LIBRARY UNIVERSITY OF CALIFORNIA. BIOLOGY LIBRARY G Class BOOKS BY B. P. COLTON Physiology: Experimental and Descriptive. For High Schools, Normal Schools, and Colleges. 440 pages. Illustrated in colors. Physiology : Briefer Course. For High Schools. 400 pages. Illustrated in colors. Elementary Physiology and Hygiene. For grades below the High School. 320 pages. Illustrated. Zoology: Descriptive and Practical. PART I. DESCRIPTIVE. 376 pages. Illustrated. PART II. PRACTICAL. 234 pages. D. C. HEATH & CO., PUBLISHERS BOSTON NEW YORK CHICAGO ZOOLOGY DESCRIPTIVE AND PRACTICAL BY BUEL P. COLTON, A.M. AUTHOR OF " PHYSIOLOGY, EXPERIMENTAL AND DESCRIPTIVE," " PHYSIOLOGY ILLUSTRATED BY EXPERIMENT," " ELEMENTARY PHYSIOLOGY," "PRACTICAL ZOOLOGY"; , AND PROFESSOR OF NATURAL SCIENCE IN THE ILLINOIS STATE NORMAL UNIVERSITY I DESCRIPTIVE ^' Of THE UNIVERSITY OF BOSTON, U.S.A. D. C. HEATH & CO., PUBLISHERS 1907 THE VOICE OF THE SEA LIBRARY "The child holds a shell to his ear and hears the roaring of the sea. Do not yet tell him that the sound he hears is only the echo of the rushing of blood in his own head. In a higher sense the child is right. To him it speaks of the sea, its home. It brings the inland child a message from the vast ocean the distant the mysterious. It widens his narrow horizon; it takes him to the shore whose waters wash all other shores. He is no longer isolated, but put in touch with all the world. And this typifies the broad principle that one fact considered in all its relations involves the whole universe." COPYRIGHT, 1903, BY BUEL P. COLTON. PREFACE. THE PLAN. The general plan of the book is to introduce each of the larger groups of animals by the careful study of a typical repre- sentative. It is the aim to present a fairly complete picture of the life of this type, its place of living ; its manner of securing food ; its enemies and its means of protection ; its mode of locomotion ; the processes of digestion, circulation, and respiration ; its sense organs ; its development ; its relations to the plant world, to other animals, and to man. Following the study of the type is a general account of representative forms The characteristics of the group are given in summarized form. Each chapter closes with a tabular classification of the group. TIME FOR THE STUDY OF ZOOLOGY. Of the three seasons during which school is in session, winter is the least desirable for the study of animals. Many of the birds have migrated ; most of the insects have been killed ; those that remain alive are in close hiding and are hard to find, and still more so are their eggs, larvae, or pupae. A large number of animals are hibernating. Animal life is at low ebb. The choice of time, then, is practically limited to fall and spring. While there is an abundance of life in the spring and some forms can better be studied then, on the whole animal life is at its highest activity in the fall. Again, since spring is preferred for botany, the fall seems the best time for zoology. THE ORDER OF STUDY. The chief aim is to understand the lives of animals. To know them it is necessary to study them in relation to their surroundings. To do this to the best advantage they should be studied when at the hight of their activity. These points, then, must largely determine the order of study. For instance, if zoology is begun in the fall, one finds insects active and abundant. Many forms are laying their eggs to produce the generation of the following spring. 212402 iv Preface. They should be studied before the season of frosts. On the other hand, fishes can as well, or better, be studied later. Since the natural history point of view is prominent, the general principle regulating the order of study should be, " follow the season." The birds, too, should receive attention during the first part of the term, for many of them migrate early. It is not necessary, nor always desirable, to complete the study of one group before beginning another. Two lines of work can profitably be pursued on alternate days or weeks. P'or fall work, the order here given has been found satisfactory. But circumstances call for considerable variation ; it is not necessary to follow any given order with slavish fidelity. If the work begins in the spring, the teacher may prefer to begin with the crayfish, clam, fish, or frog. There are some advantages in beginning with the lowest animals and studying them in the ascending order. This gives the clearest idea of the natural sequence of the animal kingdom. Other things being equal, it would be better to study animals in their logical sequence, just as we prefer to learn historical facts in their chronological order. But there are very serious objections to this order. First, it involves the use of the microscope at the outset. This is impossible for many schools. Further, the use of the microscope is like a new language, which must be translated. Even if the student has a microscope and has mastered its technique, he still has difficul- ties. What he sees is very different from his previous observations. All our knowledge is knowledge of relation. Until the new is related to that already known, it means nothing. The very simplicity of the Protozoan makes it hard to understand If, however, the teacher decides upon this course, the work may begin with Chapter XVIII. ' By following the remaining chapters and then beginning with Chapter I, the ascending order will be followed with a few slight exceptions. But, as before stated, the teacher should not be tied down to any fixed order. Zoology is the study of animals. For most schools, the best time to study animals is when they can be most easily collected, for two reasons. First, it involves expense to keep them on hand to use at a later date. Second, and more impor- tant, the sooner they are studied after collection, the better. At this time some of the facts as to their source will appear, even if the students have not assisted in the collecting. The study of the home life and natural surroundings is of vital importance, if the student is to get Preface. v beyond morphology into the fields of natural history, ecology, and economic relations. THE PLACE OF NATURE STUDY. Many teachers of natural his- tory are accused, often very justly, of placing too high a value on the subject. The true teacher will try to see the real place of his subject in the course of study. Natural history cannot claim the highest place. Interesting as are the actions of animals, they cannot compare with the deeds of men. History is above natural history as man is above the other animals. But the student who has formed the habit of seeking the meanings of facts in natural history will carry this habit into the study of history. The study of natural history should come first, for children are interested in animals. The habits of observation and interpretation once formed will be carried through life and applied in every line of thought. To cultivate these habits should be the con- stant aim of the teacher. The study of animals especially lends itself to such training, because of the child's inherent interest in the subject, and because of the varied adaptations to ^eir surroundings that animals everywhere exhibit. THE INTERPRETATION OF NATURE. The study of the relations of animals to their surroundings is a constant investigation of cause. The student must ask why an animal has a certain color, form, or habit. He must first learn to observe the facts that come within the range of his experience. Next, he must seek an explanation of these facts. He must become possessed by the idea that every fact has a meaning, and that it" is worth while to think out this meaning. At first he must be helped ; but he is to learn that he must rely mainly on himself for the solution of the problems of animal life. CLASSIFICATION. It is highly important that the student learn how to classify animals ; that he commits to memory a system of classifica- tion is of doubtful value. To classify is simply to sort, or to arrange, things according to their likenesses. The child sorts his blocks; that is, he puts those of a kind together. Those of different kinds are separated. This is classification, a grouping according to resem- blances and differences. But the child cannot sort blocks unless he has them. Neither can the student classify animals unless he knows them. It is impossible to classify the unknown. vi Preface. As the facts concerning the different kinds of animals become known, they must be sorted and arranged according to some system. The basis of classifying animals is structure. Of course the beginner cannot go deep into anatomy, but he must know some of the more important facts of structure or else his attempt at classification is com- paratively useless. Since it is usually impracticable to study animals in systematic order, the student must learn to arrange his knowledge as he proceeds. This is not different from mental growth in other lines. Our experiences do not come to us classified. Just as an orderly merchant sorts his new goods, and arranges them on shelves with previously acquired articles of the same kinds, so the student must arrange in systematic order his ever increasing stock of knowledge. At the close of the volume will be found the classification of the animal kingdom according to Parker and Haswell, whose arrangement is considered the most authoritative of recent works. THE VALUE OF THE STUDY OF TYPES. Real knowledge comes through experience. What one learns through another is information. The teacher must distinguish between first-hand knowledge and second- hand knowledge. Now the number of animals that any student can examine is small in comparison with the number in existence. The study of the animal kingdom is greatly simplified by the fact that, with all the variety of animal forms, there are actually but few different plans of structure. One important part of the teacher's work is to select the best types for careful study. On the. foundation thus laid much infor- mation may be built. If one had never seen a Crustacean, he would get little from reading about Crustaceans. But, after studying a cray- fish, a fairly clear idea of a lobster or a crab may be obtained by read- ing, for a foundation has been laid in sense perception. The knowledge of a type may ba compared to a peg in a wall ; if it is driven in solid, it will hold many facts of information. The types selected, their number, and the thoroughness with which they are studied will naturally vary with the locality, season, the age of the student, the time allotted to the study, and various other circumstances. DEFINITIONS. The student should be taught to make definitions. By comparing a number of related forms, as suggested in the practical work on insects, the student should see what characteristics they have Preface. vii in common. Thus he is enabled to distinguish groups. Memorized definitions have comparatively little value. "A neat definition is a very attractive thing. It seems to offer the sum and substance of wisdom in portable form. But to understand it, to comprehend what it includes and what it excludes, the thoughts of the master must be gone over again in the mind of the disciple, and then he no longer needs the definition." But definitions, however made, are often mis- leading. The fact is that nature has not sharply and distinctly sepa- rated animals into groups. There are usually no -hard and fast lines between them. If we try to establish a dividing line, we almost always fi:^ ; t cutting across some intermediate forms. Since the groups of animals overlap, and gradually shade off one into another, it is better not to try to think of them as having definite boundary lines. We should rather consider each group as arranged about a type at the center. PRACTICAL WORK. It has been thought best to place the practical work in the latter part of the book. But this work should, of course, precede the assignment of lessons in the descriptive text. Effort has been made to correlate the two parts so that they may be used together to good advantage. The author is well aware that in many schools the facilities for field and laboratory work are very limited. He has, there- fore, thought best to err on the safe side and give rather full descrip- tions. But the teacher should see to it that the student himself solves as many as possible of the problems. The teacher may find help in the " Suggestions to the Teacher of Zoology," which is issued in pamphlet form by the publishers of this book. ECONOMIC IMPORTANCE OF ANIMALS. The common schools aim primarily at intellectual acquisition and training rather than at indus- trial application. Still, the economic side of the study of animals should be kept clearly in mind. The public has a right to demand that the knowledge gained in school shall have some practical value. The economic side, too, is one of the most interesting, and should receive attention for this reason, if for no other. This is a line of work in which collateral reading may be most profitably followed. There are many Reports of the Department of Agriculture which may be obtained free on application to the Department of Agriculture, Wash- viii Preface. ington, D.C. These pamphlets may serve as the nucleus of a reference library. These reports, and as many other books as the school can afford, should be accessible to the student, and he should be encouraged to use them freely. ACKNOWLEDGMENT. The manuscript, entire or in part, has been critically read by Professors M. A. Bigelow, Teachers College, Columbia University; H. Carman, State College of Kentucky; F. R. Lillie, University of Chicago ; T. H. Montgomery, University of Pennsyl- vania; M. M. Ricker, Burlington, Iowa; and J. M. Tyler, Amherst College. The manuscript has been corrected by Miss Chestine Gowdy, teacher of grammar, Illinois State Normal University. The proofs have been read by Professors M. F. Arey, State Normal School, Cedar Falls, Iowa ; A. C. Boyden, State Normal School, Bridge- water, Massachusetts; M. J. Elrod, University of Montana; J. W. Folsom, University of Illinois ; H. Carman, State College of Kentucky ; W. S. Jackman, University of Chicago ; H. S. Jennings, University of Michigan ; J. M. Johnson, Peter Cooper High School, New York ; S. J. Hunter, University of Kansas; Louis Murbach, Detroit High School; Frank Smith, University of Illinois; H. B. Ward, University of Nebraska. To all of these the author extends his most sincere thanks. Their criticisms have weeded out many errors ; but for those that remain they are in no way responsible. In most cases the sources of the cuts are indicated in the captions. About forty of the cuts" are original. The drawings of the clam were made by Mr. Frank J. George, now a teacher in the Philippines. Most of the other original drawings were made by Miss Esther Mohr. NORMAL, ILLINOIS, February 19, 1903. CONTENTS. CHAPTER PAGE I. BRANCH ARTHROPODA Class Insecta i II. BRANCH ARTHROPODA Class Insecta {Continued) . . 25 III. BRANCH ARTHROPODA 54 Class i. Myriapoda 54 Class 2. Arachnida 55 IV. BRANCH ARTHROPODA Class Crustacea 61 V. BRANCH ARTHROPODA Class Crustacea (Continued) . . 77 VI. BRANCH ANNULATA The Segmented Worms ... 87 VII. BRANCH MOLLUSCA Class Pelecypoda 102 VIII. BRANCH MOLLUSCA Class Gastropoda 127 IX. BRANCH MOLLUSCA Class Cephalopoda ... 138 X. BRANCH CHORDATA 148 Subbranch Urochorda . 148 Subbranch Vertebrata 151 Class i. Cyclostomata . 153 Class 2. Pisces 154 XI. BRANCH CHORDATA Class Pisces (Continued) . . .168 XII. BRANCH CHORDATA Class Amphibia 181 XIII. BRANCH CHORDATA Class Reptilia 196 XIV. BRANCH CHORDATA Class Aves 208 XV. BRANCH CHORDATA Classification of Aves . ... . 222 XVI. BRANCH CHORDATA Class Mammalia 246 XVII. BRANCH CHORDATA Classification of Mammalia . . . 256 XVIII. BRANCH PROTOZOA The One-celled Animals . . . 286 XIX. BRANCH PORIFERA The Sponges . ..... 307 XX. BRANCH CCELENTERATA 313 Class i. Hydrozoa 317 Class 2. Scyphozoa 323 Class 3. Actinozoa . 325 Contents. CHAPTER PAGE XXI. BRANCH ECHINODERMATA . . . . . . .331 Class i. Asteroidea . 331 Class 2. Ophiuroidea ....... 337 Class 3. Echinoidea . 338 Class 4. Holothuroidea 343 Class 5. Crinoidea 345 XXII. BRANCH PLATYHELMINTHES The Flatworms . . . 348 BRANCH NEMATHELMINTHES The Roundworms . . . 351 BRANCH TROCHELMINTHES The Rotifers . . . . 352 BRANCH MOLLUSCOIDA . . 353 XXIII. CLASSIFICATION OF THE ANIMAL KINGDOM .... 355 INDEX . . -359 ZOOLOGY: DESCRIPTIVE AND PRACTICAL. PART I. DESCRIPTIVE. CHAPTER I. BRANCH ARTHROPODA. CLASS INSECTA. Example. The Grasshopper. The Life of an Animal. In order to understand the life of any animal, try to get answers to such questions as these : Where does it live? How is it adapted to its surround- ings? What does it "eat, and how does it get its food? What are its enemies, and how does it escape them ? What is its chief mode of locomotion ? What is it doing most of the time ? What seems to be its main object in life ? What changes does it undergo in its growth ? Does it eat the same kind of food, breathe in the same way, move in the same way, or live in the same conditions dur- ing the different stages of its development ? How does it affect plant life ? What is its influence on other animals ? Is it useful, either directly or indirectly, to man ? Is it either directly or indirectly injurious to man ? Home Life of a Grasshopper. As indicated in its name, we find this insect on plants. So well does its color har- i Insecta. 3 monize with its surroundings that we often fail to see the grasshopper when it is right before our eyes. Even when we -have frightened a grasshopper, and watch its jump or flight, on going to the place where we saw it alight we do not always readily discover it. The plant on which the grasshopper rests serves both as food and as shelter ; it is its home, so far as it can be said to have a home. Food usually being abundant, the grasshopper moves about but little, and leads a rather sluggish life. Locomotion of the Grasshopper. The grasshopper has three modes of locomotion, crawling, jumping, and flying. The wings and legs are moved by the strong, white, striated muscles, which are situated chiefly in the thorax. Crawling. This is accomplished mainly by the first and second pairs of legs, the hind pair making fewer movements in the ordinary slow crawl. The hooked claws enable the grasshopper to retain a firm hold while crawling. Jumping. The length and strength of the hind legs fit the grasshopper for powerful jumping. The spines on the hind border of the tibia keep it from slipping. The Wings and Flying. The anterior pair of wings serve mainly as covers for the hinder pair, and their com- parative thickness and toughness fit them well for this use. The hinder pair of wings are much wider, being folded like a fan when not in use and wholly covered and pro- tected by the anterior pair. The hinder pair are more delicate in their texture, but still are sufficiently strong for their work in flight, being stiffened by the hollow veins which radiate through them. The grasshopper is crawling through the grass or resting quietly on stems and leaves most of the time, and is flying only a small part of the FIG. 2. EXTERNAL FEATURES OF A GRASSHOPPER, DORSAL VIEW. From Packard's Zoology. Insecta. 5 time. So we can see the fitness of having the flying wings folded compactly and placed close to the sides and guarded. The wings are kept from mutilation, and the whole insect is much less conspicuous than he would be with the wings outspread. Some grasshoppers fly high in the air and travel long distances. Respiration in the Grasshopper. The spiracles are shown in Fig. I ; two pairs of thoracic and eight pairs of abdominal openings. From these spiracles, tubes, FIG. 3. CROSS SECTION OF INSECT. a = Digestive Tube. called tracheae, run inward to a trachea extending length- wise on each side of the body. There is also a pair of dorsal and a pair of ventral air tubes. There are, then, six air tubes running lengthwise, in communication with the outside air through the spiracles, and connected with each other by branches. From these main tubes branches extend which subdivide, finely permeating every part of the body, even, to a limited extent, the legs and the larger veins of the wings (see Figs. 3 and 4). In addition to the air tubes there are two rows of air sacs, which add to the 6 Descriptive Zoology. buoyancy during flight. The work of respiration depends on the abdomen, as the thorax is rigid. The abdomen is made smaller by the action of its muscles, and expands again when they relax. Expiration seems to be accom- plished by active effort, and inspiration by elastic reaction, just the reverse of the breathing* process in man. Circulation in the Grasshopper. The circulatory system of the grasshopper is not highly developed. The only dis- tinct organ is the heart (see Figs. 3 and 4), extending along Dorsal air-tube Air sac FIG. 4. AIR TUBES AND AIR SACS OF GRASSHOPPER. From Hyatt's Insecta. the dorsal part of the abdomen. It is in the form of a tube, closed behind and open at the anterior end. It has several compartments, with valves, which allow the blood to pass forward only. There are also openings with valves at the sides, so that blood enters when the tube widens, and when it contracts the blood is pumped forward. The blood is colorless, or slightly yellowish or greenish, and fills all the otherwise unoccupied spaces of the body, thus bathing all the tissues. The low development of the cir- culatory system is compensated for by the high develop- Insecta. 7 ment of the respiratory system, which conveys air to all parts constantly. Thus the insect is enabled to exert its muscles powerfully and rapidly, and in general maintain the high degree of activity which is so characteristic of the group. As might be expected, the temperature of insects is high, compared with that of invertebrates in general, being several degrees above that of the surround- ing air. The Grasshopper's Food and Digestion. Eating is a large factor in the life of the grasshopper. We see it on many kinds of plants, gnawing leaves and stems with its short, strong, laterally moving jaws. The narrow gullet extends upward to about the center of the head, then turns pos- teriorly and dilates into the crop, which runs lengthwise in the thorax. At about the beginning of the abdomen the crop narrows somewhat and becomes the stomach. Alongside the crop are the branched salivary glands, whose ducts run forward to empty into the mouth. At the place where the crop joins the stomach it is surrounded by a set of six or eight double-cone-shaped pouches extending par- allel to the digestive tube itself. These bodies are the ceca. They are hollow and communicate with the cavity of the digestive tube by openings. The ceca secrete a liquid that aids in digestion ; they increase the surface of the digestive tract and probably are largely concerned in the work of absorption. The stomach extends about half the length of the abdomen. Its posterior limit is marked by a large number of slender tubes, the urinary tubes, which enter the digestive tube at the juncture of the stom- ach and intestine. The last part of the intestine is some- what dilated, forming the rectum, which, in turn, terminates in the anal opening at the upper part of the end of the abdomen. 8 Descriptive Zoology. Absorption in the Grasshopper. The absorbed food ma- terials from the digestive tube pass directly into the general blood of the body cavity, there being no special set of tubes as in man and vertebrates generally. The Excretory System of the Grasshopper. The urinary tubes (formerly called the malpighian tubes) extend into the blood of the body cavity and extract from it essen- tially the same materials as the kidneys of the higher animals do. As above stated, these tubes empty into the intestine. The Nervous System of the Grasshopper. The nervous system of the grasshopper is essentially like that of the crayfish (Fig. 49), consisting of a row of ganglions con- nected by a nerve cord lying along the floor of the body cavity. It really is composed of two rows of ganglions, each connected by its own chainlike cord ; but usually the two corresponding ganglions unite, forming what seems a single ganglion. In the grasshopper, the nerve cord is plainly double throughout the head and thorax, while in the abdomen the cord appears single. There are ten gang- lions, two belonging to the head, three in the thorax, and five in the abdomen. The first ganglion, often called the brain, is above, or rather in front, of the gullet. From this the two strands of the nerve cord pass to right and left of the gullet and again unite in the second, or infra-esophageal ganglion, forming the nerve ring (" nerve collar ") found in arthropods and mollusks. The Senses of the Grasshopper. It is very evident that the grasshopper can see and hear, and it does not require extended experiment to show that it has also the sense of touch. The large compound eyes, composed of many facets, give a wide range of vision ; but the sense of sight Insecta. is probably not very acute, especially at any considerable distance. The clear membrane on the first segment of the abdomen is the tympanum of the hearing organ. The antennae are the chief or- gans of touch. The Enemies of the Grass- hopper. Probably birds are the most formidable enemies of the grass- hopper. The grasshopper usually becomes aware of the approach of an enemy through sight or hearing, and ordinarily escapes by flight or by jumping. They sometimes escape by simply dropping to the ground. The grasshopper is largely protected by his resem- blance in color to that on which he habitually rests, some forms being usually on plants, while those that stay much of the time on the ground are more of the color of the soil. The posi- tion while on plants, parallel to the stem, makes them less conspicuous than they would be otherwise. Grass- hoppers are often subject to injury by parasites, especially certain red mites which are often to be found under the IO Descriptive Zoology. bases of the wings. They are often destroyed in large numbers by the growth of a parasitic fungus in their bodies. Every boy knows that when the grasshopper is captured he ejects from the mouth a dark liquid secreted by the crop. This is probably a means of defense. Sounds made by Grasshoppers. Sounds are produced by the males only. Some grasshoppers make the noise by rubbing the bases of the legs against the bases of the outer wings. Others, while flying, rub the under surface of the base of the outer wing over the upper surface of the base of the inner wing. The katydids and crickets make the sound, while at rest, by rubbing the wings against each other. Colors of the Grasshopper. Although the grasshopper is decidedly inconspicuous when at rest, on account of the protective resemblance in color, yet it is to be ob- served that in some species the inner wings are con- spicuously colored, making the insect very noticeable during flight. Development of the Grasshopper. The ovaries occupy the upper part of the abdomen of the female. When full of ripe eggs they take a good share of the space in the abdomen. The oviducts extend down and back, opening between the sharp points at the end of the abdomen. These four sharp points together form the ovipositor. In lay- ing the eggs the female presses the tips of the four points close together, which makes a strong and fairly good digging tool. This is thrust into the ground and the points are then separated, and by repeating this a hole is made, into which the eggs are introduced, passing out between the guides. The egg hatches out into a little grasshopper resembling the parent, but lacking wings. Insecta. ii After a time rudimentary wings appear. In all such cases as this, where the young are hatched in essentially the same form as the adult, the development is said to be direct. Injury done by Grasshoppers. Ancient history records plagues of locusts. (The name "locust" is the proper one for our common grasshopper.) And in modern times and near-by places there have been migrations of locusts in such numbers that they have darkened the sky, and, light- ing everywhere, have devastated the land by eating almost FIG. 6. GRASSHOPPER LAYING EGGS. From Hyatt's Insecta every leaf and tender stalk of grass, crops, and trees in garden and field. The Rocky Mountain locust, migrat- ing eastward, almost produced a famine in Kansas and Nebraska, and created terror beyond the limits of its actual ravages. But, fortunately, the young hatched in the lower states are not healthy, and die prematurely ; hence the plague has not spread so extensively as it threatened to do. Packard says that the Rocky Mountain locust, within a period of four years, inflicted a loss of $200,000,000 on the farmers of the West. 12 Descriptive Zoology. ORDER ORTHOPTERA. The Orthoptera. We have selected the grasshopper as 'the best available type of the class Insecta and also of the order Orthoptera. The word Orthoptera means straight - winged, probably in allusion to the mode of folding the hind wings. The first pair are thick- ened, serving as a cover for the second pair, which are folded when at rest. The mouth parts are fitted for biting. The de- velopment is direct. Protective Resemblance. The green grasshoppers, es- pecially the katydid, are note- worthy for their resemblance to leaves, both in color and form. The walking stick (Fig. 7) so closely resembles a twig that it is seldom discovered by casual observers. These in- sects afford fine examples of the advantages of protective resemblance. The green grasshoppers have a windowlike membrane on the FIG. 7. A WALKING STICK INSECT tibia of each fore leg that is (Diapheromerafemorafa) ON TWIG. supposed to be an organ o f From Jordan and Kellogg' s Animal Life. , hearing. Classification of Orthoptera. The families are : the short- horned grasshoppers (locusts), which we have studied ; Insecta. 13 the long-horned grasshoppers (usually green), including the katydid ; the crickets ; the cockroaches, including the "croton bug," so common about water pipes; the walking sticks ; and the mantids. ORDER ODONATA. The Dragon Fly. The dragon fly has a long, straight abdomen, and large eyes. The two pairs of net-veined wings are alike in texture and nearly of the same size. The wings are never folded, but when at rest are held out at right angles to the body, ready for instant use. There is a pair of strong jaws, which are nearly covered by the large under and upper lips. The dragon fly feeds on in- sects, which it catches on the wing, being one of the swiftest and strongest flying of insects. Dragon flies are most abundant in marshy places, where they may be seen flying over the water or perched on a leaf or stem above the water, on the alert for a passing mosquito or other small insect. The females lay the eggs in the water, and may often be seen hovering over the water with the tip of the abdomen dipping beneath the surface. . An egg hatches into a form called a nymph, with strong jaws. It immedi- ately begins to prey upon other insects and larvae that it finds. When it has attained its growth it crawls up the stalk of some water plant, splits along the back, and the dragon fly emerges, leaving the empty skin still clinging to the stalk. The development is here also called direct. While living in water the larva breathes by taking water into the hind part of the digestive tube. Other dragon fly larvae have rudimentary gills. Some of the smaller dragon flies, when at rest, place the wings close together, just above the body. These are called damsel flies. Dragon flies are 14 Descriptive Zoology. also called darning needles, devil's needles, snake feeders, snake doctors, spindles, and mosquito hawks. In the FIG. 8. DRAGON FLY AND MAY FLY. From Hyatt's Insecta. Northern states children and ignorant adults believe that these insects sew up people's ears, and in the South the Insecta. 15 same classes think they bring dead snakes to life. It is easy to see how these stories arise. The long abdomen is supposed to hold a correspondingly long sting ; while its mode of laying eggs (people not knowing what it is doing) gives it the name applied in the South. The name mos- quito hawk is the most significant of its life and habits, for it has no sting, and is entirely harmless ; but, on the other hand, it benefits man by destroying mosquitos and other insects. Characteristics of Odonata. The dragon flies represent the order Odonata. The chief characteristics of the order are : wings net-veined, the two pairs equal or nearly so ; mouth parts fitted for biting ; abdomen long and slender ; development direct. COMPARISON OF GRASSHOPPER AND DRAGON FLY. GRASSHOPPER. DRAGON FLY. On land Home Over water Plants Food. Insects Numerous Enemies Few Strong for jumping Legs . . Weak, merely for perching Two pairs Wings, number . Two pairs First pair thick Wings, texture of .... Both pairs gauzy. Fold close to body . 1 Wings, position, j Extended at right angle First pair covering 2d f resting (..... Not overlapping Crawl through grass .} . f . . . . Dart after insects r Position enables to \ Elude observation . . J I Exposure less dangerous Adaptation to Mode of Life. In addition to the above tabular representation of some of the most striking differ- ences between the grasshopper and dragon fly, let us consider what characteristics each has that fit it for its particular mode and place of life, and which unfit it for 16 Descriptive Zoology. the mode of life of the other. Let us suppose that they trade places. It is not unfair to make this supposition, for they are not extremely unlike. Both have strong biting jaws, two pairs of strong wings, and a long abdomen. In the first place, let us suppose that the dragon fly can subsist on vegetable food, and that it takes up its life as a grasshopper. It finds its long, projecting wings in the way. They not only hinder it as it attempts to crawl into narrow places, but are apt to be torn, for, though strong, their texture is delicate. So it will naturally turn the wings back alongside of the body, and for compact- ness will probably let one pair rest upon the other. It will further protect them if the outer wings become harder and tougher, but this change will be something of a sacrifice in flying power. Again, when the wings are thus folded, the insect covers less area and is less conspicuous and therefore more likely to elude the eyes of birds o.f other enemies. Its legs, which are light and weak, having been used merely for support, need greater strength to enable it to crawl and jump. The eyes are not required to be so keen and naturally may become smaller, and as it leads a lazier life it becomes more corpulent and^ clumsy. To make up for the loss of flying power in the front wings, the hinder ones become wider ; this necessitates their being folded when at rest in order that the narrower front wings may completely cover them. Let us now consider how the grasshopper would fare in the endeavor to lead the life of the dragon fly. In the first place, the grasshopper lacks the flying power requisite to capture lively little insects on the wing It must have both pairs of wings developed for active use ; and it can afford to do this, as it does not need to have the front pair Insecta. 17 thickened, as in its situation covers are not needed. It should have wings constantly poised, ready to dart in- stantly after its prey. There is no objection to having the wings continually spread, as it lives in open spaces and does not have to crawl through grass and twigs ; and the increased area due to the spread does not especially endan- ger it by making it more conspicuous, since it has compara- tively few enemies. The body is too heavy, and it must " train down " until it can handle itself better. The legs are too heavy, especially the hind pair ; and, as it uses them very little except to perch upon a leaf or twig, waiting for something to turn up, this matter takes care of itself, for any unused organ is likely to dwindle away. It needs keener eyes, for it no longer feeds on plants which are sure to stay in place while it crawls upon them ; it is another matter to discern small insects at some d.*- tance. So it develops better eye power to discover its food, as well as better wing power to overtake it after seeing it. It had fairly good jaws before, but they become some- what enlarged and better adapted to the new work. The enlargement of the jaws and the eyes make the whole head bigger than it was before. Of course insects do not trade places in this manner; nor does any insect suddenly change its habits. But we can easily imagine that these two forms have descended from the same ancestors and have gradually grown dif- erent, each becoming fitted for the situation in which it is placed. It is no longer supposed that all the forms of life we now see on the earth have been distinct from the begin- ning, for we see evidences that many forms have arisen by the increase in numbers which establishes competition, and which in turn has compelled dispersion and forced 1 8 Descriptive Zoology. adaptation to new surroundings and a gradual advance- ment to changed conditions of life. ORDER HEMIPTERA. The Giant Water Bug. This is the largest of the bugs, being two and one half inches long. It lives in the water of our lakes and rivers, but was not very generally known until electric lights became common. The light attracts them, and they are frequently found where they have fallen under the lamps. Consequently many people call them FIG. 9. GIANT WATER BUG. From Hyatt's Insecta. the "Electric Light Bugs." They are more- abundant in river towns that are lighted by electricity, and a good way to collect them is to look for them under the lamps late in the evening. By preserving them in alcohol enough may be ac- cumulated to supply a class. They serve admirably to show the chief characteristics of bugs, and are large enough to dis- sect if the student wishes to learn the internal structure. The head is relatively small and the neck is not con- spicuous. The prothorax is large and broad. The outer wings are narrow in front, being separated by a triangular elevation of the mesothorax, called the scutellum. Then Insecta. 19 for a short distance the two outer wings meet in the middle line ; beyond this the wings are wider and overlap each other. The hinder part of the wings is much thinner than the front part. The inner wings are much thinner and are folded. The mouth parts are united to form a strong pierc- ing and sucking tube, which is bent back under the head, between the bases of the front legs. The features thus far described are common to nearly all bugs. But while the majority of bugs live in the air, the water bug lives under the water most of the time, though it can, and sometimes does, come out and fly about. To fit it for swimming under the water the body is flat and boat-shaped; the second and third pairs of legs are flattened, especially the tibia and tarsus, making admirable paddles. The front legs are of no use in swimming, but are used in grasping. The water bug hides under leaves and sticks in the water, and when an unwary insect, small fish, frog, or tadpole comes near, darts out, seizes it with its powerful fore legs, and kills it by piercing it with its sharp beak. It then sucks its blood, having no jaws for chewing solid food. The entomologists do not describe any poison glands in these insects, but it would appear that they have a poison- ous effect, since they seem to kill their victims so quickly ; and since this and numerous other bugs, some aquatic and some not aquatic, inflict painful wounds on man. In fact, the collector who is gathering minnows in a net is often bitten by aquatic bugs, and sometimes the hand and arm become painfully swollen as a result. Water bugs may be seen coming to the surface, where they project the tip of the abdomen into the air. They breathe through the anal pair of spiracles. In attempting to spread the outer wing, one usually meets difficulty, the wing seems to be caught. There is an in- 2O Descriptive Zoology. genious catch, consisting of a little projection or hook on the side of the thorax, that catches into a groove in the under surface of the front edge of the wing. There are two forms of water bugs common. Belostoma americanum has a groove in the femur of each front leg, into which the tibia shuts like a knife blade into a handle. The other form, Benacu s gt iseus, lacks this groove. The Squash Bug. Although smaller than the giant water bug, the squash bug has the advantage of being more abundant. If the former cannot be obtained, the latter should be studied. Like the water bug, it has a small head with a sharp beak, bent back under the head and thorax. The outer wings, too, have a thickened base, with the thin hind portions of the hind wings overlapping each other. The thinner inner wings are folded lengthwise. The legs are adapted to crawling. The prothorax is large and triangular. On the under surface of the thorax are glands which secrete an ill-smelling liquid. This is a rather common characteristic of Hemiptera, and brings the "bugs " into disrepute. This is a further reason why we should not use the term "bug" indiscriminately for the term "insect." It is incorrect, and as unfair as it would be to designate all mankind by the name of one of the most disagreeable tribes of savages that could be found. As is well known, the squash bug lives upon plants, suck- ing their juices through its strong, piercing beak, doing con- siderable damage, especially to plants of the gourd family. The eggs are laid on the under surface of the leaves about the first of July, and in August the young may be seen with the wings in all stages of development. The Cicadas. These insects are often improperly called "locusts." Probably they are best known by the shrill SQUASH BUG FIG. 10. SQUASH BUG, STRUCTURE AND DEVELOPMENT. at, antenna ; la, labium ; mx, maxilla ; oc, simple eye ; su, sucking tube. From Hyatt's Insecta. 22 Descriptive Zoology. sound made by the males. Under the abdomen of the males are two circular disks. Under these is the appa- ratus by which the sound is produced. Both pairs of wings are membranous, the hinder pair being much the smaller. The larva is a grublike form which lives under the ground, sucking the juices from the roots of trees. When ready to appear in the upper world, it crawls up the trunk ; and while it still clings to the bark its back splits open, and the winged insect emerges, leaving FIG. ii. CICADA: HARVEST FLY. From Hyatt's Insect a. the empty skin adhering by the claws. Here the shed skin may remain for weeks, until washed off by the rain or brushed off by a passing animal. The dogday harvest fly (Fig. 1 1) has a very broad head with eyes projecting at its angles, and is rather greenish. His shrill sound is suggestive of the dry, hot, August mid- day. The periodical cicada (the correct name for what is usually called the " seventeen-year locust") spends from thirteen years in the Southern form to seventeen in the Northern in the larval state. This cicada is distinctly nar- rower-headed than the summer cicada, and is darker in color. J nsecta. Order Hemiptera. Among the many exceedingly interesting He- miptera we may briefly mention the chinch bugs, so well and so unfavor- ably known, and the plant lice, which are so common on many plants, especially on house plants. Noticeable among the plant lice is the FIG. 13. PLANT LOUSE, WING Natural size. LESS LARVAL FEMALE. FIG. 12. PLANT LOUSE, ADULT WINGED FEMALE. From Hyatt's Insecta. On maple On osage orange FIG. 14. MAPLE SCALE INSECT. From Hyatt's Insecta. 24 Descriptive Zoology. grape phylloxera, so injurious to the grapevine. The scale bugs, or bark lice, are very injurious to trees ; some of them are among the worst y pests of the fruit grower, and tax his utmost ingenuity to prevent their spreading. The females are scalelike, and sometimes to be seen project- ing from beneath the scale is the cottony egg cluster so frequently observed on maples. Two kinds of bugs are worthy of mention as useful to man, the cochineal insect, furnishing a dye, and the lac insect, from which we get shellac. Lastly we refer to the parasitic Hemiptera, such as the vari- ous forms of lice, bedbugs, etc. Most of these forms are very degen- erate in their structure, having lost their wings as a result of their parasitic habits. Characteristics of Hemiptera. The mouth parts form a piercing and sucking tube ; the prothorax is prominent ; fore wings often thickened at the base ; many are ill-smell- ing ; development direct. ORDER NEUROPTERA. The order Neuroptera is a small order. The only ex- ample here presented is the ant lion (Figs. 15 and 16). FIG. 15. ANT LION, ADULT. FIG. 16. ANT LION, LARVA. From Hyatt's Insecta. CHAPTER II. BRANCH ARTHROPODA. CLASS INSECTA (Continued}. ORDER LEPIDOPTERA. The Monarch, or Milkweed, Butterfly. This common butterfly is of a brown color, with black veins and wing borders. There are about two rows of white spots in the black border. This butterfly has a wing spread of about four inches. The larva is greenish yellow, with distinct bands of shiny black, and feeds on milkweeds. The chrys- alid is suspended by the tip, as shown in Fig. 17. One of the most noticeable features of the butterfly is the presence of scales on the wings and body. The scales are modified hairs, and on the body they are slender. The scales shed water, strengthen the wing, and serve as an ornament. The wings are large, and in flying act together as one wing, the wing motion being slow. Another distinctive character is the long coiled sucking tube by which the butterfly sucks nectar from the flowers. When not in use, this tube is coiled like a watch spring and concealed between the labial palps. The sucking tube consists of the two maxillae, much lengthened and each grooved along its inner surface, so that when the two are closely applied to each other they form a tube. The man- dibles are but slightly developed. In September or October great swarms of these butter- flies may be seen, and this is a good time to collect them. 25 26 Descriptive Zoology. At night they settle on trees, hanging in great clusters from the leaves. It is not easy to see them at such times. FIG. 17. STRUCTURE AND DEVELOPMENT OF THE MONARCH BUTTERFLY. From Hyatt's Insecta. They look like dead leaves. In the morning, when they are chilled, they may be taken in a net. Insecta. 27 The Cabbage Butterfly. One of the easiest of the butter- flies to capture and to rear in confinement is the cabbage butterfly. It is white or slightly yellowish above and yellowish below. Both sexes have black tips on the an- FIG. 18. CABBAGE BUTTERFLY, MALE. FIG. 20. CABBAGE BUTTERFLY. a, larva, b, pupa. FIG. 19. CABBAGE BUTTERFLY, FEMALE. From Hyatt's Insecta FIG. 21. CABBAGE BUTTERFLY. Pupa. terior wings ; the male has a round black spot near the outer border of each wing, while the female has two spots on each anterior wing. In the early fall, watch the female laying eggs on cabbage leaves ; gather some of the leaves and watch the larvae come out of the eggs ; feed the larvae till full grown ; keep the chrysalids till the butterfly ap- pears. Describe all the changes and note the dates of all the moltings and transformations. 28 Descriptive Zoology. The Hawk Moth. This moth is well known by its habit of poising like a humming bird over the flower from which it is extracting the nectar by means of its long sucking tube. It is also called the humming miller, or humming bird moth. The hawk moths have long, sharp-pointed wings and strong powers of flight. Their larvae are usu- ally large green " worms," one of the most common being the so-called tomato worm. The pupa is often plowed up in gardens, and is distinguished by the tongue case, which is bent around to one side of the body, like a pitcher handle. The hawk moths usually fly at twilight. The hawk moths are also called sphinx moths, from the fact that the larva often rests for a long time with the anterior end held erect. DIFFERENCES BETWEEN MOTHS AND BUTTERFLIES. BUTTERFLIES. MOTHS. 1 . Day-flying, usually. I . Night-flying, usually. 2. Wings erect when resting. 2. Wings sloping when resting. 3. Antennae knobbed. 3. Antennae not knobbed. 4. Pupa a chrysalid. 4. Pupa (often) in a cocoon. Development of Lepidoptera. The egg hatches into what is commonly called a " worm." But no true worm has jointed appendages, while in these larvae each of the first three segments back of the head bears a pair of jointed legs. These three segments become the three segments of the thorax. In addition to these legs the caterpillar, as it is usually called, has several pairs, commonly five, of soft, fleshy legs on segments farther back, almost always a pair on the last segment. These prolegs have a sort of cleft at their ends by means of which they aid in crawling. Some caterpillars are smooth, others are densely hairy. FIG. 22. HAWK MOTH OR SPHINX MOTH, ADULT. From Hyatt's Insecta. Larva of another species. 30 Descriptive Zoology. The larvae eat voraciously and grow rapidly, molting sev- eral times before reaching full size. When ready to trans- form, the butterfly larva assumes a harder coat, commonly ornamented with silvery or gold markings (hence such a pupa is called a " chrysalid "), while the larva of the moth may spin a cocoon of silk, adding to it the hairs from its body, though some moths have a simple, dull-colored pupa which is buried in the ground. The larva has a silk gland which opens on the under lip, though many larvae spin little or none, some making one or two loops to support themselves when changed to chrysalids, alongside or under some protecting cover, such as a limb, fence-board, etc. It should be noted that the larvae have strong, laterally mov- ing jaws, and eat greedily, subsisting on solid food, whereas the adult is a dainty eater, and lives on liquid food, which it takes through the sucking tube. It is common to speak of the Lepidoptera as undergoing a " complete " meta- morphosis, while the grasshopper is said to have an " in- complete " metamorphosis. But as the development of the locust is just as complete as that of the butterfly, we should call the development of the grasshopper " direct," and that of the butterfly "indirect." Kinds of Lepidoptera. The butterflies are generally most conspicu- ous, as they fly in the daytime, but many of the moths are very beauti- ful. One group of butterflies are called from the form of their wings the swallow-tails. Though we associate the word " butterfly " with warm weather and sunny days, one species, the White Mountain butterfly, is found only high in the mountains, and the writer has been delightfully surprised to find these beautiful creatures above "timber line," near snowbanks, on the chilly mountain tops. Perhaps most noted among the moths is the silkworm, a native of China. But we have a number of native American silkworm moths ; of these the Cecropia and Polyphemus are perhaps best known. The larva of the codling moth is often found in apples. There is a large Insecta. 31 number of related moths whose larvae roll leaves, and are known as "leaf rollers." The ''measuring worms" are larvae of moths. Last, but not least in importance, is the clothes moth, which departs from the usual custom of living on vegetable food. Mimicry. The viceroy butterfly, which is sometimes eaten by birds, is protected by its resemblance to the ined- ible monarch butterfly. This is a case of mimicry. FIG. 25. THE MONARCH BUTTERFLY. FIG. 26. THE VICEROY BUTTERFLY, WHICH MIMICS THE MONARCH. From Kellogg's Zoology. General Characters of Lepidoptera. The moths and butterflies have two pairs of scaly wings, which are large and slow in motion. The parts of the body are distinct. 32 Descriptive Zoology. The long, coiled sucking tube, composed of the two max- illae, is a noticeable feature. The legs are small and weak, some forms having but two pairs, others having the 'anterior pair but not using them. ORDER DIPTERA. The House Fly. The house fly has but one pair of developed wings, the second pair being represented by a pair of bodies resembling pins, that is, consisting of a threadlike stalk with a knob at the end. They are called balancers ; their function is supposed to be sensory. When the fly is at rest the wings are extended backward and held horizontally over the back, lapping over each other at the inner borders, but are not folded, in the strict sense of that term; that is, are not thrown into folds, as are the inner wings of the grasshopper. The mandibles and maxillae are rudimentary, and the proboscis is composed mainly of the labial palps, which are developed into broad plates, which are thus adapted not only for lapping but also for rasping. They cannot bite, though they often light on the human skin to lap up the perspiration. The wing movements are very rapid, making as many as 330 vibrations in a second. The sound produced by flies is mainly made by the vibrations of the wings; but when the fly is held by the wings, there is still heard a faint buzzing noise, and this is supposed to be due to the pas- sage of air through the spiracles. Development of the House Fly. House flies lay their eggs in stable manure, each female laying about 150 eggs. In favorable weather, the eggs hatch in about one day. Inead Horse fly FIG. 27. HORSE FLY, STRUCTURE AND DEVELOPMENT. at, antenna; la, labium; md, mandible; mx, maxilla. From Hyatt's Insecta. 34 Descriptive Zoology. The legless larva is called a maggot. After living in this state about a week, it becomes a pupa, remaining in its old larval skin, which is called a puparium. (See Fig. 27.) In a week more it emerges as a fly. There may be, therefore, ten or a dozen generations in a single summer. A small number live over winter, hiding in crevices in walls and similar places. House flies are worse than mere nuisances, they are spreaders of disease. On the other hand they do much good as scavengers. How Flies Crawl. The fly has many little hairlike pro- jections on its feet. These secrete a sticky substance from their ends, by means of which the fly adheres to smooth walls and ceilings. Other Kinds of Flies. The stable flies closely resemble the house flies, but have a sharp, piercing sucking tube. They sometimes rind their way into houses, especially on warm, rainy days in the fall. On the other hand many of the flies seen about stables are house flies. The horseflies are well known, the most common being known as the "greenhead"; a still larger form is dull black, and in the West is called " bulldog, 11 from its size and persistency ; still smaller than either are those with banded wings, and these usually have the wings spread wider so that the fly looks FIG. 28. THE BEE KILLER. triangular; some of these are called u deer flies. 11 It is a surprise to find r rom Hyatt s Insecta. the big black horseflies abundant and annoying in the cold air of the high tops of the Rocky Mountains. Among the forms that annoy man and beast are the black flies, or midges, often swarming in the Adirondacks. On account of their smallness the Indians call them " no-see-ems. 11 To guard himself against these pests the hunter and the fisher often anoint the face and the hands with a mixture of tar and oil of pennyroyal. Insecta. 35 Every one has noticed the big fly that occasionally is found in houses, as it attracts attention by its loud buzzing and its bluish abdomen. It is the blowfly, that lays its eggs on meat. It is a disgusting sight to behold flesh " alive with maggots, 1 ' but when one reflects he sees Breathing tubes Pupa. Larva. FIG. 29. DEVELOPMENT OF THE MOSQUITO. what a wise provision of nature it is that such decaying matter should be so promptly and effectually disposed of. Let the hunter sit down to eat his lunch of biscuit and meat in any part of the Rocky Moun- tains, and the chances are that before he has finished the blowflies will have discovered the presence of flesh, and come buzzing around him. The botfly lays its eggs on the hairs of horses 1 fore legs and shoul- ders. The horse gets them into the mouth from scratching itself by biting, and swallows them. The larva attaches itself by means of hooks to the inner wall of the stomach. Later it passes on through the intes- tine, and the pupa completes its development in the dung. " Skippers " are the larvae of black flies, about half the size of the house fly, that lay their eggs on cheese, ham, and bacon. Bills received from packing houses often specify that they do not guarantee their goods against skippers. There are also flies that injure plants. Among these the Hessian fly is well known. The larva is to be found between the sheath of a blade of wheat and the stalk, where it does its damage. There is also a " wheat midge " which causes considerable loss. Nearly every one must have noticed on the ends of willow twigs a gray cone-shaped growth. This is caused by the developing larva of the "pine cone" gall gnat. The Mosquito. The mosquito lays its eggs on stagnant water. The larvae are known as " wrigglers," and their well-known habits justify the 36 Descriptive Zoology. name. The larva breathes by a tube at the hinder end of the body. The pupa is also active ; it breathes air through two tubes which grow out of the thorax. The piercing and sucking tube of the adult consists of several mouthpieces which fit snugly together. Only the female bites. She is a cheerful individual, singing as she goes about her work. Some excellent authorities believe that mosquitoes are the chief agents in intro- ducing the germs of malaria into the human system. Pouring kerosene on the water in which mosquitoes are breeding will kill them, and this is probably a more practical method of reducing their number than might be at first supposed, for kerosene, like any other oily substance when on water, spreads out in an exceedingly thin film, a little of it going a long way. Diptera. This order of insects receives its name from the fact that its members have but two wings, as seen in the flies and mosquitoes. The life history of the house fly is fairly typical. The knobbed balancers (rudimentary hinder wings) are called "halteres." ORDER COLEOPTERA. The May Beetle. This brown fellow is well known, but more commonly under the incorrect name "June bug." You will hardly need to hunt for a specimen, for if you leave your window open as you sit by your lamp on an evening in May or June, he will come to you. Instead of picking him up and throwing him out of the window, as you have been in the habit of doing, lay down your book and study him, for he will teach you more about himself than you could possibly learn from any book in the same length of time. At his best he is a poor flier, and, bewildered by the glare of light, he is more clumsy than ever ; if he bumps against the lamp and falls upon the table, you will have a good look at him. Note the order in which the legs are moved in crawling. Try to pick him up and find how he antenna mandi ^ maxilla t4x JJ Hay-beetle FIG. 30. THE MAY BEETLE, STRUCTURE AND DEVELOPMENT. From Hyatt's Insecta. 38 Descriptive Zoology. holds on so well. Observe another one flying, see how he holds the wing covers up and out at the sides. As soon as he lights, see how these wing covers come down over the membranous flying wings, which at first project behind the wing. Watch him tuck the wings under the wing covers ; can you tell how he does it ? After the membranous wings have been withdrawn from sight, pick him up and note that the wing covers meet in a straight line along the middle of the back, entirely concealing the true wings. Note also the large prothorax. The head is small, but has strong mandibles and two pairs of maxillae. The enlarged ends of the antennae consist of a series of leaflike plates, giving the name to a large group, the Lamellicorn beetles. Watch him as he starts to fly again. In order to give the flying wings free play, the wing covers must be held well up and forward. In this position they make con- siderable resistance to flight, and it is easy to see that this kind of insect cannot be a first-class flier. These beetles sometimes do considerable damage, by eating the leaves, especially of the cherry. In the early evening one may see swarms of May beetles and later hear them buzzing about the foliage. The eggs are laid in the ground and hatch out into white "grubs." Every boy knows them well and uses them for bait, and often he learns that the blackbirds know enough to follow the plow and pick up the grubs that are left in the furrow. The grub usually has a dark head, with a white body, the first three segments bearing each a pair of jointed legs that correspond to the three pairs of legs of the adult beetle. The hinder part of the body is often dark from the dirt that has been eaten. Every one knows how they lie curled up and in the ground; they generally rest on their backs. They often do great Insecta. 39 injury by eating the roots of grasses, strawberry plants, corn, grain, and other plants. The larva lives in the ground e FIG. 31. THE COLORADO POTATO BEETLE AND ITS DEVELOPMENT. a > eggs; 3, larvae; c, pupa (underground); d, adult; e, wing cover; f, leg. From Hyatt's Insecta. two or three years. The last of its stay is passed in a pupa state, when it is inactive, lying in a smooth, oval cavity it has made for itself. The Colorado Potato Beetle. This is too well known to need description. It is a native of the Rocky Mountain region, where it lived on a species of Solanum (to which genus the potato belongs) ; when the potato began to be cultivated near its home, the beetle transferred to the new plant, and, starting in 1859, it spread east- ward till it reached the Atlantic coast in 1874. The Ground Beetles. Among the most common of our beetles are the ground beetles, to be found under logs, boards, and stones, or running about on FIG. 32. COMMON GROUND BEETLE. From Hyatt's Insecta. 40 Descriptive Zoology. the ground in the summer and fall. The caterpillar hunter has green wing covers and is over an inch long. The fiery hunter has on the wing covers rows of red or copper-colored spots. The Tiger Beetles. These beetles get the name from their active predaceous habits, as well as from their bright-colored and yellow-barred wing covers. They run actively and fly well for beetles. They are often to be seen on the ground, especially on sand along streams. When you attempt to capture one it may remain quiet till you get near it, when it darts away, flying a short distance, and usually lights with its head toward you. The Borers. There are many beetles whose larvae bore into trees, where they do great damage. Among these, perhaps the locust borer FIG. 33. HICKORY TREE BORER; LARVA, PUPA, AND ADULT. From Hyatt's Insecta. and the painted hickory borer are found as frequently as any. The woodpeckers do good service in destroying these grubs. The Stag Beetles. Many children know these beetles as "pinch bugs." The large, incurved mandibles are very characteristic. The larvae usually live in decaying wood. The Dung Beetles. No boy or girl who has spent much time in the country has missed seeing these odd beetles, called "tumble-bugs." On the way to and from the district school the child meets the pairs of beetles rolling the big ball that they have made from the drop- pings of horses and cattle. It is interesting to see them, one pushing and one putting; as he patiently follows and watches them, he sees them at last bury the ball. Later the child learns that the female lays eggs in the ball, which the larvae consume as food. The "Weevils." Some of these are small beetles, not more than one fifth of an inch long. They lay their eggs on the pea pods ; the Insecta. 41 larvae bore their way into the pea, and eat out to the skin through which the adult easily makes his way when ready to emerge. Blister Beetles. A large family of beetles has a blistering substance which is used in making blistering plasters. The "Spanish fly 11 be- longs to this group. One of the most common of our blister beetles is a black fellow abundant on goldenrod flowers. Carrion Beetles. These usually have club-shaped antennae. The; are well known, as both the larvae and the adults feed on decaying flesh. Some of these beetles are called "sexton beetles 11 from the fact that they bury small animals. The Rove Beetles. These are odd forms, with short wing covers, which hardly conceal half of the abdomen. This is long and flexible, and is often carried turned up as if threatening to sting, which it has no power to do. 4 The Ladybugs. All children who live in the country know these hemispherical beetles, with their smooth and often brightly colored and spotted backs. Most of them are predaceous, and one of the greatest triumphs of economic entomology was the introduction of a species of ladybug from Australia into California, where it largely checked the ravages of a scale insect, which was making havoc with the fruit trees. The Carpet Beetles. Some of these destroy carpets. Others are the greatest pests of museums, destroying the stuffed specimens. The best remedy is bisulphide of carbon, whose fumes are fatal to eggs, larvae, and adults. The Click Beetles. Boys know them as "spring beetles, 11 "snap- ping bugs, 11 " skipjacks, 11 etc. Lay one on its back, and soon it gives a spring, with a click, that raises it perhaps several inches. If it lights on its back, it soon tries again. These beetles, like many others, " play possum. 11 Their larvae are " wire worms, 11 and do great damage, eat- ing the roots of corn, grain, grasses, and other plants. One of our largest click beetles, the eyed elater, is gray, and has on the prothorax two large black spots resembling eyes. The Snout Beetles. These beetles (the true weevils) are very odd in having the head prolonged into a long beak, sometimes longer than the body. Most of these are known as curculios. They bore a hole with the end of the snout, deposit the egg, and then push the egg to the bottom of the hole with the snout. They destroy many fruits and nuts. 42 Descriptive Zoology. The Fireflies. These, too, are beetles. Children do not need to be told that they emit light, and' the most learned scientist cannot tell just how the light is produced. The females of some fireflies are wing- less, and are called " glowworms. 1 ' Water Beetles. Not least interesting among beetles are the water beetles. We shall notice three kinds. First, the whirligig beetles, which nearly everybody has observed on the surface of the water, whirl- ing round and round in swarms. Like the other water beetles, they have a flattened body, and the hinder legs are paddle-shaped. The whirligig beetles occasionally dive. They have each eye divided into two parts, one of which looks up and the other down, so that one would s.iy they had two pairs of eyes. The predaceous diving beetles have oval bodies, somewhat wider behind. They are more abundant in stagnant water. When at rest they come to the surface and remain with the head down and the tip of the abdomen projecting into the air. Like the water bugs, they breathe by taking air under the wings, and when a new supply is needed they again come to the surface. The spiracles are on the upper surface of the abdomen. They are very voracious, and eat other insects and even small fishes. The larvae are spindle-shaped, with sharp, incurved mandibles, and are known as "water tigers" on account of their fierce- ness. Both larvae and adults may be kept and fed on meat. The water scavenger beetles are elliptical. They do not breathe as do the predaceous water beetles, but come to the surface head up and take air under the body, where it is carried as a film, which gives a sil- very gleam when seen from beneath. They are supposed to feed mainly on decaying vegetable matter, but some are known to catch live insects and eat them. They may be distinguished from the predaceous water beetles by their shape, and by a long, sharp spine that projects back- ward from the under surface of the thorax. Catch one of these beetles by one of the hind legs and you will probably find out the use of this spine. Though all these beetles have the power of flight, they, do not usually try to escape from ajar of water. It is easy to catch them by scooping in ponds with a dip net. They may be kept in glass jars (candy jars are very convenient), and watched from below as well as from above. If they have no solid surface on which to crawl, they are not likely to get away. It would seem that they -cannot start to fly from the surface of the water, but must have some solid object from which to rise into the air. Insecta. 43 Coleoptera. The beetles are called Coleoptera, mean- ing sheath-winged, from the hard, horny wing covers. The hind wings are membranous, and are usually consid- erably longer than the wing covers. To enable the beetle to protect them there is a joint in the anterior edge of the wing so that it can be folded crosswise as well as length- wise. This is accomplished by moving the abdomen down- ward and backward, then upward and forward to draw the wing under the covers. Some beetles lack true wings and are unable to fly. The mouth parts are fitted for biting. All insects have chitin in the skin to stiffen it, but the beetles have this most fully developed, and are the hardest and firmest bodied of insects. This is in keeping with their mode of life, as many of them crawl into crevices, under stones, logs, etc. They are the strongest of insects, and the load they can carry, in proportion to their weight, is marvelous. Beetles have compound eyes, but almost always lack the simple eyes that are present in most insects. As the under surface of the abdomen is subject to fre- quent pressure, it needs to be hard and unyielding. How, then, can respiration be effected? It is secured by having the upper surface of the abdomen more soft and flexible ; by the in-and-out movement of this region the air is taken in and sent out through the spiracles, which, except in water beetles, may usually be seen along the abdomen. In a former chapter we saw how the dragon fly would have to change if he were to assume the life of a locust. Go a step farther and it will be evident that the beetle, forcing his way into crevices and into narrow places, has acquired the hard, smooth body which he requires to fit him for such a life. There is great variety in the habits of beetles ; they live in air and in water; are carnivorous and herbivorous; some 44 Descriptive Zoology. are parasitic ; the larvae are found in the earth, in decay- ing wood, in the living wood of hard trees, in manure, in carrion, in fruits and seeds. Many are injurious; others are beneficial, as the lady- bugs, which destroy injurious insects. ORDER HYMENOPTERA. The Honeybee. Our honeybee is of European origin, and has long been domesticated. Occasionally escaped swarms live in a wild state. The three parts of the body, namely, head, thorax, and abdomen, are very distinct ; but it should be noticed that the prothorax, instead of being immovably connected with the rest of the thorax, as in the fly and many other insects, is movable. Another feature, peculiar among insects, is the transferring of one segment from the abdomen to the thorax, what appears to be the last segment of the thorax being really the fore- most segment of the abdomen. The second segment of the abdomen (apparently the first) is slender, and allows the abdomen to be bent sharply forward under the thorax ; and nearly every one has learned, in a way that he will not forget, how and why the bee does this. The two pairs of wings are membranous, the hind pair being much smaller than the anterior. Along the front margin of the hind wings is a row of hooks which catch on a ridge at the hind edge of the front wings, so that in flight the two wings work as one, in fact until the wings are unhooked there seems to be but one pair. The mouth parts are peculiar. In most insects the mouth parts are fitted either for biting or for sucking. In the bee we find both sorts of structures. Mandibles are present, and sometimes are strongly developed. But the food of head Honey-bee FIG. 34. THE HONEYBEE, STRUCTURE AND DEVELOPMENT, From Hyatt's Insecta. 46 Descriptive Zoology. the honeybee is liquid, and the tongue is the conspicuous organ. The two nlaxillae, with the two labial palps, form the sucking tube, within which the cylindrical tongue moves up and down. The antennae are like an arm bent at right angles at the elbow. The pollen " basket " (see Fig. 34) is on the out- side of the tibia of the hind legs of the workers, and is simply a flattened segment surrounded by stiff hairs. The sting is a modified ovipositor, consisting of several pieces closely fitting together, constituting a tube, through which the poison is conveyed from the poison gland within the tip of the abdomen. FIG. 35. HONEYBEE. a, drone or male; b, worker or infertile female; c , queen or fertile female. From Jordan and Kellogg's Animal Life. Kinds of Bees in a Hive. There are three forms of honeybees, the queen or female, the drones or males, and the workers, which are undeveloped females. There is but one queen in a hive most of the time, and compara- tively few drones, the great majority being workers. The average hive consists of from twenty-five thousand to thirty- five thousand bees, but there may be as many as fifty thou- sand. The drones have broad, blunt bodies, and have no stings ; and may be further distinguished by their large eyes, which make up most of the head. They may be found in the hive in the early summer, but after the swarming Insecta. 47 season is over they are driven out or killed by the workers. The workers are the smallest of the three kinds, and are provided with " pollen baskets" and stings. The queen is larger than the workers, and has a long, pointed abdomen. She has 2 sting, but never uses it except against a rival queen. The average life of a worker is about five weeks. Workers may live eight months, while a queen has been known to live five years. The Work of the Hive. As indicated in the name, the management of the hive falls chiefly on the workers. In the first place, the workers make honey. They gather nectar from flowers ; this is taken into the honey stomach, but not mainly for the sustenance of the worker. It is trans- ferred to the cells, loses some water by evaporation, and becomes honey. The workers make the wax from which the comb is made. The wax is a secretion from the glands on the under surface of the abdomen. When wax is needed a large number of workers gorge themselves with honey and hang like a curtain, clinging to each other, remaining quiet. As the wax exudes from the glands, other workers gather it and construct the comb. The economy of mate- rial is well known, but the cells are not always mathemati- cally exact, as is commonly supposed. The workers also collect a gummy substance from buds, which forms propolis, or " bee glue," with which they cement crevices and make similar repairs. Pollen is also gathered in a " basket " on each hind tibia. Of this pollen "bee bread " is made for feeding the young. Development. For the rearing of the young special cells are made which constitute the "brood comb." This brood comb may be afterward used for storing honey. The queen deposits an egg at the bottom of each cell, and after they hatch, the larvae are fed by the workers till ready to 4 8 Descriptive Zoology. Larv go into the pupa state, when the cell is capped over till the pupae transform into adult (or imago) bees. The drones, being larger than the workers, are developed in larger cells. Queen cells are larger than other cells. At the season of the year when the bees gitfe regular attention to rearing queens, Egg ^-^r^^^^^^^ tne queen cells are usually built at the bottom or ends of the comb. But if the bees are obliged to produce a queen out of the regular swarming season, the queen cells are made by tearing out the partitions and com- bining three cells into one, which is built out and hangs vertically in front of the comb. In the egg state there is no difference be- tween the queen and the Queen cell FIG. 36. CELLS CONTAINING EGGS, LAR- v*:, AND PUP,* OF THE HONEYBEE. The large, irregular cells are queen cells.- From Worker, but the larva that Jordan and Kellogg's Animal Life. j g ^ become a queen j s f e( J on specially prepared food. In the early part. of the sum- mer several queen cells are made ; as soon as a new queen is hatched the old queen tries to kill her ; but the workers protect the new. queen, and the old queen, followed by a part of the workers, departs to establish a new colony, and this is called " swarming." If a number of new queens are hatched at the same time, they may fight for leadership, and the one survivor rules supreme. Or, often, several young queens depart with a swarm. The queens that are thus killed are carried out by the workers, and they do the same for any that die in the hive. Insecta. 49 All dirt and rubbish are carefully removed, the hive being a model of neatness. In warm weather a number of workers may be observed stationed at the entrance, fanning vigorously with their wings ; they do this to ventilate the hive. Bumblebees. The queen is the only one of a colony that lives over the winter. Selecting some convenient place for a nest, usually an old nest of a field mouse, she gathers a mass of pollen and lays some eggs upon it. As the eggs hatch out the larvae eat into the pollen, and when fully developed spin silken cocoons for themselves. After these cocoons have served as cradles they are strengthened with wax and used for storing honey. Every country boy has robbed the nests of the bumblebee ; he likes the honey and is willing to pay the price for it. Nearly the whole colony of bumblebees may be captured by pouring water into the nest, which renders them unable to fly ; or if a jug partly filled with water be set near the nest, when they are disturbed they usually enter the jug, and, getting into the water, are easily taken ; or the whole colony may be chloroformed. Being larger than the honey- bee, they offer some advantages for study. Other Bees. The honeybees and bumblebees are called social bees in distinction from other kinds of bees that lead a solitary life. Among the solitary bees is the carpenter bee, that tunnels into wood, sometimes a foot or more. Some bees cut out circular pieces of leaves with which to line their holes. Others dig holes in the ground ; some mine into the sides of banks, one group of the mining bees being called the " short-tongued " bees. There are also several parasitic bees. Wasps. As with the bees, some of the wasps are social, while others are solitary. In colonies there are three kinds of individuals, males, females, and workers, all winged. The wings, unlike those of bees, are folded into plaits, as in a fan. They build nests either in the ground or on trees and buildings. Nearly everybody has seen the large nests suspended from trees, about the size and shape of a football ; and perhaps many have vivid recollections of the warm reception they received when they knocked abruptly at the door of this lively commu- nity. The hornet, or yellow jacket, need not be described to a country lad. " Eternal enmity 1 ' is sworn between them, and each knows there is no use of showing a white flag. Still, the skillful teacher may capture 50 Descriptive Zoology. the entire colony by quietly slipping an insect net over the nest and tying the, net to inclose them. Later a hole may be made in the tip of the net, and a single hornet at a time may be allowed to pass under a tumbler inverted on a plate. After being kept awhile they will be hungry, and if a drop of sugar water be introduced, the proud captive will not hesitate to let his enemies see how he eats. The entrance to these nests is below, while within are horizontal combs. The wasps make the nests out of wood fibers, which they tear off stumps, fences, and unpainted buildings. They chew these fibers into a pulp and make a coarse gray paper. They probably are the original paper makers. Another wasp builds a single layer of comb, which is held horizon- tally under some protecting object by a narrow stalk, the comb not being surrounded by a case as with the yellow jackets. The wasps that make nests in the ground also make paper to line the nest. Among the solitary wasps some are diggers, and it is interesting to see one of them digging a hole, throwing the dirt back as it digs very much as a dog does. Others make tunnels into the stems of plants, where the young are reared. The mud dauber wasps are slender-waisted, and wear a suit of shiny dark blue. - They have the habit of nervously jerking their wings. They are often seen lighting on the mud about horse troughs, where they are gathering mud for their nests. They make a nest of several cells, in which the eggs are deposited. We see these cells on rafters, under eaves, etc. Some wasps store the cells with spiders and insects for the larva to feed on till it emerges. Often the insect is stung so as to paralyze, but not quite kill it. Ants. Here, again, we have a communistic society with perhaps a still more perfect division of labor. The males and females at first have wings, but the males are short-lived, and the females soon bite off their wings. The work is done by the workers, who are wingless. Some make a nest in the ground, while others tunnel into decaying wood. In a disturbed nest we sometimes see the workers carrying eggs. The large white objects which they carry are cocoons. Ants are very strong for their size and do a variety of work. They care for the larvae, protect the nest from invasion by enemies ; some species make slaves (and it is interesting to note that the masters are light-colored and the slaves dark). They keep cows (aphides) from which they get a sweet liquid (honeydew), and some build a covsr for their herds Insecta. 51 (cow sheds). In some forms the masters are so dependent upon their slaves that they perish unless cared for by them. Some of the ants that keep the plant lice as cows are injurious through the action of the plant lice, which feed on the roots of corn and other plants. The ants carry the plant lice, or their eggs, into holes in the ground where they survive the winter, which they probably would not otherwise be able to do. Yellow ants often invade houses, making a nest within a wall where it is almost impossible to dislodge them; these are -often called "red ants." Though fond of sweets, ants are almost omnivorous. Other Hymenoptera. Among the other Hymenoptera we may notice the sawflies whose leaf-eating larva? are known as the rose slug, pear tree slug, currant worm, etc. Various forms of Hymenoptera sting their eggs into the stems and leaves of plants. Around the egg is formed a FIG. 37. LARVA OF A HAWK MOTH, WITH COCOONS OF A PARASITIC ICH- NEUMON FLY. From Kellogg's Zoology. swelling known as a gall In this the larva develops, finally eating its way out. There are many kinds of galls, and the entomologist knows the kind of insect from the characteristic form of the gall, and the adult insects are known as "gallflies. 1 ' The ichneumon flies have an ovipositor consisting of long, slender (usually three) threads, by means of which the eggs are deposited, usually in the trunks of trees, where these larvae prey on the larvae of other boring insects. In the fall one occasionally sees a sluggish caterpillar covered with little oval bodies resembling eggs ; examined more closely, these little bodies are seen to have a silky finish ; they are the cocoons of a para- 52 Descriptive Zoology. site. A group of parasitic Hymenoptera (the Braconids) deposit their eggs on the caterpillar ; the little larvae bore their way into the big larvae, and after consuming the tissues of the caterpillar, eat their way out and add insult to injury, attaching their cocoons to the outside of the skin. Sometimes the chrysalid of a cabbage butterfly fails to trans- form, and a hole may be discovered where the adult " Braconids " have made their escape. Characteristics of Hymenoptera. The Hymenoptera have two pairs of membranous wings, the hind pair being smaller than the front. The mouth parts are fitted both for biting and for sucking. The female usually has a sharp ovipositor, which in many cases is used simply as a sting. Development indirect. General Characteristics of Insects. i. Insects have a segmented external skeleton, i.e. consisting of a series of rings. 2. These rings are grouped in three sets, head, thorax, and abdomen. The head bears one pair of an- tennae. The thorax bears three pairs of legs and usually two pairs of wings. The abdomen does not usually have jointed appendages. 3. Insects have air tubes, branching through the thorax and abdomen, by which they breathe. Harm done by Insects. i. They destroy crops, and the damage to our field and garden produce is almost beyond computation. 2. They convey disease both by getting on diseased matter and conveying it to our food, and also by introducing disease germs in biting (mosquito). 3. They injure stock (flies, mosquitoes, botflies, etc.). 4. They injure buildings (ants and white ants). 5. They are often annoying, when not injurious, to man. ^ Good done by Insects. They benefit us (i) by making silk; (2) by making honey; (3) by furnishing material for making ink (galls); (4) furnish dyestuff (cochineal); (5) they are used in medicine (blister beetles); (6) their use Insecta. 53 in fertilizing flowers is unknown to many, but is essential to man in certain crops ; (7) they serve as scavengers (flies, beetles, maggots, etc.); (8) many kinds are very useful in killing injurious insects, as ichneumon flies that destroy borers, ladybugs that eat scale insects, etc. On the whole it would be difficult for a jury to say whether insects do more harm than good ; and it is per- haps best to regard them as having their place in the world to fill. And yet we must not submit tamely to their ravages, for we may outwit the robbers and turn other robbers against them. We should make it a study to turn insects, as well as other groups of animals, to the best account, and thus make the lower forms of animal life serve man, who is deservedly at the head of creation so long as he shows his fitness to rule. ORDERS OF INSECTS. Thysanura Springtails. Neuroptera Ant Lions. Odonata Dragon Flies. Lepidoptera Butterflies. Orthoptera Locusts. Diptera Flies. Hemiptera Bugs . Coleoptera Beetles. Hymenoptera Bees. CHAPTER III. BRANCH ARTHROPODA. CLASS MYRIAPODA. Myriapoda. The myriapods (" thousand legs" and cen- tipeds) have a wormlike form, but, like other Arthropods, have a more or less hardened external skeleton, and possess jointed appendages. The head is distinct, but after it the segments are alike, there being no distinction of thorax and abdomen. On the sides or ventral surface of most of the segments are the spiracles or breathing pores, which lead to the air tubes, or tracheae, as in the insects. FIG. 38. CENTIPED. The head, as in insects, appears to be composed of sev- eral segments, fused together ; it bears a pair of many- jointed antennae, a pair of eyes, and two or three pairs of jaws. There are two principal groups, the centipeds and the millipeds. The centipeds have flattened bodies, with one pair of legs to each segment. They are carnivorous, and have a poison gland opening at the tips of the first pair of legs, which act with the mouth parts. The millipeds, or thousand legs, have cylindrical bodies, and may be recog- 54 Myriapoda. 55 nized by their habit of coiling into a spiral when disturbed ; they have two pairs of legs to each segment. They are vegetarian and not poisonous. FIG. 39. SKEIN CENTIPED. Both of these forms are usually to be found by over- turning stones and logs ; the centipeds seek safety by run- ning briskly away, while the millipeds coil up and lie still. CLASS ARACHNIDA. The Spiders. The body of a spider consists of two parts, connected by a constricted waist, the unsegmented cephalothorax and ^, large, soft, unsegmented abdomen. There are six pairs of appendages : first, the jaws, each jaw ending in a sharp, incurved segment at whose apex opens the duct of a poison gland ; second, the palps, which are sometimes mistaken for a pair of legs ; and lastly, four pairs of legs. Spiders have from one to four pairs of simple eyes vari- ously arranged on the top or front of the head. Spi- ders have a well-developed sense of sight, and their sense of touch is very delicate. Of their other senses little is known. Descriptive Zoology. FIG. 40. JUMPING SPIDER. They suck the blood of insects, which they kill by means of the poison introduced through the biting jaws. Their bite is seldom serious to man, though one of the larger spiders is said to kill small birds. There is a strong sucking stomach which is worked by special muscles. In addition to breathing by air tubes, as in the case of insects, spiders also have what are called lungs, or, from their peculiar structure, "lung books." The openings to these lungs are under the abdomen. The cavity to which the opening leads is somewhat like the inside of a pocketbook, with a number of com- partments. Blood flows around the out- side of this lung book, and within the plates or leaves of the "book." Thus the blood and the air come near each other, separated only by a thin mem- brane, and by the folding an increase of surface is secured. This is the same general plan of all lungs and gills, but the details of the plan are carried out in various ways. Like crustaceans, spiders molt, and one may often find their cast skins, looking like dead spiders, but closer exami- nation will reveal the difference. Spinning. One of the most interesting of the habits of spiders is their web making. There is a great difference among spiders in this regard. Some spiders spin very little, leading a wandering life. Among these are tne "jumping spiders," so named from their habit of creeping stealthily close to their victims, and then suddenly pounc- ing upon them. These forms are common, and their habits are exceedingly interesting. But probably most people are rather more familiar with the spiders that make Arachnida. 57 the conspicuous webs. These kinds lead a rather seden- tary life, preferring to set traps for their game rather than actively hunt for it. The spinning apparatus consists externally of two or three pairs of short segmented appendages under the tip of the abdomen. Each of these spinnerets has many short, hairlike projections, with a perforation at the tip of each. FIG. 41. THE SPINNERETS OF THE COMMON GARDEN SPIDER. Within the abdomen are glands which secrete a liquid sub- stance of which the web is made. When the spider wishes to spin it presses the spinnerets against some surface, and the exuded liquid adheres ; then as the liquid is drawn out into a slender thread it hardens as it is drawn, making a thread often of hundreds of strands united. The feet of the spiders have blunt claws with a series of teeth, by means of which they can easily walk on the web without tearing it. In spinning the webs with radiating and concen- tric lines, such as we have often noticed, the spider first spins a few foundation threads, then the radiating threads. 58 Descriptive Zoology. After this it begins at the center and proceeds spirally outward ; but when this spiral web is completed it begins once more at the outside, and takes up this spiral and replaces it with a spiral spun in the reverse direction. It bites off the first spiral, and, rolling it up into little balls, drops them to the ground, hence it was formerly supposed to eat the web. The web is not placed quite vertically, FIG. 42. HEAD AND MANDIBLES OF COMMON GARDEN SPIDER. The spots above are eyes. and the spider hangs on the under side, so that when a fly is caught it can run to a point over it and drop down and quickly catch it. It is usually the female that is on the web, while the male may be hidden near by. The male is sometimes much smaller than the female and generally brighter-colored. We have often wondered how it is that on some bright, warm summer days there is so much spider web, or " gossamer," floating in the air. This is mostly formed by small spiders. They climb up on a fence or stump, or other place where there is an up current of air, caused by the heat of the sun. Standing with the tip of the abdomen pointing upward a thread is started ; the current carries it upward as it is formed, and after awhile the current bears up, not only the thread, but the thread maker, the spider itself, and they may often be seen by the hundreds float- ing along, so many tiny, unpatented airships. Arachnida. 59 It is said that these gossamer webs are a sign of fair weather ; so these little creatures seem to have forerun mankind in forecasting the weather as well as in aerial navigation. Some spiders construct funnel-shaped webs, and remain concealed at the small end of the funnel, ready to rush out when their delicate sense of touch informs them that some- thing is shaking the web, as when an insect is caught. Gently disturb such a web, and see the occupant dart forth. Another use of the web, and almost the only use in some spiders, is as an envelope for the eggs. The web forms a silky but tough covering, usually deposited in some place of safe-keeping, but rarely carried by the mother. There FIG. 43. SPIDER, WITH COCOON ATTACHED TO SPINNERETS. are many eggs in one such case, and when hatched the little spiders sometimes become cannibals, each eating as many as it can of its brothers and sisters. Kinds of Spiders. There are many kinds of spiders ; among the largest is the tarantula ; the bite of this and of some other large spiders is very painful to man, but most of the stones told of spider bites are gross exaggerations. The trapdoor spider is an interesting form ; it lives in a hole in the ground, lines its hole with web, and makes a lid which it hinges with the web. One spider lives under water, forming an arched web, under which it stays, carry- ing down bubbles of air which are introduced beneath the web. 60 Descriptive Zoology. Scorpions. Scorpions are found in warm countries, reaching their greatest size in tropical America and Africa. The form shown in Fig. 44 occurs from North Carolina to Florida. Other species are found in the southwestern United States as far north as Kansas. The body consists of a short, unsegmented cephalothorax, followed by a twelve-segmented abdomen. The anterior part of the ab- domen is broad, the hinder part narrow, ending in the poi- FIG. 44. SCORPION. son sting. The sting is painful and serious to man, but seldom fatal. The scorpions are nocturnal, and feed on the blood of insects. Respiration in the scorpions is by means of lung books, as in the spiders. Harvestmen. The harvestmen, or daddy longlegs, are similar to spiders, but with extremely long legs. They frequent shady places, and live chiefly on small insects, such as plant lice. Mites and Ticks. These are small and often degenerate forms of Arachnids. Many of them are parasites, sucking the blood of mammals, as ticks on dogs, cattle, and even man. Among the mites is the "itch mite," which has been made rare by the spread of "soap and civilization." CHAPTER IV. BRANCH ARTHROPODA. CLASS CRUSTACEA. Example The Crayfish. Occurrence. Crayfishes are found fairly abundant in streams and ponds in many parts of the United States. They may be seen crawling about on the muddy bottom, but, being nocturnal in their habits, they usually escape observation during the daytime by hiding in holes, under stones, and especially under ledges of rocks, overhanging banks, or where the stream has washed out the soil about the roots of trees standing on the banks. Crayfish Holes. Crayfishes are also found in holes which they dig, usually in low ground. When the water dries up from the ponds and creeks, crayfishes often dig down to water, and, at this season, live in these holes. The holes are frequently many feet deep. The soil and clay are brought up in pellets, and with these a "chimney" is built up around the mouth of the hole. How the Crayfish Walks. The crayfish walks by means of the last four pairs of thoracic legs. Each of these legs has seven segments ; and the successive joints admit of motions in different planes, so that the whole appendage has great freedom and variety of movement. The cray- fish usually walks slowly, holding out the big pinchers in front. It can, however, walk sideways or backward. When taken ^out of water the crayfish walks with a heavy, awk- 61 62 Descriptive Zoology. ward movement, frequently bumping its body upon the floor ; it evidently needs the buoyancy of the water to sup- port its weight. How the Crayfish Swims. Swimming is the most rapid action of the crayfish, and it probably seldom resorts to this means of locomotion except to escape enemies. The side parts of the " tail fin " are spread out as wide as possible, and the whole abdomen is suddenly and forcibly bent down, under, and forward. This makes a powerful stroke, and drives (or rather pulls) the crayfish swiftly backward. The whole of the under surface of the abdomen is concave, thus getting a good hold on the water. As the animal darts backward the resistance is greatly reduced by the convexity and smoothness of the dorsal surface of the abdomen. Again, since the big pinchers rather necessarily extend forward, it would be difficult for the crayfish to move for- ward with any considerable speed ; but when it darts back- ward the big claws drag along in the wake without any special resistance. It should be further observed that when the crayfish is frightened, the chances are that it is on or near the bottom, which in most cases is more or less muddy ; when the powerful tail ^stroke is made, it would naturally sweep close to, if not actually touch, the muddy bottom. This stirs up the mud, and thus makes the water turbid between the pursuer and the pursued, and greatly favors the chances of escape. The Muscles of Locomotion. The muscles which move the appendages are inclosed in the framework along the ventral surface of the cephalothorax. The muscles which flex and extend the abdomen in the act of swimming fill most of the space in the abdomen. As would be expected, the extensor muscles are much smaller than the flexors. The extensors arise from the side walls of the thorax, and FIG. 45. EXTERNAL FEATURES OF THE LOBSTER. From Packard's Zoology. 6 4 Descriptive Zoology. extend back into the abdomen, being attached to the an- terior edges of the abdominal rings in the upper part of the abdomen. When these muscles shorten they pull the an- terior edge of each tergum under the posterior edge of the preceding tergum, and thus straighten the abdomen. The extensor muscles lie above the intestine. Below the intes- tine, and filling out most of the space of the abdomen, are the flexor muscles. These are very complicated. Like the Extensor muscle. Abdominal artery. Tergum. Intestine. Flexor muscles. Epimerum. Ventral l^t W// \ Pleurum. abdominal artery. ^1^ Tpf Nerve cord. Sternum. 19, one of the swimmerets. FIG. 46. CROSS SECTION OF ABDOMEN OF CRAYFISH. From Huxley's Crayfish. extensor muscles, they originate in the thorax, and extend back and are inserted on the sternums ; and when they shorten, they flex the abdomen, giving the powerful stroke by which the animal swims backward so rapidly. Food of the Crayfish, and Mode of Eating. The crayfish lives largely on worms, the larvae of insects, with which most waters abound, snails, etc. The crayfish is carnivorous by choice, yet by necessity may be almost omnivorous. It is a greedy eater, and does not disdain carrion. It is de Crustacea. cidedly useful as a scavenger, disposing of a great amount of dead and decaying material which would polluce the water, ^ such as dead fish, clams, etc. In eating, the big pinchers may tear the food to pieces, and then the smaller pinch- ers of the second and third pairs of legs may transfer the pieces to the mouth, the entrance to which is sur- rounded by the maxillipeds. Or, instead of this process, the crayfish may apply the mouth directly to the food, and gnaw it off in bits by means of the mandibles and maxillipeds. Crayfishes are frequently guilty of cannibalism. The Digestive System of the Crayfish. The mouth of the crayfish is on the under surface instead of at f the front of the head, as in many animals. There are six pairs of mouth parts, the mandibles, two pairs of maxillae, and three pairs of maxillipeds. These jaws all move sidewise ; and when all of them are closed, the third or hindmost pair of maxillipeds cover all the others. The short gUlet passes straight up from the mouth to 66 Descriptive Zoology. the stomach, which is situated in the head. The stomach is very complicated. It has in its walls a set of arms or levers so jointed together as to support the walls of the stomach. Further, these bars, which are composed of chitin, are acted on by sets of muscles on the outside. There are teeth on the inner walls of the stomach, some projecting inward from each side and some from the upper surface. Certain muscles attached to the outside of the stomach act in such a manner as to make these teeth work together and masticate food in the stomach. The function of the stomach is wholly masticatory, and it has no digestive function. At the hinder part of the stomach there is a series of stiff hairs which act as a strainer, so' that only very fine particles are allowed to pass on into the intestine. Alongside the stomach on each side is the large digestive gland. Each of these opens by a duct into the intestine just back of the stomach. These glands were formerly called livers, but in function they more closely resemble a pancreas, their secretion digesting proteids and fats, and perhaps also starches. Beyond the stomach the intestine extends in a nearly straight course along the upper part of the abdomen, ending in the anus on the under surface of the telson. Respiration in the Crayfish. The crayfish breathes by means of the plumelike gills, which are covered by the sides of the carapace. Each gill has two blood tubes in its stem, through one of which the blood enters, while it returns through the other tube. In the feathery branches of the gill the blood is separated from the water by merely a thin membrane, so that the blood and the water make an exchange, the blood getting oxygen from the water, and giving to the water the waste products such as carbon dioxid which it contains. Crustacea. 67 There are Two Sets of Gills. One row is attached to the bases of the thoracic appendages ; these are the foot gills. A second row arises from the joints by which the FIG. 48. CROSS SECTION OF A CRAYFISH THROUGH THE HEART. Showing the gills, blood currents, and water currents. thoracic appendages are attached to the thorax; these are the joint gills. (In the lobster there is a third set, 68 Descriptive Zoology. higher still, arising from the side of the thorax, and called the wall gills.) The lowest set, the foot gills, have leaflike extensions along their borders, which perhaps serve to keep the filaments of the gills from becoming entangled with one another. The gills all have their free ends extending upward. The direction in which the gills extend is in keeping with the fact that the water which bathes the gills enters about the bases of the legs, and, passing over the gills, escapes near the anterior end of the cephalothorax, back of the base of the antenna of each side. It has been observed that the cephalic groove marks the distinction between the head and the thorax. This groove also marks the anterior limits of each gill chamber. In the extreme anterior part of the gill chamber, extending obliquely up- ward and backward, is the gill paddle or gill scoop. It is a part of the second maxilla. It is attached by its middle part, and each end is a somewhat spoon-shaped paddle. By a constant back-and-forth motion this paddle continu- ally bails the water out at the anterior end of the gill chamber, and thus draws more water in at the lower border of the gill cover, between the bases of the thoracic legs. Circulation in the Crayfish. The heart is situated in the dorsal part of the cephalothorax. From its anterior end arise five arteries : a single artery in the middle line supplies the eyes ; back of this a pair run to the antennae ; and, still further back, a pair lead to the digestive glands of the two sides. At the posterior end of the heart arises one artery, which almost immediately divides into two branches; the first branch runs straight back, just above the intestine, and is called the dorsal abdominal artery; the other branch extends downward, passing through the nerve cord. After passing through the nerve cord it again divides into two branches, one running forward, the sternal Crustacea. 69 artery, and the other extending backward, the ventral ab- dominal artery. All these arteries divide and subdivide, forming capil- laries. But the capillaries do not reunite, forming veins; they empty into more or less irregular spaces in the body, around the muscles and other internal organs. All these spaces, or sinuses, as they are called, lead into one main channel, the sternal sinus, which extends along the middle of the ventral region. From this sinus, passageways con- duct the blood to each gill. In each gill one tube, the afferent vein, conveys the blood to the gill filaments ; while another tube, the efferent vein, returns the blood to another set of veins, called the branchio-cardiac veins, which lead to the pericardium. There are no tubes to convey the blood into the heart, but the blood enters the heart directly through three pairs of holes, one on each side, a pair on top, and another pair below. These holes have lips on the inside, which act as valves, allowing the blood to enter freely, but preventing a reflow through the holes. Thus the beating of the heart causes a constant flow of blood in one direction : first to the tissues of the body in general, where it gives up oxygen and food materials and picks up carbon dioxid ; then to the gills, where it gives off carbon dioxid and gains oxygen ; then back again to the heart. The blood is colorless, but after exposure to the air it turns bluish. Excretion in the Crayfish. In connection with the study of the gills we have seen how the carbon dioxid is removed from the body. But the nitrogenous wastes are excreted by a pair of kidneys, which are called, on account of their color, the green glands. They are situated in the head, just below and in front of the stomach. The gland proper is a button-shaped body, lying close to the ventral body yo Descriptive Zoology. wall. This leads into a thin sac, which serves as a bladder, and it in turn opens by a duct to the exterior, through the apex of a hard, white, conical papilla, on the ventral surface of the base of each antenna. It is worthy of notice that the current of water coming from the gills passes directly by this other exit of waste, so that one stream carries away all the waste products, avoiding duplication of machinery. The Nervous System of the Crayfish. The nervous sys- tem consists of a nerve cord which lies on the floor of the body cavity, extending the whole length of the body in the middle line. It is a white cord, composed of a ganglion for each segment, connected in line by nerve fibers. The cord is really double, but the two rows of ganglions have consolidated, so that there appears to be but one row of ganglions. The cord itself, between the successive gan- glions, while apparently single, is actually double. And in two places the double nature of the cord is manifest. The two parts of the cord pass on the right and left of the gullet, forming what is called the esophageal ring, or esophageal collar ; again, the sternal artery passes between the two halves in the interval between two of the gan- glions. Though there is a ganglion for each segment, there is a consolidation, so that there are but thirteen dis- tinct ganglions for the twenty (or twenty-one) segments. The first ganglion, called the brain or the cerebral ganglion, is the result of the fusion of three pairs of ganglions. Back of the gullet, and connected to the brain by the two com- missures passing on either side of the gullet, is a large ganglion, which is evidently composed of the ganglions of the last three cephalic segments united with the ganglions of the first three segments of the thorax. Following this are five more distinct ganglions in the thorax and six in the Crustacea. abdomen. In the abdomen the nerve cord is in plain view when the abdominal muscles have been removed. But in the thorax the cord is concealed in a groove made by the Antennule nerve Antenna nerve Nerve ring around gullet Sternal artery Ganglion 7 Anus FIG. 49. NERVOUS SYSTEM OF CRAYFISH. From Huxley's Crayfish. inward projecting framework which supports the muscles which move the appendages. From each ganglion nerves radiate to supply the adjacent muscles and sense organs. 72 Descriptive Zoology. The Senses of the Crayfish. The crayfish appears to have the senses of touch, sight, taste, and smell. The Sense of Sight The eyes are on movable stalks. The advantage of being able to project the eyes is ap- parent. The protection afforded by withdrawing the eyes is almost equally apparent when we consider that cray- fishes fight fiercely with each other, besides being frequently under the necessity of protecting themselves from enemies outside of their own race. The projecting rostrum and the sharp blade of the lamina of the antenna need no ex- planation as to their use. The eye of the crayfish is a typical compound eye. It is made up of distinct parts, each of which is called a facet, or cornea. The Sense of Touch. One does not need to experiment long with crayfishes to be sure that they feel as well as see. The general surface of the body is more or less sensitive to touch, but with such a hard covering this sense can hardly be other than a very dull sense over most of the area. But the antennae are specially adapted for this sense, and their long, slender, tapering form and jointed structure render them convenient to apply to surrounding objects. Smell and Taste. Certain hairs of the external branch of the smaller antennas are believed to be connected with the sense of smell. There is in the basal joint of each antennule a sac, formed by the depression of its outer surface, so that free communication is left with the surrounding water. This was long supposed to be an organ of hearing, but is now regarded as the seat of the sense of equilibrium. There is no doubt that the crayfish discriminates in choice of food, and we have good reason to believe that the sense of taste is present. Crustacea. 73 The Enemies of the Crayfish. Various carnivorous fishes, such as black bass, eat crayfishes, hence the fisher- man also becomes an enemy of the crayfish by capturing it for bait. Raccoons are very fond of crayfishes. Both of these animals are nocturnal in their habits ; so when the crayfish sets out in the evening to get a lunch, the raccoon lunches on the luncher. One who frequents the woods may see the raccoon tracks along the creeks where it has been seeking this and other aquatic animals for food. Muskrats and crows are also among the more important enemies of the crayfish. How the Crayfish escapes its Enemies. In the first place its nocturnal habits keep it out of sight of some enemies. Second, its color is in close harmony with its surroundings, so that it is very inconspicuous. Dull shades of green, brown, and red are the prevailing colors. Though the senses of the crayfish are none of them very acute, they plainly are useful in making the animal aware of the approach of enemies. Then it is usually near the bottom, where there are many places of refuge. And last, but not least, this creature has one kind of locomotion that is speedy, that of swimming. The hard covering may make the crayfishes objectionable as food to many animals that otherwise would eat them. The big pinchers, too, which he knows so well how to use, are no mean defense against his lesser foes. And further, the threatening atti- tude which the crayfish assumes when cornered, may intimidate some would-be assailants who do not like the looks of the bristling claws, and fear that the " bite will be as bad as the bark." The Eggs of the Crayfish. The eggs are extruded as usual, but instead of being left in some place of de- posit, are attached to the mother by being glued to the 74 Descriptive Zoology. swimmerets. The eggs are small and smooth, reddish or dark, and in the mass suggest the appearance of a berry ; hence the mass of eggs is called the "berry." A lobster with the eggs attached is called a " berry lobster." From the eggs hatch the little crayfishes, which have the form of the adult. These little fellows have incurved hooks on the ends of their claws, by means of which they take fast hold of the swimmerets of the mother and remain so attached for some time. Rate of Growth of Crayfishes. The crayfish is about a quarter of an inch long when hatched. At the end of the first year it is about an inch and a half long. After the first year it grows more slowly, and seldom becomes more than five or six inches in length. Molting. Since the hard parts are on the outside, such creatures would soon reach a limit of growth unless some special provision were made. This is provided for by the shedding of the entire outer hard covering at stated periods. The hard shell splits across the dorsal surface at the junction of the cephalothorax and abdomen. The carapace also usually splits part way forward from the transverse opening above mentioned. By severe effort the cephalothorax and its appendages are first extracted ; then the abdomen is pulled out of its hard covering. This is a critical period in the life of the crayfish. Sometimes the big pinchers are broken off in the effort to get them out of the old case. Crayfishes sometimes perish in the struggle to get free from their "hide-bound" condition. And for some time after molting the body is soft, and hence almost defenseless. At this time the animal is un- usually timid, and lives in hiding till its skin again hardens by the addition of limy matter. After shedding, the cray- fish is doubly helpless; not only is his body soft and easily Crustacea. 75 injured, but his claws, being soft, are. useless as weapons of defense. In molting, the hard lining of the stomach, with the stomach teeth, is also shed. Crayfishes molt several times the first year, the number of molts gradually decreas- ing till in adult life the molt probably takes place but once a year. "Crab's Eyes." Previous to the time of molting there appear on the sides of the stomach two button-shaped bodies of limy material. In molting they are shed into the cavity of the stomach, together with the lining of the stomach. It is believed that they break up, become dis- solved, and are absorbed and then deposited as stiffening matter in the chitin, which makes the basis of the envelop- ing crust. Restoration of Lost Limbs. Crayfishes often lose their legs while fighting. Sometimes also they seem to drop them or throw them off when badly frightened, but perhaps they are merely snapped off in the violent effort to escape. The legs seem to break off always at the same place, where the leg is most narrow, and this is the easiest place to heal. The blood quickly coagulates, and such loss seems not to be dangerous or even serious. The mutilated stump at once begins to grow a new leg, but for a long time it is smaller than its mate. If one looks over a number of crayfishes, he is pretty sure to find some in this condition. The big fighting limbs are ordinarily the ones that have been lost. Are Crayfishes Beneficial or Injurious to Man ? Crayfishes are good to eat, the only part, of course, being the muscle, most of which is in the abdomen. They are used as food to a considerable extent in Europe, but they are little used in this country. Crayfishes are very useful as scavengers, eating dead fish, etc. Crayfishes are said to benefit some heavy, clayey land by the holes they dig, perhaps by mak- ing the soil more porous and helping to drain it. 76 Descriptive Zoology. On the other hand, crayfishes often do very great damage by digging holes in the dikes and levees along the lower Mississippi. These holes gradually become enlarged, perhaps by muskrats, and may finally cause the levee to give way, inundating vast tracts of land which are protected by the dikes-, and causing immense loss of property and sometimes of life. Distribution of Crayfishes. Crayfishes are fairly common through- out the United States, more especially in the central and southern por- tions. They are usually more abundant in regions where there is plenty of limestone, and are less abundant where granite rock prevails, as in New England. They are to be found in Ireland and England and on most of the continent of Europe, in Australia, New Zealand, Madagas- car, and Japan. But they occur in very limited areas in Asia and South America. In Africa none have ever been found. Origin of Crayfishes. It is supposed that the crayfishes are descend- ants of marine crustaceans ; that some of these forms lived about the mouths of rivers, gradually became accustomed to partly freshened water, and in time to fresh water, and ascended the streams and entered lakes. We do not know any living salt-water crustacean from which the crayfish is supposed to have been derived. CHAPTER V. BRANCH ARTHROPODA. CLASS CRUSTACEA (Continued}. Lobsters. With a few unimportant exceptions, the structure of the lobster is essentially the same as that of the crayfish. The lobster may be said to be a big salt- water crayfish, or the crayfish a small fresh-water lobster. Lobsters are an important food product of the North At- lantic, both to the old world and the new. From twenty to thirty millions are caught annually along the coasts of New England and Canada. They are captured by sinking large wooden traps, which are called " lobster pots." These are baited with refuse fish. A buoy is attached to each trap to mark its place, and to serve as a means of taking up the trap. The lobsters thus caught average less than four pounds in weight, but specimens have been found that weighed as high as thirty-nine pounds. Shrimps and Prawns. Two other marine crustaceans that are largely used as food are the shrimps and prawns. These are essentially like the crayfish, but differing from it more than the lobster. They are caught in large numbers, and eaten fresh or canned, as is the lobster. Prawns have a permanent hump on the dorsal surface of the abdomen ; and the dorsal surface rises as a sharp ridge, perhaps to diminish resistance, and thus increase its speed when swim- ming. Most of our so-called shrimps, out of which the famous salad is made, are really prawns, and not shrimps. 77 7 8 Descriptive Zoology. Crabs. Though differing considerably in appearance, crabs have the same essential structure as crayfishes and lob- sters. The cephalothorax is broad instead of being rela- tively long and narrow. The abdomen is kept folded under the cephalothorax, and is not used in swimming, almost its only use being to protect the eggs in the female. As in the preceding forms, there is the hard protecting crust ; stalked eyes; several mouth parts ; five pairs of large thoracic ap- pendages, the first pair armed with big pinchers ; gills on FIG. 50. SHRIMP. the sides under cover of the carapace ; and the same general manner of life. Crabs are great scavengers ; and if, while at the seaside, one wishes to clean a skeleton, if he puts it into a box guarded by slats, with spaces just wide enough to let crabs in, they will do the rest. Crabs may be caught by tying a piece of meat to a string and letting it down off almost any wharf or rock into the water. When the crab takes hold with the pinchers he will usually hold on till he reaches the surface ; and while he may be lifted out on the wharf or bank, it is safer to use a net when he is brought to the surface. Though most crabs are good to eat, and many kinds are so used, the one most eaten is the blue crab Crustacea. 79 (Callinectes kastatus), often called the " edible crab." Just after they molt they are esteemed good, cooked whole, under the title " soft-shelled crabs." Swimming crabs, such as the blue crab, have the last pair of thoracic legs developed as paddles, by means of which they swim sideways with considerable rapidity. In the Swimming legs. FIG. 51. LADY CRAB, NATURAL SIZE. case of crabs that do not swim, the last legs are not flat- tened, but end in a point like the other legs. The little oyster crab is often found in an oyster stew (Fig. 52). Development of the Crab. It is very interesting to note that the crab, when first hatched, has nearly the form of the crayfish, with an extended abdomen and a relatively narrow body, but that gradually the cephalothorax widens, and the abdomen becomes folded under the body. Crabs 8o Descriptive Zoology. are regarded as the highest, and probably the latest, of the crustaceans. While the development of the individual does not recapitulate the development of the race quite so fully as in some other groups, it serves very well to illustrate the general law that the development of the individuals of the highest group is an epitome of the development of the group as a whole; and often is a recapitulation of the order of geo- logical succession. FIG. 52. OYSTER CRAB. Cephalization. By this term is meant the higher development of the head, and of the appendages belonging to and immediately surrounding the head. In the lower forms of crustaceans the head does not predominate as in the crabs. The diameter is ap- proximately the same from one end to the other. Even in the crayfish, the ganglion at the anterior end is very little larger or better developed than those of the abdomen. In the crabs there is a much greater con- centration of the ganglions in the thoracic region. This principle will be illustrated in other groups of animals, but it can be seen here that the higher in the scale, the greater is the development of the head regions. The Sand Crab. This crab, with numerous others, lives out of the water considerable of the time. It is sandy in color, and lives out on the beach. It seems to be rather keen sighted, and runs at a lively rate when pursued. It usually attempts to escape, and often succeeds, by burying itself in the sand. This it does in a wonderfully short time. With a few quick, jerky motions of its legs it buries itself, usually leaving only the tips of its two eyes projecting above the surface. It is practically concealed, so much so that one who has pursued it, unless he looks closely, may lose sight of it ; but the crab has its enemy in sight all the time. Its means of escape is ingenious, and the color is a fine example of protective resemblance. The Fiddler Crab. This little crab, about two inches wide, has one big and one small pincher, suggesting the fiddle and bow. These very interesting little fellows are sometimes so thick on the shore, along the water line, that they crowd each other for crawling room, and make a very noticeable rustling noise as they elbow each other while retreating from the inquisitive biped, of whose motives they are suspicious. Crustacea. 81 Blind Crayfishes. In the Mammoth Cave, and some other caves, are found blind crayfishes. This does not mean that in all cases eyes are completely lacking, in fact, in most cases rudiments of eyes are present, but useless. How long these animals have thus lived in dark- ness we do not know ; but we find that an organ that is no longer used may lose its function and even dwindle away. We here see illustrations of the general law that disuse leads to deterioration in both structure and function, often resulting in complete uselessness, and perhaps com- plete atrophy as well. Hermit Crabs. These crabs back into an empty univalve shell, which they carry around with them for protection. The abdomen, and all the FIG. 53. BLIND CRAYFISH OF MAMMOTH CAVE, NATURAL SIZE. parts except the head and projecting appendages, become soft, and de- pendent upon a continuance of such protection. When the crab gets too big for the shell, he hunts for a bigger one. It is said that these crabs sometimes fight over shells. One hermit meeting another crab that has a shell that he thinks would fit him better than the one he has, ejects the other fellow, perhaps only to find that he has gotten a misfit after all, and so goes back to his old shell, a wiser if not a better crab. Barnaeles. If one lies down on the edge of almost any stone pier or wharf along the coast and looks down into the water, he may see a 82 Descriptive Zoology. general wavelike motion as if hundreds of hands, with feathery fingers, were constantly opening and closing. Looking closer, he will see that these feathers are in clusters, each projecting from the apex of a cone-shaped body whose base is attached to the rock wall. These are acorn barnacles. Disturb them and they will draw in their feathery appendages and close the shelly valves that guard the opening. They resemble -bivalve mollusks, and in fact were regarded as mollusks until it was discovered that when young they are like the young of the lower Crustacea. After leading a free-swimming life for a time, they attach FIG. 54. HERMIT CRAB IN SHELL OF SEA SNAIL. themselves by the head end to a rock, and thenceforth live anchored to this one spot. They have given up locomotion, and become sessile. The law of progress in evolution is toward greater freedom, as illus- trated in many forms of animal life ; but here we have a good example of retrograde development, or degeneration. Almost the only ready indication of its crustacean relationship is the segmentation of the appendages. Another form of barnacle is the goose barnacle, which has a body resembling a clam, attached by a soft, flexible stalk to some solid object, frequently to a piece of floating timber. When actively feeding, the shell opens and the feather-like feet extend in lively motion, but Crustacea. 83 they are withdrawn and shut in if the animal is disturbed. In its devel- opment the goose barnacle has about the same history as the acorn barnacle. Other Degenerate Crustaceans. Degenerate as are the barnacles, there are still lower crustaceans. Various crustaceans have become parasites, living attached to whales, fishes, etc., and have become so degenerate as to have lost all likeness to the typical crustacean struc- ture, so that no one would, without pro- longed investigation, even suspect that they belonged to this group. All of the above cases, blind crayfish, hermit crab, barnacles, and parasitic crus- tacea, illustrate one general principle, that disuse leads to atrophy, and that parasitic habits involve degeneration in structure as well as in function. Classification of Crustacea. The crus- tacea are divided into two subclasses, the Entomostraca and the Malacostraca. The Entomostraca are of comparatively FlG " 55 ' GooSE BARNACLES - simple structure, usually small, sometimes ^^Lgy^"^ 6 microscopic. The number of segments is variable, and the appendages are very similar throughout. We may briefly consider some of the leading orders. Some of the Phyllopoda are covered by a flat, shield-shaped carapace ; others have a bivalve shell which does not inclose the head. Some Phyllopods have no carapace. In some forms the body is unsegmented, and there are leaflike, lobed, swimming feet. The Ostracoda are small and the head as well as the rest of the body is inclosed in a bivalve shell, somewhat resembling a little clam. The Copepoda may be represented by the cyclops, or water flea. Fig. 56. This form is common in sluggish streams and ditches. It is white, large enough to be seen by the naked eye, and swims by a jerky motion of the antennae, which are its largest and strongest appendages. The female bears two large egg masses. The Cirripedia comprise the barnacles above mentioned. The Malacostraca comprise the higher Crustacea. They are usually of considerable size, and the number of segments is rather constant, instead of variable as in the Entomostraca. There may or may not be Descriptive Zoology. a carapace, and the head may consist of but one piece, formed by the consolidation of several segments (usually five). The thorax has eight segments and the abdomen usually seven. Without attempting to enumerate the orders, we may mention the Amphipoda, and illustrate them by the beach fleas and sand hoppers, FIG. 56. WATER FLEA (CYCLOPS). Female with egg sacs. There is a single eye with two facets. which have a laterally compressed body, the anterior legs bearing gills, and the posterior used for jumping. The Isopoda have a body flattened from above, and bear gills on the abdominal appendages, as in the sow bug, shown in Fig. 57. The Drcapoda. or ten-footed Crustacea, are so named from the five large pairs of thoracic appendages observed in the crayfish, which serves as an example of the group. The Decapods are somet ^ mes further divided into the Macrura, or long-tailed forms, such as the crayfish and lobster, and the Brachyura, or short-tailed forms, such as the crabs. FIG. 57. Sow BUG (Crustacean). Characters of Crustacea. i . The crustaceans have a hard cuticle, formed by the underlying skin. The cuticle consists largely of a substance called chitin, which is tough and more or less elastic. The chitin becomes more or less infiltrated by carbonate of lime, and is thus made harder. Crustacea. 85 2. But the limy material is not deposited everywhere in the cuticle. Certain places are left for joints. At these places the chitin remains flexible. Hence we have a series of segments joined together, five in the head, consolidated, eight in the thorax, and usually seven in the abdomen, twenty being the typical number in the higher forms. 3. Not only is the body segmented, but normally each segment bears a pair of appendages, which are themselves segmented. The eyes are no longer regarded as append- ages, but outgrowths of the head, which later become movable by means of a joint. 4. Most crustaceans have gills and lead an aquatic life. Some of the simpler forms breathe by the whole surface of the body, and a few forms which have gills live out of water, but usually in damp places. The gills remain moist, a small amount of water serving to transmit the oxygen from the air to the blood within the gills. 5. Crustacea normally possess two pairs of antennae. 6. Most crustaceans have compound eyes. 7. Crustaceans are an active group, but, as above noticed, some are sessile, and others parasitic. The King Crab. The king crab, or horseshoe crab, has a body shaped somewhat like a horseshoe. A six-sided abdomen fits into a deep notch in the posterior margin of the cephalothorax, and ends in a long, tapering spine. On the cephalothorax is one pair of simple and one pair of compound eyes. The mouth is in the center of the under surface, between the bases of the legs, and a series of leaflike gills are to be found under the abdomen. The king crab is found along our Atlantic coast, often burrowing in the sand. It molts by splitting the shell along the anterior margin. The hard crust, the molting, the gills, and general mode of life would seem to ally the king crabs to the Crus- tacea, but later researches place them nearer the spiders. They have some points of relationship with the extinct trilobites, and are especially interesting as the only known survivors of their race. 86 Descriptive Zoology. CHARACTERISTICS OF ARTHROPODS. 1. Arthropods have an external skeleton, or exoskeleton. 2. This skeleton consists of a series of rings, movable upon one another, i.e. the skeleton is segmented. 3. Some of these rings, or segments, bear appendages that are segmented. CLASSIFICATION OF ARTHROPODA. ARTHROPODA. Crustacea (Class I). (Tracheata.) i. Aquatic (generally) breathe i. Aerial breathe by air tubes by gills. or " lungs." 2. Antennae 2 pairs. 2. Antennas I pair (or none) . (Class II) (Class III) (Class IV) Arachnida. Myriapoda. Insecta. i. Head. Parts of ^ i i. Head-thorax. , Two ... Many. Body. ( 2. Abdomen. Other rings r I. Head. all alike. Three < 2. Thorax. 2. Body worm- ( 3. Abdomen. like. Legs. 4 pairs. Many pairs. . 3 pairs. Antennae. None. i pair. i pair. Jaws. 2 pairs. 2 or 3 pairs. 2 pairs. CHAPTER VI. BRANCH ANNULATA. THE SEGMENTED WORMS. Example The Earthworm. Habits of Earthworms. The name " earthworm " is so appropriate that no one questions its fitness. As every one knows, the earthworm burrows through the soil, usually making the hole deep enough to reach moist earth. The first portion of the burrow is usually vertical, but deeper its course is somewhat irregular. The worms swallow the soil, and from it they derive a considerable part of their food, digesting out of it the organic matter, which is largely composed of decaying plant material. The earthworm has the advantage of utilizing as food the material which it must excavate to make its burrow. In this respect it has a decided advantage over such animals as the mole or pouched gopher, which, as they proceed, are obliged to carry out or push aside the soil without deriving any immediate benefit from it. Earthworms are nocturnal in their habits, and the fact that they are seldom seen except when dug up leads most people to suppose that they spend their whole lives beneath the soil. But this is not the case, for if one searches for them with a lantern, they may be found in summer nights, sometimes wholly out of their holes, sometimes partly out, holding fast to the sides of the burrow by the tail end, and ready to retreat at the approach of danger. If they are found crawling about in the day- 87 88 Descriptive Zoology. time, except after a heavy rain, it is pretty good evidence that they are diseased. Of ten % in such cases it is found that they have been parasitized by a fly. Nearly every one must have noticed in the morning the fresh excrement, at the mouths of their burrows. These coiled "castings," as they are called, are the residue of digestion, and as the amount of nourishment in the soil is not great, and since the worm must do considerable excavating, the amount of the "castings" is necessarily considerable. In dry wea- ther the worms dig deep, and may be several feet from the surface. But when the ground is fairly moist they often remain during the day near the surface, with one end near the end of the hole. In winter they hibernate below the reach of frost. Form of the Earthworm. The end that usually goes foremost is the anterior end, and the hinder end is the posterior end. When crawling on the ground the surface on which the worm rests is the ventral surface, and the surface uppermost is the dorsal surface. If the earthworm were split lengthwise in the middle line by a vertical plane, the right and left halves would be counterparts of each other, that is, the earthworm is bilaterally symmetrical. The earthworm is approximately cylindric, the anterior end being more pointed, and the posterior end somewhat flattened, especially on the ventral surface. The division of the body into rings, or segments, is very evident. Toward the anterior end is a region of about six segments in which the sides and dorsal portions of the segments are swollen and more or less fused together, forming a wide girdle called the clitellum, the function of which is to secrete the capsule in which the eggs are laid. General Plan of Structure. As just noted, the body of the earthworm is cylindric. At the anterior end is the mouth and Annulata. at the posterior end is the anus. These are the two ends of the digestive tube, which runs straight through the body, being, on the average, about half the diameter of the body. The body, then, consists of two tubes,the outer wall,or body wall, and the digestive tube; the outer tube, or body wall, narrowing till it joins the inner tube. Between these two tubes is a space, the body cavity, or celom. In most of the higher animals we find a similar space around the digestive tube and within the body wall. In the earthworm the body cavity is divided into many compartments by the par- titions that extend between the inner and outer tubes at the constrictions, seen on the outside, between the successive segments. The Body Wall. This consists of two coats, each of which is made up of two or more layers. Outside is the skin, and within this the muscular coat. 90 Descriptive Zoology. The Skin. This consists of two layers. Outside is the cuticle, a thin layer, usually showing a beautiful iridescence. The cuticle often peels off in specimens that have been in alcohol. Underneath the cuticle is the epidermis (often 1 called the hypodermis). The Muscular Coat. The muscular coat is very much thicker than the skin. It consists of two layers, an outer layer of circular muscle fibers, and an inner layer of fibers running lengthwise. The inner layer is much thicker than the outer. The Bristles. The bristles, or setce, are short, stiff, chi- tinous spines, in four rows along the ventral surface and lower part of the sides. They are outgrowths of the skin, and are lodged in infoldings, or pockets, of the cuticle, which are called setigerous glands. As the bristles are worn out and become useless, they are replaced by others ; and in the same sac may be found bristles in various stages of development. Each row of bristles is double ; and each segment, except the first and last, has four pairs of them. Special muscles are attached to the base of the sac hold- ing the bristles, so that the bristles can be turned and held in various directions. The bristles can also be protruded and withdrawn. How the Earthworm Crawls. When the worm wishes to crawl forward, the spines are turned backward. Then the longitudinal muscles shorten, and the posterior end of the body is pulled forward, the whole body becoming shorter and thicker. Next the circular muscular fibers are short- ened ; this narrows and elongates the body ; but as the spines prevent any part from being pushed backward, the result is a forward movement. By a repetition of these acts the worm effects its slow locomotion. If it wishes to Annulata. 9 1 travel with the pos- terior end fore- most, as it does occasionally, it has but to point the spines forward, and the same action of the muscles will | propel it posterior end foremost. If * w the worm were jf lying on a perfectly | 3 smooth surface, on ^ which there was 1" C C/2 no friction what- * ever, the shorten- | " O ^ ing and lengthen- jg ing of the body | would avail noth- ... See Figs. 63 > Close the shell. - 2. Posterior adductor. > and 65. 3. Protractor pulls the foot and body forward and downward. 4. Anterior retractor pulls foot and body upward and backward. 5. Posterior retractor pulls foot and body upward and backward. When the foot is imbedded in the sand or mud, the shortening of the retractors, whose fibers spread over the body and foot, pull the shell forward instead of retracting the foot. Structure of the Clam Shell. If a shell is roasted thor- oughly, its structure may more easily be learned. The first fact to be noted is that the shell consists of layers ; the next, that these layers are in two sets, the dividing plane between which starts from the mantle line and extends toward the umbo. The shell is an outgrowth of the outer layer, or epidermis, of the mantle. But the layers of the shell made by the part of the mantle outside of the mantle line are not directly continuous with the layers formed by that part of the mantle which is dorsal to the mantle line. The mantle line is really a row of small muscle scars where no Descriptive Zoology. the muscular border of the mantle is attached to the shell. The edge of the mantle, it was observed, is attached to the edge of the shell. The outermost layer of the shell, the Umbo FIG. 66. STRUCTURE OF CLAM SHELL. Cross section. periostracum, is formed by the edge of the mantle, and is horny in composition. Inside this is the prismatic layer, and innermost is the laminated pearly layer. Growth of the Clam Shell. The successive concentric lines of growth seen on the outside of the shell mark the growth, each line of growth having once been the ventral edge of the shell. The layers are formed by the mantle, and each new layer is a little wider and longer than the one preceding, and outside of it. The muscles grow and gradu- ally move outward, hence the muscle scar continually widens, forming a triangle. But as the muscles move on, the scar of former years is covered by the new layers formed by the mantle. Uses of the Clam Shell. The fresh-water clams are little used as food, but their shells are used largely in making buttons. This is an industry of considerable extent along the Mississippi River and some of its tributaries. Respiration in the Clam. The current of water which we saw entering and leaving the clam brings oxygen as well Pelecypoda. in as food. The blood circulates in the walls of the gills, and thus the water current and the blood current are brought very close to each other. Oxygen passes from the water into the blood ; and from the blood, carbon dioxid and other waste matters pass into the water through the thin layer of the wall of the gill surrounding the blood tubes. There is also an active circulation of blood in the mantle, and a con- siderable share of the work of respiration is undoubtedly accomplished here. The Structure of the Gills. Each gill has the appearance of a thin, single-layered membrane ; but in reality each gill Artery \ Anterior adduc- \ tor muscle Auricle Ventricle i ! Posterior adductor muscle Gill FIG. 67. BODY OF CLAM. Left valve removed. is double walled, and a cross section is like a letter V. Each gill is a long, narrow, V-shaped pocket or trough, though divided into many compartments by cross partitions. The two gills of each side are united so as to form, in cross section, a W, the upper margin of the outer wall of the outer gill being attached to the mantle, the upper edge of 112 Descriptive Zoology. the inner wall of the outer gill joining the upper edge of the outer wall of the inner gill, while the upper edge of the inner wall of the inner gill is sometimes attached to the body or sometimes free. Back of the body the upper edges of the inner gills of the two sides unite with each other, thus sepa- rating the lower, or gill, cavity, into which the water first FIG. 68. CLAM, SIDE VIEW. Water currents to the mouth and through the gills. enters, through the lower incurrent siphon, from the upper, or cloacal, chamber, from which the water passes out. The question presents itself, " How does the water pass from the one cavity into the other ? " The sides of the gills are perforated, so much so that they are compared to a sieve or trelliswork. The vibrations of the myriads of cilia with which the gills are covered drive Pelecypoda. 113 the water that lies outside of the gill through these openings into the space within the gill. The water then passes up through the open top of the gill into the cloacal chamber, and back out of the excurrent siphon. The four gills are so many narrow, V-shaped troughs with their sides full of holes. Instead of filling at the top and leaking out at the holes in the sides, these troughs are filled through the holes Ventricle Cross section through heart. Cross section through posterior adductor muscles. Section at A . Section at B. FIG. 69. CLAM. Water currents through the gills. Compare with Figs. 68 and 71. in the sides, and overflow above, only the water cannot run down the sides of the trough, but must pass back and out through the upper siphon. (Figs. 68, 69, and 70.) The Food of the Clam, and how Obtained. The clam lives on microscopic plants and animals and on minute par- ticle^ oj[ w organic matter. This material is supplied by the current*of water which is continually passing into the lower Descriptive Zoology. and out of the upper siphon. The current is produced by the vibration of the cilia which cover the outside of the gills and the inner surface of the mantle. The entering current passes forward around the body and gills. The palps are also ciliated ; and between the two palps of each side the minute particles are caught and passed on into the mouth, Blood tubes Blood currents FIG. 70. STRUCTURE OF CLAM'S GILL. whose upper lip is formed by a continuation of the two outer palps meeting across the middle line, the two inner palps similarly forming a lower lip. The Digestive System of the Clam. The mouth is just back of the anterior adductor muscle. A short, wide gullet extends upward and backward to the large spherical Pelecypoda. stomach. On each side of the stomach is a large, greenish, digestive gland, often called the liver, whose secretion passes into the stomach. From the stomach the intestine passes downward and backward, making one or two coils in the abdomen and foot, then passes upward back of the stomach, near the dorsal margin ; it then turns posteriorly, parallel to the dorsal margin, passes through the ventricle Digestive gland Anus Intestine FIG. 71. DIGESTIVE AND EXCRETORY ORGANS OF A CLAM. of the heart, over the posterior adductor muscle, just back of which it ends, thus discharging the refuse of digestion where the outgoing current of water will catch it and sweep it out of the body through the dorsal siphon. The digestive tube is hard to trace in a fresh specimen, less difficult in one which has been boiled or hardened in alcohol. The whole tube may be injected with a colored starch injection and thus readily followed. In the fall the intestine is often found to contain a cylindrical body of 1 1 6 Descriptive Zoology. clear material having the consistency of a gumdrop. This is the " crystalline rod," and is thought by some to be a store of food material. Others regard it as a secretion to protect the lining of the intestine from injury. The Circulatory System of the Clam. From the gills and mantle of each side the blood passes up into the cor- responding auricle (Figs. 67 and 69). The auricles are wide at the base, where they arise from the upper margins of the gills, but narrow as they approach the ventricle, so that the lateral view gives a triangular appearance. The auricles are thin-walled, delicate structures. They open into the sides of the median ventricle. From the ventricle arise two arteries, one carrying blood forward above the intestine, the other extending backward beneath the intes- tine (Fig. 67). After leaving the arteries, the blood passes into irregular and ill-defined channels, supplying all parts except the shell. The blood collects in a caval vein under the floor of the pericardium, then passes through the kidneys, and to the gills once more. In the gills and mantle the blood loses carbon dioxid and gains oxygen. As it passes through the kidneys it loses nitrogenous waste matter, and from the digestive tube it absorbs new food material for the support of the life processes. The Kidneys. The kidneys are ill-defined, dark-colored organs, lying just beneath the floor of the pericardium and in front of the posterior adductor muscle. Each kidney consists of a tube doubled on itself, the bend being near the adductor muscle. One end of the tube communicates with the bottom of the anterior part of the pericardium, the other end opens on the side of the abdomen, near the upper edge of the inner wall of the inner gill, and above the tip of the corresponding palp. Here the excretion is poured out, and is carried away by the water current. Pelecypoda. 117 Nervous System of the Clam. There are three pairs of ganglions, which are connected by nerve trunks, called commissures : 1. The cerebral ganglions, one on each side of the mouth, just above the outer palp of each side; these are connected by a nerve cord which passes over the gullet. 2. The two pedal ganglions, lying closely side by side, deeply imbedded in muscle, near the middle of the foot. Each of these is connected with the cerebro-pleural gan- glion of its side. Gullet Visceral Ganglions FIG. 72. CLAM, NERVOUS SYSTEM. 3. On the under surface of the posterior adductor are the two visceral ganglions, apparently forming one double ganglion. These ganglions are much easier to find than the others. Each of these is connected with the cerebral ganglion of its side by a nerve cord, which runs along in the dorsal part of the body for a good share of its length. From all of these ganglions nerves extend to supply the adjacent regions. n8 Descriptive Zoology. The Sense Organs. The sense of touch is preeminent. This sense is best developed in the palps, along the margin of the mantle, especially that part of it which forms the borders of the siphons, and in the foot. There is no sense of sight, but the tentacles around the siphons seem somewhat sensitive to light. On a nerve near the pedal ganglion is the so-called "ear sac," of doubtful use. At the base of the gills is an organ sometimes called the "smelling patch," which, perhaps, has the office of testing the quality of the water. The sense of taste is doubtful, though it is probable that there is some discrimination as to what should be taken as food. The clam is sensitive to vibrations communicated either through the soil or the water. The Reproductive Organs. These are diffuse glands enveloping the coils of the intestine in the abdomen. The glands in the two sexes (ovaries and spermaries) are so similar that it usually requires microscopic examination to distinguish them. The ducts, both in the male and female, open on the side of the body near the opening of the duct from the kidneys. The eggs, when mature, pass out of the duct and lodge in the gills (more often the outer gills) of the female. They are fertilized by the sperms, which have been set free in the water and are drawn in by the same current that brings the food particles. The males and females may sometimes be distinguished by the greater convexity of the shell in the female, the valves being more bulging to accommodate the accumulation of eggs and young clams in the outer gill. Development of the Clam. The young usually develop during the fall and winter. When liberated, the young clams are called Glochidia. They are of different shape from the adult, being ovate, with the hinge at the wider Pelecypoda. 119 end. There is but one adductor muscle ; the foot is yet undeveloped, but from the foot region project long threads, the " byssus," by which it becomes attached. At the tip of each valve there is an incurved hook by which the little clam usually catches hold of the fin or gill of a fish, whereby it is protected from enemies and kept in fresh water. Soon after it thus becomes attached it is covered by a growth of the skin (a diseased growth) which still FIG. 73. YOUNG CLAM, STILL WITHIN THE EGG MEMBRANE. m, adductor muscle ; /, hooks by which it attaches itself to the gills or fins of fishes ; b, byssus ; s, sense organs. further protects the parasite. When sufficiently mature, the young clam drops off, soon becomes like the adult in form, and shifts for itself. Salt-water Clams. Although several kinds of marine clams are used as food, there are two that are more largely eaten in this country. One is Venus mercenaries, found from Texas to Cape Cod, but rare north of that point; the other Mya arenaria, found generally along the coasts of the Eastern states, but rather distinctively more Northern than the other. So when Massachusetts people speak of clams they mean the Mya, commonly designated elsewhere as the "soft clam," "soft-shelled clam," "long-necked clam," or "long clam." Whereas, when New Yorkers mention clams, without any qualifying adjective, they have 120 Descriptive Zoology. in mind Venus mercenaries, which, farther north, and away from the coast, would be designated as the " hard clam," "round clam," or "quahog." Both are frequently found in the markets inland. The Soft-shell Clam. This clam lives in a vertical burrow with the anterior end down. Instead of having short siphons like the fresh- water clam, the posterior margins of the mantle lobes are extended and grown together to form a long double tube, which reaches to the surface of the sand or mud, the body being sometimes a foot from the surface. The two mantle lobes are united along their entire edges, except at the two siphon apertures and an anterior opening, for the projection of the foot. The ventral channel is the incurrent and the smaller dorsal one the excurrent. As in the clam we have studied, the incurrent siphon has a fringed margin and is very sensitive. The border is also dark colored, so that it is not readily seen, and if disturbed it is withdrawn into the hole. At low tide the tube is generally so re- tracted. At this time clams are hunted and dug up. As the clam grows, it deepens and widens its burrow. The foot is small, and the old clam, dug up and left on the surface, has difficulty in making a new FIG. 74. LONG CLAM, BURIED IN THE MUD. The arrows show the currents in the siphons. From Kingsley's Zoology. Pelecypoda. 121 burrow. The internal structure is essentially the same as in the fresh-water clam. To accommodate the long siphon tube when it is retracted, there is a deep indentation of the mantle line in the posterior region. The shell of My a can- not be snugly closed, there being a. gap both anteriorly and posteriorly. Probably this may be accounted for by the more protected position and the need of having the siphon FIG. 75. HARD CLAM; ROUND CLAM; QUAHOG. With foot, siphons, and edge of mantle extended. tube extended most of the time. The siphon tube, with its black tip, is commonly called the " head," but this clam is as headless as its fresh-water relative. % The Hard Clam. The hard clam, or quahog, is also an important sea-coast food, especially where the soft clam is not obtainable. It is oval, with a thick shell. It bur- rows but a short distance, hence the siphons are not long, and the two tubes are partly separated. The foot is well developed, and the clam crawls more or less like the fresh- 122 Descriptive Zoology. water clam. These clams may be picked up at low tide, but are ordinarily taken by means of long rakes or tongs. The smaller or medium-sized ones are preferred. The border of the inner surface of the shell is usually purplish, and this part was made into the beads which constituted the more valuable purple wampum of the Indians of New England. The Oyster. One essential difference between the oyster and the clam is that the oyster is stationary, being firmly attached by one valve to some solid object, a rock, or another oyster so attached. The oyster lies on the left side, and the lower valve is much more concave than the upper, which is nearly flat, serving as a lid. As the oyster does not travel, it needs no foot and has none, hence is less tough than the clam. The hinge is at the pointed end of the shell, and the two mantle lobes are free from each other, except near the hinge. There are no siphons, the water entering all along the more curved bor- der of the shell and passing out on the straighter side near the larger end of the shell. The water is propelled by cilia and passes through the gills as in the clam. There is but one adductor muscle. Development of the Oyster. The eggs and young are not carried nor protected as in the clam, but the eggs are fertilized after being set free in the water. The egg becomes many-celled by the growth and repeated division of thft one cell w-hich constituted the egg. This becomes ciliated and swims by means of these cilia. After a few days of this free swimming life, during which time the shell and other organs are gradually developing, the little oyster attaches itself by its left valve to some submerged object, to which it becomes firmly cemented by the deposit of limy material which makes the hard part of the shell. Pelecypoda. 123 Comparison of Clam and Oyster. It will be noticed that the hinge in the oyster is at on.e end of the shell. This end corresponds to the anterior end of the clam. The oyster shell can open but slightly. The shells are rougher than those of clams. The green spot in the oyster is the digestive gland (often improperly called the liver), and not the digestive tube or its contents, as commonly sup- posed. Oysters and other salt-water mollusks are often left above water at low tide. Distribution of Oysters. Oysters are abundant along the Atlantic coast, south of Cape Cod, and in the Gulf of Mexico. In former times they occurred north of Cape Cod, but are now rare. Other species are found on the Pacific coasts and on the coasts of Europe, at the Cape of Good Hope, in Japan, and Australia. Chesapeake Bay is the center of the oyster industry, and the British market is now largely supplied from our beds, as we have not only the most abundant supply, but. ours are the best in the world. The Oyster Season. The common saying that oysters are good only in months containing the letter " r," is partly wrong and partly right. Oysters are good to eat at any time of the year when freshly taken from the water. But during their breeding season June to August they do not bear handling so well, and are more likely to spbil. It is more profitable, too, to leave them undisturbed at this time, that they may increase enough to maintain their numbers. The Shipworm. As the name implies, this mollusk is wormlike. It sometimes becomes ten inches long and half an inch thick. It bears a small bivalve shell at its larger end. It burrows in wood, doing great damage to ship timbers, buoys, wharves, etc. The first stages of devel- opment are like those of many other bivalves. If the larva cannot find I2 4 Descriptive Zoology. wood, it soon dies. The hole by which the larva enters the wood is hardly larger than a pin head, but as the animal grows it excavates a constantly widening tube, thus imprisoning itself for life. Just how it burrows is not certainly known. It does not feed upon the wood, the fine sawdust being carried off through the excurrent siphon. Its food consists of microscopic plants and animals, which are brought in by FIG. 76. RAZOR SHELL CLAM. currents, as in the clam, and its only communication with the outer world is through the small hole by which it first entered the wood. Shipworms work rapidly, often completely honeycombing the wood. But no matter how many of them there are in the wood, their tubes never interfere with one another, but there is always left a thin partition between. They avoid iron rust, so timbers are protected by driving them thickly with broad-headed nails. The copper sheathing of hulls of ships is the best protection. Shipworms caused the famous dam break in Holland at the beginning of the last century. The Razor Shell Clam. The razor shell clam has a shell somewhat resembling in shape and size the handle of a razor. The foot projects at the anterior end, the siphons at the posterior end. These clams make vertical holes in the sand and can dig rapidly. At low tide the posterior end may be seen projecting from the sand, but unless the col- lector approaches quietly and seizes the clam quickly, it is FIG. 77. MUSSEL. With threads by which it is attached. almost sure to escape. They seem to be very sensitive to vibrations, and probably be- come aware of approach through these rather than through hearing or sight, although they are somewhat sensitive to light. The Salt-water Mussel. One of the most common marine bivalves is the mussel. The shell is usually dark or purplish, and rather thin Pelecypoda. 125 and weak. The mussel is found attached to rocks by means of a num- ber of yellowish threads, the byssus, which grow from the base of the small foot. Mussels are found widely distributed along the coasts in most seas. They are used to a considerable extent as food in some countries. The Giant Clam. Probably the largest bivalve known is a marine clam of the genus Tridacna, found in Eastern seas. The soft body sometimes weighs twenty pounds, and the two valves of the shell together may weigh five hundred pounds. The Scallop. The outline of the shell as seen from one side is nearly circular. The two valves are not equal, one being less convex FIG. 78. SCALLOP. The crusaders' badge. than the other, sometimes perfectly flat. While at rest the scallop lies on the bottom with its valves widely gaped open. The scallop has a row of eyes along the margin of each mantle lobe. When an enemy approaches, the shell is quickly and powerfully shut by the one strong adductor muscle. This forcibly ejects the water, and by reaction the scallop is driven through the water, hinge foremost. The foot is rudi- mentary or lacking. The scallop is used for food ; the adductor muscle. 126 Descriptive Zoology. however, is the only part eaten. It has a sweetish taste. The scallop shell was worn as a badge by the crusaders, as evidence of having visited the Holy Land. Pearls. These are formed of nacre, the material which constitutes the inner layer of the shell. They begin as deposits around grains of sand or other foreign objects that have gained entrance within the shell. They are usually found between the mantle and the shell, but may be in almost any of the soft parts. It is said that the Chinese introduce little images into the cavity of the pearl oyster, leaving them to become coated over with nacre. The most valuable pearls are usually obtained from the pearl oyster, but they are often found in certain species of fresh -water clams. The most celebrated pearl fisheries are in the Persian Gulf. Characteristics of the Bivalve Mollusks. The clam and most of the other bivalve mollusks have the following characteristics, and have received various names, accord- ing as any given writer places special emphasis on one characteristic or another : 1. There is no head; hence some designate the group Acephala. 2. There are large, leaflike gills, from which comes the name Lamellibranchiata. 3. There is usually a muscular, tongue-shaped or hatchet- shaped foot, giving rise to the term Pelecypoda. 4. The mantle consists of two. lobes, each lobe lining a valve ; hence they are called Bivalve Mollusks. CHAPTER VIII. Spires forming whorl Sutures BRANCH MOLLUSCA. CLASS GASTROPODA. THE gastropods include the snails and slugs. They are of many kinds, terrestrial and aquatic, in fresh water and in salt water, shelled and shell-less, symmetrical and unsym- metrical, herbivorous and carnivorous. The Shell. The shells of gastropods are usually of one piece, therefore they are often called univalves in distinc- tion from the bivalves. Ape x This one-pieced shell is almost always in the form of a cone. Some- times the cone is nearly straight, as in the tooth- shells ; again it is in the form of a very low, wide cone, as in the limpets ; but in the great majority the cone is twisted into a spiral, making a thick, short cone out of a long and slender one. Some- times this primary cone is wound upon itself to form a plane spiral like a watch spring, as in Planorbis. But ordinarily the spiral is an ascending spiral, which may be illustrated by holding the outer end of a watch spring and pushing the inner end out 127 Lines of growth -Lip .. Aperture FIG. 79. PARTS OF A SNAIL SHELL. 128 Descriptive Zoology. at right angles to the plane of the flat spiral. By pushing out the center, first to the right and then to the left, we may illustrate both the right-handed and the left-handed shells. A very good substitute may be made by winding a narrow strip of paper around a lead pencil at one end. This, unwound, forms a flat spiral, representing the discoid shell. By pushing the center, first to one side and then the other, illustrate the right- and left-hand shells. Lay snail shells alongside a common wood screw ; those having the whorls run the same way as the threads of the screw are right- Left-hand shell Flat spiral or Right-hand shell FIG. 80. COMPARISON OF KINDS OF SNAIL SHELLS. hand shells ; those with the whorls twisting in the opposite direction are left-hand shells. The structure and composition of the shell are essentially the same as in clams, the lines of growth usually showing plainly parallel to the border of the lip. The Operculum. Nearly all sea snails, and many fresh- water snails, have a trap door attached to the hinder part of the foot, with which they close the aperture of the shell when the body is drawn in. This covering is the opercu- Gastropoda. 129 lum, and grows by concentric rings to keep pace with the continually widening aperture. The Lingual Ribbon. In the floor of the mouth is a rib- bon-shaped membrane bearing on its upper surface many rows of fine, sharp teeth. This ribbon passes over a pad of cartilage, being pulled forth and back by muscles. It acts like a rasp, wearing away the surfaces to which it is applied. As it is worn away in front, it is pushed forward by a new growth behind. In addition to the lingual ribbon, many FIG. 8 1. FIG. 82. FIG. 83. THREE SPECIES OF POND SNAILS. In Figs. 82 and 83 the aperture is closed by an operculum. mollusks of this group have also one or more jaw plates in the mouth, against which the ribbon works. The Foot. The foot in the gastropods is broad and flat. Resting upon this wide foot, the animal creeps or glides, leaving behind a slimy trail of mucus, which is abundantly secreted. The foot is symmetrical, and the anterior end is more or less distinctly marked off as the head. The Digestive System. The mouth opens on the front or under surface of the head. Watch a snail in an aqua- rium to see how the mouth works. From the mouth ex- tends a short gullet, sometimes dilated into a crop, to the i jo Descriptive Zoology. stomach, which in turn is followed by the intestine. The intestine is usually twisted around so as to end in the mantle chamber near the edge of the aperture of the shell. Salivary glands are almost always present, and there is a large digestive gland around the stomach, as in the clams. The Circulatory System. This is on essentially the same plan as in clams. The blood comes from the gills, or lung, to the heart, and is thence pumped to the other parts of the body. There is usually but one auricle in place of two found in the clam. The Excretory System. The gastropods have kidneys essentially like those of clams, whose ducts open into the mantle cavity. Owing to the one-sided development, usu- ally only one kidney is retained. The Nervous System. The nervous system is primarily about the same as that of the clam, consisting of several pairs of ganglions connected by nerve cords. The twisting of the body in many of the univalves involves the nervous system so that the nerve loop becomes twisted into the shape of a figure 8. Sense Organs of Gastropods. The eyes of the snail are described below. It is doubtful how well a snail can see, but it can discern light from darkness and can perceive quick movements. A sense of touch belongs to the whole surface of the body, but is more acute in the tentacles. At the base of the gills are organs called "osphradia," or "smelling patches," being perhaps organs for testing the quality of the water. Land snails can detect odors, arid the seat of the sense of smell seems to be in the tentacles. Respiration in Gastropods. The majority of the gastro- pods breathe by means of gills. Between the mantle and Gastropoda. 131 the body, near the aperture of the shell, is a space called the mantle cavity. In this space lie the gills, but in many cases but one gill is developed. Air-breathing Gastropods. In land snails, slugs, and numerous fresh-water snails, the mantle chamber becomes lore shut in, leaving a narrow opening, which is near the right side in right-hand snails, and on the left in the left- hand snails. Through this opening, which is kept closed most of the time, air is taken into the cavity, which acts as a lung. The blood circulates around the walls of the lung cavity, and is thus brought close to the air, so that an inter- change can take place between the two. The Land Snails. These are abundant in damp woods, especially in limestone regions. Their shells are usually thin. Land snails have two pairs of tentacles, with eyes at the tips of the upper or longer pair. The eyes can be pulled in, the tip disappearing first, as when in pulling off a glove the tip of the glove finger sticks to the end of the finger. If the tip of one of these tentacles is cut off, it will be reproduced, and it is said that this has been done twenty times in succession. Land snails usually have no operculums ; but at the ap- proach of winter, or of a period of drouth, they bury them- selves in the ground, and pull the body in until the foot is even with the edge of the aperture. A layer of mucus is secreted which completely closes the aperture. In some cases limy material is added, and, in any case, the covering soon hardens. Sometimes the snail then withdraws still farther, and makes another such barrier, or even several. In the spring, or at the return of moisture, the temporary door is cast off, and the snail resumes its activity. Snails have great vitality, and have been known to survive in this shut-in condition for six years without food. 132 Descriptive Zoology. Most kinds of snails lay their eggs in strings, masses, or clusters ; but the land snails deposit theirs singly, burying them or depositing them in moist places. The French follow the usage of the Romans in eating the land snails, and they are now imported into the United States .from Europe by Eastern dealers. In Europe snails do considerable damage in gardens, but they do not seriously affect us. Slugs. Slugs are air-breathing, terrestrial gastropods, almost always destitute of a shell. They are to be found in moist woods, especially under the bark or in the decaying trunks of fallen trees. On the anterior dorsal surface is a fleshy plate, the mantle, and near the right edge of this is the breathing pore, lead- Mamie FIG. 84. SLUG. Near the lower border of the mantle is the respiratory pore. ing to the lung. As in the land snail, there are two pairs of tentacles, with eyes at the ends of the upper (longer) pair. The body is elongated ; but when the animal is dis- turbed, it draws up into a short, compact lump. Slugs are nocturnal, hence are less conspicuous than snails. They do considerable damage in gardens, rasping off the surfaces of the leaves. Their presence is also in- dicated by the slimy trails which they leave behind. One of the most effective ways of checking them is to sprinkle coal ashes over and around the plants they are attacking. Gastropoda. 133 The Pond Snails: The pond snails have the mantle cavity transformed into a lung, as in the land snails. They frequently come to the surface of the water to get air, and may be seen first to emit a bubble of the contained air, take a new supply, and again descend to resume their FIG. 85. FIG. 86. POND SNAILS CREEPING. The largest part extending from the shell is the foot. There are three other protruding organs: (i) the proboscis, in the center; (2) the two tentacles, with an eye at the base of each; (3) outside the tentacles, the respiratory tubes, one of which takes' in water, the other sending it out. In Fig. 85, the dark semicircle back of the shell is the operculum. eating. They are exclusively herbivorous, and in an aqua- rium may be observed cleaning off the layer of green scum, mostly consisting of algae, which grows on the sides of the aquarium. FIG. 87. VARIATIONS IN A COMMON POND SNAIL. After Morse, from Packard's Zoology. There is but one pair of tentacles, at the bases of which are the eyes. Only a few pond snails have operculums. 134 Descriptive Zoology. The eggs are laid in clusters, usually enveloped in a gelat- inous mass ; and in an aquarium are usually deposited on the side of the glass in a very favorable place for watching their development. There are three common genera, Limnea, a right-hand shell ; Planorbis, a discoid shell, or flat spiral ; and Physa, a left-hand spiral (Fig. 80). The River Snails. These are not entirely distinct from the pond snails ; still, they nearly all breathe by means of gills, and most of them have operculums. Being gill breathers, they of course do not come to the surface to breathe, hence are not usually so conspicuous. Some of them have a projecting tube on each side of the neck, the water entering through one of the tubes to the gill, and passing out through the other. The eyes are like those of the pond snails in being borne at the bases of the one pair of tentacles. In some of the river snails the young are brought forth alive. Sea Snails. These are found chiefly along the shore, not often in very deep water. They are numerous in kinds and individuals, and vary greatly in both color and form. In size they vary from almost microscopic to a foot and a half or more in length. They also vary greatly in shape, from globu- lar (Fig. 88) to slender tapering forms resembling screws. The shell is usually right-handed, and the majority have operculums. Nearly all breathe by means of gills. FIG. 88. A LARGE SEA SNAIL (NATICA). It feeds on clams, etc., boring through their shells. Gastropoda. '35 A Drilling Sea Snail. Natica (see Fig. 88) is common on the New England coast. It is one of the largest of the snails found along the northern shores, sometimes reaching a length of five inches. Natica is carnivorous, and lives mostly on clams and other bivalves. It burrows in the mud or sand ; and when it finds a clam, it uses the lingual riobon and bores a hole through the shell, rotating its own body meanwhile. Tentacles Gills FIG. 89. A SEA SNAIL (NATICA) CRAWLING. Showing the very large foot "(surrounding the shell). It produces as neat a countersunk hole as any made by a drill for the head of a screw such as may be seen in any door hinge. After the hole is made through the shell, the soft body of the clam is eaten. Sea Slugs. Sea slugs are found near shore, on rocks or among seaweeds. Many of them are devoid of shells when adult, but all. have shells in their earlier stages. Many of them are symmetrical externally, but few are so in their internal structure, the intestine, for example, usually ending on the right side. In some the gills are covered, in others exposed. The gills often project as leaflike appendages on the posterior part of the dorsal sur- face ; and the whole animal, in form and color, has such a close resemblance to the seaweeds, on which it crawls and feeds, that it escapes the enemies to which, in its defenseless condition, it would be an easy prey. Some of the sea slugs can swim, and usually do so inverted, with the flat surface of the foot at the surface of the water. When the adult has a shell, it sometimes has its edges covered by the overlapping mantle, and some- times is completely inclosed by a sac like mantle. FIG. 90. NAKED MOLLUSK. From Kingsley's Comparative Zoology. 136 Descriptive Zoology. Limpets. Along the shore there are to be found gastro- pods with low conical shells, clinging close to the surface of the rocks. They may be scraped off by a quick motion with a dull knife, but if they are first alarmed they draw down and adhere so firmly to the rock that one is likely to break the shell in the attempt to dislodge them. The keyhole limpet is so named from the shape of the hole at the apex. The Ear-shell or Abalone. Closely related to the limpets is the " ear-shell " found on the California coast. There is FIG. 92. ABALONE OR EAR-SHELL. Furnishes mother-of pearl for inlaid work. FIG. 91. LIMPET. Surface view and side view. FlG. 93. RED CHITON (kl'tSn). a row of perforations near one margin of the shell, through which tentacles project. The interior of the shell is pearly and of beautifully variegated color. It is known as " aba- lone," and is much used for inlaid work. A Multivalved Mollusk. Chiton is a very peculiar marine mollusk. It is low and flat, creeping like the lim- pets. But the shell consists of a series of eight pieces over- lapping one another from the anterior to the posterior end. The animal is completely symmetrical, both internally and externally (Fig. 93). Gastropoda. 137 CHARACTERISTICS OF THE GASTROPODA. 1. The gastropods have a foot which is developed as a broad, flat, creeping disk. 2. There is usually a well-developed bead, with eyes and tentacles. 3. The majority have a univalve shell, but this is some- times lacking. 4. Body often unsymmetrical. 5. There is a lingual ribbon. CHAPTER IX. BRANCH MOLLUSCA. CLASS CEPHALOPODA. THE cephalopods include such forms as the squid, cuttlefish, and chambered nautilus. The Squid. The squid is the best example of the group. It is abundant along the Atlantic coast. Squids swim in schools, and are frequently found following schools of young herring and mackerel, on which they feed. They FIG. 94. COMMON SQUID. From Packard's Zoology. are chiefly nocturnal, though not infrequently seen in the daytime. After a storm the writer has seen the beaches on Cape Ann covered with them in the morning, where they have been left stranded by the receding tide. The Form of the Squid. Seen from above the body ap- pears cylindrical. At the anterior end is a well-developed Cephalopoda. 139 head and a distinct neck. At the tail end are two triangu- lar fins which together present the appearance of a dia- mond-shaped arrow point. Seen from below the body is conical or fusiform, ending in a distinct point behind, the tail fin covering about one third of the body. The fins are attached at the sides of the dorsal part of the hinder part of the body, and can be wrapped more or less around the tapering posterior end. The common kinds of squids sel- dom attain a length of a foot. The Head. From the front of the head project five pairs of arms, arranged in a circle around the mouth. Four pairs of these arms are short, and taper to a point. One pair are much longer, being nearly as long as the body, and are enlarged near the ends. On the inner surfaces of the short arms, and on one side of the club-shaped end of the long arms, are rows of suckers. These are button- shaped or saucer-shaped bodies, attached to the arms by stalks. The outer surface is hollow, and when applied to any surface the center can be retracted by the muscular stem by which it is attached, thus making a strong hold- fast. The long arms are sometimes called the "grasping arms." On the sides of the head are the two large eyes, the most highly developed eyes among the invertebrates. The Mantle. There is an opening all around the neck where it projects from the mantle cavity. The whole external envelope of the body is the mantle, inside which is the conical body, with a space extending nearly all around it except along the dorsal line, where the outside of the body mass is attached to the inside of the mantle. The mantle is muscular and very powerful. The Pen. The squid has no external shell, and the only representative of one is a horny structure, somewhat 140 Descriptive Zoology. similar in shape to a feather. This is imbedded in the dor- sal part of the mantle, extending nearly the whole length of the back. It is wholly inclosed in a capsule in the thick- ness of the mantle wall. The Siphon or Funnel. Projecting from the mantle cavity under the head is a funnel whose narrow end opens forward and whose wide end points back into the mantle cavity. How the Squid Swims. Water is taken into the mantle cavity through the open space around the neck. Then the edge of the mantle is contracted and is fastened to th<5 neck and sides of the base of the funnel by a set of ca~- tilages that have a sort of " hook and eye " arrangement. Then by the contraction of the mantle the water is forced out through the siphon, and by reaction the squid is rapidly driven backward through the water. So swift is its move- ment that it has received the popular name of " arrow fish." Squids sometimes dart clear out of the water, and, when kept in aquariums, thus jump over the sides. Their mo- tion is amazing, not only on account of its swiftness, but because there is no manifest cause of the motion. They propel themselves by the outgush of water, which is in- visible, and the change in size from the contraction of the mantle is so slight as to be unnoticed. To the uninstructed it is as inexplicable as the motion of a trolley car is to a savage. When the squid wishes to move slightly, it does so by gently flapping the tail fins. The Ink Bag. The squid has an ink bag, which lies near the rectum, and which opens near the anal opening, near the inner end of the funnel. When in flight from a pursuing fish, a discharge of ink is sent out in the strong gush of water through the siphon. This makes a dark cloud in the water, under cover of which the chances of Cephalopoda. 141 escape are greatly increased. This ink is the original "sepia" used as ink by the Chinese and Japanese. Some of this ink, from the fossil squid, has been used to make a drawing of the animal from which the ink was taken. The Color of the Squid. Ordinarily the dead squid is of a pale color, tinted with purplish. In the living animal the color is very changeable, passing quickly from red to blue or purple, and one part may have one of these colors while other parts have another color. This change of color is due to several different sets of colored cells, called "chro- matophores " ; these expand and relax under the control of muscles, which are in turn governed by nerves. The color changes in quick flashes, exceeding the quickness of blushing and pallor observed in the human face. This change of color is undoubtedly for the sake of protection, though one is inclined to wonder why such intense hues should be employed. As a school of squids are swimming along they are often seen to change their color abruptly, according to the bottom over which they are passing. Methods of Escape from Enemies. (i) The squid may elude observation by taking on the color of its surround- ings. (2) By speedy flight. (3) In flight its chances of escape are increased by the discharge of ink, which makes the water turbid. The Digestive System. The brown beak projects from the center of the circle of arms in front of the head. It consists of a pair of hard, horny jaws, somewhat resem- bling the beak of a parrot, except that the upper jaw is much smaller than the lower, into which it shuts. In addition to the beak there is a lingual ribbon, as in the snails. From the mouth extends a long, narrow gullet. Well back in the body is the muscular stomach, which has a large cecum. The intestine then extends forward, 142 Descriptive Zoology. ending in the mantle cavity near the large inner end of the funnel. The excrement, as in the clam, is swept out by the water current. There are salivary glands ; and a large digestive gland, often called the "liver," pours its secretion into the cecum. How the Squid captures its Prey. The squid is a voracious animal and lives largely on small fishes. It sometimes stealthily approaches a fish by almost imper- ceptible motions of its fins, until it is within grasping dis- tance, when it suddenly seizes the fish and quickly kills it by biting it in the back of the neck. Again it swims swiftly, and suddenly darts among a school of fishes, and turns and kills its prey by a quick snap of its powerful jaws. It also eats crabs and other animals. While it is pursuing the smaller fishes, it may, in turn, be chased by larger fishes. Respiration and Circulation in the Squid. The squid has two plumelike gills attached to the under surface of tne body, extending along the. mantle cavity. The circu- latory system is more highly developed than in any of the other mollusks. The Nervous System. The nervous system, too, is highly developed and concentrated, consisting of several pairs of ganglions in the head, forming a central brain, from which nerves extend to the other parts of the body. There is a protecting case of cartilage, a rudimentary cra- nium, supporting and partly surrounding the brain. The Senses of the Squid. The eyes are highly devel- oped, and evidently have keen sense of sight. A number of squids may be lying side by side in the water, perfectly motionless, perhaps relying on their quietness and protec- tive color. A sudden motion on the part of a person ob- Cephalopoda. 143 serving them may cause them to dart off like so many arrows. There is a rudimentary ear. Some authors say that the squid has the five senses which are best known in our bodies. The Squid used as Bait. Squids are used very extensively as bait in the cod fishery, a single small vessel sometimes using eighty thou- sand in six weeks. They are caught mainly by means of nets. They are either kept fresh for this use, or may be " pickled" in brine. They are also used in fishing for bluefish. FIG. 95. OCTOPUS, FROM BRAZIL. From Packard's Zoology. Giant Squids. Some species of squids have a body over nine feet long, with arms thirty feet in length. Some of these may have given rise to the stories of "sea serpents." The Octopus. As the name indicates, these forms have eight arms instead of ten, as in the squids and cuttles. The body is short and nearly spherical. Though the octopus can swim, it is very much less active than the preceding forms, spending most of the time crawling over the bottom, resting on the basis of the circle of arms with the body held above. The arms are more or less connected by webs at the base. There is neither internal nor external shell. A Pacific coast octopus has body a foot long, the arms having a radial spread of twenty-eight feet. 144 Descriptive Zoology. Many weird tales are told of the octopus, most of which have little or no foundation. In fact, there is no satisfactory evidence that an octopus ever intentionally attacked a human being. In countries adjacent to the Mediterranean the octopus is largely used as food. The Nautilus. The nautilus is closely related to the squids and cuttlefishes, but has the body inclosed in a flat-spiral shell. From time to time the animal moves forward and partitions off the space in the shell which it formerly occupied, the live animal occupying only the FIG. 96. CHAMBERED NAUTILUS. Showing chambers with soft body in outer chamber. From Packard's Zoology. outermost space in the shell. It retains its hold on the smallest and oldest portion of the shell, however, by means of a slender fleshy cord which passes through a series of holes left in the partitions. The inner, abandoned spaces are filled with gas. From this fact of growth the animal is commonly called the chambered nautilus, though it is also called the pearly nautilus, from the pearly lining. It lives in the South Seas. Fossil Chambered Shells. While the nautilus is almost the only living form of this peculiar plan of growth, there are many fossil cham- bered shells. Two of the most noteworthy of these are the Ammon- Cephalopoda. 145 ites, a spiral form very similar to the nautilus, and a perfectly straight conical shell, hence named Orthoceras. The Cuttlefish. In the cuttlefish the lateral fins extend along the whole of the length of the side, and the body is less sharply conical. Though essentially like the squid, they are less swift in their flight. In the sharp prow of the squid one sees the build of a racing shell, while the greater width of the cuttlefish suggests the increased breadth of beam in an ordinary rowboat. Cuttlefishes feed on crabs, clams, and fishes. The internal shell of the cuttlefish is calcareous, instead of horny as in the squid, and is well known from its use in fur- nishing limy material to canary birds. The ink of the cuttlefish is the basis of the pigment sepia. Cuttlefishes live near shore and are used extensively as food (in the Old World) as well as for the ink and cuttle bone. CHARACTERISTICS OF THE CEPHALOPODA. 1. There is a distinct head with highly developed eyes. 2. The foot has developed around the head (hence the name Cephalopoda), and is divided into a number of arms. 3. Part of the foot develops into a funnel-like siphon. 4. The shell may be external, internal, or lacking. 5. Chromatophores are found in the skin. 6. There is a beak and a lingual ribbon. CHARACTERISTICS OF THE MOLLUSKS. There is such a great diversity among the mollusks that it is very difficult to make any concise statement of their common characteristics. Some have shells, others none ; some are aquatic, others terrestrial ; some live in fresh water, others in the sea ; some breathe by gills, others by lungs ; some are herbivorous, some carnivorous ; some are free, others sessile; the limpet, though free, practically is glued to its place on a rock ; the slug is so slow that we have borrowed his name to make a common adjective, 146 Descriptive Zoology. while the scallop swims actively ; clams and oysters feed on microscopic forms swept in by currents of water, while the cephalopods prey upon the most active fishes ; there is strong contrast between the monotonous existence- of the headless clam, burrowing in the mud, and the free life of the cuttlefish, with its distinct head and highly developed eyes ; the oyster is fixed to his spot, almost as passive as a sponge, while the squid darts so swiftly that it is called the arrow fish. Nevertheless the following characteristics belong in common to the various classes of mollusks : 1. Aside from the shell the body is soft; hence the name "mollusk," soft. 2. The body is unsegmented, in distinction from the arthropods, the vertebrates, and many worms. 3.- There is an extension of the skin called the " mantle," which usually produces a shell, univalve, bivalve, or rarely multivalve. 4. There is usually a ventral muscular extension, the foot, which, in most forms, serves in locomotion. 5. They are mostly bilaterally symmetrical, but some are much distorted. 6. The nervous system consists of about three pairs of ganglions, connected by nerve cords. CLASSIFICATION OF THE MOLLUSCA. As all earlier classifications are based on superficial characteristics, it was to be expected that the first classifi- cations of mollusks would be by their shells. Hence the science of Conchology. But now we class the mollusks, as other groups, by their general plan of structure, mainly of the soft parts, for these parts make the shell, and the shell does not mould them. Cephalopoda. 147 They have been classed according to the head into Acephala (headless, clams), Cephalophora (head-bearing, snails), and Cephalopoda (head-footed, squids). The classification here adopted is based on the foot and presents three chief classes : 1. Pelecypoda (hatchet-footed) ; example, the clam. 2. Gastropoda (stomach-footed) ; example, the snail. 3. Cephalopoda (head-footed); example, the squid. CHAPTER X. BRANCH CHORDATA. THIS branch is mainly composed of the vertebrates, or backboned animals, that is, fishes, amphibians, reptiles, birds, and mammals. But it is now found necessary to class with them certain other animals formerly regarded as inverte- brates. Hence the old branch Vertebrata is made a sub- branch, and, with two other subbranches, included in the branch Chordata. The chordate animals are characterized by the possession of a dorsal chord or notochord. This is a supporting rod extending along the dorsal region between the body cavity and the main nervous system or spinal cord. While the notochord is always present in the young, it is, with a few exceptions, replaced in the adult by a seg- mented cartilaginous or bony axis, which is known as the spinal or vertebral column. In other words, the notochord is a sort of forerunner of the backbone. Subdivisions of Chordata. The branch Chordata is divided into three subbranches : 1 . Adelochorda, wormlike, marine forms (Balanoglossus). 2. .Urochorda, the tunicates or ascidians. 3. Vertebrata, lancelet to mammals. Division A. Acrania, the lancelets. (a) Cyclostomata, without jaws (lampreys). Division B. Craniata. (b) Gnathostomata, with jaws (true fishes to mammals). 148 Chordata. 149 SUBBRANCH UROCHORDA. As an example of the urochordates we may take the common ascidian. Such forms are sometimes called "sea peaches" or "sea pears," indicating the size, shape, and general appearance. They are attached by one end to rocks or shells or even to a muddy bottom. There are two holes, one at, and the other near, the free end. When the living animal is disturbed, it ejects water from both of these holes, hence the more common name, "sea squirt." The tough muscular external coat, or tunic, also gives the name tunicata. They are all marine. Structure of an Ascidian. Inside the outer wall, or tunic, is a lining, the pharynx, which hangs free below its attach- ment near the larger opening, the mouth. The pharynx is perforated by many small apertures through which water is driven by cilia. From the space around the pharynx, the peribranchial chamber, the water passes out through the second, or exhalant, aperture. From the lower end of the pharynx arises the gullet, which soon enlarges into the stomach. A relatively short intestine empties into the peribranchial chamber, where the outgoing water current catches, the refuse of digestion. There is a simple tubular heart, which is unique in its action. After pumping the blood in one direction for a few beats, it reverses its action and sends the blood the other way. The nervous system is very simple, consisting mainly of a ganglion between the two apertures (see Fig. 97). Development of Ascidians. In the above account of the structure of an ascidian there is no trace of relationship to the other chordates, and so long as the structure of the adult only was known, no one even guessed at its real affinities. But the study of its development threw light on 150 Descriptive Zoology. the subject. It was found that the larval ascidian possesses a long tail in which is a distinct notochord and an elongated nerve cord. But early in life the larva attaches itself by its head, the tail gradually disappears, and the elongated nerve cord becomes shortened to a mere ganglion. In the Mouth Nervous system Water exit Heart FIG. 97. DIAGRAM OF A TUNICATE OR ASCIDIAN (SEA SQUIRT). From Kingsley's Zoology. sessile adult animal no trace remains of the primitive noto- chord. This illustrates what is called " retrograde devel- opment " ; or, in simple words, the ascidian is a degenerate chordate, perhaps even a degenerate vertebrate. This is one instance of degeneration in which the real relationship is indicated by the structure of the young rather than by that of the adult. Acrania. 151 Other Tunicates. Some tunicates are minute and free- swimming by means of a vibratile tail. Other small forms are barrel-shaped, and exhibit a marked " alternation of generations." Many of the tunicates live and multiply by budding in colonies. SUBBRANCH VERTEBRATA. The Lowest Vertebrate. To the beginner it would seem easy to determine whether or not an animal has a back- bone, and so to decide whether it is a vertebrate or an invertebrate. But let us take a glance at what is by many authors regarded as the simplest of the vertebrates. The Lancelet. The lancelet (Branchiostoma, or Amphi- oxus) is fishlike in form and general appearance, only two FIG. 98. DIAGRAM OF LANCELET. Above (dotted) is the nervous system; below it (cross-lined) the notochord; the mouth is sur- rounded by a circle- of tentacles; below the notochord is a row of gill slits; the vent is near the posterior (right) end below. From Kingsley's Zoology. or three inches long, and nearly transparent. It is marine, being found in warm waters. Specimens are taken along the south Atlantic coast. The lancelet has a notochord extending to the anterior end, or the snout. There is a nerve cord along the dorsal side of the notochord, but the anterior end is hardly well enough developed to deserve being called a brain. It has blood tubes, but no heart. There is a tail fin, but no limbs, not even paired fins. The mouth is surrounded by a circle of fringelike tentacles. Back of the mouth extends the capacious pharynx, whose walls are perforated by numerous ciliated gill slits. At the 152 Descriptive Zoology. posterior end of the pharynx the intestine continues to the anus, situated posteriorly and ventrally. By the action of the cilia water is taken into the mouth, passes through the slits in the wall of the pharynx, and enters a space around the pharynx, called the atrial or peribranchial chamber, whence it escapes to the exterior through a ventral opening called the atrial pore. The lancelet usually lies buried in the sand, with only the mouth projecting. It gets both food and oxygen from the water, which is circulated through the body by means of ciliary action. The lancelet occasionally swims by fishlike movements. Classification of the Lancelet. It might, at first thought, seem strange that so simple an animal should be classed with a group having such complex structure as the verte- brates. The lancelet has, in fact, been placed with the mollusks, and later with the fishes, but is now located at the foot of the vertebrate series, chiefly on account of the possession of the notochord and the dorsal nervous system. It is really hard to locate an animal with colorless blood, and with neither skull, brain, heart, auditory organs, paired eyes, nor paired fins. The student who gets his ideas of classification almost entirely from reading is apt to think that the animal king- dom is divided into groups separated by clear and distinct dividing lines. But when he undertakes the actual exami- nation of any considerable series of animals, he often finds that two groups, which he regarded as distinct, actually merge one into the other so gradually that he finds it diffi- cult to see just where the line of division should be drawn. The line of demarcation must frequently be so drawn that it cuts across some intermediate forms, part of whose char- acteristics lie on one side and part on the other. In some cases the intermediate forms are living ; in other cases the Cyclostomata. 153 "connecting links" are represented only by fossil forms, as, for example, the extinct animals that connect the reptiles and the birds. The lancelets are plainly on the threshold of the verte- brate household. By some authorities they are denied admittance, and must wait just outside. Others allow them barely to cross the threshold and humbly take their place by the door, the lowest of the great branch at whose head stands man. Distinction of the Lancelet from Other Vertebrates. On account of the poorly developed brain and the absence of a cranium, the lancelet is placed by itself in a division called Acrania, while all the other vertebrates are desig- nated as Craniata, from the presence of a skull and the higher development of the brain. CLASS CYCLOSTOMATA. The lowest of the craniate vertebrates are the Cyclo- stomata. This class includes the lampreys, or lamprey eels, as they are often called, and the hagfishes. They are eel-like in form, without scales, and with smooth, slimy skins. They have no jaws, but a round, sucking mouth, hence they are sometimes called the " round-mouthed eels." There is a single nostril on top of the head. They have dorsal and caudal fins, but no paired fins. There are sev- eral pairs of purse-shaped gills, hence they are called by some authors Marsipobranchii. The skeleton has no trace of bone, being wholly cartilaginous and very imperfectly developed. The internal organs are, in many features, similar to those of the true fishes. Lampreys are rather widely distributed. They are found along the Atlantic coast and ascend the rivers. Descriptive Zoology. Some appear to live permanently in our large lakes. "By their sucking mouths . they attach themselves to fishes, FIG. 99. LAMPREY EEL. After Goode. -< From Kingsley's Zoology. sucking their blood, or even penetrating their bodies. They are the only vertebrates known to live a. parasitic life. In Europe the sea lampreys are valued as food. CLASS PISCES. Example. The Ringed Perch. Life of a Perch. If one stops to consider what are the chief objects in life with a fish, he soon sees that it is well expressed in the words " to eat and not be eaten." ANAL FIN FIG. ioo. EXTERNAL FEATURES OF A PERCH. In order to secure food and escape enemies the fish must have sense organs and organs of locomotion. Pisces. 155 How the Fish Floats. Before taking up the question of locomotion in fishes, let us first consider how it is that the fish can keep its place in the water without effort, neither rising nor sinking. A freshly killed fish usually sinks, showing that its body is slightly heavier than water. Almost every one knows that after a fish has been dead a short time it usually floats (commonly with the ventral surface upward). This is due to the development of gases in the intestines. Most fishes have air bladders (or swim bladders), by means of which they can regulate their position in water. By shortening the muscle fibers in the walls of the air bladder, or in the walls of the abdomen, the air bladder is made smaller and the fish sinks. By relaxing the muscles the air expands, the fish as a whole is relatively lighter, and consequently rises. Most fishes have swim bladders, and stay in midwater, that is, do not rest most of the time on the bottom. On the other hand, many fishes that rest most of the time on the bottom are without a swim bladder. In some fishes, as the perch, the air bladder is attached to the walls of the abdomen. In others, for example, suckers, the air bladder is free from the walls of the abdomen and is readily removed, and in dressing the fish the air bladder is taken out with the other internal organs. Locomotion of Fishes. Most fishes have the body com- pressed ; that is, flattened from side to side. The thickest part of the body is in front of the middle. The longer taper is toward the tail, and this gives greater flexibility and freedom of motion to this part. When the fish wishes to swim, it makes a sideways and backward stroke of the tail. This sends the body ahead and sideways ; that is, if the tail is struck back and to the right it pushes the fish 156 Descriptive Zoology. forward and to the left. But the fish quickly makes an- other stroke in the opposite direction, and as a result of the two he may go straight ahead. The fish may simply make the double stroke, right and left, and without further strokes dart straight forward, but usually there is a suc- cession of strokes by which it is enabled to pursue a straight course. It should be noted that nearly all fishes that can swim rapidly have a pointed snout to diminish the resistance. Resistance to the motion of the fish is still further reduced by the mode of overlapping the scales and the coating of mucus. The fins, too, point backward. How the Perch Eats. The perch feeds on minnows, worms, water insects, and larvae of various sorts, which it catches and swallows alive. The extensibility of the mouth is very great. The upper jaw can be protruded so that the opening of ' the mouth is a wide circle, nearly as large as the greatest circumference of the fish at any point. It has been noticed that when the fish keeps the mouth closed the snout presents a sharp point ; this is in marked con- trast with the large opening shown when the fish is about to ingulf its prey. It must be kept in mind that the fish has no special organs of prehension, but must do all the work of catching with the mouth alone. There are numerous teeth, but they are not large, serving merely to hold the struggling captive, and used little, if any, for either tearing or masticating it. Digestive Organs of the Perch. The mouth narrows back into the wide gullet, which is kept closed except when swallowing. The gullet leads into a fair-sized stomach, which ends blindly behind. The intestine arises from one side of the anterior end of the stomach. At the begin- ning of the intestine are three short blind tubes, the ceca. The intestine takes one or two turns and terminates in Pisces. 157 the anal opening. As the perch is carnivorous, we should naturally ex- pect a relatively short in- testine. In the anterior part of the body cavity lies the liver. On its posterior surface is the bile sac, which may be greenish or yellowish, or, if empty, have little color. It is then hard to discover, and appears like a small worm-shaped appendage to the liver. A duct conveys the bile into the intestine. Circulatory System of the Perch. The heart of "the perch is almost literally "in his throat." The heart is in a sepa- rate cavity, the pericar- dial chamber, with a firm partition between it and the main body cav- ity. The heart consists of three parts, through which the blood passes in order from behind. The venous sinus re- ceives the blood from all parts of the body ; from 158 Descriptive Zoology. the sinus the blood enters the auricle, which also is thin- walled ; from the auricle it passes into the ventricle, whose walls are thick and muscular, and by whose contraction the blood is pumped clear around the whole circuit to the heart again. From the 'anterior end of the ventricle runs for- ward the artery leading to the gills. The first part of the artery is often enlarged and is sometimes called the arterial cone or arterial bulb. This artery divides into four branches on each side, one to each gill. After traversing the gills, the blood-tubes (still called arteries) unite on each side, and later the two arteries thus formed unite to form one dorsal artery which supplies all parts of the body. The small arteries subdivide and form capillaries, which pervade all the tissues. The capillaries unite to form the veins, which again bring blood to the heart. How the Perch Breathes. When watching a live fish one sees that the mouth and gill openings open and close alternately. It can easily be proved that water enters the mouth and passes out through the gill openings ; thus a pretty constant current of water flows over the gills. Each gill consists of a bony arch, hinged at the upper and lower ends and jointed in the middle. Along the posterior border of each gill is a red fringe, the red color being due to the red blood within, which shows through the thin, delicate coverings of the gill filaments, as the individual parts of the fringe are called. As the blood comes up into the gill from the artery below, it goes off into small side branches running out into the filaments ; when it returns along the other margin of the gill filament, it enters another artery to pass out at the upper end of the gill. Thus it is clear that there is a constant flow of blood in very narrow, thin-walled tubes in the thin-covered gill, filaments; there is also a stream of fresh water flowing Pisces. 159 over the outside of the filament. The blood entering the gills has lost oxygen in passing through the muscles and other working tis- sues of the body ; so, in passing through the gills, -it absorbs oxygen from the water through the comparatively thin wall that separates it from the water. On the other hand, the blood entering the gills is loaded with carbon di- oxid and other waste matter that it has picked up in the mus- cles and other tissues ; this passes out into the water and is carried away. It should be noted that the current of water is in the right direction to keep the delicate gill fringe evenly extended, in- stead of matting and tangling it together, as it would be likely to do if the water current were reversed. 160 Descriptive Zoology. The Protection of the Gills. The gills are really ex- ternal organs. From the nature of their work they must have very thin external coatings, and so are correspond- ingly delicate. Hence the strong yet flexible gill cover. The more technical name for this is the opercle. It con- sists of several parts, the opercle proper, subopercle, preopercle, and interopercle (see Fig. 100). Overlapping from front to back, and being under muscular control so that they can be held down with considerable force when necessary, they constitute a very good shield. In addition to the opercle there is a gill cover below, called -the bran- chiostegal membrane. It is a tough, yet thin, mem- brane supported by several small curved bones, the branchiostegal rays. A fish carries about its head organs that are of vital importance and of most delicate texture, yet it dashes among more or less rough aquatic plants and after fishes that are well armed with spines. It is safe in doing this because of the double set of gill covers, one soft and one bony. When the perch swallows a spiny fish, still struggling, will not the soft gills be torn from the inside, producing serious injury ? The use of the bony, toothlike gill rakers projecting on the inner surface of the gill arches is now apparent. The gill rakers also serve as a strainer in swallowing smaller particles of food, and some authorities say that the gill rakers serve, to a certain extent, as teeth in crushing the food. When the fish seizes its prey, it of course takes water into the mouth with it; but this is allowed to pass out through the gill openings, and probably only a little is swal- lowed with the food. The Sense Organs of the Perch. The perch has well- developed eyes, but without movable lids. If any one Pisces. 161 doubts their keenness of sight, let him fish for trout or black bass before rendering his verdict. The sense of touch seems well developed. Numerous fishes have tactile bar- bels about the mouth, as the catfish, sturgeon, and codfish. The lateral line is considered a sense organ. There is an internal ear, but it does not appear that fishes hear ordinary sounds made out of water, like human speech, unless they are loud ; on the other hand, fishes have a keen perception of any sound vibrations that are directly transmitted to the water, such as splashing in the water, noises made by the grating of oars in the oarlocks or by hard objects striking the bottom or sides of a boat. The semicircular canals are now understood to be connected with a sense of equilibrium. Smell is probably, pretty well developed, in some fishes at least. The nostrils have nothing to do with respiration in any fishes below the lungfishes. The nostrils do not open into the mouth, but are simply openings into a cavity around which the nerves of smell are distributed. Some fishes have a single nostril on each side. In others, as in the perch, there are two openings on each side. The two nostrils of one side connect with a common cavity, the water entering through one aperture and leaving through the other. The sense of taste is probably less distinct. Excretory Organs of the Perch. The gills excrete car- bon dioxid. For the removal of nitrogenous waste matter, there is a pair of slender red kidneys which extend the whole length of the body cavity. They can be seen through the dorsal wall of the air bladder. There is an enlargement at the anterior end in front of the air bladder. At the posterior end there is a tube, the ureter, to convey the excretion to the exterior ; this duct joins a small uri- nary bladder and opens just back of the opening of the ovi- duct, so that the three openings at this place are, in order 1 62 Descriptive Zoology. from the front, the anus, the opening of the oviduct, and the opening of the ureter. In most of the higher fishes these three openings are separate. Development of the Perch. The ovary is an elongated body, occupying, when the eggs are mature, a large part of the space in the body cavity. The outlet of the ovary is the oviduct, whose external opening is just back of the anus. The ovary shows that it is really a double organ by its forked anterior end. In the male the two white sper- maries unite in one sperm duct, which reaches the exterior just behind the anal opening. The eggs are fertilized after they have been laid. They are left without care on the part of the parents. The eggs contain a store of nour- ishment which is not yet completely absorbed when the tiny fish begins to swim. The young fishes feed at first on small crustaceans and other minute forms of life. Both the eggs and the young fishes are eaten in great numbers by many kinds of fishes and other voracious water animals. Scales. Scales are developments of the deeper skin or dermis, serving for protection, or ornament, or both. The scales usually overlap each other so much that only a small part of each scale is exposed, and this part is covered by the epidermis. The scales are usually of horny material and not bony, except in a few fishes, such as ganoids. Kinds of Fish Tails. When the tail is completely sym- metrical, inside and outside, it is called diphycercal. In most fishes the tail, while externally symmetrical, is not so within, the spinal column being turned up as it joins the tail fin ; such a tail is homocercal. When the tail is unsym- metrical, with the spinal column extending into the upper lobe, the tail is said to be heterocercal. It is noteworthy that the tails of nearly all young fishes are heterocercal. Pisces. 1 63 The Fins. The ordinary fin has a set of fanlike rays supported by a series of bones at the base of the fin. Fins are designated as " soft-rayed " or " spiny-rayed," according to the nature of the supporting rays. The dorsal, anal, and caudal fins are called median, as they are in the middle plane of the body. The pectoral and pelvic are spoken of as " paired fins," and are com- parable to the two pairs of limbs of the higher vertebrates. Uses of the Different Fins. As already noted, the tail fin is the chief propelling power. It also serves as a rud- der in guiding the direction of movement. The paired fins serve as balancing organs and also serve in elevating or depressing the body. The dorsal and anal fins act like the keel of a boat in steadying and guiding the movement. The Air Bladder. The air bladder is generally consid- ered as comparable with the lung of the higher forms. It certainly acts as an organ of respiration in the lungfishes and some of the ganoids. But in most fishes the air bladder acts as an organ for maintaining the fish's position in the water, and hence is more appropriately spoken of as a " swim bladder." In the lungfishes and some ganoids the air bladder has a wide and direct connection with the gullet ; in many other fishes the opening persists, but is less direct. On the other hand, in many fishes the duct is entirely closed. The air bladder may have thin walls or thick ; it may be in one section or divided into several sections ; it may be attached to the body wall or lie freely in the body cavity. Flatfishes. Fishes may be flattened in two ways : (i) from side to side, that is, laterally, when they are said to be " compressed," as in the ordinary fish, more mark- edly shown in the fresh-water sunfishes; (2) a fish that is flattened from above, or dorso-ventrally, is said to be 164 Descriptive Zoology. . "depressed," as with the rays. The flounders are com- pressed, but have turned down on one side. Electric Fishes. These fishes have the power of giving an electric shock when touched. The electrical apparatus is a modification of the muscular system, and, like the muscles, is under the control of the nervous system. It is a point to be noted that the electric fishes are devoid of scales. The torpedo of the Atlantic coast and of the Mediterranean belongs to the rays. An African catfish has the same power, and in South America is found the electric eel. It is said that in South Africa the natives drive herds of horses into the pools, and after the electric eels have exhausted their " shocking power " on the horses, the eels may be caught and handled with impunity. Colors of Fishes. The colors of fishes are due to two factors, the nature of the scales and the pigment in the epidermis. The scales often are striated or polished to give various colors, especially the gleam so often seen on the sides of a fish. Aside from this kind of appearance the color is chiefly due to pigment. As in most animals, the color 's darker on the back than below, where we often find white. The olive or dark back of most fishes makes it difficult to see them when looking down into the water, while the white color beneath might make a fish less con- spicuous to an enemy below him. In the breeding season many fishes, especially the males, assume much brighter colors, most accented on the fins. Many fishes, notably catfishes, change their color considerably in conformity with their surroundings, like the amphibians and lizards. Care of the Eggs and Young. Most fishes give no care whatever to the eggs or young. Some deposit the eggs in a place of comparative safety. The stickleback builds a nest for the eggs and the male defends them carefully. Pisces. 165 But the eggs of many fishes are eaten by thousands by many kinds of fishes and other animals. The very great num- ber of eggs laid by most fishes is in keeping with the fact that the chances are many to one against their success- ful development. Indeed, if the eggs all developed, it is easy to see that the ocean would be overrun. For instance, the codfish is said to lay about eight million eggs yearly ; .if each of these eggs developed, it would not take long literally to fill the ocean. Contrast this " infant mortality" with that of the fulmar petrel. This is said to be the most numerous bird in the world, though it lays but a single egg ; but the conditions are such that the chances of this single egg for reaching maturity are ex- tremely favorable. Migration of Fishes. The salmon, shad, and sturgeon pass from the sea up rivers to spawn. The eels pass from rivers into the sea to lay their eggs. Aside from migrat- ing to find suitable breeding grounds, fishes migrate more or less in search of food. With some kinds their move- ments are pretty regular and well known ; in other cases their location at any given season is very uncertain, depend- ing on their food and other conditions not accounted for. Deep-sea Fishes. Most fishes are found near shore or in comparatively shallow water. Of those found in deeper waters, it is interesting to observe that, as the water be- comes deeper, and the amount of light consequently less, the fishes usually have larger eyes, or else a better develop- ment of the organs of touch. In the deepest water many are phosphorescent, and blind fishes, or fishes with rudi- mentary eyes, are found. The Food Fishes. Among the principal food fishes are the codfish, salmon, haddock, shad, mackerel, hake, smelt, sardine, menhaden, mullet, lake trout, whitefish, sturgeon, 1 66* Descriptive Zoology. halibut, flounder, herring, catfish, various kinds of bass, both fresh-water and marine, pike, pickerel, sucker, buffalo, carp, and many others. Space will not permit an account of them here, but the student is referred to the Riverside Natural History, and other works of the same scope. Artificial Propagation and Distribution of Fishes. In late years much has been done toward protecting and propagating our edible fishes. With the increase of popu- lation the food question will gradually become a more and more serious one. An excellent authority has said that an acre of water ought to supply as much food as an acre of land. The time has passed when the privilege is extended to any one to fish anywhere and at any time. Common sense dictates fhat fishes should not be caught during their breed- ing season, and that they should not be caught under a cer- tain size, etc. ; hence laws limiting the fishing season, and requiring that seines must have meshes not less than a given size. Killing fishes by the use of dynamite is prohibited. Also it is provided that there shall be no obstruction to the free passage of fishes up and down streams ; and that where dams are necessary, side channels (fish ways) shall be provided. Most of the states have enacted laws for the protection of its native fishes. A number of states have made appro- priations for the establishment and maintenance of fish hatcheries, where fish are artificially hatched. These are shipped, to be introduced into various waters where it is thought they will thrive, sometimes to replenish a stock that is diminished by overfishing or other causes ; in other cases to introduce them where they do not naturally occur. The United States government has also taken the matter in hand, and many valuable results have been obtained. This industry is comparatively in its infancy, but it promises Pisces. to increase greatly the world's food supply. It remains to be seen what can be done toward getting rid of the more voracious fishes that destroy so many of the young of the food fishes. The pikes, including the pickerel and mas- calonge of the tributaries of the Mississippi and St. Law- rence, must greatly reduce the numbers of more valuable fishes. If they were to increase rapidly, they might nearly deplete the waters, so active ajid voracious are they. CHAPTER XI. BRANCH CHORDATA. CLASS PISCES (Continued). The Elasmobranchs. THE sharks and rays are the chief representatives of the subclass designated Elasmobranchii. They are nearly all marine. One of the best representatives is the shark known as the "dogfish," which is caught in large numbers along the New England coast for the sake of the oil ob- tained from the livers. It differs from the " true fishes " in the following points : 1. The skeleton is cartilaginous, never bony. 2. There is no gill cover, the gill slits (usually five) opening separately. 3. The mouth and nostrils" open ventrally. 4. The scales are small and separate, making the skin rough. 5. The tail is heterocercal, that is, the spinal column extends up into the upper lobe. 6. The eggs are few and large, inclosed in a tough case, the walls being strengthened by chitin. In some sharks, as the dogfish, the young are brought forth alive. 7. There is no air bladder. The Sharks. The typical shark has a spindle-shaped body, and is exceedingly active. The mouth is far back under the head instead of in front, as in most bony fishes. 1 68 Pisces. 169 The gill openings are separate. The teeth are flat, three- cornered, and sharp. There is a constant succession of teeth, so that as those of the front row are lost, others take their place from behind. Though sharks are very vora- cious, it does not follow that they always attack human FIG. 103. SHARK (DOGFISH). Showing separate gill slits. Tail heterocercal. beings. For instance, on the coast of North Carolina sharks are abundant and of large size ; yet they do not attack man. This is probably because fishes are abundant and the sharks have an ample supply of food. But in some parts of the world sharks are exceedingly dangerous. The Rays. The skates and rays have a broad body, partly due to the merging of the body into the large, horizontally flattened pectoral fins. The bo'dy is usually A FIG. 104. SHARK (DOGFISH), VENTRAL VIEW. Showing nostrils, mouth, gill slits, and anus. rhomboidal, often wider than long. One form is called the "barn-door skate." They live on the bottom, feeding on mollusks, and have pavement teeth. Some have sharp 170 Descriptive Zoology. spines above the base of the tail, and are called " thorn- backs " and " sting rays." Perhaps the largest of them is the "devilfish," sometimes attaining a width of eighteen feet and a weight of several tons. Some of the rays have a complicated electric apparatus, FIG. 105. COMMON SKATE (RAY). Jaws and teeth (above); mouth and gill slits (below). From Packard's Zoology. with which they can give a strong shock to an animal with which they come in contact. This serves both as a means of defense and for securing prey. The one electric ray found on the Atlantic coast has the scientific name Torpedo and the common names " crampfish " and "numbfish." THE BONY FISHES. The great majority of fishes differ from the sharks and rays as follows : I. The skeleton is bony instead of cartilaginous. Pisces. 171 2. The gills are protected by a gill cover, so that there is but one external opening. 3. The eggs are small and numerous. The Spiny-rayed Fishes. The perch is typical of a large group of fishes, all of which have spiny rays. The perch is widely distributed in fresh-water lakes and streams ; the sea perch, or cunner, is common along the Atlantic coast, and is so nearly like the yellow or "ringed" perch that the descriptions and directions for dissection will apply fairly well to it. In the same family with the perch is the pike perch, better known as the " wall-eye " or wall-eyed pike, an excellent food fish. Among the perches are also the darters, a most interesting family on account of their small size and peculiar* habits. They rest on the bottom, never poising in the water like ordinary fishes ; they are found in streams, in rapid currents, getting their food under FIG. 106. MACKEREL. stones, etc. They swim by means of their pectoral fins, coming to rest after the quick, darting motion that gives them their name. One species is only from an inch to an inch and a half long. Yet in some respects they are to be classed among the most highly developed of fishes. They may be caught in a minnow seine by taking pains to "keep the lead line down s " that is, by being careful to drag very 172 Descriptive Zoology. close to the bottom. In keeping with the fact that they stay on the bottom is the fact that most of them lack an air bladder. They feed mostly on insect larvae. The sunfishes are a closely related family ; these are well known as having short, deep bodies, usually with bright colors. More active than the sunfishes proper, though in the same family, is the black bass, so well known as a game fish. There are also the white bass, striped bass, and yellow bass in fresh waters, and various kinds of sea bass. Two important families of the spiny-rayed fishes are the mackerels and the codfishes. FIG. 107. CODFISH. Most of these fishes are very active and reckoned among the " game fishes " on account of their resistance to being caught and the skill required to capture them. The Black Bass. The black bass is probably more sought by the scientific angler than any other fish in the Central States. It is a fine type of the spiny-rayed fishes. " The black bass is eminently an American fish ; he has the faculty of asserting himself and making himself com- pletely at home wherever placed. He is plucky, game, brave, unyielding to the last when hooked. He has the Pisces. '73 arrowy rush and vigor of a trout, the untiring strength and bold leap of a salmon, while he has a system of fighting tactics peculiarly his own. I consider him, inch for inch and pound for pound, the gamest fish that swims." J. A. HENSHALL. The Catfishes. The catfishes are scaleless ; they have long, tapering barbels ("feelers") around the mouth; the mouth is wide, and the head low and flat, adapting the fish for a groveling life, skimming along the bottom. The dorsal and the pectoral fins each have for the first ray a very strong, stiff spine, with a jagged edge, by means of FIG. 108. CATFISH; CHANNEL CAT. which they inflict painful and probably poisonous wounds. They seem to be lovers of muddy streams, and lead a rather sluggish life. They abound in the Mississippi Val- ley, where some species reach a weight of 150 pounds. They are esteemed as food, as the flesh is of fair quality and unusually free from bones. The Suckers. In this family are a number of forms, such as the various suckers, the buffalo fishes, and carps, including some carps that have been introduced from Europe. The scales are large, with smooth borders ; such scales are called cycloid scales. They all have a scaleless 174 Descriptive Zoology. head and a sucking mouth, toothless, with soft lips capable of downward extension ; they feed to a large extent on vegetable matter, hence have a long intestine, in marked contrast with the short intestine of the carnivorous perch. The air bladder is large, and is constricted into two or three compartments, linked together sausagelike. The air bladder communicates with the digestive tube. They ascend streams in the spring to lay their eggs. Their flesh is rather tasteless and full of bones ; still, they are largely used as food, as they cost less than other fishes, being caught in immense numbers in seines. Their sluggishness contrasts sharply with the alertness of the game fishes. FIG. 109. ATLANTIC SALMON. From Kingsley's Zoology. The Salmon Family. The salmon is well known both from its commercial importance and from its remarkable migrations up rivers to spawn. It passes swift rapids and leaps falls of considerable height. To this family also belong the trout and the whitefish of the great lakes. The Trout. One of the daintiest of fishes, as well as one of the most delicately flavored, is the trout. On account of its wariness it is sought by the angler who wishes to overmatch its cunning. " This is the last generation of trout fishers. The chil- dren will not be able to find any. Already there are well- Pisces. 175 trodden paths by every stream in Maine, in New York, and in Michigan. I know of but one river in North America by the side of which you will find no paper collar or other evidence of civilization. It is the Nameless River. Not that trout will cease to be. They will be hatched by machinery and raised in ponds, and fattened on chopped liver, and grow flabby and lose their spots. The trout of FIG. no. THE RAINBOW TROUT. From Kellogg's Zoology. the restaurant will not cease to be. He is no more like the trout of the wild river than the fat and songless rice bird is like the bobolink. Gross feeding and easy pond life enervate and deprave him. The trout that the chil- dren will know only by legend is the gold-sprinkled living arrow of the white water, able to zigzag up the cataract, able to loiter in the rapids, whose dainty meat is the glanc- ing butterfly." MVRON W. REED. The Flatfishes. As an example of this group we may select the flounder found along the Altantic coast. These fishes keep near the bottom, swimming on one side, and the two eyes are both on the side that is uppermost. Per- haps the most interesting fact concerning these odd fishes is their development. At first they are symmetrical, with ij6 Descriptive Zoology. an eye on each side, and erect like other fishes ; gradually the body turns over to one side, the cranium becomes twisted, and the eye of the side that turns down travels over to the upper side ; the upper side becomes dark, while the under side is white or nearly so, whereas in the young flounder both sides were colored alike. The sole and the plaice belong to this family. The most important member, FIG. in. WINTER FLOUNDER. From Kingsley's Zoology. however, is the halibut, which sometimes reaches a weight of three or four hundred pounds. Eels. The eels have elongated, cylindrical bodies, with minute scales or none. They have no ventral fins, and swim or crawl through the mud by a snakelike motion. They are active and very voracious, pushing their way under stones and into holes after small fishes and crustaceans, on which they feed. It is said that they can crawl a consider- able distance on land, through wet grass, and that they pass around falls and other obstructions in this way. Flying Fish. Certain marine fishes are called " flying fishes." They do not really fly, but, by means of their long pectoral fins, make long flying leaps through the air. They Pisces. '77 make these leaps better against the wind than in the same direction as the wind. Their leaps are probably somewhat like the " sailing" of birds. THE GANOIDS. We have in the United States four kinds of ganoids, the gar pike, the sturgeon, the mudfish, and the spoonbill catfish. FIG. 112. GAR PIKE; GAR. The gar pike has a cylindrical body covered by rhom- boidal bony scales. These scales are coated with enamel, making a very strong and complete armor. The jaws ex- tend, forming a long bony snout, the nostrils being at the tip of the upper jaw. The teeth are sharp, and the fish is voracious, but of rather sluggish habits. The tail is slightly heterocercal. Three species are common in the Mississippi and some of its tributaries : the long-nosed gar (Fig. 112); the short-nosed gar; and the alligator gar, which is said sometimes to attain a length of ten feet. FIG. 113. COMMON STURGEON. After Goode. From Kingsley's Zoology. The sturgeon is decidedly like a shark in general ap- pearance, with its strongly heterocercal tail, its projecting snout, with the mouth well back on the ventral surface, and 178 Descriptive Zoology. its cartilaginous skeleton. The skin is also rough like that of a shark ; but in addition to the separate scales that give roughness, there are several rows of bony plates, each with a central projecting point. These rows of scales are not set close together, one row of large scales being along the back, with rows of smaller scales along the sides. The sturgeon has a projectile toothless mouth, and feeds along the bottom, sucking up worms, larvae, etc., from the mud. The spoonbill catfish very much resembles a catfish, being smooth-skinned, but has a long, paddle-shaped upper jaw with which to stir up the mud from which it gets its food. The mudfish, or bowfin, is, in the Mississippi Valley, commonly called the " dogfish," an unfortunate term that FIG. 114. MUDFISH; BOWFIN; GRINDLE. Dogfish (of Central States, but should not be confused with the shark called dogfish). is likely to confuse it with the shark called by the same name. The mudfish, as the name implies, lives in shallow water, and is a very voracious fish. It is more nearly like the ordinary bony fishes than the other ganoids, having a pretty complete bony skeleton. Its flesh is soft, and gen- erally considered as wholly unfit for food, but of late it is beginning to be used. In some waters of the Mississippi system it is very abundant. These four fishes do not present many characteristics in common, hence it is not strange that the authorities differ greatly as to their classification. In the first place, it should Pisces. 179 be noted that there are but few living ganoids ; these are the survivors of a host that existed in earlier geologic periods. Many of these fossil forms possess a heavy armor, of which the gar shows a sample. It is also noteworthy that North America has a majority of the survivors. Most of them have heterocercal tails. The most valuable feature for our consideration is the air bladder, which is present in all, and in all is connected with the gullet by a persistent open duct This duct opens on the dorsal side of the gullet except in one instance. Further, the air bladder in most has an unusual supply of blood, so that it serves to a considerable extent as a lung. Both the mudfish and the gar pike often come to the sur- face and emit bubbles and take in a fresh supply of air, FIG. 115. LUNGFISH. After Boas. From Kingsley's Zoology. very much as do the mud puppy and the tadpole after the lungs begin to develop. These two fishes are very tena- cious of life when removed from the water, undoubtedly because of the ability of the air bladder to act as a lung. The ganoids thus foreshadow the lungfishes, as, in turn, the lungfishes anticipate the Amphibia. THE LUNGFISHES. In the Jungfishes the development of the air bladder as a lung is much more complete than in any of the ganoids. The nostrils open into the mouth cavity, which is not the 180 Descriptive Zoology. case with, any other fishes. There is also a pulmonary artery and a pulmonary vein, making the circulation much more perfect. In keeping with this, the auricle is partially divided into two compartments. There are only three or four species, one in Australia, one in Africa, and one or two in South America. The Australian form has a single lung; the others have the lungs double. The African lungfish secures protection during the dry season by burying itself in the mud, where it remains in a snugly inclosed cavity. These " mud nests," as they are called, have been dug up and the fish taken alive and uninjured to Europe. Gills are present and permanently kept. It is a general belief among naturalists that the Amphibia originated from such lunged fishes as these we have been considering. Why, indeed, should we hesitate to believe that a race of animals has gradually changed from an aquatic to a terrestrial life in long course of time, when we have all seen this change take place in the individual frog in a relatively short time ? Whether they were first led to do this from the drying up of the water or from pollution of the water, making it unfit for respiration, or whether they were forced to adopt a land life from the competition for a living in the water, or from some other causes or conditions, who shall say ? SUBCLASSES OF PISCES. 'Subclass i. Elasmobranchii, sharks and rays. f Teleostei, the bony _,. Subclass 2. Teleostomi. \ fishes. Pisces. | _ . , . t . , [ Ganoidei, "ganoids. Subclass 3. Dipnoi, the lungfishes. CHAPTER XII. BRANCH CHORDATA. CLASS AMPHIBIA. Example. The Frog. Where Frogs Live. Frogs are usually found in or near water. In the spring they congregate in ponds and pools to lay their eggs. Later in the season they scatter, and may be found at some distance from the water, but still in moist places, such as near springs, swampy meadows, etc. Even when they are spending most of the time in the water they come out on the banks to catch insects. How the Frog Progresses. The frog has three modes of locomotion jumping, swimming, and creeping or walk- ing. The latter mode is seldom used except to change its position or climb up something on which to rest. The long, muscular thighs enable the frog to make powerful leaps, by which it rapidly escapes to the water when it is on shore and alarmed. In swimming it folds the fore limbs along- side the body and by the simultaneous strokes of the two hind limbs, with the long, broad, webbed feet, makes rapid progress. It is a model swimmer. The Frog's Food and Method of Eating. The frog feeds chiefly on insects, though it also eats slugs, worms, and various kinds of larvae. The writer has found the remains of a mouse in the stomach of the common frog, and in the stomach of a bullfrog a small bird entire ; but these cases are exceptional. The frog catches insects its main 181 182 Descriptive Zoology. food by means of the tongue. The tongue is attached in front and free behind. Insects are caught by turning the tongue forward quickly, the sticky mucus with which the tongue is covered holding them securely. There are fine teeth on the upper jaw and the roof of the mouth, but these serve merely to hold the insect or slimy worm, while it is being swallowed, and are not used for masticating the food. The wide mouth narrows into the gullet, which is really wide, since the animals captured are swallowed FIG. 116. PLAN OF FROG'S STRUCTURE, SIDE VIEW. whole, but is kept closed by being " puckered up," as it were. Back of the gullet is the rather large stomach. The stomach narrows as it extends backwards, and is con- tinued into the intestine, which, after one or two turns, suddenly widens into the cloaca. Alongside the stomach is the lobed liver ; between two of the lobes is the bile sac, whose duct empties into the intestine a short distance behind the stomach. The duct from the small pancreas joins the bile duct a little before the latter enters the intestine. Amphibia. '83 How the Frog Breathes. The adult frog breathes chiefly by means of lungs. In dissecting, the lungs may be found collapsed; in which case they are small and dark-colored. When inflated they are of considerable size and of a beau- tiful pinkish color, owing to the blood in the capillaries. A frog's limg is not a mere air sac, with transparent walls, as with most fishes. There is blood circulating in the wall, and the wall is somewhat thickened, and has ridges extending on the inside, which, to a limited extent, parti- FIG. 117. PLAN OF FROG'S STRUCTURE, VENTRAL VIEW. tion off the space into air vesicles, thus increasing the area of the inside of the lungs, and consequently exposing more blood to the action of the air contained within the lung. In watching the breathing movements of the frog, three actions are seen : first, the in-and-out movement of the floor of the mouth ; second, occasional movements of the side of the body ; third, opening and closing of the nos- trils. When the floor of the mouth is lowered and the nostrils are opened, air is taken into the mouth cavity ; if, now, the nostrils are closed and the floor of the mouth 184 Descriptive Zoology. raised, air is forced into the lungs. The gullet is kept firmly closed so that air does not enter it, and the glottis, a longitudinal slit in the floor of the mouth just back of the tongue, being opened at the right time, air freely enters the lungs. The windpipe, or trachea, is extremely short, dividing almost immediately to enter the two lungs. The less frequent movements of the sides of the body seem to be for driving air out. This is accomplished by the action of the muscles of the sides of the abdomen. From the above it may be understood why a frog may be suffocated by having its mouth held open for any considerable time. The frog also breathes to a limited extent by means of the skin. It has been noticed that the skin is always moist, a condition necessary for this function. In cool weather it will be noticed that frogs kept in aquariums frequently sink to the bottom and remain there for a long time. Of course the breathing movements then cease. The diminished activity is accompanied by a reduced re- spiratory need, and the blood,, circulating in the skin, absorbs all the oxygen that is required. Circulation of Blood in the Frog. The heart consists of one ventricle and two auricles. The right auricle receives blood through the .caval veins from all parts of the body except the lungs; this blood is dark because it has been deprived of its oxygen by the working tissues of the body ; it is loaded with impurities which the tissues have given to it. The left auricle receives blood from the lungs ; this blood is bright-colored from the oxygen just obtained in the lungs ; it has also lost some carbon dioxid. The two auricles contract at the same time and .send these two kinds of blood into one ventricle. How is one ventricle to send the purer blood to the organs that need it, and the impure blood to the organs whose work it is to Amphibia. 185 remove impurities ? Without attempting here to explain this in detail, it may be stated that, owing to the way in which the arteries branch from the ventricle, and to an ingenious valve arrangement, ( I ) the best blood is sent to the head, (2) the next best blood (somewhat mixed) is sent to the body, and (3) the most impure to the lungs and skin. The Lymphatic System. In skinning the frog it is very noticeable that the skin is attached only occasionally, leaving a free space between the skin and muscles over the greater part ot the body. In these spaces is a more or less watery liquid, the lymph. Lymph is also found in the body cavity around the internal organs. The lymph system is part of the blood system. Lymph may be described as part of the liquid of the blood that has soaked out of the regular blood tubes and gotten into the lymph spaces. There are two pairs of contractile ' lymph hearts, 11 one, whose pulsations may have been observed, near the anus. The other pair is between the transverse processes of the third and fourth vertebrae, and cannot readily be found. Excretion of Impurities. The lungs and skin remove carbon dioxid from the blood as it circulates through them. The nitrogenous waste matter is taken from the blood as it flows through the kidneys. From each kidney a tube called the ureter passes back to open into the cloaca on its dorsal surface. The Colors of the Frog. The prevailing colors are green and brown, though some are marked by black spots, and sometimes these black spots are made more distinct by a whitish border. The frog does not frequent bare ground, but is usually to be found near plants, whether in water or on land. Its colors are generally similar to the surround- ings, so that it is not a very conspicuous object, and some% times keen eyesight is needed to discover it even when in plain view. By distending its lungs the frog easily floats in water. When so floating only the top of the head is out of water, with its three projecting points, the snout and 1 86 Descriptive Zoology. the two eyes. In some kinds of frogs the head is more distinctly green than other parts, so a little practice is required before the collector readily discovers it as it rests in the water, with the top of the head appearing among green leaves. The color is due to pigment cells in the deep layer of the skin. These cells are branched, but can change their shape and vary the color somewhat in accordance with the sur- roundings. These cells may easily be observed in the skin of the frog's web, and can hardly escape observation when the circulation in the web is studied. The Frog's Enemies. Most of the larger snakes eat frogs when they can get them. Many fishes take them greedily, hence the frog is used as bait. A number of birds capture frogs, including some of the hawks, certain waders, and perhaps others. The frog's color undoubtedly often keeps it from being discovered, and when it is approached it can make use of one, or both, of its two speedy modes of locomotion to make good its escape ; concealment by protective resemblance and escape by flight are its two safeguards, for it has no weapons of defense. How Frogs spend the Winter. At the approach of freez- ing weather frogs reassemble at the shore, and perhaps for some time may be found at the surface during the warmer part of the day, but stay at the bottom during the night or during colder days. They finally dive deep into the mud, which is their winter resort. Here they hibernate, motion- less, eyes closed, lungs emptied, with no breathing move- ments, the heart beating feebly and slowly, till they are revived by the returning warmth of spring. Warm-blooded vs. Cold-blooded Animals. The frog's nor- mal temperature during the season when it is active is a Amphibia. 187 little above the surrounding air or water. Its temperature varies with the degree of its activity. In the winter when it is buried in the mud its temperature sinks nearly to the freezing point, for the lower layers of water have a tem- perature of about 40 F. In other words, the frog's tem- perature is variable, instead of constant as in the case of mammals. The Nervous System of the Frog. The widest part of the brain consists of the two optic lobes. In front of these are the two cerebral hemispheres. Barely separated from the anterior ends of the cerebral hemispheres by a slight groove are the olfactory lobes ; they seem to be a part of the cerebral hemispheres. Back of the optic lobes, sepa- rated by a depression, is the cerebellum, a narrow trans- verse band. Beyond the cerebellum is the spinal bulb (see also Fig. 167). There are ten pairs of cranial nerves. There are also ten pairs of spinal nerves. The Senses and Sense Organs of the Frog. The promi- nence of the frog's eyes has already been noticed. The upper lid is thick and drops with the eye when it is with- drawn. The thin under lid can be drawn more completely over the eye and is often used when the upper lid remains stationary. Back of the eye the eardrum is conspicuous. From the inner surface of the tympanum extends the bony rod called the " columella " to the inner ear, to which it transmits the vibrations received by the tympanum. The sense of taste is apparently well developed. All parts of the skin seem to possess the sense of touch. The nostrils open directly into the front of the mouth. Of the sense of smell less is known than of the other senses. Development of the Frog. The eggs are formed in the ovaries. When the eggs are mature the ovaries become much folded and plaited and the egg-masses occupy a large i88 Descriptive Zoology. share of the space in the body cavity. The eggs finally are set free in the body cavity ; they find their way to the open- Nasal sac Eye Cerebrum Spinal bulb t Boundary between I Spinal cord - Spinal nerves ,. Branches connecting ,' t Sympathetic gan- *' glions Sympathetic gan- / glion Olfactory nerve Optic nerve Ganglion of fifth nerve Fifth nerve Ganglion of vagus nerve Vagus nerve First spinal nerve Brachial nerve (arm) Sympathetic nerve trunk . Sympathetic gan- glions Sciatic nerve (thigh) FIG. 118. NERVOUS SYSTEM OF FROG, VENTRAL VIEW. Amphibia. 189 ing at the inner end of the oviduct and as they pass along the duct are coated with a layer of gelatinous material which swells up after the eggs are laid, so that each egg appears as a small, spherical, glassy body, with its upper part of a dark color, and surrounded by a spherical mass of clear, jellylike substance. In a few weeks the form of the body begins to appear. The tail begins to vibrate, the sur- rounding mucus breaks up and the tadpole emerges with gills very much like a tiny fish. For a short time there is no mouth opening, and the little tadpole attaches itself to water- weeds by suckers near the place where the mouth is to FIG. 119. DEVELOPMENT OF A TOAD. From Packard's Zoology. appear. After the mouth, with horny lips and jaws, is developed, the tadpole feeds greedily on waterweeds and grows rapidly. The external gills disappear and are replaced by internal gills, which are concealed by a fold of skin which incloses a gill chamber. There is an opening on the left side of the body for the water to escape. The limbs de- velop as little projections, like buds, on the sides of the body ; but the anterior limbs are for a long time concealed by the gill chamber and therefore appear to develop later than the hinder pair. At first the tadpole swims, fishlike, wholly by means of the tail, and it continues to do so long after the limbs appear. It holds the limbs close by the side 190 Descriptive Zoology. of the body and swims by the sidewise movements of the tail. At this time the intestine is long and coiled spirally. Then for a time the tadpole quits eating. It fasts, but is maintained by the material from its tail, which is being absorbed while a great transformation is taking place. The horny lips and jaws are shed, the mouth becomes wider and develops true jaws with teeth. The long, coiled intestine becomes relatively short. The anterior limbs are pushed out through the fold of the skin that inclosed them. Lungs are developed, although they are at first but little used, the tadpole coming to the surface occasionally to get a mouth- ful of air ; respiration is still chiefly accomplished by the Gills FIG. 120. THE SIREN ; MUD EEL. Gills persistent. gills, but the lungs come to be used more and the gills less until finally the gills disappear. It was herbivorous ; now it is carnivorous. Formerly strictly aquatic, it is now am- phibian. In short, our tadpole has become a frog. CLASSIFICATION OF AMPHIBIA. The Siren. The lowest of the amphibians is the siren or mud eel. It is eel-like in form, having gills that persist through life, and one pair of legs (the anterior). It lives in the swamps of the Southern states and sometimes is three feet long. Amphibia. 191 The Mud Puppy. The mud puppy, or water dog, is a little higher than the siren, having two pairs of legs. It also has persistent external gills. It is found in the streams FIG. 121. NECTURUS; MUD PUPPY (NORTH); WATER DOG (SOUTH). Gills retained thruout life. of the Mississippi Valley and in the lakes of central New York. It sometimes 'attains a length of two feet. FIG. 122. SPOTTED SALAMANDER. The Salamanders. The salamanders are still a step higher. They have gills in the earlier stage, but shed them when adult. They retain the tail, and, in swimming, fold 192 Descriptive Zoology. the two pairs of limbs close to the body and swim by lat- eral movements of the vertically flattened tail. Most of the salamanders li^e on land, but they seek moist places. The salamanders are often incorrectly called liz- ards. They are pretty well distributed in temperate and tropical regions. Most of them are of rather small size. One form is used as food by the Mexicans. In some forms the larva is larger than the adult. In unfavorable conditions some of the larvae fail to transform, but perma- nently, or at least indefinitely, retain the gills. Some European forms fail to develop lungs. Many of the salamanders reproduce the legs or tail when these members have been lost. Like the other amphibians, the salamanders go to the water to lay their eggs, and all sala- manders, whether they lead a terrestrial life later or not, spend their early life in the water, breathing by means of gills. One family of salamanders are called newts or efts. None of o'ur amphibians are in any way poisonous or inju- rious to man, though several of them are reputed to be so. Frogs and Toads. These are the highest of the amphib- ians. They have lost, not only the gills, but also the tail. They are not only fitted to live a truly terrestrial life, like the salamanders, but are much more active than the latter, having the hind limbs well developed for leap- ing, whereas the two pairs of limbs in the salamander are nearly equal, and it can, at best, only crawl. One of the commonest of the frogs is the leopard frog, so named from its spots. Quite similar to it in general appearance is the pickerel frog. The green frog is green- ish and brownish, with small dark spots. The bullfrog is well known from its size and heavy voice. The common toad has a rough-looking, warty skin, in which are glands that secrete an irritating liquid for pro- Amphibia. 193 tection. The toes are .webbed, but not so completely as in the frog. The hind limbs are less fully developed, and so the toad merely hops, instead of j&mping like the frog. The frog has teeth in the upper *jaw only, the toad in neither jaw. The toad lives away from the water ; still it goes to the water to lay its eggs, and the young tadpoles pass through the same stages of development as the frog. The toad lays its eggs in strings, while those of the frog are in masses. The tadpoles of the toad are usually darker than those of the frog. The toad has the same kind of tongue as the frog and catches insects in the same way. The toad is usually of a duller color, corresponding with its surroundings. The tree toads or tree frogs are somewhat warty and thus get the name " toads," but they are in a different family from either frogs or toads. They are peculiar in having the tips of the ringers and toes dilated into disks, which adhere and thus aid in climbing. No matter how high and dry they may live in trees, they return to the water to lay their eggs. As is well known, they can change their color through a considerable range, from nearly white to nearly black, in keeping with the surface on which they are resting. The hind limbs are elongated as in other frogs, but, since they jump little, if any, the muscles of these limbs are slightly developed, making them slender instead of strong and muscular. Though the larynx is poorly developed, nearly all the frogs and toads have voices. The males have louder voices, and most of these are well known, from the faint " peep " of the little frogs and the shrill " trill " of the tree toad to the heavy bass notes of the bullfrog. Some Peculiar Forms of Development. In some of the islands of the ocean where there are no marshes, the development is direct, the 194 Descriptive Zoology. young being hatched in the form of the adult. A few forms bring forth the young alive. CHARACTERISTICS OF AMPHIBIA. The Amphibia breathe by gills in the larval state, but generally develop lungs in becoming adult. They have no fin rays as with the fishes, but usually have paired limbs with distinct fingers and toes. Aquatic Life vs. Terrestrial Life. Several lines of investigation converge to prove that at one time the globe was entirely covered by water. Of course until there was land there could be no land life. What were the first forms of life on the land ? Did some of the forms of aquatic animals gradually become fitted for living on land and then desert the water ? The study of the amphibia seems to throw some light on these ques- tions. In the ganoid fishes we saw that the swim bladder had some cir- culation of blood in its walls and that there was an opening from the. gullet into the swim bladder, which is, in action at least, a sort of rudi- mentary lung. The lungfishes have the air bladder still more com- pletely developed as a lung. The lungfishes came to the very door of land life, but remained aquatic. The Amphibia boldly stepped over the threshold and were, probably, among the first of the animal kingdom to emerge from the water to live upon the land. This transition from life in the water to life upon the land marks a great step upward. Perhaps it would be hard to believe that any group of animals had made such a profound change, if it were not for the fact that we see this same change in the individual life of every amphibian. Gradation among the Amphibia. It is interesting and instructive to observe the successive progress in the various groups of amphibians. If we consider in succession the siren, mud puppy, salamander, and frog, we see that they all have traveled along the same road, only some have gone farther than others. They all start as limbless tadpoles, with gills, practically in the same stage of development as the fishes. The siren develops one pair of legs, retains the legs and gills, although developing lungs, and goes no farther. The mud puppy makes a slight advance by developing another pair of legs. It retains the two pairs of legs and the gills, at the same time breathing, in part, by means of lungs. The salamander takes a decided step upward when it sheds the gills and Amphibia. breathes by means of lungs. The frog goes through all these stages, but rises to a still higher level by getting rid of the tail which it had in its larval life. In short, each of these forms has gone through all the stages represented by the forms below it in the scale, but has discarded certain features and has advanced to a higher plane and leads a more active life. The life history of the frog, therefore, serves to review all the other forms of amphibians below it in the scale. The temporary stages of the frog's life represent the permanent form of the lower kinds of Amphibia. To put it in another way, they all start at the foot of the same stairs at the fish level, so to speak ; the siren climbs up on the first step and stops there ; the mud puppy makes one more step and rests content ; the salamander mounts still higher by a step and has reached its high- est point ; while the frog takes all of these steps and reaches out once again and tops the series by getting on the highest step of the stairs. This series illustrates a law which, though general, does not appear so clear in some other groups. The stages of development of the individuals of the higher groups recapitulate the development of the group as a whole; or, in other words, "the development of the individ- ual epitomizes the development of the race. 11 DIFFERENCES BETWEEN FISHES AND AMPHIBIANS. FISHES. AMPHIBIANS. Persist through life Gills . Air bladder respiratory in lungfishes . Lungs i Auricle, i Ventricle .... Heart . May disappear in adult Present in adult 2 Auricles, i Ventricle Fins with fin rays Limbs Scales (usually) .... Exoskeleton Not open to mouth (except lungfish) Nostrils . Limbs with digits Skin smooth (usually) . Open into mouth Class Amphibia . ORDERS OF AMPHIBIA. r Order i. Urodela . { Order 2. Anura I Order 3. Gymnophiona Salamander Frog Blind-snake CHAPTER XIII. BRANCH CHORDATA. CLASS REPTILIA. THERE are four principal forms of reptiles, represented by the lizard, snake, turtle, and alligator. THE LIZARDS. General Characters of Lizards. Lizards are scaly rep- tiles, having, in the typical forms, two pairs of limbs and an elongated body, with a long, tapering tail, frequently twice as long as the rest of the body. The middle of each vertebra of the tail has a thin layer of cartilage, at which places the tail easily breaks off. The advantage of this arrangement is readily seen. When attacked by an enemy the chances are the lizard will be seized by the tail, for he is probably trying to escape by flight. The brittle tail breaks off, and as this constitutes the greater part of the length, the pursuer thinks he has the main part ; at any rate, while he is holding this the curtailed lizard may make good his escape. But the tail grows out again. In capturing lizards, which often lie basking in the sun, it is best to creep stealthily upon them till within arm's length, and quickly dart the hand forward. Unfortunately, in thus grasping them, the tail is in most cases broken off. There are five toes, with claws, on each foot. There are no external ears, but the tympanum is sunken, leaving 196 Reptilia. 197 a depression back of the eye. The eyes have movable upper and lower lids. The teeth are attached to the ridge or edge of the jaws, and are not set in sockets. Lizards feed on insects, worms, and other small animals, though a few forms are herbivorous. Lizards are active in habits, some being called " swifts." They are found on the ground, more often in sandy soils, on rocks, trees, walls, etc., being most abundant in warm countries. There are not many north of latitude 40. A few live more or less in the water, but they do not have gills at any stage of their lives. Lizards lay eggs of com- paratively large size, which are covered by a tough leathery or limy shell. Many lizards are bril- liantly colored, and some have power to change their color; most noted of these are the chameleon, of the old world, and the Anolis (Fig. 123), found in the Carolinas and Florida, which readily changes from a bright green to a dull brown FIG. 123. GREEN LIZARD. From Kingsley's Comparative Zoology, according to its surround- ings. Put one of these fellows in a box with a lot of dead pine needles, and note the color change. This lizard is often sold under the name "chameleon." 198 Descriptive Zoology. The Chameleon. The true chameleon is found in Africa. Its power to change its color has been mentioned. It has a laterally compressed body, with a prehensile tail. Its feet are fitted for climbing by having two toes on one side and three on the other. The two eyes can move independently of each other, and the tongue can be darted out four or five inches after insects. The Horned Toad. This is a lizard with a broad, relatively short body, with spines on the back of the head. It is found in the dry regions of the Western and Southwestern states. FIG. 124. THE GILA MONSTER. The only poisonous lizard. From Kellogg's Zoology. The "Gila Monster." This is the largest of the lizards found in the United States, being about eighteen inches long. It is found from New Mexico south and west. It is brown, with red markings. Its bite is poisonous, though seldom fatal to man. The Iguanas. In Central and South America and the West Indies are found the lizards called iguanas. They are about three feet long, and are found on the lower branches of trees. They are used as a food by the natives, and are said to be excellent eating. The Monitors. The monitors are found in Africa, Australia, and the East Indies. They are the largest of living lizards, being five or six feet long. Differences between a Salamander and a Lizard. Salamanders are commonly called lizards. The two animals have a general resemblance in form, both having elongated bodies, with two ^ pairs of limbs and a long tail. The following tabular statement shows important points of difference : SALAMANDER (Amphibian). LIZARD (Reptile). Smooth Skin Scaly Unarmed Toes With claws Present in young Gills No gills at any stage A metamorphosis Development Young like adult Reptilia. 199 The Joint-snake. Every one has heard of the glass-snake or joint- snake, which is by no means rare in the Central states. The commonly accepted story is that when struck it flies to pieces, and that the pieces come together again, making the animal whole as before. The facts are as follows : The glass snake is a lizard without legs, and with a tail two or three times as long as the body proper; hence it looks very much like a snake. A closer examination would show that it can shut its eyes, which no snake can do. There is also a depression marking the ear, not found in snakes. A groove along each side of the body is also a feature never found in snakes. The tail is very brittle, as in all lizards. When struck, the tail is easily broken off and broken into several pieces, the short body usually crawling quickly away. No part of the tail lives. The disappearance of the pieces of the tail is easily accounted for by any one who knows how many animals are on the lookout for something to eat. To one who knows the animal's struc- ture an explanation is easy ; it is also easy to comprehend how the ignorant usually accept the popular story. If one can be obtained, carefully compare it with a snake. THE SNAKES. Characteristics of Snakes. The absence of limbs is not distinctive, since the glass-snake is a legless lizard, and some snakes have rudiments of hind limbs. In snakes there are no movable eyelids, the eyes being covered by the thin, transparent epidermis. The mouth is very dilat- able, the lower jaw being held by extensible ligaments, and the two halves of the lower jaw are also loosely con- nected so they can be stretched apart during swallowing. The tongue is long, soft, cylindric, and forked at the tip ; it serves as an organ of touch, and has nothing to do with the poison apparatus. The teeth are relatively small, pointed backward, and serve to hold the prey and to aid in swallowing. There is no breastbone. The number of vertebrae is great, in the boa over four hundred. Ribs begin on the second vertebra and continue the whole length of the body cavity. 2OO Descriptive Zoology. Locomotion of Snakes. The chief mode of locomotion in a sinuous line is so well known that a double curve is desig- nated as " serpentine. " It should first be noted that along the whole length of the ventral surface is a series of broad, overlapping plates, the scutes or ventral plates. By means of these the snake "gets hold" of rough places, for on a perfectly smooth surface it can make no progress. By the winding, wavelike motion of its body it both pulls and pushes itself along. The absence of limbs enables it to glide through grass and weeds and into crevices and holes. Snakes also glide along with the body straight. This is accomplished by rhythmically drawing the ribs and scutes forward and pushing them backward, or, as some express it, by "walking on the ribs." Food of Snakes. Snakes are carnivorous and take only living prey. This they swallow whole. The constrictors wind the body around the victim and crush it. Our com- mon black snake (blue racer) is a good example of a con- strictor. Our commoner snakes feed on toads, frogs, birds, etc. Garter snakes sometimes eat earthworms. Water snakes catch fish, frogs, and other aquatic animals. Process of Swallowing. Birds are usually swallowed head first. If the snake catches a frog by a hind leg, that part leads the way in. The backward-pointing teeth prevent escape. The two halves of the lower jaw are alternately pushed forward and drawn backward, and the victim is thus slowly drawn in. Meanwhile the salivary glands lubricate the object. The Organs of Digestion. The gullet is as wide as the mouth, and there is no constriction or line of demarcation between it and the storm rh. The posterior end of the stomach is glandular. About halfway back in the body Reptilia. 201 cavity the stomach ends and is continued into the intestine, which pursues nearly a straight course. Near the posterior part of the body cavity it widens, forming the cloaca. Alongside the stomach is the long, narrow liver ; from its hinder end the bile duct extends back to the bile sac, and from this a duct empties into the intestine a little way back of the stomach. The pancreas, a pale, roundish organ, also pours its secretion through a duct into the intestine. Digestion is a slow process, as might be guessed from the condition in which the food is swallowed, and the snake lies stupid and inactive for a long time after such a "bolted" meal. How the Snake Breathes. The right lung is long and nar- 202 Descriptive Zoology. row, and continues back, as a transparent air sac, through most of the length of the body cavity. The left lung is rudimentary, sometimes being so small it is difficult to see. The windpipe is long, beginning very close to the front of the floor of the mouth. This is regarded as an adaptation to the mode of eating, so that the snake may not be suffo- cated during the long and tedious process of swallowing. Circulatory System. The heart beat is slow and the circulation not very active. The heart continues to beat long after the head is severed. The temperature of the blood varies with that of the surroundings. Excretory Organs. In the posterior part of the body cavity are the two long, slender kidneys, whose ducts open into the cloaca. The Eggs and the Young. Eggs are produced in two long, narrow ovaries; the oviducts also open into the cloaca. Some snakes deposit their eggs in the earth, though probably a majority bring forth the young alive. Senses of Snakes. Sight and touch are fairly well de- veloped, though a study of snakes does not reveal a keen sense of sight. Some snakes are affected by music, show- ing a sense of hearing. Of their senses of smell and taste we know but little. Adaptations of Internal Organs to External Form. We have seen how the external form is adapted to the mode of life. Let us now see how the internal organs are fitted to the necessarily long, narrow space allotted to them. In the first place the body cavity is so long that a moderately long digestive tube is accommodated without the necessity of coiling it, as in many animals. But one lung is developed, and that one is long and narrow, whereas our bodies admit of two relatively wide lungs placed side by side. The liver Reptilia. 203 is long and slender, and its bile sac is behind it. Not only are the ovaries (and spermaries) and kidneys slender, but they are not directly opposite each other ; in short, every- thing is arranged on the tandem plan. Yet the snake is bilaterally symmetrical, in its fundamental plan, like other vertebrates and the vast majority of animals. Poisonous Snakes? Some of the front upper teeth of these snakes, called " fangs, " are especially adapted for in- troducing poison. They are longer than the other teeth, FIG. 126 DIAMOND RATTLESNAKE. From photograph by W. H. Fisher. From Recreation, by permission of G. O. Shields. can usually be erected or folded back, and have a hollow, or groove, by which poison passes from the poison sac into the wound by muscular pressure on the sac. The poison gland is a modified form of salivary gland. This poison is not a stomach poison, but a violent blood poison. Our chief poisonous snakes are the rattlesnake, now becoming rare in all thickly settled regions, the copperhead, and the water moccasin of the South. Their abundance and the danger from them are both grossly exaggerated. As an 204 Descriptive Zoology. antidote, a hypodermic injection of permanganate of potash (i to 100), is by many now preferred to alcoholic liquor. In India the cobra kills several thousand persons yearly. (See The American Natural History. Hornaday.) How Snakes protect Themselves. ( i ) By their color, (2) by flight, (3) by their odor, (4) by their poison. Many snakes are colored so like their surroundings as to be decidedly inconspicuous, and this is of advantage both in escaping enemies and in securing their prey. By their noiseless mode of locomotion they can, unobserved, ap- proach a victim or elude a pursuer. We are so familiar with their stealthy move- ments that we are not sur- prised when we learn that the words snake and sneak are of the same origin ; nor do we wonder that there has been a long-standing enmity between man and serpent. Yet the majority of snakes are entirely harmless, and are as much surprised as we are when we " meet by chance." Many snakes have a disagreeable odor which probably serves to protect them from some enemies. Lastly, the poisonous snakes use their poison to secure food and to protect themselves. Among the enemies of snakes are to be reckoned several kinds of birds, such as the shrikes and hawks, hogs, wild and domesti- cated, bears (occasionally), and various other animals. Molting. At least once a year snakes shed the epi- dermis over the entire body, even over the eyes. During this process they are dull-colored and inactive. FIG. 127. DISSECTION OF RATTLESNAKE. HEAD OF Showing fangs and poison sac ( /). From Kingsley's Comparative Zoology. Reptilia. 205 DIFFERENCES BETWEEN A SNAKE AND A "GLASS SNAKE." SNAKE. GLASS SNAKE. No lids ........ Eyes Movable lids Dilatable Mouth Not dilatable Extensible Tongue . . '. . . Not extensible Invisible externally Ear Visible externally Broad plates Ventral scales Small Short, strong Tail Long, brittle Absent Lateral groove Present THE TURTLES. General Characters of Turtles. In turtles the relatively short and broad body is inclosed between two bony shields, the dorsal one being called the carapace, and the ventral, the plastron. The carapace is made up of (i) the widened spines of the thoracic vertebrae, (2) the ribs, which have widened and grown together, and (3) a series of. marginal plates. There is no breastbone, but the plastron is made of a set of bony plates. Both carapace and plastron are covered by a set of horny, epidermal scales which do not coincide with the underlying bony plates. The "tortoise shell " of commerce is made of the epidermal plates of the big sea turtle known as the hawkbill turtle. There are no teeth, but instead the jaws are horny. The neck and tail are the only movable parts of the spinal column, and these, with the legs, can be withdrawn so as to be protected by the shell. In the boxshell turtle there is a hinge in the plastron to make the protection more complete by closing the shell. The sea turtles have pad- dles, while the land turtles have feet, with more or less distinct toes. Some of the sea turtles weigh as high as a thousand pounds. The green turtles, so valued for soup, are caught in the West Indies at night, when they come 206 Descriptive Zoology. ashore to lay their eggs. Among the more noticeable of our inland turtles are the fierce snapping turtle, the soft- shell turtle, and the " gopher " of the South, which burrows in the ground. The terrapins of Chesapeake Bay are noted for their quality as food. All turtles bury their eggs, and our northern forms all hibernate in the mud. THE ALLIGATORS. General Features. The alligators and crocodiles are like lizards in general form, but differ from them in several important points. They swim well by means of the verti- cally flattened tail. The skin is covered with horny scales, those of the back having corresponding underlying bony plates. The teeth of alligators are set in sockets, which is true of no animals below it in scale. The heart is also more complete than in the other reptiles, having a complete partition separating the ventricle into two parts. The temperature is about that of the surrounding air or water. The brain, though more highly developed than in other reptiles, is small relative to the size of the body and the skull. The alligators have a muscular, gizzardlike stomach. The young feed on fishes and small animals, but the full-grown alligators seize mammals, for which they lie in wait at the edge of the water until the animals come down to drink or swim. The nostrils, eyes, and ears are at the top of the head, so these reptiles can lie concealed, with their main sense organs extending into the air to discover their prey ; they very much resemble a stranded log. The nostrils can be closed by a valve, which is done when a victim is dragged under water to drown. Alligators dig holes in the banks, in which they lay their eggs, which are sometimes as large as those of a goose. The alligators of our Southern states grow to a length of Reptilia. 207 ten or twelve feet. Alligators are confined to the western hemisphere, occurring in the Southern states, Central and South America. Crocodiles are found in both the old world and the new. One species is found in southern Florida. Extinct Reptiles. In earlier geologic ages reptiles were very much more numerous than at present. Not only were they more abundant, but there were more kinds ; and many of them were large, some being eighty feet in length. Some were lizardlike, with long, slender necks. Others were fishlike. Some had resemblances to birds. The tracks of many of these ancient reptiles in the mud have hardened into rock, and have often been called " fossil bird tracks.' 1 Perhaps the most remark- able were the flying reptiles. They are supposed to have been rather batlike in appearance. The remains of these reptiles are found in rocks in many parts of the world, and the age in which they were most preva- lent is called by geologists the " Age of Reptiles." General Characteristics of Reptilia. Reptiles are cold- blooded vertebrates, covered with scales, and when toes are present they end in claws. There is no metamorphosis after leaving the egg. There are no gills at any stage of life. Reptiles produce large eggs which are covered by a tough limy or leathery shell. Some reptiles are ovo- viviparous. Reptiles show a decided advance beyond amphibians in the development of the nervous system ; in the respiratory system, since they breathe by lungs after leaving the egg ; and in the circulatory system, the heart of the alligator having four cavities, as in birds and mammals. CLASSIFICATION OF REPTILIA. f Lacertilia lizards. {Order i. Squamata. j ..... . (Ophidia snakes. Order 2. Chelonia turtles. Order 3. Crocodilia alligators. CHAPTER XIV. BRANCH CHORDATA. CLASS AVES. Example. The Common Pigeon. Adaptation for Flight. The pigeon is fitted for flying : (i) by the wings, which, with their wide, strong, yet elastic feathers, are air paddles of marvellous efficiency ; (2) by the powerful breast muscles which move the wings; (3) by the lightness of the skeleton ; (4) by the air sacs through- out the body, which render it more buoyant; (5) and, not least, by the shape, -being double pointed, so as to penetrate the air with the least resistance. Structure of a Feather. Let us consider the structure of one of the quill feathers. It consists primarily of two parts, the shaft and the vane, or flattened part. The shaft is solid so far as the vane extends, but the basal part is hollow, and is called the quill. The two sides of the vane are unequal in width, and the feathers overlap so that the wider side of the vane is beneath. The vane is made up of side branches called barbs, arranged in a close row. From each side of each barb arise secondary branches, called barbules ; and the barbules of adjacent barbs interlock by little hooked ends, so that the whole vane is firm. Feathers are developed from papillae of the skin. In a growing feather it can be seen that the quill is full of pulp supplied with blood. In the fully developed feather the 208 Aves. 209 dry, pithy remains of this pulp are found in the quill, which is now narrowed at the base, but still shows an aperture. Kinds of Feathers. There are four principal kinds of feathers : ( I ) The quills found on the wings and tail. (2) The contour feathers, which have the same general structure as the quills, but are smaller, and lie close to the body. They protect the body from bruises, and also from cold, being the very best of non-conductors of heat. Their mode of overlapping serves admirably for shedding rain and for retaining the heat when flying through cold air. (3) Downy feathers, which differ from the above , in not having the barbs fastened together by hooked barbules ; the result is a loose, soft feather, well suited for retaining heat. These feathers, when present, are inside the contour feathers, where we should expect to find them. The young pigeon has downy feathers, but they disappear in the adult. (4) The pinfeathers are fine, hairlike feathers, usually left after the pigeon is plucked, and usually removed from fowls by singeing. They show that they are feathers by a little tuft of barbs at the tip. Distribution of Feathers. Feathers are not evenly dis- tributed over the surface of the body ; but there are certain areas from which they grow, and certain other areas from which feathers never grow. By separating the feathers on a bird's breast it may readily be seen that no feathers de- velop there. There are also bare places on the sides of the neck and in other places ; but the length of the feathers and their mode of overlapping cover these bare spots, so that most people hardly know of their existence. The Pigeon's Wing. The wing, like our arm, consists of three parts, the arm, forearm, and hand. The similarity of the first and second of these to the corresponding part of our arms is so evident that it needs no explanation. The Descriptive Zoology. sui. FIG. 128. EXTERNAL FEATURES OF A BIRD. From Kellogg's Zoology. Aves. 2 1 1 front angle of the wing, or " bend of the wing," as it is called, corresponds to our wrist ; but the hand is sharply bent back upon the forearm when the wing is folded, a posi- tion we cannot assume. When the wing is folded, the arm, forearm, and hand lie alongside of each other like this, z. Further, the hand is reduced to two fingers, bound together, and the thumb, which every one has seen in the plucked fowl. The thumb, with its feathers, is called the false wing. The feathers borne on the hand are called primaries, and those supported by the forearm are the secondaries. In some cases a few of the inner feathers of the forearm are called tertiaries. The wing is concave on the inside, mak- ing it fit the body closely when the wing is folded. The Flying Muscles. To use such a wing effectively as an air paddle, it is evident that there must be very strong muscles. These we find in the breast. The bulk of the breast is made up of two powerful muscles, which cover nearly the whole of the ventral surface of the body. To support these large muscles, and supply a basis for their attachment so they can work, it is equally clear that a con- siderable extent of bone is also a necessity ; hence the large breastbone. Not only is the breastbone very large, but along its middle line is a high ridge, the keel. Lying between the body of the breastbone and the keel, and attached to both, there is on each side the large pectoral muscle, the two together constituting about one fifth of the entire weight of the body. At the anterior end, each pec- toral muscle narrows into a tendon, which is attached (in- serted) to the bone of the upper arm (humerus). By the shortening of this muscle the wing is pulled downward. Two points must now be kept in mind: (i) the wing is concave beneath, which enables it to " catch " the air ; (2) the wider side of the vane of each quill is on the under ^^rT J - 212 Descriptive Zoology. side, so when the wing is struck against the air, the resist ance presses the vanes together in one continuous layer, through which the air cannot pass. The result is that a strong " push " is made against the air, and by reaction the bird is propelled upward or forward according to the direc- tion of the wing stroke. In seeking the muscle that raises the wing, one would naturally look on the dorsal surface in the region of the shoulder ; but, oddly enough, the muscles that raise the wings are also on the breast. Every one has noticed in the well-cooked breast of a bird that the meat of the breast separates into two parts, the outer part being large and flat, the pectoral muscle just described. Inside of this, lying in the angle between the body of the breast- bone and the keel, is a slender muscle, somewhat triangu- lar in cross section. This is the subclavian muscle. At its anterior end it narrows into a tendon, which passes up through a hole left between the bones that make the shoulder; the tendon then turns and is attached to the upper (dorsal) surface of the arm bone (humerus). When the subclavian muscle shortens, this tendon acts as a pulley, and elevates the wing. In raising the wing it is desirable that there should be as little resistance as possible. This condition is secured ( i ) by the convex outer surface of the wing; (2) by the fact that pressure on the outside of the wing separates the quills and allows the air to pass through with very little resistance. The Legs and Feet. The pigeon is a model flier. It uses the feet but little, hence the legs and feet are small and weak. Heavy legs and feet would be to the pigeon a useless burden. The hind limb consists of three parts, thigh, leg, and foot. The true heel is some distance from the toes, where we cut off the foot in dressing a bird. The part between the toes and the heel, usually covered with Aves. 213 scales, is the tarsus. The pigeon has four toes, one extend- ing backward and having two joints. Of the three front toes, the inner has three joints, the middle four, and the outer five. Each toe ends in a claw. It should be noted that the hip joints are not only far apart, but are very high on the body, being near the dorsal surface. This enables the body of the bird to swing be- tween its two points of support, somewhat like an ice- pitcher on its two pivots. Since the bird is obliged to put its head to the ground so frequently, the convenience of this arrangement is apparent. When we stoop we realize that we are awkwardly built for soich a position. It would at first seem that the bird's center of gravity is too far forward, but the length of the toes must be taken into account. Perching. It is to be noticed that when a bird's leg is drawn up close to its body, the toes are clenched at the same time. This is due to the action of a tendon that passes over the joints of the leg in such a way that when the limb is bent the tendon is put on a strain and thus the toes are flexed. So when the bird settles on its perch the toes grasp the perch without active muscular effort ; this helps answer the question, " How does a bird stay securely on its perch when asleep?" There are also muscles by which the bird can voluntarily clutch without depending on this purely mechanical arrangement. The Pigeon's Shoulder Braces. With such strong pull- ing as the breast muscles give the wing, it will be seen that the shoulder needs to be firmly braced, especially against the strong pull of the pectoral in making the down stroke of the wing. In the first place, the shoulder is braced like our own by the collar bones, or clavicles, the two collar bones uniting near their attachment to the anterior end of the keel, together making the "wishbone." In addition 214 Descriptive Zoology. to this brace there is an additional bone alongside of each half of the wishbone, the coracoid bone, much stronger than the collar bone itself. On the back the shoulder is braced by the strong, curved shoulder blade. To strengthen the body for the work of flying, the verte- brae of the trunk are consolidated, the only parts of the spinal column that are flexible being the neck and the tail. The Head and Neck. In many birds the beak is the only organ capable of being used for grasping, hence the long, flexible neck, which makes up for the above-mentioned stiffness of the trunk. The bird must be able to reach the ground, hence the length of the neck is proportioned to that of the legs ; the head must also be able to reach any part of the body. Some birds have as many as twenty- four cervical vertebrae. In many birds the head must be darted forward quickly to secure prey or in defense. The horny beak is strong, yet light, and serves as a hand in picking up small objects. Because of the quick motion of a bird's head, as it picks objects out of the dirt, soft lips would be too delicate. A head that requires such quick handling needs to be light ; and in keeping with this re- quirement there is an entire absence of teeth in all exist- ing birds, though in a few cases rudiments of teeth are found in the embryo. In the plucked bird it is found that the neck is more slender than would appear from the out- side, the feathers filling the angle between the neck and the body, and making on the exterior a gradual transition, where in the bare bird there is an abrupt change. The Pigeon's Food and Digestive System. Pigeons feed chiefly on grains and other seeds. These are swallowed whole, and pass into the crop, an enlargement of the gullet situated in tront of the breast. Here seeds are moistened and well soaked before they go farther. The crop serves Aves. 215 as a storing sac during the hasty gathering of food. In- side of the body cavity is the stomach, which consists of two very distinct parts ; the first part is the glandular stomach, or proventriculus, and the second is known as the gizzard. The gizzard is very strong, having thick muscular walls. In it the seeds, only partially softened, are to be ground. To aid this process small pebbles are swallowed. It is clear, therefore, that its inner wall needs to be tough ; FIG. 129. INTERNAL ANATOMY OF A PIGEON. it will not do to have the soft glands here, hence they are placed out of the way, a little higher up the digestive tube where the secretion can trickle down upon the food in the grinding stomach. The intestine arises from the gizzard ; first there is a long loop, the duodenum, in which lies the pancreas. Its secretion is poured into the duodenum. The liver is adjacent and the bile duct also empties into the duodenum. The transition from the small intestine to the large intestine is marked by two small, blind side branches, 2i6 Descriptive Zoology. the ceca. The terminal portion of the digestive tube is widened, and is called the cloaca. It receives three sets of products, (i) the residue of digestion, (2) the eggs, and (3) the excretion of the kidneys. The Circulatory System of the Pigeon. The circula- tion of blood is very rapid in birds because of their great activity. The heart is proportionally large ; it is com- pletely divided into two halves, so that the blood moves through one half of the heart from the lungs to the body, and through the other half from the body to the lungs, being pumped twice in the circuit instead of once as in fishes. An important point to note is that the aorta turns to the right instead of to the left as in our bodies. How the Pigeon Breathes. Respiration is exceedingly active in a bird. Imagine yourself taking such violent ex- ercise as that required for a bird tq fly through the air at the rate of a mile a minute. Would you not be "out of breath"? The bird's lungs are of fair size; in addition there are air sacs in all parts of the body, communicating with the lungs, the bronchial tubes continuing on through the lungs into these sacs. The lungs do not lie free in the body cavity as in our bodies, but are attached to the dorsal wall, fitting closely between the ribs. The air sacs are also in communication with the hollows of the bones, which adds to the buoyancy. The temperature of birds is higher than that of any other animals, being about 110 F. The movements of respiration in birds is peculiar, in that expiration is accomplished by active muscular effort, and inspiration by elastic reaction, just the opposite of the processes of our bodies. The Excretory System of the Pigeon. The lungs serve as organs of excretion, throwing off carbon dioxid. The Aves. 217 kidneys are paired organs, lying embedded in the hollow of the pelvis, each kidney being in three sections. The Oil Gland. On the rump, at the base of the tail, is the conical oil gland. It is concealed by feathers, but when the bird wishes to oil the feathers, oil is taken from the gland by the beak and spread over them. The oil glands are the only skin glands possessed by the bird, there being no glands distributed over the skin as in many other animals. Nervous System of the Pigeon. The brain is relatively large. It is also wide in proportion to its length as com- pared with the brains of reptiles and amphibians. The anterior part of the brain consists of the two cerebral hemi- spheres (see Fig. 167). Back of these, in the middle line, is the rather large cerebellum, marked by transverse grooves. On the sides of the cerebellum are the two optic lobes. The whole nervous system is relatively large, the brain and spinal cord in some of the smaller birds constituting a greater proportion of the weight than in any other animals. The Senses of the Pigeon. Sight is the most highly developed of the bird's senses. The eye is very large in proportion to the size of the head. The outer coat (sclerotic) of the eye is strengthened by stiff sclerotic plates. The sense of sight is keen, enabling the bird to discover food and to escape enemies. The sense of hearing is acute, the inner ear being well developed. There is no outer ear, but the depression lead- ing to the tympanum is easily to be found back of the eye, though usually more or less concealed by feathers. The sense of touch is general over the body. Taste is appar- ently not very acute. While it is pretty generally believed that birds, especially carrion eaters, have a keen sense of 2i 8 Descriptive Zoology. smell, yet experiment seems to show that this is not so acute as supposed. The Pigeon's Voice. The cooing of the pigeon is pro- duced by air vibrations made in the windpipe, but not, as in most animals with a true voice, in a larynx at the upper part of the windpipe. In birds the organ of the voice is at the lower end of the windpipe, where it forks to form the two bronchi ; and it is called a syrinx instead of a larynx. The bird uses the voice to utter cries of warning, to call the young, and to attract attention in the mating season. It is worthy of notice that the sweetest singers are not to be found among the highly colored birds, but among those of more subdued tints. Origin of the Domesticated Pigeon. All other varieties of domesticated pigeons appear to have descended from the rock pigeon of the old world. By carefully selecting pigeons having certain peculiarities, and breeding from these to the exclusion of other forms, in time we have produced a large number of varieties of pigeons, known as carriers, pouters, fantails, etc. This production of vari- eties by interfering with the natural selection of mates is known as artificial selection. A Bird's Egg. Birds' eggs are proportionately large. This might naturally be expected, since there is deposited within the egg sufficient nourishment to form the chick in resemblance to the adult. The eggs are formed in the ovary, and it is interesting to find that but one ovary (the .left) is developed, though the right ovary is represented by a rudiment. The eggs as produced by the ovary consist simply of the yolk. On one side of the yolk is the germ spot. As the yolk, which is the real egg, passes along the oviduct, it has added to it first an enveloping mass of transparent substance which is termed the " white of the Aves. 219 egg," or albumen. The word "albumen" (from album, white) now stands for the class of substances having the same essential composition as the clear part of the egg. After the albumen is added to the yolk, the oviduct secretes a limy shell which completes the egg. The eggs pass from the oviduct through the cloaca on their way out. Incubation. Most birds incubate the eggs. They are sometimes laid on the bare ground, but generally in a more or less carefully prepared nest. These nests vary from a simple platform of sticks to the elaborate hanging nest of the oriole, woven of grass and soft fibers, or the still more ingenious nest of the tailor bird. It is to be noted that the nest is " simply a cradle and not a home." The germ spot always turns uppermost, so that the developing embryo gets the heat from the body of the incubating bird. During incubation there is an increase in the amount of blood circulating in the area in contact with the eggs, a provision for affording heat to them. The Colors of Birds. The colors of feathers are due to two factors, first to certain coloring matters, or pigments, and second to the structure of the feather, most of the luster and iridescence being due to the latter. As a class birds are highly ornamented. The males are usually more highly ornamented than the females. Perhaps this is because the females are safer, during incubation, with dull colors. But in many families the sexes are colored alike. The young generally resemble the adult female. Molting. Birds shed their feathers and renew them at least once a year. If the molting takes place but once a year, it is usually in the fall, but some birds also renew their plumage in the spring. In rare cases there is a third molt. Most birds shed their wing quills in pairs, succes- sively, so that they are at no time deprived of the use of 22O Descriptive Zoology. the wings ; but the ducks shed their wing quills all at once and for a time are unable to fly. Some birds shed the claws, and the puffin sheds the outer covering of the beak. Migration of Birds. Comparatively few of the birds that we see during the year reside with us permanently. If one makes a list of the birds that remain through the winter, he misses many of his summer acquaintances. The crow, jay, nuthatch, chickadee, some of the woodpeckers, several sparrows, the hawks and owls, and a few others are left, when the rest have flown southward. Why do they go ? The common answer is, " Because they cannot endure the cold." But if one examines the feathers he finds little difference between the robin and the jay, or the bluebird and the sparrow. It is chiefly a question of food. The robin and the bluebird live mostly on insects and worms. As winter approaches these birds can no longer find this sort of food in northern latitudes, and they seek a warmer climate, not so much because they cannot stand the cold as because insects and worms cannot stand the cold. Woodpeckers are insectivorous, yet remain ; but they can get the larvae from the trees about as well dur- ing the winter as in the summer. The large majority of the birds that remain with us during the winter are either seed-eating birds, like the grouse and sparrows, or car- nivorous, as the hawks and owls. Some are omnivorous, like the crows and jays. Some birds, such as the swal- lows, are very regular in the times of their migrations. Others are irregular, and some birds migrate or not, according to varying conditions. We must keep in mind the bird's marvelous power of flight ; in a short time he can cover a very great distance. Parasitic Birds. Perhaps the most common example of the parasitic habit is seen in the common cowbird. Aves. 221 It lays its eggs in the nests of smaller birds. The eggs, being larger than those of the owner of the nest, receive the most heat, and are likely to hatch first and prevent the development of the rightful heirs ; thus the usurper suc- ceeds. Our cuckoo builds its own nest and should not be confused with the English cuckoo, whose bad reputation is sometimes transferred to his American namesake. CHAPTER XV. BRANCH CHORDATA. CLASSIFICATION OF AVES. EXISTING birds are divided into two great groups. All flying birds have the keeled breastbone, and from this fact of structure are placed together in the division Carinatae, meaning " keeled." The ostrich has no keel on the breast- bone, hence is placed in the division Ratitae, from a word meaning " raftlike," referring to the shape of its breastbone. DIVISION I. RATITAE. The best-known representative of this division is the African ostrich. It cannot fly, the wings being small ; but it is a swift runner, equaling a horse in speed. The breast- bone is not only without a keel, but is relatively very small, as might be expected since there are no large flying muscles. The feathers on the wings and tail have no booklets on the barbules ; the result is a plume instead of a firm vane as in the flying birds. These plumes have been valued as ornaments from the earliest time, and now the rearing of ostriches for the plumes is an important industry in South Africa and southern California. The ostrich is also noteworthy from its size, being the largest of existing birds, standing from six to eight feet high. It has but two toes on each foot. In the same division are also the South American ostrich, the emu of Australia, the cassowary of Australia and the East Indies. The kiwi of New Zealand has bristlelike feathers, Aves. 223 so that it appears to be covered with hair, and the nos- trils open at the tip of the long beak. The Ratitae are " overgrown degenerate birds that were once on the right road for becoming flying fowl, but through greediness and FIG. 130. SOUTH AMERICAN OSTRICH. From Kingsley's Zoology. idleness never reached the 'goal/ went back, indeed, and lost their sternal keel, and almost lost their unexercised wings" (Parker). DIVISION II. This division includes all flying birds. All of the birds in this part of the world are carinate. The breastbone 224 Descriptive Zoology. is large and keeled to support the flying muscles. The barbules have booklets which unite the barbs, forming a firm vane. The Carinatae are divided into a number of orders. The Diving Birds. The diving birds have webbed (or lobed) feet and are expert in swimming and diving. The wings are usually small or rudimentary. In many the tail is rudimentary. Our local examples are the grebes and loons, though these are little seen except by the field naturalist, hunter, or fisher. Their legs are set far back in adaptation to their main use, the result being that they must stand upright and can hardly walk. The plumage is thick and well oiled, to fit them for diving. Water does not penetrate be- tween the feathers, so the skin is not wet. The grebes have lobed toes and are about the size of our smallest ducks. They dive like a flash when alarmed, but it is not true that they can dive between the flash of a gun and the time that the shot can reach them. The grebe is commonly called " hell-diver." The loon is our largest diver. Its peculiar cry, sometimes resembling a hysterical laugh, has given rise to the expression, " crazy as a loon." The loon does not try to escape pursuers by flight, but dives and swims long distances under water, so that it is seldom shot. FIG. 131. PIED-BILLED GREBE OR HELL-DIVER. From Eckstorm's The Bird Book, Aves. 225 The auks and puffins are found in vast numbers on the coast of Labrador and northward, some having great powers of flight. FIG. 132. THE LOON. From Eckstorm's The Bird Book. The penguins are correspondingly characteristic of Pata- gonia and the Antarctic regions. Their wings are small and paddlelike, and ^ are covered with scale- like feathers. The Long-winged Swimmers. This group includes the gulls and terns. They are web-footed and have long wings and tail, with remarkable power of flight. They occasionally rest upon the water, coming on shore only to lay their eggs. They are mostly sea birds, though some frequent inland lakes and rivers, and any one FIG. 133. HERRING GULL. From Eckstorm's The Bird Book. 226 Descriptive Zoology. who has* taken a trip by steamer has watched them and wondered at their tireless flight. The gulls have hooked beaks, while those of terns are pointed and nearly straight ; in both the bills are often bright-colored. They feed chiefly on fishes, but some are scavengers, following ships. The Tube-nosed Swimmers. To this order belong the petrels, which resemble the gulls except in having the nos- FIG. 134. PETREL. From Eckstorm's The Bird Book. trils open as two parallel tubes on the top of the beak. Perhaps best known, or at least most read about, are the stormy petrels, or " Mother Carey's chickens." Closely related also is the albatross of the southern hemisphere, which has a spread of ten feet. Aves. 227 The Totipalmate Birds. As the name indicates, the birds of this order have full-webbed feet ; that is, there are not merely two webs between the three front toes, as in ducks and most web-footed birds, but there are three full webs, the hind toe being connected by a web with the FIG. 135. THE CORMORANT. From Eckstorm's The Bird Book. inner front toe. Our most familiar examples are the cor- morants, but they are shy birds, found in the lakes and larger streams. They are voracious fish eaters. Nearly every one has seen the pelican, as it is frequent in zoologi- cal gardens and menageries. The cormorant has a rudi- ment of the throat pouch so conspicuous in the pelican 228 Descriptive Zoology. In the East Indies the pelican is tamed and used in fish- ing, as is the cormorant in China. The Ducks and Geese. These birds have webbed feet, with heavy, oily plumage. The body is flattened, and all are fine swimmers. The bill is frequently broad, with a sort of saw edge. The tongue is fleshy. In the geese and fish ducks the bill is narrow. The swans belong to this FIG. 136. HEAD OF PELICAN. From Eckstorm's The Bird Book. group. Our domesticated duck closely resembles the wild mallard, from which it is descended. The downy feathers are much used for pillows, etc. Some ducks dive well, and live largely on fish, which diet gives their flesh a rank, fishy flavor ; but the fine flavor of the canvasback is thought to be due to the wild celery on which it feeds. The wood duck, and a few others, are exceptional in nesting in trees, though, of course, near water. Ducks and Avcs. 229 geese attract attention by their migration in large flocks, especially in the spring. But their former vast numbers have been reduced, mainly by those who shoot them for market. All the above-described orders are often classed together as the " swimming birds." Herons and Storks. These are slender-bodied, long- legged, and long-necked, with long, sharp bills, living about the water and feeding chiefly on fishes, etc. They are fitted for wading, not only by their long legs, but also FIG. 137. WOOD DUCK. From Kingsley's Zoology. by the fact that the feathers extend only part way down the tibia. The long neck is ordinarily kept bent in an S-shape, and can be quickly darted out to seize food. Among the herons are the big blue heron, seen along the rivers and creeks, the white egret, the bittern or stake driver, the night heron, and the little green heron. In the breeding season the head bears long plumes that are much sought as ornaments. 230 Descriptive Zoology. The Cranes and Rails. This group also consists of marsh birds, usually with long legs and necks. The cranes are large, the white or whooping crane having a very long windpipe coiled in a hollow in the breastbone. The rails are smaller birds, not larger than a hen. These are seldom seen except in reedy swamps. The coot, or mud hen, is common in marshes and reedy lakes ; it has a bill like a hen. It is an excellent swimmer, but has lobed instead of webbed feet. The flesh is rather rank ; but as ducks are becoming more scarce, the coot is not unfrequently substituted. The Shore Birds. This order includes the snipes, plovers, etc. Like the two preceding orders, its members usually have long bills, neck, and legs. The three orders are often spoken of together as the " waders." The long, slender bill is often soft and sensitive at the tip, to fit it for probing in the mud for worms. Several of the snipes are highly esteemed by epicures, especially the woodcock and "jacksnipe." The plovers are found rather more on dry land ; they have no hind toe. The golden plover is often seen in large flocks during its migration, and nearly every one knows the killdeer by the cry from which it gets its name. The Gallinaceous Birds. The Gallinae, or fowls, have robust bodies, well-developed legs, strong, blunt bills and claws. The hind toe is elevated, that is, is attached higher than the other toes. They are poor fliers, having relatively short wings. They are essentially ground birds, none making their nests in trees. They feed chiefly on seeds and grains, the crop and gizzard being well developed. On account of their plump bodies and the excellent quality of their flesh, they are valued as food. Other animals thari man prey upon them ; and as they live on the ground, where prowling enemies can gain easy access to them, we should expect to find them colored for protection ; and, in Aves. 23 1 fact, they wear grays, browns, and blended colors resembling grass, weeds, and brush. The turkey is a native American, though bearing a foreign name. Except the turkey, all our native Gallinae belong to the grouse family. The quail is widely known as "bob-white." It is very cunning, and holds its own fairly well when properly pro- tected by law. The partridge, or ruffed grouse, lives in the woods. On account of its wildness, it persists where native forest still stands. It makes a loud noise by beating its wings rapidly (drumming). The prairie hens once abounded on the prairies of the Central states, but are fast disappearing. Even though protected by law eleven months of the year, they seem doomed to extermination. They lack the cunning of the quail, and their size is a disadvantage. The cock has a bare colored spot on each side of the neck. This is inflated while making his booming noise in the mating season, and gives him the appearance of having an orange on each side of the neck. The sage grouse (sage hen) is found on the Western plains among the sage brush. Sage hens are very good to eat early in the season, but later are often tainted by eating sage leaves, which makes the flesh bitter. The sage hen is peculiar in lacking a gizzard. One of the most interesting of the grouse is the ptarmi- gan. It is a rock grouse. The American species is found in the Rocky Mountains, living on the rocks above timber line. The legs and feet are fully feathered down to the base of the claws. It has in summer a mixed gray and brown color that makes it inconspicuous on lichen-covered rocks. In the winter it turns pure white, and in fall and spring is partly gray and partly white in transition. 2J2 Descriptive Zoology. Our common fowl are descendants of the jungle fowl of India, which our ancestors took from a wild state and do- mesticated. The guinea fowl, peafowl, and turkey are other domesticated gallinaceous birds, these domesticated forms all belonging to the pheasant family. It is remark- FIG. 138. THE RUFFED GROUSE. From Eckstorm's The Bird Book, able that the breast muscles should retain their large size when they are so little used. Of late, pheasants from the old world have been introduced in various parts of this country. The Gallinae are undoubtedly the most valuable to man of any order of birds. Aves. 233 The Doves. The doves- are characterized by a soft, swollen membrane, or cere, overhanging the nostrils at the base of the bill. They are strong fliers, with heavy flying muscles and small, weak legs. This is a small order. The wild pigeon, formerly existing in countless numbers, is now well-nigh extinct. The turtledove, or mourning dove, how- ever, remains abundant in the Central and Western states, finding abundant feed in the grain fields. The Birds of Prey. Birds of prey usually have stout, hooked beaks and sharp, curved claws, fitting them for clutching and tearing their prey. They do not have a gizzard, not needing such a stomach for digesting flesh. The colors are usually dull, the sexes generally being colored alike. The females are usually larger than the males. There are three principal forms of Raptorcs, illus- trated by the hawk, the owl, and the vulture. The hawks are the best examples of the order. They are keen-eyed, strong of wing and leg. There is much un- grounded prejudice against them, for, with the exception of Cooper's hawk and the sharp-shinned hawk, most of them do more good than harm, killing large numbers of mice, especially field mice. The eagles belong to the same family (Falconidae) as the hawks. The so-called " bald- headed eagle " is not bald ; but in old age the feathers of the head and neck are white, making the name "white- headed eagle " appropriate. The adult is smaller than the younger eagle. This bird hardly deserves to be chosen as the emblem of this country, as he is a notorious robber. Often he perches, waiting and watching, till an osprey, or fishhawk, has captured a fish ; then he swoops down upon him and snatches away the prize. The golden eagle is a distinct species, characterized by being full-feathered down to the toes. 234 Descriptive Zoology. The owls have both eyes facing forward. The eyes are large, and have very dilatable pupils, thus enabling them to see well at night. Owls have a soft plumage and an almost noiseless flight. They depend more on stealth than on swiftness for securing their prey. They do much good by FIG. 139. THE MARSH HAWK. From Grinnell's Our Feathered Friends. destroying rats and mice. They swallow birds and mice nearly whole ; later the bones, hair, and any other indigesti- ble portions are ejected from the mouth. Many owls have tufts of feathers called "ears," "ear tufts," or "horns," but these probably are merely ornamental. The great horned owl is well known by its hoot, " hoo-hoo, hoo-hoo, Aves. 235 hoo-hoo, hoo-hoo," the last note prolonged with a circum- flex accent. The common little screech owl shows an interesting varia- tion in color. Two colors are found, a gray and a reddish. It was at first thought they belonged to different species, but these two colors have been found in young of the same brood. The difference seems to have no relation to age, FIG. 140. TURKEY BUZZARD. From Grinncll's Our' Feathered Friends. sex, or geographical distribution, nor do there seem to be intermediate individuals. There are evidently two styles of dress with the screech owls. This occurrence of two styles of plumage is known as "color dimorphism." The vultures are degenerate Raptores, usually carrion eaters. The head and neck are usually bare, and the bill and claws weaker than in the above-described forms. Many 23 6 Descriptive Zoology. of them are large, and soar gracefully hour after hour high in the sky ; but when they descend to earth they show their disgusting nature. Yet they are useful as scavengers, and are wisely protected by law, especially in the South. Our only example in the Northern states is the turkey buzzard, which has a spread of six feet. In the South is found also the carrion crow. This must not be confused with our common crow, which, though carnivorous, is classed with FIG. 141. CAROLINA PARRAKEET. From Kingsley's Zoology. the Passeres, or perching birds. The condor of the Andes is a vulture ; though feeding chiefly on carrion, it sometimes kills lambs and other small animals. Exaggerated accounts of its size and ferocity are common ; measurements do not show that it exceeds a spread of eleven or twelve feet. The Parrots. Parrots have a soft, fleshy, mobile tongue, and can learn to talk. They have the toes in pairs, and can climb well. The bill is large and so strong they can Aves. 237 crack hard nuts. Most of the group are tropical birds, as the macaws and cockatoos, and have gorgeous colors. The only example of the order found in the United States is the parrakeet of Florida. The Cuckoos. The cuckoos have the toes in pairs, the outer front toe having been turned backward. In the same group are placed the kingfishers, though this order is confessedly a " mixed lot " that were thrown out of the old group of "climbing birds." The Woodpeckers. The woodpeckers are typical climbers, the feet being zygodactyl, that is, with two toes turned forward and two back- ward. In climbing, the stiff tail feathers assist by bracing against the tree below. The bill is straight, hard, and chisel- like, the strong neck muscles using it to drill a hole through bark and wood after insect larvae. When the larva is reached, it is secured by the slender tongue, hard and barbed at the tip, which is darted out and withdrawn with force and pre- cision. The mechanism for projecting the tongue can hardly be understood without actual examination. There FIG. 142. DOWNY WOODPKCKER. From Grinnell's Our Feathered Friends. 23 8 Descriptive Zoology. are two slender cartilaginous rods which pass backward from the tongue under the angle of each jaw, up and for- ward on top of the head, in some cases even nearly to the tip of the bill. The cartilaginous rods furnish stiffness, so that a muscular sheath can be effective. Woodpeckers do good by destroying borers. Only one kind, the true sap sucker, or yellow-bellied wood- pecker, uses the wood or sap, thus being somewhat injurious. The Swifts and Humming Birds. The birds of this order have long, pointed wings, the primaries being especially elon- gated. The feet are small and weak. The swifts are well known to every one under the name " chimney swallows," but they are not closely related to the true swallows. The humming birds are the smallest of birds and among the most beautifully colored. The tongue is long and extensible, and is used in securing insects from tubular flowers, over which they are often seen hovering. The nighthawk and whip-poor-will are in this order. They are fitted for catching insects on the wing by the very wide mouth, the gape extended far along each cheek, while the bill itself is small and weak. These birds fly at night or at dusk. When they light on a branch, they always sit lengthwise, never crosswise, and, as they lie quite flat and are of a grayish tint, they are very hard to see. FIG. 143. NIGHTHAWK. From Packard's Zoology. Aves. The Perching Birds. This is the largest order of birds. Its members have the toes fitted for perching, with three toes turned forward and one backward, all on the same level; most of them are "tree" birds, and are small or medium-sized. There are usually twelve tail feathers and nine or ten primaries. The flycatchers include the kingbird and pewee. The crows and jays are known by their harsh voices, omnivo- rous appetites, and thievish habits. They do harm by eating the eggs and young of many birds. The black- birds and orioles form a well-known family, including the parasitic cowbird, the bobolink, and meadow lark. The sparrows, or finches, are the largest family of perchers. They have stout, cone-shaped beaks, with the " corners of the mouth drawn down." Most of the sparrows are of rather dull colors, streaked grays, drabs, and browns pre- vailing, as in the tree sparrow, chipping sparrow, and snow- bird. Still, many of these have patches of yellow, white, or chestnut feathers. Some are conspicuously, colored, as the purple finch, wild canary, or thistle bird, the indigo bird, and the cardinal and rose- breasted grosbeaks. The English sparrow was introduced into the United States about 1850, with the hope that it might check the ravages of the "cankerworm" and other tree-infesting caterpillars. The importation was a failure. It is doubt- ful if these sparrows do much good in the way of eating FIG. 144. KINGBIRD. From Packard's Zoology, 240 Descriptive Zoology. obnoxious insects. Certain it is that the English sparrow drives away many birds that were very useful in destroy- ing such insects. The English sparrow is a bold, pugna- cious bird ; he makes himself at home, but drives from home many of our fine birds, such as the bluebird, pewee, and wren. This sparrow, like most sparrows, is mainly a seed eater, and does considerable damage in this way. A further charge against him is his dirty habits. The swallows are another interesting family, comprising the " swallow-tailed " barn swallow, the eave swallow, the FIG. 145. BUTCHER BIRD ; SHRIKE. From Miller's My Saturday Bird Class. bank swallow, which makes its nest in long, horizontal holes in steep banks, and the half-domesticated martin. The shrikes are hawklike in appearance and in habits, having a hooked beak and sharp claws. They catch mice, frogs, small birds, snakes, grasshoppers, etc., and impale them on the thorns of hedges and other trees. From these habits they are also called mouse hawks and butcher birds. A large family of small birds called warblers live in tree tops, and are not well known except to those who take special pains to study them. The sprightly wrens are placed in the same family with the mocking bird, catbird, and brown thrush. These last three are superb singers. Another fine songster is the wood thrush ; though placed in Aves. 241 a different family, it resembles the brown thrush in hav- ing a tawny back and a light-colored breast, with brown spots, the tail being shorter than that of the brown thrush. The mocking bird is more southern, occurring mainly south of the latitude of the mouth of the Ohio River. The nuthatch and chickadee remain through the winter, as they feed on insects found beneath the bark of trees. The nut- hatch has the climbing habits of a woodpecker, but its FIG. 146. BLUE JAY. From GrinnelFs Our Feathered Friends. toes are arranged as in perchers. It is not excelled as a climber, going sideways or head downward, as well as up- ward. Among the highest in development of all birds is the bluebird, which, unfortunately, is growing rare in the Central states, especially about towns, where it was formerly common. Perhaps no bird ranks higher in its general organization than that bird so dear to every American child, the robin. 242 Descriptive Zoology. Fossil Birds. In rocks in various parts of the world have been found remains of various extinct birds. Some of them were larger than any existing, ten feet in height. One egg has been found, the capacity of which equaled one hundred and fifty hen's eggs. But more interesting than the great size is the peculiar structure of some of these ancient birds. Many of them possessed teeth, and some FIG. 147. MEADOW LARK. From Grinnell's Our Feathered Friends. of these teeth were set in sockets, a feature we did not find till we reached the highest of the reptiles. One fossil, found in Bavaria, had not only teeth, but also a long tail, consisting of many vertebrae, with a pair of feathers extending out on each side from each joint. Relations of Birds and Reptiles. Not only do fossil remains show points of structure in common between these Aves. 243 two groups, but if we compare the structure of modern birds and reptiles, we find likenesses that are not apparent on superficial examination. Feathers and scales are of the same origin ; the bird has both. The feathers of the wing of the penguin are scalelike. The head joins the first ver- tebra in the same way in both by a single occipital condyle, FIG. 148. BALTIMORE ORIOLE AND NEST. From Grinnell's Our Feathered Friends. that is, the head pivots on a single rounded process, instead of on two, as in our bodies. The tongue of a snake is supported in the same way as in a bird, and both are more or less protrusible. Both lay large eggs, and there are points of development in common that cannot be con- sidered here. All these facts, here scarcely hinted at, go to show that birds have descended (or ascended) from 244 Descriptive Zoology. reptiles. Hence many authors include birds and reptiles in the one group, Sauropsida, just as the fishes and am- phibians are placed together in the group Ictyhyopsida. Game Birds'. The principal game birds are the various kinds of grouse (the quail, prairie hen, partridge, sage hen), the ducks and geese, and various wading birds, including snipe, rails, plovers, etc. But the food value of these is not great. All sportsmen who wish a continuation of these game birds should agree in enacting such laws as shall protect them so their numbers may not be greatly reduced. The general sentiment is that they ought not to be killed for market purposes, nor during the jreeding season. Value of Birds. The value and importance of game birds sinks into insignificance in comparison with the smaller birds. When we stop to consider the ravages of insects, those that infest the fields and orchards, forests and groves, the many larvae at the roots and on the foli- age, the caterpillars, cankerworms, etc. ; and on the other hand the multitude of birds mostly of small size the robin and bluebird, the cuckoos and warblers, flitting about in the tree tops all day long in search of these noxious insects, when all these facts are weighed, we may well raise the question whether, if all bird life on the globe were destroyed, the earth would long continue habitable by man. As it is, occasional plagues of insects strip large areas of plants and bring on local famine. These birds should be fully protected by law. Till lately the number of many of these birds has rapidly 'decreased, owing to their being killed for their plumage, to the collection of eggs, and to wanton and aimless destruction. Besides game birds none should be killed, except for scientific purposes, unless they are themselves noxious, as crows and jays, the English sparrow, a few hawks, and possibly a few others. Aves. 2 45 General Characteristics of Birds. The possession of feathers is sufficient to distinguish birds from all other animals. The consolidation of the thoracic ,vertebrae and the pelvis is peculiar. The bones of the cranium are united in one, the sutures disappearing early. The ribs are provided with flat braces extending to adjoining ribs. The breastbone is large, and usually has a well-developed keel. The two collar bones (clavicles) unite to form a wish- bone. Air sacs are connected with the lungs. The tem- perature of the blood is high. The red corpuscles are elliptical and have nuclei. The brain is relatively large, the eye especially being large in proportion to the size of the head. The organ of the voice is at the lower end of the windpipe, instead of at the upper. Class Aves CLASSIFICATION OF BIRDS. ORDERS. EXAMPLES. Division Ratitae i. Struthiones Ostrich 2. Pygopodes Loon 3. Longipennes ..... Gull 4. Turbinares Petrel 5. Steganopodes .... Pelican 6. Anserrs Duck 7. Herodiones Heron 8. Paludicolae . . . . Crane Division Carinatae i 9. Limicolae Snipe 10. Gallinae . . . . . . Quail 11. Culumbas Pigeon 12. Raptores ...... Hawk 13. Psittaci Parrot 14. Coccyges Cuckoo 15. Pici Woodpecker 16. Macrochires Nighthawk 17. Passeres Robin CHAPTER XVI. BRANCH CHORDATA. CLASS MAMMALIA. Example. The Common Rabbit. Habits. The common gray rabbit is familiar to many under the name of " cottontail." This name is due to the white fur of the ventral surface of the tail. As the tail is held erect, the white part is very conspicuous when the rabbit is running away from the observer. Our rabbit unlike the English rabbit does not burrow, though it sometimes takes to holes to escape pursuit, and perhaps lives in them when other shelter is not convenient. In pleasant weather the rabbits stay most of the time in rather open spaces, hiding in bunches of grass. They do not make any nest at such places, but simply find, or make, an opening in a convenient tuft of grass, where they squat. Such place is called a " form." In colder weather, especially when there is snow, they find a more complete protection in brush heaps, hedges, and patches of weeds, or even in burrows. They are nocturnal, sitting quiet all day, or coming out only in the cool part of the summer mornings and evenings. But at night they come out and run about for food, and many observers think they are very social and enjoy playing together. Covering of the Rabbit. The rabbit has a covering of hair. The bulk of the covering, the fur, is made up of short, soft hairs. Among these, and more deeply embedded 246 Mammalia. 247 in the skin, are a number of long, straight hairs with dark tips. They make an admirable covering during the cold of winter. The feet are also covered by hairs, and the inside of the cheek is hair-lined. The Rabbit's Mode of Locomotion. It should first be observed that the hind limbs are much larger and stronger than the fore limbs. The back and loins are well-muscled, all fitting the rabbit for running. When it is undis- turbed, and moving about in search of food, it simply hops. But when frightened, it runs swiftly. In running, the chief propelling power is the hind limbs, which, when straightened, are efficient means in pushing the body for- ward. Before each leap the body is doubled, or arched. Then the body straightens by the action of the muscles of the back and the hind limbs. At the end of the long leap the rabbit alights on the front feet, but the long hind legs swing forward, one on each side, straddling the fore legs, so that the foremost tracks, in the set of tracks made at each leap, are made by the hind feet, and the two smaller tracks, which are closer together, are made by the front feet, as follows : o hind o front o o feet o o o feet o Not unfrequently the rabbit sits erect, resting on the whole length of the hind feet. Ordinarily the rabbit walks or runs on the toes only. The true heel in the rabbit is off the ground in running, and is where we usually cut off the foot when dressing the rabbit. Food of the Rabbit. The rabbit is herbivorous, eating clover, grass, etc., with an especial liking for many garden vegetables. It is, therefore, commonly found around gar- 248 Descriptive Zoology. dens and orchards. The rabbit likes such places, not only on account of the food there found, but also because of the shelter afforded by the grass and bushes. In winter, when fresh vegetation is scarce, the rabbit eats twigs, especially the buds and bark ; thus a brush heap of fresh cuttings from such trees as the apple affords the rabbit both shel- ter and food. The Rabbit's Teeth. At the front of the mouth are two pairs of chisel-shaped teeth, the incisors. These teeth are mainly composed of dentine. On their front surfaces is a layer of hard enamel. The result of this hard front edge is that in gnawing, the hinder edges of the teeth are worn away faster and the teeth are kept constantly beveled ; in other words, they are self-sharpening. These teeth grow at the base of the roots as fast as they are worn away at the outer ends. If one of these teeth should be broken off, or otherwise destroyed, the opposing tooth would no longer be worn down and would grow too long, and sooner or later interfere with the process of eating and cause starvation. Many cases of this kind among rodents have been known. Back of the upper incisors is another, smaller pair of teeth, also regarded as incisors, an arrangement pe- culiar to the rabbits and not found in other rodents. Back of the incisors is a considerable space without any teeth, before the grinding teeth, or molars, are reached. This space undoubtedly enables the rabbit to manage the mouth better in gnawing, just as in most of our pinchers we have a widened space back of the nipping jaws. The same arrangement is found in the horse, cow, etc. The molars are six above and five below, set in close rows, and having ridges running crosswise. The direction of these ridges must be considered in relation to the joint by which the lower jaw articulates witn the skull. This 250 Descriptive Zoology. joint is not a regular hinge joint, such as we find in a cat, which allows of little more motion than a door hinge. The rounded knob at the upper end of each jawbone fits into a groove which runs front-and-back, thus allowing the jaw to be moved forward and back. If one watches a rabbit chewing, he will see that this motion is character- istic in place of the more decidedly lateral movement seen when a cow is ruminating. The ridges of the upper and lower molars, therefore, are drawn back and forth over each other, thus effectively grinding the food. The Process of Digestion. There are four pairs of salivary glands on each side of the head, which pour their secretions into the mouth to aid in digestion. At the base of the tongue is the epiglottis, a cartilaginous cover which turns down over the opening into the windpipe when the food passes over it on the way to the stomach. The gullet extends through the thorax, piercing the diaphragm, and enters the large stomach, which lies back of the diaphragm, partly separated from it by the liver. On the liver is the bile sac, from which the bile is poured into the first part of the intestine, called the duodenum. The long, coiled small intestine finally joins the large intestine, and at their junction is a long, blind tube, or sac, the cecum. Near the stomach is the pale pancreas, which empties its secretion by a duct into the duodenum. Since the rabbit eats food that is relatively poor in nour- ishing material, it is obliged to eat a large amount ; and as vegetable food, especially with a good deal of cellulose, is difficult of digestion, we should expect to find the digestive tube both long and capacious, and this is the case. The intestine is about ten times the length of the rabbit's body. While the rabbit sits in concealment during the day, the slow process of digestion is going on. Mammalia. 251 The Circulation of Blood in the Rabbit. The rabbit's circulation is essentially as in our bodies. The heart is completely divided into two parts, the right and left halves. The right half pumps the blood to the lungs, whence it returns to the left half of the heart to be pumped to all the other parts of the body through the main artery, called the aorta. The heart is within a pericardium, situated between the two lungs, and resting against the diaphragm, near the ventral body wall. How the Rabbit Breathes. The rabbit's respiration, too, is very like ours. The diaphragm is a thin sheet of muscle that arches across the body at about the pos- terior border of the longer ribs, separating the body cavity completely into two cavities, the anterior con- taining the heart and lungs, the posterior con- taining the stomach and intestines, with the liver, pancreas, kidneys, blad- der, etc. By the shorten- ing of its muscle fibers FlG ' I 5- CROSS SECTION OF ABDOMEN . j OF MAMMAL. the diaphragm is moved backward, thus drawing in the air. The muscles which move the ribs in and out also do part of the work. The lungs are similar to ours, being light (hence called "lights") and porous, all the air vesicles being reached by minute branches of the bronchial tubes, which fork from the windpipe. The temperature of the rabbit's blood is considerably higher than our own, averaging 103 or 104 F. 252 Descriptive Zoology. The Excretory Organs of the Rabbit. The lungs act as excretory organs, throwing off carbon dioxid as well as ab- sorbing oxygen. The kidneys also are organs of excretion. The kidneys are bean-shaped bodies attached to the dorsal wall of the abdominal cavity. To each kidney runs a branch of the aorta, supplying it with blood, and from the kidney a vein returns the blood to the postcaval vein. As the blood flows through the kidney in fine tubes called capillaries, the kidney removes from it certain impurities, especially the waste matter that contains nitrogen. The excretion is con- veyed backward by a tube called the ureter, and emptied into the urinary bladder, an organ not possessed by the birds or reptiles. Enemies of the Rabbit Among the enemies of the rab- bit are dogs, wolves, foxes, cats, both wild and domesticated, minks, weasels, hawks, owls, and perhaps many others. In addition to these larger foes, the rabbit is usually infested by parasites, such as fleas, tapeworms, etc. How the Rabbit escapes his Enemies. The rabbit has claws, but they are not very efficient as a means of defense. Rabbits use their teeth in fighting one another, but these avail nothing against their enemies. The rabbit is practi- cally defenseless, and relies upon two means for protec- tion, the first is its color, and the second its speed of flight. The prevailing color of the rabbit is gray, varied with some blackish, and more or less tinged with yellowish brown. In the summer he appears rather more rusty or tawny. He is so like his surroundings that it takes a keen and practiced eye to detect him when he sits perfectly quiet in his form. This he usually does, relying on his color to protect him. Besides his color, his position is an aid in concealment, for he is snugly doubled up, the ears folded down closely along the back, and the white tail is out of sight. He generally Mammalia. 253 sits in the center of a tuft of grass, and frequently he appears to select a small bunch of grass, just large enough to cover him scantily, perhaps thinking that he will not be looked for in such slight cover. Sometimes a rabbit will start from his form when an enemy is at a distance, especially if much noise is made ; at other times he may be approached closely, and almost touched, before he will stir. When he does start, it is usually with a dash ; and he generally runs with great speed to another cover, often running through hedges and other places that will prove an obstruction to pursuers. If followed, especially by dogs, the rabbit fre- quently runs in a circle, and after completing the circle, suddenly jumps far to one side, thus throwing the follower off the scent. Though speedy, the rabbit is not an enduring runner. He carries too much weight. The bulky food and the large amount he eats prove a handicap. His paunch suggests that of the cow. A dog has the advantage. Being a meat eater, he has a short intestine, whereas that of the rabbit is long. The dog's food is concentrated, nutritious, and quickly digested ; hence the dog is light in the abdo- men, where the rabbit is heavy. Further, the heart of the dog is stronger relatively, and a strong heart is the chief factor in long-windedness. But in spite of his relative short- windedness, his running and his cunning often enable him to escape. Injury done by the Rabbit. Rabbits do considerable harm by gnawing the bark of young trees in orchards, and in some places it is necessary to build a protection around the trees to save them. The English rabbit, introduced into Australia, has become a plague. In spite of all the means that man has been able to devise, they multiply beyond any checks that can be applied. High rewards have been offered for any means that will exterminate 254 Descriptive Zoology. them, and bounties are continually paid for killing them ; they thrive in spite of all that can be done. The intro- duction of contagious diseases has not been a success. Uses of Rabbits. In this country they are used only for food, and that to a very slight extent ; but in Australia and some other parts of the world the fur is saved and used in making felt. This is an important industry, as practically all our " derby " hats are made of rabbit fur. Most of the fur goes to London to be dyed. Development of the Rabbit. The ovaries are small ovoid bodies attached to the dorsal wall of the abdominal cavity, posterior to the kidneys. The eggs are microscopic, and when set free from the ovary, enter the free opening of the oviducts, as in the case of the frog. The posterior end of each oviduct is developed into an organ called the uterus, for holding and nourishing the egg, which is here retained till development to the form of the parent is reached. The young are born alive, and for a time after birth they are nourished by milk from the mammary glands of the mother. From four to seven are usually in a litter, more commonly five or six. As several litters may be produced during a year, the rate of their increase is very rapid ; but their fa- talities are enough to keep their numbers down in this part of the world. The little " cottontails " are concealed in a fur-lined nest, which is a pocketlike hole in the ground. The Nervous System of the Rabbit. The brain is fairly well developed, but the rabbit has not a high intelligence; and as in the other lower orders, the surface of the brain is nearly smooth instead of convoluted, as is the case with brains of the higher animals. The principal parts of the brain are the cerebrum, with its two hemispheres tapering forward into the olfactory lobes (see Fig. 167). Back of the cere- brum is the irregular cerebellum, with a central and lateral Mammalia. 2 55 Jobes. From the ventral surface of the brain the spinal bulb arises, and continues into the spinal column as the spinal cord. From the brain arise twelve pairs of cranial nerves, and from the spinal cord a series of paired spinal nerves which supply the body. The Senses of the Rabbit. Sight and hearing are es- pecially well developed. The eyes are prominently placed on the sides of the head, so that the rabbit can see an enemy approach from any direction. The ears are long, and can be moved by muscles so as to turn in any direction to catch the sound. Rabbits may not unfrequently be seen to sit erect and prick up the ears as if suspicious of danger. When at rest in concealment, the ears are laid flat on the back. The sense of smell seems well developed. The nos- trils are longitudinal slits at the end of the nose, and between them is a cleft, from which fact we borrow the term " hare- lip." This arrangement apparently gives greater mobility to the lips in feeding, and in sniffing there is considerable range of movement of the upper lip and nostrils. Taste also appears to be fairly keen, judging by the rabbit's dis- crimination in choice of foods. Microscopic examination of the tongue shows essentially the same taste organs and nerve supply as in our tongues. The sense of touch ap- pears to be distributed all over the body, though prob- ably more keen about the nose, especially through the long, stiff hairs which we commonly call the "whiskers." CHAPTER XVII. BRANCH CHORDATA. CLASSIFICATION OF MAMMALIA. SUBCLASS I. PROTOTHERIA. THERE are two subclasses of mammals, the Prototheria and the Theria. The Prototheria nourish the young with milk. They also show that they are mammals by their hairy covering. But they reveal their relationship to birds and reptiles by the fact that they lay eggs. FIG. 151. DUCKBILL. From Packard's Zoology, after Liitken. In this subclass there is but one order, the Monotremata. The order contains but three or four species, and there are two chief forms, the duckbill and spiny ant-eater, both lim- ited to Australia and adjacent islands. 256 Mammalia. 257 The duckbill has a horny bill similar to that of a duck. Its habits are similar to those of a muskrat. It lives in water, and has holes in the bank, which it can enter beneath the water. The body is about as big as a cat's, though it presents a " squatty " appearance, the legs being very short. The feet are webbed and the tail is flattened. It is covered by a soft, fine fur. The duckbill has rudiments of teeth in the early stages of its life, but in the adult state neither the duckbill nor the spiny ant-eater has any teeth. The ant-eater is of about the same size as the duckbill. The hairs are developed into strong, stiff, sharp spines. The bill is conical, and a small mouth at the end permits the extension of the slender tongue, with which it licks up ants like other ant eaters. It lives in rocky ground. SUBCLASS II. THERIA. The Theria include all the remaining mammals. In this subclass the young are born alive, in the form of the adult. The Marsupials. Our only marsupial is the opossum. This odd animal is well known, at least by report, on account of its habit of feigning death when attacked. The marsupials get the name from their most marked charac- teristic, the possession of a pouch, or infolding of the skin of the abdomen. Two peculiar bones extend forward from the pelvis, toward the pouch ; they are called the mar- supial bones, as they support the pouch. The young are born in a very immature condition, and are transferred to the pouch, where they are nursed. The young are kept a long time developing in the pouch, and, after they become self-helpful, occasionally take refuge in the pouch. The opossum is almost omnivorous, eating insects, eggs, and birds, the teeth being of the carnivorous type. The opossum is a good climber, and has a hairless, scaly, prehensile tail. 258 Descriptive Zoology. Opossums are very tenacious of life, and it is commonly reported that after a " possum " has been severely pounded and " every bone in its body broken," it later gets up and crawls away. The following are some facts of structure FIG. 152. OPOSSUM. From photograph from Recreation, by permission of G. O. Shields. that may explain such reports. First, the skin and hair make a thick protective covering, under which is usually a thick layer of fat. The chewing muscles extend far up on the top of the head, meeting in the middle line. The Mammalia. 259 skull is therefore well protected, so that it may receive a severe mauling and not be much the worse, except for external bruises. The opossum is of a low order of intelli- gence, and appears stupid, both when free and in confine- ment. It has not sense enough to become a pet. The kangaroo is another well-known marsupial. The story of its development is about the same as that of the opossum, but the mode of life is different. The hind legs are excessively developed, and the animal hops with "record-breaking" power, seldom putting the feeble fore legs to the ground. When standing, the strong, muscular tail aids in supporting the body, forming a third leg, so to speak. The kangaroo is entirely herbivorous. There are many other marsupials in Australia, and, in fact, with the exception of the opossums, all the living marsupials are confined to ^he Australian region. Many countries yield fossil remains of marsupials, some of large size, showing that Australia contains the remnants of this peculiar, but once widely distributed race. It is further interesting to note that Australia has no other native mammals than the marsupials, except possibly the dingo, or wild dog, which some believe to have been introduced. PLACENTAL MAMMALS. All the mammals above the marsupials are born in a more mature condition. The Edentates. This order includes the sloths, arma- dillos, etc. They are" not wholly toothless, as the name would indicate, but the teeth, when present, are simple or imperfect. They are mostly tropical, one armadillo occur- ring in southwestern Texas. The sloths are herbivorous and tree-inhabiting. They climb, hanging under limbs by their hooked claws, and as 26o Descriptive Zoology. they proceed, strip off the leaves. On the ground they are almost helpless. The extinct slothlike megatherium was as large as a rhinoceros. The armadillos have a scaly or horny development of the skin for protection ; some have also the power of roll- ing themselves into a ball, still further securing safety. The ant-eaters lack teeth ; they secure insects by pro- truding the long, sticky tongue. The Gnawers. The gnawers, or rodents, are character- ized by chisel-shaped incisor teeth, which keep wearing away at the tip and as continually growing from the root. FIG. 153. NINE-BANDED ARMADILLO. From Packard, after Liitken. In all but the hares the incisors are two above and two below. There are no canine teeth, and there is a wide space between the incisors and the molars. They are chiefly herbivorous, and the digestive tube is long. They constitute the largest family of mammals, and are espe- cially numerous in individuals. The Hares. The general characteristics of this family have been illustrated in the description of the rabbit. Besides our common gray rabbit, there are found in the Southern states the marsh hare and the water hare ; in the North, the northern hare, which turns white in winter; on the Western plains, the big jack rabbit. Mammalia. 261 Porcupines. The porcupines are distinguished by hav- ing sharp spines, which are really modified hairs, and are scattered among the longer hairs of the ordinary type so that the spines are ordinarily not very conspicuous. The spines are especially developed on the tail and on the pos- terior parts of the body. When the porcupine is attacked by an enemy, and especially if cornered, he turns his back toward his pursuer and draws the skin of the body forward, so that the quills point outward in all directions, and any attempt to seize him is met by a quick side stroke of the tail. The quills have a very sharp tip, near which are a series of backward-projecting barbs. They are also very loosely attached at the base. The result is that the quills readily pierce the soft skin of an enemy, become detached from the porcupine, and remain sticking in the wound. These facts are the sole foundation of the once widely ac- cepted belief that the porcupine has the power to shoot his quills into his pursuer. In the West cattle often come in contact with porcupines and have their legs and noses stuck full of quills. On account of the backward-project- ing barbs the quills cannot fall out, but keep working their way in deeper and deeper, making bad festering sores. On this account stockmen hate porcupines and usually shoot them on sight. In the lumber regions of the North porcupines also prove a nuisance, in another way, how- ever. They gnaw into the handles of axes, oars, or any wooden-handled implement, especially those that have been used, apparently for the sake of the salt that comes from perspiration. Hence tools are not left lying on the ground, but axes are stuck into trees with the handles standing far out, oars are laid up in bushes, etc. Porcupines are very stupid, being so well protected by their spines that they do not need to use their wits to escape an enemy. 262 Descriptive Zoology. Rats and Mice. The rats and mice are of many kinds and of vast numbers. Man has adopted some kinds of animals, but these creatures may be said to have adopted man. They are universal attendants on civilization and are as cosmopolitan as man himself. The length of time that they have been associated with man is hinted at by the fact that the word for mouse, in essentially the FIG. 154. CHIPMUNK. From photograph from Recreation, by permission of G. O. Shields. same form, is found in many languages. Though they have many enemies besides man, it seems impossible to exter- minate them, for they are protected in many ways, espe- cially by their nocturnal habits, and, as Coues says, by their very insignificance. Beavers. The largest rodent found in the United Mammalia. 263 States is the beaver. It has webbed hind feet and a broad, flat, scaly tail. All have read of its remarkable intelli- gence and skill in felling trees and in constructing dams. It was formerly widely distributed, but is now rare, owing not merely to the fact that it has been trapped for its fur, but also to the spread of civilization itself. Squirrels. The squirrels are a very interesting group, not only on account of their active and graceful movements, FIG. 155. COMMON MOLE. but also on account of their human trait of laying up pro- visions and their human mode of eating. Most attractive are the tree squirrels, including the fox squirrel, the gray squirrel, the red squirrel, and the flying squirrel. The woodchuck, prairie dog, and gophers live in the ground. The true gophers have large cheek pouches in which they carry out the soil in digging their burrows. The Insect Eaters. This order is best represented by our common mole, whose work of raising a ridge of sod is 264 Descriptive Zoology. familiar to all. They make these ridges in burrowing for earthworms and grubs, which are their main food. They are well fitted for digging by the very large front feet and strong muscles of the front legs. Since they live in dark- ness, the eyes have become rudimentary, sometimes con- cealed by the skin. The teeth are like those of a diminu- tive flesh eater. The nose is long, bare at the tip, and very sensitive. There are no external ears. The shrews are mouselike and are probably often mistaken for mice, as the front feet are not enlarged as in the moles ; but the nose is more pointed, and one look at the teeth would show that a shrew is not a "gnawer." This order also includes the hedgehog of the old world, which has the hairs devel- oped as sharp spines. The fact that both the hedgehog and porcupine have sharp spines leads to confusion. It is unfortunate that many writers are either uninformed or careless in this matter and further extend an already wide- spread error. The two animals are entirely distinct, and the following tabular statement may aid in showing their points of difference : DIFFERENCES BETWEEN A HEDGEHOG AND A PORCUPINE. HEDGEHOG. PORCUPINE. Insectivora Order Rodentia Conical points Teeth . . . Chisel-shaped incisors Insects, etc Food Herbage Not barbed } ~ . ( Barbed Firmly attached f ^ } . . . . Loosely attached Less than a foot Size .... Two feet or more Old world Habitat . . Both old world and new The Bats. The bats of this country are insectivorous, and would undoubtedly be classed with the preceding order if they were not flyers. The wing is a fold of skin Mammalia. 265 supported by the arm and the excessively elongated fingers ; the fold in our bats extends to and includes the tail. The thumb is free from the wing mem- brane and has a hooked claw by which the bat can hang, but usually when at rest it hangs head down- ward by the hooked claws of the hind limbs. Every one is familiar with the flight of our bats as they zigzag after insects. Bats are chiefly nocturnal. There is much super- stition concerning them. There are in the tropics some blood- sucking bats, but ours ^ are not only harmless P but beneficial. Our bats <& hibernate in caves, hoi- ^ low trees, etc. The large bats of the East Indies, > known as flying foxes, are fruit eaters. The Whales. Though living con- tinually in water, whales are true mammals ; they bring forth their young alive and nourish them by means of milk. The fore limbs are developed into flippers. The tail is horizontally flattened, and its two lobes are called flukes. Whales are devoid of hair. The whalebone whale has in its mouth a long series of fringed baleen plates (whalebone), which serve as strainers. The whale ingulfs whole schools of crustaceans, jelly- 266 Descriptive Zoology. fishes, etc., and the water passes through these strainers and out at the sides of the mouth. Underneath the skin is a thick layer of fat which furnishes the whale oil. Such a layer of fat protects this warm-blooded animal in the icy water of the arctic seas. Since the discovery of our oil fields the whale fishery has declined. The "spouting" of whales is not due to a column of water, but to mucus and the condensed moisture of the breath. Whales over fifty feet long are not often taken, though the sperm whale is sometimes seventy-five feet, and the " sulphur-bottom," found in the Pacific, is said to reach even a hundred feet. It is the largest living animal. Porpoises are smaller members of the same group. The Sea Cows. Some authors class these with the whales, but they are herbivorous animals, having grinding molars and a hairy covering. They seem to stand between the whales and the ungulates. They live in the mouths of large rivers ; the manatee is found in Florida and on the west coast of Africa, the dugong in India and Australia. They are sometimes killed for their flesh, which is said to be very much like beef. The Hoofed Mammals. The horse and cow may stand as examples of this order, the ungulates. The hoofs are excessive developments of what correspond to our nails or the claws of other animals. In many forms the hoof en- cases the whole of the lower surface of the foot. It appears to be a special adaptation for the support of heavy animals, many of which have to run rapidly over rough or even rocky ground. The number of toes is typically five, though no living ungulate has more than four. They are all digitigrade, that is, they walk on the toes. They are all herbivorous, with teeth adapted for grinding. This is a large order, and its members are of a large average size. Mammalia. 267 In its domesticated forms it is probably the most useful of any order to man, as from it are derived beasts of burden. Members of this order also furnish us with food (meat, milk, cheese, butter), leather, etc. The domestication of the horse, cattle, sheep, etc., dates so far back that we know not what were the wild forms from which they have descended. The ungulates are divided into two groups, according as the number of toes is odd or even, the odd-toed group being called Perrissodactyls, and the even-toed, Artiodactyls. The Perissodactyls. These forms have an odd number of toes, as shown in the horse, rhinoceros, and tapir. The Horse. The horses now in this country are not natives, but were introduced from the old world; the Indians did not know the horse till after what we call the " discovery " of America. Still, America did have horses in earlier geologic periods, and the history of the develop- ment of the horse, as shown by fossil remains (largely found in this country), is exceedingly interesting. The earliest form was about the size of a fox, and had four well-developed toes in front, with a rudiment of a fifth and three toes behind. Later appears a form with four toes in front and three behind. Then came a horse about as large as a sheep, with only three fully developed toes in front, the fourth represented by a rudiment, but still having three toes in the hind foot. Later still the outer toe became reduced to a mere remnant. Then came a form about the size of a donkey, with three toes all around ; the middle toe persisting and the two on each side becom- ing dwarfed. Finally, the one-toed horse was evolved, the single toe being the middle one of the five, that is, corre- sponding to our middle toes and middle fingers. The Tapir. The tapirs are found in South America and Sumatra. They have four toes in front and three 268 Descriptive Zoology. behind. The snout is prolonged, suggesting the proboscis of the elephant, but its relationship is plainly with the hors'e. The Rhinoceros. The rhinoceros has three toes all Mammalia. 269 around. It is peculiar in having a horn on the top of the snout. In some species there are two horns, not paired, however, but one in front of the other. These animals are found in Africa. and East India. The Artiodactyls. The artiodactyls, or even-toed un- gulates, have either two or four toes. These are symmetri- cally arranged on each side of a median cleft ; hence they are spoken of as " cloven-footed" animals. Lowest among the even-toed ungulates are the hippopotamus and the swine. A species of wild hog, the peccary, inhabits Central and South America, extending into Texas. It is a slender, active, fearless animal, in marked contrast to our inactive, fat-burdened domestic hog. The swine are omnivorous, the other ungulates are almost strictly herbivorous. Except the camel, nearly all the artiodactyls have four toes, two well developed and two rudimentary. The well- developed toes are the third and fourth, the first toe (cor- responding to our great toe and thumb) being wanting. The second and fifth toes are small, but usually with distinct hoofs ; they are shorter and back of the two main parts of the hoof. These rudimentary hoofs are commonly called the " dewclaws." They do not ordinarily reach the ground, and are of little if any use, except in the reindeer. The Ruminants. With the exception of the hippopota- mus and the swine, all the even-toed ungulates are cud chewers and have complex stomachs. As an example, let us consider the cow. There are no upper incisors ; grass and herbage are bitten or broken off by pressing the lower incisors against the hard, toothless pad of the upper jaw. The molars are well developed, and the lateral chewing motions of the jaw are well known. In keeping with this lateral motion, the ridges on the crowns of the molars run lengthwise in wavy lines. The stomach consists of four 270 Descriptive Zoology. compartments. When the food is cropped it is swallowed without chewing. It passes into the large paunch, or first stomach ; when the ruminant lies down to rest, the soaked fodder is passed into the small second stomach, the honey- comb or reticulum, where it is formed into distinct masses and returned to the mouth for thorough mastication. It again goes down the gullet, this time to the third stomach, the psalterium, or manyplies, whence it enters the true stomach, or fourth stomach, sometimes called the rennet. The intestine is very long, be- tween twenty and thirty times the length of the body. The ruminants need a large quantity of food, hence it is easy to see how it is of advantage to them to be able to gather their food quickly, retire to a place of con- cealment, and digest it at their leisure, as many of them are comparatively defenseless. The males of all the ruminants, except the camels, have horns, and in many species the females also possess them, though usually much smaller than those of the male. The Hollow-horned Ruminants. In cattle, sheep, goats, and antelopes, the horn consists of a bony core, covered with a layer of horn, which is not shed except in the case of the pronghorn antelope of our Western plains. Sheep. The rams have large, curved horns, which they use for butting when fighting. Our native sheep is the Rocky Mountain, or bighorn sheep, so named from its immense horns. These, in the old rams, become very much FIG. 158. t>IAGRAM OF THE STOMACH OF A RUMINANT. Showing the course of the food. From Kingsley's Comparative Zoology. Mammalia. 271 battered. Hence arose the story, long widely accepted, that they jump down precipices, alighting on their horns. Since the ewes and lambs can go anywhere the rams can, the absurdity of the account is evident. They are remark- Lamb Ram. Ewe. FIG. 159. MOUNTAIN SHEEP FAMILY. From photograph of some of the author's trophies. able climbers, walking securely on a narrow ledge, perhaps over a sheer precipice of a thousand feet, with the utmost unconcern. They are wary animals, usually having a sen- 272 Descriptive Zoology. tinel, commonly an old ram, posted on a high point of rock, on the lookout for enemies. They seem to expect attack from below, so the hunter tries to get above them. They stay most of the time above timber line. Goats. The Rocky Mountain goat dwells in equally inaccessible mountain tops. Its color is pure white, though its coat is usually dingy from the habit of sunning itself in a bed of dust. Its white coat seems odd for a wild animal. But when one sees it in its home, up among snow banks FIG. 160. ROCKY MOUNTAIN GOAT. From photograph of specimen mounted by L. L. Dyche, in Camp Fires of a Naturalist. By permission of D. Appleton & Co. and light-colored rocks, it seems well adapted to its sur- roundings. It has small, smooth, black horns. Mountain goats are rather stupid animals. The main difficulties in hunting them are due to the steepness of ascent and the rarefied condition of the air. The Buffalo. The American bison, usually called " buffalo," is now nearly extinct. Buffaloes once roamed Mammalia. 273 in countless herds over the plains and prairies of almost all of the United States; to-day probably the only wild herd in the country is in the Yellowstone Park, and it numbers hardly more than fifty. There are probably a limited number in British Columbia. Once the mainstay of the Indians, furnishing them with food, clothing, and tents (tepees), they were doomed to give way before an advancing civilization. The Antelope. The prong- horn, or antelope of our Western plains, is a peculiar animal, the only member of its family. It stands be- tween the cattle and the deer families. It has hol- low horns, which are shed annually. The bony core is a projection from the skull and is never shed. It is very swift-footed and wary, keen of eye and nose. Like most of our wild ruminants, it has a white rump. When hunted it usually runs to a ridge and stops to watch. Instead of getting out of sight of its pursuer, its policy is to keep its enemy in sight, but at a safe distance. The antelope is rapidly disappearing and is doomed to extermination. The Solid-horned Ruminants Deer. The deer family in this country includes three species of deer, and the elk, moose, and caribou. Except in the caribou, only the males have horns. The horns, which are solid, are shed annually, FIG. 161. ANTELOPE. From Forest and Stream. 274 Descriptive Zoology. usually in December or January. They grow out again, with an added prong for each of the first six or eight years. Till fully grown the horns, or antlers, as they are often called, are covered with a soft fur, and are said to be " in the velvet." When the horns are mature this skin dies FIG. 162. WHITETATL DEER. HORNS IN THE " VELVET.' From Recreation, by permission of G. O. Shields. and peels off, the owner assisting by rubbing them against shrubs and small trees. The two common species of deer are the whitetail and the blacktail deer. The whitetail deer is probably identical with the Virginia deer or red deer. It is the most widely distributed form, extending from Maine to Florida, and westward to the Rocky Moun- Mammalia. 275 tains, usually keeping in lowlands. The term "red deer" is inappropriate, as all our deer are red when in their summer coat, turning grayish in the fall. The blacktail is Western, preferring mountains or hilly country. The tip of the tail is black. This deer is also called " mule deer," on account of its very large ears. The horns of the FIG. 163. BLACKTAIL DEER. From Forest and Stream. two species branch differently (see Figs. 162 and 163). The elk (see Frontispiece) is larger than the other deer, sometimes weighing eight hundred and perhaps a thousand pounds. A bull elk surpasses any of the stags of the old world. Elk are being reduced in number and bid fair to be exterminated, since they cannot hide so. cunningly as deer. 276 Descriptive Zoology. The deer family is peculiar in lacking the bile sac. Deer shed their coats, in the summer time being reddish, or "in the red," as the hunters say; while in the winter they are grayish, or "in the blue." In the summer the males of the elk and deer keep by themselves, ranging FIG. 164. MOOSE. From Forest and Stream. high on the mountain sides, often upon the rocks near timber line, while the does and fawns are more likely to be found on lower slopes or in the valleys. In hunting squirrels, the hunter has only two senses to guard against, sight and hearing. But in hunting deer the Mammalia. 277 hunter must not only keep out of sight and out of hearing, but must also avoid detection by a third sense, that of smell. If he attempts to approach this game from the windward side, they are almost sure to detect him and to escape, often without his being aware of their presence, unless he afterward discovers their tracks. The moose is an awkward-looking animal, with its long hump nose. The antlers are spread out into a flattened " blade " near the tips. The moose lives in marshy for- ests. There is a considerable number in northern Maine, Nova Scotia, Alaska, and in British Columbia. A few remain in Idaho, in the northwestern part of Montana, and in the region of Yellowstone Park. The moose and deer feed almost entirely on twigs and leaves, that is, they "browse," while elk feed to a considerable extent on grass, like our domesticated cattle. The Camel. The camel has but two toes, with large, soft pads. The hump is a storehouse of fat. They can go without water longer than most animals, but this is no more than might be expected of an animal accustomed to living in a desert country. The Giraffe. The giraffe is remarkable for the extreme length of its neck. Nevertheless, it has but seven cervical vertebrae, the same number that we have, the increase being due to the lengthening of the individual vertebrae. The Elephants. The elephants are essentially ungu- lates, having five toes, each incased in its own hoof; but on account of the peculiar development of the nose into a trunk, or proboscis, most authors place them in a separate order. The excessively long snout is flexible, very muscu- lar, and serves as a hand in conveying food to the mouth. This arrangement seems especially desirable for an animal 278 Descriptive Zoology. with long, stiff legs and a very short neck. Even if he were not stiff-legged and short-necked, it would be incon- venient for him to dispense with the trunk so long as he retains the tusks. These are the long upper incisors, which are of solid ivory, the slight amount of enamel which originally covered the tips soon wearing away. Elephants are herbivorous and have one large grinding tooth in each half-jaw. The skull is not heavy in proportion to its size, as it has many large air spaces. The skin re- tains a few scattered hairs, with a distinct tuft at the end of the tail. Two species of elephants are found, one in India, the other in Africa. Still larger than the elephants were their (now extinct) relatives, the mastodon and the mammoth. The Flesh Eaters. The flesh eaters, or beasts of prey, are fitted for their life (i) by their activity; (2) by their sharp teeth, especially the long canines; (3) by the claws, usually sharp and strong ; (4) by their color, usually in har- mony with their surroundings. The lower jaw is so hinged that only an up-and-down, or true hinge motion, is per- mitted ; this should be considered in comparison with the lateral jaw movements of ungulates and the gliding for- ward-and-back of the rodents. Instead of being flat-topped, the molars are somewhat like saw-teeth, the upper and lower shutting past each other like shear blades. The flesh eaters have simple stomachs and relatively short in- testines, as the digestion of flesh is short and easy as com- pared with that of vegetable food. The senses are generally very acute. As there is considerable variation in adapta- tion to the conditions of life, let us consider four types of flesh eaters as represented by the cat, dog, bear, and seal. The Cats. Cats are distinguished from the other beasts of prey by having the claws retractile, that is, they can be Mammalia. 279 withdrawn into a sheath, where they are kept most of the time, the animal walking on pads developed on the next to the last joint of each toe. These pads enable the cats to walk noiselessly, and this is an important trait, as they capture their prey by lying in wait or by creeping near it stealthily, then suddenly pouncing upon it. In a bright light the pupils are reduced to a narrow vertical slit. In the dark they dilate widely ; thus they are fitted for their nocturnal habits. Our biggest cat is the cougar or puma, also called the American panther, and in the West known altogether as the mountain lion. Its body is about as thick as that of a sheep and somewhat longer, with a long tail. It is tawny brownish yellow above, paler beneath. Though fierce when wounded or cornered, it is a sneaking, cowardly creature, few instances being known of its attacking a human being. It follows mountain sheep and other mam- mals, ready to seize the young or the sickly or wounded adults. It is found from British Columbia to Patagonia. The wild-cat and lynx are smaller and are short-tailed, being in some localities called " bobcats." Other cats are the lion, tiger, leopard, jaguar, etc. The Dogs. Dogs have the nose more pointed than the cats. The claws are blunt and not retractile. The dog- like form includes the wolves, jackals, and foxes. Most of this group capture their prey by running it down, instead of by stealth as in the cat tribe, though the fox is rather catlike in this respect Proverbial for his cunning, the fox remains in thickly settled districts, not disdaining birds that are domesticated. We have two species of wolves. The prairie wolf, or coyote, has a sneaking, cowardly dis- position. When an Indian wishes to express his utmost contempt for an individual he calls him a coyote. The 280 Descriptive Zoology. timber wolf is larger and does considerable injury by kill- ing calves and lambs. A bounty is paid for wolf scalps. Wolves are little to be feared in this country. The hyenas are between the cats and the dogs. They have heavy shoulders and fore limbs, also strong jaws and FIG. 165. GRIZZLY BEAR, FROM PHOTOGRAPH. From Recreation, by permission of G. O. Shields. teeth to crush bones. They are the scavengers among the beasts of prey, like the vulture among the birds of prey. Both the cats and the dogs walk on the toes, hence are said to be digitigrade. The Bears. Bears walk on the whole flat of the foot and are therefore called plantigrade. Bears are less distinctly carnivorous than the above groups. They live largely on berries when they can get them. They eat many insects, Mammalia. 281 turning over logs and stones and devouring the beetles, worms, and larvae. They are, in fact, omnivorous and not only in their food, but in their mode of feeding, re- semble hogs. The ferocity of bears is greatly exaggerated. They are extremely -shy animals, usually on the lookout for danger ; even when feeding they look around at short intervals. One common mode of hunting them is to watch a carcass of some large animal. When a bear discovers such a "feast" he feeds greedily, and either stays in the neighborhood or returns regularly till it is all consumed. The hunter lies in wait or approaches when the bear is feeding, usually at dawn or at dusk. The approach must be made with the utmost care from the leeward, or the bear is gone without being seen. A bear has no wish to culti- vate man's acquaintance. But a wounded bear is a most desperate and dangerous foe. He is quick on his feet and strikes like a prize fighter, a single blow from his mighty arm, with its long claws, often completely disemboweling a victim. In rare instances a bear, when discovered feed- ing, becomes enraged and shows fight. Aside from these conditions almost the only occasion when a bear " begins a fight " is when a female with cubs is met ; even then she often ignominiously takes to flight. Though clumsy in appearance, the bear is a swift runner. In the fall bears usually become very fat. Through most of the winter they hibernate, or "hole up," as the hunters say, in a cave of rocks or under the roots of a big tree. North America has four kinds of bears: the polar bear; the grizzly, including the silvertip ; the black bear, including the cin- namon bear ; and the big brown bear of Alaska. The raccoon is very mudi like a diminutive bear, not only in its plantigrade feet, but also in its food habits. Coons are shrewd creatures, and make good pets. 282 Descriptive Zoology. The Weasels. These are by some placed with the bears, while others ally them to the cats. In this family are the weasel, mink, ermine, marten, ferret, otter, badger, wolver- ine, skunk. All are valuable for their fur. The weasel turns white in winter. Most of these have strong scent glands. Several of them are excellent swimmers and divers, living largely on fish. One otter lives in the sea. The Seals. The seals are fitted for aquatic life by hav- ing the hands and feet developed as paddles or " flippers," the limbs being very short. The sea lion can walk on all fours ; others have the hind limbs permanently turned backward, forming a sort of "tail fin," so that they swim very much like the fishes, on which they feed. Seals are sometimes said to be pinnigrade (walking by fins) in con- trast to the digitigrades and plantigrades. No seals in- habit the tropics. The seal grounds of the southern hemisphere have been depleted by indiscriminate killing, and the northern fields bid fair to meet the same fate. The Primates. This order, highest of all the mam- mals, includes the monkeys, apes, and man. There is a great range from the little squirrel-like marmoset to the massive gorilla, and from the horizontal-bodied, four-footed . lemur to the erect biped, man. But structure is the basis of classification, and many of these lower forms have almost bone for bone and muscle for muscle similar to those of man. The higher apes are tailless. The form differs greatly, the facial angle of the ape being almost that of a dog, while the Caucasian has an angle of about 95. As we approach man in the scale the body becomes more erect and is supported on the flat sole, instead of on the outer edges as in the lower forms. Man alone has a well-developed hand, and he distances all other forms in having the power of speech, although some authors think Mammalia. Duodenu apes have a language. The name orang-utan means " man of the woods." Anatomists do not agree as to which is nearer man, the chimpanzee or the gorilla. It must be borne in mind that in the animal world classification is based on structure, and that the zoological point of view does not take into con- sideration the intellectual, Gullct moral, or spiritual quali- stomach ties. Characteristics of Mam- mals. (i) Mammals have a hairy covering. (2) The young are born alive. (3) The young are nour- ished by milk from mam- mary' glands. (4) There is a diaphragm separating the body cavity into thorax and abdomen. (5) All have teeth set in sockets. (6) Two pairs of limbs are usually present. (7) There are usually seven cervical vertebrae. (8) The lower jaw articu- lates directly with the skull and not by the inter- vention of a separate bone (quadrate bone) as in birds. (9) There is an epiglottis covering the opening (glottis) to the windpipe. (10) The blood is warm, and of a nearly constant temperature. (11) The heart is completely divided by a partition into right and left halves. FIG. 166. Rectum STOMACH AND INTESTINES OF MAN. 284 Descriptive Zoology. CLASSIFICATION OF MAMMALS. SUBCLASSES. ORDERS. 2. Theria^j (Placentals) i. Prototheria i. Monotremata Duckbill and' Spiny Ant-eater f (Nonplacentals] . 2. Marsupialia Opossum, Kangaroo 3. Edentata Sloth, Armadillo 4. Rodentia Rabbit, Squirrel 5. Insectivora Mole, Shrew 6. Cheiroptera Bat 7. Cetacea Whale, Porpoise 8. Sirenia ; Sea Cow 9. Ungulata Horse, Cow, Deer 10. Proboscidea Elephant 11. Carnivora Cat, Dog, Bear, Seal 12. Primates Lemur, Ape, Man CHARACTERISTICS OF CHORDATA. 1. There is a notochord, a long skeletal rod, a sort of forerunner of the backbone. 2. There are gill slits opening from the throat to the outside. 3. The central nervous system is a hollow tube and is wholly dorsal to the digestive tube. CHARACTERISTICS OF VERTEBRATA. In the Vertebrata the characters given for the Chordata are distinctly displayed, and a permanent backbone is de- veloped. A cross section of a vertebrate shows two cavities (see Fig. 150), the dorsal containing the cerebro-spinal nervous system, and the ventral containing the digestive, circulatory, and respiratory organs. In the vertebrates a liver is always present. The nervous system is usually well developed. Classification of Animals. An early classification divided animals into two groups, the vertebrates, or the animals having backbones ; and the invertebrates, those lacking a Mammalia. backbone. A. comparatively recent grouping is into Pro- tozoa, or one-celled animals, and Metazoa, or many-celled animals. Each of these groupings simply characterizes one group (one system taking the lower end and the other the higher end of the animal series) and lumps off all the rest in one negatively named group. Neither of these sys- tems pretends to do anything more than call attention to the presence or absence of a single feature of structure. Fish Toad Snake Sparrow Mouse Olfactory lobe ? Cerebrum Mid brain - Cerebellum Spinal bulb Spinal cord .. FIG. 167. DIAGRAM OF BRAINS OF VERTEBRATES. From Kellogg's Zoology. The Basis of Classification of Animals. The basis of classi- fication of animals is structure, only so many branches being recognized as there are distinct plans of structure. It is generally understood that the structure considered is that of the adult, since many animals change greatly during their development. But in some cases, especially of degenerate forms, the larval form shows, more clearly than the adult, the true relationship. Consequently embryology must be called in as an aid in classification. Fossils also clear up many doubtful points in classification. CHAPTER XVIII. BRANCH PROTOZOA. THE ONE-CELLED ANIMALS. Amoeba. The Proteus Animalcule. One of the sim- plest -forms of animal life is the Amoeba. It is found in the slimy coating usually found on submerged leaves and stems in standing water, or in the slimy ooze resting on the mud at the bottom. If this ooze be examined under a high power of a microscope, amoebae may usually be found, though occasionally one has to search for some time Endoplasm Ectoplasm Pseudopods extending Pseudopods retracting Contractile vacuole Water vacuoles Food vacuoles FIG. 168. AMCEBA. before he is successful. And it is difficult for a begin- ner to be certain, at first, whether what he has found is really an amoeba. An amoeba is a speck of clear, color- less, jellylike substance called protoplasm, with a distinct/ though delicate, outline. There can usually be discerned a clearer outer layer, the ectoplasm, and a more Dotted cen- tral portion, the endoplasm ; but there is nfl distinct line between the two. Sometimes one can see a more dense 286 Protozoa. 287 appearing portion, the nucleus, and occasionally there ap- pears a clear space, the contractile vacnole. If the object is an amoeba, it. will usually soon betray itself by its motion. First there is a bulging out on one side, and this projection may be prolonged into a distinct lobe, called a pseudopod. The amoeba may form several of these pseudopods at the same time, so that it may have little central body and nearly all of its substance may be in the pseudopods These pseudopods may be extended and retracted without changing the place of the amoeba. But more often after a pseudopod has been protruded, the vest of the body follows it, seeming to flow into it ; by '-<.*3$3JJ FIG. 169. AMOZBA: CHANGES IN FORM, DRAWN AT SHORT INTERVALS. repetition of this process the amoeba changes its place, and thus exhibits not only motion, but locomotion. If watched for some time the amoeba may be seen to change its shape considerably and to make slow progress, some- times for a considerable time in the same direction. Patient watching may reveal how the amoeba takes its food. If a small plant or animal cell or portion of such matter lies in its way, a pseudopod is pressed against it and it becomes embedded in the endoplasm. With any such food material there is usually taken a small amount of water. The space occupied by the .water and absorbed food is called a food vacuole. Usually a number of these food vacuoles may be seen in an amoeba After a time the water and other matter disappear, having been digested and absorbed and assimilated into the substance of the 288 Descriptive Zoology. amoeba. Occasionally a grain of sand, or other indiges- tible matter, is taken in ; in this case it is finally passed out of the body, usually being left behind as the amoeba moves on. There is no mouth ; food may be taken in at any part of the surface. There is no stomach ; the space occupied by the ingested food is an improvised stomach. There is no anus, residual matter being passed out at the point most convenient. Still, as the amoeba moves about in search of food, the surface that happens to be foremost is likely to take in the new matter, and the part that is, for the time, rearmost serves as the place of exit. The amoeba may be said to flow around its food, and to flow away from, and so leave behind, its waste matter. The work of moving about involves the expenditure of energy. This energy is produced by the oxidation of the substance constituting the amoeba. Oxygen is constantly being absorbed through the surface to supply this need, which varies according to the degree of activity. The oxi- dation of the matter of the body of the amoeba produces carbon dioxid and water, which are passed off, invisibly, through the surface. The new food taken replaces the loss by such oxidation. This taking in of oxygen and giving out carbon dioxid is respiration, in its simplest form. In the oxidation heat is produced, which probably is given off to the water about as fast as it is produced in excess of the temperature of the surrounding medium. Actively moving amoebae warm the water in which they move, as truly as we warm the water in which we are bathing, or the air in which we are performing active muscular work. And as we taint the air with our waste products and need a constant renewal of the surrounding air, so the amoeba must not be confined too closely in a limited quantity of water that is sealed from the air. Protozoa. 289 The amoeba shows that it has a sense of touch, for it frequently avoids solid objects with which it comes into contact, passing to one side. It has the characteristic termed irritability. This characteristic does not involve any special degree of sensitiveness, but simply the power to receive impressions through contact with external objects. If stimulated by slight electric shocks, the amoeba may be made to withdraw its pseudopods and remain quiet in a spherical form. It is said to have contracted, and is said to be endowed with the property of contractility, but it is simpler merely to say that it has changed its form. But the amceba does not always wait to be stimu- lated from without to make it move. It sometimes appears to move " of its own accord," as we say. That is, it is automatic, in the sense of self-moving. , mm FIG. 170. AMCEBA DIVIDING. ,,, If amoebae are well nourished, they are likely to mul- tiply. They do this by simple division. An amoeba becomes constricted in the middle. The constriction increases until the individual is divided into two. Encysted Amoeba. Sometimes an amoeba, when sub- jected to drouth, or perhaps other unfavorable conditions, forms a tough outer wall, and remains in a quiet condi- tion. The tough covering is called a "cyst," and the amoeba is said to be "encysted." It may thus remain 290 Descriptive Zoology. dormant for a long time, until more favorable conditions return, when it ruptures the cyst, crawls out, and once more renews its former active life. SUMMARY OF THE CHARACTERISTICS OF AMCEBA 1. It eats ; it takes in material through its surface from the surrounding water. 2. It digests ; the material thus taken in is made soluble so that it can be used in building up the body of the amoeba. 3. It assimilates ; after suitable preparation the mate- rial is taken into the actual substance of the amoeba ; it is "made like," as the word "assimilate" signifies. 4. It grows, as a result of assimilation. Growth is the increase in size and substance of a living thing as a result of taking material from the outside and making it over into its own body. Growth should be distinguished from the mere increase in size of such dead objects as an icicle or a crystal by the accretion of more material on the outside. 5. It moves ; it has power, not to change its bulk, but to change its shape. It is able to rearrange its particles, which is what is meant by the term "contract." Contrac- tility does not mean ability to occupy less space. Distinc- tion must be made between "motion" and "locomotion"; when an amoeba extends a pseudopod and then withdraws it, this is motion; when an amoeba changes its place, or moves on," this is not only motion, but also locomotion. 6. It breathes ; the energy of motion is maintained by a process of oxidation going on within the substance of the amoeba. Oxygen is absorbed through the outer surface and unites with the materials of the body of the amoeba. Its energy is furnished by this oxidation as truly as the Protozoa. 291 energy by which a train is moved is furnished by the burning (oxidation) of coal in the engine. 7. It produces heat; heat is another form of energy which always results from oxidation. We are always pro- ducing some heat, even when we are as quiet as possible, and we know that when we are more active we breathe faster and produce more heat. So with the amoeba. But the amoeba should be classed with the so-called " cold- blooded " animals. It should be noted that not only do all such animals have a rather low temperature, but it is a variable temperature and usually only slightly above the temperature of the surrounding air or water. The amoeba is constantly producing heat, but gives it off to the water about as fast as it is made. 8. It gives off waste matter, i.e. it excretes. All .oxidation produces waste matter. Oxidation of wood or coal pro- duces carbon dioxid, water, and ashes. Our breathing produces carbon dioxid, water, and other wastes which we throw off continually. The carbon dioxid, water, and other wastes thrown off by the amoeba are small in amount, and, being invisible, pass out into the water unnoticed. 9. It feels ; when a foreign body comes into contact with an amoeba it usually moves. A slight electric shock causes it to assume the spherical form. There is good evidence that amoebae have the sense of touch. They also seem responsive to light and heat. 10. It reproduces its kind ; this we have seen is done in the simplest way imaginable ; that is, merely by separating into two parts, each of which is then a complete individual. Multiplication takes place by division. Paramecium, the Slipper Animalcule. The slipper ani- malcule is usually to be found in the water collected for amoebae. In aquariums where clams have been kept, 292 Descriptive Zoology. or in vases where flowers have been standing for some time, a film of scum is likely to appear. Just underneath this film is a good place to look. Often the naked eye may detect small white objects moving about. These are paramecia. On examining some of the water with a low power of the microscope, one discovers that these tiny white specks are oval or elliptical, that they swim actively, Course of food vacuoles Contractile vacuole Contractile vacuole Ventral view "","""111111111181111111111 ANTERIOR MACRO- MICRO- ^UTH GULLET END NUCLEUS NUCLEUS SPOT CONTRACTILE VACUOLE POSTERIOR END Mouth gullet Food ball FK5, 171. PARAMECIUM, THE SLIPPER ANIMALCULE. usually with the same end foremost, and that when they run against an obstruction they back off quickly. They evidently have the power of moving and the sense of touch. Looked at with a higher power, the shape may be determined more definitely. They are somewhat flattened, and one end is more pointed than the other. The dif- ference between the clear ectoplasm and the more granular endoplasm is more marked than in the amoeba. Protozoa. 293 There is also a rather distinct layer, or cuticle, forming the outer layer of the ectoplasm. The whole surface is covered with small, hairlike projections called cilia. These are prolongations of the protoplasm which makes the body of the paramecium. These have the power of actively lashing back and forth, acting like so many pad- dles, by means of which the paramecium swims. At the more pointed end, usually kept in the rear, there is a bunch of longer cilia, which seem to serve as a rudder. Sometimes the animal reverses its direction and proceeds with the pointed end foremost, but ordinarily only for a short time, to back out of a tight place and to get a new start in another direction. How Paramecium Eats. Along the flat surface is a groove, which at one end forms a blind passageway dip- ping into the body. Both the groove and the tube, which is a gullet, are lined by cilia. By their vibrations these cilia collect small one-celled plants and animals, or other particles of organic matter, which accumulate at the inner end of the gullet. From time to time -this inner end is cut off by constriction, and a collection of food particles, with some water, is pushed into the soft protoplasm of the body. It then is what is termed a food ball, or some- times the space with its contents is designated a food vacuole. These food vacuoles may be regarded as so many improvised stomachs. The masses slowly rotate around in the body in the manner indicated by the arrows in the accompanying figure. At a point about opposite their starting-point any undigested residue is expelled through a weak place in the wall, there being no permanent anal opening. Excretion in Paramecium. There are usually two clear spaces in a paramecium, one near each end. These may 294 Descriptive Zoology. be seen to contract at tolerably frequent intervals, appar- ently discharging liquid to the exterior. Around each of these " contractile vacuoles " is a series of radiating canals. After the vacuole has become obliterated by emptying its contents, it is gradually filled again by these surrounding canals, which get watery material from the various parts of the body. Thus certain waste material is thrown out. The Nucleus. Paramecium has two nuclei, a larger body called the macronucleus and a smaller called the micronucleus. How Paramecium protects Itself. In the outer part, or cortex, are many small sacs, each containing a tiny thread. When a paramecium is irritated, it discharges these thread-cells, which appear to produce a stinging or benumbing effect on small animals. Multiplication of Paramecia. Like the amoeba and the vorticella, the paramecium forms new individuals by division. The constriction is transverse, at about the middle, and finally separates the one into two. Both the macronucleus and the micronucleus divide, a part going with each half, which soon after separating becomes a complete paramecium. VorticeJa, the Bell Animalcule. Another interesting protozoan is Vorticella or the bell animalcule. It is found on submerged stems and leaves in stagnant water, sometimes appearing like a delicate white fringe. Under a low power of the microscope a vorticella is seen to be bell-shaped, attached by a slender, flexible stalk, which joins the handle end of the bell-shaped body to some solid object. When the animalcule is disturbed, the stalk be- comes coiled, jerking the body up close to its support, where it is much more secure than when extended. Protozoa. 295 Examination with a higher power shows more of the structure of the body. The bell-shaped body is not hol- low, but is made up of protoplasm. Across the mouth of the bell is a disk, which is slightly narrower than the mouth of the bell. Between the disk and the rim of the bell is a circular groove. At one point the groove dips down into the body of the bell, forming a mouth and a gullet. The borders of 'the disk and the bell are fringed Vestibule Cilia Gullet Contractile vacuole Endoderm ' Ectoderm Disk Groove Macronucleus Micronucleus Stalk ... Contractile axis FIG. 172. VORTICELLA, THE BELL ANIMALCULE. with cilia, which by their vibrations create water currents and thus accumulate food material in the inner end of the gullet. The food material consists largely of minute plants and animals or fragments of larger forms. As in the paramecium, the collection of food particles becomes pushed farther into the body, becoming a food ball, or food vacuole, which, with others preceding and following, rotate around the body in regular order. At the outer end of the gullet is a space called the vestibule. Into this any undigested residue is passed, and thus swept out by the 296 Descriptive Zoology. currents maintained by the cilia. There is also a con- tractile vacuole, which is near the vestibule and empties into it. The vorticella has a C-shaped nucleus. How Vorticella protects Itself. When a vorticella is disturbed it is at once jerked up close to its mooring by the coiling of its stalk. At the same time the body changes its shape. The disk is drawn in, the rim of the bell turns in, the cilia are inclosed, and the body becomes pear-shaped or even spherical, there being no opening left at the free end. After the disturbance has ceased, the stalk elongates, the bell opens, the disk protrudes, the cilia extend, and the operations of active life are all resumed. Development of Vorticella. Vorticella multiplies by longitudinal division. For some time two bells are attached to the stalk, but one finally breaks loose and swims away by means of its cilia. Later it becomes attached and develops a stalk. GENERAL CHARACTERISTICS OF PROTOZOA. 1. The protozoans are the simplest animals. Most of them are one-celled. As a group, they are the smallest of animals. 2. They are the most numerous, in individuals, of any branch of animals. It is not true, as commonly believed, that every drop of water swarms with animal life. One would find few animalcules in ordinary well or spring water. But they usually abound in stagnant water. There is room for vast numbers of these lowly forms which occupy so little space. 3. They multiply the most rapidly of all animals. In most cases multiplication consists simply of division into Protozoa. 297 two equal parts, each of which is very soon a complete individual, ready again to divide in the same manner. Their great number is due to their rapid multiplication, to their small size, which makes it easy for them to find hiding places, and, further, to their complete adaptation to the conditions in which they live. Multiplication does not depend wholly on division. There is occasionally what is called "conjugation"; that is, two individuals come together and more or less completely fuse. At any rate, it seems to be proved that the species could not con- tinue to live indefinitely without the occasional occurrence of conjugation. And this is supposed to be true of most of the Protozoa. 4. They are the oldest of animals ; that is, they are supposed to have been on the earth longer than any other kind of animals. We find their remains in very early geologic formations. Some of them are supposed to have changed but little as time passed, the conditions of their surroundings being comparatively stable, while other groups of animals have been greatly modified by changes in their surroundings. 5. They are the most independent of animals. The conditions of their lives are such that they could live with- out the larger animals, while many of the latter could not live without them. Kinds of Protozoans. There are many kinds of pro- tozoans, some of them widely different from any of the three forms we have studied. Some are parasitic. One of the parasitic forms causes malaria when introduced into the blood by the proboscis of a mosquito. Some proto- zoans, instead of having cilia, possess a few longer vibratile projections called flagella. In the one-celled forms there is usually one flagellum, or, at most, two. But the colonial 298 Descriptive Zoology. protozoans are composed of several or many cells, each of which may have a pair of flagella. Thus there are three principal modes of locomotion among protozoans : (i) slow creeping by means of pseudopods, as in amoeba; (2) swim- ming by cilia, as in paramecium ; (3) more active swimming by flagella, this mode being not very unlike the second. The Shell-bearing Protozoans. Many protozoans have shells. Some of these shells are composed of lime, others of silica, while still others are formed of grains of sand which the protozoan glues together by a secretion from its protoplasm. Most of these shelled forms live in the ocean. Some of the shells are borne where we should expect them, on the outside, the animal being able to withdraw into the shell and project again at will through an opening. But in many the ani- mal cannot thus withdraw itself completely into the shell. Many of the shells are perforated by nu- FIG. 173. NOCTILUCA. merous minute openings, through A phosphorescent marine protozoan. which fine threads of protoplasm are extended, these projecting threads sometimes forming a network outside of the shell. In many forms the proto- plasm increases in amount, flows out of the main opening of the shell, and forms a new shell, larger than the old one, but attached to it. In this way it proceeds, making a series spirally arranged, similar in general appearance to a spirally coiled snail shell, or the chambered nautilus. Chalk. One of the most abundant and best known of geologic formations is made by protozoans. Chalk is made up of the shells, such as above described, of a kind of protozoan known as Globigerina. Myriads of these protozoans live in the ocean. When they die, their skele- Protozoa. 299 tons slowly settle to the bottom. Dredgings from the bottom of the Atlantic Ocean contain a gray mud which, under the microscope, is found to be largely composed of these shells. So where we find chalk rock on land, we know that region was once the bed of the ocean. This once soft mud has become hardened, by drying or by pressure, sometimes by both, into hard rock, a variety of limestone known as chalk. A generation ago the car- FIG. 174. A SHELL-BEARING PROTOZOAN (GLOBIGERINA). From Packard. penter and the schoolboy used a rough broken lump of the chalk rock. The ordinary school crayon, however, usually contains no chalk. Any one who has used the old lump chalk will recall that occasionally he struck a hard, flinty place, due to the mixture of other material. Silicious Earth. Other kinds of protozoans form their shells of silica. Beds of this material are found in various parts of the world and are used as polishing material, under the names Tripoli, Barbadoes earth, etc. Many of the shells of silica are exceedingly beautiful in form. joo Descriptive Zoology. Distribution of Protozoa. All protozoans are aquatic, though some might seem to be exceptions, living as they do in damp moss ; but they are probably in thin films of water on the surface. Protozoans are the most widely distributed of animals, occurring almost all over the globe, in fresh water and in the ocean, in lakes and rivers, ponds and creeks, pools and ditches. In the ocean they are more abundant in shallow water, but are also found at considerable depths and at the surface of the deeper seas. The Importance of Protozoa. Protozoans are highly important in two respects: (i) they have contributed much to rock-making, and are still making deposits on the ocean bottom ; (2) as a source of food to the animals of the ocean, it is difficult to overestimate their importance. In countless myriads they serve as food for animals some- what larger and higher in the scale than themselves. These animals, in turn, are the food for still higher animals. The protozoans, then (with the protophytes or one-celled plants), may truly be said to be the food foundation of all the higher marine animals. PROTOZOA AND METAZOA. Protoplasm. Protoplasm is the living substance of animals and plants. It is a clear, jellylike substance, which does not dissolve in water nor readily mix with it. When seen in water its outlines are usually quite distinct. It may appear more or less dotted on account of various kinds of matter suspended in it. An amoeba is a mass of protoplasm, and the properties of protoplasm were con- sidered in connection with amoeba. Protoplasm has the power of movement, is capable of being stimulated, i.e. is irritable, it eats, grows, breathes, throws off waste matter, or excretes, and has the power of reproduction. Protozoa. 301 Protoplasm is killed by very high temperature, killed or its activity checked by low temperature, and, in general, requires the conditions that we usually recognize as neces- sary for life. In its chemical composition protoplasm is exceedingly complex. Protoplasm is a living substance, and any attempt to analyze it kills it; hence its exact composition cannot be known. But the dead material left when it has been killed can be analyzed, and consists largely of a sub- stance called proteid. This consists of carbon, hydrogen, oxygen, and nitrogen, with some sulphur, traces of iron, and compounds of phosphorus, potassium, calcium, and magnesium. Protoplasm seems to be a very unstable compound, as we should naturally expect from its com- plexity. Then, too, in its life and growth, it is constantly changing, and, undoubtedly, changes more or less in its composition from time to time. The Cell. Sometimes protoplasm occurs in a consider- able mass, without any separation into distinct parts. But usually it is found in more or less distinct particles, .and these distinct particles of protoplasm are called " cells." There may be a cell wall distinct from the mass of proto- plasm, but this is not essential to a cell. Within the cell is a more dense appearing portion called the "nucleus." A cell living independently tends to be spherical, though since it has the power of changing its shape, it often departs from the typical form. When an amoeba goes into the resting stage it assumes the spherical form. Protozoa and Metazoa. The protozoans are typically one-celled animals. The other animals are many-celled and are called metazoans. Their greater size is not due to their having larger cells, but to the increased number of cells. 302 Descriptive Zoology. Development of Metazoa. Every metazoan begins life as a single cell (except in multiplication by budding). It starts as an egg (ovum or egg cell), having very much the same characteristics as an 'amoeba. After being fer- tilized it soon divides into two parts, but these halves, instead of separating, as in the case of the amoeba, re- main together. These halves divide into quarters, and so on, into 8, 16, 32, 64, 128, etc., parts, until they become too numerous to be counted. After a time these numer- ous cells, still remaining together, arrange themselves in the shape of the animal that produced the egg cell. Division of Labor in Communities. A solitary back- woodsman has to do everything for himself. He gets and prepares his own food, provides needed shelter, makes his own clothing. But if he has a partner, there is sure to be some division of their labor. One can do some things better than the other, and they find that it is advantageous for each to do what he can do best. In an Indian family the men do the hunting and fighting, while the squaws pre- pare the food, dress the hides for clothing and lodges, etc. It is hardly necessary to call attention to the saving, of time that results from such a division of labor, or to note the finer quality and finish of the various articles of common use when they are made by one who acquires skill by the con- stant practice which comes from devoting himself entirely to one kind of work. It is evident that no one man can do many things and do them all as well as when the work is divided. Physiological Division of Labor. An amoeba does every- thing for itself. Of course it lives. very well in its simple way, and is well adapted to its mode and place of life. But it does too many things to do any of them very well. It can move but slowly, it is dull of sensation, etc. Sup- pose that, when an amoeba divides, the two parts remain Protozoa. 303 adhering to each other, and that it divides again, making four parts, and each of these divides, making eight parts remaining in one mass. It is easy to see how one might attend to the moving, another to the work of feeling, a third to eating and digesting, a fourth to breathing, a fifth to the work of dividing for the spread of the species, while the other three became more or less flattened and spread out over the others to protect them. This will serve to give an idea of what actually takes place when the egg cell of a metazoan has, by division, become a many-celled mass. Each cell has primarily all the characteristics common to an amoeba, that is, they all have power to move, eat, digest, feel, breathe, divide. But such a large mass would be unwieldy unless it had some support ; hence some cells may, to the advantage of the whole, become harder and stronger to hold the soft cells in place. In this now heavier mass there is more danger of mechani- cal injury to the outside, and the outside layer by harden- ing will serve to protect the inner, more delicate cells from harm. If the outside cells harden, the animal will no longer be able so well to absorb oxygen for the interior cells, nor can it now take in food at any point. Special arrangement must be made to take oxygen and food into the interior, where soft cells can do the work of preparing it for use in the body. These inner cells have now more work than before, for they must prepare the material for building and maintaining the cells that have given up their power of digesting that they might fit themselves for pro- tection. In proportion as any given cell devotes itself to one kind of work, it must lose more or less the ability to do the other kinds of work that it primarily could do. This is what is meant by physiological division of labor. All the cells resulting from the division of a metazoan egg 304 Descriptive Zoology. cell are at first essentially alike in structure and function. To fit themselves for the different kinds of work that they have to do, they grow different. This growing different is called differentiation. Each becomes fitted for one special work ; this is specialization. Tissues. In the higher metazoans there are many cells devoted to each of the different kinds of work to be done. This we should naturally expect, for in such a body there are myriads of cells, but only comparatively few kinds of work. As has already been made clear, an amoeba can do nearly all the kinds of work that any animal can do, though in a much simpler way. The func- tions of animals are summed up in saying they move, feel, eat, grow, breathe, protect themselves, and reproduce their kind. Stated more formally, the functions of animals are included in the processes of motion, sensation, support, pro- tection, reproduction, and nuttition (nutrition including digestion, absorption, circulation, respiration, and excretion). For instance, muscle cells are cells devoted to the work of motion ; they have largely given up the other functions that they originally possessed. The nerves have lost the ability to change their form, in devoting themselves to the special work of sensation. So, too, with the cells of the supporting and protective tissues. A tissue is a group of cells having the same structure and function. An amoeba consists of a single cell, but it can do a number of kinds of work. A tissue consists of many cells, but they all do the same kind of work. In other words, an amoeba is simple in structure, but complex in function ; a tissue is complex in structure, but simple in function. Organs. In addition to the differentiation of cells into tissues, there is a still further division of labor by having Protozoa. 305 certain distinct parts of the body devoted to a special work ; for instance, the hand is adapted to the work of grasping ; it is an organ and its special work, or function, is prehension. But the hand is composed of several kinds of tissues. It is supported by bony tissue, the muscular tissue gives motion to the fingers, the nerves are composed of nervous tissue, connective tissue makes up the tendons and part of the muscle, and the skin is another kind of tissue. In addition there is usually some fat, which is considered a still different tissue. The higher animals are organisms, that is, they are made up of organs, each of which has its special function to perform. In other words, each organ works for every other organ in the organism, and every other organ works for it. The Colonial Protozoa. This name is given to the protozoans that have more than one cell, some of them being actually many-celled. The simplest of these proto- zoans are little more than an aggregation of cells, each of which leads a nearly independent life, doing its own diges- tion, etc. There is almost no division of labor among them. Others form a true colony, and there is a rather gradual series in development until in the higher forms there is a division of labor approaching that found in the simpler Metazoa. The cells in the simpler colonial proto- zoans lead lives so nearly independent of their associates that we might imagine the colony falling to pieces and each cell again taking up an independent life, like that of the amoeba. Not so, however, with the metazoans. After their differentiation in structure and specialization in function they are so modified that they could no longer live independently. In developing one function each cell has neglected other functions till now it is no longer able to perform them. In other words, it has become dependent. 306 Descriptive Zoology. Each cell lives and works, not merely for itself, but for all. In their cooperation these units of a lower order have become so united as to form " a unit of a higher order," as the mathematician expresses it. The cell is the unit of structure in animals, and where the cells unite and specialize they form a many-celled in- dividual, in the strict sense of the word, that is, it can- not now be divided without destroying the life of the whole complex individual. There is one exception : the egg cells can, and do, live separately. This is their work, to separate from the body as a whole, for the express purpose of growing into new individuals. CHAPTER XIX. BRANCH PORIFERA. THE SPONGES. The Simplest Sponge. The simplest sponge is a vase- shaped body attached by the base. It is hollow, and has an opening (osculum) at the free end. Through the wall are many small holes, and water is constantly entering these holes (inhalant pores) and passing out of the mouth of the vase. The cause of this current is the vibration of many flagella, which project inward from the cells lining the cavity. This current of water brings oxygen and food, consisting of minute plants and animals, and remains of larger animals and plants. The vaselike body is supported by a large number of three-rayed spicules, embedded in the wall of the vase. These are composed of carbonate of lime, and they constitute the skeleton, making the body fairly firm, and yet leaving it flexible and elastic. An outer layer of cells constitutes the ectoderm, the lining cells are the endoderm, while between these is a thin layer called the mesoderm, in which the spicules are embedded. (See Fig. 176.) More Complex Sponge. Somewhat higher is a sponge that is vase-shaped, or cylindric, in which the inhalant 307 FIG. 175. SIMPLE SPONGE, MARINE. Water enters minute holes in the sides and passes out of the opening at the top of the tube. 308 Descriptive Zoology. pores do not lead directly into the main cavity (as shown in Figs. 176 and 177), but do so indirectly. The cells bearing the flagella, instead of lining the main cavity, are here in the radiating canals that open into the main cavity, and receive the water through cross openings from the incurrent canals. As in the simpler sponge, there are supporting spicules in the walls. The Highest Sponges. The general plan of structure of the highest sponges may be illus- trated by Fig. 178. The most noticeable peculiarities are two : ( i ) The cilia are limited to cer- tain cavities, or enlargements, along the course of the passages from the outside to the main cavity. These cavities are called the "ciliated chambers." (2) The whole sponge is no longer a vase or cylinder, but a mass, in which the cavities are less con- spicuous. This is due to the increase of the middle layer, or ONE OF THE^LEST SPONGES, esoderm, a gelatinous mass of Caicoiynthus primigenius. cells. As before, the outer layer (After Haeckei.) i s the ectoderm, and the lining the endoderm. Kinds of Skeletons. Sponges may be classed, according to the nature of their skeletons, into three groups : i. Calcareous sponges, whose skeletons consist of A part of the outer wall is cut away to show the inside. From Jordan and Kellogg's Animal Life. Porifera. 309 spicules of carbonate of lime, as seen in the simple sponge described. These spicules have various forms, but the three-rayed form is most common. They often resemble crystals. 2. The silicious sponges, with spicules of silica or flint. These skeletons often appear to be made of spun glass, and many of them are of great beauty, one of the most noted being the Venus's flower basket, found about the Philippine Islands. 3. The horny sponges, or sponges of commerce. These skeletons are composed of a substance called spongin, whose chemical composition resembles that of silk. Its fine, threadlike fibers branch and interweave, forming a feltlike structure, with which all are familiar. Its chief value consists in its absorbing power, and this, in turn, depends on its softness, fineness, and elasticity. Its durability is also a factor in its value. Some sponges have both silicious spicules and horny fibers. The Commercial Sponge at Home. If one could "call upon " one of these sponges, he would find it attached to rock at the bottom of a warm sea. He would see a round- ish mass with a smooth exterior, in color and finish not unlike a dark-colored kid glove. He might see several large openings, from which currents of water are emerg- ing, bearing carbon dioxid and other impurities. Over the surface he might discover smaller holes, into which the water flows, bearing oxygen and food. If he were to dis- FIG. 177. CROSS SECTION OF SIMPLE TUBULAR SPONGE. Showing Ci) three-pointed spicules (skele- ton) , (2) cilia which bring in water through (3) the holes in the sides of the tube. 3io Descriptive Zoology. turb the sponge, these smaller openings would close, and perhaps the larger ones also. If he now tried to pick it up, it would be found firmly attached. Effort to detach it by pulling would probably crush it, and show that the whole has about the consistency of beef liver. It is easy to squeeze out all of the soft tissue and leave the elastic skeleton. Source of Commercial Sponges. The most valuable of the sponges of commerce come from the Mediterranean ; many also come from the Red Sea, Florida, and the West Indies. Water Exit FIG. 178. DIAGRAM OF A COMMERCIAL SPONGE. Collecting Sponges. Sponges are collected by divers, or by the use of rakes, or by dragging hooks. They are piled on shore to allow the soft tissues to decay, after which they are washed, dried, sorted, trimmed, and shipped to market. The finer ones are usually bleached. Sometimes, in trimming away the base where they are attached to the rock, enough is cut away to leave a large hole ; this is the lower end of the cloaca, or main cavity. Fresh-water Sponges. Most of the sponges are marine, but there is one family of sponges in fresh water. It is not uncommon to find them in lakes and rivers, where they Porifera. 311 form a coating on logs and rocks, usually greenish or yellowish green. In still water they branch and may reach considerable height, but in swift streams form a low, spreading mat. They are of no commercial value. Some- times in reservoirs supplying drinking water they give an unpleasant taste to the water. Relations of Sponges to Other Animals. None of the larger animals eat sponges. This may be due to the pres- ence of the sharp spicules, or to an unpleasant taste or odor. Many small animals bore into or crawl into them, some for a safe hiding place, doing no direct injury to their host. Others are perhaps parasitic. While no sponge is a parasite, some injure shells, as oysters, by bor- ing into them. Certain sponges are found only on the shells inhabited by hermit crabs, where they pay for their transportation by concealing their bearer. Reproduction and Development of Sponges. Sponges have two ways of multiplying, by budding and by eggs. In budding, a group of cells, called a " gemmule," is formed, which becomes detached, and develops into a sponge. Fresh-water sponges form these gemmules in the fall. The gemmules lie dormant over winter, and begin growth in the spring. Sponges produce eggs. These eggs are cells, which are produced by the middle layer of the sponge (mesoderm). Other cells, called sperm cells (or sperms), are produced by some other part of the mesoderm, or perhaps by the mesoderm of another sponge. After the egg cell is ferti- lized by the sperm cell, it begins to divide, and forms a number of cells which cohere. Part of these cells have cilia, and by their vibration the embryo sponge swims about, until finally it settles, attaches itself, and remains fixed the rest of its life. While it is small and free, the 312 Descriptive Zoology. vibration of cilia propels it through the water; after it becomes attached, the vibration of cilia creates water currents, which bring it food and oxygen. Rank of Sponges. The sponges are many-celled and evidently higher than the colonial protozoans. But there is no high degree of differentiation of parts. The cells bearing flagella and the egg and sperm cells are differ- ent from the others. But there are no special distinct organs for the performance of special functions. In com- paring them with other forms, it may be seen that they are plainly the lowest of the metazoa. CHAPTER XX. BRANCH CCELENTERATA. [This branch includes the Hydroids, Jellyfishes, Sea Anemones, and Coral Polyps.] Example. The Fresh-water Polyp, Hydra. Naked-eye Appearance of Hydra. In examining a jar of aquatic plants one may find attached to them slender cylindric bodies about half an inch long and of the thick- ness of a needle. Extending from the free end are several fine, threadlike tentacles, which may be as long as the body itself. Hydras are often white or colorless, but occa- sionally brown or green ones are found. If undisturbed, the body and tentacles may occa- sionally sway gently to and fro. If disturbed, a hydra usually shortens until it is a tiny ball. The tentacles also shorten until they look like a circle of tiny buds. Structure Of Hydra. -Micro- scopic examination is required to learn much of the structure of hydra. The cylindric body is hollow, and the hollow extends through the tentacles, which are closed at their tips. Above the circle of tentacles rises a cone-shaped body called the hypostome, at the apex of which is the mouth. The body wall consists of two layers, the outer being the ectoderm, and the inner the endoderm. Between these two is a layer called the mesoglcea. 313 HYDRA EXTENDED. Descriptive Zoology. The Ectoderm. The cells of the ectoderm are clear, and more uniform in size than those of the endoderm. At their inner ends they are narrower, and usually end in slender prolongations, which bend at a right angle to the main axis of the cell, and help make a sort of middle layer between the endoderm and ectoderm. These prolonga- Tentacle . Spermary Bud Cross section FIG. 180. HYDRA, LONGITUDINAL SECTION. tions are called muscle processes and are the chief agents in shortening and moving the body. Between the nar- rowed bases of the larger ectoderm cells are smaller cells, which are supposed to be sensitive, and may perhaps be properly called nerve cells. Stinging Cells. Among the cells of the ectoderm, both of the body and of the tentacles, are peculiar bodies called Coelenterata. 315 thread capsules, stinging cells, or nematocysts. These are elliptical, and before being disturbed have a fine thread coiled within. When the hydra is irritated, the nematocysts are discharged and the threads are suddenly darted out. At the base of each thread, close to the capsule, are a few fine barbs, and it is supposed that a Cell containing thread capsule Thread capsule partly discharged FIG. 181. STINGING CELLS OF HYDRA, HIGHLY MAGNIFIED. Thread capsule fully discharged poisonous substance is contained within the capsule. At any rate, the result of coming in contact with this sort of apparatus is a stinging sensation, like that caused by nettles, but, of course, the hydra is so small that it does not produce much effect except on very small animals. But let a small crustacean, such as a water flea, swim against a hydra's tentacle, and it is usually paralyzed at once. Then the tentacles draw the victim to the mouth and it is swallowed. Descriptive Zoology. The Endoderm. The cells of the endoderm are larger than those of the ectoderm. They are also less uniform in size. They are darker colored, sometimes containing brown coloring matter. The green hydra contains chloro- phyll. The endoderm cells often exhibit amoeboid move- ments, and frequently show food particles and large contractile vacuoles, such as noticed in amoeba. Project- ing from these cells into the cavity are sometimes found large flagella. Digestion in Hydra. When food is taken into the central cavity it is supposed to be partly digested here, this often being called the digestive cavity. But, at any rate, parti- cles not completely digested are taken into the endoderm cells, where no doubt digestion takes place ; and from the material digested by the endoderm cells the ectoderm gets its nourishment. We here see a division of labor, the outer layer producing the motion, obtaining the food, and pro- tecting the whole, while the inner cells do the work of digestion. Locomotion. While the hydra is pretty firmly attached by means of a sticky substance secreted by the cells of the base, it can let go and move away. It sometimes bends over, attaches itself by the tentacles, and then lets go at the base and pulls the base up close to the place where the tentacles are fastened, and by repeating this action crawls along like a "measuring worm." Or it may bend over, attach itself by the tentacles, let go at the base, and turn the base clear over, thus turning a complete somersault, though slowly, instead of with a spring. Sometimes, also, it appears to crawl slowly by means of the tentacles alone. But hydra is not a great traveler, preferring to wait for something to turn up, rather than hunt for food. We see how well fitted it is for a sedentary life, for with the long, Coelenterata. 317 outstretched tentacles, with their many stinging cells, it has a trap continually set for the unwary small swimmers that abound in such places as the hydra inhabits. Recovery after Mutilation. One very remarkable fact about hydra is its ability to live and grow after injury. If cut into several pieces, each grows into a complete hydra. Multiplication by Budding. Hydra multiplies by bud- ding. A small part of the wall bulges out and forms a cylindric branch, with a double wall continued from the two layers of the body, and the hollow of the branch is continuous with that of the body (see Figs. 179 and 180). After a while, a circle of tentacles is formed at the end of the branch, and an opening appears at the end for a mouth. Finally the base of the branch is constricted and the branch separates and is an independent hydra. Multiplication by Eggs. Among the cells of the ecto- derm, we noticed that certain cells are smaller and lie deeper than the others. Some of these cells develop into egg cells, or eggs. They are covered by the outer cells, but make a marked bulging. This is the ovary (from ova, eggs) and is usually found at about one third of the length from the foot of the hydra (see Fig. 180). A somewhat similar growth occurs near the tentacles, but the contained cells are different. Instead of spherical cells like the egg cells, here are produced cells resembling a miniature tad- pole, with an oval head and a vibrating tail. These are the sperm cells, or sperms, and the enlargement in which they are developed is called a spermary. CLASS I. HYDROZOA. Hydroids. Most of the members of this class are called hydroids, and, as the name implies, they are hydralike. 318 Descriptive Zoology. But instead of being simple most of them are compound, or, as it is more commonly expressed, they live in colonies. We have seen that hydra multiplies by budding. Imagine a hydra in which the budding continues indefinitely, the new individuals remaining connected with the parent, and FIG. 182. A HYDROID. After Allman. From Kingsley's Zoology. you have the hydroid colony. The relation between these members of the colony is more than a mere mechanical connection, for the internal cavity is continuous through the colony, so that whatever one individual takes as food may serve to nourish any one or all the other members of the community. Coelenterata. 319 The idea of community life is well carried out in that there is a well-marked division of labor among the mem- bers. Some, called nutritive individuals, devote themselves to the work of obtaining and preparing food for the whole ; some develop the stinging cells and protect the others ; while still others are specialized for the work of reproduc- tion, and depend on other members for nourishment and protection. General Appearance of Hydroids. Most of the hydroids are plantlike in appearance, hence are often called zoo- phytes. Some resemble tufts of moss, others are simply branched and trailing like the ground pine. They vary greatly in color, from white to dark brown, while some are of a beautiful pink. A form that will serve well for example is whitish or brownish, and forms a downy or furry coating on the wooden piles of wharves, piers, etc. Many threads creep along the surface, while others rise at right angles to the surface and end in budlike swellings. Examined more closely, these terminal enlargements are found to be bell-shaped. These are the individuals borne on the connecting and supporting stalks. The unit, or zooid, as it is called, is very much like a hydra. The body is hollow, with a circle of arms surrounding the mouth, which is at the free end. It is unlike the hydra in at least three respects. First, the base, instead of being closed, opens into the supporting tube, and this is in communica- tion with all the other zooids of the colony. Second, the tentacles are solid instead of hollow ; but they are like the tentacles of the hydra in being flexible and provided with stinging cells that serve for securing food. Third, the mouth is distinctly raised above the bases of the tentacles, and is capable of closing into a cone-shaped mass, the hypostome, or opening into a bell-shaped entrance. '320 Descriptive Zoology. A Tubularian Hydroid. The general appearance of a zooid of a tubularian hydroid may be seen from Fig. 182. The body is hydralike, but with a prolonged mouth. There are two layers of the body, the ectoderm and the endo- derm. The ectoderm -of the tentacles is provided with nettle cells. Structure of the Stem. The structure of the common stem is similar to that of the zooid. The outer covering of chitin is called the perisarc, while the soft tube within, con- sisting of ectoderm and endoderm, is called the cenosarc. The endoderm cells have flagella. Action of a Live Zooid. The live zooid captures small animals by stinging them as does the hydra. It uses the tentacles to draw them into the mouth. After the food is softened and reduced to a liquid, it is circulated by the vibrations of the flagella of the cells of the endoderm. The nettle cells serve for protection as well as in securing food. When the zooid is disturbed, it withdraws into the protect- ing cup, or hydrotheca, and may thus remain for some time. Development of a Zooid Budding. The colony in- creases in extent by budding. A bud forms on the side of a main stem. The bud consists of the same layers as the stem, namely, the perisarc and cenosarc. The bud swells into a knob, the cavity of the main stem extending into it, and the nutritive liquid circulates in the bud. After a time the perisarc ruptures at the end and expands into the cup, the cenosarc forms a mouth at the end, tentacles develop around the mouth, and a new zooid is complete. How a New Colony is formed Medusa Buds. By a continuation of the process just described /the colony is increased in extent, but no new colony is formed, for none Coelenterata. 321 of these parts separate from the colony. But certain buds differ from the above. Usually near the base of the colony are to be found longer buds which develop differ- ently. They become long and club-shaped. The soft cenosarc, blastostyle, develops circular side buds, called medusa buds, which finally become detached and swim away, passing out of a hole which is formed at the end of the gonotheca, as the perisarc is here called. Medusae. The medusa bud when developed becomes an umbrella-shaped body, and is called a medusa, or often a hydromedusa. It is, in fact, a small kind of jellyfish. The outside of the umbrella is called the exumbrella and the inside the subumbrella." Hanging from the center of the subumbrella surface is a short handle, the manubrium. It is hollow, and the opening at its end is the mouth. The cavity extends up through the handle, and continues as four radiating tubes to the margin of the umbrella. These four radiating tubes, or canals, are connected by a circular canal, running around near the margin. Food is taken in at the mouth, digested, and circulated through this system of canals. From the margin of the umbrella a short fold or shelf extends inward horizontally, and is called the veil (velum). Around the margin are numerous tentacles, and on the margin certain spots supposed to be organs of a sense of direction. Some medusae have around the mar- gin of the umbrella a series of black spots, which are rudi- mentary eyes. The umbrella has the power of expanding and contracting, and by this means the medusa swims. Sometimes it turns inside out. How a Medusa Multiplies. Suspended from the sub- umbrella surface, close to the four radial canals, are four spherical bodies. These are the gonads. In one indi- vidual the gonads produce eggs (ova), and in another 322 Descriptive Zoology. individual they produce sperms. The gonads set free their contents in the water, and the eggs are fertilized by the sperms. After fertilization, the egg develops first into a simple hydralike polyp, and later, by budding, into a branched hydroid like the form that produced the medusa. Alternation of Generations. Thus we see that these hydroids have two forms, and neither one is complete. The hydroid form can spread as a colony, but it can form no new colony. But by means of the medusae, which are free-swim- ming, it forms new colonies, which may be at a distance from the original colony. This peculiar process of development, hydroids giving off medusae, and medusae, in turn, producing eggs which develop into hydroids, is known as "alternation of generations." It is found in some other lower ani- mals, and among the Arthropods. Other Forms of Hydrozoa. The great majority of Hydrozoa have an alternation of generations as described. But there are others in which there is only a medusa form, no polyp form appearing, the eggs produced by the medusa developing directly into a medusa form. In others the medusa buds are produced, but are not set free. While remaining attached, they produce and set free the eggs FIG. 183. PORTUGUESE MAN-OF-WAR. Coelenterata. 323 and sperms, which develop into polyp form. The siphon- ophores are in colonies, but, instead of being fixed, are free. Some swim by means of bell-shaped zooids, resem- bling a cluster of medusae, while other zooids in the group devote themselves to nutrition, and others to the work of protection. In other kinds of siphonophores there is a bladderlike float, and locomotion depends upon the wind and current. The Portuguese man-of-war is an example. All forms are well provided with stinging cells, and one who handles them carelessly finds that this whole branch may well be designated "the sea nettles." CLASS II. THE SCYPHOZOA. Jellyfishes. This class is mostly made up of the larger jellyfishes. One of the most common on the New Eng- land coast is the common white jellyfish, known as Aurelia. It is saucer-shaped and frequently is a foot or more in diameter. It is gelatinous and semitransparent. In the center of the subumbrella is a short stalk, or manubrium. At the end of this is the square mouth, from the corners, of which extend four delicate processes, the oral arms. The short gullet leads from the mouth to a roomy stomach, whose four gastric pouches extend halfway to the margin. There are many fine radiating canals and a small, circular marginal canal. On the floor of each gastric pouch is a brightly colored gonad, whose contents, eggs or sperms, are "discharged into the stomach and pass out through the mouth. Along the inner border of each gonad is a row of delicate gastric filaments, well supplied with stinging cells, whose function is to paralyze the animals taken in as food. The margin has a fine fringe of tentacles. Evenly distributed on the margin are eight peculiar sense organs. Descriptive Zoology. Development of the Scyphozoa. The egg, after being fertilized, divides into many cells. These finally arrange themselves into a two-layered sac. This becomes cylin- drical and attaches itself by one end. The other end opens to form a mouth, around which tentacles develop, FIG. 184. JELLYFISH. The four long projections are the oral (mouth) appendages. The slender hanging projections are the marginal tentacles. thus forming a hydralike or polyp form. This elongates and becomes constricted transversely so that it resembles a pile of saucers, each of which is scalloped. These saucer-shaped parts become detached in order from the Coelenterata. 325 top, each, except the first, forming a jellyfish. The sur- face that was uppermost becomes the subumbrella. Other Jellyfishes. Most of the jellyfishes are essen- tially similar to Aurelia, though they differ considerably in their shape, some being conical instead of saucer-shaped. They often are seen in great schools, swimming lazily by gently opening and closing the umbrella, or floating at the surface ; or they may sink out of sight at will. They are mostly marine, and most are free-swimming, though a few are permanently or temporarily attached by the exum- brella surface. They are all carnivorous, feeding largely on Crustacea. Most of them are very beautiful, being like cut glass, or brightly colored, many being beautifully phos- phorescent. The great blue jellyfish of the New England coast sometimes is seven feet in diameter with tentacles a hundred feet long. Smaller specimens of this sort, when seen by transmitted light, as when in an aquarium, resemble immense amethysts. CLASS III. ACTINOZOA. Sea Anemones. To this class belong the sea anemones and most of the coral polyps. The common sea anemone is hydralike, that is, it is cylindric, attached by the base. The tentacles are numerous and are borne on a disk sur- rounding the mouth at the free end. The mouth is an elongated slit. The internal structure differs considerably from that of the hydra. In the first place, the mouth does not open directly into a simple body cavity, but is continued as a tubular gullet, which extends halfway down the body. A series of radiating partitions run the whole length of the body, extending from the outside of the gullet to the body wall. Below the lower end of the 326 Descriptive Zoology. gullet the free inner edges of these partitions, the mesen- teries, may be seen. Digestion in the Sea Anemone. Small animals, such as crustaceans, mollusks, and fishes, which come in contact with the tentacles, are partially paralyzed. They are then drawn into the mouth and passed through the gullet into the digestive cavity below, which may perhaps be called FIG. 185. SEA ANEMONE. After Emerton. From Kingsley's Zoology. the stomach. On the edges of the mesenteries below the gullet are many threadlike projections, called the mesen- terial filaments. These filaments are richly provided with nettle cells, which complete the killing of the prey. The filaments are also furnished with gland cells, which supply the liquid for digesting the food. The liquefied food ma- terial may pass up into all the spaces between the mesen- Coelenterata. 327 teries^* or intermesenteric spaces, as they are called. There are holes through the mesenteries near the top, so these chambers may communicate with one another. Be- tween the mesenteries are ridges, extending inward from the outer wall, but not reaching the gullet. These are incomplete or secondary mesenteries. Change of Form of the Sea Anemone. When undis- turbed the animal is cylindrical, sometimes long, some- times broad, so that many of them resemble the flowers of the chrysanthemum, daisy, anemone, and sunflower. They well deserve the name, for many of them are beautifully colored. The tentacles are often banded with variegated colors. It is hard for one who has lived all his life inland to realize that such brilliantly colored, flowerlike forms are actually animals and not plants. But disturb one of these flowerlike animals and it shows its real nature. It at once begins to shorten, to withdraw its tentacles, and shrink into a rounded mass lying close to its attachment. The mesenteries are well supplied with longitudinal mus- cles, whose shortening draws the body down close. Near the margin of the disk are strong circular muscles which shorten and shut in the free end, over the retracted ten- tacles, like a bag with a draw-string, so that all that appears resembles an old felt hat, with, perhaps, a little indication of a hole at the apex. After the disturbance ceases the sea anemone may gradually expand again. Development of the Sea Anemone. Sea anemones lay eggs, which are developed in the mesenteries near their free edges. The later development resembles that of the jellyfishes, but there is no alternation of generations. General Characteristics of Sea Anemones. Sea anem- ones are all marine. They are all single, that is, they do not form colonies. They have no true skeleton. Some 328 Descriptive Zoology. sea anemones attach themselves to the shells inhabited by hermit crabs. They thus get transportation, and are more secure of getting food. In return they protect the crab, for few animals care to eat so tough and nettling an animal as a sea anemone. Coral Polyps. The coral polyps are essentially like the sea anemone in their structure. But, unlike the sea anemones, they are almost always in colonies. They are unlike the sea anemone, too, in secreting carbonate of lime at the base. The single coral makes a cup or circular FIG. 186. A CLUSTER OF NEW ENGLAND CORAL POLYPS. They secrete but little coral. wall, with radiating partitions, these radiating partitions alternating with the mesenteries. In the colonies these individual cups fuse more or less together, making im- mense masses of coral. Kinds of Coral Polyps. Coral polyps are usually classed in two groups, according to the number of ten- tacles. In the sea anemone the tentacles are some mul- tiple of six. Some authors call these Hexacoralla. To this group, besides the sea anemone, belong all the true corals which produce coral reefs and islands. As is well Coelenterata. 329 known, they cannot build coral in cold water, being limited to about the temperature of 60 F. The other group have the tentacles on the plan of eight, and are sometimes therefore called Octocoralla. They make little coral, but form whiplike and fanlike colonies, the sea FIG. 187. RED CORAL POLYPS. fans, and sea pens, or sea whips. These have a horny core with loose limy material on the outside. To this group belongs the well-known red coral of the Mediterra- nean. The polyps of many of the corals are exceedingly brilliant. GENERAL CHARACTERISTICS OF CCELENTERATA. 1. There is no digestive tube separate from the body cavity. 2. Stinging cells are almost always present. 3. The body is usually radially symmetrical, but in some there are traces of bilateral symmetry. 330 Descriptive Zoology. 4. In addition to producing eggs, many multiply by bud- ding, which often results in (5), 5. Colonies, often showing marked division of labor among the differentiated individuals, or zooids. 6. The body consists of three layers : an ectoderm, and endoderm, and a middle, supporting layer, called the meso- glea. 7. The ccelenterates are mostly marine. CLASSIFICATION OF CCELENTERATA. Class i. Hydrozoa; examples, hydra and the hydroids- Class 2. Scyphozoa ; examples, most of the large jelly- fishes. Class 3. Actinozoa ; examples, the sea anemones and most stony corals. Class 4. Ctenophora, the " comb jellies." CHAPTER XXI. BRANCH ECHINODERMATA. THE echinoderms include the starfishes, brittle stars, sea urchins, sea lilies, feather stars, and sea cucumbers, all exclusively marine. CLASS I. ASTEROIDEA. Example. The Common Starfish. Occurrence. The common starfish is found all along the Atlantic coast from Labrador to Florida. It is more abundant in the shallower water, especially on the oyster beds. Other kinds of starfishes are found deeper. General Appearance. The common starfish is a five- rayed star. The central body is called the disk and the arms are the rays. In the center of the more flattened surface is the mouth ; hence this surface is called the "oral" surface in distinction from the opposite "aboral" surface, which is more convex. The Skeleton. One of the noticeable features of the starfish is its roughness. This is due to the limy skeleton, which consists of many small pieces (ossicles) of calca- reous material loosely and, in the main, irregularly joined together by more or less muscular tissue, so that the star- fish can turn or twist the rays about to a considerable ex- tent. The skeleton is embedded in the tough body wall, which is more or less ciliated, externally and internally. Many of the ossicles bear rigid projecting spines, while on Descriptive Zoology. the oral surface, especially along the borders of the grooves on the oral surfaces of the rays, are movable spines attached to the ossicles of the body wall. On the aboral surface are many small pinchers, consist- ing of a short stalk bearing two calcareous blades. The FIG. 188. COMMON STARFISH. stalks are flexible, and the blades of the pinchers may be seen opening and closing. It is thought they are for the purpose of keeping the body clean by picking up and re- moving small particles. These pinchers are called pedi- cellariae. The Water Tube System. Before we can understand how the starfish locomotes we must get an idea of the water tube system, or water vascular system, as it is usually called. In the first place, an examination of a live starfish will show the rows of soft, flexible, cylindric tube feet in the grooves in the rays. By watching the live animal it Echinodermata. 333 will be seen that these tube feet are retracted, extended, and variously moved about. For protection the feet can be withdrawn into the groove. But commonly the feet are applied to the surface on which the starfish is creep- ing. Each tube foot is a hollow cylinder, containing water, and is connected by a slender tube, passing be- tween the ossicles, with a water bulb in the cavity of the ray. Both the foot and the bulb are muscular, so when the bulb contracts it forces more water into the foot and .Madreporic plate Stone canal Radial canal FIG. 189. WATER TUBE SYSTEM OF STARFISH. extends it ; and when the foot shortens it can send the water back into the bulb. Around the mouth is a circular water tube, which sends a tube along each ray ; and side branches from these radiating tubes supply the tube feet. On the outside of the aboral surface, between the bases of two of the rays, there is a wartlike body. This is the madreporic plate. It is perforated. Water enters it and 334 Descriptive Zoology. passes down through a madreporic canal or stone canal (made of the same material as the skeleton), and this stone canal empties into the circular water tube around the mouth. Thus water, filtered through the madreporic plate, is supplied to the whole water tube system. There is also a series of water bulbs opening into the circular water ring ; these are the Polian vesicles. How the Starfish Crawls. When the starfish wishes to crawl, it distends the tube feet by the action of the water bulbs (or water sacs, called ampulla) along the inside of the rays. The flattened disklike ends of the feet are closely applied to the surface on which it is crawling. Then the center of the disk is somewhat retracted, making a sort of " sucker," by which the foot holds firmly. When many feet are thus holding there is considerable power, and when the feet are now shortened the body as a whole is pulled along. The starfish can climb vertical walls or even cling to the under side of a horizontal surface. And so strongly can it hold that sometimes, when the collector tries to pull it away he simply tears the starfish in two. The starfish can crawl with any ray foremost. The Digestive System of the Starfish. The mouth opens into a large stomach which fills nearly all the space in the central body, and has, in addition, a large lobe extending a short distance into each ray. The stomach is thin-walled and very extensible. This wide part of the stomach is called the cardiac portion. The stomach narrows above, and again widens to form the pyloric portion. Into this portion is poured the secretion of ten digestive glands, a pair in each ray. The ducts of the two glands in each ray unite, so there are five ducts entering the pyloric stomach. These glands are like long bunches of small grapes. The glands are held in place by thin folds of the Echinodermata. 335 lining membrane of the ray, and are called mesenteries. From the pyloric stomach a slender intestine extends up to the aboral wall, a little to one side of the center. Its opening is hard to find and in some starfishes is entirely obliterated. There are no jaws nor any teeth in the starfish. The Starfish's Food and Mode of Eating. Starfishes feed chiefly on mollusks, especially on oysters and mussels. The starfish arches the body over the oyster, and then turns its stomach inside out and around the soft body of the oyster, and, after digesting it, withdraws the stomach again. This seems an odd way of eating, but certainly it is an economical way, for the starfish takes only what it can digest and absorb. Damage done to Oysters. The starfish is a very vora- cious animal, and the injury done by it to the oyster indus- try is very great. The oystermen have learned that they must make effort to keep the oyster beds clear of starfishes. How Starfishes recover after Mutilation. A starfish torn in two will grow, and may make two complete star- fishes. The oystermen know that it will make a bad matter worse to tear the plunderer into pieces and throw them back into the water. Experiments show very great power of recovery after mutilation. Frequently one finds starfishes with one ray missing, or even two or three. Occasionally the collector finds a specimen with but one fully developed ray, the other four having been lost. Four new rays may, perhaps, be started, which in 1 course of time will grow to full size. The Body Cavity. The starfish is a decided advance on the ccelenterate type of structure in having a distinct body cavity, separate from the digestive tube. 33 6 Descriptive Zoology. Circulation. There is no well-developed circulatory system, such as we find in the higher animals. There are blood corpuscles in the liquid contained in the general body cavity. This liquid pervades all parts, and is set in motion by the cilia of the lining membrane, and by the general movements of the stomach and the bending of the rays ; these movements seem to suffice to circulate the contained liquid, which probably directly receives the absorbed prod- ucts of digestion. Respiration in Starfishes. There is no very complete system of respiration in starfishes. In fact, no such system is needed, for the whole body, inside and out, is constantly bathed in sea water. Still, it is thought by many authors that the tube feet are the chief agents in absorbing oxygen from the water and giving off the waste. There are also many holes through the aboral wall, from which extend slender projections of the thin, soft lining membrane of the body cavity. These are now supposed to be gills. The Nervous System and Senses. The nervous system is near the surface, and can be seen without dissection. Around the mouth is a five-angled nerve ring, which gives off a radial nerve along each ray. It may readily be seen by separating the tube feet along the middle line. At the extreme end of each ray is an eye spot, which shows as a distinct red spot in a fresh specimen of the common starfish. In alcoholic specimens it is hard to see. Close to the eye is what appears to be a tube foot, but without the disk at the end. This is called a tentacle, and is now believed to be an organ of smell. The sense of smell seems to be a much better guide than sight in bring- ing the starfish to its food. There is undoubtedly some sensitiveness to touch, but of this and any other senses little is known. Echinodermata. 337 Development of the Starfish. The female has a pair of ovaries at the base of each ray. They are like slender bunches of tiny grapes. The eggs pass out of minute pores in the angles between the bases of the rays. In the males the spermaries occupy a similar position and resemble the ovaries in form, but are lighter colored, usually white. The young starfish goes through a remarkable transformation, the young no more resembling the adult than in the case of many insects with which we are familiar. The most strik- ing fact is that the young is very distinctly bilaterally sym- metrical, showing no traces of radial symmetry. Other Forms of Starfishes. Most starfishes are five-rayed, but in some the rays are so short that the whole animal is a pentagon, the rays hardly extending beyond the disk. Some are brilliant, exhibiting beautifully complementary colors of purple and orange. The number of rays may be as many as twenty. A Pacific starfish sometimes becomes two feet in diameter. FIG. 190. BRITTLE STAR; SAND STAR. CLASS II. OPHIUROIDEA. The Brittle Stars. The ophiuroids are represented by the brittle stars. Their general form is similar to that of the starfishes. But the central disk is more distinct and the arms relatively slender. The arms are more flexible and the brittle star locomotes by active lateral movements of the arms, making rapid progress compared to a starfish. 338 Descriptive Zoology. The arms are not hollow as in the starfish, there is no ambulacral groove and the tube feet project on the side instead of on the oral surface. On account of the taper- ing arms, with their active wriggling movements, the brittle stars are sometimes called serpent stars. They are also called sand stars. In some ophiuroids the arms are branched as in the common basket star, whose arms are many times branched, and become so inrolled as to give the name basket-fish. CLASS III. ECHINOIDEA. Occurrence. Sea urchins are found along the Atlantic coast from low-water mark to fifty fathoms, being more common among rocks. They are also found clinging to the piles of wharves. The northern form is greenish, with slender spines, somewhat resembling a chestnut bur. The more southern form is of a dark color, with fewer and stouter spines. General Form of a Sea Urchin. The common sea urchin is apple-shaped, the mouth being where the stem of an apple is, and the anus at the opposite end, or pole, as the ends are termed. Running from the mouth to the anus are meridians, marked especially by the five double rows of tube feet, which, when fully extended, are long and slender, reaching beyond the tips of the longest spines. For some considerable space around the mouth is a leathery mem- brane, the peristome, where the skeleton is undeveloped. The Skeleton. As in the starfish, the leathery body wall abounds in limy plates, or ossicles ; but instead of being loosely attached to each other, as in the starfish, they are, in the sea urchin, firmly cemented together, constituting a rigid shell. These shells are sometimes sold under the Echinodermata. 339 name of sea eggs. In a cleaned shell, or corona, as it is sometimes called, there are found ten double rows of cal- careous plates, making twenty in all. Every alternate double row is closely perforated for the passage of the tube feet. These perforated plates are called the ambu- FIG. 191. SEA URCHIN. The heavy projections are the spines; the long, slender ones are the tube feet. lacral plates. Both the ambulacral and the interambula- cral plates bear rounded elevations, on which the spines were borne. Each spine has a hollow in its base, which fits over an elevation on the shell, making a ball-and-socket 340 Descriptive Zoology. joint, and is capable of a limited motion in any direction by means of muscles attached around the base. Between the spines are the pincherlike pedicellariae, as in the star-- fish, only here they have three blades instead of two. The Water Tube System. The sea urchin has a water tube or water vascular system essentially like that of the starfish. There is a water ring around the gullet, with radiating tubes between the rows of feet along the ambu- lacral rows. Inside the shell are water bulbs, or ampullae, as in the starfish, and the mechanism for the operation of these parts is as described for the starfish. How the Sea Urchin Locomotes. The injected feet are extended and attached by means of the suckerlike action at the end of each foot. Then the muscular shortening of the feet pulls the sea urchin along. This means of pro- gression is also aided considerably by the movements of the spines. The sea urchin can climb perpendicular surfaces. When placed on the aboral surface, it can turn over, though it is a very slow process. Sea urchins are sometimes found in deep holes in rocks, and it is believed that they have gradually made the holes. Digestive System of the Sea Urchin. Projecting from the mouth are usually to be seen five hard, white teeth. These teeth are movable, not being set in sockets, but held in a very complicated apparatus, somewhat like a five-angled top, known as Aristotle's lantern. The whole apparatus is under muscular control. Through the center of the whole runs the gullet. Above the tooth apparatus the intestine runs around the body wall, then reverses, making in all about two and a half turns around the body wall. It then extends up to the apex, where it ends in the anus, guarded usually by four calcareous plates. It is held in place by a thin membrane, the mesentery. Echinodermata. 341 The food is varied. Sea urchins sometimes eat sea- weeds. At other times they are found eating fish, etc., that have been thrown out as refuse by the fishermen. Sea urchins are of no special economic importance, neither being of any use nor doing any damage. Respiration in the Sea Urchin. Around the mouth, on the leathery membrane known as the peristome, are some specially modified tube feet which are supp9sed to act as gills. But, as in the starfish, the whole body, inside and outside, is so thoroughly bathed in water that there hardly seems a need of any special organs of respiration. The Nervous System of the Sea Urchin. This, too, is very similar to what we have seen in the starfish. There is a nerve ring around the gullet, from which a radial nerve passes along the ambulacral line, between the rows of tube feet, just within the body wall. At the end of the series of ambulacral plates is a single plate, known as the ocular plate, on which is an eye, at the very tip of each radial nerve. There are also, over the surface of the body, a number of small spherical bodies, borne on movable stalks. These bodies (spheridia) have ganglion cells in them, and are regarded as sense organs. Development of the Sea Urchin. The ovaries are situ- ated in the aboral part of the body cavity and are placed in the interambulacral spaces. A duct from each ovary opens through a plate at the end of the series of interam- bulacral plates. These plates with the genital pores are called the " genital plates," and alternate with the ocular plates that have been described as occurring at the apex of the series of ambulacral plates. In the male the sperma- ries occupy a similar position, and have similar genital pores. In the Southern sea urchin the ovaries are red Descriptive Zoology. from the color of the contained eggs, while the spermaries are white. The ovaries and spermaries are similar in form, resembling small bunches of grapes ; and if it were not for the difference in color, it would require microscopic exami- nation to distinguish the two sexes. Both the eggs and sperms are discharged into the water. The sperms are microscopic, tadpole-like bodies, swimming actively by the vibration of their tails. If the sperms do not gain access to the eggs, the eggs do not develop, but soon die. But usually the sperms surround the eggs, there being, ordi- narily, many sperms to each egg. One sperm gains en- trance to an egg, at least the head fusing with part of the egg. The egg is now said to be fertilized. After fertilization, the egg mass contracts, leaving a clear space around it inside the "outer coat, or cell wall. Soon the egg mass within divides into two equal parts, each of these halves again divides into two, the four then become eight, sixteen, thirty-two, and so on until the num- ber can no longer be counted and the egg looks like a spherical mulberry. This process of division is known as segmentation. The berry like mass now becomes hollow, consisting of a single layer of cells. Next one side is pushed in like a rubber ball with one side punched in ; it now has a wall made of two layers of cells. On the outside are little hairlike projections of the cells, called cilia, which by their vibrations propel the body through the water. A set of needlelike rods develop within the embryo, which soon make a skeleton, shaped somewhat like a common chair. This skeleton has a covering of soft tissue, and the projections, which correspond to the legs of the chair, are covered with strong cilia for locomotion. The digestive tube has at first but one opening, that made by the doubling in of the outer wall, as above mentioned, Echinodermata. 343 and the cavity of this depression forms the digestive cavity. The mouth is formed later by a new opening made through the outer wall into the first cavity, and the original opening becomes the anus. So far the young sea urchin is very unlike the adult ; but after a time this larva begins to transform into the real sea urchin, and soon the little sea urchins, about the size of pins' heads, are found crawling up the sides of the glass vessels in which they are kept. It should be noted that the larval sea urchin is bilaterally symmetrical, whereas the adult is, apparently at least, radially symmetrical. Other Forms of Echinoids. In addition to the common apple-shaped sea urchins, we find very greatly flattened forms, such as the sand cake, or sand dollar, also called cake urchin. The mouth is central, but the anus is at one edge. Slightly different is the key- hole urchin, with narrow open- ings through the shell (not communicating with the body cavity). There are some elon- gated urchins, showing rather marked bilateral symmetry. FIG. 192. SAND DOLLAR; CAKE URCHIN. The spines are removed from most of the surface. CLASS IV. HOLOTHUROIDEA. Sea Cucumbers. Our larger holothurians are cucumber- shaped, hence the common name, sea cucumber. The mouth is at one end and the anus at the other. Around the mouth is a 'circle of tentacles, with which food is taken. Along the sides, usually in five distinct rows, are 344 Descriptive Zoology. the tube feet. Sometimes the radial symmetry is more or less altered, for some of these forms so habitually rest, or creep, on one side that they are said to have a dorsal and a ventral surface. A sea cucumber may be compared to a sea urchin that has been drawn out in the direction of the poles that is, from mouth to anus and further to have lost most of the ossicles in the body wall so that it is now flexible instead of being rigid. There are many Tube feet Tentacles FIG. 193. SEA CUCUMBER. microscopic spicules in the integument that give it rough- ness and sometimes some degree of stiffness. Various forms of holothurians are found along the Atlantic coast. Some of the holothurians are so extremely elongated that they are frequently mistaken for worms. Among the Chinese and other West Pacific peoples, sea cucumbers, under the name trepang, are variously prepared for food. They are used principally for soups, and are considered a great delicacy. Echinodermata. 345 CLASS V. THE CRINOIDEA. Sea Lilies. The stalked crinoids are borne on a slender stalk of calcareous disks, so connected as to allow of con- siderable freedom of motion. The body is flowerlike, with branching arms surround- ing the central mouth. Most of the living crinoids are found in deep seas, and are known as the sea lilies. In shallow water is found a form that is stalked in its earlier life, but later the body, with its feathery arms, is set free and swims away by the motions of the arms. These are known as the feather stars. Crinoids. Many fossil crinoids are found in the Mississippi Valley. The heads are less common, perhaps be- cause, being softer, they have been ground to powder. But it is common to find portions of the stems, which FIG. 194. A CRINOID, OR look like a series of buttons piled one upon another, with a more or less evident hole running through the center. These appear to have been so abundant in the seas of former ages that they have formed whole strata of limestone rock. 346 Descriptive Zoology. GENERAL CHARACTERISTICS OF ECHINODERMATA. 1 . The body and its various organs are radially arranged. But many show more or less bilateral symmetry. 2. In their development they all undergo a marked meta- morphosis, the young being bilaterally symmetrical, and only in a later stage acquiring the radiate arrangement. 3. The surface has an exoskel- eton of calcareous plates, with movable spines. 4. There is a well-developed digestive tube, distinct from the body cavity. 5. There is a peculiar system of water tubes by which tube feet are extended and locomotion effected in the free forms. 6. They reproduce by means of eggs, and do not bud. 7. They do not occur in colonies. 8. They are all rather sluggish. 9. They are all, without exception, marine. 10. They have remarkable power of regeneration after mutilation. The echinoderms were formerly classed with the coelenterates on ac- count of the radial arrangement of the parts of the body ; but the echinoderms differ sharply from the coelenterates in having a digestive tube distinct from the body cavity, and in having a much higher devel- opment, as shown in the variety and perfection of their FIG. 195. STONE LILY (CRINOID). From Packard's Zoology. Echinodermata. 347 organs. The echinoderms are a very distinct group, standing apart from all other branches of the animal kingdom. CLASSES OF ECHINODERMATA. Class I. Asteroidea Starfishes. Class II. Ophiuroidea Sand Stars and Brittle Stars. Class III. Echinoidea Sea Urchins and Cake Urchins. Class IV. Holothuroidea Sea Cucumbers, or Sea Slugs. Class V. Crinoidea Sea Lilies and Feather Stars. CHAPTER XXII. BRANCH PLATYHELMINTHES. The Flatworms. [THE word " worm " is used in a very loose and indefi- nite way. In popular language it is applied indiscrimi- nately to the legless earthworm, the insect larva with segmented appendages (caterpillar), and to the elongated mollusk styled the shipworm. All that is required to merit the title is a soft, elongated, bilaterally symmetrical body. This superficial view makes no distinction as to whether the body is segmented or unsegmented, whether appendages are present or absent, whether the form is that of an adult or only in the larval stage, and asks no questions as to internal structure. The old group of " Worms " had no fundamental unity in plan of structure ; in fact, they had nothing in common except a general simi- larity in form. Hence it is natural that an increasing knowledge should break up the old branch " Vermes." In its stead we find what were formerly reckoned as classes of the branch elevated to the rank of branches, as follows : Platyhelminthes, the flatworms ; Nemathelmin- thes, the roundworms ; Trochelminthes, the rotifers or Wheel Animalcules ; the Molluscoida ; and the Annulata, the segmented or ringed worms, such as the earthworm.] The Platyhelminthes. As the name indicates, the body is flattened. They are bilaterally symmetrical, and with- out skeleton or body cavity. There is no system of blood- tubes. The body has three embryonic layers, ectoderm, 348 Platyhelminthes. 349 mesoderm, and endoderm. Many of them are parasites, and some wholly lack a digestive tube. When present the digestive tube has but one opening, the mouth. They show a tendency to reproduction by self-division, and most of them when cut in two develop two individuals. The Tapeworm. Probably the most widely known of the flatworms are the tapeworms. These are parasites in the digestive tube of various verte- brates, including man. As the name indicates, the body is ribbon-shaped, sometimes attaining a length of thirty feet. The body consists of segments, or proglottids, a tapeworm ten feet long having about eight hundred segments. There is no mouth nor digestive tube ; none is needed, as the worm lives surrounded by material digested by another animal, and the parasite simply absorbs nourishment through its skin. There is a distinct head, whose chief work is that of at- taching the worm to the lining of the intestine ; this is secured by a circle of hooks at the end of the head and four sucking disks on the sides. For a short distance from the head the body is unsegmented ; then segments are formed by constrictions at intervals ; farther on, the segments grow larger. Development of the Tapeworm. The hinder segments of the tapeworm contain embryos. These segments drop off and the embryos are set free, passing out with the excrement. They are eaten by another animal, the hog, for instance; in the intestine the embryo bores through the FIG. 196. TAPEWORM ( Tcenia solium) . In upper left hand corner of figure the head much mag- nified. After Leuckart. From Jordan and Kel- logg's Animal Life. 350 Descriptive Zoology. wall of the intestine into the muscles or other tissues. Here it becomes flask-shaped (bladder worm) and develops a head with hooks and suckers ; but in this condition it must remain unless eaten by some other animal. If the flesh be cooked, the bladder worm (cysticercus) will be killed. The danger comes in eating raw or half-raw meat. If taken into the intestine of another animal, it attaches by hooks, or suckers, or both, and the body elongates by the formation of segments as above noted. Kinds of Tapeworms. Man is infested by at least three different kinds of tapeworms, one obtained from pork, another from beef, and a third from fish ; but the latter kind is seldom, if ever, found in this country. Various animals have their own kinds of tapeworms, usually getting them from a certain kind of animal on which they prey ; thus the dog has tapeworms which have passed their larval stage in the muscles of the rabbit. The cat gets a tapeworm from the mouse. The Liver Fluke. This is another of the flatworms. It is a parasite in the liver of the sheep, living in the larger bile ducts. The eggs develop into embryos which escape with the excrement. Then they pass into the bodies of snails. Here they reach the larval stage. After leaving the snail, they attach them- FIG. 197. LIVER FLUKE. * Atrematodeworm. SelvCS tO dam P S raSS under water. If eaten by sheep, they become fully developed worms like the adult from whose eggs they developed. In England it was esti- mated that 3,000,000 sheep were killed by the liver fluke in 1880, and that the average yearly loss is 1,000,000. Nemathelminthes. 351 CLASSES OF PLATYHELMINTHES. [Class i. Trematoda Liver Fluke. Platyhelminthes. .-j Class 2. Turbellaria (ciliated). [ Class 3. Cestoda Tapeworm. BRANCH NEMATHELMINTHES. THE ROUNDWORMS. The roundworms have long, cylindrical bodies. They are not segmented, but some of them have the appear- ance of segmentation. Some are parasites in animals and plants, while others live a free life. Most of the round- worms belong to the class Nematoda. Hair Worms. These are often found as parasites in grasshoppers and other insects, but later they live free outside. They are by many ignorant people believed to be horsehairs that have "come to life" by soaking in water. The Vinegar Eel. This is another small roundworm . . , . FIG. 198. HAIR WORM. which is well known. Intestinal Worms. Two forms of roundworms are not uncommon in the human intestine, especially in those of children. The eggs or larvae have been swallowed with food. The pinworm is well known ; it is small and white and usually inhabits the rectum. The other is larger, sometimes somewhat resembling an earthworm in size and general appearance, though lacking the segments. It belongs to the genus Ascaris. Trichina. The most dangerous of the parasitic round- worms is Trichina. It is small, not exceeding an eighth 35* Descriptive Zoology. of an inch in length. It is sometimes called the " pork- worm." As is well known, this parasite is obtained by eating raw or partially raw pork, and there is no danger when the flesh is thoroughly cooked. If they gain access to the intestine of the pig, the females bring forth alive a FIG. 199. TRICHINA ENCYSTED IN HUMAN MUSCLE. Highly magnified. From Packard's Zoology. large number of young. These bore their way outward into the muscles and there inclose themselves in a sac or capsule, where they may remain an indefinite time. If this pork, uncooked, is eaten by man, the capsule is di- gested and the larvae are set free. The young soon bore through into the muscles and each worm gets into a muscle cell and coils up in a case or "cyst," which it forms for itself. The Guinea Worm. In the East Indies occurs another parasite, the guinea worm. It is sometimes found two feet long, embedded in the connective tissue under the human skin. It is supposed that the eggs or larvae are introduced in drinking water. BRANCH TROCHELMINTHES. THE ROTIFERS. The Wheel Animalcule. The word "Rotifer" means wheel bearer, from the two circular disks at the anterior end, around the borders of which are circles of cilia whose Molluscoida. 353 motions resemble the rotation of a wheel. These disks can be retracted when the animal wishes. The common name for one of these animals is the " wheel animalcule." As implied by the term animalcule, the animals are small, usually not exceeding a thirtieth of an inch in length. They occur in fresh water, and are usually to be found when looking over minute water plants under the micro- scope. They are transparent and are easily examined, all their organs showing without dissection. Though small, they are highly organized, having a complete digestive system, the food being swept to the mouth by the cilia bordering the disks. There is also a nervous system, with one or more eyes. They can swim by the action of the cilia and they also progress by a looping movement, attaching alternately by FIG. 200. WHEEL ANIMALCULE (ROTIFER). From Packard's Zoology, the two ends of the body. The posterior part of the body is a segmented " tail " which can be withdrawn like a telescope. It is said that after being dried for years, they -will revive when placed in favorable conditions, though some authors think it is contained eggs that survive instead of the adults. BRANCH MOLLUSCOIDA. This group gets its name from the fact that some of the forms were once supposed to be mollusks. There are two principal classes. 354 Descriptive Zoology. The Polyzoa. These are chiefly, though not entirely, ma- rine and are known as the "sea mats" or "corallines." They are also known as the "moss animals." These names come from the fact that they grow in colonies like mosses. They often incrust rocks with their skeletons, which are either gelatinous, chitinous, or calcareous. Each individual is frequently contained in a sort of cup, into which it can retract or from which it can protrude to a certain extent. There is a row of tentacles around the mouth. One of our fresh-water forms (Pectinatella) has a gelatinous basis or common body, which is found in spher- ical masses as large as a man's head, being attached to branches in the water. The living animals are on the outside. Such masses are often called "sponges" by the fishermen. The Brachiopods. These are in- closed in a bivalve shell, and are named the " lamp shells." Their resemblance to mollusks is very superficial, the FIG. 201. LAMP SHELLS internal structure of the two being (BRACHIOPODS). ^^jjy un]ike There ig usuaUy a circle of tentacles somewhat as in the Polyzoa. The brachiopods are exclusively marine. They are attached by a stalk which extends through the larger valve near the hinge. There are many fossil brachiopods. CHAPTER XXIII. CLASSIFICATION OF THE ANIMAL KINGDOM. (Parker and Haswell.) BRANCH I. PROTOZO'A. Class I. Rhlzop'oda Amoe ba, Globigeri'na. Class II. Mastigoph'ora Eugle'na, Vol'vox, Noctil'uca. Class III. Sporozo'a Gregari'na. Class V. Infuso'ria Parame'cium, Vorticel'la. BRANCH II. POR!F'ERA. Class I. PorTfera sponges, fresh-water and marine. BRANCH III. CffiLENTERA'TA. Class I. Hydrozo'a Hy'dra, sea anemone. Class II. Scyphozo'a jellyfish. Class III. Actinozo'a corals. Class IV. Ctenoph'ora (ten-off-o-ra) comb jellies. BRANCH IV. PLATYHELMIN'THES. Class I. Turbella'ria planarian worms. Class II. Tremato'da liver fluke. Class III. Cesto'da tapeworm. BRANCH V. NEMATHELMIN'THES. Class I. Nemato'da roundworms, Trichina. BRANCH VI. TROCHELMIN'THES. Class I. Rotlfera wheel animalcules. 355 356 Descriptive Zoology. BRANCH VII. MOLLUSCOI'DA. Class I. Polyzo'a sea mats. Class II. BrachiSp'oda lamp shells. BRANCH VIII. Asteroi'dea starfish. Ophiuroi'dea brittle stars. Class I. Class II. Class III. Echinoi'dea sea urchins. Class IV. Holothuroi'dea sea cucumbers. Class V. Crinoi'dea sea lilies. BRANCH IX. ANNULA'TA. Class I. Chsetop'oda (ke-top'-o-da) earthworm. Class II. Gephyre'a (jef-e-re'-a). Class III. Hn-udin'ea leech. Class I. Class II. Class III. Order Order Order Order Order Order Order Order Order Class IV. BRANCH X. ARTHROP'ODA. Crusta'cea crayfish, crab, barnacle, cyclops. Myrlap'oda centiped, milliped. Insec'ta grasshopper, dragon fly, water bug, butterfly. Thysanu'ra small, wingless insects. Orthop'tera grasshopper, cricket, cockroach. III. Odona'ta dragon fly, damsel fly. IV. Hemfp'tera water bug, squash bug, cicada. Neurop'tera ant-lion. Lepidop'tera butterfly, moth. DTp'tera housefly, horse fly, flesh fly, mosquito. Coleop'tera May beetle, potato beetle, tiger beetle. Hymenop'tera bee, wasp, ant, gallfly, ichneumon fly. V VI VII VIII IX Arach'nTda spiders, ticks, mites, daddy longlegs. BRANCH XL MOLLUS'CA. Class I. Pelecyp'oda clam, oyster, scallop, mussel. Class II. Amphineu'ra chl'ton (ki'-ton). Class III. Gastrop'oda snails, fresh-water and marine. Class IV. Cephalop'oda squid, cuttlefish, oc'topus, nau'tilus. Classification of the Animal Kingdom. 357 BRANCH XII. CHORDA'TA (kor-da'-ta). Subbranch I. Adelochor'da Balanoglos'sus. Subbranch II. Urochor'da sea squirts. Subbranch III. Vertebra' ta. Division A. Acra'nia (without cranium) lancelet. Division B. Crania'ta all other vertebrates. Class I. Cyclostom'ata lamprey eels. Class II. PIs'ces (pts'-sez) fishes. Subclass I. Elasmobran'chii shark, ray. Subclass II. Hdloceph'ali Chimera. Subclass III. Teleos'tomi. Order I. Crossopterygii Polyp'terus. Order II. Chondrostei sturgeon. Order III. Holostei gar pike, dogfish (of Central states). Order IV. Teleos'tei most bony fishes, such as catfish, salmon, herring, mackerel, codfish, perch. Subclass IV. Dip noi lungfish. Class III. Amphib'ia. Order I. Urode'la mud puppy, siren, salamander. Order II. Anu'ra frog, toad. Order III. Gymnophio'na blind snake. Class IV. Rgptfl'ia. Order I. Squama'ta lizard, snake. Order II. Chelo'nia (ke-lo'-ni-a) turtle. Order III. Crocodll'ia alligator, crocodile. Class V. A'ves. Division A. Rati'tae (breastbone without keel) emu, ostrich. Division B. Carina'tae (breastbone keeled). Order I . Pygop'odes loon, grebe. Order II. Impen'nes penguins. Order III. Turbina'res pet/rels. Order IV. Steganop'odes cormorant, pelican. Order V. Herodio'nes heron, stork. Order VI. An'seres duck, goose. Order VII. AccTp'itres hawk, owl, vulture. Order VIII. Crypturi tinamou. Order IX. Galll'nae grouse, quail, turkey. Order X. Gral'lae rail, crane. Order XI. Ga'vias gull, tern. 358 Descriptive Zoology. Order XII. Limlc'olae snipe, plover. Order XIII. Pterocle'tes sand grouse. Order XIV. Colum'bae pigeon, dove. Order XV. Psit'taci (sit'-a-si) parrot, cockatoo. Order XVI. Stri'ges (stri'-jez) owls. Order XVII. Pica'riae woodpecker, cuckoo, humming bird. Order XVIII. Pas'seres robin, lark, sparrow, thrush, crow. Class VI. Mamma'lia. Subclass I. Protothe'ria duckbill, spiny ant-eater. Subclass II. The'ria. Section A. Metathe'ria (marsupials) opossum, kangaroo. Section B. Euthe'ria. Order I. Edenta'ta sloth, ant-eater Order II. Ceta'cea whale, porpoise, dolphin. Order III. Sire'nia manatee, dugong. Order IV. Ungula'ta:- Odd-toed (PerTssodac'tyls) horse, tapir, elephant. Even-toed (Artiodac'tyls) ox, sheep, deer, pig. Order V. Carnlv'ora dog, cat, bear, wolf, fox, seal. Order VI. Roden'tia rat, mouse, rabbit, squirrel, Order VII. Insectiv'ora mole, shrew, hedgehog. Order VIII. Chirop'tera bat. Order IX. Prfmates lemur, baboon, ape, man. INDEX TO PART I. Abalone, 136. Abdomen of grasshopper, 2. Aboral surface of starfish, 331. Acrania, 148, 153. Actinozoa, 325. Adaptation, 15. Adelochorda, 148. Air bladder of fish, 155, 163. Sacs of grasshopper, 5. Of pigeon, 216. Of snake, 201. Tube of grasshopper, 5. Albatross, 226. Albumen, 219. Alligator, 206. Gar, 177. Alternation of generations, 322. In tunicates, 151. Ambulacral plate, 339. Ammonites, 144. Amoeba, 286. Dividing, 289. Encysted, 289. Amphibia, 181. Amphioxus, 151. Amphipoda, 84. Ampullae, 333. Angle, facial, 282. Animalcule, bell, 294. Slipper, 291. Wheel, 352, 353. Annulata, 87. Anolis, 197. Ant, 50, 51. Ant-eater, 256, 257, 260. Ant lion, 24. Antelope, 273. Antenna of grasshopper, 4. Anthropoidea, 282. Antidote for snake bites, 204. Antlers, 274. Anura, 195. Aortic arches of earthworm, 95. Aperture of snail shell, 127. Apes, 282. Aphids, 23, 50. Appendix vermiformis, 283. Arachnida, 55. Arches, aortic, 95. Aristotle's lantern, 340. Armadillo, 259, 260. Arms, oral, of jellyfish, 323, 324. Of squid, 139. Arrowfish, 140. Arteries of crayfish, 68. Arthropoda, i, 54, 77, 86. Artificial selection, 218. Artiodactyls, 267, 269. Ascaris, 351. Ascidians, 148, 149. Assimilation in amoeba, 290. Asteroidea, 331, 347. Auks, 225. Aurelia, 323. Automatic action, 289. Aves, 208. Badger, 282. Balancers, 32, 36. Balanoglossus, 148. Baleen plates, 265. Barb of feathers, 208. Barbadoes earth, 299. Barbels of catfish, 173. Barbules of feather, 208. Bark lice, 24. Barnacles, 81, 82. Basket fish, 338. Star, 338. Bass, 166. Batrachia, 181. Bats, 264, 265. Beach fleas, 84. Beak of pigeon, 214. 359 3 6 Index. Beak of squid, 141. Bear, 279, 280, 281. Beavers, 262. Bedbug, 24. Bee glue, 47. Bees, short-tongued, 49. Bell animalcule, 294. Belostoma, 20. Benacus, 20. Bend of wing, 209. Berry lobster, 74. Bighorn sheep, 270. Bile duct of pigeon, 215. Sac of snake, 201. Bill of woodpecker, 237. Bird, external features of, 210. Birds, fossil, 242. Game, 244. Value of, 244. Bison, 272. Bittern, 229. Black bass, 172. Blackbirds, 239. Black snake, 200. Black tail deer, 274, 275. Bladder of crayfish, 70. Urinary, of perch, 157. Bladder worm, 350. Blastostyle, 321. Blind snake, 195. Blister beetle, 41, 52. Blood of earthworm, 94. Blood tubes in earthworm, 94. Blowfly, 35. Bluebird, 240, 241. Blue racer, 200. Bobcat, 279. Bobolink, 239. Bob-white, 231. Body cavity of earthworm, 89. Of hydra, 314. Of starfish, 335. Borers, 40. Botfly, 35. Bowfin, 178. Boxshell turtle, 205. Brachiopods, 354. Brachyura, 84. Braconids, 52. Brain of fish, 285. Brain of mouse, 285. Of pigeon, 217. Of snake, 285. Of sparrow, 285. Of toad, 285. Of vertebrates, 285. Branchiostegal membrane, 160. Branchiostoma, 151. Breastbone of pigeon, 211. Bristles of earthworm, 90. Brittle stars, 331, 337. Brood comb, 47. Browsing, 277. Bud of hydra, 314. Budding of hydra, 317. Of hydroid, 320. Buffalo, 272. Buffalo fish, 166, 173. Bugs, 20. Bulb, spinal, 285. Bumblebees, 49. Butcher bird, 240. Byssus, 119, 125. Cabbage butterfly, 27. Cake urchin, 343. Calcareous sponge, 308. Camel, 277. Canal, marginal of jellyfish, 323. Canvasback, 228. Capsule, egg, of earthworm, 88. Thread of hydra, 315. Carapace, 205. Carinatae, 222, 223. Carnivora, 278. Carp, 166, 173. Carpet beetles, 41. Carrion beetles, 41. Crow, 236. Eaters, 217. Cassowary, 222. Catbird, 240. Catfish, 166, 173. Cats, 278. Caucasian, 282. Ceca of grasshopper, 7, 9. Of perch, 157. Of pigeon, 216. Cecropia, 30. Cecum of man, 283. Index. 361 Cecum of rabbit, 250. Cell, 301. Wall, 301. Celom, 89. Cenosarc of hydroid, 320. Centiped, 54. Skein, 55. Cephalization, 80. Cephalopods, 138. Cerebellum, 285. Cerebrum, 285. Cestoda, 351. Chalk, 298. Chameleon, 198. Channel cat, 173. Chickadee, 241. Chimney swallows, 238. Chinch bug, 23. Chipmunk, 262. Chitin, 84. Chiton, 136. Chordata, 148, 246, 284. Chromatophores of squid, 141. Cicada, 20, 22. Cilia of earthworm, 96. Of paramecium, 293. Of rotifer, 353. Of vorticella, 295. Ciliated chambers, 308, 310. Circulation in clam, 116. In crayfish, 68. In earthworm, 94. In frog, 184. In grasshopper, 6. In perch, 157, 159. In pigeon, 216. In rabbit, 251. In snail, 130. In snake, 202. In squid, 142. In starfish, 336. Cirripedia, 83. Clam, foot of, 105. Fresh-water, 102. Giant, 125. Hard, 121. Long, 120. Muscles of, 109. Razor-shell, 124. Round, 121. Clam, siphons of, 105, 108. Soft, 1 20. Clam shell, 102, 103. Growth of, no. Structure of, 109, no. Clavicle of pigeon, 213. CJaws of cat, 278. Of dog, 279. Click beetles, 41. Climbing birds, 237. Clitellum of earthworm, 88. Cloaca of pigeon, 216. Of snake, 201. Of sponge, 310. Cloven-footed animals, 269. Clypeus of grasshopper, 2. Cochineal insect, 24, 52. Cockatoo, 237. Cockroaches, 13. Cocoons of ants, 50. Of lepidoptera, 30. Of spider, 59. Codfish, 165, 172. Codling moth, 30. Coelenterata, 313. Cold-blooded animalsj 291. Coleoptera, 36, 43, Collar bones of pigeon, 213. Colon, ascending, 283. Descending, 283. Transverse, 283. Colonial protozoans, 305: Colony of hydroids, 318. Color dimorphism, 235. Of fishes, 164. Of frog, 185. Of jellyfishes, 325. Of rabbit, 252. Of squid, 141. Colorado potato beetle, 39. Colors of birds, 219. Commercial sponge, 309, 310. Conchology, 146. Condor, 236. Condyle, occfpital, in bird, 243. Conjugation of protozoans, 297. Constrictors, 200. Contour feathers, 209. Contractile vacuole, 286, 287, 295. Contractility, 289. 362 Index. Copepoda, 83. Copperhead, 203. Coracoid bone, 214. Coral islands, 328. Polyps, 325, 328. Red, 329. Reefs, 328. Corallines, 354. Cord, spinal, 285. Cormorant, 227. Corpuscles of birds, 245. Of earthworm, 94. Cougar, 279. Cow, 269. Cowbird, 220, 239. Coxa of grasshopper, 2, 4. Coyote, 279. Crabs, 78. Development of, 79. Fiddler, 80. Hermit, 81. Horseshoe, 85. King, 85. Oyster, 79, 80. Sand, 80. Swimming, 79. Crab's eyes, 75. Crampfish, 170. Cranes, 230. Craniata, 148, 153. Crayfish, 61, 65. Blind, 81. Distribution of, 76. Enemies of, 73. Holes, 61. Crayons, 299. Crickets, 13. Crinoidea, 345, 347. Crocodiles, 206, 207. Crop of earthworm, 89, 93. Of grasshopper, 7. Of pigeon, 214, 215. Croton bug, 13. Crows, 239. Carrion, 236. Crustacea, 61. Cubs, 281. Cuckoos, 221, 237. Cud chewers, 269. Gunner, 171. Curculios, 41. Currant worm, 51. Cuticle of vorticella, 295. Cuttlefish, 145. Cyclops, 83, 84. Cyclostomata, 148, 153. Cyst, 289. Cyst of trichina, 352. Cysticercus, 350. Daddy longlegs, 60. Damsel flies, 13. Darning needles, 14. Darters, 171. Decapoda, 84. Deer, 273, 274. Deer flies, 34. Development of ascidians, 149. Of clams, 118. Of crabs, 79. Of earthworm, 97. Of frog, 187, 189. Of grasshopper, 10. Of honey bee, 47, 48. Of house fly, 32. Of hydroid, 320. Of jellyfish, 324. Of lepidoptera, 28. Of metazoa, 302. Of oyster, 122. Of perch, 162. Of rabbit, 254. Of retrograde, 150. Of sea anemone, 327. Of sea urchin, 341. Of sponge, 311. Of starfish, 337. Of tapeworm, 349. Of vorticella, 296. Devilfish, 170. Devil's needles, 14. Dewclaws, 269. Diamond rattlesnake, 203. Diaphragm of rabbit, 249, 251. Differentiation, 304. Digestion in amoeba, 290. In crayfish, 65. In hydra, 316. In sea anemone, 326. Digestive gland in clam, 115. Index. 363 Digestive gland in starfish, 334. Digestive system of clam, 115. Of crayfish, 65. Of earthworm, 89, 92. Of frog, 181, 183. Of grasshopper, 7. Of perch, 156. Of pigeon, 214. Of rabbit, 250. Of sea urchin, 340. Of snail, 129. Of snake, 200, 201. Of squid, 141. Of starfish, 334. Digitigrade animals, 280. Dingo, 259. Diphycercal tail, 162. Diplocardia, 95. Dipnoi, 180. Diptera, 32. Discoid shell, 128. Disk of starfish, 331. Of tapeworm, 349. Distribution of crayfishes, 76. Of earthworms, 97. Of feathers, 209. Of fishes, 166. Of oysters, 123. Of protozoans, 300. Diving birds, 224. Division of amoeba, 289. Of labor, 302, 303. Dogday harvest fly, 22. Dogfish, 168, 169, 178. Dogs, 279. Doves, 233. Down, 209. Dragon fly, 13, 15. Drones, 46. Duckbill, 256. Ducks, 228. Dugong, 266. Dung beetles, 40. Duodenum of man, 283. Of pigeon, 215. Eagles, 233. Ears of owls, 234. Ear-shell, 136. Earthworms, 87. Earthworms, distribution of, 97. Muscles of, 89. Eating in amoeba, 290. In crayfish, 64. In paramecium, 293. In ruminants, 269. In starfish, 335. Echinodermata, 331, 346. Echinoidea, 338, 347. Ectoderm of hydra, 313. Of sponge, 308. Of vorticella, 295. Ectoplasm, 286. Edentates, 259. Eels, 176. Lamprey, 153. Round-mouthed, 153. Efts, 192. Eggs of birds, 218. Of crayfish, 73. Of earthworm, 97. Of fishes, 164. Of hydra, 317. Of jellyfish, 323. Of medusa, 321. Of snail, 134. Of snake, 202. Of sponges, 311. Shell, 219. Egret, 229. Elasmobranchii, 168, 180. Electric fishes, 164. Light bugs, 18. Ray, 170. Elephant, 277. Elk, 273, 275 (Frontispiece). Embryo of sponge, 311. Of tapeworm, 349. Emu, 222. Enamel of rabbit's teeth, 248. Encysted amoeba, 289. Endoderm of hydra, 313. Of sponge, 308. Of vorticella, 295. Endoplasm, 286. Entomostraca, 83. Epicranium of grasshopper, 4. Epidermal plates of turtle, 205. Epidermis of clam, 109. Epiglottis of rabbit, 250. 364 Index. Equilibrium sense of crayfish, 72. Of perch, 161. Ermine, 282. Esophageal collar, 70. Of grasshopper, 8, 9. Ring, 70. Ewes, 271. Excretion in amoeba, 291. In crayfish, 69. In earthworm, 95. In frog, 185. In grasshopper, 8. In paramecium, 293. In perch, 161. In pigeon, 216. In rabbit, 252. In snail, 130. In snake, 202. Exumbrella, 321. Eyed elater, 41. Eyes of grasshopper, 8, 9. Of snail, 133. Of snake, 199. Of squid, 139. Facial angle, 282. Falconidae, 233. Fangs of snakes, 203, 204. Feathers, development of, 208. Distribution of, 209. Kinds of, 209. Structure of, 208. Feather stars, 331, 345, 347. Feet of pigeon, 212. Femur of grasshopper, 4. Ferret, 282. Fertilization of sea urchin's egg, 342. Filament, gastric, of jellyfish, 323. Mesenterial, 326. Finches, 239. Fins of fishes, 163. Of perch, 154. Firefly, 42. Fish, 154, 170. Brain, 285. Hatcheries, 166. Laws, 166. Fish ways, 166. Flagella, 297. Of hydroid, 320. Flagella of sponges, 307. Flatfishes, 163, 175. Flatworms, 348. Flesh eaters, 278. Flight of pigeon, 208. Flippers of seals, 282. Floating of fish, 155. Flounder, 166, 175, 176. Flukes of whale's tail, 265. Flycatchers, 239. Flying fish, 176. Foxes, 265. Muscles of pigeon, 211. Food of clam, 113. Of crayfish, 64. Of earthworm, 92. Of frog, 1 8 1. Of perch, 156. Of pigeon, 214. Of rabbit, 247. Of sea urchin, 341. Of snake, 200. Of squid, 142. Of starfish, 335. Food balls of paramecium, 292, 293. Food fishes, 165. Food vacuole, 286, 287. Foot of clam, 105, 106, 108. Of snail, 129. " Form " of rabbit, 246. Fossils, 285. Birds, 242. Bird tracks, 207. Brachiopods, 354. Crinoids, 345. Reptiles, 207. Fox, 279. Fresh-water clam, 102. Sponges, 310. Frogs, 181, 192. Function, 305. Functions of animals, 304. Fur of rabbit, 246. Gall, 51. Flies, 51. Gnat, 35. Gallinaceous birds, 230. Gallinae, 230. Game birds, 244. Index. 365 Game fishes, 172. Ganglions of clam, 117. Of crayfish, 70,71. Of frog, 188. Of grasshopper, 8. Ganoids, 177. Gar pike, 177. Garter snake, 200. Gastric filaments of jellyfish, 323. Pouches of jellyfish, 323. Gastropods, 127. Geese, 228. Gemmule, 311. Genital plates of sea urchin, 341. Gephyrea, 101. Giant water bug, 18. Gila monster, 198. Gill chamber of crayfish, 68. Paddle of crayfish, 68. Rakers of perch, 160. Scoop of crayfish, 68. Gills of clam, HI, 113. Of crayfish, 66, 67. Of dragon-fly larva, 13. Of mud puppy, 191. Of perch, 158. Of sea slug, 135. Of siren, 190. Of snail, 134. Of tadpole, 189. Giraffe, 277. Gizzard of earthworm, 89,93. Of pigeon, 215. Gland cells of sea anemone, 326. Glands, digestive, of crayfish, 65, 66. Digestive, of starfish, 334. Green, of crayfish, 69. Salivary, of rabbit, 250. Scent, 282. Setigerous, 90. Glass-snake, 199, 205. Globigerina, 298, 299. Glochidia, 118. Glowworm, 42. Gnathostomata, 148. Gnawers, 260. Goats, 272. Gonads of jellyfish, 323. Of medusa, 321. ' Gopher, pouched, 263. Gopher turtle, 206. Gorilla, 282, 283. Gossamer, 58. Grasshopper, i, 12, 15. Grebes, 224. Grizzly bear, 281. Grosbeak, cardinal, 239. Rose-breasted, 239. Ground beetle, 39. Grouse, 231. Growth of amoeba, 290. Lines of clam, 103. Of clam shell, no. Of crayfishes, 74. Grubs, 38. Guinea fowl, 232. Worm, 352. Gullet of cow, 270. Of earthworm, 89, 93. Of man, 283. Of paramecium, 292. Of perch, 157. Of rabbit, 250. Of sea anemone, 325. Of snake, 201. Gulls, 225. Gymnophiona, 195. Haddock, 165. Hagfishes, 153. Hair worms, 351. Hake, 165. Halibut, 166, 176. Halteres, 36. Hand, 282. Hare lip, 255. Hares, 260. Harvestmen, 60. Hawk, cooper's, 233. Fish, 233. Sharp-shinned, 233. Hawkbill turtle, 205. Hawk moth, 28, 29. Head of pigeon, 214. Of squid, 139. Of tapeworm, 349. Heart of crayfish, 68, 69. Of grasshopper, 6. Of rabbit, 249, 250, 251. Heat-production in amoeba, 291. 366 Index. Hedgehog, 264. Heel of pigeon, 212. Hell-diver, 224. Hemiptera, 18. Hermit crab, 81, 82. Herons, 229. Herring, 166. Hessian fly, 35. Heterocercal tail, 162. Hexacoralla, 328. Hibernation of frog, 186. Hind wing of grasshopper, 4. Hinge ligament of clam, 103, 106, 107. Teeth of clam, cardinal, 104. Lateral, 104. Hippopotamus, 269. Hive of honey bees, 46. Hog, 269. Hollow-horned ruminants, 270. Holothuroidea, 343, 347. Homocercal tail, 162. Honey, 47. Bee, 44, 45. Comb, 47, 48. Comb of cow, 270. Dew, 50. Hoofs, 266. Hooks of tapeworm, 349. Horned toad, 198. Hornets, 49. Horns of ungulates, 270, 273. Horny sponges, 309. Horse, 267. Fly, 33, 34- House fly, 32. Humming bird, 238. Moth, 28. Humming miller, 28. Hydra, 313. Hydroids, 317, 318, 319. Hydrotheca, 320. Hydrozoa, 317. Hyena, 280. Hymenoptera, 44. Hypostome of hydra, 313. Of hydroid, 319. Ichneumon flies, 51. Iguana, 198. Incisors of rabbit, 248. Incubation, 219. Indigo bird, 239. Individual, 306. Ink bag of squid, 140. Ink galls, 52. Insecta, I. Insect eaters, 263. Interambulacral plates of sea urchin, 339- Intestinal worms, 351. Intestine of clam, 115. Of crayfish, 64, 66. Of frog, 182, 183. Of man, 283. Of perch, 157. Of pigeon, 215. Of rabbit, 249, 250. Of snake, 201. Of starfish, 335. Irritability, 289. Isqpoda, 84. Itch mite, 60. Jackal, 279. Jack rabbit, 260. Jacksnipe, 230. Jaguar, 279. Jay, 239. Jellyfishes, 323, 324. Joint-snake, 199. June bug, 36, 37. Kangaroo, 259. Katydid, 12. Keel of pigeon, 211. Keyhole urchin, 343. Kidneys of clam, 115, 116. Of crayfish, 69. Of earthworm, 96. Of frog, 182, 185. Of perch, 157, 161. Of pigeon, 215, 217. Of rabbit, 249, 252. Of snail, 130. Of snake, 201, 202. Killdeer, 230. Kingbird, 239. King crab, 85. Kingfisher, 237. Kiwi. 222. Index. 367 Labrum of grasshopper, 4. Lac insect, 24. Ladybug, 41, 44. Lake trout, 165. Lamb, 271. Lamp shells, 354. Lamprey eels, 153. Lancelet, 151. Language, 283. Larva of dragonfly, 13. Lateral line of perch, 154. Leaf rollers, 31. Leech, 100. Left-hand shells, 128. Lemur, 282. Leopard, 279. Lepidoptera, 25. Lice, 24. Limestone, 299. Limnea, 134. Limpet, 136. Lingual ribbon, 129. Lion, 279. Mountain, 279. Sea, 282. Lip of snail shell, 127. Liver of frog, 182. Of pigeon, 215. Of rabbit, 249, 250. Of snake, 201. Liverfluke, 350. Lizard, 196, 197. Lobster, 63, 77. Pot, 77. Locomotion of amoeba, 287, 290. Of clam, 108. Of crayfish, 62. Of earthworm, 91. Offish, 155. Of frog, 181. Of grasshopper, 3. Of hydra, 316. Of rabbit, 247. Of sea urchin, 340. Of snake, 200. Of starfish, 332, 334. Locust, it, 12. Long-winged swimmers, 225. Loon, 224, 225. Lung-book of spider, 56. Lung-fish, 179. Lungs of frog, 182, 183. Of pigeon, 215, 216. Ol rabbit, 249, 251. Of snake, 201. Of spider, 56. Lymphatic system of frog, 185. Lynx, 279. Macaws, 237. Mackerel, 165, 171. Macronucleus of paramecium, 292. Of vorticella, 295. Macrura, 84. Madreporic body, 332. Canal, 334. Plate, 333. Maggot, 34. Malacostraca, 83. Mallard, 228. Mammalia, 246, 256. Mammoth, 278. Man, 282. Manatee, 266. Mandible of grasshopper, 2, 4. Mantid, 13. Mantle of clam, 104. Lines, 109. Of squid, 139. Manubrium, 321. Manyplies, 270. Maple scale insect, 23. Marmoset, 282. Marsipobranchii, 153. Marsupial, 257. Bone, 257. Marten, 282. Martin, 240. Mascalonge, 167. Mastodon, 278. Maxilla of grasshopper, 4. May fly, 14. May beetle, 36. Meadow lark, 239, 242. Measuring worm, 31. Medusa bud, 320. Medusae, 321. Megatherium, 260. Menhaden, 165. Mesenterial filaments, 326. 3 68 Index. Mesenteries of sea anemone, 326. Of starfish, 335. Mesentery of rabbit, 251. Mesoderm of sponge, 308. Mesogloea of Hydra, 313. Mesothoiax of grasshopper, 2. Metamorphosis, 30. Metathorax of grasshopper, 2. Metazoa, 300. Mice, 262. Micronucleus of paramecium, 292. Of vorticella, 295. Mid brain, 285. Midges, 34. Migration of birds, 220. Of fishes, 165. Milkweed butterfly, 25. Milliped, 54. Mimicry, 31. Mink, 282. Mite, 9, 60. Mocking bird, 240, 241. Molars of rabbit, 248. Mole, 263. Mollusca, 102. Molluscoida, 353. Monarch butterfly, 25, 26, 31. Monitor, 198. Monotremata, 256. Moose, 273, 276, 277. Mosquito, 35. Hawk, 14. Moss animals, 354. Mother Carey's chickens, 226. Mother-of-pearl, 136. Moths and butterflies, 28. Motion of amoeba, 287, 290. Molting of birds, 219. Of crayfishes, 74. Of king crab, 85. Of snakes, 204. Of spiders, 56. Mountain lion, 279. Sheep, 271. Mourning doves, 233. Mouse brain, 285. Hawk, 240. Mouth of earthworm, 92. Of hydra, 313, 314. Mud eel, 190. Mud fish, 178. Nest, 180. Puppy, 191. Mule deer, 275. Mullet, 165. Multiplication of amoeba, 289. Of hydra, 317. Of hydroids, 321. Of paramecium, 294. Of protozoa, 296. Muscle pectoral of pigeon, 211. Scars of clarn shell, 103, 104. Subclavian of pigeon, 212. Muscles of clam, 106, 109. Of crayfish, 62. Of earthworm, 89, 92. Of grasshopper, 3. Of sea anemone, 327. Of starfish, 331. Mussel, salt-water, 124. Myriapoda, 54. Natica, 134, 135. Nautilus, 144. Neck of pigeon, 214. Necturus, 191. Nemathelminthes, 351. Nematocysts of hydra, 315. Nereis, 99. Nerve collar of earthworm, 89. Nerve ring of crayfish, 71. Of earthworm, 96. Nervous system of clam, 117. Of crayfish, 70, 71. Of earthworm, 96. Of frog, 187, 188. Of grasshopper, 8. Of pigeon, 217. Of rabbit, 249, 254. Of sea urchin, 341. Of snail, 130. Of squid, 142. Of starfish, 336. Nettle cells of sea anemone, 326. Neuroptera, 24. Newts, 192. Nighthawk, 238. Noctiluca, 298. No-see-ems, 34. Notochord, 148. Index 369 Nucleus, 286, 287, 301. Of paramecium, 294. Numbfish, 170. Nuthatch, 241. Nymph, 13. Octocoralla, 329. Octopus, 143. Odonata, 13, 15. Odor of snakes, 204. Oil gland of pigeon, 215, 217. Olfactory lobe, 285. One-celled animals, 286. Opercle of perch, 154, 160. Operculum of snail, 128, 129. Ophiuroidea, 337, 347. Opossum, 257, 258. Oral arms of jellyfish, 323. Surface of starfish, 331. Orang-utan, 283. Organism, 305. Organs, 304. Orioles, 239, 243. Orthoceras, 144. Orthoptera, 12. Osculum of sponge, 307. Osphradia of snails, 130. Osprey, 233. Ossicles of sea urchin, 338. Of starfish, 331. Ostracoda, 83. Ostriches, 222, 223. Otter, 282. Ovary of bird, 218. Of crayfish, 65. Of earthworm, 89, 91. Of frog, 182, 183. Of grasshopper, 10. Of hydra, 313, 317. Of perch, 157. Of sea urchin, 341. Of snake, 201. Oviduct of crayfish, 65. Of earthworm, 97. Of frog, 182, 183, 189. Of grasshopper, 10. Of perch, 157, 162. Of pigeon, 215, 219. Of snake, 201. Ovipositor of grasshopper, 10. Ovum, 302. Owls, 234, 235. Oyster, 122. Crab, 79, 80. Distribution of, 123. Season, 123. And starfish, 335. Palp of clam, in, 114. Palpus of grasshopper, 4. Pancreas of pigeon, 215. Of rabbit, 249, 250. Of snake, 201. Panther, American, 279. Paramecium, 291, 292. Parasites of grasshopper, 9. Of rabbit, 252. Parasitic arachnids, 60. Birds, 220. Crustacea, 83. Hymenoptera, 52. Protozoa, 297. Worms, 349, 351, 352. Parrakeet, 236, 237, Parrots, 236. Partridge, 231. Paunch of cow, 270. Peafowl, 232. Pear-tree slug, 51. Pearls, 126. Peccary, 269. Pectinatella, 354. Pedicellariae of sea urchin, 340. Of starfish, 332. Pelecypoda, 102. Pelican, 228. Pen of squid, 139. Penguins 225. Perch, 154. Development of, 162. Fins of, 154. Opercle of, 154, 160. Ringed, 154. Sea, 171. Perching, 213. Birds, 239. Pericardium of clam, 115. Periodical cicada, 22. Perisarc of hydroid, 320. Perissodactyls, 267. Index. Peristaltic action, 94. Peritoneum of rabbit, 251. Petrels, 226. Pewee, 239, 240. Pharynx of earthworm, 89, 92. Pheasants, 232. Phyllopoda, 83. Phylloxera, 24. Physa, 134. Pickerel, 166, 167. Pigeon, 208. Origin of, 218. Pigment in fishes, 164. Pike, 166, 167. Perch, 171. Pinchers of crayfish, 73. Of sea urchin, 340. Of starfish, 332. Pin feathers, 209. Pinnigrade animals, 282. Pinworm, 351. Pisces, 168. Placental mammals, 259. Plaice, 176. Planorbis, 127, 134. Plant lice, 23. Plantigrade animals, 280. Plastron, 205. Plates, epidermal, of turtle, 205. Genital, of sea urchin, 341. Platyhelminthes, 348. Plovers, 230. Plumes of egret, 229. Of ostrich, 222. Poison gland of honey bee, 46. Poisonous snakes, 203. Polishing powders, 299. Pollen baskets, 46. Polyp, coral, 325, 328. Fresh-water, 313. Polyphemus, 30. Polyzoa, 354. Pond snails, 129, 133. Porcupine, 261. Porifera, 307. Pork worm, 352. Porpoise, 266. Portal vein of perch, 159. Portuguese man-of-war, 322, 323. Potato beetle, 39. Prairie dog, 263. Hen, 231. Wolf, 279. Prawns, 77. Prey, birds of, 233. Primaries, 210, 211. Primates, 282. Proboscis of elephant, 277 Of snail, 133. Proglottids, 349. Pronghorn, 273. Propagation of fishes, 166. Propolis, 47. Proteid, 301. Prothorax of grasshopper, 2. Protoplasm, 286, 300, 301. Prototheria, 256. Protozoa, 286, 296, 300. Colonial, 305. Distribution of, 300. Shell-bearing, 298. Proventriculus of pigeon, 215, Psalterium of cow, 270. Pseudopod, 286, 287. Ptarmigan, 231. Puffins, 225. Puma, 279. Puparium, 33, 34. Purple finch, 239. Quahog, 121. Quail, 231. Queen, honey bee, 46. Cells, 48. Quills, 209. Of porcupine, 261. Rabbit, 246. In Australia, 253. Development of, 254. Nervous system of, 254. Structure of, 249. Raccoon, 281. Rails, 230. Raptores, 233, 235. Ratitae, 222. Rats, 262. Rattlesnake, 203, 204. Rays, 168, 169. Of starfish, 331, Index. Recovery of earthworms, 98. Of hydra from mutilation, 317. Of starfish from mutilation, 335. Rectum, 283. Red coral, 329. Deer, 274. Rennet, 270. Reproduction of amoeba, 289, 291. Reptiles, 196. Age of, 207. Extinct, 207. Respiration in amoeba, 290. In clam, no. In crayfish, 66. In earthworm, 95. In frog, 183. In gastropods, 130. In grasshopper, 5. In perch, 158. - In pigeon, 216. * In rabbit, 251. . In sea urchin, 341. In snail, 133. In snake, 201. - In squid, 142. In starfish, 336. Restoration of limbs in crayfish, 75. Reticulum of cow, 270. Rhinoceros, 268. Ribs of snake, 199, 200. Right-hand shell, 128. Ringed perch, 154, 171. Robin, 241. Rodents, 260. Rose slug, 51. Rotifers, 352, 353. Roundworms, 351. Rove beetles, 41. Ruffed grouse, 232. Ruminants, 269. Solid-horned, 273. Sage hen, 231. Salamanders, 191. Salmon, 165, 174. Sand cake, 343. Dollar, 343. Hoppers, 84. Star, 337, 338. Worm, 99. Sapsucker, 238. Sardine, 165. Sawflies, 51. Scale bugs, 24. Scales of butterfly, 25. Of fishes, 162. Of lizard, 196. Scallop, 125. Scent gland, 282. Scorpion, 60. Scutellum of grasshopper, 4. Scutes of snake, 200. Scutum of grasshopper, 4. Scyphozoa, 323. Sea anemone, 325, 326. Cucumber, 331, 343, 344. Eggs, 339. . Fans, 329. Lilies, 331, 345. Lion, 282. Mats, 354. P.ear, 149. Pen, 329. Perch, 171. Squirt, 149. Turtle, 205. Urchin, 331, 338, 339. Whip, 329. Seals, 282. Secondaries, 210, 211. Segmentation of egg, 342. Senses of clam, 118. Of crayfish, 72. Of earthworm, 97. Of frog, 187. Of gastropod, 130. Of grasshopper, 8. Of jellyfish, 323. Of perch, 160, 161. Of pigeon, 217. Of rabbit, 255. Of snake, 202. Of squid, 142. Of starfish, 336. Sepia of squid, 141. Serpent stars, 338. Setae of earthworm, 90. Seventeen-year locust, 22. Sexton beetles, 41. Shad, 165. 372 Index. Sharks, 168, 169. Shedding of horns, 273. Sheep, 270. Shell of sea urchin, 339. Shipvvorm, 123. Shore birds, 230. Shrews, 264. Shrike, 240. Shrimp, 77. Silica, 299. Siliceous earth, 299. Sponges, 309. Silkworm, 30. Silvertip bear, 281. Sinus, blood, of crayfish, 69. Siphon of squid, 140. Of clam, 105, 108. Siren, 190. Skate, 169, 170. Skeleton of arthropods, 86. Of birds, 245. Of bony fishes, 170. Of insects, 52. Of pigeon, 208, 213. Of sea urchin, 338. Of shark, 168. Of sponge, 308. Of starfish, 331. Skin of earthworm, 90. Skipjacks, 41. Skippers, 35. Skunk, 282. Slaves of ants, 51. Slipper animalcule, 291. Sloths, 259. Slugs, 132. Sea, 135. Smell in birds, 217. In crayfish, 72. In deer, 277. In rabbit, 255. In snails, 130. Smelling patches, 130. Smelt, 165. Snails, land, 131. Pond, 133. River, 134. Sea, 135. Shell, 127. Snake doctors, 14. Snake feeders, 14. Snakes, 199, 205. Brain, 285. Poisonous, 203, 204. Snipe, 230. Snout beetles, 41. Social bees, 49. Sole, 176. Solid-horned ruminants, 273, Solitary bees, 49. Sowbug, 84. Spanish fly, 41. Sparrows, 239. Brain, 285. English, 239. Specialization, 304. Speech, 282. Sperm cells of hydra, 317. Of sponge, 311. Spermary of fish, 162. Of hydra, 314, 317. Sea urchin, 341. Sperms of hydra, 317. Of jellyfish, 323. Of medusa, 322. Of sponges, 311. Sphinx moth, 28. Spicules of sponge, 307, 308, 309. Spiders, 55. Jumping, 56. Trapdoor, 59. Web, 57. Spinal bulb, 285. Cord, 285. Spindles, 14. Spines of sea urchin, 338, 339. Of starfish, 331. Of sting cells, 315. Spinnerets of spider, 57. Spinning of spiders, 56. Spiny-rayed fish, 171. Spiracles, 5. Spleen of snake, 201. Sponges, 307. Calcareous, 308. Commercial, 309,310. Development of, 311. Flagella, 307, 308. Fresh-water, 310. Horny, 309. Index. 373 Sponges, in reservoirs, 311. Siliceous, 309. Spongin, 309. Spoonbill catfish, 178. Spouting of whales, 266. Spring beetles, 41. Squash bug, 20, 21. Squid, 138. Giant, 143. Squirrels, 263. Flying, 263. Fox, 263. Gray, 263. Red, 263. Stable flies, 34. Stag-beetles, 40. Stake driver, 229. Starfish, 331, 332. Development of, 337. Sting of honey bee, 46. Cells of hydra, 314. Cells of jellyfish, 323. Rays, 169. Stomach of crayfish, 65, 66. Of frog, 182, 183. Of jellyfish, 323. Of man, 283. Of perch, 157. Of pigeon, glandular, 215. Of rabbit, 249, 250. Of ruminant, 270. Of sea anemone, 326. Of snake, 201. Of starfish, 334. Stone canal of starfish, 333, 334. Stork, 229. Striped bass, 171. Sturgeon, 165, 177. 'Subumbrella, 321. Suckers, 166, 173. Squid, 139. Sulphur-bottom whale, 266. Sunfish, 171. Sutures of snail shell, 127. Swallows, 240. Bank, 240. Barn, 240. Chimney, 238. Eave, 240. Fork-tail, 240. Swallowing in snakes, 199, 200. Swallow-tail butterflies, 30. Swarming, 48. Swifts, 197, 238. Swim bladder of perch, 155. Swimming of crayfish, 62. Of frog, 1 8 1. Of jellyfish, 321, 325. Of perch, 155. Of squid, 140. Syrinx of pigeon, 218. Tadpole, 189. Tail fin of crayfish, 62. Of squid, 140. Tails of fishes, 162. Tapeworm, 349. Tapir, 267, 268. Tarantula, 59. Tarsus of grasshopper, 4. Of pigeon, 212. Taste in crayfish, 72. Teeth of rabbit, 248. Of sea urchin, 340. Of snake, 199. Teleostei, 180. Teleostomi, 180. Temperature of amceba, 291, Oi frog, 1 86, 187. Of insects, 7. Of mammals, 251, 283. Of pigeon, 216. Of rabbit, 251. Tentacles of hydra, 313. Of jellyfish, 323. Of sea anemone, 325. Of sea slug, 135. Of snail, 130, 131. Terns, 225. Tertiaries, 210, 211. Theria, 256, 257. Thistle bird, 239. Thornbacks, 170. Thousand legs, 54. Thread capsules of hydra, 315. Thrush, brown, 240. Wood, 240. Thumb of bird, 211. Tibia of grasshopper, 4. Ticks, 60. 374 Index. Tiger, 279. Beetle, 40. Timber wolf, 279. Tissues, 304. Toads, 192. Brain, 285. Toes of pigeon, 212. Tomato worm, 28. Tongue of snake, 199. Of frog, 182. Of woodpecker, 237. Torpedo, 170. Tortoise shell, 205. Totipalmate birds, 227. Touch in amoeba, 291. In catfish, 173. In clam, 118. In crayfish, 72. In earthworm, 97. In frog, 187. In grasshopper, 9. In perch, 161. In pigeon, 217. In rabbit, 255. In snail, 130. Tracheae in grasshopper, 5. Tracks of rabbit, 247. Tree frog, 193. Toad, 193. Trematoda, 351. Trepang, 344. Trichina, 351, 352. Tridacna, 125. Trigger-hair of hydra, 315. Tripoli, 299. Trochanter of grasshopper, 2, 4. Trochantine of grasshopper, 2, 4. Trochelminthes, 352. Trout, 174. Tube feet of starfish, 332. Tube-nosed swimmers, 226. Tubularian hydroid, 320. Tunicates, 148, 149. Turbellaria, 351. Turkey, 231, 232. Buzzard, 235, 236. Turtle, boxshell, 205. Gopher, 206. Green, 205. Hawkbill, 205. Turtle, sea, 205. Snapping, 206. Turtledove, 233. Tusks of elephant, 278. Tympanum of frog, 187. Typhlosole, 92, 94. Umbo, 102, 103. Ungulates, 266. Ureter of rabbit, 249, 252. Of snake, 201. Urochorda, 148. Urodela, 195. Vacuole, 286, 292. Contractile, 295. Vane of feather, 208. Veil of jellyfish, 321. Veins of insect wing, 3. Velum of medusa, 321. Velvet of antlers, 274. Ventral plates of snake, 200. Vermiform appendix, 283. Vertebrata, 148, 284. Viceroy butterfly, 31. Vinegar eel, 351. Voice of frog, 193. Of pigeon, 218. Vorticella, 294. Vulture, 235. Waders, 230. Walking stick, 12, 13. Wall-eye, 171. Warblers, 240. Wasps, 49, 50. Water beetles, 42. Bug, 18. Bulbs, of starfish, 334. Dog, 191. Flea, 83, 84. Moccasin, 203. Snakes, 200. Tubes of sea urchin, 340. Tubes of starfish, 332, 333. Wax of bees, 47. Weasels, 282. Weevils, 40, 41. Whalebone, 265. Whales, 265. Index. 375 Wheat midge, 35. Wheel animalcule, 352, 353. Whip-poor-will, 238. Whiskers of rabbit, 255. White bass, 172. Whitefish, 165, 174. White-tail deer, 274. Whorl of snailshell, 127. Wild canary, 239. Cat, 279. Windpipe of snake, 201. Wing of pigeon, 209. Wireworm, 41. Wishbone, 213. Wolf, 279. Wolverine, 282. Woodchuck, 263. Woodcock, 230. Wood duck, 228, 229. Woodpecker, 237. Yellow-bellied, 238. Worker, honey bee, 46. Worms, 348. Intestinal, 351. Wren, 240. Yellow bass, 172. Jacket, 49. Perch, 171. Zooid, 319. Action of, 320. Zoophytes, 319. Zygodactyl feet, 237. 14 DAY USE RETURN TO DESK FROM WHICH BORROW! is due on the lastdate stampea below, or on the date to which renewed. Renewed books are subject to immediate recall. JAN 4 }96S LD 21-50w-6,'59 (A2845slO)476 General Library University of California Berkeley C ] L UNIVERSITY OF CALIFORNIA LIBRARY