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

JTIG. 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 at 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 0

,,,.,- . 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

76

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;lP: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. WThen, 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. ' '

n4 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