BIOLOGY
LIBRARY
G
-ELEMENTARY ZOOLOGY
BY
VERNON L. KELLOGG, M.S.
Professor of Entomology, Leland Stanford Junior University
SECOND EDITION, REVISED
' - -
* .' > _
NEW YORK
HENRY HOLT AND COMPANY
1902
BIOLOGY
LIBRARY
Copyright, 1901,
BY
HENRY HOLT & CO.
ROBERT DHUMMOND, PRINTED NEW YORK
PREFACE
IT seems to the author that three kinds of work should
be included in the elementary study of zoology. These
three kinds are: (a) observations in the field covering
the habits and behavior of animals and their relations
to their physical surroundings, to plants, and to each
other ; () work in the laboratory, consisting of the study
of animal structure by dissection and the observation of
live specimens in cages and aquaria ; and (c) work in the
recitation- or lecture-room, where the significance and
general application of the observed facts are considered
and some of the elementary facts relating to the classifi-
cation and distribution of animals are learned.
These three kinds of work are represented in the course
of study outlined in this book. The sequence and extent
of the study in laboratory and recitation-room are defi-
nitely set forth, but the references to field-work consist
chiefly of suggestions to teacher and student regarding
the character of the work and the opportunities for it.
Not because the author would give to the field-work the
least important place, he would not, but because of the
utter impracticability of attempting to direct the field-
work of students scattered widely over the United States.
The differences in season and natural conditions in vari-
ous parts of the country with the corresponding differences
in the * ' seasons ' ' and course of the life-history of the
221739 '
iv PREFACE
animals of the various regions make it impossible to in-
clude in a book intended for general use specific direc-
tions for field-work. Further, the amount of time for
field-work at the disposal of teacher and class and the
opportunities afforded by the topographic character of the
region in which the schools are located vary much. The
initiation and direction of this must therefore always de-
pend on the teacher. On the other hand, the work of the
other two phases of study can to a large extent be made
pretty uniform throughout the country. For dissection,
specimens properly killed and preserved are about as
good as fresh material, and by modifying the suggested
sequence of work a little to suit special conditions or con-
veniences, the examination of live specimens in the
laboratory can in most cases be accomplished.
The author believes that elementary zoological study
should not be limited to the examination of the struc-
ture of several types. The student should learn by
observation something of the functions of animals and
something of their life-history and habits, and should be
given a glimpse of the significance of his particular ob-
servations and of their general relation to animal life as a
whole. The drill of the laboratory is perhaps the most
valuable part of the work, but as a matter of fact the high
school is trying to teach elementary zoology, an ele-
mentary knowledge of animals and their life, and dissec-
tion alone cannot give the pupil this knowledge. On the
other hand, without a personal acquaintance with animals,
based on careful actual observations of their life-history
and habits and on the study of the structural characters of
the animal body by personally made dissections, the
pupil can never really appreciate and understand the life
of animals. Reading and recitation alone can never
give the student any real knowledge of it.
The book is divided into three parts, of which Part I
PREFACE V
should be * first undertaken. This is an introduction to
an elementary knowledge of animal structure, function,
and development. It consists of practical exercises in
the laboratory, each followed by a recitation in which the
significance of the facts already observed is pointed out.
The general principles of zoology are thus defined on a
basis of observed facts.
Part II is devoted to a consideration of the principal
branches of the animal kingdom ; it deals with t system-
atic zoology. In each branch one or more examples
are chosen to serve as types. The most important struc-
tural features of these examples are studied, by dissection,
in the laboratory. The directions for these dissections
consist of technical instructions for dissecting, the calling
attention to and naming of principal parts, together with
questions and demands intended to call for independent
work on the part of the student. The directions follow
the actual course of the dissection instead of being ar-
ranged according to systems of organs, and are intended
for the orientation of the student and not to be in them-
selves expositions of the anatomy of the types. The
condensation of these directions is made more feasible by
the presence of anatomical plates (drawn directly from
dissections). Following the account of the dissection of
the type are brief notes on its life-history and habits.
* This is true if a strictly logical treatment of the subject is held to. As
a matter of fact, it is often of advantage to begin with, or at least to take vip
from the beginning in connection with the indoor work, some field-work,
such as the collecting and classifying of insects and the observation of
their metamorphosis. As most schools begin work in the fall, advantage
must be taken of the favorable opportunities for field-work at the beginning
of the year. These opportunities are of course much less favorable in the
winter.
f The classification of animals used in this book is that adopted in
Parker and Haswell's " Text-book of Zoology " (2 vols., 1897, Macmillan
Co.). Exception is made in the case of the worms, which are considered
as a single branch, Vermes, instead of as several distinct branches.
vi PREFACE
Then follows a general account of the branch to which
the example dissected belongs and brief accounts of
some of the more interesting members of the branch. In
these accounts technical directions are given for brief
comparative examinations and for the study of the life-
history and habits of some of the more accessible of
these forms.
It will not be possible, of course, to undertake with any
thoroughness the consideration of all of the branches of
animals in a single year. But all are treated in the book,
so that the choice of those to be studied may rest with the
teacher. This choice will of necessity depend largely on
the opportunities afforded by the situation of the school,
as, for example, whether on the seashore or in the interior
near a lake or river, or on the dry plains, and on the re-
lation of the school-terms to the seasons of the year.
The branches are arranged in the book so that the sim-
plest animals are first considered, the slightly complex
ones next, and lastly the most highly organized forms.
But if in order to obtain examples for study it is necessary
to take up branches irregularly, that need not prove con-
fusing. The author would suggest that whatever other
branches are studied, the insects and birds, which are
readily available in all parts of the country, be certainly
selected, and with this selection in view has given them
special attention. Indeed some teachers may find these
two branches to offer quite sufficient work in classificatory
and ecological lines.
Part III is devoted to a necessarily brief consideration
of certain of the more conspicuous and interesting
features of animal ecology. It has in it the suggestion
for much interesting field-work. The work of this part
should be taken up in connection with that of Part II, as,
for example, the consideration of social and communal
life in connection with the insects, parasitism in connec-
PREFACE vii
tion with the worms, and also with the insects, distribu-
tion in connection with the birds, perhaps, and so on.
In appendices there are added some suggestions for
the outfitting of the laboratory, and a list of the equip-
ment each student should have. Here, also, is appended
a list of a few good authoritative reference books which
should be accessible to students and to which specific
references are made in the course of this book. Some
practical directions for the collecting and preserving of
specimens are also given. (Suggestions for the obtaining
of material for the various laboratory exercises outlined
in the book are to be found in "technical notes " in-
cluded in the directions for each exercise.) The author
believes that the building up of a single school-collection
in which all the pupils have a common interest and to
which all contribute is to be encouraged rather than the
making of separate collections by the pupils. Waste of
life is checked by this, and in time, with the contributions
of succeeding classes, a really good and effective collec-
tion may be built up. The ' ' collecting interest ' ' can
be taken advantage of just as well in connection with a
school-collection as with individual collections.
The plates illustrating the dissections have all been
drawn originally for the book from actual dissections.
Most of the other figures are original, either drawn or
photographed directly from nature, or from preserved
specimens. Credit is given in each case for figures not
original. The drawings for all of the figures of dis-
sections and for all original figures not otherwise accred-
ited were made by Miss Mary H. Wellman, to whom the
author expresses his obligations. The thanks of the
author are due to Mr. George Otis Mitchell, San Fran-
cisco, who kindly made the photo-micrographs of insect
structure from the author's slides; to Professor Mark V.
Slingerland, Cornell University, for electros of his photo-
viii PREFACE
graphs of insects; to Dr. L. O. Howard, U. S. Entomol-
ogist, for electros of figs. 45, 52, 56, 68, 81, 82, 83,
84, 87, 90, and 92 ; to Professor L. L. Dyche, University
of Kansas, for photographs of his mounted groups of
mammals; to Mrs. Elizabeth Grinnell, Pasadena, Calif.,
for photographs of birds; to Mr. J. O. Snyder, Stanford
University, for photographs of snakes; to Mr. Frank
Chapman, editor of " Bird-lore," for electros of photo-
graphs of birds; to Mr. G. O. Shields, editor of " Recrea-
tion," for an electro of the photograph of a bird; to the
American Society of Civil Engineers for electros of photo-
graphs of boring marine worms; to Cassell & Co., for
electros of three photographs from nature; to Geo. A.
Clark, secretary Fur Seal Commission for photographs of
seals; and to the Whitaker and Ray Co., San Francisco,
for electros of figs. 46, 59, 60, 61, 64, 65, 93, 94, 97, 98,
99, 100, 1 02, 119, and 166 to 172, published originally in
Jenkins & Kellogg's " Lessons in Nature Study." The
origin of each of these pictures is specifically indicated in
connection with its use in the book.
The author's sincere thanks are also due to Mrs. David
Starr Jordan and to Mr. J. C. Brown, graduate student in
zoology in Stanford University, for their assistance in the
correction of the MS., and in the preparation of the lab-
oratory exercises respectively. The chapters of Part II
relating to the vertebrates were read in MS. by President
David Starr Jordan, whose aid and courtesy are gratefully
acknowledged. Similar acknowledgments are due Pro-
fessors Harold Heath and R. E. Snodgrass for read-
ing the proofs of the directions for the laboratory ex-
ercises.
VERNON LYMAN KELLOGG.
STANFORD UNIVERSITY, May, 1901.
CONTENTS
PART I
STRUCTURE, FUNCTIONS, AND DEVELOPMENT OF
ANIMALS
I. THE STUDY OF ANIMALS AND THEIR LIFE.
Our familiar knowledge of animals and their life, I. Zoology and its
divisions, 2. A first course in Zoology, 3.
II. THE GARDEN TOAD (Buro LEXTIGINOSUS).
[Laboratory exercise], 5. External structure, 5. Internal structure. 7.
III. THE STRUCTURE AND FUNCTIONS OF THE ANIMAL BODY.
Organs and functions, 14. The animal body a machine, 14. The essen-
tial functions or life-processes, 15.
IV. THE CRAYFISH (CAMBARUS SP.).
[Laboratory exercise], 17. External structure, 17. Internal structure, 21.
V. THE MODIFICATION OF ORGANS AND FUNCTIONS.
Difference between crayfish and toad, 26. Ref-emblances between cray-
ri-li and toad, 27. Modification of functions and structure to fit the animal
to the special conditions of its life, 29. Vertebrate and invertebrate, 30.
VI. AMCEBA AND PARAMCLCIUM.
[Laboratory exercise], 31. Amoeba, 31. The slipper-animalcule (PARA-
MCECIUM SP.), 34.
ix
X CONTENTS
VII. THE SINGLE-CELLED ANIMAL BODY; PROTOPLASM
AND THE CELL.
The single-celled animal body, 36. The cell, 37. Protoplasm, 39.
VIII. -CELLULAR STRUCTURE OF THE TOAD (OR FROG).
[Laboratory exercise], 40. The blood, 40. The skin, 40. The liver.
41. The muscles, 41.
IX. THE MANY-CELLED ANIMAL BODY; DIFFERENTIATION
OF THE CELL.
The many-celled animal body, 43. Differentiation of the cell, 43.
X. HYDRA.
[Laboratory exercise], 46.
XL THE SIMPLEST MANY-CELLED ANIMALS.
Cell-differentiation and body-organization in Hydra, 52. Degrees in
cell-differentiation and body-organization, 54.
XII. DEVELOPMENT OF THE TOAD.
[Field and laboratory exercise], 55.
XIII. MULTIPLICATION AND DEVELOPMENT.
Multiplication, 57 Spontaneous generation, 58. Simplest multiplica-
tion and development, 59. Birth and hatching, 61. Life-history, 62.
PART II
SYSTEMATIC ZOOLOGY
XIV. THE CLASSIFICATION OF ANIMALS.
[Laboratory exercise and recitation], 65. Basis and significance 01
classification, 65. Importance of development in determining classification,
67. Scientific names, 68. An example of classification, 68. Species,
69. -Genus, 70. Family, 72. Order, 72. Class and branch, 73.
XV. BRANCH PROTOZOA : THE ONE-CELLED ANIMALS.
EXAMPLE : THE BELL ANIMALCULE (VORTICELLA SP.) [Laboratory
exercise], 75.
OTHER PROTOZOA.
Form of body, 78. Marine Protozoa, 80.
CONTENTS xi
XVI. -BRANCH PORIFERA: THE SPONGES.
EXAMPLE : THE FRESH-WATER SPONGE (SPONGILLA SP.) [Laboratory
exercise], 84.
EXAMPLE: A CALCAREOUS OCEAN-SPONGE (GRANTIA SP.) [Laboratory
exercise], 85.
EXAMPLE: A COMMERCIAL SPONGE [Laboratory exercise], 86.
OTHER SPONGES.
Form and size, 87. Skeleton, 88. Structure of body, 88. Feeding
habits, 88. Development and life-history, 89. The sponges of commerce,
90. Classification, 91.
XVII. -BRANCH CCELENTERATA: THE POLYPS, SEA-
ANEMONES, CORALS, AND JELLYFISHES.
POLYPS, SEA-ANEMONES, CORALS, AND JELLYFISHES.
General form and organization of body, 93. Structure, 94. Skeleton,
95. Development and life-history, 95. Classification, 96. The polyps,
colonial jellyfishes, etc. (Hydrozoa), 97. The large jellyfishes, etc.
(Scyphozoa), 101. The sea-anemones and corals (Actinozoa), 102. The
Ctenophora, 107.
XVIII. BRANCH ECHINODERMATA : THE STARFISHES, SEA-
URCHINS, SEA CUCUMBERS, ETC.
EXAMPLE : STARFISH (ASTERIAS SP.) [Laboratory exercise]. External
structure. 108. Internal structure, no. Life-history and habits, 113.
EXAMPLE : SEA-URCHIN (STRONGYLOCENTRUS SP.) [Laboratory exercise].
External structure, 113.
OTHER STARFISHES, SEA-URCHINS, SEA CUCUMBERS, ETC.
Shape and organization of body, 116. Structure and organs, 117. De-
velopment and life-history. 119. Classification, 120. Starfishes (Asteroi-
dea), 121. Brittle stars (Ophiuroidea), 122. Sea-urchins (Echinoidea).
123. Sea-cucumbers (Holothuroidea), 124. Feather-stars (Crinoidea), 125.
XIX. BRANCH VERMES: THE WORMS.
EXAMPLE: THE EARTHWORM ILUMBRICUS SP.) [Laboratory exercise]
External structure, 127. internal structure, 129. Life-history and habits,
133
OTHER WORMS.
Classification, 135. Earthworms and leeches (Oligochaetae , 136. Flat
worms (Platyhelminlhes). 137. Round worms (Nemathelminthes), 140.
Wheel-animalcules (Rotifera), 142.
xi i CONTENTS
XX. BRANCH ARTHROPODA : THE CRUSTACEANS, CEN-
TIPEDS, INSECTS, AND SPIDERS.
CLASS CRUSTACEA: CRAYFISHES, CRABS, LOBSTERS, ETC.
EXAMPLE; THE CRAYFISH (CAMBARUS SP.). Structure, 146. Life-his-
tory and habits, 146.
OTHER CRUSTACEANS.
Body form and structure, 147. Water-fleas (Cyclops], 148. Wood-lice
(Isopoda), 150. Lobsters, shrimps, and crabs (Decapoda), 151. Barnacle*,
XXL BRANCH ARTHROPODA (CONTINUED).
CLASS INSECTA : THE INSECTS.
EXAMPLE : THE RED-LEGGED LOCUST (MELANOPLUS FEMUR-RUBRUM^
[Laboratory exercise]. External structure, 157. Life-history and habits,
161.
EXAMPLE: THE WATER- SCAVENGER BEETLE (HYEROPHILUS SP.) [Labo-
ratory exercise]. External structure, 163. Internal structure, 166. Life-
history and habits, 169.
EXAMPLE : THE MONARCH BUTTERFLY (ANOSIA PLEXIPPUS) [Laboratory
exercise]. External structure, 171. Life-history and habits, 175.
EXAMPLE : LARVA OF MONARCH BUTTERFLY [Laboratory exercise].
Structure, 177.
OTHER INSECTS.
Body form and structure, 181. Development and life-history, 188.
Classification, 191. Locusts, cockroaches, crickets, etc. (Orthoptera), 192.
The dragon-flies and May-flies (Odonata and Ephemerida), 194. The
sucking-bugs (Hemiptera), 197. The flies (Diptera), 201. The butterflies
and moths (Lepidoptera). 205. The beetles (Coleoptera), 206. The
ichneumon flies, ants, wasps, and bees (Hymenoptera), 212.
CLASS MYRIAPODA : THE CENTIPEDS AND MILLIPEDS.
CLASS ARACHNIDA : THE SCORPIONS, SPIDERS, MITES, AND TICS.
XXII. BRANCH MOLLUSCA : THE MOLLUSCS.
EXAMPLE : THE FRESH-WATER MUSSEL (L^Nio SP.) [Laboratory exercise].
Structure, 239. Life-history and habits, 243.
OTHER MOLLUSCS.
Body form and structure, 245. Development, 246. Classification. 246.
Clams, scallops, and oysters (Pelecypoda), 246. Snails, slugs, nudi-
branchs, and "sea-shells" (Gastropoda), 252. Squids, cuttlefishes, and
octopi (Cephalopoda), 255.
CONTENTS xiii
XXIII. BKANX II CHORDATA: THE ASCIDTANS, VERTE-
BRATES, ETC.
Structure of the vertebrates, 259. Classification of the Chordata, 260.
The ascidians, 261.
XXIV. BRANCH CHORDATA (CONTINUED).
CLASS PISCES : THE FISHES.
EXAMPLE: THE GOLDEN SUNFISH EUPOMOTIS GIBBOSUS) [Laboratory
exercise]. External structure, 263. Internal structure. 265. Life-history
and habits, 270.
OTHER FISHES.
Body form and structure, 271. Development and life-history, 276.
Classification, 277. The lancelets (Leptocardii), 277. The lampreys and
hag-fishes (Cyclostomata), 278. The true fishes (Pisces), 279. The sharks,
skates, etc. (Elasmobranchii), 279. The bony fishes (Teleostomi), 281. .
Habits and adaptations, 285. Food-fishes and fish -hatcheries, 288.
XXV. BRANCH CHORDATA (CONTINUED).
CLASS BATRACHIA : THE BATRACHIANS.
Body form and organization, 292. Structure, 293. Life -history and
habits. 295. Classification, 297. Mud-puppies, salamanders, etc. (Uro-
dela), 297. Frogs and toads (Anura), 299. Coecilians (Gymnophiona),
302.
XXVI. BRANCH CHORDATA (CONTINUED).
CLASS REPTILIA: THE SNAKES, LIZARDS, TURTLES. CROCODILES, ETC.
EXAMPLE : THE GARTER SNAKE (THAMNOPHIS SP.) [Laboratory exer-
cise]. Structure, 303. Life-history and habits, 308.
OTHER REPTILES.
Body form and organization, 310. Structure, 311, Life-history and
habits, 312. Classification, 313. Tortoises and turtles (Chelonia), 314.
Snakes and lizards (Squamata\ 317. Crocodiles and alligators (Croco-
dilia), 325.
XXVII. BRANCH CHORDATA (CONTINUED).
CLASS AVES : THE BIRDS.
EXAMPLE : THE ENGLISH SPARROW i PASSER DOMES ncus) [Laboratory
exercise]. External structure, 327. Internal structure [Laboratory exer-
cise], 329. Life history and habits, 335.
OTHER BIRDS.
Body form and structure, 336. Development and life-history, 339.
Classification. 340. The ostriches, cassowaries, etc. (Rutitx), 341. The
xiv CONTENTS
loons, grebes, auks, etc. (Pygopodes), 343. The gulls, terns, petrels, and
albatrosses (Longipennes), 345. The cormorants, pelicans, etc. (Stegano-
podes), 346. The ducks, geese, and swans (Anseres), 347. The ibises,
herons, and bitterns (Herodiones). 347. The cranes, rails, and coots (Palu-
dicolse), 348. The snipes, sand-pipers, plovers, etc. (Limicolse), 349.
The grouse, quail, pheasants, turkeys, etc. (Gallinse), 358. The doves and
pigeons (Columbse), 351. The eagles, hawks, owls, and vultures (Raptores),
351. The parrots (Psittaci), 353. The cookoos and kingfishers (Coccyges),
354. The woodpeckers (Pici), 354. The whippoorwills, chimney-swifts,
and humming-birds (Macrochires), 356. The perchers (Passeres), 357.
Determining and studying the birds of a locality, 359. Bills and feet, 362.
Flight and songs, 364. Nestling and care of the young, 366. Local dis-
tribution and migration, 367. Feeding habits, economics, and protection of
birds, 370.
XXVIII. BRANCH CHORDATA (CONTINUED).
CLASS MAMMALIA : THE MAMMALS.
EXAMPLE : THE MOUSE (Mus MUSCULUS) [Laboratory exercise]. Struc-
ture, 373. Life-history and habits, 379.
OTHER MAMMALS.
Body form and structure, 381. Development and life-history, 387.
Habits, instincts, and reason, 387. Classification, 388. The opossums
(Marsupialia), 389. The rodents or gnawers (Glires), 390. The shrews
and moles (Insectivora), 391. The bats (Chiroptera), 391. The dolphins,
porpoises, and whales (Cete), 393. The hoofed mammals (Ungulata), 394.
The carnivores (Ferae), 396. The man-like mammals (Primates), 398.
PART III
ANIMAL ECOLOGY
XXIX. THE STRUGGLE FOR EXISTENCE, ADAPTATION,
AND SPECIES-FORMING.
The multiplication and crowding of animals, 404. The struggle for
existence, 406. Variation and natural selection, 406. Adaptation and
adjustment to surroundings, 407. Species forming, 408. Artificial selec-
tion, 409.
XXX. SOCIAL AND COMMUNAL LIFE, COMMENSALISM, AND
PARASITISM.
Social life and gregarkmsness, 410. Communal life, 411. Commen-
salism 413. Parasitism, 415.
CONTENTS xv
XXXI. COLOR AND PROTECTIVE RESEMBLANCES.
Use of color, 424. General, variable, and special protective resemblance,
426. Warning colors, terrifying appearances, and mimicry, 430. Alluring
coloration, 433.
XXXII. THE DISTRIBUTION OF ANIMALS.
Geographical distribution, 435. Laws of distribution, 437. Modes of
migration and distribution, 437. Barriers to distribution, 438. Faunae
and zoogeographic areas, 440. Habitat and species, 441. Species-extin-
guishing and species-forming, 442.
APPENDICES
EQUIPMENT AND METHODS
APPENDIX I. EQUIPMENT AND NOTES OF PUPILS.
Equipment of pupils, 447. Laboratory drawings and notes, 447. Field
observations and notes, 448.
APPENDIX II. LABORATORY EQUIPMENT AND METHODS.
Equipment of laboratory, 450. Collecting and preparing material for use
in the laboratory, 451. Obtaining marine animals, microscopic prepara-
tions, etc., 453. Reference-books, 454.
APPENDIX III. REARING ANIMALS AND MAKING COLLEC-
TIONS.
Live cages and aquaria, 457. Making collections, 461. Collecting and
preserving insects, 463. Collecting and preserving birds, 466. Collecting
and preserving mammals, 470. Collecting and preserving other animals,
472.
PART I
STRUCTURE, FUNCTIONS, AND DEVELOP-
MENT OF ANIMALS
CHAPTER I
THE STUDY OF ANIMALS AND THEIR LIFE
Our familiar knowledge of animals and their life.
We are familiarly acquainted with dogs and cats; less
familiarly probably with toads and crayfishes, and we
have little more than a bare knowledge of the existence
of such animals as seals and starfishes and reindeer. But
what real knowledge of dogs and toads does our familiar
acquaintanceship with them give ? Certain habits of the
dog are known to us: it eats, and eats certain kinds of
food ; it runs about ; it responds to our calls or even to
the mere sight of us ; it evidently feels pain when struck,
and shows fear when threatened. Another class of
attributes of the dog includes those things that we know
of its bodily make-up: its possession of a head with eyes
and ears, nose and mouth ; its four legs with toes and
claws; its covering of hair. We know, too, that it was
born alive as a very small helpless puppy which lived for
a while on food furnished by the mother, and that it has
grown and developed from this young state to a fully
grown, fully developed dog. We know also that our
dog is a certain kind cf dog, a spaniel, perhaps, while
2 ELEMENTARY ZOOLOGY
our neighbor's dog is of another kind, a greyhound, it
may be. We know accordingly that there are different
kinds of tame dogs, and we may know that wolves
are so much like dogs that they might indeed be
called wild dogs, or dogs called a kind of tame wolf.
But how little we really know about the dog's body and
its life is apparent at a moment's thought. We see only
the outside of the dog, but what an intricate complex of
parts really composes this animal! We see it eat and
breathe and run ; of what is done with the food and air
inside its body, and of the series of muscle contractions
and mechanical processes which cause its running, we have
but the slightest conception. We see that the pup gets
larger, that is, grows ; that it changes gradually in appear-
ance, that is, develops ; but of the real processes and
changes that take place in growth and development how
little we know ! We know that there are other kinds of
dogs; that wolves and foxes are relatives of the dog; and
we have heard that cats and tigers are relatives also,
although more distant ones. We know, too, that all the
backboned animals, some of them very unlike dogs, are
believed to be related to each other, but of the thousands of
these animals and of their relationships our knowledge is
scanty. Finally, of the relations of the dog, and of other
animals, to the outside world, and of the wonderful man-
ner in which the dog's make-up and behavior fit it to live
in its place in the world under the conditions that surround
it, we have probably least knowledge of all.
Zoology and its divisions. What things we do know
about the dog, however, and about its relatives, and
what things others know, can be classified into several
groups, namely, things or facts about what the dog does,
or its behavior, things about the make-up of its body,
things about its growth and development, things about
the kind of dog it is and thejdnds of relatives it has, and
THE STUDY OF ANIMALS AND THEIR LIFE 3
things about its relations to the outer world, and its special
fitness for life.
All that is known of these different kinds of facts about
the dog constitutes our knowledge of the dog and its life.
All that is known by scientific men and others of these
different kinds of facts about all the 500,000 or more kinds
of living animals, constitutes our knowledge of animals and
is the science zoology * Names have been given to these
different groups of facts about animals. The facts about
the bodily make-up or structure of animals constitute that
part of zoology called animal anatomy or morpJiology; the
facts about the things animals do, or the functions of
animals, compose animal physiology; the facts about the
development of animals from young to adult condition are
the facts of animal development; the knowledge of the
different kinds of animals and their relationships to each
other is called systematic zoology or animal classification;
and finally the knowledge of the relations of animals to
their external surroundings, including the inorganic world,
plants and other animals, is called animal ecology.
Any study of animals and their life, that is, of zoology,
may include all or any of these parts of zoology. Most
zoologists do, indeed, devote their principal attention to
some one group of facts about animals and are accordingly
spoken of as anatomists, or physiologists, systematists,
and so on. But such a specialization of study should be
made only after the zoologist has acquired a knowledge
of the principal or fundamental facts in all the other
branches of zoology.
A first course in zoology. The first " course," then,
in the study of animals should include the fundamental
facts in all these branches or parts of zoology. That is
what the course outlined in this book tries to cover.
* Zoology is formed from two Greek words: zoon, meaning animal, and
logos, meaning discourse.
4 ELEMENTARY ZOOLOGY
But no text-book of zoology can really give the student
the knowledge he seeks. He must find out most of it for
himself; a text-book, based on the experiences of others,
is chiefly valuable for telling him how to work most
effectively to get this knowledge for himself. And the
best students always find out things which are not in books.
Especially can the beginning student find out things not
known before, * ' new to science, "as we say, about the
behavior and habits of animals, and their relations to their
surroundings. The life-history of comparatively few kinds
of animals is exactly known; the instincts and habits of
comparatively few have been studied in any detail. The
kinds of food demanded, the feeding habits, nest-building,
care of the young, cunning concealment of nest and self,
time of egg-laying or of producing young, duration of the
immature stages and the habits and behavior of the young
animals a host, indeed, of observations on the actual life
of animals, remain to be made by the "field naturalist."
Any beginning student can be a "field naturalist" and
can find out new things about animals, that is, can add
to the science of zoology.
\
CHAPTER II
THE GARDEN TOAD (Bufo lentiginosus)
LABORATORY EXERCISE
TECHNICAL NOTE. Although this description is written for the
toad it will fit for the dissection of the frog. It will be found, after
casting aside a few ungrounded prejudices, that the toad is the
better for class dissection. Toads are best collected about dusk,
when they can be picked up in almost any garden in town or in the
country. During the spring many can be found in the ponds where
they are breeding. To kill the toad place it in an air-tight vessel
with a piece of cotton or cloth saturated in chloroform or ether.
When the toad is dead, wash off the specimen and put in a dissect-
ing pan for study. Several specimens should be placed in a nitric
acid solution for a day or so (for directions for preparing, see
p. 12) to be used later for the study of the nervous system. Also
several specimens should be injected for the better study of the
circulatory system. With an injecting mass made as directed on
p. 451 introduce through a small canula into the ventricle of the
heart. This will inject the arterial system, and with increased
pressure the injecting mass may be forced through the valves of the
heart, thus passing into the auricles and throughout the venous
system. After injecting use the specimen fresh or after it has been
preserved in 4^ formalin.
External structure. Note that the body of the toad
is divided into several principal regions or parts, as is the
human body, namely, a head, upper limbs, trunk, and
lower limbs. As you look at the toad note the similarity
of the parts on one side to those of the other, as right leg
corresponding to left leg, right eye to left eye, etc. This
arrangement of the body in similar halves among animals
is known as bilateral symmetry. As a rule animals which
show bilateral symmetry move in a definite direction.
The part that moves forward is the anterior end, while
5
6 ELEMENTARY ZOOLOGY
the opposite extremity is the posterior end. In most
animals we note two other views or aspects ; that which
is called the "back" and with most animals is, under
ordinary conditions, uppermost is the dor sum or dorsal
aspect, while that which lies below is the venter or ventral
aspect. When referring to a view from one side we speak
of it as a right or left lateral aspect. These terms hold
good for most of the animals that we shall study.
Note at the anterior end of the toad a wide transverse
slit, the mouth. What other openings are on the anterior
end ? Note the two large eyes, the organs of sight. Just
back of each eye note an elliptical, smooth membrane.
This is the tympanum of the outer ear, and through this
membrane the vibrations produced by sound-waves are
transferred to the inner ear, which receives sensations and
transmits them to the brain. Open the mouth by drawing
down the lower jaw. Note just within the angle of the
lower jaw the tongue. How is it attached to the wall of
the mouth ? On the tongue are a great many fine papilla
in which is located the sense of taste. It has now been
seen that most of the special senses of the toad have their
seat in the head. Pass a straw or bristle into one of the
nostrils. Where does it come out ? These internal
openings to the nose are the inner nares. Note in the
roof of the mouth just posterior to each of the eyeballs an
opening. These are the internal openings to the wide
Eustachian tubes, which lead to the mouth from the
chamber of the ear behind the tympanum.
Note far back in the mouth an opening through which
food passes. This is the oesophagus or gullet. Note just
below this gullet an elevation in which is a perpendicular
slit, the glottis. This is the upper end of the laryngo-
tracheal chamber, and the flaps within on either side of
the slit are the vocal cords.
Note at the posterior end of the body in the median
THE GARDEN TOAD 7
line an opening. This is the anal opening or amis. Note
the general make-up of the toad. How do its arms com-
pare with our own ? How do its fore feet (hands) differ
from its hind feet ? Note that the body is covered by a
tough enveloping membrane, the skin. In the skin are
many glands which by their excretion keep it soft and
moist.
Internal structure TECHNICAL NOTE. With a fine pair of
scissors make a longitudinal median cut through the skin of the
venter from the anal opening to the angle of the lower jaw. Spread
the cut edges apart and pin back in the dissecting-pan.
Note the complex system of muscles which govern the
movements of the tongue. Observe a number of pairs of
muscles overlying the bones which support the arms.
These are attached to the pectoral or shoulder -girdle.
Note the large sheet of muscles covering the ventral
aspect of the toad. These are the abdominal muscle 's,
which consist of two sets, an outer and an inner layer.
Note that posteriorly the abdominal muscles are attached
to a bone. This is the pubic bone of the pelvic girdle
which supports the hind legs.
TECHNICAL NOTE. With the scissors cut through the muscles of
the body wall at the pubic bone and pass the points forward to the
shoulder-girdle. Separate the bones of the shoulder-girdle and pin
out the flaps of skin and muscle to right and left in the dissecting-
pan (see fig. i). Cover the dissection with clear water or weak
alcohol.
Note two large conspicuous soft brown lobes of tissue.
These form the liver, an organ which produces a secretion
that assists in the process of digestion. Note just anterior
to the liver and extending between its two lobes a pear
shaped organ, the heart, which may yet be pulsating.
Are these pulsations regular ? How many occur in a
minute ? The lower end or apex of the heart, ventricle,
undergoes a contraction, forcing blood out into the blood-
8 ELEMENTARY ZOOLOGY
vessels. This is followed by a relaxation of the apex and
a contraction of the basal portion, the auricle. 'The heart
is surrounded by a delicate semi-transparent sac, the
pericardium. The' pericardium is filled with a watery
fluid, body-lymph, which bathes the heart. Note between
the lobes of the liver a small bladder-shaped transparent
organ of a pinkish color. This is the gall-cyst, or gall-
bladder, a reservoir for the bile, the secretion from the
liver. Separate the lobes of the liver and note, beneath,
the long convoluted tube which fills most of the body-
cavity. This is part of the alimentary canal. Is the
alimentary canal of uniform character ? The most anterior
portion of the canal, the gullet or cesopJiagus, leads to a
large U-shaped enlargement, the stomach. From the lower
end of the stomach there extends a long, slender, very
much convoluted tube, the small intestine, which is fol-
lowed by a much larger one, the large intestine. This large
intestine after one or two turns passes directly back into
the rectum, which opens at last to the exterior through the
anus. Note just ventral to the rectum a large thin-walled
membranous sac. This is the urinary bladder which acts
as a reservoir for the secretion from the kidneys. Notice
a many-branched yellow structure with a glistening
appearance, the fat-body (corpus adiposuui). Now push
liver and intestine to one side and note the pinkish sac-like
bodies (perhaps filled with air), the lungs. The lungs are
paired bodies which open into the laryngo-tracheal cham-
ber. The toad takes air into its mouth through its
nostrils, and then forces it, by a kind of swallowing action,
through the laryngo-tracheal chamber into the lungs.
Now lift the stomach and note in the loop between its
lower end and the small intestine a thin transparent tissue.
This is a part of the mesentery, which will be found to
suspend the whole alimentary canal and its attached
organs to the dorsal wall of the body. Note in the loop
THE GARDEN TOAD 9
of the stomach in the mesentery an irregular pinkish
glandular structure which leads by a small duct into the
intestine. This gland is the pancreas, and the duct is
the pancreatic duct. From it comes a secretion which
aids in the digestion of food. Near the upper end of the
pancreas note a round nodular structure, generally dark
red. This is the spleen, a ductless gland, the use of
which is not altogether known.
Make a drawing which will show as many of the organs
noted as possible.
TECHNICAL NOTE. Pass two pieces of thread under the rectum
near the pubic bone. Tie these threads tightly a short distance
apart and then cut the rectum in two between the threads. Now
carefully lift up the alimentary canal with attached organs (liver,
etc.), and cut it off near the region of the heart.
How is the heart situated with regard to the lungs ?
The heart consists of a lower chamber with thick muscular
walls, the tip, called the ventricle, and two upper thin-
walled chambers, the right and left auricles. Can you
make out these three chambers ? The purified blood from
the lungs flows into the left auricle, while the venous
blood from all over the body laden with its carbon dioxide
enters the right auricle. From these two chambers the
blood enters the ventricle. Here the pure and impure
blood are mixed. From the ventricle the blood enters a
large muscular tube on the ventral side of the heart. This
is the conus arteriosus, which gives off three branches on
each side ; the anterior ones, the carotid arteries, supply
the head, the next ones, the systemic arteries, or aortce,
carry blood to the rest of the body, while the posterior
vessels, the pulmonary arteries, go directly to the lungs
and there break up into fine vessels (capillaries) where
the carbon dioxide is given off and oxygen is taken from
the air. From the lungs the blood returns through the
puhnonary vein to the left auricle. Meanwhile the blood
10 ELEMENTARY ZOOLOGY
which has passed through the systemic arteries and body
capillaries is collected again into other vessels going back
to the heart; these are the veins, which empty into a large
thin-walled reservoir, the sinus venosus, which in turn
connects with the right auricle of the heart. Three large
veins enter the sinus venosus, namely, two pre-caval veins
at the anterior end, and a single post-caval vein at the
posterior end. Trace out the larger arteries and veins
from the heart to their division into or origin from the
smaller vessels.
TECHNICAL NOTE. Carefully remove the heart together with
the lungs. The lungs may be inflated by blowing into them through
the laryngo-tracheal chamber with a quill and tying them tightly,
after which they should be left for several days to dry. When
perfectly dry, sections may be cut through them in various places
with a sharp knife, and by this means a very good idea of the
simple lung structure of the lower backboned animals can be ob-
tained. With a sharp knife cut the heart open, beginning at the
tip (ventricle) and cutting up through the conus arteriosus and
the two auricles. Note the valves in the heart which separate
the different compartments.
Note on either side of the median line in the dorsal
region a pair of reddish glandular bodies (the kidneys).
From each kidney trace a tube (itreter) posteriorly toward
the region of the anus. The kidneys are the principal
excretory organs of the body. The blood which flows
through the delicate blood-vessels in the kidney gives up
there much of its waste products. These pass out through
small tubules of the kidneys into the ureters, which carry
the wastes toward the anus. Along one side of each
kidney may be seen a yellowish glistening mass, the
adrenal body.
In some of the specimens studied, the body cavity may
be filled with thousands of little black spherical bodies.
These are undeveloped eggs. They are deposited by the
mother toad in the water in long strings of transparent
jelly, which are usually wound around sticks or plant-
THE GARDEN TOAD
II
stems at the bottom of the pond near the shore. From
these eggs the young toads hatch as tadpoles and in their
, spheno-ethmoid
maxillary
tibio-fibula *
astragalus
FlG. 2. Skeleton of the garden toad.
life-history pass through an interesting metamorphosis.
fSee Chapter XII.)
12 ELEMENTARY ZOOLOGY
TECHNICAL NOTE. The teacher should be provided with several
well-cleaned skeletons of the toad in order that the bones may be
carefully studied. Boil in a soap solution a toad trom which most
of the muscles and skin have been removed (see p. 452). Leave in
this solution until the muscles are quite soft and then pick off all
bits of muscles and tissue from the bones. If this is carefully done,
the ligaments which bind the bones will be left intact and the
skeleton will hold together.
Note that the skeleton (fig. 2) consists of a head portion
which is composed of many bones joined together to form
a bony box, the skull; of a series of small segments, the
vertebrce, forming the vertebral column, which with the
skull forms the axial skeleton; and of the appcndicidar
skeleton, consisting of the bones of the fore and hind limbs.
Note that the skull is composed of many bones joined
together, some by sutures, while others are fused. Do
the limbs attach directly to the axial skeleton ? The
anterior limbs (arms) articulate with the pectoral or
shoulder-girdle. The arms will be seen to be made up
of a number of bones placed end to end. Note that the
uppermost, the Jiumerus, is attached to the pectoral
girdle, while at its lower end it articulates with the
radio-ulna. At the lower end of the radio-ulna is a small
series of carpal bones which afford attachments for the
slender finger-bones, \\\e plialanges or digit a I bones. The
bones of the leg are articulated with a closely fused set
of bones, the pelvic girdle. The leg-bones, proceeding
from the pelvic girdle, are named femur, tibio-filnda,
tar sal bones, and phalanges or digits. To what bones of
the arm do these correspond ? Determine the other
principal bones of the skeleton by reference to figure 2.
TECHNICAL NOTE. In a specimen which has been macerated
for some time in 20% nitric acid dissect out the nervous system.
Place the specimen in a pan ventral side uppermost and pin out.
Carefully pick away the vertebrae and the roof of the mouth-cavity,
thereby exposing the central nervous system, which will appear
light yellow.
THE GARDEN TOAD 13
Examine the brain. In front of the true brain are the
olfactory lobes, the nervous centre for the sense of smell.
The brain itself is composed of several parts. The
anterior portion consists of two elongated parts, the
cerebral hemispheres; just back of these are the optic lobes
or midbrain, consisting of two short lobes, which are fol-
lowed by the small cerebellum, which in turn is followed
by a long part, the medulla oblongata, which runs imper-
ceptibly into the long dorsal nerve, the spinal cord. Note
the large optic nerves running out to each eye. How far
backward does the spinal cord extend ? Note the many
pairs of nerves given off from the brain and spinal cord.
These nerves branch and subdivide until they end in very
fine fibres. Some end in the muscle-fibres, and through
them the central nervous system innervates the muscles.
These are motor endings. Still others pass to the surface
and receive impressions from the outside. These last are
sensory endings. Note that the spinal nerves arise from
the spinal cord by two roots, an anterior or ventral, and
a posterior or dorsal root. Trace the principal spinal
nerves to the body-parts innervated by them. These
nerves are numbered as first, second, etc., according to
the number of the vertebrae (counting from the head back-
ward) from behind which they arise.
CHAPTER III
THE STRUCTURE AND FUNCTIONS OF THE
ANIMAL BODY
Organs and functions. The body of the toad is com-
posed of various parts, such as the lungs, the heart, the
muscles, the eyes, the stomach, and others. The life of
the toad consists of the performance by it of various
processes, such as breathing, digesting food, circulating
blood, moving, seeing, and others. These various
processes are performed by the various parts of the body.
The parts of the body are called organs, and the processes
(or work) they perform are called their functions. The
lungs are the principal organs for the function of breath-
ing; the heart, arteries and veins are the organs which
have for their function the circulation of the blood ; the
principal organ concerned in the digestion of food is the
alimentary canal, the function of seeing is performed by
the organs of sight, the eyes, and so one might continue
the catalogue of all the organs of the body and of all the
functions performed by the animal.
The animal body a machine. The whole body of the
toad is a machine composed of various parts, each part
with its special work or business to do, but all depending
on cne another and all co-operating to accomplish the total
work of living. The locomotive engine is a machine
similarly composed of various parts, each part with its
special work or function, and all the parts depending on
one another and so working together as to perform satis-
14
STRUCTURE AND FUNCTIONS OF THE ANIMAL BODY 15
factorily the work for which the locomotive engine is
intended. An important difference between the locomo-
tive engine and the toad's body is that one is a lifeless
machine and the other a living machine. But there is a
real similarity between the two in that both are composed
of special parts, each part performing a special kind of
work or function, and all the parts and functions so fitted
together as to form a complex machine which successfully
accomplishes the work for which it is intended. And this
similarity is one which should help make plain the funda-
mental fact of animal structure and physiology, namely,
the division of the body into numerous parts or organs,
and the division of the total work of living into various
processes which are the special work or functions of the
various organs.
The essential functions or life-processes. The toad
has a great many different special parts in its body. Its
body is very complex. It performs a great many differ-
ent functions, that is, does a great many different things
in its living. And the structure and life of most of the
other animals with which we are familiar are similarly
complex: a fish, or a rabbit, or a bird has a body com-
posed of many different parts, and is capable of doing
many different things. Are all animals similarly complex
in structure, and capable of doing such a great variety of
things ? We shall find that the answer to this question
is No. There are many animals in which the body is
composed of but a few parts, and whose life includes the
performance of fewer functions or processes than in the
case of the toad. There are many animals which have
no eyes nor ears nor other organs of special sense.
There are animals without legs or other special organs of
locomotion ; some animals have no blood and hence no
heart nor arteries and veins. But in the life of every
animal there are certain processes which must be per-
16 ELEMENTARY ZOOLOGY
formed, and the body must be so arranged or composed
as to be capable of performing these necessary life-
processes. All animals take food, digest it, and assimi-
late it, that is, convert it into new body substance ; all
animals take in oxygen and give off carbonic acid gas;
all animals have the power of movement or motion (not
necessarily locomotion) ; all animals have the power of
sensation, that is, can feel; all animals can reproduce
themselves, that is, produce young. These are the
necessary life-processes. It is evident that the toad could
still live if it had no eyes. Seeing is not one of the
necessary functions or processes of life. Nor is hearing,
nor is leaping, nor are many of the things which the toad
can do ; and animals can exist, and do exist, without any
of those organs which enable the toad to see and hear and
leap. But the body of any animal must be capable of
performing the few essential processes which are necessary
to animal life. How surprisingly simple such a body can
be will be later discovered. But in most animals the
body is a complicated object, and is able to do many
things which are accessory to the really essential life-
processes, and which make its life complex and elaborate.
CHAPTER IV
THE CRAYFISH (Camdarus sp.)
LABORATORY EXERCISE
TECHNICAL NOTE. The crayfish, or crawfish, is found in most of
the fresh-water ponds and streams of the United States. (It is not
found east of the Hoosatonic River, Mass. In this region the lob-
ster may be used. On the Pacific coast the crayfishes belong to the
genus Astacus.} Crayfishes may be taken by a net baited with dead
fish, or they may be caught in a trap made from a box with ends
which open in, and baited with dead fish or animal refuse of any
sort. This box should be placed in a pond or stream frequented
by crayfish. If possible the student should study the living animal
and observe its habits. Crayfish which are to be kept alive should be
placed in a moist chamber in a cool place. They will keep for a
longer time in a moist chamber than in water. Some fresh specimens
should be injected by the teacher for the study of the circulatory
system. A watery solution of coloring matter or, better, of an in-
iecting mass of gelatine (see p. 451) is injected into the heart
through the needle of a hypodermic syringe. For the purpose of
injecting, a small bit of the shell may be removed from the cephalo-
thorax above the heart. Specimens which are to be kept for some
time should be placed in alcohol or 4^ formalin.
External structure (fig. 3). Place a specimen in a
pan for study. Note that the body, which of course differs
much in shape from that of the toad, is also unlike that of
the toad in being covered by a hard calcareous cxoskclcton,
which acts as a covering for the soft parts and also as a
place of attachment for the muscles, just as the internal
skeleton does in the case of the toad. The body is com-
posed of an anterior part, the cephalotJiorax, and a
posterior part, the abdomen. The cephalothorax is covered
above and on the sides by the carapace, which is divided
into parts corresponding to the head and thorax of the
17
i8
ELEMENTARY ZOOLOGY
antennule
opening of green gland
maxillipeds----f-
thorax
genital aperture
.'' anus
,.,-"uropod
telson
JT IG . 3. Ventral aspect of crayfish (Cambarus sp.), with the appendages ot
one side disarticulated.
THE CRAYFISH *9
toad by the transverse cervical suture. The abdomen
is composed of segments. How many ? The flattened
terminal segment is called the telson. Is the cephalo-
thorax composed of segments ? Where is the mouth of
the crayfish ? Where is the anal opening ?
At the anterior end of the cephalothorax note a sharp
projection, the rostrum. Where are the eyes ? Remove
one of them and examine its outer surface with a micro-
scope. A bit of the outer wall should be torn off and
mounted on a glass slide. Note that it is made up of a
great many little facets placed side by side. Each of
these facets is the external window of an eye element or
ommatidium. An eye composed in this way is called a
compound eye. In front of the eyes note two pairs of
slender many-segmented appendages. The shorter pair,
the antenmdes, are two-branched. Remove one of them
and note at its base a small slit along the upper surface.
This slit opens into a small bag-like structure which con-
tains fine sand-grains. The bag is protected by a series
of fine bristles along the edge of the slit. This bag-like
structure is believed to be an auditory organ. The longer
pair of appendages are the antennce, and in the fine hair-
like projections upon the joints is believed to be located
the sense of smell. Thus it will be seen that the sense-
organs of the crayfish, like those of the toad, are located
on the head. Beneath the basal portion of each antenna
there is a flat plate-like projection, at the base of which
on the upper edge will be noted a small opening, the
exit of the kidney, or green gland.
Make a drawing of the surface of part of an eye ; also
of an antennule ; and of an antenna.
TECHNICAL NOTE. Stick one point of the scissors under the
posterior end of the carapace on the right side, and cut forward,
thus exposing a large cavity, the gill-chamber. Remove all of the
mouth-parts, legs and abdominal appendages from the right side,
being careful to leave the fringe-like parts, the gills, attached to
20 ELEMENTARY ZOOLOGY
their respective legs. Place all of the appendages in order on a
piece of cardboard.
Examine the abdominal appendages, called pleopods,
or swimming feet. How many pairs are there ? Each
is composed of a basal part, the protopodite, and two
terminal segments, an inner one, the endopodite, and an
outer, the exopodite. In the males the first and second
pleopods of the abdomen are larger and less flexible than
the others. In the female the pleopods serve to carry
the eggs and the first two pairs are very small or absent.
Note the last set of abdominal appendages. These are
the uropods, which together with the telson form the tail.
Make a drawing of the pleopods of one side.
Examine the appendages of the cephalothorax. Like
the appendages of the abdomen the typical composition
of each includes a protopodite, an exopodite and an
endopodite, but some of these appendages are much
modified, and show a loss of one of these parts, or the
addition of an extra part. The cephalothoracic appen-
dages may be divided into three groups, an anterior group
of three pairs of mouth-parts (belonging to the head) of
which the first pair is the mandibles and the others are the
maxillcz; a second group of three pairs of foot-jaws or
maxillipeds, belonging to the thorax, and a third group of
five pairs of walking- -legs. The mandibles, lying next to
the mouth-opening, are hard and jaw-like and lack the
exopodite ; the first maxillae are small and also lack the
exopodite; the second maxillae have a large paddle-like
structure which extends back over the gills on each side
within the space, the branchial chamber, above the gills.
It is by means of this paddle-like structure (the scaphog-
nathite) that currents of water are kept up through the
gill-chambers. The maxillipeds increase in size from
first to third pair. Each pair of walking-legs except the
last bears gills. These gills are the organs by which
THE CRAYFISH 21
the blood is purified. The blood of the crayfish flows into
the large vessels on the outer sides of the gill and thence
into the fine vessels in the little leaf-like lamellae. At the
same time the air which is mixed with the water bathing
the gills passes freely through the thin membranous walls
of these lamellae and blood-vessels, and the blood gives
off its carbonic acid gas to the water and takes up oxygen
from the air in the water. Thus it will be seen that the
office of the gill is like that of the lung in the toad,
namely, to act as an organ for the elimination of carbonic
acid gas and the taking up of oxygen.
Note the pincer-like appendages of the first pair of legs.
These pincers are the chclce, with which food is torn into
bits and placed in the mouth. In the basal segment of
each of the last pair of legs of the male note the genital
pore. In the female the genital pores are in the basal
segments of the next to last pair of legs. Is the crayfish
bilaterally symmetrical ? Note the repetition of parts in
the crayfish, that is, the recurrence of similar parts in
successive segments. This serial repetition of parts among
animals is called metemerism.
Internal Structure (fig. 4). TECHNICAL NOTE. With a pair
of scissors cut through the dorsal wall of the cephalothorax into the
body-cavity. Cut the body-wall away from both sides and remove
the middle portion.
At the anterior end of the cephalothorax note the large
membranous sac, the stomach. Attached to each end of
this are sets of muscles which control its movements.
To the right and left of the stomach notice attached to
the shell large muscles which connect by stout ligaments
at their lower ends with the mandibles. Note a yellow
fringe-like structure, the digestive gland, which fills most
of the region about the stomach. It connects by a pair
of small tubes, the bile-ducts, with the alimentary canal.
Within the posterior portion of the cephalothorax note a
ELEMENTARY ZOOLOGY
THE CRAYFISH 23
pentagonal sac, the heart, contained within a delicate
membrane, the pericardium. Remove the pericardium
and note a pair of dorsal openings into the heart, called
ostia. (There are also two lateral pairs and a ventral
pair of ostia.) Note passing anteriorly from the heart
along the median line to the eyes a blood-vessel, the
ophthalmic artery. Arising from the anterior portion of
the heart are the antennary arteries, running to the
antennae. Yet another pair running anteriorly from the
heart to the stomach and digestive glands are called the
hepatic arteries. From the posterior end of the heart
arises the dorsal abdominal artery, running back to the
telson. Below this arises the sternal artery, which will
be seen later.
In the region below the heart are located the reproduc-
tive organs. They are whitish glandular masses from
each of which runs a tube which opens at the base of the
last pair of walking-legs in the male, and at the base of
the third pair of walking-legs in the female.
TECHNICAL NOTE. Cut longitudinally through the dorsal wall
of the abdomen on either side of the median line and remove the
piece of shell.
Note the powerful muscles within which flex and extend
the abdomen. By a rapid contraction of these muscles
the tail is brought beneath the body, propelling the animal
strongly backwards. When the crayfish crawls it gen-
erally goes forward, but in swimming it reverses this
direction.
Make a drawing showing, in their natural position, the
internal organs which have been studied.
Examine the alimentary canal for its whole length.
Note that the large bladder-shaped stomach is attached
to the mouth-opening by a short tube. What part of the
canal is this ? From the posterior end of the stomach is
a short thick-walled part, the small intestine, followed by
24 ELEMENTARY ZOOLOGY
a long straight tube, the large intestine, which opens to
the exterior through the anus.
TECHNICAL NOTE. Remove the alimentary canal, detaching it
from the anal end first, and working forward.
Cut the stomach open. Note an anterior portion, the
cardiac cJiamber, and a smaller posterior portion, the
pyloric chamber. Examine its inner surface. What do
you find here ? This structure is called the gastric mill.
Food, which for the most part consists of any dead
organic matter, is chewed by the ' ' stomach-teeth ' ' into
fine bits, and is then passed into the pyloric chamber. It
is here that the digestive glands empty their secretion into
the food. These glands have the same office as have the
liver and pancreas combined in the toad, and so they are
often called the hepato-pancreas. When the stomach has
been removed there will be noted in the anterior portion
of the body paired, flattened bodies, already mentioned,
which connect with openings at the base of each of the
antennae by means of wide thin-walled sacs, the ureters.
These organs are the kidneys, or green glands. Their
office is similar to that of the kidneys in the toad, namely,
the elimination of waste from the body.
TECHNICAL NOTE. Carefully remove all of the alimentary canal,
digestive glands, and reproductive organs. This process will expose
the floor of the cephalothorax. Now cut away from either side the
horny floor or bridge at the bottom of the cephalothorax. If the
specimen has not already been immersed, place it in clear water for
further dissection.
The foregoing dissection will expose the central nervous
system. It extends as a series of paired ganglia con-
nected by a double nerve-cord along the ventral median
line from the oesophagus to the last segment of the
abdomen. From what points do the lateral nerves arise ?
Anteriorly the double nerve-cord divides, the two parts
THE CRAYFISH 25
passing upward on each side of the oesophagus, where they
again meet to form the supra-oesopJiageal ganglion or
brain. Where do the nerves run which rise from the
brain ? What is the difference between the position of
the central nervous system in the crayfish and in the toad ?
Make a drawing of the nervous system.
Just beneath the nerve-cord note a blood-vessel ex-
tending the length of the body. This is the sternal
artery, which arises from the posterior end of the heart
and passes ventrally at one side of the alimentary canal
and between the nerve-cords. Here the sternal artery
divides into an anterior and a posterior branch, from
which lesser branches are given off to each one of the
appendages. The various arteries running to all parts of
the body finally pour out the blood into the body-cavity,
where it flows freely in the spaces among the various tissues
and organs. After the blood has bathed the body tissues
it flows to the gills on either side, passing up the outer
side of the gill through delicate thin-walled vessels, where
it is oxygenated as has already been described. From
the gills the purified blood flows back on the inner side
through a large chamber, sinus, into the pericardium,
through the ostia of the heart, whence it is driven into the
arteries once more. This sort of a circulatory system in
which the blood in places is not enclosed in a definite
vessel is known as an open system. In the toad we find
the blood in a dosed system, i.e., arteries leading into
capillaries which in turn lead into veins, in no case allow-
ing the blood to pass freely through the spaces of the
body.
CHAPTER V
THE MODIFICATION OF ORGANS AND FUNC-
TIONS
Differences between crayfish and toad. In the dis-
section of the crayfish one of the most important things in
the study of zoology has been learned. It is plain that
the crayfish has a body composed, like the toad's, of
parts or organs, and that most of these organs, although
differing much in appearance and actual structure from
those of the toad, correspond to similarly named organs
of the toad, and perform the same functions or processes,
although with many striking differences, essentially in the
same way as in the toad. But the structure of the body
is very different in the two animals. The toad has an
internal body skeleton to which the muscles are attached,
and a soft, yielding, outer body-covering or skin ; the
crayfish has no internal skeleton, but has its body covered
by a horny, firm body-wall to which the muscles are
attached. The toad has its main nervous chain lying just
beneath the dorsal wall of the body; the crayfish has its
main nervous chain lying just above the ventral wall of
the body. The toad has lungs and takes up oxygen from
the air of the atmosphere ; the crayfish has gills and takes
up oxygen from the air which is mixed with the water.
The toad has a single pair of jaws; the crayfish has
several pairs of mouth-parts. The toad has four legs
fitted for leaping; the crayfish has numerous legs fitted
for crawling or swimming. The crayfish's body is com-
26
THE MODIFICATION OF ORGANS AND FUNCTIONS 27
posed of a series of body-rings or segments; the toad's
body is a compact apparently unsegmented mass. The
toad has eyes each with a single large lens and capable
of moving in the head and of changing their shape and
hence their focus; the crayfish's eyes are immovable and
have a fixed focus, and are composed of hundreds of tiny
eyes each with lens and special retina of its own. And
so a long list of differences might be gone through with.
Resemblances between toad and crayfish. But on the
other hand there are many resemblances resemblances
both in structure and life-processes or physiology. Both
toad and crayfish have organs for the prehension of food,
its digestion and its assimilation. And these organs, the
organs of the digestive system, while differing in details
are alike in being composed principally of a long tube,
the alimentary canal, running through the body, open
anteriorly for the taking in of food, and open posteriorly
for the discharge of indigestible useless matter. Both
alimentary canals are divided into various special regions
for the performance of the various special processes con-
nected with the digestion and assimilation of food. Each
is adapted for the special kind of food which it is the habit
of the particular animal to take. The two sets of organs
are essentially alike and have the same essential function
or life-process to perform. But this process differs in the
details of its performance, and the organs which perform
this function and which constitute the digestive system of
each are modified to suit the special habits or kind of life
of the animal.
Both toad and crayfish have a heart w^ith blood-vessels
leading from it. In the case of the toad the heart is more
complex than in the crayfish, and the system of blood-
vessels is far more extensive and elaborate. But the heart
and blood-vessels in both animals subserve the same pur-
pose; their function is the circulation of the blood, this
28 ELEMENTARY ZOOLOGY
being the means by which oxygen and food are carried
to all growing or working parts of the body, and by
which carbonic acid gas and other poisonous waste
products are brought away from these parts. But this
function differs somewhat in its performance in the two
animals, and the organs which perform the function are
correspondingly modified in structural condition.
Both toad and crayfish have organs for respiration, that
is, for breathing in oxygen and breathing out carbonic
acid gas. But the toad takes its oxygen from the
atmosphere about it; its respiratory organs are the
lungs, the sac-like tube leading to the mouth, and
the external openings for the ingress and exit of the
gases. The crayfish, living mostly in the water, takes
its oxygen from the air which is mechanically mixed
with the water. Its respiratory organs are its gills.
There is a great difference, apparently, in the structural
.conditions of the organs of respiration in the two animals.
As a matter of fact the difference is less great than, at
first sight, appears to be the case. The lungs of the toad
are composed primarily of a thin membrane, in the form
of a sac, richly supplied with blood-vessels. Air is
brought to this thin respiratory membrane and by osmosis
the oxygen passes through the membrane and through
the thin walls of the fine blood-vessels, and is taken up
by the blood. At the same time the carbonic acid gas
brought by the blood to the lungs from all parts of the
body is given up by it and passes through the membranes
in order to leave the body. The air comes in contact
with the respiratory membrane (which is situated inside
the body) by means of a system of external openings and
a conducting chamber, and by these same openings and
chamber the carbonic acid gas leaves the body. In the
crayfish the gills are nothing else than a large number of
small flattened sacs each composed of a thin membrane
THE MODIFICATION OF ORGANS AND FUNCTIONS 29
richly supplied with blood-vessels. This respiratory mem-
brane is not, in the crayfish, situated inside the body, but
on the outer surface, although protected by being in a sort
of pocket with a covering flap, and it comes into immediate
contact with the air held in the water which freely bathes
the gills. By osmosis the oxygen of this air passes in
through the gill-membranes, while the carbonic acid gas
brought by the blood passes out through them. Exactly
the same exchange of gases is accomplished as in the
toad. But because of the great difference in the conditions
of life of the toad and crayfish, one living in \vater, the
other living out of water, the character of the performance
of the function of respiration, and correspondingly the
structural condition of the organs performing this function,
are strikingly different.
Modification of functions and structure to fit the
animal to special conditions of its life. As has been
done with the organs of digestion, circulation, and
respiration, so we might compare the other organs of the
crayfish and the toad. There would be found not only
many very marked differences between organs which have
the same general function in the two animals, but we
should find also numerous organs in the toad which are
not present at all in the crayfish, and conversely; and this
means, of course, that the toad can do numerous things,
perform numerous functions, which the crayfish cannot,
and, conversely, that the crayfish does some things which
the toad cannot. But both of these animals agree in
possessing in common the capability of performing those
processes such as taking food, breathing, reproducing,
etc., to which attention has been called as being indis-
pensable to all animal life. These processes, however,
are performed by the two animals in different ways and
the organs for the performance of these processes, although
at very bottom essentially alike, are in outer and super-
3 ELEMENTARY ZOOLOGY
ficial details of position, appearance and general structure
markedly different. Animals are fitted to live in different
places amid different surroundings by having their bodies
modified and the performance of their life-processes modi-
fied to suit the special conditions of their life.
Vertebrate and invertebrate. In selecting the toad
and the crayfish as the first animals to study and to com-
pare with each other, we have chosen representatives of
the two great groups into which the complexly organized
animals are divided, viz., the group of backboned or
vertebrate animals, and the group of backboneless or
invertebrate animals. To the vertebrates belong all those
which have an internal bony skeleton (and a few without
such a skeleton) and which have also an arrangement of
body-organs on the general plan of the toad's body. A
conspicuous feature of this arrangement is the situation of
the spinal cord or main great nerve-trunk along the back
or dorsal wall of the animal, and inside of a backbone.
All the fishes, batrachians (frogs, toads, salamanders,
etc.), reptiles (snakes, lizards, alligators, etc.), birds, and
mammals (quadrupeds, whales, seals, etc.) belong to the
vertebrates. / The backboneless or invertebrate animals
have no internal bony skeleton and have their main nerve-
trunk usually along the ventral wall of the body, some-
times in a circle around the mouth, but never in a back-
bone. To the invertebrates belong all insects, lobsters,
crabs, clams, squids, snails, worms, starfishes and sea-
urchins, corals and sponges, altogether a great host of
animals, mostly small.
7
CHAPTER VI
AMCEBA AND PARAMCECIUM
LABORATORY EXERCISE
Amoeba. TECHNICAL NOTE. Amoeba are found in stagnant
pools of water on the dead leaves, sticks and slime at the bottom.
To obtain them, collect slime and water from various puddles in sepa-
rate bottles and take them to the laboratory. Place a small drop of
slime on a slide under a cover-glass. Examine under the low power
first and note any small transparent or opalescent objects in the
field. Examine these objects with the higher power and note that
some are mere granular jelly-like specks, which slowly (but con-
stantly) change their form. These are Amoeba.
A teacher of zoology recommends the following method of obtain-
ing a large supply of A mceba : "For rearing Ama'ba place two or
three inches of sand in a common tub, which is then filled with
water and placed some feet from a north window ; three or four
opened mussels, with merest trace of the mud from the stream in
which they are taken, are partially buried in the sand and a hand-
ful of Xitclla and a couple of crayfish cut in two are added ; as
decomposition goes on a very gentle stream is allowed to flow into
the tub, and after from two to four weeks abundant Amoeba are to
be found on the surface of the sand and in the scum on the sides of
the tub ; small Amoeba appear at first, and later the large ones."
Having found an Amaba (fig. 5) note its irregular
shape, and if it moves actively observe its method of mov-
ing. How is this accomplished ? The viscous, jelly-like
substance which composes the whole body of an Amceba
is called protoplasm. The little processes which stick
out in various directions are the "false feet" (pseudo-
podia). Note that the outer portion, the cctosarc, of the
protoplasmic body is clear, while the inner, the endosarc,
is more or less granular in structure. Has Amoeba a
definite body- wall ? Do the pseudopodia protrude only
3'
32 ELEMENTARY ZOOLOGY
from certain parts of the body ? Within the endosarc
note a clear globular spot which contracts and expands,
or pulsates, more or less regularly. This is the contrac-
tile vacuole. Note the small granules which move about
within the endosarc. These are food-particles which
FIG. 5. Amceba sp. ; showing the forms assumed by a single individual in
four successive changes. (From life.)
have been taken in through the body-wall. Note how
pseudopodia flow about food-particles in the water and
how these are digested by the protoplasm. If an Amoeba
comes into contact with a particle of sand, note how it at
once retreats. Note within the endosarc an oval trans-
parent body which shows no pulsations. This is the
AMCEBA /IND PARAMCECIUM 33
nucleus, a very complex little structure of great impor-
tance in the make-up of Amceba.
Note that A moeba has no mouth or alimentary canal;
no nostrils or lungs, no heart or blood-vessels, no mus-
cles, no glands. It is an animal body not made up of
distinct organs and diverse tissues. Its whole body is a
simple minute speck of protoplasm, a single animal cell.
But it takes in food, it moves, it excretes waste matter
from the body, is sensitive to the touch of surrounding
objects, and, as we may be able to see, it can reproduce
itself, i.e., produce new Amcebce. Amoeba is the simplest
living animal.
It is only rarely that we can find an Amoeba actually
reproducing. The process, in its gross features, is very
simple. First the Amoeba draws in all of its pseudopodia
and remains dormant for a time. Next, certain changes
take place in the nucleus, which divides into equal por-
tions, one part withdrawing to one end of the protoplasmic
body, the other to the opposite end. Soon the body pro-
toplasm itself begins to divide into two parts, each part
collecting about its own half of the nucleus. Finally the
two halves pull entirely away from each other and form
two new Amoebce^ each like the original, but only half as
large. This is the simplest kind of reproduction found
among animals.
Amoeba continue to live and multiply as long as the
conditions surrounding them are favorable. But when
the pond dries up the Amcebcz in it would be exterminated
were it not for a careful provision of nature. When the
pond begins to dry up each Amoeba contracts its pseudo-
podia and the protoplasm secretes a horny capsule about
itself. It is now protected from dry weather and can be
blown by the winds from place to place until the rains
begin, when it expands, throws off the capsule and com-
mences active life again in some new pond.
34 ELEMENTARY ZOOLOGY
The Slipper Animalcule (Paramcccium sp.) TECHNICAL
NOTE. Paramcecia can be secured in most pond water where
leaves or other vegetation are decaying. However, if specimens
are not readily secured place some hay or finely cut dry clover in a
glass dish, cover with water and leave in the sun for several days.
In this mixture specimens will develop by thousands. Place a drop
of water containing Paramcecia on a slide with cover-glass over it.
Using a low power, note the many small animals darting hither and
thither in the field. Run a thin mixture of cherry gum in water
under the cover-glass. In this mixture they can be kept more quiet
and be better studied.
How does Paramcccium (fig. 6) differ from Amoeba in
form and movement ? Has the body an anterior and a
posterior end ? The delicate, short, thread-like processes,
on the surface of the body, which beat about very rapidly
in the water are called cilia, and they^are simply fine
prolongations of the body protoplasm. ^What is their
function ? Note a fine cuticle covering the body. Note
also many minute oval sacs lying side by side in the
ectosarc. These are called trichocysts and from each a
fine thread can be thrust out.
Note on one side, beginning at the anterior end, the
buccal groove leading into the interior through the gullet.
Observe also that by the action of the cilia in the buccal
groove food-particles are swept into the gullet. Rejected
or waste particles are ejected from the body occasionally.
Where ? Note about midway of the Paramcecium an
ovoid body with a smaller oval one attached to its side,
the forme^ being the macronucleus, the latter the micro-
uuclcus. Note that there are two contractile vacuoles in
the Paramcccium; also that the food-vacuoles have a
definite course in their movement inside the endosarc.
Make a drawing of a Paramcccium.
In comparing Paramcccium vyith Amccba it is apparent
that the body of the first is less simple than that of the
second. The definite opening for the ingress of food, the
two nuclei, the fixed cilia, and the definite cell-wall giving
AMCEBA AND PARAMCECIUM
35
a fixed shape to the body, are all specializations which
make Paramcecium more complex than Amoeba. But the
whole body is still composed of a single cell, and there
is, as in Amoeba, no differentiation of the body-substance
into different tissues, and no arrangement of body-parts
as systems of organs.
Paramcecium may occasionally be found reproducing.
This process takes place very
much as in Amoeba. The animal
remains dormant for a while, the
micronucleus then divides, the
macronucleus elongates and
finally divides in two, the proto-
plasm of the body becomes con-
stricted into two parts, each part
massing itself about thewithdrawn
halves of the macro- and micro-
nuclei, and lastly the whole breaks
into two smaller organisms which
grow to be like the original.
After multiplication or reproduc-
tion has gone on in this way for
numerous generations (about one
hundred), a fusion of two Para-
mcecia seems necessary before
further divisions take place. This
process of fusion, called conjuga-
tion, may be noted at some sea-
sons,
their buccal grooves together,
~, .... FIG. 6. Parama'chim sp. ;
1 wo Paramcrcia unite with buccal groove a t right. (From
life.)
part of the macronucleus and micronucleus of each passes
over to the other, and the irjxed elements fuse together
to form a new macro- and micronucleus in each half.
The conjugating Paramcccia now separate, and each
divides to form two new individuals.
CHAPTER VII
THE SINGLE-CELLED ANIMAL BODY. PRO-
TOPLASM AND THE CELL
The single-celled body. The study of Amoeba and
Paramcecium has made us acquainted with an animal body
very different from that of the toad or the crayfish. These
extraordinarily minute animals have a body so simple in
its composition, compared with the toad's, that if the
toad's body be taken for the type of the animal body,
Amoeba might readily be thought not to be an animal at
all. The body of Amoeba is not composed of organs, each
with a particular function or work to perform. Whatever
an Amoeba does is done, we may say, with its whole body.
But as we learn the things that this formless viscid speck
of matter does, we see that it is truly an animal ; that it
really does those things which we have learned are the
necessary life-processes of an animal. Amoeba takes up
and digests food composed of organic particles; it has the
power of motion ; it knows when its body comes in con-
tact with some external object, that is, it can feel or has
the power of sensation. Amoeba takes in oxygen and
gives out carbonic acid gas, and it can produce new in-
dividuals like itself, that is, it has the power of reproduc-
tion. But for the performance of these various life-pro-
cesses or functions it has no special parts or organs, no
mouth or alimentary canal, no lungs or gills, no legs, no
special reproductive organs. We have here to do with one
of the "simplest animals." With a minute, organless,
36
THE SINGLE-CELLED AWMAL BODY 37
soft speck of viscous matter called protoplasm for a body,
the simplest structural condition to be found among living
beings, Amoeba nevertheless is capable of performing, in
the simplest way in which they may be performed, those
processes which are essential to animal life.
Paramcecium has a body a little less simple than
Amoeba. The food-particles are taken into the body
always at a certain spot; this might be spoken of as a
mouth. And the body has some special locomotory
organs, if they may be so called, in the presence of the
cilia. The body, too, has a definite shape or form.
But, as in Amoeba, there is no alimentary canal, nor
nervous system, nor respiratory system, nor reproductive
system. The whole body feels and breathes and takes
part in reproduction.
A long jump has been made from the toad and crayfish
to Amoeba and Paramoecium; from the complex to the
simplest animals. But, as will later be seen, the great
difference between the bodies of these simplest animals
and those of the highly complex ones is only a difference
of degree ; there are animals of all grades and stages of
structural condition connecting the simplest with the most
complex. When animals are studied systematically, as
it is called, we begin with the simplest and proceed from
them to the slightly complex, from these to the more
complex, and finally to the most complex. There are
hundreds of thousands of different kinds of animals, and
they represent all the degrees of complexity which lie
between the extremes we have so far studied.
The cell. The characteristic thing about the body of
Amccba and Paramcecium and the other "simplest
animals ' ' for there are many members of the group of
"simplest animals," or Protozoa is that it is com-
posed, for the animal's whole lifetime, of a single cell.
A cell is the structural unit of the animal body. As
38 ELEMENTARY ZOOLOGY
will be learned in the next exercise, the bodies of all
other animals except the Protozoa, the simplest animals,
are composed of many cells. These cells are of many
kinds, but the simplest kind of animal cell is that shown
by the body of an Amoeba, a tiny speck of viscous, nearly
colorless protoplasm without fixed form. The protoplasm
composing the cell is differentiated to form two parts or
regions of the cell, an inner denser part, called the
nucleus, and an outer clearer part, called the cytoplasm.
Sometimes, as in the Paramxcium, the cell is enclosed by
a cell-wall which may be simply a denser outer layer of
the cytoplasm, or may be a thin membrane secreted by
the protoplasm. Thus the cell is not what its name
might lead us to expect, typically cellular in character;
that is, it is not (or only rarely is) a tiny sac or box of
symmetrical shape. While the cell is composed essen-
tially of protoplasm, yet it may contain certain so-called
cell-products, small quantities of various substances pro-
duced by the life-processes of the protoplasm. These
cell-products are held in the protoplasmic body-mass of
the cell, and may consist of droplets of water or oil or resin,
or tiny particles of starch or pigment, etc. The cell
cannot be said to be composed of organs, because the
word organ, as it is commonly used in the study of an
animal, is understood to mean a part of the animal body
which is composed of many cells. But the single cell
can be somewhat differentiated into parts or special
regions, each ^art or special region being especially
associated with some one of the life-processes. In
Paramoecium, for example, the food is always taken in
through the so-called mouth-opening; the fine proto-
plasmic cilia enable the cell to swim freely in the water,
the waste products of the body are always cast out through
a certain part, and so on. But this is a very simple sort
of differentiation, and the whole body is only one of those
THE SINGLE-CELLED ANIMAL BODY 39
structural units, the cells, of which so many are included
in the body of any one of the complex animals.
Protoplasm. The protoplasm, which is the essential
substance of the typical animal cell and hence of the
whole animal body, is a substance of very complex
chemical and physical make-up. No chemist has yet
been able to determine its exact chemical constitution,
and the microscope has so far been unable to reveal
certainly its physical characters. The most important
thing known about the chemical constitution of proto-
plasm is that there are always present in it certain com-
plex albuminous substances which are never found in
inorganic bodies. And it is certain that it is on the
presence of these substances that the power possessed
by protoplasm of performing the fundamental life-pro-
cesses depends. Protoplasm is the primitive physical
basis of life, but it is the presence of the complex albu-
minous substances in it that makes it so.
The physical constitution of protoplasm seems to be
that of a viscous liquid containing many fine globules of a
liquid of different density and numerous larger globules
of a liquid of still other density. Some naturalists believe
the fine globules to be solid grains, while still others
believe that numerous fine threads of* dense protoplasm
lie coiled and tangled in the clearer, viscous protoplasm.
But the little we know of the physical structure of proto-
plasm thro\vs almost no light on the remarkable properties
of this fundamental life-substance.
CHAPTER VIII
CELLULAR STRUCTURE OF THE TOAD (OR
FROG)
LABORATORY EXERCISE
The blood. TECHNICAL NOTE. The blood of a frog can be
studied as it flows through the small vessels in the membranes
between the toes while the animal is alive. Place a frog on a small
flat board which has had a hole cut near one end, and with a
piece of cloth bind it to the board. Spread the web between two
toes over the hole in the board and keep it in place with pins.
This done, examine the distended web under the compound micro-
scope first with low then with higher power, and observe the blood-
vessels and the blood circulating in them. For a further study of
the blood kill a toad or frog and place a drop of the blood on a
slide with a cover-glass over it.
Put the prepared slide under the microscope and note
that the blood, which as seen with the unaided eye
appears to be a red fluid, is made up of a great many
yellowish elliptical disks or cells, the blood-corpuscles,
floating in a liquid, the blood-plasma. Here and there
you may notice amoeboid blood-corpuscles. These are
irregular-shaped cells which move about by thrusting out
pseudopodia. They look like some of the unicellular
animals, as the Amccba. Can you distinguish a nucleus
and cell-wall in the blood-cells ?
Make drawings of these blood-cells.
The skin. TECHNICAL NOTE. Keep a live toad or frog in
water for some time and note if its skin becomes loose or begins to
slip away. If the outer skin, epidermis, comes off, take some of the
shed skin and wash it in water, then stain for three or four minutes
in a solution of methyl-green and acetic acid (seep. 451). Cut
40
CELLULAR STRUCTURE OF THE TOAD (OR FROG) 41
the pieces of stained skin into small bits and examine one of these
under the microscope.
With the low power of the microscope you will note
that the skin is made up of a great many flat cells placed
edge to edge. Each one has its cell-wall and a central
darkly stained nucleus.
Make a drawing of a portion of the toad's skin.
The liver. TECHNICAL NOTE. Cut through the fresh liver
of a toad, and with a knife-blade scrape from the cut surface some
of the liver-cells and place them on a slide with cover-glass.
Examine under the microscope and observe many
polygonal cells. Place some of the methyl-green acetic
stain under the cover-glass and note, after the cells are
stained, that they have definite boundaries and a central
nucleus.
Draw some of these scattered liver-cells.
The muscles. TECHNICAL NOTE. Take a piece of intestine
from a freshly killed toad, wash it thoroughly and place it in a con-
centrated solution of salicylic acid in 70% alcohol for 24 hours,
then gradually heat until about the boiling-point, when the muscles
will fall to pieces. Transfer the preparation to a watch-crystal and
tease small bits of isolated muscle with dissecting-needles. Place
some of the teased muscle-fibres on a slide, cover with cover-glass,
and add a drop of the methyl-green acetic acid.
' Note the small spindle-shaped muscle-fibres. Each
one of these fibres is a cell possessing all of the structures
common to cells, namely, cell-wall, nucleus, etc.
Make a drawing of a few isolated fibres of muscle.
From this study of some of the tissues in a toad it will
be noted that in the first case we had in the blood
separate cells which moved about freely in the plasma.
In the second case, that of the epidermis, the cells are
fixed edge to edge, thus forming a thin tissue; while in
the third and fourth cases, that of the liver and muscle,
the cells are not only placed edge to edge, but aggregated
42 ELEMENTARY ZOOLOGY
into vast masses or bundles, in one case to form the liver
and in the other case a muscle. The entire body of the
toad is built up of a colony of simple units (cells) com-
bined in various forms to make all the various tissues and
organs.
CHAPTER IX
THE MANY-CELLED ANIMAL BODY. DIF-
FERENTIATION OF THE CELL
The many-celled animal body. In the study of cer-
tain of the tissues and organs of the toad we have learned
that the body of this animal is composed of many cells,
thousands and thousands of these microscopic structural
units being combined to form the whole toad. This
many-celled or multicellular condition of the body is true
of all the animals except the simplest, the unicellular
Protozoa. Corals, starfishes, worms, clams, crabs, in-
sects, fishes, frogs, reptiles, birds, and mammals, all the
various kinds of animals in which the body is composed
of organs and tissues, agree in the multicellular character
of the body, and may be grouped together and called the
many-celled animals in contrast to the one-celled animals.
This division is one which is recognized by many syste-
matic zoologists as being more truly primary or funda-
mental than the division of animals into Vertebrates and
Invertebrates. The one-celled animals are called Pro-
tozoa, and the many-celled animals Metazoa.
Differentiation of the cell. It is apparent at first
glance that the cells which compose the body of a many-
celled animal are not like the simple primitive cell which
makes up the body of the Amoeba , nor are they like the
more complexly arranged cell of the Paramoecium. Nor
are they all like each other. The cells in the toad's blood
are of two kinds, the white blood-cells, which are very like
44 ELEMENTARY ZOOLOGY
the body of Amoeba, and the elliptical disk-like red blood-
cells. The cells composing the muscles are, moreover,
like neither kind of blood-cells, and the cells of which the
liver is composed are not like the cells of the muscles.
That is, there are many different kinds of cells in the body
of a many-celled animal. While the single cell which
composes the whole body of the Amoeba is able to do all
the things necessary to maintain life, the various cells in the
body of a complex animal are differentiated or specialized,
certain cells devoting themselves to a certain function or
special work, and others to other special functions. For
example, the cells which compose the organs of the
nervous system, the brain, ganglia, and nerves, devote
themselves almost exclusively to the function of sen-
sation, and they are especially modified for this purpose.
The highly specialized nerve-cells resemble very little the
primitive generalized body-cell of Amoeba. The muscle-
cells of the complex animal body have developed to a
high degree that power of contraction which is possessed,
though in but slight degree, by Amoeba. These muscle-
cells have for their special function this one of contraction,
and massed together in great numbers they form the
strongly contractile muscular tissue and muscles of the
body on which the animal's power of motion depends.
The cells which line certain parts of the alimentary canal
are the ones on which the function of digestion chiefly
rests. And so we might continue our survey of the
whole complex body. The point of it all is that the
thousands of cells which compose the many-celled animal
body are differentiated and specialized; that is, have
become changed or modified from the generalized primitive
amoeboid condition, so that each kind of cell is devoted
to some special work or function and has a special struc-
tural character fitting it for its special function. In the
Protozoan body the single cell can perform and does per-
DIFFERENTIATION OF THE CELL 45
form all the functions or processes necessary to the life of
the animal. In the Metazoan body each cell performs, in
co-operation with many other similar cells, some one
special function or process. The total work of all the
cells is the living of the animal.
CHAPTER X
HYDRA
LABORATORY EXERCISE
TECHNICAL NOTE. Hydra lives in fresh water, attached to stones,
sticks, or decayed leaves. It can be found in most open fresh-water
ponds not too stagnant, often attached to Chara. There are two
species occurring commonly, H. iriridis, the green Hydra, and H.
fuscus, the brown or flesh-colored Hydra. Both are very small
forms and have to be looked for carefully. Specimens should be
brought to the laboratory, put into a large dish of water and left
in the light. Hydra is best studied alive. Place a living specimen
attached to a bit of weed in a watch-crystal filled with water or on
a slide with plenty of water and examine with the low power of the
microscope.
Note the cylindrical body (fig. 7, A, E) with its flat
basal attachment and radial tentacles (varying in number)
which crown the upper end and surround the centrally
located mouth. Note the movements of Hydra, its powers
of contraction, and method of taking in food.
TECHNICAL NOTE. -To feed Hydra, place very small " water-
fleas" (Daphuia sp. ) in the water with it.
Observe the method by which " water-fleas " are taken
into the mouth. Food is caught on stinging cells (to be
studied later) and conveyed to the mouth by the tenta-
cles. Note that the cylindrical body encloses a cavity,
the digestive cavity. How is this connected with the ex-
terior ? If Hydra captures prey too large or is no longer
hungry, the prey is released.
46
HYDRA
47
''""' -' lth
,,,.,- . V
E
FIG. 7 A, Hydra fusca, with expanded body and a budding individual;
B, H.fiaca, contracted; C, H. fusca. part of outer surface of a tenta-
cle, greatly magnified. (A and B drawn- from live specimens. C, from a
preparatio'i; )'l), Grantia sp. (a sponge), three individuals; E, Gruntia^
sp., longitudinal section ; F, Grunlin sp., spicules. (D, E, and F
drawn from preserved specimens. )
48 ELEMENTARY ZOOLOGY
TECHNICAL NOTE. Place small slips of paper on the slide near
the Hydra, put cover-glass over the whole, and examine with the
low power of the microscope.
Note that the whole animal is made up of cells closely
joined. Are the cells in the tentacles all alike ? Note
nodule-like projections above some of the cells; these are
stinging cells, or cnidoblasts. In some cases a small hair-
like process, the trigger hair or cnidocil, may be seen pro-
jecting above the surface of the cell. Note in some of the
tentacles dark-colored particles. These are food-particles
which have been taken through the mouth into the diges-
tive cavity and have passed thence into the tentacles.
The central digestive cavity communicates freely with the
cavities in the tentacles, for the tentacles are merely
evaginations of the body-wall.
Make drawings of the Hydra expanded and of the same
individual contracted. r
TECHNICAL NOTE. From the preparation which you have under
the microscope pull out the slips of paper, thus letting the cover-
glass drop down on the specimen. With a small pipette put a
drop of anilin-acetic stain (see p. 451 ) on the slide at one side
of the cover-glass and with a piece of filter-paper draw the water
through from the other side of the cover-glass. When the stain is
diffused press down the cover-glass gently and examine the tentacles
first under a low power of the microscope, then under a high one.
Note the distortion that the animal has undergone
through the action of the reagent. Observe the cnido-
blasts of the tentacles and note that many of them have
thrown out long whip-like processes (fig. 7, C). On
what parts of the body do the cnidoblasts occur ? Care-
fully examine one of the cnidoblasts which has been dis-
charged and note a clear transparent bag-like structure
within, the nematocyst, to which is attached the long
whip-like process. In another cnidoblast cell which has
not been discharged note that the whip-like process is
coiled about inside of the bag-like structure. The whole
HYDRA 49
apparatus is like the inturned finger of a glove which can
be blown out by pressure from the inside. The mechan-
ism is simple. The cnidocil or trigger-hair is touched by
some animal, an impulse is conveyed to the delicate fibres
interspersed among the cells (nerve-cells) which stimulate
the cnidoblast cell, whereupon there is a contraction of
the contents and, the cnidoblast being compressed, the
inverted whip-like process turns wrong side out and im-
pales the animal on its points or barbs.
TECHNICAL NOTE. The teacher should be provided with micro-
scopical sections, both transverse and longitudinal, of the Hydra
stained in some good general stain (hsematoxylin or borax carmine).
If the teacher has no means of making such preparations, they may
be procured from dispensers of microscopical supplies.
From the cross-section of the Hydra make out the
general structure of the body. Note that it is a hollow
cylinder consisting of two well-defined layers of cells, an
outside ectoderm layer and an inner endoderm layer.
Between these two is yet another thin non-cellular layer
called the mesogloea.
Thus it will be seen that Hydra is made up of two
layers of cells, the outer ectoderm or skin, which is
specialized to perform the office of capturing prey as well
as that of protection, and the inner endoderm, whch sur-
rounds the digestive cavity and performs the function of
digestion. The endoderm lines the body-cavity, particles
taken in as food being digested by certain digestive cells
which thrust out amoeboid processes and ingest particles
of food. Other cells in the endoderm have long flagellate
processes which vibrate back and forth in the digestive
cavity, thereby creating currents in the water containing
food-particles.
Note, in a cross-section, that there are small ovoid or
cuboid cells at the bases of the large ectoderm cells.
These are the interstitial cells. Some of the interstitial
50 ELEMENTARY ZOOLOGY
cells become modified and pushed up between the ecto-
derm cells to form cnidoblast cells. Many of the
endoderm as well as ectoderm cells have muscle-processes
which spread out from the base of the cell and which
serve to contract and expand the body.
TECHNICAL NOTE. In the specimens which have been collected
perhaps two methods of reproduction will be observed. Place
healthy Hydrce in a wide-mouthed jar in the sunlight with plenty
of water and food. In a few days active budding will take place.
Observe the method of reproduction in Hydra. Com-
monly the parent produces small buds, which at first are
only evaginations of the body- wall, but which later
develop tentacles and a mouth of their own. Subse-
quently the bud becomes constricted at the base, separates
from the parent, and the young Hydra begins a distinct
existence.
Another mode of reproduction takes place which, in
distinction from the asexual method just mentioned, is
called sexual reproduction. This last is the method
common to most of the higher organisms. You may note
that in some Hydra there is a swelling or bulging of the
ectoderm of the body-wall in the region just below the
tentacles. These are the sperm-glands. Within these are
produced sperm-cells which break away in great clusters
to fertilize the ova, or eggs. Note a larger bulging of the
body-wall nearer the lower end of the body which, under
high power, has a granular appearance. This is the egg-
gland, in which develops a single ovum or egg. The
ovum breaks from its covering and is fertilized by sperm-
cells from another individual. In forms like Hydra,
where both sexes are represented in a single individual,
the organism is termed vioiurcunis or hermaphroditic* In
connection with reproduction Chapter XIII should be
studied.
HYDRA 51
An instructive experiment can be performed by cutting
a Hydra into two or more parts, when (usually) each of
the various parts will develop into a complete Hydra.
This process may be called reproduction by fission, but it
rarely occurs naturally,
CHAPTER Xt
THE SIMPLEST MANY-CELLED ANIMALS
Cell differentiation and body organization in Hydra.
From the examination of Hydra we have learned that
there are true many-celled animals which are much less
complex in structure than the toad and crayfish. The
body of Hydra, like the body of the toad, is composed of
many cells, but these cells are of only a few different
kinds; that is, show but little differentiation. There is
relatively little division of the body into distinct organs.
Still, certain parts of the body devote themselves princi-
pally to certain particular functions. Thus all the food is
taken in through the single "mouth-opening" at the
apical free end of the cylindrical body, and there are
certain organs, the tentacles, whose special business or
function it is to find and seize food and to convey it to the
mouth. After the food is taken into the cylindrical body-
cavity it is digested by special cells which line the cavity.
Some of these cells are unusually large, and each contains
one or more contractile vacuoles. From the free ends of
these cells, the ends which are next to the body-cavity,
project pseudopods or flagella. These protoplasmic
processes are constantly changing their form and number.
In addition to these large sub-amoeboid cells there are, in
this inner layer of cells lining the body-cavity, and
especially abundant near the base or bottom of the cavity,
many long, narrow, granular cells. These are gland-
cells which secrete a digestive fluid. The food captured
by the tentacles and taken in through the mouth-opening
disintegrates in the body-cavity, or digestive cavity as it
52
THE SIMPLEST MANY-CELLED ANIMALS 53
may be called. The digestive fluid secreted by the
gland-cells acts upon it so that it becomes broken into
small parts. These particles are seized by the projecting
pseudopods of the sub-amceboid cells and taken into the
body-protoplasm of these cells. The cells of the outer
layer of the body do not take food directly, but receive
nourishment only by means of and through the cells of
the inner layer. The body-cavity of Hydra is a very
simple special organ of digestion.
In the outer layer of cells there are some specially
large cells whose inner ends are extended as narrow
pointed prolongations directed at right angles with the
rest of the cell. These processes are very contractile and
are called muscle-processes. Each one is simply a
specially contractile continuation of the protoplasm of the
cell-body. There are also in this layer some small cells
very irregular in shape and provided with unusually large
nuclei. These cells are more irritable or sensitive than
the others and are called nerve-cells. We have thus in
Hydra the beginnings of muscular organs and of nerve-
organs. But how simple and unformed compared with
the muscular and nervous systems of the toad and crayfish !
There is no circulatory system, nor are there any special
organs of respiration.
But Hydra is far in advance of Amoeba or Paramoccium.
Its body is composed of thousands of distinct cells. Some
of these cells devote themselves especially to food-taking,
some especially to the digestion of food; some are
specially contractile, and on them the movements of the
body depend, while others are specially irritable or sensi-
tive, and on them the body depends for knowledge of the
contact of prey or enemies. In the cnidobla^t cells, those
with the stinging threads, there is a very wide departure
from the simple primitive type of cells. There is in
Hydra a manifest differentiation of the cells into various
54 ELEMENTARY ZOOLOGY
kinds of cells. The beginnings of distinct tissues and
organs are indicated.
Degrees in cell differentiation and body organization.
In the study of the cellular constitution of the tissues
and organs of the toad, we found to what a high degree
the differentiation of the cells may attain, and in the study
of the anatomy of the toad we found how thoroughly these
differentiated cells may be combined and organized into
body-parts or organs. The body of the toad is made up
of distinct organs, each composed of highly differentiated
or specialized cells. The body of Hydra is composed of
cells for the most part only slightly differentiated and
hardly recognizably grouped or combined into organs.
These two conditions are the extremes in the body-
structure of the many-celled animals. Between them
is a host of intermediate conditions of cell differentia-
tion and body organization. When we come to the
study of other members of the great branch of simple
many-celled animals to which Hydra belongs (see
Chapter XVII), it will be found that some of them
show a slight advance in complexity beyond Hydra.
Higher in the scale of animal life the forms will be found
still more and more complex, with ever-increasing differ-
entiation of the cells, with the combination of the differ-
entiated cells into distinct organs, and the co-ordination
of organs into systems of organs up to the extreme shown
by the birds and mammals. And hand in hand with this
increasing complexity of structure goes ever-increasing
complexity or specialization of function. Breathing is a
simple function or process with Hydra, where each body-
cell takes up oxygen for itself, but it is a complex business
with the toad, or with a bird or mammal, where certain
complex structures, the lungs and accessory parts, and
the heart, blood-vessels and blood all work together to
distribute oxygen to all parts of the body.
CHAPTER XII
DEVELOPMENT OF THE TOAD
FIELD AND LABORATORY EXERCISE
TECHNICAL NOTE. As the work of this chapter, or some similar
work in getting acquainted with the postembryonic development
of a many-celled animal, should be done early in the course, and
as most schools open in the fall, it will perhaps be impossible to
make this first study of development from live specimens in the field.
In such case the examination of a series of prepared specimens,
previously obtained by the teacher, must be resorted to. In the
spring the development of several kinds of animals, including the
toad, can be studied from live specimens in the field or in breeding-
cages and aquaria in the laboratory. The eggs of the toad may be
found in April and May (the toads are heard trilling at egg-laying
time) in ponds. The eggs look like the heads of black pins, and are
in single rows in long strings of transparent jelly, which are usually
wound around sticks or plant-stems at the bottom of the pond near
the shore. Bring some of these strings into the schoolroom and
keep them in water in shallow dishes. Keep them in the light, but
not in direct sunlight. In the dishes put some small stones and
mud from the pond, arranging them in a slope, thus making different
depths of water. Stones with green algae on should be selected, for
algae are the food of the tadpoles. The eggs will hatch in two or
three days, and if too many tadpoles are not kept in the dish, and
the little aquarium be well cared for, the whole postembryonic de-
velopment of the toad can be well observed. For the study of the
development from prepared specimens the teacher should have a
complete series of stages from egg to adult toad in alcohol. The
specimens may be examined by the students in connection with a
talk from the teacher on the life-history of the toad.
If the study is made from prepared specimens, make
drawings of egg-strings, and of a single egg magnified
and shaded to indicate its color. Draw each specimen of
the series of tadpoles, noting in the youngest the presence
of gills and tail and absence of legs and eyes; in the
55
56 ELEMENTARY ZOOLOGY
older the appearance of eyes, the shrivelling of the gills,
shrinking of the tail and development of legs ; in the still
older the characteristic shape, in miniature, of the adult
toad.
In observing the course of development of the living
specimens there should be made, in addition to the draw-
ings, notes showing the duration of the egg stage, and
the time elapsing between all important changes (as seen
externally) in the body of the young. Observations and
notes on the general behavior of tadpoles should also be
made ; note the swimming, the feeding, the gradual leav-
ing of the water, etc.
In addition to the easily seen external changes in the
body, very important ones in the internal organs take
place during development. Perhaps the most important
of these concerns the lungs. The young gilled toad
breathes as a fish does, but gradually its gills are lost,
while at the same time lungs develop and the tadpole
comes to the surface to breathe air like any lunged aquatic
animal. The toad on leaving the water changes its diet
from vegetable to animal food ; a tadpole feeds on aquatic
algae; a toad preys on insects. Correlated with the
change in habit, the intestine during development under-
goes some marked changes, becoming relatively dimin-
ished in length.
For an account of the development of the toad see
Gage's "Life-history of a Toad" or Hodge's "The
Common Toad. '
CHAPTER XIII
MULTIPLICATION AND DEVELOPMENT. MUL-
TIPLICATION OF ONE-CELLED ANIMALS
Multiplication. We know that any living animal has
parents; that is, has been produced by other animals
which may still be living or be now dead or, as with
Amoeba, may have changed, by division, into new indi-
viduals. Individuals die, but before death, they produce
other individuals like themselves. If they did not, their
kind or species would die with them. This production
of new animals constantly going on is called the repro-
duction or multiplication of animals. The process is
well called multiplication, because each female animal
normally produces more than one new individual. She
may produce only one at a time, one a year, as many of
the sea-birds do or as the elephant does, but she lives
many years. Or she may produce hundreds, or thou-
sands, or even millions of young in a very short time.
A lobster lays 10,000 eggs at a time. Nearly nine
millions of eggs have been taken from the body of a
thirty-pound female codfish. As a matter of fact but
very, very few of these eggs produce new animals which
reach maturity. From the 10,000 eggs produced by the
lobster each year an average of but two new mature
lobsters is produced. There is always a struggle for food
and for place going on among animals, for many more
are produced than there are food and room for, and so of
all the new or young animals which are born the great
57
5^ ELEMENTARY ZOOLOGY
majority are killed before they reach maturity. In a later
chapter more attention will be given to this great struggle
for life.
In the preceding paragraph it has been stated that
" we know that any living animal has parents ; that is, has
been produced by other animals which may still be living
or be now dead." This is a statement, however, which
has found complete acceptance only in modern times.
It is a familiar fact that a new kitten comes into the world
only through being born ; that it is the offspring of parents
of its kind. But we may not be personally familiar with
the fact that a new starfish comes into the world only as
the production of parent starfish, or that a new earth-
worm can be produced only by other earthworms. But
naturalists have proved these statements. All life comes
from life ; all organisms are produced by other organisms.
And new individuals are produced by other individuals of
the same kind. That these statements are true all
modern observations and investigations of the origin of
new individuals prove. But in the days of the earlier
naturalists the life of the microscopic organisms like
Amoeba and Paramcecium, and even that of many of the
larger but unfamiliar animals, was shrouded in mystery.
And various and strange beliefs were held regarding the
origin of new individuals.
Spontaneous generation. The ancients believed that
many animals were spontaneously generated. The early
naturalists thought that flies arose by spontaneous genera-
tion from the decaying matter of dead animals. Frogs
and many insects were thought to be generated spontane-
ously from mud, and horse-hairs in water were thought
to change into water-snakes. But such beliefs were
easily shown to be based on error, and have been long
discarded by zoologists. But the belief that the micro-
scopic organisms, such as bacteria and infusoria, were
MULTIPLICATION AND DEVELOPMENT 59
spontaneously generated in stagnant water or decaying
organic liquids was held by some naturalists until very
recent times. And it was not so easy to disprove the
assertions of such believers. If some water in which
there are apparently no living organisms, however
minute, be allowed to stand for a few days, it will
come to swarm with microscopic plants and animals.
Any organic liquid, as a broth or a vegetable infusion,
exposed to the air for a short time becomes foul through
the presence of innumerable microsccpic organisms. But
it has been certainly proved that these organisms are not
spontaneously produced in the water or organic fluid.
A few of them enter the water from the air, in which there
are always greater or less numbers of spores of micro-
scopic organisms. These spores germinate quickly when
they fall into water or some organic liquid, and the rapid
succession of generations soon gives rise to the hosts of
bacteria and one-celled animals which infest all standing
water. If all the active organisms and inactive spores in
a glass of water are killed by boiling the water, and this
sterilized water be put into a sterilized glass, and this
glass be so well closed that germs or spores cannot pass
from the air without into the sterilized liquid, no living
animals will ever appear in it. We know of no instance
of the spontaneous generation of animals, and all the
animals whose life-history we know are produced by other
animals of the same kind.
Simplest multiplication and development. The sim-
plest method of multiplication and the simplest kind of
development shown among animals are exhibited by such
simple animals as Amccba and Paramaccium. The pro-
duction of new individuals is accomplished in Amoeba by
a simple division or fission of its body (a single cell) into
two practical ly equivalent parts. An Amccba which has
grown for some time contracts all of its finger-like
60 ELEMENTARY ZOOLOGY
processes, the pseudopodia, and its body becomes con-
stricted. This constriction or fissure increases inwards
so that the body is soon divided fairly in two. There are
now two Amceba, each half the size of the original one;
each, indeed, actually one-half of the original one. The
original Amoeba was the parent; the two halves of it are
the young. Each of the young possesses all of the char-
acteristics and powers of the parent ; each can move, eat,
feel, "grow, and reproduce by fission. The only change
necessary for the young or new Avt&b'a to become like its
parent, is that of simple growth to a size about twice its
present size. The development here is reduced to a
minimum. Just as the simplest animals perform the other
life-processes, such as taking and digesting food, breath-
ing and feeling, in an extremely primitive simple way, so
do they perform the necessary life-process of reproduction
or multiplication in the simplest way shown among
animals.
In the case of Paramcecium the process of multiplication
is slightly more complex than that of Amoeba in the fact
that sometimes before the simple fission of the body takes
place the interesting phenomenon of conjugation occurs.
Paramoecium may reproduce itself for many generations
by simple fission, but a generation finally appears in which
conjugation takes place. Two individuals come together
and each exchanges with the other a part of its nucleus.
Then the two individuals separate and each divides into
two. The result of the conjugation, or the coming
together, of two individuals with mutual interchange of
nuclear substance is to give to the new Paramoecia pro-
duced by the conjugating individuals a body which
contains part of the body-substance of two distinct indi-
viduals. If the two conjugating individuals differ at all
and they always do differ, because no two individual
animals, although belonging to the same species, are
MULTIPLICATION AND DEVELOPMENT 61
exactly alike the new individual, made up of parts of
each of them, will differ slightly from both. Nature
seems intent on making every new individual differ slightly
from the individual which precedes it. And the method
of multiplication which Nature has adopted to produce
the result is the method which we have seen exhibited in
its simplest form in the case of Paramcechnn the method
of having two individuals take part in the production of
a new one.
The development of the new Paramoccia is a little more
complex than that of Amccba. Not only must the new
Paramccciinn grow to the size of the original one, but it
must develop those slight, but apparent, modifications of
the parts of its body which we can recognize in the full-
grown, fully developed Parainoccium individual. A new
mouth-opening must develop on the new individual
formed of the hinder half of the original Paramccchuu and
new cilia must be developed. Thus there is a slight
advance in complexity of development, just as there is in
complexity of structure in Paramachnn as compared with
Amccba. In the many-celled animals this complexity of
development is carried to an extreme.
Birth and hatching. When a young animal is born
alive, it usually resembles in appearance and structure the
parent, although of course it is much smaller, and requires
always a certain time to complete its development and
become mature. A young kangaroo or opossum is
carried for some time after its birth in an external pouch
on the mother's body and is a very helpless animal. A
young kitten is born with eyes not yet opened and must
be fed by the mother for several weeks. On the other
hand young Rocky Mountain sheep are able to run about
swiftly within a few hours after birth.
62 ELEMENTARY ZOOLOGY
Most animals appear first as eggs laid by the mother.
This is true of the birds, the reptiles, the fishes, the
insects, and most of the hosts of invertebrate animals,
This egg may be cared for by the parent as with the
birds, or simply deposited in a safe place as with most
insects, or perhaps dropped without care into the water as
with most marine invertebrates. The young animal which
issues from the egg may at the time of its hatching
resemble the parent in appearance and structural character
(although always much smaller) as with the birds, some
of the insects, and many of the other animals. Or it may
issue in a so-called larval condition, in which it resembles
the parent but slightly or not at all, as is the case with
the gill-bearing, legless, tailed tadpole of the frog or the
crawling, wingless, wormlike caterpillar of the butterfly,
or the maggot of the house-fly.
Life-history. Any animal which hatches from an egg
has undergone a longer or shorter period of development
within the egg-shell before hatching. The development
of an animal from first germ-cell to the time it leaves the
egg, for example, the development of the embryo chick
from the first cell to time of hatching, is called its em-
bryonic development; and the development from then on,
for example, that of the chick to adult hen or rooster,
or that of tadpole to frog, is called the post-embryonic
development. Beginning students of animals cannot
study the embryonic development (embryology} of animals
readily, but they can in many cases easily follow the
course of the post-embryonic development, and this stud}'
will always be interesting and valuable, When the
" life-history " of an animal is spoken of in this book, or
other elementary text-book of zoology, it is the history
of the life of the animal from the time of its birth or
hatching to and through adult condition that is meant,
not the complete life-history from beginning single egg-
MULTIPLICATION AND DEVELOPMENT 63
cell to the end. In all of the study of the different kinds
of animals to which the rest of this book is devoted,
attention will be paid to their life-history.
PART II
SYSTEMATIC ZOOLOGY
CHAPTER XIV
THE CLASSIFICATION OF ANIMALS
Basis and significance of classification. It is the
common knowledge of all of us that animals are classified:
that is, that the different kinds are arranged in the mind
of the zoologist and in the books of natural history, in
various groups, and that these various groups are of
different rank or degree of comprehensiveness. A group
of high rank or great comprehensiveness includes groups
of lower rank, and each of these includes groups of still
lower rank, and so on, for several degrees. For example,
we have already learned that the toad belongs to the
great group of back-boned animals, the Vertebrates, as
the group is called. So do the fishes and the birds, the
reptiles and the mammals or quadrupeds. But each of
these constitutes a lesser group, and each may in turn be
subdivided into still lesser groups.
In the early days of the study of animals and plants
their classification or division into groups was based on
the resemblances and the differences which the early
naturalists found among the organisms they knew. At
first all of the classifying was done by paying attention
to external resemblances and differences, but later when
naturalists began to dissect animals and to get acquainted
65
66 ELEMENTARY ZOOLOGY
with the structure of the whole body, the differences and
likenesses of inner parts, such as the skeleton and the
organs of circulation and respiration, were taken into ac-
count. At the present time and ever since the theory of
descent began to be accepted by naturalists (and there is
practically no one who does not now accept it), the classifi-
cation of animals, while still largely based on resemblances
and differences among them, tells more than the simple
fact that animals of the same group resemble each other
in certain structural characters. It means that the mem-
bers of a group are related to each other by descent, that
is, genealogically. They are all the descendants of a
common ancestor ; they are all sprung from a common
stock. And this added meaning of classification explains
the older meaning ; it explains why the animals are alike.
The members of a group resemble each other in structure
because they are actually blood relations. But as their
common ancestor lived ages ago, we can learn the history
of this descent, and find out these blood relationships
among animals only by the study of forms existing now,
or through the fragmentary remains of extinct animals
preserved in the rocks as fossils. As a matter of fact
we usually learn of the existence of this actual blood-
relationship, or the fact of common ancestry among
animals, by studying their structure and finding out the
resemblances and differences among them. If much alike
we believe them closely related; if less alike we believe
them less closely related, and so on. So after all, though
the present-day classification means something more,
means a great deal more, in fact, than the classification
of the earlier naturalists means, it is largely based on
and determined by resemblances and differences just as
was the old classification. Sometimes the fossil remains
of ancient animals tell us much about the ancestry and
descent of existing forms. For example, the present-day
THE CLASSIFICATION OF ANIMALS 67
one-toed horse has been clearly shown by series of fossils
to be descended from a small five-toed horse-like animal
which lived in the Tertiary age.
Importance of development in determining classifica-
tion. A very important means of determining the
relationships among animals is by studying their develop-
ment. If two kinds of animals undergo very similar
development, that is, if in their development and growth
from egg-cell to adult they pass through similar stages,
they are nearly related. And by the correspondence or
lack of correspondence, by the similarity or dissimilarity
of the course of development of different animals much
regarding their relationship to each other is revealed.
Sometimes two kinds of animals which are really nearly
related come to differ very much in appearance in their
fully developed adult condition because of the widely differ-
ent life-habits the two may have. But if they are nearly
related their developmental stages will be closely similar
until the animals are almost fully developed. For exam-
ple, certain animals belonging to the group which includes
the crabs, lobsters, and crayfishes, have adopted a para-
sitic habit of life, and in their adult condition live attached
to the bodies of certain kinds of true crabs. As these
parasites have no need of moving about, being carried by
their hosts, they have lost their legs by degeneration, and
the body has come to be a mere sac-like pulsating mass,
attached to the host by slender root-like processes, and
not resembling at all the bodies of their relatives the
crabs and crayfishes. If we had to trust, in making out
our classification, solely to structural resemblances and
differences, we should never classify the Sacculina (the
parasite) in the group Crustacea, which is the group in-
cluding the crabs and lobsters and crayfishes. But the
young Sacculina is an active free-swimming creature
resembling the young crabs and young shrimps. By a
68 ELEMENTARY ZOOLOGY
study of the development of Sacculina we find that it is
more closely related to the crabs and crayfishes and the
other Crustaceans than to any other animals, although in
adult condition it does not at all, at least in external ap-
pearance, resemble a crab or lobster.
Scientific names. To classify animals then, is to deter-
mine their true relationships and to express these relation--
ships by a scheme of groups. To these groups proper
names are given for convenience in referring to them.
These proper names are all Latin or Greek, simply
because these classic languages are taught in the schools
and colleges of almost all the countries in the world, and
are thus intelligible to naturalists of all nationalities. In
the older days, indeed, all the scientific books, the
descriptions and accounts of animals and plants, were
written in Latin, and now most of the technical
words used in naming the parts of animals and
plants are Latin. So that Latin may be called the
language of science. For most of the groups of animals
we have English names as well as Greek or Latin ones
and when talking with an English-speaking person we
can use these names. But when scientific men write of
animals they use the names which have been agreed on
by naturalists of all nationalities and which are understood
by all of these naturalists. These Latin and Greek
names of animals laughed at by non-scientific persons as
"jaw-breakers," are really a great convenience, and save
much circumlocution and misunderstanding.
AN EXAMPLE OF CLASSIFICATION.
TECHNICAL NOTE. There should be provided a small set of bird-
skins which will serve just as well as freshly killed birds, and which
may be used for successive classes, thus doing away with the neces-
sity ot shooting birds. The birds suggested for use are among the
commonest and most easily recognizable and obtainable. They may
be found in any locality at any time of the year. The skins can
THE CLASSIFICATION OF ANIMALS 69
he made by some boy interested in birds and acquainted with
making skins, or by the teacher, or can be purchased from a natur-
alists' supply store, or dealer in bird skins. The skins will cost
about 25 cents each. This example or lesson in classification can
be given just as well of course with other species of birds, or with
a set of some other kinds of animals, if the teacher prefers. Insects
are especially available, butterflies perhaps offering the most readily
appreciated resemblances and differences.
Species. Examine specimens of two male downy
woodpeckers (the males have a scarlet band on the back
of the head). (In the western States uses Gardiner's
downy woodpecker.) Note that the two birds are of the
same size, have the same colors and markings, and are
in all respects alike. They are of the same kind; simply
two individuals of the same kind of animal. There are
hosts of other individuals of this kind of bird, all alike.
This one kind of animal is called a species. The species
is the smallest * group recognized among animals. No at-
tempt is made to distinguish among the different individuals
of one kind or species of animal as we do in our own case.
Examine a specimen of the female downy wood-
pecker. It is like the male except that it does not have
the scarlet neck-band. But despite this difference we
know that it belongs to the same species as the male
downy because they mate together and produce young
woodpeckers, male and female, like themselves. There
are thus two sorts of individuals, t male and female, com-
prised in each species of animal. A species is a group of
animals comprising similar individuals which produce
new individuals of the same kind usually after the mating
together of individuals of two sexes which may differ
somewhat in appearance and structure.
* The lesser group called variety, or subspecies, we may leave out of
consideration for the present.
\ Some species of animals are not represented by male individuals ; and
in some all the individuals are hermaphrodites, as explained in chapter
XIV,
70 ELEMENTARY ZOOLOGY
Examine a male hairy woodpecker and a female ; (in
western States substitute a Harris's hairy woodpecker).
Note the similarity in markings and structure to the
downy. Note the marked difference in size. Make notes
of measurements, colors and markings, and drawings of
bill and feet, showing the resemblances and the differ-
ences between the downy woodpecker and the hairy
woodpecker. These two kinds of woodpeckers are very
much alike, but the hairy woodpeckers are always much
larger (nearly a half) than the downy woodpeckers and
the two kinds never mate together. The hairy wood-
peckers constitute another species of bird.
Genus. Examine now a flicker (the yellow-shafted
or golden-winged flicker in the East, the red-shafted
flicker in the West). Compare it with the downy wood-
pecker and the hairy woodpecker. Make notes referring
to the differences, also the resemblances. The flicker
is very differently marked and colored and is also much
larger than the downy woodpecker, but its bill and feet
and general make-up are similar and it is obviously a
' * woodpecker. ' ' It is, however, evidently another species
of woodpecker, and a species which differs from either the
downy or the hairy woodpecker much more than these
two species differ from each other. There are two other
species of flickers in North America which, although
different from the yellow-shafted flicker, yet resemble it
much more than they do the downy and hairy wood-
peckers or any other woodpeckers. We can obviously
make two groups of our woodpeckers so far studied,
putting the downy and hairy woodpeckers (together with
half a dozen other species very much like them) into one
group and the three flickers together into another group.
Each of these groups is called a germs, and genus is thus
the name of the next group above the species. A genus
usually includes several, or if there be such, many,
THE CLASSIFICATION OF ANIMALS 71
similar species. Sometimes it includes but a single known
species. That is, a species may not have any other
species resembling it sufficiently to group with it, and so
it constitutes a genus by itself. If later naturalists should
find other species resembling it they would put these new
species into the genus with the solitary species. Each
genus of animals is given a Greek or Latin name, of a
single word. Thus the genus including the hairy and
downy woodpeckers is called Dryobates; and the genus
including the flickers is called Colaptes. But it is neces-
sary to distinguish the various species which compose the
genus Colaptes, and so each species is given a name which
is composed of two words, first the word which is the
name of the genus to which it belongs, and, second, a
word which may be called the species word. The species
word of the Yellow-shafted Flicker is auratus (the Latin
word for golden), so that its scientific name is Colaptes
auratus. The natural question. Why not have a single
word for the name of each species ? may be answered thus :
There are already known more than 500,000 distinct
species of living animals ; it is certain that there are no
less than several millions of species of living animals;
new species are being found, described and named con-
stantly; with all the possible ingenuity of the word-
makers it would be an extremely difficult task to find or
to build up enough words to give each of these species a
separate name. This is not attempted. The same
species word is often used for several different species of
animals, but never for more than one species belonging
to a given genus. And the names of the genera are
never duplicated. (There are, of course, much fewer
genera than species, and the difficulty of finding words
for them is not so serious.) Thus the genus word in the
two-word name of a species indicates at once to just what
particular genus in the whole animal kingdom the species
72 ELEMENTARY ZOOLOGY
belongs, while the second or species word distinguishes it
from the few or many other species which are included in the
same genus. This manner of naming species of animals
and plants (for plants are given their scientific names
according to the same plan) was devised by the great
Swedish naturalist Linnaeus in the middle of the
eighteenth century and has been in use ever since.
Family. Examine a red-headed woodpecker (J^lela-
nerpes crytJirocepJialus) and a sapsucker (Spliyrapicus
varius) and any other kinds of woodpeckers which can be
got. Find out in what ways the hairy and downy
woodpeckers (genus Dry ob cites), the flickers (genus
Colapies) and the other woodpeckers resemble each other.
Examine especially the bill, feet, wings and tail. These
birds differ in size, color and markings, but they are
obviously all alike in certain important structural respects.
We recognize them all as woodpeckers. We can group
all the woodpeckers together, including several different
genera, to form a group which is called a family. A
family is a group of genera which have a considerable
number of common structural features. Each family is
given a proper name consisting of a single word. The
family of woodpeckers is named Picidce.
We have already learned that resemblances between
animals indicate (usually) relationship, and that classify-
ing animals is simply expressing or indicating these
relationships. When we group several species together
to form a genus we indicate that these species are closely
related. And similarly a family is a group of related
genera.
Order. There are other groups* higher or more com-
*Each of these higher groups has a proper name composed of a single
word. In the case of no group except the species is a name-word ever
duplicated. Each genus, family, order, or higher group has a name-word
peculiar to it, and belonging to it alone.
THE CLASSIFICATION OF ANIMALS 73
prehensive than families, but the principle on which they
are constituted is exactly the same as that already
explained. Thus a number of related families are grouped
together to form an order. All the fowl-like birds, in-
cluding the families of pheasants, turkeys, grouse and
quail, all obviously related, constitute the order of gal-
linaceous birds called Gallince. The families of vultures,
hawks and owls constitute the order of birds of prey,
the Raptores, and the families of the thrushes, wrens,
warblers, sparrows, black-birds, and many others con-
stitute the great order of perching birds (including all the
singing birds) called the Passeres.
Class and branch. But it is evident that all of these
orders, together with the other bird orders, ought to be
combined into a great group, which shall include all the
birds, as distinguished from all other animals, as the
fishes, insects, etc. Such a group of related orders is
called a class. The class of birds is named Aves. There
is a class of fishes, Pisces, and one of frogs and salaman-
ders, Batrachia, one of snakes and lizards called Reptilia,
and one of the quadrupeds which give milk to their young
called Mammalia. Each of these classes is composed of
several orders, each of which includes several families and
so on down. But these five classes of Pisces, Batrachia,
Reptilia, Aves and Mammals agree in being composed of
animals which have a backbone or a backbone-like struc-
ture, while there are many other animals which do not
have a backbone, such as the insects, the starfishes, etc.
Hence these five backboned classes may be brought
together into a higher group called a branch or phylum.
They compose the branch of backboned animals, the
branch Vertebrata; all the animals like the starfishes,
sea-urchins and sea-lilies which have the parts of their
body arranged in a radiate manner compose the branch
Echinodermata; all the animals like the insects and
74 ELEMENTARY ZOOLOGY
spiders and centipedes and crabs and crayfishes which
have the body composed of a series of segments or rings
and have legs or appendages each composed of a series
of joints or segments make up the branch Arthropoda.
And so might be enumerated all the great branches or
principal groups into which the animal kingdom is divided.
In the remainder of this book the classification of
animals is always kept in sight, and the student will see
the terms species, genus, family, order, etc., practically
used. In it all should be kept constantly in mind the
significance of classification, that is, the existence of actual
relationships among animals through descent.
CHAPTER XV
BRANCH PROTOZOA: THE ONE-CELLED
ANIMALS
Of this group the structure and life-history of the
Amoeba (Amceba sp.) and the Slipper Animalcule (Para-
mcecium sp.) have already been treated in Chapter VI.
Another example is the
BELL ANIMALCULE Vorticella sp.)
TECHNICAL NOTE. Specimens of Vorticella may usually be
found in the same water with Amceba and Paramcecium. The
individuals live together in colonies, a single colony appearing to
the naked eye as a tiny whitish mould-like tuft or spot on the
surface of some leaf or stem or root in the water. Touch such a
spot with a needle, and if it is a Vorticellid colony it will contract
instantly. Bring bits of leaves, stems, etc., bearing Vorticellid
colonies into the laboratory and keep in a small stagnant-water
aquarium (a battery-jar of pond-water will do).
Examine a colony of Vorticella in a watch-glass of
water or in a drop of water on a glass slide under the
microscope. Note the stemmed bell-shaped bodies
which compose the colony. Each bell and stem together
form an individual Vorticella (fig. 8.) How are the
members of the colony fastened together ? Tap the slide
and note the sudden contraction of the animals ; also the
details of contraction in the case of an individual. Watch
the colony expand ; note the details of this movement in
the case of an individual.
Make drawings showing the colony expanded and con-
tracted.
With higher power examine a single individual. Note
75
7 6
ELEMENTARY ZOOLOGY
the thickened, bent-out, upper margin of the bell. This
margin is called the peristome. With
what is it fringed ? The free end of the
bell is nearly filled by a central disk,
the epistome, with arched upper surface
and a circlet of cilia. Between the
epistome and peristome is a groove,
the mouth or vestibule, which leads
into the body. Study the internal
structure of the transparent, bell-
shaped body. Note the differentia-
tion of the protoplasm comprising the
body into an inner transparent color-
less endosarc containing various dark-
colored granules, vacuoles, oil-drops,
etc., and an outer uniformly granular
ectosarc not containing vacuoles. Is
the stalk formed of ectosarc or en-
dosarc or of both ? Note the curved
nucleus lying in the endosarc. (This
may be difficult to distinguish in some
specimens.) Note the numerous large
FIG. *. Vorticelia sp. ; circular granules, the food vacuoles.
one individual with Note the contractile vesicle, larger and
stalk coiled, and one , . A ,
with stalk extended, clearer than the food vacuoles. Note
(From life.) ^e thin cuticle lining the whole body
externally. A high magnification will show fine trans-
verse ridges or rows of dots on the cuticle.
Make a drawing showing the internal structure.
Observe a living specimen carefully for some time to
determine all of its movements. Note the contraction
and extension of the stalk, the movements of the cilia of
peristome and epistome, the flowing or streaming of the
fluid endosarc (indicated by the movements of the food
vacuoles), the behavior of the contractile vesicle.
BRANCH PROTOZOA: THE ONE-CELLED ANIMALS 77
Make notes and drawings explaining these motions.
Specimens of Vorticclla may perhaps be found dividing,
or two bell-shaped bodies may be found on a single stem,
one of the bodies being sometimes smaller than the other.
These two bodies have been produced by the longitudinal
division or fission of a single body. In this process a
cleft first appears at the distal end of the bell-shaped
body, and gradually deepens until the original body is
divided quite in two. The stalk divides for a very short
distance. One of the new bell-shaped bodies develops a
circlet of cilia near the stalked end. After a while it
breaks away and swims about by means of this basal
circlet of cilia. Later it settles down, becomes attached
by its basal end, loses its basal cilia and develops a stalk.
4 ' Conjugation occurs sometimes, but it is unlike the
conjugation of Paramcceium in two important points:
Firstly, the conjugation is between two dissimilar forms ;
an ordinary large-stalked form, and a much smaller free-
swimming form which has originated by repeated division
of a large form. Secondly, the union of the two is a
complete and permanent fusion, the smaller being
absorbed into the larger. This permanent fusion of a
small active cell with a relatively large fixed cell, followed
by division of the fused mass, presents a striking analogy
to the process of sexual reproduction occurring in higher
animals. '
OTHER PROTOZOA
Besides the Amoeba^ Paratncecium^ and Vorticella there
are thousands of other Protozoa. Most of them live in
water, but a few live in damp sand or moss, and some
live inside the bodies of other animals as parasites. Of
those which live in water some are marine, while others
are found only in fresh-water streams and lakes.
7$ ELEMENTARY ZOOLOGY
Form of body. The Protozoa all agree in having the
body composed for its whole lifetime of a single cell,*
but they differ much in shape and appearance. Some of
them are of the general shape and character of Amoeba,
sending out and retracting blunt, finger-like pseudopodia,
the body-mass itself having no fixed form or outline but
FIG. 9. Sun animalcule, a fresh-water protozoan with a siliceous skeleton,
and long thread-like protoplasmic prolongations. (From life.)
constantly changing. Others have the body of definite
form, spherical, elliptical, or flattened, enclosed by a thin
cuticle, and having a definite number of fine thread-like
or hair-like protoplasmic prolongations called flagella or
* In some Protozoa a number of similar cells temporarily unite to form a
colony, but each cell may still be regarded as an individual animal.
BRANCH PROTOZOA: THE ONE-CELLED ANIMALS 79
cilia. Many of the familiar Protozoa of the fresh-water
ponds always have two whiplash-like flagella projecting
from one end of the body. By means of the lashing of
these flagella in the water the tiny creature swims about.
Others have many hundreds of fine short cilia scattered,
sometimes in regular rows, over the body-surface. The
Protozoan swims by the vibration of these cilia in the
water.
There is no stagnant pool, no water standing exposed
in watering-trough or bar-
rel which does not contain
thousands of individuals of
the one-celled animals.
And in any such stagnant
water there may always be
found several or many dif-
ferent kinds or species. A
drop of this water examined
with the compound micro-
. scope will prove to be a
tiny world (all an ocean)
with most of its animals and
plants one-celled in struc-
ture. A few many-celled
animals will be found in it
preying on the one-celled
ones. There are sudden
and violent deaths here, and
births (by fission of the
parent) and active locomo-
tion and food-getting and
growth and all of the busi-
nesses and functions of life
which we are accustomed
world of larger animals.
which has the nucleus in the shai
of a string or chain of bead-
FIG. 10. Stcntor sp. ; a protozoan
which may be fixed, like Vortifellu,
or free-swimming, at will, and
hape
-like
bodies. The figure shows a single
individual as it appeared when fixed,
with elongate, stalked bodv, and as
it appeared when swimming about,
with contracted body. (From life.)
to see in the more familiar
So ELEMENTARY ZOOLOGY
Marine Protozoa. One usually thinks of the ocean as
the home of the whales and the seals and the sea-lions, and
of the countless fishes, the cod, and the herring, and the
mackerel. Those who have been on the seashore will
recall the sea-urchins and starfishes and the sea-anemones
which live in the tide-pools. On the beach there are the
innumerable shells, too, each representing an animal
which has lived in the ocean. But more abundant than
all of these, and in one way more important than all,
are the myriads of the marine Protozoa.
Although the water at the surface of the ocean appears
clear and on superficial examination seems to contain no
animals, yet in certain parts of the ocean (especially in
the southern seas) a microscopical examination of this
water shows it to be swarming with Protozoa. And not
only is the water just at the surface inhabited by one-
celled animals, but they can be found in all the water from
the surface to a great depth below it. In a pint of this
ocean-water there may be millions of these minute
animals. In the oceans of the world the number of them
is inconceivable. And it is necessary that these Protozoa
exist in such great numbers, for they and the marine one-
celled plants (Protophyta) supply directly or indirectly
the food for all the other animals of the ocean.
/Among all these ocean Protozoa none are more in-
teresting than those belonging to the two orders Forami-
nifera (fig. 1 1) and Radiolaria. The many kinds belong-
ing to these orders secrete a tiny shell (of lime in
the Foraminifera, of silica in the Radiolaria) which en-
closes most of the one-celled body. These minute shells
present a great variety of shape and pattern, many being
of the most exquisite symmetry and beauty. The shells
are perforated by many small holes through which project
long, delicate, protoplasmic pseudopodia. These fine
pseudopodia often interlace and fuse when they touch each
BRANCH PROTOZOA: THE ONE-CELLED ANIMALS 81
other, thus forming a sort of protoplasmic network outside
of the shell. In some cases there is a complete layer of
protoplasm part of the body protoplasm of the Protozoan
surrounding the cell externally.
When these tiny animals die their hard shells sink to
the bottom of the ocean, and accumulate slowly, in in-
conceivable numbers, until they form a thick bed on the
ocean floor. Large areas of the bottom of the Atlantic
FIG. II. Rosalina varians, a marine protozoan (Foraminifera) with calca-
reous shell. (After Schultze.)
Ocean are covered with this slimy ooze, called Forami-
nifera ooze or Radiolaria ooze, depending on the kinds of
animals which have formed it. Nor is it only in present
times that there has been a forming of such beds by the
marine Protozoa. All over the world there are thick
rock strata composed almost exclusively of the fossil shells
of these simplest animals. The chalk-beds and cliffs of
England, and of France, Greece, Spain, and America,
were made by Foraminifera. Where now is land were
once oceans the bottoms of which have been gradually
82 ELEMENTARY ZOOLOGY
lifted above the water's surface. Similarly the rock
called Tripoli found in Sicily and the Barbadoes earth
from the island of Barbadoes are composed of the shells
of ancient Radiolaria.
It is thus evident that the Protozoa is an ancient group
of animals. As a matter of fact zoologists are certain
that it is the most ancient of all animal groups. All of
the animals of the ocean depend upon the marine Protozoa
and the marine Protophyta, one-celled plants, for food.
Either they feed on them directly, or prey on animals
which in turn prey on these simplest organisms. A well-
known zoologist has said: "The food-supply of marine
animals consists of a few species of microscopic organisms
which are inexhaustible and the only source of food for all
the inhabitants of the ocean. The supply is primeval as
well as inexhaustible, and all the life of the ocean has
gradually taken shape in direct dependence on it." The
marine Protozoa are the only animals which live in-
dependently; they alone can live or could have lived in
earlier ages without depending on other animals. They
must therefore be the oldest of marine animals. By
oldest is meant that their kind appeared earliest in the
history of the world, and as it is certain that ocean life is
older than terrestrial life that is, that the first animals
lived in the ocean it is obvious that the marine Protozoa
are the most ancient of all animal groups.
As already learned in the examination of examples of
one-celled animals, it is evident that life may be success-
fully maintained without a complex body composed of
many organs performing their functions in a specialized
way. The marine Protozoa illustrate this fact admirably.
Despite their lack of special organs and their primi-
tive way of performing the life-processes, that they live
successfully is shown by their existence in such extraor-
dinary numbers. They outnumber all other animals.
BRANCE PROTOZOA: THE ONE-CFLLED ANIMALS 83
The conditions of life in the surface-waters of the ocean
are easy and constant, and a simple structure and simple
method of performing the necessary life-processes are
wholly adequate for successful life under these con-
ditions.
CHAPTER XVI
BRANCH PORIFERA: THE SPONGES
THE FRESH-WATER SPONGE (Spongilla sp.)
TECHNICAL NOTE. Fresh-water sponges may perhaps not be
readily found in the neighborhood of the school, but they occur
over most of the United States, and careful searching will usually
result in the finding of specimens. They are compact, solid-looking
masses, sometimes lobed, resting on and attached to rocks, logs,
timbers, etc., in clear water in creeks, ponds, or bayous. They
are creamy, yellowish-brown or even greenish in color and resemble
some cushion-like plant far more than any of the familiar animal
forms. They can be distinguished from plants, however, by the
fact that there are no leaves in the mass, nor long thread-like fibres
such as compose the masses of pond algae (pond scum). When
touched with the fingers a gritty feeling is noticeable, due to the
presence of many small stiff spicules. Sponges should be removed
entire from the substance they are attached to, and may be taken
alive to the laboratory. They die soon, however, and should be put
into alcohol before decay begins.
Note the form of the sponge mass. Is it lobed or
branched ? Examine the surface for openings. These
are of two sizes'; the larger are osteoles or cxhalant open-
ings, while the smaller and more numerous are pores or
inJialant openings. The sponge-flesh is called sarcode.
Examine a bit of sarcode under the microscope ; note the
spicules. Have these spicules a regular arrangement ?
Of what are they composed ?
Draw the entire sponge, showing shape and openings ;
draw some of the spicules.
Embedded in the body-substance, especially near the
base, note (if present) numerous small, yellowish, sub-
84
BRANCH PORIFERA: THE SPONGES 85
spherical or disk-like bodies, the gemmnles. These are
reproductive bodies. Each gemmule is a sort of internal
bud. It is composed of an interior group of protoplasmic
cells, enclosed by a crust thickly covered with spicules.
In winter the sponge dies down and the gemmnles are set
free in the water. In spring the protoplasmic contents
issue through an aperture in the crust, called the micro-
pyte or foraminal opening, and develop and grow into a
new sponge.
For a good account of the fresh- water sponge, see
Pott's " Fresh-water Sponges. "
A CALCAREOUS OCEAN-SPONGE (Grantia sp.) (fig, 7, D, E, F.)
TECHNICAL NOTE. For inland schools, specimens preserved in
alcohol or formalin must be used. They may be obtained from
dealers in naturalists' supplies (see p. 453). Specimens of some
species of this genus can be obtained at almost any point on the
Atlantic or Pacific coasts of this country.
Examine the external structure of a specimen. Note
the elongate, sub-cylindrical form, the attached base, the
free end. Note the large exhalant opening, osteole or
osculum, at the free end; the numerous small inhalant
openings elsewhere on the surface (best seen in dried
specimens). Note the spicules covering the surface of the
body, and the longer ones surrounding the osculum. Cut
the sponge in two longitudinally and note the simple cylin-
drical body-cavity, the gastric cavity or cloaca. Note the
thickness of the body- wall ; note the tubes running through
the body-wall from cloaca to external surface. Through
these tubes water laden with food enters the gastric cavity,
where the food is digested, the water and undigested
particles passing out through the osculum. Crush a bit of
dried sponge, or boil a bit of soft sponge in caustic potash
and mount on a glass slide. Examine under a micro-
scope and note the abundance of spicules and the variety
in their form. Two kinds may always be found, and
86 ELEMENTARY ZOOLOGY
sometimes three. These spicules are composed of car-
bonate of lime and can be dissolved by pouring on to
them a drop of hydrochloric acid.
Some of the sponges may have buds growing out from
them near the base. These buds are young sponges
developed asexually. If allowed to develop fully the
buds would have detached themselves from the parent
and each would have become a new sponge.
Make drawings showing the form of a whole sponge ;
the appearance of the inner face of the sponge bisected
longitudinally; the shape of the spicules.
A COMMERCIAL SPONGE
TECHNICAL NOTE. For the study of the skeleton of an ocean-
sponge with more complex body buy several common small bath-
sponges without large holes running entirely through them. The
teacher should have also a few specimens of small marine sponges
preserved in alcohol or formalin. Such specimens should be part
of the laboratory equipment (see account of laboratory equipment,
p. 450), and can be readily and cheaply obtained from dealers in
naturalists' supplies.
The bath-sponge or slate-sponge consists simply of the
hard parts or skeleton of a sponge animal. In life all of
the skeleton is enclosed or covered by a soft, tough mass
composed of layers of cells. Note the many openings on
the surface of the sponge. Crush a bit of the skeleton
and examine it under the microscope. Note that it is
composed of fine fibres of a tough, horny substance called
spongin, instead of tiny distinct calcareous spicules.
OTHER SPONGES
The sponges are fixed, plant-like aquatic animals.
The members of a single family live in fresh water, being
found in lakes, rivers, and canals in all parts of the world.
All the other sponges, and there are several thousand
species known, live in the ocean. They are to be found
at all depths, some in shallow water near the shore and
BRANCH PORIFERA: THE SPONGES
others in deeper water, even to the deepest depths yet
explored. They are found in all seas, though especially
abundantly in the Atlantic Ocean and Mediterranean Sea.
Form and size. The shape of the simplest sponges is
that of a tiny vase or nearly cylindrical cup, hollow and
attached at its base. At the free end there is a large
opening. But there is a great deal of variety in the form
and size of different sponges.
There is, indeed, much varia-
tion in the shape and general
character of different individuals
of the same species. Unlike
most other animals, sponges are
fixed, and the character of the
surface to which a sponge is
attached has much influence
upon its shape. If this surface
is rough and uneven the sponge
may follow in its growth the
sinuosities of the surface and so
become uneven and distorted
in shape. At best, only a few
kinds of sponges have any very
even and symmetrical shape.
Most of them are very unsym-
metrical and grow more like a
low compact bushy plant than
like the animals we are familiar
with. The smallest sponges
are only I mm. (^ in.) high,
while the largest may be over FlG - I2 - The skeleton of a
... "glass " sponge (skeleton com-
a meter (39 in.) in height. In posed of siliceous spicules) from
color living sponges may be J ;l P :xn - < From specimen, j
red, purple, orange, gray, and sometimes blue. Most
sponges have the whole body of one color.
88 ELEMENTARY ZOOLOGY
Skeleton. A very few sponges have no skeleton at
all. The others have a skeleton or hard parts composed
of interwoven fibres of the tough, horny substance called
spongin, or of hosts of fine needles or spicules of silica or
of carbonate of lime. The siliceous skeletons of some
of the so-called glass-sponges (fig. 12) are very beautiful.
The lime and siliceous sponge spicules exhibit a great
variety of outline, some being anchor-shaped, some cross-
shaped, and some resembling tiny spears or javelins.
Structure of body. The skeleton of a sponge whether
composed of interlacing fibres or of short spicules is
always invisible from the outside when the sponge is alive.
It is embedded in, or clothed by, the soft, fleshy part of
the body. The soft part of the sponge is composed
simply of two layers of cells, one constituting the external
surface of the body, and the other lining the interior
cavities and canals of the body. Between these two cell-
layers there is a mass of soft gelatinous substance all
through which protoplasm ramifies, and in which are em-
bedded numerous scattered cells. There are, as seen in
the case of Spongilla and Grantia, no systems of organs
such as characterize the higher animals. No heart, lungs,
alimentary canal, nervous system, organs of locomotion,
eyes, ears, or other organs of special sense; the sponge
has none of these. It is simply an aggregate of cells,
arranged in two layers, and supported usually by a skele-
ton of horny fibres or calcareous or siliceous spicules. Its
body is usually shapeless, unsymmetrical and without
front or back, right or left. It is not to be wondered at
that sponges were for a long time believed to be plants.
Feeding habits. The sponges feed on minute bits of
animal or plant substance and on the microscopic unicel-
lular plants or animals which float in the water which
bathes their bodies. The water entering the sponge-
body through the various openings of the surface is moved
BRANCH PORIFERA: THE SPONGES 89
along by the waving or lashing of the flagella of the cells
which line the canals, and these currents of water bear
with them the tiny organisms which are taken up by these
same cells and digested. The incoming currents of water
meet in the central cavity or cavities of tiie body and pass
out through the large opening called the osculum at the
free end of the vase-like body, or if the body is branched,
through the large openings at the tips of these branches.
The same currents of water bring also oxygen for the
sponge's breathing and carry away the carbonic acid gas
given out by the body-cells.
As a German naturalist has said, the one necessary
condition for the life of a sponge is the streaming of water
through its body. All sponges have a system of canals
for this water-current and all have means, in the waving
flagella or cilia with which these canals are lined, for pro-
ducing these currents. When a live sponge is put into a
vessel of water, currents are immediately set up, and they
always flow into the body through the many fine openings
and out of the body through the osculum.
Development and life- history. Although the sponge
in its adult condition is permanently attached by its base
to the sea-bottom or to some rock or shell, when it is first
born it is an active free-swimming creature. The sponges
reproduce in two ways, asexually and sexually. The
asexual mode of reproduction of the fresh-water sponge
by gemmules has already been described. The ocean
sponges also reproduce asexually either by forming
interior gemmules or external buds. In this latter
method a bud forms on the outer surface of the body
which increases in size and finally grows into a new
sponge individual. In some species this new sponge does
not become separated from the body of the mother,
but remains attached to it like a branch to a tree-trunk.
By the continued production of such non -separating indi-
90 ELEMENTARY ZOOLOGY
viduals, a colony of sponges is formed which has the
general appearance of a branching plant. In other
species the new sponge formed by the development and
growth of a bud falls off and becomes a distinct separate
individual.
In the sexual mode of reproduction, male or sperm-
cells and female or egg-cells are developed in the same
individual. The sperm-cells are motile and swim about
in the cavities and canals of the sponge-body until they
find egg-cells, which they fertilize. The fertilized eggs
begin to develop and pass through their first stages in the
sponge-body. Finally the embryo sponge, which is
usually a tiny oval or egg-shaped mass of cells, escapes
from the body of the parent into the water. The young
sponge has some of its outer cells provided with cilia,
and by means of these it swims about. After a while
it comes to rest on the ocean-floor or on some rock
or shell, attaches itself, and begins to take on the form
and character of the parent. It leads hereafter a fixed
sedentary life.
The sponges of commerce. The sponge-skeletons
which are the ' ' sponges ' ' that we use all belong to a few
species, not more than half a dozen. Most of the com-
mercial sponges come from the Mediterranean Sea, though
some come from the Bahama Islands, some from the Red
Sea, and a few from the coasts of Greece, Asia Minor,
and Africa. The commercial sponges do not live in very
deep water; they are usually found not deeper than 200
feet. The living sponges are collected by divers, or are
dragged up by men in boats using long-poled hooks, or
dredges. ' When secured they are exposed to the air
for a limited time, either in the boats or on shore, and
then thrown in heaps into the water again in pens or
tanks built for the purpose. Decay thus takes place with
great rapidity, and when fully decayed they are fished up
BRANCH PORIFERA: THE SPONGES 91
again, and the animal matter beaten, squeezed, or washed
out, leaving the cleaned skeleton ready for the market.
In this condition after being dried and sorted, they are
sold to the dealers, who have them trimmed, re-sorted
and put up in bales or on strings ready for exportation.
There are many modifications of these processes in differ-
ent places, but in a general way these are the essentia-
steps through which the sponge passes before it is con-
sidered suitable for domestic purposes. Bleaching-
powders or acids are sometimes used to lighten the color,
but these unless very delicately handled injure the dura-
bility of the fibres."
Classification. The sponges are classified according
to the character of the skeleton. In one group are put
all those sponges which have a skeleton of calcareous
spicules, and this group is called the Calcarea. All other
sponges are grouped as Non-Calcarea, the members of
this group either having no skeleton at all, or having a
skeleton composed of siliceous spicules or of spongin
fibres. According to the absence or presence of a skele-
ton and the character of the skeleton when it exists the
Non-Calcarea are subdivided into smaller groups.
CHAPTER XVII
BRANCH OELENTERATA: THE POLYPS, SEA-
ANEMONES, CORALS, AND- JELLYFISHES
The structure and life-history of an example of the
polyps (the Fresh-water Hydra, Hydra sp.) has been
studied in Chapters X and XI.
OTHER POLYPS, SEA- ANEMONES, CORALS, AND
JELLYFISHES
TECHNICAL NOTE. The teacher should have, if possible, several
pieces of coral and a few specimens of Coelenterates in alcohol or
formalin, which will show the external character, at least, of these
animals (see account of laboratory equipment, p. 450). If the
school is on the coast, the pupils should be shown the sea-anemones
of the tide-pools.
The animals which are included in the branch Ccelen-
terata are, at least in living condition, unfamiliar to most
of us. Like the sponges, they are almost all inhabitants,
of the ocean; a few, like Hydra, live in fresh water.
Like the sponges, too, most of the members of this
branch are fixed, and in their general appearance suggest
a plant rather than an animal. The name zoophytes, or
plant-animals, which is often applied to these animals is
based on this superficial resemblance. But many of the
Coelenterates lead an active free-swimming life. This is
true of the jellyfishes which float or swim about on or near
the surface of the ocea^P Many of the zoophytes spend
part of their life in an active free-swimming condition
before settling down, becoming attached and thereafter
92
BRANCH CCELENTERATA: THE POLYPS, ETC. 93
remaining fixed. In localities near the seashore many
animals belonging to this great group can be readily
found and observed. The beautiful sea-anemones with
their slowly-waving tentacles, the fine many-branched
truly plant-like hydroids with their hosts of little buds,
and the soft colorless masses of jelly, the jellyfishes, which
are cast up on to the beaches by the waves are all animals
belonging to the branch Coelenterata.
General form and organization of body. The general
or typical plan of body-structure for the Coelenterata,
these animals which come next to the sponges in degree
of complexity, can best be understood by imagining the
typical cylindrical or vase-like body of the simple sponges
to be modified in the following way: The middle one of
the three layers of the body- wall not to be composed of
scattered cells in a gelatinous matrix, but to be simply a
thin non-cellular membrane; the body-wall not to be
pierced by fine openings or pores, but connected with the
outside only by the single large opening at the free end,
and this opening to be surrounded by a circlet of arm-like
processes or tentacles, which are continuations of the
body-wall and similarly composed. Such a body-struc-
ture, which we saw well shown by Hydra, is the funda-
mental one for all polyps, sea-anemones, corals, and
jellyfishes. The variety in shape of the body and the
superficial modifications of this type-plan are many and
striking, but after all the type-plan is recognizable through-
out the whole of this great group of animals.
C The two chief body-shapes represented in the branch
are those of the polyps on the one hand, and the jelly-
fishes or medusae oTT the other. The polyp-shape is that
of a tube with a basal end blirrS^or closed, attached to
some firm object in the water ana with the free end with
an opening, the mouth-opening. At this mouth-end
there is a circlet of movable, very contractile tentacles.
94 ELEMENTARY ZOOLOGY
The mouth may open directly into the interior of the
which interior may be called the digestive cavity
may lead into a simple short tube produced by t
vagination or bending in of the body-wall, which m
looked on as the simplest kind of oesophagus,
oesophageal tube opens into the body-cavity or dige^u\/e
cavity. This cavity may be incompletely divided by
longitudinal partitions which project from the sides in'.o
the cavity.
The jellyfish or medusoid body-form corresponds^ *,.
general to an umbrella or bell. Around the edge of this
umbrella are disposed numerous threads or tentacles
(corresponding to the circlet of tentacles in the polyp).
The mouth-opening is at the end of a longer or shorter
projection which hangs down from the middle of the
under side of the umbrella. The interior body-cavity or
digestive cavity extends out into the umbrella-shaped
part of the body, usually in the condition of canals radiat-
ing from the centre and a connecting canal running
around the margin of the umbrella.
Structure. Although the Ccelenterata show little in-
dication of the complex composition of the body out of
organs, as it exists^ among the higher animals, yet they
do show an nr|rnfcfokribLe- advance on the simple, almost
organless body of the sponges. This is chiefly shown by
the differentiation among the cells which compose the
body. In the polyps and jellyfishes some of the cells are
specialized to be nnrnjgfal'aKlp muscle-cells, some to be
\ nerve-cells and fibres, and so on. A very simple nervous
system consisting of small groups of nerve-cells connected
by nerve-fibres exists. Some very simple special sense-
organs may occur. The digestive system, although in
the simpler Coelenterates consisting merely of the cylin-
drical body-cavity enclosed by the body- wall and opening
by the single hole at the free end of the body, in some is
BRANCH CCELENTERATA : THE POLYPS, ETC. 95
complex and is composed of different parts. Those
iterates which are not fixed but lead an active, free-
zing life, viz., the jellyfishes or medusae, are the
highly organized.
ie tentacles which surround the mouth-opening and
U* j to grasp food and carry it into the mouth, and the
stinging or lasso threads with which these tentacles are
provided are special organs possessed by most of these
jials.
^ Skeleton. Like the sponges, some of the Ccelenterata
possess a hard skeleton. This skeleton is always com-
posed of calcium carbonate and is called coral. Those
polyps which form such a skeleton are called the corals.
Coral will be described in connection with the account of
the coral-polyps.
_yc Development and life-history. The polyps and jelly-
fishes reproduce both asexually and sexually. The
asexual mode is usually that of budding. On a polyp a
bud is formed by a hollow outgrowth of the body-wall.
The bud grows, an opening appears at its distal end, a
circlet of tentacles arises about this mouth-opening and a
new polyp individual is formed. This individual may
separate from the parent or it may remain attached to it.
By the development of numerous buds, and the remaining
attached of all of the individuals developing from these
buds, a colony of polyp individuals may be formed, plant-
like in appearance. The various polyp individuals of a
colony may differ somewhat among themselves, and these
differences are correlated with a division of labor. Thus
some of the individuals may devote themselves to getting
food for the colony, and these have mouth and tentacles.
Others may be devoted to the production of new indi-
viduals by budding or by producing germ-cells, and may
not have any mouth-opening or any food-grasping
tentacles.
96 ELEMENTARY ZOOLOGY
In case of many polyps all or some of the new indi-
viduals which arise by budding do not become polyps, but
develop into medusae or jellyfish, which separate from the
fixed polyp and swim off through the water. These
medusae or jellyfish produce sperm-cells and egg-cells.
The sperm-cells fertilize the egg-cells and a new indi-
vidual develops from each fertilized egg. This new indi-
vidual is at first an active free-swimming larva called a
planula, which does not resemble either a medusa or polyp.
After a while it settles down, becomes fixed and develops
into a polyp. Thus a polyp may produce a medusa or
jellyfish which, however, produces not a new jellyfish, but
a polyp. This is called an alter nation _gf generations .
and is not an uncommon phenomenon among the lower
animals, j It results from such an alternation of genera-
tions that a single species of animal may have two distinct
forms. This having two different forms is called diino}'-
pJiism. Sometimes, indeed, a species may appear in
more than two different forms ; such a condition is called
polymorphj^tn .
Not all medusae or jellyfish are produced by polyp indi-
viduals, nor do jellyfish always produce polyps and not
jellyfishes. There are some jellyfishes (we might call
them the true jellyfishes) which always have the jellyfish
form, producing new jellyfishes either by budding or by
eggs, and there are some polyps which always have the
true polyp form, producing new individuals, either by
budding or by eggs, always of polyp form and never of
jellyfish form. That is, some species of Ccelenterata
exist only in polyp form, some species exist only in jelly-
fish form, while some species (those having an alternation
of generations) exist in both polyp and jellyfish form, ]
these two forms appearing as alternate generations.
/ Classification. The branch Ccelenterata is divided f
^ four classes: (i) the Hydrozoa, including the fresh-
BRANCH CCELENTER/1T/I : THE POLYPS, ETC.
97
water polyps, numer-
ous marine polyps,
many small jellyfishes
and a few corals ; (2)
the Scyphozoa, includ-
ing most of the large
jellyfishes; (3) the Ac -
tinozoa, including the
sea-anemones and
most "of the stony
corals; (4) the Cte-
nophora, including
certain peculiar jelly-
fishes. -
The polyps, colonial
jellyfishes, etc. (Hy-
drozoa). To the class
Hydrozoa belongs the
Hydra already studied .
There are a few other
fresh-water polyps and
they all belong to this
class. The most in-
teresting members of
the class are the "co-
lonial jellyfishes,"
constituting the order
Siphonophora. These
FIG. 13. -The Portuguese M;m-of-War (Physalia sp.). (From specimen
98 ELEMENTARY ZOOLOGY
colonial je-llyfishes are floating or swimming colonies of
polypoid and medusoid individuals in which there is a
marked division of labor among the individuals, ac-
companied by marked differences in structural charac-
ter. The individuals are accordingly polymorphic,
that is, appear in various forms, although all belong
to the same species. Because these various individuals
forming a colony have given up very largely their
individuality, combining together and acting together like
the organs of a complex animal, they are usually not
called individuals, nor on the other hand organs, but
zooids, or animal-like structures. The beautiful " Portu-
guese man-of-war " (fig. 13) is one of these colonial jelly-
fishes. It appears as a delicate bladder-like float, brilliant
blue or orange in color, usually about six inches long,
and bearing on its upper surface which projects above the
water a raised parti-colored crest, and on its under surface
a tangle of various appendages, thread-like with grape-
like clusters of little bell- or pear-shaped bodies. Each
of these parts is a peculiarly modified polyp- or medusa-
zooid produced by budding from an original central zooid.
The Portuguese man-of-war is very common in tropical
oceans, and sometimes vast numbers swimming together
make the surface of the ocean look like a splendid flower-
garden.
Usually the central zooid in a Siphonophore to which
the other zooids are attached is not a bladder-like float,
but is an upright tube of greater or less length. In the
Siphonophore shown in figure 14, the compound body is
composed of a long central hollow stem with hundreds
or thousands of variously shaped parts, each of which is
reducible to either a polyp or medusazooid, attached
around it. The upper end is enlarged to form an air-
filled chamber, a sac-like boat, by means of which the
whole colony is kept afloat. Around the uprjer end of the
BRANCH CCELEKTERATA: THE POLYPS, ETC.
99
central stem are many medusoid structures, the swimming-
bells, by means of
whose opening and
closing the whole col-
ony is made to swim
through the water.
Each swimming - bell
is a modified medusa-
zooid, without tenta-
cles, without digestive
or reproductive or-
gans, but exercising
the power of swim-
ming by contracting
and forcing the water
out of the hollow bell
just as is done by
the free medusae. Be-
low the swimming-
bells, at the lower end
of the central stem,
are grouped many
structures presenting
at first sight a confu-
sion of variety and
complexity, but on
careful examination
revealing themselves
to be polyp- and me-
dusa-zooids modified
to form at least five
kinds of particularly .
FTG. 14. A colonial jelly fish (Siphonophora).
functioning Struc- (After Haeckel.)
tures. There are many flattened scale-like parts whose
function is simply that of affording a passive protection,
ioo ELEMENTARY ZOOLOGY
in times of danger, to the other structures. These pro-
tecting-scales are greatly modified medusa-zooids, each
consisting of a simple cartilage-like gelatinous mass
penetrated by a food-carrying canal. Under the broad
leaves of these protecting-zooids are a number of pear-
shaped bodies which have a wide octagonal mouth-open-
ing at their free end, and possess in their interior certain
digestive glands. Each one is provided with a very long
flexible tentacle which bears many fine stinging-threads.
The tentacle waves back and forth in the water, and
on coming in contact with an enemy or with prey its
poisonous stinging-threads shoot out and paralyze or
wound the unfortunate animal. These pear-shaped bodies
are the feeding structures, each being a modified polyp-
zooid. Scattered among these dangerous structures are
many somewhat similarly shaped but wholly harmless
structures, the sense-structures. Each of these has a
pear-shaped body but without mouth-opening, and also
a long, very sensitive, tentacle-like process. The sense
of feeling is highly developed in these tentacles, and they
discover for the colony the presence of any strange body.
These sense-structures are modified polyp-zooids. Finally
there are two other kinds of structures, usually arranged
in groups like bunches of grapes, which are the repro-
ductive structures, male and female. They are modified
medusa-zooids grown together and without tentacles.
This whole colony, or this compound animal, floats or
swims about at the surface of the ocean, and performs all
of the necessary functions of life as a single animal com-
posed of organs might. Yet the Siphonophore is more
truly to be regarded as a community in which the hundreds
or thousands of animals, representing five or six kinds of
individuals, all of one species, are fastened together. Each
individual performs the particular duties devolving upon
its kind or class. Thus there are food-gathering indi-
BRANCH CCELENTERATA : THE POLYPS, ETC. ior
viduals, locomotor individuals, sense individuals, and
reproductive individuals. The modifications of the various
kinds of individuals are more extreme than in the case of
the various kinds of individuals composing a bee-com-
munity, for example, but the holding together or fusing
of all into one body or corporation is a condition which
makes this greater modification necessary and not un-
expected. And there is no difficulty in seeing that each
of these parts is really, structurally considered, a modified
polyp or medusa.
The large jellyfishes, etc. (Scyphozoa). To the class
Scyphozoa belong most of the common large jellyfishes.
FIG. 15. A jellyfish or medusa, Gonionema vertens, eating two small
fishes. (From specimen from Atlantic Coast.)
When one walks along the sea-beach soon after a storm
one may find many shapeless masses of a clear jelly-like
102 ELEMENTARY ZOOLOGY
substance scattered here and there on the sand. These
are the bodies or parts of bodies of jellyfishes which have
been cast up by the waves. Exposed to the sun and
wind the jelly-like mass soon dries or evaporates away to
a small shrivelled mass. The body-substance of a jelly-
fish contains a very large proportion of water; in fact
there is hardly more than I per cent of solid matter in it.
The jellyfishes occur in great numbers 6n the surface of
the ocean and are familiar to sailors under the name of
"sea-bulbs." Some live in the deeper waters; a few
specimens have been dredged up from depths of a mile
below the surface. They range in size from " umbrellas "
or disks a few millimeters in diameter to disks of a
diameter of two meters (2\ yards). 'They are all car-
nivorous, preying on other small ocean animals which
they catch by means of their tentacles provided with
stinging-threads. The tentacles of some of the largest
jellyfishes "reach the astonishing length of 40 meters, or
about 130 feet." Many of the jellyfishes are beautifully
colored, although all are nearly transparent. Almost all
of them are phosphorescent, and when irritated some
emit a very strong light.
The sea-anemones and corals (Actinozoa). Almost
everywhere along the seashore where there are rocks and
tide-pools a host of various kinds of sea-anemones can be
found. When the tide is out, exposing the dripping sea-
weed-covered rocks, and the little sand- or stone-floored
basins are left filled with clear sea-water, the brown and
green and purple "sea-flowers " may be found fixed to
the rocks by the base with the mouth-opening and circlet
of slowly-moving tentacles hungrily ready for food
(fig. 1 6). Touch the fringe of tentacles with your finger-
tip and feel how they cling to it and see how they close in
so as to carry what they feel into the mouth-opening. A
host of individuals there are, and scores of different kinds;
BRANCH CCELEHTERATA : THE POLYPS, ETC. 103
some small, some large, some with the body covered out-
side with tiny bits of stone and shell so that they are
hardly to be distinguished from the rock to which they
FIG. 16. Sea anemones, Bunodes californica, open and .closed individuals.
The closed- individuals in upper right-hand corner show the external
covering of small bits of rock and shell, characteristic of most individu-
als of this species. (From living specimens in a tide-pool on the Bay
of Monterey, California.)
cling; some of bright and showy colors. These are the
most familiar members of the class Actinozoa.
But in other oceans, along the coasts of other lands,
especially those of the tropics and sub-tropics, there are
104 ELEMENTARY ZOOLOGY
some other members of the class which are of unusual
interest. They are the corals, or coral polyps. We
know these animals chiefly by their skeletons (fig. 17).
The specimens of corals which one sees in collections, or
made into ornaments, are the calcareous skeletons of
various kinds of the coral polyps. Some of the corals
live together in enormous numbers, forming branching
colonies fixed as closely together as possible, and secrete
while living a stony skeleton of carbonate of lime. These
skeletons persist after the death of the animals, and
\)f cause of their abundance and close massing form great
reefs or banks and islands. These coral reefs and islands
occur only in the warmer oceans. In the Atlantic they
are found along the coasts of Southern Florida, Brazil
and the West Indies ; in the Pacific and Indian Oceans
there are great coral reefs on the coast of Australia^
Madagascar and elsewhere, and certain large groups of in-
habited islands like the Fiji, Society, and Friendly Islands
are exclusively of coral formation. Coral islands have a
great variety of form, although the elongated, circular,
ring-shaped and crescent forms predominate. How such
islands are first formed is described as follows by a well-
known student of corals:
"A growing coral plantation, with its multitudinous
life, oftentimes arises from great depths of the ocean, and
the sea-bed upon which it rests is probably a submarine
bank or mountain, upon which have lodged and slowly
aggregated the hard skeletons of pelagic forms of life.
W T hen, through various sources of increase, this submarine
bank approaches the depth of from one hundred to one
hundred and fifty feet from the surface of the water, there
begins on its top a most wonderful vital activity. It is
then within the bathymetric zone of the reef-building
corals. Of the many groups of marine life which tnen
'cake possession of the bank, corals are not the only
BRANCH CCELEUTERATA : THE POLYPS, ETC. 105
animals, but they are the most important, as far as its
subsequent history goes. As the bank slowly rises by
their growth, it at last approaches the surface of the
water, and at low tide the tips of the growing branches
of coral are exposed to the air. This, however, only
takes place in sheltered localities, for long before it has
reached this elevation it has begun to be more or less
FIG. 17. Skeleton of a branching coral, Madrepora cervicornis. (From
specimen.)
changed and broken by the force of the waves. As the
submarine bank approaches the tide level, the delicate
branching forms have to meet a terrific wave-action.
Fragments of the branching corals are broken off from
the bank by force of the waves, and falling down into the
midst of the growing coral below fill up the interstices,
io6 ELEMENTARY ZOOLOGY
and thus render the whole mass more compact. At the
same time larger fragments are broken and rolled about
by the waves and are eventually washed up into banks
upon the coral plantation, so that the island now appears
slightly elevated above the tides. This may be called a
first stage in the development of a coral island. It is,
however, little more than a low ridge of worn fragments
of coral washed by the high tides and swept by the larger
waves a low, narrow island resting on a large submarine
bank."
When the coral island rises thus a little above the sur-
face of the water, the waves break up some of the coral
into fine sand, which fills in the interstices, and offers a
sort of soil in which may germinate seeds brought in the
dried mud on the feet of ocean birds or carried by the
ocean currents. With the beginning of vegetable growth
the soil is more firmly held, is fertilized and ready for the
seeds of plants which need a better soil than lime sand.
Flying insects find their way to the island, especially if
it be near the mainland, birds begin to nest on it, and
soon it may be the seat of a luxuriant plant and animal
life.
For an account of coral islands see Darwin's "The
Structure and Distribution of Coral Reefs."
I There are over 2000 kinds of coral polyp known, and
/ their skeletons vary much in appearance. Because of the
appearance of the skeleton certain corals have received
common names, as the organ-pipe coral, brain coral, etc.
The red coral, of which jewelry is made, grows chiefly in
the Mediterranean. It is gathered especially on the
western coast of Italy, and on the coasts of Sicily and
Sardinia. Most of this coral is sent to Naples, where it is
cut into ornaments.
There are other interesting members of the class
f Actinozoa like the beautiful sea-pens, sea-feathers and
BRANCH CCELENTERATA : THE POLYPS, ETC. 107
sea-fans, delicate, branching, tree-like forms found all
over the world.
J Ctenophora. The members of this class are mostly
small, peculiar jellyfishes which do not form colonies, and
are extremely delicate, being usually perfectly trans-
parent. They swim by means of cilia. They never
appear in a polyp condition, but are always medusoid in
shape.
CHAPTER XVIII
BRANCH ECHINODERMATA : STARFISHES,
SEA-URCHINS, SEA-CUCUMBERS
STARFISH (Asterias sp.)
TECHNICAL NOTE. The species of Asterias are widely dis-
tributed on both coasts of the United States and may be procured
on almost any rocky shore at low tide. Teachers in inland schools
can obtain preserved material from the dealers mentioned on p.
453. Most of the specimens should be placed in alcohol or 4$
formalin. If fresh material can be had it is well to place at least .
one specimen for each student in a 20% solution of nitric acid in
water for two or three hours, when all of the calcareous parts will
have been dissolved, and after a thorough washing the specimen
will be ready for use.
External structure (figs. 18 and 19.) In a fresh
specimen or one which has been preserved in alcohol or
formalin note the raying out of parts of the body from a
common centre. This is characteristic of the body or-
ganization of all Echinoderms, and is known as radial
symmetry. The lower surface of the body is called the
oral (because the mouth is on this surface), while the
upper is called the aboral surface. The central part of
the body is called the disk. Note on the aboral surface
of the disk a small striated calcareous plate, the madre-
porite or madrcporic plate. In the middle (or very
nearly in the middle) of this surface of the disk there is
a small pore, the anal opening. The entire aboral sur-
face as well as a greater part of the oral side is thickly
studded with the calcareous ossicles of the body-wall.
These ossicles support numerous short stout spines ar-
ranged in irregular rows. Note that some of the ossicles
108
BRANCH ECH1NODERMATA : STARFISHES, ETC. 109
support certain very small pincer-like processes, the pedi-
cellarice. In the interspaces between the calcareous plates
are soft fringe-like projections of the inner body-lining, the
-eye spot
''cardiac stomach
r^V^" " - intestinal caecu.
pyloric caecuik
' muscles of tht pyloric caeca
eye spot--'
FIG. 18. Dissection of a starfish (Asterias sp.).
respiratory cceca. Note at the tip of each arm or ray a
cluster of small calcareous ossicles and within each cluster
a small speck of red pigment, the eye-spot or ocellus.
no ELEMENTARY ZOOLOGY
Make a drawing of the aboral surface showing all these
parts.
On the oral surface note the centrally-located mouth,
the ambulacral groove 's, one running longitudinally along
each ray, and in each groove two double rows of soft
tubular bodies with sucker-like tips. These are called
the tube-feet and are organs of locomotion. Make a
drawing of the oral surface.
Internal structure (figs. 18 and 19). TECHNICAL NOTE.
Take a specimen which has been immersed for some time in the nitric
acid solution, and with a strong pair of scissors, or better, bone-
cutters, cut away all the aboral wall of the disk except that immedi-
ately around the madreporite and the anus. Now begin at the tip
of each ray and cut away the aboral wall of each, leaving, however,
a single arm intact. When the roof of each arm has been carefully
dissected away the specimen should appear as in fig. 18.
Note the large alimentary canal, which is divided into
several regions. Note the short cesophagus leading from
the mouth on the oral surface directly into a large mem-
branous pouch, the cardiac portion of the stomach. By
a short constriction the cardiac portion is separated from
the part which lies just above, i.e., the pyloric portion of
the stomach. From the pyloric portion large, pointed,
paired glandular appendages extend into each ray.
These are the pyloric cceca. Their function is digestive,
and oftentimes they are spoken of as the digestive glands
or "livers." The pyloric caeca, as well as the cardiac
portion of the stomach, are held in place by paired muscles
which extend into each arm. Note two sets of these
muscles, one set for thrusting the cardiac portion of the
stomach out through the mouth and another for pulling it
back, the protractor muscles and retractor muscks,
respectively. The starfish obtains its food by enclosing
it in its everted stomach and then withdrawing stomach
and food into the body. Note that the pyloric portion of
the stomach opens aoove into a short intestine terminating
BRANCH ECHINODERMATA : STARFISHES, ETC. in
in the anus, and observe that there is attached to the in-
testine a convoluted many-branched tube, the intestinal
ccecum.
Carefully remove a pair of pyloric caeca from one of the
rays and note the short duct which connects them with
the pyloric chamber of the stomach. Note in the angle
of each two adjoining rays paired glandular masses which
empty by a common duct on the aboral surface. These
glands are the reproductive organs. Note the small bulb-
like bladders extending in two double rows on the floor
of each ray. These are the water-sacs or ampulla, and
each one is connected directly with one of the locomotor
organs, the tube-feet.
Make a drawing of the organs in the dissection which
have so far been studied.
TECHNICAL NOTE. For a careful study of the locomotor organs
a fresh starfish should be injected. This can usually be accom-
plished by cutting one ray off squarely, and inserting the needle of
a hypodermic syringe (which has been previously filled with a
watery solution of carmine or Berlin blue), into the end of the
radial water-tube which runs along the floor of the ray. By
injecting here, the whole system of vessels, tube-feet, and ampullae
are filled.
Note a ring-shaped canal which passes around the
alimentary canal near the mouth from which radial vessels
run out beneath the floor of each ray and from which a
hard tube extends to the madreporite. This hard tube is
the stone canal, so called because its walls contain a series
of calcareous rings, while the circular tube is the ring
canal or circum-oral water-ring from which radiate the
radial canals. In some species of starfish there are
bladder-like reservoirs, Polian vesicles, which extend
interradially from the ring canal.
Note that the ampullae and tube-feet are all connected
with the radial canals. By a contraction of the delicate
112
ELEMENTARY ZOOLOGY
muscles in the walls of the ampullae the fluid in the cavity
is compressed, thereby forcing the tube-feet out. By the
contraction of muscles in the tube-feet they are again
shortened while the small disk-like terminal sucker clings
to some firm object. In this way the animal pulls itself
calcareous spine respiratory caeca
epithelium of the body
cavity ^
mesentery-
pyloric caecumr-
lacral ossicle
ectodermal covering*
-ossicles
ampulla
pedicellaria U / / ^tube fool
.radial ''canal /
radial blood-vessel
KIG. 19. Semi-diagrammatic figure of cross-section of the ray of a starfish,
Asterias sp.
along by successive " steps." This entire system, called
the water-vascular system, is characteristic of the branch
Echinodermata. In addition to the fluid in the water-
vascular system there is yet another body-fluid, the peri-
visceral fluid, which bathes all of the tissues and fills the
body-cavity.
TECHNICAL NOTE. Take a drop of the perivisceral fluid from a
living starfish and examine under high power of microscope, noting
the amoeboid cells it contains.
The perivisceral fluid is aerated through outpocketings
oi the thin body-wall which extend outward between the
calcareous plates of the body. These outpocketings have
'BRANCH ECHINODERMATA : STARFISHES, ETC. 113
already been mentioned as the respiratory caeca (see
p. 109). Surrounding the stone canal is a thin mem-
branous tube, and within it and by the side of the stone
canal is a soft tubular sac. The function of these organs
is not certainly known.
Work out the nervous system; note, as its principal
parts, a nerve-ring about the mouth, and nerves running
from this -ring beneath the radial canals along each arm.
Life-history and habits. The starfishes are all marine
forms. They hatch from eggs, and in their early stages
are very different in appearance from the adults. At first
they are bilaterally symmetrical, their radial symmetry
being acquired later. Thousands of eggs and sperm-cells
are extruded into the sea-water, where fertilization and
development take place. The young swim freely in the
open sea, feeding on microscopic organisms, and then
undergo very radical changes in the course of their
development. The adults are for the most part carniv-
orous, feeding on crabs, snails, and the like. The live
prey is surrounded by the extruded stomach which secretes
fluids that kill it, after which the soft parts are digested.
(See general account of the life-history of Echinoderms
on p. 1 19.)
THE SEA-URCHIN (Strongylocentrotiis sp.)
External Structure. TECHNICAL NOTE. If fresh or alco-
holic specimens or even the dry "tests" of the sea-urchin (fig. 20)
are to be had, the general characteristics of the external structure
can be made out.
How does the external surface of the sea-urchin differ
from that of the starfish ? Can you find the very long
tube-feet ? Where is the mouth-opening ? With what is
it surrounded ? Each tooth is enclosed in a calcareous
framework. The whole structure is known as " Aristotle's
lantern. ' '
n 4 ELEMENTARY ZOOLOGY
TECHNICAL NOTE. Remove the spines from the underlying
shell or test (fig. 21) and wash the test until perfectly clean, or place
in a solution of lye for a short time and then wash.
Note, the characteristic radial symmetry of the shell or
test. Note on the aboral aspect, diverging from the
medial anal aperture, five double rows of pores. What
are these for ? Each of the five divisions set with pores
FIG. 20. A sea-urchin, Strongylocentrotus franciscanns. (From specimen
from Bay of Monterey, Calif. )
is called an ambulacral area, while the intervening seg-
ments which support the long spines are called the
inter ambulacral areas. Note on the aboral surface, sur-
rounding the median-placed anal aperture, a series of
small plates. Those which are located in the interambu- ]
lacral areas are the genital plates. Through these plates
the ducts from the reproductive organs open by small
pores. Note a very much enlarged plate with a striated j
appearance. This is the madreporite, which, as in the j
starfish, is the external opening of the stone canal and!
water-vascular system. Note the small ocular plate at |
the tip of each ambulacral area. The ocular plates con-]
BRANCH ECHINODERMATA : STARFISHES, ETC. 115
tain small pigment-cells and communicate with the
nervous system.
From a general inspection of the sea-urchin's shell the
Echinoderm characteristics, namely, radial symmetry and
the presence of the water-vascular system, are readily
seen. While at first glance there is apparent little
similarity between the starfish and sea- urchin, neverthe-
less careful examination shows that the two animals are
FIG. 2i. "Test" of Sea-urchin, Strongylocentrotus franciscanus, with
spines removed. (From specimen.)
alike in their fundamental structure. Both are radially
symmetrical. The position of the anal opening makes
both starfish and sea-urchin slightly asymmetrical. In
both the madreporite and anus are on the aboral side,
while the mouth is centrally located on the oral side!
In the starfish we noted five ambulacral areas, one on the
under side of each arm ; similarly we find five in the sea-
urchin. In both cases also we find the ocular spots at
the tips of the ambulacral areas. The genital apertures
are situated interradially in the starfish. In the sea-
urchin they are similarly placed. The dissimilarity
between the two forms is largely due to the very much
developed outer spines and the dorso-ventral thickening
of the disk in the sea-urchin. The starfish is carnivorous,
while the sea-urchin lives on vegetable matter consisting
n6 ELEMENTARY ZOOLOGY
for the most part of green algae and the red sea-weeds.
Correlated with this difference in food-habits there are
certain differences in the structure of the internal organs.
For example, the alimentary canal in the sea-urchin winds
in about two and one-half turns within the body-cavity
before it reaches the anus.
OTHER STARFISHES, SEA-URCHINS, SEA-CUCUMBERS,
ETC.
Without exception all the Echinoderms, under which
term are included the starfishes, sea-urchins, brittle-stars,
feather-stars, and sea-cucumbers, live in the ocean. Some
of them, the starfishes and sea-urchins, are among the
most common and familiar animals of the seashore. Most
of them are not fixed, but can move about freely, though
slowly. Some of the feather-stars are fixed, as the
sponges and polyps are.
Shape and organization of body. The body-shape of
the Echinoderm varies from the flat, rayed body of the
starfish to the thick, flattened egg-shape of the sea-urchin,
the melon-like sac of the sea-cucumber and the delicate
many-branched head of the sea-lily sometimes borne on
a slender stalk* But in all these shapes can be seen more
or less plainly a symmetrical, radiate arrangement of the
parts of the body. The Echinoderm body has a central
portion from which radiate separate arm or branch-like
parts, as in the starfishes and sea-lilies, or about which
are arranged radiately the internal body-parts, although
the external appearance may at first sight give no plain
indication of the radiate arrangement. This is the case
with the sea-urchins and sea-cucumbers, yet, as has been
seen in the sea-urchin, the radiate arrangement can be
readily perceived by closer exanrnation of the surface of
the egg- or sac-like body. The radiating parts of the
BRANCH ECHINODERMATA : STARFISHES, ETC. 117
body are usually five. In the body of an Echinoderm
can be usually recognized an upper or dorsal surface and
a lower or ventral surface. The mouth is usually situated
on the ventral side and the anal opening on the dorsal.
Echinoderms agree also in having a calcareous outer
skeleton or body-wall usually in the condition of definitely-
shaped plates or spicules fitted either movably or rigidly
together. This outer body-wall or exoskeleton may bear
many tubercles or spines. These spines are sometimes
movable. The body-wall of the sea-urchin shows very
well the exoskeleton composed of plates on which are
borne movable strong spines.
Structure and organs. As has been learned from the
dissection of the starfish, the Echinoderms have well-
developed systems of organs. The body-structure in its
complex organization presents a marked advance beyond
the structural condition of the polyps and jellyfishes.
There is a well-organized digestive system with mouth,
alimentary canal, and anal opening. The alimentary
canal is either a simple spiral or coiled tube, or it is a tube
in which can be recognized different parts, namely,
oesophagus, stomach, intestine, caeca, and special glands
secreting digestive fluids. This alimentary canal is not,
as in the polyps, simply the body-cavity, but it is an in-
closed tubular cavity lying within the general body-cavity.
At the mouth-opening there is in some Echinoderms,
notably the sea-urchins, a strong masticating apparatus
consisting of five pointed teeth which are arranged in a
circle about the opening. ["The nervous system consists
of a central ring around the oesophagus or mouth, from
which branches extend into the radiately arranged arms
or regions of the body. There is no brain as in the
higher animals, but the central nerve-ring is composed of
both nerve-cells and nerve-fibres as in the nerve-centres
of higher forms. Of organs of special sense there are
n8 ELEMENTARY ZOOLOGY
special tactile or touch organs in all the Echinoderms,
and the starfishes have very simply composed eyes or
eye-like organs at the tips of the rays.
While some of the Echinoderms breathe simply through
the outer body-wall, taking up by osmosis the air mixed
with the water, some of them have special, though very
simple, gill-like respiratory organs. These organs con-
sist of small membranous sacs which are either pushed
out from the body into the water, or lie in cavities in the
body to which the water has access. There is also a dis-
tinct circulatory system, but the " blood" which is
carried by these organs and which fills the body-cavity
consists mainly of sea-water, although containing a
number of amoeboid corpuscles containing a brown pig-
ment. There is no organ really corresponding to the
heart of the higher animals. There are distinct organs
for the production of the germ or reproductive cells. The
sexes are distinct (except in a few species), each individual
producing only sperm-cells or egg-cells, but the organs
or glands which produce the germ-cells are very much
alike in both sexes. There is no apparent difference
between male and female Eehinoderms except in the
character or rather in the product of the germ-cell pro-
ducing organs. A few species are exceptions, certain
starfishes showing a difference in color between males and
females.
As all of the Echinoderms except some of the feather-
stars can move about, they have organs of locomotion,
and well-defined muscles for the movement of the loco-
motory organs. The external organs of locomotion, the
tube-feet (in the sea-urchins the dermal spines aid also in
locomotion), are parts of a peculiar system of organs
characteristic of the Echinoderms, called the ambulacral
or the water-vascular system. This system is composed
of a series of radial tubular vessels which rise from a cen-
BRANCH ECH1NODERMATA : STARFISHES, ETC. 119
tral circular or ring vessel and which give off branches to
each of the tube-feet. The water from the outside enters
the ambulacral system through a special opening, the
madreporic opening, and flowing to the tube-feet helps
extend them. The tube-feet usually have a tiny sucking
disk at the tip, and by means of them the Echinoderm
can cling very firmly to rocks.
Development and life-history. Differing from the
sponges and the polyps and jellyfishes, the reproduction
of the Echinoderms is always sexual ; young or new indi-
viduals are never produced by budding, or in any other
asexual way. The new individual is always developed
from an egg produced by a female and fertilized by the
sperm of a male. The eggs are usually red or yellow,
are very small (about ^ in. in diameter in certain
starfishes), and are fertilized by the sperm-cells of the
males after leaving the body of the female. That is, both
sperm-cells and unfertilized egg-cells are poured out into
the water by the adults, and the motile sperm-cells in
some way find and fertilize the egg-cells.
From the egg there hatches a tiny larva which does
not at all resemble the parent starfish or sea-urchin. It
is an active free-swimming creature, more or less ellip-
soidal in shape and provided with cilia for swimming.
Soon its body changes form and assumes a very curious
shape with prominent projections. The larvae of the
various kinds of Echinoderms, as the starfishes, sea-
urchins, sea-cucumbers, etc., are of different characteristic
shapes. The naturalists who first discovered these odd
little animals did not associate them in their minds with
the very differently shaped starfishes and sea-urchins, but
believed them new kinds of fully developed marine
animals, and gave them names. Thus the larvae of the
starfishes were called Bipinnaria, the larvae of the sea-
urchins Pluteus, and so on. These names are still used
120 ELEMENTARY ZOOLOGY
to designate the larvae, but with the knowledge that
Bipinnaria are simply young starfishes, and that a Pluteus
is simply a young sea-urchin. From these larval stages
the adult or fully developed starfish or sea-urchin develops
by very great changes or metamorphoses. The Echino-
derms have in their life-history a metamorphosis as strik-
ing as the butterflies and moths, which are crawling
worm-like caterpillars in their young or larval condition.
Most of the Echinoderms have the power of regenerat-
ing lost parts. That is, if a starfish loses an arm (ray)
through accident, a new ray will grow out to replace the
old. And this power of regeneration extends so far in
the case of some starfishes that if very badly mutilated
they can practically regenerate the whole body. This
amounts to a kind of asexual reproduction. Some-
species, too, have the peculiar habit of self-mutilation.
1 * Many brittle stars and some starfishes when removed
from the water, or when molested in dfny way, break off
portions of their arms piece by piece, until, it may be,
the whole of them are thrown off to the very bases,
leaving the central disc entirely bereft of arms. A central
disc thus partly or completely deprived of its arms is
capable in many cases of developing a new set; and a
separated arm is capable in many cases of developing a
new disc and a completed series of arms." In some of
the sea-cucumbers "it is the internal organs, or rather
portions of them, that are capable of being thrown off and
replaced, the oesophagus ... or the entire alimentary
canal, being ejected from the body by strong contrac-
tions of the muscular fibres of the body-wall, and in
some cases, at least, afterwards becoming completely
renewed. "
Classification. The Echinodermata are divided into
five classes, viz., the Asteroidea or starfishes, "free
Echinoderms with star-shaped or pentagonal body, in
BRANCH ECHINODERMATA : STARFISHES, ETC. 1 21
which a central disc and usually five arms are more or
less readily distinguishable, the arms being hollow and
each containing a prolongation of the body-cavity and
contained organs"; the OgJiLurojdea, or brittle-stars,
"star-shaped free Echinoderms, with a central disc and
five arms, which are more sharply marked off from the
disc than in the Asteroidea and which contain no spacious
prolongations of the body-cavity ' ' ; the Echinoidea, or
sea-urchins, ' ' free Echinoderms with globular, heart-
shaped, or disc-shaped body enclosed in a shell or corona
of close-fitting, firmly united calcareous plates"; the
Holuthuroidea, or sea-cucumbers, "free Kchinoderms
with elongated cylindrical or five-sided body, . . . with a
circlet of large oral tentacles "; and the Crinoic]ea, or
feather-stars, * ' temporarily or permanently stalked Echi-
noderms with star-shaped body, consisting of a central disc,
and a series of five bifurcate or more completely branched
arms, bordered with pinnules."
Starfishes (Asteroidea). The starfishes feed on other
marine animals, especially shell-fish and crabs. They
are also reputed to destroy young fish. By means of their
sucking-tubes, or tube-feet with sucker tips, they can
seize and hold their prey firmly. They do much injury
to oyster-beds by attacking and devouring the oysters.
When attacking prey too large to be taken into the mouth
the starfish everts its stomach over the prey and devours
it. The stomach is afterward drawn back into the body-
cavity by special muscles.
Starfishes vary much in size, color and general appear-
ance, although all are readily recognizable as starfishes
(fig. 22). The number of arms or rays varies from five
to thirty or more in different species; some have the
interradial spaces filled out nearly to the tips of the rays,
making the animal simply a pentagonal disc. In size
starfishes vary from a fraction of an inch in diameter to
122
ELEMENTARY ZOOLOGY
three feet; in color they are yellow or red or brown or
purple.
Brittle-stars (Ophiuroidea) . The brittle-stars, or ser-
>.\>'ttJ&>
*&&$
" : ^r5-^ r >
pent-stars (fig. 22) as
they are also called,
resemble the starfishes
in external appearance,
that is, they are flat and
FIG. 22. A group of Echinoderms; the composed of a Central
upper one. a starfish, Asterina mineata , . , ,.
the one at -the right a starfish, Asterias dlSC Wltn radiating arms
ocracia, at the left a brittle-star, spe-
(always five in number,
although each arm
, -
cies unknown, and at bottom two sea-
urch ins, Strongylocentrotn*. franciscanus.
(From living specimens in a tide-pool on
the Bay of Monterey, California.)
branched). The central
disc is always sharply distinguished from the arms, and
the arms are usually slender and more or less cylin-
BRANCH ECHINODERMATA : STARFISHES, ETC. 123
drical. The distinguishing difference between the brittle-
stars and the starfishes is that the body-cavity and the
stomach which extend out into the arms in the star-
fishes are in the brittle-stars limited to the central disc, or
to the disc and bases of the arms. The tube-feet also
have no suckers at the tips. More than 700 species of
brittle-stars are known. They feed on marirjfe shell-fish,
crabs and worms. /'
Sea-urchins (Echinoidea). The sea-urchins (figs. 20, 2 1
and 22) of which more than 300 species are known, have
no arms or rays, and they are usually not flat like the star-
fishes but globular, with poles more or less flattened. As
has been noted in the examination of the body-wall or
* ' shell, ' ' the radiate character of the body is shown by the
five radiating zones of tube-feet. The mouth, with its five
strong "teeth," is on the ventral surface, and the anal
opening and madreporic opening are on the dorsal sur-
face. The calcareous plates (seen distinctly in a specimen
from which the spines have been removed) which consti-
tute the firm part of the body- wall, are more or less
pentagonal in shape and are usually firmly united at the
edges. The spines which are so characteristic of the
sea-urchins vary much in size and number and firmness,
but are present in some form on all of them.
\Yhile most of the sea-urchins live near the shore,
being very common in tide-pools, some live only on the
bottom of the ocean at great depths. Their food consists
of small marine animals and of bits of organic matter
which they collect from the sand and debris of the ocean
floor. Many of the sea-urchins are gregarious, living
together in great numbers. Some have the habit of
boring into the rocks of the shore between tide-lines. I
have seen thousands of small beautifully colored purple
sea-urchins lying each in a spherical pit or hole in hard
conglomerate rock on the California coast. How they
124 ELEMENTARY ZOOLOGY
are enabled to bore these holes is not yet known.
There is great variety in size and color among the sea-
urchins. The colors are brown, olive, purple red, greenish
blue, etc.
A few kinds of sea-urchins have a flexible shell or test.
The Challenger expedition dredged up from sea-bottom
some sea-urchins, and when placed on the ship's deck
<4 the test moved and shrank from touch when handled,
and felt like a starfish. ' ' The cake-urchins or sand-
dollars are sea-urchins having a very flat body with short
spines. They lie buried in the sand, and are often very
brightly colored. Their hollow bleached tests with the
spines all rubbed off are common on the sands of both
the Atlantic and Pacific coasts.
Sea-cucumbers (Holothuroidea). The sea-cucumbers
(fig. 23) show at first glance little resemblance to the
other radiate animals. The body is an elongate, sub-
cylindrical sac, resembling a thick worm or sausage or
cucumber in shape. At one end it bears a group of
branched tentacles which are set in a ring around the
mouth-opening. The body-wall is muscular and leathery,
but contains many small separated calcareous spicules.
There are usually five longitudinal rows of tube-feet. In
some species, however, tube feet are wholly wanting; in
others they are scattered over the surface.
Although there are known about five hundred species
of sea-cucumber's many of which live along the shores,
they are much less familiar to us than the starfishes and
sea-urchins. They usually rest buried in the sand by day,
feeding at night. Some of them attain a large size. A
great orange-red species of the genus Cuciimaria, which
is found in the Bay of Monterey, California, is three feet
long.
The people of some nations use sea-cucumbers as food.
They are called " trepang " in the orient. The trade of
BRANCH ECHINODERMA TA : S TARFISHES, ETC. 125
preparing the trepang is almost entirely in the hands of
the Malays, and every year large fleets set sail from
FIG. 23. A sea-cucumber, Pentacta frondosa. (After Emerton.)
Macassar and the Philippines to the south seas to catch
sea-cucumbers.
Feather-stars (Crinoidea) . The feather-stars or sea-
lilies or crinoids (fig. 24), as they are variously called, differ
from the other Echinoderms in having the mouth on the
upper side of the central disc, and in the fact that all of
the species are fixed, either permanently or for a part of
their life, being attached to rocks on the sea-bottom by
a longer or shorter stalk which is composed of a series of
rings or segments. The central disc is small and the
126
ELEMENTARY ZOOLOGY
radiating arms are long, slender, sometimes repeatedly
branched, and all the branches bear fine lateral projec-
tions called pinnulae. Most of the feather-stars live in
deep water and are thus only seen after being dredged
up. They feed on small crab-like animals, and on the
marine unicellular animals and plants.
FIG. 24. A crinoid or feather-star, Pentacrinus sp. (After Brehm.)
CHAPTER XIX
BRANCH VERMES:* THE WORMS
THE EARTHWORM (Lumbricus sp.).
TECHNICAL NOTE. Obtain live earthworms of large size, killing
some in 30^ alcohol and hardening and preserving them in 8o# alco-
hol, and bringing others alive to the laboratory. The worms may
be found during the daytime by digging, or at night by searching
with a lantern. They often come above ground in the daytime
after a heavy rain. Live specimens may be kept in the laboratory
in flower-pots filled with soil. " They may be fed on bits of raw
meat, preferably fat, bits of onion, celery, cabbage, etc., thrown on
the soil."
External structure (fig. 25). Examine the external
structure of live and dead specimens. Which is the ventral
and which the dorsal surface ? Which the anterior and
which the posterior end ? Note the segmented condition
of the body; the number of segments or somites, and their
relative size and shape. Note absence of appendages such
as limbs and the presence of locomotor seta (short bristles).
How many setae are there on each segment and what is
their disposition ? The moutJi is covered by a dorsal
projection called the prostomium. The anal opening is
situated in the posterior segment of the body. The broad
thickened ring or girdle including several segments near
* The author recognizes the untenability of the group Vermes as a group
co-ordinate with the other branches of the animal kingdom, and that
"Vermes" has been discarded in modern text-books. But because of the
very scant consideration whic^i can he given the various kinds of worm like
animals the course of the older text-books will be followed, and all of the
worm-like animals, as far as referred to in ihis book, be considered under
the group name Vermes.
127
128
ELEMENTARY ZOOLOGY
retractor and protractor
muscles of the phq/ry
cesophageal pouches-
reproductive organs =
reproductive organs -
:erebral ganglion
pharynx
^esophagus
JT IG . 25. Dissection of the earthworm, Lumbricus sp.
BRANCH YERMES: THE IVOR MS 129
the anterior end of the body is the clitellum, agkrtidular
structure which secretes the cases in which the 'eggs are
laid. On the ventral surface of the fourteenth and
fifteenth segments (in most species) are two pairs of small
pores ; two other pairs of small openings (usually difficult
to find), one between segments 9 and 10, and one between
segments 10 and 11, are present. All these are the
external openings of the reproductive organs.
Make drawings showing the external structure of the
earthworm.
Examine a live specimen placed on moist paper or
wood. Note the characteristics of its locomotion, and
the movements of its body-parts. How do tfie setae aid
in locomotion ?
Internal structure (figs. 25, 26 and 28). TECHNICAL
NOTE. With a fine-pointed pair of scissors make a dorsal median
incision, not too deep, behind the clitellum and cut forward as far
as the first segment. Put the specimen into dissecting-dish, care-
fully pin back the edges of the cut and cover with clear water or,
better, 50^ alcohol.
Note the long body-cavity divided by the thin septa
which have been torn away for the most part by the
pinning process. Note the thin transparent covering of
the body, the cuticle. Just beneath this note a less trans-
parent layer, the epidermis, and underneath this a layer
of muscles. The muscular layer is made up of two
clearly recognizable sets, an outer circular layer and an
inner longitudinal layer the fibres of which are continuous
with the septa.
Note, as the most conspicuous internal organ, the long
alimentary canal, of which a number of distinct parts may
be recognized. Most anteriorly is a muscular pJiarynx,
which is followed by a narrow oesophagus, leading directly
into the thin-walled crop; next comes the muscular
130 ELEMENTARY ZOOLOGY
gizzard, and next the intestine wtyich opens externally in
the terminal segment through the anus. The anterior end
of the alimentary canal is more or less protrusible, while
the posterior portion is held more firmly in place by the
septa which act as mesenteries. Surrounding the narrow
oesophagus are the reproductive organs, three pairs of
large white bodies and two pairs of smaller sacs.
Note the dorsal blood-vessel lying along the dorsal
surface of the alimentary canal, from the anterior por-
tion of which arise several circumcesophageal rings or
"hearts." These hearts are contractile and serve to
keep the blood in motion tfirough the blood-ve-ssels (see
later). In the most anterior of the body segments note
the pear-shaped brain or cerebral ganglion.
TECHNICAL NOTE. Lilt carefully to right and left the repro-
ductive organs, thus exposing the oesophagus.
Note three pairs of bag-like structures projecting from
the oesophagus. The front pair is the oesopJiageal pouches;
the next two pairs are the oesopJiageal or calciferous
glands. They communicate with the alimentary canal,
and their secretion is a milky calcareous fluid.
Make a drawing that will show all the parts so far
studied.
TECHNICAL NOTE. Cut transversely through the alimentary
canal in the region of the clitellum and carefully dissect the anterior
portion of the canal away from the surrounding organs.
Note the dorsal fold of the intestine, typJilosole, ex-
tending into the lumen. This fold gives a greater surface
for digestion, and in it are a great many hepatic or special
digestive cells. The entire alimentary canal is lined with
epithelium. Observe just beneath the alimentary canal
the ventral blood-vessel, and still beneath this blood-
vessel the ventral nerve-cord. There is a slight swelling
on the nerve-cord in each segment of the body. These
BRANCH YERMES: THE WORMS I3 1
swellings are the ganglia. How many pairs of nerves
are given off from each ganglion ? Observe in each seg-
ment, posterior to the first three or four, the successive
Dorsal blood vessel
lyphlosole
intestine
nepkrostome
ventral nerve cord
FIG. 26. Dissection to show alimentary canal in section and nephridia
of earthworm.
pairs of convoluted tubes, the nephridia, or organs of
excretion. Each nephridium opens internally through a
ciliated funnel, the nepJirostome, within the body-cavity,
while it opens externally by a small excretory pore
between the setae on the ventral surface of the segment
behind that in which the nephridium chiefly lies. The
function of the nephridia is to carry off waste matter
from the fluid which fills the body-cavity.
Trace the ventral nerve-cord forward to its connection
with the cerebral ganglion. Note the threat nerve-ring
or circumccsophageal collar connecting the ventral cord
with the brain.
Make a drawing of the nervous system showing its
relation to other organs.
Life- history and habits. The earthworm lives in soft
moist soil which is rich in organic matter. Its food is
I 3 2
ELEMENTARY ZOOLOGY
taken into the mouth mixed with dirt and sand. As this
mixture passes through the long alimentary canal the
organic particles are taken up and digested. As we have
already seen, there are in each worm two sets of reproduc-
tive glands, namely, male and female organs. Each
earthworm produces both egg-cells and sperm-cells, but
nephridium dorsal blood vessel
\ hepatic cells I
\ \ I longitudinal muscle
\ \ /i Circular muscle fibres
' epidermis
V V ^ \ \^ ^^^cuiicle
', ! \ nerve* cor d\
lephndipore ! nephrostome \
* D
body cavily
typhlosole
ventral vessel
FIG. 28. Cross-section of earthworm.
the sperm-cells of one worm are not used to fertilize the
eggs of the individual producing them. When the eggs
are ready to be discharged from the bod)/, the clitellum
becomes very much swollen and its glands begin an active
secretion which hardens and forms a collar-like structure
about the body of the worm. As this collar moves
forward toward the anterior end of the body it collects the
eggs and also the sperm-cells previously received from
BRANCH VERMES: THE WORMS 133
another worm, and finally slips off the head end of the
animal. The entire structure with the contained eggs
and sperm-cells as it passes off from the body becomes
closed at both ends, thus forming a horny capsule which
lies in the earth until the young worms emerge. Only a
part of the eggs develop in each capsule, the rest being
used as food for the growing young. The young earth-
worms, though of very small size, are fully formed before
they leave the egg-capsule. Earthworms are more or less
gregarious, large numbers often being found together.
For an interesting account of the habits of earthworms
see Darwin's- " The Formation of Vegetable Mold."
OTHER WORMS.
The branch Vermes comprises so large a number of
kinds of animals presenting such great differences in struc-
ture and habit that it is impossible to give a brief state-
ment in general or summary terms of their external
body-characters, of the structural and functional condition
of their various organs and systems of organs, and of the
course of their development and life-history as has been
done for the preceding branches. Many zoologists,
indeed, do not include all the worms or worm-like animals
in one branch, but consider them to form several distinct
branches.
In certain very general characters all of the animals
which compose the branch Vermes do agree. All, or
/ nearly all, have an elongate body which is bilaterally
\ symmetrical, that is, which could be cut by a median
longitudinal cutting in two similar halves. In most of
J them also the body is composed of a number of successive
\ segments or somites which are more or less alike. This
kind of segmented or articulated body is also possessed by
13 J ELEMENTARY ZOOLOGY
the insects and crabs. Almost all of the worms have the
power of locomotion ; usually that of crawling. For
this crawling they do not have legs composed of separate
segments or joints as do the higher articulated animals,
FIG. 29. A group of marine worms; at the left a gephyrean, Dendrostomum
cronjhelmi, the upper right-hand one a nereid, Nereis sp., the lower
right-hand one, Polynoe brevisetosa. (From living specimens in a
tide-pool on the Bay of Monterey, California.)
the crabs and insects, but either have fleshy unjointed
legs, or various kinds of bristles or spines, or suckers, or
even no external organs of locomotion at all. As regards
their internal structure they have well-organized systems
of organs, which show great variety in character and
degree of complexity. The special sense-organs are
usually of simple character and low degree of functional
development. Reproduction occurs both sexually and
asexually; in some species the sexes are distinct, while
in others both sperm-cells and egg-cells are produced by
the same individual. Asexual reproduction is by budding
or by a kind of simple division or fission. The worms
live either in salt or fresh water, or in moist, muddy or
slimy places or as parasites in the bodies of other animals
or in plants. While most worms feed on animal sub-
BRANCH VERMES: THE WORMS 1 35
stance either living or dead, some feed on living or
decaying plant matter.
Classification. There is great lack of agreement
among zoologists in the matter of the classification of the
worms. Not only are the various groups which by some
are called classes held by others to be distinct branches,
co-ordinate in rank with the Echinodermata, Ccelenterata,
etc., but the limits of these groups are also constantly
called in question. It will require a great deal better
knowledge of the structure and life-history of these diverse
animals before the matter of their classification is satisfac-
torily settled. We shall consider briefly four of the
various groups (which we may consider as classes) which
include worms either specially familiar to us or of special
interest or importance. One or two examples of each
group (the groups being selected primarily because of the
examples) will be described in some detail. By this
means we may get an idea of the extremely diverse char-
acter of the animals which are included in the heteroge-
neous branch Vermes.
Earthworms and leeches (Oligochaetae) . The various
species of earthworms, an example of which has been
studied are found in all parts of the world; they occur in
Siberia and south to the Kerguelen Islands. They are
absent from desert or arid regions, and some can live
indifferently either in soil or in water. Some near allies
ot the earthworms are aquatic, living in fresh or brackish
water, some in salt water near the shore. In size earth-
worms vary from I mm. (fa in.) to 2 metres (2^ yds.) in
length. All show the distinct segmentation of the body
noticeable in the common earthworm already studied.
The leeches, some of which are familiar animals, are
closely related to the earthworms, although at first glance
the similarity in structure is not very noticeable.
I3 ELEMENTARY ZOOLOGY
TECHNICAL NOTE. Some common water-leeches, alive or pre-
served in alcohol, should be examined by the class. The animals
are not unfamiliar to boys who "go in swimming" in the small
streams of the country. The body of a leech should be examined
carefully, and drawings of it showing the external structural charac-
ters should be made.
The body of a leech is flattened dorso-ventrally, instead
of being cylindrical as in the earthworm, and tapers at
both ends. In the live animal the body can be greatly
elongated and narrowed or much shortened and broad-
ened. It is composed of many segments (not as many
as there are cross-lines however; each segment is trans-
versely annulated), and bears at each end on the ventral
surface a sucker, the one at the posterior end being the
larger. These suckers enable the leech to cling firmly
to other animals. The mouth is at the front end of the
body on the ventral surface and is provided with sharp
jaws. Leeches live mostly on the blood of other animals
which they suck from the body. The common leech
"fastens itself upon its victim by means of its suckers,
then cuts the skin, fastens its oral sucker over the wound
and pumps away until it has completely gorged itself with
blood, distending enormously its elastic body, when it
loosens its hold and drops off. ' ' Its biting and sucking
cause very little pain, and in olden days physicians used
the leeches when they wanted to " bleed " a person. A
common European species of leech much used for this
purpose is known as the "medicinal leech." All
leeches are hermaphroditic, that is, the sexes are not dis-
tinct, but each individual produces both sperm-cells and
egg-cells. Most of the leeches lay their eggs in small
packets or cocoons. This cocoon is dropped in soil on the
banks of a pond or stream so that the young may have a
moist but not too wet environment. The young issue
from the eggs in four or five weeks, but they grow very
BRANCH HERMES: THE WORMS 137'
slowly and it is several years before they attain their full
size. Leeches are long-lived animals, some being said
to live for twenty years.
Flat worms (Platyhelminthes). TECHNICAL NOTE.
Collect some live fresh-water planarians (see fig. 30), which are to be
found on the muddy bottom of most fresh-water ponds, and examine
them while alive in watch-glasses of water. Make drawings show-
ing the external appearance, and as much of the internal anatomy
as can be seen. The branching alimentary canal can be seen in
more or less detail, and with higher power of the microscope parts
of the nervous system can be seen also. Have also a tapeworm
preserved in alcohol or formalin to show the very flat and many-
segmented body.
The flatworms include a large number of forms which
vary much in shape and habits. They are all, however,
FIG. 30. A fresh water planarian, Planaria sp. (From a living specimen.)
characteristically flat; in some this condition is very
marked. Some are active free-living animals, as the
planarians (figs. 30 and 31), while many live as parasites
in the alimentary canal of other animals, as do the sheep-
fluke and the tapeworms.
The fresh- water planarians (fig. 30), which live com-
monly in the mud of the bottom of ponds, are small,
being less than half an inch long. They are very thin
and rather broad, tapering from in front backwards. On
the upper surface near the front they have a pair of eyes ;
the noouth is on the under surface a little behind the
middle of the body. The alimentary canal is composed
of three main branches, each with numerous small side
branches. One main branch runs forward from the
mouth, and the other two run backwards, one on each
side of the body. There is no anal opening, and the
138 ELEMENTARY ZOOLOGY
alimentary canal thus forms a system of fine branches
closed at the tips, and extending all through the body.
The nervous system is composed of a ganglion or brain
in the front end of the body from which two main branches
extend back throughout its whole length. From these
main longitudinal branches arise many fine lateral
branches.
Of the parasitic flatworms the tapeworms are the best
known. There are numerous species of them, all of
FIG. 31. A marine planarian, Leptoplana californica. (From a living
specimen.)
which live in the bodies of vertebrate animals. In the
adult or fully developed stage the tapeworms live in the
alimentary canal, holding on to its inner surface by hook-
like clinging organs and being nourished by the already
digested food by which they are bathed. In the young
or larval stage tapeworms live in other parts of the body
of the host, and usually, indeed, in other hosts not of the
same species as the host of the adult worm.
BRANCH YERMES: THE WORMS 139
The common tapeworm of man, Tcenia solinm (there
are several other species of Tcenia which infest
man, but solium is the common one), may serve as an
example of the group. In the adult condition its body,
which is found attached to the inner wall of the intestine,
is like a long narrqw ribbon : it may be two or three
metres long. It is attached by one end, the head, which
is very small and provided with a score of fine hooks.
Behind the head the thin ribbon-like body grows wider.
The body is composed of many (about 850) joints called
proglottids. There is no mouth or alimentary canal, the
liquid food being simply taken in through the skin. Each
proglottid produces both sperm-cells and egg-cells ; one
by one these proglottids or joints with their supply of
fertilized eggs break off and pass from the alimentary
canal with the excreta. If now one of these escaped
proglottids or the eggs from it are eaten by a pig, the
embryos issue from the eggs in the alimentary canal of
the pig, bore through the walls of the canal and lodge in
the muscles. Here they increase greatly in size and
develop into a sort of rounded sac filled with liquid. If
the flesh of the pig be eaten by a man, without its being
first cooked sufficiently to kill the larval sac-like tape-
worms, these young tapeworms lodge in the alimentary
canal of the man and develop and grow into the long
ribbon-like many-jointed adult stage.
The life-history of the other tapeworms which infest
the various vertebrate animals is of this general type.
There is almost always an alternation of hosts, the larval
tapeworm living in a so-called intermediate host, and the
adult in a final host. Of the domestic animals the dog
is the most frequently attacked. At least ten different
species of tapeworms have been found in the dog. The
intermediate hosts of these dog tapeworms include
rabbits, sheep, mice, etc. Some of the domestic fowl,
140
ELEMENTARY ZOOLOGY
ducks, geese and chickens, for instance, are also infested
by tapeworms, and the intermediate hosts in these cases
are usually insects or small aquatic crustaceans like the
familiar Cyclops.
Roundworms (Nemathelminthes) . TECHNICAL NOTE.
Vinegar-eels from mouldy vinegar, and hair-worms from fresh-
water pools, can usually be readily obtained. They should be
examined, and drawings should be made of them, showing their
shape and simple external structural character. If a specimen of
trichinosed pork be obtained, the encysted stage of
the Trichina, described in the following account, can
be shown.
The roundworms are slender, smooth,
cylindrical worms pointed at both ends.
They are all very long in proportion to their
diameter, although their actual length may
be short. Some species are of microscopic
size; as the Trichina worm, which is about
^ in. long; while the guinea-worm, one of
the worst parasites of man, may reach a
length of six feet. Many of the round-
worms are parasites living in the various
organs of other animals. Some, however,
lead an independent free life in water or in
damp earth.
Familiar examples of roundworms are the
so-called vinegar-eels (Anguilluld) (fig. 32)
to be found in weak vinegar, and other
species of this same genus which live in water
or moist ground or in the tissues of plants,
doing much injury. The hair-worms (Gor-
dius) or horse-hair snakes, which are believed
by some people, to be horse-hairs dropped
into water and turned into these animals, are
also familiar examples of roundworms. They
are often found abundantly in little pools after a rain, and
FIG. 32. A
vinegar eel,
Anguiilula
sp. (From
a living
specimen.)
BRANCH HERMES: THE WORMS
141
it is sometimes said that these worms come down with the
rain. They have in reality come from the bodies of insects
in which they pass their young or larval stages as parasites.
The hair-worms all live as parasites during their larval
stage, and as free independent animals in their adult stage.
Some of them require two distinct hosts for the comple-
tion of their larval life, living for a while in the body of
one, and later in the body of
another. The first host is
usually a kind of insect which is
eaten by the second host. The
eggs are deposited by the free
adult female in slender strings
twisted around the stems of
water-plants. The young hair-
worm on hatching sinks to the
bottom of the pond, where it
moves about hunting for a host
in which to take up its abode.
The terrible TricJiina spiralis
(fig- 33)' which produces the
disease called trichinosis, is
another roundworm of which
much is heard. This is a very
small worm which in its adult
condition lives in the intestine
of man as well as in the pig and
other mammals. The young,
which are borne alive, burrow
through the walls of the intes-
tine, and are either carried by the blood, or force their
way, all over the body, lodging usually in muscles.
Here they form for themselves little cells or cysts in
which they lie. The forming of these thousands of tiny
cysts injures the muscles and causes great pain, sometimes
FIG. 33. Trichina spiralis, en-
cysted in muscle of a pig.
(From specimen.)
142 ELEMENTARY ZOOLOGY
death, to the host. Such infested muscle or flesh is said
to be "trichinosed," and the flesh of a trichinosed
human subject has been estimated to contain 100,000,000
encysted worms. To complete the development of the
encysted and sexless Trie hince the infested flesh of the
host must be eaten by another animal in which the worm
can live, e.g. the flesh of man by a pig or rat, and that
of a pig by man. In .such a case the cysts are dissolved
by the digestive juices, the worms escape, develop repro-
ductive organs and produce young, which then migrate
into the muscles and induce trichinosis as before. But
however badly trichinosed a piece of pork may be,
thorough cooking of it will kill the encysted Trichina, so
that it may then be eaten with impunity. Some people,
however, are accustomed to eat ham, which is simply
smoked pork, without cooking it, and in such cases there
is always great danger of trichinosis.
Wheel animalcules (Rotifera). TECHNICAL NOTE.- Live
specimens of Rotifers can be found in almost any stagnant water
Examine a drop of such water with the compound microscope, and
find in it a few small, active, transparent creatures, larger than the
Paramcccium and other Protozoa in the water and which have the
appearance shown in fig. 34. They may be known by the constant
whirling, or rather vibrating, circlet or wheel of cilia at the larger
or head end of the body. These wheel animalcules may be studied
alive by the class. Although usually darting about, the animalcules
occasionally cease to move, when, because of their transparency,
almost the whole of their anatomy can be made out. Their feeding
habits can also be readily observed, and the food itself watched
as it moves through the body. Make drawings showing as much
of the anatomy as can be worked out. Note especially the "mas-
tax " or gizzard-like masticating apparatus in the alimentary canal.
The wheel animalcules (fig. 34) or Rotifers look little
like the other worms we have studied. But they are
nevertheless more nearly related to the worms than to
any other branch of animals. They are all small, about
mm. long, and have a compact body. They are aquatic
and feed on smaller animals and plants or on bits of or-
BRANCH I/ERMES: THE WORMS
ganic matter which they capture by means of the currents
produced by the vibrating cilia of the " wheel. " Small as
they are they have a complex
body-structure, with well-or-
ganized systems of organs.
For a long time, however,
they were classed by natural-
ists with the Protozoa on ac-
count of their size. They are
found all over the world,
mostly in fresh w r ater; a few
are marine. More than 700
species of them are known.
An interesting thing about
the Rotifers is their remark-
able power to withstand dry-
ing-up. When the water in
a pond or ditch evaporates
some of the Rotifers do not
FIG. 14. A wheel animalcule. ... -11 i T
Rotifer sp. (From living sped- die, but simply dry up and he
men, Stanford University.) j n t l ie dust, shrivelled and
apparently lifeless, yet really in a state of suspended
animation. On being put into water they will gradually
fill out to their full size and shape, and finally resume all
their normal activities. In this dried-up condition Rotifers
may persist for a long time, several years even, although
otherwise their natural life is short, being probably of not
over two weeks' duration. Certain other of the lower
animals have this same power of withstanding desiccation.
CHAPTER XX
BRANCH ARTHROPODA: CRUSTACEANS, CEN-
TIPEDS, INSECTS, AND SPIDERS
I THE great branch Arthropoda includes a host of
"T familiar animals. It contains more species than any other
branch of the animal kingdom. To it belong the cray-
fishes, shrimps, crabs, lobsters, water-fleas, and other ani-
mals which compose the class Crustacea ; the centipeds
and thousand-legged worms which compose the class
Myriapoda ; the true or six-footed insects forming the class
Insecta, which includes nearly two-thirds of all the known
species of animals; and the scorpions, mites, ticks, and
spiders which constitute the class Arachnida. There is
also a fifth class in the branch Arthropoda which includes
a few species of animals unfamiliar to us but of great
interest to zoologists.
All these varied kinds of animals have a body on the
^ annulate or segmented type-plan, like -that shown by most
worms, but they differ from the worms in possessing
jointed appendages, used for locomotion or food taking.
There is typically or racially one pair of these jointed or
segmented appendages on each segment of the body, but
in all of the Arthropoda some of the segments have lost
their appendages. The body is covered by a firm cuticle
or outer body-wall called the exoskeleton. This exo-
skeleton serves not only to enclose and protect the soft
parts of the body but also for the attachment of the body
144
BRANCH ARTHROPODA: CRUSTACEANS 145
muscles. It may be flexible as in the sutures between
the body-segments in most insects, or hard and rigid as
in the sclerites of the segments. The firmness is due
primarily, and in the insects usually solely, to a deposit in
the cuticle of chitin, a substance probably secreted by the
underlying cells of the true skin, or it maybe due chiefly,
as in the crabs, to a calcareous deposit. In such cases it
becomes a veritable armor. The internal organs of the
Arthropods show a more or less obvious segmentation
corresponding with the segmentation of the body- wall.
The alimentary canal runs longitudinally through the
center of the body from mouth to anal opening. The
nervous system consists of a brain lying above the
oesophagus and a double nerve-chain running backward
from beneath the oesophagus, along the median line of
the ventral wall, to the posterior extremity of the body.
This ventral nerve-chain consists of a pair of longitudinal
commissures or cords and a series of pairs of ganglia,
arranged segmentally. The two ganglia of each pair are
fused more or less nearly completely to form a single
ganglion, and the nerve-cords are partially fused, or at
least lie close together. In addition there is a smaller
sympathetic system composed of a few small ganglia and
certain nerves running from them to the viscera, this sys-
tem being connected with the main or central nervous
system. In this group the organs of special sense reach
for the first time a high stage of development. Com-
pound eyes are peculiar to Arthropoda. The heart lies
above the alimentary canal. Respiration is carried on by
gills in the aquatic forms, and by a remarkable system of
air-tubes or tracheae in the land forms (insects). The
sexes are usually distinct, and reproduction is almost uni-
versally sexual. Most of the species lay eggs.
The Arthropods are animals of a high degree of organ-
ization. The extremely diverse life-habits of the various
146 ELEMENTARY ZOOLOGY
kinds among them have led to much modification and to
great specialization of structure. The course of develop-
ment, too, is made very complicated by the elaborate
metamorphosis undergone by many of the members of the
branch.
We shall study the Arthropoda by getting acquainted
with a few examples of each class and thus learning the
special class characteristics.
CLASS CRUSTACEA: CRAYFISHES, CRABS, LOBSTERS,
ETC.
THE CRAYFISH (Cambarus sp.)
Structure. The structure of the crayfish has been
already studied (see Chapter IV and figs. 3 and 4).
Life- history and habifs. Crayfish frequent fresh-water
lakes, rivers, and springs in most parts of the United
States. Many of them perish whenever the small prairie
ponds dry up. But some burrow into the earth when the
dry season comes. There may be noticed in meadows
where water stands for certain seasons of the year many
scattered holes with slight elevations of mud about them.
These are mostly the burrows of crayfish. During the
dry season the crayfish digs down until it reaches water,
or at least a damp place, where it rests until wet weather
brings it to the surface once more. One of these burrows,
followed in digging a mining shaft, extended vertically
down to a distance of twenty-six feet, where the crayfish
was found tucked snugly away.
The eggs are carried by the female on her abdominal
appendages. Previous to the laying of the eggs the
female rubs off all foreign matter from the appendages,
thus preparing them for the reception of the eggs. This
cleaning is done with the fifth pair of legs. When the
BRANCH ARTHROPODS: CRUSTACEANS 147
eggs arc ready to be laid, which is during the last of
March or in April in the Central States, a sticky secretion
passes out of the openings at the base of the walking legs
and smears the pleopods of the abdomen. The eggs as
they pass out are fertilized and caught on the pleopods,
where they remain attached in clusters. After some
weeks the young crayfishes issue from the eggs. In
general appearance they are not very unlike the adults.
They grow very rapidly at this stage. As the animal is
enclosed in a hard shell, growth can only take place
during the period just following the molt, for the crayfish
casts its skin periodically, and it is while the new shell is
forming that the animal does its growing. The crayfish
when it molts casts not only the exoskeleton, but also the
lining of part of the alimentary canal. After the females
have hatched their young many die in the shallow pools,
in which places the dried-up skeletons are noticeable
during the summer months.
OTHER CRUSTACEANS.
Most of the crustaceans live in water, a few being found
- in damp soil or in other moist places. Some are fresh-
water animals and some marine. They vary in size from
the tiny water-fleas, a millimeter long, to crabs two feet
across the shell or sixteen feet from tip to tip of legs.
They present great differences in form and general ap-
pearance of body, being adapted for various conditions
of life. Some crustaceans live as parasites on other
animals, in some cases on other crustaceans. Such
parasitic species have the body much modified and are
hardly to be recognized as members of the class.
Body form and structure. In structural character and
body organization the Crustaceans show, of course, the
general characteristics already attributed to the Arthro-
nnrta thf brnnrh tn \vhtrh fViPV Hplnnrr The character-
M s ELEMENTARY /.OOLOGY
istics which distinguish them from other Arthropods are
the possession of gills for respiration (some insects have
gills, but of a very different kind as will be seen later),
and the bi-ramose condition of the body appendages, each
appendage (excepting the antennules) consisting of a
single basal segment from which arise two branches made
up of one or more segments. Of the form of the crus-
tacean body few generalizations can be made.
'There is no [other] class in the animal kingdom
which presents so wide a range of organization as the
Crustacea, or in which the deviations in structure from the
4 type form ' are so striking and so interesting from their
obvious adaptation to the mode of life. ' ' For this reason
no attempt will be made to discuss in general terms the
form of ther crustacean body, but brief accounts will be
given of a few of the more familiar kinds of Crustacea
which will serve to illustrate this remarkable diversity of
body form.
Similarly impossible* is it also to give a general account
f the development of the crustaceans. The sexes are
distinct in most Crustacea, and there is often great differ-
ence in form between the male and female. A certain
amount of metamorphosis takes place in the development
of all crustaceans; that is, the young when hatched from
the egg differs, often decidedly, in appearance and structure
from the parent x and in the course of its post-embryonic
development undergoes more or less striking change
or metamorphosis. This metamorphosis is often very
marked.
Water-fleas (Cyclops). TECHNICAL NOTE. The water-
fleas are common in the water of ponds or of 'slow streams; they
may often be found in the school aquarium. They are, though
small (about i mm. long), readily seen with the unaided eye ; they
are white, rather elongate, and have a rapid jerky movement. Ex-
amine specimens alive in water in a watch glass. Note the "split
pear " shape, broadest near the front, tapering posteriorly, flat be-
BRANCH ARTHROPODS: CRUSTACEANS
149
neath, convex above; note the forked stylets at tip of abdomen ; also
the two pairs of antennae, the single median eye, the mandibles, two
pairs of maxillae, and five pairs of legs (last pair very small). There
are no gills. Some of the specimens, females, may have attached to
the first abdominal segment on either side an egg sac. Make
drawings showing all these structural details. Watch the Cyclops
capturing and feeding on Paramcecium or other small animals.
The water-fleas (Cyclops) (fig. 35) are among the
\smallest of the Crustacea. They are extremely abundant,
7
FIG. 35. A water- flea, Cyclops sp. Female with egg-masses.
(From living specimen.;
having great power of multiplication. "An old Cyclops
may produce forty or fifty eggs at once, and may give
birth to eight or ten broods of children living five to six
i5- ELEMENTARY ZOOLOGY
months. As the young begin to reproduce at an early
age, the rate of multiplication is astonishing. The
descendants of one Cyclops may number in one year
nearly 4,500,000,000, or more than three times the total
population of the earth, provided that all the young reach
maturity and produce the full number of offspring. ' ' The
Cyclops feed on smaller aquatic animals such as Protozoa,
Rotifera, etc. .They in turn serve as food for fishes; and
because of their immense numbers and occurrence in all
except the swiftest fresh waters ' ' they form the main food
of most of our fresh-water fishes while young. ' ! Many
aquatic insect larvae feed almost exclusively on them.
Related to the Cyclops are a host of other kinds of
minute Crustaceans. Among these the so-called fish-lice
are specially interesting because of their parasitic habits
and greatly modified and degenerate structure. There
are many kinds of these parasitic crustaceans infesting
fishes, whales, molluscs, and worms. " As on land almost
every species of bird or mammal has its own parasitic
insects, so in the water almost every species of fish or
larger invertebrate has its parasitic crustaceans." Some
of the most common of these parasites attach themselves
to the gills of fishes. Here they cling, sucking the blood
or animal juices from the host. In form of body they do
not at all resemble other Crustaceans, but are strangely
misshapen. They are often worm-like, or sac-like, with-
out legs or other locomotory appendages. As with other
parasites (see Chapter XXX) an inactive dependent life
results in the atrophy and loss by degeneration of the
body-parts concerned with locomotion and orientation.
Wood lice (Isopoda). TECHNICAL NOTE. Specimens of
wood lice, pill bugs, or damp bugs, as they are variously called, may be
readily found in concealed moist places, as under stones or boards on
damp soil. They are often common in houses, near drains or in dark,
damp places. Examine some live wood lice, and some dead speci-
mens (killed by chloroform or in an insect-killing bottle).
BRANCH ARTHROPODA : CRUSTACEANS 151
Note the division of the body into the head, thorax, and abdomen ;
find the eyes, the antenna; and the mouthparts (mandibles and maxillae
are usually pressed closely together). All the locomotory append-
ages are adapted for walking or running, not swimming. Note the
number of pairs of legs ; the structure of a leg ; find gills and gill-
covers. Some females may be found with eggs on the under side
of the thorax near the bases of the legs, the eggs being covered by
thin membranous plates. Make drawings snowing the general
form and character of body and details of legs, gills, etc. Compare
with the crayfish and Cyclops.
The wood-lice (fig. 36) are among the few Crustacea
which have a wholly terrestrial life. They run about
quickly and feed chiefly on decaying
vegetable matter. They are night
scavengers. They have the body
oval and convex above, rather pur-
plish or grayish brown, and smooth.
Although they do not live in the
water they breathe partly at least by
means of gills (though they may
breathe partly through the skin).
It is therefore necessary for them to
live in a damp atmosphere so that the
facoi seci^Tnot ^1 S il1 membranes may be kept damp.
specnot
termined. (From sped- if no t kept moist they could not
men.)
serve as osmotic membranes.
Lobsters, Shrimps and Crabs (Decapoda). TECHNICAL
NOTE. Teachers living near the sea-shore can get specimens of
live and dead, lobsters, shrimps, and crabs in the markets. Schools
in the interior should have a few preserved specimens for examina-
tion. These specimens should be compared with the crayfish ;
although differences in shape of body are evident, the character
and arrangement of body parts will be found to be very similar.
The largest and most familiar Crustaceans, as the cray-
fishes, lobsters, shrimps, prawns and crabs, all belong
to the order Decapoda, or ten-legged Crustacea. The
members of this order have, including the large claws,
ten walking feet; they all have eyes on movable stalks,
152 ELEMENTARY ZOOLOGY
and the front portion of the body is covered by a horny
fold of the body-wall called the carapace.
The lobsters are large ocean-inhabiting crustaceans
which are very like the fresh-water crayfish in all struc-
tural characters. They live on the rocky or sandy ocean-
bottom at shallow depths. They feed largely on decaying
[ animal matter. They are caught in great numbers in
so-called " lobster pots, " a kind of wooden trap baited
with refuse. "The number thus taken upon the shores
of New England and Canada amounts to between twenty
and thirty million annually. " Live lobsters are brownish
i or greenish with bluish mottling; they turn red when
boiled. A single female will lay several thousand eggs.
The eggs are greenish and are carried about by the mother
until the young hatch. The young are free-swimming
larvae, until they reach a length of half an inch.
^j The shrimps and prawns are mostly marine, though*
some species live in fresh water. They are, like the
lobsters, used for food. Some of the species are gregari-
ous in habit, occurring in great " schools " of individuals.
Like the lobsters they crawl about on the sea-bottom
feeding on decaying animal matter. Shrimps are very
abundant near San Francisco, where extensive "shrimp
fishing " is done by the Chinese.
.JkThe crabs (fig. 37) differ from the lobsters and cray-
fishes and shrimps in having the body short and broad,
instead of elongate. This is due to the special widening
of the carapace and the marked shortening of the
abdomen. The abdomen, moreover, is permanently bent
underneath the body, so that but little of it is visible from
the dorsal aspect. The number of abdominal legs or
appendages is reduced. When the tide is out the rocks
and tide-pools of the ocean shore are alive with crabs.
They "scuttle " about noisily over the rocks, withdraw-
ing into crevices or sinking to the bottom of the pools
BRANCH ARTHROPODA: CRUSTACEANS 153
when disturbed. They move as readily backward or
sidewise, "crab-fashion," as forward. They are of
various colors and markings, often so patterned as to
FIG. 37. Some crabs and barnacles of the Pacific coast; the short sessile
acorn barnacles in the upper left-hand corner belong to the genus Bal-
anus; the stalked barnacles in the upper right-hand corner are of the
species Pollidpes polymenus; the largest crab (upper left-hand) is
Brachynotus nudus; the one in left-hand lower corner is a young rock-
crab, Cancer prodiictus; the crab in the sea-weed at the right is a kelp-
crab, Epialtus prodnctus, while the two in snail-shells in lower corner
are hermit-crabs, Pagnms samuelis. (From living specimens in a tide-
pool on the Bay of Monterey. California.)
harmonize very perfectly with the general ^cplor and ap-
pearance of the rocks and sea-weeds among which they
154 ELEMENTARY ZOOLOGY
live. The spider-crabs are especially strange-looking crea-
XTHtures with unusually long and slender legs and a com-
paratively small body-trunk. They include the Macro-
cJieira of Japan, the largest of the crustaceans. Specimens
of this crab are known measuring twelve to sixteen feet
from tip to tip of extended legs ; the carapace is only as
many inches in width or length. The soft-shelled crab
is a species common along our Atlantic coast. It is
"soft-shelled " only at the time of molting, and has to
be caught in the few days intervening between the shed-
ding of the old hard shell and the hardening of the new
body-wall. The little oyster-crabs (Pinnotheres] which
live with the live oyster in the cavity enclosed by the
oyster shell are well-known and interesting crabs. They
are not parasites preying on the body of the oyster, but
are simply messmates feeding on particles of food brought
into the shell by the currents of water created by the
oysters.
^~ Among the most interesting crabs are the hermit crabs
(fig. 37), familiar to all who know the seashore. There
are numerous species of these crabs, all of which have the
habit of carrying about with them, as a protective covering
into which to withdraw, the spiral shell of some gastropod
mollusc. The abdomen of the crab remains always in
the cavity of the shell ; the head and thorax and legs
project from the opening of the shell, to be withdrawn
into it when the animal is alarmed or at rest. The
abdomen being always in the shell and thus protected
loses the hard body- wall, and is soft, often curiously
shaped and twisted to correspond to the cavity of the
shell. It has on it no legs or appendages except a pair
for the hindmost segment which are modified into hooks
for holding fast to the interior of the shell. As the
hermit crab grows it takes up its abode in larger and
larger shells, sometimes killing and removing piece-meal
BRANCH ARJHROPODA: CRUSTACEANS '55
the original inhabitant. Some hermit crabs always have
attached to the shell certain kinds of sea-anemones. It
is believed that both crab and sea-anemone derive advan-
tage from this arrangement. The sea-anemone, which
otherwise cannot move, is carried from place to place by
the crab and so may get a larger supply of food, while
the crab is protected from its enemies, the predaceous
fishes, by the stinging threads of the sea-anemone, and
also perhaps by the concealment of the shell its presence
affords. This living together by two kinds of animals to
their mutual advantage is called commensalism. ^r sym-
biosis (see Chapter XXXj. The hermit crabs are not true
crabs, but are more nearly related to the crayfishes and
shrimps than to the true broad-bodied, short-tailed crabs.
Barnacles. TECHNICAL NOTE. Specimens of barnacles may
be got readily from the tide rocks or from piles in a harbor. In-
terior schools should have, if possible, specimens preserved in
alcohol or formalin for examination. The " shells " of acorn (ses-
sile) barnacles may often be found on oyster shells (get at restau-
rants).
/ Crustaceans which at first glance are hardly recogniz-
able as such are the stafked^or sessile barnacles (fig. 37)
which live fixed in great numbers on the rocks between
the tide lines, or on the piles supporting wharves, or on
the bottom of ships or even on the body-wall of whales
and other ocean animals. In the stalked forms the stalk
is a flexible stem or peduncle covered with a blackish
finely-wrinkled skin bearing at its free end the greatly
modified body of the barnacle. This body is enclosed in
a sort of bivalved shell or carapace formed by a fold of
the skin and stiffened by five calcareous plates. Within
this curious shell is the compact, rather worm-like body-
mass, showing little or no indication of segmentation.
The legs, of which there are usually six pairs, are much
modified, being long, feathery, and divtcTecT nearly to the
156 ELEMENTARY ZOOLOGY
base. These feathery feet project from the opened shell
when the animal i^undisturbed, and waving about in the
water catch small animals which serve as the barnacle's
food. When disturbed the barnacle withdraws its feet
and closes tightly its strong protecting shell. The acorn-
barnacles have no stalk, but look like a low bluntly-
pointed pyramid, this appearance being due to the
converging arrangement of six calcareous plates in its
body-wall.
The barnacles present several unusual conditions with
regard to the internal organs. They have no heart nor
any blood-vessels ; most of the species are hermaphroditic ;
and there are other indications of a degenerate condition.
This degeneration of the barnacles is due to their fixed
Hfe, the results of which are like those of a parasitic life.
The young barnacles when hatched from the egg are free-
swimming larvae as with the other Crustacea. They
finally attach themselves and undergo the changes, some
of them of degenerative nature, which produce the body-
structure of the adult. It was long a belief among many
people that the barnacle produced the barnacle goose.
Pictures in ancient books show the young barnacle geese
issuing from the* opened shell of the barnacle. The early
naturalists believed barnacles, on account of the shell, to
be a kind of shell-fish or mollusc, but when their develop-
ment was thoroughly worked out, it became evident that
they belong to the Crustacea.
CHAPTER XXI
BRANCH ARTHROPODA (continued}; CLASS IN-
SECTA: THE INSECTS
THE LOCUST (Melanoplus sp.)
TECHNICAL NOTE. Locusts or grasshoppers are common and
familiar insects all over the country. The genus Melanoplus in-
cludes numerous species, one or more of which are to be found in
almost any locality. The common red-legged locust (M. femur-
rubruni} of the East, the Rocky Mountain migratory locust (M.
spretits], of the West, the large differential (M. differentialis} and
two-striped (M. bivittatus} locusts of the Southwest, are especially
common species. All the members of the genus have their hind
wings uncolored, and the front wings marked with a longitudinal
series of small dots more or less distinct, or with a longitudinal line.
There is a small blunt spine or process projecting from the ventral
aspect of the prothorax. If a species of Melanoplus cannot be
found, any other locust may be used, although there are some slight
variations in the external structure of the various species. Fresh
specimens killed in a cyanide bottle (for preparing see p. 463) are
preferable in the study of the external structure, but specimens
preserved in alcohol will do.
External structure (fig. 38). Note that the body of
the grass-hopper is composed of successive rings or seg-
ments grouped into thre^ regions, the head (anterior),
thorax (median), and abdomen (posterior). In which
region of the body are the segments most readily distin-
guished ? Of how maji}t-srgmeris <-i oes the head appear
to be composed ? The thorax is composed of three
segments of which the most anterior, to which is attached
the front pair of legs, differs from the succeeding two,
being freely movable and bearing a large hood- or saddle-
shaped piece on its dorsal aspect. To the other two
thoracic segments the second and third pair of legs are
157
158 ELEMENTARY ZOOLOGY
attached, as are also the two pairs of wings. The re-
maining segments of the body compose the abdomen.
Note the smooth, rather firm and horny character of
antennae
/\
auditory organ
ocellus I
head compound eye \
-ovipositor
femur*
tibia/
tar sal segments
FIG. 38. The red-legged locust. Mclanoplus femitr rubnim, to show ex-
ternal structure.
the body. This is due to the fact that the skin is every-
where covered with a cuticle in which is deposited a
horny substance called chitin. The cuticle is not uni-
formly firm over the body. At the junction of the body
segments in the abdomen, in the neck and between the
segments of the legs, in fact, wherever motion is desir-
able, the cuticle is flexible, thus making bending of the
body-wall possible. Elsewhere, however, it is hard and
stiff, serving not only as a protective coat or armor over
the body, but also affording firm places for the attachment
of muscles.
Insects (and all other Arthropods) have no * internal
skeleton, but, in this firm cuticle, an exoskeleton,
Although the head is apparently a single segment, it
* There are in many forms a few internal projections from the exterior
cuticle which act as internal skeletal pieces.
BRANCH ARTHROPODS; CLASS INSECTS: THE INSECTS 159
is really composed of six or seven body segments greatly
modified and firmly fused together. Note that it bears
a pair of large compound eyes and three much smaller
simple eyes or ocelli.
TECHNICAL NOTE. Strip off a bit of the outer covering of a
compound eye, mount on a glass slide and examine under the
microscope.
Note that, as in the crayfish, each compound eye is
composed externally of many small hexagonal facets, the
outer covering, the cornea, being simply the cuticular cover-
ing of the body, in this place transparent and divided into
small facets. Besides the eyes, the head bears also several
movable appendages, namely the antennce, and the
mouth-parts. Note the number, place of insertion, and
segmented character of the antennae. These antennae are
sense-organs and are used for feeling, smelling, and, in
some insects, for hearing. Note that the mouth-parts
consist of an upper, broad, flap-like piece, the *labrum; of
a pair of brown, strongly chitinized, toothed jaws or
mandibles; of a second pair of jaw-like structures, the
maxillce, each of which is composed of several parts ; and
of an under, freely-movable flap, the labium, also com-
posed of several pieces. Each maxilla bears a slender
feeler or palpus composed of five segments. The labium
bears a pair of similar palpi, which are, however, only
three-segmented. The mandibles and maxillae, which
are the insect jaws, move laterally, riot vertically as with
most animals.
Make drawings of the lateral aspect of the head ; of a
bit of the cornea ; of the dissected out mouth-parts.
Of the three segments of the thoracic region of the
body, the most anterior one is called the prothorax. It
is freely movable and has a large hood or saddle-shaped
* The labrum differs from the other mouth -parts in not being composed of
a pair of body appendages ; it is simply a fold or flap of the skin of the head.
160 ELEMENTARY ZOOLOGY
piece, the pronotnm, on its dorsal aspect, and a blunt-
pointed tubercle on the ventral aspect. The foremost
pair of legs is attached to the prothorax. The next
segment is the me so thorax, which is immovaly fused to
the next thoracic segment. What appendages does it
bear ? The third segment is the metathorax, which
besides being fused with the mesothorax in front, is
similarly fused with the foremost abdominal segment
behind. What appendages does the metathorax bear ?
Examine one of the fore legs and note that it is com-
posed of a series of unequal parts or segments. The
segment nearest the body is sub-globular and is called
the coxa; the second segment is smaller than the coxa
and is called the trochanter; the third, known as the
femur, is the largest of all ; the fourth, tibia, is long and
slender; and the next three, the last of which is the
terminal one and bears a pair of claws and between them
a little pad, the pulvillus, are called the tarsal segments.
Most insects have five tarsal segments. Note the great
size of the hindmost or leaping legs. Determine the seg-
ments of the middle and hindmost legs. Make a draw-
ing of a fore leg.
Examine the wings. In what ways do the front wings
differ from the hind wings ? The front wings are known
as the wing covers or tegmina. Note how the hind wings
fold up like a fan, and are covered and protected by the
wing covers. Draw the wings.
The abdomen is composed of a number of segments
most of which resemble each other. The first segment
(immediately behind the metathorax) has its dorsal and
ventral parts widely separated by the cavities for the in-
sertion of the hindmost legs. The ventral part of this
segment is dovetailed into the ventral part of the meta-
thorax and appears to be part of it. In the dorsal part
of this segment there is on each side a spot where the
BRANCH ARTHROPOD A; CLASS IN SECT A : THE INSECTS 161
cuticle is only a thin membrane. At these places are
the auditory organs or ears of the locust. The thin
membranes are the tympana. Only the various kinds of
locusts and those insects closely related to them have ears
of this kind. Most other insects are believed to have the
sense of hearing situated in the antennae.
The abdominal segments from second to eighth are ring-
like in form and are without appendages. There is on
the side of each of these segments near its front margin a
tiny opening or pore called a spiracle. These spiracles
are the breathing pores of the locust, which does not take
in air through its mouth or any other opening in the head.
There is a spiracle near each ear in the first abdominal
segment, and one on each side of the mesothorax near
the insertion of the middle legs.
The terminal segments of the abdomen are provided
with certain processes which are different in male and
female. The female has at the tip of its abdomen two
pairs of strong, curved pointed pieces which compose the
ovipositor, or egg-laying organ. The opening of the
oviduct lies between the pieces. The male has a swollen
rounded abdominal tip, with three short inconspicuous
pieces on the dorsal surface.
Make a drawing of the lateral aspect of the abdomen
of a female locust; also, of a male.
For a more detailed account of the external anatomy of
a locust see Comstock and Kellogg's " Elements of In-
sect Anatomy," chap. II.
The external structure of the grasshopper should be
carefully compared with that of the crayfish; pay special
I attention to the mouth-parts and legs.
The teacher should point out the homologies and
; modifications.
Life-history and habits. The eggs of the locust are
\ laid in the autumn in the ground in bare dry places,
1 62 ELEMENTARY ZOOLOGY
as roadsides, closely-grazed pastures, etc. The female
thrusts her strong ovipositor into the soil, and by opening
and shutting it, thus boring, pushes in the abdomen for
about two thirds its length. The eggs, about one hun-
dred, are then deposited in a capsule or pod. The young
locusts hatch in the following spring. When just
hatched they resemble the parent locust in general
appearance and structure except that they lack wings,
and are of course very small. The young locusts are
gregarious, congregating in warm and sunny places.
They feed on green plants and travel about by walking
and hopping. At night they try to find shelter under
rubbish in the fields. They feed voraciously and grow
rapidly, reaching maturity in about two months. During
this post-embryonic development and growth they molt
(shed the chitinous exoskeleton) five times. After the
first molt indications of the wings appear in the shape of \
small backward and downward prolongations of the pos-
terior margins of the dorsum of the mesothorax and
metathorax. With each succeeding molt these wing-
pads, or developing wings, are larger and more wing-like,
until after the last molting they appear fully developed.
With each molting, too, there is a marked increase in
size of the locust, the average length of the body just
before the first moult being 4.3 mm., before the second
6.8 mm., before the third 9 mm., before the fourth 14
mm., before the fifth 17 mm., and after the fifth (the full-
grown stage) about 26 mm.
The molting is an interesting process, and can be
readily observed. The young locust ready for its last
molt crawls up some post, weed, grass stalk, or other
object, and clutches this object securely with the hind
feet. The head is generally downward. The locust
remains motionless in this position for several hours, when
the skin suddenly splits along the back from the middle
BRANCH ARTHROPODA ; CLASS IN SECT A : THE INSECTS 163
of the head to the base of the abdomen. By steady
swelling and contracting and slight wriggling, lasting for
half an hour to three-fourths of an hour, the old skin is
completely shed, and the wings spread out. In an hour
the wings are dry and the new chitinized exoskeleton
firm enough for flying, or crawling about, and in another
hour the locust begins to eat.
The red-legged locust does considerable damage to
cultivated crops, but its injuries are insignificant compared
with the tremendous losses occasioned by a near relative,
the Rocky Mountain Locust (Melanoplus spretus}. This
locust has its breeding-grounds on the high plateaus of
the Rocky Mountain region, but it sometimes migrates in
countless numbers southeast over the plains and into the
great grain-fields of the Mississippi valley. Such migra-
tions occurred in 1866, 1867, 1874 (in this year eighteen
hundred and forty two families in Kansas were reduced
to destitution by the utter wiping out of their crops by
the locusts) and 1876. With the settling-up of the
regions injvvhich the Rocky Mountain locust breeds, there
seems to have come a change of conditions, so that no
great migrations have occurred since 1876.
THE GREAT WATER-SCAVENGER BEETLE (Hydrophilus sp.)
TECHNICAL NOTE. The great water-scavenger beetles are
large, black, elliptical insects common in quiet pools where they
may be found swimming through the water, or crawling among the
plants growing on the bottom. They are an inch and a half long
and are readily distinguishable from all other water insects except
the predaceous diving beetles (Dytictts). The antennae of Hydro-
philus, however, are thickened (clavate) at the tip, while those of
Dyticus are thread-like for their whole length. The beetles may
be readily collected with a water-net, and kept alive in glass jars
or aquaria in water containing decaying vegetation.
External structure (fig. 39). Is the body of the water-
beetle composed of segments ? Can you make out three
body-regions, head, thorax and abdomen / As in the
locust the metathorax is fused with the first abdominal
164
ELEMENTARY ZOOLOGY
labial
labium j
compound eye-
mouth-parts
palpi
head
coxa
trochanler-
femur-'
tibia
tarsal segments
~prothorax
-jnesothora
metathorax
abdom
FIG. 39. Ventral aspect of male great water-scavenger beetle,
ffydrophilus sp
BRANCH ARTHROPODS ; CLASS INSECTS: THE INSECTS 165
segment and with the mesothorax, while the prothorax
is freely movable, and is covered above by a strong shield.
The chitin armor of the whole body is specially heavy
and strong, affording a great protection to the insect.
On the flattened head note the compound eyes and the
peculiarly-shaped nine -segmented antenna. Are there
any ocelli ? Dissect out the mouth-parts. The beetle's
mouth is fitted for biting, the mouth-parts being in general
character like those of the locust, with distinct flap-like
labnun, dentate mandibles, jaw-like maxillce with long,
slender, four-segmented palpi and lip-like labium with
three-segmented palpi. Make drawings of the antennae
and mouth-parts.
Note the character of the thoracic segments. Ex-
amine the wings and legs. The fore wings are modified
into strong horny sheaths, or elytra, which completely
cover and protect the folded hind wings. The hind wings
are large and membranous. How are they folded ? Note
the adaptation of the middle and hind legs for swimming.
Determine the various segments of the legs, i.e. coxa,
trocJiantcr, fcmnr, tibia and tarsus. Note the long longi-
tudinal median keel on the ventral aspect of the thorax.
The abdomen articulates with the metathorax by the
full width of the broad first abdominal segment. It is
composed of a series of segments without appendages, of
about equal length but decreasing in width from in front
backwards. Of how many segments does the abdomen
seem to be composed when viewed from the ventral
aspect ? From the dorsal ?
Make a drawing of the ventral aspect of the whole
body.
TECHNICAL NOTE. After examining the abdomen thus far, re-
move it from the rest of the body, and boil it in dilute potassium
hydrate (KOH) in a test-tube. This will soften and partially bleach
the body wall,
1 66 ELEMENTARY ZOOLOGY
Examine the softened specimen, and note that at least
two additional segments are to be found retracted or tele-
scoped into the apparently last segment. The character
of these terminal abdominal segments differs in male and
female individuals, and specimens of both sexes should be
examined. (The males can be distinguished from the
females by the peculiar pad-like expansion of the last
tarsal segment of the fore legs.) Pull out the retracted
segments, and note that they are unevenly chitinized,
parts of their surface being simply membranous. Project-
ing backwards are several long-pointed processes. The
female has but one retracted- segment. Though the
females of many insects possess more or less elaborately
developed egg-laying organs, this is not the case with the
beetles. Look for spiracles near the lateral margins of
the dorsal surface of the abdomen. How many pairs are
present ?
Internal Structure (fig.4o). TECHNICAL NOTE. If fresh speci-
mens are to be had, kill by dropping into the cyanide bottle (see p.
463). Specimens preserved in a 5$ solution of chloral hydrate may
be used if necessary. When putting specimens into this solution a
small slit should be cut through the body wall to allow the preserv-
ative to enter the body cavity. When ready to dissect a specimen
cut off the elytra and wings close to the base, and carefully remove
all of the dorsal wall of the abdomen and thorax and the median
portion of the dorsal wall of the head. Pin ou% ventral side down,
under water in a dissecting-dish.
Note in the median dorsal line of the abdomen a pale
transparent longitudinal vessel, the heart or dorsal vessel.
Note on each side of it six prominent triangles or " Vs "
with apex of each directed laterally, the posteror three
smaller than the anterior three of each side. These tri-
angles are formed by respiratory tubes or trachea. From
each spiracle or breathing-pore there extends into the
body a respiratory tube or trachea. These lateral tracheae
join a main longitudinal trachea on each side, from which
BRANCH ARTHROPODA; CLASS INSECT A : THE INSECTS 167
are given off branches, which in turn repeatedly subdivide,
until all parts of the body are ramified by tracheae, large
and small, bringing air to all the tissues. The oxygen is
brain
oesophagus
muscles
.....crop
elytron
alimentary
canal
ventral nerve
chain
wing
. , ,, %. \ '^ N . Malpighian
accessory glands^' fectum ^L\ ^Jr *' intestine tubules
\receptaculum~seminalis
FIG. 40. Dissection of female great water-scavenger beetle, Hydrophilus
sp., the heart and tracheae being cut away.
taken up from this air, and carbonic-acid gas is given up
to it, when it passes out of the body again through the
spiracles. Thus in the insects oxygen and carbonic-acid
1 68 ELEMENTARY ZOOLOGY
gas are not carried by the blood but by special air-tubes.
The respiratory system of insects is very different from
that of other animals.
Mount a bit of trachea in glycerine on a glass slide and
examine under the microscope. Note the fine spiral line
(looking like transverse annular striations) which is a
thickening of the chitinous inner wall of the tube and
which by its elasticity keeps the tracheal tubes open.
The heart, already noted, is composed of a longitudinal
series of very thin-walled chambers, each with a pair of
lateral openings into the body-cavity and with terminal
openings into the adjacent chambers. The blood, which
is colorless or greenish or yellowish, is sent forward
through the successive heart chambers by regular contrac-
tions until it finally pours from the most anterior chamber
freely into the body-cavity. Here it bathes the body-
tissues, flowing perhaps in regular paths, giving up food
to the tissues and taking up food from the alimentary
canal, until it finds its way through the lateral openings
into the heart chamber again. There are no arteries or
veins.
Note the large mass of muscles in the metathorax.
Note, by attempting to remove it, that the anterior part
of the muscle mass is attached to a chitinous partition-wall
between the meso- and meta -thorax. Remove this parti-
tion-wall (and one between the metathorax and abdomen)
and note that certain muscles run deeply down into the
body. By pulling on the bits of chitin to which the
muscles are attached, the muscles (if they have not been
cut) can be stretched to the length of three-quarters of an
inch. When released they will contract. (This stretch-
ing and contracting takes place only in fresh specimens.)
What are these large and numerous muscles of the thorax
for?
Remove the thin membrane stretching over the abdomen
BRANCH ARTHROPODA ; CLASS INSECT A: THE INSECTS 169
and in which the heart and tracheal " Vs " lie, and note
immediately underneath it the large coiled intestine with
a knot of greenish yellow threads in the centre. Carefully
uncoil and pin out the intestine, cutting away the tying
tracheae, but being careful not to cut other structures.
Work out the full length of the alimentary canal, noting
the oesophagus, the widened crop behind it, and the long
intestine. From the intestine arise several greenish
yellow threads, the Malpigliian tubules. These are the
excretory organs of the insect. What is the total length
of the alimentary canal ?
The reproductive organs, consisting of a pair of glands
(egg-glands or sperm-glands) \vith a pair of tubes which
unite before reaching the body-wall and have a common
external opening, may now be seen. These should be
removed, thus exposing the ventral nerve-chain in the
abdomen. To expose the chain in the thorax it will be
necessary to pick away carefully the muscles. As in the
crayfish, the central nervous system in the beetle consists
of a ventral nerve-chain, a brain or supra-ccsopJiageal
ganglion and a pair of circum-acsophagcal commissures
connecting the brain and the foremost ganglion (infra-
ccsophageal) in the ventral chain. There are, in the
ventral chain, four ganglia in the thorax and four in the
abdomen. The large nerves running from the brain to
the compound eyes and to the antennae can be traced.
Make a drawing showing the nervous system.
Life-history and habits. The eggs, usually about
one hundred, are deposited in a silken sac or case which
is spun by the female, and either floats freely or is attached
to the under sides of the leaves of aquatic plants. This
egg-case is not wholly filled with eggs but has a consider-
able air-chamber in it, causing it to float. It is oval in
shape, and has a peculiar curved horn-like projection at
the upper end. In sixteen or eighteen days the young
170 ELEMENTARY ZOOLOGY
water-scavenger beetles hatch as elongate, wingless,
active larvae, provided with three pairs of legs and strong
jaws. They remain for a short time after hatching in the
egg-case, feeding on each other ! After they issue from
the case they feed on flies or other insects which fall into
the water, and on snails. They breathe through a pair
of spiracles situated at the posterior tip of the abdomen,
coming to the surface and thrusting this tip up so that the
spiracles are out of water. They grow rapidly, molting
three times before becoming full grown. They attain a
length of nearly three inches. -When full grown they
leave the water, crawling out on the damp shore of the
pond or stream, and burrow into the soil for a few inches.
Here they molt again, or pupate as it is called, changing
to a non-feeding, quiescent stage called the pupal stage.
The pupa is the stage in which the great changes from
wingless, crawling and swimming, short-legged, long,
slender-bodied larva to winged, swimming and flying,
long-legged, compact, broad-bodied adult are completed.
Late in the summer or in the fall the pupal skin breaks
and the adult issues. It works its way to the surface of
the ground, and betakes itself to the nearest water.
The water-scavenger beetle shows in its post-embryonal
development a " complete metamorphosis " as contrasted
with the "incomplete metamorphosis" of the locust.
Wherever among insects similar changes occur, the young
issuing from eggs as larvse only remotely resembling the
parent, and these active feeding larvae changing finally
into more or less quiescent, strictly non-feeding pupae,
which finally change into the active adults, a complete
metamorphosis is said to exist. All the beetles, the
butterflies and moths, the two-winged flies, the ants, bees
and wasps, and certain other groups of insects undergo in
their post-embryonic development a complete metamor-
phosis. The crickets, katydids, the sucking bugs, the
BRANCH ARTHROPODA; CLASS INSECT A : THE INSECTS ij 1
May-flics, the white ants and numerous other insects
have, like the locust, an incomplete metamorphosis, that
is, the young when hatched resemble in most respects,
except in the absence of wings,' their parents.
The adult water-scavenger beetle feeds chiefly on
decaying vegetation in the water, but instances of the
taking of other insects and of snails have been noted.
Although an aquatic insect the beetle, like its larva, has
no gills for breathing the air which is mixed with the
water, but has to come to the surface occasionally to
obtain air. This it does in an interesting way, which
should be carefully observed by the pupils. The air is
received and held by a covering of fine hairs on the ven-
tral surface of the body, so that a considerable supply may
be carried about by the* beetle while underneath the sur-
face. The beetles often leave the water by night, flying
abroad to other ponds or streams. In winter the beetles
hibernate, burying themselves in the banks of the ponds
which they inhabit.
For a good account, with illustrations, of the water-
scavenger beetle's life-history see Miall's " Natural His-
tory of Aquatic Insects," pp. 61-87.
THE MONARCH BUTTERFLY (Anosia plexippns}
TECHNICAL NOTE. The Monarch or Milkweed butterfly is dis-
tributed ail over the country. It is large, and red-brown in color,
and lays its eggs on milk weeds where the greenish yellow and black-
banded larvae (caterpillars) may be found feeding. The covering
of scales conceals the outlines of the various external parts, but
these scales may be easily removed with dissecting needle and a
small brush. In brushing the scales from the head care must be
taken not to break of the mouth-parts.
External structure (fig. 41). Note the three body-
regions, Jicad, tJiorax and abdomen. Is the body seg-
mented ? Note the dark color and firm character of the
chitinized cuticle.
I7 2 ELEMENTARY ZOOLOGY
Note on the head the large compound eyes. Note the
tumid convex clypens which composes most of the anterior
aspect of the head. Are ocelli present ? Compare the
antenna with those of the locust and water-beetle. Com-
pare also the mouth-parts and note that they differ radi-
cally from those of the locust and beetle. They are not
fitted for biting, but for sucking up liquid food (the nectar
of flowers). Note the absence of a movable flap-like
labrum (a minute narrow stiff piece, bearing at each lateral
compound eye,
antennae. /...
prothorax\
labial
palpi
proboscis''
tarsal segments
FIG. 41. Body of the monarch butterfly, Anosia plexippus, with scales re-
moved to show the external parts.
end a small group of fine brown hairs, represents the
labrum), the entire absence of mandibles, and the absence
of a movable flap-like labium. The labiiim is a fixed
chitinized triangular piece forming part of the floor of the
head. Note the long slender proboscis coiled up like a
watch-spring. (In fresh specimens- this proboscis can be
uncoiled and will be found flexible. If dried or alcoholic
specimens are being studied, the head of the butterfly
BRANCH ARTHROPODS; CLASS INSECTA : THE INSECTS i?3
should be removed and softened in warm water before the
mouth-parts are examined.) On either side of this
proboscis is a peculiar pointed process which rises from
the under side of the head. These processes are the
labial palpi and serve to protect the sucking proboscis.
The proboscis itself is composed of the two greatly modi-
fied maxillce. Instead of being short, jaw-like and com-
posed of several pieces as in the locust, in the butterfly
each maxilla is a slender, flexible half tube applied against
its mate on the opposite side in such a way as to form a
perfect tube long enough to reach into the nectaries of
flowers when in use and capable of being compactly coiled
up at other times. Cut across the proboscis and note the
canal in the centre. Try to separate the two maxillae
which compose it.
Make a drawing of the frontal aspect of the head with
the eyes and appendages.
Compare the thorax with that of the beetle and that of
the locust. The prothorax is a freely movable narrow
ring or collar. The mesothorax and metathorax are fused
to form a large convex mass, of which fully five-sixths is
mesothorax and only one-sixth metathorax. Try to dis-
tinguish the boundaries of the two segments. Note the
three pairs of legs; the differences in size among them,
and the differences between them and the legs of the
locust and water-beetle. In one of the legs determine
the coxa, trochantcr, femur, tibia and tar sal segments.
Note the differences between the wings of the butterfly
and those of the locust and beetle. Note that the wings
are membranous, but are covered with many fine scales
(fig. 42), as is, indeed, the whole body. Rub off some of
these scales on a glass slide and examine ; note shape,
little stem or pedicel of insertion, and longitudinal stria-
tions. Examine under microscope a bit of wing from which
some of the scales have been rubbed. How are the scales
i 7 4
ELEMENTARY ZOOLOGY
attached to the wing 1 membranes ? How are the scales
arranged ? Note that the wing is colorless where the
scales have been removed. All the colors and patterns
of the wings of butterflies are produced by the scales.
Make drawings of scales; of parts of denuded wings,
and of bit of wing covered with scales.
Remove all or nearly all the scales from a wing and
note the arrangement of the veins (venation). Compare
with venation in wings of locust.
Make drawing showing venation in the butterfly's
wings.
The venation of insects' wings is much used in insect
classification, and the
various veins have been
given names. The
names of the veins in
the butterfly's wings are
given in fig. 43. When
the veins in the wings
of all the various groups
of insects are studied, it
is evident that the prin-
cipal ones are the same
in all insects, so that
FIG. 42-Bit of wing of monarch butterfly, the COSta, Sllb-CUSta, ra-
Anosia plexippus, magnified to show the dius, media, Cubitus and
scales; some scales removed to show the
anal veins of the butter-
insertion-pits and their regular arrange-
ment. (From specimen.) fly's wings can be com-
pared with the corresponding veins in the wings of a
beetle or wasp or fly. Noting the differences in the num-
ber and character of branching of these principal veins,
and the number and disposition of the cross-veins which
connect the longitudinal veins, the various kinds of insects
can be to a large extent properly grouped or classified.
A detailed account of the wing-veins of insects is given
BRANCH ARTHROPODA; CLASS IN SECT A : THE INSECTS i?5
in Comstock and Kellogg's " Elements of Insect Anat-
omy," chap. VII.
Of how many segments is the abdomen composed ?
The first or basal segment is depressed, while the others are
more or less compressed. The spiracles are, as in the locust,
situated on the lateral aspects of the abdominal segments.
What segments bear spir-
acles ? The terminal seg-
ments of the abdomen
differ in the two species.
In the female the dorsal
part of the Apparently)
last segment is longer
than the ventral part and
is bent down over it form-
ing a sort of hood over a
space enclosed partly by
this hood, partly by a
bluntly-pointed projection
from the ventral surface,
and party by the lateral
margins of the segment.
In this chamber lies the
Opening from which the FIG. 43. Wings of monarch butterfly,
eggs issue. In the male Anosiaplexippas to show venation ;/
costal vein ; sc, sub-costal vein; r, radial
there are several back- vein; r, cubital vein; a, anal veins.
.- i In addition most insects have a vein
ward - projecting, horny, ^^ the sub costal and ra _
thin processes. dial veins called the median vein.
Make a drawing of the lateral aspect of the whole body.
Life-history and habits. The tiny, conical, yellowish-
green eggs of the monarch butterfly are deposited on the
under side of the leaves of milkweeds (Ascleptas} and
when examined under the microscope are seen to be very
beautiful little objects finely ribbed with longitudinal and
transverse striae. The eggs are laid in April and May
(depending on the lacitude and season) by females which
176 ELEMENTARY ZOOLOGY
have hibernated in the adult condition. From the eggs
the minute, cylindrical, pale-green, black-headed larvae
hatch in four or five days. As soon as hatched the
larva devours the eggshell from which it has escaped and
then feeds voraciously on the milkweed leaves. It grows
'rapidly, and in three or four days a blackish band or ring
appears on each segment, and for the rest of its life it is
very conspicuously colored with its black rings on a
yellowish-green background. It molts three times, and
in from twelve to twenty days is ready to pupate, or
change to a chrysalis.
When ready to pupate the larva usually leaves the
milkweed plant, and seeks some such protected place as
the under side of a fence-rail or jutting rock. Here it
attaches its posterior extremity by a small silken web to
the rail or rock, and casting its larval skin appears as a
beautiful pale-green chrysalis with ivory black and golden
spots. It hangs motionless, and of course without taking
food, for from a week to two weeks (according to
season and temperature), when the pupal cuticle breaks
and the great red-brown butterfly (fig. 165) issues.
The butterfly feeds fas is indicated by the structure of
its mouth-parts) very differently from the larva; it sucks
up by means of its long tubular proboscis the nectar of
flowers, nor does it confine itself at all to the flowers of
milkweeds. It is a fine flyer and a great traveller. Many
thousands of these butterflies often make long flights or
migrations together. At other times tens of thousands
of these butterflies congregate in a certain limited area,
clinging sometimes to the branches of a few trees in such
numbers and so closely together as to give the tree a
brown color. Such a " sembling " of monarch butterflies
occurs every year near the Point Pinos lighthouse on
the Bay of Monterey, California. The object of this
assembling together is not understood. Both the larvae
and adults of the monarch butterfly are distasteful to birds,
BRANCH ARTHROPODA; CLASS IN SECT A : CHE INSECTS *77
by their possession of an acrid body-fluid. The species
is thus protected against the most dangerous enemies of
butterflies, a fact which chiefly accounts for the great
abundance and wide distribution of the monarch (see
p. 137). For a full account of the life-history of the
monarch butterfly, see "Scudder's Life of a Butterfly."
LARVA OF MONARCH BUTTERFLY (Anosia plexippus)
TECHNICAL NOTE. For directions for finding and identifying the
larvae of the monarch butterfly see p. 171. If larvae (caterpillars) of
Anosia cannot be found, those of any other butterfly or moth will
do. Use naked, smooth kinds like cutworms, cabbage worms and
the like, rather than hairy or spiny ones. Use large specimens.
Kill the caterpillar with ether or in a cyanide bottle.
Structure (fig. 44). As we have learned from the study
of the life-history of the locust, water-beetle and butterfly,
some insects are hatched from the egg in a condition
resembling that of the parents in most structural charac-
ters. This is true of the locust. Other insects, as the
beetle and butterfly, are hatched in a form and condition
apparently very different from that of the parents. The
external appearance of a beetle or butterfly larva differs
much from that of the adult or imago of the same indi-
vidual. It will be of interest to examine more particu-
larly the structural condition of one of these larvae and to
compare it with the structure of the adult.
Is the body segmented ? Is the body composed of
head, thorax and abdomen? Note the soft, flexible,
weakly-chitinized condition of the body-wall. How many
pairs of legs are there ? Where are they situated ? Is
there any difference in the various legs ? If so, what is
the difference ? Which of the legs of the larva correspond
with the legs of the butterfly ? Why ? The prothoracic
segment and the abdominal segments I to 8 each bear a
pair of spiracles (small blackish spots on the sides). Are
both compound and simple eyes present ? How many eyes
I 7 8
ELEMENTARY ZOOLOGY
Q3
BRANCH ARTHROPODA ; CLASS INSECT A : THE INSECTS 179
are there ? Are there antenna ? Dissect out the month-
parts. How do they differ from those of the butterfly ?
Are they more like the mouth-parts of the butterfly or
more like those of the locust ?
With fine sharp-pointed scissors make a shallow longi-
tudinal incision along the whole length of the dorsal wall.
In a freshly-killed specimen a drop of pale greenish blood
will issue as the scissors' point is first thrust through the
skin. Put a droplet of this blood on a glass slide, cover
with cover glass and examine with high power of the
microscope. Note that the blood is a fluid containing
numerous sub-circular or elliptical bodies, the blood-
corpuscles. Note at least two kinds of corpuscles : most
abundant a granular, circular kind, the true blood-corpus-
cles ; and rarer, a larger, clear, usually elliptical or oval,
but sometimes irregular and amoebiform kind, generally
spoken of & fat -cells.
Make a drawing of the corpuscles in the field of the
microscope.
After making the dorsal longitudinal incision pin out
the caterpillar in the dissecting-dish with dorsal aspect
uppermost. When the edges of the skin are pinned back,
the organs most conspicuous in the body-cavity will be
the flocculent masses of adipose tissue, the large, simple,
tubular alimentary canal usually dark or greenish because
of the color of its contents, and the numerous silvery
tracJieal tubes. In those caterpillars which spin a silken
cocoon, the silk or spinning-glands are usually long and
prominent. They lie on either side of the anterior part
of the alimentary canal, and open by a common duct on
the labium. Rising from behind the middle of the ali-
mentary canal maybe found the long, whitish, folded and
twisted MalpigJiian tubules. By picking away the fat
masses, expose the full length of the alimentary canal.
Note its great size (large diameter). Is it divided into
i8o ELEMENTARY ZOOLOGY
distinct regions such as crop, proventriculus, stomach,
intestine, etc. ? How is it held in place ? Trace the
principal longitudinal trachea! trunks. Find, if you can,
a pair of small compact bodies usually somewhat elongate,
one lying on each side of the posterior part of the alimen-
tary canal. These are the rudimentary reproductive
organs.
Remove the alimentary canal by cutting it off at its
posterior tip and also in the prothoracic segment. Work
out now the ventral nerve-cord and ganglia, and the
supra-asophageal (brain) and infra-oesophageal ganglia
and the commissures in the head.
In the body of the caterpillar we have found the same
general disposition of organs as in the body of an adult
insect, but several differences are nevertheless noticeable,
viz., the presence of a large quantity of fatty tissue, the
great size and simple character of the alimentary canal,
and the undeveloped condition of the reproductive organs.
OTHER INSECTS
The class Insecta includes those Arthropods which
have one pair of antennae (sense appendages), three pairs
of mouth-parts (oral appendages), and three pairs of legs
(locomotory appendages). The insects, in further con-
tradistinction to the crustaceans, are mostly land animals
and breathe by means of tracheae or tracheal gills. They
are the most familiar of land invertebrates, and, as already
mentioned, include more species than are comprised in all
the other groups of animals taken together. Beetles,
moths and butterflies, flies, wasps and bees, dragonflies
and grasshoppers are familiar members of the class of
insects, but spiders, mites, scorpions, centipeds and
thousand-legged worms are not true insects and should
BRANCH ARTHROPOD/1; CLASS 1NSECTA : THE INSECTS 181
not be so miscalled. These last belong to the branch
Arthropoda but to other classes than the class Insecta.
While insects are found living under most diverse condi-
tions on land, that is, on the ground, in the leaves, fruits
and stems of plants, in the trunks of trees or in dead
wood, in the soil, in decaying animal or plant matter, as
parasites on or in other animals, and in all fresh-water
ponds and streams, they do not live in ocean water. A
few species live habitually on the surface of the ocean, and
a few other forms are found habitually on the water-
drenched rocks and seaweeds between tide lines. The
varied habits of insects, their economic relations with
man. the beauty and grace of many of them, and the
readiness with which they may be collected, reared and
studied, renders them unusually fit animals for the special
attention of beginning students of zoology.
Body form and structure. The segments composing
the body of an insect
are grouped to form
three body-regions, the
head, thorax, and abdo-
men. The head of an
adult insect appears to
be a single segment or
body-ring, but in reality
it is composed of several
segments, probably
seven, completely fused.
The head bears the eyes,
antennae and the mouth-
parts. The thorax is
made up of three seg-
ments, each segment
bearing a pair of legs.
From the dorsal side of the hinder two thoracic segments
FIG. 45. A wingless insect; the American
spring-tail. Lepidocyrtus americanus,
common in dwelling-houses. The short
line at the right indicates the natural
size. (From Marlatt.)
182 ELEMENTARY ZOOLOGY
arise the two pairs of wings which are the most striking
structural features of insects. Not all insects are winged,
(fig. 45), and of those which are a few have only one pair
of wings, but the great majority of them have two pairs of
well-developed wings (fig. 46), which give them, as com-
pared with the other animals we have studied, a new and
most effective means of locomotion. The great numbers
FIG. 46. A four- winged insect; a stone fly, Per la sp., common about
brooks. (From Jenkins and Kellogg.)
of insects and their preponderance among living animals
is undoubtedly largely due to the advantage derived from
their power of flight. The hindmost part of the body,
the abdomen, is composed of from seven to eleven seg-
ments, only the last one or two of which are ever provided
with appendages. When such posterior abdominal
appendages are present they form egg-laying or stinging
or clasping organs.
BRANCH ARTHROPODA; CLASS INSECT A : THE INSECTS 1^3
The body-wall is usually firm and rigid, with thinner
flexible places between the segments and body-parts for
the sake of motion. The body-wall is composed of a
cellular skin or hypoderm, and an outer non-cellular
cuticle in which is deposited a horny substance called
chitin. This chitinous cuticle or exoskeleton serves as
an armor or protective covering for the soft body within,
and also as a point of attachment for the many muscles
of the body.
Insects vary a great deal in regard to shape and ap-
pearance of the body, and certain of the external organs
are greatly modified in different insects to adapt them to
the varied conditions under which they live. Especially
interesting and important are the variations in the char-
acter of the mouth-parts and wings, the organs of food-
getting and locomotion. In our consideration later of
some of the more important groups of insects the modifica-
tion of these parts will be specially referred to. Despite
the great number ol insects, however, and their varied
habits of life, a strong uniformity of body-structure is
noticeable, all of them holding pretty closely to the
typical body-plan.
The most interesting feature of the internal anatomy of
the insect body is the respiratory system. Insects breathe
through tiny paiied openings, called spiracles, in the sides
of the abdominal (and sometimes the thoracic) segments
(the number and disposition of the pairs of spiracles varying
much in different insects). These spiracles are the external
openings of an elaborate system of air-tubes or tracheae
(fig. 47) which ramify throughout the whole body and carry
air to all the organs and tissues. The blood has apparently
(nothing to do with respiration as it has in the' vertebrate
animals, where it carries oxygen to all the body tissues.
The other systems of organs are well developed and in
many respects more complex and elaborate than those of
ELEMENTARY ZOOLOGY
any
of the
The alimen-
FIG, 47. Piece
other invertebrates. The muscular system
comprises a large number of distinct mus-
cles, usually small and short, which are
disposed so as to make very effective the
various complex motions of antennae,
mouth-parts, legs, wings, and egg-laying
organs. The muscles appear to be
very delicate, being almost colorless
when fresh, but they have a high
contractile power,
tary canal is di-
vided into various
special re-
gions, a s
pharynx, cesopha-
of gus, crop, fore
stomach or gizzard,
the giant-crane- digesting Stomach,
fly. (Photo-micro- .
graph by Geo. O. and small and large m-
Mitchell.) testine. From the canal
just at the point of union of the digesting
stomach (ventriculus) and the small in-
testine rise the so-called Malpighian
tubules, which are excretory organs.
They are long slender diverticula of the
alimentary canal, and are typically six
(three pairs) in number. The circula- FlG - 48. The anten-
na of a carrion bee-
tory system is composed of a tubular tie, with the termi-
vessel running longitudinally through the
body in the median line just under the
dorsal wall. It is composed of a series
of chambers or segmental parts, which
by a rhythmic contraction and expansion
propel the blood anteriorly and into a
short, narrow, unsegmented anterior portion of the vessel
nal three segments
enlarged and flat-
tened, and bearing
many ' smelling-
pits/' the antenna
thus serving as an
olfactory organ.
(Photo -micrograph
by Geo. O.Mitchell.)
BRANCH ARTHROPOD A; CLASS MSECTA : THE INSECTS 185
which may be called the aorta. There are no other
arteries or veins, the blood simply pouring out of the
anterior end of the dorsal vessel into the body-cavity. It
bathes the body tissues, flowing usually in regular channels
without walls. It re-enters the dorsal vessel through
paired lateral openings in the chambers.
The main or central nervous system consists of a large
ganglion, the "brain," situated in the head above the
FIG. 49. A section through the compound eye (in late pupal stage) of the
blow-fly, Calliphora romitoria. In the centre is the brain, with optic
loin-, and on the right-hand margin are the many ommatidia in longi-
tudinal section. (Photo-micrograph by Geo. O. Mitchell.)
oesophagus, which sends nerves to the antennae and eyes >
a ganglion in the head below the oesophagus connected
with the brain by a short commissure on each side of
the oesophagus, and sending nerves to the mouth-parts ;
and a ventral nerve-chain composed of a pair of longitudinal
]86 ELEMENTARY ZOOLOGY
commissures lying close together and running from the
head to the next to the last abdominal segment, which
bears a series of segmentally disposed ganglia, each
ganglion being composed of two ganglia more or less
nearly completely fused. There is, in addition, a lesser
system called the sympathetic system, which comprises a
few small ganglia and certain nerves which run from
them to the viscera. The function of the nervous system
of insects reaches a very high development among the
so-called "intelligent insects" and certain extraordi-
narily complex and interesting instincts are possessed by
many forms. The social or communal habits of the ants,
bees, and wasps and the habits connected with the deposi-
tion of the eggs and the care of the young exhibited by
the digger wasps and other insects are of extreme
specialization. The organs of special sense are highly
specialized, the sense of smell (fig. 48) reaching in par-
ticular a high degree of perfec-
tion. One of the compound eyes
(figs. 49 and 50) may contain as
many as 30,000 distinct eye-
elements or ommatidia, but the
sight is probably in no insect
very sharp or clear. Among
insects there are organs of hear-
ing of two principal kinds. In
FIG. 50. -Part of cornea, snow- one kind the organ for taking up
ing facets, of the compound ^ ie sound-waves is a PTOUD of
eye of a horse-fly (Therioplec- &
tes sp.). (Photo-micrograph vibratile hairs usually situated on
by Geo. O. Mitchell.) the antennJE> as j s the case with
the mosquito; in the other kind, it is a stretched mem-
brane or tympanum such as is found in the fore leg of a
cricket or katydid or on the first abdominal segment of
the locust (fig. 51)
The sexes are distinct in insects, and there is often a
BRANCH ARTHROPODA; CLASS INSECT A : THE INSECTS 187
marked sex dimorphism ; in numerous species the males
are winged while the females are wingless, and in a few
cases this condition is reversed. Where there is a
difference in size between male and female, the females
FIG. 51. The auditory organ of a locust (Melanoplus sp.). The large clear
part in centre of the figure is the thin tympanum, with the auditory
vesicle (small black pear-shaped spot) and auditory ganglion (at left of
vesicle and connected with it by a nerve) on its inner surface. (Photo-
micrograph by Geo. O. Mitchell.)
are usually the larger. Fertilization of the egg takes
place in the body of the female and, strangely, this fertil-
ization is effected after the eggshell has been formed. In
all insect eggs there is a minute opening in one pole of
the eggshell called the micropyle through which the
sperm-cells enter. In a few cases the young are born
alive, but such a viviparous condition is exceptional. In
i88 ELEMENTARY ZOOLOGY
a few species, too, young are produced parthenogeneti-
cally, that is, are produced from unfertilized eggs. And
in the case of a few insect species male individuals are
not known.
Development and life-history. The young insect
when just hatched from the egg either resembles, except
for the absence of wings, its parent in general appearance
as in the case of the locust, or it may, as in the butterfly,
emerge in a form very unlike the parent. In the first
case the young has simply to grow, that is, to increase
FIG. 52. The young (at left) and adult (at right) of the bed-bug, Acanthia
lectularia, a wingless insect with incomplete metamorphosis. (After
Riley.)
in size, to develop wings, and to make some other not
very obvious developmental changes in order to become
fully grown. But in the case of the butterfly, and
similarly in the case of all other insects as the flies,
beetles, bees et aL, whose young hatch in a larval condi-
tion differing markedly from the adult, some radical and
striking developmental changes occur before maturity is
reached. Such insects are said to undergo complete
metamorphosis in their development, while those insects
like the locusts, the sucking-bugs, white ants, and others,
BRANCH ARTHROPODA ; CLASS IN SECT A : THE INSECTS 189
the just hatched young of which resemble their parents,
are said to have an incomplete metamorphosis (fig. 52).
In the case of insects with complete metamorphosis,
the young hatches as an active grub or worm-like feeding
larva which increases in size, casting its skin or molting
several times in its growth. Finally after the last larval
molt (fig. 53) called pupation the insect appears in a
FIG. 53. The larva of the violet tip butterfly, Polygonia interragationis*
making its last molt, i.e. pupating. (Photograph from life.)
quiescent non-feeding stage called the pupa (fig. 54), and
encased in an extra thick and firm chitinous exoskeleton.
The immovable pupa is sometimes concealed underground,
sometimes enclosed in a silken cocoon spun by the larva
just before pupation, or is in some other way specially
protected. It is in this pupal condition that the great
changes from wingless, often legless, worm-like larva to
190
ELEMENTARY ZOOLOGY
winged, six-legged, graceful imago of adult stage are
completed, and with the molting of the chitinous pupal
cuticle the metamorphosis or development of the insect
is completed. As a matter of fact many of the special
organs of the adult, the legs and wings, for example,
begin to develop as little buds or groups of cells in the
body of the larva, and when the larva is ready to pupate
FlG. 54. Chrysalid (pupa) of the violet tip butterfly, Polygonia interraga-
tionis. From this chrysalid issues the full fledged butterfly. (Photo-
graph from life.)
these imaginal wings and legs are drawn out to the
external surface of the body, and may be readily recog-
nized as they lie on the ventral surface of the pupa folded
and closely pressed to the body surface. In recent years
the study of the post-embryonic development of insects
with complete metamorphosis has revealed some re-
markable changes of the internal organs which result in
a nearly complete disintegration or breaking down of
BRANCH ARTHROPODA; CLASS IN SECT A : THE INSECTS 191
most of the internal organs of the larva (fig. 55) and a
rebuilding of the organs of the adult from primitive be-
ginnings.
The habits of the larvae of insects with complete meta-
morphosis and of the young of some insects with incom-
plete metamorphosis often differ markedly from the
FIG. 55. A cross-section of the body of the pupa of a honey-bee, showing
the body cavity filled with disintegrated tissues, and (at the bottom) a
budding pair of legs of the adult, the larva being wholly legless.
(Photo-micrograph by Geo. O. Mitchell.)
habits of the adults, and as the habits and instincts of
insects are remarkably specialized, the study of their be-
havior and of the structural and physiological modifica-
tion which their varied habits of life have brought about
is of much interest and significance. In later paragraphs
this phase of insect study will be again referred to.
Classification. Much attention has been paid to the
classification of insects and the 300,000 (approximately)
known species have been variously grouped together into
orders by different entomologists. A subdivision of the
class Insecta into five orders was proposed by Linnaeus
about 1750 and was used until comparatively recently.
Since then, however, numerous other arrangements have
been proposed, all of them agreeing in increasing the
I9 2 ELEMENTARY ZOOLOGY
number of orders by breaking up some of the old ones
into two or more new ones. The classification adopted
in the text-book * of zoology which we have made our
reference in classification is an 8-order system. The
latest English t text-book, in entomology adopts a
9-order system, while the principal American J text-book
on this subject divides the insects into nineteen orders.
The classification depends chiefly on the character of
the post-embryonic development, that is, on whether the
metamorphosis is complete or incomplete, and on the
structural character of the mouth-parts and wings. In
the following paragraphs a few of the larger insect orders,
with some special representatives of each, will be briefly
considered.
The best American text-book of the classification and
habits of insects is Comstocks' "Manual of Insects."
For an account of the structure of the wings and mouth-
parts of various insects see Comstock and Kellogg 's
" Elements of Insect Anatomy."
Orthoptera : the locusts, cockroaches, crickets, katy-
dids, etc. TECHNICAL NOTE. Obtain specimens of crickets or
katydids, and cockroaches, and compare the external body struc-
ture with that of the grasshopper; examine especially the wings,
mouth-parts, legs, and egg-laying organs. Note that the hindmost
legs of the cockroach are not fitted for leaping but for running. Note
the sound-making (stridulating) organs on the bases of the fore wings
of the male katydids and crickets. Note the auditory organs (tym-
pana) in the fore tibiae of the katydids and crickets. Crickets can
be easily kept alive in breeding-cages in the laboratory and their
feeding habits and much of their life-history observed. The growth
of the young and the development of the wings can be noted, and
will be found to be essentially similar to the conditions already
found in the case of the locust.
The locust studied as one of the examples of the class
Insecta belongs to the order Orthoptera, which also in-
* A Text-book of Zoology, Parker & Haswell, 1897.
f The Cambridge Natural History, vol. V, 1895. vol. VI, 1899.
| A Manual for the Study of Insects, J. H. and A. B. Comstock, 1897.
BRANCH ARTHROPODA; CLASS 1NSECTA : THE INSECTS *93
eludes the cockroaches, crickets (fig. 56), katydids and
green grasshoppers, the walking-stick or twig insects, the
praying mantis and others.
The members of this order all
have an incomplete metamor-
phosis, and in all the mouth-
parts are fitted for biting and
the fore wings are more or
less thickened and modified to
serve as covers or protecting
organs for the broad, plaited,
membranous hind wings, which
are the true flight organs. The
hind legs of locusts, grasshop- FIG. 56. The house cricket,
pers, crickets, and katydids are ^) and female (*) ( From
very large, and enable the in-
sects to leap; the legs of the cockroaches are fitted for
swift running; the fore legs of the praying mantis are
fitted for grasping other insects which serve as their food,
and the legs of the walking-stick (fig. 162) are long and
slender and fitted for slow walking. The shrill singing of
the crickets and katydids and the loud "clacking" of
the locusts are all made by stridulation, that is, by
rubbing two roughened parts of the body together. The
sounds of insects are not made by vocal cords in the
throat. The male crickets and katydids (for only the
males sing) have the veins of the fore wings modified so
that when the bases of the wings are rubbed together
(and when the cricket or katydid is at rest the base of
one fore wing overlaps the base of the other) a part of
one wing called the ' ' scraper ' ' rubs against a part of the
other called the "file" and the shrilling is produced.
The sounds of locusts are produced by the rubbing of
the inside of the hind leg against the outside of the fore
wing when the insect is at rest, or by striking the front
i 9 4
ELEMENTARY ZOOLOGY
margin of each hind wing against the hind margin of each
fore wing when the locust is flying. For hearing the
Orthoptera are provided with auditory organs having the
character of tympana or vibrating membranes. In the
locusts these ears (fig. 51) are situated on the dorsal
surface of the first abdominal segment; in the katydids
and crickets they are in the tibiae
of the fore legs. The food of
locusts, crickets, and katydids is
vegetable, being usually green
leaves ; the cockroaches eat either
plant or animal substances fresh
or dry, while the praying mantis
is predaceous, feeding on other
insects which it catches in its
strong grasping fore legs. The
walking-stick or twig insect is an
excellent example of what is called
1 ' protective resemblance ' ' among
animals. Indeed most of the
FIG. 57. A bird louse, Mr- Orthoptera are so colored and
mus prcest an s, irom a tern,
Sterna maxima. Most birds patterned as to be almost indistin-
w^nglest^bitin'g 11 inlets! guishable when on their usual rest-
called bird-lice, which are ing- or feeding-grounds. Some
external parasites feeding , ., . ^ ,.
on the feathers of the bird f the tropical Orthoptera carry
host. The bird louse to a marvelous degree this modi-
figured is about T V in. long. -..''/'
(Photo-micrograph by Geo. fication for the sake of protection.
O. Mitchell.) j n t hi s connection read Chapter
XXXI referring to ' Protective Resemblances ".)
Odonata and Ephemerida : the dragon-flies and May-
flies. TECHNICAL NOTE. Obtain specimens of adult and imma-
ture dragon-flies. The young dragon-flies (fig. 59) may be got by
raking out some of the slime and aquatic vegetation from the bottom
of a small pond. Compare the external structure of the adult dragon-
flies with that of the grasshopper ; note the large eyes, the narrow
nerve-veined wings, the biting mouth-parts, and the short antennae.
BRANCH ARTHROPODA ; CLASS INSECT A : THE INSECTS *95
Compare the young dragon-flies with the adults ; note the devel-
oping wings and the peculiar modification of the lower lip into a
protrusible, grasping organ which when at rest is folded like a mask
over the face. Examine the interior of the posterior part of the
alimentary canal to find the rectal gills. Obtain specimens of adult
and young May-flies. The young may be found on the under side
of stones in a " riffle " in almost any stream. They live also in ponds.
They may be recognized by reference to fig. 61. Compare adult
May-flies with the dragon-flies ; note the weakly chitinized, delicate
body-wall, and the difference in size between fore and hind wings ;
note the biting mouth-parts of the young and their absence or
presence in vestigial condition only in the adults.
The young of both dragon-flies and May-flies may easily be kept
alive in the laboratory aquarium (fruit-jars or battery-jars with pond
water in), and their feeding habits, their swimming, their respiration,
and much of their development observed. The young May-flies
should be got from ponds, not running streams. Put one ot these
semi-transparent May-fly nymphs into a watch-glass of water, and
examine under the microscope. The movements of the gills, heart,
and alimentary canal, and much of the anatomy can be readily made
out. The emergence of the adult from the nymphal skin can be
seen if close watch is kept. The young dragon-flies may be seen to
capture and devour their prey. They may also transform into adults,
but for this it will be necessary to obtain nymphs nearly ready for
transformation.
Among the most familiar and interesting insects are the
dragon-flies (fig. 58), sometimes called "devil's darning-
needles." They are commonly seen flying swiftly about
over ponds or streams catching other flying insects. The
dragon-flies are the insect-hawks ; they are predaceous and
very voracious, and are probably the most expert flyers
of all insects. There are many species, and their bright
iridescent colors and striking wing-patterns make them
very beautiful. The young dragon-flies (fig. 59) are
aquatic, living in streams and ponds, where they feed
on the other aquatic insects in their neighborhood.
They catch their prey by lying in wait until an insect
comes close enough to be reached by the extraordi-
narily developed protrusible grasping lower lip (fig. 60).
When at rest this lower lip lies folded on the face so as
to conceal the great jaws. The young dragon-flies breathe
196
ELEMENTARY ZOOLOGY
by means of gills which do not project from the outside
of the body, as do the gills of other aquatic insects, but
line the inner wall of the posterior or rectal part of the
FIG. 58. A dragonfly. Sympetrum FIG. 59. The young (nymph) of the
illotum, common in California. dragon-fly, Sympetrum illotum.
(From life.) (From Jenkins and Kellogg.)
alimentary canal. Water enters the canal through the
anal opening and bathes these gills, bringing oxygen to
them and taking away carbonic acid gas. The aquatic
FlG. 60. Young (nymph) dragon-fly, showing lower lip folded and ex-
tended. (F_rom Jenkins and Kellogg.)
immature life of the dragon-flies lasts from a few months
to two years. When ready to change to adult, the young
crawls out of the water and clinging to a rock or plant
makes its last molt.
BRANCH ARTHROPOD A; CLASS INSECT A : THE INSECTS 197
Other abundant and interesting pond and brook insects
are the May-flies. The young May-flies (fig. 61) are
aquatic, living in streams and
ponds and feeding on minute
organisms such as diatoms and
other algae. The immature life
lasts a year, or even two or three
in some species, and then the
May-fly crawls out of the water
upon a plant-stem or projecting
rock and, molting, appears as the
winged adult. The adult May-
fly, having its mouth-parts atro-
phied (a few May-flies have func-
tional mouth-parts), takes no food,
and lives only a few hours or at
most perhaps a few days. It has
the shortest life (in adult stage)
of all insects. The female drops
her eggs into the water.
Hemiptera : the sucking- bugs.
TECHNICAL NOTE. Obtain speci-
FIG. 61. Young (nymph) of
May-fly, showing (g) tra-
cheal gills. (From Jenkins
and Kellogg.)
mens of water-striders (narrow elongate-bodied insects with long
spider-like legs which run quickly about on the surface of ponds
or quiet pools in streams), water-boatmen (mottled grayish insects
about half an inch long which swim and dive about in ponds and
stream-pools), back-swimmers (which are usually in company with
the water-boatmen, but which swim with back downwards and
are marked with purplish-black and creamy white patches), cicadas
(the dog-day locusts), and plant-lice (the green fly "of rose-bushes
and other cultivated plants). Compare the external structure of
some of these Hemiptera with the other insects already examined ;
note especially the sucking beak, composed of the elongate tube-
like labium in which" lie the greatly modified flexible needle-like
maxillae and mandibles, the whole forming an equipment for pierc-
ing and sucking. Obtain immature specimens of some of these
insects (distinguished by their smaller size and the wing-pads) ; note
that the metamorphosis is incomplete, the young resembling the
parents in general appearance. Both immature and adult specimens
of water-boatmen (Corisa), back-swimmers (Notonecta), and water-
198
ELEMENTARY ZOOLOGY
striders (Hygrotrechus} can be easily kept in the laboratory aquaria-
and their swimming, breathing, and feeding habits observed. Note
especially the carrying of air down beneath the water.
The Hemiptera are characterized particularly by their
highly specialized sucking mouth-parts, no other of the
sucking insects having the proboscis composed in the
FIG. 62. The female red orange scale
insect, Aspidiotus aurantii, very injuri-
ous to orange-trees. It has no wings,
legs, nor eyes, but remains motionless
on a leaf, stem, or fruit, holding fast by
its long slender beak, through which it
sucks up the plant-sap. The male is
winged, and has no mouth-parts, taking
no food. (Photo-micrograph by Geo.
O. Mitchell.)
FIG. 63. The female rose-
scale, Diaspis rosa, a
pest of rose-bushes, with-
out eyes, wings, or legs,
but with slender sucking
proboscis. The male is
winged and without
mouth-parts. (Photo-mi-
crograph by Geo. C).
Mitchell.)
same manner. The palpi of both maxillae and labium
are wholly wanting in Hemiptera and the flexible needle-
like maxillae and mandibles are enclosed in the tubular
labium. This order is a large one and includes many
well-known injurious species, as the chinch-bug (Blissns
leucopterus), which occurs in immense numbers in the
grain-fields of the Mississippi valley, sucking the juices
from the leaves of corn and wheat, the grape Phylloxera
(Phylloxera vastatrix), so destructive to the vines of
Europe and California, the scale insects (Coccidce] (figs.
BRANCH ARTHROPODA; CLASS INSECT A : THE INSECTS 199
62 and 63), the worst insect pests of oranges, the squash-
bugs and cabbage-bug and a host of others. Some of
the Hemiptera, for example, the lice and bed-bugs, are
predaceous, sucking the blood of other animals.
The water-striders (fig. 64) catch other insects, both
those that live in the water
and those which fall on to
its surface, and holding the
prey with their seizing
fore legs they pierce its
body with their sharp
beak and suck its blood.
They lay their eggs in the
spring glued fast to water-
plants. The young water-
striders are shorter and
stouter in shape than the
adults.
The Water-boatmen FIG. 64. A water-strider, Hygrotrechns
(fig. 6 5 ) and back-swim- SP " (F-m Jenkins and Kellogg.,
mers swim and dive about in the water, coming more
or less frequently to the surface to get a supply of air.
This air they hold under the
wings, or on the sides and
under part of the body en-
tangled in the fine hairs on
the surface. The insects
appear to have silvery spots
on the body, due to the
presence of this air. The
FIG. 65. A water-boatman, Corisa* "rowing " legs of the water-
sp. (From Jenkins and Kellogg., boatmen (Corisd] are the
hindmost pair; in the back-swimmers (Notonecta) they
are the middle legs.
The cicadas (fig. 66) are the familiar insects of summer
20O
ELEMENTARY ZOOLOGY
which sing so shrilly from the trees, the seventeen-year
cicada (Cicada septendecini) (oftentimes called locust)
being the best known of
this family. Its eggs
are laid in slits cut by
the female in live twigs.
The young, which hatch
in about six weeks, do
not feed on the green
foliage, but fall to the
ground, burrow down to
the roots of the tree and
there live, sucking the
juices from the roots, for
FIG. 66. The seventeen-year cicada, Ci- sixteen years and ten or
cada septendecim ; the specimen at left , ,, iiru
showing sound-making organ, ,./., ven- eleven months. When
tral plate; /, tympanum. (From speci- about to become adult,
men.)
the young cicada crawls
up out of the ground and clinging to the tree-trunk molts
for the last time, and flies to the tree-tops.
The plant-lice (Aphididce) are small soft-bodied
Hemiptera which have both winged and wingless indi-
viduals. In the early spring a wingless female hatches
from an egg which, laid in the preceding fall, has passed
the winter in slow development. This wingless female,
called the stem-mother, lays unfertilized eggs or more
often perhaps gives birth to live young, all of which are
similarly wingless females which reproduce partheno-
genetically. This reproduction goes on so rapidly that
the plant-lice become overcrowded on the food-plant and
then a generation of winged * individuals is produced from
* It has been shown by experiment that the winged individuals, which are
able to leave the old food-plant and scatter over new plants, do not appear
until the food-supply begins to run short. At the insectary of Cornell Uni-
versity ninety -four successive generations of wingless individuals were bred,
BRANCH ARTHROPODA; CLASS JNSECTA : THE INSECTS 201
time to time. These winged plant-lice fly away to new
plants. In the autumn a generation of males and females
is produced ; these individuals mate and each female lays
a single large egg which goes over the winter, and pro-
duces in the spring the wingless agamic stem-mother.
Plant-lice produce honey-dew, a sweetish substance much
liked by ants, and the lice are often visited, and sometimes
specially cared for, by the ants for the sake of this honey-
dew. Small as they are, plant-lice occur in such numbers
as to do great damage to the plants on which they feed.
The apple-aphis, cherry-aphis, pear-aphis, cabbage-aphis
and others are well-known pests. The most notoriously
destructive plant-louse is the grape PJiylloxera, which
lives on the roots and leaves of the grape-vine. Im-
mense losses have been caused by this pest, especially in
the wine-producing countries of southern Europe.
Diptera : the flies. TECHNICAL NOTE. Obtain specimens
of the adult and young stages of the blowfly and the mosquito. All
the young stages of the blowfly may be obtained, and its life-history
studied, by exposing a piece of meat to decay in an open glass jar.
The larvae of the mosquito are the familiar wrigglers of puddles
and ponds, and by collecting some of them and keeping them in a
glass jar of water covered with a bit of mosquito-netting, the life-
history of the mosquito is easily studied. If the eggs can be ob-
tained from the pond so much the better ; they are in little black
I masses floating on the surface of the water, and resemble at first
j glance nothing so much as a floating bit of soot. The external
structure of the adult flies should be compared with that of the
other insects studied, noting especially the condition of mouth-parts
and wings, and the substitution of balancers for the hind wings.
The mouth-parts of the mosquito are in the form of a long proboscis
composed of six slender needle-like stylets lying in a tube narrowly
open along its dorsal surface. The tube is the labium, and the
stylets are the two maxillae, two mandibles, and two other parts
known as the epipharynx and the hypopharynx. Two additional
thicker elongate segmented processes lying outside of and parallel
with the tube are the maxillary palpi. The male mosquito (distin-
guished from the female by the more hairy or bushier antennae) lacks
In taking care to provide a constantly abundant supply of food. This ex
it was continued for more than lour years.
202 ELEMENTARY ZOOLOGY
the pair of needle-like mandibles. The mouth-parts of the blowfly
are composed almost exclusively of the thick fleshy proboscis-like
labium, which is expanded at the tip to form a rasping organ
The Diptera or true flies are readily distinguishable
from other insects by their having a single pair of wings
instead of two pairs, the hind wings being transformed
into small knob-headed pedicels called balancers or
halteres. The flies undergo complete metamorphosis,
and their mouth-parts are fitted for piercing and sucking
(as in the mosquito) or for rasping and lapping (as in the
blowfly). Nearly 50,000 species of flies are known, more
than 4,000 being known in North America alone.
The blowfly (CallipJiora vomitoria) is common in
houses, but can be distinguished from the house-fly by its
larger size and its steel-blue abdomen. It lays its eggs
on decaying meat (or other organic matter) and the white
footless larvae (maggots) hatch in about twenty-four
hours. They feed voraciously and become full grown in
a few days. They then change into pupae which are
brown and seed-like, being completely enclosed in a uni-
form chitinized case which wholly conceals the form of the
developing fly. The house-fly has a life-history and im-
mature stages like the blowfly, but its eggs are deposited
on manure.
The mosquito (Culcx sp.) (fig. 67) lays its eggs in a
sooty-black little boat-shaped mass which floats lightly on
the surface of the water. In a few days the larvae, or
" wrigglers," issue and swim about vigorously by bend-
ing the body. The head end of the body is much broader
than the other, the thoracic segments being markedly
larger than the abdominal ones. The head bears a pair
of vibrating tufts of hairs, which set up currents of air that
bring microscopic organic particles in the water into the
wriggler's mouth. At the posterior tip of the body are
two projections, one the breathing-tube (the wriggler
BRANCH ARTHROPODS; CLASS 1NSECTA : THE INSECTS 2 3
coming often to the surface to breathe), and the other
the real tip of the abdomen. The wriggler, although
heavier than water, can hang suspended from the surface
film by the tip of its breathing-tube. It changes in a few
FIG. 67. The mosquito, Culex sp. ; showing eggs Con surface of water),
larvae (long and slender, in water), pupa (large headed, at surface),
and adult (in air). (From living specimens.)
204
ELEMENTARY ZOOLOGY
change to the adult mosquito the pupa (which, unlike the
wriggler, is lighter than water) floats at the surface of the
water, back uppermost. The chitinous cuticle splits
along the back and the delicate mosquito comes out, rests
FIG. 68. The house-flea, Pulex irritans; a, larva; , pupa; t, adult.
(The fleas are probably more nearly related to the Diptera than to any
other order of insects. (After Beneden.)
on the floating pupal skin until its wings are dry, and
then flies away. Only the female mosquitoes suck blood.
If they cannot find animals, mosquitoes live on the juices
of plants. They are world-wide in their distribution,
being serious pests even in Arctic regions, where they are
often intolerably numerous and greedy. Recent investi-
gations have shown that the germs which cause malaria
in man live also in the bodies of mosquitoes, and are in-
troduced into the blood of human beings by the biting
BRANCH ARTHROPODA; CLASS IN SECT A : THE INSECTS 205
(piercing) of the mosquitoes. It is probable also that the
germs of yellow fever are distributed by mosquitoes in the
same way. By pouring a little kerosene on the surface
of a puddle no mosquitoes will be able to escape from
the water.
Lepidoptera: the moths and butterflies. TECHNICAL
NOTE. Obtain specimens of a few moths, and compare with the
butterfly already studied ; note especially the character of antennae.
Obtain miscellaneous specimens of larvae, pupae, and cocoons of any
moths or butterflies. Note the variety in colors, markings, and
skin covering's of the larvae ; note the shape and markings of the
pupae. Rear from eggs, larvae, or pupae in breeding-cages any
moths and butterflies obtainable (for directions for rearing moths
and butterflies see Chapter XXXIV), keeping note of the times of
molting and of the duration of the various immature stages. If
the eggs of silkworms can be obtained the whole life cycle of the
silkworm moth can be observed in the schoolroom. The larvae
(worms) feed on mulberry or osage orange leaves, feeding vora-
ciously, growing rapidly and making no attempts to escape. The
molting of the larvae can be observed, the spinning of the silken
cocoon, and the final emergence of the moth. The moths after
emergence will not fly away, but if put on a bit of cloth will mate,
and lay their eggs on it. From these eggs, which should be kept
well aired and dry, larvae will hatch in nine or ten months (if the
race is an " annual ").
The Lepidoptera (figs. 69-74) include all those insects
familiarly known to us as moths and butterflies ; they are
characterized by their scale-covered wings (fig. 69) and
long nectar-sucking proboscis composed of the two inter-
locking maxillae. They undergo a complete metamorpho-
sis (fig. 70) and their larvae are the familiar caterpillars of
garden and field. These larvae have biting mouth-parts
and feed on vegetation, some of them being very injurious,
for example the army-worms, cut-worms, codlin moth
worms, etc. The adult moths and butterflies take only
liquid food, or no food at all, and are wholly harmless to
vegetation. The structure and life-history of a butterfly
has already been studied, and in the more general condi-
206 ELEMENTARY ZOOLOGY
tions of structure and life-history there is much similarity
in the many insects of this order. The eggs are usually
laid on the food-plant of the larva ; the larva feeds on the
FIG. 69. A small, partly denuded part, much magnified, of a wing of a
" blue" butterfly, Lyceena sp., showing the wing,scales and the pits in
the wing-membrane, in which the tiny stems of the scales are inserted.
(Photo-micrograph by Geo. O. Mitchell.)
leaves of this plant, grows, molts several times, and
pupates either in the ground or in a silken cocoon or
simply attached to a branch or leaf. There are about
six thousand species of moths and butterflies known
in North America, and they are our most beautiful in-
sects.
Coleoptera : the beetles. TECHNICAL NOTE. Obtain
specimens of various beetles, among them some water-beetles and
June-beetles with their young stages, if possible ; if not, then the
young stages and adults of any beetle common in the neighborhood
of the school. Of the swimming and diving water-beetles there are
three families, viz., the Gyrinida? or whirligig beetles, with four eyes
(each compound eye divided in two), the Hydrophilidas, or water-
scavengers with two eyes and antennas with the terminal segments
BRANCH ARTHROPOD/1; CLASS IN SECT A : THE INSECTS 207
thicker than the others, and the Dytiscidae or predaceous water-
beetles with two eyes and slender thread-like antennae. Try to
find Dytiscidae, large, oval, shining black beetles ; the larvae are
called water-tigers and are long, slim, active creatures with six legs
FlG. 70. The forest tent-caterpillar moth, Clisiocampa disstria, in its
various stages; m, male moth; /", female moth; />, pupa; e, eggs (in a
ring) recently laid; g. eggs hatched; r, larva or caterpillar. Moths
and caterpillar are natural size, eggs and pupa slightly enlarged.
(Photograph by M. V. Slingerland. )
and slender curving jaws (see fig. 76). The June-beetles are the
heavy brown buzzing "June-bugs" and their larvae are the common
"white grubs "found underground in lawns and pastures. Have
live water-tigers and predaceous water-beetles in the aquarium.
Note their feeding and breathing. Compare the external structure
of the beetles with that of the other insects, noting especially the
biting mouth-parts, and their thickened horny fore wings serving
as covers for the folded membranous hind wings.
208 ELEMENTARY ZOOLOGY
The Coleoptera is the largest insect order, probably
100,000 species of beetles being known, of which 10,000
FIG. 71. A trio of apple tent-caterpillars, Ctisiocampa americana, natural
size. These caterpillars make the large unsightly webs or ;i tents " in
apple-trees, a colony of the caterpillars living in each tent. (Photograph
from life by M. V. Slingerland.)
species are found in North America. They pass through
a complete metamorphosis (figs. 75 and 76), the larvse of
the various kinds showing much variety in form and habit.
BRANCH ARTHROPODA; CLASS IN SECT A : THE INSECTS 209
The pupae are quiescent and are mummy-like in appear-
ance, the legs and wings being folded and pressed to the
ventral surface of the body. Among the familiar beetles
are the lady-birds, which are beneficial insects feeding on
plant-lice and other noxious forms ; the beautifully colored
FIG. 72. A. family of forest tent-caterpillars (Clisiocampa disstria , resting
during the day on the bark, about one-third natural size. (Photograph
from life by M. V. Slingerland.)
tiger-beetles, predaceous in habit; the "tumblebugs " and
carrion beetles, which feed on decaying organic matter;
the luminous fire-flies with their phosphorescent organs
on the ventral part of the abdomen; the striped Colorado
potato-beetle and the cucumber-beetles and numerous
other destructive leaf-eating kinds; the various weevils
210
ELEMENTARY ZOOLOGY
(fig. 78) that bore into fruits, nuts and grains, and the
many wood-boring beetles, destructive to fruit-trees as
well as to shade- and forest-trees.
The predaceous water-beetles (Dyticus sp. ) are common
in ponds and quiet pools in streams. When at rest they
hang head downward with the tip of the abdomen just
projecting from the water. Air is taken under the tips of
FIG. 7v Moths of the peach-tree borer, Sanninoidea exitiosa, natural size;
the upper one and the one at the right are females. (Photograph by
M. V. Slingerland.)
the folded wing-covers (elytra) and accumulates so that
it can be breathed while the beetle swims and feeds under
water. When the air becomes impure the beetle rises to
the surface, forces it out, and accumulates a fresh supply.
The beetles are very voracious, feeding on other insects,
and even on small fish. The eggs are laid promiscuously in
the water, and the elongate spindle-form larvae (fig. 77)
FIG.
74- Army- worms, larvae of the moth, Leucania ^^n^pllncta, on corn.
(Thotoeranh by M. V. Slingerland.)
212
ELEMENTARY ZOOLOGY
called water-tigers are also predaceous. They suck the
blood from other insects through their sharp-pointed
sickle-shaped hollow
mandibles. When a larva
is fully grown it leaves
the water, burrows in
the ground, and makes a
round cell within which it
undergoes its transforma-
tions. The pupa state
lasts about three weeks
in summer, but the larvae
that transform in autumn
remain in the pupa state
all winter.
The June-beetles (June-
bugs) (Lachnosterna sp.)
feed on the foliage of
trees. Their eggs are
laid among the roots of
grass in little hollow balls
of earth, and the fat slug-
gish white larvae feed on the grass-roots. They some-
times occur in such numbers as to injure seriously lawns
and meadows. The larvae live three years (probably)
before pupating. They pupate underground in an earthen
cell, from which the adult beetle crawls out and flies up
to the tree-tops.
Hymenoptera : the ichneumon flies, ants, wasps, and
bees. TECHNICAL NOTE. Obtain specimens of wasps, both
social (distinguished by having each wing folded longitudinally) and
solitary (wings not folded longitudinally), and if possible of both
queens (larger) and workers (smaller) of the social kinds ; of ants
both winged (males or females) and wingless (workers) individ-
uals ; also of honey-bees, including a queen, drones, and workers,
and some brood comb containing eggs, larvae, and pupae. The bee
FIG. 75. The quince-curculio (a beetle),
Conotracheliis cratcegL natural size and
enlarged. (Photograph by M. V.
Slingerland.)
BRANCH ARTHROPOD A; CLASS IN SECT A : THE INSECTS 213
specimens can be got of a bee raiser. Compare the external struc-
ture of ants, bees, and wasps with that of other insects ; note the
pronounced division of the body into three regions (head, thorax,
abdomen) ; note the character of the mouth-parts having mandibles
fitted for biting (ants and wasps) or moulding wax (honey-bees) and
having the other parts adapted for taking both solid and liquid
food ; note the sting (possessed by the females and workers only).
Observe the behavior of bees in and about a hive ; note the coming
and going of workers for food. Observe bees collecting pollen at
flowers ; observe them drinking nectar. Examine the honey-bee
FIG. 76. Immature stages of the quince curculio, Conotrachelus crattzgi;
at the left, the larva natural size and enlarged ; at the right, the pupa.
The beetle lays its eggs in pits on quinces, and the larva lives inside
the quince as a grub; the pupa lives in the ground. (Photograph by
M. V. Sliugerland.)
in its various stages, egg, larva, pupa, adult. Note the special
structure of the adult worker fitting it to perform its various special
labors ; the pollen-baskets on the hind legs ; the wax-plates on the
ventral surface of the abdomen, the wax-shears between tibia and
tarsus of hind legs ; the antennas-cleaners on the fore legs ; the
hooks on front margin of hind wings, etc.
The Hymenoptera include the familiar ants, bees, and
wasps, and also a host of other four- winged, mostly
small, insects, many of which are parasites in their larval
stage on other insects. All Hymenoptera have a com-
2T4
ELEMENTARY ZOOLOGY
plete metamorphosis, and their habits and instincts are,
as a rule, very highly specialized. The parasitic Hymen-
optera such as the ichneumon flies,
chalcid flies, etc., are stingless but
have usually a piercing ovipositor
(the sting being only a modified
ovipositor). The general life-history
of these ichneumons is as follows:
the female ichneumon fly, finding
one of the caterpillars or fly or beetle
larvae which is its host, settles on it
and either lays an egg or several
eggs on it, or thrusting in its ovi-
positor, lays the eggs in the body;
the young ichneumon hatching as
a grub burrows into the body of its
caterpillar host, feeding on the body-
tissues, but not attacking the heart
FIG. 77._Water-tiger, the or nervous system, so that the host
larva of the predaceous
water-beetle, Dyticus sp.
(From specimen.)
is not soon killed ; the ichneumon
pupates either inside the host, or
crawls out and, spinning a little silken cocoon (fig. 160),
pupates on the surface of the
body or elsewhere.
Some of the stingless Hymen-
optera are not parasites, but are
gall-producers. The female with
its piercing ovipositor lays an
egg in the soft tissue of a leaf or FIG. 78. The plum curcutio,
stem, and after the larva hatches ConotraMus nenuphar a
beetle very injurious to plums.
the gall rapidly forms. The (Photograph by M. v. Slin-
larval insect lies in the plant- landt)
tissue, having for food the sap which comes to the rapidly
growing gall. It pupates in the gall, and when adult
eats its way out.
BRANCH ARTHROPODS; CLASS INSECTA : THE INSECTS 215
The ants, bees, and wasps are called the stinging
Hymenoptera, although the ants we have in North
America have their sting so reduced as to be no longer
usable. Among these Hymenoptera are the social or
communal insects, viz., all the ants, the bumblebees and
honey-bee, and the few social wasps, as the yellow-jacket
FIG. 79. The currant-stem girdler, Janus integer, a Hymenopteron at
work girdling a stem after having deposited an egg in the stem half an
inch lower down. (Photograph by M. V. Slingerland.)
and black hornet. There are many more species of non-
social or solitary bees and wasps than social ones, and
their habits and instincts are nearly as remarkable.
The solitary and digger wasps do not live in com-
munities as the hornets do, but each female makes a nest
or several nests of her own, lays eggs and provides for
216 ELEMENTARY ZOOLOGY
her own young". The nest is usually a short vertical or
inclined burrow in the ground, with the bottom enlarged
to form a cell or chamber. In this chamber a single egg
is laid, and some insects or spiders, captured and so stung
by the wasps as to be paralyzed but not killed, are put in
for food. The nest is then closed up by the female,
and the larva hatching from the egg feeds on the enclosed
helpless insects until full grown, when it pupates in the cell
and the issuing adult gnaws and pushes its way out of the
ground. Each species of wasp has habits peculiar to itself,
making always the same kind of nest, and providing
always the same kind of food. Some of these wasps make
their nests in twigs of various plants, especially those with
pithy centres in the stems. For interesting accounts of
the habits of several digger wasps see Peckham's 4< The
Solitary Wasps."
The solitary bees, of which there are similarly many
kinds, are like the solitary \vasps in general habit, only
they provision the nest with a mixture of pollen and nectar
got from flowers instead of with stung insects. Some-
times many individuals of a single species of solitary bee
will make their nests near together and thus form a sort
of community in which, however, each member has its
own nest and rears its own young. In the case of certain
small mining bees of the genus Halictus, a step farther
toward true communal life is taken by the common build-
ing and use by several females of a single vertical tunnel
or burrow from which each female makes an individual
lateral tunnel, at the end of which is a brood-chamber.
Perhaps half a dozen females will thus live together, each
independent except for the common use of the vertical
tunnel and exit.
The bumblebees (J^ombus sp.) are truly communal in
habit. All the eggs are laid by a queen or fertile female,
which is the only member of the colony to live through
BRANCH ARTHROPODS; CLASS IN SECT A : THE INSECTS 2*7
the winter. In the spring she finds a deserted mouse's
nest or other hole in the ground, gathers a mass of pollen
and lays some eggs on it. The larvae, hatching, feed on
the pollen, dig out irregular cells for themselves in it,
pupate, and soon issue as workers, or infertile females.
These workers gather more pollen, the queen lays more
eggs, and several successive broods of workers are pro-
duced. Finally late in the summer a brood containing
males (drones) and fertile females (queens) is produced,
mating takes place, and then before winter all the workers
and drones and some of the queens die, leaving a few
fertilized queens to hibernate and establish new communi-
ties in the spring.
The yellow-jackets and hornets (Vespidae), the so-
called social wasps, have a life-history very like that of
the bumblebees. The communities of the social wasps
are larger and their nests are often made above ground,
being composed of several combs one above the other
and all enclosed in a many-layered covering sac open
only by a small hole at the bottom. This kind of nest
hangs from the branch of a tree and is built of wasp-paper,
which is a pulp made from bits of old wood chewed
by the workers. The brood-cells are provisioned with
killed and chewed insects, the larvae of both solitary and
social wasps being given animal food, while the larvae
of both solitary and social bees are fed flower-pollen and
honey. As in the bumblebees, all the members of the
community except a few fertilized females die in the
autumn, the surviving queens founding new colonies in
the spring. The queen builds a miniature " hornet's
nest ' ' in the spring, lays an egg in each cell and stores
the cells with chewed insects. The first brood is com-
posed of workers, which enlarge the nest, get more food,
and relieve the queen of all labor except that of egg-
laying. More broods of workers follow until the fall
2l8
ELEMENTARY ZOOLOGY
brood of males and females appears, after which the
original process is repeated.
The honey-bees and ants show a highly specialized
communal life, with a well-marked division of labor and
an individual sacrifice of independence and personal
advantage which is remarkable. Their communities are
large, including thousands of individuals, and the struc-
tural differences among the males, females, and workers
are readily recognizable. With the ants the workers may
be of two or more sorts, a distinction into large and small
workers or worker majors and worker minors being not
uncommon.
A honey-bee community, living in hollow tree or hive,
includes a queen or fertile female, a few hundred drones
or fertile males, and ten to forty thousand workers, in-
fertile females (fig. 80). The number of drones and
FIG. 80. The honey-bee, Apis mellifica ; A, queen, B, drone, C, worker.
(From specimens.)
workers varies, being smallest in winter. Each kind of
individual has a certain particular part of the work of the
whole community to do; the queen lays all the eggs, that
is, is the mother of the entire community; the drones act
simply as the royal consorts, fertilizing the eggs; while
the workers build the comb, produce the wax from
which the cells are constructed, bring in all the food con-
BRANCH ARTHROPODA; CLASS INSECT A : THE INSECTS 219
sisting of flower-pollen and nectar, care for the young
bees, fight off intruders, and in fact perform all the many
labors and industries of the community except those of
reproduction. There is a certain not very well understood
and perhaps not very sharply defined division of these
labors among the worker individuals, the younger ones
acting specially as " nurses," feeding and caring for the
young bees (larvae and pupae), the older ones making the
food-gathering expeditions. The queen lays her eggs one
in each of many cells (fig. 81). These eggs hatch in three
days, and the young bee appears as a white, soft, footless,
helpless grub or larva that is fed at first by the nurses with
FIG. 81. Worker brood and queen cells of honey-bee ; beginning at the
right end of upper row of cells and going to the left is a series of egg,
young larvae, old larvae, pupa, and adult ready to issue ; the large
curving cells below are queen cells. (From Benton.)
a highly nutritious substance called bee-jelly which the
nurses make in their stomachs and regurgitate for the
larva. After two or three days of this feeding the larvae
are fed pollen and honey. After a few days a small mass
of this food is put into the cell, which is then " capped "
or covered with wax. The larva after using up this food-
supply pupates, and lies quiescent in the pupal stage for
220 ELEMENTARY ZOOLOGY
thirteen days, when the, fully developed bee issues, and
breaking through the wax cap of the cell is ready for the
labors which are immediately assigned it. The bee with
the kind of life-history just described is a worker. It has
been demonstrated that the eggs which produce workers
and those which produce queens do not differ, but if the
workers desire to have a queen produced they tear down
two or three cells around some one cell, enlarging this
latter into a large vase-shaped cell. When the larva
hatches from the egg in this cell it is fed for its whole
larval life with bee-jelly. From the pupa into which this
larva transforms issues not a worker but a new queen.
The eggs which produce drones or males differ from those
which produce queens and workers in being unfertilized,
the queen having the power to lay either fertilized or
unfertilized eggs. When a new queen appears or when
several appear at once there is great excitement in the
community. If several appear they fight among them-
selves until only one survives. It is said that a queen
never uses its sting except against another queen. The
old queen now leaves the hive accompanied by many of
the workers. She and her followers fly away together,
finally alighting on some tree-branch and massing there
in a dense swarm. This is the familiar act of 4< swarm-
ing. " Scouts leave the swarm to find a new home, to
which they finally conduct the whole swarm. Thus is
founded a new colony. "This swarming of the honey-
bee is essential to the continued existence of the species ;
for in social insects it is as necessary that the colonies be
multiplied as it is that there should be a reproduction of
individuals. Otherwise as the colonies were destroyed
the species would become extinct. With the social wasps
and with the bumblebees the old queen and the young
ones remain together peacefully in the nest; but at the
close of the season the nest, is abandoned by all as an
BRANCH ARTHROPOD A; CLASS IN SECT A : THE INSECTS 221
unfit place for passing the winter, and in the following
spring each young queen founds a new colony. Thus
there is a tendency towards a great multiplication of
colonies. But with the honey-bee the habit of storing
food for winter, and the nature of the habitations of these
insects, render it possible for the colonies to exist in-
definitely, and thus if the old and young queens remained
together peacefully there would be no multiplication of
colonies and the species would surely die out in time.
FIG. 82. Honey-bees building comb. (From Benton.)
We see, therefore, that what appears to be merely
jealousy on the part of the queen honey-bee is an instinct
necessary to the continuance of the species."
For the special labors of gathering food, making wax,
building cells, etc., the \vorkers are provided wit'i special
structures, as the pollen-baskets on the outer surface
of the widened tibia of the hind legs, the wax-shears
between the tibia and first tarsal joint of the hind legs,
the wax-plates on the ventral surface of the abdomen,
etc. A great many interesting things connected with the
222
ELEMENTARY ZOOLOGY
life and industries of a honey-bee community can be
learned by the student from observation, using for a guide
some book such as Cowan's "Natural History of the
Honey-bee."
The gathering of food from long distances, the details
of wax-making and comb-building, of honey-making (for
FIG. 83. Comb of the tiny East Indian honey-bee, Apis jlorea, one-third
natural size. (From Benton. )
the nectar of flowers is made into honey by an interesting
process), the storing of food, how the community protects
itself from starvation when winter sets in or food is
scarce by killing the useless drones and the immature
bees in egg and larval stage, and many other phenomena
of the life of the bee community present good opportuni-
ties for careful observation and field study. Although
the community is a persistent or continuous one, the indi-
viduals do not live long, the workers hatched in the
spring usually not more than two or three months, and
BRANCH ARTHROPODA; CLASS INSECTA : THE INSECTS 223
those hatched in the fall not more than six or eight
months. But new ones are hatching while the old ones
are dying and the community as a whole always persists.
A queen may live several years, perhaps as many as five.
She lays about one million eggs a year.
There are more than two thousand known species of
ants (fig. 84), all of which live in communities and show a
truly communal life. The ant workers are specially dis-
tinguished in structure from the males and females by
being wingless, and in numerous species there are two
sizes or kinds of workers known as \vorker majors and
worker minors. The life-history and communal habits of
ants are not so thoroughly known as are those of the
honey-bee, but they show even more remarkable speciali-
zations. The ant nest or formicary is with most species an
elaborate system of underground galleries and chambers,
special rooms being used exclusively for certain special
purposes, as nurse-rooms, food-storage rooms, etc. The
food of ants comprises many animal and vegetable sub-
stances, but the favorite food with many species is the
4 'honey-dew" secreted by the plant-lice (Aphididae)
and scale insects (Coccidae). To obtain this food an ant
strokes one of the aphids with its antennae, when the fluid
is excreted by the insect and drunk by the ant. In order
to have a certain supply oi this food some species of ants
care for and defend these defenseless aphids, which have
been called the 4< cattle" of the ants. In some cases
they are even taken into the ants' nests and food provided
for them. "In the Mississippi Valley a certain kind of
plant-louse lives on the roots of corn. Its eggs are
deposited in the ground in the autumn and hatch the fol-
lowing spring before the corn is planted. Now the
common little brown ant (Lasius flaws] lives abundantly
in the cornfields, and is especially fond of the honey
secreted by the corn-root louse. So when the plant-lice
224
ELEMENTARY ZOOLOGY
hatch in the spring before there are corn-roots for them
to feed on, the little brown ants with great solicitude
carefully place the plant-lice on the roots of a certain
kind of knot-weed which grows in the field and protect
them until the corn germinates. Then the ants remove
the plant-lice to the roots of the corn, their favorite food-
FIG. 84. The little black ant, Monomorium mimitum; a, female, b, female
with wings, <r, male, </, workers, e, pupa, f. larva, g, egg of worker,
all enlarged. (From Marlatt.)
plant. In the arid lands of New Mexico and Arizona the
ants rear scale insects on the roots of cactus. "
The ants are among the most warlike of insects.
Battles between communities of different species are
numerous, and the victorious community takes possession
of the food-stores of the conquered. Some species of ants
live wholly by war and robbery. In the case of the
BRANCH ARTHROPOD A; CLASS INSECT A : THE INSECTS 225
remarkable robber-ant (Ecitori], found in tropical and sub-
tropical regions, most of the workers are soldiers, and no
longer do any work but fighting. The whole community
lives exclusively by pillage. Some kinds of ants go even
farther than mere robbery of food-stores: they make
slaves of the conquered ants. There are numerous species
of these slave-making ants. They attack a nest of
another species and carry into their own nest the eggs
and larvae and pupae of the conquered community, and
when these come to maturity they act as slaves of the
victors, collecting food, building additions to the nest,
and caring for the young of the slave-makers.
As with the honey-bee the larval ants are helpless
grubs and are cared for and fed by nurses. The so-called
44 ants' eggs," the little white oval masses which we often
see being carried in the mouths of ants in and out of an
ants' nest, are not eggs, but are the pupae which are
being brought out to enjoy the warmth and light of the
sun or being taken back into the nest afterward.
There are in this country numerous species of ants
showing much variety of habit and offering excellent
opportunities for most interesting field observations. For
an account of several of the common species see Corn-
stock's 4< Manual of Insects," pp. 633-643. Ants may
be readily kept in the schoolroom in an artificial nest or
formicary and their life-history and habits closely watched.
For full directions for making and keeping a simple and
inexpensive formicary see Comstock's 44 Insect Life,"
pp. 278-281. For an interesting account of some of the
habits of the social insects see Lubbock's "Ants, Bees,
and Wasps. ' '
226
ELEMENTARY ZOOLOGY
CLASS MYRIAPODA : THE MYRIAPODS, OR CENTIPEDS
AND MlLLIPEDS.
Belonging to the branch Arthropoda, with the classes
Crustacea and Insecta, are three other classes, of which
one, the Onychophora, is represented by a single genus
Peripatus (Fig. 85), of extremely interesting animals.
However, as these animals are not found
in the United States we cannot study
them. The other two classes are the
Myriapoda, including the centipeds and
millipeds or thousand-legged worms, and
the Arachnida, including the scorpions,
spiders, mites, and ticks. All these
animals are often spoken of as insects,
but though related to them they are not
true insects.
TECHNICAL NOTE. From under stones or
logs obtain specimens of millipeds, or thousand-
legged worms (large blackish, cylindrical, worm-
like animals with each body-segment back of the
fourth bearing two pairs of jointed legs) ; also
specimens of centipeds or hundred-legged worms
(flattened, usually brownish or pale worm-like
animals with the body-segments bearing only one
pair of legs each) in the same places. Examine
the external structure ; note number of body-
rings ; division into body-regions ; presence of
FIG. 85. Peripatus antennae; character and number of eyes; charac-
eiseni (Mexico), ter of mouth-parts ; character and arrangement
(From specimen.) o f j e g S> j n tne centipeds the first pair of legs is
modified to form a pair of poison-fangs. They appear to belong to
the mouth-parts. The internal anatomy will be found to be, if
examined, much like that of insects and can be studied from the
account of the anatomy of the water-scavenger beetle and butterfly
larva. Compare the Myriapods with the Hexapods or true insects.
What are the points of resemblance ? what are the points of differ-
ence ?
The Myriapoda are land-animals breathing by means
of tracheae like the insects. In them the body-segments
BRANCH AR THRU POD A ; CLASS M YRIAPODA : M YRIAPODS 227
are nearly uniform in character with the exception of the
head, which, as in the insects, bears the mouth-parts and
antennae. There is no grouping of the body-segments
into regions except as the head is opposed to the rest of
the body. (In a few myriapods there are indications of
a division of the hind body into thorax and abdomen.)
The presence of true legs on all the
segments of the hinder region of the
body and the lack of the three-region
division of the body are the principal
external structural characteristics which
distinguish myriapods from insects. The
internal anatomy corresponds in general
character with that of insects.
The most familiar myriapods are the
millipeds, and the lithobians and centi-
peds. The millipeds are cylindrical in
shape, have two pairs of legs on most
of the body-segments and are vegetable
feeders, though some may feed on dead
animal matter. The galley-worms
{Julus) (fig. 86), large, blackish, cylin-
drical millipeds found under stones and
logs and leaves and in loose soil, are
familiar forms. They crawl slowly and when disturbed
curl up and emit a malodorous fluid. They can easily be
kept alive in shallow glass vessels with a layer of earth in
the bottom, and their habits and life-history may thus be
studied. They should be fed sliced apples, green leaves,
grass, strawberries, fresh ears of corn, etc. They are not
poisonous and may be handled with impunity. They lay
their eggs in little spherical cells or nests in the ground.
An English species of which the life-history has been
studied lays from 60 to 100 eggs at a time. The eggs
of this species hatch in about twelve days.
FIG. 86. A galley-
worm (milliped),
Julits sp. (From
specimen.)
228
ELEMENTARY ZOOLOGY
The lithobians and centipeds are flattened and have
but a single pair of legs on each body-ring. They are
predaceous in habit, catching and killing insects, snails,
earthworms, etc. They can
run rapidly, and have the first
pair of legs modified into a
pair of poison-claws, which
are bent forward so as to lie
near the mouth. The com-
FIG. 87. The skein centi-
ped, Scutigera forceps, nat-
ural size, common in houses
and conservatories. (From
Marlatt.)
FIG. 88. Acentiped, Scolo-
pendra sp. (From speci-
men.)
mon ''skein" centiped (Scutigera forceps] (fig. 87) is
yellowish and has fifteen pairs of legs, long 4O-segmented
antennae, and nine large and six smaller dorsal segmental
BRANCH ARTHROPODA ; CLASS ARACHNID A : SPIDERS 229
plates. The true centipeds (Scolopcndra) (fig. 88) have
twenty-one to twenty-three body-rings, each with a pair
of legs, and the antennae have seventeen to twenty joints.
They live in warm regions, some growing to be very
large, as long as twelve inches or more. The " bite " or
wound made by the poison-claws is fatal to insects and
other small animals, their prey, and painful or even
dangerous to man. The popular notion that a centiped
" stings " with all of its feet is fallacious. It is recorded
by Humboldt that centipeds are eaten by some of the
South American Indians.
CLASS ARACHNIDA: THE SCORPIONS, SPIDERS, MITES,
AND TICKS.
TECHNICAL NOTE. Obtain specimens of various spiders ; the
running or hunting spiders may be found on the ground, especially
under stones and boards, the web-makers on their snares. Get
also spiders' " cocoons " (egg-sacs). Examine the external structure
of the spider ; note the two body-regions ; the number and character
of legs ; the absence of antennas ; the number and arrangement of
the eyes (which are simple, not compound) ; the mouth-parts, espe-
cially the large mandibles ; the spinnerets at the tip of the abdomen
(examine a cut off spinneret under the microscope to see the spin-
ning-tubes) ; note the breathing openings or spiracles on under side
of abdomen. Obtain also a scorpion if possible, and some ticks and
mites. Compare with the spiders and note that in the scorpion
the body is plainly seen (especially in the abdomen) to be composed
of segments. Note the extreme fusion of the segments and body-
regions in the mites and ticks. The common red spider of hot-
houses and gardens is a mite ; ticks may sometimes be found on
dogs. Observe various kinds of spider-webs, and try to observe
the process of web-making (this can be observed early in the morn-
ing or about dusk) by one of the orb-weaving garden-spiders.
Live spiders can be kept in the schoolroom and their feeding
habits and perhaps web-making habits observed.
The class Arachnida is composed of Arthropods whose
body-segments are grouped into two regions, a cephalo-
thorax bearing the mouth-parts, eyes, and legs, and an
abdomen. The segments composing these two parts are
210
ELEMENTARY ZOOLOGY
so fused that, except in the scorpions, they are usually
indistinguishable. There are no
antennae, the eyes are simple, the
mouth-parts fitted for biting, and
there are four pairs of legs. In
their internal anatomy the arach-
nids show in some forms a pecu-
liar modification of the respiratory
organs, the tracheae being flat and
leaf-like and massed together in a
few groups rather than being tubular
and ramifying through the body.
The dorsal vessel or heart usu-
ally has a few blood-vessels or
arteries running from it. This class
is divided into three orders, the
FIG. 89. A scorpion Cen- Arthrogastra, or scorpions, the
trurus sp., from Cali- A r ~ r : nQ
fornia. (From specimen.) 1 ld >
o r mites
and ticks, and the Araneina, or
spiders.
The scorpions (fig. 89) have
the posterior six segments of
the abdomen much narrower
than the seven anterior seg-
ments and forming a tail which
bears at its tip a poison-fang or
sting. This sting is used to kill
prey, insects and other small
animals. The tail can be darted
forwards over the body to strike
prey which has been previously FlG .
seized by the large pincer-like
maxillary palpi. Scorpions are
common in warm regions, about twenty species being
cheese-mite, Ty-
roglyphus siro, greatly en-
larged. (After rk-rlese.)
BRANCH ARTHROPODS , CLASS ARACHNID A : SPIDERS 231
known in southern North America. Their sting though
painful is not dangerous to man. The young are born
alive and are carried about by the mother for some time
after birth.
The mites (figs. 90 and 91) and ticks (fig. 92) are
mostly small obscure animals, which live more or less
parasitically. The common red spider of house-plants
as well as the sugar- and cheese-mites, the dreaded
FIG. 91. Bird mite, species undetermined, from the gnome-owl, Glauci-
dium gnomus. (Photo-micrograph by Geo. O. Mitchell.)
itch-mite and the chigger are familiar examples of these
degraded arachnids, and the wood-ticks, dog- and
chicken-ticks are common examples of the larger blood-
sucking forms. The body in both mites and ticks is very
compact, the two body-regions, cephalothorax and ab-
domen, being closely fused.
The spiders have the abdomen distinctly set off from the
cephalothorax. The eyes (fig. 93) vary in number and
arrangement, the mandibles are large, each being com-
posed of two parts, a basal hair-covered part, the falx, and
a terminal smooth, shining, slender, sharp-pointed part,
ELEMENTARY ZOOLOGY
the fang, which is movably articulated with the falx
(fig. 93 \ In the falx is a poison-sac from which poison
FIG. 92. The dog or wood tick, Dermacentor americanus male, the most
common tick in the Northern States. (After Osborn.)
flows through the hollow fang and out at its tip. The
legs vary in relative length in different spiders, and each
is made up of seven joints. The spinnerets
(fig. 94), which are situated at the tip of the
abdomen, are six in number (a few spiders
have only four), and are like little short
fingers. They have at their tips many fine
FIG. 93. The little spinning-tubes from each of which a
showh" d ^fafx ^ ne S1 *^ en thread issues when the spider is
and fang of a spinning. These many fine threads fuse as
Jenkins ^ a ^^ issue to form a single strong cable or
Kellogg.) sometimes a flat rather broad band. The
spinnerets are movable, and by their manipulation the
desired kind of line is produced. The silk comes from
BRANCH ARTHROPODS ; CLASS ARACHNID A : SPIDERS 233
many silk-glands in the abdomen, from each of which a
fine duct runs to a spinning-tube.
The spiders may be divided into two groups according
to their habits, viz., the wandering or hunting spiders,
FIG. 94. The six spinner-
ets (below) of a spider,
with one spinneret en-
larged (above) to show
the spinning "spools"
or tubes. (From Jenkins
and Kellogg.)
FIG. 95. A long-legged spider,
Tetragnatha sp., on its web.
(From life.)
which do not spin webs to catch their prey, and the
sedentary or web- weaving spiders, which spin snares to
catch their prey. The wandering spiders can spin silk,
however, and often do so to line their burrows, to make
nests, or to make egg-sacs.
The hairy tarantulas and the trap-door spiders of
similar appearance are among the most interesting of
234
ELEMENTARY ZOOLOGY
the hunting spiders. They live in vertical burrows or
tunnels in the ground which are lined with silk, and which
in the case of the trap-door spider are covered with a door
or lid made of silk and soil. The top of this door is
FIG. 96. A running spider (Ly.osidse;. (From life.)
always covered with soil or bits of leaves or twigs so that
it is nearly indistinguishable from the surface of the
ground about it. When the nest is in ground covered
with moss the spider covers the door with moss. The
FIG. 97. A female running spider (Lycosidse) carrying its egg-sac about
attached to its spinnerets. (From Jenkins and Kellogg. )
tarantulas hunt at night and rest in the burrow in the
daytime. They are very large, sometimes having an
expanse of legs of 6 inches.
The common, rather large swift black spiders found
BRANCH ARTHROPOD A ; CLASS ARACHNID A : SPIDERS 235
under stones and boards are hunting spiders, belonging
to the family Lycosidae and are called the running spiders
(fig. 96). They -live in burrows in the ground, coming
out to stalk and chase their prey. The eggs are laid in
globular egg-sacs which are often carried about, attached
to the spinnerets, by the female (fig. 97). The young
spiderlings after hatching, in some species, climb on to
the mother's back and are carried by her for some time.
Other kinds of wandering or hunting spiders are the crab-
spiders (Thomisidae) (fig. 98), which run sidewise or back-
ward as well as forward, and the black and red, fierce-
FIG. 98. A crab-spider (Thomi- FIG. 99. A jumping spider (Atti-
sidae). (From Jenkins and Kellogg.) dae.) (From Jenkins and Kellogg.)
eyed, stout-bodied little jumping spiders (Attidae) (fig. 99),
which leap on their prey.
The sedentary or web-weaving spiders are of various
kinds. They may be grouped according to their spinning
habits into cobweb weavers (Therididae), small slim-
legged spiders which make the familiar unsymmetrical
cobwebs of houses and outbuildings ; funnel-web weavers
(Agalenidae), larger long-legged spiders of meadow and
field which spin a flat or concave horizontal web in the
grass with a silken tube leading down to the ground;
the curled-thread weavers (Dictynidae), which use in addi-
tion to the usual lines peculiar broad lines made of waved
or curled threads in their irregular webs made in fence-
236 ELEMENTARY ZOOLOGY
corners and on plants ; and finally orb-weavers (Epeiridae)
(fig. 100), the host of variously colored and patterned
stout-bodied garden-spiders which spin the beautiful sym-
metrical circular webs familiar to all (fig. 101). If a
complete uninjured orb web be examined it will be found
to consist of a small central hub either open or closed,
from which run radii to the outer edges of the web.
Around the hub is an open or free zone, and farther out
a spiral zone, so called because a line running in close
FIG. 100. Argiope sp., a large orb- weaver (Epeiridse). (From Jenkins
and Kellogg.)
spiral turns fills in the space between the radii. This is
the real prey-catching part of the snare, and the silken
line here is sticky, while the radii and some other parts
of the web are made of silk that is not sticky. The
web is supported by strong foundation-lines, attached to
leaves, stems, or whatever is firm in the neighborhood of
the web. The spider either rests on the web, usually in
the centre, or lies concealed in a nest or tent near at hand
from which a special path-line runs to the centre of the
web. The building of one of these orb webs is a great
BRANCH ARTHROPOD/. ; CLASS ARACHNID A : SPIDERS 237
work, and is done with extraordinary nicety of manipula-
tion by the use of feet and spinnerets. For account of
FIG. ioi. Spider and its web in a rose-bush. (Photograph from life by
Cherrv Kearton; from "Wild Life at Home," by permission of Cassell
&Co.).
web-making, etc., see McCook's "American Spiders and
their Spinning Work."
The habits and instincts of spiders in connection with
the care of the young, the building of webs and nests,
ballooning by means of silken lines, the active stalking
and catching of prey, etc., are very interesting and offer
23 8
ELEMENTARY ZOOLOGY
a good field for independent observation and study by the
student.
FPG. 102. The triangle spider, Hyptiotes sp. (California), with its web; the
spider rests on the taut guy-line, with a loop of the line held between
its fore and hind legs; when an insect gets into the web the spider
loosens the hold of its hind feet on the guy-line, thus allowing the web
to spring forward sharply and further entangle the prey. (From
Jenkins and Kellogg.)
CHAPTER XXII
MOLLUSCA: THE MOLLUSCS
THE FRESH-WATER MUSSEL
Structure (fig. 103). TECHNICAL NOTE. The fresh-water 01
river mussel lives commonly in the streams and lakes or ponds in
the United States. It frequents muddy or sandy bottoms. Speci-
mens can often be secured with a long-handled rake from the shore
or picked up in shallow streams with the hand. If possible to keep
the animals alive until ready for use, some of their habits may be
observed. Place them in a tub or trough with water and mud ;
when they have settled themselves put some powdered carmine,
starch, or similar substance in the water near them, and note the
water-currents.
Living mussels which have been placed in a dish with
mud several inches deep and covered with water will be
seen to travel in a definite direction. The end which is
in front is the head end. Note the process of thrusting
out and retracting the fleshy/^/ which extends between
the two valves of the shell. Note that the two valves are
held together along the upper, or dorsal, surface by a
horny structure, the hinge -ligament. Note near the hinge-
line a prominence (umbo) in each valve from which ex-
tends a series of concentric lines of growth. The umbo
is the oldest part of the valve. Note at the lower edge
of the valves a soft membrane with a fringe along its free
border. This is the edge of the mantle-lobes, flaps of the
body-wall which cover the body and which aid in the
functions of respiration and nutrition.
239
240 ELEMENTARY ZOOLOGY
TECHNICAL NOTE. Specimens which are to be dissected should
be killed by dropping them for a few seconds into warm water, when
the muscles will relax enough so that a chip may be thrust between
the valves. If specimens are to be kept for some time before dis-
secting they should be preserved in alcohol or 4^ formalin. In a
dead specimen carefully remove the left valve. This is accomplished
by slipping in a thin knife-blade close to the inner edge of the left
valve and carefully cutting the two large adductor muscles which
bind the valves together. The dissection should be made under
water.
Before the removal of the valve, as just described,
notice a portion of the mantle adhering to the Inner face
of the valve, along a line of attachment indicated by a
crease. This is the pallial line. After the left valve has
been removed, the mantle being carefully separated from
it, note the large conical projections from the valves, the
hinge teeth, which fit into each other. Note the large
muscle impression just in front of the hinge-teeth ; this is
the point of attachment of the anterior addtictor muscle,
while just behind and adjoining it is the impression of the
anterior retractor muscle. Note posterior to the adductor
and below the retractor a small impression which affords
attachment for the protractor muscles of the foot. At
the other end of the valve, note the large impression of the
posterior adductor muscle with the impression of the small
posterior retractor muscle just above it.
TECHNICAL NOTE. Lift back the left mantle-lobe, thus exposing
the body parts underneath.
Note the projecting muscular foot, the movements of
which are governed by the retractor and protractor
muscles attached to the impressions just mentioned.
Note a pair of flattened plate-like structures composed of
thin, ribbed, membranous folds. These are the gills.
Note just beneath the anterior adductor muscle a small
opening leading into the soft visceral mass of the body.
This is the mouth. Note near the mouth two pairs of
olate-like structures much smaller than the gills. These
MOLLUSC/1: THE MOLLUSCS 253
second or hinder pair), and the respiratory pore. Note the streak
of mucus left by the slugs in crawling about.
Some sea-shells can be got from private collections of " curios"
to illustrate the variety of form of the univalve shells.
Perhaps one-half of all the known species of molluscs
are snails and slugs (fig. 108). Snails are either aquatic or
terrestrial in habit, but in either case they (the true pulmo-
nate snails) breathe not by means of gills, as do most of
the other molluscs, but by means of a so-called " lung."
This lung is a sac with an external opening on the right
side of the body and with its inner sutjace richly furnished
with fine blood-vessels. The exchange of gases between
the blood and the outer air takes place through the thin
walls of the blood-vessels. Most snails which live in the
water, as the pond-snails and the river-snails, have to
come occasionally to the surface to breathe. These fresh-
water and land-molluscs which possess a lung-sac instead
of gills constitute the order Pulmonata. The pulmonate
pond- and land-snails and slugs are vegetable feeders and
where they occur in large numbers do much injury to
vegetation. While the common pond-snails have but
one pair of feelers, at the base of which are found the
eyes, most of the land-snails and slugs have two pairs of
' * horns, ' ' the eyes being on the tips of the second pair.
The lung-sac, besides serving as a breathing organ, also
enables the snail to rise or sink according as the animal
varies the size of the sac and consequently the amount of
air in it. All the Pulmonata are hermaphroditic, each
individual producing both sperm- and egg-cells. The
eggs of the pond-snail " are laid in gelatinous transparent
capsules, half an inch to an inch in length, flattened and
linear or oblong in outline. After a few snails have been
kept a short time in a small vessel of water with their
appropriate food, these egg-capsules may be looked for
on the bottom and sides of the vessel or closely adherent
254 ELEMENTARY ZOOLOGY
to the stems or leaves of plants placed in the water.
They are so transparent as to be easily overlooked."
Young snails may be reared from these eggs.
There are other snails common in ponds, also called,
like the pulmonate forms, pond-snails, which have gills
and no lung-sac. These pond-snails belong to a different
order of molluscs, and live on the bottom of the pond,
crawling about in the soft mud and feeding on animal
instead of vegetable food.
The shells of the various kinds of snails vary much.
In many of the land-snails the spiral is not spire-shaped
or conical, but is flat. In some the whorls of the spiral
run from left to right (dextral) when the shell is looked
at with apex held toward one, while in others the whorls
run from right to left (sinistral).
Of the hosts of marine Gastropods we can notice only
a few kinds. The nudibranchs (fig. 109) are a group of
FlG. 109. Three Pacific Coast nudibranchs; Doris tuberculata (in lower
left-hand corner), Echinodoris sp. (upper one), and Triopha modes ta
(at right). (From living specimens in a tide-pool on the Bay of Mon-
terey, California.)
beautiful forms in which the shell is wholly wanting and f
the mantle is usually absent. The gills are thus exposed
and are usually in the shape of delicate freely projecting
V
MOLLUSCS: THE MOLLUSCS 241
are the labial palpi, and it is by their action that food-
particles which have been brought in with the water are
conveyed to the mouth. Note at the posterior part of
each mantle-lobe a fringed portion which, together with
a corresponding part on the other side, forms the inhalant
sipJion. The cilia of the fringes carry water and food-
particles into the space enclosed by the mantle- lobes;
this space is the mantle-cavity. After the food has been
taken o^it and the water has passed through the finely
striated gills it is collected in a common cavity which
extends above the two sets of gills on each side. This
space is called the supra-branchial cavity. This cavity
is continuous posteriorly with a space between the right
and left mantle-lobes, which is connected with the
exterior by an opening above the inhalant siphon called
the exlialant sip/ion. The function of the gills is partly
to produce currents of water carrying the food to the
mouth, and partly respiratory^ The mantle is an impor-
tant organ of respiration. /
Make a drawing showing the organs described ^TT^
TECHNICAL NOTE. Carefully cut away the mantle and gills
from the leftside, and also the labial palpi, being careful not to dis-
turb the visceral mass.
Note two openings along the line where the gills and
foot come together. The uppermost is the opening of the
ureter giving exit to the excretion from the kidneys; the
lower is the opening of the duct frofn the reproductive
organs and is called the genital aperture. The products
from both of these organs are carried out through the
exhalant siphon^
Note that th* mouth leads by a short tube (oesophagus
or gullet) into a large cavity, the stomach, which is sur-
rounded by a greenish mass, the digestive gland.
TECHNICAL NOTE. Carefully cut the delicate covering of the
dorsal portion of the visceral mass and expose a cavity.
242 ELEMENTARY ZOOLOGY
The cavity thus exposed is the pericardium. Note
within the pericardium a long tube extending through it.
This is a portion of the alimentary canal, the rectum,
which opens posteriorly through the anus into the supra-
branchial chamber. Note a muscular sac about the
rectum midway of its course through the pericardium.
This is the unpaired ventricle of the heart. Attached to
each side of the ventricle are thin-walled sacs, the right
and left auricles, which are entered by fine blood-vessels,
the efferent branchial veins, from the right and left gills.
The blood brought through these blood-vessels from the
gills flows into the auricles and from them into the un-
paired muscular ventricle, from which it is forced anteriorly
and posteriorly through two main arteries, the anterior
and posterior aortas, to all parts of the body. After
bathing the body-tissues the blood is collected into a
median longitudinal vein beneath the pericardium called
the vena cava. From the vena cava the blood passes
through the kidneys and gills to be returned at last to the
heart. The mantle acts as an organ for the aeration of
the blood, and the blood it receives or at least part of it
passes directly back to the heart without passing through
the kidneys and gills.
Note the delicate membranous dark-colored sac on the
floor of the pericardium, the kidneys or nepJiridia. These
are paired structures which appear as two U-shaped tubes
lying side by side. Each consists of a lower portion with
thick folded walls, the kidney proper, and an upper thin-
walled portion, the ureter. The kidneys open internally
through a pair of reno-pericardial openings into the peri-
cardium, while the ureters communicate with the mantle-
cavity by an opening on the side of the body beneath the
gills as already mentioned. The kidneys are profusely
supplied with fine blood-vessels and carry off the waste
matter from the blood.
MOLLUSCS: THE MOLLUSCS 243
Beneath the posterior adductor muscles note a small
white spider-shaped body, the more or less united visceral
ganglia of the nervous system. Posteriorly these ganglia
give off nerves to the mantle and gills, while anteriorly
there proceed two nerves, the ccrcbro-visceral connectives,
running forward, one on either side of the foot close to
the visceral mass, to the cerebro-pleural ganglia, paired
ganglia lying near the mouth. A delicate commissure
running over the gullet connects these ganglia.
TECHNICAL NOTE. Cut away the skin and outer muscular layer
from the left side of the foot.
Note the large stomach-cavity, surrounded by the
digestive gland. Trace the convolutions of the alimentary
canal through the foot to the anal exit. Note in the
anterior portion of the foot a fused pair of ganglia similar
to the visceral ganglia. These are the pedal ganglia,
which are connected by a pair of delicate commissures,
the cerebro-pedal connectives, with the cerebro-pleural
ganglia. Note the glandular tissue which fills the cavity
of the foot and surrounds the loops of the alimentary
canal. This is the reproductive organ, which has its exit
leneath the gills on each side of the foot. The sexes of
ihe mussel are separate, but the reproductive organs are
very similar.
Life-history and habits. The eggs (ova) of the female
pass first into the supra-branchial chamber, whence, after
being fertilized, they drop into the outer pair of gill-
chambers. These outer gills serve as brood-pouches, and
here it is that the embryonic stages are passed through.
The embryo when ready to issue has a soft body enclosed
in two triangular valves. At this stage it is called a
glochidium. The glochidium on being discharged through
the exhalant siphon of the parent fails to the bottom,
where it remains for a time, when it attaches itself to some
2,44 ELEMENTARY ZOOLOGY
fish by the lower hook-like projections of the valves and
leads a truly parasitic life for two months, after which it
undergoes a metamorphosis and falls to the bottom again,
there to begin an independent existence. Mussels often
congregate in favorite mud or sand banks. Their food
consists primarily of small organisms, both plants and
animals, which are taken from the water entering the
mantle-cavity. Mussels move about slowly over the
muddy bottom of the stream by means of the muscular
foot.
OTHER MOLLUSCS.
The branch Mollusca includes the fresh-water mussels,
the clams, oysters, snails, and slugs, the cuttlefishes, and
all that host of animals we call ' ' shells ' ' or shell-fish, which
we know familiarly only by the shell which they make,
live in, and leave at death to tell the tale of their exist-
ence. Not all the molluscs, however, form shells, that
is, external shells which serve as houses. The familiar
slugs do not, nor do a number of ocean forms called
nudibranchs, which are somewhat like the land-slugs, only
much prettier and more attractive. All the cuttlefishes
and octopi are also without the hard calcareous shell.
But most of the molluscs are shell-bearing animals. The
shell may be bivalved, as in the mussel and clam, or uni-
valved, that is, composed of a single piece which may be
spirally twisted, as with the snail, or otherwise curiously
shaped. The variety in the form, colors, and markings
of the shells indicates the great diversity among molluscs.
Molluscs live on land, in fresh water and in the ocean.
No depths of the ocean abysses are too great for the
octopi, no coast but has its many shells, hardly a pond
or stream is without its mussels and pond-snails, and in
all regions the land-snails and slugs abound.
MOLLUSCA : THE MOLLUSCS 245
Body form and structure. The molluscs are not to
be mistaken for any other of the lower animals ; they
have a structure peculiarly their own. In them the body
is not articulated or segmented as with the worms and
arthropods, nor radiate as in the echinoderms, nor plant-
like as with the sponges and polyps. (Where the typical
molluscan body is well developed it is composed of four
principal parts: a head, with the mouth, feelers, eyes, and
other organs of special sense; a trunk containing the
internal organs; a foot which is a thick muscular mass not
at all foot- or leg-like in shape, but which is the organ
of locomotion by means of which the mollusc crawls ; and
a mantle which is a fold of the skin enclosing most of the
body and which produces the shell. Such a typical
molluscan body is possessed by most of the snails. But
in most of the other molluscs one or more of these four
body-regions are so fused with some other region as to
be indistinguishable. In the mussels and clams the head
is not at all set off from the rest of the body, the cuttle-
fishes and octopi have no foot, the slugs have no shell. In
the case of some of the molluscs without external shell there
are inside the body the rudiments or vestiges of a shell.
With regard to the internal organs we note the constant
presence of three pairs of ganglia, viz., the brain, lying
above the pharynx, which sends nerves to the feelers^
eyes, and auditory organs ; the pedal ganglion, which sends
nerves to the foot, and the visceral ganglion, which sends
nerves to the viscera. This is a condition of the nervous
system characteristic of all molluscs. The heart is a well-
developed pulsating sac in the upper part of the body
composed of either two or three chambers, and there is a
well-defined closed system of arteries and veins, specially
complete in the cuttlefishes and octopi. This highly
developed condition of the circulatory system also distin-
guishes the molluscs from the other invertebrates.
246 ELEMENTARY ZOOLOGY
Development. Reproduction among the molluscs is
always sexual. Multiplication by budding or by the
parthenogenetic production of eggs is not known to occur.
The eggs are usually laid in a mass held together by a
gelatinous substance. In most species the young mollusc
on hatching from the egg does not resemble its parent,
but is a free-swimming larva called a vcliger. It is
provided with cilia for organs of locomotion. It must
undergo a radical change in order to reach the adult
stage. Thus metamorphosis occurs in this branch as well
as among the Arthropods and Echinoderms. In the
development of some molluscs, however, there is little or
no metamorphosis, the young being hatched in a condi-
tion much resembling, except in size, the parent.
Some of the special characteristics of structure, life-
history, and habits of the molluscs will be noted in our
consideration of the various kinds.
Classification. The branch Mollusca is divided into
five classes, three of which include the more familiar
kinds. These three classes are the Pelecypoda, including
the mussels, cockles, clams, scallops, oysters, etc., mol-
luscs with a shell composed of two pieces, one on each
side of the body and hinged together; the Gastropoda,
including the snails, slugs, periwinkles, whelks, and a host
of other univalved shell-fish, that is, molluscs which have
a shell composed of a single piece ; and the Cephalopoda,
including the squids, cuttlefishes, octopi, and the pearly
nautilus.
Clams, scallops, and oysters (Pelecypoda). TECHNICAL
NOTE. Shells of scallops, oysters, and sea-rnussels should be had for
examination ; also specimens of Teredo or Pholas in alcohol or for-
malin, and pieces of pile bored by Teredo. Make drawings of vari-
ous bivalve shells, and of Teredo.
The fresh-water mussel which we have studied is an
example of the bivalve molluscs. The members of this
hinge ligamt
reno-pericardial aperture
renal aperture v
genital aperture ^
right auricle i
anterior aorta \ ,
umbone-
hinge tooth
stomach-
digestive gland
gullet-
wrebro-pleural ganglion - ->
mouth /
anter adductor*' \ .
;
'.
anter retractor ,'*\
pedal ganglion.
foof~ "-^
intestine*'
typhlosole
\ mm
,$
FIG. 103. Dissection oa
ventricle
/ pericardium
rectum
/
^kidney
palhal aperture
--- posterior aorta
post, retractor
post adductor
. ~ amis
mantle cavity
-water mussel. Unio sp.
- visceral ga nglion
exhalant siphon
super branchial chamber
- right gill ^
inhalant siphon
'shell
palliai groove
MOLLUSCS: THE MOLLUSCS 247
class show a range in size from the little fresh-water
Cyclas about I cm. long to the giant clam of the Indian
and Pacific islands "which is sometimes 60 cm. (2 feet)
in length and 500 pounds in weight." They show also
some variety in the form and appearance of the shell, but
not anything like the degree of variety shown by the
shells of the Gastropods.
The edible clams are of several different species. The
hard-shell clam (Venus mercenaria), or "quohog "as it
is often called, is found along the Atlantic coast from
Texas to Cape Cod. It is "common on sandy shores,
living chiefly on the sandy and muddy plots, just beyond
low-water mark. ... It also inhabits estuaries, where it
most abounds. It burrows a short distance below the
surface, but is frequently found crawling at the surface
with the shell partly exposed. " The shells of this edible
clam are white. The soft-shell clam (My a arenaria],
" the clam par excellence, which figures so largely in the
celebrated New England clam-bake, is found in all the
northern seas of the world. . . . All along the coasts of
the eastern States, every sandy shore, every mud flat, is
full of them, and from every village and hamlet the clam-
digger goes forth at low tide to dig these esculent
bivalves. The clams live in deep burrows in the firm
mud or sand, the shells sometimes being a foot or fifteen
inches beneath the surface. When the flats are covered
with water his clamship extends his long siphons up
through the burrow to the surface of the sand, and
through one of these tubes the water and its myriads of
animalcules is drawn down into the shell, furnishing the
gills with oxygen and the mouth with food, and then the
water charged with carbonic acid and fcecal refuse is
forced out of the other siphon. When the tide ebbs the
siphons are closed and partly withdrawn." Ocean clams
and mussels have furnished food for man' for ages, and
248 ELEMENTARY ZOOLOGY
along coasts are found here and there great mounds
made of heaps of clam-shells which have become covered
over with soil and vegetation. Such mounds are the old
feasting-places of the early coast inhabitants, and the
archaeologist often finds in these "kitchen-middens," as
FlG. 104. A group of marine Pacific Coast molluscs; in upper left-hand
corner. Piirpura saxicola; next to the right, Littorina scutiilata,',
farthest to right, limpets, Acmara spectrum; left-hand lower corner,
Mytilus calif orni anus; in right-hand lower corner the black shells just
above the large clam-shell, Chlorostomum fitncbralc. (From living
specimens in a tide pool in the Bay of Monterey, California.)
they are called, various relics of the early natives of the
continent.
Even more widely known that the clams are the oysters
(Ostrea virginiana], also members of this class of mol-
luscs. The oyster is carefully cultivated by man in many
countries. It has its two shells or two shell-halves dis-
similar, one valve being hollowed out to receive the body,
while the other is nearly flat. The oyster is attached to
the sea-bottom by the outside of the hollowed-out valve.
When first hatched the young oyster swims freely by
means of its cilia; after a few days it attaches itself to
MOLLUSCA: THE MOLLUSCS 249
some solid object and grows truly oyster-like. Much care
has to be taken in cultivating oysters to furnish proper
conditions for growth and development. The young
oysters when first attached are called ' * spat ' ' ; when a
little older this "spat," now called "seed," may be
transplanted to new beds, which are stocked in this way.
In fact some beds have constantly to be thus restocked,
the young oysters produced on them not finding good
places to attach themselves, and so swimming away.
Sometimes pieces of slate, pottery, etc., are strewed about
the oyster-beds to serve as ' ' collectors, ' ' that is, as
places for the attachment of the young oysters. The
FIG. 105. Dactylus sp.. a mollusc, excavating granite. (Photograph by
C. H. Snow; permission of Amer. Soc. Civil Engineers.)
extent of the acreage of the American oyster-beds is
larger than that .of any other country. "The Baltimore
oyster-beds on the Chesapeake River and its tributaries
cover 3,000 acres, and produce an annual crop of 25,000, -
ooo bushels."
The " pearl-oyster " is not a true oyster, that is, not a
member of the family to which the edible oysters belong,
250
ELEMENTARY ZOOLOGY
but it is a member of the same class, that is, it is a bivalve
mollusc. Pearls are obtained from a number of different
" pearl-oysters, ' ' but the finest pearls and mother-of-pearl
come from the tropical species Meleagrina margaritifera.
This pearl-oyster "has an extensive distribution, being
found in Madagascar, the Persian Gulf, Ceylon, Australia,
Philippine Islands, South Sea Islands, Panama, West
Indies, etc." Mother-of-pearl is simply the inner lining
of the shell, which is composed of numerous thin layers of
carbonate of lime so arranged that the edges of the suc-
cessive layers produce many fine striae very close together.
The beautiful iridescence of this inner shell-lining is
caused by the complicated diffraction and reflection (inter-
ference effects) of the light by the fine striae and the
translucent superposed thin plates of shell material.
Pearls are simply isolated deposits of shell material usually
around some particle of foreign substance which has found
FIG. 106. Pholas sp., a mollusc, burrowing in sandstone. (Photograph
by C. H. Snow; permission of Amer. Soc. Civil Engineers.)
lodging in the mantle-cavity. Sometimes small objects
are purposely introduced into the shell in order to stimu-
late the formation of pearls. The pearl-fishers go out in
boats and dive to the bottom, filling baskets with pearl-
oysters. These are piled up in a bin and left to die and
MOLLUSC A : THE MOLLUSCS 251
decompose. " When the flesh is pretty thoroughly dis-
integrated, it is washed away with water, great care being
taken that none of the pearls loose in the flesh are lost.
When the washing is concluded the shells themselves are
examined for pearls which may be attached to the interior
of the valves. ' ' The principal pearl-fishery is that on the
coast of Ceylon ; pearl-fishing has been carried on here
for over 2000 years.
The ship-worm (Teredo) is an interesting member of
this class of bivalve molluscs, because of its unusual
FIG. 107. Martesia xylophaga, a Pholad, in Panama mahogany. (Photo-
graph by C. H. Snow; permission of Amer. Soc. Civil Engineers.)
habits, and strangely modified body form. The teredo
is long and worm-like in general appearance, with a small
bivalve shell at one end and two elongated siphons at the
other. The young teredo is a free- swimming ciliated
embryo like the young of the other bivalve molluscs, but
it soon settles on a piece of submerged wood, usually the
pile of a wharf, or the bottom of a ship, and burrows into
this wood. As it grows it enlarges and deepens its tube-
like burrow, and lines it with a calcareous deposit. The
burrow may be a foot long or longer, and when thousands
of teredos attack a pile or the bottom of a ship, the wood
soon becomes riddled with holes. These boring molluscs
252 ELEMENTARY ZOOLOGY
do great damage to wharves and ships. In Holland
where they were first discovered they caused such injuries
to the piles and other submerged wood which supported
FIG. 108. The giant yellow slug of California, Ariolimax californica.
This slug reaches a length when outstretched of 13 inches. (From
living specimen.)
the dikes and sea-walls that they seriously threatened the
safety of the country.
Snails, slugs, nudibranchs and " sea-shells " (Gas-
tropoda). TECHNICAL NOTE. Pond-snails can be readily found
clinging to submerged stems, leaves, or pieces of wood in almost
any pond. Collect some and carry alive, in a jar of water, to the
schoolroom. Observe the habits of these live snails in the school aqua-
rium. Note the movements, the coming to the surface to breathe,
the eating (by scraping the surface of the leaves with the " radula "
or tongue ; provide fresh bits of cabbage or lettuce-leaves), the "use
of the feelers. Make drawings illustrating these habits. Examine
the shell ; note that it is univalved, that is, composed of one piece.
Do the whorls of all the shells turn the same way ? Make a draw-
ing of the shell, naming such parts as the apex, spire (all the whorls
taken together), the aperture, the columella (the axis of the spire),
the lip (outer edge of the aperture), the lines of growth (parallel to
the tip), the suture (the spiral groove on the outside). Examine the
snail ; note the character of the foot ; note the protrusible tentacles
or feelers, the eyes (dark spots at bases of the tentacles), the mouth,
the respiratory opening (on right side of body in the edge of the
mantle which protrudes beneath the lip when the snail's body is ex-
tended), the radula or ribbon-like tongue with fine teeth. Compare
with the body of the mussel.
Slugs may be found during the day concealed under boards or
elsewhere ; they are nocturnal in habit. If specimens can be ob-
tained, compare with the pond-snails, noting the. absence of a shell,
and the fleshy mantle on the dorsal surface near the head ; note the
presence of two pairs of tentacles (the eyes being at the tips of the-
MOLLUSC/I: THE MOLLUSCS 253
^
second or hinder pair), and the respiratory pore. Note the streak
of mucus left by the slugs in crawling about.
Some sea-shells can be got from private collections of" curios"
to illustrate the variety of form of the univalve shells.
Perhaps one-half of all the known species of molluscs
are snails and slugs (fig. 108). Snails are either aquatic or
terrestrial in habit, but in either case they (the true pulmo-
nate snails) breathe not by means of gills, as do most of
the other molluscs, but by means of a^so-^alled "lung."
This lung is a sac with an external Opening on the right
side of the body and with its inner surface richly furnished
with fine blood-vessels. The exchange of gases between
the blood and the outer air takes place through the thin
walls of the blood-vessels. Most snails which live in the
water, as the pond-snails and the river-snails, have to
come occasionally to the surface to breathe. These fresh-
water and land -molluscs which possess a lung-sac instead
of gills constitute the order Pulmonata. The pulmonate
pond- and land-snails and slugs are vegetable feeders and
where they occur in large numbers do much injury to
vegetation. While the common pond-snails have but
one pair of feelers, at the base of which are found the
eyes, most of the land-snails and slugs have two pairs of
' ' horns, ' ' the eyes being on the tips of the second pair.
The lung-sac, besides serving as a breathing organ, also
enables the snail to rise or sink according as the animal
varies the size of the sac and consequently the amount of
air in it. All the Pulmonata are hermaphroditic, each
individual producing both sperm- and egg-cells. The
eggs of the pond-snail ' ' are laid in gelatinous transparent
capsules, half .an inch to an inch in length, flattened and
linear or oblong in outline. After a few snails have been
kept a short time in a small 'vessel of water with their
appropriate food, these egg-capsules may be looked for
on the bottom and sides of the vessel or closely adherent
254 ELEMENTARY ZOOLOGY
to the stems or leaves of plants placed in the water.
They are so transparent as to be easily overlooked. ' '
Young snails may be reared from these eggs.
There are other snails common in ponds, also called,
like the pulmonate forms, pond-snails, which have gills
and no lung-sac. These pond-snails belong to a different
order of molluscs, and live on the bottom of the pond,
crawling about in the soft mud and feeding on animal
instead of vegetable food.
The shells of the various kinds of snails vary much.
In many of the land-snails the spiral is not spire-shaped
or conical, but is flat. In some the whorls of the spiral
run from left to right (dextral) when the shell is looked
at with apex held toward one, while in others the whorls
run from right to left (sinistral).
Of the hosts of marine Gastropods we can notice only
a few kinds. The nudibranchs (fig. 109) are a group o f
FIG. 109. Three Pacific Coast nudibranchs; Doris tuberculata (in lower
left-hand corner), Echinodoris sp. (upper one), and Triopha modesta
(at right). (From living specimens in a tide-pool on the Bay of Mon-
terey, Califorria.)
beautiful forms in which the shell is wholly wanting and
the mantle is usually absent. The gills are thus exposed
and are usually in the shape of delicate freely projecting
MOLLUSC si; THE MOLLUSCS 255
tufts arranged in rows along the back. The body is often
strikingly and variedly colored. These soft, naked " sea-
slugs ' ' live near the shore, creeping about among the
rocks and seaweeds. About a thousand species of nudi-
branchs are known.
Among the shell-forming marine Gastropods there is
great variety in the size and shape and coloring of the
shells. Many are beautifully colored and patterned ;
others are oddly and fantastically shaped. The cowries,
or porcelain shells, familiar in collections of ocean curiosi-
ties, have a large body whorl and a very short flat spire,
and the brightly colored shell looks as if enamelled.
Some of the coast tribes of Africa once used, and perhaps
still use to some extent, cowries as money. The limpets
(fig. 104) are among the most abundant of the seashore
molluscs, their low, broadly conical shells being plenti-
fully scattered over the rocks between tide-lines. The
* ' oyster-drills ' ' are Gastropods with odd spiny shells which
do much harm in oyster-beds by settling down on the
oysters, boring holes through the shells and eating the
soft parts within. The helmet-shells, from which shell
cameos are cut, are composed of layers of shell material
of different colors. Among the specially beautiful shells
are the cone-shells, the olive-shells, the ivory-shells, etc.
Squids, cuttlefishes, and octopi (Cephalopoda).
TECHNICAL NOTE. Small squids preserved in alcohol or formalin
can be had of all dealers in biological supplies (see p. 453), and
specimens should be examined.
The squids (fig. no), cuttlefishes, octopi or "devil-
fishes," and the three living species of Nautilus constitut-
ing the class Cephalopoda are very different from the other
molluscs in appearance, and are in fact different in im-
portant structural characters. They can move swiftly,
have strangely modified organs of prehension, strong biting
mouth-parts, and eyes of very complex organization.
256 ELEMENTARY ZOOLOGY
They are the most highly organized molluscan forms, and
their predaceous habits and the great size to which some
of them attain have given them distinction among the
fierce and dangerous creatures of the sea. They are all
strictly marine in habitat, and are all carnivorous. Most
of them have no shell, or where the shell is present it is
internal in all but a very few forms. The tentacle-like
arms or feet surrounding the mouth which occur in all the
Cephalopods are provided with sucking organs or suckers,
in some cases with a horny toothed rim. These long,
powerful, grasping, tentacular feet, with the suckers and
five hooks, are very effective means of securing prey, and
the pair of strong, sharp, cutting mandibles or beaks are
equally effective in tearing to pieces. The eyes of the
Cephalopods are almost as highly developed as those of
the vertebrates. They are unusually large and staring,
and add much to the terrifying appearance of the " devil-
fishes." Cephalopods have the power of quickly chang-
ing color, because of the presence in the skin of many
pigment-cells which can expand so as nearly to touch
each other, thus producing a uniform tint over the whole
body, or which can contract so as to destroy this uniformity
of color. There are several sets of these color-carrying
cells or chromatophores, each set of a color different from
the others. The purpose of this change of color is pro-
tective, the animal being thereby able to make its color
so harmonize with that of its immediate surroundings as
to become indistinguishable.
There are two principal groups of Cephalopods, viz.,
the Decapods and the Octopods. The Decapods, as their
name indicates, have ten feet or arms surrounding the
mouth, and in them the body is usually elongate, con-
taining a horny "pen" or calcareous "bone." This
group includes the cuttlefishes or sepias, from which are
obtained sepia ink and the cuttlefish bone used to feed
MOLLUSCS: THE MOLLUSCS 257
canary birds. The ink is a secretion which the cuttlefish
discharges when attacked to create a cloud in the water
and thus escape unperceived. The squids (Loligo) com-
monly used as bait by fishermen belong to the Decapoda.
The two extra feet or arms which the Decapods have in
addition to the eight possessed by the Octopods, differ
from the others in being longer and slenderer and having
suckers only on the distal extremities which are expanded
into "clubs " (fig. no).
The Octopods have a short, sac-like, sub- spherical body
and neither external nor internal shell. To this group
FlG. I jo. The giant squid, Ommatostrephes californica. (From specimen
with body (exclusive of tentacles) four feet long, thrown by waves on
shore of the Bay of Monterey, California.)
belong the famous devil-fishes (Octopus], whose strange
and terrifying appearance combined with their frequently
great size has furnished the basis for many a weird tale of
the sea. Octopi have been killed having tentacles more
than 30 feet in length. The largest members of the
class, however, are probably the giant squids (belonging
to the Decapoda) specimens of which have been captured
with a body-length of twenty feet, and arms thirty-five
feet long.
The beautiful paper sailor or argonaut (Argonauta argo).
258 ELEMENTARY ZOOLOGY
which secretes a thin shell (not homologous with the
shell of the other molluscs) to protect her eggs, is a mem-
ber of the Octopod group. In fine weather the argonauts
sail in fleets on the surface of the ocean.
The pearly nautilus (Nautilus pompilius) is a Cephalo-
pod with four gills instead of two, as with the Decapoda
and Octopoda, and is the only existing member of what
was in the earlier times of the earth's history a large
group of animals. The nautili live in rather shallow
water usually creeping over the bottom feeding on small
marine animals. They make a many-chambered spiral
shell with its inner surface lined with beautiful pearly
nacre.
CHAPTER XXIII
BRANCH CHORDATA: THE VERTEBRATES,
ASCIDIANS, ETC.
THE branch Chordata includes all the backboned
animals or vertebrates, comprising the fishes, salamanders,
frogs and toads, lizards, crocodiles, turtles and snakes,
birds, and all the quadrupeds or mammals, and includes
also a few small unfamiliar ocean animals which do not
look at all like the backboned animals, but which agree
with them in possessing a peculiar structure called the
notochord. This notochord consists of a series or cord of
cells extending longitudinally through the body from head
to tail, above the alimentary canal and below the spinal
nerve-cord. In all the vertebrates excepting a few low
forms, the notochord while present in the young, is re-
placed in the adult by a segmented bony or cartilaginous
axis, the spinal or vertebral column. But in the ascidians
or sea-squirts (called also tunicates) it persists throughout
life. In addition to this characteristic notochord, nearly
all the Chordata are marked by the presence, either in
embryonic or larval stages only, or else persisting through-
out life, of a number of slits or clefts in the walls of the
pharynx which serve for breathing, and which are called
gill-slits.
Structure of the vertebrates. As the backboned or
vertebrate animals make up almost the whole of the
branch Chordata, and as the few other chordates are
animals the special structures of which we shall not under-
take to study in this book, we may note here some of the
other more obvious structural characteristics of the true
259
260 .ELEMENTARY ZOOLOGY
vertebrates. The possession of a backbone or bony
(sometimes cartilaginous) spinal column is the character-
istic by which we distinguish them from the invertebrate
or backboneless animals. Furthermore, all of the verte-
brates possess an internal skeleton which is in most cases
composed of bone, and is firm and strong. In some of the
lower fishes, as the sharks and sturgeons, the skeleton is
made up of cartilage, tough but not hard. The vertebrate
skeleton consists typically of an axial portion comprising
the spinal column and head, and of two pairs of append-
ages or limbs, variously developed as fins, wings, legs
and arms. In some vertebrates these limbs are repre-
sented by mere rudiments, and in the lowest fish-like
forms, the lancelets and lampreys, there is not the
slightest trace of limbs. A part of the central nervous
system, the spinal cord, runs longitudinally through the
body on the dorsal side of the alimentary canal ; the cir-
culatory system is closed, the blood being always confined
in the heart and in vessels called arteries, veins, and capil-
laries, and the blood is red in color owing to the presence
of numerous red corpuscles or blood-cells. The nervous
system is highly developed, with a large brain in all the
typical forms, and with complex and usually highly
efficient special sense-organs. Respiration is carried on
by means of external gills, or by internal lungs which
communicate with the outside through the mouth and
nostrils. To the lungs and gills the blood is brought to
be "purified," i.e., to give up its carbonic-acid gas and
to take up oxygen.
Classification. The Chordata are variously divided
by zoologists into eight or ten classes, of which (in the
eight-class system) the five classes* Pisces (fishes),
* The animals included by some zoologists in the single class Pisces, are
held by other zoologists to constitute three distinct classes, thus making a
subdivision of the branch into ten classes.
BRANCH CHORD AT A : THE VERTEBRATES, ETC. 261
Batrachia (batrachians), Reptilia (reptiles), Aves (birds),
and Mammalia (mammals), belong to the true vertebrates.
These classes will be considered in the five following
chapters.
The remaining three classes include a number of strange
marine forms which until recent years were considered as
worms, but which are now known to be the nearest living
allies of the earliest or primitive vertebrates. The rela-
tionship of these forms to early types is manifest, not in
the appearance or structure of the adult stage, but only
during embryonic or larval stages.
The ascidians. The sea-squirts, or Ascidians, com-
mon on the seashore, compose one class of these primitive
FIG. m.-^-An ascidian or sea-squirt from the coast of California. (After
Jordan and Kellogg.)
chordate animals. They possess a simple, sac-like body
(fig. ill), fastened to the rocks by one end, the other being
262 ELEMENTARY ZOOLOGY
provided with two openings, one for the ingress and the
other for the exit of water, a strong current of which flows
constantly through the body. By means of this current
the ascidian obtains food. Usually sea-squirts live
together in large colonies, and in some cases a number of
individuals enclose themselves in a common gelatinous
mass, forming what is called a compound ascidian.
The ascidian when born is a tiny, free-swimming, tad-
pole-like creature with a slender finned tail. It swims
about freely for only a few hours, however, soon attach-
ing itself to a rock, and in its further development becom-
ing degenerate. It loses its tail and with it the short
notochord possessed by the larva; the eye and the auditory
organ are lost, and the nervous system and alimentary
canal become much reduced and simplified. Sea-squirts
in their adult stage are very simple degenerate animals,
with low functional development, yet their embryonic and
larval conditions show a considerable degree of structural
specialization, and the presence of the notochord in these
early stages reveals their affinity with the backboned
animals.
CHAPTER XXIV
BRANCH CHORDATA (Continued}'. CLASS PISCES
(THE FISHES)
THE GOLDEN SUNFISH OR PUMPKIN SEED (Apomotts sp.)
TECHNICAL NOTE. The species of sunfish named, or some closely
related species, can be obtained in any brook or stream in the
United States. Gibbosus lives in all streams north of Dubuque,
Chicago, Pittsburg, and along the eastern coast north of Charleston.
Closely allied species live in all the other parts of the countn
except in the higher Rocky Mountains west of Bismarck, Pueblo,
and Santa Fe. One species is found in the streams of California,
but none occurs in Washington or Oregon. In the few places
where a sunfish cannot be had, any species of bass or perch may
be used. Sunfish live in ponds and sluggish streams in deep holes
under a log or at the foot of a stump. They take eagerly a hook
baited with a worm, or they may be caught in nets. When sun-
fish cannot be kept fresh for study in class, specimens may be
preserved in alcohol or 4^ formalin. But if possible to keep some
alive for a time in a jar or tub with plenty of fresh water, the colors
of the living fish, together with its manner of swimming and mode
of breathing, can be observed.
External structure* (fig. 1 12). Examine the general
configuration and make-up of the body. Note the deep,
laterally flattened trunk and paddle-like tail. The head
is closely fitted to the trunk without any neck. Note that
* The author wishes to call the attention of teacher and student to the
plan (referred to in the Preface, page v) adopted in writing the directions
for the dissections. The sequence of the references to the various organs
depends on the actual course of the dissection, and not upon the association
of organs in systems. And the directions are so much condensed that they
are hardly more than a means of orienting the student, leaving him to work
out independently, or by the aid of more detailed accounts (sometimes
specifically referred to), the details of the dissection.
263
264 ELEMENTARY ZOOLOGY
the body is thickly covered with firm, hard scales, arranged
like the shingles on a roof. Remove one of these scales
and examine it under a hand lens. What sort of an edge
has it ? Such a scale is said to be ctenoid.
The body of the sunfish terminates behind in the
caudal fin, a series of cartilaginous rays connected by thin
skin and attached to a bony plate at the end of the back-
bone. Along the median dorsal line will be noted another
fin composed anteriorly of spines and posteriorly of soft
rays jointed and branched. This is the dorsal fin. How
many spines has it ? Anterior to the caudal fin on the
ventral surface is a median unpaired anal fin. How many
spines has it ? Anterior to the anal fin are the ventral
fins, while on the sides of the body back of the head in
a line with the mouth are found the pectoral fins. The
ventral fins, attached to a rudimentary pelvis, correspond
to the hind legs of the other vertebrates. The pectoral
fins, attached to the shoulder girdle, correspond to the
arms. In front of the anal fin note a small pit-like open-
ing, the opening from the kidneys and reproductive organs,
and just anterior to this a large aperture, the amis. At the
anterior end of the head note the broad moutli, surrounded
by a complicated system of bones. Note the large eyes
surrounded by a series of small bones, the orbital chain.
Just anterior to the eyes are two pairs of openings, one
pair of each side opening into a closed sac. What are
these openings ? Note the presence of various bones on
the side of the head, each covered with a thin layer of
skin. These are membrane bones, characteristic of fishes.
Are there any external ears in the fish ? Examine the in-
side of the mouth. Is there a tongue f If so, of what char-
acter ? Are there teeth f If so, where are they situated ?
Note along each side extending to the base of the tail
a line of modified scales, on each scale a little mucous
tube, the whole series constituting the lateral line. These
BRANCH CHORD AT /I; CLASS PISCES: THE FISHES 265
scales are intimately associated with a large nerve (the
vagifs), and probably serve an important part, not yet
clearly understood, in the life of the fish.
Lift up the flap in front of one of the pectoral fins.
This is the opercular flap which covers the gills that lie
beneath. Bend this forward and find four gill-arches,
each with its double fringe of gills. Note the gill-rakers,
short and blunt, on the first gill-arch. Note also on the
under side of the flaps turned back, delicate red gill-like
structures covered by a membrane. These are t\\z false
gills or psendo-branchice, larger in most fishes than in the
sunfish. The gills in the fish subserve the same function
as the gills of the crayfish, that of purifying the blood
by eliminating carbonic-acid gas from it and taking up
oxygen from the air mixed with or dissolved in the water.
Organs subserving the same purposes in different kinds of
animals as, for example, the gills in fish and in crayfish,
are called analogous structures. But there is an important
morphological difference between the fish's gills and the
gills of the crayfish. In the latter animal they are out-
growths of the basal segments of the walking-legs ; in the
fish they are outgrowths from the alimentary canal. The
internal gills of the young toad (tadpole) arise in the same
way as those of a fish. Structures which are identical in
their origin, like the gills of tadpole and fish, are called
Jioinologous structures.
Make a drawing of the sunfish from a lateral aspect,
showing the external parts named.
Internal structure. TECHNICAL NOTE. Insert one point
of the scissors a little to one side of the anus and cut dorsally on the
left side of the body to the backbone. Now cut anteriorly from the
anus along the ventral wall to where the jaws unite, and cut, also
anteriorly, along the dorsal wall until the left side of the body can
be removed. Bend the opercular flap backward over the eye and
pin the entire fish, uncut side down, to the bottom of the dissecting-
pan, covering it with water.
266 ELEMENTARY ZOOLOGY
The above operation will have severed the large power-
ful muscles forming the body-wall and extending along
the sides. Note a membranous sac completely filling a
large dorsal cavity. This is the swim- bladder, a float
filled with air which tends to give the fish the same weight
as the water it displaces. It arises as a diverticulum from
the alimentary canal, but soon becomes permanently shut
off from it. Beneath the swim-bladder is a large cavity
filled with various organs, collectively known as the
viscera. In vertebrate animals the cavity which contains
the viscera is generally called the peritoneal cavity. It is
lined by the peritoneum, a delicate membrane, part of
which is deflected as the mesentery over the alimentary
canal and the other organs, thus suspending them all from
the dorsal wall. Note in the anterior end of the peritoneal
cavity a large bi-lobed gland, the liver, red in fresh,
yellowish in alcoholic specimens. Its function, like that
of the liver of the toad, is to store up nutriment for the
blood and to secrete a digestive fluid called bile. Behind
the liver note a long, convoluted tube. What is this tube ?
Unfold this tube, separating it from its enveloping mem-
brane, the mesentery. Thrust a probe down the throat
and note that it passes into a thick-walled sac, the
stomach. The mouth and gill-slits open into the front
part of the alimentary canal called the pharynx, which
leads by a short tube, the cesopJiagus, into the stomach.
Note the large, thickened portion of the alimentary canal
leading from the stomach. This is the pylorus, and to its
walls are attached a number of finger-like projections, the
pyloric cceca. The pyloric caeca secrete a fluid which is
poured into the alimentary canal and which assists in the
process of digestion somewhat as does the secretion from
the pancreas of the toad. From the pylorus, passing
backwards in one or two loops, is the small intestine.
Trace this to its exit. Lying within the mesentery near
BRANCH CHORDATA; CLASS PISCES: THE FISHES 267
the posterior end of the body-cavity note a small red
glandular mass, the spleen.
At the anterior end of the body in front of the liver
and between the sets of gills note the small pcricardial
cavity within which is contained the heart. The peri-
cardial cavity is separated from the peritoneal cavity by
a thick muscular wall against which the liver abuts. The
heart consists of four parts. The posterior part is a thin-
walled reservoir, the sinus venosus, into which blood
enters through the jugular vein from the head and through
the cardinal vein from the kidney. From the sinus
venosus it passes forward into a large chamber, the
aiiride. Next it flows into the ventricle, where, by the
contraction of the walls, rhythmical pulsations force it into
the conns arteriosus, thence into the ventral aorta, and
lastly into the gills, where it is purified. After passing
through the capillaries in the fine gill-filaments it is again
collected, now pure, by paired arteries from each pair of
gills, which arteries unite to form the dorsal aorta ex-
tending backward just below the backbone to the end of
the tail. From the dorsal aorta a pair of arteries, the
subclavian, are given off to the pectoral fins. At this
point two other arteries branch off ventrally, the first being
the cardiac artery, which distributes blood to the stomach
and pyloric caeca. The second divides into several long
mesenteric arteries supplying blood to all parts of the in-
testine and spleen. In the caudal region blood is taken
up through the caudal vein and carried forward to the
kidneys. These strain out the impurities arising from
waste of tissues, after which the blood is carried back to
the sinus venosus through the cardinal vein. From the
intestine it is gathered into the large portal vein as in the
toad. The portal vein carries blood to the liver, where
nutriment may be stored up, and from thence it flows back
268 ELEMENTARY ZOOLOGY
to the sinus venosus through a very short thin-walled
vessel, the hepatic sinus.
The kidneys, more or less united in one mass, lie in the
posterior part of the body-cavity along the dorsal wall.
Note running from each side of the kidney a ureter which
unites with its fellow and opens into a small urinary
bladder which discharges through a small opening im-
mediately back of the anus.
The reproductive organs lie below the swim-bladder
near the posterior end of the body-cavity. If the fish are
caught in the spring, the greater part of the body-cavity
of the female is found to be filled with small eggs. When
mature, these eggs are deposited by the mother fish in the
gravel of the stream-bed where they are fertilized by the
sperm-cells poured over them by the male and left float-
ing in the water.
The nervous system of fishes is best studied in a speci-
men treated with nitric acid. Carefully remove the roof
of the skull, thereby exposing the brain. Most anteriorly
make out, as in the toad, the paired olfactory lobes.
These are attached by long stalks to the cerebrum or
forebrain, which is followed by two large hollow lobes,
the midbrain or optic lobes. Behind the midbrain is the
cerebellum. Following the cerebellum is the elongate
medulla oblongata, which tapers backward into the spinal
cord. How far backward does the spinal cord extend ?
On each side of the brain-case about opposite the cerebel-
lum are located the auditory organs, each consisting of
three semicircular canals which lie in different planes, and
of the vestibule. These parts are filled with liquid, and
suspended in the liquid in the vestibule are small calcareous
bodies called otoliths or ear-stones. Running out beneath
from the midbrain are the optic nerves, which cross, the
left one connected with the right eye, the right one with
the left eye. From each side of the medulla oblongata
BRANCH CHORD AT /I; CLASS PISCES: THE FISHES 269
there is given off a large nerve, the vagus, which sends
branches to the lateral line organs on either side, and
extends backward to the stomach and viscera.
For further study of the nervous system see Parker's
' Zootomy, ' ' pp. 1 2 2-1 30.
Make a drawing of the nervous system as worked out.
TECHNICAL NOTE. To make a good skeleton immerse a fresh
or preserved specimen for some time in a hot soap solution. When
the muscles have commenced to soften remove the body from the
solution, pick the flesh away, and leave to dry.
Note that the main axis of the skeleton is composed of
vertebra placed end to end. How many vertebrae are
there ? What vertebra: bear ribs f The ribless ones
beyond the body-cavity are called caudal vertebra. Note
the inter spinal bones which support the fins, with large
muscles on either side to control their action. Note that
the group of bones supporting the pectoral fin is attached
to the back of the brain -case and makes up the shoulder
girdle. The ventral fins are attached to a rudimentary
pelvic girdle^ attached in front to the shoulder girdle, as
the shoulder girdle is in turn attached to the skull. It
will be seen that the sunfish has no neck and we may say,
also, no back. Its skeleton consists only of a tail attached
to the skull. The brain-case is made up of a number of
bones closely joined together. From it is suspended the
lower jaw, which comprises a number of bones but loosely
attached to each other. Overlying these is the system
of membrane bones already mentioned, including the
opercle or gill-cover.
For a detailed study of the fish-skeleton see Parker's
"Zootomy," pp. 86-101, or Parker and Hasvvell's
4 * Zoology, " vol. II. pp. 183-195.
Life-history and habits. The sunfish or 4< pumpkin-
seed" lives in quiet corners of the brooks and rivers,
preferably under a log or at the root of an old stump. It
270 ELEMENTARY ZOOLOGY
is a beautiful fish, shining "like a coin fresh from the
mint." Its body is mottled golden, orange and blue,
with metallic lustre, darker above, pale or yellowish
below. Its fins are of the same color. The tip of its
opercle is prolonged like an ear and jet black in color,
with a dash of bright scarlet along its lower edge. Nearly
all the thirty species of sunfish found in the United States
have this black ear, but some have it long, some short,
and in some it is trimmed with yellow or blue instead of
scarlet.
The sunfish lays its eggs in the spring in a rude nest it
scoops in the gravel, over which it stands guard with its
bright fins spread, looking as big and dangerous as
possible. When thus employed it takes the hook savagely,
perhaps regarding the worm as a dangerous enemy. The
young fishes soon hatch, looking very much like their
parents, although more transparent and not so brightly
colored. They grow rapidly, feeding on insects and
other small creatures, and reach their growth in two or
three years. They do not wander far and never willingly
migrate. Students should verify this account on the
different species. A more exact study of the nests of the
different species and the fishes' defence of them would be
a valuable addition to our knowledge. The most striking
traits of the habits of this fish are its vivacity and courage ;
it reveals its great muscular strength when captured.
The sexes are similar in appearance and both defend the
nest alike.
OTHER FISHES.
Fishes constitute the largest class of vertebrate animals
and are to be found eveTywhereFTn ponds, streams, or
ocean. About 15,000 species offish are known, of which
3,000 live in North America. Thejargest ofjil^ fishes is
the basking shark (Cetorhinus), which- reaches a length
lateral line
opercular flap \
gill-rakers
i
gall bladder I
1
nostrils
pericardia! cavity
I ventricle
conus arteriosub
ventral fin
intestine
body cavity
FIG. 112. Dissection
fin ^ / Cat7 % f ^e swim-bladder
^- , X kidney
"un-nary bladder
' opening from kidneys
body muscles
fthe sunfisli, Apomotis sp.
BRANCH CHORD AT A ; CLASS PISCES: THE FISHES 271
of thirty-six feet. The smallest is the dwarf goby
i . 1 /is tic I i thys )7~te s s than half an inch long, found in Luzon,
one of the Philippine Islands. Between these extremes
is every variety in size, form, and relative proportions.
The body, for example, may be greatly elongated and
almost cylindrical as in the eels; or long and flattened
from side to side as in the ribbon-fishes; or the head may
be very large, wider and higher than the rest of the body
as in the anglers, or may have a great beak as in the
sword-fish.
Body form and structure. When we consider the fish
as a whole, we find first a body formed for progression in
the water, the typical fish being pointed at each end (the
shorter point in front), and having the sides flattened, the
back and belly rather narrow, and the motive power
located in the fin on the tail. From this typical form
diverge all conceivable variations, adaptations to every
sort offish life.
Most fishes have the body covered with seal eg, although
many have the skin naked or covered with small scales
so hidden in the skin as to be hardly visible. The scales
are small horny or bony plates which fit into small pockets
or folds of the skin, and are usually arranged shingle-
fashion, overlapping each other. They are of various
shapes, mostly classified as of three kinds, namely, squarish
enamelled scales called ganoid, roundish smooth-edged
called cycloid, and roundish tooth-edged called ctenoid.
The skeleton of the fish is relatively complex. Its
bones are comparatively soft, having little lime in them,
indeed in many cases they are mere cartilage. The
vertebral column is made of twenty-four vertebrae in the
typical fishes, the number in the others being variously
increased, or sometimes diminished. These vertebrae are
of two classes, abdominal or body, and caudal or tail
vertebrae. The former have a neural arch which encloses
27 2 ELEMENTARY ZOOLOGY
the spinal cord and from which projects a spine. Below,
the processes spread apart, surrounding the kidneys and
partly enclosing the air-bladder. To these processes ribs
are loosely attached. The caudal vertebrae have no ribs
and leave no room below for viscera. Their lower arch
(hsemal), similar to the dorsal (neural) arch, surrounds a
blood-vessel. The fins of a fish are composed of bony
rods or rays joined by membrane. Some of these rays
may be unbranched and unjointed, being then known as
spines, and usually occupy the front part of the fin.
Other rays are made up of little joints and are usually
branched toward their tip. Such ones are called soft
rays. Soft rays make up the greatest part of most fins.
The vertical fins are on the middle line of the body.
These are the dorsal above, anal below, and caudal form-
ing the end of the tail. The paired pectoral and ventral
fins are ranged one on each side corresponding to the
arms and legs of higher animals. The pectoral fin or
arm is fastened to a series of bones called the shoulder
girdle. These bones do not correspond to those in the
shoulder girdle of the higher animals, and the various
parts in the two structures are differently named. The
uppermost bone of the shoulder girdle is usually attached
to the skull. To the lowermost is attached the rudimen-
tary pelvis, which supports the hinder limb or ventral fin.
Usually the pelvis is farther back and loose in the flesh,
but sometimes it is placed far forward, being occasionally
attached at the chin.
The head contains the various bones of the cranium,
usually closely wedged together and not easily distin-
guished. The jaws are each made of several pieces ; the
lower one is suspended from the skull by a chain of three
flat bones. The jaws may bear any one of a great variety
of forms of teeth or no teeth at all, and any of the bones
of the mouth-cavity and throat may have teeth as well.
BRANCH CHORD AT A; CLASS PISCES: THE HSHES ?73
On the outside of the head are numerous bones called
membrane bones, because they are made up of ossified
membrane. The most important of these is the operclc
or gill-cover. Within are the tongue with the fivejjill-
arches attached to it below and to the floor of the skull
a5ove~ the last arch being usually modified to form the
pharyngeal jaw.
The^stomach may be a blind sac with entrance and exit
close together, or it may have the form of a tube or
siphon. At its end are often found the large glandular
tubes called pyloric caeca which secrete a digestive fluid ;
and to its right side is attached the red spleen. Theliver
is large, having usually, but not always, a gall-bladder;
it "pouTs its secretion into the upper intestine. In fishes
which feed on plants the intestine is long, but it is short
in those which eat flesh, because flesh is digested in the
stomach, not in the intestines. The kidney is usually a
long slender forked gland showing little variation. The
egg-glands differ greatly in different sorts of fishes, the size
and number of eggs varying equally. The air-bladder is
a lung which has lost both lung structure and respiratory
function, being simply a sac filled with gas secreted from
the blood, and lying in the upper part of the abdominal
cavity. It is subject to many variations. In the gar
pike, bow-fin and the lung-fishes of the tropics, the air-
bladder is a true lung used for breathing and connected
by a sort of glottis with the oesophagus. In others it is
rudimentary or even wholly wanting, while in still others
its function as an air-sac is especially pronounced, and in
many it is joined through the modified bones of the neck
to the organ of hearing.
The blood of the fish is purified by circulation through
its gills. These are a series of slender filaments attached
to bony arches. Among them the blood flows in and out,
coming in contact with the water which the fish takes in
274 ELEMENTARY ZOOLOGY
through its mouth and which passes across the gills to be
expelled through the gill-openings. The blood is received
from the body into the first chamber of the heart, a mus-
cular sac called the auricle. From here it passes into the
ventricle, a chamber with thicker walls, the contraction
of which sends it to the gills, thence without return to the
heart it passes over the body. The circulation of blood
in fishes is slow, and the blood, which receives relatively
little oxygen, is cold, being but little warmer than the
water in which the individual fish lives.
Inside the cranium or brain-case is the brain, small and
composed of ganglia which are smooth at the surface and
contain little gray matter. At the posterior end of the
brain is the thickened end of the spinal cord, called the
medulla oblongata. Next overlapping this is the cere-
bellum, always single. Before this lie the largest pair of
ganglia, the optic lobes or midbrain, round, smooth, and
hollow. From the under side of these, nerves run to the
eyes with or without a chiasma or crossing. In front of
the optic lobes and smaller than them is the cerebrum or
forebrain, usually of two ganglia but sometimes (in the
sharks) united into one. In front of these are the small
olfactory lobes which send nerves to the nostrils.
The sense organs are well developed. The sense of
touch has in some fishes special organs for its better
effectiveness. For instance certain fin-rays in some
fishes, or, as in the catfish, slender, fleshy, whip-like
processes on the head, are developed as feelers or special
tactile organs. Other fishes, the sucker and loach for
example, have specially sensitive lips and noses with
which they explore their surroundings. The sense of
taste does not seem to be well developed in this group.
Taste-papillae are often present in small numbers on the
tongue or on the palate. The sense of smell is good.
The olfactory organs, one on each side of the head, are
BRANCH CHORD AT A; CLASS PISCES: THE FISHES 275
hollow sac-like depressions, closed at the rear. In
cases each sac has two openings or nostrils. The sense
oj" hearing is not very keen. The ears are fluid-filled sacs
buried in the skull, and without external or (except in a
few cases) internal opening. Fishes are far more sensi-
tive to sudden jars or sudden movements than to any
sound. They possess what is generally believed to be a
special sense organ not found in other animals. This is
the lateral line which extends along the sides of the body
and which consists of a series of modified scales (each one
with a mucous channel) richly supplied with nerves. The
eyes jire usually large and conspicuous. They differ
mainly from the eyes of other vertebrates in their myopic
spherical crystalline lens, made necessary by the density
of the medium in which fishes live. There are usually no
eyelids, the skin of the body being continuous but trans-
parent over the eyes. Being near-sighted, fishes do not
discriminate readily among forms, their special senses
fitting them in general to distinguish motions of their
enemies or prey rather than to ascertain exactly the
nature of particular things.
The colors of fishes are in general appearance protec-
tive. Thus most individuals are white on the belly,
mimicking the color of the sky to the enemy which
pursues them from below. Seen from above most of them
are greenish, like the water, or brownish gray and
mottled, like the bottom. Those thaf live on sand are
sand-colored, those on lava black, and those among rose-
red sea-weeds bright red. In many cases, especially
among kinds that are protected by their activity, brilliant
colors and showy markings are developed. This is
especially true among fishes of the coral reefs, though
species scarcely less brilliant are found among the darters
of our American brooks.
Among fresh-water fishes bright colors, crimson,
276 ELEMENTARY ZOOLOGY
scarlet, blue, creamy white, are developed in the breeding
season, the then vigorous males being the most highly
colored. Many of the feeble minnows even become very
brilliant in the nuptial season of May and June. Color in
fishes is formed by minute oil-sacs on the scales, and it
often changes quickly with changes in the nervous condi-
tion of the individuals.
Development and life-history. The breeding habits
of fishes are extremely varied. Most fishes do not pair,
but in some cases pairing takes place as among higher
animals. Ordinarily fishes lay their eggs on the bottom in
shallow water, either in brooks, lakes, or in the sea. The
eggs of fishes are commonly called spawn, and egg-laying
is referred to as spawning. The spawn of some fishes is
esteemed a special food delicacy. Spring is the usual time
of spawning, though some fishes spawn in summer and
some even in winter; generally they move from their usual
haunts for the purpose. The eggs of the different species
vary much in size, ranging from an inch and a half in
diameter (barn-door skate) down to the tiniest dots, like
those of the herring. The number of eggs laid also varies
greatly. The trout lays from 500 to i ,000, the salmon
about 10,000, the herring 30,000 to 40,000, and some
species of river fish 500,000, while certain flounders,
sturgeons, and others each lay several millions of eggs.
The adults rarely pay any attention to the eggs, which are
hatched directly by the heat of the sun or by heat absorbed
from the water. The length of incubation varies much.
When the young fish leaves the egg-shell it carries, in the
case of most species, a part of the yolk still hanging to
its body. Its eyes are very large, and its fins are repre-
sented by thin strips of membrane. It usually undergoes
no great changes in development from the first, resembling
the adult except in size. But some of the ocean fishes
BRANCH CHORD AT A i CLASS PISCES: THE FISHES 277
show a metamorphosis almost as striking as that of insects
or toads or frogs.
Some fishes build nests. Sticklebacks build elaborate
nests in the brooks and defend them with spirit. Sun-
fishes do the same, but the nests are clumsier and not
so well cared for.
The salmon is the type of fishes which run up from the
sea to lay their eggs in fresh water. The king salmon of
the Columbia River, for example, leaves the sea in the
high waters of March and ascends without feeding for over
a thousand miles, depositing its spawn in some small
brook in the fall. After making this long journey to lay
the eggs, the salmon become much exhausted, battered
and worn, and are often attacked by parasitic fungi. They
soon die, probably none ofthem ever surviving to lay eggs
a second time.
Classification. A fish is an aquatic vertebrate, fitted
to breathe the air contained in water, and never develop-
ing fingers and toes. Accepting this broad general
definition we find at once that there are very great differ-
ences among fishes. Some differ more from others than
the ordinary forms differ from rabbits or birds. So
although we have entitled this chapter as if all fishes
belonged to the class Pisces, we cannot arrange them
satisfactorily in less than three classes.
The lancelets (Leptocardii). The lowest class of fish-
like animals is that of the lancelets, the Leptocardii.
These little creatures, translucent, buried in the sand, of
the size and form of a small toothpick, are fishes reduced
to their lowest terms. They have the form, life, and ways
of a fish, but no differentiated skull, brain, heart, or eyes.
Moreover they have no limbs, no jaws, no teeth, no
scales. The few parts they do have are arranged as in a
fish, and they show something in common with the fish
278 ELEMENTARY ZOOLOGY
embryo. Lacking a distinct head, the lancelets are put
by some zoologists in a group called the Acrania, as
opposed to the Craniata, which includes all the other
vertebrates. Lancelets have been found in the North
Atlantic and Mediterranean, on the west coast of North
America, on the east coast of South America and on the
coasts of Japan, Australia, New Zealand, the East Indies
and Malayan Islands. The best-known members of the
group belong to the genus Amphioxiis. There are but
one to two other genera in the class.
The lampreys and hag-fishes (Cyclostomata). The
next class of fish-like animals is that of the lampreys (fig.
FlG. 113. A lamprey, Petromvzon martnus. (After Goode.)
113) and hag-fishes, the Cyclostomata. The lampreys
and hags are easily distinguished from the true fishes by
their sucking mouth without jaws, their single median
nostril, tHeir eel-like shape and lack of lateral appendages
or paired fins. The hag-fishes (Myxine), which are
marine, attach themselves by means of a sucker-like mouth
to living fishes (the cod particularly), gradually scraping
and eating their way into the abdominal cavity of the fish.
These hags or "borers " "approach most nearly to the
condition of an internal parasite of any vertebrate. ' ' The
lampreys, or lamprey-eels as they are often called because
of their superficial resemblance to true eels, are both
marine and fresh-water in their habitat, and most of them
attach themselves to live fishes and suck their blood.
They also feed on Crustacea, insects, and worms. The
BRANCH CHORD AT A; CLASS F>1$CES : THE PISHES
brook -lamprey, Lampetra wilder! , is never parasitic. It
reaches its full size in larval life and transforms simply
for spawning. The sea- and lake-lampreys ascend small
fresh-water streams when ready to lay their eggs, few
living to return. Sometimes small piles of stones are
made for nests. The young undergo a considerable
metamorphosis in their development. The largest sea-
lampreys reach a length of three feet. The common
brook-lampreys are from eight to twelve inches long only.
The true fishes (Pisces). All the other fish-like ani-
mals are grouped in the class Pisces. They are charac-
terized, when compared with the lower fish-like forms just
referred to, by the presence of jaws, shoulder girdle, and
pelvic girdle. The class^includes both the cartilaginous
and bony fishes, and is divided into three sub-classes,
namely, the Elasmobranchii, including the sharks, rays,
skates, torpedoes, etc., the Holocephali, including the
chimaeras (a few strange-bodied forms), and the Teleos-
tomi, including all the other fishes, as the trout, catfishes,
darters, bass, herring, cod, mackerel, sturgeons, etc., etc.
The sharks, skates, etc. (Elasmobranchii). --The
sharks and skates are characterized by the possession of
a skeleton composed of cartilage and not bone, as in
the bony fishes; they have no operculum; their teeth
are distinct, often large and highly specialized, and their
eggs are few and very large. There are two principal
groups among Elasmobranchii, viz., the sharks, which
usually have an elongate body, and always have the gill-
openings on the sides, and the rays or skates, which have a
broad flattened body with the gill-openings always on the
under side. All the members of both groups are marine.
The sharks are active, fierce, usually large fishes, which
live in the surface-waters of the ocean and make war on
other marine animals, all of the species except half a
dozen being fish-caters. The shark's mouth is on the.
2&o . ELEMENT A kY ZOOLOGY
under side of the usually conical head, and the animal
often turns over on its back in order to seize its prey.
The largest American sharks, and the largest of all fishes,
are the great basking-sharks (CctorJiinus}, which reach a
length of nearly forty feet. They get their name from
their habit of gathering in numbers and floating motion-
less on the surface. They feed chiefly on fishes.
The hammer-headed sharks (Sphyrna] are odd sharks
which have the head mallet or kidney shaped, twice as wide
as long, the eyes being situated on the ends of the lateral
expansions of the head. The man-eating or great white
sharks (Carcharodon) are nearly as large as the basking-
sharks, and are extremely voracious. They will follow
ships for long distances for the refuse thrown overboard.
They do not hesitate to attack man. Among the more
familiar smaller sharks are the dog-fishes and sand-sharks
of our Atlantic coast.
The rays and skates are also carnivorous, but are with
few exceptions sluggish, lying at the bottom of shallow
shore-waters. They feed on crabs, molluscs, and bottom-
fishes. The small common skates, /'tobacco-boxes"
(Raja erinaced] (fig. 114), about twenty inches long, and
the larger "barn-door skates" (R. hcvis), are numer-
ous along the Atlantic coast from Virginia northward.
Especially interesting members of this group, because of
the peculiar character of the injuries produced by them,
are the sting-rays and torpedoes or electric-rays. The
sting-rays (Dasyatis) have spines near the base of the tail
which cause very painful wounds. The torpedoes (Narcine)
have two large electrical organs, one on each side of the
body just behind the head, with which they can give a
strong electric shock. "The discharge from a large in-
dividual is sufficient to temporarily disable a man, and
were these animals at all numerous they would prove
dangerous to bathers. ' ' Very different from the typical
BRANCH CHORD AT A; CLASS PISCES: THE FISHES 281
rays in external appearance are the saw-fishes ( Pristis
pcctinatis), which belong to this group. The body is
elongate and shark-like, and has a long sa\v-like snout.
This sa\v, which in large individuals may reach a length
of six feet and a breadth of twelve inches, makes its
owner formidable among the small sardines and herring-
FIG. 114. The common skate, Raja erinacea. (From Kingsley.)
like fishes on which it feeds. The saw-fishes live in tropi-
cal rivers, descending to the sea.
The bony fishes (Teleostomi). The bony or true fishes
are distinguished from the lampreys and sharks and rays
by having in general the skeleton bony, not cartilaginous,
the skull provided with membrane bones, and the eggs
small and many. In this group are included all the
fishes of our fresh- water lakes, ponds, and streams as well
as most of the marine forms. Fish life, being spent under
2&2 . ELEMENTARY ZOOLOGY
water, is not familiar to most of us, and beginning students
are rarely helped enough in getting acquainted with the
different kinds and the interesting habits of fishes. But
they offer a field of study which is really of unusual interest
and profit. We can refer in the following paragraphs to
but few of the numerous common and readily found kinds,
and to these but briefly.
Closely related to the sunfish, studied as example of
the bony fishes, are the various kinds of bass, as the
"crappie " (Pomoxis annularis), the calico bass (P. sepa-
roidcs), the rock-bass (Ambloplitcs rupcstris) and the
large-mouthed and small-mouthed black bass (Micropterus
salmoides and M. dolomieu respectively). All the mem-
bers of this sunfish and bass family are carnivorous fishes
especially characteristic of the Mississippi valley.
Another family of many species especially common in
the clear, swift, and strong Eastern rivers is that of the
darters and perches. The darters are little slender-bodied
fishes which lie motionless on the bottom, moving like a
flash when disturbed and slipping under stones out of sight
of their enemies. Some are most brilliantly colored, sur-
passing in this respect all other fresh-water fishes.
Unlike the sunfishes and darters are the catfishes,
composing a great family, the Siluridae. The catfish
(Ameturus) gets its name from the long feelers about its
mouth ; from these feelers also come its other names of
horned pout, or bull-head. It has no scales, but its spines
are sharp and often barbed or jagged and capable of mak-
ing a severe wound.
Remotely allied to the catfish are the suckers, min-
nows, and chubs, with smooth scales, soft fins and soft
bodies and the flesh full of small bones. These little fish
are very numerous in species, some kinds swarming in
all fresh water in America, Europe, and Asia. They
usually swim in the open water, the prey of every carniv-
BRANCH CHORDATA; CLASS PISCES: THE FISHES 283
orous fish, making up by their fecundity and their insig-
nificance for their lack of defensive armature. In some
species the male is adorned in the spring with bright
pigment, red, black, blue, or milk-white. In some cases,
too, it has bony warts or horns on its head or body. Such
forms are known to the boys as horned dace.
Most interesting to the angler are the fishes of the
salmon and trout (fig. 115) family, because they are gamy,
FIG. 115. The rainbow-trout, Salmo iri..ens. (From specimen.)
beautiful, excellent as food and above all perhaps because
they live in the swiftest and clearest waters in the most
charming forests. The salmon live in the ocean most of
their life, but ascend the rivers from the sea to deposit
their eggs. The king salmon (Oncorhynchus tschawy-
tscha) of the Columbia goes up the great river more than
a thousand miles, taking the whole summer for it, and
never feeding while in fresh water. . Besides the different
kinds of salmon, the black-spotted or true trout, the charr
or red-spotted trout of various species, the whitefish
(Coregonus), the grayling ( Thymallus signifer) and the
famous ayu of Japan belong to this family.
In the sea are multitudes of fish forms arranged in many
families. The myriad species of eels agree in having no
ventral fins and in having the long flexible body of the
snake. Most of them live in the sea, but the single
284 ELEMENTARY ZOOLOGY
genus (Anguilla] or true eel which ascends the rivers is
exceedingly abundant and widely distributed. Most eels
are extremely voracious, but some of them have mouths
that would barely admit a pin-head. The codfish (Gadus
callarias) is a creature of little beauty but of great useful-
ness, swarming in all arctic and subarctic seas. The
FIG. 116. The winter flounder, Pseudopleuronectes americanus.
(After Goode. )
herring (Clupea Jiarengiis]^ soft and weak in body, are
more numerous in individuals than any other fishes. The
flounders (fig. 116) of many kinds lie flat on the sea-
bottom. They have the head so twisted that the two
eyes occur both together on the uppermost side. The
members of the great mackerel tribe swim in the open
sea, often in great schools. Largest and swiftest of these
is the sword-fish (Xipliias gladius), in which the whole
upper jaw is grown together to form a long bony sword,
a weapon of offence that can pierce the wooden bottom
of a boat.
Many of the ocean fishes are of strange form and ap-
pearance. The sea-horses (Hippocampus sp.) (fig. 117)
are odd fishes covered with a bony shell and with the
head having the physiognomy of that of a horse. They
are little fishes rarely a foot long, and cling by their
BRANCH CHORD AT A; CLASS PISCES: THE FISHES 285
curved tails to floating seaweed. The pipefish (Syn-
nat/uis fnsanti) is a sea-horse straightened out. The
porcupine-fishes and swellfishes (Tctraodontidce) have the
power of filling the stomach
with air which they gulp from
the surface. They then escape
from their pursuers by floating
as a round spiny ball on the
surface. The flying-fishes (Exo-
ccetns) leap out of the water and
sail for long distances through
the air, like grasshoppers. They
cannot flap their long pectoral
fins and do not truly fly;
nevertheless they move swiftly
through the air and thus escape
their pursuers. In its structure
a flying-fish differs little from a
pike or other ordinary fish.
Foi an account of the fishes
of North America see Jor-
dan's "Manual of Vertebrates, "
eighth edition, ' pp. 5-173 . and
Jordan and Kvermann's - Fishes
of North and Middle America,"
where the 3,127 species known from our continent are
described in detail with illustrative figures.
Habits and adaptations. The chief part of a fish's life
is devoted to eating, and as most fishes feed on other
fishes, all are equally considerably occupied in providing
for their own escape.
In general the provisions for seizing prey are confined
to sharp teeth and the strong muscles which propel the
caudal fin. But in some cases special contrivances
appear. In one large group known collectively as the
Goode.)
2 86 ELEMENTARY ZOOLOGY
" anglers " the first spine of the dorsal fin hangs over the
mouth. It has at its tip a fleshy appendage which serves
as a bait. Little fishes nibble at this, the mouth opens,
and they are gone. In the deep seas, many fishes are
provided with phosphorescent spots or lanterns which
light up the dark waters, and enable them to see their
prey. In storms these lantern-fishes sometimes lose their
bearings and are thrown upward to the surface.
In general the more predatory in its habits any fish is
the sharper its teeth, and the broader its mouth. Among
brook-fishes the pickerel has the largest mouth and the
sharpest teeth. It has been called a " mere machine for
the assimilation of other organisms. ' ' The trout has a
large mouth and sharp teeth. It is a swift, voracious, and
predatory fish, feeding even on its own kind. The sunfish
is less greedy and its mouth and teeth are smaller, though
it too eats other fish.
As means of escape, most fishes depend on their speed
in swimming. But some hide among rocks and weeds,
disguising themselves by a change in color to match their
surroundings. Others, like the flounders and skates, lie
flat on the bottom. Still others retreat to the shallows
or the depths or the rock-pools or to any place safer than
the open sea. Some are protected by spines which they
erect when attacked. Some erect these spines only after
they have been swallowed, tearing the stomach of their
enemy and killing it, but too late to save themselves.
Again in some species the spines are armed with poison
which benumbs the enemy. Sometimes an electric battery
about the head or on the sides gives the biting fish a
severe shock and drives him away. Such batteries are
found in the electric rays or torpedo, in the electric eel
of Paraguay, the electric catfish of the Nile, the electric
stargazer and other fishes.
Some fishes are protected by their poor and bitter flesh.
BRANCH CHORD AT 4; CLASS PISCES: THE FISHES 287
Some have bony coats of mail and sometimes the coat of
mail is covered with thorns, as in the porcupine-fish.
This fish and various of its relatives have the habit of filling
the stomach with air when disturbed, then floating belly
upward, the thorny back only within reach of its enemies.
Many species (cling fishes) attach themselves to the
rocks by a fleshy sucking-disk. Some (Remora) (fig. 1 1 8)
cling to larger fishes by a strange sucking-disk on the head,
a transformed dorsal fin, being thus shielded from the
FIG. 118. The remora, or cling fish, Remoropsis brachyptera. Note sucker
on top of head. (After Goode.)
attacks of fish smaller than their protectors. Some small
fishes seek the shelter of the floating jellyfishes, lurking
among their poisoned tentacles. Others creep into the
masses of floating gulf-weed. Some creep into the shell
of clams and snails. In the open channel of a sponge,
the mouth of a tunicate and in similar cavities of various
animals, little fishes may be found. A few fishes (hag-
fishes) are parasitic on others, boring their way into the
body and devouring the muscles with their rasp-like
teeth.
Some fishes are provided with peculiar modifications of
the gills which enable them to breathe for a time out of
water. Such fish have the pectoral fins modified for a
rather poor kind of locomotion on land, thus enabling
them to move from pond to pond or from stream to stream.
In cold climates the fishes must either migrate to warmer
latitudes in winter, as some do, or withstand variously the
cold, often freezing weather. Some fish can be frozen
288 ELEMENTARY ZOOLOGY
solid, and yet thaw out and resume active living. Some
lie at the bottoms of deep pools through the colder periods,
while many others, such as the minnows, chubs, and
other kinds common in small streams, bury themselves in
the mud, and lie dormant or asleep through the whole
winter. On the other hand in countries where the long
intense rainless summers dry up the pools, some fishes
have the habit of burying themselves in the mud, which,
with slime from the body, forms about them a sort of tight
cement ball in which they lie dormant until the rains
come. " Thus a lung-fish (called Protopterus), found in
Asia and Africa, so completely slimes a ball of mud
around it that it may live for more than one season, per-
haps many; it has been dug up and sent to England, still
enclosed in its round mud-case, and when it was placed
in warm water it awoke as well as ever."
Food-fishes and fish-hatcheries. Most fishes are suit-
able for food, though not all. Some are too small to be
worth catching or too bony to be worth eating. Some
of the larger ones, especially the sharks, are tough and
rank. A few are bitter and in the tropics a number of
species feed on poisonous coelenterates about the coral
reefs, becoming themselves poisonous in turn. But a fish is
rarely poisonous or unwholesome unless it takes poisonous
food. Where fishes of a kind specially used for food gather
in great numbers at certain seasons of the year, fishing is
carried on extensively and with an elaborate equipment.
Such fisheries, some of which have been long known, are
scattered all over the world. Along the shores of the
Mediterranean Sea, and on the coasts of Norway, France,
the British Isles and Japan are numerous great fishing-
places. But " nowhere are there found such large fisheries
as those along the northern Atlantic coasts of our own
continent, extending from Massachusetts to Labrador.
Especially on the banks of Newfoundland are codfish,
BRANCH CHORD AT A; CLASS PISCES: THE FISHES 289
herring, and mackerel caught. ' ' Among our fresh-water
fisheries the great salmon fisheries of the Penobscot and
Columbia rivers and of the Karluk and other rivers of
Alaska are the best known. The whitefish of our Great
Lakes is also one of the important food-fishes of the world.
In many places fishes are raised in so-called hatcheries,
not usually for immediate consumption but for the purpose
of stocking ponds and streams either in the neighborhood
of the hatchery or in distant waters which the special
species cultivated has not been able naturally to reach.
The eggs of some fishes are large and non-adherent, two
features which greatly favor artificial impregnation and
hatching. In the hatcheries the eggs are put first into
warm water, where development begins; they are then
removed into cool water, which arrests development with
out injury, making shipment possible. The eggs of
salmon and trout in particular can be sent long distances
to suitable streams or ponds. The eggs of the shad have
been thus carried from the East to the streams of Cali-
fornia and trout have been distributed to many streams in
our country which by themselves they could never have
reached.
The salmon is a conspicuous example of those fishes
which can be artificially propagated. The eggs of the
salmon are large, firm, and separate from each other. If
the female fish be caught when the eggs are ripe and
her body be pressed over a pan of water the eggs will
flow out into the water. By a similar process the milt or
male sperm-cells can be procured and poured over the
eggs to fertilize them. The young after hatching are kept
for a few days or weeks in artificial pools, till the yolk-
sacs are absorbed and they can take care of themselves.
They are then turned into the stream, where they drift tail
foremost with the current and pass downward to the sea.
All trout may be treated in similar fashion, but there are
2 90 . ELEMENTARY ZOOLOGY
many food-fishes which cannot be handled in this way.
In some the eggs are small or soft, or viscid and adhering
in bunches. In others the life-habits make artificial fer-
tilization impossible. Such species are artificially reared
only by catching the young and taking them from one
stream to another. To this type belong the black bass,
the sunfish, the catfish and other familiar forms.
CHAPTER XXV
BRANCH CHORDATA (Continued). CLASS BA-
TRACHIA: THE BATRACHIANS
THE structure, life-history, and habits of the garden-
toad (Bnfo Icntiginosus} have already been studied (see
Chapter II and Chapter XII).
OTHER BATRACHIANS.
The class Batrachia includes the animals familiarly
known as coecilians, sirens, mud-puppies, salamanders,
toads, and frogs. Although differing plainly from fishes
in appearance and habits, the batrachians are really closely
related to them, resembling them in all but a few essential
characters. Among the distinctive characters of ba-
trachians may be noted the absence of fins supported
by fin-rays, the presence usually of well-developed legs
for walking or leaping, and the absence or reduction of
certain bones of the head connected with the gills and
lower jaw and which are well developed in the fishes.
The batrachians stand in somewhat intermediate position
between the fishes and the reptiles, showing some of the
characters of both. They are, like fishes and reptiles,
cold-blooded. In their adult condition some are terres-
trial and some aquatic as to habitat, but all have an aquatic
larval life. The water-inhabiting young breathe at first
by means of gills, later lungs begin to develop, and for a
time both gills and lungs are used in respiration. Finally
in the adult condition in almost all of the forms the gills
291
292 ELEMENTARY ZOOLOGY
are wholly lost and breathing is done by the lungs and
skin solely. Correlated with the change of habits from
larval to adult stage there is usually a well-marked meta-
morphosis in post-embryonic development. This meta-
morphosis is specially striking among the frogs and toads.
None of the aquatic forms is marine, salt water always
killing eggs, larva? or adults. Batrachians are found all
over the world, although there are few in the extreme
North. They are most abundant in warm and tropical
lands.
Body form and organization. The body varies from
a long and slender, truly snake-like form as in the tropical
ccecilians through the usual salamander (fig. 119) shape,
where it is more robust but still elongate and tailed, to
the heavy, squat, tailless condition of the toads. Legs,
FIG. 119. The tiger salamander. (From Jenkins and Kellogg.)
with five digits, are usually present, and are used for
swimming, walking, or leaping. The legs are longest
and best developed in the short tailless frog and toad
forms which are mostly terrestrial, and are short and weak
in the tailed salamander forms, many of which are aquatic.
The skin is almost always naked, showing a marked differ-
ence from the scaled condition of reptiles and most of the
fishes, and its cells secrete a slimy, sticky, usually whitish
fluid, which in some cases is irritating, or even poisonous.
BRANCH CHORDATA: CLASS BATRACHIA 293
The skin is sometimes thrown up into folds or ridges, and
in some species is elevated to form a kind of fin on the
tail or back. This unpaired fin differs from the dorsal fin
(and other fins) of fishes in not being supported by rayed
processes of the skeleton. There are in some batrachians
traces of an exoskeleton in the presence of scale-like
structures in the skin or in the horny nails on the digits,
but these cases are rare. The skin contains pigment-cells
and many of the batrachians are brilliantly colored and
patterned ; some of the pigment is carried by special con-
tractile or expansile cells, the chromatophores (see
account of chromatophores of the Cephalopoda, p. 256),
so that the animal can change its tint and markings more
or less rapidly. All the batrachians possess external gills
in their aquatic larval stage, and in a few forms, as the
sirens and mud-puppies, gills are retained all through life.
These gills are branched folds of the skin abundantly
supplied with blood-vessels.
In the organization of the batrachian body the usual
vertebrate characters appear, the body-organs being
arranged with reference to a supporting and protecting
internal bony skeleton. The head is plainly set off from
the rest of the body and bears the mouth and the organs
of hearing and sight. Certain so-called lateral sense
organs, the function of which is not exactly known, occur
arranged in three lines on each side of the body of some
of the forms. Both pairs of limbs are present and func-
tional in almost all of the species. In the coecilians the
limbs are wholly wanting ; in the sirens only the fore legs
are present.
Structure. The most obvious skeletal differences
among batrachians are those due to variations in external
form. While there are as many as 100 vertebra,* in some
of the elongate long-tailed salamanders (even 250 in the
strange snake-like ccecilians), there are but 10 (the last
294 ELEMENTARY ZOOLOGY
or tenth being the rod-shaped bone called the urostyle)
in the short, tailless frogs and toads. To any of the
vertebrae except the first (the single cervical vertebra) and
the last, ribs may be attached and the ccecilians have
about as many pairs of ribs as vertebrae. In the frogs
and toads, however, the ribs are lost. In any case they
are never fastened by their lower ends to the breast-bone.
The alimentary canal is usually not much longer than
the body and is plainly divided into mouth, pharynx,
oesophagus, small intestine, large intestine or rectum,
and anal opening. The teeth when present occur on both
the jaws and the palate. They are small, sharp, point
backward and are fused to the bones. They are wholly
wanting in the toad and in some other allied forms. The
tongue may be wanting, or may be immovably fixed to
the floor of the mouth, or as in the frogs, fastened at its
front end but free behind, so that the hinder end can be
protruded far from the mouth for the purpose of catching
insects.
The organs of respiration are gills, external and in-
ternal, lungs, trachea or windpipe, and the skin. In the
earliest larval stages all batrachians have gills; later, in
most cases, the gills become reduced and disappear, while
at the same time lungs are developing. In some sala-
manders the lungs never develop, but the animals, in their
adult stage, breathe wholly by means of the skin. In a
few cases, as in the siren and mud-puppies, gills are
retained through the whole life, although lungs are also
present in the adult stage. The lungs are two in number,
a right and a left lung, and are simple sacs with the walls
more or less folded or thrown into ridges and richly sup-
plied with blood-vessels. The front end of the lungs
opens directly into the pharynx or, in the more elongate
batrachians, is connected with it by a tubular trachea or
windpipe. In the frogs and toads there are vocal cords
BRANCH CHORD AT A: CLASS BATRACHIA 295
stretched across the short windpipe; the vibration of
these cords produces the croaking.
The heart is always three-chambered, consisting of the
right and left auricles and a single ventricle. The circu-
lation of the more generalized salamanders like the mud-
puppies is essentially like that of a fish. In the frogs and
toads there is a distinct advance beyond this condition.
The red corpuscles of the blood are oval in shape and are
the largest found among any of the vertebrates.
In the nervous system the small size of the hindbrain
or cerebellum is noticeable. The sense organs are fairly
well developed. The skin of the whole body is provided
with tactile nerve-endings. There are special taste organs
on the lining membrane of the tongue and mouth-cavity.
The eyes have no lids in some of the lower forms ; most
of the frogs and toads have an upper lid but no under one,
although a thin membrane, called the nictitating mem-
brane, arises from the lower margin of the eye and can be
drawn up over it. The ears have no external parts, other
than the thin tympanic membranes. The nostrils of frogs
and toads can be closed by the contraction of certain
special muscles.
Life-history and habits. The sexes are distinct, and in
most cases the young hatch from eggs. A few of the sala-
manders give birth to free young. The eggs are usually in
strings or chains enclosed in a clear gelatinous substance;
these chains of eggs are either simply dropped into the
water or are fastened to water-plants. The young, called
tadpoles (fig. 120), in their earlier larval stages are ex-
tremely fish-like in character, long-bodied, tailed, swim-
ming freely about by means of the fin-like flattened tail, and
breathing by means of external gills. Nor do they show
any sign of legs. As the tadpoles grow and develop the
legs begin to appear, the hind legs first in the frogs and
toads, the fore legs first in the salamanders ; lungs develop
296 . ELEMENTARY ZOOLOGY
and the gills disappear (except in the cases of the few forms
which retain gills through life). The tail shortens and
finally disappears in the frogs and toads ; with the salaman-
ders the tail-fin only is lost. At the same time the change
from water to land is made. Further growth is very
FIG. 120. Tadpoles. (Photograph from life by Cherry Kearton; per-
mission of Cassel & Co.)
slow; frogs are not really adult, that is, capable of pro-
ducing young, until they are five years old, and they may
continue to increase in size until they are ten years old.
The food of the adult batrachians is almost exclusively
small animals, particularly insects and worms. Crus-
taceans, snails, and young fish are also eaten. The tad-
poles also eat vegetable matter. Almost all batrachians
are nocturnal in habit, remaining concealed by day. In
the zones in which cold winters occur they hibernate or
pass the winter in a torpid condition, or state of " sus-
pended animation," or, as it is said, they sleep through
the winter. Frogs burrow into the mud at the bottom of
ponds at the approach of winter and come forth early in
BRANCH CHORD AT A: CLASS B AT R A CHI A 297
the spring- to lay their eggs. Most batrachians are very
tenacious of life, being able to withstand long periods of
fasting and serious mutilation, and most of them can
t>
regenerate certain lost parts, such as the tail or legs.
Classification, The living Batrachia are divided into
three orders, viz., the Urodela, including the sirens, mud-
puppies, salamanders, and newts, batrachians which retain
the tail throughout life, having generally two pairs of limbs
of approximately equal size, and sometimes possessing
gills or gill-slits in the adult condition ; the Anura, or
frogs and toads, with no tail in the adult condition, with
short and broad trunk, with hind limbs greatly exceeding
the fore limbs in size, and never with gills or gill-slits
in the adult stage; and the Gymnphiona, or ccecilians,
snake-like batrachians having neither limbs nor tail, with
a dermal exoskeleton and without gills or gill-slits in the
adult.
Mud-puppies, salamanders, etc. (Urodela). TECHNI-
CAL NOTE. If possible obtain specimens of mud-eels (Siren], com-
mon in the South, or mud-puppies (Necturus], common in the cen-
tral North, as examples of batrachians with gills persisting in the
adult stage. One or more species of Amblystoma may be found in
almost any part of the country, and larvae of large size may be found
with the external gills. For an example of the general long-tailed
or Urodelous type of batrachian any salamander or newt occurring
in the vicinity of the school may be used. The little green triton or
eft (Diemyctylus viridiscens} of the eastern States, or its larger
brown-backed congener of the Pacific coast (D. torosus] is common
in water, while another eft, the little red-backed salamander,
(Plethodon} is common in the woods under logs and stones. The
external characters of the body should be compared with those of
the toad. The skeleton should be prepared by macerating away
the flesh (for directions, see p. 452), and the presence of the many
caudal vertebrae and the ribs, the equality in size of the legs, and
other points should be noted. Compare with skeleton of toad.
Make drawings. It will be well, also, to dissect out and examine
the various internal organs of the salamander, comparing them with
the same organs in the toad. The salamander,, indeed, is in many
ways better than the toad as an example of the class. Its body is
less adaptively modified and shows the essentially fish-like charac-
ter of the batrachian structure.
298 ELEMENTARY ZOOLOGY
The batrachians which retain external gills in the adult
stage are the members of two families of which the
American representatives are known as mud-eels (Siren}
and mud-puppies or water-dogs (Necturus)* The mud-
eels, which are found * * in the ditches in the swamps of
the southern States from South Carolina to the Rio Grande
of Texas and up the Mississippi as high as Alton, Illinois, ' '
are blackish in color, have no hind legs and are long and
slender, with the tail shorter than the rest of the body.
They reach a length of nearly three feet. The mud-
puppies, found in the Great Lakes and in the rivers of the
upper Mississippi valley, are brown with colored spots,
and are about two feet long when full grown. They have
both fore and hind legs.
A few salamanders, while not possessing external gills
when adult, have a spiracle or small circular opening in
the side of the neck which leads into the throat. The
best-known American salamander of this kind is the
large heavy-bodied blackish water-dog or ' ' hellbender ' '
(Cryptobranchus) of the Ohio River. It is about two feet
long, and is <4 a very unprepossessing but harmless
creature." It has a conspicuous longitudinal fold of skin
along each side of the body. The largest known ba-
trachian, the giant salamander of Japan (Megalobatrachus\
reaching a length of three feet, is related to the water-
dog.
Of all the salamanders the most interesting are the
blunt-nosed salamanders (Amblystoma}. A dozen or
more species of A mblystoma occur in North America, of
which tigrimim, a dark-brown species with many irregular
yellow blotches sometimes arranged in cross-bands, is the
most widespread. The larvae of some Amblystoma retain
their gills until they have reached a large size, and in one
or two species the usual metamorphosis is very long
delayed and the salamanders produce young while in the
BRANCH CHORD AT A : CLASS BATRACHIA 299
larval condition, that is, while retaining the gills and a
compressed fin-like tail. In the case of a certain Mexican
species (A. maculatunt) it is believed that the final meta-
morphosis never occurs. The Mexicans call these gilled
larval Amblystoma axolotls, and use them for food. For
FIG. 121. The Western brown eft, or salamander, Diemyctyhis torosus.
(From living specimen.)
a long time naturalists supposed the Amblystoma larvae
which produce young to be the adults of a species of sala-
manders which retained their gills through life, like the
sirens and mud-puppies, and classified them in a distinct
genus.
Of the various common salamanders or newts some are
found in streams, ponds, and ditches, and some under
logs and stones in the woods. The aquatic forms have
the tail compressed (flattened from side to side), while
the land forms have the tail cylindrical, tapering to a
point. Most of the land-salamanders produce their young
alive, while the water forms lay eggs which are usually
attached to a submerged plant-stem. The salamanders
are, almost without exception, found only in the northern
hemisphere.
Frogs and toads (Anura). There are about a dozen
species of frogs in the United States. The largest of
these, and indeed the largest of all the frogs, is the well-
known bullfrog (Rana catesbiand], which reaches a length
(head to posterior end of body) of eight inches. It is
found in ponds and sluggish streams all over eastern
300 ELEMENTARY ZOOLOGY
United States and in the Mississippi valley. It is green-
ish in color with the head usually bright pale green. Its
croaking is very deep and sonorous. The pickerel-frog
(R. palustris], which is bright brown on the back with two
rows of large oblong square blotches of dark brown on
the back, is found in the mountains of eastern United
States. The little pale reddish-brown wood-frog (R. syl-
vaticd) with arms and legs barred above is common in
damp woods and is "an almost silent frog." The
peculiar and infrequently seen frogs known as the ' * spade-
foots ' ' (Scaphiopus} are subterranean in habit and usually
live in dry fields or even on arid plains and deserts.
They pass through their development and metamorphosis
very rapidly, appearing immediately after a rain and lay-
ing their eggs in temporary pools. At this time of egg-
laying they utter extraordinarily loud and strange cries.
Some frogs in other parts of the world live in trees, and
the eggs of one species are deposited on the leaves of
trees, leaves which overhang the water being selected so
that the issuing young may drop into it.
The true tree-frogs or tree-toads (Hylidae) constitute a
family especially well represented in tropical America.
They have little disk- or pad-like swellings on the tips of
their toes to enable them to hold firmly to the branches
of the trees in which they live. Some, like the swamp
tree-frog and the cricket-frog, are not arboreal in habit,
remaining almost always on the ground. The common
tree-frog of the eastern States (Hyla vcrsicolor) is green,
gray, or brown above with irregular dark blotches, and
yellow below. It croaks or trills, especially at evening
and in damp weather. Pickering's tree-frog (Hyla
pickeringii} makes the "first note of spring" in the
eastern States. This tree-frog is the one most frequently
heard in the autumn too, but "its voice is less vivacious
than in the spring and its lonely pipe in dry woodlands is
BRANCH CHORD AT A: CLASS BATRACHIA 301
always associated with goldenrods and asters and falling
leaves. ' ' The tree-frogs of North America lay their eggs
in the water on some fixed object as an aquatic plant, in
smaller packets than those of the true frogs, and not in
strings as do the toads.
The toads (Bufonidae) differ from the true frogs in
having no teeth and in not having, as the frogs do, a
cartilaginous process uniting the shoulder-bones of the
two sides of the body. The absence of this uniting
process makes the thoracic region capable of great expan-
sion. There are only a few species of toads in North
America, but one of these species, the common American
toad (Bufo lentiginosus), is very abundant and wide-
spread. It appears also in two or three varieties, the
common toad of the southern States differing in several
particulars from that of the northern. The toad is a
familiar inhabitant of gardens, and does much good by
feeding on noxious insects. It is most active at twilight.
Its eggs are laid in a single line in the centre of a long
slender gelatinous string or rope, which is nearly always
tangled and wound round some water-plant or stick near
the shore on the bottom of a pond. The eggs are jet
black and when freshly laid are nearly spherical. At the
time of egg-laying the toads croak or call, making a sort
of whistling sound and at the same time pronouncing deep
in the throat " bu-rr-r-r-r. " The toad does not open its
mouth when croaking, but expands a large sac or resonator
in its throat. The toad-tadpoles are blacker than those
of frogs or salamanders, and undergo their metamorphosis
while of smaller size than those of frogs. When they
leave the water they travel for long distances, hopping
along so vigorously that in a few days they may be as far
as a mile from the pond where they were hatched. They
conceal themselves by day, but will appear after a warm
shower; this sudden appearance of many small toads
3 2 ELEMENTARY ZOOLOGY
sometimes gives rise to the false notion that they have
fallen with the rain.
Coecilians (Gymnophiona). The third order of ba-
trachians, the ccecilians, includes about twenty species of
slender worm- or snake-like limbless forms which are
confined to the tropics. Some of them are wholly blind
and the others have only rudimentary eyes. In them the
skin is folded at regular intervals so that the body appears
to be rigid or segmented, and in some species there are
small concealed horny scales in the skin.
CHAPTER XXVI
BRANCH CHORDATA (Continued}. CLASS REP-
TILIA: THE SNAKES, LIZARDS, TURTLES,
CROCODILES, ETC.
THE GARTER SNAKE (Thamnophis sp.)
TECHNICAL NOTE. Garter snakes may be found almost any-
where during the spring and summer months. If possible each
student should have a specimen, but in case it is difficult to get
enough snakes two students can use a single specimen. If garter
snakes are rare, take any other snake. Snakes will live a long time
without feeding and specimens should be kept alive until ready to
use. Kill with chloroform as directed for the toad (p. 5). After
completing the study of the external characters place each specimen
in a dissecting-pan and with a pair of scissors cut through the scales
on the ventral side, passing backwards from the eighteenth to the
fortieth. Pin back the edges of the cut and thus expose the heart.
Through its lower end, the ventricle, insert a large canula; inject
with a fairly large syringe the glue mass which is described on
p. 452. This injection will fill the entire arterial system. To inject
the venous system make another cut through the ventral scales, cut-
ting forward from the anal scale through about forty of them. Note
the injected mass in some of the vessels already filled. Take one
of the large vessels still containing blood and pass two ligatures
beneath it. Get ready a small canula and cut a slit in the vessel,
elevating the head so that the blood will run out as much as possi-
ble. Now wash the blood off, insert the canula in the slit and tie
one ligature about the vessel containing the canula ; have the other
ready to tie after the vein has been injected. Use a new color for
the venous system. Leave specimen in cold water for a time until
the injection is hard. Then continue the cut from the anal plate
forward to the lower jaw and pin out the edges of the cut on both
sides in the dissecting-pan.
Structure (fig. 122). Note that the snake is covered
with horny scales somewhat as the fish is. How do these
scales differ from those of the fish ? In snakes the scales
303
3^4 ELEMENTARY ZOOLOGY
are not bony, but are true skin structures. Note the modi-
fication of the scales on the head, back, and ventral sur-
face. Those on the dorsal surface often have minute
ridges, the keels. How do the ventral scales differ from the
dorsal ones and others ? By a system of muscles these
ventral scales are rhythmically moved and as their posterior
edges are pushed back against some resisting object the
body glides forward. On the head note the pair of eyes.
Are there eyelids ? In front of each eye note an opening.
What are these openings ? Thrust a bristle into the
opening and see where it enters the mouth-cavity through
the internal nares. Does the snake have external ears ?
Observe the very long jaws and note that they are loosely
hinged. Examine the inside of the mouth. Are there
teeth? If so where are they situated, and how arranged?
Note that all of the teeth point backwards. Food is not
chewed. When some object of prey, a frog, or mouse,
for example, is seized, the teeth hold it fast to the roof of
the mouth and by a backward and forward movement of
the lower jaws it is gradually drawn into the large
oesophagus. What is the character and situation of the
tongue f Just behind the tongue note the narrow slit,
glottis, opening into the tvindpipc, or trachea. Back o/
the trachea opens the oesophagus.
When the snake is laid open the elongate heart will
be conspicuous in the anterior third of the body. Insert
a blowpipe or quill into the glottis just back of the tongue,
and inflate the lung, which is a long, thin- walled bag
extending from the region of the heart posteriorly for
two-thirds of the length of the body. There is but one
developed lung, the right ; note at the anterior end of the
lung a small mass of tissue, the atrophied left lung.
Running forward from the lung is a long tube composed
of incomplete cartilaginous rings, connected by mem-
brane, the trachea. Note the long straight alimentary
BRANCH CHORDATA: CLASS REPTILIA 305
tonal. Distinguish the oesophagus, stomach, intestine,
rectum and the anus.
In the region of the lung is an elongated dark-red
glandular mass, the liver. The secretion from the liver
passes down through the long Jiepatic duct to the oval-
sha 
