the organic matter, thus
enriching the soil with the minerals of which the growth of
extensive crops may have deprived it. Darwin determined
the rate at which objects once upon the surface gradually
sink to lower depths. Layers of cinders, chalk, stone, and
the like were strewn upon small fields, and trenches were
dug from year to year to ascertain the progress of the earth-
worms' activity. In fields of ordinary fertility, having an
average supply of worms, the amount of earth brought to
the surface and spread out more or less evenly is one fifth
of an inch a year. In the course of comparatively few years
this is sufficient to conceal from sight objects of considerable
size. Indeed, Darwin witnessed a sterile, stony field with
flints "as large as a child's head" transformed into a fertile,

250 GENERAL ZOOLOGY

grass-covered pasture, "so that after thirty years (1871) a
horse could gallop over the compact turf from one end of
the field to the other, and not strike a single stone with its
shoes. This was certainly the work of worms, for, though
castings were not frequent for several years, yet some were
thrown up month after month, and these gradually in-
creased in numbers as the pasture improved/ '

Estimates which Darwin based on careful observations
indicate that over fifty thousand earthworms find plenty of
working room in an acre of ground, and that these bring
to the surface annually from fourteen to eighteen tons of
earth.

CHAPTER XXII

ALLIES OF THE EARTHWORMS : ANNELIDA

Sinuous, glittering worm of the sea,
Wondrous in sheen of ruby and green.

The Sandworm. One of the commonest of the animals liv-
ing in the mud and sand at tide level in protected bays and
inlets of all the oceans is the sandworm, known more defi-
nitely by its scientific name Ne'reis vi'rens (Fig. 131). It
lives in burrows lined with a thick mucus. This unites the
grains of sand into a tough, black tube. The depth of these
burrows depends on the length of the animal, which is
sometimes as great as two feet. Like earthworms, sand-
worms often rest with the head near the opening during the
day. Sometimes at night they leave their burrows to swim
at the surface. It is likely, however, that in most cases they
do not withdraw the entire body from the burrow, but
reach out in all directions for prey that comes near them.
When driven from their burrows in the daytime they swim
away, and at that time look very beautiful, as the couplet
above suggests. Nereis has two horny jaws, sharp-pointed,
and bending to meet at the tips. The jaws are concealed by
the infolded pharynx when not in use. When about to
seize its prey, which consists chiefly of small, living sea
animals, the sandworm suddenly everts the pharynx, and
the jaws, thus freed, at once spread horizontally and seize
the victim.

Comparison of the external appearance of the sandworm
with that of an earthworm brings out some points of differ-
ence, as well as some points of similarity. We observe the

251

252

GENERAL ZOOLOGY

same division into somites of approximately uniform struc-
ture throughout the body. Fully developed locomotor
organs, and a distinct head with eyes and tactile sense
organs, serve to adapt Nereis to its environment.

The Tube Worm. The name "tube worm " applies equally
well to many genera of slender animals in the sea that live

i

Fig. 131. Living sandworm. ^Reduced)

continuously in tubes of mud, sand, or limy secretions. In
Amphitri'te orna'ta (Fig. 132) the gills occur only at the
anterior end, where they may obtain oxygen from the cir-
culating water above the animal. To counterbalance the
disadvantage of a fixed habitat, Amphitrite has many long
tentacles which extend out over an area sometimes of three
square feet. These tentacles are covered with scattered, fine
bristles and with many cilia; the cilia are waving con-
stantly toward the animal's mouth, carrying in the micro-
scopic food present in the water. At the same time the
bristles, aided by mucus which is secreted from glands on

ALLIES OF THE EARTHWORMS

253

the tentacles, catch up grains of sand. These are added to
the little hummock that conceals the mouth of the tube.

The Leech. Most species of leeches are known to be
temporary parasites on other animals. Placobdel'la rugo'sa
(Fig. 133) feeds very
commonly upon the
blood of turtles. It is
about two inches long
and broader near the
posterior end than
elsewhere. The an-
terior and posterior
sucking disks on the
ventral surface are
used for holding on to
a support and for lo-
comotion. Placobdella
"loops" itself along,
but it cannot swim,
as some other species
of leech can, although
no leeches have ap-
pendages.

The body of a leech
is divided into thirty-
four somites, while

these are superficially divided into two and sometimes more
rings. Two eyes lie close together on the dorsal surface of
the third somite. The mouth is on the ventral surface in the
anterior sucking disk. The pharynx can be rolled out as in
Nereis. The color of Placobdella is described by Professor
Moore, of the University of Pennsylvania, as a "pepper-
and-salt mixture of various light and dark browns, yellows,
and greens." Around the margin are light-colored patches.

Fig. 132. Photograph of a tube worm.
(Slightly reduced)

1, thread-like gills; 2, tentacles

254

GENERAL ZOOLOGY

The digestive system of a leech secretes substances that
prevent the blood used as food from clotting. This is in-
teresting because after a leech is filled with blood it has
enough food to last it for several months. When gorged

with blood a leech is relatively inac-
tive, staying in some secluded place
until ready to seek new prey.

Leeches of a different genus
(Pisci'cola) frequently become
parasitic on fishes. The horseleech
(Hsemop'is marmora'tis) lives only
part of the time in water and
spends much time burrowing in
the soil. This species is largely
a scavenger, though it also feeds
snails, earthworms, and other
small animals, and
frequently becomes a
bloodsucker. Some
species in the tropical
countries live on land
permanently and are a
great nuisance to pe-
destrians in the forests.
There are two differ-
ent kinds of wounds
made by leeches. Some
leeches have three saw-like jaws which cut a Y-shaped open-
ing in the skin. The jawless leeches have a conical lancing
organ in the pharynx with which they pierce the skin.

Bloodsuckers feed upon human blood of bathers in
fresh-water streams and lakes of many regions. In the not
very distant past leeches were commonly used by physi-
cians as a relief from many diseases. Blood-letting was then

Fig. 133. Leech. (Slightly reduced)

ALLIES OF THE EARTHWORMS 255

considered good medical practice, and living leeches of a
species known as the medicinal leech were regularly carried
in stock by the apothecary shops.

Leeches are hermaphroditic. Placobdella rugosa carries
its eggs in a gelatinous mass on the ventral surface. When
the young hatch they live for several weeks attached by the
posterior sucker to the parent, as shown in the picture.

Definition of Annelida (Lat. annulus, "ring "). The earth-
worm, sandworm, tube worm, and leech have certain char-
acters in common. The body is divided into somites of
nearly uniform shape, the characteristic form being a ring.
From that resemblance the name of the phylum Annel'ida
is derived. A conspicuous space, the body cavity, or ccelom,
lies between the digestive tract and the body wall in every
somite.

CHAPTER XXIII

ROUNDWORMS: NEMATHELMINTHES

Very close and diligent looking at living creatures, even through the best
microscope, will leave room for new and contradictory discoveries.

George Eliot

Ascaris. As'caris lumbricoi'des is often found as a para-
site in the intestine of man. The body, which is cylindrical
and tapering at both ends, is frequently over ten inches in
length and in diameter as large as an ordinary lead pencil.
The sexes are separate, and the male is always considerably
smaller than the female. For a long time it was thought that
this parasite was relatively harmless. Very recently it has
been found that the young when taken into the digestive
tract with food or water do not become established there at
once as parasites. They first wander around, boring their
way through various organs of the body. In young pigs
they pierce the lungs in such numbers as to cause a dis-
ease resembling pneumonia. In the human being, Ascaris
is especially likely to occur in small children. This is due
to the fact that young children are not careful about what
goes into their mouths. Food dropped onto polluted soil con-
taining Ascaris eggs readily brings the eggs into a child's
mouth. Whether we are interested in saving children or
pigs from the ravages of Ascaris the same methods apply.
Sanitary surroundings are not favorable for the worms.

The structure of Ascaris is very simple. The digestive
tract runs as a straight tube throughout the length of the
body. The cavity between the digestive tract and the body
wall is filled with the coils of the reproductive organs.

256

ROUNDWORMS

257

Trichina. Trichinel'la spira'lis (Fig. 134, 1) is one of the
most dangerous of parasites. Like the tapeworm it requires
two hosts to complete its development. The adult trichina
may be found in the intestine of a pig, rat, or of man. The
female trichina, about three millimeters (one eighth of an
inch) long, bores into the wall of the
intestine and brings forth her young
alive. The young worms are carried
by the blood and lymph streams to
all parts of the body. When they
reach muscle tissue they come to rest,
and inclose themselves in a thick,
tough membrane or cyst (Fig. 134, 2),
remaining encysted until the muscle
is eaten by another animal. Then the
cyst dissolves, permitting the young
and still undeveloped trichinae to
grow and reach maturity in the in-
testine of the second host. If the
first host is the pig, the second host
may be the human being.

The danger to the human being
comes while the young are making
their way into the muscular tissue.
The boring of thousands and some-
times millions of these larval parasites
in the muscles disintegrates the tissue and causes a fever,
which is very frequently fatal. A simple preventive remedy,
which everyone should apply, is to see that all the pork that
is eaten is thoroughly cooked. Human beings are infected
less frequently by the trichina since the Bureau of Animal
Industry of the United States Department of Agriculture
established the system of inspecting packing houses (see
page 266).

Fig. 134. Trichina.
(Much enlarged)

1, parasite; 2, membrane

of cyst ; 3, muscle fiber of

pig. (After Leuckart)

258

GENERAL ZOOLOGY

Hookworms. One of the most spectacular members of
this group of roundworms is the hookworm. There are two
species, known, respectively, as the Old World hookworm

{Ancylos'toma duodena'le)
and the New World hook-
worm (Neca'tor america'-
nus). The story of the
conquest of the latter in
the southern part of the
United States is one of
the brightest chapters in
the history of preventive
medicine in this country.
The hookworms live
in the large intestine of
man. Though each hook-
worm is only about one-
half inch long, when they
are present in consider-
able numbers they pro-
duce serious diseased
conditions (Fig. 135).
These conditions are due
chiefly to two causes.
First, the mouth of the
worm is provided with
sharp tooth-like struc-
tures which pierce the
wall of the intestine and
cause constant loss of blood, upon which the worms feed.
In the second place, they produce poisons, which seriously
interfere with normal physical and mental development of
the infected person. The patient becomes lazy and shiftless
and, if a young person, fails to develop properly. A young

Fig. 135. The effects of hookworm

Two boys of about the same age, the one on
the left suffering from hookworm. (Photo-
graph by courtesy of the International
Health Board)

ROUNDWORMS 259

man of twenty may have the size and all the appearances
of a child about twelve or fourteen years old. It was long
thought that the shiftless and indolent "white trash" of the
South were lazy by choice. During the present generation it
was shown largely through the important works of Professor
C. W. Stiles that they suffered from a disease produced by
hookworms. Studies on the life history of the parasite and
its methods of getting into the human body were carried on.
It was found that only in unsanitary surroundings can the
hookworm disease exist, for the young worms get into the
soil only when it is polluted by the feces of a hookworm
patient. From the polluted soil the young worms come into
contact with bare hands and feet and bore their way into
the skin. Here they find blood vessels or lymph spaces and
are carried by the blood or lymph to the heart. From the
heart the larvae are pumped with the blood into the lungs.
The minute worms by boring their way through the capil-
laries get into the air sacs of the lungs. They then crawl up
the air passages into the mouth. The worms reach their
final abode in the intestine only after completing this journey
through the lungs. After being swallowed they pass in turn
from the mouth into the esophagus and thence through the
stomach into the intestine.

It was a triumph of medicine and of zoology when it was
discovered that hookworm can be prevented by correcting
unsanitary habits and living conditions, and educating the
people in proper preventive measures. An equal triumph
was the discovery of a simple cure for the disease. With the
removal of the worms, the patient not only is saved from
the disease but recovers his mental and physical devel-
opment as well. The American Hookworm Commission,
operating under the generous support of Mr. John D.
Rockefeller, has carried on an extensive program of educa-
tion in the South. In recent years Dr. M. C. Hall of the

260 GENERAL ZOOLOGY

Department of Agriculture in Washington discovered that
carbon tetrachloride is a much more effective cure for hook-
worm patients than any drug previously used.

Hair Snakes. A myth believed at least for a time by most
children in rural communities maintains that hair from a
horse's tail, if allowed to stand in water, turns into a hair
snake or hairworm. Many people think they have carried
on a scientific experiment when they put a hair into a water-
ing trough, and later find there a living, wriggling creature
very much like a hair in appearance. The performer of such
an experiment may not be aware that in the meantime a
grasshopper or a cricket has fallen into the watering trough
and from its body has crawled the long hair-like worm. The
Gor'dius, or hair snake, lives, as an adult, free in watering
troughs and streams. The female deposits long strings of
eggs, which hatch into microscopic larvae, each provided
with a peculiar boring spine. By use of this spine the larva
drills its way through the body wall of a cricket or a grass-
hopper and comes to lie in the body cavity. Here it com-
pletes its growth but is not able to reproduce unless the
insect bearing it gets into water. Then the " snake " emerges
ready to continue life as a free individual.

Definition of Nemathelminthes. All the roundworms whose
bodies are not segmented but contain a body cavity belong
to the phylum Nemathelmin'thes (Gr. nema, "thread";
helmins, "worm").

The roundworms include some of the most important
enemies of man. As parasites they destroy his domestic
animals and crops and many attack man directly. They
produce disease and in some localities reduce the inhabit-
ants to the lowest physical and economic standards of ex-
istence. Knowledge of these worms has been scanty until
recently.

CHAPTER XXIV

THE PLANARIANS, FLUKES, AND TAPEWORMS:
PLATHELMINTHES (FLATWORMS)

He prayeth best, who loveth best
All things both great and small ;
For the dear God who loveth us,
He made and loveth all.

Coleridge, The Rime of the Ancient Mariner

A Planarian. On the lower surface of submerged stones,
near the margin of ponds, there are many little black, or
white, flatworms. The most of these belong
to a genus called Plana'ria. Quite often a
larger specimen (10 mm. to 15 mm.) is found
among the others. This is most likely to
belong to the species Procot'yla fluviat'ilis
(Fig. 136). It is nearly colorless except for
a clouded middle region. Upon examination
with a simple lens an observer may distinguish
the organs of the interior with remarkable
clearness. The mouth is in the middle of the
under surface. It is at the end of a short pro-
boscis (the pharynx) which may be rolled
inside out. Microscopic food entering the
mouth may pass forward through a slender
tube, and into all the many branches, or it
may pass backward by two tubes and into
their branches. Branches from the digestive system carry
food directly to every part of the body. No separate cir-
culatory system has been developed. At the anterior end
beneath, there is a shallow sucker for holding on to stones

261

Fig. 136. A pla-
narian. (x 10)

262 GENERAL ZOOLOGY

or plants. Above there is a pair of small eyes of very simple
structure. The body is not divided into somites. Each indi-
vidual is hermaphroditic, but in many instances reproduc-
tion takes place asexually. In asexual reproduction the body
becomes constricted and separates into two parts, each of
which then grows the missing portion. Thus by fission two
complete individuals result from the division of a single
specimen. In addition to this normal means of asexual
reproduction planarians have extreme powers of recovery
from injury. Even a small fragment cut from the body of
one of these worms has the ability to produce a complete
new individual through the powers known as regeneration.
The class to which the planarians belong is called Turbel-
la'ria (Lat. turbo, a "whirling," referring to the movement of
water about the mouth). In all members of this class the
body is covered with minute hair-like structures called cilia.

Parasitic Flatworms

Though planarians may on occasion live as parasites,
there are two other classes of flatworms, the flukes, or trema-
todes, and the tapeworms, or cestodes, which are unable to
live in any manner other than as parasites. It is not un-
common for these parasitic flatworms to produce disease in
their hosts. Especially when they parasitize man or his
domestic animals they may be of very great economic
importance.

Trematodes. There are many kinds of trematodes, rang-
ing in size from microscopic creatures barely visible to
the naked eye to large, flat, leaf-like worms more than an
inch long. Since they commonly live within other animals,
they are but rarely seen except by students of zoology
and medical men.

The Liver Fluke. In North America one of the most im-
portant trematodes from the economic point of view has

THE PLANARIANS, FLUKES, AND TAPEWORMS 263

-Mouth

Ventral sucker

Eggs

— Ovary

been the sheep liver fluke {Fasci'ola hepat'ica). This animal
(Fig. 137) lives in the liver and bile ducts of sheep, pro-
ducing a disease known as liver rot. This disease is not
uniformly present over the
country because of certain
peculiarities in the life his-
tory of the worm. It was early
noted that sheep grazing on
lowlands were apt to contract
this disease, while those kept
in upland pastures away from
water were free from attack.
This is due to the fact that
the parasite cannot be passed
directly from one sheep to
another. The adult trema-
tode produces eggs which are
carried from the body of the
sheep along with the drop-
pings. From each egg a mi-
croscopic larva is hatched.
This larva dies unless it finds
a certain kind of snail into
whose body it can bore its
way and carry on the next
stage of its development.
After two additional larval
generations in the body of
the snail, great numbers of minute tailed larvae are pro-
duced and finally liberated into the water. These minute
worms, after a period of free-swimming life, come to rest on
blades of grass and other vegetation. Each forms a pro-
tective shell about itself and becomes an inactive cvst. If
such a cyst is eaten by a grazing sheep, the young fluke is

Testes

-Intestine

Fig. 137. Photograph of a sheep

liver fluke stained for microscopic

study. (x8)

264 GENERAL ZOOLOGY

set free from its cyst in the digestive tract and is given
the chance to grow to maturity. All the higher trematodes
pass through a life history similar to this. In each species
a vertebrate serves as host to the adult worm, and the
young worm cannot enter another vertebrate directly but
must first undergo a series of stages at least one of which is
passed in the body of a snail. Draining of swamps, fencing,
and care in the selection of grazing range have done much
to reduce the ravages of this parasite.

Human Flukes. In tropical countries, and especially in
the Orient, trematodes become serious enemies of man.
Blood flukes (Schistoso'ma) are especially common in Asia
and in Africa. They are small worms, less than one-half
inch long, living in the blood vessels of man. They cause
disease by blocking the blood vessels. The eggs, which are
provided with sharp spines, bore their way through the
tissues. There are other flukes of grave importance in the
Orient. A lung fluke (Paragon' imus) causes a disease very
similar to tuberculosis. Liver flukes and various intestinal
flukes also produce diseases in man.

The Simplest Flukes. The simplest of all the trematodes
live on the body surface and gills of the lower vertebrates,
especially of fish. Hooks and spines on the posterior end
catch into the skin of the host and prevent the worm's
being dislodged easily. Frequently muscular organs known
as suckers also aid in this attachment. These external
parasites, or ectoparasites as they are called, undergo di-
rect sexual development. Nothing but accidental dislodg-
ment would prevent the young from immediately becoming
a parasite of the same individual host which sheltered its
parent. There are no free larval stages and no complicated
life history in these ectoparasitic trematodes.

Tapeworms. Tapeworms are likewise exclusively para-
sitic. There are but few species of animals from fish on up

THE PLANARIANS, FLUKES, AND TAPEWORMS 265

the scale through man that are free from attack by the
various species of these worms.

The Beef Tapeworm of Man. The best-known tapeworm is
the one that is sometimes found to inhabit the intestine of
man, Tse'nia sagina'ta (Fig. 138).
This parasite frequently grows
to the length of many feet. The
figure seems to show that the
body is divided into somites, but
these divisions are not consid-
ered true somites. The head of
the animal is, except for the nar-
row neck behind it, the smallest
portion of the body ; the poste-
rior portion is the oldest part of
the parasite, except the head it-
self. New somite-like divisions
of the body form just behind the
head, and as they grow older and
larger are pushed backward by
newer ones. The tapeworm is an
interesting example of a parasite
that has become so completely
dependent on its host that one of
the most important systems of
the body has totally disappeared,
namely the digestive system.
The parasite maintains its hold "

on the inner wall of the intestine by four sucking disks on
the head ; the body floats free in the intestine, and food
can be absorbed from all sides.

Every tapeworm has in each division both eggs and
spermatozoa. When the embryos reach a certain stage, a
few terminal divisions of the adult separate from the rest,

Fig. 138. Tapeworm. Left-
hand drawing, reduced; right-
hand drawing, enlarged

After Leuckart

266 GENERAL ZOOLOGY

and pass out with the undigested portion of the person's
food. Sometimes the embryos, inclosed in their thick mem-
branes, are swallowed by cattle while drinking at pools. In
the intestine of the cattle the membrane of the embryo is dis-
solved, and the freed larva bores its way through the wall of
the intestine, and finally comes to rest in the muscular tissue.
It remains there until the muscle is consumed by man. If
the larva has not been killed by cooking, it develops in man's
intestine into the mature tapeworm.

Other Tapeworms of Man. Another species of tapeworm
(Tse'nia so' Hum) found in human beings comes from un-
cooked pork. Tapeworms are not necessarily fatal. The
annoyance is considerable, however, until, by a period of
fasting and medical treatment, the head of the parasite is
removed from the intestine. The fish tapeworm of man is of
restricted distribution, for it occurs in only a few localities
near lakes where the inhabitants eat raw fish containing the
living larva?.

Prevention. Government inspection of meat in the pack-
ing houses has been an important agency in reducing the
numbers of cases of beef tapeworm and pork tapeworm in
man, for these worms get into the human body only when
raw or partially cooked beef or pork containing living larva?
is eaten. Government inspectors examine the hogs and
cattle in the packing houses which are under federal in-
spection, and if larval tapeworms are found the animal is
not sold for meat.

The class to which the tapeworms belong is called
Cesto'da (Gr. kestos, " girdle"; eidos, "form").

Definition of Plathelminthes (Gr. platys, "flat"; helmins,
"worm"). The members of the phylum Plathelmin'thes
are worms with flattened bodies that are not divided into
somites. Almost all the species are hermaphroditic. All
the flatworms lack a body cavity.

CHAPTER XXV

THE FRESH-WATER POLYP AND SOME ALLIES:

CCELENTERATA

To-day the many-hued anemone
Waving, expands within the rock-pools green,
And swift, transparent creatures of the sea
Dart throu' the feathery sea-fronds scarcely seen.

Sir Lewis Morris

The Fresh- Water Polyp. There are several species of fresh-
water polyps (Fig. 139). These are so small that the casual
observer would seldom be aware of their existence, even
though they were abundant in his aquarium. Two common
species are Hy'dra viridis'sima, the green hydra, and Hydra
oligac'tis, the brown hydra.

The green hydra lives among green fresh-water plants
in places where there is abundant sunlight. At rest, it
holds to a plant with its aboral surface, the remainder of
the body floating outward or downward. The body, which
is cylindrical in form, is about 3 mm. (■§- in.) long and
.4 mm. (^o in-) in diameter. A little practice will enable
a person to distinguish one in an aquarium, for speci-
mens frequently leave the green plants and crawl up the
side of the glass nearest the light. They can move either
by a slow, creeping movement on the aboral surface, or by
the process of "looping," like a measuring worm. Hydras
exist for a long time in an aquarium, provided there is an
abundance of their food animals, which are usually small
Crustacea.

The number of tentacles which a specimen of the green
hydra may have depends upon its size, and also upon its age.

267

268

GENERAL ZOOLOGY

The small individuals are generally the youngest; these
have four tentacles. The larger, older ones gain in the
number of tentacles, up to the extreme number of eleven ;
but there is a greater percentage of individuals with six

tentacles than with any
other number.

Internally, the hydra is
the simplest animal we
have studied. There is no
distinct alimentary canal
separate from a body cav-
ity. Those animals that
do not have a body cavity
and an alimentary canal
have but one cavity to
take their place ; this cav-
ity is called the gastrovas-
cular cavity, because in
the same space food is di-
gested and carried about.
The fact that food and
oxygen can pass into any
portion of the body, even
into hollow tentacles,
accounts for the absence
of a circulatory system,
which usually serves the
purpose of transporting
oxygen, digested food, and also waste products from part
to part in the animal body. The mouth (Fig. 140) opens
into a cylindrical cavity with no indication of gullet. The
cavity extends by slender tubes out into each tentacle, and
in all parts only two layers of cells separate it from the
water outside. The inner one of these two layers is the

Fig. 139. Hydra capturing a fish.
(Enlarged)

Courtesy of the American Museum of
Natural History

FRESH-WATER POLYP AND SOME ALLIES 269

endoderm, and the outer one, the ectoderm. Cells of the
endoderm secrete fluid for digesting food, and even take
up small particles of food, digesting them inside the cell
substance. The ectodermal cells are modified into nettle
cells, nerve cells, muscle cells, and general surface cells.

. Ectodermal cells
- Endodermal cells

Older bud

Forming bud--

Spermatozoa forming
r. . . Gastrovascular cavity

Egg forming

Fig. 140. Longitudinal section of a Hydra. (Much enlarged to

show structure) *

In capturing food (Fig. 139) the hydra makes use of very-
effective organs called nettling cells (Fig. 141). These organs
are found only in the phylum to which the hydra belongs.
By the aid of the nettling cells the prey is paralyzed or
killed, and then the tentacles push it into the mouth.
The nettling cells, which are of several different sizes, are

1 Modified from Parker's Elementary Biology.

270

GENERAL ZOOLOGY

found both on the tentacles and on the body. Each cell
(Fig. 141) consists of a minute microscopic sac within
which is coiled a hollow thread. A small hair-like projec-
tion from the surface of the body near
each nettling cell may control the action
of the cell. When this hair is touched
the coiled thread within the sac is shot
out with force sufficient to pierce the
shell of a small crustacean. The thread
carries with it a fluid which paralyzes
the prey.

Reproduction may take place by the
sexual method, or by budding. Eggs
(Fig. 140) are developed in the ecto-
derm near the aboral end. In the same
individual spermatozoa (Fig. 140) are
formed in the ectoderm nearer the oral
end, and these on escaping fertilize the
eggs, which remain in the ectoderm for
some time as embryos. Then the em-
bryos separate from the parent, and
after swimming about for a variable
period develop into organisms like the
parent. Nonsexual reproduction is the
more frequent method, however. Buds
involving both ectoderm and endoderm
form on the side of the body ; four ten-
tacles appear, the mouth forms, and
the base of the bud constricts, setting
the young hydra free to begin its own
career. This asexual method is so effec-
tive that hydras become extremely numerous in some lakes.
In fish hatcheries hydras sometimes become so abundant as
to destroy the very young fishes (Fig. 139).

Fig. 141. Nettle cells
of a hydra. (Much en-
larged)

A, nettle cell, with un-
discharged nettling cap-
sule ; B, nettle cell, with
discharged nettling cap-
sule ; 1 , nettling capsule;

2, nucleus of nettle cell ;

3, bristle of nettle cell;
U, hollow filament of
nettling capsule. (After

Schneider)

FRESH-WATER POLYP AND SOME ALLIES 271

Hydroids and Medusae. There is a large group of animals
closely allied to the hydra, that live in the sea. A portion
of one of them, Bougainvil'lia
frutico'sa, is shown in Fig. 142.
It looks very much like a plant,
owing to its habit of branching.
The colony may contain many
polyps, each of which is con-
nected indirectly with every
other by means of the continu-
ous body wall.

There are two different kinds
of individuals in such a colony.
One of these very closely re-
sembles the Hydra. The other
is a minute jellyfish, or medusa,
which is formed by the colony,
but later separates from the col-
ony and leads an independent,
free-swimming existence. At the
base of the colony, root-like
branches from a stem-like struc-
ture cling to floating timbers or
buoys. Although the colony
reaches the height of two inches,
the individual polyps are micro-
scopic in size. Each polyp has
about fourteen tentacles amply
provided with nettling capsules,
which aid in capturing small
pelagic animals. The mouth is
at the center of the circle of ten-
tacles (Fig. 142, 1) ; it opens directly into the gastrovascular
cavity. As the branches are terminated by feeding polyps,

Fig. 142. Hydroid. (Much
enlarged)

1, tentacles; 2, 3, k, stages in the

formation of medusa. (After

Allman)

272

GENERAL ZOOLOGY

the cells of the branches are probably supplied with food
by the polyps nearest at hand.

Reproduction in Bougainvillia may be a mere increase in
the number of polyps by a process of budding similar to
that described for the hydra. Occasionally, however, a bud

develops into a structure totally dif-
ferent from an ordinary polyp, and
after a series of stages, indicated in
Fig. 142, 2, 3, 4, finally becomes sepa-
rated from the colony and floats
away as a free-swimming individual
(Fig. 143). This is called the medusa
stage of the animal. The medusa is
shaped something like an umbrella.
The structure hanging within the
cavity of thebell is called ihemanubri-
um. The mouth is located at the end
of the manubrium (Fig. 143, 8). The
gastrovascular cavity sends out four
slender tubes (Fig. 143, 4) radially
to the margin of the body, where a
circular canal joins them. Tentacles
(Fig. 143, 2) stream downward from
the margin, and at their bases are
minute sense organs (Fig. 143, 5).
There are male and female medusa?. The ovaries and the
spermaries .of Bougainvillia are located on the manubrium.
When the eggs and spermatozoa are ripe, they pass out
through the mouth, and fertilization takes place in the
water outside. The embryo swims about for a time and
then settles to some fixed or floating object, attaches itself,
and soon another colony of the hydroid (hydra-like) stage
is developed by budding. The life history of Bougainvillia
illustrates alternation of generations. The fixed, colonial,

Fig. 143. Medusa. (Much
enlarged)

1, bell ; 2, tentacle ; 3, manu-
brium ; 4, radial tubes ; 5,
sense organs. (After Allman)

FRESH-WATER POLYP AND SOME ALLIES 273

nonsexual hydroid stage alternates with the free-swimming,
single, sexual medusa stage, and together they complete
the life cycle.

Definition of Hydrozoa (Gr. Hydra, the fabulous monster;
zoa, "animals"). The class Hydrozo'a includes the genus
Hijdra and many thousands of species of hydroids. The life
history described for
Bougainvillia does not
apply to all species
of hydroids, but it is as
characteristic as any.
Hydrozoa are small
animals occurring sin-
gly and in colonies.
There is but one cavity
in the body, and that
is continuous with the
mouth opening. There
are but two layers of
cells, the ectoderm and
theendoderm. In some
members of the class
the two layers are sep-
arated by a jelly-like mass secreted by the cells. The body
is radially symmetrical. Tentacles with nettling capsules in
their ectodermal cells are the organs of offense and defense.

Larger Jellyfishes. Although the name "jellyfish " is some-
times applied to the medusa? of the class Hydrozoa, it is
more commonly given to the larger, saucer-shaped, or bell-
shaped, animals that swim at or near the surface in har-
bors and bays of all oceans. The species most frequently
found from Massachusetts southward is Aure'lia flavid'ula
(Fig. 144). This jellyfish reaches the diameter of fifteen
inches.

Fig. 144. Photograph of a jellyfish.
(Reduced)

274 GENERAL ZOOLOGY

In various details of structure Aurelia resembles the
medusa of certain hydroids, and also the sea anemone, the
coral polyp, and the fresh- water polyp. The mouth opens at
the center of the under-surface into a large cavity which
branches freely into many tubes running to the circum-
ference, where they join the circular canal. Between the
ectoderm covering the body, and the endoderm lining the
gastro vascular cavity, is a great mass of jelly secreted by
the cells of the two layers. Hanging from about the mouth
are four broad ribbon-like appendages called "lips." These
and the delicate fringe of tentacles at the rim of the bell are
covered with nettle cells.

A very noticeable detail of structure that one observes in
watching these animals in the water, especially in the late
summer, is the set of four partial rings about the center,
yellowish in color in the males and reddish in the females.
These rings are the gonads. They are sacs which contain
the eggs or sperm until these cells are ready to be discharged.
On the rim of the bell, at eight equidistant points, are small,
rounded balancing organs. The most important muscle is
a circular band near the rim. The nerve cells are grouped
near the sense organs, and connect the latter with the
muscle band. When the circular muscle contracts, the
bell becomes more convex, and the resulting action of
the water in the hollow of the bell against the water that
is outside sends the animal along in a slow, periodic, pul-
sating movement.

The development of Aurelia is very different from that of
the hydroids. The simple, free-swimming larva of Aurelia
sinks to the bottom, attaches itself to some fixed object,
and takes on a form resembling Hydra. The formation of
circular grooves below the tentacles develops a series of
saucer-like divisions, one within another. These separate
and, swimming away with the convex, aboral surface upper-

FRESH-WATER POLYP AND SOME ALLIES 275

most, grow into the adult form. The fixed stage is com-
parable with the hydroid generation of Hydrozoa.

Aurelia is but slightly more dense than the sea water
itself. According to one authority there is less than one
eighth of 1 per cent of protein material present. Thus
over 99 per cent is water. The small amount of protein
material in the body of Aurelia makes it very unlikely
that many animals depend on them for food. After a
storm in summer great numbers of aureliae may be found
on the shore. In a few hours only scattered films are left on
the sand to show where the animals lay. The destruction
of many aureliae is to be expected because of their general
helplessness, but annihilation of the species is prevented by
the enormous number of young produced.

Aurelia and its giant relative Cya'nea, which sometimes
grows to a diameter of eight feet, might threaten to fill the
ocean with their bodies, were it not for the fact that neither
lives over the winter. The young start their development
in the autumn and complete it in the spring. It is a self-
evident fact, in this instance at least, that death is a benefit,
not only to all other forms of sea life, but even to the race
of Aurelia itself. The adults swallow everything that can
be taken into the mouth, but probably their most abundant
food is small pelagic Crustacea similar to Cyclops (Fig. 92).

The class of which Aurelia flavidula is a representative is
called Scyphozo'a (Gr. skyphos, "cup"; zoa, "animals").

The Sea Anemone. The best-known sea anemone of the
North Atlantic coast is Metrid'ium marginatum (Figs. 145,
146). The picture of the tide pool shows sea anemones
in various attitudes. Metridium has the power of moving
by creeping along on its base, but it seldom changes its
place of attachment, even in the coldest weather.

The form of Metridium is nearly cylindrical. The oral
end of the column-shaped body, or polyp, expands into a

FlG. 145. Tide-pool study of sea anemones, East Point,
Nahant, Massachusetts

FRESH-WATER POLYP AND SOME ALLIES 277

crown of many small, slender tentacles. At the middle of
the oral surface is the mouth, which is a slit-like open-
ing. The skin of the body is soft, but it is rather tough.

Fig. 146. Dissection of a sea anemone. (Natural size)

1, zone between tentacles and mouth; 2, lip; 3, ciliated groove in gullet ; 4, gul-
let ; 5, inner end of gullet ; 6, edge of mesentery ; 7, cavity within tentacle ;
8, 9, internal openings between chambers; JO, primary mesentery; 11, muscle
of primary mesentery; 12, abnormal tertiary mesentery; 13, secondary mesen-
tery; Ik, tertiary mesentery; 15, quaternary mesentery; 16, gonad; 17, mes-
enterial filament; 18, opening for mesenterial filament

The mouth opens to receive the food, which is sometimes
quite large, and the gullet (Fig. 146, 4) passes it down by
ciliary action aided by muscular activity in the gullet- wall.
At the inner end (Fig. 146, 5) of the gullet, food passes into

278 GENERAL ZOOLOGY

a large space which extends radially between mesenteries
(partitions) (Fig. 146, 12, 13) to the body wall.

There are usually six pairs of principal mesenteries in
Metridium marginatum. They are thin, radial partitions
extending from the gullet outward and downward to the
body wall. These six pairs are called the primary mesen-
teries (Fig. 146, 10, 11). In the arcs between the sets of pri-
mary mesenteries there are secondary mesenteries, also in
pairs (Fig. 146, 13), arising from the body wall and extend-
ing part way toward the gullet. The tertiary mesenteries
(Fig. 146, 14) and the quaternary mesenteries (Fig. 146, 15)
extend shorter distances into the gastrovascular cavity, but
all unite with the body wall of the oral and the aboral ends,
and in the latter place meet at the center. Occasionally a
mesentery grows beyond the usual width and becomes
attached to the gullet, as in Fig. 146, 12.

At the free edge of the widest mesenteries below the end
of the gullet there are to be found coiled masses which are
composed chiefly of mesenterial filaments (Fig. 146, 17,18).
These filaments are thickly set with microscopic nettle cells,
like those shown in Fig. 141. When the animal is disturbed
greatly, the mesenterial filaments stream out through the
mouth and through small invisible openings in the body
wall. It is likely that the most frequent use of the mesen-
terial filaments is for defense.

The Coral Polyp. The only coral polyp of the North
Atlantic coast is Astran'gia da'nse (Fig. 147). It occurs in
colonies of many individuals and incrusts rocks or pebbles
in shallow water near the shore line from Massachusetts to
North Carolina.

A polyp of Astrangia is about one eighth of an inch in
diameter and of variable length. It bears a very obvious
resemblance to a sea anemone. The columnar form, the flat-
tened aboral surface resting on a support, and the oral end

FRESH-WATER POLYP AND SOME ALLIES 279

with its crown of tentacles prove the relationship. Besides,
examination of the interior reveals the presence of mesen-
teries arranged very much as in Metridium. One important
structure of Astrangia, however, is never found in the sea
anemone, and that is the carbonate of lime "skeleton."
This structure at the base of the polyp is more definitely
referred to under the name corallite, for it is not a true

Fig. 147. Colony of coral polyps. (Enlarged)

skeleton. Several corallites are shown in the lower portion
of the figure. The hard, radial plates repeat the number of
pairs of mesenteries of the polyp, since each plate is formed
between the members of pairs of mesenteries.

Definition of Anthozoa (Gr. anihos, "flower" ; zoa, "ani-
mals"). The members of the class Anthozo'a are alike in hav-
ing a soft, generally cylindrical body. The plan of structure
is bilaterally symmetrical, as indicated in the arrange-
ment of mesenteries in the gastrovascular cavity. Super-
ficially, however, as indicated by the arrangement of the
tentacles, there is radial symmetry. Into the single, par-
tially divided gastrovascular cavity the mouth opens, and

280 GENERAL ZOOLOGY

through it food enters and unused particles are discharged.
Nettling capsules, which are the organs of offense and
defense, are at the surface of the tentacles and on the mes-
enterial filaments.

Coral Islands. Ever since Charles Darwin from 1831 to
1836 made his famous journey around the world in the
Beagle, scientific explorers have engaged from time to time
in the study of the life and structure of coral reefs and
islands. We know from their researches that coral reefs are
formed of great masses of carbonate of lime, largely as the
result of the secretion of that substance by polyps.

Just as with other organisms, reef-forming polyps flour-
ish wherever they become adapted to external conditions.
The food they need is probably abundant anywhere in the
seas, but they cannot endure the temperature common to
regions outside the torrid zone. They can live in situations
where the tide recedes from them for two or three hours,
or in depths as great as fifty fathoms (300 feet), but the most
general limit of depth for the greatest number of species is
about twenty fathoms. A condition which checks their dis-
tribution near large bodies of land is the presence of silt, as
in the fresh water that flows from the mouths of rivers.
Fresh water itself when free from impurities is not especially
detrimental to the growth of coral polyps. The most famous
coral formations are found in the neighborhood of the Ba-
hama Islands, in the Great Barrier Reef of Australia, in the
Fiji Islands of the South Pacific Ocean, and in the Maldive
Islands of the Indian Ocean.

When conditions permit, young coral polyps attach them-
selves to the sea bottom near a body of land, and by the
process of secreting carbonate of lime, as described for
Astrangia, extend upward toward the surface in the form of
a long, narrow ridge skirting the land. When the ridge is
so near the land that it leaves no channel, it is called a

FRESH-WATER POLYP AND SOME ALLIES 281

fringing reef. If by subsequent changes, or as originally
formed, a navigable channel lies between the ridge and the
land, it is called a barrier reef. If the formation surrounds
a body of water, which it nearly or completely cuts off from
the sea, it is called an atoll. The most remarkable examples
of atolls are the Maldive Islands.

Many theories have been advanced to account for the
historical connection which is thought to exist between
fringing reefs, barrier reefs, and atolls. Two of the more
important of these theories will be discussed. Darwin be-
lieved that an atoll begins as a fringing reef surrounding an
oceanic island, which may be of volcanic or other origin,
and that as the island sinks from internal causes, the coral
polyps build up carbonate of lime as long as they are within
their range of favorable depth. The reef that at first was
a fringing reef becomes a barrier reef, on account of the in-
crease in distance between it and the decreasing area of
sinking land. At last the top of the island disappears be-
neath the water, and the atoll remains. Professor J. D.
Dana, and others, have published evidence in support of
Darwin's subsidence theory, but the erosion theory suggested
by Sir John Murray, leader of the exploring expedition of
the Challenger (1850), has probably more adherents at the
present day. The erosion theory has been modified and
extended, chiefly by Dr. Alexander Agassiz. According to
this theory coral polyps may form a fringing reef about an
oceanic island. The reef continues to grow, while the soil or
rock of the island is carried away by rains and by rivers.
The solution of the soil and rock is caused by the tempo-
rary chemical union of these substances with carbon dioxide
derived from dead animals and plants. The idea is that in
the course of a few centuries an entire island could be worn
away, and the atoll left with its lagoon of water partially
connected with the sea.

282 GENERAL ZOOLOGY

Dr. Murray suggested also the probability of atolls being
formed without the preliminary stages of fringing and bar-
rier reefs. If coral polyps were to attach to a submerged
plateau not too deep for them to live on, the small colony
would grow upward and extend itself radially, something
like the flaring sides of a shallow washbasin. As the mass
grows larger the polyps at the center would be killed by the
detritus collecting from the broken pieces of coral rock at
the wave-beaten margin, and the rock already formed at
the center would be worn and scooped out by erosion with
coral sand.

Coral atolls are imperishable bulwarks against the sea,
and in some cases have formed the beginning of strips of
land sufficiently wide for wild races of men to live upon.

Definition of Coelenterata (Gr. koilos, ' ' hollow " ; enteron,
"intestine ")• Arranged in the order of their increasing de-
gree of specialization, the three classes that make up the phy-
lum Coelentera'ta are Hydrozoa, Scyphozoa, and Anthozoa.
The classes constitute a fairly distinct phylum by including
animals with radially symmetrical bodies (at least in ex-
ternal appearance) in which there is but one cavity. This
cavity, joining the mouth opening, is the digestive cavity,
and is not separated from a body cavity, as in higher ani-
mals (whence the derivation of the name of the phylum).
The body has but two germ layers, — the ectoderm and the
endoderm. In this particular it is different from every
phylum of animals heretofore described. The characteristic
organs of offense and defense are the nettling cells.

CHAPTER XXVI

THE BATH SPONGE AND SOME ALLIES: PORIFERA

The unending shapes of plants, the rainbow's varied hues,
All these the lowly sponge on ocean's bed renews.

Habitat and Form. Sponges live in the ocean both in shal-
low and in deep waters, and members of one family live in
fresh water. Some kinds have no characteristic shape of
their own, for they merely form crusts over rocks or other
objects (Fig. 148). Some have a definite cup-like shape,
while others grow as branching structures or are solid
rounded masses. Sponges are animals of a very low type of
organization. They have no organs of locomotion. In fact
they have no highly specialized organs of any sort. As a
consequence in general appearance they rather closely re-
semble plants.

Structure. One of the most characteristic features of a
sponge is the practically solid body penetrated by numerous
openings (Figs. 148, 149) which lead into an internal sys-
tem of spaces or tubes. There are no true body cavities.
The systems of openings and tubes penetrating the body
are simply channels for the surrounding water to pass
through (Fig. 149). In passing through the body, the water
brings food to the tissues. The form of the body is largely
due to supporting or skeletal material. In many of the
sponges the skeleton is made up of spicules of lime or of a
glass-like (silicious) material. Another type of framework,
or skeleton, in sponges is a soft fibrous material arranged in
the form of a network running all through the body. The
sponges used in house-cleaning and usually sold under the

283

284

GENERAL ZOOLOGY

name "bath sponges" are but the skeletons of sponges of
this last type. The tissues of the dead sponge are allowed
to disintegrate and fall away leaving only the skeleton
or framework of fibers as the part desired for market.

A fresh-water sponge

Upper portion of figure natural
size, lower portion enlarged

In the living sponge two dif-
ferent kinds of openings are
usually recognizable. These
are the very numerous small

pores scattered over the surface of the body, and a few larger
openings. Each of the larger openings is called an osculum
(Lat., "little mouth"), because it was long thought that
this opening was the mouth leading into a digestive canal.
Examination of a living sponge shows that this is not true.
Water bringing minute particles of food" passes in through
the small pores and leaves the body of the sponge by way

THE BATH SPONGE AND SOME ALLIES 285

of the osculum. Many of the sponges are really colonies
produced by budding around the base of a single individual.

Some of the spaces within a sponge are lined with spe-
cialized cells which were part of the endoderm during em-
bryonic development. These endoderm cells are furnished
with long'thread-like appendages called flagella. When these
flagella vibrate they force the water out through the oscu-
lum and thus draw in a fresh supply of water through
the pores in the surface of the body. Food particles con-
tained in the water are taken directly into the protoplasm
of the endoderm cells. Digestion takes place inside the
cells, not in a digestive cavity such as has been described
for all other free-living animals treated before in this text.

Reproduction. Reference has already been made to the
fact that budding occurs in the sponges. They also repro-
duce sexually. Eggs and sperms are produced in the mature
sponge. Fertilization takes place inside the body of the
parent. The egg develops into an ovoid larva covered with
flagella. After leaving the body of the parent the larva
swims about for a while, finally settling down on some
solid object, where it transforms and grows into an adult
sponge.

Fresh-Water Sponges. The sponge of Fig. 148 (Hetero-
meye'nia ry'deri) is found quite generally in ponds and
quiet brooks, at least as far west as the Mississippi River.
It grows on the under side of overhanging submerged rocks,
and on dead sticks and leaves. The largest specimens are
not usually more than one inch across. Each mass of sponge
clings flat against the supporting substance, and seldom is
more than one eighth of an inch thick. The sponge yields
slightly on being pressed with the finger. The surface looks
rough, but to the touch it is smooth. The color is grayish ;
occasionally specimens are found with a part or all of the
mass green. This is due to the presence of a green alga

286

GENERAL ZOOLOGY

growing in the sponge. Besides the species here described,
there are numerous other species of sponges living in
fresh water.

In addition to sexual reproduction, fresh-water sponges
reproduce also by means of special organs called gem-
mules, which are about one fiftieth of an inch in diameter
(Fig. 148). These structures are produced in the sponge
mass during the summer. Their use is to carry the spe-
cies over the unfavorable season after the destruction of

the parent sponge,
which usually takes
placeinthefall. The
gemmules are really
buds within the tis-
sue of the sponge
which become sur-
rounded by a pro-
tective covering.

Relation to Envi-
ronment. Perhaps
no group of animals
has so wide a distribution in water as sponges. In fresh water,
and in the sea from the very margin of low tide to the great-
est depth of ocean yet explored, and in all zones, various
species of sponges are found. They live in every conceiv-
able situation, adapting themselves in form of mass to the
particular place in which they grow. Branched species, like
Microci'ona prolif'era, in the frontispiece, vary much in
form and arrangement of branch. Incrusting species on
rocks, as in the frontispiece, follow every turn of the sup-
porting substance. One species of Clio'na grows on shells
of mollusks, and through the agency of a secretion its pro-
toplasm consumes the substance of the shell and grows to
fill the space thus made. In regions where the ocean bottom

Section of fresh-water sponge.
(Much enlarged)

a, surface ; b, dermal pores ; c, ampullae, lined with
collar cells ; d, osculum. (After Huxley)

THE BATH SPONGE AND SOME ALLIES 287

is muddy, sponges grow stalks that keep the mass away from
the mud, which if stirred up would smother the colony.

Many marine sponges, being thick and massive, and of
loose texture, like the sulphur sponges, are very convenient
harbors of refuge for myriads of small animals, chiefly Crus-
tacea and worms. Undoubtedly the odor of living sponges,
described by one investigator as resembling garlic, drives
away fishes and other ravenous animals of large size that
might feed on the little guests, or even on the sponge itself.

Economic Importance of Sponges. Some idea of the value
of sponges is gained from the fact that $715,000 worth of
sponges were sold in the chief sponge market at Tarpon
Springs, Florida, during the season of 1925. In some of the
shallow waters of the warm oceans, sponges are picked up
from the ocean floor with long-handled rakes and tongs.
Most of the market sponges are now gathered by divers
who can work in the deeper waters.

Definition of Porifera (Lat. porus, " pore" ; ferre, "bear ").
By most investigators the sponges are considered a distinct
phylum, Porifera, including but a few classes (see page 307).
It is evident that the Porifera are lower in organization than
the Ccelenterata, for members of the phylum do not show
indications of muscle cells, of nerve cells, or of sense organs.
Neither are there special organs of offense. Protection is
afforded by the spicules and the characteristic odor.

CHAPTER XXVII

AMOEBA AND SOME ALLIES: PROTOZOA

Gradual, from these what numerous kinds descend,

Evading even the microscopic eye!

Full nature swarms with life, — one wondrous mass

Of animals, or atoms organized.

James Thomson, Summer

Protozoa. There are untold millions of animals which
are so very small that most people are not aware of their
existence, for they may be seen only with a microscope.
The simplest and many of the smallest of these are called
Protozoa. They exist under every conceivable condition
that will support life, and some even have the power, though
dried up completely and blown with the dust, of coming
to active life again if they get into suitable surroundings.
Stagnant pools teem with these minute forms. Even most
drinking water is populated with them, though fortunately
most of them are harmless. Some inhabit the soil, and many
species live as parasites in the bodies of other animals. In
spite of their microscopic size each of these organisms carries
on the same functions of life that are characteristic of the
higher animals. In the higher animals there are special
organs for metabolism, for reproduction, for movements,
and for the various other functions performed by living
animals. In the Protozoa all the functions of life are car-
ried on by the parts of the smallest unit of living matter —
a single cell. This cell feeds, moves, and produces other in-
dividuals like itself just as effectively as does man with his
complicated organization. Thus, in spite of its minute size,
each cell is a complete individual.

288

AMCEBA AND SOME ALLIES 289

The Amoeba. The amoeba (Amoe'ba pro'teus, Fig. 150) is
common in stagnant water of all lands, but it is so minute
that it is impossible to be sure of its presence in a given
place until examination has been made with a compound
microscope.

One of the best ways to find large specimens of the amoeba
is to remove carefully from the bottom of a well-stocked
fresh- water aquarium a few dead leaves. A medicine-dropper

full of material from the ^

surface of one of the leaves ,*•>. /$&££■)

may yield several speci- vlSftfPr''

mens. A short time after v^lsilf;!

a few drops of the water fSPfe>^ -^ i:l§te

have been mounted on a

glass slide the amcebas will

exhibit their characteristic

structure and activities.

The usual diameter of an

amoeba is about .5 mm. Fig. 150. Amoeba. (Much enlarged) *

(^o inch).

Structure and Appearance. The simplest structure en-
countered in any living animal is that found in an amoeba.
Under the microscope this minute animal is seen as a drop-
let of practically colorless jelly-like fluid only with difficulty
distinguished from the water surrounding it. The granular
protoplasm of which this body is composed is usually in
motion, stretching out here and there as small lobes in-
creasing in size until the whole tody seems to flow along.
The projections which produce this movement are called
pseudopodia (false feet). The entire body is surrounded by
a very thin nongranular layer called the ectoplasm, which
contains within it a more fluid granular mass, the endo-
plasm. Part of the granular nature of the endoplasm is due

1 From Sedgwick and Wilson's General Biology.

290 GENERAL ZOOLOGY

to the presence of food in all the stages of digestion and as-
similation, and waste materials that are to be expelled from
the body. There are two fairly conspicuous bodies within
the endoplasm, the nucleus, which controls most of the acts
of the cell, and the contractile vacuole, in which the liquid
wastes are accumulated until the vacuole reaches its capac-
ity. Then the vacuole bursts through the ectoplasm, throw-
ing the liquid waste out of the body. In its functioning
this contractile vacuole goes through regular cycles of
gradual increase in size, followed by sudden disappearance.

In the life functions, oxygen dissolved in the surrounding
water is absorbed directly by the protoplasm in the process
of respiration. At the same time the carbon dioxide pro-
duced by the protoplasm is taken up by the surrounding
water.

Microscopic plants and animals and parts of larger or-
ganisms serve the amoeba as food. When a moving amoeba
approaches a food particle, pseudopodia extend on each
side of the particle. As the animal flows along, the pseudo-
podia completely surround the object being taken as food,
which becomes recognizable as a food vacuole within the
endoplasm. Though a food vacuole lies in the protoplasm
it is not part of the living amoeba. The food must first
undergo digestion under the influence of the surrounding
protoplasm and become assimilated in a manner exactly
similar to the processes that take place in the higher animals.

As an amoeba continues to feed, it grows, but soon reaches
a limit in size. It then undergoes reproduction. The nucleus
divides into two equal parts, and the cytoplasm becomes
separated into two masses. Each mass of cytoplasm sur-
rounds a nucleus and becomes a new individual.

There are many species of Amoeba and amoeba-like forms,
mostly living in stagnant water and having relatively little
economic importance. In contrast with these some others

AMCEBA AND SOME ALLIES 291

are highly important as parasites of man and other higher
animals. In man one type of dysentery is produced by an
amoeba, and many diseased conditions are due to amoeboid
forms.

Euglena. A relative of Amoeba, found in the same situ-
ations, is Eugle'na vir'idis (Fig. 151) ; it also is composed of
one cell. Euglena has a more fixed arrangement of parts
than Amoeba. There is a blunt anterior end with a short,
funnel-shaped mouth. Out of the mouth extends a long
lash, or flagellum, which by its whip-like vibrations carries

Fig. 151. Euglena. (Much enlarged)
After Saville Kent

the animal through the water. Behind the mouth is a small
red eye-spot, which lies beside a clear space. This clear space
has been found to be sensitive to light. The nucleus is near
the middle of the body, and can be seen easily in the liv-
ing animal, although the cytoplasm immediately about it is
colored quite green with chlorophyll, — a coloring matter
found in the green parts of plants.

Many biologists believe that Euglena is indeed a plant
because, through the agency of its chlorophyll, it can use
carbon dioxide as a raw food material, retaining the carbon
and giving off oxygen when the organism is in the light.
This creature illustrates the fact that it is impossible to
classify all organisms as plants or animals.

As a rule Euglena moves with the lash forward, but the ani-
mal can turn in any direction, and can even change the shape

292

GENERAL ZOOLOGY

Wr-7

%-8--m

d'-mm,

6-4

of its body considerably, but it does not form pseudopodia.
Sometimes when being experimented on Euglena ceases mov-
ing, contracts into a ball, and encysts itself, just as it does
in nature when it is surrounded by unfavorable conditions.

Paramecium. Perhaps no
member of the phylum
under discussion in this
chapter has been ob-
served by more students
than has the slipper ani-
malcule, Parame'cium cau-
da'tum (Fig. 152 A, B) ;
and no member of its
phylum has been so fre-
quently made the basis
of scientific discussions of
cell structure and cell
physiology. Paramecium
lives in stagnant pools of
fresh water in all lands.
Specimens may be ob-
tained in countless num-
bers by placing a quantity
of hay in a jar of ordi-
nary water and leaving
it to stand for a few
weeks. The bacteria de-
veloped in the decaying hay furnish a food supply favor-
able for rapid growth and reproduction of Paramecium.
There are several species of Paramecium, differing from
each other slightly in form and in size. Most of these live
in all sorts of standing fresh water but become most abun-
dant if the water is stagnant.

1 From Sedgwick and Wilson's General Biology.

Fig. 152. Paramecium.
enlarged)

A, leftside; B, ventral surf ace ; 1, cilia;
2, mouth ; 3, gullet ; -4, food vacuole form-
ing ; 5, food vacuole in cytoplasm ; 6, anus ;
7, contractile vacuole ; 8, macronucleus ;
9, micronucleus 1

AMCEBA AND SOME ALLIES 293

As in Amoeba and Euglena, the entire body of Para-
mecium is a single cell. The cell when moving freely has a
definite shape, although it changes constantly in outline,
owing to the fact that the irregularities in the body are
whirled into view as the animal swims along in a slender
spiral path.

Paramecium is about 0.2 mm. (xW5 m0 m length. The
anterior end is rounded and the posterior end pointed.
Right and left sides are, as indicated in the figures, deter-
mined by the position of the mouth (Fig. 152, 2), which is
on a surface called the oral surface. The entire surface of
the ectoplasm is covered with great numbers of short, hair-
like structures, called cilia (Fig. 152, 1). The cilia are the
organs of locomotion. They wave backward toward the
posterior end, propelling the animal forward. A few cilia
somewhat longer than the others lie in the groove that leads
diagonally across the ventral surface to the mouth. Their
function is to carry the food down the short gullet into the
endoplasm.

The endoplasm, which, as already explained, is that por-
tion of the cytoplasm lying between the nucleus and the out-
side layer of ectoplasm, is soft and semifluid. Food is passed
into it by the gullet (Fig. 152, 3), and immediately begins to
float away from that point, surrounded by a little drop of
water. These masses are called food vacuoles (Fig. 152, 4, 5).
While the current in the cell protoplasm is carrying the food
vacuoles around, digestive fluid formed by the protoplasm
is breaking up the food, liquefying it, and changing it chem-
ically for the process of assimilation or building up into pro-
toplasm. The indigestible particles are discharged from the
cell by a small opening, the anus (Fig. 152, 6). The waste
derived from the food and protoplasm that is used up in the
work of the animal is probably discharged in the form of
liquid from two special organs, one near either end at the

294

GENERAL ZOOLOGY

dorsal surface. These are contractile vacuoles (Fig. 152, 7).
It is supposed that the liquid waste, when formed, flows
through the protoplasm along somewhat definite channels
to the point where it collects in a gradually increasing vacu-
ole. Soon the maximum size is attained, and the vacuole

bursts at the surface, the waste pour-
ing into the water outside. The two
contractile vacuoles alternate in con-
tracting.

Paramecium has two nuclei ; the large
one is called the macronucleus (Fig. 152,
8), and the small one the micronucleus
(Fig. 152, 9). The macronucleus is
thought to be the seat of control of the
general activities of the cell, while the
micronucleus is the seat of control of
the important process of reproduction.
Paramecium divides into two equiv-
alent cells (Fig. 153), with half the
macronucleus and half the micronu-
cleus in each, probably because the
volume of the cell becomes too great
to be kept alive by the protoplasm
of the relatively decreasing surface.
As many as three or four generations
of paramecia may be produced in a
single day. The frequency of division of the cell depends
upon the kind and abundance of food obtainable, upon
temperature, and also upon a process known as conjuga-
tion (Fig. 154). This complicated process was worked out
in great detail in 1888 by Maupas, a French librarian, who
in his spare time studied the life history of Paramecium
and other unicellular organisms.

1 From Sedgwick and Wilson's General Biology.

Fig. 153. Paramecium
dividing. (Much en-
larged)

1, mouth and gullet; 2,
macronucleus dividing ;
3, micronucleus dividing x

AMCEBA AND SOME ALLIES

295

In conjugation two paramecia unite temporarily in the
manner indicated in the figure. A fraction of the micro-
nucleus of each passes through the two contiguous layers of
ectoplasm and unites with a similar fraction in the other
animal. When this and certain other less essential phenom-
ena have taken place, the individuals
separate and continue the process of
transverse division, but with greater
frequency than before. Professor L.
L. Woodruff of Yale University has
found that conjugation is not neces-
sary to the life of Paramecium. By
isolating single specimens of Parame-
cium he kept watch so that each time
the animal divided the parts were
separated. In this manner conjuga-
tion was entirely avoided for ten
years. During this time there were
twelve thousand generations. Since
the animals showed no ill effects we
must conclude that Paramecium can
continue to reproduce indefinitely
without conjugation.

The Malarial Parasite. Many one-
celled animals are parasitic. One of
the most studied in recent years is one
of the malarial parasites of man (Plas-

mo'&ium mala'rix, Fig. 155). There are several different
species of malarial parasite. These differ one from another
in appearance and in the nature of the diseases which they
produce. While the most generally known species cause
human malaria, other species live in birds and in other ani-
mals. The life history of these organisms is so long and com-
plicated that we can give but a brief account of it here.

Fig. 154. Paramecia con-
jugating. (Much en-
larged)

After Saville Kent

296

GENERAL ZOOLOGY

In its simplest form the animal resembles an extremely
small amoeba. In that stage it is found in the red corpuscles
of human blood. There the parasite increases in size until it

Mosquito

USfc..

Fig. 155. Stages in the development of the parasite which causes malaria

Stages a to e occur in the human blood. The parasite lives in the red blood cor-
puscles, (a to d). When blood from a malarial patient is taken into the body of a
mosquito the spores develop into germ cells (h and i). After fertilization (j), the
parasite enters the tissues of the mosquito (I) and multiplies rapidly (m and n),
forming myriads of small spores (o) ready to infect other human beings when the
mosquito bites them, p shows the stomach of a mosquito with swellings pro-
duced by the parasite. (After Gruenberg)

almost fills the corpuscle (Fig. 155, c) ; then it divides into
small bodies called spores (Fig. 155, d). The process of
spore formation causes the chill that accompanies malaria.
When the spores burst from their spore cases (Fig. 155, e)

AMCEBA AND SOME ALLIES 297

and from the blood corpuscles, a quantity of poisonous ma-
terial is released and mingles with the liquid of the blood.
This poisonous material induces the fever which always fol-
lows the chill. The released spores may enter red corpuscles
again and, in forty-eight hours in one type of malaria and
seventy-two hours in another, form spores once more.

Some of the amoebulse (amceba-like stages) of the parasite
have a different history. While most of them in the red cor-
puscles of a person go on reproducing nonsexually, as just
described, some develop into a form which, by comparison
with higher animals, we call the female cell (Fig. 155, h2)r
and others into male cells (Fig. 155, i). If now the person
be exposed to the bite of a mosquito of the genus Anopheles,,
the male and female cells of Plasmodium reach their full
development in the human red blood corpuscles, as these
rest in the stomach of the mosquito. Leaving the corpuscles,
the two cells unite to form a worm-like cell (Fig. 155, k),
which penetrates to the outer wall of the stomach of the
mosquito, where it increases in size to form a large sphere
(Fig. 155, p). In a short time the sphere subdivides into
countless extremely minute blasts (Fig. 155, m). These
make their way through the body cavity of the mosquito to
the salivary glands (Fig. 155, n). Penetrating to the interior
of those glands, the blasts enter the ducts, and are carried
outward and down the insect's proboscis by the saliva when
the mosquito bites another person. Then in the human
blood the blasts enter the red corpuscles and become amoe-
bulse, thus completing a cycle.

Prominent among the scientific men who since 1896 have
discovered the facts of the life history of the malarial para-
site are Dr. Ross, of India, and Professor Grassi, of Italy.
Upon their discoveries, and those of others, are based the
numerous operations against the mosquito in the vicinity
of large cities.

298 GENERAL ZOOLOGY

Definition of Protozoa (Gr. protos, "first"; zoa, "ani-
mals"). The four members of the phylum described in this
chapter were selected as representatives of the four classes
that make up the phylum : Amoeba proteus, of the class Sar-
codi'na ; Euglena viridis, class Mastigoph'ora ; Paramecium
caudatum, class Cilia'ta; and Plasmodium malarise, class
Sporozo'a.

Although in each class the genera differ widely, all the
members of the four classes agree in being composed of
single cells. Nearly all species are microscopic in size.

Reproduction is brought about by division of the cell, and
in some cases by specialized germ cells, as in the higher
animals.

In all the Protozoa discussed in this text, the body con-
sists of a single cell. However, in many species the cells,
after division, remain united in clusters. These groups, in
some instances, are only temporary and finally break apart
into entirely independent individuals. In other species, the
cells remain united permanently. Such groups, whether per-
manent or temporary, are called colonies. Division of labor
or specialization occurs in many of these colonies, for only
certain of the cells are capable of reproduction while the other
cells care for the nutrition and locomotion of the colony.

CHAPTER XXVIII

THE PAST HISTORY OF INVERTEBRATES AND THE
BEGINNINGS OF THE VERTEBRATES

I wrote the past in characters

Of rock and fire the scroll,

The building in the coral sea,

The planting of the coal.

Emerson, Song of Nature

Vertebrates and Invertebrates. However various in form
and structure the members of the phyla thus far discussed
are, they have in common at least this negative character,
that in none of them has a backbone been developed. For
this reason they are collectively termed Invertebrates (Lat. in,
:'not" ; vertebratus, "vertebrate") ; the animals which have
a backbone are called Vertebrates. It will be worth our while,
before beginning the study of the vertebrates, to consider
some general questions of interest in connection with the
evolution of the invertebrate phyla, and then to describe
briefly some peculiar forms which appear to stand between
the invertebrates and the vertebrates.

The Invertebrates of Past Ages

Sources of Information. There are three sources of in-
formation which the zoologist may draw upon in his en-
deavor to discover the relationship which the animals of the
past and the present bear to each other throughout the
long series from the lowest to the highest. These sources of
information are the geological record of species, compara-
tive anatomy or morphology, and the stages in the develop-
ment of the individual. We shall consider first the record of

299

300 GENERAL ZOOLOGY

geology, and in order to do this intelligently we shall have
to begin far back, for perhaps more than any other science
geology requires of the mind of man vast sweeps of the
imagination to form even faint conceptions of the illimitable
processes that have brought the earth to its present state.
Scarcely less awe-inspiring is the contemplation of the
changes that must have taken place in living things since
life began in the ocean and on the land. Great as the time
and changes were before the earth had life upon it, greater
still may be the time that the processes of evolution have
required to develop all the forms of life in their complexity.
Archaean Time. The earliest period of the earth's geo-
logical history is termed the Archaean Era (Gr. archaios, "an-
cient"). At first all the substances, including the water which
now covers three quarters of the earth's surface, were held
suspended in the atmosphere, owing to the high tempera-
ture. Later there came a time when the waters condensed,
and the surface, cooled still further, permitted the water to
cover the rocks of the early crust entirely or in part. Stu-
pendous volcanic upheavals must have been frequent as fire
and water struggled for the mastery. During this time, of
course, no life was possible. As the crust continued to cool
it was upheaved and formed land. When the waters had
cooled sufficiently to permit of it, life appeared, but in what
form we do not know. It is thought that this early life must
have been plant rather than animal in its nature. Plants are
able, with the exception of the fungi (mushrooms, bacteria,
and the like), through their green substance, called chlo-
rophyll, to manufacture their food materials out of simple
chemical substances. All animals lack this power and con-
sequently depend upon green plants to manufacture their
food for them. Flesh-eating animals get their food indi-
rectly from plants, for the food manufactured by plants
is eaten by plant-eating animals, and these in turn become

PAST HISTORY OF THE INVERTEBRATES 301

the prey of the flesh-eaters. It stands to reason that the
first living things must have been able to provide for them-
selves and therefore must have been plants. As regards the
temperature at which life became possible, it is known that
plants live now in the hot springs of the West in water
reaching 180° F.

There is very little direct evidence to indicate the charac-
ter of the life in the Archaean Era, but in all probability it
was of the simplest structure, even simpler than the single-
cell organisms of today. Although fossil remains of that
time are wanting, beds of limestone and graphite which were
formed then, point to the existence of life, for similar beds
formed in later eras are known to have been made through
the agency of organisms (polyps, mollusks, and the like, and
plants).

The Age of Invertebrates. Following the Archaean Era,
several succeeding geological periods may be, for our pur-
pose, grouped under the general term, Age of Invertebrates,
from the predominance of these forms of life. The era was
very long, undoubtedly to be reckoned in millions of years.
We have no knowledge of the exact time that the different
species appeared, nor of the exact length of time each ex-
isted. Neither do we know from actual specimens all the
stages of evolution through which the early forms of life may
have passed in coming to the form and structure in which
we know their kin today. The intermediate types have been
lost on account of one catastrophe or another in the history
of the world.

In the beginning of the era, life was marine, as far as fossil
records indicate. The earliest fossils are of sponges, corals,
sea lilies, worms, mollusks, and trilobites. Subsequently land
animals made their appearance in forms like the arachnids
and the insects. Before the close of the era a class of ver-
tebrate animals, the fishes, had come into existence.

302 GENERAL ZOOLOGY

Evidence from Embryology and Morphology. Frequently
the only way the zoologist may know of the kinship of cer-
tain groups is by studying their early stages of development.
Since all the animals composed of more than one cell repro-
duce at one time or another by means of eggs and sperms,
we see that all animals, however great the differences be-
tween the adults may be, are alike in being composed of one
cell at the beginning of development. Furthermore, the
degree to which the young of two different groups of ani-
mals resemble each other in the details of their development
is believed to be a measure of the relationship existing be-
tween the groups. This theory is based upon the very
generally accepted belief that each individual in the course
of its development repeats in an extremely short time the
history of its race. The Recapitulation Theory is the name
by which this generalization is commonly known.

All those animals which have few organs show relatively
few changes in development, in comparison with those ani-
mals which have numerous complicated organs. A hydra,
for example, is a very simple form compared with an earth-
worm. Not only has a hydra fewer organs than an earth-
worm, but reference to the latter's development will show
that the two layers of cells which constitute an entire hy-
dra represent a very early stage in the development of an
earthworm.

The third germ layer, the mesoderm, offers a beginning
place for organs not developed in the ectoderm and endo-
derm, and groups of animals possessing it develop more
kinds of organs than those which do not have it ; that is to
say, they show greater differentiation. All animals except
the Protozoa and the ccelenterates have a mesoderm.'

If we were to begin at once to arrange all animals in a
regular graded series, on the basis of what we learn from
morphology and from embryology, we should have a diffi-

PAST HISTORY OF THE INVERTEBRATES 303

cult task. The number of facts that it is necessary to know
is so considerable that even today systematic zoologists are
not agreed on important details of grouping animals in a
complete system of classification. Besides, the doctrine of
evolution takes into account the fact that the phyla of ani-
mals have not developed in a direct line, but as branches
from a previously existing stem. The whole system of
animals might be represented by a stem and a series of
branches resembling a tree ; but whereas in a tree we can
trace down one branch and out any other, in the diagram
suggested some of the branches would not be connected with
the stem at all, because the organisms which would stand in
the connecting places have disappeared both in living and
in fossil form.

However, we can see very clearly that the Protozoa, being
composed of a single cell, are the lowest of all animals ; and
that the Porifera, with their structure showing no sign of
digestive organs, muscle cells, nerve cells, or sense organs,
are the simplest of the many-celled animals (Metazoa).

After considering all facts of structure and development,
we may arrange the phyla in a series going from the sim-
pler animals to the more complex (see page 307). But in
doing this we must keep in mind that in some instances one
group may be simpler than another in regard to certain
organs or structures but more complex in other respects. It
then becomes necessary to decide which of the differences is
the most important. Furthermore, it is not unusual to find
that some simple animals are really degenerate examples of
a group that is relatively complex.

Invertebrates which resemble the Vertebrates. All the
animals which have been discussed in the preceding chap-
ters lack a backbone. The name "invertebrate" is there-
fore applied to them in contrast with the highest animals,
or 'vertebrates." For a long time a few animals which

304

GENERAL ZOOLOGY

lack a backbone have been admitted to resemble the
vertebrates in other important respects. These peculiar
forms show so many points of agreement with the verte-
brates that zoologists now uniformly agree that they should
be united with them in a larger group to which the name
:'chordate" is applied. This name is taken from the fact
that a soft, rod-like structure called the notochord occurs in
the position which is occupied by the backbone of a verte-
brate. There are three of these groups of low chordates
(Figs. 156, 157, 158) represented by the fish-like lancelet,
the sac-shaped tunicate, and the worm-like Balanoglos'sus.

Nerve cord

Notochord

Atrium

Fig. 156. The lancelet. (x2)
Modified from Kowalevsky

The Lancelet. The lancelet (Amphiox'us lanceola'tus,
Fig. 156) is a fish-like animal about two inches long. It
lives almost embedded in the sand at the sea bottom in
Chesapeake Bay and in other warm ocean waters.

The mouth of the lancelet opens into a long pharynx,
which has many pairs of gill slits. When water and food
pass in at the mouth, the water passes through the gill slits,
giving up oxygen to the blood in the gills, and then passes
into a chamber partially surrounding the pharynx, called
the atrium, and to the outside by the atrial pore ; the food
goes down the intestine.

Immediately above the intestine is the structure which
corresponds in position to the backbone of higher animals ;
it is called the notochord. The notochord is soft throughout
life, but it is sufficiently strong to act as a supporting rod

PAST HISTORY OF THE INVERTEBRATES 305

for the body. Parallel with the notochord and above it is the
spinal cord, lying near the dorsal wall. The characteristics
of structure which permit zoologists to consider Amphioxus
a chordate are the presence of gill slits, a notochord above
the intestine, and a spinal cord dorsal to the notochord.

Fig. 157. Photograph of living sea squirts. (Natural size)

A, Styela; B, Cynthia

The Sea Squirt. As far as outward appearance indicates
the sea squirts, Sty'ela and Cyn'thia (Fig. 157, A, B), seem
to have nothing in common with vertebrates. Sea squirts
live attached to rocks and wharves, and once attached
never leave the place. The body is covered with a tough
coat, or tunic, which gives the class its name, Tunica'ta.
The food and oxygen are drawn through the opening in
the upper tube, and the excess water and wastes are dis-
charged by the lower tube. There is a pharynx with gill

306

GENERAL ZOOLOGY

Proboscis

openings, and a nervous system, but there is no indication

of a notochord in the adult animal.

The adult tunicate is simpler in structure than the larva.

The larva has very much the form of a frog tadpole, and it

swims about. Its locomotor or-
gan is a fin-like tail. In the
larva there are structures which
indicate vertebrate relationship.
Extending through the middle
of the tail is a notochord which
is evidently a supporting organ.
Dorsal to the notochord is the
nerve cord. Below the notochord
is the alimentary canal, and close
by are the beginnings of the
gills, with openings which, how-
ever, are not gill slits. When the
larva reaches a certain stage of
development, it fastens itself by
adhesive papillx to some fixed
object. Then begins the process
of degeneration of all distinctly
chordate structures; the tail is
absorbed, the notochord also
disappears, and the nerve cord
changes form. If it were not for

what is known of the larva, the vertebrate relationship of

tunicates would never be suspected.

The Acorn-Tongue Worm. The acorn-tongue worm, Bala-

noglos'sus (Fig. 158) is found in the sand of seashores. It

has a proboscis with a collar-like band at the base, both

organs together somewhat resembling an acorn in its cup.
The mouth, at the base of the proboscis, opens into a

pharynx, from which many pairs of gill slits open to the

Fig. 158. Acorn-tongue worm.
(Enlarged)

Modified from A. Agassiz

PAST HISTORY OF THE INVERTEBRATES 307

exterior. There is a dorsal nerve cord and a ventral nerve
cord. A notochord-like structure extends into the middle
of the proboscis.

A Synopsis of the Animal Kingdom

The relative positions of the phyla are shown in the ac-
companying table. As regards the brief diagnosis of char-
acters listed for each class it is of course assumed that, in
addition, the statements made for the phylum apply to all
the members of each class within that phylum. Attention
should be called to the fact that in this table many of the
less important or less well-known classes have been omitted.
This applies especially to the Arthropoda and to the various
phyla of worm-like forms.

The lowest chordates are sometimes called the Prochor-
dates. In the following table the phylum Chordata is in-
cluded. This makes it possible for us to have a complete
list of the phyla contained in the entire animal kingdom,
even though the higher chordates are not treated until later
in the book.

PHYLA AND CLASSES OF THE ANIMAL KINGDOM

Phylum I. Protozoa: chiefly single-celled animals.

Class 1. Sarcodina: move by pseudopodia. Ex. Amoeba

proteus.
Class 2. Mastigophora: move by flagella. Ex. Euglena

viridis.
Class 3. Ciliata: move by cilia. Ex. Paramecium caudatum.
Class 4. Sporozoa: reproduce by spores, entirely parasitic.

Ex. Plasmodium malarias.
Phylum II. Porifera (sponges) : body with numerous pores, no organs.
Class 1. Calcarea: with limy spicules. Ex. Grantia.
Class 2. Hexactinellida: with silicious spicules. Ex. Eu-

plectella.
Class 3. Demospongia: with fibrous skeleton and frequently

with silicious spicules. Ex. Heteromeyenia ryderi.

308 GENERAL ZOOLOGY

Phylum III. Coelenterata : radially symmetrical, two cell layers, ten-
tacles with stinging cells, with a single cavity serving
as both digestive cavity and body cavity.
Class 1. Hydrozoa: usually two forms — polyp and medusa,
the former with no folds in endoderm. Ex.
Hydra viridissima.
Class 2. Scyphozoa: usually polyp and medusa, of which
latter is larger, former with four folds in en-
doderm. Ex. Aurelia flavidula.
Class 3. Anthozoa: polyp only, endoderm with many
folds. Ex. Metridium marginatum.
Phylum IV. Ctenophora: similar to medusa with eight bands of cilia
for locomotion, but a single pair of tentacles. Ex.
Pleurobrachia pileus (sea comb) .
Phylum V. Plathelminthes (flatworms) : body flat, bilaterally sym-
metrical, no body cavity.
Class 1. Turbellaria: free-living, body covered with cilia.

Ex. Procotyla fluviatilis.
Class 2. Trematoda (flukes) : always parasitic, digestive

tract present. Ex. Fasciola hepatica.
Class 3. Cestoda (tapeworms) : always parasitic, no diges-
tive organs. Ex. Taenia saginata.
Phylum VI. Nemathelminthes (roundworms) : round, not segmented,
with a digestive system and a body cavity.
Class 1. Nematoda: characters as for phylum. Ex.
Ascaris lumbricoides.
Phylum VII. Trochelminthes (wheel animalcules) : many-celled, minute,

with wheel of cilia about mouth.
Class 1. Rolifera: characters as for phylum. Ex.Hydatina.
Phylum VIII. Annelida (jointed worms) : body segmented, with dis-
tinct body cavities.
Class 1. Chsetopoda: bristles for appendages. Ex. Lum-

bricus terrestris.
Class 2. Hirudinea (leeches) : no bristles. Ex. Placob-
della rugosa.
Phylum IX. Molluscoidea: with a crown of ciliated tentacles on an-
terior end of body.
Class 1. Bryozoa (moss animals) : usually colonial, diges-
tive system complete. Ex. Plumatella.
Phylum X. Echinoderma : radially symmetrical, with body cavity,
locomotion usually by tube feet, limy plates in skin.
Class 1. Asteroidea (starfishes) : a central disk with five
or more arms, body cavity extending into
arms. Ex. Asterias vulgaris.

PAST HISTORY OF THE INVERTEBRATES 309

Class 2. Ophiuroidea (serpent stars) : a disk and five

slender or branched arms, no body cavity in

arms. Ex. Gorgonocephalus.
Class 3. Echinoidea (sea urchins) : hemispherical, or flat

disk without arms. Ex. Strongylocentrotus

drobachiensis.
Class 4. Holothuroidea (sea cucumbers) : long soft body

with feathery tentacles about mouth. Ex.

Cucumaria chronhjelmi.
Class 5. Crinoidea (sea lilies) : a cup with movable arms,

attached by a stalk. Ex. Pentacrinus blakei.

Phylum XI. Mollusca: not segmented, usually covered with a shell.

Class 1. Acephala (clams) : no head, shell usually in two

parts. Ex. Mya arenaria.
Class 2. Gasteropoda (snails) : head with tentacles, a

single shell, usually coiled. Ex. Physa.
Class 3. Cephalopoda: with a circle of arms about the

mouth, shell usually internal, free-swimming.

Ex. Ommastrephes illecebrosus (squid). .
Phylum XII. Arthropoda: body with an exoskeleton, segmented, with

body cavity, and with paired jointed appendages.
Class 1. Crustacea: skeleton limy, two pairs of antennae.

Ex. Cambarus limosus.
Class 2. Arachnida (spiders and ticks) : no antennae,

usually four pairs of legs. Ex. Miranda

aurantia.
Class 3. Diplopoda (thousand legs) : land-living, most of

segments with two pairs of legs each. Ex.

Spirobolus.
Class 4. Chilopoda (centipeds) : one pair of legs to each

of many somites, body flattened. Ex. Scu-

tigera forceps.
Class 5. Hexapoda (insects) : one pair of antenna?, three

pairs of legs, tracheae for respiration. Ex.

Melanoplus femur-rubrum.
Phylum XIII. Chordata: with backbone -or a rod called the notochord

in its place, gill slits in either adult or embryo, nerve
cord dorsal to digestive tract.

A. The Prochordates : never having any backbone. Ex.

Amphioxus lanceolatus.

B. Vertebrates, with a bony or cartilaginous backbone.
Class 1. Pisces (fishes) : breathe by gills, body

usually covered with scales. Ex. Perca
flavescens.

310 GENERAL ZOOLOGY

B. Vertebrates (Continued)

Class 2. Amphibia: breathe by gills or lungs, skin,
moist, usually two pairs of legs. Ex. Rana
clamitans.

Class 3. Reptilia: breathe by lungs, body covered
with dry scales, heart with three cham-
bers. Ex. Sceloporus undulatus.

Class 4. Aves: breathe by lungs, body covered with
feathers, heart with four chambers. Ex.
Columba livia.

Class 5. Mammalia: breathe by lungs, body covered
with hair, heart with four chambers, suckle
young. Ex. Sciurus carolinensis.

CHAPTER XXIX

THE YELLOW PERCH

Give me some observations and directions concerning the Pearch for they say-
he is both a very good and a bold biting fish, and I would fain learne to fish for him.

Izaak Walton, The Compleat Angler

Habitat and Distribution. Brilliant in coloration, abun-
dant and easy of capture, and possessing a firm, white flesh
of delicate flavor, it is no wonder that the yellow perch
{Per'ca flaves'cens, Fig. 159) is one of the best known of the
fresh-water fishes of the United States. Though found in
streams, especially in those with quiet reaches of water, the
yellow perch is more truly a creature of ponds and lakes.
There it prefers a pebbly or sandy bottom. Its range ex-
tends from Labrador to Georgia in the fresh-water rivers
and the lakes along the Atlantic coast, and westward in the
region of the Great Lakes and upper Mississippi Valley.
Though originally absent from the Far West, it has been in-
troduced with success into the lakes of Washington, Oregon,
and California. In structure and habits our yellow perch
very closely resembles the perch of Europe, referred to in the
quotation at the head of this chapter, and by some authors
it is considered to be identical with the latter species.

External Structure. The body of the perch is elongate,
slightly compressed from side to side, and tapers toward
both ends. Three divisions are apparent, the head, trunk,
and tail ; several appendages, the fins, are attached to the
body. The covering is a smooth skin, containing pigment
cells, to which the colors are due, and glands which secrete
mucus. Within pouches in this skin are transparent scales,

311

312 GENERAL ZOOLOGY

which overlap, like the shingles on the roof of a house, and
form a coat of mail, incasing the fish from head to tail.
Along a clearly defined lateral line the scales are somewhat
modified, and beneath them are sense organs the functions
of which have been variously stated. These organs are sensi-
tive to mechanical jars of a low rate of frequency, thus stand-
ing between organs of touch proper and those of hearing.

Fig. 159. Yellow perch1

At the anterior end of the head are the jaws, armed with
teeth for seizing food. The eyes have no eyelids. Just in
front of the eyes are the nostrils, two on either side. They
have no communication with the mouth. Behind the eyes,
on each side of the body, is a movable flap called the oper-
culum, beneath which are the red comb-like gills.

There are five fins, three unpaired and two in pairs. Of
the unpaired fins those on the back are called the dorsal
fins, the one on the under side the anal fin, and the one at the
tail the caudal fin. The more anterior of the paired fins are
the pectoral fins ; the more posterior and lower, the ventral, or

iFrom The Fishes of Illinois, by S. A. Forbes and R. E. Richardson.

THE YELLOW PERCH 313

pelvic, fms. The fins are supported by fin rays of two sorts,
the one hard, unsegmented, and unbranched (Fig. 160) ; the
other soft, segmented, and branched.

The Digestive System. The mouth is large. Teeth are
borne not only on the jaws but also on the roof of the mouth
(Fig. 160). On the ventral surface of the mouth is a rather
large, fleshy tongue. Behind the tongue is the pharynx, with
gill slits on both sides, which allow water from the mouth
to pass into the gill chamber. From the pharynx a short
esophagus leads to the stomach. Several pyloric cseca open
into the intestine, increasing its absorbing and secreting sur-
face. The intestine ends ventrally at the anal opening an-
terior to the anal fin. The liver-secretion, called bile, is
stored in a gall bladder attached to the posterior surface of
the liver, and finds its way into the alimentary canal through
the bile duct. Close to the alimentary canal, but not open-
ing into it, is a bright-red organ called the spleen, the func-
tion of which is not positively known.

The Circulatory System. The heart is placed in a large
pericardial cavity, the posterior wall of which forms a thin
membrane separating the heart from the other organs of
the body cavity. Two divisions of the heart may be clearly
distinguished, an auricle and a ventricle (Fig. 160). The
blood, driven from the heart by the contraction of the ven-
tricle, is forced through an artery (the aorta) with a bul-
bous base (bulbus aortae) to the gills, where it gives off its
carbon dioxide and takes on oxygen. After leaving the gills
the blood is collected into a dorsal artery, which carries
it through the body, giving off branches to the various
organs. In the capillaries of the different organs it gives
up its oxygen, collects waste products, and makes its way
through the veins to the auricle, whence it enters the ven-
tricle to repeat its circulation. Valves in the heart and in
the course of the venous circulation prevent the backward

314 GENERAL ZOOLOGY

flow of the blood. In addition to the blood, a white fluid
(lymph) circulates through the body in vessels called lym-
phatics. The function of the lymph is supplementary to that
of the blood.

The Respiratory System. The principal organs of respira-
tion are the gills, eight in number, four on either side. Each
gill consists of a bony arch, on the anterior surface of which
are teeth-like gill-rakers; on the posterior surface are the
delicate gill filaments. In this position the filaments are
constantly bathed by a current of water, which passes from
the mouth cavity out beneath the operculum. In the dorsal
part of the body cavity is a large air bladder (Fig. 160). In
the lining of the wall of the air bladder is a network of
blood vessels, grouped into gland-like "red bodies." By
the absorption and formation of gas by these blood vessels
the weight of the fish can be maintained nearly equal to
that of the water it displaces. The air bladder is probably
useful also as a reservoir of air, for it has been found that in
a perch suffocated in stagnant water the oxygen in the air
bladder, which normally amounts to about one fifth of the
volume of the inclosed gas, had been entirely absorbed and
replaced by carbon dioxide and nitrogen. In some fishes
the air bladder communicates with the alimentary canal by
means of a tube called the pneumatic duct. In the perch
this duct is present in early life, but it soon closes, remain-
ing, however, as a fibrous cord.

The perch, like other fishes, is usually spoken of as cold-
blooded, since its body temperature is little above that of
the surrounding medium. Compared with the higher ver-
tebrates, — the birds, for example, — very little oxygen is
required for respiration, and the circulation is compara-
tively slow.

The Excretory System. The principal organs of excretion
are the kidneys, placed just above the air bladder and below

Teeth in lower jaw, TMh f». roof <* m?uih

Tongue

Optic nerve

Pharynx

Bulbus aortse

Ventricle of heart
Auricle of heart ~

Cord from) Uver
air bladder^

to
alimentary

canal

Gall bladder-
Stomach

Bile duct

Pyloric csecum-

Spleen-

Fat-
mass

Ventral
fin

Urinary bladder -
Urinogenital opening

i Teeth in upper jaw

— -Nostril

Olfactory tract

Cerebrum-
Optic lobes

Cerebellum
— - . -Cranium

■Spinal cord

Interspinal bone

Kidney

Hard

spines

Anal fin

—Air
bladder

Ureter

Vertebra

— Soft ray

Fig. 160. Dissection of the yellow perch. (Reduced)

316 GENERAL ZOOLOGY

the backbone. From the kidneys two tubes, the ureters,
lead, after union, to the urinary bladder. The contents of
the urinary bladder are carried to the surface of the body
at the urinogenital opening, just posterior to the anal
opening.

The Skeletal System. So far in our study of the animal
kingdom the skeletal, or protecting and supporting, parts
have been found chiefly on the outside ; in the fish there is
a well-developed internal skeleton formed of bones com-
posed largely of phosphate of lime. Running from head to
tail through the body is the backbone, or vertebral column,
consisting of a number of separate bones called vertebrse
(Fig. 160) and continued into a brain case, or cranium, at
the anterior end. Bones also form the foundation of the
upper and lower jaws, and support the gills and tongue.
Attached to the backbone are a number of ribs, which in-
close and protect the organs of the body cavity. A row of
small bones (interspinals) supports the unpaired fins. The
pectoral and ventral fins are each supported by a framework
of bones forming respectively a shoulder girdle and a hip or
pelvic girdle.

The Nervous System. Four divisions are quite clearly
marked in the brain, — the cerebrum (Fig. 160) ; the two
large rounded optic lobes ; the medially and dorsally placed
cerebellum; and the medulla oblongata, the latter tapering
posteriorly into the spinal cord (see Fig. 160, where the
medulla is shown though not labeled). Anteriorly the brain
is prolonged into the olfactory tracts, which communicate
with the nostrils ; nerves extend to the different sense organs
and to the various parts of the body.

The ears of the perch consist of two closed cavities on
opposite sides of the cranium, containing concretions of car-
bonate of lime, called otoliths, or ear stones. No one knows
exactly to what extent fishes hear. Some, at least, are

THE YELLOW PERCH

317

capable of appreciating sound vibrations. The ears also
serve as organs of equilibration, by aid of which the fish is
able to maintain its balance. The sense of touch is located
in the skin generally, and in the lateral-line organs. The
sense of taste is not greatly developed in the perch, and
the eyes are not adapted for vision at any great distance.
The organ of smell of fishes is peculiar
among vertebrates in that it has no con-
nection with the respiratory system.

The Muscular System. The muscular sys-
tem consists principally of a
long, thick muscle on either
side, stretching from head to
tail. In the young fish this
muscle is divided into seg-
ments extending vertically
and corresponding in number
with the vertebrae. As the
young fish begins active ex-
istence the muscle segments
are bent and twisted, so that
for a portion of their extent
they seem to run zigzag.

The Reproductive System.
Both the ovary of the female (Fig. 160) and the spermaries
of the male are of large size in the mature perch. They
open to the surface at the urinogenital opening.

Development. Early in the spring the adult perch, which
have spent the winter in the deepest waters of ponds or
lakes, often without feeding very much, draw toward the
shore. The colors, especially on the males, begin to brighten,
till an adult perch in the full glory of his breeding colors is
one of the most beautiful objects in his domain. The time
of spawning varies with the climate : in the South it begins

Fig. 161. Eggs of perch before and
after laying. (Reduced)

From Bulletin United States Fish
Commission

318 GENERAL ZOOLOGY

as early as March ; in New England, in May. The eggs are
laid in shallow water in a ribbon-like mass (Fig. 161), which,
after absorption of water, is sometimes six or seven feet
long and two inches in diameter. This great mass, which
contains thousands of eggs (over a hundred thousand have
been counted in a two-pound perch), is fertilized by the
male emitting his sperm (milt) over it. The eggs form a
large part of the food of other fishes and aquatic birds.
In from two to four weeks, depending on the temperature,

the young perch hatches

from the egg, at first with

the yolk sac attached to

the ventral surface (compare

Fig. 162). After absorption

Fig. 162. Young sturgeon with of the yolk sac, which soon

yolk sac. (Enlarged) occurs, the young perch dif-

After Ryder fers from the adult chiefly in

its smaller size and lighter
color, and in the relatively greater size of head and eyes as
compared with the rest of the body.

Relation to Environment. The whole organization of the
perch marks it at once as one of the predatory type of ani-
mals, — those which hunt their food and depend upon their
superior strength or agility to obtain it. As Izaak Walton
long ago said of its European relative, the yellow perch is
'one of the fishes of prey that, like the Pike and Trout,
carries his teeth in his mouth, not in his throat, and dare
venture to kill and devour another fish." The shape of the
body is precisely that which offers least resistance to mo-
tion in the water. The strong lateral muscles give great
power to the caudal fin, which, by a slight lateral motion,
drives the fish forcibly forward. Lateral and median fins
assist in maintaining equilibrium, in steering, and in raising
and lowering the fish in the water.

THE YELLOW PERCH 319

The colors of most fishes are protective in their nature,
and the perch is no exception to this general rule. From
above, the olivaceous back is with difficulty distinguished
from the water itself or the bottom below ; from beneath,
the white under parts are colored like the surface of the
water or the atmosphere above. The mottled sides also
serve to render the perch less conspicuous in lights and
shadows among weeds and rocks on the bottom. It has
been noted that in some instances where perch live both in
a large lake and in its tributaries, as in Lake Michigan and
the rivers which flow into it, the lake fish have a tendency to
lighter general coloration and to disappearance of the dark
vertical bands. It has been suggested that this difference in
color is due, in part at least, to the smaller amount of light
in the lake, combined with the absence of dark lurking-
places.

Sight is probably the best-developed sense, though, as al-
ready stated, the eyes are not adapted to vision at a great
distance. To test the power of sight discrimination, an
observer dropped into an aquarium pieces of wireworms
(larvae of click beetles) alternately with similar bits of
earthworms. Nearly every time one or more of the bits of
wireworm were seized by the perch, only to be dropped a
moment later. The fishes did not seem to make any per-
manent association between the appearance of the wire-
worm and its inedible character.

Perhaps the clearest way to picture the limitations in
the mental organization of a fish is to sum up, as Professor
Sanford does, some characters in which the fish differs from
man:

No fish is ever conscious of himself ; he never thinks of himself
as doing this or that, or feeling in this way or that way. The
whole direction of his mind is outward. He has no language and
so cannot think in verbal terms ; he never names anything ; he

320 GENERAL ZOOLOGY

never talks to himself. As Huxley says of the crayfish, he " has
nothing to say to himself or anyone else." He does not reflect ;
he makes no generalizations. All his thinking is in the present
and in concrete terms. He has no voluntary attention, no voli-
tion in the true sense, no self-control.

The food of the young perch at first consists entirely of
small, delicate crustaceans, such as Cyclops and its allies ;
from the time the perch are about an inch and a half in
length they begin to add insects to the bill of fare. Adult
perch have a still more varied diet, consisting of the larger
crustaceans, mollusks, and other fishes. The young are
gregarious, and those of about the same size tend to keep to-
gether, so that every farmer boy knows his chances of catch-
ing "a big one" are small indeed when he has his hook in a
swarm of little fishes. He has, however, this consolation, —
that the supply of the one size is likely to last ; for

Perch, like the Tartar clans, in troops remove,
And, urged by famine or by pleasure, rove ;
But if one prisoner, as in war, you seize,
You'll prosper, master of the camp, with ease
For, like the wicked, unalarmed they view
Their fellows perish, and their path pursue.

Oppian, Halientica

CHAPTER XXX

THE ALLIES OF THE PERCH: PISCES

Halcyon prophecies come to pass
In the haunts of bream and bass.

Maurice Thompson

Definition of Pisces (Lat. piscis, "fish"). The perch is a
member of the class Pisces. Fishes are cold-blooded verte-
brates, adapted to life in the water. In the lower forms the
notochord persists as a continuous rod ; in the higher fishes
it is replaced by the vertebrae. The body is covered with
a skin, in which are numerous mucous glands. Scales are
usually present, set in pouches in the skin. In the great
majority of forms, gills are the only organs of respiration.
Locomotion is usually effected by means of fins. With very
few exceptions, fishes lay eggs from which the young are
hatched ; that is, they are oviparous. Some of the sharks
as well as some of the higher fishes produce living young.

Sharks and Rays. The sharks and rays, or Elasmobran'chii
(Gr. elasmos, "metal plate"; branchia, "gills"), are fishes
with a cartilaginous skeleton and with gills which commu-
nicate with the surface by several openings, instead of being
covered by an operculum, as in the perch. The tail is usually
unequally lobed, the dorsal division being the larger.

The sharks (Fig. 163) are, with the exception of one
species found in Lake Nicaragua, marine animals, and are
developed to the greatest extent in the tropics. The rays,
or skates, are more flattened forms, adapted to a life on
the bottom of the sea, which they often resemble in color.
Fig. 164 shows a species common on the North Atlantic

321

322

GENERAL ZOOLOGY

coast, which grows to be about two feet in length. The
most famous of the rays are the torpedoes, so called from

Fig. 163. Photograph of a shark
American Museum of Natural History

their power of giving an electric shock. One species is
sometimes' found on the eastern coast of the United States.

Economic Importance
of Sharks. In some
lands, sharks, and es-
pecially their fins, are
considered a delicacy.
Some species are used
in producing leather
for the manufacture
of novelties. The sha-
green, used in the arts
for polishing woods
and for ornamental
work, is made from
the skin of sharks.
Their livers produce
oils, and the bodies are fig. 164. Photograph of a skate

used in the manufac-
ture of fertilizer. But these uses do not offset the damage
with which the sharks are charged. They destroy great

THE ALLIES OF THE PERCH

323

numbers of valuable food fishes and lobsters, and are a great
bother to the set lines and nets of commercial fishermen.

Bony Fishes. The bony fishes, or Teleos'tomi (Gr. teleos,
" complete " or " perfect " ; stoma, " mouth "), in the higher
forms, of which the perch is an example, have the skeleton
ossified (converted into bone) and the body usually covered
with scales (Fig. 165) ; in
the lower forms the body
may be covered with bony
plates, and the skeleton may
be hardly more ossified than
in the group which has just
been considered. Inalltele-
ostomes, however, the gills
open beneath a protecting
operculum. Most of our
present-day fishes belong
to this order.

The gar pikes of Ameri-
can waters illustrate one
type of body covering, con-
sisting of bony, enameled,
closely set plates, which form
a complete coat of armor.
The sturgeons (Fig. 166) il-
lustrate another type, in
which the armor is greatly reduced, the teeth absent, and
the animals adapted to bottom feeding by the development
of a beak, and by barbels for feeling for their food in the
mud. Sturgeons are found in Europe as well as in the United
States and Canada. One of the European species grows to
be over twenty feet long.

The remaining bony fishes have fully ossified skeletons.
The eels are forms in which the body is greatly elongated

Fig. 165. A scale from a muskel-
lunge. (Greatly enlarged)

The numbered rings are annual growth
rings, showing that the fish bearing this
scale was in its eleventh year. (Photo-
graph by Dr. Alvin R. Cahn)

324 GENERAL ZOOLOGY

and the scales reduced to almost invisible rudiments. Loco-
motion is effected by snake-like movements of the body. The
common eel (Anguil'la chrys'ypa) of North America is found
along the Atlantic coast from Newfoundland to Central
America, and in most streams and ponds in the Eastern
states which are accessible from the sea. The young are
hatched at or near the surface of the ocean. They are so en-
tirely different from the adult eel that for a long time they
were thought to be a distinct genus of fish. After about a year

Fig. 166. A sturgeon1

of life in the ocean waters, drifting here and there without
feeding, they find their way in countless numbers up the va-
rious streams. Here they complete their development and
return to the sea to spawn. After providing for the new
generation the adult eels die, never returning to fresh water.
Life of the Salmon. David Starr Jordan of Stanford Univer-
sity is one of the world's greatest authorities on fishes. He
states, " Of all the families of fishes, the one most interesting
from almost every point of view is that of the Salmonidx,
the Salmon family." There are several species of salmon
on the Pacific coast and one species on the Atlantic. In
1925 the salmon canneries, especially in Oregon, Wash-
ington, and Alaska, produced canned salmon of more than
$47,000,000 value. This is just about one half of the value
of the total canned-fish industry of the entire country.

1 From The Fishes of Illinois by Forbes and Richardson.

THE ALLIES OF THE PERCH

325

The adult salmon live in the ocean. When sexually ma-
ture they leave the ocean and by way of the rivers seek lakes
and streams as spawning grounds. It seems fairly certain
that the adult fishes return to the same waters where they
were born. The mature salmon which escapes the fisher-
man makes its way upstream, frequently for several hun-
dred miles. No food is taken after the fish enters fresh water.

Fig. 167. Flatfish
From Report of Fur-Seal Investigations

It seems to have but one object, that of reaching the breed-
ing grounds. Waterfalls and even some types of dams do
not deter the migration, for by persistent effort some individ-
uals finally succeed in leaping over such obstacles. After the
eggs have been laid and fertilized the adults of both sexes
die, never living to return to the sea. From the spawning
grounds the young salmon migrate to the sea, where they
live for from three to five years before becoming mature
and ready to ascend the streams to the breeding grounds.
Flatfishes. The flatfishes (including among other fishes
the flounders and halibuts) are a family of compressed
fishes, dark on one side and light on the other, which lie on
their light side on the bottom of the sea (Fig. 167). When

326

GENERAL ZOOLOGY

thus placed the dark surface is protectively colored and the
eyes are both on the upper side, which is sometimes the
right side and sometimes the left side of the body. When
they are hatched they have an eye on either side and they

swim like other fishes, though

with a slight leaning to one

side, which becomes more and

more marked as they develop,

till they finally turn entirely over. The eye

on the light side has meanwhile worked its

way slowly round to the dark side, where

it remains with its fellow, looking upward

when the fish lies on the bottom.

Care of Eggs and Young. In most fishes the
parents take no care of the eggs or young.
In some of the fresh-water fishes, such as
the sunfishes, for example, the males con-
struct a rough nest which is often no more
than a hollow in the gravel. Here the fe-
male deposits her eggs and the male dis-
charges sperm into the water to fertilize
them. During development of the eggs the
male stands guard to defend them against
all intruders, even against the female as
well as against outside enemies.

Lungfishes. The lungfishes (Fig. 168), or

Dip'noi (Gr. di-, "two" ; pnoe, "breath"),

Fig. 168. Lungfish
After Dean

in place of the air bladder have a true lung,
or pair of lungs, opening from the ventral side of the ali-
mentary canal. Dipnoans differ from other fishes, too, in
the fact that the heart is incompletely divided into three
chambers. These animals are interesting as the possible
ancestors of the toads, frogs, and their allies, which we shall
consider later. Though numerous in earlier times there are

THE ALLIES OF THE PERCH 327

but three genera now in existence, one each in the rivers of
Queensland (in Australia), Brazil, and tropical Africa.

Economic Importance of Fishes. The value to a people of
an abundant and cheap fish supply cannot be overestimated.
Recognizing its importance, the United States government
has long maintained a Bureau of Fisheries, which has been
active along both practical and scientific lines. A very ex-
tensive laboratory is maintained by the Bureau of Fisheries
at Woods Hole, Massachusetts, for the study of marine life.
Much of the work on problems of fresh-water life has been
carried on by the Bureau through its laboratory on the
Mississippi River, at Fairport, Iowa. Among the subjects
which are considered by the Bureau are the resources of our
inland and coastal waters, the geographical distribution of
the economically important fishes inhabiting them, and the
study of the natural history of fishes, their enemies, diseases,
and the remedies therefor. Perhaps most important of all,
it has carried on the artificial propagation and distribution
of valuable species. According to statistics for 1925 more
than 191,000 persons in the United States and Alaska are
engaged in fishing as a business. They receive close to
$98,000,000 annually for their products.

Hatcheries have been established in many places for
rearing the young from fish eggs. In these hatcheries eggs
are gently pressed from the bodies of mature fishes, or
gathered from the nests where they are deposited in ponds
and streams. The fertilized eggs are placed in jars of water
through which a small water current is passed, or in wire-
bottom trays set into troughs of running water. The young
fishes after hatching are kept in troughs and ponds until they
are ready for transplanting to the lakes and rivers. Until
very recently fishes were liberated when but a few inches
long. The result was that many were destroyed by larger
fishes. A very recent plan of operation calls for fish nurs-

328

GENERAL ZOOLOGY

eries to carry the young fish for a few months after they
leave the hatcheries to insure their ability to care for them-
selves when transplanted to the lakes and streams.

Some idea of the extent of the operations conducted
to restock our streams and lakes is given by the fact
that more than five billion fish and fish eggs were distrib-
uted by the United States Bureau of Fisheries in 1926.

Fig. 169. Inshore with the haul of a large commercial seine on the

Mississippi River

Protection and Conservation. Most states have definite
laws for the protection of fishes. When these laws are wisely
formulated and obeyed they protect the fishes at the breed-
ing season and regulate the methods of catching. The game
fishes, especially the black basses and various species of trout,
are very generally protected from commercial fishing and
are thus preserved for the disciples of Izaak Walton. In most
regions the game fishes may be taken only by hook and line
and their sale is forbidden. Another conservation measure
is the protection of many species by making it illegal to take

THE ALLIES OF THE PERCH 329

fish below certain lengths. In some locations the numbers
allowed each fisherman per day are limited.

Power dams and pollution of the streams by sewage and
factory wastes are probably the greatest factors in reduc-
ing the fish population of our streams. Public sentiment
against, and knowledge of, these destructive conditions are
necessary before adequate laws may be passed and enforced
to protect the life of our streams. There are many very
worthy organizations whose chief object is the enlisting of
public sentiment in favor of conservation. Some states set
apart streams as fish refuges. In these refuges fishing is
either prohibited or very rigidly restricted.

The lives of many thousands of fishes are saved annually
by the rescue crews operating in the backwaters after
streams have been flooded. The relation of this rescue
work to mussel propagation was mentioned on page 205.

Indirect Value of Fishes. In judging the value or impor-
tance of the various kinds of fishes their use as food for man
is not the only relationship to be considered. The gizzard
shad (Doroso'ma) is rarely used for human food. Yet in
many streams it is very abundant, living very largely on
microscopic plants and animals. In turn it serves as one of
the most abundant food supplies of game fishes, which are
unable to use the food upon which the gizzard shad thrives.
Other species are noteworthy because of their destructive
habits. The gar pikes are outlaws, for they have voracious
appetites and live almost wholly on small fishes and the
young of species which are valuable as food for man.

Mosquito Control by Fishes. Goldfishes and several species
of minnows feed very largely on insect larvae. In many
regions where ponds and swamps are the breeding places of
hordes of mosquitoes the mosquito problem has been solved
by introducing goldfishes, and minnows (especially of the
genus Gambu'sia), into the water.

330

GENERAL ZOOLOGY

Geographical Distribution of Fishes. A simple and seem-
ingly natural classification of fishes, as regards their hab-
itat, is a division into fresh-water and marine forms. This
will serve our purpose if it be remembered that there has
been much interchange of species between the two.

There are three common divisions of the ocean fauna, —
the littoral, or shore fauna, the pelagic, or open-sea fauna, and
the abysmal, or deep-sea fauna. The shore fishes never ven-
ture far into the open
sea. Among them are
to be included the
large members of
the salmon family
already referred to.
The pelagic fishes are
mostly hunters of
other animals in the
sea and are strong
swimmers, as befits
their environment.
Typical fishes of this
type are many of
the sharks.
The most peculiar forms belong to the deep-sea fauna.
There, of course, the conditions are unusual ; life must be
adapted to an enormous pressure, to a low temperature (not
far above freezing), and to absolute darkness, except where
it is lit up by some phosphorescent animal. Hence the fishes
found in the deep waters are most bizarre, characterized by
uniformity of color pattern, often black, though brighter
colors are sometimes developed ; by modifications of the
eyes, which are either very large in proportion to the size
of the fish or entirely absent ; by the development of tactile

1 From Gunther's Fishes.

Fig. 170. A deep-sea fish1

THE ALLIES OF THE PERCH

331

and phosphorescent organs. Increase in size of mouth, jaws,
and stomach enables the fish to swallow an animal larger
than itself. Fig. 170 shows one of these species.

Fishes of Past Ages. The earliest known remains of verte-
brates are those of fossil fishes. The oldest of the fossil
fishes were covered with a heavy shell, or armor, and in
appearance somewhat resembled arthropods. These fossil

,— ;- T",X^-',TW^?*^*^-v^^vy^t

Fig. 171. Two examples of fossil fishes

fishes are found in rocks of that period of the earth's his-
tory which is known as the Age of Invertebrates. Geologists
very commonly call the following age the Age of Fishes, for
then many different kinds of fishes made their appearance.
Some of these were not very different from present-day
fishes (Fig. 171), while others represent groups unlike any
that exist today. Paleontologists tell us that fishes first ap-
peared on the earth about twenty-five million years ago. At
that time they were the highest animals on the face of the
earth. But we should hardly recognize as fishes some of
the species of that day.

CHAPTER XXXI

THE GREEN FROG

Cardanus undertakes to give reason for the raining of Frogs ; but if it were
in my power, it should rain nothing but Water Frogs, for those, I think, are not
venomous. — Izaak Walton, The Compleat Angler

Habitat and Distribution. The green frog (Ra'na clam'-
itans, Fig. 172) is one of the commonest species of frogs in
the eastern United States. It frequents the neighborhood
of springs and meadow brooks and may be distinguished
from its larger relative, the bullfrog {Rana catesbia' no) , by
the presence of two glandular folds of skin along the sides
of the back.

In many regions the most abundant frog is a smaller
species commonly called the leopard frog {Rana pip'iens).
The following descriptions of structure agree equally well
for bullfrog or leopard frog, though the green frog is the
species actually described.

External Structure. The body is divisible into a head and
trunk ; there is no visible tail. The body covering is a soft,
smooth skin without scales, abundantly supplied with mu-
cous glands. There are two pairs of appendages, — the limbs :
the anterior of which are divisible into upper arm, forearm,
and hand ; the posterior, into thigh, lower leg, and foot. The
hand ends in four short fingers ; the foot, in five toes, joined
by a web. Both fingers and toes are often spoken of as
digits. The eyes are situated prominently on the top of
the head, and possess, in addition to an upper eyelid, a
thin fold of skin called the nictitating membrane, which can

be drawn across the eyeball from below. There is no true

332

THE GREEN FROG

333

lower eyelid. In front of the eyes, near the anterior end of
the head, are the external openings of the nostrils ; posterior
to the eyes are smooth, round spots, the tympanic mem-
branes, which are the outer portions of the frog's ears.

The Digestive System. The wide mouth cavity (Fig. 173)
narrows into the short, straight esophagus. Conical teeth
are placed along the edge of the upper jaw and on the roof

Fig. 172. The green frog. (Reduced)
Photograph by Elwin R. Sanborne, courtesy of the New York Zoological Society

of the mouth. A thick, fleshy tongue, notched posteriorly,
is attached by its anterior margin to the ventral surface of
the mouth cavity. The tongue can be thrust out suddenly
to quite a distance to capture food, which consists largely
of insects, worms, and mollusks. Two openings lead from
the mouth to the nostrils, and two openings (the Eustachian
tubes, Fig. 173) communicate with the ears. The stomach
is a thick- walled sac tapering gradually into the coiled small
intestine. Beyond the small intestine the alimentary canal
suddenly increases in diameter, forming the large intestine,

334 GENERAL ZOOLOGY

or rectum, which passes without change of diameter into
the terminal cloaca. Between the lobes of the liver lies a
large gall bladder. Another gland, the pancreas, also fur-
nishes a digestive fluid. The spleen is red and globular.

The Circulatory and Respiratory Systems. The heart in-
closed in its sac, the pericardium (Fig. 173), has one chamber
more than the heart of the perch, by the division of the
auricle into two parts, a right and a left auricle. The blood
is aerated in the lungs, the walls of which are traversed by
the capillaries of the blood system. The lungs communicate
with the exterior by means of the windpipe, or trachea,
opening into the mouth by a narrow slit, the glottis.

Owing to the additional chamber in the heart and the
presence of lungs, the course of circulation in the frog is
somewhat different from that in the perch. The aerated
blood returned from the lungs by the pulmonary veins is
poured into the left auricle ; the nonaerated blood from all
over the body is returned to the right auricle. The auricles
contract at the same instant, forcing both venous and arte-
rial blood into the ventricle, which in turn contracts before
there has been much mixing of the two kinds of blood,
emptying its contents into the arterial circulation, the be-
ginnings of which are shown in Fig. 173. As the arterial
system takes its rise from the right side of the ventricle, the
first blood to enter the arteries is nonaerated. Owing to
the less pressure in the arteries which supply the lungs and
skin, and the presence of valves which cut the blood off
from easily entering the arteries that supply the head and
body, most of the nonaerated blood goes to the lungs and
skin. The blood which follows is a mixture of aerated
and nonaerated blood. When the pressure is raised by
the presence of nonaerated blood in the capillaries of the
lungs and skin, this blood forces the valves aside and
makes its way to the different parts of the body, except the

Cartilage in loiver jaiy

Left branch of artery

leaving the heart

Right branch of artery

leaving the heart

Opening of

Eustachian tube —

Medulla — 84

Tongue Mouth cavity

Teeth on upper jaiv
Posterior nostril

Small intestine
Pancreas

Spleen - -

Mesentery-

I

Rectum — ^7
Urinary bladder -Ufe

Cloaca- -
Muscles of left leg

Muscles of right leg

i L-: I '

Socket of femur Aperture of bladder
Fig. 173. Dissection of the green frog. (Enlarged)

Nasal bone
Olfactory lobe

-Cerebrum
Cerebellum

- -Trachea

'Esophagus

-Skin

: Spinal cord

Blood vessels
of skin

Left lung

Vertebra

-Right lung
—Fat body

Spermary

-Kidney

Urostyle

Right ureter

Aperture of right ureter
into cloaca

Cloacal opening

336 GENERAL ZOOLOGY

head. In the course of the artery leading to the head is a
structure (the carotid gland) which temporarily obstructs
the flow of blood till the body arteries have become filled.
The supply of mixed blood having become exhausted,
the head receives only aerated blood. The impure blood
from the organs of the body cavity and from the hind legs
returns either through the liver or the kidneys ; while that
from the head, the forelimbs, and from the skin and muscles
generally, is poured directly into the right auricle.

The frog breathes with the mouth closed. By depressing
the tongue, air is drawn into the mouth cavity through the
nostrils. When the tongue is raised the nostrils close by
valves and the air is forced into the lungs. Considerable
exchange of gases takes place through the soft, moist skin,
which is well supplied with blood vessels.

The lymphatic system is well developed in the frog, and
the lymph is assisted in its circulation by two pairs of lymph
hearts, one at the posterior end of the body, and one in the
region of the shoulders. The pulsations of the posterior
lymph hearts can be observed externally in the living frog.

Excretory System. The kidneys (Fig. 173) are a pair of
oval, dark-red bodies lying in the dorsal part of the body
cavity. The ureters open from them into the cloaca. The
urinary bladder is a large, thin-walled sac projecting ven-
trally from the cloaca and is a very different organ from
the urinary bladder of the perch, which is a dilatation of
the ureter. The function of the two organs, is, however, the
same, that of receiving the liquid nitrogenous waste from
the kidneys.

The Skeletal System. In general, the skeleton of the frog
(Fig. 174) is built upon the plan seen in the perch, but its
appendages are considerably more specialized. The skull
is flattened and the cranium articulates with the first verte-
bra by two rounded contact surfaces, or condyles. The

Phalanges of foreleg

v Skull

,' Radius
and ulna

Metacarpals' ,' „--'
,' Pelvic girdle' . "

Carpus y ..•■■•■' ""-»

Femur

— j- -Tibia and fibula

__ , - Tarsus

Rudimentary toe

- -Metatarsals

-" ;*5*- Phalanges of hind leg

v. Vertebral
/ column

Urostyle

Fig. 174. Skeleton of frog. (Natural size)
Modified from Duges

338 GENERAL ZOOLOGY

vertebral column consists of nine vertebrae, terminated by a
long bone called the urostyle (tail bone).

The bones of the arms are attached to a shoulder girdle
consisting of the shoulder blades, or scapulse, two coracoids,
and two collar bones, or clavicles. A broad breastbone
(sternum) extends a short distance along the median ven-
tral line. Each of the anterior limbs contains one bone in
the upper arm, called the humerus ; one bone in the fore-
arm, composed of two bones united, ■ — the radius and ulna ;
six bones in the wrist region, or carpus ; four complete sets
of bones in the palm (metacarpals) ; and four complete sets
of finger bones (phalanges). The metacarpals and phal-
anges of the inner digit are rudimentary.

The leg bones are attached to the vertebral column by
means of a hip or pelvic girdle, of peculiar shape. The skele-
ton of each leg consists of one bone in the upper leg, the
femur ; one bone in the lower leg, formed from two bones
united, the tibia and fibula ; five bones in the ankle region,
or tarsus ; and five complete sets of phalanges. A sixth rudi-
mentary digit is also present, consisting of one metacarpal
bone and two phalanges.

The Nervous and Muscular Systems. The nervous system
is similar in general plan to that of the perch. The brain has
large cerebral hemispheres (cerebrum, Fig. 173), each of
which is prolonged anteriorly into an olfactory lobe. The
optic lobes are also large, but the cerebellum is small. Be-
hind the cerebellum is the medulla oblongata, at the posterior
end of which the spinal cord arises. The nerves are not shown
in the dissection. The muscles are arranged in bands, or
spindle-shaped masses, instead of in segments, and the frog
is capable of much more complex movements than the perch.

The Reproductive System. The spermaries of the male
frog (Fig. 173) are bean-shaped bodies lying beneath the
kidneys, to which they are attached. The ovaries of the

THE GREEN FROG 339

female frog when mature fill a large portion of the body
cavity. Attached to the anterior end of the spermaries and
ovaries are the fat bodies, — lobed organs which attain
their fullest development in the spring. These organs are
believed to be of use as storehouses of reserve material, ren-
dering possible the formation of large numbers of sperma-
tozoa or eggs without complete exhaustion of the animal.
After the spawning season the fat bodies decrease in size.

Development. The eggs of frogs (Fig. 175) are laid early
in the spring in shallow water in large, jelly-like masses.
They are fertilized by the male as they leave the body of the
female. Within a week or ten days they hatch, the time re-
quired depending largely upon the temperature of the water.
At first the young is blind, and is without gills or a mouth ;
it fastens itself to weeds and other objects in the water
by means of a crescent-shaped, adhesive apparatus at the
anterior end. Certain areas of the body are covered with
cilia, by the vibration of which the animal is able, even
without using its tail, to go forward in the water. Eyes,
external gills, and a mouth provided with horny jaws soon
appear, and the young, now the familiar tadpole, begins
to feed on plant food. The alimentary canal is long and
coiled, as it usually is in animals which feed upon plant
material. The heart has two chambers.

As the tadpole increases in size the first, or primary, gills
are replaced by secondary gills, which soon become covered
with a fold of skin, the operculum. The growth of the oper-
culum continues till the gill openings are covered, leaving a
small hole usually on the left side. In this fish-like condition
the tadpole continues through the summer, and on the
approach of cold weather buries itself in the mud, where it
hibernates. In the leopard frog and some other species the
tadpole develops into the adult form in the course of a
single season.

340

GENERAL ZOOLOGY

If the adult condition has not been reached, the tadpole
continues its growth the following summer. The hind legs
appear and grow to be about an inch long, when the fore-
legs suddenly appear. The front legs are really formed as
early as the hind legs, but they are kept beneath the skin

Fig. 175. Development of a frog1

A, eggs in water ; B to E, stages in the division of the egg and arrangement of
the cells to form the embryo ; F, recently hatched tadpoles clinging to water
plants ; G and H, full-grown tadpoles with hind legs developing ; I and J, trans-
formation of tadpole into adult form showing gradual loss of tail; K, fully

formed frog

for a while. The broad and compressed tail, which forms
the tadpole's chief organ of locomotion, is gradually ab-
sorbed, and the young frog finally hops out on land with
only a stump of a tail remaining. In the time these changes
have been taking place externally, important changes have
gone on inside : the gills have been replaced by lungs ; one

1 Reprinted by permission from Textbook of General Zoology, by W. C. Curtis
and M. J. Guthrie, published by John Wiley & Sons, Inc.

THE GREEN FROG 341

of the chambers of the heart has been divided ; the intes-
tine has become shorter, fitting the frog better for an
animal diet; and the horny jaws have given place to a
wide mouth with teeth. This metamorphosis is retarded
by cold and accelerated by rest and freedom from disturb-
ance of the water. The frog grows for several years without
further metamorphosis, except the gradual disappearance
of the stump of the tail. Throughout life the outer skin is
cast periodically in a single piece and immediately devoured.

Tadpoles fed on thyroid gland transform to frogs long
before their natural time, and tadpoles from which the
thyroid is removed by an operation never undergo meta-
morphosis.

Relation to Environment. The dark-green and brown
colors of the upper surface afford considerable protection
among the water plants and along the muddy or grassy
margins of ponds and streams, and the white under surface
may be similarly useful in the water.

The green frog is a voracious feeder and varies its diet
with almost every kind of small creature that comes its
way, not hesitating in the least to devour smaller individ-
uals of its own kind. Usually only moving objects are seized,
and it has been said that the frog may starve to death in the
midst of an abundance of food if there is no movement to
attract its attention. The eyes are situated high on the top
of the head, where they maintain a wide survey. Every boy
in the country knows of the difficulty of approaching these
alert creatures, and he knows, too, how to capture them
by dangling a hook with a piece of red flannel in front of
them. Even if well fed the frog seems to find the moving
object irresistible, and seizes it with wide-open mouth.
The tongue is covered with a sticky substance and can be
swiftly extended with unerring aim to a distance of several
inches.

342 GENERAL ZOOLOGY

While the frog depends very largely on the sense of sight
to warn it of approaching enemies or enable it to distinguish
food, the sense of hearing is also of considerable value.
Dr. R. M. Yerkes of Yale University, who has studied the
sense of hearing in frogs both in the laboratory and in the
field, says that he is convinced that sounds which are of
importance in the life of the animal, as the splash made by
a frog jumping into the water, are not only heard, but that
such sounds serve to put other frogs on their guard. The
croaking of male frogs in the spring is undoubtedly heard
by the female and serves to make mating more certain.

The observer just cited does not give the green frog
credit for much intelligence, since his experiments seem to
show that nearly all the frog's actions are repeated with
machine-like accuracy, and new habits are learned very
slowly. He is inclined to think that even the perch learns
more rapidly than the frog. He also notes that the frog is
very timid, and that fright tends to lengthen the process
of learning.

When suddenly touched, the frog may do one of several
things : it may jump, using the strong hind legs sometimes
with force enough to carry it several feet ; it may remain
perfectly quiet; or it may crouch with its head close to
the ground, at the same time puffing itself out. This last
action, Dr. Yerkes has noticed, more often takes place when
the animal is touched in front and is probably useful to
render seizure difficult, or to prevent it altogether. If the
frog leaps away, it is usually into the water with a loud
" plunk." A few swift strokes of the hind legs serve to carry
the animal to shelter beneath protecting debris in the water.
There it is able to remain for a considerable period without
the necessity of rising to the surface for oxygen, owing to
the low state of all its life processes. The frog has numer-
ous enemies, among which are owls, "hawks, and herons,

THE GREEN FROG 343

many snakes and other reptiles, and several fur-bearing
creatures which come to the water in search of food.

During the winter, green frogs, like some other frogs,
hibernate in the mud at the bottom of pools. With return-
ing spring they congregate to lay their eggs, and the males
may then be heard calling to the females in an unmusical
"chung," "chung," which is not as familiar a sound, per-
haps, as the bass voice of the bullfrog or the high-pitched,
insistent note of the spring "peepers." After providing for
the reproduction of the species, the green frog spends the
rest of the summer in its rather solitary life on the bank of
some stream or spring hole.

CHAPTER XXXII

THE ALLIES OF THE FROG: AMPHIBIA

Blue dusk, that brings the dewy hours,
Brings thee, of graceless form in sooth

Dark stumbler at the roots of flowers,
Flaccid, inert, uncouth.

Edgar Fawcett, A Toad

Definition of Amphibia (Gr. amphibios, "capable of living
in both air and water")- The frog belongs to the class
Amphib'ia, to which belong also the toads, newts, and
salamanders. Amphibians are cold-blooded vertebrates
covered with a smooth or rough, moist skin, in which are
numerous mucous glands. In the immature state most am-
phibians are adapted to a life in the water and breathe
by gills ; when adult the gills are in the majority of cases
absorbed, and the animals breathe by lungs. Four limbs
are usually present. Nearly all amphibians lay eggs, from
which the young develop.

Two out of the three orders into which the class is divided
will be discussed here. One of these orders includes the sal-
amanders and newts, the other the toads and frogs.

Salamanders and Newts. The Urode'la (Gr. oura, "tail"; de-
los, "conspicuous") are elongate forms, with a tail through-
out their lives. They are often, but erroneously, called lizards,
and resemble the latter only in external form. The eggs are
laid usually in the water in strings, or in large masses re-
sembling frogs' eggs, or singly, attached to the leaves of
water plants.

The red-backed salamander (Pleth'odon cine' reus) and a
number of other species spend their entire life in moist

344

THE ALLIES OF THE FROG 345

places, under logs and stones. They do not even go to the
water to lay their eggs but deposit them among moist leaves
and in rotten wood. Salamanders and newts hatch as tad-
poles, which develop into the adult form without a strongly
marked metamorphosis. The young of most species may be
distinguished from the tadpoles of the toad, and from those
of our various species of frogs, by their more elongate form.
The gills are usually visible externally for a longer period
than is the case with the toad and the frogs. Some species
retain their gills throughout life, though the lungs are also
functional ; in others, though the gills are absorbed in adult
life, the gill openings are retained ; in still others all traces
of gills and gill slits disappear; and, finally, a few species
lose their lungs also, when mature, depending entirely upon
the skin for respiration.

The genus Ambys'toma includes some of the largest of our
species, known by the common name of blunt-nosed sala-
manders. The color is black, spotted with yellow. As these
salamanders are protected by an acrid secretion from the
mucous glands of the skin, the conspicuous colors are pos-
sibly to be interpreted as warning coloration. The adults
live in damp places and lay eggs in the water in large masses
resembling frogs' eggs, though the jelly-like mass which sur-
rounds them is more opaque. The young keep their gills
for a considerable period, and one species (Ambystoma
tigri'num) may even breed in the gill-bearing larval stage.
These immature forms, called the axolotl, live in the
water, growing to be eight or nine inches long, or, in excep-
tional cases, even larger, and may continue in this condi-
tion for years, without ever changing to the adult form.

Like some other amphibians these salamanders can regen-
erate lost limbs. This, according to Professor Gadow of
Cambridge, England, takes place more certainly and quickly
the younger the animal is. In one case quoted by this

346

GENERAL ZOOLOGY

authority the hand of an axolotl ten years old was removed,
and it was replaced within twelve weeks.

The newts, or tritons, are carnivorous salamanders which
are more or less aquatic in their habits when adult, or, at
least, during the breeding season, at which time also the
colors of the males in some species become brighter, and a
crest is developed along the back. The common species of
the eastern United States {Tritu'rus virides'cens, Fig. 176)
is olive green or reddish in color, with a compressed tail and
a row of small orange-colored spots along the right and left

c ~ d

Fig. 176. Development of newt. (Reduced)

A, egg on water plant ; B, larva, in August ; C, young, in autumn ; D, about

two years old ; E, adult. (After Gage)

sides of the body. It grows to the length of three and a
half inches. The eggs (Fig. 176, A) are laid during April,
May, or June, usually in the axils of leaves of water plants,
and the leaves are drawn together and made into a compact
mass by a secretion from the oviduct. As a general rule one
egg is laid at a time ; occasionally two are inclosed in the
same mass. The young hatch in from twenty to thirty-five
days, depending on the temperature. In August they re-
semble Fig. 176, B. Late in the fall they leave the water
and live on land in damp places beneath logs and leaves in
the woods. They are then of a beautiful red color and have
a cylindrical tail (Fig. 176, C). Several years are required
to produce the aquatic adult form (Fig. 176, E), which, as
will be seen, differs considerably from the young.

THE ALLIES OF THE FROG

347

The mud puppy, or water dog {Nectu'rus Fig. 177), lives
permanently in the water and never loses its gills. This
form is the most primitive of present-day amphibians. The
adults are more than a foot in length.

Toads and Frogs. The members of the order Anu'ra (Gr.
an-, "without"; our a, "tail") undergo a well-marked
metamorphosis. From eggs they hatch as tadpoles, and

Fig. 177. Necturus in an aquarium
Photograph by Elwin R. Sanborne, courtesy of the New York Zoological Society

later change to the adult condition by the development
of legs and the gradual absorption of the tail (Fig. 175).
Many examples of peculiar breeding habits are known.
The female of a Brazilian species of tree frog (Hy'la fa'ber)
lays her eggs within a circular wall of mud which she con-
structs on the bottom of a shallow pool of water. Within
this nursery the tadpoles develop, unless liberated by the
rain or other accident. Several species lay their eggs on the
leaves of trees above the water, into which the young fall
when hatched. The male of the obstetrical toad of Europe
(Al'ytes obstet'ricans) winds the eggs around his legs, and,
seeking a safe place, guards them till they hatch. In a

348 GENERAL ZOOLOGY

South American species, the famous Surinam toad (Pi'pa
pipa), the eggs are spread by the male over the back of the
female, where each egg becomes covered with a growth of
skin, forming a pouch with a lid. Here development goes
on, and the entire metamorphosis takes place within the
egg. In a Chilean species (Rhinoder1 'ma dar'wini) the eggs
are transferred by the male to vocal sacs at the side of the
mouth, which become greatly developed at the breeding
season. Metamorphosis takes place within these sacs, and
the young escape in the adult condition. In half a dozen
species of tree frogs from South America (Nototre'ma) the
females possess dorsal pouches in which the eggs are placed.
The young appear either as tadpoles or as perfect frogs.

The tree frogs, or tree toads, are forms adapted to life in
trees. They possess soft pads on the ends of the fingers and
toes. Many of them, like our common tree toad (Hyla
ver'sicolor, Fig. 178), are protectively colored, and have the
power of changing their color through various shades of gray
and green. Several of our smaller species of tree toads,
called "peepers" in the country, give utterance to shrill
notes, which are among the first sounds of spring. In that
season they seek the ponds to mate and lay their eggs.

The common toad (Bu'fo americanus) is one of the
farmers' most valuable allies in the destruction of injurious
insects. Usually the toads feed continuously throughout
the night. It has been estimated that in a single night a
toad consumes insects enough to equal four times the ca-
pacity of its stomach. Despite the prejudice which its
appearance still excites among those who do not understand
it, the animal is a most interesting object for study. There
is no truth in the oft-repeated statements of its poisonous
qualities, except in so far as the acrid secretion of the skin,
which is a protection to many amphibians, might be in-
jurious if it got on sensitive surfaces, such as the lining of

THE ALLIES OF THE FROG

349

the eyelids. The dark-colored eggs are laid in long strings,
like a string of beads, in shallow water, usually in April, in
the latitude of New York. They hatch in two or three
weeks into small black tadpoles, which transform and become
minute toads within
about two months.

Use as Food. Sev-
eral different species
of the larger frogs, the
bullfrog and the green
frog especially, are
frequently caught for
market. The hind legs
of frogs are by many
considered a great
delicacy.

Amphibians of the
Past. Since the am-
phibians are the lowest
animals having limbs
similar to those of
mammals, man has
been much interested
in their beginnings.
The first fossil remains
of amphibians date to
that period of the

earth's history when there was a very luxuriant growth of
tropical fern-like trees. During this time there were many
regions where movements of the earth's crust caused these
forests to be covered by water and turned into coal. The
swamps of that time are the coal beds of today, and the
period is known as the Carboniferous Age, or Age of Coal
Plants. Though fishes and many invertebrate forms were

Fig. 178. Photograph of a tree frog on the
bark of a tree. (Natural size)

350 GENERAL ZOOLOGY

abundant, progress had been made over preceding periods
in the development of backboned creatures adapted to
breathing air. These were amphibians, and from the prev-
alence of species of this order the period is often called the
Age of Amphibians. There were snake-like forms without
limbs, and forms with every degree of limb development.
Some species grew to be as large as alligators of the present
time.

This age when the amphibians represented the highest
development of life upon the earth came to a close about
the time that the Appalachian Mountains were being
formed. Up to the close of this age the eastern portion of
what is now the United States had undergone frequent
changes of level. Part of the time the land areas stood well
above the water, but the land was frequently overflowed by
the sea. With the formation of the Appalachian Moun-
tains, conditions became more permanently suited for land
animals. In the following ages new forms of life began to
come into existence.

CHAPTER XXXIII

THE PINE LIZARD AND ITS ALLIES: REPTILIA

I only know thee humble, bold,

Haughty, with miseries untold,

And the old curse that left thee cold,

And drove thee ever to the sun

On blistering rocks.

Bret Harte, The Rattlesnake

The Pine Lizard

Habitat and Distribution. The pine lizard (Scelop'orus un-
dula'tus, Fig. 179), or " swift" as it is often called, is found
in the eastern United States as far north as Michigan, prefer-
ring the more sandy areas covered with pine. It is a graceful
little creature about seven inches long, gray in color above,
with faint undulating black stripes, and silvery white below.
The male is ornamented with lustrous patches of blue or
green, edged with black on the sides of the throat and under
surface of the body. Old fences which border pinelands are
favorite resorts, and here it pursues and captures countless
insects. Like others of its kind this lizard loves the sun, and
is to be found active only in the hottest part of the day.
During the cold weather it hibernates, at least in the north-
ern part of its range.

External Structure. The body is elongate in form, resem-
bling that of the salamanders, but the skin is covered with
scales instead of being smooth, and there are no mucous
glands. The digits of the four legs are long and slender, and
have sharp claws, which are admirably fitted for clinging to
inequalities in the bark of trees. The gray color of the back

is protective when the lizard is at rest, and its movements

351

352

GENERAL ZOOLOGY

are so quick that it is difficult for the eye to follow them.
When alarmed the scales can be raised, the throat patches
swollen, and the head elevated. The harmless little creature
then looks quite formidable. In order to provide for growth
the scaly skin is cast periodically.

Internal Structure. The internal structure is, in general,
similar to that of the amphibians, but in several respects it

2*7

Fig. 179. The pine lizard. (Reduced)

indicates a higher type of animal. Thus the lizard
breathes by lungs at all periods of its life. The
heart has a longitudinal partition extending par-
tially through the posterior chamber (Fig. 180),
so that there is an incomplete separation into
right and left ventricles. The heart is thus three-
chambered, being composed of one ventricle and two auri-
cles. The arteries leading out from the ventricles are so
arranged that impure blood returning from the tissues of
the body is not completely mixed in the ventricle with the
purified blood from the lungs. When both auricles contract,
the blood is forced into the ventricle. But the purified blood
from the left auricle does not mix completely with the im-
pure blood from the right auricle. Arteries which open from
the left side of the ventricle receive most of the blood from

Cartilage in loiver jaiu— -7-fS" Teeth

Posterior nostril

Glottis

Trachea

Opening of Eustachian tube

Thymus gland

Artery to head and arms—i ^j

Tongue

A

>/...

I

-

Left auricle
Ventricle -
Pericardium
Gall bladder- —
Liver- %

Stomach

Vein from alimentary canal
to liver

Pancreas

Bile duct--

Small intestine

Rectum-
Anterior division of cloaca.

Posterior division of cloaca ~~*

Opening of sperm duct into cloaca 1*-

Aperture of right ureter into cloaca

Cranial cavity

Olfactory lobe

- -,- ;- - Optic nerve

~J? -Cerebrum

W — Optic lobe

■ - - Cerebellum

-'-Medulla

Pulmonary artery

:- — Vein to right auricle

Pulmonary vein

-
||---/ Left lung

| : -.-/r — Edge of stomach
— -<--—»■?-- Artery supplying

- Dorsal aorta

— Spleen

Spinal cord
- - Vertebra

if

if- Left spermary

stomach

Kidney

--Left sperm duct
— Left ureter

Fig. 180. Dissection of the pine lizard. (Enlarged)

354 GENERAL ZOOLOGY

the left auricle, and thus they carry aerated blood almost
exclusively to the tissues of the body. In similar manner
when the impure blood from the right auricle enters the
ventricle most of it is forced directly into the pulmonary
artery, which carries it directly to the lungs. The nervous
system, especially the brain, is also more highly differen-
tiated than in the amphibians, and the bones are more com-
pletely ossified. In discussing the frog mention was made of
the fact that the skull moves on the first vertebra by two
rounded prominences called condyles. In the lizard and
other reptiles there is but a single condyle at the base of the
skull. A study of Fig. 180 will make clear the relation of the
most important organs.

Development. The female pine lizard lays her eggs in the
ground, a short distance below the surface ; ten or fifteen
eggs are deposited in each lot. The eggs are elongated, from
14 to 18 mm. (a little over | in.) in length, and are roughened
on the surface, which causes dirt to adhere to them. They
increase in size as the embryo develops, finally hatching in
about two months. The young resemble the adult quite
closely in everything but size. They are able to take care
of themselves from the first.

The Allies of the Pine Lizard : Reptilia

Definition of Reptilia. The pine lizard will serve as an ex-
ample of the class Reptil'ia (Lat. repere, "creep"), which
includes also snakes, turtles, tortoises, alligators, crocodiles,
and many forms, the dinosaurs, for example, of which there
are no living examples. Reptiles are cold-blooded verte-
brates covered with scales or plates ; they breathe by lungs
throughout their life. A few reptiles are viviparous, but
most of them lay eggs, from which the young hatch in the
form of the adult.

THE PINE LIZARD AND ITS ALLIES 355

Lizards. Most of the Lacertil'ia (Lat. lacerta, "lizard")
are, like the pine lizard, elongate reptiles with four limbs and
movable eyelids. A few families have, however, lost one or
both pairs of limbs in connection with their adoption of a
burrowing life, and the eyes have disappeared beneath the
skin. The covering of scales, so characteristic of reptiles, has
also in some cases become much reduced. Legless lizards
(Fig. 181) may be distinguished from the snakes, which they

Fig. 181. The glass snake, a legless lizard. (Reduced)

resemble, by the fact that they are incapable of opening the
mouth to so great an extent as snakes are. Ear openings on
the sides of the head and eyelids which are capable of clos-
ing are found in the legless lizards but not in snakes. One of
the legless lizards (Ophisau'rus ventra'lis (Fig. 181)) is called
the glass snake because its body breaks so readily. There are
many fables regarding the ability of the glass snake to fly
to pieces when struck and later to reassemble its parts and
crawl away. The portion of the tail broken off is replaced,
but only by the slow process of regeneration and growth.

Many lizards possess the power, when seized suddenly, of
snapping off the tail, which may be left in possession of the

356

GENERAL ZOOLOGY

captor, while the creature hurries away to safety. Fig. 183
shows a Mexican species of iguana which had thus responded
to the efforts of the photographer to take its picture. The
same animal before mutilation is shown in Fig. 182. The
tail is usually reproduced, at least so far as the flesh and

skin are concerned ;
new vertebrae are not
developed. The pat-
tern of the scales on
the newer portion of
the tail is usually sim-
pler, sometimes ap-
parently reverting to
an ancestral type.

The chameleons of
the Old World are
noted for their color
changes, but this
power is possessed to
a greater or less extent
by nearly all lizards.
It is accomplished by
the shifting of pig-
ment granules in cells
in the deeper layers of
the skin, toward or away from the colorless outer skin. The
movement of the granules, though affected by external con-
ditions, such as color and temperature of surrounding ob-
jects, is said to be largely under the control of the animal.
On the islands off the Malay coast lizards close to twenty
feet long have recently been discovered.

Only one genus of lizard found in North America is pois-
onous. These are the Gila monsters (Heloder'ma) which live
in the deserts of our southwestern states.

Fig. 182. Photograph of a Mexican iguana

THE PINE LIZARD AND ITS ALLIES

357

Snakes. The snakes, which belong to the class Ophid'ia
(Gr. ophis, " serpent "), are usually very easily distinguished
externally by the absence of eyelids and limbs, although
rudimentary hind legs are found in a few forms, such as the
pythons. Teeth are present in all snakes, and are of two
types, — the ordinary teeth, used for seizing food, and the
poison fangs, which are perforated, forming a passage for

Fig. 183. Photograph of a Mexican iguana with broken tail

the poison secreted in a gland at their base. Both kinds of
teeth are shown in the illustration of the skull of the rattle-
snake (Fig. 184), which shows also the gland where the
poison is secreted (Fig. 184, 9), and the reserve fangs
(Fig. 184, 11) which replace the first pair when the former
are broken or shed. In the nonpoisonous species the num-
ber of teeth is much greater than in the rattlesnake.

The tongue of a snake is a long, slender, forked structure,
used principally as an organ of touch, not as a fang as many
people believe. The lower jaw is joined to the upper jaw
in such a way (Fig. 184) as to admit of so much freedom
of movement that the snake's mouth can be opened wide

358 GENERAL ZOOLOGY

enough to swallow animals greater in diameter than itself.
The passage of food into the esophagus is facilitated by an
abundant secretion from salivary glands, and escape of the

^~~ _.„j prey is prevented by the

s ":^^^^^^&~; - 4 sharp, backward-pointing

5 TT^^?§^#I^ teeth in both jaws. The

6 ^ J^J/ union of the two sides of

£^fj^ the lower jaw in front is

so loosely made by a

^^^^^yjj^^- cartilaginous connection

s ifl^^^^^^KvS^v"^7'""7^ that each side of the jaw

^^^&^PR^?>g^ can ^e pushed forward

6 ^ ^J^W^>^^S independently, thus get-

^^^^0^^ ting a fresh hold on the

7 ^g^^ food. Some of the larger

^r-^^^%v snakes, as the pythons

10 .^^JgjjjJHJg ^-~m and boas, kill their prey

r^^^^x . N^^i^P^ by constriction : the non-

\a\ x •'' poisonous species may

6 :Sk •" swallow theirs alive ; the

12 J\ poisonous species gener-

Fig. 184. Skull of rattlesnake, showing ally kill the animal, un-

poison fangs » jess jt be a small one.

I, 2, bones of cranium ; 3, prefrontal bone ; Jn captivity many of
k, quadrate bone; 5, maxillary bone; . ,

6, fang.; 7, bones of lower jaw; s, tip of the large snakes refuse to

snout; 9, poison gland; 10, poison duct; eat. In zoological gar-

I I, reserve fangs; 1 2, tip of fang; 13, tern- , ., , ,

porai muscle dens tne extremely large

pythons are held by sev-
eral men and a whole animal as large as a rabbit is poked
down the throat with a probe.

Snakes crawl by means of muscles attached to the ribs
and scales of the under side. These scales have a free
posterior edge, which can be inserted into rough places.

1 From Baskett's Story of the Amphibians and Reptiles.

THE PINE LIZARD AND ITS ALLIES

359

There are more than twenty-three hundred species of
snakes in the world. Of these, less than 1\ per cent are
poisonous. In North America a still smaller percentage
are poisonous. Several species of rattlesnakes (Fig. 185),
copperheads, water moccasins, and coral snakes are poison-
ous, but together they cause only a few deaths a year. This
is in sharp contrast to conditions in India and some regions
of South America. It is
estimated that in Brazil
alone about nineteen thou-
sand persons are bitten
annually by snakes, and
of these close to forty-
eight hundred die.

The poisons produced by
different kinds of snakes
act in entirely different
manners on the human
body. Some destroy the
blood corpuscles. Others
produce paralysis. The
old idea that whisky is an

antidote for any kind of snake bite is absolutely false. The
most successful treatment is by use of a serum called anti-
venin. By injecting small doses of the poison of a given
kind of snake into horses, their blood produces a serum
which counteracts the effects of the poison when injected
into a person bitten by the same species of snake.

The poisonous snakes of the United States are the pret-
tily colored coral snake {Micru'rus ful'vius, Fig. 186) and
the water moccasin (Agkis'trodon pisciv'orus) of the South-
ern states ; the copperhead (Agkistrodon mok'aseri), found
from New England to Wisconsin and southward; and
more than a dozen species of rattlesnakes (Fig. 185), found

Fig. 185. Photograph of a rattlesnake

360

GENERAL ZOOLOGY

mostly in the arid regions of the West and Southwest. The
use of the peculiar horny appendage, or rattle, at the end of
the tail of the rattlesnake has occasioned much discussion.
By some it has been thought to be a means of terrifying
its prey, so that escape may be rendered impossible; by
others it has been regarded as a sex call for its mate, or
even as a lure for birds. Many naturalists consider that

/

.'.

Fig. 186. Coral snake
Photograph by courtesy of the American Museum of Natural History1

its function is similar to that of the yellow and black colora-
tion of wasps, or the distinctive red markings of poisonous
spiders, — features which serve to mark the possessor as
having unusual means of defense. It is thought many con-
flicts are avoided which might prove disastrous to the rat-
tlesnake, even if the attacker were killed in the contest. As
it is, an animal must have some confidence in its powers if
it disregards the warning rattle. A diamond-back rattle-
snake in captivity in the New York Zoological Park grew a
new "button" to the rattle every three months, on each
occasion of shedding its skin.

1 From R. L. Ditmar's Reptiles of the World, with the permission of The
Macmillan Company.

THE PINE LIZARD AND ITS ALLIES

361

Of the nonpoisonous snakes of this country the little
green snake (Liopel'tis verna'lis) is one of the most interest-
ing and beautiful. When kept in confinement it is a harm-
less and interesting pet. As much cannot be said for our
water snakes (Na'trix), which are of irritable disposition and
disposed to strike when handled. Blacksnakes (Coluber)

Fig. 187. A king snake
Photograph by courtesy of the American Museum of Natural History1

have been kept in captivity and handled freely after they
have become accustomed to their new surroundings. Many
snakes are not only harmless but are even actually beneficial.
The fox snakes (Ela'phe) and bull snakes (Pituo'phis) feed
largely on rats, mice, and other rodents. They are worth
protecting around barns and corn cribs. Many of the
smaller snakes feed chiefly on insects and worms, while
those which live near water commonly add fishes to their
diet. Some of the king snakes (Lampropel'tis, Fig. 187) are
beneficial because they feed on poisonous snakes.

1 From R. L. Ditmar's Reptiles of the World, with the permission of The
Macmillan Company.

362 GENERAL ZOOLOGY

Some snakes produce eggs with a tough shell, others bring
forth living young. Some water snakes (Natrix) and garter
snakes (Tham'nophis) give birth to large families. As many
as seventy-five young may be given birth at one time by a
female garter snake. The old superstition that snakes
swallow their young to protect them is absolutely false. It
probably had its origin in the fact that unborn young are
sometimes found in the bodies of dead snakes.

Turtles and Tortoises. The turtles and tortoises, Chelo'nia
(Gr. chelone, ' tortoise "), are externally the best protected
of all the reptiles, being incased in a shell formed of plates
firmly fixed to the vertebras and ribs. Chelonians have no
teeth, but the rim of the jaws is covered with a horny skin.
The limbs are sometimes modified into flippers for locomo-
tion in the water, though the land and fresh-water species
have digits with claws.

The green turtle (Chelo'nia my'das) of the warmer por-
tion of the Atlantic, Indian, and Pacific oceans and the
hawkbill (Eretmoch'elys imbrica'ta), also widely distributed
in warm ocean waters, are economically important, — the
first as an article of food, the second as the source of tortoise
shell. These turtles lay their eggs in immense numbers on
sandy beaches in holes dug for the purpose by the female.
As many as two hundred eggs may be laid by a single female.
Within about six weeks they hatch, having been incubated
by the heat of the sun. These turtles are captured by the
natives of different parts of the world, by diving or by nets
or harpoons. A peculiar method of capturing them is fol-
lowed by natives of such widely separated regions as Torres
Strait, Madagascar, and Cuba. This method consists in
utilizing the services of the sucking fish. This fish is pro-
vided with a sucker-like attachment on the top of the head.
It is borne from place to place by larger fishes, especially
sharks and swordfishes, leaving its host occasionally to

THE PINE LIZARD AND ITS ALLIES

363

procure food. A string is attached to one of these sucking
fishes, which is then liberated in the vicinity of turtles. It
soon attaches itself to the under surface of the shell, holding
on so tenaciously that the turtle can be drawn gently to the
surface. The method was noticed by Columbus or one of

Fig. 188. Photograph of a box tortoise

his companions, and was described in 1671, in the follow-
ing quotation from Ogilby's America :

Somewhat further he [Columbus] saw very strange Fishes,
especially of the Guaican, not unlike an Eel, but with an extra-
ordinary great Head, over which hangs a skin like a bag. This
Fish is the Natives Fisher, for having a Line or handsom Cord
fastned about him, so soon as a Turtel, or any other of his Prey,
comes above Water, they give him Line ; whereupon the Guaican,
like an Arrow out of a Bowe, shoots toward the other Fish, and then
gathering the Mouth of the Bag on his Head like a Purse-net, holds
them so fast that he lets not loose till hal'd up out of the Water.

A common species of tortoise in the eastern United States
is the box tortoise (Terr ape' 'ne, Fig. 188), which lives en-

364 GENERAL ZOOLOGY

tirely on land. These tortoises have a very convex upper
shell ; the lower portion is provided with a transverse hinge,
which makes it possible for the animal to bring the two
parts of the shell closely together, thus forming a box,
within which are concealed head, neck, legs, and tail. A
remarkable sex dimorphism occurs; the eyes of the male
are red, those of the female, brown. More flattened species,
like the painted tortoise (Chrys'emys), are better adapted to

Fig. 189. Photograph of an alligator. (Greatly reduced)

an aquatic existence. The snapping turtles {Chely'dra)
have extremely powerful jaws. In some localities both the
snapper and the soft-shelled turtle (Am'yda) are used as
food.

Alligators and Crocodiles. The large reptiles known as alli-
gators and crocodiles belong to the Crocodiria (Lat. croco-
dilus, "crocodile"). The heart in the crocodilians is highly
specialized, having four separate chambers by the complete
separation of the ventricle into two chambers. Alligators
(Fig. 189) differ from crocodiles in having the canine teeth
of the lower jaw fitting into pits in the upper jaw ; in the
crocodiles they fit into notches in the side of the jaw. A
species of each kind is found in Florida, though both have
been sought so eagerly for the teeth and skin that they are
now found only in the more inaccessible places. Crocodil-

THE PINE LIZARD AND ITS ALLIES

365

ians are also found in China, Africa, southern Asia, and
South America. They frequent the edge of rivers, ponds,
and lakes, lying in wait for their prey with only the tip of
the snout exposed, or concealed in the vegetation at the
edge of the water. They feed at night, and during the day
bask in the sun on sand banks or on logs.

Fig. 190. Reconstruction drawing of the fossil reptile Ceratosaurus.

(Greatly reduced)

Reptiles of Past Ages. During the Age of Amphibians a
great part of the interior of North America was one vast
swamp, in which stretches of black water alternated with
drier areas covered with the characteristic vegetation of the
period, the whole bathed in the heat of a tropical climate.
Under conditions similar to these the reptiles first came into
existence in the latter part of the Carboniferous Age. They
developed in numbers, size, and form, and became in the
succeeding period so characteristic a part of the world's
fauna that the age is named, from them, the Age of Reptiles.
This forms the third great division of geological time, called
Mesozoic Time, or the Era of the Medieval Forms of Life.

366 GENERAL ZOOLOGY

Fossil remains of the later part of the Carboniferous Age
link the reptiles with the amphibians. Some of the reptiles
possessed certain skeletal characteristics of the fur-bearing
animals, and they are called theromorphs (beast-formed) on
that account.

On land many species of dinosaurs (terrible lizard) were
found ; some of them were, with the exception of some

Fig. 191. Photograph of a model of a dinosaur (Triceratops).

(Greatly reduced)

American Museum of Natural History

whales, the largest animals ever developed on the earth,
reaching, in one case, the possible length of eighty or more
feet and the height of nearly twenty feet. This animal was
so great in bulk that it is considered hardly possible for it to
have' supported such a vast amount of flesh on land, and
it is therefore thought that it was aquatic or semiaquatic
in its habits. Some of the dinosaurs, as Ceratosau'rus
(Fig. 190), were particularly fitted to walk on their hind legs,
using the tail as a support. Members of this genus grew to
be seventeen feet in height. Hundreds of the footprints of
dinosaurs have been found in the sandstone of the Con-
necticut valley. Fig. 191 shows a well-known dinosaur,

THE PINE LIZARD AND ITS ALLIES

367

Tricer'atops, with formidable armature. One species reached
a length of more than twenty feet, and stood eight feet
high. An American scientific expedition into Asia has re-
cently unearthed many interesting fossils. Among the
most noteworthy finds was the discovery of dinosaur eggs.

Fig. 192. Restoration drawings of bird-like reptiles, or pterosaurs1

Some of the ancient reptiles (the flying lizards, or ptero-
saurs, Fig. 192) were capable of flight by means of skin
stretched between the front and hind limbs and tail. Most
of the bones were hollow and the skull was quite bird-like.
Reptiles which are apparently related to the alligators and
crocodiles, and to the turtles and tortoises, have also been
found in the rocks of this period, so that these groups are
very ancient. Most of the lizards and snakes belong to a
later day.

1 From Seeley's Dragons of the Air.

CHAPTER XXXIV

THE DOMESTIC PIGEON

A hundred wings are dropt as soft as one.
Now ye are lighted — lovely to my sight
The fearful circle of your gentle flight,
Rapid and mute, and drawing homeward soon ;
And then the sober chiding of your tone
As there ye sit from your own roof arraigning
My trespass on your haunts, so boldly done,
Sounds like a solemn and a just complaining !

Charles Tennyson Turner, On Startling Some Pigeons

Habitat and Distribution. The domestic pigeon is known
under many varieties, all of which, it is now believed,
have been bred by artificial selection from the rock dove
(Colum'ba liv'ia, Fig. 193), a bird widely distributed through-
out the European north-temperate realm. In its wild state
the rock dove nests in the crevices of rocks, usually along
seacoasts. The different domesticated varieties (Fig. 97)
have been still more widely scattered over the earth
through man's influence.

External Structure. In the pigeon we can distinguish a
head, neck, trunk, and tail. All over the body the skin is
closely set with feathers. There are two pairs of appendages :
the anterior, or wings, are used for flight, and the posterior,
or legs, for support. The wings consist of an upper arm,
forearm, and hand, as in the amphibians and reptiles, though
the digits are joined together and reduced in number
(Fig. 195). The legs also show divisions similar to the hind
legs of amphibians and reptiles ; that is, thigh, lower leg, and
foot, the latter being covered with scales and ending in four

toes, which bear claws resembling those of the lizard.

368

THE DOMESTIC PIGEON

369

The mouth is inclosed by a toothless, horny beak, above
which are situated the two nostrils, set in a mass of soft,
fleshy skin called the cere. The eyes are large and have an
upper and a lower eyelid and a nictitating membrane. The
external openings to the ears are a little behind and below
the eyes and are surrounded with specially modified feath-
ers. At the base of the
tail on the dorsal surface is
a gland which secretes an
oil for keeping the feathers
in good condition.

The feathers are not scat-
tered uniformly over the
body, but are arranged in
definite tracts separated by
areas in which grow only a
few hair-like feathers. As
an example of a fully de-
veloped feather we may
choose one of the large
flight feathers (Fig. 194, A)
which occur on the wings
and tail. It consists of
a hollow base, the quill

(Fig. 194, A, 1), from which extends a portion called the vane.
Through the center of the vane runs the rachis (Fig. 194,
A, 2), which gives off branches called barbs. From the barbs
run interlocking structures (barbules) bearing hooks which
serve to bind the vane into one continuous surface. At the
junction of quill and rachis on the under surface of the
feather a tuft of down, the aftershaft (Fig. 194, A, 3), is
often found. The surface of the body is covered with con-
tour feathers, which overlap each other, forming a close
covering. Scattered among the contour feathers are down

Fig. 193.

Photograph of a rock dove.
(Reduced)

370

GENERAL ZOOLOGY

feathers (Fig. 194, C), with which the nestling pigeon was
covered, and hair-like feathers, or filoplumes (Fig. 194, B).
Down feathers differ from contour feathers in having no bar-
bules, so that the barbs are not held together, but make a
fluffy mass. Filoplumes have only a main axis with few barbs.

The Digestive Sys-

tern. The mouth is
without teeth. Sali-
vary glands opening
into the mouth fur-
nish a fluid which
assists in swallow-
ing the food. There
is a large tongue
(Fig. 195), pointed
at its anterior end.
From the pharynx
there are openings
to the nostrils and
to the ears, as in
reptiles and am-
phibians. A short
esophagus leads to a
large crop, in which
the food, consisting
largely of grain, is
somewhat softened
before passing into the glandular stomach behind it. Glands
in the lining walls of the stomach pour out a digestive fluid
which serves further to soften the food, which then enters
the gizzard, an organ with a yellow, horny lining surrounded
by a thick mass of muscle. The gizzard contains small
stones swallowed for the purpose of assisting in grinding
the food ; this process is accomplished by movements of the

Fig. 194. Feathers of pigeon

A, flight feather; 1, quill; 2, rachis ; 3, aftershaft;
B, filoplume ; C, down feather

THE DOMESTIC PIGEON

371

muscular walls. Beyond the gizzard the small intestine forms
a loop inclosing the pancreas, which discharges its secretion
into the intestine through three ducts, one of which is shown

Tongue

Posterior nostril

Trachea

Esophagus

m$\~"'-Cere

Medulla-

Pulmonary artery
Left branch of pulmonary vein
Esophagus
-Left lung

-Olfactory lobe
■'%^-Glottis

'.x-Optic nerve
S""V" Cerebrum
~^ji}~~Optic lobe
^-Cerebellum
™ -Cranium

— Spinal cord

First digit (thumb)
Second digit - - - -^3.

Crop

Right branch of aorta
Left branch of aorta

Aorta
Left auricle --

Left ventricle —
Pericardium

Liver-
Sternum
Spleen
Glandular stomach

Gizzard —
Leg-

Intestine
Pancreas

Dorsal aorta
Spermary

Sperm duct
Ureter
Kidney
Csecum

Oil gland
Terminal vertebra

Bile duct
Pancreatic duct

Vesicula seminalis
Aperture of ureter into cloaca

Fig. 195. Dissection of common pigeon. (Reduced)

in Fig. 195. The liver is large and opens into the intestine
by two bile ducts. The posterior end of the intestine {rectum)
passes without change of diameter into the cloaca. The
junction between the rectum and cloaca is marked by the

372 GENERAL ZOOLOGY

presence of two caeca. The spleen is bright red, and is
attached to the walls of the glandular stomach.

The Circulatory System. The heart is a large, four-
chambered organ inclosed in the pericardium (Fig. 195).
It consists of two auricles and two ventricles, the latter sep-
arated by a complete partition. The circulation is double,
and the aerated and nonaerated blood come nowhere in
contact, except in the capillaries. The blood is sent to the
lungs from the right ventricle, through the pulmonary artery.
Freed of its carbon dioxide, the blood returns through the
pulmonary vein to the left auricle, whence it passes to the
left ventricle and thence into the aorta, which distributes
it to all parts of the body. The blood from the body returns
to the right auricle, whence it enters the right ventricle,
completing its circuit. Lymph circulates through the body
of the pigeon in vessels of the lymphatic system.

The Respiratory System. The organs of respiration are the
larynx, which opens out to the pharynx by a slit-like glottis ;
the trachea ; the bronchial tubes, which ramify through the
tissue of the lungs ; and the lungs themselves. The trachea
is kept open by rings of cartilage in its wall. At the junction
of the bronchial tubes and trachea is a slight enlargement,
forming the syrinx, the organ of voice. The well-known
sounds are produced by the vibration of a fold of membrane
at this place. Many of the bones are hollow, and there is
a system of air sacs scattered through the body and com-
municating with the bronchial tubes. By these means the
air available for respiration is greatly increased and the
weight of the body is lessened. Breathing is accomplished
by movements of the muscles of the thoracic region, by
which air is driven almost completely out of the lungs at each
expiration. The aeration of the blood is complete, and a prac-
tically constant high temperature, 37° C. (100° F.), is main-
tained. The pigeon is therefore said to be warm-blooded.

THE DOMESTIC PIGEON 373

The Excretory System. The kidneys (Fig. 195) are dark,
three-lobed organs fitting closely into cavities beneath the
backbone. The ureters open into the cloaca.

The Skeletal System. The skull (Fig. 196) is large, with
a comparatively large, rounded cranium. The articulation
of the cranium with the first vertebra is made by a single
condyle, as in the reptiles. The vertebrae of the neck, or
cervical region, are free ; those of the thoracic region, pelvic
region, and caudal region are more or less united. There
are several pairs of ribs. The caudal vertebras are termi-
nated by a peculiar bone called, from its shape, the plow-
share bone. The shoulder girdle is composed of a pair of
narrow scapulas, to which are attached two coracoids, con-
necting the scapulas and the sternum, and a V-shaped bone,
the wishbone, formed from the union of the two clavicles.
A greatly enlarged sternum with a prominent ridge, or keel
(Fig. 196), serves as a surface for attachment of the mus-
cles of flight. The hip girdle is united to the vertebras of
the pelvic region. A study of Fig. 196 and comparison with
the skeleton of the frog will make clear in what respects the
appendages are different.

The Nervous and Muscular Systems. The brain is larger
in the pigeon, in proportion to the size of the animal, than
in the amphibians and reptiles. The cerebrum (Fig. 195)
and the cerebellum are especially large. One of the principal
functions of the cerebellum is to control the muscles which
bring about the balancing of the body. It is apparent that
this is of greater importance in the birds and fishes than in
the broader-bodied amphibians and reptiles. The optic lobes,
pressed to one side by the large cerebrum, are also well
marked, in correlation with the unusually large eyes and the
dependence of the pigeon on the sense of sight. The olfactory
lobes are relatively small, and the sense of smell is not at all
keen. The medulla is bent downwards, as in the reptiles.

374

GENERAL ZOOLOGY

The muscular system shows many adaptations to the
aerial life of the pigeon. The great mass of muscle by which
the downward stroke of the wings is accomplished occupies
almost all the space on the prominent, keeled breastbone.
Its position, low down on the body, makes overturning in

Skull — ;

Upper
mandible-

-Cranium

/Cervical (neck) vertebra

Ulna
Radius

Thumb

Lower
mandible

Humerus
Clavicles (wishbone)-
Coracoid —

Keel of sternum—

TJwracic
region

Scapula

End bone of
second finger

Bone LB<me of
of second
third finger
finger

-Plowshare
bone

Bone of second toe

Caudal region

-—Ankle and foot
Bone of first toe

Fig. 196. Skeleton of pigeon. (Reduced)

the air almost an impossibility. The muscle which raises the
wing is also situated beneath the breastbone, and is inserted
on the dorsal surface of the humerus by a tendon which
passes through an opening at the shoulder. The tendon thus
acts as a pulley in raising the wing. The muscles which
bend the toes in perching are so arranged that the mere
weight of the bird keeps them contracted, so that even when
the pigeon is asleep the toes firmly grasp the perch.

THE DOMESTIC PIGEON 375

The Reproductive System. The spermaries (Fig. 195) are
oval bodies attached to the kidneys. The ovary of the right
side is not developed, but the left ovary is a large organ
situated near the kidneys.

Development. Unlike most of our domestic animals,
pigeons choose their mates for life. After fertilization the
ova, or " yolks," pass down the oviduct and are covered with
secretions from glands in different regions, first with the
white, or albumen, then with a thin membrane, and lastly
with a white, limy shell. The eggs are laid in a roughly
made nest, and are incubated by both parents in turn for
about two weeks, when they hatch. The young bird breaks
through the shell by means of a hard structure on the tip of
its beak, and makes its appearance covered with a fine down.
It is interesting to note in this connection that Darwin says
that some of the short-beaked tumbler pigeons, which have
been developed by artificial selection, have beaks so short
that they are unable to get out of the shell alone, and re-
quire therefore to have the help of the pigeon-fanciers. For
a few days after hatching, the young bird is fed by both
parents with a milky secretion afforded by the crop and
called "pigeon's milk/'

At first the young are deaf and the eyes are closed, but
both sight and hearing are acquired within a few days. The
young birds rapidly acquire the power to make coordinated,
or connected, muscular movements, and in a few days the
voice develops. The independent life of the pigeon, in some
cases, begins about the thirty-fourth day after hatching.

Relation to Environment. The form of the pigeon is well
adapted to cleaving the air, and the feathers form a light
waterproof covering which serves to retain the body heat in
the rapid flights in the cold atmosphere. "It is worthy of
notice," say Parker and Haswell, "that birds agree with
insects, the only other typically aerial class, in having the

376 GENERAL ZOOLOGY

inspired air distributed all over the body, so that the aera-
tion of the blood is not confined to the limited area of an
ordinary respiratory organ." Other important structural
peculiarities are the light, toothless beak and the small
number of digits in the anterior extremities. Still other
characters have been referred to in the discussion of the in-
ternal anatomy.

The many varieties of the domestic pigeon afforded Dar-
win much material for his book The Variation of Animals
and Plants under Domestication. From this study he ob-
tained many of the conclusions which led to the statement
of the principle of natural selection. These domestic varie-
ties differ among themselves in appearance far more than
many species in nature. Some well-known varieties are the
pouters, fantails, tumblers, and carriers. The pouters are
large birds with elongate body and legs, and often with in-
flated crop and esophagus. The fantails are known by the ex-
traordinary development of tail feathers. The tumblers have
the remarkable habit of turning somersaults backward in the
air from a considerable height nearly to the ground.

The carriers have the "homing faculty" developed to
such an extent that they are useful as messengers. Though
shut within a basket and removed long distances from their
home, they have been able to find their way back. Carriers
have, been used by man for many centuries. During the
World War homing pigeons were much used at the front
when other communication was entirely cut off. In one in-
stance a pigeon carried and delivered a message a distance
of almost twenty-five miles in just twenty-five minutes, al-
though one leg had been shot off and the breast injured by a
machine gun.

CHAPTER XXXV

THE ALLIES OF THE PIGEON: AVES

Robins and mocking-birds that all day long

Athwart straight sunshine weave cross-threads of song.

Sidney Lanier

Definition of Aves (Lat. avisf "bird"). The pigeon is a rep-
resentative of the class A'ves. Birds are warm-blooded ver-
tebrates adapted as a class to an aerial existence. They are
covered with feathers, which are, in their origin, modified
scales. Birds breathe by lungs. The young are always
hatched from eggs in a form closely resembling the parent.
There is remarkable uniformity of structure in the class,
making classification extremely difficult.

The following groups, which are some of the most impor-
tant of the many divisions into which birds have been di-
vided, are not all entitled to rank as separate orders, though
often treated as orders.

The Ostrich and Allies. The group Struthio'nes (Gr. stru-
thion, "ostrich") contains the ostrich of Africa, the rheas, or
South American ostriches, and the emus and cassowaries
of Australia, New Guinea, and adjacent islands. They are
all large birds with rudimentary wings, and with only two
or three toes on each foot. They have no ridge, or keel, on
the sternum, a structure which in most birds serves as an
attachment for the muscles of flight ; hence the struthious
birds cannot fly, though there is evidence that they have
descended from ancestors that had functional wings. The
legs are large, and the birds run with great speed. Most of
them live in open desert places, though cassowaries inhabit

377

378 GENERAL ZOOLOGY

forest regions. The eggs are laid in a deep depression in the
sand, or in a rough nest in the case of the cassowary. The
ostrich is the best known of the group, largely on account of
the beautiful wing and tail plumes, which have been used
for ornaments from very early times. Ostriches are now
raised for the sake of the plumes on "farms" in California
and South Africa.

Diving Birds. The group Pygop'odes (Gr. pyge, "rump" ;
pous (pod-), "foot") includes various species of water birds
with webbed or lobed toes (Fig. 197). Their scientific name
refers to the fact that the legs are placed very far back, so
that when standing, an erect position is assumed. The tail is
very short. The beak is sharp and pointed and fitted for cap-
turing fishes, which constitute a large part of their food.
They are expert divers and can swim under water with only
the tip of the bill exposed. The nest is generally nothing
more than a floating mass of decaying vegetation, attached
perhaps to some reeds in shallow water. Our northern lakes
and ponds are often visited by the loon, a characteristic
diving bird.

Gulls and Terns. The group Longipen'nes (Lat. longus,
"long" ; penna, "feather") includes long- winged water birds
with sharply pointed or hooked beaks* The colors are usually
gray above and lighter below. The three front toes are con-
nected by a web (Fig. 197). These birds are strong and
graceful fliers, and spend much of their time on the wing.
All the members of the group are gregarious, occupying
nesting sites on sandy beaches, in marshes, or on rocky
shores. They obtain the greater part of their food from
the ocean and lakes, and are useful as scavengers. Terns
(Fig. 198) may be distinguished from gulls by their usually
deeply forked tail and straight bill. Gulls are generally
pelagic, and they often follow ships for the sake of the
refuse thrown overboard ; terns frequent the shores of

Fig. 197. Specialization in the legs of birds

Although the legs of all birds are constructed on th -^^PJf ^^
many distinctive features that correspond to ^^^^ ^^ts . thelonKlegs
are the webbed toes of water birds - gull, loon alba ross pehca , the long eg_
of wading birds - heron ; the sharp claws of *"*«?£ »^^ f oot of
hawk. Contrast the climbing foot of the woodpecker with ™Pg™m*
the parrot and the ground foot of the sparrow or partridge

380

GENERAL ZOOLOGY

both fresh and salt water. Owing to the forked tail and
graceful flight, the terns are often called sea swallows.

Petrels and Allies. The petrels and their allies are strong-
winged pelagic birds, many of which externally resemble
the gulls and terns. They may be distinguished from other
water birds by the nostrils, which are inclosed in tubes lying

Fig. 198. Photograph of a tern on its nest

on the dorsal or lateral surface of the upper mandible ; hence
their scientific name, Tubina'res (Lat. tubus, "tube" ; naris,
"nostril"). The beak is usually strongly and sharply hooked.
The food consists of fishes and other small animals which
live near the surface of the ocean. The birds often follow
ships, like the gulls, to pick up refuse. They occupy various
nesting sites along shores. The wandering albatross (Dio-
mede'a ex'ulans, Fig. 197) of southern oceans is the best-
known species. It is the largest of sea birds, measuring
over twelve feet between the tips of the wings. One of the

THE ALLIES OF THE PIGEON

381

traditions among sailors concerning the albatross is referred
to in Coleridge's Ancient Mariner. Other members of the
group, called stormy petrels and Mother Carey's chickens,
are also regarded by many sailors with superstitious dread.
Pelicans and Allies. The members of the group Steganop'-
odes (Gr. steganos, "covered"; pons (pod-), "foot") differ

Fig. 199. Colony of brown pelicans and young on nesting site

The female near the center is protecting the young from the sun. (Photograph

by Dr. Alvin R. Cahn)

from all other web-footed birds in that all four toes are
connected by a web (Fig. 197). They are aquatic and
feed mainly on fishes. To this group belong the pelicans
(Fig. 199), remarkable for the pouch beneath the bill, which
is used as a scoop to capture food or as a storage reservoir.
There are about a dozen species of pelicans distributed
over the world, of which two species, the brown and the
white pelican, are found in the United States. White peli-
cans have the habit of surrounding schools of small fishes

382 GENERAL ZOOLOGY

and driving them with loud beatings of wings into shallower
water, where they can be scooped up in the great pouch
and devoured at leisure.

Ducks, Geese, and Swans. The group An'seres (Lat. anser,
" goose") is made up of water birds which have the three front
toes webbed and the tail comparatively well developed. The
ducks, geese, and swans are included here. The bill is usu-
ally flattened and is furnished with transverse tooth-like
ridges on both upper and lower mandibles. In the species
which frequent rivers and ponds, feeding largely on vege-
table food or on small mollusks, crustaceans, and larvae of
insects, these ridges act as a strainer through which the
water runs off when the bill is closed, leaving the food be-
hind; in the harbor species and sea-haunting, fish-eating
species the ridges are useful in holding the slippery food.
The nest is usually placed on the ground near the water.

Wild geese have long excited interest on account of their
peculiar manner of migrating in a flock arranged in a long,
V-shaped group, keeping up the continual, sonorous "honk,
honk." Among the geese and swans the sexes are usually
alike, but in many of the ducks the male is specially orna-
mented with brilliantly colored plumage. Well-known spe-
cies of ducks are the canvasback duck, dear to the epicure ;
and the mallard, the ancestor of the common domestic duck.

Herons, Storks, and Allies. The birds of the group Hero-
dio'nes (Gr. erodios, "heron"), often spoken of as wading
birds, are long-legged species, with four toes placed on about
the same level, and slightly or not at all webbed (Fig. 197).
The bill and neck are long and slender. Crests and decora-
tive plumes often ornament the head and neck. Herons
haunt the edge of ponds, lakes, and rivers, where they feed
on fishes and frogs, which they capture with their long, sharp
beaks. They nest in great colonies, usually in trees. The
nests are clumsy affairs made of sticks in an untidy mass.

THE ALLIES OF THE PIGEON

383

One of our largest species is the great blue heron, which
stands nearly five feet high. Several herons, called egrets
(Fig. 200), which have the misfortune to grow beautiful
dorsal plumes, or "aigrets," at the breeding season, have
been practically exterminated by man for the sake of their
plumes for women's hats. Fortunately, federal laws now

Fig. 200. Photograph of egrets

prohibit the slaughter of these birds and the sale of their
feathers. Egrets were formerly common in Florida and
along the Gulf coast. Storks are natives of the Old World,
frequenting wooded regions or open country. The white
stork has been tamed in some countries, where it frequently
occupies nesting sites on houses.

Cranes and Allies. Though superficially like the herons,
in that they have a long bill, neck, and legs, the cranes and
their allies may nevertheless be distinguished from the herons
by the elevation of the hind toe above the level of the others.
The cranes are scattered widely over the globe, though we

384 GENERAL ZOOLOGY

have but three species in North America. They frequent
marshes and open plains (their scientific name, Paludic'olse,
means "marsh inhabitants"), and feed on both vegetable
and animal food, the latter consisting largely of small rep-
tiles and amphibians.

Erect and tall, they may be seen striding swiftly along with
head thrown back, or strutting around their mates; while in
spring they often stand in rows and proceed to stalk about in
single file, or dance to meet one another with nodding heads,
necks advanced, and wings widely outspread. Thereafter they
bow toward the ground, jump in the air, and perform graceful
antics of all descriptions. The chosen spot for these dances is
commonly near water. The male courts his spouse in somewhat
similar fashion, and twigs or feathers are often tossed in the air in
sport, to be caught again ere they touch the ground.1

Snipes, Sandpipers, Plovers, and Allies. The well-known
shore birds, included in the group Limic'olae, usually have
long, slender legs, with the hind toe, when present, elevated
above the others (Fig. 197). The scientific name refers to
their habitat (Lat. limus, "mud" ; colere, "dwell"). The bill
is usually long and slender and more or less soft, especially
at the tip. With their bills these birds probe the mud and
sand of pond and river margins and the seacoast for their
food, which consists of small crustaceans, worms, and mol-
lusks. The plumage is usually brown or gray, with some
white intermixed. During the breeding season many species
give utterance to more or less musical cries. At other sea-
sons a number of species have shrill call notes or whistles.
The eggs are usually laid on the sand in a hollow scraped for
the purpose. They are very often protectively colored. Like
the domestic fowl, the young are able to take care of them-
selves from the very first. Their nestling plumage is also
protectively colored.

1 Cambridge Natural History, Vol. IX.

THE ALLIES OF THE PIGEON

385

One of the best known is the woodcock, which frequents
low, moist, wooded regions. The tip of the upper mandible
can be moved upward, so that it is of use in feeling for and
seizing worms in the ground. The Wilson's snipe of fresh-
water meadows and swamps, and the upland plover of higher
and drier pastures, are other familiar species of shore birds.

Grouse, Quail, Tur-
keys, Pheasants, and
Allies. The gallinace-
ous birds, Galli'nae
(Lat. gallina, "hen"),
commonly known as
scratching birds, have
a stout, convex beak
with which they pick
up seeds of plants,
which form a large
part of their food. The
wings are short and
rounded, and the
short, stout legs have
strong toes adapted to
scratching (Fig. 197).

Nearly all species are terrestrial in habit. Here are included
the larger part of the game birds of the world. By far the
best known of the group is our domestic fowl, of many races,
all of which are descended from the jungle fowl (Gal'lus, Figs.
201, 202) of India, Sumatra, Celebes, and the Philippines.

The best known of the grouse in the eastern United
States is the ruffed grouse (Bona'sa umbel'lus), usually, but
wrongly, called "partridge" in New England. It is about
the size of the domestic fowl, and has pronounced black
ruffs on the sides of the neck. The male produces a loud
drumming sound by beating the air rapidly with the wings.

Fig. 201. Photograph of male and female
jungle fowl

386

GENERAL ZOOLOGY

The sound is a call to the female, though it is indulged in
occasionally at other seasons than in the spring. The quail-
like bobwhite (Coli'nus Virginia' nus) is also, but errone-
ously, called "partridge" in the Southern states. It is a
smaller bird than the ruffed grouse, reddish brown in color,
and without the ruff about the neck. Neither of these birds
should be called "partridge," since that name is already in
use for Eurasian species of gallinaceous birds. The same

statement is true of the
term "quail," which is
often applied to our bob-
white. The pheasants
are magnificently colored
birds, native to south-
eastern Asia and adjacent
islands. The Hungarian
partridge and the ring-
necked pheasants have
been introduced in vari-
ous regions in the inter-
ests of the sportsman.
Pigeons and Doves. The Colum'bae (Lat. columba, "dove")
are closely related to the gallinaceous birds, but the nostrils
open into a fleshy cere. The domestic pigeons belong to
this group. We have in the eastern United States but one
species of wild dove, the mourning, or turtle, dove. The
passenger pigeon was formerly present in immense num-
bers in the wooded regions of the eastern LTnited States.
In the early years of the eighteenth century flocks were
seen which stretched far across the sky, and which required
hours to pass a given point. Owing to the increased demand
for both young and adults as food they were slaughtered in-
discriminately and have since, to our disgrace as a civilized
nation, been entirely exterminated.

Fig. 202. Young of jungle fowl

THE ALLIES OF THE PIGEON

387

Hawks, Eagles, Vultures, and Allies. The Rapto'res (Lat.
raptor, "robber ") are generally spoken of as birds of prey,
though the term is equally applicable to some members of
other groups, the gulls among the long-winged swimmers,
for example. The beak is stout, strong, and sharply hooked
(Fig. 203) ; the toes, arranged three in front and one be-
hind, are provided with strong, sharp, curved claws
(Fig. 197) with which to seize their living prey, except in
the vultures, which
feed on carrion. All
the Rap tores possess
great powers of flight.
The female is larger
than the male. The
nests are generally
bulky and are com-
posed of sticks and
placed in tall trees or
on rocky cliffs.

The red-shouldered
and the red-tailed

hawks are generally termed "hen hawks," or "chicken
hawks/' by farmers. Though they occasionally levy tribute
on the chicken yard, their propensities in this direction are
not so marked as is the case with some of the other hawks,
which do not sail so conspicuously in the air. Except in
some localities, hawks undoubtedly do more good than
harm by destroying large numbers of mice and other small
mammals. The vultures are, generally speaking, scaven-
gers, though they may attack weak and disabled animals.
The black vulture and the turkey buzzard are invaluable
as scavengers in the Southern states. They have been
protected for this reason, and have become very tame in
many places.

Fig. 203. Head of golden eagle

388

GENERAL ZOOLOGY

The owls (Fig. 204) are birds with large eyes and soft,
fluffy plumage. They feed almost exclusively on mice and
other rodents, though some species are guilty of eating song
birds. The great horned owl is even convicted of stealing
poultry. The screech owl and most of the other species are
not only harmless but render real service in keeping down

the population of rats
and mice. While feed-
ing they usually swal-
low their prey entire.
After the food is di-
gested the hair and
bones are formed in-
to compact masses
and ejected from the
mouth. Owl roosts are
frequently located by
the presence of these
hard pellets on the
ground beneath the
trees.

Parrots and Cocka-
toos. ThePsit'taci(Gr.
psittakos, ' * parrot ' ' )
are generally birds of gaudy colors, with a very stout,
strongly hooked beak, which is used for climbing, as well as
for crushing seeds. They have four toes, arranged two in
front and two behind, with strong, curved claws (Fig. 197).
Most species inhabit forests; they are all good climbers.
A great many species can learn to talk, but the red-tailed
gray parrot of Africa is considered the best talker. The
cockatoos are often ornamented with crest feathers of vari-
ous colors. They are restricted to Australia, Tasmania, and
the Philippines. A New Zealand parrot, the kea (Nes'tor

Fig. 204. Photograph of a barred owl

THE ALLIES OF THE PIGEON 389

nota'bilis), has of late years become carnivorous in its habits,
alighting on the backs of live sheep and digging deep into
the flesh for the fat surrounding the kidneys. "The pro-
pensity is said to have originated from the bird's pecking
at sheepskins hanging outside country stations." We have
only one member of the group in the United States, the
Carolina paroquet, and that has been almost exterminated.

Woodpeckers. The group Pi'ci (Lat. picus, " woodpecker")
forms a well-marked assemblage of climbing birds, with
two toes in front and two behind (except in the three-toed
woodpeckers, Fig. 197).

Woodpeckers have a strong, straight bill, with which they
dig into wood for insects, and a long, barbed tongue, spear-
pointed at the end, which enables them to draw their food
from beneath the bark of trees. The tail feathers are usu-
ally stiff and pointed, and form a support to rest on while
the bird is engaged in feeding. The usual coloration in the
group is black and white, but red often appears on the head.
The nests are made in holes in trees, and the eggs are white
in color. By far the greater number of the woodpeckers are
beneficial to the farmer, but the yellow-bellied woodpecker,
or sapsucker (Sphyrapi'cus va'rius, Fig. 205), girdles trees
with numerous small holes to get at the sap beneath the
bark. The flickers (Colap'tes) have lost some of the habits
of the family, and have descended to picking up part of
their food on the ground of fields and pastures. For much
of the year their food consists very largely of ants.

Perching, or Singing, Birds. The passerine type (Lat. passer,
1 sparrow ") is exemplified in more than half the birds of the
world. The characteristics which serve to distinguish the
Pas'seres, or perching birds, from other groups are the pres-
ence of four toes without webs, placed at the same level,
three in front and one behind (Fig. 197, sparrow). The
perchers are birds of small or medium size. Among them

390

GENERAL ZOOLOGY

are included all our well-known songsters. The nesting
habits are various, but a great number build complicated
and often beautiful nests (Fig. 206) in which to rear their

Fig. 205. Photograph of yellow-bellied sapsuckers
American Museum of Natural History

young. The young when hatched are always in a helpless
condition, requiring the care of the parent for a time (com-
pare Figs. 207 and 202). The sexes may be alike, or the male

THE ALLIES OF THE PIGEON

391

may be specially ornamented. The bright colors of the male
are generally believed to be due to sexual selection, and his

Fig. 206. Photograph of nest and eggs of catbird

ability to sing is accounted for in a similar manner. The
perching birds are the familiar birds of forest, field, and gar-
den, and are those with
which the young stu-
dent will naturally be-
gin his study in the
field. They are so nu-
merous that very few
can be referred to here.
The flycatchers (Ty-
ran'nidae Fig. 208) are

pert little birds with a Fig. 207. Recently hatched young of catbird
slightly hooked bill,

provided with bristles at its base. From some convenient
perch they watch for insects, which they snap at on the
wing, returning to the perch after each flight. The bristles

392

GENERAL ZOOLOGY

at the base of the bill serve to entangle insects and make
their capture more certain. The brightly colored warblers
(Mniotil'tidae), as Mr. Chapman says, are "at once the
delight and the despair of field students." The many
species are insect-eaters, getting their food almost exclu-
sively from the leaves or bark of trees, though some cap-
ture it on the wing, after the manner of the flycatchers.

Fig. 208. Flycatchers
American Museum of Natural History

The vireos (Vireon'idae) are to be found in much the same
places as many of the warblers, industriously picking insects
from the leaves of trees, or from crevices in the bark. Vireos
are small, greenish-colored birds, which build cup-shaped,
hanging nests of plant fibers, lined with pine needles and
similar material. The white-eyed vireo has the habit of
often weaving a piece of newspaper into the structure of its
nest ; hence it is called "the politician " in some parts of the
country. A cast snake's skin is also a favorite object for this
purpose.

Our familiar crow and our almost equally familiar blue
jay are members of the family Cor'vidae. The family is

THE ALLIES OF THE PIGEON 393

considered by ornithologists to be unusually intelligent, and
by some is even considered the highest bird group. Closely
allied to the crows and jays are the blackbirds and orioles
(Icter'idae). In this family is the cowbird, which has the
habit of laying its eggs in the nests of other birds, which are
usually smaller than itself, and of leaving the egg to be
hatched by its foster parent. A South American cowbird
lays its eggs in the nest of another species of cowbird, which
does not possess this parasitic habit fully developed, since
the latter sometimes builds its own nest and sometimes lays
its eggs in the nests of other birds. The orioles are remark-
able for their elaborately interwoven hanging nests, much
deeper than the somewhat similar hanging nests of the
vireos.

The finches and sparrows (Fringiriidae) are the largest
family of birds. However varied the members of this group
are in form and color, they agree, usually, in the possession
of a stout, conical bill, adapted to crushing seeds. The Eu-
ropean house sparrow, often called the English sparrow
{Pas'ser domes' ticus), is well known to dwellers in nearly
every town and city in the United States. Introduced from
Europe into this country in the neighborhood of Brooklyn,
in 1851 and 1852, the house sparrow has since spread so
widely that it may now be said that its conquest of the cen-
ters of population in our country is almost complete. It has
made itself at home in our city streets, and has managed to
pick up a living where another bird would starve to death.
Most of the sparrows belong to the fields and hedges, where
their brownish coloration serves to make them inconspicuous.

Our American robin belongs to the family of thrushes
(Tur'didae). Though not a gifted songster, like some of its
near relatives, the robin is dear to all dwellers in the country.
With the bluebird and the song sparrow it shares the honor
of being spring's harbinger among the birds in eastern North

394 GENERAL ZOOLOGY

America. Its habits, song, and call notes offer an interesting
subject for study.

Migration of Birds. The phenomena of migration are es-
pecially noteworthy among birds, and the birds of a region
may be roughly classified in connection with this habit.
Those species which remain in a region all the year are
spoken of as permanent residents of that region. They may
be more or less migratory as individuals ; that is, the birds
seen in the summer may not be the same individuals that
appear in the autumn or winter. The great majority of the
birds of the northern hemisphere leave in the autumn to
pass the winter in the south, returning in great bird waves
in the spring. These birds are the summer residents of the
region. The summer residents of the eastern United States
may pass the winter in the Southern states, or they may (like
the bobolink) go as far as Brazil (Fig. 209). When the great
hordes of the summer residents have passed to the south,
other birds come down from the north ; these are winter visi-
tants. Often a bird loses its way, or is blown out of its regu-
lar line of travel to other regions ; such birds are accidental
visitants to those regions.

The great migratory movements of birds are fairly regular
year after year, and they are participated in by thousands
upon thousands of individuals. When the appropriate time
comes each species gathers in large flocks, or the individuals
separately move off on their long trip. The larger birds, with
special means of defense, as the large hawks and cranes,
choose daylight in which to travel. Ducks and geese mi-
grate in flocks, flying either by day or by night. Some of
the smaller birds which are also rapid and untiring fliers,
like the swallows, also carry on their migrations during the
day, but most of the smaller birds migrate at night. A foggy
night causes the death of large numbers of birds ; over fif-
teen hundred individuals have been picked up at the foot

THE ALLIES OF THE PIGEON

395

of the Statue of Liberty in New York Harbor after a dark
night in the migration period. Attracted by the bright
light the birds had dashed against the glass in their
swift flight. Birds are exposed to other dangers on their

Fig. 209. Map showing migration of the bobolink
Courtesy of the United States Department of Agriculture

migration flight. They are fed upon by other animals, or are
blown out to sea, where they fall exhausted into the water.
It is not thoroughly understood how birds find their way
over such great stretches of territory. The "fly lines" of
some swallows are ten thousand miles long. The golden

396 GENERAL ZOOLOGY

plover breeds in arctic America and winters in Patagonia.
The bobolink spends the summer in the northern part of the
United States and Canada but winters in Brazil. The paths
which the bobolinks follow in their two trips a year fall be-
tween the two broken lines shown on Fig. 209. By some
ornithologists the ability to travel these great distances is
ascribed to the possession of a sixth sense, — that of direc-
tion. In some cases rivers and coast lines are followed. It
has been observed that there are instances in which birds
now follow the outlines of old, submerged coast lines.

While members of some species cover great distances in a
single day the migration speed is rarely more than fifty miles
an hour, and for all our species the average rate of migra-
tion is not much more than twenty miles a day, for there are
frequent stops of one or more whole days for feeding.

The causes which underlie these great movements cannot
yet be stated with certainty. One very careful student of
bird migration has observed that in the spring migration the
appearance of greatest numbers of individuals and "first ar-
rivals" follows after a day of high temperature and winds
from the south when areas of low barometric pressure are
moving northward. It has been stated that the return to
the north is due to the desire of the birds to regain their old
home, or to their desire for seclusion during the breeding
season. The origin of the habit has been looked for in the
geological history of the world. During the Glacial Epoch
a great part of the northern hemisphere was shrouded in a
mass of ice, which came down from the north upon a region
which was then almost tropical in its climate. With the on-
ward advance of the ice, the birds, like all other forms of
life, were driven south, returning whenever the melting of
the ice permitted. Geology tells of many periods of alter-
nate progression and regression of the ice sheet, with ac-
companying changes of climate. It may well be that the

THE ALLIES OF THE PIGEON 397

northerly and southerly movements then begun among the
birds have been continued till today.

Bird-Banding. In the past few years much valuable in-
formation about movement and migration of birds has been
obtained by banding. Small metal bands are placed on the
feet of young birds before they leave the nest and of old birds
captured in traps. These bands bear numbers and instruc-
tions to notify the Biological Survey at Washington, D.C.,
in case the bird is killed or trapped. By this means it has
been determined that in many species individuals return
year after year to exactly the same nesting site. Migration
routes are also studied in this manner.

Economic Importance of Birds. Leaving out of considera-
tion their value to man as a source of food, birds are chiefly
important economically in connection with their destruction
of insects injurious to vegetation. Of course not all birds
are beneficial in this respect ; whether they are beneficial or
injurious depends largely on the character of their food.
What we know of the food of birds has come not only from
the observation of the birds in the field but also from the
examination of the contents of their stomachs. The Bureau
of Biological Survey of the Department of Agriculture has
performed a most useful task in collecting, tabulating, and
publishing observations from all parts of the country. The
diagram (Fig. 210) shows the proportion of different sorts
of food in the young and the adult of the common crow.

Some of the conclusions of Dr. Judd, who studied the
birds of a Maryland farm for the Biological Survey, are as
follows :

. . . the English sparrow, the sharp-shinned and Cooper hawks,
and the great horned owl are, as everywhere, inimical to the
farmers' interests and should be killed at every opportunity. The
sapsucker punctures orchard trees extensively and should be shot.
The study of the crow is unfavorable in results so far as these

398

GENERAL ZOOLOGY

particular farms are concerned, partly because of special condi-
tions. Its work in removing carrion and destroying insects is
serviceable, but it does so much damage to game, poultry, fruit,
and grain that it more than counterbalances the good, and should

Seven days or less

One to two weeks old

Three weeks and older Adult

Fig. 210. Diagrams showing relative amounts of different kinds of food

eaten by crows of different ages1

be reduced in numbers. The grackle appears to be purely bene-
ficial to these farms during the breeding-season, and feeds ex-
tensively on weed-seed during migration, but at the latter time
it is very injurious to grain. The remaining species probably do
more good than harm and, except under unusual conditions,

1 From Judd's Birds of a Maryland Farm.

THE ALLIES OF THE PIGEON 399

should receive encouragement by the owners of the farms. Cer-
tain species, such as flycatchers, swallows, and warblers, prey to
some extent upon useful parasitic insects ; but on the whole the
habits of these insectivorous birds are productive of considerable
good to man. Together with the vireos, cuckoos, and woodpeckers
(exclusive of the sapsuckers), they are the most valuable con-
servators of foliage on the farms. The quail, meadow-lark,
orchard-oriole, mocking bird, house-wren, grasshopper-sparrow,
and chipping sparrow feed on insects of the cultivated fields,
particularly during the breeding-season, when the nestlings of
practically all species eat enormous numbers of caterpillars and
grasshoppers.

Bird Protection. The first steps toward bird protection
were taken at the instance of the sportsmen, in whose inter-
est laws were passed prohibiting the destruction of game
birds except at stated seasons of the year. These laws were
in the interest, too, of the hunter who shot for the market,
since they secured for the birds freedom from the molesta-
tion of man during the period of bringing up their young,
without which protection their extinction would, in many
cases, have been only a matter of time. Of late years great
interest has been aroused in ornithology, and the value of
birds to agriculture or as scavengers has been more generally
recognized. People generally have begun to take pleasure
in having birds about, for their beauty of form, or color, or
movement, and for their song, so that an aesthetic argument
has been added to the others. The separate states have
shown the effect of this general awakening by the improve-
ment of old laws or the passage of new ones for the protection
of the insectivorous song birds and other birds which have
not been proved to be directly injurious. As one result of the
interest in the study of birds in the schools several states
have set apart Bird Day, which is observed after the fashion
of Arbor Day, and oftentimes in connection with it. The
first Bird Day was observed in Pennsylvania, May 4, 1894.

400 GENERAL ZOOLOGY

The greatest single act for the protection of our bird life
was a treaty entered into by the Canadian government and
the United States in 1916. By the terms of this treaty game
birds may not be killed in the spring, which is the breeding
season, and the sale of migratory birds is prohibited every-
where in the United States and Canada. This treaty recog-
nizes the fact that migratory birds are not the property of
the state where they happen to reside for a few months of
the year, and places their protection in the hands of the
federal government. Before this treaty became effective
water fowl were on the verge of extermination in many parts
of the country. Since 1916 there are strong evidences of
increasing numbers.

Our national parks and forests in addition to furnishing
a playground for citizens of this country are under an ad-
ministration which furnishes protection not only to game
animals but to many kinds of birds as well. In addition to
the federal government, the various states and numerous
private organizations have set apart regions where birds are
given complete protection. These sanctuaries, or refuges, as
they are called, now number close to one hundred and are
scattered over the entire country. Some of them are small,
but a few acres in extent, while others cover several thou-
sands of acres. In many of the larger sanctuaries wardens
are constantly on guard to protect the birds from depre-
dations of wild animals and their even greater enemy, man.
In some of the private sanctuaries remarkable work has
been done. Jack Miner on his Canadian estate feeds thou-
sands of ducks and geese, which he claims are not wild
except as we make them so.

Increased interest in our wild life has led to the planting by
many persons of fruit-bearing trees and shrubbery to attract
the birds. In the winter many find pleasure in keeping feeding
stations provided with food to attract the winter residents.

THE ALLIES OF THE PIGEON

401

Geographical Distribution of Birds. Because of their strongly
developed powers of flight, birds have fewer barriers to their
distribution than exist for most other animals. As a result
the same species frequently occur over large areas. In the
United States, the Rocky Mountains are a distinct bar-
rier to many species of birds. Except where barriers exist,
regions offering similar conditions for life may have the
same species of birds even though they be widely separated
geographically. Thus the en-
tire area east of the Rocky
Mountains has practically the
same species of bird inhabit-
ants, while west of the Rockies
there are many species differ-
ent from those of the Eastern
United States.

When a given species of bird
occurs over a wide area, there
are often minor differences such
as of color or of size which dis-
tinguish the individuals of one
region from those of another.
These differences mark off the

varieties within a species, as mentioned on page 108. Thus,
though song sparrows occur from one coast to the other,
they represent a considerable number of varieties.

Birds of Past Ages. The earliest remains of birds of which
we have any knowledge come from the Age of Reptiles.
The oldest of these remains is the famous fossil known as
Archseop'teryx (Fig. 211), two specimens of which have been
found in Bavaria. The ancestry of all known birds is there-
fore to be traced back, at least so far as our knowledge goes,
to these two specimens. Archseopteryx was a land bird
about the size of a crow, probably arboreal in its habits,

Fig. 211. Reconstruction draw-
ing of the primitive fossil bird,
Archseopteryx

After Pycraft

402 GENERAL ZOOLOGY

though not necessarily a good flier. It had true feathers,
but it was very different from the birds of today in that it
possessed teeth and a long, lizard-like tail of about twenty
vertebrae. These last characteristics are strikingly reptilian,
and such considerations point to the fact that the birds
developed from the reptiles. As the development was un-
doubtedly gradual, we should expect to find forms possess-
ing the characters of both groups.

Many remains of birds have been found, especially in the
rocks on the eastern slope of the Rocky Mountains, in
Kansas and Colorado. These belong to species which lived
later in the period. These birds are of at least two different
types, differing in the arrangement of the teeth. One group
had the teeth set in separate sockets; the other had the
teeth in grooves. Some of the birds found in the rocks of
this age in New Jersey seem to have been toothless, like
birds today. It is interesting to note that even thus early
the bird type had become quite well advanced, having lost
not only the teeth but also the long tail of earlier forms.
The time of this period was great enough to permit the de-
velopment of species of birds with highly developed wings,
as well as others with degenerate wings.

In the next succeeding period, to which we shall refer at
the close of a later chapter, the birds were all toothless and
related to those of today. There were woodpeckers, parrots,
swallows, cranes, and many others.

CHAPTER XXXVI

THE GRAY SQUIRREL

Up the oak-tree, close beside him,
Sprang the squirrel, Adjidaumo,
In and out among the branches,
Coughed and chattered from the oak-tree,
Laughed, and said between his laughing,
"Do not shoot me, Hiawatha."

Longfellow, The Song of Hiawatha

Habitat and Distribution. The gray squirrel {Sciu'rus caro-
linen'sis, Fig. 212) was formerly found all over the wooded
region of the eastern United States, and still exists, though in
much diminished numbers, wherever its numerous enemies
permit. It does not extend farther west than Minnesota and
Wisconsin. It lives in those regions where hardwood trees
grow, seldom being found in the depths of coniferous forests.

External Structure. The elongate body is covered with a
skin bearing soft hair, and is clearly divisible into a head,
neck, trunk, and tail. There are two pairs of appendages, the
legs. In addition to their use in running and in climbing,
the fore legs are used in grasping objects and bringing them
up to the mouth. The hind legs serve for making the long
leaps so characteristic of the squirrel's method of progres-
sion in trees. Both pairs of legs show the divisions which we
have already noted in the amphibians, reptiles, and birds,
and they are provided at the end with digits ending in horny
claws. The nostrils (Fig. 215) are situated at the anterior
extremity, just above the mouth. The eyes are large, and
furnished with an upper and a lower eyelid and a nictitating

membrane. About the mouth and eyes are long, sensitive

403

404

GENERAL ZOOLOGY

hairs called vibrissa. At the back of the head are movable
flaps of skin (external ears, or pinnae) placed at the opening
of the ears. The long and bushy tail is useful in a number
of ways : it is an ornament ; it is useful as a balancing or-
gan in the long leaps from branch to branch ; and it serves
to keep the squirrel warm in its nest in cold weather.

The Digestive Sys-
tem. The mouth is pro-
vided with fleshy lips,
which assist in seizing
and holding food. On
the ventral surface of
the mouth rests a
large, fleshy tongue
(Fig. 215), with nu-
merous nerve endings
of the organ of taste
(papillae) scattered
over the surface. The
front teeth, called in-
cisors (Fig. 215), are
long, sharp, and chisel-
shaped, and are fitted
for gnawing ; those in
the back of the jaw, separated from the incisors by quite
a space, are shorter, broader, and flattened on top, and are
fitted for grinding (Fig. 213). The incisors are four in num-
ber, two in each jaw ; the grinding teeth in an adult squirrel
may be eighteen in number, — four on either side of the
lower jaw and five on either side of the upper jaw. Of the
grinding teeth the last three on either side in both jaws are
termed molars, the others premolars. One of the premolars
in the upper jaw is very likely to be minute, or even missing,
having been shed in early life.

Fig. 212. Photograph of a gray squirrel

THE GRAY SQUIRREL 405

A tooth contains a pulp cavity (Fig. 214, 4), supplied with
blood vessels and nerves and surrounded by a mass of firmer
tissue, or dentine (Fig. 214, 3), which makes up the bulk of
the tooth. The dentine is usually covered, where the tooth
projects from the gum, with a very hard, smooth substance
called enamel (Fig. 214, 1) ; below there is a bony substance,
the cement (Fig. 214, 2), surrounding the root of the tooth.

Fig. 213." Skull of a squirrel

In the molar teeth of the squirrel the pulp cavity, which is at
first open at the base, as in the case of man (see Fig. 214, B),
becomes inclosed and develops a root (see Fig. 214, C), after
which all growth of the tooth stops. In the incisors of the
squirrel the pulp cavity persists throughout life, remaining
open so that the tooth continues to grow as fast as it is worn
away. The enamel is confined to the front surface of the in-
cisors, so that when the tooth is used on hard substances
the softer dentine wears away more quickly and the tooth
becomes sharper and more like a chisel the more it is used.
In most fur-bearing animals the lower jaw is articulated
to the upper by means of transverse condyles, but in the

406

GENERAL ZOOLOGY

squirrel and its allies the condyles are parallel with the long
diameter of the head, thus allowing some backward and
forward motion of the lower jaw. The advantages of these
special adaptations of the structure of teeth and jaws to the

life of a gnawing animal like
the squirrel are obvious.

The ducts of four pairs of
salivary glands open into the
mouth. A muscular flap,
called the soft palate, to dis-
tinguish it from the roof of
the mouth, or hard palate,
separates the mouth from the
pharynx (Fig. 215). Embed-
ded in the soft tissues of the
soft palate are the tonsils, two
small oval bodies, the func-
tion of which is unknown.
The nostrils open posteriorly
into the pharynx. The Eu-
stachian tubes from the ears
enter the pharynx at the
sides.

A short, straight esophagus
(Fig. 215) leads to the sac-
like stomach, passing through
a muscular partition called
the diaphragm, which separates the heart and lungs in the
thoracic cavity from the organs of the abdominal cavity.
In the first fold of the intestine is the pancreas, an extended
mass of spongy tissue roughly suggesting a bunch of grapes.
The liver is large and is divided into several lobes. The in-
testine is very long and much coiled. A clearly marked

1 From Flower and Lydekker's Mammals.

Fig. 214. Sections of teeth

A, incisor, or tusk, of the elephant ;

B, human incisor during develop-
ment ; C, human incisor completely
formed ; D, human molar ; E, molar
of ox ; 1, enamel ; 2, cement ; 3, den-
tine; .4, pulp cavity1

Nostril
Incisor tooth of lower jaw.

Thyroid gland

Thymus gland
Sternum

Aorta -

Left auricle

Left ventricle — -

Pericardium
Diaphragm-
Bile duct
Liver
Stomach
Small intestine—
Pancreas

Blood vessels --
of intestine

Aperture of urethra
Penis—

Cowper's gland
Spermary

PJiarynx
r_iJ Posterior nostril

\^L Cranium

^- -Olfactory lobe

I i — \- - Optic nerve

\m» w A cranial
■ u\ nerve

-%~ Cerebrum

r}/^- Cerebellum
-r Medulla,

Jfiijl ^^ of ear
I ~$~~f~ ' 'Spinal cord
f-y-~ w Esophagus

-^--[----Trac/iea

- - -A nterior vena cava
-|- Pulmonary artery
4 --Pulmonary vein
I Posterior vena cava-

Left lung

H — Dorsal artery

A 7 7

- -Adrenal capsule
- Left kidney

Hfi&frr-Mesorchium

Scrotum
Urinary bladder
Prostate gland

Sperm duct

- Uterus masculinus
Urethra
- -Rectum

First tail vertebra

Fig. 215. Dissection of the gray squirrel

408 GENERAL ZOOLOGY

anterior portion, the small intestine, can be distinguished
from the posterior portion, or rectum. At the junction of
the small intestine and rectum is the cxcum, from which
projects a closed finger-like vermiform appendix.

Ductless Glands. Several glands, called ductless glands
(owing to the absence of a duct leading from them), are
present in vertebrates. With the single exception of the
spleen (mentioned in each case in the course of the state-
ments concerning the digestive system) they have not been
referred to in our brief discussion of the internal anatomy
of the classes of vertebrates, but as they show plainly in the
squirrel attention may be called to them at this time. They
are, besides the spleen (Fig. 215), the adrenal capsules, just
anterior to the kidneys, the thymus gland and the thyroid
gland. In addition to these, there are other ductless glands
of much smaller size. Among these are the parathyroids,
closely associated with the thyroid, and the hypophysis in
the ventral part of the brain. Groups of cells in the gon-
ads, called the interstitial cells, have nothing to do with the
formation of germ cells but regulate the development of the
secondary sexual characters. Though their functions are
but imperfectly known the ductless glands are coming to be
considered among the most important organs of the body.
They regulate and control the actions of many other organs.

The Circulatory System. The heart is inclosed in a pericar-
dium (Fig. 215) and is of the four-chambered type found
in the birds. There is a complete double circulation of the
blood in the squirrel, as in birds. The lymphatic vessels of
the abdomen, called lacteals, which carry from the intestine
the absorbed fatty materials of food, unite to form a thoracic
duct, which extends anteriorly and empties into the venous
system near the heart.

The Respiratory System. At the anterior end of the larynx
is a cartilaginous flap called the epiglottis (Fig. 215). The

THE GRAY SQUIRREL 409

lungs are larger and more extensible than in the birds and
hang free in the thoracic cavity. Respiration is effected
mainly by movements of the diaphragm and the ribs, thus
altering the size of the thoracic cavity and causing air to
enter and to leave the lungs.

The Excretory System. The kidneys (Fig. 215) are bean-
shaped bodies in the dorsal part of the abdominal cavity.
The ureters lead from them to the urinary bladder, whence
the waste products are carried to the surface by the urethra.

The Skeletal System. The skeleton is, in general, built
upon the plan with which we have become familiar in the
study of the frog, the lizard, and the pigeon. The cranium
(Fig. 215) is articulated to the vertebrae by two condyles, as
in the amphibians. All the vertebrse, except those in the
pelvic region, are free.

The Nervous and Muscular Systems. The nervous system
is similar to that of the bird, but the cerebrum (Fig. 215) is
considerably more differentiated. The muscles, especially
those in the hind legs, form a complex system adapted to
strong and rapid movement.

The Reproductive System. The organs of reproduction in
the male consist of oval spermaries (Fig. 215) and a penis ;
in the female, of ovaries with their oviducts.

Development. The squirrel is viviparous. The ovum pro-
duced in the ovary passes into the oviduct, where it becomes
fertilized. In that portion of the duct called the uterus, it
develops into the young squirrel. The young is born in
a condition resembling the adult, though the hair is not com-
pletely formed and the eyes are closed. In the Southern
states the first of two or three litters appears early in March,
and four young are usually produced at a birth. The nest
is usually in a hollow tree in the colder portions of the squir-
rel's range, and exposed on the branches in the warmer
regions. The female keeps the male away from the young

410 GENERAL ZOOLOGY

during their period of infancy and feeds them on milk,
which is secreted by the mammary glands on her ventral

surface.

Relation to Environment. When the young have been
reared, the winter nest in a hollow tree is usually deserted
for a structure of leaves and twigs built high among the
branches of a tree. This outside nest is occupied (at least in
the colder regions) throughout the summer.

The food of the squirrel in the spring consists largely of
buds, especially of the maple and elm. In the summer, fungi
and berries are added to the bill of fare, and in the fall nuts
form a large part of the diet. The gray squirrel has been
accused of varying its vegetable diet with such animal food
as the young and the eggs of song birds, but it is probably
not as frequent an offender as the red squirrel, whose bad
habits in this respect are well known. The nuts of autumn
are gathered and stored in secret places beneath stumps and
in hollow trees, and many are separately buried in the
ground. Some observers are inclined to think that their
sense of smell guides them to the buried food, though it is
doubtful if these individual hoards are always located again.

When winter comes on, gray squirrels are likely to be
later in rising in the morning, preferring to come out in the
warmest part of the day, and on some inclement days they
may not venture forth at all. There is no evidence, how-
ever, that they truly hibernate.

Gray squirrels have been known to travel in bands from
place to place. Of late years, either on account of their
much diminished numbers or because of change in the food
supply, we see little of the great migrations which formerly
occurred. Many such visitations have been recorded.
Pennsylvania was overrun with squirrels in 1749, and a
bounty of threepence a head was offered for their destruc-
tion. It is estimated that about six hundred and forty

THE GRAY SQUIRREL 411

thousand squirrels were killed at that time. In their migra-
tions bodies of water were crossed by swimming, though
ordinarily squirrels are not lovers of water. The cause of
the migrations is probably to be looked for in scarcity of
food supply.

The general color of the gray squirrel's fur is protective,
and the animal has the habit of flattening itself on the upper
side of a horizontal branch, so that it is invisible from below.
Of their enemies, the hawks probably give them most
trouble. It is said that the red-tailed hawks hunt them in
pairs, thus making futile their habit of dodging to the far
side of a branch.

Spread over a large area from Maine to Minnesota and
south as far as Florida, it is to be expected that the different
individuals will vary considerably. In general, it is found
that the colors increase in intensity southward and in
regions of copious rainfall, while the legs, tail, and ears show
a tendency to increase in length. In all parts of their range
individuals are sometimes born in which the normal
coloring matter of the hairs is replaced by black pigment,
and others in which the pigment is lacking, leaving the fur
white. The black individuals are examples of melanism;
the white, of albinism. Both conditions are quite common
among squirrels.

The calls of the gray squirrels to each other may often be
heard in the woods, especially in the fall. The "barking," as
it is termed, consists of a series of notes ending in a longer
snarl. It expresses anger, alarm, or warning. Gray squirrels
have sometimes been encouraged to make their homes in
city parks, where they soon learn to accept and finally to be
largely dependent on contributions of food from human
visitors.

CHAPTER XXXVII

THE ALLIES OF THE SQUIRREL: MAMMALIA

They say,
The solid earth whereon we tread

In tracts of fluent heat began,

And grew to seeming-random forms,
The seeming prey of cyclic storms,

Till at the last arose the man.

Tennyson, In Memoriam

Definition of Mammalia (Lat. mamma, "breast"). The
squirrel serves to introduce the Mammalia, the highest class
of the animal kingdom. Man himself belongs to this class.
Therefore all facts of structure and of function mentioned
in the preceding chapter have especial interest for us. All
mammals are much alike in their anatomy and physiology.

Mammals are warm-blooded vertebrates covered with
hair. Generally two pairs of appendages are present, the
anterior of which are never absent in any member of the
class. Mammals breathe by lungs. Teeth are almost in-
variably present. In the majority of cases the "milk teeth ,:
of the young are shed and an entirely new set develops in
the adult. Mammals bring forth their young alive and feed
them on milk, except in the very few cases to be referred to
under the Monotremata below.

The principal orders into which the class is divided are
mentioned in the following pages.

The Duckbill and Allies. The duckbill (Ornithorhyn'chus
anati'nus, Fig. 216) and two or three species of spiny ant-
eater (Echid'na), mammals of the size of a rabbit and found
only in Australia, Tasmania, and New Guinea, have many

412

THE ALLIES OF THE SQUIRREL

413

special characteristics. The name "Monotrem'ata" is given
to them in reference to the fact that these mammals possess
but a single opening (cloaca) through which the contents of
the intestine and the urinary and reproductive products pass
outward, as in the case of amphibians, birds, and reptiles.
Monotremes also stand alone among mammals in the fact

Fig. 216. Duckbill1

that they lay eggs inclosed in a white, flexible shell, much
like the egg of a reptile. The duckbill gets its name from its
peculiar duck-like beak, which is toothless when the animal
is full grown, the teeth being shed after they have been used
for a while. The male has a hollow spur on the heel, which
is connected with a poison gland in the thigh. The duckbill
is semiaquatic, and lives in burrows in the banks of ponds
and streams. Its food consists of mollusks, small insects,

1 From Lydekker 's Geographical History of Mammals.

414

GENERAL ZOOLOGY

worms, and crustaceans. Spiny anteaters are inhabitants
of elevated rocky districts and feed on ants. They are pro-
tected by a covering of spines intermixed with the hairs.

Kangaroos, Opossums, and Allies. The order Marsupia'lia
(Lat. marsupium, " pouch ") contains a large number of
species, most of which are confined to Australia and the

Fig. 217. Photograph of an opossum

surrounding islands. The mammals comprising it are of
various external form, but the females of nearly all species
have an abdominal fold of skin forming a pouch in which the
almost helpless young are placed by the mother when born ;
they are then carried about with her until they are able to
take care of themselves. The kangaroos vary from the size
of a rabbit to that of a sheep. The hind legs are developed
for jumping. The Virginian opossum (Didel'phys Virginia' 'na,
Fig. 217) of our Southern and Middle Atlantic states is the
most northern member of the opossum group, many species
of which are found in South and Central America. It has the

THE ALLIES OF THE SQUIRREL 415

habit of feigning death when in danger of capture, hence the
expression, "playing possum. "

Fossils from the rocks of the latter part of the Age of Rep-
tiles show that marsupials were widely distributed over the
earth at that time. Then came the separation of the Austra-
lian continent from the land to the north, isolating the mar-
supial fauna from the larger and more diversified land areas.
The Australian fauna evolved along various lines, produc-
ing herbivorous, insectivorous, and carnivorous forms which
resemble in outward appearance the members of the higher
orders of mammals, though they are in reality marsupial in
structure. Over the rest of the world, with the exception of
America, the marsupials were entirely destroyed and their
places taken by more highly specialized types. Marsupials
retained a foothold in South America owing to the absence
of overpowering enemies, and on account of their adaptation
to climatic and general environmental conditions. They
afford an illustration of discontinuous distribution.

Sloths, Armadillos, and Allies. Both terrestrial and ar-
boreal animals are included in the order Edenta'ta (Lat. e,
" out " ; dens, " tooth "). Edentates have incompletely de-
veloped teeth, or if the teeth are well developed, they are
of simple structure ; true incisors are never present. Many
members of the order have a covering of scales formed from
the hardening of the skin.

The armadillos (Fig. 218) are terrestrial American forms
which are protected by the scaly covering just referred to.
The tail and head are generally exposed, but the animals can
roll themselves into a ball, thus offering a hard surface in
every direction.

The sloths of South and Central America are nocturnal,
arboreal animals ; their natural attitude during the day is
hanging from a branch back downward. The hair is gray,
but in some species it offers a lodgment for a green alga, a

416 GENERAL ZOOLOGY

plant of low organization, which gives the hair a green tinge
like that of the masses of vegetation of the tropical forest.
Sloths rarely descend from the branches of trees. On the
ground they are almost helpless.

Whales, Dolphins, Porpoises, and Allies. The whales,
dolphins, and porpoises are true mammals, though so
adapted to their aquatic life that they seem, on superficial

Fig. 218. Photograph of an armadillo

examination, to be fishes. The name of the order, Ceta'cea,
is derived from the Latin cetus, "whale."

Flower and Lydekker, in their book on Mammals, thus
review the principal peculiarities of the group :

The external fish-like form is perfectly suited for swimming
through the water ; the tail, however, is not placed vertically as
in fishes, but horizontally, a position which accords better with
the constant necessity for rising to the surface for the purpose of
breathing. The hairy covering characteristic of all mammals,
which, if present, might interfere with rapidity of movement
through the water, is reduced to the merest rudiments, — a few
short bristles about the chin or upper lip, — which are often
present only in very young animals ; and the function of keeping
the body warm is performed by the "blubber." The fore limbs,

THE ALLIES OF THE SQUIRREL 417

though functionally reduced to mere paddles, with no power of
motion except at the shoulder- joint, have beneath their smooth
and continuous covering all the bones, joints, and even most of
the muscles, nerves, and arteries of the human arm and hand ;
the rudiments of hind legs, found buried deep in the interior of the
animal, apparently subserve no useful purpose, but point an in-
structive lesson to those who are able to read it.

Cetaceans are found in all seas, and feed on fishes, crus-
taceans, and the smaller floating animal life of the ocean

Fig. 219. Comparison of the size of an elephant with that of a whale1

generally. They vary from four to eighty feet in length,
some of the whales being the largest of existing animals
(Fig. 219). There is every reason to believe that the group
is descended from land mammals. The whalebone whales
are species without teeth, but with a development of baleen,
or whalebone, in the upper jaw, which acts as a strainer. By
means of the closely set, flexible strips of whalebone the
small animals on which they feed are retained, while the
water is forced out. Several species_are found in the Atlantic
and Pacific oceans. The sperm whale (Physe'ter macro-
ceph'alus) has a square head, within which is a cavity con-
taining oil which, on being refined, yields spermaceti.

Hoofed Mammals. The great assemblage of animals called
Ungula'ta (Lat. unguis, "nail") includes the hippopota-

1 From R. S. Lull's Organic Evolution. Used by permission of The MacMillan
Company.

418

GENERAL ZOOLOGY

muses, pigs, camels, deer, the giraffes, antelopes, oxen, goats,
sheep, rhinoceroses, horses, and elephants. All these mam-
mals have the toes ending in either a blunt nail or a fully
developed hoof, both of which structures are formed from
the thickening of the skin of the toes. In ungulates like the
cow and sheep there are two divisions in the hoof, and the
animals really walk on the tip of the third and fourth dig-
its, the others being
much reduced in size.
In the horse and its
allies this reduction
has [gone much far-
ther, so that the tip
only of the third digit
is used for support.
The elephants have
five toes, each incased
in a short nail. The
living species of ele-
phants undoubtedly
would have been re-
moved to a separate order if fossil forms had not been dis-
covered possessing characters intermediate between these
mammals and other ungulates.

Ungulates are adapted to a terrestrial life and feed almost
entirely on vegetable food. Four kinds of teeth are present,
— incisors, canines, premolars, and molars. The first kind
and the last two kinds will be recognized from the study of
the squirrel ; the canines, so named because they are well-
developed in the dog (Lat. canis, " dog"), fill the space be-
tween the incisors and premolars. The canines are often
elongated to form tusks for defense or for obtaining food ;
the incisors serve to crop the herbage ; the molars and pre-
molars are flattened for grinding.

Fig. 220. Head of rhinoceros
American Museum of Natural History

THE ALLIES OF THE SQUIRREL

419

Horns for defense have been de-
veloped in many species of ungulates.
They are of various sorts. The rhi-
noceroses (Fig. 220) have one or more
median horns, which are composed
of a thickened and hardened portion
of the skin and hair, covering a short
protuberance of the skull. In the
giraffes there are one or two pairs of
horns consisting of a layer of skin
over bony processes of the skull.
Neither in the rhinoceros nor the
giraffe are the horns ever shed. In
the North American pronghorn an-
telope {Antiloca'pra america'na) the
horns are branched and consist of
a hardened and thickened skin on a
bony core. The thickened skin is shed
periodically but the core is retained.
The horns in true antelopes and in
oxen, sheep, and goats, are of similar
structure but are never shed. They
are usually found in both sexes. In
the deer family (Fig. 221) the horns,
called antlers, consist of outgrowths
of bone covered each year during the
period of growth with a sensitive skin
called "the velvet." When the an-
nual growth is completed the supply
of blood to the antlers ceases and the
velvet peels off, leaving the bone
bare. After a time the antlers sepa-
rate from the skull and are shed. In
most deer this takes place annually.

Fig. 221. Series of antlers

American Museum of Natu-
ral History

420 GENERAL ZOOLOGY

In some members of the family the antlers remain simple
throughout life; in others they become much branched in
successive annual growths (Fig. 221). It is interesting to
note that, in a broad way, this was the order of development
of antlers in geological time, the earliest deer of which we
have any knowledge being without them. Horns and antlers
are used in the battles of the males for the possession of the
females, as well as for defense of themselves and their band.
The presence of these organs is usually ascribed to the ac-
tion of sexual selection.

A large number of the ungulates have learned the ad-
vantage of cooperation and live in herds, which possess
an organized power of resistance far greater t.han any indi-
vidual has. In many cases, especially among the deer, scent
glands are developed on the head below the eyes, and as
the sense of smell is extremely acute, notice of the presence
of other members of the herd is given by the odor of the
secretion from these glands. Often the tail and rump are
conspicuously marked with white, showing plainly when the
animal is in flight, and probably serving as a recognition
or signaling mark.

The structural peculiarities already referred to form the
basis for separating the ungulates into three divisions, —
those with an even number of toes, as the cow ; those with
an odd number of toes (one or three), as the rhinoceros and
horse; and the long-nosed forms (Proboscid'ea), including
the elephants. Of the even-toed ungulates the families of
camels (Cameridae), deer (Cer'vidae) and antelopes, goats,
sheep, and oxen (Bo'vidae) have the stomach (Fig. 222)
divided into a digestive and a nondigestive or storage
region, forming a complex organ of several compartments.
The food is taken into the first two of these divisions, the
reticulum, or honeycomb bag, and the rumen, or paunch,
where it remains till the animal has finished grazing and has

THE ALLIES OF THE SQUIRREL 421

leisure for its digestion. The food is then raised to the mouth
in a somewhat softened condition and is there ground be-
tween the molar teeth and moistened with saliva, after
which it is again swallowed, this time into the psalterium, or
manyplies, so called from the numerous folds in its lining
membrane. The food slowly filters through the manyplies
into the true digestive stomach, or abomasum. This very

Fig. 222. Diagram of the stomach of a ruminant
Arrows and dotted lines show the course of food (After Wiedersheim)

characteristic habit of chewing the cud has suggested the name
of ruminants (Lat. rumen, "throat") for these ungulates.

Most of the so-called wild horses are in reality horses
which have escaped from domestic breeds. The tarpan of
Central Asia is an exception. It seems to be truly wild, not
feral. This horse closely resembles the pictures of horses
made by man on walls of caverns and those carved on bone,
which date back long before the beginnings of real history.
The interesting story of the geological development of the
horse is told farther on.

Of the Proboscidea the elephants alone require mention.
There are two common present-day species, the Asiatic
(El'ephas in'dicus) and the African elephant (Elephas afri-

422 GENERAL ZOOLOGY

ca'nus). The latter can be distinguished from the former
by its very large ears. The Asiatic species has long been
domesticated and many stories are told of its intelligence.
The African species was used by the Romans in battle and
circus games, but in modern times these animals have been
hunted so persistently for their ivory that there is danger of
their being exterminated. Steps are now being taken to pre-
vent their complete destruction.

Gnawing Mammals. The Roden'tia (Lat. rodere, " gnaw ")
are the most numerous in point of species and are the most
widely distributed of all the mammals. Here belong the
hares, rabbits, guinea pigs, porcupines, mice, rats, beavers,
woodchucks, prairie dogs, and squirrels. Rodents are dis-
tinguished by the absence of canine teeth and the presence
of chisel-shaped incisors, which grow from persistent pulps
(Fig. 214). They are mostly terrestrial animals, though a
few, like the beaver, are modified for an aquatic existence,
and others, like the squirrels, for life in the trees.

The hares are distinguished from all other rodents by the
presence of a second pair of incisor teeth behind the first pair
in the upper jaw. Well-known American species are the cot-
tontail, or gray rabbit, of the East (Sylvila'gus florida'nus),
the varying hare (Le'pus america'nus) of the North, and the
northern jack rabbit (Lepus campes'tris) of the West. The
cottontail is so named from the white tail, which is plainly
shown in flight and probably serves as a signal or recogni-
tion mark. The varying hare is a larger and more northern
species, which grows a white coat of fur in winter. The north-
ern jack rabbit also changes to white in the northern part of
its range ; farther south the change is only partial or entirely
wanting. The domestic rabbit is descended from the com-
mon rabbit of the Mediterranean basin (Lepus cunic'ulus).

The porcupine (Erethi'zon dorsa'tus) is a sluggish, stupid
animal, which, having spines for protection, relies on them

THE ALLIES OF THE SQUIRREL 423

to such an extent that it hunts its food in the daytime, —
a habit which most rodents have had to give up (if they
ever possessed it) on account of their lack of protection and
means of defense against numerous enemies. The squirrels
have solved the problem in another way by the development
of extreme watchfulness. There is no truth in the oft-
repeated statement that the porcupine can shoot its quills,
the fact being that, as they are loosely attached, they are
likely to come out on slight pressure.

So much has been written on the beaver and its works
that its habit of felling trees for its dam or for food, its win-
ter storage of branches or twigs beneath the ice, and the
habits developed in connection with its communal life are
pretty well known to everybody. In the communal life of
the beaver, as among the bees and wasps, instinctive actions
are performed with a high degree of perfection. The beaver
also has capabilities of meeting new conditions, and it has
been credited with a considerable degree of intelligence.
It has been hunted so persistently for its fur and scent
bags that it is now greatly reduced. In some localities where
it is given protection, it is again becoming well established.

Flesh-Eating Mammals. The carnivorous mammals, Car-
mVora (Lat. caro (cam-), "flesh"; vorare, "devour"), are
the flesh-eaters par excellence. The incisor teeth are small
and sharp ; the canines are generally long, strong, and coni-
cal, fitted for tearing; and the premolars and molars are
raised into more or less sharp ridges... The toes are sheathed
in claws, often fitted for grasping, and in one family, the
cats, are capable of being retracted and thus kept sharp by
being saved from constant friction. The group has divided
along two main lines of development, one adapted to terres-
trial, the other to aquatic, life. To the first belong the family
of cats (Fe'lidae), including the lion, tiger, leopard, lynx, jag-
uar, and puma ; the hyenas (Hyam'idae) ; the dogs, wolves,

424 GENERAL ZOOLOGY

and foxes (Can'idae) ; the bears (Ur'sidae) ; and the raccoons
(Procyon'idae). To the second division belong the seals and
walruses.

The jaguar is a South American cat resembling in general
appearance the leopard of Africa, and, like it, an inhabitant
of wooded regions, where it spends much of its time in trees.
The irregular markings resemble in a general way the pat-
terns of light and shade beneath the leaves of a forest. The
markings are usually spoken of as an illustration of aggres-
sive resemblance. The dun-colored lion and the gayly
striped tiger are mentioned as similar examples, the one re-
sembling the brown of desert places and the other the ver-
tical shadows of reeds and grasses in tropical jungles. The
origin of our domestic cat and dog, like that of some of our
other domestic animals, is uncertain, but it is generally
believed that the cat is descended from the Egyptian, or
Caff re, cat (Fe'lis caf'fra), an African and Asiatic species
domesticated by the Egyptians and held in veneration by
them ; the dog is variously thought to be the descendant of
some wild species now extinct, or of one of several wolves
or jackals, or a mixture of several species. The great length
of time since the dog first became the companion of man,
and the numerous races which have arisen, render the
question extremely complicated.

Of our smaller wild carnivores none is more generally
known and feared than the skunk (Mephi'tis), of which
there are many species in the United States. Their powerful
means of defense is a pair of glands secreting a strong-
smelling fluid, which they are able to eject for a distance
of several feet. Though they are destroyed by the farmer
for robbing his henroosts, they are on the whole beneficial, .
as they feed largely on injurious insects. Those who have
observed them most say that they make interesting and
cleanly pets, even without the removal of the scent glands,

THE ALLIES OF THE SQUIRREL 425

and that they are not prone to defend themselves except
under great provocation. The presence of this means of
defense has had its effect upon the skunk's character, so
that if a person comes upon it in the daytime it is
likely to make no special effort to escape, but goes about
its business leisurely, secure in the confidence that it will
not be molested. The Eastern species are black animals
about the size of a cat, with prominent white stripes down
the back and a white patch on the forehead. The white
markings on the black ground are usually cited as an ex-
ample of warning coloration. It has been asserted that it is
advantageous to the skunk to be thus marked, for if it had
a uniform black color, it might be mistaken in the uncertain
light for other night prowlers and be pounced upon and
killed by an enemy before it had an opportunity to use its
peculiar method of defense.

Among the aquatic carnivorous forms the Alaskan fur
seal (Callota'ria alasca'nus) has been the subject of inter-
national discussion on account of the value of its fur as an
article of commerce. This is a truly migratory species of
mammal, bringing up its young on the Pribilof, or Fur Seal,
Islands (Fig. 223) in the summer, and going far to sea in the
winter. The males do not reach their full size and strength
till about the seventh year, and until that age the young
males herd by themselves, being forbidden the general herd
by the older males. The females mature in two years.
Early in May the full-grown males appear at the islands,
and the females a few weeks afterward. Each male im-
mediately collects as many females as he can guard, and
battles are frequent before the groups are made up. From
twenty to one hundred females, or "cow" seals, are included
in a single harem.

The government-owned seal herd in the Pribilof Islands
is the world's chief supply of sealskin. This herd now totals

426

GENERAL ZOOLOGY

more than 723,000 animals. Only three-year-old " bachelor "
males, who have not started a harem, are killed for the fur.
In 1925 the Bureau of Fisheries supervised the taking of
twenty thousand skins.

Insect-Eating Mammals. The insect-eating mammals, In-
sectiv'ora, are usually of small size. The teeth are sharp and
numerous, and the molars have sharp points for crushing

Fig. 223. A colony of fur seals in Alaska
From United States Bureau of Fisheries

the bodies of insects. The eyes are often small and hidden
in the fur, especially in the forms which, like the moles and
shrews, burrow in the ground. The star-nosed mole {Con-
dylu'ra crista'ta) is a common American species living in
peat swamps and rich land near ponds and streams. They
make great burrows, and the earth thrown up may some-
times make a pile a foot or more in diameter. The name is
given from a fleshy filamentous appendage on the nostrils,
which is probably used as an organ of touch. Some of the

THE ALLIES OF THE SQUIRREL

427

shrews are the smallest mammals known. They generally
live in burrows like the moles. They somewhat resemble
mice, from which they can be distinguished by the different
plan of the teeth.

Bats. The Chirop'tera (Gr. cheir, "hand"; pteron,
"wing") are marked off from all other mammals by the
possession of wings, which are
formed of skin stretched over
the bones of the arm, includ-
ing also the legs and some-
times the tail.

. So well adapted for aerial
locomotion have the bats (Fig.
224) become that progress on
the ground is almost impos-
sible. The sense of touch is
greatly developed not only on
the muzzle but on the wings as
well, so that the animals are
able to avoid obstacles in their
nocturnal flights. During the
day bats hang themselves up
by their legs in caves and in
hollow trees to sleep. Some
species feed on insects, others
on fruit, and some, the vam-
pire bats of Central and South America, feed on blood. The
latter have the teeth peculiarly adapted to cutting the skin
of animals. The esophagus is so narrow that no solid mat-
ter can pass down it.

Primates. The Prima'tes (Lat. primus, " first") include
the monkeys, apes, and man. The teeth are generally
adapted to a diet of both plant and animal food ; the five
toes and fingers are separate and are usually provided with

Fig. 224. Photograph of a bat

428

GENERAL ZOOLOGY

nails ; the thumb is opposable to the other digits, and the
eyes are directed forward.

The spider monkeys (At'eles, Fig. 225) of South and Cen-
tral America are representative forms of the New World

Fig. 225. Photograph of a spider monkey
American Museum of Natural History

monkeys. They have a long tail, which serves as an organ
of prehension. The most man-like of the monkeys are the
orang-utan (Sim'ia sat'yrus) of Borneo and Sumatra, and
the gorilla {Goril'la goril'la) and chimpanzee (Anthro-
popithe'cus troglody'tes) of equatorial Africa. Of these the
chimpanzee (Fig. 226) is the most gentle in disposition and

THE ALLIES OF THE SQUIRREL 429

the most intelligent. All these monkeys lead a more or less
arboreal life and build nests in trees, where the young are
produced.

That man belongs zoologically in the same group with
the monkeys is now universally admitted, for in the struc-
tural characters upon which classification largely depends,
as Professor Huxley pointed out many years ago, he differs
less from the apes, which resemble him most, than they do
from other monkeys. The principal anatomical characters
are the possession of a relatively larger brain case and less-
developed canine teeth, the adaptation of the vertebral
column to an erect posture, the greater length of the lower
as compared with the upper extremities, and absence of
the power to oppose the great toe to the other toes. The
similarity between man and the apes does not mean that
man has descended from the apes. In fact through various
discoveries of fossil apes and fossil man we have considerable
knowledge about what each was like in past ages. We like-
wise know that there was a time when neither apes nor
man existed on the earth. Before either of these animals
came into existence there were other animals which were
neither ape nor man but the common ancestor of both. In
view of these facts it is no more nearly true to say that man
came from apes than to say that apes came from man.
Neither came from the other.

Intelligence of Mammals. There are many who ascribe
to the birds and to the mammals Jbelow man mental attri-
butes, including a power of reasoning, differing from the
attributes of man not in kind but in degree.

In the past few years there have been many students
working on the problem of intelligence in the lower animals.
In the earlier period of this study emphasis was placed upon
the attempt to discover whether animals below man really
have intelligence, or are simply machines reacting in a

430

GENERAL ZOOLOGY

mechanical manner to outside forces. Finally, after many
hundreds of experiments and many conflicts in definition of
terms, the students in animal behavior have come to the
conclusion that man is not the only animal possessing an
intellect. In the animals below man we find the beginnings
of reason and the various emotions. Very recently much
attention has been directed to the study of the intelligence

of some of the higher
apes, especially the
chimpanzee and the
orang-utan. In a book
entitled Almost Hu-
man, Professor R. M.
Yerkes of Yale Uni-
versity has reviewed
a good many observa-
tions and interesting
experiments on the
higher apes. In one
experiment a banana
is placed above the
reach of a chimpan-
zee. He piles boxes one on top of another until he can
climb high enough to grasp it. Is it possible to explain
such behavior as accidental, requiring no mental activity?
Economic Importance of Mammals. The mammals come
into more intimate relations with man than any other group
of animals except the insects. From them he gets materials
for dress, — wool, leather, and furs ; food in the shape of
butter, cheese, and meat of different kinds. They are his
beasts of burden the world over, and they furnish a long
line of miscellaneous products, such as horn, bone, ivory,
perfumes, whalebone, oils, fats, and material for fertilizers.
The following paragraphs tell of other relations.

Fig. 226. Portrait of a young chimpanzee

Photograph by Elwin R. Sanborn, courtesy of
the New York Zoological Society

THE ALLIES OF THE SQUIRREL 431

Mammals in the War on Disease. Even a brief summary
of the facts regarding the importance of mammals to man
must include some mention of the role which mammals have
played in the development of modern medicine. By far the
greatest advance in our war on disease has been in the direc-
tion of the prevention of disease. Much that we now know
about human ills has resulted from laboratory studies in
which rabbits, guinea pigs, and other laboratory animals
have been used in experiments. Further than this, many
mammals have aided directly in curing and in preventing
human disease by producing serum and antitoxin.

In the blood of cows the germs of cowpox are produced.
These are very nearly like the germs of the dreaded small-
pox. When cowpox germs are introduced into the human
body by vaccination they cause the blood to become immune
to the more dreaded and highly fatal smallpox.

When the germs which cause diphtheria are injected into
a horse, the blood of the horse produces substances called
antitoxins. These neutralize the effects of the poisons, or
toxins, formed by the germs. The blood of the horse pro-
duces more antitoxin than is needed to kill the germs that
were introduced into it. When antitoxin from the blood of
the horse is injected into a diphtheria patient, the disease
is checked. Furthermore, it has been discovered that diph-
theria may be avoided altogether. When a mixture of the
antitoxin and a small amount of the toxin of diphtheria are
injected into the blood of a child, the antitoxin prevents the
toxin from injuring the child, but at the same time the toxin
causes the blood to produce its own antitoxin. When this
toxin-antitoxin treatment is given, the child becomes im-
mune to diphtheria.

In some diseases the dead germs introduced into the hu-
man body produce immunity to the disease. The germs of
typhoid are grown, or "cultured," in the laboratory. After

432 GENERAL ZOOLOGY

these germs have been killed, a fluid containing the dead
bacteria is injected into the body of a man. The presence
of the dead germs in this instance causes the blood to manu-
facture antitoxins for this particular germ. As a conse-
quence of this treatment the individual becomes immune to
typhoid.

Rabies, scarlet fever, and lockjaw are others of the list
of dreaded diseases from which immunity may be secured.
Experiments on animals have thus relieved man from some
of his most dangerous enemies.

Fur-Farming. As the country has become more densely
populated the natural supply of furs taken in the wilds by
trappers has steadily decreased. In recent years an entirely
new industry has been developed. Various kinds of wild
and domesticated animals are being bred and raised in
captivity for furs. Fox-farming has become an important
industry in many localities. Skunks, minks, and rabbits, as
well as many other animals, are being raised for their skins.

Mammals as Pests. Next to the insects the mammals in-
clude some of man's worst enemies. In the frontier days of
our own country wolves, bears, foxes, and coyotes caused
great damage to flocks and herds of domestic animals.
Skunks, minks, and weasels prey upon birds, including do-
mestic fowls. Rabbits and other rodents destroy trees,
shrubs, and vegetable gardens. Coyotes, prairie dogs, and
woodchucks by their burrows damage fields and pasture
lands and frequently are the cause of injury to horses and
cattle which step into their burrows. Rats have become so
destructive that it is estimated that every rat eats at least
two dollars' worth of food a year. In addition the rats are
a necessary link in the chain for spreading one of the most
dreaded of human diseases, — bubonic plague.

Wild-Life Sanctuaries. In addition to the bird protection
mentioned earlier, our national parks and forests give pro-

THE ALLIES OF THE SQUIRREL 433

tection to many of our game animals. In separate reserva-
tions, as well as in parks and forests, many of our big-game
animals are being given a new lease of life and kept from
extermination. Bisons or buffaloes, elk, antelopes, and deer
have been given special attention, and reservations have
been set apart for their protection. When natural condi-
tions demand it, the herds are supplied with food and thus
kept from starving in severe winters.

Mammals of Past Ages. With the upheaval of the Rocky
Mountain system at the close of Mesozoic time the North
American continent assumed practically its present out-
line, with the exception of a strip along the southeastern
coast, which was still beneath the level of the ocean. In
connection with this disturbance of level and the accom-
panying climatic changes the great reptiles so characteris-
tic of the period became extinct and left the field clear for
the development of the mammals. The succeeding period
is therefore called the Age of Mammals. As we have already
seen, representatives of each group of animals have ap-
peared before the age which bears its name, so the first
mammals of which we have any knowledge are to be cred-
ited to the Age of Reptiles. They were nearly all of small
size and allied to the marsupials and monotremes of today, —
groups which we have noticed as being the lowest of the class.

During the Age of Mammals there were extensive areas
of fresh-water lakes in western North America. It is from
these deposits that much of our information regarding the
early mammals of America has been obtained. The Ameri-
can Museum of Natural History in New York City has on
exhibition a large series of fossils from this region. Many of
the specimens discovered are of generalized structure. They
possess the characteristics of several different groups of to-
day, without much modification to a particular kind of life
or food. It is among such animals that we must look for the

434

GENERAL ZOOLOGY

ancestors of the species of today, for no species of mammal
which was in existence in the Age of Mammals has lasted
through to the present time.

Of few other animals have we so complete and satis-
factory a geological record as of the horse. From fossil
remains found in the western part of the United States we

Fig. 227. Reconstruction of an early fossil horse (Eohippus)
American Museum of Natural History

are able to trace its evolution from an ancestor (Eohip'pus,
Fig. 227) a little larger than a cat, with four toes on the
front feet and three on the hind feet. The figure of Eohip-
pus is photographed from a water color by Mr. Charles
R. Knight, based on skeletal material at the American
Museum of Natural History. The markings are drawn as
they are supposed to have existed on the animal. There is
reason to believe that the undiscovered ancestors of this
early form had five toes on each foot. The transition to the

THE ALLIES OF THE SQUIRREL 435

horse of today has been accomplished by a gradual increase
of size, a reduction in the number of toes, and a reduction in
number and an increase of complexity in the teeth. The
main steps in the evolution of the horse are shown in
Fig. 228. The changes in the limbs fit the animal for rapid
locomotion over level, grassy ground. The teeth become
more complex and more efficient grinding organs. In the
latter part of the Age of Mammals, North America was
broadly connected with Asia, and the horse is known to have
inhabited plains of all the continents excepting Australia.
After the horse had reached practically its present state of
development (in the early part of the next succeeding period,
the Age of Man) it seems to have disappeared entirely from
America, owing to causes not thoroughly understood, though
generally ascribed to the oncoming cold of the Glacial Epoch.
The horse persisted, however, in Europe and was one of the
animals which primitive man domesticated. The various
uses to which the horse could be put were gradually learned
by man, for Professor Osborn of the American Museum of
Natural History says there is "abundant proof that man
first hunted and ate, then drove, and finally rode the ani-
mal. " It was reintroduced into America by the Spaniards
at the time of their conquest, and soon ran wild.

The carnivores were early represented by generalized
types, and later by dogs and saber-toothed cats. The latter
get their name from their lengthened canine teeth. Insec-
tivorous mammals, rodents, bats, ungulates of many kinds,
and even the Primates, also occurred, and in the waters of
the oceans were found cetaceans of different species.

The Age of Mammals began in North America with a
warm climate, as in the case of previous periods, but toward
its close frigid conditions began to prevail, probably due to
the gradual elevation of the continental land-mass. The on-
coming cold produced in the northern part of both America

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and the Eurasian land-mass conditions so severe that to the
period the name Glacial Epoch is given. During its contin-
uance all of North America north of a line drawn from
New York through Pennsylvania, Indiana, Missouri, South
Dakota, Montana, and Oregon was covered at different
times with a layer of ice, which in certain regions grew to be
a mile thick over the land, destroying all life or forcing it to
migrate southward to escape the rigors of the climate. As
there were several invasions and retreats of the ice, there
may be said to have been several glacial epochs, separated
by long periods of warmer weather, when the animal and
plant life could slowly work its way back on the edge of the
retreating glaciers. There is a peculiar interest to this period,
inasmuch as it introduces the last of the great geological eras,
the Quaternary Period, or the Age of Man.

A conspicuous feature of the mammalian life of the Age
of Man was the great size of many of the species. After the
opening glacial epoch the climate became mild again, and
this seems to have forced the development of abundant
vegetation and great mammalian forms. One of the largest
and most widely distributed species was the mammoth
(El'ephas yrimiqe'nius, Fig. 229), a proboscidean larger than
the elephant of today and covered with a thick coat of hair,
an adaptation to cold temperate regions. Its remains have
been found frozen in the ice of Siberia, the hair and flesh
perfectly preserved. Early man knew of this great mammal,
for a drawing of the creature is in existence, made on a piece
of its own tusk (Fig. 230). The mastodons were somewhat
similar to the mammoths, but fitted on the whole for a
warmer climate. There are over thirty species of mastodons
known, of nearly world-wide distribution. They have be-
come extinct within so short a time, geologically speaking,
that traditions of their existence as living animals occur
among men.

THE ALLIES OF THE SQUIRREL

439

The remains of giant edentates have been found in South
America. Recent discoveries seem to show that some of
them were living within the period of man on that continent,
for some of the tribes of South American Indians have tra-
ditions respecting these monsters. In Europe and Asia there
were lions, hyenas, bears, rhinoceroses, and gigantic un-
gulates. In Australia, as will be expected from what has
been said of the distribution of the group, there were mar-
supials of various species, but none of the higher mammals.

Fig. 230. Drawing of a mammoth made by prehistoric man

on mammoth tusk1

But the great interest of the Age of Man centers about
man himself. If it is not yet possible to prove to the sat-
isfaction of everyone the existence of man in the Glacial
Epoch in North America, it is certain that he was in ex-
istence in Europe at that time. It would be interesting
to know, if possible, how far distant we should place this
period, and where man first appeared on the earth, but to
neither of these questions can any satisfactory answer be
given. Regarding the time, estimates have been made in
various ways, reaching conclusions which vary greatly. A
conservative estimate is that the Glacial Epoch began two
million four hundred thousand years ago and ended eighty

1 From Lucas's Animals of the Past.

440 GENERAL ZOOLOGY

thousand years ago. Regarding the place of man's origin,
some have believed that his earliest home was Africa, be-
cause the great apes, which most resemble him, live there
today. Others have maintained that it was somewhere in
equatorial regions, where the vegetation is abundant and the
climate quite similar throughout the year; others claim
that it was on some of the high plains of the temperate zone,
like those of Persia and Tibet.

Primitive man was a savage, living in caves. His princi-
pal means of defense, in addition to those with which nature
had provided him, were a stone picked from the ground or a
bough broken from a tree. At an early stage in his develop-
ment he learned the use of fire, made clothing of the skins of
wild beasts to keep himself warm, and fashioned rude imple-
ments out of bone, shell, horn, wood, and stone. In those
places where such easily worked metals as copper and zinc
were accessible man early learned their use and made from
them implements of bronze, a compound of the two metals.
From a hunting existence arose the nomadic or wandering
life, with property in the shape of herds of domesticated or
semidomesticated animals, and the more fixed agricultural
condition in which the main dependence for food was on the
products of the field. We see people today in each of these
conditions of existence. Along with the advance in the mode
of life has gone a mental and moral evolution as man's con-
quest of nature has been pushed through wider and wider
fields.

CHAPTER XXXVIII

THE HISTORICAL DEVELOPMENT OF ZOOLOGY

The history of the transformation of opinion in reference to living organisms
is an interesting part of the story of intellectual development.

W. A. Locy, Biology and its Makers

The Science of Zoology and its Divisions. This is a text-
book of zoology because it attempts to give, in orderly
fashion, facts about animals. But not all of these facts are
obtained from one kind of study. When in the foregoing
chapters we were examining the general form of animals we
were dealing with morphology. When the study of form went
into the form and arrangements of the individual organs or
parts we were taking up that branch of morphology which is
called anatomy. When parts or organs of two different ani-
mals were compared or contrasted we were delving into a
field of zoology called comparative anatomy. But structure
is of live interest only when we come to see what the in-
dividual organ or part does. This field of zoology treating
of function is called physiology. Before we were able to talk
about either the form or function of the parts we found it
necessary to call the animal by some name. This division of
zoology is called systematic zoology, or taxonomy. When we
discussed the relations of the various animals to their en-
vironment we were attacking one phase of the field of ecol-
ogy. When we have discussed the animal life of the past we
have been delving into the field of paleontology.

From the foregoing it becomes apparent that zoology is

not a simple aggregate of facts, but these facts may be

grouped into a great number of different subdivisions or sub-

441

442 GENERAL ZOOLOGY

sciences. Many of these in turn are capable of still further
division. We shall turn now to the history of zoology. After
seeing the many avenues along which animal studies may be
approached we are in a position to appreciate the fact that
the history of such a diversified science cannot be simple.

The Background of Zoological History. We have proof that
man has known something about animals since before the
dawn of history. There are caves in southern France where
man lived long before the period of which we have any
consecutive record, or history. On the walls of these caves
are pictures of deer and of horses. These pictured animals
are entirely different from any of the animals now living,
but like the ones of a past geological period. Doubtless
these were the animals which primitive man hunted. The
drawings in the caves and the carvings on bone from these
same ancient homes of prehistoric man show us that he
had a considerable knowledge of animals. But there was no
zoology at that early period, for in our definition we must
include the statement that zoology is the science of animals.
The knowledge which the ancient races of mankind had
concerning animals merely furnished the foundation on
which zoology could be built in later generations. For a
science consists not alone of facts but requires that these
facts shall be arranged in such manner as to show how they
are related to one another.

No one knows when these facts with which primitive man
must have been familiar became knit together into a science
of zoology. The earliest person of whom we definitely know
as a writer on animals is the Greek philosopher Aristotle
(Fig. 231), who lived in the fourth century B.C.

Zoology in the Middle Ages. In spite of its venerable be-
ginnings in the period of Greek culture and learning,
zoology never prospered as a separate science and profession
until modern times. Throughout the important epochs of

HISTORICAL DEVELOPMENT OF ZOOLOGY 443

Greek and Roman history and on down through the
Middle Ages zoology and most of the other sciences devel-
oped as mere appendages of the medical profession.

Discovery of the Microscope. Interesting as they are, the
discoveries as late as those of the sixteenth and seventeenth
centuries merely paved the
way for the real development
of the various branches of
zoology. About the opening
of the seventeenth century
the microscope was invented.
A Dutch spectacle-maker,
named Zacharias Jensen, is
usually credited with its in-
vention. The development
of this instrument opened
an entirely new field of en-
trancing interest. Then for
the first time man became
aware of the teeming world
of minute life. So also was
the way opened for an un-
derstanding two centuries
later of the structure of the
animal body.

Beginnings of Classification. All through the centuries there
had been no uniformity in the names used for the various
animals. As knowledge spread and interest in living things
grew this lack of uniformity in names became more and more
apparent. To the Swedish scientist Carl Linnaeus (1707-1778)
we are indebted for a system of exact naming. He is gener-
ally called the father of systematic zoology (Fig. 232). He
devised a system called binomial nomenclature wherein each
kind of animal is known by a name composed of two words,

Fig. 231

444

GENERAL ZOOLOGY

— the name of a larger group, or genus, plus a name for the
species. His system of names (first published in 1735 and
finally perfected in 1758) is recognized as the basis of all
modern classification of both plants and animals.

Comparative Anatomy and Paleontology. In the early part of
the nineteenth century a French naturalist, Georges Cuvier

(1769-1832), greatly
influenced the devel-
opment of zoology. In
his studies of fossils he
recognized them as the
remains of animals of
past times and related
to the animals of to-
day. Thus he founded
the science of paleon-
tology. Furthermore
he realized the impor-
tance of anatomical
structure in classifica-
tion, and is recognized
as the father of com-
parative anatomy.

The Cell and Proto-
plasm. In the two
hundred years follow-
ing the invention of the microscope many observations on
the minute structure of living things were published. Most of
these were scattering observations. In 1838 a botanist named
Schleiden, and one year later a zoologist named Schwann,
became convinced that the tiny units which various people
had observed in both plant and animal tissue are the funda-
mental units of which all living matter is composed. Thus
arose one of the most important generalizations in biology

Fig. 232. Linnasus

HISTORICAL DEVELOPMENT OF ZOOLOGY 445

up to that time. Later work by the German scientist Max
Schultze showed that not only are plants and animals com-
posed of similar units (the cells), but the actual living ma-
terial, or protoplasm, is identical in plants and in animals.

The Origin of Species. One of the outstanding contribu-
tions of the nineteenth century to scientific thought was the
serious study of evolution.
As a philosophical prin-
ciple evolution had been
discussed since the days
of Aristotle. No one per-
son has had greater effect
in stimulating thought
and research in natural sci-
ence than Charles Darwin
(Fig. 233), whose works
have been discussed in
another chapter.

He brought together
huge volumes of facts
from nature in support
of his arguments. Such an
array of facts was never
before assembled. This
statement may be more

readily appreciated when we understand the methods used in
science from its beginnings on down through the Middle Ages.
In all branches of learning, as well as in the sciences, the proof
of a statement or the validity of an expression rested upon
the statements of older writers. The words of an authority
passed for fact and were unquestioned. Science owes a debt
to the philosopher Roger Bacon for altering this manner of
getting at truth. Through his teaching in the thirteenth
century, — that we arrive at facts only by observation of

Fig. 233. Charles Darwin

446 GENERAL ZOOLOGY

nature and by experiment, — he brought about a complete
change of attitude toward the nature of truth. Authority,
except when it depends upon facts obtainable by any other
searcher after truth, has no place in science. Our whole
development of laboratory science and research resulted
from the application of Bacon's principles of philosophy.

Spontaneous Generation of Life. The origin of life has
been a problem on which man has speculated since his
earliest history. Until fairly recently it was commonly be-
lieved that living animals are being continuously formed
out of lifeless matter. By simple observation men witnessed
that cheese placed in a cupboard seemed to turn into mice.
Further, when meat was allowed to stand in the open, it
soon gave rise to blowflies. Such observations were com-
mon enough and unchallenged by most persons. At that
time no one understood how mice develop or how flies
come only from eggs. In fact, the idea that lifeless matter
could turn into living beings was not finally disproved
until the time of Pasteur. About 1860 Pasteur performed
experiments which proved that even the simplest organisms
are developed only from other living beings of their own

kind.

Zoology in America. Various agencies have contributed
to the advance of zoology in America. One of the most out-
standing of these has been the support accorded to zoolog-
ical research through federal and state funds. Our federal
government from an early date has recognized the service
of science to humanity. Through its Bureaus of Entomol-
ogy, Fisheries, Animal Industry, and Biological Survey
many economic problems have been solved. These bureaus
have not confined their attention to the control of destruc-
tive or harmful animals. A program of researches in pure
science has been carried out by all these bureaus in addition
to their programs of economic work. Frequently the re-

HISTORICAL DEVELOPMENT OF ZOOLOGY 447

searches on structure or habits or life history of an animal
have furnished information of value in controlling animal
pests, and also in protecting and propagating desirable
animals or those of direct value to man. The United States
Public Health Service has rendered immeasurable services
to zoology in investigating the relations of parasites to the
health of the nation.

In similar manner many of the states support, from taxes,
laboratories which return to the people many times the
amounts invested in protection of human lives and in bet-
tering the economic conditions of many industries. The
office of state entomologist, the numerous natural-history
surveys, departments of health, water surveys, and other
organizations supported by many states not only yield a
return in valuable discoveries in economic zoology but have
also been large factors in the advancement of pure science.

Societies. Public interest in animals has been stimulated
in many ways, of which societies and museums are prominent
examples. The Audubon societies were named in honor of
our pioneer student and bird artist, J. J. Audubon. These
societies scattered throughout the country and numerous
other nature-study organizations are responsible in large
measure for much of our legislation designed to protect
birds. More recently sportsmen and all others interested in
our native wild life have formed various societies and or-
ganizations, of which the Izaak Walton League is typical.
Through the efforts of such groups, popular sentiment for
conservation is being fostered.

Natural History Museums. Museums have played no small
part in the advancement of science. Most of them render
a service in educating the public in the wonders of nature,
and some become centers for research and study. The
National Museum, supported by our federal government,
and private institutions such as the American Museum

448

GENERAL ZOOLOGY

of Natural History in New York and the Museum of Com-
parative Zoology at Harvard are examples of these insti-
tutions. They perform the double service of educating the
public and at the same time, through expeditions and a
corps of scientific workers, serve as research centers.

Teaching of Zoology
in America. Any dis-
cussion of the teach-
ing of zoology in this
country always starts
with the name of Louis
Agassiz (1807-1873).
A Swiss by birth,
Agassiz (Fig. 234)
came to this country
when thirty-nine years
of age. He was the
founder of one of the
greatest research insti-
tutions in the United
States, the Museum
of Comparative Zool-
ogy at Harvard. His
summer laboratory at
Penikese in 1873 was
the forerunner of the
marine laboratories. His slogan, "Study nature, not books,"
was largely responsible for the introduction in colleges of
laboratory work in the sciences in place of textbook work
alone. Since his time there have been many notable teach-
ers of zoology in this country. Professor E. L. Mark of
Harvard and Professor E. B. Wilson of Columbia might
be mentioned as two who have played an unusual part in
the training of teachers of zoology since Agassiz's time.

Fig. 234. Louis Agassiz

HISTORICAL DEVELOPMENT OF ZOOLOGY 449

Practically every educational institution of any size and
importance has made contributions to the advancement of
zoology through its teachers and its students. In addition
to these, many privately controlled and endowed labora-
tories have furnished the facilities for some of the funda-
mental contributions to zoology. The International Health
Board has been very active in public health work both here
and abroad. Much of what we know of human heredity has
come from a laboratory at Cold Spring Harbor, New York,
under the direction of Dr. C. B. Davenport. Marine labora-
tories where teachers and students may spend summers in
study and research have been great factors in zoological
progress. The pioneer laboratory at Woods Hole, Massa-
chusetts, and several on the Pacific coast deserve mention.

In the foregoing paragraphs some of the many agencies for
the advancement of the zoological sciences in this country
have been passed in hasty review. These serve only as ex-
amples to show what diversity of interest and what variety
of means have been enlisted in directing the growth of zo-
ology in America. A complete list of the factors would re-
quire a large volume.

Science and Human Welfare. We live in an age which is
commonly referred to as the Age of Science. Man has
learned how to make use of and to control the forces of
nature. No other beings have ever been able to make
nature serve them in such manner. Most of the things
which we have come to consider as conveniences or even
necessities in our everyday life were unknown to our fore-
fathers of a few generations ago. In most of the countries
of the earth we find evidence that our civilization and our
culture have extended back only a few thousands of years.
Before that period most of our ancestors were what we
today should call savages. All of us are aware that in
America our modern civilization dates only from the seven-

450 GENERAL ZOOLOGY

teenth century. There are evidences that a rather high type
of civilization flourished on this continent at an early period,
but when the white settlers first arrived they found the
Indians in a stage of development which is commonly called
the Stone Age. This means that they formed stones into
spearheads and arrowheads by chipping off pieces until the
desired shape was attained. Weapons and most of the
implements which they used were formed in this way. In
some instances they had discovered how to use metal for
making implements and decorations, but stone was the
common material for all such purposes.

In Europe and Asia modern civilization was established
long before it was in America. Yet even in these countries
many remains of primitive man are still found. In the caves
where men dwelt before they began to build shelters of their
own many stone implements similar to those found in
America have been discovered. Objects of the same sort
found in the gravel deposits along streams give evidence
that these early implements date from a time during or
just following the geological period known as the Ice Age.
These oldest signs of man's occupation of the earth are
thought to date back several hundred thousand years.

It is only a few hundred years since superstition and
magic played the greatest role in human thinking. Even
as recently as two or three generations ago the causes of
disease were attributed to evil spirits, as they still are by
uncivilized tribes at the present day. The unknown to
these people was shrouded in mystery. No attempt was
made to understand what was not known. Though there
are many things of which we today are still ignorant, we
do not look upon many of these as unknowable. Much of
this change in our attitude is due to the influence of science
upon our thinking. Our highly trained physician with his
laboratory for discovering the cause of disease has replaced

HISTORICAL DEVELOPMENT OF ZOOLOGY 451

the witch doctor with his charms to conquer the evil spirits.
Swampy regions where the "bad air" caused yellow fever
and malaria in the days of our grandfathers have become
healthful dwelling places since man through science has
learned that mosquitoes, not the air, are responsible for the
malaria and yellow fever. The United States succeeded in
building the Panama Canal after other nations had been
forced to admit defeat in the attempt, not so much because
of superior engineering skill but as a result of knowledge
of the manner in which certain diseases are spread. The
diseases which killed off the workmen in the earlier attempts
were controlled by the American engineers through a scien-
tific knowledge of their causes which was not available
before.

Through the information which the sciences have fur-
nished us we now look upon the entire universe as gov-
erned by definite laws. Ignorance and superstition fall
before the attack of knowledge. In the advance of our
learning and of science each generation witnesses the dis-
covery of new laws and principles governing nature. Many
of these new laws and principles have application for living
things as well as for lifeless material. Through these dis-
coveries man has learned how to make the forces of nature
serve him. In this discussion it is not worth while to go into
the details of how man discovered that the waterfall might
be harnessed and made to turn his machinery or to produce
electricity. In this mechanical age we frequently forget
that only a few thousand years ago there were no machines
of any kind. All work that was then performed for man was
done by his own hands or by his domestic animals.

Tremendous progress has been made in the past two or
three generations toward applying the discoveries of science
to the enriching and conserving of human life. So much has
been accomplished in this direction that we may rightly raise

452 GENERAL ZOOLOGY

the question if there is a limit beyond which man may not
go. Rapid transportation and ready communication are
only samples of the commonplace experiences of today
which we owe to the development of the physical sciences.
Control and prevention of disease and improvement of liv-
ing conditions are among the things for which advancement
of the biological sciences is responsible.

There is one direction in which the limit of application
of the discoveries of science is not even in sight, — that of
race improvement. It is impossible to imagine what the
future holds in store for the human race if man is able to
make full use of all the knowledge contributed by science.

INDEX

Abomasum, 421

Aboral surface, 222

Absorption, 7, 120

Abysmal fauna, 330

Acephala, 206, 309

Acorn-tongue worm, 306

Acquired characters, 187

Aftershaft, 369

Agassiz, Alexander, 281

Agassiz, Louis, 448

Age, of Amphibians, 350; of Coal
Plants, 349 ; of Fishes, 331 ; of In-
vertebrates, 301 ; of Mammals, 433 ;
of Man, 435; of Reptiles, 365; of
Science, 449

Aggressive resemblance, 23, 424

Agramonte, 102

Aigrets, 383

Air bladder, 314

Air sacs, 8

Albatross, 380

Albinism, 411

Alligators, 354, 364

Alluring coloration, 23

Alternation of generations, 272

Amber, 114

Ambulacral groove, 222

Ambystoma, 345

American Museum of Natural His-
tory, 433, 447

Amoeba, 289-291, 293, 297

Amoebocytes, 243

Amoebulae, 297

Amphibia, 310, 344 ; Age of, 350

Amphioxus, 304, 309

Ampulla, 224

Anabolism, 124

Anatomy, 441

Anemone, 275

Animal kingdom, 109

Annelida, 251, 255, 308

Annulus, 154

Anseres, 382

Ant, cornfield, 33, 91

Anteater, spiny, 412

Antelopes, 418, 419, 420, 433

Antennae, 2, 146

Antennules, 146

Anthozoa, 279, 308

Antitoxin, 431

Antlers, 419

Ants, 89 ; agricultural, 92 ; cornfield,

33, 90-91 ; honey, 92 ; slave-making,

92 ; white, 110
Anura, 347
Apes, 427

Aphids, 33, 99, 184 ; corn-root, 33, 91
Appendages, 2
Appendix, vermiform, 408
Arachnida, 144, 301, 309
Archaean Era, 300
Archaeopteryx, 401
Aristotle, 442
Armadillos, 415
Arms of starfish, 221
Arthropoda, 157, 171, 309
Artificial selection, 173-174

Asexual reproduction, 127, 262, 270

Assimilation, 120

Asteroidea, 308

Atoll, 281

Atrium, 304

Audubon, J. J.-, 447

Auricles, 194, 206, 313, 334, 352, 354

Australian realm, 116

Aves, 310, 377

Axolotl, 345

Back swimmer, 41

Bacon, Roger, 445

Balancers, 69

Balancing organs, 146, 274

Balanoglossus, 306

Baleen, 417

Barbels, 323

Barbs, 369

Barbules, 369

Barnacles, 166

Barrier, 114, 401

Basipodite, 150

Basket stars, 231

Bats, 427 ; vampire, 427

Beaks, sucking, 30

Bears, 424

Beavers, 422, 423

Beebread, 83

Bees, bumble, 86; carpenter, 89;

guest, 86; honey, 83; leaf-cutter,

89; solitary, 89

453

454

GENERAL ZOOLOGY

Beetles, 43 ; buffalo, 52 ; buprestid,
52 ; click, 49 ; Colorado potato, 50 ;
diving, 47 ; flat-headed, 52 ; Japa-
nese, 45 ; June, 43 ; lady, 48 ; lady-
bird, 48 ; long-horned, 52 ; May, 43 ;
sacred, 45 ; scavenger, 47 ; snout,
51; tiger, 46; water, 46; whirligig,
46 ; wood-boring, 52

Beriberi, 125

Binomial nomenclature, 443

Biological Survey, 397

Bird Day, 399

Bird-banding, 397

Birds, 377 ; banding, 397 ; geographical
distribution of, 401 ; migration of,
394 ; protection of, 399

Black snakes, 361

Blackbirds, 393

Blastula, 134, 230

Blowflies, 71

Bluebottle flies, 71

Boatman, water, 41

Bobolink, 396

Bobwhite, 386

Boll weevil, 51

Botflies, 71 ; horse, 71 ; sheep, 72

Bovidae, 420

Bristles, 238

Brittle stars, 231

Britton, Dr., on insect pests of stored
food, 101

Bronchial tubes, 372

Brood pouch, 164

Brooks, W. K., 199

Bryozoa, 308

Bubonic plague, 104, 432

Budding, 270, 272, 285

Buffalo beetles, 52

Buffaloes, 433

Bugs, 30 ; chinch, 40 ; squash, 39 ;
water, 41

J3ull snakes, 361

Bumblebees, 86, 106

Buprestids, 52

Bureau, of. Animal Industry, 446; of
Biological Survey, 446 ; of Entomol-
ogy, 446; of Fisheries, 204, 327, 446

Butterflies, 54 ; cabbage, 59 ; check-
ered white, 60 ; economic impor-
tance of, 60 ; milkweed, 54 ; mon-
arch, 54 ; swallowtail, 58 ; viceroy,
58 ; zebra, 59

Buzzard, 387

Byssus, 196

Caddis flies, 184

Caeca, 6, 372 ; gastric, 6 ; pyloric,

227 ; intestinal, 227
Caecum, 6
Calcarea, 307

Calciferous glands, 240

Camelidae, 420

Camels, 418

Canal, circular, 272; radial, 224;
ring, 224 ; stone, 224

Canidae, 424

Capillaries, 122, 193, 242, 313, 334

Caprella, 165

Capsule, adrenal, 408; egg, 247

Carapace, 146

Carbohydrates, 118

Carbon tetrachloride, 260

Carboniferous Age, 349

Carnivorous mammals, 423

Carpenter bees, 89

Carroll, 102

Cassowaries, 377

Caterpillars, 56

Cats, 423 ; domestic, 424

Cell, 129; division of, 132; struc-
ture of, 129

Cement gland, 12

Centipeds, 169, 309

Centrosome, 131

Cephalopoda, 219, 309

Cephalothorax, 137, 145

Cerebellum, 316, 338, 373

Cerebropleural ganglia, 195

Cerebrum, 316, 338, 373

Cervidae, 420

Cestoda, 266, 308

Cetacea, 416

Chaetopoda, 308

Chameleons, 356

Chapman, Frank, on warblers, 392

Chelicerae, 137

Chelipeds, 148

Chelonia, 362

Chiggers, 143

Chilopoda, 309

Chimpanzee, 428

Chinch bug, 40

Chiroptera, 427

Chitin, 2

Chlorophyll, 291

Chordata, 307, 309

Chordate, 304

Chromatin, 131, 133, 179

Chromosomes, 131, 179 ; numbers of,
132

Chrysalis, 56

Cicadas, 30; periodical, 30

Cilia, 192, 194, 252, 262, 293, 307

Ciliata, 298, 307

Clam, 189, 309 ; long-neck, 189 ; soft-
shell, 189

Classes, 109

Classification, 107, 443

Clavicles, 338, 373

Cleavage, 134 ; spindle, 131

INDEX

455

Click beetles, 49

Clitellum, 239, 246

Clothes moths, 67

Cochineal, 38

Cockatoos, 388

Cockroaches, 19, 101, 164

Cocoon, 61

Codling moth, 66

Ccelenterata, 267, 282, 308

Ccelom, 255

Coleoptera, 53

Collembola, 109 110

Colloids, 119

Colonies, 298

Colorado potato beetle, 50

Coloration, alluring, 23 ; warning, 48,

49, 58
Columbae, 386
Commensalism, 91
Commissures, 195
Comparative anatomy, 441
Compound eyes, 2
Conchologists, 213
Condyles, 336, 354, 373
Conjugation, 294
Conservation, 328
Contractile vacuole, 290, 294
Control of crop pests, 99
Copperhead, 359
Coracoid, 338, 373
Coral, 278 ; islands, 280 ; reefs, 281
Coral snake, 359
Corn borer, 67
Cornfield ant, 33, 90, 91
Corn-root aphids, 33, 91
Corvidae, 392
Cotton boll weevil, 51
Cottontail, 422
Cottony scales, 36
Cow, 418, 420
Cowpox, 431
Coxopodite, 150
Crabs, 160; blue, 162; edible, 162;

fiddler, 163; hermit, 160; oyster,

200 ; spider, 162
Crane flies, 76
Cranes, 383

Cranium, 316, 336, 373
Crayfishes, 145; as food, 156
Crickets, 18 ; house, 18 ; mole, 19
Crinoidea, 309
Crinoids, 231
Crocodiles, 354, 364
Crocodilia, 364
Crop, 6, 239, 370
Crop pests, control of, 99
Crow, 392

Crustacea, 166, 168, 309 ; parasitic, 166
Crystalline style, 192
Crystalloids, 119

Ctenophora, 308
Cuckoos, 399
Cuvier, Georges, 444
Cyclops, 165
Cytoplasm, 130, 291

Daddy-long-legs, 141

Damsel flies, 27

Dana, J. D., on coral reefs, 281

Darning needles, 24

Darwin, Charles, on earthworms,
249 ; natural selection of, 182, 3 85 ;
on the origin of species, 445; pi-
geons and natural selection of, 376 ;
sexual selection of, 186

Darwin, Erasmus, 187

Davenport, C. B., 449

Death, feigning, 415

Deer, 418, 433

Degeneration, 112

Demospongia, 307

Devil's darning needles, 24

Digestion defined, 118

Dimorphism, 59 ; sexual, 59 ; seasonal,
59

Dinosaurs, 354, 366

Diplopoda, 309

Dipnoans, 326

Diptera, 76

Disease, insects as cause of, 74, 101

Diseases : bubonic plague, 104 ; dys-
entery, 102 ; sleeping sickness, 71 ;
trench fever, 103; typhoid fever,
70, 102 ; typhus, 103 ; yellow fever,
74, 102, 103

Disk, 222

Distribution of insects, 114

Diving beetles, 47

Division of cell, 132 ; of nucleus, 131

Dogs, 423 ; domestic, 424

Dolphins, 416

Dominant, 177

Dorsal, 4

Dorsal vessel, 8

Doves, 386; mourning, 386; turtle,
386; wild, 386

Dragon flies, 24

Drill, oyster, 212

Drones, 83

Drosophila, 179

Drum, 30

Duckbill, 412

Ducks, 382; canvasback, 382 ; domes-
tic, 382 ; mallard, 382

Dysentery, 102

Eagles, 387
Earthworm, 238
Echinoderma, 221, 237, 308
Echinoidea, 309

456

GENERAL ZOOLOGY

Ecology, 441

Ectoderm, 136

Ectoplasm, 289

Edentata, 415

Edentates, 439

Eel, 324

Egg, 11, 127, 133, 318, 339, 354, 375, 413

Egg capsule, 247

Egrets, 383

Eigenmann, Professor, on blind

crayfishes, 155
Elasmobranchii, 321
Electric-light bug, 42
Elephants, 418
Elimination of unfit, 183
Elk, 433
Elytra, 43, 53
Embryo, 133-134, 151
Embryology, 127
Emus, 377

Endocrine glands, 127
Endoderm, 136
Endoplasm, 289
Endopodite, 150
Energy, forms of, 122 ; potential, 123 ;

kinetic, 123
Entomology, 95
Enzymes, 118
Eohippus, 434
Ephemerida, 29
Epiglottis, 408
Epipharynx, 6
Erosion theory, 281
Ethiopian realm, 116
Euglena, 291
European corn borer, 67
Evolution, 173; study of, 188
Excretion, 10, 124, 125
Existence, struggle for, 183
Exopodite, 150
Exoskeleton, 95

Facet, 2

Family, 109

Fangs, 357 ■

Fat bodies, 339

Fats, 118, 129

Fatty acid, 119

Fauna, 116; abysmal, 330; littoral,

330 ; pelagic, 330
Faunal realms, 116
Feathers, contour, 369; down, 369;

flight, 369
Feces, 125
Feign death, 415
Felidae, 423
Femur, 4, 338
Fertile, 108

Fertilization, 12, 127, 133
Fertilized egg, 12, 127, 134

Fertilizers, 430

Fibula, 338

Filoplumes, 370

Finches, 393

Fins, 311 ; anal, 312 ; caudal, 312 ; dor-
sal, 312 ; pectoral, 312 ; pelvic, 313 ;
ventral, 312

Fireflies, 49

Fish lice, 166

Fish moths, 109

Fisheries, Bureau of, 327

Fishes, 309 ; Age of, 331

Fission, 262

Fittest, survival of, 183

Flagellum, 285, 291, 307

Flatfishes, 325

Flatworms, 261, 308

Fleas, rat, 104; water, 165

Flesh flies, 71

Flickers, 389

Flies, 69; bluebottle, 71; crane, 76;
flesh, 71; fruit, 72; Hessian, 76;
house, 69; hover, 73; tsetse, 71.
See also Botflies ; Blowflies

Flounders, 325

Flower and Lydekker on whales, 416

Flowers and insects, 104

Flukes, 261, 308; blood, 264; hu-
man, 264 ; liver, 262 ; lung, 264

Flycatchers, 391, 399

Food, classes of, 118

Food vacuole, 290, 293

Forbes, S. A., on man versus insects,
98

Fossil animals, 181, 219, 231, 331, 350,
366, 401, 433; insects, 113

Fowl, jungle, 385; domestic, 385

Fox-farming, 432

Fox snakes, 361

Foxes, 424

Fringillidae, 393

Frog, 332; bull, 332; green, 332;
leopard, 332 ; tree, 347

Fruit flies, 72

Fur-farming, 432

Gadow, Professor, on regeneration,

345
Gallflies, 92
Gallinae, 385
Ganglia, 10
Gar pike, 323
Garter snakes. 362
Gasteropoda, 214, 309
Gastric mill, 151
Gastrula, 134
Geese, 382
Gemmules, 286
Gene, 179
Generalized insects, 111, 112

INDEX

457

Generation, alternation of, 272 ; spon-
taneous, 446

Genus, 107

Germ cells, 133

Giant water bug, 42

Gila monster, 356

Gill chamber, 148

Gill slits, 304

Gill-bailer, 148, 152

Gill-rakers 314

Gills, blood, 95 ; tracheal, 28, 95

Giraffes, 418

Gizzard, 6, 370

Gizzard shad, 329

Glacial Epoch, 435, 437

Glands, calciferous, 240; green, 146,
153; silk, 62

Glass snake, 355

Glochidium, 203

Glottis, 372

Glycerin, 119

Glycogen, 123

Goats, 418

Goldfishes, 329

Gonads, 11, 127, 128, 154

Gorilla, 428

Grasshoppers, 1 ; common red-legged,
1, 107; control of, 15; lesser, 1,
107; long-horned, 17 ; meadow, 18;
Rocky Mountain, 1, 107

Grassi, Professor, on malaria, 297

Green gland, 146, 153

Grouse, 385

Grubs, white, 44

Guest bees, 86, 88

Guinea pigs, 177, 422

Gulls, 378

Gypsy moth, 66

Habitat, 1, 107

Haemoglobin, 122

Hair snakes, 260

Halibut, 325

Hall, M. C., on cure for hookworm,

259
Halteres, 69
Hares, 422
Harvest fly, 30
Harvest mites, 143
Harvestmen, 141
Hawk moths, 64
Hawkbill, 362
Hawks, 387

Health Board, International, 449
Hemiptera, 30, 42
Hereditary characters, 134
Heredity, 173 ; Mendel's law of, 176
Hermaphroditic, 206, 210, 245
Herodiones, 382
Herons, 382

Hessian fly, 76

Heterozygous, 178

Hexactinellida, 307 »

Hexapoda, 95, 309

Hinge ligament, 189

Hippopotamus, 417

Hirudinea, 308

History of zoology, 441

Holothuroidea, 309

Homing pigeons, 376

Homologous, 151

Homology, 150

Homoptera, 30, 38

Homozygous, 178

Honey, 83

Honeybee, 83

Honeydew, 33

Hoofed mammals, 417

Hookworm Commission, 259

Hookworms, 258

Hopperdozer, 16

Horn, 430

Hornets, 79

Horns, 419

Horses, 418, 434, 437

House cricket, 18

House flies, 69

Hover flies, 73

Howard, L. O., on malaria, 102

Huxley on man and apes, 429

Hybrids, 108

Hydra, 267, 308

Hydroids, 271

Hvdrozoa, 273, 308

Hyenas, 423

Hymenoptera, 94

Hypopharynx, 3, 6

Hypophysis, 128

Ichneumon flies, 92

Icteridse, 393

Iguana, 356

Imaginal disks, 96

Imago, 14, 96

Incisors, 404

Insect, behavior of, 96 ; control of, 99

Insecticides, 100

Insectivora, 426

Insects, 95, 309 ; control of, 99 ; dis-
ease-causing, 101 ; distribution of,

- 114; economic importance of, 99;
fossil, 113; generalized, 111; house-
hold, 101; pollination by, 105;
relation of, to flowers, 104; sim-
plest, 109; specialized, 111; versus
man, 98

Instinctive action, 97

Intelligence, 98

Internal secretions, 127

Interstitial cells, 128

458

GENERAL ZOOLOGY

Invertebrates, 299 ; of past, 299
Islands, coral, 280
Isoptera, 110
Itch mites, 144
Ivory, 422

Jackals, 424
Jaguar, 423
Japanese beetle, 45
Jaws, 312
Jay, 392
Jellyfish, 273

Jensen and invention of microscope
443 H '

Jordan, David Starr, 184, 324
Judd, Dr., on birds, 397
June beetles, 43
Jungle fowl, 385

Kangaroo, 414
Katabolism, 124
Katydid, 17
Kea, 388

Kinetic energy, 123
King snakes, 361

Knight, Charles R., drawings of fos-
sil horse, 434

Labium, 3

Labrum, 3

Lacertilia, 355

Lacteals, 408

Lady beetles, 48

Ladybird beetles, 48

Ladybugs, 48

Lancelet, 304

Larva, 44, 96

Larynx, 372

Lateral line, 312

Lazear, 102

Leaf-cutter bees, 89

Leech, 253, 308

Leopard, 423

Lepidoptera, 68

Lice, as carriers of disease, 103: fish.

166; plant, 33
Life and protoplasm, 133
Life processes, 117
Limicolae, 384

Linnjeus, Carl, 108, 443-444
Lion, 423

Littoral fauna, 330
Living matter, 129
Lizard, 351; legless, 355; pine, 351
Lobster, 157
Lockjaw, 432
Locustidae, 109

Locusts, 1, 30; Rocky Mountain, 1;
seventeen-year, 30 ; thirteen-year, 30
Long-horned beetles, 52

Long-horned grasshoppers, 17

Longipennes, 378

Loon, 378

Lung books, 137

Lungfishes, 326

Lymph hearts, 336

Lynx, 423

Macronucleus, 294
Madreporic body, 224
Maggots, 69
Malaria, 74, 101, 295

Malarial parasite, 295

Malpighian tubes, 10

Mammalia, 310, 412

Mammary glands, 410

Mammoth, 437

Man, 427 ; Age of, 435

Mandibles, 3

Mange, 144

Manna, 38

Mantids, 21

Mantle, 191

Mantle cavity, 192

Mantle folds, 191, 202

Manubrium, 272

Mark, Professor E. L., 448

Marsupialia, 414

Mastigophora, 298, 307

Mastodons, 437

Maturation, 133

Maupas on conjugation, 294

Maxillae, 3, 54, 77, 149

Maxillipeds, 149

May beetles, 43

May flies, 27

Meadow grasshopper, 18

Measuring worm, 67

Medulla, 316, 338, 373

Medusa, 271, 308

Melanism, 411

Mendel, Gregor, 176

Mendel's law, 176

Mesenterial filaments, 278

Mesenteries, 278

Mesoderm, 136, 302

Mesothorax, 4

Mesozoic time, 365

Metabolism defined, 124

Metacarpals, 338

Metamorphosis, 23, 340; complete,

53, 96 ; incomplete, 23, 96
Metathorax, 4
Metazoa, 303
Mice, 422
Micronucleus, 294
Microscope, discovery of, 443
Migration of birds, 394
Milkweed butterfly, 54
Millipeds, 170

INDEX

459

Mimicry, protective, 58, 73

Miner, Jack, and birds, 400

Minks, 432

Minnows, 329

Mites, 141; harvest, 143; itch, 144

Mitosis, 131

Mniotiltidae, 392

Moebius, Professor on the oyster, 200

Molars, 404

Mole cricket, 19

Moles, 426

Mollusca, 207, 220, 309

Molluscoidea, 308

Molt, 13, 146, 158

Molting, 10, 23, 158

Monarch butterfly, 54

Monkeys, 427 ; spider, 428

Monotremata, 413

Morphology, 112, 441

Mosaic vision, 3

Mosquitoes, 73; control of, 74, 329

Moss animals, 308

Mother Carey's chickens, 381

Mother of pearl, 192

Moths, 61 ; American, 63 ; Chinese
silkworm, 62 ; clothes, 67 ; codling,
66 ; corn-borer, 67 ; giant silkworm,
63; gypsy, 66; hawk, 64; silk-
worm, 61 ; tussock, 65 ; under-
wings, 63 ; yucca, 105

Motor nerve cell, 245

Mucous glands, 321

Mud dauber, 79

Mud puppy, 347

Murray, Sir John, on coral islands, 281

Museum, of Comparative Zoology
(Harvard), 448; of Natural His-
tory, 447

Museums, American, 447

Mussel, fresh water, 202

Mutant, 173

Mutation, 173

Mutation theory, 188

Nacreous layer, 191
Nagana, 71

National Museum, 447
Natural selection, 182
Nauplius, 167
Nautilus, 217
Nearctic realm, 116
Necturus, 347
Nemathelminthes, 256, 308
Nematoda, 308
Neotropical realm, 116
Nephridia, 193, 243
Nerve cell, 245
Nerve cord, 306

Nervous system, 10 ; peripheral, 244 ;
radial, 229

•Nettling cells, 269

Neuters, 78

Newts, 344

Nictitating membrane, 332, 369

Nitrogenous wastes, 10

Noguchi, Professor, and yellow
fever, 102

Nomenclature, 107 ; binomial, 443

Nostrils, 312

Notochord, 304

Nucleus, 130; division of, 131 ; func-
tion of, 130

Nudibranch, 214

Nymph, 13, 96

Ocelli, 3

Octopus, 217

Odonata, 27

Odors, repellent, 40

Olfactory lobes, 316, 338, 373

Operculum, 312

Ophidia, 357

Ophiuroidea, 309

Opossum, 414

Optic lobes, 316, 338, 373

Oral surface, 222, 293

Orang-utan, 428, 430

Order, 23, 109

Organ systems, 117

Oriental realm, 116

Orioles, 393

Ornithologists, 395

Orthoceras, 218

Orthoptera, 23

Osborn, Professor, on prehistoric

man, 435
Osculum, 284
Osmosis, 120
Ostriches, 377
Otocyst, 146
Otoliths, 316
Ova, 375, 409
Ovaries, 12, 154, 230, 245, 317, 338,

375, 409
Overpopulation, 183
Oviduct, 12
Oviparous, 321
Ovipositor, 6, 18, 77
Owls, 388
Oxen, 418
Oxidation, 122

Oyster, 196 ; drill, 212 ; farms, 198
Oyster-shell scale, 36

Palsearctic realm, 116
Palate, 406
Paleontologists, 181
Paleontology, 441
Palpi, 4, 149, 192
Paludicola?, 384

460

GENERAL ZOOLOGY

Pancreas, 119, 371

Paramecium, 292

Parasites, 71, 203, 262, 288, 295

Parathyroid gland, 128

Paroquet, 389

Parrots, 388

Parthenogenesis, 34

Partridge, 385

Passeres, 389

Pasteur, 446

Pearls, 205

Peckham, Dr. and Mrs., on habits of

wasps, 81
Pedal ganglion, 195
Pedicellariae, 222
Pedipalps, 137
Pelagic fauna, 330
Pelicans, 381
Pelvic girdle, 316, 338
Peptone, 119
Perch, 311
Perching birds, 389
Perfumes, 430
Pericardium, 193, 372
Periostracum, 191
Peripheral nervous system, 244
Periwinkle, 213
Permeable membrane, 120
Petrels, 380
Phagocytes, 96
Phalanges, 338
Pheasants, 385
Phyla, 109
Physiology, 441
Pici, 389

Pigeons, 368, 386; carrier, 376; do-
mestic, 368; passenger, 386
Pigs, 418
Pike, gar, 323
Pill bug, 163
Pisces, 309
Plague, 104
Planarian, 261
Plant lice, 33

Plathelminthes, 261, 266, 308
Plovers, 384
Plowshare bone, 373
Pneumatic duct, 314
Polian vesicles, 229
Pollen baskets, 86
Pollination by insects, 105
Pollution, 329
Polymorphism, 59
Polyp, 267, 308
Porcupines, 422
Porifera, 283, 287, 307
Porpoises, 416
Potato beetle, 50
Potential energy, 123
Prairie dogs, 422, 432

Prawn, 160

Premolars, 404

Primates, 427

Prismatic layer, 191

Proboscidea, 420

Proboscis, 54, 261

Prochordates, 307, 309

Propolis, 83

Prostomium, 239

Protection, 328

Protective color, 14, 319

Protective mimicry, 58, 73

Protective resemblance, 18, 20, 64

Protein, 118, 129

Prothorax, 4

Protoplasm, 118, 129

Protopodite, 150

Protozoa, 288, 297, 307

Psalterium, 421

Pseudopodium, 289, 307

Ptyalin, 118

Public Health Service, 447

Pulvillus, 4, 14, 69

Puma, 423

Pupa, 44, 96

Pygopodes, 378

Quail, 385

Quaternary Period, 436
Queen bee, 83
Quill, 369

Rabbits, 422, 432

Rabies, 432

Raccoons, 424

Rachis, 369

Radial canals, 224

Radial nerve, 229

Radially symmetrical, 222

Radius, 338

Raptores, 387

Rats, 422, 432

Rattlesnakes, 359

Rays, 321

Rays of fins, 313

Realms, 116

Reasoning, 98

Recapitulation Theory, 302

Recessive, 177

Reed, Dr., on yellow fever, 102

Reefs, 281

Reflex action, 97, 245

Regeneration, 159, 230, 262, 345

Repellent odors, 40

Reproduction, methods of, 127 ; mi-
tosis in, 133

Reptiles, Age of, 365

Reptilia, 310, 351

Resemblance, aggressive, 23; protec-
tive, 18, 20, 64

INDEX

461

Respiration denned, 121

Reticulum, 420

Rheas, 377

Rhinoceros, 418, 419, 439

Ring canal, 224

Robin, 393

Rocky Mountain spotted fever, 143

Rodentia, 422

Rodents, 422

Ross, Sir Ronald, on malaria, 101, 297

Rostrum, 146

Rotifera, 308

Roundworms, 256, 260, 308

Royal jelly, 84

Rumen, 420

Ruminants, 421

Sacred beetle, 45

Salamanders, 344

Salmon, 324

Sanctuaries, wild-life, 432

Sand dollars, 232

Sandpipers, 384

Sandworm, 251

Sanford, Professor, on intelligence
of fish, 319

San Jose scale, 36

Saponification, 119

Sapsuckers, 389

Sarcodina, 298, 307

Sawflies, 93 ; American, 93 ; currant,
93

Scale insects, 35 ; cottony, 36 ; oyster-
shell, 36 ; San Jose, 36

Scales, insect, 54; fish, 311

Scallop, 200

Scapulas, 338, 373

Scarabaeus, 45

Scarabs, 44, 45

Scarlet fever, 432

Scavenger beetles, 47

•Schleiden, 444

Schultze, Max, 445

Schwann, 444

Science, 442

Scientific name, 107

Scorpions, 144

Scudder, S. H., on butterflies, 56

Scurvy, 125

Scyphozoa, 275, 308

Sea anemone, 275

Sea combs, 308

Sea cucumber, 234, 309

Sea lily, 231, 309

Sea squirt, 305

Sea urchin, 232, 309

Seals, 424, 425

Seasonal dimorphism, 59

Secondary sexual characters, 128

Secretions, 10 ; internal, 127

Selection, artificial, 173-174 ; natural,

182 ; sexual, 186
Sense organs, 96
Sensory nerve cell, 245
Serpent stars, 231, 308
Serum, 431

Seventeen-year locust, 30
Sewage contamination, 199
Sexual dimorphism, 59
Sexual selection, 186, 391
Shad, gizzard, 329
Shagreen, 322
Sharks, 321
Sheep, 418
Shellac, 38
Shipworms, 201
Shoulder girdle, 316, 338
Shrews, 427
Shrimp, 160
Sieve plate, 224
Silk glands, 62
Silkworm moths, 61 ; American, 63 ;

Chinese, 62 ; giant, 63
Silverfish, 109
Simplest insects, 109
Sinuses, 7, 152
Siphon, 192, 216
Skate, 321
Skippers, 61
Skunk, 424, 432
Sleeping sickness, 71
Slipper animalcule, 292
Sloths, 415
Slug, garden, 211
Smallpox, 431

Snail, 309 ; land, 211 ; pond, 207
Snake feeders, 24
Snakes, 354, 357; black, 361; bull

361 ; copperhead, 359 ; coral, 359

fox, 361; garter, 362; green, 361

king, 361; moccasin, 359; water,

361
Snipes, 384
Snout beetles, 51
Snow fleas, 110
Societies, 447
Soft-shell clam, 189
Solitary bees, 89
Somites, 2, 238
Sow bug, 163
Sparrows, 393
Specialized insects, 111, 112
Species, 1, 14, 107
Specific name, 107
Sperm cells, 11, 127, 133
Sperm ducts, 154
Sperm whales, 417
Spermaries, 12, 154, 230, 245, 317,

338, 375, 409
Spermatozoa, 133, 154, 195, 198, 339

462

GENERAL ZOOLOGY

Spicules, 283

Spiders, 137, 309 ; garden, 138 ; taran-
tula, 140; trapdoor, 141; wolf, 140

Spinal cord, 305

Spindle, 131

Spinnerets, 137

Spiracles, 4 m

Sponges, 283 ; boring, 200 ; fisheries,
287

Spontaneous generation of life, 446

Spores, 296

Sporozoa, 298, 307

Sport, 173

Spotted fever, 143

Springtails, 109, 110

Squame, 146

Squash bug, 39

Squid, 215

Squirrel, 403, 422

Starch, 119, 129

Starfish, 221, 308; basket, 231;
brittle, 231 ; serpent, 231

Steapsin, 118

Steganopodes, 381

Stiles, C. W., on hookworms, 259

Sting, 77, 144

Stone Age, 450

Stone canal, 224

Storks, 382

Struggle for existence, 183

Struthiones, 377

Sturgeon, 323

Subesophageal ganglion, 11

Subimago, 28

Subsidence theory, 281

Sugars, 119, 129

Sunfishes, 326

Supraesophageal ganglion, 11

Suprarenal gland, 128
Survival of the fittest, 183
Swallowtail butterflies, 58
Swans, 382
Swarming of bees, 85
Swimmerets, 150
Symbiosis, 91
Syrinx, 372
Systematic zoology, 441

Tadpoles, 339

Tapeworms, 261, 264, 308 ; of man, 265

Tarantulas, 140

Tarpan, 421

Tarsus, 4, 338

Taxonomy, 441

Teleostomi, 323

Telson, 150

Termites, 110

Terns, 378

Texas fever, 143

Theromorphs, 366

Thirteen-year locust, 30

Thousand legs, 309

Thrushes, 393

Thymus gland, 408

Thyroid gland, 128, 408; metamor-
phosis and, 341

Thysanura, 109

Tibia, 4, 338

Ticks, 141, 309 ; cattle, 143 ; wood, 143

Tiedemann's vesicles, 229

Tiger, 423

Tiger beetles, 46

Tissues, 130

Toads, 347; obstetrical, 347; Suri-
nam, 348 ; tree, 348

Tobacco worm, 65

Tomato worm, 65

Tonsils, 406

Torpedoes, 322

Tortoises, 354, 362 ; box, 363 ; painted,
364

Toxin-antitoxin treatment, 431

Toxins, 431

Tracheae, 8, 95, 137

Tracheal gills, 28, 95

Tree frogs, 347

Tree toads, 348

Trematoda, 308

Trematodes, 262, 264, 308

Trench fever, 103

Triceratops, 367

Trichina, 257

Trichinella, 257

Trilobites, 168

Tritons, 346

Trochelminthes, 308

Tropism, 97

Trypanosomes, 71

Trypsin, 118

Tsetse flies, 71

Tube feet, 222, 231, 232, 235

Tube worm, 252

Tubinares, 380

Tunicata, 305

Turbellaria, 262, 308

Turdidse, 393

Turkeys, 385

Turtles, 354, 362 ; green, 362 ; hawk-
bill, 362; snapping, 364; soft-
shelled, 364

Tusks, 418

Tussock moths, 65

Tympanic membrane, 333

Tympanum, 6

Typhoid fever, 70, 102, 431

Typhus fever, 103

Tyrannidaa, 391

Ulna, 338
Umbo, 189

INDEX

463

Underwings, 63

Unfit, elimination of, 183

Ungulata, 417-419, 435

Unit character, 177

United States Bureau of Fisheries,

204, 327, 446
Ureters, 316, 409
Urethra, 409
Uric acid, 123, 193
Urine, 125

Urinogenital opening, 316
Urodela, 344
Urostyle, 338

Vaccination, 431

Vacuoles, 290 ; contractile, 290 ; food,

290
Vampire, 427
Vane, 369
Variation, 173
Varieties, 108, 401
Ventral sinus, 8

Ventricle, 194, 206, 313, 334, 352, 372
Vertebra?, 316
Vertebral column, 316
Vertebrates, 299, 309
Vibrissa?, 404
Vireonidae, 392
Vireos, 392
Vitamins, 125
Vries, Hugo de, 177, 188
Vultures, 387

Walking leaves, 21

Walking sticks, 20

Walruses, 424

Walton, Izaak, 328; on perch, 318

Walton, Izaak, League, 447

Warblers, 392

Warning coloration, 48, 49, 58, 345

Wasps, 77 ; digger, 80 ; paper-making,
79 ; potter, 82 ; social, 77 ; solitary, 79
Water beetles, 46
Water boatman, 41
Water bugs, 41 ; giant, 42
Water dog, 347
Water fleas, 165
Water moccasin, 359
Water snakes, 361
Water-vascular system, 224
Wax of bees, 86 *
Wax pockets, 86
Weevil, cotton boll, 51
Whalebone, 417, 430
Whales, 416
Wheel animalcules, 308
Whip scorpions, 144
Whirligig beetles, 46
White ants, 110
White grubs, 44
Wild-life sanctuaries, 432
Wilson, E. B., 448
Wireworms, 49
Wolves, 423
Wood tick, 143
Wood-boring beetles, 52
Woodchuck, 422, 432
Woodcock, 385
Woodpeckers, 389

Woodruff, L. L., on Paramecium, 295
Workers, 78, 83
Wrigglers, 74

Yellow fever, 74, 102, 103

Yerkes, R. M., on intelligence in

frogs, 342 ; on apes, 430
Yucca moth, 105

Zoological history, 442
Zoology, 441