5 hth uu AN Pew Dork Htate College of Agriculture At Cornell University Bthaca, N. P. Librarp ornell University Libra First lessons in zoology, (CSiziqpynwuide vIpsMory ‘satgads auo 3y} je Jo eel asoyp, ‘coOL Jo Jowuns ay} ul—uvad(y 9ylorg oy} ul purest aan J USAT peaytsla |. SOUA ERIN sy JouwWeoys MOTs Ue) yst Ss “(a ot} usy a ‘Aysaaa tay} ‘[ ‘Jorg Aq opuw yd Soyoyd y) ‘spaiq uvaso Jo Bury ‘ssoajvqye ay2 Jo spunois-Bunsay Pio. ESS: O NS IN LOOLOGY BY VERNON L. KELLOGG Professor in Leland Stanford Junior University NEW YORK HENRY HOLT AND COMPANY 1903 Copyright, 1903, BY MENRY HOLT AND COMPANY ROBERT DRUMMOND, PRINTER, NEW YORK. PREFACE Tuis book, an introduction to the study of animals and their life, is intended for use in grammar schools and in those high schools which are not equipped with laboratories or which do not care to undertake the study of zoology by having the pupil dis- sect a series of types or examples. For high schools prepared to take up this college method of zoological study the author’s Elementary Zoology is intended. In preparing a text-book for the guidance of teachers and pupils in high schools without laboratory equipment and in grammar schools and classes of younger pupils, the author has believed it better to write a new book, rather than to shorten and ‘‘ simplify ’’ the text intended for larger high schools and older pupils. He has believed it better to make the life-history and habits of familiar animals the basis for a beginning study of zoology by young pupils rather than to make the study of structure and classification such a basis. But this is not a reading book, or nature-study story book. It is a guide and outline for constant, specific personal work in observation, and answering questions by means of this observation, on the part of the pupils, and only such telling of facts is included as seems necessary to make significant and coherent and related the self-made discoveries of the pupils. The actual method of use of the book will be obvious to any teacher into whose hands it may fall. The succession of chap- ters is one that seems natural and useful to the author; for any teacher it will be, of course, a simple matter to modify and re- arrange the course of work as outlined. In fact the opportu- nities for obtaining material for study offered 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 the rela- tion of the school terms to the seasons of the year, and other special and varying conditions, will dictate in large measure the Vv vi PREFACE teacher’s actual procedure. The numbered parts of the book indicate the classification of the study of animals into particular phases or kinds of study rather than a definite linear arrange- ment or sequence of this study. The lessons or subjects of Part IV, for example, should be interpolated wherever the teacher finds fittest opportunity in connection with the study of special animals or groups of animals. Chapters VI, VII, and VIII of Part II have to do with that part of the study of animals which, as usually treated, demands the facilities of equipped laboratories. As here treated no laboratory work is required, but these chapters have been arranged to call for the continuous and thoughtful ‘‘seeing why’’ of facts mostly already familiar to the pupil. In this way the author believes that what little knowledge of the internal anatomy of animals young people can get will have a maximum of worth, The author wishes to express his special obligations to Dr. O. P. Jenkins, professor of physiology in Stanford University, for the first draft of Chapters VI, VII, and VIII of Part II, and to thank Mrs. D.S. Jordan and Miss Isabel McCracken for their critical reading of the MS. and proof-sheets, respectively, of the book. For aid and courtesy in the matter of illustrations the author’s thanks are due Miss Mary Wellman, who made all the drawings for figures whose origin is not elsewhere specifically indicated, and to Professors M. V. Slingerland of Cornell Uni- versity and L. L. Dyche of Kansas State University, Dr. L. O. Howard, U. S. Entomologist, Mr. Geo. O. Mitchell of San Francisco, Mrs. Elizabeth Grinnell of Pasadena, California, Mr. J. O. Snyder, Stanford University, Mr. Frank Chapman, editor of ‘‘Bird-Lore,’’ Mr. G. O. Shields, editor of ‘‘ Recreation,”’ Mr. Geo. A. Clark, secretary U.S. Fur Seal Commission, the American Society of Civil Engineers, Cassell & Co., the Out West Publishing Co., Camera Craft, ‘‘ The Condor,’’ and the Whitaker and Ray Co. of San Francisco. ‘The illustrations got from these various sources are all specifically indicated in connection with their special use. VERNON LYMAN KELLOGG, STANFORD UNIVERSITY, May, 1903. CONTENTS PART | THE LIFE HISTORY OF ANIMALS I—MOSQUITOES, SILKWORMS, AND DRAGON.-FLIES Animals not fully developed at birth, 1.—Mosquitoes, 2,—The eggs and hatching, 2.—The wrigglers or larve, 4.—The pupz, 6.—The winged or imago stage, 7.—Distribution of mosquitoes, 8,—Silkworms, 9.—How to get silkworm eggs, 9..-The eggs and hatching, 11.—The larve or silk- worms, 11.—The cocoon and pupa, 15.—The moths and egg-laying, 17.— Other moths and butterflies, 20.—Dyragon-flies. 21.—The adults, 21.—Egg- laying, 23.—Nymphs, 23.—The transformation to winged stage, 25. Il.—TOADS AND TADPOLES The eggs and hatching, 27.The tadpoles, 28.—Toads and frogs 31. Ill. A BIRD’S NEST AND OTHER ANIMAL HOMES A bird’s nest, 34.—Homes of insects and spiders, 36.—Homes of the backboned animals, 42. PART II THE PARTS OF ANIMALS AND HOW THEY ARE USED IV. THE GRASSHOPPER AND THE SNAIL An animal’s body composed of parts, 47.—The grasshopper or locust, 48. —The pond snail, 52. vii vill CONTENTS V. THE SUNFISH AND THE SPARROW The sunfish, 54.—The English sparrow, 58. VI. THE MOTIONS OF ANIMALS AND THE SKELETON AND MUSCLES Motion and locomotion, 64.—Muscles and skeleton, 68. VII. HOW ANIMALS CHANGE FOOD AND AIR INTO FLESH AND ENERGY Necessity of oxygen and food, 77.—How animals breathe, 79.—How animals obtain and digest food, 86.—How the blood circulates, 93. VIII. HOW ANIMALS KNOW THINGS AND CONTROL THEIR MOTIONS The central nervous system, 100.—The special senses and their organs, 103. PART Il VARIOUS KINDS OF ANIMALS AND THEIR LIFE IX. THE AMCEBA, HYDRA, AND OTHER SIMPLE ANIMALS Amceba, 114.—Other one-celled animals, 116.— Ocean Protozoa, 119,— Hydra, 122. X. OCEAN ANIMALS: SPONGES, SEA-ANEMONES, JELLY FISHES, CORALS, STARFISHES, OYSTERS, CLAMS, AND SEA-SHELLS Sponges, 125.—Sea-anemones and corals, 126 —Jellyfishes, 131.—Star- fishes and sea-urchins, 134.—Oysters, clams, and sea-shells, 139. XI. WORMS, CRAYFISHES, CENTIPEDS, AND OTHER SMALL LAND ANIMALS Earthworms and leeches, 144.—Vinegar-eels, hair-worms, and trichine, 146,—The crayfish, 149.—Lobsters and crabs, 154.—Pill-bugs and water- fleas, 157-—Thousand-legged worms and centipeds, 159. XI. INSECTS Pond and brook insects, 163.—Moths and butterflies, 171.—Aphids, ants, and aphis-lions, 174.—Cicadas, katydids, crickets, and the sounds of in- sects, 179.—The solitary bees and digger-wasps, 182. 1x XITI.—SPIDERS AND THEIR WEB-MAKING Collecting spiders, 190.—The make-up of the spider body, 192.—The hunting spiders, 193.—The web-weaving spiders, 196.—Life-history of spiders, 207. XIV.—FISHES, BATRACHIANS, AND REPTILES The fishes, 210.—The batrachians, 215.—The reptiles, 219. XV.—BIRDS The English sparrow, 230.—The beginning study of birds, 231.-—Classi- fication and identification, 233.—Birds and the seasons, 238.—Structure and habit, 244.—Feeding habits, economics, and protection of birds, 250. XVI.—MAMMALS The house mouse, 254.—Classification, 256.—The opossums and kanga- roos (Marsupialia), 256.—The rodents and gnawers (Glires), 258.—The shrews and moles (Insectivora), 261.—The bats (Chiroptera), 261.—The dolphins, porpoises, and whales (Cete), 262.—The hoofed mammals (Ungu- lata), 263.—The carnivorous mammals (Fere), 266.—The man-like mam- mals (Primates), 269. PART IV ANIMALS IN RELATION TO EACH OTHER, AND TO THE OUTSIDE WORLD XVII.—THE STRUGGLE FOR FOOD AND ROOM, AND SPECIAL MEANS FOR FOOD-GETTING AND PROTECTION The multiplication of animals, 273.—The struggle to live, 274.—Se- lection by nature, 275.—Special means to get food, 275.—Special means for protection, 277.—Examples to be looked for by pupils, 279. XVIII.—THE COLORS AND MARKINGS OF ANIMALS, AND THEIR USES The scales and colors of butterflies’ wings, 281.—Colors of other animals, 285.—Uses of color, 285.—Special protective resemblance, 287.— Warning colors, 288.—Mimicry, 291.—Other uses of color and marking not yet understood, 291. XIX.—ANIMAL PARASITES Degeneration of parasites, 293.—Internal parasites, 295.—Parasitic in- sects, 297. x CONTENTS XX. THE HONEY-BEE AND OTHER SOCIAL ANIMALS The life of a honey-bee, 302.—Ants, 309.—Wasps and bumble-bees, 315. —Other social animals, 318. XXIL—HOW ANIMALS ARE DISTRIBUTED OVER THE WORLD Animals limited to particular regions, 319.—Barriers, 320.— How animals spread, 321.—Map showing the distribution of animals, 322. APPENDICES APPENDIX I.—NOTE-BOOKS, DRAWINGS, AND REFERENCE BOOKS, 325. APPENDIX II.—REARING ANIMALS, AND MAKING COLLEC.- TIONS Live-cages and aquaria, 329.—Making collections, 333.—Collecting and preserving insects, 335.—Collecting and preserving birds, 338.—Collecting and preserving mammals, 342.—Collecting and preserving other animals, 344. APPENDIN III.—CLASSIFICATION OF ANIMALS, 345. PART | THE LIFE-HISTORY OF ANIMALS CHAPTER I MOSQUITOES, SILKWORMS, AND DRAGON- FLIES Animals not fully developed at birth.—lIt is fa- miliar knowledge of us all that any animal when just born differs from its parents more or less. The downy little chick, just from the egg, is very different from the old hen or crowing rooster; a kitten with its unopened eyes and helpless little legs differs plainly from the strong, large mother cat. These differences are due to the fact that the chick and the kitten are not fully developed, or, as we say, not full grown. And such differences are even greater in some other animals, as, for example, butterflies and frogs. Butterflies’ eggs hatch, not into butterflies, but into worm-like caterpillars, while newly hatched frogs are not frog-like at all, but are the little, long-tailed, fish-like creatures we call tadpoles. But the caterpillar will develop into, or grow up to be, a butterfly, just like the splendid one which laid the egg from which it hatched, and each tadpole will grow to be a frog. What is true of cats and chickens, frogs and butterflies, is true of all other animals; that is, every animal has to go through more or less growth and development in order to become 2 FIRST LESSONS IN ZOOLOGY like its parent. The story of an animal's birth, its growth and gradual change or development into a mature or adult individual, is called its life-story or /¢/e-Arstory. In the following studics of insect life-histories the growth and development of the insects from hatching to maturity can be readily observed in the schoolroom. The particular insects chosen are selected because they can be easily obtained and reared indoors, and because they present especially interesting changes in their de- velopment. But other insect life-histories may be ob- served, either completely or in part, if it is so desired. Various caterpillars and chrysalids can be kept alive and watched as they develop into moths or butterflies, and various grubs that live in the ground can be kept until they become beetles. Flesh-flies may be allowed to lay their eggs on decaying meat, and the hatching of the maggots, their change into brown seed-like pupa, and the final emergence from these of the blue and green flies all carefully noted. MOSQUITOES The eggs and hatching.—Mosquitoes’ eggs are usually laid in small blackish masses, which float on the surface of water. (In the case of some species the eggs are laid y.) These sooty egg-masses are composed of a single layer of slen- in groups of only a few, or even deposited sing] der elongate eggs standing on end and loosely fastened together to form a narrow, irregular, little raft, slightly concave on the upper surface, and wholly unsinkable. They are to be found on small pools of standing water, or in watcring-troughs or exposed barrels—wherever in- deed there is quiet or stagnant water. These ege- masses should be brought into the schoolroom and kept in glass tumblers, with some of the water on which they are found floating (fig. 1). Examine an egg-mass with D DRAGON-FLIES 3 a hand lens to note the arrangement and appearance of the eggs. How many are there in the mass? The eggs should be kept under pretty constant obser- Fic. 1.—The mosquito, Cu/ex sp.; showing eggs (on surface of water), larvee (long and slender, in water), pupa (large-headed, at surface), and adult (in air). (From living specimens. ) vation, for hatching is likely to take place soon after they are brought into the schoolroom. Ordinarily they hatch in from twelve to twenty-four hours after they are laid. They may, of course, hatch at night. But if the hatching occurs during the day it can be easily observed. 4 FIRST LESSONS IN ZOOLOGY From which end of the egg does the young mosquito emerge? It may not be easy to find the egg-masses on the pools ; in that case the wrigglers or larvae (described in the next paragraph) should be sought for and brought into the schoolroom in tumblers or jars containing water taken from the pool in which they are found. The life- history can be studied from this point on. The tumblers must not be kept in places too cool or dark, or the young mosquitoes will develop abnormally slowly. The ‘‘wrigglers’’? or larvea.—The newly hatched mosquito bears no resemblance to the familiar winged fly which we call by that name. In this first stage of its life, or second stage, if we call the egg stage the first, it is familiarly known as a ‘“wriggler,” but is called /arva by naturalists. The active young stage of any insect which differs markedly from the fully developed or mature one is called the larval stage. The larva swim actively about. By what means do they swim? If they cease swimming do they sink deeper in the water or rise to the surface? Is the body of the larva more or less dense than the water? that is, is it heavier or lighter than water ? Note that some of them hang quietly from the surface, and that each one comes occasionally to the surface and rests there for a while to breathe. Every animal has to breathe; that is, to take up oxygen from the air and to give off from its body carbon dioxide (CO,). There is always some air mixed with or dissolved in water, and some aquatic ani- mals—fishes for example—have special structures called gills which enable them to take up this dissolved oxygen, and thus to breathe under water. But the mosquito larva has no gills, and therefore has to come occasionally to the surface to breathe. Examine with a hand lens one of the larvae ina watch- glass of water. Distinguish the head end of the body ; MUSYUIIUES, SILAWURKMS, AND DRAGON-FLIES 5 note the eyes (two small black spots), the feelers, or antenne, and a pair of tufts or brushes of hair on the head which vibrate rapidly and constantly. These brushes by their vibration create currents in the water setting toward the mouth, which lies between them, and thus bring food to it. This food consists of any tiny animalcules and microscopic bits of organic matter in the water. Are there any legs or wings? Examine the _ posterior end of the body and note its division into two parts— one the end of the hind body or abdomen, the other a breathing-tube projecting from the next to last body- ring. Make a drawing of the larva, showing and naming all these parts. Observe again the larve in the jar. When they hang from the surface note that only the tip of the breathing- tube reaches it. Note the vibration of the mouth-brushes. The larvz feed busily for most of the time. If they sink in the water when they stop “ wriggling,” i.e., swimming, how is it that they can rest quietly at the surface? For this reason: the tip of the stem-like breathing-tube pro- jects slightly above the surface when the wriggler comes up to breathe, so that the expanded edges of its mouth are caught by the tense surface film and the wriggler’s body being but slightly heavier than water, is thus sup- ported or suspended by the film. It is easier to prove the existence of this film than to explain it. If you care- fully lay a clean needle on the surface of the water it will not sink, although much denser, i.e., heavier than water, but will be supported by the surface film. If you fill a tumbler to its brim you can still add more water carefully and so heap it up above the level of the brim. This is because the surface film extending over the water from edge to edge holds it in place. If you dip your finger in and then lift it up the water does not all run off, but a large drop will remain hanging to your finger. 6 FIRST LESSONS IN ZOOLOGY The tense surface film holds the little mass together in the form of a drop. The mosquito larva takes advantage of the surface film and is able to keep itself at the surface when breathing by hanging from it. Water-striders and the numerous little flies which run quickly and safely about on the surface of the water are supported by the film. Their feet make little dents or depressions on the water’s surface, but do not break through. It is probable that the movements of the feeding-brushes also help to keep the wriggler at the surface, as the wrigglers seem to be able to balance themselves, i.e., keep from sinking, in the water by these movements. Observing the larve or ‘“‘wrigglers ’’ from day to day it will be noted that they increase in size, that is, are growing. They breathe and feed and swim and grow. And some keenly observant pupil may see that they occasionally cast their skin, or moult. That the larve do moult one or more times is certain; how many times, however, has not yet been found out. The pupz.—After several days—just how many each pupil should determine for himself—the long slender larve enter upon another stage in the mosquito’s life called the pupal stage, and the young mosquitoes are now called pupe. In this stage the head end is large and bulbous, the hind body is usually curled underneath the head, and the creature spends most of its time floating at the surface. It can swim, and does so when disturbed, by a peculiar straightening and folding of its body. When it stops swimming what happens to it? In what way must the pupa differ from the larva in its relation to the density of water ? Examine with a hand lens one of the pup in a watch- glass of water. Note the two tubes or horns which project upwards from the back or dorsal part of the bulbous head end of the body, and the pair of flaps at MOSQUITOES, SILKWORMS, AND DRAGON-FLIES 7 its posterior tip. What are the dorsal tubes for? With what do they correspond in the larve? The pupa takes no food at all, and usually floats quietly at the surface. Why then does it swim at all? What is the use of the flaps at the end of the body? Note the indications of legs and wings folded on the under side of the head end. Make a drawing showing and naming these parts. In two or three days the pupa suddenly changes into the full-fledged winged mosquito. That is, the cuticle or outer skin wall of the body splits along the middle line of the back, and the winged mosquito emerges through this opening. What part of the body appears first? What parts next? While the mosquito is emerging the pupal skin serves as a raft upon which the soft-bodied damp insect is partly supported until its wings and legs are un- folded and dried and hardened, and it is ready to fly away. Sometimes the body rests simply on the surface of the water, being supported by the surface film. This transformation of pupa into fully developed mosquito can be readily observed, and each pupil should see it. The winged or imago stage.—The mosquito is now full-grown and fully developed ; and in this fully devel- oped stage it is called an zmago, to distinguish it from larva and pupa. It is of course the same insect, a mos- quito all the time, but we commonly apply that name only to the winged stage or imago. A few of the winged mosquitoes should be killed in a ‘‘killing-bottle ’’ (see page 335), and examined under a hand lens. Two kinds may be distinguished; one with many long hairs on their feelers or antenne, the other with fewer and much shorter hairs ; the latter are females, the ones with bushy antenne males. These antenne are the mosquito’s organs of hearing. How many wings has the mosquito ? How many pairs of legs? Can you find behind the 8 FIRST LESSONS IN ZOOLOGY wings a pair of delicate little knobbed processes projecting from the body? These are called balancers and they aid the mosquito in directing its flight. Note the long, piercing and sucking beak (fig. 2) by means of which the mosquito gets its food, which is either the blood of animals or the sap of plants. The male mosquitoes never (or very rarely) suck blood. On each side of the beak, and arising at its base, is Fic. 2,—Deak of female mosquito 4 pair of feelers or palpi, pre- dissected to show the piercing sumably organs for smelling needle-like parts, and_ their : ; sheath; mx.p, the maxillary and tasting, or which at least palpi, or feelers of the mouth. gid in determining the charac- ter of the food. These palpi are as long as the beak in the males, but less than half as long in the females. What are the large black spots on the head? Make a drawing of a mosquito, showing and naming these parts. If some of the mosquitoes are kept alive in jars filled with water and covered with netting the females may perhaps lay eggs on the surface of the water. But it is not at all certain that they will ; indeed, they seem to lay eggs only rarely when thus kept in confinement. Ifa slice of banana be put in the jar the mosquitoes may be seen to suck the sap from it, and they may be kept alive for many days if given fresh banana every three or four days. If the egg-laying occurs, the life-history of our mosquitoes is completed. A new cycle is about to begin. Distribution of mosquitoes.-—Mosquitocs are distrib- uted all over the world, being found in cnormous numbers in arctic regions and on high mountain ranges as well as in the tropics, and in swamps and marshy valleys. About MOSQUITOES, SILKWORMS, AND DRAGON-FLIES 9 three hundred and fifty species, or different kinds, of mos- quitoes are known, nearly fifty of which are found in North America. Besides the irritation caused by their “‘bite,’’ i.e., piercing with the sucking beak, it has been proved that mosquitoes are the conveyers and distributors of the germ of malarial fever. Only certain kinds of mosquitoes, however, are malaria-carriers. These all belong to the genus Anopheles ; most of them may be distinguished by the possession of spotted wings, while the innocuous kinds have the wings clear. There are a few innocuous or non-malarial kinds with spotted wings, however, but no malaria-carrying kinds with wholly clear wings. Other kinds of mosquitoes are almost certainly the distributors of the germs of yellow fever, and the same kinds convey a terrible tropical disease called elephantiasis. The most effective remedy against mosquitoes is to pour a little kerosene on the surface of the pool in which the larvae and pupe live. The kerosene will spread out and form a thin, oily film over the surface of the water, and no winged mosquito will be able to emerge alive through this film, contact with kerosene being fatal to almost all insects, and especially so just after a moult. For a full and excellent account of the life of mosquitoes see ‘“‘ Mosquitoes,” by Dr. L.O. Howard. (See page 327 for list of reference books with publishers’ names and price.) SILKWORMS How to get silkworm eggs.—Live eggs of the silk- worm moth, Bombyx mort, are regularly sold by dealers in Japan,* and sometimes can be got in curiosity shops in this country. They may also be obtained wherever there is a silkworm-rearing establishment in this * Silkworm eggs can be obtained from the Kioto Agricultural School, Kioto, Japan, or from the Nishigahara Agricultural Experimental Station, Silk Culture Dep’t, Tokio, Japan, or from Mr. S. I. Kuwana, Buzen, Kiu- shiu, Japan. 10 FIRST LESSONS IN ZOOLOGY country, though unfortunately there are but few now. The author will be glad to send* a few eggs, say twenty-five, once to any teacher who will defray the cost of postage. From the first lot of eggs moths may be raised and new eggs obtained, and a gen- eration thus be reared each year. There are four kinds or races of silkworms, one of which, known as annuals, produces but one generation a year, the second kind, called bivoltins, produces two, the third, the trivoitins, produces three, while the fourth, found in India, produces six or seven generations each year. The eggs which the author can furnish are those of the annual race, and will naturally hatch in the Middle and Eastern States from April 15 to May 1. By keeping them at a temperature of 40° F., or below, the hatching may be postponed as long as desired. Under no circumstances should it be allowed to take place before the first mulberry or osage orange-leaves appear in the spring. If it is more convenient to rear the silkworms in the fall, the eggs may be kept in some re- frigerator or cold-storage room through the summer. But the natural hatching-time will be found to coincide fairly with the leafing of the mulberry and osage-orange trees, and no special care in keeping will be necessary. As the silkworms will feed on no other than mulberry or osage- orange leaves, a supply of these must be available, or some other moth chosen for this life-history study. _How- ever, both these trees are spread over the whole country, and one or the other is to be found in nearly every locality. The advantage of using the mulberry silkworm moth for this life-history study lies in the « domesticity ” of the in- sect ; the worms have no tendency to crawl away but will remain quietly in open shallow trays as long as food is provided them, and the moths, although winged, do not * Address V. L. Kellogg, Stanford University, California. cents in stamps for postage. Send five MOSQUITOES, SILKWORMS, AND DRAGON-FLIES II fly. The larve are not hairy and all their markings, their changes during growth, and their behavior can be fully observed. And finally, the moths are obliging enough to lay their eggs on whatever is provided them, and do not insist on flying away into the fields ; thus the process of egg-laying can be observed and the age of the eggs be exactly known. The eggs and hatching.—The eggs of the silkworm moth are nearly spherical, a little flattened, and about the size of a mustard-seed. When first deposited they are yellow, but soon become grayish or slate-colored and in- dented on top. Each female moth lays about 300 eggs. These remain unchanged in appearance, after the first change from yellow to gray, until about the hatching time, when they become paler. The tiny worm or larva inside, for the silk ““worm”’ is of course simply the larva or first young stage of the silkworm moth, gnaws its way through the thin egg-shell and crawls out ready to begin feeding. Some newly hatched larve of moths and butter- flies have the curious habit of eating the egg-shells as soon as they issue from them. Do the young silkworms do this ? The larva, i.e., ‘‘silkworms’’ (figs. 3 and 4).—As soon as the eggs begin to hatch fresh leaves of the mulberry or osage orange must be supplied to the young larve. These leaves must not be wet, for the tiny silkworms seem to have rather delicate stomachs which object to cold damp food. They should be cut into pieces, the bits being evenly spread about in the shallow tray or box-cover in which the worms are to live. Watch the young larve crawl and feed. Note that they bite out little crescents and semicircles in the edges of the leaves. Does the silk- worm have any particular way of moving its head when biting off bits of leaf-tissue? Examine one of the tiny worms with a hand lens. Note that its body is composed of aseries of segments or rings. How many pairs of legs 12 FIRST LESSONS IN ZOOLOGY are there and on what body-rings are they? Note the scattered long hairs sparsely covering the body. Can Fic. 3.—Silkworms feeding on mulberry leaves. (From life.) you see the jaws and eyes on the head? Make a draw- ing of a worm as seen from the side. Silkworms will eat a surprisingly large amount of food, and fresh leaves must be given them at least two or three times a day. Scatter the new leaves over the little pile of worms, dried old food and excrement, and the worms Fm. 4 Sileween en malbersy Tea Will soon crawl out and on showing front view of head and thorax. to the new. It is advis- Pees, able to keep the feeding- tray as clean as possible, for the larvae are readily subject to disease. In order to remove the waste matter, spread a bit of large-meshed mosquito netting over the tray and throw the fresh food on top of it. The worms. will crawl up through the meshes to the fresh leaves when MOSQUITOES, SILKWORMS, AND DRAGON-FLIES 13 the netting can be lifted up and the tray emptied. The larve will grow rapidly, plainly increasing in size each day. After eight or nine days they will cease feeding and crawling around. Each one stands on the legs of the middle of the body, and usually holds up the head and forepart of the body, and sometimes the tail. It is preparing to moult, i.e., to cast the skin. The moulting should be observed in detail. After moulting each larva will be noticeably larger and paler, and the long hairs of the body will be replaced by short ones. The feeding begins again, and larger and larger supplies of leaves will be found necessary to keep the worms well fed. The larval stage of the silkworm lasts about forty-five days, with a moulting once every nine days (or eight or ten). It is easy to see why these successive moultings are necessary. The true skin of an insect is always cov- ered over outside by a cuticle in which a horny substance called chztzz is deposited. This chitin makes the cuticle nearly inelastic, so that the growing insect finds its body confined within a non-stretchable case. There is then but one way out of this dilemma, and that is the simple way of breaking out! And so in the life-history of all insects the phenomenon of moulting takes place. In nearly all cases the cuticle splits along the middle of the back from the head to about half way to the end of the tail, and through this rent the body issues with new cuticle. The cast skin being very light and thin, and usually color- less, soon disappears from view, and unless the insect be seen precisely at each moulting time it is not easy to ascertain how many moults occur in the life of any par- ticular species. The silkworms breathe through very small openings, called spzracles, on the sides of the body. One pair of spiracles occurs on each of nine of the body-rings. What rings are these? Each spiracle opens into an air-tube FIRST LESSONS IN ZOOLOGY 14 “yout ayy oyuT uado ‘apis yoea uo auO ‘spur]3-y]IS OY, *saqn}-ITe 10 KBaysvsy Jo woysks oy} Aptepnonaed ajoNy “SULSIO [VULI}UL S}T MOYS 0} papassIp WAOMHLIS WY—"S “OT i Ay = p , ‘ wnyrat ' tgaynqny wnrybedyoyy youve Ravyuawmrp MOSQUITOES, SILKWORMS, AND DRAGON-FLIES 15 inside the body, and these various side-tubes lead into a main longitudinal tube running along each side from head to tail (fig. 5). From these main longitudinal trunks branches and sub-branches go to all parts of the body, the air being distributed in the insect’s body by a distinct system of air- tubes called ¢rachee, and not entering a pair of lungs (fig. 6). Silkworms devour an _ enor- mous amount of leaves during the last few days of larval life, much more indeed than they need at that time. Later we shall see the reason for this over- eating. They have thick, heavy bodies and reach a length of two and a half inches. Make a draw- ing of a full-grown larva from a lateral view, showing all the legs of one side, nine breathing holes (tiny openings each surrounded Fic. 6. — Diagram of tracheal ‘ system in body of beetle; by a black ellipse), and the dor- sp, spiracles; ¢, trachez. sal spine on the posterior end, (After Kolbe.) The cocoon and pupa.—About a week or nine days after the fourth moult the silkworms stop feeding and prepare for the fifth and final one. (Occasionally a silk- worm moults six times.) But unusual preparations are made this time; each larva crawls alongside the edge of the tray, or approaches some object in it, and begins to spin silken thread from its mouth (fig. 5.) All of this spinning should be watched closely. At first the thread is attached irregularly and apparently aimlessly to the objects near by, but when a sort of loose and irregular net or web of silk has been made, the spinning becomes more regular, 16 FIRST LESSONS IN ZOOLOGY and it is plain that the larva is making a silken case or cocoon about itself. The spinning lasts about three days and results in a thick, firm, white or yellowish (rarely greenish) silken closed cocoon, within which the larva moults. Cut one of the cocoons open a few days after its making and there will be found within it the cast skin of the larva and the pupa which appears after the final larval moulting. In what habit does this pupa resemble that of the mosquito? In what habit does it differ? The pupal stage in the development of insects is a stage in which the insect takes no food, is usually quiescent, and is undergoing the final changes from worm- or grub-like larva to winged adult. The silkworm pupa lies quiescent in its silken case for about two weeks, sometimes a little longer, when the pupal cuticle splits, and one end of the silken cocoon is dissolved by a fluid secreted by the insect within. Through this opening out crawls the moth, damp and crumpled-looking, with the wings all compressed into short thick pads or sacs. But these slowly expand, the scales and hairs covering the body dry, and soon the robust fully developed white moth walks slowly about. Make a drawing of a net and cocoon just begun, show- ing the larva inside at work spinning ; also a drawing of a completed cocoon; and of a cocoon cut open showing the mummy-like pupa within. As the silkworm takes no food in the pupal stage (this is true of the mosquito also) and as a great deal of devel- opment goes on in this stage during which the wingless larva is transformed into the very different winged imago, it is plain that the pupa must live on food stored in the body. It is for this reason that the larval mosquito, the wriggler, and the larval silkworm moth, the silkworm, devote themselves so steadily to cating and cat more than they need for their own use. The extra food eaten is changed into fat, or is in some way stored in the body MOSQUITOES, SILK WORMS, AND DRAGON-FLIES 17 as reserve material on which the pupa draws during its quiescent and fasting life. Fic. 7.—The forest tent-caterpillar moth, CZiséocampa disstria, in its various stages; m, male moth; 7, female moth; /, pupa; e, eggs (in a ring) recently laid; g, eggs hatched; ¢, larva or caterpillar. Moths and caterpillar are natural size, eggs and pupa slightly enlarged. (Photo- graph by M. V, Slingerland.) The moths and egg-laying.—When the silkworm moths issue from the cocoons they make no attempt to fly although each is provided with four wings. Some of them, however, will be seen to keep up a rapid gentle fluttering of the wings; these are usually males, which are more active than the females. The males and females are alike in color and marking, but the antenna, or feelers, of the male are wider or bushier than those of the female ; that is, the side branches or “ pectinations,’’ suggesting 18 FIRST LESSONS IN ZOOLOGY feathers in appearance, are longer in the males than in the females. Fic. 8.—A trio of apple tent-caterpillars, CZ/s/ecampa americana, natural size. These caterpillars make the large unsightly webs or ‘‘tents ” in apple-trees, a colony of the caterpillars living in each tent. (Photo- graph from life by M. V. Slingerland.) examine a moth, noting the number of wings, number of legs, the antennz: and eyes, and the scales or hairs which cover the body and wings. Make a drawing, from dorsal view, of a moth with wings outspread. MOSQUITOES, SILKWORMS, AND DRAGON-FLIES 19 The moths will soon pair, and the females will begin laying eggs at about the end of the first day. Each female will lay about 300 eggs. Provide small pieces of cloth ; place the moths on the cloths and the eggs will be laid on them. After laying the eggs the moths soon die. They take no food at all, indeed their mouth-parts Fic. 9.—The larva of the violet-tip butterfly, Polygonta interrogationis, making its last moult, i-e., pupating. (Photograph from life, by the author. ) are incomplete and not able to suck flower nectar which is the usual food of moths and butterflies. The pieces of cloth covered with eggs should be put away in a closed box and kept in a fairly cool place until the following spring. When the mulberry leaves appear again, lay out the egg-cloths in trays in a warm bright room. In a few days the hatching will begin, and with it a new life- cycle. 20 FIRST LESSONS IN ZOOLOGY Other moths and butterflies.—The life-history of the silkworm moth serves as an example of the life of all moths, and of butterflies too, which are closely related to moths. In every case there hatch from the eggs not small moths and butterflies, but worm-like larve, which we call caterpillars (figs. 7 and 8). These larve feed mostly on green leaves, grow rapidly, moult several times, and | Fic. 10,—Chrysalid (pupa) of the violet-tip butterfly, Podvgonia interroga- tionts, From this chrysalid issues the full-fledged butterfly. (Photo. graph from life, by the author.) finally change to pup, i.e., pupate. Before pupating some spin a silken cocoon as the silkworm does, some may burrow into the ground, and some simply crawl into a sheltered spot, or hang from some twig and change into a naked pupa or chrysalid (figs. 9 and 10). In this latter case the color of the chrysalid usually harmonizes so well with the surrounding leaves or bark that it is almost indistinguishable. Almost any caterpillars that are found MOSQUITOES, SILKWORMS, AND DRAGON-FLIES 21 may be reared in the schoolroom or at home ifthe proper food is known and can be obtained. While some of them will eat almost any kind of leaves most of them feed only on one or two particular kinds. Whatever plant the caterpillar selects outdoors is the kind of food plant it prefers or must have. Directions for making breeding-cages for caterpillars are given on p. 330; so that any caterpillar found may be brought home alive and an attempt made torear from it the moth or butterfly of which it is only a young stage. Excellent books about the life of butterflies and moths are ‘Moths and Butterflies,’’ by Mary C. Dickerson, “Every-day Butterflies,’’ by S. H. Scudder, and “ Cater- pillars and Their Moths,’’ by Ida Eliot and Caroline Soule. DRAGON-FLIES The adults.—Dragon-flies (fig. 11), or ‘ devil’s darning- needles,’’ are familiar insects in any locality not wholly without ponds or streams. These long, slender-bodied, swiftly flying insects are to be seen any bright day from early spring to late autumn darting hither and thither over a pond or along a stream bank. They are usually bril- liantly colored with blue or green or red, and the wings are often strongly marked with blackish bars or blotches. When they thus dart swiftly about they are capturing and devouring their prey—the little gnats and midges which dance in the air over the pond or near its shores. Dragon-flies are the hawks of the insect world. If one of these swift flyers can be caught in an insect net it may be taken out and handled without fear, for despite popular prejudice it is wholly harmless to any- thing except small insects; these it catches in its wide mouth and crushes with its strong jaws. But it has no sting, nor any piercing beak or poisonous jaws. Note the 22 FIRST LESSONS IN ZOOLOGY long, slender hind body or abdomen, made up of several segments or body-rings ; in flight this hind body acts as a rudder to help steer the dragon-fly in its quick turnings and swift dashes. Note the two pairs of long wings, transparent and delicate, but firmly supported by a com- plex skeleton of longitudinal and cross veins ; no other insect surpasses this one in flight. Note the three pairs of slender weak legs; it uses its legs only occasionally for perching, but it ses the two front pairs to form a little sort of trap or basket which aids the great mouth in catching and holding small insects when the dragon-fly is ‘‘ hawk- ing.”’ Note the great head, so loosely attached to the body behind it that it can be turned in any direction, and caneven be so twisted on the neck that the top of the head will be direct- ed downward with the : mouth facing directly up- (From life.) ward. This head is com- posed chiefly of two great shining compound eyes each made up of many thousand eye-elements. When exam- if Lap ea pms BS a Vic. 11.—A drayon-tly. ined under a good hand lens the shining outer surface of these eyes is seen to be composed of thousands of tiny facets, each facet being the window or transparent outer wall of one of these eye-clements. Each facet and the eye-element behind it sce one small part of the object looked at, so that the image produced in the sensitive part of the back of the eye is composed of thousands of scparate small parts, which make a sort of mosaic of the object looked at. This seeing by compound eyes, MOSQUITOES, SILKWORMS, AND DRAGON-FLIES 23 which is the kind of sight possessed by almost all insects and crustaceans (crabs, lobsters, crayfishes, etc.), but by no other animals, is called mosaic vision, and cannot be so exact or truthful as our own. Examine the mouth of the dragon-fly and notice the large flap-like under lip which folds over the opening, and behind it the strong brown jaws. Make a drawing from dorsal view of an adult dragon- fly with wings outspread. Make a drawing of the head from front view. Egg-laying.—If you watch dragon-flies darting over a pond in summer occasionally some may be seen to swoop down quite to the water’s surface and to strike it repeat- edly with the tip of the abdomen. Theseare laying eggs, and each time the water is touched a few eggs are liber- ated and sink slowly to the bottom. If one of these ovi- positing females can be caught alive the egg-laying may be observed and the eggs obtained for the school aqua- rium by holding the dragon-fly by the wings and touch- ing the tip of her abdomen to the surface of some water ina saucer. The eggs should then be poured into the aquarium (for directions for making simple school aquaria see p. 332) where, if all goes well, they will hatch into young dragon-flies. But as this hatching will not occur until late in the summer, and as the young dragon-flies, called nymphs, grow very slowly and donot change into winged adults for about a year, it will be better to find nymphs in the pond and stock the aquarium with these already partially developed individuals. Nymphs.—With a rake or stout water-net (see p. 335) scrape over the bottom of a pond and find in the mud and slime drawn out a number of flattened, heavy- bodied, broad-headed, six-legged creatures like the one shown in figure 12. These are the nymphs of dragon- flies. Each nymph will have on its back four conspicu- 24 FIRST LESSONS IN ZOOLOGY ous wing-pads; the larger these are the older is the nymph, and the more nearly ready to change into the adult form. April and May are the best months for col- lecting nymphs because the oldest ones found then are nearly ready to change into winged flies, and this they may do in the schoolroom. A careful observer of these creatures gives the following directions for bringing the nymphs to maturity. ‘ Place them [the collected nymphs] in a wooden pail or tub. If the sides are so smooth that they cannot crawl up to transform, put some sticks in the water for them to Fic. 12.—The young (nymph) of a crawlout on. Tie mosquito dre -fly. (F snkins and ; : celine eee netting tightly over the top, or better, make a screen cover; leave three or four inches of air between the water and the netting ; feed at least once a week; set them where the sun will reach them; and after the ad- vent of warm spring weather look in on them early every morning to see what is going on.”’ To feed the nymphs provide them with smaller live insects. Mosquito wrigglers, May-fly nymphs, small water-bugs, and any tiny swimming “beasties ’’ that can be caught in stagnant water should be dropped alive into the tub. The nymphs, like the adult dragon-flies, are ex- clusively carnivorous in diet. Observe how they catch their prey. Note that they rarely come to the surface of the water, and that there is no indication of breathing. In fact they breathe under water by means of gills which are not external, but which line the posterior third of the MOSQUITOES, SILKWORMS, AND DRAGON-FLIES 25 intestine. Water, carrying air dissolved in it, enters through the anal opening at the posterior tip of the body, and, after giving up its air to the gills inside, is ejected again. The opening is guarded by some flaps which may be seen to open and close occasionally. If a nymph be taken out it may eject water with considerable force from this opening. Kill a nymph in a killing-bottle and examine it care- fully. Note the wing-pads ; note the long, strong legs; also the large head with conspicuous compound eyes and short delicate antenne. Examine especially the mouth- parts, and note how the long under lip is folded over the mouth-opening, but can be unfolded and extended from a third to half an inch ; note the two grasping parts at its tip (fig. 13). This long, grasping under lip is the prey-catch- ing organ of the nymph, while the pair of strong jaws which open and shut laterally are the organs which crush the body of its prey and force its blood into the hungry Fic. 13.—Young (nymph) dragon-fly, showing lower lip folded and extended. (From Jenkins and Kellogg.) mouth of the destroyer. Make a drawing of a nymph from dorsal view, with its under lip extended and pinned out. Make a drawing of the front of the head, with the under lip folded like a mask over the face. The transformation to winged stage.—During the life of the nymph it grows and develops from a very small creature without wing-pads to a much larger one with conspicuous pads. During this growth it moults several times. iust as the growing silkworm does. Imme- 26 FIRST LESSONS IN ZOOLOGY diately after moulting the body wall is very soft, and light greenish or grayish in color, but it gradually hardens and darkens. When its growth and development is com- pleted the nymph will climb out of the water on some firm object, and, fixing its feet solidly, will proceed to transform, by means of a final moult, into the adult or imago stage. The cuticle or horny outer-skin layer splits along the middle of the back of the head and front part of the body, and out of this crack the winged dragon-fly slowly emerges. When this trans- formation takes place out- doors it usually occurs early in the morning. ‘If one can be out at the pond by six o’clock some clear morning, when the adults of some dragon-fly that is known to be common are_ beginning (Natural to appear, he may be sure Fic. 14. — Damsel-flies (narrow- winged dragon-flies). size; from life.) of finding them transform- ing. There will be some nymphs crawling up the banks, imagos pulling themselves out of their old nymph skins, others drying their wings, others ready to fly, and all within a few feet of the margin of the water. At noon one would find only dry and empty nymph-skins clinging to the sedges. And there, unless beaten down by wind or rain, each empty husk still clings, useless now, or sometimes furnishing a night's shelter to some mendicant plant-bug, until the festive, sportive, aerial life of its former occupant has run its swift course.” or a good account of dragon-flics see pp. 54-72, in “ Outdoor Studies,” by James G. Needham. CHAPTER II TOADS AND TADPOLES While the life-history of most of the backboned animals shows no such startling transformations or met- amorphoses as that of the insects we have studied, yet among toads, frogs, and salamanders, forming the class of backboned animals known as amphibians or batrachians, there is an interesting and well-marked metamorphosis. A newly hatched bird is much smaller and weaker than its parents, its feathers are different, and it usually has to be cared for and fed for some time, but it is unmistakably bird- like in appearance, and its development to adult form is gradual and without startling changes. The same is true of kittens and puppies, or young lions or camels, and true, also, for the most part, of fishes and of snakes and lizards. But the young toad or frog, which we call tadpole, looks, and truly is, much more like a fish than like its parent, and therefore in its growth and development it undergoes a marked transformation. The eggs and hatching.—In the spring, April and May, the frogs and toads begin their croaking and trill- ing, and then is the time to look in the ponds for the eggs. Indeed the ponds had better be watched as soon as the ice goes out. Hunt in the shallow water along the banks. Toads’ eggs lie in long strings of a gelatinous, jelly-like substance, usually wound about submerged sticks or the stems of water-plants, while those of the frog are found in small bunches or masses of the jelly. They are small, 27 28 FIRST LESSONS IN ZOOLOGY shining, black, and bead-like, and in the toad strings are arranged in single rows. If they have been recently laid, the enclosing jelly mass will be clean and clear, but it soon becomes partly covered with fine mud, when the eggs are not so easily seen. Bring some egg masses to the schoolroom and keep them in water in a light warm place, but not in the direct sunlight. Fic. 15.—Garden toad. (From life.) Examine the eggs several times a day, as hatching occurs in two or three days after they are laid. The developing embryo can be clearly seen through the trans- parent jelly. Watch for their first movements and note their change in form. Finally they wriggle out from the jelly mass and swim freely in the water, or attach them- selves, by means of a little V-shaped sucker on the head, to some solid object. They are not like adult frogs or toads at all, but are the familiar little fish-like tadpoles (fig. 16). The tadpoles.—To rear tadpoles successfully in the schoolroom requires some pains. First, a proper little artificial pond must be made. Professor Gage, of Cornell University, who has successfully reared many broods, gives the following directions for caring for them: TOADS AND TADPOLES 29 “To feed the tadpoles it is necessary to imitate nature as closely as possible. To do this a visit to the pond where the eggs were found will give the clue. Many plants are present, and the bottom will be seen to slope gradually from the shore. The food of the tadpole is the minute plant-life on the stones, the surface of the mud, or on the outside of the larger plants. Make an artificial Fic. 16.—Tadpoles. (Photograph from life by Cherry Kearton ; permis- sion of Cassell & Co.) pond in a small milk-pan, or a large basin or earthenware dish. Put some of the mud and stones and small plants in the dish, arranging all to imitate the pond, that is, so it will be shallow on one side and deeper on the other. Take a small pail of clear water from the pond to the schoolhouse and pour it into the dish to complete the artificial pond. The next morning when all the mud has settled and the water is clear, put thirty or forty of the little tadpoles which hatched from the egg string, into the artificial pond. Keep this in the light, but not very long at any one time in the sun. 3° FIRST LESSONS IN ZOOLOGY ‘One must not attempt to raise too many tadpoles in the artificial pond or there will not be enough food, and all will be half-starved. While there may be thousands of tadpoles in a natural pond, it will be readily seen that, compared with the amount of water present, there are really rather few. “ Every week, or oftener, a little of the mud, and _per- haps asmall stone covered with the growth of microscopic plants, and some water should be taken from the pond to the artificial pond. The water will supply the place of that which has evaporated, and the mud and stones will carry a new supply of feed.” The tadpoles will begin to change very soon. Make a drawing of one just hatched from the egg, examining it with a hand lens. Note the gills on the sides of the neck, the V-shaped sucker on the head, and the absence of legs and eyes. Watch sharply for the first changes. What are they ? It takes a tadpole about two months from the time of hatching to complete its development and hop out of the water as a little toad or frog. In this process of develop- ment the following changes occur : eyes appear ; the gills are lost ; four legs develop; the tail is gradually lost, and lungs are formed inside the body. The development of the lungs cannot be actually seen, but its course is made apparent by the behavior of the tadpoles. While at first they remain under the water nearly all the time, breathing by means of their gills the air dissolved in the water, as they grow older they come more and more often to the surface and gulp down air through the mouth. Lungs are developing, and are being more and more used for breathing air from the limitless supply above. Observe carefully the process of the disappearance of the tail. Does it drop off suddenly ? Is it lost before the legs develop ? Which pair of legs appears first ? The order TOADS AND TADPOLES 31 of their appearance differs in the toad tadpoles and the frog tadpoles ; if both kinds are being reared determine this by observation. Make a drawing of a tadpole just after its legs appear, and compare with the drawing of the newly hatched tadpole ; make also a drawing of a little toad or frog when it first finishes the tailed tadpole stage and hops out of the water. While the development of the tadpoles is going on in the schoolroom observations on the growth and changes of those in the natural ponds outdoors should be made. Does development go on more rapidly indoors than out ? Where do the little toads and frogs go after they leave the outdoor ponds?) On what do they feed now ? Toads and frogs.—Adult toads and frogs are carniv- orous, instead of feeding on tiny plants as in their tadpole stage. They snap up all kinds of insects, worms, and snails ; when full grown they will eat younger frogs, cray- fish, small turtles, and fish, and may also occasionally capture small birds. A few grown-up toads and frogs should be kept in the school- “4 room in a box with at least one glass-side and covered over with netting. Keep q Fic. 17.—Garden toad. (From life.) dish of water in the box, and the bottom covered with clean moist sand. Feed the toads live insects, worms, and snails, or bits of raw meat. How does the toad catch its prey or seize the offered food ? Both toads and frogs do much good by destroying many insects. One observer, quoted by Professor Gage, reports that a single toad disposed of twenty-four cater- pillars in ten minutes, and that another ate thirty-five 32 FIRST LESSONS IN ZOOLOGY celery-worms within three hours. This observer esti- mates that a good-sized toad will destroy nearly ten thousand insects and worms in a single summer. The garden can have no more desirable animal inhabitants than toads; not only should they not be killed but it would be worth while to introduce them in flower and vegetable gardens where they are not naturally present. For a good account of tadpole-rearing see ‘‘ The Life of a Toad,’’ by Professor 5. H. Gage. CHAPTER III A BIRD’S NEST, AND OTHER ANIMAL HOMES The animals whose life-history we have so far studied do not take care of their young, though making certain provision for them nevertheless. The female mosquito, although an aerial creature, is careful to lay her eggs on the surface of water so that the young will find them- selves at the moment of hatching in their proper element ; the female silkworm moth, although she never takes food herself, in nature would certainly lay her eggs on mulberry trees, where the young, on hatching, could find at hand their proper food. Such is the habit of all moths and butterflies. Some of them indeed take food in their adult stage, but this is always liquid nectar from flowers, or other sweet juices, and water, and their mouth-parts are formed into a long, flexible, coiling, sucking proboscis. They could not eat green leaves if they would ; and yet each moth and butterfly mother seeks out, at egg-laying time, that particular plant, unknown to her as food, the green leaves of which the young caterpillars must live upon ; truly a remarkable instinct! But beyond this care in laying their eggs in suitable places the butterflies and moths have nothing to do with their young. And so it is with most of the lower or simpler animals, and with many of the vertebrates (backboned animals), most of the fishes for instance, the amphibians, and the reptiles. These animals pay little or no attention to 33 34 FIRST LESSONS IN ZOOLOGY their young after birth ; indeed many of the lower ones die before the young are hatched, and those that do not may have gone a long distance away before that time. But among the higher vertebrates, the birds and mam- mals, and among a few particularly interesting inver- tebrates, as the social insects and others, the parents give much care and protection to their young, building homes for them, providing them with food, and teaching them to help themselves. Almost all animal homes are built primarily for the protection and housing of the young, although the parents, may, and during the rearing of the young naturally do, largely live in them themselves. Asan example of an animal home, we may observe the construction of a bird’s nest, together with the egg-laying and incubation and the care of the fledglings. A Bird’s nest.—In spring and early summer, the nesting-times, find close to the schoolroom a pair of birds that have begun a nest. By keeping sharp watch in trees and bushes they will surely be found, though most birds hide their nests as effectively as possible. Robins are especially good birds to watch, because they are not easily frightened from their work, because they build a large nest, and because they gather their nesting materials mostly in the near vicinity of the nest. Be- cause the robin’s nest is in a tree, it may not be so easy to watch as the nest of some bird that builds in hedges or bushes. Find a robin or other bird carrying a straw in its bill and trace it ““home,”’ In observing the nest-building, egg-laying, and incu- bation try to answer the following questions: Do both birds take active part in building, or but one, and if one, which one, the male or female, and what does the other do? What materials are used? Is the nest composed chicfly of one kind of material, or nearly equally of sev- ral? What ‘tools’ of the bird are used in building ? A BIRD’S NEST, AND OTHER ANIMAL HOMES 35 When does building begin? How long does it last? How soon after finishing the nest are the eggs laid? Are all the eggs laid at one sitting ? Do both birds take part in incubation, i.e., sitting, or but one, and if but one, is it the male or the female? What does the other do? How long before the eggs hatch? Do they all hatch at the same time? After hatching the care of the fledglings should be well watched. Do both parents bring food? How many times is food brought in one hour, or ifso much time can be given to continuous watch- ing, in two or three?) What is the food? Is the nest cleaned? If so, how often ? When are the first flying lessons given? How long do the young birds continue ae Bs yeas fe ee nade of sycamore down (one-half to come back to the nest at natural size). night after they first leave it? Other incidents in the course of nest-building incu- bation, and care of the young birds will certainly be noted if sufficient observation to answer the above ques- tions is given. Attacks by cats and bluejays (fig. 19), disputes between the parent birds, accidents from high winds or other causes are all likely to enter into the course of nesting. And the behavior of the parent birds under such more or less unnatural circumstances will be interesting to observe and record. While some pupils are watching a robin’s nest others should observe the nesting of other kinds of birds—the 30 FIRST LESSONS IN ZOOLOGY bluebird, wren, groundbird, catbird—any familiar kind that can be found at work. In Chapter XV_ of this book, which is devoted to suggestions for studying the life of birds, further attention is given to nesting and care of the young. See Chapters XVII-XXI in Baskett's ‘The Story of the Birds,’’ and Chapter VI in Chapman’s “ Bird-life.” Fic, 19.—Oriole’s nest with skeleton of bluejay suspended from it; the bluejay probably came to the nest to eat the eggs, became entangled in the strings composing the nest, and dicd by hanging, (Photograph by S. J. Hunter.) Homes of insects and spiders.—The insects which build the most elaborate homes and take the greatest care of their young are the so-called social insects—the communal ants, bees, and wasps. As a later chapter (Chapter XX) in this book is entirely devoted to the life-history and habits of these insects, we may omit any account of them here. But only a few species of bees, namely, the bumble-bees and the honey-bee, live in com- A BIRD’S NEST, AND OTHER ANIMAL HOMES 37 munities, and similarly only a few kinds of wasps. All the ants, however, and more than 2000 living species of them are known, have acommunal life. But the solitary Fic. 20.—An oak-gall (California) home of a small four-winged gall insect; in upper figure the gall on oak-branch; in lower, the gall cut open to show the inside. (Upper figure slightly reduced; lower figure, natural size; from specimen.) bees and wasps give more or less special attention to their young, all of them building homes for them, and providing them with food either by storing it in a closed nest and leaving the young to supply themselves from it, or by leaving the nest open and bringing food daily after 38 FIRST LESSONS IN ZOOLOGY the larva: hatch. The instincts connected with nest- making and caring for the young shown by the non- social or digger wasps and the solitary bees are remark- able, and offer an intensely interesting field of outdoor observation and study. (See the special account of these habits in Chapter XII on insects.) Many insects make for themselves simple burrows or nests in the ground or wood. When not feeding they can retire to these burrows and lie there somewhat pro- tected from their enemies, the birds and the predaceous insects. The eggs of many insects are thrust by the female into the soft tissue of leaves and stems, or even into bark and hard wood. When the young hatch they burrow about in the plant or tree, feed- ing on the juices or other plant substance, and re- maining out of sight and reach of their outside enemies. The larve of certain moths burrow about in the soft inside tissue of leaves, the whole life of the moth except its short adult stage being : assed _ insi leaf. Fic. 21.—Egg-cocoon of the labyrinth , nside the spider, with side removed to show These moths are called egy-packets and chambers. (Two and 7, Sa eee one-half times natural size; after Snod- leaf-miners. The larvae of grass. ) some moths and of many small four-winged hymenopterous midges live through their immature life in galls (fig. 20) on live plants. Th mother, with a tiny, pointed ovipositor, thrusts her eggs into soft plant tissuc, which closes over them. When the oO 1 A BIRD’S NEST, AND OTHER ANIMAL HOMES 39 larve hatch, their wriggling and feeding irritate the sen- sitive tissue so that it grows in an abnormal way and forms a gall, often very large, about the insects. All these burrows and galls may be looked on as the simplest kinds of houses or homes, the young insects living in them, and being protected by them. Most spiders spin silken cocoons (fig. 21), or sacs, in which to deposit their eggs. Some spiders carry this egg-filled cocoon (fig. 22) about with them for the sake of protecting the eggs. After hatching the spiderlings remain in it a short time, feeding on each other! Thus only the strongest survive and issue from the cocoon to Fic, 22.—A female running spider (Zycoside) carrying its egg-sac about attached to its spinnerets. (From Jenkins and Kellogg.) earn their living in the outer world. With certain species of spiders the young after hatching leave the cocoon and gather on the back of the mother and are carried about by her for some time. In connection with their webs or snares many spiders have silken tunnels or tubes in which to lie hidden, a sort of sheltering nest. Those that live on the ground make for themselves cylindrical burrows or holes in the ground, usually lined with silk, in which they hide when not hunting for food. Espe- cially interesting among these many kind of nests are the burrows of the various trap-door spiders (figs. 23 and 24). These spiders are common in California and some other far Western States. Their burrow or cylindrical hole is closed above by a silken, thick, hinged lid or door, a little larger than the hole in diameter, and neatly beveled on the edge, so as to fit tightly into and perfectly cover 40 FIRST LESSONS IN ZOOLOGY the hole when closed. Its upper surface is covered with soil, bits of leaves, and wood, and resembles very exactly the ground surface about it. We have found these trap- door nests in California in moss-covered ground, and Fic. 23.—Trap-door spider (California) with two burrows, one with door 3 P I : , : open, one with door closed. (Natural size; from life and specimens. ) here the nest lids were always covered with green, growing moss. An English naturalist who studied the habits of these spiders found that if he removed the soil and bits of bark and twigs, or the moss, from the upper surface of the lid the spider always recovered it. It is of course plain that by means of this covering the nest is perfectly concealed, the surface of the closed door not differing from the sur- rounding ground surface. This naturalist finally removed the moss not only from the surface of a trap-door, but also from all the ground in a circle of a few fect about the nest. The next day he found that the spider had brought moss from outside the cleared space and covered the A BIRD’S NEST, AND OTHER ANIMAL HOMES 41 door with it, thus making it very conspicuous in the cleared ground space. The spider’s instinct was not ca- pable of that quick modification to allow it to do what a reasoning animal would have done—namely, to cover the trap-door only with soil to make it resemble the cleared ground about it. Another interesting species is the turret- spider, that builds up a little tower of sticks and soil and moss above its burrow (fig. 25). The sticks are an inch or two in length, fastened to- gether with silk and so arranged as to make a five-sided turret two or three inches high. This turret - building spider carries about its egg- cocoon. A female of this : : ee ee Fic. 24.—Burrow of trap-door spider species in captivity was cut open to show interior. (One-half observed to pay much _ natural size; from specimen.) attention to caring for the cocoon. “If the weather was cold or damp she retired to her tunnel; but if the jar in which she lived was set where the sun could shine upon it she soon reappeared and allowed the cocoon to bask in the sunlight. If the jar was placed near a stove that had a fire in it the cocoon was put on the side next the source of warmth ; if the jar was turned around she lost no time in moving the cocoon to the warmer side. Two months after the eggs were laid the 42 FIRST LESSONS IN ZOOLOGY young spiders made their appearance and immediately perched upon their mother, many on her back, some on her head, and even on her legs. She carried them about with her and fed them, and until they were older they never left their mother for a moment.” Fic. 25.—‘ Turret” or above-ground part of nest of turret-spider, (Natural size; from specimen. ) Homes of the backboned animals.—Among the fishes, the lowest of the backboned animals, most species con- tent themselves with the laying of many eggs in a situa- tion best suited for their safe hatching. But some species show interesting domestic habits. The female catfish swims about with her brood much as a hen moves about with her chickens. Some of the larger ocean catfish of the tropics receive the eggs or the young within the mouth for safety in time of danger. Certain sunfishes care for their young, keeping them together in still places in the brook. They also make some traces of a nest, which the male A BIRD’S NEST, AND OTHER ANIMAL HOMES 43 defends. The male salmon scoops out gravel to make a shallow nest, in which the female deposits her eggs, after ‘JSoUu SH pure (szevuusgupy) ysysory W—"9z ‘OI (‘Teg ‘sajesuy sot “od Burystqng Isai NO Jo uolssttusad Ag) se : Ase ee ete ie which he covers the eggs. The males of the species of pipe-fish and sea-horses receive the eggs of the female 44 FIRST LESSONS IN ZOOLOGY into a groove or sac between the folds of skin on the lower part of the tail, Here they are kept until the little fishes are large enough to swim about for themselves. The brave little stickleback builds a tiny nest about an inch and a half or two inches in diameter, with a small opening at the top. In this nest the eggs are laid, and the young fish remain in it some time after hatching. The male parent jealously guards it and fights bravely with would-be intruders. The frogs and salamanders (batrachians) and the lizards and snakes (reptiles) rarely show any care for their young, the eggs of most batrachians being laid in the water and left by the female. The males of the Surinam toad receive the eggs in pits of the spongy skin of the back, where they remain until the young hatch. Snakes’ eggs are laid under logs or buried in sand, and no fur- ther attention is given them by the parent. Among the birds, as we know, nest-building and care of the young are the rule. But not all birds make nests. On the rocky islets of the northern oceans, where thou- sands of puffins and auks and other maritime birds gather to breed, the eggs are laid on the bare rock (fig. 27). At the other extreme is the tailor-bird of India, which sews together leaves with fibrous strips, plucked from a growing plant, to form a long, bag-like nest. The nests of the orioles and bush-tits are also good examples of elaborate nest-making. In the degree of care given the nestlings there is also much difference. The robin brings food to the helpless young for many days, and finally teaches it to fly and to hunt for food for itself. Young chickens are not so helpless as the nesting robins, but are able to run about, and, under the guiding care of the hen mother, to pick up food for themselves. Among the mammals the young are always given some degree of care. Excepting in the case of the egg-laying T, AND OTHER ANIMAL HOMES 45 A BIRD’S NES Fic. 27.—-Murres on Walrus Island, Behring Sea. Note the eggs scattered about over the bare rocks, lite by the Fur Seal Commission.) (Photograph from 46 FIRST LESSONS IN ZOOLOGY duck-bills, the lowest of the mammals, the young are born alive—that is, not hatched from eggs laid outside the body—and are nourished after birth, for a shorter or longer time, with milk drawn from the body of the mother. The nests or homes of mammals present varying degrees of elaborateness, from a simple cave-like hole in the rocks or ground to the elaborately constructed villages of the beavers, with their dams and conical several-storied houses. The wood-rat piles together sticks and twigs in what seems, from the outside, a most haphazard fashion, but which results in the construction of a convenient and ingenious nest. The moles and pocket-gophers build underground nests composed of chambers and galleries. The prairie-dogs make burrows in groups, forming large villages. We are familiar with the devotion to their young dis- played by birds and mammals. The parent will often risk or suffer the loss of its own life in protecting its off- spring from enemies. Many mother-birds have the in- stinct to flutter about a discovered nest, crying, and apparently broken-winged, thus leading away the preda- tory fox or weasel to fix his attention on them and to leave the nest unharmed. See Beard’s ‘Curious Homes and their Tenants.”’ PART II THE PARTS OF ANIMALS AND HOW THEY ARE USED CHAPTER IV THE GRASSHOPPER AND THE SNAIL An animal’s body composed of parts.—The body of every animal, except the very simplest ones, is composed of a few or many parts, each part having some special use or thing to do. A dog has its body made up of head, trunk, legs, and tail—the head comprising skull with brain inside, jaws with teeth, tongue, eyes, ears, etc.; the trunk comprising a host of internal parts, as the back- bone, heart, lungs, stomach, intestines, etc., and the legs in turn composed of a series of bones to which are attached muscles, among which run nerves and blood-vessels, the whole being covered with a hairy skin. The study of the parts, external and internal, of an animal is called anat- omy, and the study of the uses or functions of the parts is called physiology. In earlier years anatomy and physi- ology were studied wholly separately, as they still some- times are. But we know that the things animals do, and the ways in which they do them, depend upon the parts of the body and upon the special character of these parts. We know also that these parts are specially developed and fitted to do certain things or perform certain functions 47 48 FIRST LESSONS IN ZOOLOGY Thies Fic. 28.—Locusts on wild oats. (Nat- ural size; from life. ) in special ways. That is, the structure of a part and its function or business are closely related. A grass- hopper’s hind legs are spe- cially long and strong so as to enable the grasshopper to hop; or we may put it differ- ently and say that the grass- hopper can hop because its hind legs are specially long and strong. In whichever way we look at this relation between the power of an animal to do some- thing in a special way and its posses- sion of parts specially fitted for doing this something, whether it be hopping, or flying, or singing, or breathing under water, it must be kept always plainly in mind that such a close re- lation does exist. Therefore when we study the make-up of an animal, ex- amining carefully the various parts of the body, we should always remember that this particular make-up or structure is closely connected with the things the animal can do, and the special manner in which it does them. The grasshopper. — Grasshoppers, better called locusts, of some kind can be readily found along roadsides or in fields (fi mens, kecping some alive and dropping g. 28). Collect several speci- the others into the killing-bottle (see p. 335). Examine carefully a dead speci- THE GRASSHOPPER AND THE SNAIL 49 men. Note thatthe body is made up of rings or segments. In what part of the body are these rings plainest? The legs are attached to the middle part of the body called the thorax, of which the front part (to which the front legs are attached) is movable and is covered over by a sort of saddle-shaped hood, while the hinder part is solid and box-like. How many pairs of legs are there? Examine a single leg and make a drawing of it, showing of how many parts it is composed and how each part appears. Of what use are the claws and the little pads on the under surface of the foot? To what part of the body are the wings attached? Note how the narrow thicker fore wing covers and protects the plaited delicate hind wing when the wings are folded. When the locust flies for long distances it rises high into the air, until it finds an air current; then it simply lets its large outspread hind wings act as flat sails to hold it up, thus allowing it to float for many miles. In this way the Rocky Moun- tain locusts sail or fly sometimes a thousand miles; all the way from Wyoming to Kansas. Note the many veins in the wings. What are these for? Draw a front wing and a hind wing. On the head find two large compound eyes (see p. 22), three very small simple eyes, a pair of many- jointed feelers or antennz, used both for feeling and prob- ably also for smelling, and a set of mouth parts consisting of an upper lip, a pair of hard, blackish-brown jaws or mandibles, a second pair of jaw-like parts called maxille, each made up of several small pieces and a small palpus or feeler, and an under lip bearing two more small palpi. With the mandibles the locust bites off, and with the help of the other parts, chews bits of leaves, green stems, etc. The palpi are believed to be organs for feeling and tast- ing the food. Draw the front of the head, naming the different parts. 5° FIRST LESSONS IN ZOOLOGY Note that almost the whole outer surface of the body is covered with a firm, smooth coat, the chitinized cuticle, that is, the horny outer layer of the skin. The skin of the neck, however, and that at the bases of the legs and wings is soft. Why is this necessary ? What is the most obvious use of this hard outer covering? Note that the soft skin of the neck is well protected by the projecting Antenne “nr auditory organ i ‘ocellus / f head compound eye 1 ' pronolum } as Ldhorar 7 ges \ COra i Vrochanter T femur . tibia” 7h a iarsal segments Vic. 29.—-Locust with external parts named, saddle-shaped horny picce on the front thoracic body- ring. Another use of the firm cuticle, or exo-skeleton, as it is called, is to afford solid points of attachment for the many muscles of the body, the locust having no bones or any kind of internal skeleton. (In a few places there are processes or continuations of the exo-skeleton projecting internally.) That part of the body behind the thorax is called the abdomen. [xamine the upper side of the first (nearest the thorax) body-ring of the abdomen, and find two small, nearly circular, thin places looking like little windows. These are the hearing organs, or tympana, of THE GRASSHOPPER AND THE SNAIL 51 the locust. The sound-waves striking against these thin tightly stretched bits of the body wall, set them into vibration, and these vibrations stimulate a tiny nerve which touches each tympanic membrane on the inside and leads to one of the internal nerve-centers. This is a much simpler kind of ear than we possess, and the locust probably cannot hear nearly as well as we can. Note on each side of each abdominal body-ring (except the last) a tiny blackish spot. These are breathing pores or spiracles like those of the silkworm (see p. 13). The locust does not take in air through nostrils en the head or through the mouth, but through these numerous pores. There is also a spiracle near each tympanum, and one on each side of the thorax near the insertion of the middle legs. At the very tip of the abdo- men are several small projecting parts which differ in the male and female. The female has two pairs of strong, curved, pointed pieces called the ovipositor or egg-laying organ. When the locust is ready to lay its eggs, by means of this strong ovipositor it bores a hole in the ground into which the abdomen is pushed and the eggs laid at the bottom. The male locust has a swollen, rounded, abdominal tip, with a few short inconspicuous pieces on the upper surface. Examine now a live locust and see how it uses its legs in walking and hopping ; how it moves its jaws sidewise, not up and down as with us; how its antenne keep ‘‘feeling” about in front of it when it is walking; how the abdomen keeps up a slight but distinct and regular expanding and contracting. This movement forces air in and out of the body through the spiracles; it is the breathing motion. Make a drawing from lateral view of the whole body of the locust, showing and naming all the parts studied. For a more detailed account of the external structure 52 FIRST LESSONS IN ZOOLOGY of the locust see Comstock and Kellogg's ‘‘ Elements of Insect Anatomy,’’ Chap. II. The pond snail.—Pond snails may be found in almost any pond, and live specimens may be easily kept in the schoolroom aquarium or simply in bowls or glass jars of water (fig. 30). They should be fed pieces of lettuce or cabbage leaves. Observe the habits of the snails; a i ry z i) liv Ty i ae E i i if} Fic. 30.— Pond snails in a battery-jar aquarium. (One third natural size; from life.) how they come to the surface to breathe ; how they crawl about; how they eat by rasping off bits of the leaves with the rough, horny tongue; how they protrude from and withdraw into the shell; how the feelers move in and out. Ikxamine a specimen with body extended from the shell, and note that it is not made up of segments or rings, but is a soft, unsegmented mass with a firm, muscular, flattish disk on its lower side called the foot. How does THE GRASSHOPPER AND THE SNAIL 53 the snail ‘‘walk’’ by means of this ‘‘ foot”? The body is covered by the mantle, an edge of which may be seen just at the margin of the shell. The soft, flexible body and firmer muscular foot can both be withdrawn into the protecting shell. Find on the head a pair of extensible tentacles, the feelers, with the eyes (dark spots) at their bases. Most other snails and slugs have two pairs of tentacles or horns, the eyes being on the tip of the second pair. Find also the mouth, and examine with a lens the pecul- iar ribbon-like radula or tongue, which is covered with fine curved teeth. The radula is drawn back and forth across the food, and by it small particles of the leaf are rasped off. Leaves which have been fed on will show the rasped or scraped places. Find also, usually just at the surface of the water, when the snail has come up to breathe, a small hole on the right side of the body; this is the breathing pore, and air entering here passes into a small sac-like space, a simple kind of lung. Examine a shell and note the following parts: the aperture at the large end, the apex or pointed end, the lip or outer edge of the aperture, the lines of growth parallel with the lip, the suture or spiral groove on the outside, the spire comprising all the whorls or turns, and the columella or inner axis of the spire. Do the whorls of all the shells turn the same way? What is the use of the shell? Make a drawing of the right-hand side of a snail and its shell representing the animal fully extended; name all the parts of the snail and shell. If pond snails cannot be found, garden snails or slugs may be studied. The slug is a snail-like animal without a shell. CHAPTER V THE SUNFISH AND THE SPARROW The two animals whose external structure we have studied are both backboneless or invertebrate animals. Most of the smaller animals are without internal bony skeletons and hence without backbones. This is true of the sponges and sea-anemones, the starfishes, the worms, the crayfishes, crabs and lobsters, the centipedes, and the spiders, as well as of the insects and the snails, slugs, and clams. Contrasted with these backboneless animals are the backboned ones, or vertebrates, including the fishes, amphibians, reptiles, birds, and mammals or quadrupeds. We shall now examine the external struc- ture of two backboned animals, a fish and a bird. The sunfish (fig. 31)—Some kind of sunfish can be found in the streams of any part of the United States, except in Washington and Oregon, and in the higher Rocky Mountains. Where sunfishes cannot be obtained, bass or perch or gold-fish may be used for study. Speci- mens should be taken alive if possible, and kept in a large jar or tub of fresh water. Examine a live sunfish. Note the deep, flattened trunk of the body, and the paddle-like tail. The head is closely fitted to the trunk without any neck. How are the scales arranged? Remove a scale and examine it under a hand Jens. What sort of an edge has it? Ex- amine the fin, called the dorsal fin, on the back. Note that its front part is composed of spines, and its posterior 54 55 THE SUNFISH AND THE SPARROW Fic. 31.—A sunfish. (One-half natural size; from specimen.) 56 FIRST LESSONS IN ZOOLOGY part of soft rays jointed and branched, both spines anc rays being connected by and supporting a thin skin. At the end of the tail is the caudal fin; in front of the tail on the under surface is the anal fin, while still in front of this is the pair of ventral fins, and on the sides of the body back of the mouth are the pectoral fins. How is each of these fins composed? The ventral fins correspond to the hind legs of other backboned animals, while the pectoral fins correspond to the forelegs, wings, or arms. Watch the fish swim and determine the use of each kind of fin. Professor Needham gives the following directions for doing this: ‘‘ To learn the use of the pectoral and ventral fins catch the fish with the hand, avoiding the sharp spines at the front of the pectoral and anterior dorsal fins; fold the pectoral fins backwards, flat against the sides of the body; pass a rubber band back over the head and around these fins to keep them so. Keep the fish under water while attempting to depress the pectoral spines, for in air it will keep them rigidly erect. Pass another rubber band about the ventral fins. Then liber- ate the fish and watch it. What position does its body assume? Release the paired fins and fasten down the dorsal and anal fins with rubber bands. Liberate the fish again, and observe how it gets along without the use of these fins. What kind of a course does it take through the water?’”’ Examine the eyes. Are there eyelids? In front of the eyes are two pairs of nostrils. Examine the inside of the mouth. Is there a tongue? Where are the teeth situated, and in what direction do they point? What advantage to the fish is it to have the teeth pointing as they do? Lift up the flap, called opercular flap, in front of one of the pectoral fins and bend it forward. Under it are four gill arches, each with a double fringe of gills. The THE SUNFISH AND THE SPARROW 57 cavities enclosed by the gills are called gill-pouches. Note the gill-rakers, short and blunt, on the first gill arch. Note also, on the under side of the flaps turned back, delicate red gill-like structures covered by a mem- brane. These are the false gills. The true gills are organs by means of which the fish breathes under water. Note the fish continually gulping water. This water with air dissolved in it passes through the mouth into the gill-pouches and out under the operculum. Thus the dissolved air in the water comes in contact with the gills passes through the delicate gill membranes and into the blood, which runs in many fine capillaries through the gills, while at the same time the blood itself gives up carbonic dioxide, which passes out through the gill membranes into the water. In this way the blood is purified. Make a drawing from lateral view of the sunfish, show- ing and naming the parts studied. Professor Needham gives the following directions for seeing the flow or circulation of the blood in the caudal fin of a fish: ‘« Wrap the fish in a wet towel, leaving the caudal fin exposed, and place it ona low box beside the microscope, with its caudal fin extending across the center of the microscope stage. Spread the fin out flat on a glass slip upon the stage, so as to bring a thin portion of it into the field, and examine it with low power. If the fish refuses to lie quietly, pour a little chloroform on the towel near its mouth. ‘Observe the conspicuous, dark, irregular pigment cells scattered throughout the epidermis of the fin. “The larger blood-vessels are of two kinds; (1) arteries, bringing blood out into the fin, and (2) veins, conveying the blood back to the body again. The smaller ones are the capillaries connecting the arteries 58 FIRST LESSONS IN ZOOLOGY with the veins, and distributing the blood throughout the tissues of the fin. ‘© Observe that the blood consists of a fluid plasma, in which floats numerous corpuscles. Observe that the blood appears red in the arteries and veins, where the corpuscles are accumulated, but only slightly reddish or yellowish in the capillaries, where the corpuscles form but a thin layer. “Does the blood travel faster in the arteries and veins, or in the capillaries ? “ Place a bit of cover-glass over a very thin portion of the fin and study it with higher power. Find two kinds of corpuscles in the blood: (1) red corpuscles (red only when a number are seen together), very numerous, and carried along in the center of the larger currents closely packed together; and (2) white corpuscles, . . . not very numerous, and usually seen trailing along the edges of the blood currents, or escaping out into the tissues.’ The English sparrow (fig. 32).—As the English spar- rows, which have spread over the whole country, are almost universally held to be pests, the shooting of a few to serve as specimens for the study of the external parts of a bird may be looked on more leniently than the killing of other birds should be. The habits of the live birds may be studied as the pupils go and come from school. Examine a dead specimen. Note the division of the body into head, trunk, and appendages—namely, wings and legs. Note that the sparrow is covered with feathers, some long, some short, in some places thick and in others thin, but all fitting together to form a complete covering for the body. Only the bill and feet are exposed, and these are covered in one case (bill) with a horny sheath, and in the other (feet) with horny scales. The feathers and the horny covering of bill and feet are simply modi- THE SUNFISH AND THE SPARROW 59 Fic. 32.—English sparrows at a drinking-place; note the black cheeks and throat of the males. (One-half natural size; from life.) 60 FIRST LESSONS IN ZOOLOGY fied portions of the skin. Of what uses are the feathers to the bird? The feathers are of several kinds or types, each of which has a name. In the wings and tail are long, stiff feathers called quill feathers; those which overlie the whole body and bear the color pattern are called contour feathers; the small soft ones which cover the body more or less completely (being, however, mostly hidden by the contour feathers) are called down feathers or plumules, while, finally, the scattered, slender, soft, or stiff hair-like ones, with the thin bare stem and small terminal tuft of branches, are called thread feathers or filoplumes. Pull a quill feather from the wing and examine it in detail. Note the central stem or shaft, composed of two parts, a basal hollow transparent quill, which bears no web and by which the feather is inserted in the skin, and a longer terminal four-sided part, the rachis, which bears on either side a web or vane. Examine the vane with a lens and see that it is composed of many narrow linear plates called barbs, and that each barb is fringed in turn with smaller branches called barbules. Finally, each barbule bears many fine barbicels or hamules, which can be seen with a micro- scope. The barbs compris- ing the vanes are inter- locked with each other (fig. 33), thus forming a true web and giving the vanes, com- Fic. 33.—Bit of bird’s feather, greatly maynified; s, shaft; 4, barb; 4/, posed of small, weak parts, Darbule; 4, hamule. (From = speci- men.) much strength and power of resistance. Rub the feathers from tip to base, and, examining the vanes with THE SUNFISH AND THE SPARROW 61 the lens, find out what has happened ; now rub from base to tip, and note, under a lens, the result. Examine a plucked-out contour feather. How does it differ from the quill feather? Can you understand its structure from your study of the quill feather ? Note that the tip of the feather is colored and marked while the base is not especially patterned. Why is this? Ex- amine a down feather. How does it differ in make up from a quill feather? From a contour feather ? What is the special use of the down feathers ? Finally, pluck out one of the hair-like thread feathers from the base of the bill and examine it with the lens to determine its structure. Make a careful drawing of each of the four kinds of feathers, naming all the parts. In classifying birds reference is made in the manuals of classification to differences in the shape and character of many parts of the body and to differences in the plumage of various body-regions. To understand these references it is necessary to become acquainted with the names applied to these various small parts and regions, and so in fig. 34 the names of them all are given. Examine the bill or beak. It is composed of an upper and a lower mandible or jaw; the meeting line of the mandibles is called the commissure, and the corner of the mouth is called the rictus; the bristles at the rictus are the rictal bristles; the median ridge of the upper mandible is the culmen, and the median keel of the lower mandible the gonys. Note just above the bill two openings. What are they? How are they connected with the mouth? Note the eyes, and at the inner angle of each the delicate nictitat- ing membrane, which can be drawn over the ball. Does the bird have external ears? The names of the regions of the head which are commonly referred to in describing its markings will be learned from fig. 34. ,Culmen 62 FIRST LESSONS IN ZOOLOGY Examine a wing; determine by reference to fig. 34 what feathers compose the primaries, secondaries, tertiaries, Upper mandible ‘Lower mandible Forehead -- Outer Toe Fic. 34.—Outline of bird’s body, with names of external parts and regions. (Hallux ) Heel joint (Suffrago) Lateral rectrix so greater, middle, and lesser coverts. How many primaries are there?) How many secondaries? At the bend of the THE SUNFISH AND THE SPARROW 63 wing and lying partly over the upper greater coverts is a tuft of short quills, the spurious quills ; underneath the wing at its junction with the body are some long, narrow feathers, the axillars. Spread the wing out and note where the quill feathers are inserted. Note how perfectly the feathers fit together and overlap, both when the wing is outspread and when folded. The wing corresponds to our arm and hand, the primaries being inserted on the hand (in the bird there is only one large finger, two very small ones not showing except in the skeleton), the secondaries on the forearm and the tertiaries on the upper arm. With what part of the fish does the wing of the bird correspond? If a cleaned and mounted skeleton of a bird can be had for examination the bones of the wing should be studied and drawn. The names of the various regions of the trunk can be learned by reference to fig. 34. How many rectrices or tail feathers are there? What is the use of the tail? Note the oil gland above the base of the tail. What is the use of the oil? How is it put on the feathers? Observe this in a chicken. Examine a leg. It is composed of thigh, shank, and foot, the foot comprising the long slender tarsus and four toes with claws. What parts of the leg are feathered? Note the covering on the unfeathered parts. What are the toes well fitted for? There is much variety in the shape and character of birds’ legs, including differences in the length of the various parts, in the covering, in the number and position of the toes, and in the size of the claws. All these differences, as well as the many in the shape and character of the bill, are correlated with habits, especially the feeding habits of the birds, and offer a most interesting subject for study. Special attention is given this subject in Chapter XV. CHAPTER VI THE MOTIONS OF ANIMALS, AND THE SKEL- ETON AND MUSCLES Motions and locomotion.—Our attention is usually first attracted to an animal by the movements it makes. These are the plainest proof that it is alive. For the animal itself the ability to move is essential to existence. Most animals move in search of food, to escape from their enemies, to find and build their homes, to seek their mates, and care for their young. In the higher forms the organs of motion constitute the great bulk of the body. The shape and size of such an animal are determined largely by these organs. The heart and blood-vessels, the lungs and digestive system, are principally concerned with supplying the organs of motion with materials necessary for their working, and by far the larger part of the work of the sense organs and nervous system is to put these organs into action, and to direct and control them. We can see therefore that they have much to do with both the structure and physiology of animals. Indeed the most marked difference between animals and plants is the pos- session by the former of the organs of motion and their controlling organs, the sense organs, the brain and nerves. True, plants have the power of motion and are sensitive to light, heat, and other influences as are animals, but to a far less degree. 64 THE MOTIONS OF ANIMALS 65 Among the movements made by animals, the moving of the body from place to place, usually spoken of as lo- comotion, generally requires the greatest energy or power. The other motions are those of parts of the body, as the arms, legs, head, etc. We shall here consider a few examples of the motion of animals illustrating the character of locomotion in different forms. There are three different ways in which locomotion takes place, that is, by swimming in water, crawling or walking or leaping on some solid object, as the ground or the trunk of a tree, and by flying in the air. In each of these three cases the body must first be sup- ported, then either pushed or pulled along or perhaps both pushed and pulled. In swimming the body is supported by the water. In animals that swim it is either lighter than water, asin the duck, or just as heavy or only a little heavier, as in fishes, so that it is wholly or almost wholly held up by the water, and the full power of the leg, fin, or tail used in the motion can be devoted to pushing the animal along. Animals crawling on the bottom in water also have very little to do in holding up the body, the water supporting them. But those that move on land or fly, with their bodies immersed in air alone, have the body only very slightly supported by the air. These animals must there- fore devote energy to supporting the body as well as to moving it along, and they have special means for this. As already said the body is moved by pushes or pulls. In by far the most cases motion results from pushes given by a part of the body against something outside. Now it is plain that air is a very poor. thing to push against as compared with water or a solid. Naturally since water is a liquid it gives way readily to a push, but its heaviness offers much greater resistance to motion than does the air. The solid ground, of course, offers most of all. Currents 66 FIRST LESSONS IN ZOOLOGY in water and air are of peculiar help in this matter. Water currents may carry an animal for great distances without any work on its part; while air currents make it possible for birds to soar with little effort. Flight by the vibration of wings, as in birds and insects, requires the greatest expenditure of energy, since the pushes against the thin air must be made quickly and with great force and be rapidly repeated to be effective for support and loco- motion. Man in making locomotive machines, railway engines, automobiles, steamships, etc., has met the same conditions as the animals; but the difficulties of aerial locomotion are so great that he has not yet been successful in inventing a mechanism for it such as has been developed in the birds. The simplest and what may be called the most imper- fect mode of locomotion is shown by the simplest ani- mals. These, the Protozoa (see Chapter IX), are ex- tremely minute, and mostly live in water. A single drop of stagnant water may contain hundreds of them. Among these simplest animals we can readily find forms illus- trating at least four different modes of motion; all, how- ever, are really but different forms of the same action, that is, the contracting or shortening and thickening of a part or the whole of the animal. In the Amceba (see Chapter IX) the body is composed of a minute bit of soft, jelly- like living substance called protoplasm, without any spe- cial parts at all. By the varying contracting and relaxing of the soft body portions of it are protruded and with- drawn again, a slow and imperfect locomotion being accomplished by this means (fig. 35). In the most rapidly moving Amceba the motion is very slow, while in the slower ones it would take some hours to proceed a single inch. Some kinds of Protozoa show what is called streaming motion. This is seen in forms in which the central por- tion of the body protoplasm will flow along for a while in THE MOTIONS OF ANIMALS 67 one direction, then stop and flow the opposite way. It is not easy to understand the exact method by which this motion is produced. In some of the Protozoa, instead of the whole or a large part of the body taking part in an ill-defined movement, Fic, 35.—Ameba sp.; showing the forms assumed by a single individual in four successive changes, (Greatly magnified; from life.) there are definite organs of motion. Small, hair-like parts of the body, called cilia or flagella, are extended into the water and struck or pushed against it. Among the ciliate and flagellate Protozoa we find some with the body cov- ered all over with cilia, as in Paramcecium (fig. 36), and some with only very definite cilia-covered areas, or even with but one or two cilia, these being usually long and 68 FIRST LESSONS IN ZOOLOGY whiplash-like. In some the cilia seem to be in constant rhythmic motion, in others they seem to move only when the animal wills it. Motion by the contraction of a fiber is seen in the peculiar Protozoan called Vorticella (fig. 37). Fic. 36.—Laramecium sp.; Fic. 37.— Vorticella sp.; one buceal groove at right. individual with stalk coiled, (Greatly magnified; from and one with stalk extended. life. ) (Greatly magnified; from life.) This animal has a tiny bell-like body on the end of a slender stalk. The stalk is made up of an outer rather firm elastic substance with a contractile fiber in the core. When the fiber contracts the stalk is drawn up into a spiral and thus becomes shortened, Muscles and skeleton.—The living elements in the body of the higher animals are small parts called cells, THE MOTIONS OF ANIMALS 69 and all of the above-described kinds of motion are found in some of these. But motion is produced mainly by the contraction of fibers, which are grouped into masses called muscles. In the higher groups of animals the great mass of the body consists of muscles composed of con- tractile fibers, which are to be thought of as modifications of a fiber such as exists in the stalk of the Vorticella, one of the smallest and simplest of living animals. It is as if the contractile substance had appeared under different forms, but having proved most useful in the form of fibers as animals rose higher in the scale this form became very extensively used. In such forms as the hydroids and jellyfishes the con- tractile fibers are not gathered together into such definite muscles as in the higher animals, nor are there such well- developed firm body-parts for the fibers to pull against. These contractile fibers are only extensions of) certain body-cells, as in Hydra (see Chapter IX), or form a more or less scattered net-work, gathered into ill-defined bands or sheets, as in the sea-anemones and jellyfishes. From the starfishes and worms, through the crabs and insects, the muscular parts become more and more definite in form and prompt in action, and there appears more and more perfect development of firm parts. Some of these serve as points of attachment from which the muscles can pull, and some act as levers to make a push on the external water, earth, or air. The swift, strong, and accurate motions of the insects and of the backboned animals require rigid levers, firm points for levers to work against, or fulcra, and other firm points for the attach- ment of muscles from which to exert their pull. These firm solid parts, the levers, fulcra, and attachment points of muscles, constitute the skeleton of the animal body. The skeleton of a backboneless or invertebrate animal differs from that of a backboned or vertebrate one not in 7° FIRST LESSONS IN ZOOLOGY the use made of it but in its arrangement and in the part of the body from which it is mainly developed. The skeleton of the invertebrate is developed from the skin, and forms a hard casing over the whole or part of the body. It is therefore called an exoskeleton. How this outside skeleton serves as levers, fulcra, and points of at- tachment may well be seen in the case of insects (fig. 38), a ——— Se H vit . wT : Vv.in.c. Fic. 38.— Left middle leg Fic, 39.—Diagram of cross-section through of cockroach, with exo- the thorax of an insect to show the muscles skeleton partly — re- of the wings and legs; 4, heart; alc, moved, showing mus- alimentary canal; v.#.c, ventral nerve cles. (Much enlarged; cord; w, wing; 7, leg; m, muscles. after Miall and Denny.) (Much enlarged; after Graber.) or crayfishes. The wall of the thorax, or carapace (fig. 39), is the central strong portion from which the great pulls are exerted, while each joint of a leg is a lever, a fulcrum for the next part, and a point of attachment for muscles. The whole system of muscles is so arranged inside the exoskeleton that the flying, crawling, and swimming of the various animals, as well as the particular THE MOTIONS OF ANIMALS 71 motions of the eyes, feelers, and respiratory organs are well performed. In the vertebrates the skeleton is mainly developed from tissues within the body and is called in consequence the endoskeleton. Even more than in the invertebrates it is a system (fig. 40) of levers, fulcra, and points of attachment for muscles to work with, and is as important a part of the organs of motion as is the muscular system itself. : To illustrate the use of the skele- Sea ton of a vertebrate we may examine arm of man; to show the bones of the hind legs of a cat how bones and muscle act as levers, (After (fig. 41). The upper bone, the femur, Jenkins.) is attached by a joint to the large irregularly shaped bone called the ilium, which is firmly bound to the backbone. Below the femur are two bones, the largest, called tibia, being bound by a joint to the femur. Below the tibia are a group of bones, the tarsal bones, pretty firmly fastened to- gether. The largest makes a joint with the tibia. Each of the four tarsal bones toward the toes make a a joint with a slender Fy. 41,—Skeleton of cat. (After Reighard bone in the body of and Jennings.) the foot. These are the metatarsals. At the end of each metatarsal is a series of three bones which form the skeleton of the toes. All of these bones together consti- tute a system of levers which the muscles of the leg can draw up in a somewhat folded position, and then straighten out with quickness and force. Since during 72 FIRST LESSONS IN ZOOLOGY such movements the toes rest on the solid ground, the body is lifted and thrown forward. There are a number of strong muscles which make the pulls for these motions, but a single pair may be studied as an cxampile of the method of attachment and action of all. Fig. 42 shows the large muscles of the fore leg of a cat. Each consists of a large central mass formed of the muscular or contractile substance proper bound up into a compact body by connective tissues, with strings or bands of connective tissue at the ends fastening the muscular mass to the bones. These fastenings are tendons. When the muscular sub- stance contracts it of course pulls on the two tendonous ends. If one end of a muscle in the hind leg is attached to the hip-bone it cannot move, but the one fastened to the tibia moves this bone as a lever, with its fulcrum at the end of the femur. The tibia is brought toward the femur and we say that the /g) limb is flexed. Another muscle in con- 7)} y # tracting will act on the tibia as a lever 5 also, but it brings the tibia back again Fic. 42.—Muscles on Into a straight line with the femur. a Bee ne This motion is called extension. For hard and = Jen- each part of the limb from hip to toe are vie groups of muscles which flex and extend that part, the bones being levers and fulcra and points of attachment. Most of these levers are of the kind called in mechanics levers of the third class. By them quickness of motion is magnified. Thus by noting first what motions an animal makes, and then, by dissection, examining the muscles, the bones, and their points and means of attach- ment, we may come to understand clearly the uses of the muscles and skeleton in any animal. THE MOTIONS OF ANIMALS 73 The plan of the skeleton in the vertebrates is the same throughout the whole great group, which includes the fishes, amphibians, reptiles, birds, and mammals. The differences lie in the varying development of the differ- ent parts and in the modification in the size and form of these parts. The plan includes a central axial portion, the spinal column, made up of a series of elements called vertebre. In a completely developed skeleton, as that of a cat (fig. 41), the groups of vertebre are the cervical, i.e., those of the neck; dorsal, those to which the ribs are attached; lumbar, just posterior to the dorsal; sacral, the group to which the ilium is bound, and caudal or tail vertebrae. In the higher vertebrates the vertebra of the sacral group are fused into one bone, the sacrum; while the caudal vertebre, posterior to the sacrum, are fused into one or a few bones in animals without a tail and in them named the coccyx. The bones of the spinal column are firmly bound together, constituting a somewhat flexible but very firm axis, to which the head and limbs are attached and from which the main pulls on these parts can be exerted. The head skeleton consists of a central group of bones in front of the axial skeleton, being an extension of it, and around it are placed the other bones of the head. To the axial skeleton are attached two pairs of limbs; an anterior pair, joined to the axis by a group of bones known as the shoulder girdle, and a posterior pair joined to the axis by the pelvic girdle. The leg of the cat, already described, may be taken as a represent- ative limb. Now if we examine a series of vertebrate skeletons, representative of the different groups from the lowest forms of fishes through to the highest mammals, we can see that notwithstanding the different forms and sizes of the various animals and their different ways of locomotion —swimming, flying, crawling, running, walking, and leap- 74 FIRST LESSONS IN ZOOLOGY ing—they all make use of the same plan of levers, each kind of animal, however, having it specially adapted for its peculiar motions. To see this more clearly com- Fic, 43.—Bones of fore limb of various backboned animals; A, horse; B, bird; C, man; D, dog; £, fish; F, reptile. pare the skeleton of the fin of a fish with the fore leg of a lizard, the wing of a bird, the fore leg of a horse, the fore leg of a dog, and the arm of man (fig. 43). If we carefully remove the skin from the side of a fish such as a black bass or sunfish, there is shown a mass of flesh (fig. 44). The great bulk of this is one large muscle, the contraction of which makes the THE MOTIONS OF ANIMALS 75 body curve to the same side and thus gives a stroke of the tail fin. A similar muscle on the opposite side pro- duces a stroke in the opposite direction. These alternating strokes are the propelling power which forces the fish through the water. At the base of each of the other fins are found a few small strips of muscle. These give their varied and more gentle movements which keep the body in any particular position and aid in directing its Fic. 44.—Side view of a dogfish (shark) with a strip of skin removed to show muscles. (After Parker.) locomotion. About the head are other muscles which move the jaws, eyes, and gill-covers. If we take the skin from the side of a body of a dog and dissect out all the muscles we find a large number of well-developed ones. The great muscular mass on the side of the fish’s body used for one or a few motions is replaced in the dog by a great number of muscles used to produce a number of various movements. The few comparatively weak muscles of a ventral fin are replaced by the many large, strong, and definite ones of the hind limb of the dog, while the small group working the pectoral fin finds its representative in the large and varied group moving the fore leg. Further differences are seen in comparing the head of the fish with that of the dog, as well as in every other part of the two bodies. These differences all show that in the dog there is a separation of the muscular system into more numerous and more definite forms of muscles, with the possibility of more numerous and more accurate motions than in the fish. If we compare the muscles 76 FIRST LESSONS IN ZOOLOGY and bones of the human hand and arm with those of the fore limb of other animals we find an advance in complexity over the fin of a fish or the fore limb of a salamander or even the fore leg of a dog, although all are made up on the same plan and out of the same elements. If we now go further and compare the organs of motion in the human body with the means of motion in Amceba we see what a wonderful advance the highest animal exhibits over the lowest both in structure of the motor organs and in the possibilities of movement. CHAPTER VII HOW ANIMALS TURN FOOD AND AIR INTO FLESH AND ENERGY Necessity of oxygen and food.—In the organs of motion just studied the muscles and bones are only the machinery for motion. They make use of energy but cannot themselves provide it. Just as an engine and all the wheels and levers connected with it make use of heat, which is one of the forms of energy, to produce the needed motions, so the muscles and bones make use of some form of energy to produce the motions of the animal body. In the steam-engine the special form used is heat, gen- erated by the burning of coal, oil, or wood; by means of this heat, which expands the steam, i.e., the vapor of water, energy is applied to the piston in the form of a push. The motion of the piston is passed over to the wheels and levers of the shop, and by them are given all the different directions and velocities required by the different machines of that particular shop. In the animal body the muscle is the engine, for in it the energy is generated. In a way we do not yet ex- actly understand this energy makes the muscular sub- stance contract and give a pull on the tendon, with the same effect as the push of the steam on the piston, that is, to set the rest of the machinery, the bones, in motion. The bones apply the motion in the way required for the movement of the animal. A striking difference, how- ever, between the animal body and a shop is this, that 77 78 FIRST LESSONS IN ZOOLOGY while in even a very large shop there may be but one engine generating energy to run all the different machines, in the body every muscle is a separate engine, and one bone may be connected with a number of them. Never- theless the essential facts are the same in both cases. The muscle-engine, like the steam-engine, produces a form of energy and applies it to machines so as to lift weights or to move things from place to place. But we learn in physics that we can get any form of energy only by changing some other form into the one desired. The forms of energy are heat, light, electricity, chemical en- ergy, and that of a body in motion. Now the only way to get heat, for example, is by a change from one of the others. We can make a piece of iron hot by striking it with a hammer; here the energy of a moving body is con- verted into heat. Or the energy of the electric current may be converted into heat or motion. Man’s most com- mon way of getting heat is to take coal, wood, or oil, and apply some heat to start with, when the oxygen of the air will unite with carbon and hydrogen, substances in the coal, wood, or oil, to make two new substances, one of these being carbon dioxide, the other water. This is chemical action; it results in changing chemical energy into heat. In ordinary language this union of oxygen with carbon or hydrogen is spoken of as ‘‘ burning '’ or ‘‘ combustion.’ An animal cannot make the least motion without using a certain amount of energy. And it has been shown by investigation that the energy possessed by an animal is derived from the chemical energy resulting from the union of oxygen with the carbon, hydrogen, and nitro- gen in other substances. The muscles are the engines in which this energy is made use of for motion. This brings us now to see how essential it is that the animal should have in its body oxygen and substances for the oxygen to combine with. FOOD AND AIR TURNED INTO FLESH AND ENERGY. 79 The animal body, however, not only needs a constant supply of the substances from which this energy may be produced, but also a constant supply of those substances which compose its body. In every young animal there is a growth, an increase of size and weight, and in the adult a constant replacing of body material. And by far the greater part of an animal body is made up of just those things, namely, oxygen, carbon, hydrogen, and nitrogen, that are used in the supply of energy. How animals breathe.—The animal gets its oxygen from the free air, or from the air mixed with water, by a process called respiration. It obtains from its food all the other substances used. Food is prepared for use by the process of digestion. Oxygen obtained by respiration and the substances obtained from food are distributed throughout the body by the process of circulation. We may now consider the ways in which respiration, diges- tion, and circulation are carried on among animals. As to respiration, mention has been made only of its service in providing the animal with oxygen. It has, however, one other object. When oxygen combines with carbon, carbon dioxide is formed; if this remains in the muscle or other tissue cells it interferes with the activity of those cells. It is therefore just as necessary for the carbon dioxide to be removed as for the oxygen to be supplied. Carbon dioxide, like oxygen, is soluble in water. Blood, which is composed largely of water, and which can carry the one serves also to carry the other. Further- more, since carbon dioxide is made by a combination with oxygen, it arises just where it can be carried away by the very apparatus that has brought the necessary oxygen. Thus the respiratory apparatus manages both the supply of oxygen and the disposal of carbon dioxide. The fundamental fact in the process of respiration is that gases, whether free or dissolved in water, will readily 80 FIRST LESSONS IN ZOOLOGY pass through a thin, moist membrane. Thus if a closed sac made of thin membrane filled with water in which carbon dioxide is dissolved be immersed in water in which oxygen is dissolved, carbon dioxide will pass out of the sac and oxygen into it until there is the same amount of each outside and inside. If the water outside is con- stantly replaced all the carbon dioxide will be finally removed. If the oxygen inside the sac is constantly used up and the supply outside is always renewed, oxygen will be constantly going in and carbon dioxide going out. This is just what happens in the living animal. Animals get their oxygen from the air, of which it is a part. The air may be free or dissolved in water. Carbon dioxide is made in the cells of the body. Respiration takes place through the membranes covering all or part of the surface of the body. It requires the constant re- newal of free air or water containing air on the outside, and the constant passage of fresh blood on the inside sur- face of the membrane. This end is attained in a variety of ways among animals. In the simplest forms, the Protozoa, where we have the most primitive means of motion, we find also the simplest means of respiration. The Amccba (see Chap- ter IX) simply relies on its whole external surface for breathing, the thin outside layer of the body acting as a membrane through which the oxygen passes in and the carbon dioxide out. During periods of activity the pro- cesses protruding from the body increase the amount of respiratory surface sufficiently to provide for the increased respiration demanded by the activity. In ciliated forms the cilia greatly increase the surface area and respiration is further assisted by the constant contact of the moving body with fresher water. Even in more complex animals, the common earthworm and the larvic of some insects for example, the whole external skin is sometimes the FOOD AND AIR TURNED INTO FLESH AND ENERGY 81 only respiratory surface. Such animals have only sluggish and weak motions however. Much increase in size and activity make certain demands on the surface of the body which unfit it for respiration. The hard covering of in- sects, crabs, and other animals necessary in connection with locomotion and for protection from injuries illustrate this. Again, while in a minute form like Amceba, the slight increase of surface attained by its protruded pro- cesses answers the increased respiratory needs, the sur- face of a large animal would fall far short of doing so, because, according to a familiar law of physics, the mass or bulk of a body increases as the cube of the diameter while the surface increases only as the square. There- fore the larger animals must have special respiratory sur- faces with special respiratory apparatus to move the air or water over these surfaces externally, and special cir- culatory apparatus to move the blood over them internally. Special respiratory surface is provided for in two ways. One is by the extension of a portion of the surface exter- nally; thus gills are formed. The other is by the exten- sion of the surface within the body in the form of tubes, as the trachez in insects, or of sacs, as the lungs in the vertebrates. Water-breathers have gills and air-breathers have trachee or lungs. In crayfishes or crabs the gills have the form of feather- like projections from one of the upper leg joints, and extend up into a cavity formed by a projection of the car- apace over the sides. It is interesting to note that these animals have a paddle for bailing the water out of the gill cavity, and that by it a constant current is kept flowing over the gills. Fishes breathe by means of gills, of which they have four pairs (fig. 45). These are placed on the sides of the head and consist of minute projections of the skin appearing as a fine red fringe. They are supported by bony or cartilaginous arches. The heart lies close to 82 FIRST LESSONS IN ZOOLOGY the gills and pumps the blood directly into and through them into vessels that carry it all over the body. The fish keeps a current of water passing over its gills. First it opens the mouth, spreading the gill covers, when the water rushes in, after which it closes the mouth drawing the Fic. 45.—Head of trout with gill cover bent Covers together so that forward to show gills. (From specimen.) the water is forced back over the gills. This operation is constantly repeated. If the mouth of an active fish like a sunfish is fastened open it will die, since it can no longer breathe. It must be added that the fins of most fishes no doubt aid somewhat in respira- tion since they are well supplied with blood and the skin on them is very thin. Insects are mostly air-breath- ers. Many, the bee and dragon- fly for example, show very great activity, demanding much oxy- gen. They have an elaborate system of tubes, called trachee (figs. 46, 47, and 48), which penetrate every part of the body, reaching in some cases every muscle cell. These open lic. 46,—Diagram showing tra- J : ; cheal system of a beetle; sf, to the air by means of pairs spiracles: ¢r, trachew. (After of small holes, called spiracles, Kolbe.) in most of the body segments. Air is made to come in FOOD AND AIR TURNED INTO FLESH AND ENERGY 83 and go out through these by an alternate contraction and expansion of the body readily seen in a bee or dragon-fly at rest. The walls of the trachee are in part supported by a fine spirally wound elastic thread which keeps the tubes always open to the air. The spiracles are often guarded by little tufts of hairs, which being oily prevent Fic. 47. Fic. 48, Fic. 47.—Diagram of trachee in head of a cockroach; note branches to all mouth parts and feelers; ¢, trachez or air-tubes. (After Miall and Denny.) Fic. 48.—Piece of trachea (air-tube) from an insect. (Photomicrograph by Geo. O. Mitchell.) water from entering easily, though oil will enter readily, and a drop of oil running over the spiracles will quickly kill an insect. Very fine dust will also choke up the spiracles and smother it. Some ‘‘ insect powders ’’ act in this way. The amphibians, which class includes frogs, toads, and salamanders, are water-breathers during their young life and in this period have gills. But early in the tad- pole stage there develops by growth from a point in the throat what is first a pouch, later a small pair of lungs, which are soon put in use. By the time the animal 84 FIRST LESSONS IN ZOOLOGY leaves the water the gills have disappeared and the lungs are well developed. A few of the amphibians, however, may retain the gills in addition throughout the adult stage. Such forms live in water or in very moist places. Moreover, most amphibians make use of the skin, thin and moist like that of the frog, for respiration, and thus have no necessity of great lung development. The air-bladder of fishes has the position of a lung, but is used ordinarily to regulate the weight of the body. Still in a few forms, the garpike for example, it serves sometimes as a lung. In the higher vertebrates the exterior skin surface is not adapted for respiration, which, together with the generally greater activity of these animals, necessitates a much greater development of the lungs. Thus instead of the two simple lung sacs of the frog the lizard has a com- plex double sac enlarged by tube-like extensions into the body cavity. This arrangement gives a much increased respiratory surface. In birds and mammals the extent of surface is immensely increased. It is estimated that the inner surface of a man’s lungs amounts to a thousand square feet in area, or one hundred times the external sur- face of the body. The windpipe gives off one large branch to cach lung; these branches divide again and again, the last divisions bearing on their ends very small sacs of thin membrane about which is clustered a net- work of capillary blood-vessels. Through the walls of these small sacs the oxygen and carbon dioxide pass. So far we have seen only how increase of surface is brought about. Accompanying this we find improved means for passing the air over the exterior and bringing the blood to the interior surface. A frog or salamander breathing quietly enlarges the mouth cavity by lowering its floor, and the air comes in through the nostrils; this air is then squeezed by the upward pressure of the floor of FOOD AND AIR TURNED INTO FLESH AND ENERGY 85 the mouth, the valves in the nostrils close, and it is thus pushed down into the lungs. The muscles in the walls of the body now contract and squeeze upon the air in the lungs, the nostril valves open, and the air is forced out. This method is gradually improved upon in the vertebrates until in the mammals we find a bony basket of ribs and sternum, the thorax (fig. 49), containing the lungs, with two sets of mus- cles between the ribs, which by their alternate contractions and expansions first elevate and extend the ribs, then lower and draw them in, thus enlarging and _ diminishing the thoracic cavity. We find further a muscular partition in the thorax, the diaphragm, separating it from the ab- heart, and diaphragm of mouse. dominal cavity. When the (f'0™ specimen.) diaphragm, which is convex on the upper side, contracts it lowers the floor of the thorax, thus enlarging the thoracic cavity; the muscles in the walls of the abdomen then contract and press upon the stomach, intestines, and liver, pushing up the floor of the thorax and so diminishing the thoracic cavity. Thus in two ways this is enlarged, and in two ways diminished. As it enlarges, the pressure of the outside air expands the elastic sacs of the lungs; as it diminishes, the air is pressed out again. Along with great increase of surface and great complexity of mechanism for moving the air goes, as has been pointed out, a perfecting of the circulatory apparatus for bringing the blood to the respiratory surface, and a pro- portionate complexity of the nervous system for producing and regulating the movements necessary. It is to be kept in mind, however, that the respiratory apparatus 86 FIRST LESSONS IN ZOOLOGY only brings oxygen to the respiratory surface, and before the real respiration at the tissue-cell can take place the oxygen must be carried by the blood to the cell. This process we shall later discuss under the head of circulation. Now having seen how animals get the necessary oxygen we may next inquire how they obtain and make use of the equally necessary substances to be oxidized and to build the body out of, that is, their food. How animals obtain and digest food. into the ways by which animals obtain and use food we may consider the processes under three heads, obtaining food, eating it, and digesting it. In obtaining food all the sense and motor organs are employed, that is, the instincts and ingenuity of the animal are brought into play as well as the parts of its body. In eating it the mouth is employed in mastication and the throat in swal- lowing. Digestion is carried on by liquids secreted by parts of the alimentary canal. In examining In the parts used for obtaining food we necessarily find the greatest range of variation on account of the great variety of food materials made use of. The food of animals consists of other animals or plants. Of the plants it may be leaves, stem, wood or bark, roots or fruit or seeds. That particular part desired may be deep in the ground, high in the air, or buried in a thick cover- ing of its own. The plant sought may grow in a marsh, on a plain, on a mountain, or immersed in the ocean. It may be fit for food at a certain season only. To get it the animal must have the necessary equipment of wings, or legs, claws, beaks, teeth, etc., as well as eyes, ears, and organs of smell, touch, and taste, besides some means for searching out the places where it grows, selecting the proper parts and deciding upon ways of securing these parts. Acts like these last are performed by the nervous system and arise from instinct or intelligence. FOOD AND AIR TURNED INTO FLESH AND ENERGY 87 In the case of carnivorous animals where prey is to be captured, the same adaptations must exist, being neces- sarily even more complex than those demanded for the securing of vegetable food. Some of the special adap- tations of animals for food-getting are described in Chapter XVII. But food once obtained and ready to be eaten appears under very many forms and there is accordingly great variety of structure among the parts employed in eating. Ameceba eats without a mouth. It extends any part of its soft body over the little plant or animal it feeds upon. In many Protozoa, however, there is a definite mouth- place, as in Paramcecium, where the food particles are gathered together in a little ball by the cilia, and then pushed through the body-wall. The body of the fresh- water hydra (see Chapter IX), incloses a digestive cavity, the mouth being but an opening to this. In the higher animals we find mouths arranged for cutting, filing, sucking, crushing, gnawing, grinding, chiseling, pierc- ing, sawing; in fact almost every device one could think of for working in wood, bone, shell, flesh, liquid, soft and hard material of many forms. The study of the mouth parts of animals belonging to one group shows how the same parts may take on such different forms as to make very different kinds of appa- ratus. For example among the insects, the bee (fig. 50), mosquito (fig. 51), tiger-beetle, dragon-fly (fig. 52), moth (fig. 53), and squash-bug, while exhibiting great variety of mouth parts show each the same pieces, but in each so changed in form as to make up a combination pe- culiar to it. Among birds there is not so great a range of difference; still, the various beaks and bills of chickens, cranes, sparrows, ducks, curlews, hawks, cross-bills, puffins, and horn-bills illustrate how one form may be adapted to many operations. Birds do not use the mouth 88 FIRST LESSONS IN ZOOLOGY for mastication. Where mastication is necessary there is an expansion of the alimentary canal called crop or craw, which acts as a reservoir for the hard seeds or grains, and further along the gizzard, which with its strong muscular wall and hard inner coat, assisted by the small stones picked up in eating, sufficiently grinds up the Mic, 50. Fic. 51. lic. 5§0.—Head and mouth parts of honey-bee; note the short trowel-like mandibles for moulding wax when building comb, and the extended proboscis for sucking flower nectar. (Much enlarged; from specimen.) Fic. §1.—Piercing and sucking beak of the mosquito (female) dissected to show its parts. (Much enlarged; from specimen. ) food. Among mammals the same large extent of variety in the mouth structure exists as among insects and birds. Compare the teeth and other mouth parts of a rat, beaver, cat, pig, horse, sheep, and man, noting how they vary in number, size, and form, and then consider how each is used in the process of cating. To understand the process of digestion some knowledge of the nature of food substances is necessary. In consid- FOOD AND AIR TURNED INTO FLESH AND ENERGY 89 ering the production of energy and making of body mate- rial we saw that the same substances provided for both. In fact whatever the form of food, animal, or plant, the elementary substances are the same, being conveniently classified into two great groups, organic and inorganic substances. Inorganic food substances are water and certain minerals of which common salt is one. Organic food substances are of three kinds or groups. The first group, called the Fic. 52.,—Mouth, with prehensile under lip, of young dragon-fly. (From Jenkins and Kellogg. ) proteids, of which the white of egg is an example, forms a large part of the tissues of animals; the second group is made up of the fats and oils; the third, known as the carbohydrates, consists of the starches and sugars. Now digestion consists in changing all these substances into soluble form so that they can be absorbed into the body, circulate with the blood, if there be any, and then pass into the living cells for their use. This change is accomplished by certain liquids called digestive fluids. The digestive apparatus varies like other parts of the ani- mal organism, being most simple in some forms and very complex in others. In Amceba the food particles are retained in spaces in the cell until they are digested. So in other Protozoa. The simple digestive cavity of the hydra has been referred to (fig. 54). In the polyps and jelly-fishes (see Chapter X), this cavity is extended, the digestive surface being much increased by partitions, FIRST LESSONS IN ZOOLOGY Worms (figs. 55 and 56), crabs, and_ snails Fic. §3.—Sucking proboscis of a sphinx have a definite alimentary canal with certain parts set apart for special processes. In the verte- brates the digestive apparatus varies from a relatively simple straight tube to the very long and complex alimentary canal of the cow (fig. 57). All these forms depend much on the nature of the food of the individual animal, and the processes necessary to turn it into body material. To illustrate what complexity of the digestive system may be reached let us consider somewhat in detail the structure of the ali- mentary canal of a small mammal a rabbit, for example. First is Fic. 54.—Diagram of sec- tion through a simple polyp, Odea, showing moth; in small figure the proboscis is digestive cavity 5 my shown coiled up on the under side of the mouth-opening ; al.c, ali- head, the normal position when not in use. mentary cavity, (After (One-half natural size; from specimen.) Parker and Haswell.) the mouth with its parts; the walls of the mouth are furnished with minute tube-like extensions or glands, FOOD AND AIR TURNED INTO FLESH AND ENERGY 91 which secrete mucus to aid the animal in swallowing dry substances. Other larger glands, the salivary glands, empty into the mouth, saliva being also necessary for the purpose of swallowing. Behind the mouth come the pharynx and gullet, which together make a _ tube with muscular walls which perform the movements of swallowing. Both pharynx and gullet are furnished with numerous mucous glands. The gullet leads to the stomach, an enlargement of the alimentary canal acting mainly as a reservoir. Its walls also are filled with small glands secreting gastric juice which makes proteid foods soluble, that is, carries on the proteid digestion. Next to the stom- ach is the small intestine, a very long tube in the first part-of which is ac- _ complished the digestion of starches and fats. Its walls are lined with numerous glands, and besides these, two very large glands, the pancreas and liver, pour into it large quantities of liquid. The pancreatic juice di- gests the starch and fat and also any left-over proteids. The liver fur- nishes the bile, but its functions being Fic. 55. — Common mainly other than digestive, they need not be discussed here. The walls of the small intestine fur- nish the principal surface for the absorp- tion of digested food. This surface is earthworm dissected to show alimentary canal, a straight and nearly simple tube through the middle. (Natural size; after Jordan and Kellogg.) greatly increased by millions of small projections called 92 FIRST LESSONS IN ZOOLOGY villi, in which are blood-vessels, and other absorbent ves- sels for taking up the digested food. The small intestine empties into the large intestine, which has an enlargement called the cecum. The large intestine and the caecum together form the last section of the alimentary canal and Fic, 56. Fic. 57. Fic. 56,—A flatworm (/7anarta) to show branched alimentary canal, a/c. (About natural size; after Hatshek. ) Fic. 57.—Alimentary canal of a cow; a, rumen (left hemisphere); 4, rumen (right hemisphere); ¢, insertion of ceso- phagus; d, reticulum; e, omasum; /, abomasum; , duodenum; / and 7, jejunum and Ay ileum, 7, cecum; 4, colon with its various convolutions; /, rectum; the whole canal about 150 fect long. retain the remaining food substances for some time to allow of more complete absorption of the digested foods. The alimentary canal of the rabbit, with all its folding and branchings into large glands and millions of small ones, furnishes a surface for secretion and absorption very many times the external surface of the body. In brief, the area FOOD AND AIR TURNED INTO FLESH AND ENERGY 93 concerned with the taking in of food as well as of oxygen is immensely increased in the higher animals. We have now to consider that process which has to do with carrying oxygen and food from the respiratory and digestive surfaces to all parts of the body. This process is the circulation, and the organs for performing it com- pose the circulatory system. How the blood circulates.—It has already been shown that increase of size and activity in animals necessitates blood and a means of circulating it through the body. The uses of the circulation are: to bring oxygen from the respiratory surface to every cell, to take carbon dioxide from every cell to the respiratory surface, to carry digested food substances from the absorbing surface of the alimentary canal to every cell, and, further, to remove from every cell the injurious and waste substances formed by its activity to where they may be either ex- creted from the body or otherwise disposed of. Circula- tion is accomplished by the moving of a liquid through a system of tubes and spaces channeling the whole body. In the very smallest and most sluggish of animals there is no circulatory system. In those which are of compara- tively large size and very active, and which therefore need a great amount of energy, much oxygen and food must be supplied and a large amount of waste substance is produced which must be removed. Here the circulatory system is found to be highly developed and to work with great efficiency. In Amceba, because of its small size and the constant flowing of the body-substance there is no circulatory sys- tem. In some Protozoa the contents of the body-cell seem to have a definite movement, but there are no such organs as heart and blood-vessels. In most animals we find blood and a system of tubes and spaces for it to circu- late in. In some, as the insects (fig. 58), only part of the 94 FIRST LESSONS IN ZOOLOGY circulatary system consists of definite tubes; these open into loose ill-defined spaces in the body-cavity. In such the blood is moved gradually throughout the animal, but not so definitely and quickly as in others where the blood runs in definite vessels. In the earthworm there is no such heart as in higher animals, but the blood- vessel along the dorsal line and some of its branches around the sides have muscular walls and ‘‘ beat’? by a wave of contraction running toward the head. In insects the dorsal blood-vessel beats in the same way, but generally more vigor- ously. In the young larva of a mosquito or nymph of a May-fly with transparent Fic. 58.—Diagram ; : of circulatory skin the beating can be easily seen under system of young le soy: dragon-y; inthe microscope. In molluscs there is a middle is the well-developed heart; it can be well seen chambered dor- , sal vessel or heart in the fresh-water mussel. The crustacea with single ar- alsq have a heart. This can be seen at tery; arrows in- ; : dicate direction Work in a water-flea under the microscope, of blood currents. ale i (After Kolbe.) OF CaN be readily demonstrated inacrab or crayfish killed with chloroform or ether. In vertebrates the blood circulates in a definite system of tubes through which it is pumped bya heart. The fishes (fig. 59) have the heart consisting of two parts, with muscular walls, a single auricle and a single ventricle. The auricle receives the blood pouring from all the tissues of the body through the veins. It contracts and forces the blood into the ventricle. This then contracts and drives it into a short vessel called the ventral aorta, which gives off a branch artery for each gill-arch. The gill-arteries divide up into capillaries in the gills, whence, after aeration, the blood is gathered by another artery and carried to the dorsal aorta, from which branch arteries FOOD AND AIR TURNED INTO FLESH AND ENERGY. 95 distribute it to the capillaries of the general body-tissues. From these it is gathered by the veins and carried back to the auricle to begin again. In the course of circu- lation the blood reaches every part of the body, picking up certain substances here, leaving others there, thus accomplishing the results already pointed out as the objects of the circulation. In the circulation of the higher vertebrates the most striking difference from that of the fish is in the structure Ss AE PRY CRE —- ae oS iS = Fic. 59.—Diagram of circulatory system of a fish; v, ventricle; a, auricle. (After Parker and Haswell.) of the heart, which adapts the circulation to lungs instead of gills, and in the more perfect control and regulation of the action of heart and blood-vessels by the nervous system. The circulation of a gilled frog tadpole is on the same plan as that of a fish. In the adult frog, however, there is no longer a circulation through gills but one through the lungs. Moreover, the adult has two auricles instead of one (fig. 60). Of these the right receives the blood from veins draining the tissues, the other blood from the lungs. All this blood, however, is thrown together into the one ventricle, from which, mixed as it is, it is sent out both to the lungs and to the tissues through arteries. In reptiles there are two auricles, as in the frog, and a partition partially separates the ventricle into halves (fig. 61), so that the blood coming from the tissues is kept 96 FIRST LESSONS IN ZOOLOGY partly separate from that out of the lungs. This separa- tion allows the blood from the lungs to be sent to the tissues without much mixing with the impure blood from the tissues. In birds and mammals the separation of the two halves of the ventricle is complete, the blood from the lungs being sent out unmixed to the tissues and that from the tissues returned without delay to the lungs. Fig. 62 gives the plan of the circulation in the mammals. ra la Yv viv Fic. 60.—Diagram of heart of Fic. 61.—Diagram of heart of amphibian; 7.a, right auricle; a reptile; 7,a, right auricle; Z.a, left auricle; v, ventricle. /.a, left auricle; 7,7, ventricles, (After Ritzema-Bos.) (After Ritzema-Bos, ) It shows how the blood is driven through the lungs by a special pump, the right ventricle, which is devoted to that purpose alone. It also makes clear how the blood is made to pass from the left ventricle to all parts of the body (fig. 63). It may be asked how, since the blood remains in vessels during circulation, the tissue-cells receive any- thing from it. The blood as such does not reach the tissue- cells. These are surrounded by a liquid, called lymph, which fills the spaces between them. The capillary blood-vessels run through this liquid and may not actu- ally touch the cells themselves at all, or at only a few points. The walls of the capillaries being very thin, however, the substances needed by the cells diffuse from the blood through the walls into the liquid and thence to the cells themselves. On the other hand, substances from FOOD AND AIR TURNED INTO FLESH AND ENERGY 97 the cells—carbon dioxide and other waste matters—diffuse into the liquid and from this to the blood through the capillary walls. In fact each tissue-cell feeds, like cer- tain one-celled animals, by absorption from a liquid Y 10 ThastiaaR I \\ Wj ® yw iS Ss FIG, 63. Fic. 62.—Diagram of the circulation of the blood in a mammal; a, auricles; 4, lung; /, liver; ~, portal vein bringing blood from the intestine; 7, ventricles; the arrows show the direction of the current; the shaded (From Kingsley.) vessels carry venous blood, the others arterial blood. Frc. 63.—-Heart of cat, dorsal view; a, right ventricle; 4, left auricle; c, right auricle; d, vena cava inferior; ¢, vena cava superior; /, aorta. (After Reighard and Jennings. ) medium, but by means of the circulation this liquid has a prepared food constantly brought to it. We may ask how the blood carries the oxygen. In the vertebrates part of the blood consists of little bodies called the red corpuscles. The color of these is due to a chemical substance called hemoglobin. This has the 98 FIRST LESSONS IN ZOOLOGY capacity of absorbing oxygen at the lungs and of giving Fic. 64.— Lower fore- leg and foot of cat, showing arteries (dotted lines), veins (black lines), and nerves (thin lines). (After Reighard and Jennings. ) it up to the tissues. The blood of vertebrates and of many invertebrates possesses a re- markable property that should be noticed, that is, of forming a jelly- like mass called a clot when a vessel is broken. In other words, it is able to close the opening with a solid plug made up of its own sub- stances. In higher vertebrates there is a very perfect regulation of the heart- beat, and of the narrowing or enlarg- ing of the small by the influence of the nervous system on their muscular walls. By this means and the peculiar structure of vein and arteries, and the use of valves, the flow of blood is nicely regulated to arteries the needs of each part of the body during its activity. CHAPTER VIII. HOW ANIMALS KNOW THINGS AND CONTROL THEIR MOTIONS. Thus far we have considered the mechanisms animals have for motion and for obtaining oxygen and food.