Elementary Zoology, Second Edition

by Vernon L. Kellogg

BRANCH CHORDATA: THE VERTEBRATES, ASCIDIANS, ETC.

The branch Chordata includes all the backboned animals or vertebrates, comprising the fishes, salamanders, frogs and toads, lizards, crocodiles, turtles and snakes, birds, and all the quadrupeds or mammals, and includes also a few small unfamiliar ocean animals which do not look at all like the backboned animals, but which agree with them in possessing a peculiar structure called the notochord. This notochord consists of a series or cord of cells extending longitudinally through the body from head to tail, above the alimentary canal and below the spinal nerve-cord. In all the vertebrates excepting a few low forms, the notochord while present in the young, is replaced in the adult by a segmented bony or cartilaginous axis, the spinal or vertebral column. But in the ascidians or sea-squirts (called also tunicates) it persists throughout life. In addition to this characteristic notochord, nearly all the Chordata are marked by the presence, either in embryonic or larval stages only, or else persisting throughout life, of a number of slits or clefts in the walls of the pharynx which serve for breathing, and which are called gill-slits.

Structure of the vertebrates.—As the backboned or vertebrate animals make up almost the whole of the branch Chordata, and as the few other chordates are animals the special structures of which we shall not undertake to study in this book, we may note here some of the other more obvious structural characteristics of the true vertebrates. The possession of a backbone or bony (sometimes cartilaginous) spinal column is the characteristic by which we distinguish them from the invertebrate or backboneless animals. Furthermore, all of the vertebrates possess an internal skeleton which is in most cases composed of bone, and is firm and strong. In some of the lower fishes, as the sharks and sturgeons, the skeleton is made up of cartilage, tough but not hard. The vertebrate skeleton consists typically of an axial portion comprising the spinal column and head, and of two pairs of appendages or limbs, variously developed as fins, wings, legs and arms. In some vertebrates these limbs are represented by mere rudiments, and in the lowest fish-like forms, the lancelets and lampreys, there is not the slightest trace of limbs. A part of the central nervous system, the spinal cord, runs longitudinally through the body on the dorsal side of the alimentary canal; the circulatory system is closed, the blood being always confined in the heart and in vessels called arteries, veins, and capillaries, and the blood is red in color owing to the presence of numerous red corpuscles or blood-cells. The nervous system is highly developed, with a large brain in all the typical forms, and with complex and usually highly efficient special sense-organs. Respiration is carried on by means of external gills, or by internal lungs which communicate with the outside through the mouth and nostrils. To the lungs and gills the blood is brought to be "purified," i.e., to give up its carbonic-acid gas and to take up oxygen.

Classification.—The Chordata are variously divided by zoologists into eight or ten classes, of which (in the eight-class system) the five classes[15] Pisces (fishes), Batrachia (batrachians), Reptilia (reptiles), Aves (birds), and Mammalia (mammals), belong to the true vertebrates. These classes will be considered in the five following chapters.

The remaining three classes include a number of strange marine forms which until recent years were considered as worms, but which are now known to be the nearest living allies of the earliest or primitive vertebrates. The relationship of these forms to early types is manifest, not in the appearance or structure of the adult stage, but only during embryonic or larval stages.

Fig. 111.—An ascidian or sea-squirt from the coast of California. (After Jordan and Kellogg.)

The ascidians.—The sea-squirts, or Ascidians, common on the seashore, compose one class of these primitive chordate animals. They possess a simple, sac-like body (fig. [111]), fastened to the rocks by one end, the other being provided with two openings, one for the ingress and the other for the exit of water, a strong current of which flows constantly through the body. By means of this current the ascidian obtains food. Usually sea-squirts live together in large colonies, and in some cases a number of individuals enclose themselves in a common gelatinous mass, forming what is called a compound ascidian.

The ascidian when born is a tiny, free-swimming, tadpole-like creature with a slender finned tail. It swims about freely for only a few hours, however, soon attaching itself to a rock, and in its further development becoming degenerate. It loses its tail and with it the short notochord possessed by the larva; the eye and the auditory organ are lost, and the nervous system and alimentary canal become much reduced and simplified. Sea-squirts in their adult stage are very simple degenerate animals, with low functional development, yet their embryonic and larval conditions show a considerable degree of structural specialization, and the presence of the notochord in these early stages reveals their affinity with the backboned animals.

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[CHAPTER XXIV]

BRANCH CHORDATA (Continued): CLASS PISCES (THE FISHES)

THE GOLDEN SUNFISH OR PUMPKIN SEED (Apomotis sp.)

Technical Note.—The species of sunfish named, or some closely related species, can be obtained in any brook or stream in the United States. Gibbosus lives in all streams north of Dubuque, Chicago, Pittsburg, and along the eastern coast north of Charleston. Closely allied species live in all the other parts of the country except in the higher Rocky Mountains west of Bismarck, Pueblo, and Santa Fe. One species is found in the streams of California, but none occurs in Washington or Oregon. In the few places where a sunfish cannot be had, any species of bass or perch may be used. Sunfish live in ponds and sluggish streams in deep holes under a log or at the foot of a stump. They take eagerly a hook baited with a worm, or they may be caught in nets. When sunfish cannot be kept fresh for study in class, specimens may be preserved in alcohol or 4% formalin. But if possible to keep some alive for a time in a jar or tub with plenty of fresh water, the colors of the living fish, together with its manner of swimming and mode of breathing, can be observed.

External structure[16] (fig. [112]).—Examine the general configuration and make-up of the body. Note the deep, laterally flattened trunk and paddle-like tail. The head is closely fitted to the trunk without any neck. Note that the body is thickly covered with firm, hard scales, arranged like the shingles on a roof. Remove one of these scales and examine it under a hand lens. What sort of an edge has it? Such a scale is said to be ctenoid.

The body of the sunfish terminates behind in the caudal fin, a series of cartilaginous rays connected by thin skin and attached to a bony plate at the end of the backbone. Along the median dorsal line will be noted another fin composed anteriorly of spines and posteriorly of soft rays jointed and branched. This is the dorsal fin. How many spines has it? Anterior to the caudal fin on the ventral surface is a median unpaired anal fin. How many spines has it? Anterior to the anal fin are the ventral fins, while on the sides of the body back of the head in a line with the mouth are found the pectoral fins. The ventral fins, attached to a rudimentary pelvis, correspond to the hind legs of the other vertebrates. The pectoral fins, attached to the shoulder girdle, correspond to the arms. In front of the anal fin note a small pit-like opening, the opening from the kidneys and reproductive organs, and just anterior to this a large aperture, the anus. At the anterior end of the head note the broad mouth, surrounded by a complicated system of bones. Note the large eyes surrounded by a series of small bones, the orbital chain. Just anterior to the eyes are two pairs of openings, one pair of each side opening into a closed sac. What are these openings? Note the presence of various bones on the side of the head, each covered with a thin layer of skin. These are membrane bones, characteristic of fishes. Are there any external ears in the fish? Examine the inside of the mouth. Is there a tongue? If so, of what character? Are there teeth? If so, where are they situated?

Note along each side extending to the base of the tail a line of modified scales, on each scale a little mucous tube, the whole series constituting the lateral line. These scales are intimately associated with a large nerve (the vagus), and probably serve an important part, not yet clearly understood, in the life of the fish.

Lift up the flap in front of one of the pectoral fins. This is the opercular flap which covers the gills that lie beneath. Bend this forward and find four gill-arches, each with its double fringe of gills. Note the gill-rakers, short and blunt, on the first gill-arch. Note also on the under side of the flaps turned back, delicate red gill-like structures covered by a membrane. These are the false gills or pseudo-branchiæ, larger in most fishes than in the sunfish. The gills in the fish subserve the same function as the gills of the crayfish, that of purifying the blood by eliminating carbonic-acid gas from it and taking up oxygen from the air mixed with or dissolved in the water. Organs subserving the same purposes in different kinds of animals as, for example, the gills in fish and in crayfish, are called analogous structures. But there is an important morphological difference between the fish's gills and the gills of the crayfish. In the latter animal they are outgrowths of the basal segments of the walking-legs; in the fish they are outgrowths from the alimentary canal. The internal gills of the young toad (tadpole) arise in the same way as those of a fish. Structures which are identical in their origin, like the gills of tadpole and fish, are called homologous structures.

Make a drawing of the sunfish from a lateral aspect, showing the external parts named.

Internal Structure.—Technical Note.—Insert one point of the scissors a little to one side of the anus and cut dorsally on the left side of the body to the backbone. Now cut anteriorly from the anus along the ventral wall to where the jaws unite, and cut, also anteriorly, along the dorsal wall until the left side of the body can be removed. Bend the opercular flap backward over the eye and pin the entire fish, uncut side down, to the bottom of the dissecting-pan, covering it with water.

The above operation will have severed the large powerful muscles forming the body-wall and extending along the sides. Note a membranous sac completely filling a large dorsal cavity. This is the swim-bladder, a float filled with air which tends to give the fish the same weight as the water it displaces. It arises as a diverticulum from the alimentary canal, but soon becomes permanently shut off from it. Beneath the swim-bladder is a large cavity filled with various organs, collectively known as the viscera. In vertebrate animals the cavity which contains the viscera is generally called the peritoneal cavity. It is lined by the peritoneum, a delicate membrane, part of which is deflected as the mesentery over the alimentary canal and the other organs, thus suspending them all from the dorsal wall. Note in the anterior end of the peritoneal cavity a large bi-lobed gland, the liver, red in fresh, yellowish in alcoholic specimens. Its function, like that of the liver of the toad, is to store up nutriment for the blood and to secrete a digestive fluid called bile. Behind the liver note a long, convoluted tube. What is this tube? Unfold this tube, separating it from its enveloping membrane, the mesentery. Thrust a probe down the throat and note that it passes into a thick-walled sac, the stomach. The mouth and gill-slits open into the front part of the alimentary canal called the pharynx, which leads by a short tube, the œsophagus, into the stomach. Note the large, thickened portion of the alimentary canal leading from the stomach. This is the pylorus, and to its walls are attached a number of finger-like projections, the pyloric cæca. The pyloric cæca secrete a fluid which is poured into the alimentary canal and which assists in the process of digestion somewhat as does the secretion from the pancreas of the toad. From the pylorus, passing backwards in one or two loops, is the small intestine. Trace this to its exit. Lying within the mesentery near the posterior end of the body-cavity note a small red glandular mass, the spleen.

At the anterior end of the body in front of the liver and between the sets of gills note the small pericardial cavity within which is contained the heart. The pericardial cavity is separated from the peritoneal cavity by a thick muscular wall against which the liver abuts. The heart consists of four parts. The posterior part is a thin-walled reservoir, the sinus venosus, into which blood enters through the jugular vein from the head and through the cardinal vein from the kidney. From the sinus venosus it passes forward into a large chamber, the auricle. Next it flows into the ventricle, where, by the contraction of the walls, rhythmical pulsations force it into the conus arteriosus, thence into the ventral aorta, and lastly into the gills, where it is purified. After passing through the capillaries in the fine gill-filaments it is again collected, now pure, by paired arteries from each pair of gills, which arteries unite to form the dorsal aorta extending backward just below the backbone to the end of the tail. From the dorsal aorta a pair of arteries, the subclavian, are given off to the pectoral fins. At this point two other arteries branch off ventrally, the first being the cardiac artery, which distributes blood to the stomach and pyloric cæca. The second divides into several long mesenteric arteries supplying blood to all parts of the intestine and spleen. In the caudal region blood is taken up through the caudal vein and carried forward to the kidneys. These strain out the impurities arising from waste of tissues, after which the blood is carried back to the sinus venosus through the cardinal vein. From the intestine it is gathered into the large portal vein as in the toad. The portal vein carries blood to the liver, where nutriment may be stored up, and from thence it flows back to the sinus venosus through a very short thin-walled vessel, the hepatic sinus.

The kidneys, more or less united in one mass, lie in the posterior part of the body-cavity along the dorsal wall. Note running from each side of the kidney a ureter which unites with its fellow and opens into a small urinary bladder which discharges through a small opening immediately back of the anus.

The reproductive organs lie below the swim-bladder near the posterior end of the body-cavity. If the fish are caught in the spring, the greater part of the body-cavity of the female is found to be filled with small eggs. When mature, these eggs are deposited by the mother fish in the gravel of the stream-bed where they are fertilized by the sperm-cells poured over them by the male and left floating in the water.

The nervous system of fishes is best studied in a specimen treated with nitric acid. Carefully remove the roof of the skull, thereby exposing the brain. Most anteriorly make out, as in the toad, the paired olfactory lobes. These are attached by long stalks to the cerebrum or forebrain, which is followed by two large hollow lobes, the midbrain or optic lobes. Behind the midbrain is the cerebellum. Following the cerebellum is the elongate medulla oblongata, which tapers backward into the spinal cord. How far backward does the spinal cord extend? On each side of the brain-case about opposite the cerebellum are located the auditory organs, each consisting of three semicircular canals which lie in different planes, and of the vestibule. These parts are filled with liquid, and suspended in the liquid in the vestibule are small calcareous bodies called otoliths or ear-stones. Running out beneath from the midbrain are the optic nerves, which cross, the left one connected with the right eye, the right one with the left eye. From each side of the medulla oblongata there is given off a large nerve, the vagus, which sends branches to the lateral line organs on either side, and extends backward to the stomach and viscera.

For further study of the nervous system see Parker's "Zootomy," pp. 122-130.

Make a drawing of the nervous system as worked out.

Technical Note.—To make a good skeleton immerse a fresh or preserved specimen for some time in a hot soap solution. When the muscles have commenced to soften remove the body from the solution, pick the flesh away, and leave to dry.

Note that the main axis of the skeleton is composed of vertebræ placed end to end. How many vertebræ are there? What vertebræ bear ribs? The ribless ones beyond the body-cavity are called caudal vertebræ. Note the interspinal bones which support the fins, with large muscles on either side to control their action. Note that the group of bones supporting the pectoral fin is attached to the back of the brain-case and makes up the shoulder girdle. The ventral fins are attached to a rudimentary pelvic girdle, attached in front to the shoulder girdle, as the shoulder girdle is in turn attached to the skull. It will be seen that the sunfish has no neck and we may say, also, no back. Its skeleton consists only of a tail attached to the skull. The brain-case is made up of a number of bones closely joined together. From it is suspended the lower jaw, which comprises a number of bones but loosely attached to each other. Overlying these is the system of membrane bones already mentioned, including the opercle or gill-cover.

For a detailed study of the fish-skeleton see Parker's "Zootomy," pp. 86-101, or Parker and Haswell's "Zoology," vol. ii. pp. 183-195.

Life-history and habits.—The sunfish or "pumpkin-seed" lives in quiet corners of the brooks and rivers, preferably under a log or at the root of an old stump. It is a beautiful fish, shining "like a coin fresh from the mint." Its body is mottled golden, orange and blue, with metallic lustre, darker above, pale or yellowish below. Its fins are of the same color. The tip of its opercle is prolonged like an ear and jet black in color, with a dash of bright scarlet along its lower edge. Nearly all the thirty species of sunfish found in the United States have this black ear, but some have it long, some short, and in some it is trimmed with yellow or blue instead of scarlet.

The sunfish lays its eggs in the spring in a rude nest it scoops in the gravel, over which it stands guard with its bright fins spread, looking as big and dangerous as possible. When thus employed it takes the hook savagely, perhaps regarding the worm as a dangerous enemy. The young fishes soon hatch, looking very much like their parents, although more transparent and not so brightly colored. They grow rapidly, feeding on insects and other small creatures, and reach their growth in two or three years. They do not wander far and never willingly migrate. Students should verify this account on the different species. A more exact study of the nests of the different species and the fishes' defence of them would be a valuable addition to our knowledge. The most striking traits of the habits of this fish are its vivacity and courage; it reveals its great muscular strength when captured. The sexes are similar in appearance and both defend the nest alike.

OTHER FISHES.

Fig. 112.—Dissection of the sunfish, Apomotis sp.

Fishes constitute the largest class of vertebrate animals and are to be found everywhere in ponds, streams, or ocean. About 15,000 species of fish are known, of which 3,000 live in North America. The largest of all fishes is the basking shark (Cetorhinus), which reaches a length of thirty-six feet. The smallest is the dwarf goby (Mistichthys), less than half an inch long, found in Luzon, one of the Philippine Islands. Between these extremes is every variety in size, form, and relative proportions. The body, for example, may be greatly elongated and almost cylindrical as in the eels; or long and flattened from side to side as in the ribbon-fishes; or the head may be very large, wider and higher than the rest of the body as in the anglers, or may have a great beak as in the sword-fish.

Body form and structure.—When we consider the fish as a whole, we find first a body formed for progression in the water, the typical fish being pointed at each end (the shorter point in front), and having the sides flattened, the back and belly rather narrow, and the motive power located in the fin on the tail. From this typical form diverge all conceivable variations, adaptations to every sort of fish life.

Most fishes have the body covered with scales, although many have the skin naked or covered with small scales so hidden in the skin as to be hardly visible. The scales are small horny or bony plates which fit into small pockets or folds of the skin, and are usually arranged shingle-fashion, overlapping each other. They are of various shapes, mostly classified as of three kinds, namely, squarish enamelled scales called ganoid, roundish smooth-edged called cycloid, and roundish tooth-edged called ctenoid.

The skeleton of the fish is relatively complex. Its bones are comparatively soft, having little lime in them, indeed in many cases they are mere cartilage. The vertebral column is made of twenty-four vertebræ in the typical fishes, the number in the others being variously increased, or sometimes diminished. These vertebræ are of two classes, abdominal or body, and caudal or tail vertebræ. The former have a neural arch which encloses the spinal cord and from which projects a spine. Below, the processes spread apart, surrounding the kidneys and partly enclosing the air-bladder. To these processes ribs are loosely attached. The caudal vertebræ have no ribs and leave no room below for viscera. Their lower arch (hæmal), similar to the dorsal (neural) arch, surrounds a blood-vessel. The fins of a fish are composed of bony rods or rays joined by membrane. Some of these rays may be unbranched and unjointed, being then known as spines, and usually occupy the front part of the fin. Other rays are made up of little joints and are usually branched toward their tip. Such ones are called soft rays. Soft rays make up the greatest part of most fins. The vertical fins are on the middle line of the body. These are the dorsal above, anal below, and caudal forming the end of the tail. The paired pectoral and ventral fins are ranged one on each side corresponding to the arms and legs of higher animals. The pectoral fin or arm is fastened to a series of bones called the shoulder girdle. These bones do not correspond to those in the shoulder girdle of the higher animals, and the various parts in the two structures are differently named. The uppermost bone of the shoulder girdle is usually attached to the skull. To the lowermost is attached the rudimentary pelvis, which supports the hinder limb or ventral fin. Usually the pelvis is farther back and loose in the flesh, but sometimes it is placed far forward, being occasionally attached at the chin.

The head contains the various bones of the cranium, usually closely wedged together and not easily distinguished. The jaws are each made of several pieces; the lower one is suspended from the skull by a chain of three flat bones. The jaws may bear any one of a great variety of forms of teeth or no teeth at all, and any of the bones of the mouth-cavity and throat may have teeth as well. On the outside of the head are numerous bones called membrane bones, because they are made up of ossified membrane. The most important of these is the opercle or gill-cover. Within are the tongue with the five gill-arches attached to it below and to the floor of the skull above, the last arch being usually modified to form the pharyngeal jaw.

The stomach may be a blind sac with entrance and exit close together, or it may have the form of a tube or siphon. At its end are often found the large glandular tubes called pyloric cæca which secrete a digestive fluid; and to its right side is attached the red spleen. The liver is large, having usually, but not always, a gall-bladder; it pours its secretion into the upper intestine. In fishes which feed on plants the intestine is long, but it is short in those which eat flesh, because flesh is digested in the stomach, not in the intestines. The kidney is usually a long slender forked gland showing little variation. The egg-glands differ greatly in different sorts of fishes, the size and number of eggs varying equally. The air-bladder is a lung which has lost both lung structure and respiratory function, being simply a sac filled with gas secreted from the blood, and lying in the upper part of the abdominal cavity. It is subject to many variations. In the gar pike, bow-fin and the lung-fishes of the tropics, the air-bladder is a true lung used for breathing and connected by a sort of glottis with the œsophagus. In others it is rudimentary or even wholly wanting, while in still others its function as an air-sac is especially pronounced, and in many it is joined through the modified bones of the neck to the organ of hearing.

The blood of the fish is purified by circulation through its gills. These are a series of slender filaments attached to bony arches. Among them the blood flows in and out, coming in contact with the water which the fish takes in through its mouth and which passes across the gills to be expelled through the gill-openings. The blood is received from the body into the first chamber of the heart, a muscular sac called the auricle. From here it passes into the ventricle, a chamber with thicker walls, the contraction of which sends it to the gills, thence without return to the heart it passes over the body. The circulation of blood in fishes is slow, and the blood, which receives relatively little oxygen, is cold, being but little warmer than the water in which the individual fish lives.

Inside the cranium or brain-case is the brain, small and composed of ganglia which are smooth at the surface and contain little gray matter. At the posterior end of the brain is the thickened end of the spinal cord, called the medulla oblongata. Next overlapping this is the cerebellum, always single. Before this lie the largest pair of ganglia, the optic lobes or midbrain, round, smooth, and hollow. From the under side of these, nerves run to the eyes with or without a chiasma or crossing. In front of the optic lobes and smaller than them is the cerebrum or forebrain, usually of two ganglia but sometimes (in the sharks) united into one. In front of these are the small olfactory lobes which send nerves to the nostrils.

The sense organs are well developed. The sense of touch has in some fishes special organs for its better effectiveness. For instance certain fin-rays in some fishes, or, as in the catfish, slender, fleshy, whip-like processes on the head, are developed as feelers or special tactile organs. Other fishes, the sucker and loach for example, have specially sensitive lips and noses with which they explore their surroundings. The sense of taste does not seem to be well developed in this group. Taste-papillæ are often present in small numbers on the tongue or on the palate. The sense of smell is good. The olfactory organs, one on each side of the head, are hollow sac-like depressions, closed at the rear. In most cases each sac has two openings or nostrils. The sense of hearing is not very keen. The ears are fluid-filled sacs buried in the skull, and without external or (except in a few cases) internal opening. Fishes are far more sensitive to sudden jars or sudden movements than to any sound. They possess what is generally believed to be a special sense organ not found in other animals. This is the lateral line which extends along the sides of the body and which consists of a series of modified scales (each one with a mucous channel) richly supplied with nerves. The eyes are usually large and conspicuous. They differ mainly from the eyes of other vertebrates in their myopic spherical crystalline lens, made necessary by the density of the medium in which fishes live. There are usually no eyelids, the skin of the body being continuous but transparent over the eyes. Being near-sighted, fishes do not discriminate readily among forms, their special senses fitting them in general to distinguish motions of their enemies or prey rather than to ascertain exactly the nature of particular things.

The colors of fishes are in general appearance protective. Thus most individuals are white on the belly, mimicking the color of the sky to the enemy which pursues them from below. Seen from above most of them are greenish, like the water, or brownish gray and mottled, like the bottom. Those that live on sand are sand-colored, those on lava black, and those among rose-red sea-weeds bright red. In many cases, especially among kinds that are protected by their activity, brilliant colors and showy markings are developed. This is especially true among fishes of the coral reefs, though species scarcely less brilliant are found among the darters of our American brooks.

Among fresh-water fishes bright colors, crimson, scarlet, blue, creamy white, are developed in the breeding season, the then vigorous males being the most highly colored. Many of the feeble minnows even become very brilliant in the nuptial season of May and June. Color in fishes is formed by minute oil-sacs on the scales, and it often changes quickly with changes in the nervous condition of the individuals.

Development and life-history.—The breeding habits of fishes are extremely varied. Most fishes do not pair, but in some cases pairing takes place as among higher animals. Ordinarily fishes lay their eggs on the bottom in shallow water, either in brooks, lakes, or in the sea. The eggs of fishes are commonly called spawn, and egg-laying is referred to as spawning. The spawn of some fishes is esteemed a special food delicacy. Spring is the usual time of spawning, though some fishes spawn in summer and some even in winter; generally they move from their usual haunts for the purpose. The eggs of the different species vary much in size, ranging from an inch and a half in diameter (barn-door skate) down to the tiniest dots, like those of the herring. The number of eggs laid also varies greatly. The trout lays from 500 to 1,000, the salmon about 10,000, the herring 30,000 to 40,000, and some species of river fish 500,000, while certain flounders, sturgeons, and others each lay several millions of eggs. The adults rarely pay any attention to the eggs, which are hatched directly by the heat of the sun or by heat absorbed from the water. The length of incubation varies much. When the young fish leaves the egg-shell it carries, in the case of most species, a part of the yolk still hanging to its body. Its eyes are very large, and its fins are represented by thin strips of membrane. It usually undergoes no great changes in development from the first, resembling the adult except in size. But some of the ocean fishes show a metamorphosis almost as striking as that of insects or toads or frogs.

Some fishes build nests. Sticklebacks build elaborate nests in the brooks and defend them with spirit. Sunfishes do the same, but the nests are clumsier and not so well cared for.

The salmon is the type of fishes which run up from the sea to lay their eggs in fresh water. The king salmon of the Columbia River, for example, leaves the sea in the high waters of March and ascends without feeding for over a thousand miles, depositing its spawn in some small brook in the fall. After making this long journey to lay the eggs, the salmon become much exhausted, battered and worn, and are often attacked by parasitic fungi. They soon die, probably none of them ever surviving to lay eggs a second time.

Classification.—A fish is an aquatic vertebrate, fitted to breathe the air contained in water, and never developing fingers and toes. Accepting this broad general definition we find at once that there are very great differences among fishes. Some differ more from others than the ordinary forms differ from rabbits or birds. So although we have entitled this chapter as if all fishes belonged to the class Pisces, we cannot arrange them satisfactorily in less than three classes.

The lancelets (Leptocardii).—The lowest class of fish-like animals is that of the lancelets, the Leptocardii. These little creatures, translucent, buried in the sand, of the size and form of a small toothpick, are fishes reduced to their lowest terms. They have the form, life, and ways of a fish, but no differentiated skull, brain, heart, or eyes. Moreover they have no limbs, no jaws, no teeth, no scales. The few parts they do have are arranged as in a fish, and they show something in common with the fish embryo. Lacking a distinct head, the lancelets are put by some zoologists in a group called the Acrania, as opposed to the Craniata, which includes all the other vertebrates. Lancelets have been found in the North Atlantic and Mediterranean, on the west coast of North America, on the east coast of South America and on the coasts of Japan, Australia, New Zealand, the East Indies and Malayan Islands. The best-known members of the group belong to the genus Amphioxus. There are but one to two other genera in the class.

Fig. 113.—A lamprey, Petromyzon marinus. (After Goode.)

The lampreys and hag-fishes (Cyclostomata).—The next class of fish-like animals is that of the lampreys (fig. [113]) and hag-fishes, the Cyclostomata. The lampreys and hags are easily distinguished from the true fishes by their sucking mouth without jaws, their single median nostril, their eel-like shape and lack of lateral appendages or paired fins. The hag-fishes (Myxine), which are marine, attach themselves by means of a sucker-like mouth to living fishes (the cod particularly), gradually scraping and eating their way into the abdominal cavity of the fish. These hags or "borers" "approach most nearly to the condition of an internal parasite of any vertebrate." The lampreys, or lamprey-eels as they are often called because of their superficial resemblance to true eels, are both marine and fresh-water in their habitat, and most of them attach themselves to live fishes and suck their blood. They also feed on crustacea, insects, and worms. The brook-lamprey, Lampetra wilderi, is never parasitic. It reaches its full size in larval life and transforms simply for spawning. The sea- and lake-lampreys ascend small fresh-water streams when ready to lay their eggs, few living to return. Sometimes small piles of stones are made for nests. The young undergo a considerable metamorphosis in their development. The largest sea-lampreys reach a length of three feet. The common brook-lampreys are from eight to twelve inches long only.

The true fishes (Pisces).—All the other fish-like animals are grouped in the class Pisces. They are characterized, when compared with the lower fish-like forms just referred to, by the presence of jaws, shoulder girdle, and pelvic girdle. The class includes both the cartilaginous and bony fishes, and is divided into three sub-classes, namely, the Elasmobranchii, including the sharks, rays, skates, torpedoes, etc., the Holocephali, including the chimæras (a few strange-bodied forms), and the Teleostomi, including all the other fishes, as the trout, catfishes, darters, bass, herring, cod, mackerel, sturgeons, etc., etc.

The sharks, skates, etc. (Elasmobranchii).—The sharks and skates are characterized by the possession of a skeleton composed of cartilage and not bone, as in the bony fishes; they have no operculum; their teeth are distinct, often large and highly specialized, and their eggs are few and very large. There are two principal groups among Elasmobranchii, viz., the sharks, which usually have an elongate body, and always have the gill-openings on the sides, and the rays or skates, which have a broad flattened body with the gill-openings always on the under side. All the members of both groups are marine. The sharks are active, fierce, usually large fishes, which live in the surface-waters of the ocean and make war on other marine animals, all of the species except half a dozen being fish-eaters. The shark's mouth is on the under side of the usually conical head, and the animal often turns over on its back in order to seize its prey. The largest American sharks, and the largest of all fishes, are the great basking-sharks (Cetorhinus), which reach a length of nearly forty feet. They get their name from their habit of gathering in numbers and floating motionless on the surface. They feed chiefly on fishes.

The hammer-headed sharks (Sphyrna) are odd sharks which have the head mallet or kidney shaped, twice as wide as long, the eyes being situated on the ends of the lateral expansions of the head. The man-eating or great white sharks (Carcharodon) are nearly as large as the basking-sharks, and are extremely voracious. They will follow ships for long distances for the refuse thrown overboard. They do not hesitate to attack man. Among the more familiar smaller sharks are the dog-fishes and sand-sharks of our Atlantic coast.

The rays and skates are also carnivorous, but are with few exceptions sluggish, lying at the bottom of shallow shore-waters. They feed on crabs, molluscs, and bottom-fishes. The small common skates, "tobacco-boxes" (Raja erinacea) (fig. [114]), about twenty inches long, and the larger "barn-door skates" (R. lævis), are numerous along the Atlantic coast from Virginia northward. Especially interesting members of this group, because of the peculiar character of the injuries produced by them, are the sting-rays and torpedoes or electric-rays. The sting-rays (Dasyatis) have spines near the base of the tail which cause very painful wounds. The torpedoes (Narcine) have two large electrical organs, one on each side of the body just behind the head, with which they can give a strong electric shock. "The discharge from a large individual is sufficient to temporarily disable a man, and were these animals at all numerous they would prove dangerous to bathers." Very different from the typical rays in external appearance are the saw-fishes (Pristis pectinatis) which belong to this group. The body is elongate and shark-like, and has a long saw-like snout. This saw, which in large individuals may reach a length of six feet and a breadth of twelve inches, makes its owner formidable among the small sardines and herring-like fishes on which it feeds. The saw-fishes live in tropical rivers, descending to the sea.

Fig. 114.—The common skate, Raja erinacea. (From Kingsley.)

The bony fishes (Teleostomi).—The bony or true fishes are distinguished from the lampreys and sharks and rays by having in general the skeleton bony, not cartilaginous, the skull provided with membrane bones, and the eggs small and many. In this group are included all the fishes of our fresh-water lakes, ponds, and streams as well as most of the marine forms. Fish life, being spent under water, is not familiar to most of us, and beginning students are rarely helped enough in getting acquainted with the different kinds and the interesting habits of fishes. But they offer a field of study which is really of unusual interest and profit. We can refer in the following paragraphs to but few of the numerous common and readily found kinds, and to these but briefly.

Closely related to the sunfish, studied as example of the bony fishes, are the various kinds of bass, as the "crappie" (Pomoxis annularis), the calico bass (P. separoides), the rock-bass (Ambloplites rupestris) and the large-mouthed and small-mouthed black bass (Micropterus salmoides and M. dolomieu respectively). All the members of this sunfish and bass family are carnivorous fishes especially characteristic of the Mississippi valley.

Another family of many species especially common in the clear, swift, and strong Eastern rivers is that of the darters and perches. The darters are little slender-bodied fishes which lie motionless on the bottom, moving like a flash when disturbed and slipping under stones out of sight of their enemies. Some are most brilliantly colored, surpassing in this respect all other fresh-water fishes.

Unlike the sunfishes and darters are the catfishes, composing a great family, the Siluridæ. The catfish (Ameiurus) gets its name from the long feelers about its mouth; from these feelers also come its other names of horned pout, or bull-head. It has no scales, but its spines are sharp and often barbed or jagged and capable of making a severe wound.

Remotely allied to the catfish are the suckers, minnows, and chubs, with smooth scales, soft fins and soft bodies and the flesh full of small bones. These little fish are very numerous in species, some kinds swarming in all fresh water in America, Europe, and Asia. They usually swim in the open water, the prey of every carnivorous fish, making up by their fecundity and their insignificance for their lack of defensive armature. In some species the male is adorned in the spring with bright pigment, red, black, blue, or milk-white. In some cases, too, it has bony warts or horns on its head or body. Such forms are known to the boys as horned dace.

Most interesting to the angler are the fishes of the salmon and trout (fig. [115]) family, because they are gamy, beautiful, excellent as food and above all perhaps because they live in the swiftest and clearest waters in the most charming forests. The salmon live in the ocean most of their life, but ascend the rivers from the sea to deposit their eggs. The king salmon (Oncorhynchus tschawytscha) of the Columbia goes up the great river more than a thousand miles, taking the whole summer for it, and never feeding while in fresh water. Besides the different kinds of salmon, the black-spotted or true trout, the charr or red-spotted trout of various species, the whitefish (Coregonus), the grayling (Thymallus signifer) and the famous ayu of Japan belong to this family.

Fig. 115.—The rainbow-trout, Salmo iridens. (From specimen.)

In the sea are multitudes of fish forms arranged in many families. The myriad species of eels agree in having no ventral fins and in having the long flexible body of the snake. Most of them live in the sea, but the single genus (Anguilla) or true eel which ascends the rivers is exceedingly abundant and widely distributed. Most eels are extremely voracious, but some of them have mouths that would barely admit a pin-head. The codfish (Gadus callarias) is a creature of little beauty but of great usefulness, swarming in all arctic and subarctic seas. The herring (Clupea harengus), soft and weak in body, are more numerous in individuals than any other fishes. The flounders (fig. [116]) of many kinds lie flat on the sea-bottom. They have the head so twisted that the two eyes occur both together on the uppermost side. The members of the great mackerel tribe swim in the open sea, often in great schools. Largest and swiftest of these is the sword-fish (Xiphias gladius), in which the whole upper jaw is grown together to form a long bony sword, a weapon of offence that can pierce the wooden bottom of a boat.

Fig. 116.—The winter flounder, Pseudopleuronectes americanus. (After Goode.)

Many of the ocean fishes are of strange form and appearance. The sea-horses (Hippocampus sp.) (fig. [117]) are odd fishes covered with a bony shell and with the head having the physiognomy of that of a horse. They are little fishes rarely a foot long, and cling by their curved tails to floating seaweed. The pipefish (Syngnathus fuscum) is a sea-horse straightened out. The porcupine-fishes and swellfishes (Tetraodontidæ) have the power of filling the stomach with air which they gulp from the surface. They then escape from their pursuers by floating as a round spiny ball on the surface. The flying-fishes (Exocœtus) leap out of the water and sail for long distances through the air, like grasshoppers. They cannot flap their long pectoral fins and do not truly fly; nevertheless they move swiftly through the air and thus escape their pursuers. In its structure a flying-fish differs little from a pike or other ordinary fish.

Fig. 117.—A sea-horse, Hippocampus
heptagonus. (After
Goode.)

For an account of the fishes of North America see Jordan's "Manual of Vertebrates," eighth edition, pp. 5-173, and Jordan and Evermann's "Fishes of North and Middle America," where the 3,127 species known from our continent are described in detail with illustrative figures.

Habits and adaptations.—The chief part of a fish's life is devoted to eating, and as most fishes feed on other fishes, all are equally considerably occupied in providing for their own escape.

In general the provisions for seizing prey are confined to sharp teeth and the strong muscles which propel the caudal fin. But in some cases special contrivances appear. In one large group known collectively as the "anglers" the first spine of the dorsal fin hangs over the mouth. It has at its tip a fleshy appendage which serves as a bait. Little fishes nibble at this, the mouth opens, and they are gone. In the deep seas, many fishes are provided with phosphorescent spots or lanterns which light up the dark waters, and enable them to see their prey. In storms these lantern-fishes sometimes lose their bearings and are thrown upward to the surface.

In general the more predatory in its habits any fish is the sharper its teeth, and the broader its mouth. Among brook-fishes the pickerel has the largest mouth and the sharpest teeth. It has been called a "mere machine for the assimilation of other organisms." The trout has a large mouth and sharp teeth. It is a swift, voracious, and predatory fish, feeding even on its own kind. The sunfish is less greedy and its mouth and teeth are smaller, though it too eats other fish.

As means of escape, most fishes depend on their speed in swimming. But some hide among rocks and weeds, disguising themselves by a change in color to match their surroundings. Others, like the flounders and skates, lie flat on the bottom. Still others retreat to the shallows or the depths or the rock-pools or to any place safer than the open sea. Some are protected by spines which they erect when attacked. Some erect these spines only after they have been swallowed, tearing the stomach of their enemy and killing it, but too late to save themselves. Again in some species the spines are armed with poison which benumbs the enemy. Sometimes an electric battery about the head or on the sides gives the biting fish a severe shock and drives him away. Such batteries are found in the electric rays or torpedo, in the electric eel of Paraguay, the electric catfish of the Nile, the electric stargazer and other fishes.

Some fishes are protected by their poor and bitter flesh. Some have bony coats of mail and sometimes the coat of mail is covered with thorns, as in the porcupine-fish. This fish and various of its relatives have the habit of filling the stomach with air when disturbed, then floating belly upward, the thorny back only within reach of its enemies.

Fig. 118.—The remora, or cling fish, Remoropsis brachyptera. Note sucker on top of head. (After Goode.)

Many species (cling fishes) attach themselves to the rocks by a fleshy sucking-disk. Some (Remora) (fig. [118]) cling to larger fishes by a strange sucking-disk on the head, a transformed dorsal fin, being thus shielded from the attacks of fish smaller than their protectors. Some small fishes seek the shelter of the floating jellyfishes, lurking among their poisoned tentacles. Others creep into the masses of floating gulf-weed. Some creep into the shell of clams and snails. In the open channel of a sponge, the mouth of a tunicate and in similar cavities of various animals, little fishes may be found. A few fishes (hag-fishes) are parasitic on others, boring their way into the body and devouring the muscles with their rasp-like teeth.

Some fishes are provided with peculiar modifications of the gills which enable them to breathe for a time out of water. Such fish have the pectoral fins modified for a rather poor kind of locomotion on land, thus enabling them to move from pond to pond or from stream to stream. In cold climates the fishes must either migrate to warmer latitudes in winter, as some do, or withstand variously the cold, often freezing weather. Some fish can be frozen solid, and yet thaw out and resume active living. Some lie at the bottoms of deep pools through the colder periods, while many others, such as the minnows, chubs, and other kinds common in small streams, bury themselves in the mud, and lie dormant or asleep through the whole winter. On the other hand in countries where the long intense rainless summers dry up the pools, some fishes have the habit of burying themselves in the mud, which, with slime from the body, forms about them a sort of tight cement ball in which they lie dormant until the rains come. "Thus a lung-fish (called Protopterus), found in Asia and Africa, so completely slimes a ball of mud around it that it may live for more than one season, perhaps many; it has been dug up and sent to England, still enclosed in its round mud-case, and when it was placed in warm water it awoke as well as ever."

Food-fishes and fish-hatcheries.—Most fishes are suitable for food, though not all. Some are too small to be worth catching or too bony to be worth eating. Some of the larger ones, especially the sharks, are tough and rank. A few are bitter and in the tropics a number of species feed on poisonous coelenterates about the coral reefs, becoming themselves poisonous in turn. But a fish is rarely poisonous or unwholesome unless it takes poisonous food. Where fishes of a kind specially used for food gather in great numbers at certain seasons of the year, fishing is carried on extensively and with an elaborate equipment. Such fisheries, some of which have been long known, are scattered all over the world. Along the shores of the Mediterranean Sea, and on the coasts of Norway, France, the British Isles and Japan are numerous great fishing-places. But "nowhere are there found such large fisheries as those along the northern Atlantic coasts of our own continent, extending from Massachusetts to Labrador. Especially on the banks of Newfoundland are codfish, herring, and mackerel caught." Among our fresh-water fisheries the great salmon fisheries of the Penobscot and Columbia rivers and of the Karluk and other rivers of Alaska are the best known. The whitefish of our Great Lakes is also one of the important food-fishes of the world.

In many places fishes are raised in so-called hatcheries, not usually for immediate consumption but for the purpose of stocking ponds and streams either in the neighborhood of the hatchery or in distant waters which the special species cultivated has not been able naturally to reach. The eggs of some fishes are large and non-adherent, two features which greatly favor artificial impregnation and hatching. In the hatcheries the eggs are put first into warm water, where development begins; they are then removed into cool water, which arrests development without injury, making shipment possible. The eggs of salmon and trout in particular can be sent long distances to suitable streams or ponds. The eggs of the shad have been thus carried from the East to the streams of California and trout have been distributed to many streams in our country which by themselves they could never have reached.

The salmon is a conspicuous example of those fishes which can be artificially propagated. The eggs of the salmon are large, firm, and separate from each other. If the female fish be caught when the eggs are ripe and her body be pressed over a pan of water the eggs will flow out into the water. By a similar process the milt or male sperm-cells can be procured and poured over the eggs to fertilize them. The young after hatching are kept for a few days or weeks in artificial pools, till the yolk-sacs are absorbed and they can take care of themselves. They are then turned into the stream, where they drift tail foremost with the current and pass downward to the sea. All trout may be treated in similar fashion, but there are many food-fishes which cannot be handled in this way. In some the eggs are small or soft, or viscid and adhering in bunches. In others the life-habits make artificial fertilization impossible. Such species are artificially reared only by catching the young and taking them from one stream to another. To this type belong the black bass, the sunfish, the catfish and other familiar forms.

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[CHAPTER XXV]

BRANCH CHORDATA (Continued). CLASS BATRACHIA: THE BATRACHIANS

The structure, life-history, and habits of the garden-toad (Bufo lentiginosus) have already been studied (see Chapter [II] and Chapter [XII]).

OTHER BATRACHIANS.

The class Batrachia includes the animals familiarly known as cœcilians, sirens, mud-puppies, salamanders, toads, and frogs. Although differing plainly from fishes in appearance and habits, the batrachians are really closely related to them, resembling them in all but a few essential characters. Among the distinctive characters of batrachians may be noted the absence of fins supported by fin-rays, the presence usually of well-developed legs for walking or leaping, and the absence or reduction of certain bones of the head connected with the gills and lower jaw and which are well developed in the fishes. The batrachians stand in somewhat intermediate position between the fishes and the reptiles, showing some of the characters of both. They are, like fishes and reptiles, cold-blooded. In their adult condition some are terrestrial and some aquatic as to habitat, but all have an aquatic larval life. The water-inhabiting young breathe at first by means of gills, later lungs begin to develop, and for a time both gills and lungs are used in respiration. Finally in the adult condition in almost all of the forms the gills are wholly lost and breathing is done by the lungs and skin solely. Correlated with the change of habits from larval to adult stage there is usually a well-marked metamorphosis in post-embryonic development. This metamorphosis is specially striking among the frogs and toads. None of the aquatic forms is marine, salt water always killing eggs, larvæ or adults. Batrachians are found all over the world, although there are few in the extreme North. They are most abundant in warm and tropical lands.

Fig. 119.—The tiger salamander. (From Jenkins and Kellogg.)

Body form and organization.—The body varies from a long and slender, truly snake-like form as in the tropical cœcilians through the usual salamander (fig. [119]) shape, where it is more robust but still elongate and tailed, to the heavy, squat, tailless condition of the toads. Legs, with five digits, are usually present, and are used for swimming, walking, or leaping. The legs are longest and best developed in the short tailless frog and toad forms which are mostly terrestrial, and are short and weak in the tailed salamander forms, many of which are aquatic. The skin is almost always naked, showing a marked difference from the scaled condition of reptiles and most of the fishes, and its cells secrete a slimy, sticky, usually whitish fluid, which in some cases is irritating, or even poisonous. The skin is sometimes thrown up into folds or ridges, and in some species is elevated to form a kind of fin on the tail or back. This unpaired fin differs from the dorsal fin (and other fins) of fishes in not being supported by rayed processes of the skeleton. There are in some batrachians traces of an exoskeleton in the presence of scale-like structures in the skin or in the horny nails on the digits, but these cases are rare. The skin contains pigment-cells and many of the batrachians are brilliantly colored and patterned; some of the pigment is carried by special contractile or expansile cells, the chromatophores (see account of chromatophores of the Cephalopoda, p. [256]), so that the animal can change its tint and markings more or less rapidly. All the batrachians possess external gills in their aquatic larval stage, and in a few forms, as the sirens and mud-puppies, gills are retained all through life. These gills are branched folds of the skin abundantly supplied with blood-vessels.

In the organization of the batrachian body the usual vertebrate characters appear, the body-organs being arranged with reference to a supporting and protecting internal bony skeleton. The head is plainly set off from the rest of the body and bears the mouth and the organs of hearing and sight. Certain so-called lateral sense organs, the function of which is not exactly known, occur arranged in three lines on each side of the body of some of the forms. Both pairs of limbs are present and functional in almost all of the species. In the cœcilians the limbs are wholly wanting; in the sirens only the fore legs are present.

Structure.—The most obvious skeletal differences among batrachians are those due to variations in external form. While there are as many as 100 vertebræ in some of the elongate long-tailed salamanders (even 250 in the strange snake-like cœcilians), there are but 10 (the last or tenth being the rod-shaped bone called the urostyle) in the short, tailless frogs and toads. To any of the vertebræ except the first (the single cervical vertebra) and the last, ribs may be attached and the cœcilians have about as many pairs of ribs as vertebræ. In the frogs and toads, however, the ribs are lost. In any case they are never fastened by their lower ends to the breast-bone.

The alimentary canal is usually not much longer than the body and is plainly divided into mouth, pharynx, œsophagus, small intestine, large intestine or rectum, and anal opening. The teeth when present occur on both the jaws and the palate. They are small, sharp, point backward and are fused to the bones. They are wholly wanting in the toad and in some other allied forms. The tongue may be wanting, or may be immovably fixed to the floor of the mouth, or as in the frogs, fastened at its front end but free behind, so that the hinder end can be protruded far from the mouth for the purpose of catching insects.

The organs of respiration are gills, external and internal, lungs, trachea or windpipe, and the skin. In the earliest larval stages all batrachians have gills; later, in most cases, the gills become reduced and disappear, while at the same time lungs are developing. In some salamanders the lungs never develop, but the animals, in their adult stage, breathe wholly by means of the skin. In a few cases, as in the siren and mud-puppies, gills are retained through the whole life, although lungs are also present in the adult stage. The lungs are two in number, a right and a left lung, and are simple sacs with the walls more or less folded or thrown into ridges and richly supplied with blood-vessels. The front end of the lungs opens directly into the pharynx or, in the more elongate batrachians, is connected with it by a tubular trachea or windpipe. In the frogs and toads there are vocal cords stretched across the short windpipe; the vibration of these cords produces the croaking.

The heart is always three-chambered, consisting of the right and left auricles and a single ventricle. The circulation of the more generalized salamanders like the mud-puppies is essentially like that of a fish. In the frogs and toads there is a distinct advance beyond this condition. The red corpuscles of the blood are oval in shape and are the largest found among any of the vertebrates.

In the nervous system the small size of the hindbrain or cerebellum is noticeable. The sense organs are fairly well developed. The skin of the whole body is provided with tactile nerve-endings. There are special taste organs on the lining membrane of the tongue and mouth-cavity. The eyes have no lids in some of the lower forms; most of the frogs and toads have an upper lid but no under one, although a thin membrane, called the nictitating membrane, arises from the lower margin of the eye and can be drawn up over it. The ears have no external parts, other than the thin tympanic membranes. The nostrils of frogs and toads can be closed by the contraction of certain special muscles.

Life-history and habits.—The sexes are distinct, and in most cases the young hatch from eggs. A few of the salamanders give birth to free young. The eggs are usually in strings or chains enclosed in a clear gelatinous substance; these chains of eggs are either simply dropped into the water or are fastened to water-plants. The young, called tadpoles (fig. [120]), in their earlier larval stages are extremely fish-like in character, long-bodied, tailed, swimming freely about by means of the fin-like flattened tail, and breathing by means of external gills. Nor do they show any sign of legs. As the tadpoles grow and develop the legs begin to appear, the hind legs first in the frogs and toads, the fore legs first in the salamanders; lungs develop and the gills disappear (except in the cases of the few forms which retain gills through life). The tail shortens and finally disappears in the frogs and toads; with the salamanders the tail-fin only is lost. At the same time the change from water to land is made. Further growth is very slow; frogs are not really adult, that is, capable of producing young, until they are five years old, and they may continue to increase in size until they are ten years old.

Fig. 120.—Tadpoles. (Photograph from life by Cherry Kearton; permission of Cassel & Co.)

The food of the adult batrachians is almost exclusively small animals, particularly insects and worms. Crustaceans, snails, and young fish are also eaten. The tadpoles also eat vegetable matter. Almost all batrachians are nocturnal in habit, remaining concealed by day. In the zones in which cold winters occur they hibernate or pass the winter in a torpid condition, or state of "suspended animation," or, as it is said, they sleep through the winter. Frogs burrow into the mud at the bottom of ponds at the approach of winter and come forth early in the spring to lay their eggs. Most batrachians are very tenacious of life, being able to withstand long periods of fasting and serious mutilation, and most of them can regenerate certain lost parts, such as the tail or legs.

Classification.—The living Batrachia are divided into three orders, viz., the Urodela, including the sirens, mud-puppies, salamanders, and newts, batrachians which retain the tail throughout life, having generally two pairs of limbs of approximately equal size, and sometimes possessing gills or gill-slits in the adult condition; the Anura, or frogs and toads, with no tail in the adult condition, with short and broad trunk, with hind limbs greatly exceeding the fore limbs in size, and never with gills or gill-slits in the adult stage; and the Gymnophiona, or cæcilians, snake-like batrachians having neither limbs nor tail, with a dermal exoskeleton and without gills or gill-slits in the adult.

Mud-puppies, salamanders, etc. (Urodela).—Technical Note.—If possible obtain specimens of mud-eels (Siren), common in the South, or mud-puppies (Necturus), common in the central North, as examples of batrachians with gills persisting in the adult stage. One or more species of Amblystoma may be found in almost any part of the country, and larvæ of large size may be found with the external gills. For an example of the general long-tailed or Urodelous type of batrachian any salamander or newt occurring in the vicinity of the school may be used. The little green triton or eft (Diemictylus viridiscens) of the eastern States, or its larger brown-backed congener of the Pacific coast (D. torosus) is common in water, while another eft, the little red-backed salamander, (Plethodon) is common in the woods under logs and stones. The external characters of the body should be compared with those of the toad. The skeleton should be prepared by macerating away the flesh (for directions, see p. [452]), and the presence of the many caudal vertebræ and the ribs, the equality in size of the legs, and other points should be noted. Compare with skeleton of toad. Make drawings. It will be well, also, to dissect out and examine the various internal organs of the salamander, comparing them with the same organs in the toad. The salamander, indeed, is in many ways better than the toad as an example of the class. Its body is less adaptively modified and shows the essentially fish-like character of the batrachian structure.

The batrachians which retain external gills in the adult stage are the members of two families of which the American representatives are known as mud-eels (Siren) and mud-puppies or water-dogs (Necturus). The mud-eels, which are found "in the ditches in the swamps of the southern States from South Carolina to the Rio Grande of Texas and up the Mississippi as high as Alton, Illinois," are blackish in color, have no hind legs and are long and slender, with the tail shorter than the rest of the body. They reach a length of nearly three feet. The mud-puppies, found in the Great Lakes and in the rivers of the upper Mississippi valley, are brown with colored spots, and are about two feet long when full grown. They have both fore and hind legs.

A few salamanders, while not possessing external gills when adult, have a spiracle or small circular opening in the side of the neck which leads into the throat. The best-known American salamander of this kind is the large heavy-bodied blackish water-dog or "hellbender" (Cryptobranchus) of the Ohio River. It is about two feet long, and is "a very unprepossessing but harmless creature." It has a conspicuous longitudinal fold of skin along each side of the body. The largest known batrachian, the giant salamander of Japan (Megalobatrachus), reaching a length of three feet, is related to the water-dog.

Of all the salamanders the most interesting are the blunt-nosed salamanders (Amblystoma). A dozen or more species of Amblystoma occur in North America, of which tigrinum, a dark-brown species with many irregular yellow blotches sometimes arranged in cross-bands, is the most widespread. The larvæ of some Amblystoma retain their gills until they have reached a large size, and in one or two species the usual metamorphosis is very long delayed and the salamanders produce young while in the larval condition, that is, while retaining the gills and a compressed fin-like tail. In the case of a certain Mexican species (A. maculatum) it is believed that the final metamorphosis never occurs. The Mexicans call these gilled larval Amblystoma axolotls, and use them for food. For a long time naturalists supposed the Amblystoma larvæ which produce young to be the adults of a species of salamanders which retained their gills through life, like the sirens and mud-puppies, and classified them in a distinct genus.

Fig. 121.—The Western brown eft, or salamander, Diemyctylus torosus. (From living specimen.)

Of the various common salamanders or newts some are found in streams, ponds, and ditches, and some under logs and stones in the woods. The aquatic forms have the tail compressed (flattened from side to side), while the land forms have the tail cylindrical, tapering to a point. Most of the land-salamanders produce their young alive, while the water forms lay eggs which are usually attached to a submerged plant-stem. The salamanders are, almost without exception, found only in the northern hemisphere.

Frogs and toads (Anura).—There are about a dozen species of frogs in the United States. The largest of these, and indeed the largest of all the frogs, is the well-known bullfrog (Rana catesbiana), which reaches a length (head to posterior end of body) of eight inches. It is found in ponds and sluggish streams all over eastern United States and in the Mississippi valley. It is greenish in color with the head usually bright pale green. Its croaking is very deep and sonorous. The pickerel-frog (R. palustris), which is bright brown on the back with two rows of large oblong square blotches of dark brown on the back, is found in the mountains of eastern United States. The little pale reddish-brown wood-frog (R. sylvatica) with arms and legs barred above is common in damp woods and is "an almost silent frog." The peculiar and infrequently seen frogs known as the "spade-foots" (Scaphiopus) are subterranean in habit and usually live in dry fields or even on arid plains and deserts. They pass through their development and metamorphosis very rapidly, appearing immediately after a rain and laying their eggs in temporary pools. At this time of egg-laying they utter extraordinarily loud and strange cries. Some frogs in other parts of the world live in trees, and the eggs of one species are deposited on the leaves of trees, leaves which overhang the water being selected so that the issuing young may drop into it.

The true tree-frogs or tree-toads (Hylidæ) constitute a family especially well represented in tropical America. They have little disk- or pad-like swellings on the tips of their toes to enable them to hold firmly to the branches of the trees in which they live. Some, like the swamp tree-frog and the cricket-frog, are not arboreal in habit, remaining almost always on the ground. The common tree-frog of the eastern States (Hyla versicolor) is green, gray, or brown above with irregular dark blotches, and yellow below. It croaks or trills, especially at evening and in damp weather. Pickering's tree-frog (Hyla pickeringii) makes the "first note of spring" in the eastern States. This tree-frog is the one most frequently heard in the autumn too, but "its voice is less vivacious than in the spring and its lonely pipe in dry woodlands is always associated with goldenrods and asters and falling leaves." The tree-frogs of North America lay their eggs in the water on some fixed object as an aquatic plant, in smaller packets than those of the true frogs, and not in strings as do the toads.

The toads (Bufonidæ) differ from the true frogs in having no teeth and in not having, as the frogs do, a cartilaginous process uniting the shoulder-bones of the two sides of the body. The absence of this uniting process makes the thoracic region capable of great expansion. There are only a few species of toads in North America, but one of these species, the common American toad (Bufo lentiginosus), is very abundant and widespread. It appears also in two or three varieties, the common toad of the southern States differing in several particulars from that of the northern. The toad is a familiar inhabitant of gardens, and does much good by feeding on noxious insects. It is most active at twilight. Its eggs are laid in a single line in the centre of a long slender gelatinous string or rope, which is nearly always tangled and wound round some water-plant or stick near the shore on the bottom of a pond. The eggs are jet black and when freshly laid are nearly spherical. At the time of egg-laying the toads croak or call, making a sort of whistling sound and at the same time pronouncing deep in the throat "bu-rr-r-r-r." The toad does not open its mouth when croaking, but expands a large sac or resonator in its throat. The toad-tadpoles are blacker than those of frogs or salamanders, and undergo their metamorphosis while of smaller size than those of frogs. When they leave the water they travel for long distances, hopping along so vigorously that in a few days they may be as far as a mile from the pond where they were hatched. They conceal themselves by day, but will appear after a warm shower; this sudden appearance of many small toads sometimes gives rise to the false notion that they have fallen with the rain.

Cœcilians (Gymnophiona).—The third order of batrachians, the cœcilians, includes about twenty species of slender worm- or snake-like limbless forms which are confined to the tropics. Some of them are wholly blind and the others have only rudimentary eyes. In them the skin is folded at regular intervals so that the body appears to be rigid or segmented, and in some species there are small concealed horny scales in the skin.

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[CHAPTER XXVI]

BRANCH CHORDATA (Continued). CLASS REPTILIA: THE SNAKES, LIZARDS, TURTLES, CROCODILES, ETC.

THE GARTER SNAKE (Thamnophis sp.)

Technical Note.—Garter snakes may be found almost anywhere during the spring and summer months. If possible each student should have a specimen, but in case it is difficult to get enough snakes two students can use a single specimen. If garter snakes are rare, take any other snake. Snakes will live a long time without feeding and specimens should be kept alive until ready to use. Kill with chloroform as directed for the toad (p. 5). After completing the study of the external characters place each specimen in a dissecting-pan and with a pair of scissors cut through the scales on the ventral side, passing backwards from the eighteenth to the fortieth. Pin back the edges of the cut and thus expose the heart. Through its lower end, the ventricle, insert a large canula; inject with a fairly large syringe the glue mass which is described on p. 452. This injection will fill the entire arterial system. To inject the venous system make another cut through the ventral scales, cutting forward from the anal scale through about forty of them. Note the injected mass in some of the vessels already filled. Take one of the large vessels still containing blood and pass two ligatures beneath it. Get ready a small canula and cut a slit in the vessel, elevating the head so that the blood will run out as much as possible. Now wash the blood off, insert the canula in the slit and tie one ligature about the vessel containing the canula; have the other ready to tie after the vein has been injected. Use a new color for the venous system. Leave specimen in cold water for a time until the injection is hard. Then continue the cut from the anal plate forward to the lower jaw and pin out the edges of the cut on both sides in the dissecting-pan.

Structure (fig. [122]).—Note that the snake is covered with horny scales somewhat as the fish is. How do these scales differ from those of the fish? In snakes the scales are not bony, but are true skin structures. Note the modification of the scales on the head, back, and ventral surface. Those on the dorsal surface often have minute ridges, the keels. How do the ventral scales differ from the dorsal ones and others? By a system of muscles these ventral scales are rhythmically moved and as their posterior edges are pushed back against some resisting object the body glides forward. On the head note the pair of eyes. Are there eyelids? In front of each eye note an opening. What are these openings? Thrust a bristle into the opening and see where it enters the mouth-cavity through the internal nares. Does the snake have external ears? Observe the very long jaws and note that they are loosely hinged. Examine the inside of the mouth. Are there teeth? If so where are they situated, and how arranged? Note that all of the teeth point backwards. Food is not chewed. When some object of prey, a frog, or mouse, for example, is seized, the teeth hold it fast to the roof of the mouth and by a backward and forward movement of the lower jaws it is gradually drawn into the large œsophagus. What is the character and situation of the tongue? Just behind the tongue note the narrow slit, glottis, opening into the windpipe, or trachea. Back of the trachea opens the œsophagus.

When the snake is laid open the elongate heart will be conspicuous in the anterior third of the body. Insert a blowpipe or quill into the glottis just back of the tongue, and inflate the lung, which is a long, thin-walled bag extending from the region of the heart posteriorly for two-thirds of the length of the body. There is but one developed lung, the right; note at the anterior end of the lung a small mass of tissue, the atrophied left lung. Running forward from the lung is a long tube composed of incomplete cartilaginous rings, connected by membrane, the trachea. Note the long straight alimentary canal. Distinguish the œsophagus, stomach, intestine, rectum and the anus.

In the region of the lung is an elongated dark-red glandular mass, the liver. The secretion from the liver passes down through the long hepatic duct to the oval-shaped green gall-bladder and into the intestine.

Technical Note.—The bile-duct may be injected through the gall-bladder with some colored injecting mass.

Note that the duct running off from the gall-bladder to the intestine passes through a pink glandular organ, the pancreas. At the anterior end of the pancreas is a dark-red nodular structure, the spleen. The alimentary canal, the liver and the spleen are all suspended from the dorsal wall of the body-cavity by a delicate sheet of tissue. What is this? This condition we have also noted in the toad and fish.

Toward the posterior end of the body cavity are two long, dark-red glands, the kidneys, which are the principal excretory organs of the body. Through a long, slender tube (the ureter) each of the kidneys passes off its wastes. Where do the ureters open?

Anterior to the kidneys are the reproductive organs. The eggs, produced by the female snake, after being fertilized, pass backward through the egg-tubes. During the breeding season these tubes are much distended. This is due to the presence of the developing eggs, for the young snakes are hatched in the egg-tubes.

A successful injection as directed in the first technical note will have filled both arterial and venous systems. How does the general shape of the snake's heart compare with that of the toad? The heart consists of two ventricles, incompletely separated, and two auricles. In the snake the conus arteriosus is very much shortened and is not visible. Note two large vessels arising from the median portion of the ventricle. The one on the left side is the left aortic artery or left aortic arch, while the right gives off two branches. Where does the anterior one of these run? The main branch, or right aortic arch, passes back to meet its fellow, the left aortic artery, forming with it the dorsal aorta, which runs posteriorly to the end of the tail. Note the various branches given off by the dorsal aorta and trace some of them. Arising from the ventricles beneath the two aortic arches is the pulmonary artery, which goes to the lung. There the blood is purified, after which it is taken up by the pulmonary vein and carried back to the left auricle, whence it passes into the ventricle to be mixed with the impure blood from the right auricle. From the arteries the blood flows to all parts of the body through fine capillaries, bathing the tissues, giving off oxygen and taking up the carbonic acid gas. From these capillaries it passes into veins and so back to the heart; from the anterior end of the body through the jugular veins and from the posterior portion of the body through the postcaval vein. Flowing forward from the tail in the caudal vein, the blood enters the capillaries of the kidneys, where the waste matter is taken from it. This part of the circulatory system is known as the renal-portal circulation. From the kidneys the blood flows through the postcaval vein anteriorly to the heart.

The blood which passes out from the dorsal aorta to all parts of the alimentary canal is again collected into veins which unite to form the mesenteric vein. This vein runs to the liver, where it breaks up into capillaries. Thence the blood is carried into the postcaval vein, which leads directly to the heart. This part of the circulatory system which collects blood from the alimentary canal and carries it to the liver is called the hepatic-portal system.

Just in front of the heart will be noted a nodular structure, the thyroid gland, while a little in advance of the thyroid may be seen a long glandular mass, the thymus gland. The functions of these glands are not certainly understood.

Remove the alimentary canal and muscles from a part of the body and note that the axial skeleton, like that of the other vertebrates studied, consists of a series of vertebræ placed end to end. Are there arms or legs? Are shoulder and pelvic girdles present? How many of the vertebræ bear ribs? The ribs connect at their lower ends with the ventral scales. Note the great number of the vertebræ and ribs as compared with those of the toad or fish. What are those vertebræ called which bear no appendages or ribs? Examine carefully the elongated skull of the snake, especially the modified jaws. A detailed study of the skeleton may be made by referring to the account of the skeleton of the lizard in Parker's "Zootomy," pp. 130 et seq.

The nervous system may be worked out in a specimen which has been immersed in 20 per cent nitric acid. The description of the nervous system of the toad (see pp. [12]-[13]) will suffice for a guide to the study of the nervous system of the snake. The special sense organs, as eyes and ears, should be examined and compared with those of the fish and toad.

Life-history and habits.—The garter snakes are more or less aquatic in habit and are good swimmers. They are often found far from water, but in greatest abundance where the cat-tails and rushes grow thickest. They feed on frogs, salamanders, and field-mice, which they swallow whole. All the garter snakes are ovoviviparous, i.e., hatch eggs within the body-cavity. The eggs, often as many as eighteen or twenty, are enclosed within widened portions of the oviducts during embryonic existence; when the young are born they are able to shift for themselves. During cold weather the garter snake hibernates, hiding then in some gopher-hole, or, in the warmer climates, under some log or stone, there to lie dormant until the warm days of spring come, when it resumes activity.

The garter snake sheds its skin at least once a year, sometimes oftener. This process may be observed in snakes kept in confinement. For some time before molting the animal remains torpid, the eyes become milky, and the skin loses its lustre. After a few days it conceals itself, the skin about the lips and snout pulls away and the animal slips out of its entire skin. The snake not only sheds the skin of the body but also the covering of the eyes. Snakes have no eyelids, as we have already noted, that which represents the eyelid being a transparent membrane which covers the eyeball.

No species of the garter snake group is poisonous. Sometimes a garter snake may appear to be vicious, but its teeth are very short and at best it can only make a small scratch scarcely piercing the skin.

Fig. 122.—Dissection of the garter snake, Thamnophis sp.

OTHER REPTILES.

The class Reptilia includes the lizards, snakes, tortoises, turtles, crocodiles, and alligators. Although popularly associated in the common mind with the batrachians, the reptiles are really more nearly related to the birds than to the salamanders and frogs. In general shape they more nearly resemble the batrachians, but in the structural condition of the internal body organs they are more like the birds. They are cold-blooded, and breathe exclusively by means of lungs, the forms which live in water coming to the surface to breathe. They are covered with horny scales or plates, which with the entire absence of gills after hatching readily distinguish them from all the batrachians. While most reptiles live on land, some inhabit fresh water and some the ocean. As the young have the same habitat and general habits as the adult, there is no such metamorphosis in their life-history as is shown by the batrachians. The reptiles are widespread geographically, occurring, however, in greatest abundance in tropical regions, and being wholly absent from the Arctic zone. They are not capable of such migrations as are accomplished by the birds and many mammals, but withstand severely hot or cold seasons by passing into a state of suspended animation or seasonal sleep or torpor.

Fig. 123.—A lizard in the grass. (Photograph from life by Cherry Kearton; permission of Cassell & Co.)

Body form and organization.—The chief variations in body form among the reptiles are manifest when a turtle, lizard, and snake are compared. In the turtles, the body is short, flattened, and heavy, and provided always with four limbs, each terminating in a five-toed foot; in the lizards the body is more elongate and with usually four legs, but sometimes with two only, or even none at all; while in the snakes the long, slender, cylindrical body is legless or at most has mere rudiments of the hinder limbs. With the reptiles locomotion is as often effected by the bending or serpentine movements of the trunk as by the use of legs. Among lizards and snakes the body is covered with horny epidermal scales or plates, while among the turtles and crocodiles there may be, in addition to the epidermal plates, a real deposit of bone in the skin whereby the effectiveness of the armor is increased. The epidermal covering of snakes and lizards is periodically molted, or, as we say, the skin is shed. The bright colors and patterns of snakes and of many lizards are due to the presence and arrangement of pigment-cells in the skin. Among some reptiles, notably the chameleons, the colors and markings can be quickly and radically changed by an automatic change in the tension of the skin.

Structure.—In reptiles, as in batrachians, the chief variations in the body skeleton are correlated with differences in external body form. In the short compact body of the turtles and tortoises the number of vertebræ is much smaller than in the snakes. Some turtles have only 34 vertebræ; certain snakes as many as 400. The reptilian skull, in the number and disposition of its parts and in the manner of its attachment to the spinal column, resembles that of the birds, although the cranial bones remain separate, not fusing as in the birds. In the snake the two halves of the lower jaw are not fused in front but are united by elastic ligaments, which condition, together with the extremely mobile articulation of the base of the jaws, allows the snakes to open their mouths so as to take in bodies of great size. All of the reptiles, except the turtles, are provided with small teeth which serve, generally, for seizing or holding prey and not for mastication. The poisonous snakes have one or more long, sharp, and grooved or hollow fangs (fig. [131]). In the legless reptiles both shoulder and pelvic girdles may be wholly lacking; in the limbed forms both girdles are more or less well developed.

The tongue of many reptiles, notably the snakes, is bifid or forked, and is an extremely mobile and sensitive organ. The œsophagus is long and in the snakes can be stretched very wide so as to permit the swallowing of large animals whole. Reptiles breathe solely by lungs, of which there is a pair. They are simple and sac-like, the left lung being often much smaller than the other. In turtles and crocodiles the lungs are divided internally by septa into a number of chambers. Because of the rigidity of the carapace or "box" of turtles the air cannot be taken in the ordinary way by the use of the ribs and rib-muscles, but has to be swallowed. The reptilian heart consists of two distinct auricles and of two ventricles, which in most reptiles are only incompletely divided, the division into right and left ventricles being complete only among the crocodiles and alligators, the most highly organized of living reptiles.

The organs of the nervous system reach a considerable degree of development in the animals of this class. The brain in size and complexity is plainly superior to the batrachian brain and resembles quite closely that of birds. Of the organs of special sense those of touch are limited to special papillæ in the skin of certain snakes and many lizards. Taste seems to be little developed, but olfactory organs of considerable complexity are present in most forms, and consist of a pair of nostrils with olfactory papillæ on their inner surfaces. The ears vary much in degree of organization, crocodiles and alligators being the only reptiles with a well-defined outer ear. This consists of a dermal flap covering a tympanum. Eyes are always present and are highly developed. They resemble the eyes of birds in many particulars. All reptiles, excepting the snakes and a few lizards, have movable eyelids, including a nictitating membrane like that of the birds. With the snakes the eye is protected by the outer skin, which remains intact over it, but is transparent and thickened to form a lens just over the inner eye. Turtles and lizards have a ring of bony plates surrounding the eyes similar to that of the birds. In addition to the usual eyes there is in many lizards a remarkable eye-like organ, the so-called pineal eye, which is situated in the roof of the cranium, and is believed to be the vestige of a true third eye, which in ancient reptiles was probably a well-developed organ.

Life-history and habits.—Most reptiles lay eggs from which the young hatch after a longer or shorter period of incubation. Usually the eggs are simply dropped on the ground in suitable places (although certain turtles dig holes in which to deposit them), where they are incubated by the general warmth of the air and ground. However, some of the giant snakes, the pythons for instance, hold the eggs in the folds of the body. In the case of some snakes and lizards the eggs are retained in the body of the mother until the young hatch; such reptiles are said to be ovoviviparous, because the young, although born alive, are in reality enclosed in an egg until the moment of birth. Among reptiles the newly hatched young resemble the parents in most respects except in size, yet striking differences in coloration and pattern are not rare. But there is in this class no metamorphosis such as characterizes the post-embryonic development of the batrachians.

The food of reptiles consists almost exclusively of animal substance, although some species, notably the green turtles and certain land-tortoises, are vegetable-feeders. The animal-feeders are mostly predaceous, the smaller species catching worms and insects, while the larger forms capture fishes, frogs, birds, and their eggs, small mammals, and other reptiles.

Classification.—The living Reptilia are divided into four orders, of which one includes only a single genus, Hatteria, a peculiar lizard found in New Zealand. The other three are the Squamata, which includes the lizards and snakes,[17] distinguished by the scaly covering of the body, the Chelonia, which includes the tortoises and turtles, distinguished by the shell of bony plates which encloses the body, and the Crocodilia, which includes the crocodiles and alligators, whose bodies are covered with rows of sculptured bony scutes.

Tortoises and turtles (Chelonia).—Technical Note.—Obtain specimens of some pond- or land-turtle common in the vicinity of the school. The red-bellied and yellow-bellied terrapins (Pseudemys) or the painted or mud-turtles (Chrysemys) are common over most of the United States. (Pseudemys is found south of the Ohio River and Chrysemys north of it.) They may be raked up from creek-bottoms or fished for with strong hook and line, using meat as bait. They will live through the winter if kept in a cool place, without food or special care of any kind. Observe their swimming and diving, the retraction of head and limbs into the shell, the use of the third eyelid (nictitating membrane), and the swallowing of air.

Examine the external structure of a dead specimen (kill by thrusting a bit of cotton soaked with chloroform or ether into the windpipe; see opening just at base of tongue). Note shell consisting of a dorsal plate, the carapace, and ventral plate, the plastron, and the lateral uniting parts, the bridge. Note legs, and head with horny beak but no teeth. Compare with snake. The examination of the internal structure of the turtle can be readily made by sawing through the bridge on either side and removing the plastron. Note the ligaments which attach the plastron to the shoulder and pelvic girdles. Note muscles covering these bones. Note just behind the shoulder girdle the heart (perhaps still pulsating) and the dark liver on each side of it. Work out the alimentary canal, the trachea and lungs, and other principal organs, comparing them with those of the snake. The skeleton can be studied by dissecting and boiling and brushing away the flesh which still adheres to the bones. The comparison of the skeleton of the turtle with that of the snake is very instructive; marked differences in the skeletons of the two kinds of reptiles are obviously correlated with the differences in habits and shape of body. Note in the skeleton of the turtle especially the shoulder and pelvic girdles and limbs (absent in the snake) and small number of vertebræ and ribs.

Among the common turtles and tortoises of the United States are several species of soft-shelled turtles (Trionychidæ) with carapace not completely ossified and both carapace and plastron covered by a thick leathery skin which is flexible at the margins; the snapping-turtle (Chelydra serpentina), common in streams and ponds, with shell high in front and low behind and head and tail long and not capable of being withdrawn into the shell; the red-bellied and yellow-bellied terrapins (Pseudemys), red and yellow, with greenish-brown and black markings, common on the ground in woods and among rocks and also near water and sometimes in it; the pond- or mud-turtle (Chrysemys), also brightly colored and usually confined to ponds and pond-shores; and the box-tortoise (Cistudo carolina), common in woods and upland pastures and readily recognizable by its ability to enclose itself completely in its shell by the closing down of the lids of the plastron. All of these fresh-water and land-turtles except the soft-shelled turtles belong to one family, the Emydidæ, but have somewhat diverse habits. Most of them are carnivorous, but few catch any very active prey. While some are strictly aquatic, others are as strictly terrestrial, never entering the water. The eggs of all are oblong and are deposited in hollows, sometimes covered in sand. The newly hatched young are usually circular in shape, and vary in color and pattern from the parents.

The "diamond-back terrapin" (Malaclemmys palustris), used for food, is a salt-water form "inhabiting the marshes along the Atlantic coast from Massachusetts to Texas. About Charleston [and Baltimore] they are very abundant and are captured in large numbers for market, especially at the breeding season, when the females are full of eggs. Further north they are dug from the salt mud early in their hibernation and are greatly esteemed, being fat and savory."

Fig. 124.—The giant land-tortoise of the Galapagos Islands, Testudo sp. These tortoises reach a length of four feet. (Photograph from life by Geo. Coleman.)

Strongly contrasting with the usually small land- and fresh-water turtles are the great sea-turtles, such as the leather-back, the loggerhead and the green turtles. Some of these animals reach a length of six feet and more and a weight of nine hundred pounds, and have the feet compressed and fin-shaped for swimming. They live in the open ocean, coming on land only to lay their eggs, which are buried in the sand of ocean islands. These egg-laying visits are almost always made at night, and the turtles are then often caught by "turtlers." The flesh of most of the sea-turtles is used for food, and from the shell of certain species, notably the "hawk-bill" (Eretmochelys imbricata) the beautiful "tortoise-shell" used for making combs and other articles is obtained. The common green turtle (Chelonia mydas) of the Atlantic coast is the species most prized for food. It is a vegetarian, feeding on the roots of Zostera, the plant known in New England as eel-grass, though farther south it is called turtle-grass. When grazing the turtles eat only the roots, the tops thus rising to the surface, where they indicate to the turtler the animal's whereabouts. The turtler, armed with a strong steel barb attached to a rope and loosely fitted to the end of a pole, carefully rows up to the unsuspecting animal, and with a strong thrust plunges the barb through its shell, withdraws the pole, and, grasping the rope, now firmly attached to the turtle's back, lifts the animal to the surface. Here, with assistance, he turns it into the boat, where it is rendered helpless by being thrown on its back and by having its flippers tied. These turtles are also caught on their breeding-grounds, being found on the sand at night by the turtler, turned over on their backs, and left thus securely caught until assistance comes to help get them into the boats.

Snakes and lizards (Squamata).—Technical Note.—A snake has already been dissected and studied. It will be instructive to compare the external structures, at least, of a lizard with that of the snake. Specimens of some species of the common swift (Sceloporus) are obtainable almost anywhere in the United States. The "pine-lizards" of the east belong to this genus. Lizards may be sought for in woods, along fences, and especially on warm rocks.

Fig. 125.—The blue-tailed skink, Eumeces skeltonianus. (From living specimen.)

The group of lizards is a very large one, about 1,500 species being known, but it is represented in the United States by comparatively few species. Lizards are especially abundant in the tropics of South America. The strange and fantastic appearance presented by some of them has made certain species the object of much interest and often fear on the part of the natives of tropical lands. In those regions are current extraordinary stories and beliefs regarding the habits and attributes of certain lizards like the basilisk and chameleon. Lizards are all more or less elongate and some are truly snake-like in form. The legs, though usually present and functional, are in many cases much reduced, and in some forms, as the glass-snake, either one or both pairs are so rudimentary as to have no external projection whatever. Although lizards are often regarded as being poisonous, only one genus, Heloderma, the Gila Monster, is really so. All others are perfectly harmless as far as poison is concerned, and most of them are unusually timid. They vary in size from a few inches to six feet in length. Most of them are terrestrial, some arboreal, and some aquatic.

Fig. 126.—The Gila monster, Heloderma horridum, the only poisonous lizard. (Photograph from life by J. O. Snyder.)

Among the lizards of this country the swifts and ground-lizards are familiar everywhere. In certain regions the glass-snake or joint-snake (Opheosaurus ventralis) is common. This animal, popularly considered to be a snake, has no external limbs, and its tail is so brittle, the vertebræ composing it being very fragile, that part of it may break off at the slightest blow. In time a new tail is regenerated. It lives in the central and northern part of the United States, and burrows in dry places. In the western part of the country horned toads (Phrynosoma) are common, about ten different species being known. These are lizards with shortened and depressed body and well-developed legs. The body is covered with protective spiny protuberances, and in individual color and pattern resembles closely the soil, rocks, and cactus among which the particular horned toad lives. All the species of Phrynosoma are viviparous, seven or eight young being born alive at a time.

In New Mexico, Arizona, and northern Mexico the only existing poisonous lizards, the Gila Monster (Heloderma) (fig. [126]) is found. This is a heavy, deep-black, orange-mottled lizard about sixteen inches long. There is much variance of belief among people regarding the Gila Monster, but recent experiments have proved the poisonous nature of the animal. The poison which is secreted by glands in the lower jaw flows along the grooved teeth into the wound. A beautiful and interesting little lizard found in the South is the green chameleon (Anolis principalis). Its body is about three inches long with a slender tail of five or six inches. The normal color of the chameleon is grass-green, but it may "assume almost instantly shades varying from a beautiful emerald to a dark and iridescent bronze color."

In the tropics many of the lizards reach great size and are of strange shape and patterns. The flying dragons (Draco) have a sort of parachute on each side of the body composed of a fold of skin supported by five or six false posterior ribs. These lizards live in the trees of the East Indies and "fly" or sail from tree to tree. They are very beautifully colored. The iguanas (Iguana) of the tropics of South America are commonly used for food. They live mostly in trees, and reach a length of five or six feet. The monitor (Varanus niloticus) is a great water-lizard that lives in the Nile, and feeds on crocodiles' eggs, of which it destroys great numbers. It is the principal enemy of the crocodile. When full grown it reaches a length of six feet or even more.

About 1,000 living species of snakes are known. Usually they have the body regularly cylindrical, and without distinct division into body regions. Legs are wanting, locomotion being effected by the help of the scales and the ribs. No snake can move forward on a perfectly smooth surface and no snake can leap. In some forms, such as the pythons, external rudiments of the hind limbs are present, but do not aid in locomotion. The mouth is large and distensible so that prey of considerably greater size than the normal diameter of the snake's body is frequently swallowed whole. The sense of taste is very little if at all developed, as the food is swallowed without mastication. The tongue, which is protrusible and usually red or blue-black, serves as a special organ of touch. Hearing is poor, the ears being very little developed. The sense of sight is also probably not at all keen. Snakes rely chiefly on the sense of smell for finding their prey and their mates. The colors of snakes are often brilliant, and in many cases serve to produce an effective protective resemblance by harmonizing with the usual surroundings of the animal. The food of snakes consists almost exclusively of other animals, which are caught alive. Some of the poisonous snakes kill their prey before swallowing it, as do some of the constrictors. While most snakes live on the ground, some are semi-arboreal and others spend part or all of their time in water. Cold-region snakes spend the winter in a state of suspended animation; in the tropics, on the contrary, the hottest part of the year is spent by some species in a similar "sleep."

Fig. 127.—A garter snake, Thamnophis parietalis. (Photograph from life by J. O. Snyder.)

There are so many common snakes in the United States that only a few of the more familiar forms can be mentioned. The non-poisonous species of America belong to the family Colubridæ, while all but one of the poisonous species belong to the family Crotalidæ, characterized by the presence of a pair of erectile poison-fangs on the upper jaw. Among the commonest of the Colubridæ are the garter snakes (Thamnophis) (fig. [127]), always striped and not more than three feet long. The most widespread species is Thamnophis sirtalis, rather dully colored with three series of small dark spots along each side. The common water-snake (Natrix sipedon) is brownish with back and sides each with a series of about 80 large square dark blotches alternating with each other. It feeds on fishes and frogs, and although "unpleasant and ill-tempered" is harmless. One of the prettiest and most gentle of snakes is the familiar little greensnake (Cyclophis æstivus), common in the East and South in moist meadows and in bushes near the water. It feeds on insects and can be easily kept alive in confinement. A familiar larger snake is the blacksnake or blue racer (Bascaniom constrictor), "lustrous pitch black, general color greenish below and with white throat." It is "often found in the neighborhood of water, and is particularly partial to thickets of alders, where it can hunt for toads, mice, and birds, and being an excellent climber it is often seen among the branches of small trees and bushes, hunting for young birds in the nest." The chain-snake (Lampropeltis getulus) of the southeast and the king-snake (also a Lampropeltis) (fig. [128]) of the central States are beautiful lustrous black-and-yellow spotted snakes which feed not only on lizards, salamanders, small birds and mice but also on other snakes. The king-snake should be protected in regions infested by "rattlers." The spreading adder or blowing viper (Heterodon platirhinos), a common snake in the eastern States, brownish or reddish with dark dorsal and lateral blotches, depresses and expands the head when angry, hissing and threatening. Despite the popular belief in its poisonous nature this ugly reptile is quite harmless. It specially infests dry sandy places.

Fig. 128.—A king-snake, Lampropeltis boylii. (Photograph from life by J. O. Snyder.)

Fig. 129.—The gopher-snake, Pituophis bellona. (Photograph from life by J. O. Snyder.)

With the exception of the coral or beadsnake (Elaps fulvius), a rather small jet-black snake with seventeen broad yellow-bordered crimson rings, found in the southern States, the only poisonous snakes of the United States are the rattlesnakes and their immediate relatives, the copperhead and water-moccasin. These snakes all have a large triangular head, and the posterior tip of the body is, in the rattlesnakes, provided with a "rattle" composed of a series of partly overlapping thin horny capsules or cones of shape as shown in figure [130]. These horny pieces are simply the somewhat modified successively formed epidermal coverings of the tip of the body, which instead of being entirely molted as the rest of the skin is, are, because of their peculiar shape, loosely attached to one another, and by the basal one to the body of the snake. The number of rattles does not correspond to the snake's years for several reasons, partly because more than one rattle can be added to the tail in a year, and especially because rattles are easily and often broken off. As many as thirty rattles have been found on one snake. There are two species of ground-rattlesnakes or massasaugas (Sistrurus) in the United States and ten species of the true rattlesnakes (Crotalus). The centre of distribution of the rattlesnakes is the dry tablelands of the southwest in New Mexico, Arizona, and Texas. But there are few localities in the United States outside the high mountains in which "rattlers" do not occur or did not occur before they were exterminated by man. The copperhead (Agkistrodon contortix) is light chestnut in color, with inverted Y-shaped darker blotches on the sides, and seldom exceeds three feet in length. It occurs in the eastern and middle United States from Pennsylvania and Nebraska southward. It is a vicious and dangerous snake, striking without warning. The water-moccasin (Agkistrodon piscivorous) is dark chestnut-brown with darker markings. The head is purplish black above. It is found along the Atlantic and Gulf coasts from North Carolina to Mexico, extending also some distance up the Mississippi valley. It is distinctively a water-snake, being found in damp swampy places or actually in water. It reaches a length of over four feet and is a very venomous snake, striking on the slightest provocation. The common harmless water-snake is often called water-moccasin in the southern States, being popularly confounded with this most dangerous of our serpents. The poison of all of these snakes is a rather yellowish, transparent, sticky fluid secreted by glands in the head, from which it flows through the hollow maxillary fangs. The character and position of the fangs are shown in figure [131]. Remedial measures for the bite of poisonous snakes are, first, to stop, if possible, the flow of blood from the wound to the heart, by compressing the veins between the wound and heart, then to suck (if the lips are unbroken) the poison from the wound, next to introduce by hypodermic injection permanganate of potash, bichloride of mercury or chromic acid into the wound, and finally perhaps to take some strong stimulant as brandy or whiskey.

Fig. 130.—The rattles of the rattlesnake; the lower figure shows a longitudinal section of the rattle.

Fig. 131.—Dissection of head of rattlesnake; f, poison-fangs; p, poison-sac.

Of the kinds of snakes not found in this country perhaps the most interesting are the gigantic boa constrictors, anacondas, and pythons. Pythons are found in India, the islands of the Malay archipelago, and Australia, while the boas and anacondas live in the tropics of America. The largest pythons reach a length of thirty feet and some of the boas are nearly as large. These snakes feed on small mammals such as fawns, kids, water-rats, etc., and birds. The prey is swallowed whole, being first encircled and crushed to death in folds of the body. After a meal the python or boa lies in a sort of torpor for some time. A famous snake is the deadly cobra-da-capello of India. These snakes are so abundant and the bite is so nearly certainly fatal that thousands of persons are killed each year in India by it. Other extremely poisonous snakes are the vipers (Vipera cerastes), which live in the hot deserts of northern Africa. Over each eye there is a scaly spine or horn, from which the name horned viper is derived. The most poisonous snake of South Africa is the large and ugly puff-adder, which puffs itself up when irritated. An interesting group of snakes is that of the Hydrophidæ or sea-snakes, which swim on the surface of the ocean by means of their flattened and oar-like tails. These forms live in the tropical portions of the Indian and Pacific oceans, ranging as far north as the Gulf of California, and spend their whole life in the water, "out of which they appear to be blind and soon die." They are extremely venomous, but are all of small size, rarely two feet long.

Crocodiles and alligators (Crocodilia).—The crocodiles and alligators are reptiles familiar by name and appearance, though seen in nature only by inhabitants or visitors in tropical and semitropical lands. In the United States there are two species of these great reptiles, the American crocodile (Crocodilus americanus), living in the West Indies and South America and occasionally found in Florida, and the American alligator (Alligator mississippiensis), common in the morasses and stagnant pools of the southern States. The alligator differs from the crocodiles in having a broader snout. It is rarely more than twelve feet long. The best-known crocodile is the Nile crocodile, which is not limited to the Nile, but is found throughout Africa. In the Ganges of India is found another member of this group of reptiles called the gavial. It is among the largest of the order, reaching a length of twenty feet. The crocodiles, alligators, and gavials comprise not more than a score of species altogether, but because of their wide distribution, great size, and carnivorous habits they are among the most conspicuous of the larger living animals. They live mostly in the water, going on land to sun themselves or to lay their eggs. They move very quickly and swiftly in water but are awkward on land. Fish, aquatic mammals and other animals which occasionally visit the water are their prey. The gavial and Nile crocodile are both known to attack and devour human beings, and these species annually cause a considerable loss of life. But few such fatalities, however, are accredited to the American alligator.

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[CHAPTER XXVII]

BRANCH CHORDATA (Continued). CLASS AVES: THE BIRDS

THE ENGLISH SPARROW (Passer domesticus)

Technical Note.—The English sparrow may be found now in cities and villages all over the United States. It has become a veritable pest, and the killing of the few needed for the laboratory may be looked on as desirable rather than deplorable, as is the killing of birds in almost all other cases. The males have a black throat, with the other head-markings strong and contrasting (black, brown, and white), while the females have a uniform grayish and brownish coloration on the head.

Specimens are best taken alive, as shooting usually injures them for dissection. One can rely on the ingenuity of the boys of the class to procure a sufficient number of specimens. Observations on the habits of the birds should be made by the pupils as they go to and from school. For dissection use fresh specimens if possible. If desirable a pigeon or dove may be used in place of the sparrow.

External structure.—Note in the sparrow the same general arrangement of body parts as in the toad, the body being divided into head, upper limbs, trunk, and lower limbs. In the toad, however, all of the limbs are fitted for walking and jumping, whereas in the sparrow the anterior pair of appendages, the wings, are modified to be organs of flight, and the posterior limbs are specially adapted for perching. Note that the sparrow is covered with feathers, some long, some short, in some places thick and in others thin, but all fitting together to form a complete covering for the body. Note also that the anterior end of the head is prolonged into a hard bony structure, the bill, covered with horny substance. This horny substance together with the feathers and horny covering of the feet are modified portions of the skin. Note the long quill-feathers attached to the posterior edge of the wing. By these the bird sustains its flight. Other long quill-feathers are attached to the posterior end of the body, forming the tail. By a system of muscles connected with these feathers they act together, serving as a rudder during flight and as a balancing contrivance when perching. Note just above the bill two openings protected by tufts of feathers. What are these openings? How are they connected with the mouth? Note the large eyes, and at the inner angle of each the delicate nictitating membrane which can be drawn over the ball. Does the bird have external ears? Lift the feathers just above the tail (the upper tail-coverts) and note a small median gland, the oil-gland, from which the bird derives the oil with which it oils its feathers. Beneath the tail note the opening from the alimentary canal and from the kidneys and reproductive organs. This is called the cloacal opening.

Examine in detail some of the feathers. In one of the quill-feathers note the central stem or shaft composed of two parts, a basal hollow quill, which bears no web and by which the feather is inserted in the skin, and a longer, terminal, four-sided portion, the rachis, which bears on either side a web or vane. Each vane is composed of many narrow linear plates, the barbs, from which rise (like miniature vanes) many barbules. Each barbule bears many fine barbicels and hamuli or hooklets. The barbs of the feather are interlocked. How is this effected? The feathers which overlie the whole body and bear the color pattern are called contour-feathers. How do they differ from or correspond with the quill-feathers in structure? Soft feathers called down-feathers or plumules, cover the body more or less completely, being, however, mostly hidden by the contour-feathers; the barbs of these are sometimes not borne on a rachis, but arise as a tuft from the end of the quill. Certain other feathers which have an extremely slender stem and usually no vane, except a small terminal tuft of barbs, are called thread-feathers, or filoplumules. They are rather long, but are mostly hidden by the contour-feathers. In certain birds they stand out conspicuously, as the vibrissæ about the nostrils.

In the determination of birds by the use of a classificatory "key" (see p. [359]) it is necessary to be familiar with the names applied to the various external regions of the body and plumage, and with the terms used to denote the special varying conditions of these parts. By reference to figure [133] the names of the regions or parts most commonly referred to may be learned. A full account of all of the external characters with definitions of the various terms used in referring to them may be found in Coues's "Key to North American Birds."

Fig. 133.—Diagrammatic outline of bird's body with names of external parts and regions.

Technical Note.—Pull the feathers from the body, being careful not to tear the skin.

In the fish and toad, already studied, the head is closely joined to the trunk. How is it with the bird? Observe that the knee of the sparrow is covered by feathers and that it is the ankle which extends down as the bare unfeathered part to the digits. How many digits have the feet of the bird? How are they arranged?

Internal structure (fig. [132]).—Technical Note.—With a pair of scissors cut just beneath the skin anteriorly from the cloacal opening to the angle of the lower jaw. Pin the sparrow on its back by the wings, feet, and bill. Push back the skin from both sides and pin out.

Fig. 132.—Dissection of the English sparrow, Passer domesticus.

Note the large powerful pectoral muscles. Note a hard median projection of bone, the sternum, which is a large keel-shaped bone with lateral expansions to which are attached the ribs. Where are the largest and most powerful muscles of the toad located? Where are they in the fish? In the bird the most powerful muscles are these pectoral muscles, which move the wings in flight.

Technical Note.—Cut the pectoral muscles from the left side of the sternum, push back and pin to one side. With a strong pair of scissors cut through the ribs on the left side of the sternum and through the overlying bones. Lift the whole sternum, with the right pectoral muscle attached, to the left side of the pan and pin it down. Cut through the membrane which covers the viscera and cover the dissection with water.

In this operation note the V-shaped wishbone in front of the sternum. It is composed of the two clavicles with their inner ends fused. Note the stout coracoid bones extending from the anterior end of the sternum to the shoulder.

Note near the middle of the body the heart with the large blood-vessels proceeding from it. Behind the heart lies the large reddish-brown liver, and on the left side below the liver is the large gizzard or muscular stomach. Note the viscera folded over themselves in the body-cavity. Push them temporarily aside and note in the dorsal region under the heart large pinkish spongy sacs, the lungs. These are attached by short tubes, the bronchi, to the long cartilaginous trachea. At the union of the bronchi with the trachea is a small expansion with cartilaginous walls, within which are stretched small bands of muscles. This organ is the syrinx, the song- or voice-apparatus of the bird. It should be cut open and carefully examined. Trace the trachea forward to its anterior end. It opens by a glottis into the larynx, a slightly swollen chamber with cartilaginous walls. Note the U-shaped hyoid bone surrounding the front of the glottis. Through a blowpipe or quill inserted into the glottis blow air into the trachea and observe the inflation of the lungs and of certain large air-sacs in the abdomen, which communicate with them.

Beneath the trachea note the long œsophagus. Inflate the œsophagus with a blowpipe and note how distensible is its lower end near the breast. This distensible portion is called the crop. If the alimentary canal be drawn out straight the œsophagus will be found to run as an almost straight tube down the left side of the body to the gizzard. This latter organ has very thick muscular walls and in it the food is ground up among the small bits of gravel it contains. Extending from the gizzard near the entrance of the œsophagus note the long pyloric loop of the intestine called duodenum. Within this loop is a long pinkish gland, the pancreas, which empties by a duct into the duodenum. Into the duodenum also the overlying liver empties its secretion of bile from the median-placed gall-bladder. From the duodenum the small intestine or ileum extends with many convolutions to its exit through the cloacal aperture. On the intestine near the cloacal opening note a pair of glandular structures, the cæca. The short part of intestine between the cæca and cloaca is called the rectum. On the left side of the body beneath the gizzard note a dark glandular structure, the spleen.

Make a drawing of the dissection as so far worked out.

Technical Note.—Remove the alimentary canal, cutting it free posteriorly at the cæca and anteriorly just above the muscular gizzard. Cut open the gizzard and note its structure. The contained sand and gravel grains are picked up by the bird as it eats.

On either side of the throat note the well-defined thyroid gland; in young sparrows will be noted on each side of the neck a mass of tissue, the remains of the thymus gland, which disappears in the adult.

Cut transversely through the lower end of the heart and note that the ventricles are wholly distinct, whereas in the toad and snake they are incompletely separated. In the bird there is a complete double circulation. Its blood is not mixed, the pure with the impure, as in the toad and snake. Blood passing through the right auricle and ventricle goes to the lungs; on its return to the heart purified, it enters the left auricle and left ventricle thence to pass out over the body through the arteries.

Note the large aorta given off from the left ventricle. Note the two large branches, the innominate arteries, given off by it near its origin. Each innominate divides into three smaller arteries, a carotid, branchial, and pectoral. The aorta itself turns toward the back and continues posteriorly through the body as the dorsal aorta. To the right auricle come three large veins, the right and left præcavæ and the postcava. Each præcava is formed by three veins, the jugular from the head, the branchial from the wing, and the pectoral from the pectoral muscles. The postcava comes from the liver. From the right ventricle go the short right and left pulmonary arteries to the lungs, and from the lungs the blood is brought to the left auricle through the right and left pulmonary veins.

Technical Note.—For a detailed study of the circulation of the bird the teacher should inject the blood system of some larger bird, as a pigeon or fowl, for a class-demonstration. (For a guide, use Parker's "Zootomy," p. 209, or Martin and Moale's "How to Dissect a Bird," pp. 135-140 and pp. 148, 149.)

In the posterior dorsal region of the body-cavity will be found large three-lobed organs fitting into the spaces between the bones of the back on either side. These are the kidneys, and from their outer margins on each side a ureter runs posteriorly into the cloaca. Overlying the anterior ends of the kidneys are the reproductive organs. In the male these glands consist of firm, whitish, glandular bodies. From each runs a long convoluted vas deferens, which enters the cloaca. This tube corresponds to the egg-duct of the female. In the female the right egg-gland and egg-duct or oviduct are wanting. The left egg-gland appears as a glandular mass; during the breeding season yellow ova or eggs in various stages of development project from its surface. The oviduct opens by a funnel-shaped mouth near the egg-gland and runs thence to the cloaca. The eggs pass from the egg-gland into the body-cavity, where they are caught in the upper end of the oviduct and carried down and out through the cloacal opening. It is in the oviduct that the egg derives its accessory covering, which consists of a white or albuminous portion, together with several enveloping membranes and the hard shell enclosing all.

Remove the top of the skull and note the large brain. What portions of the brain make up the greater part of it? Note the differences between this brain and that of the toad. Trace the principal cranial nerves. Work out the spinal cord and principal spinal nerves. For an account of the nervous system of the sparrow see Martin and Moale's "How to Dissect a Bird," pp. 150-163.

Technical Note.—For a study of the skeleton of the sparrow a specimen should be cleaned by boiling in a soap-solution (see p. [452]).

In the sparrow's skeleton note the compactness of the skull and the fusion of its bones. Observe the long cervical vertebræ which support the skull, also the thoracic vertebræ bearing the ribs and sternum. How many of each of these kinds of vertebræ are there? The vertebræ posterior to the thorax are more or less fused together to form the sacrum, which, with the pelvic girdle, supports the leg-bones. The bones of the tail consist of a number of very small vertebræ, some of which are fused together. Note the correspondence between the bones of the leg and those of the wing. What are the names of each of the bones of each limb, and what are the corresponding bones in the two limbs? The wings and legs being modified for different uses, their various bones have assumed different relations to each other and to the body, for they are bent at directly opposite angles and the attachment of muscles is different. Compare the skeleton of the bird with that of the toad. (For a detailed account of the skeleton of the bird see Parker's "Zootomy," pp. 182-209, or Martin and Moale's "How to Dissect a Bird," pp. 102-125.)

Life-history and habits.—The English sparrow was first introduced into the United States in 1850, and since that time has rapidly populated most of the cities and towns of the country. On account of its extreme adaptability to surroundings, its omnivorous food-habits and its fecundity it survives where other birds would die out. It also crowds out and has caused the disappearance or death of other birds more attractive and more useful. The sparrow annually rears five or six broods of young, laying from six to ten eggs at each sitting. Had it no enemies a single pair of sparrows would multiply to a most astonishing number. The sparrow has, however, a number of enemies, most common among them perhaps being the "small boy," but birds and mammals play the chief part in the destruction. The smaller hawks prey upon them, and rats and mice destroy great numbers of their young and of their eggs whenever the nests can be reached. The sparrow is omnivorous and when driven to it is a loathsome scavenger, though at other times its tastes are for dainty fruits. Its senses of perception are of the keenest; it can determine friend or foe at long range. The nesting habits are simple, the nests being roughly made of any sort of twigs and stems mixed with hair and feathers and placed in cornices or trees. A maple-tree in a small Missouri town contained at one time thirty-seven of these nests.

OTHER BIRDS.

Birds are readily and unmistakably distinguishable from all other kinds of animals by their feathers. They are further distinguished from the reptiles on one hand by their possession of a complete double circulation and by their warm blood (normally of a temperature of from 100-112° F.), and from the mammals on the other by the absence of milk-glands. There are about 10,000 known species of living birds; they occur in all countries, being most numerous and varied in the tropics. Birds are exceptionally available animals for the special attention of beginning students, because of their abundance and conspicuousness and the readiness with which their varied and interesting habits may be observed. The bright colors and characteristic manners which make the identification of the different kinds easy, the songs and flight, and the feeding, nesting and general domestic habits of birds are all excellent subjects for personal field-studies by the students. We shall therefore devote more attention to the birds than to the other classes of vertebrates, just as we selected the insects among the invertebrates for special consideration.

Body form and structure.—The general body form and external appearance of a bird are too familiar to need description. The covering of feathers, the modification of the fore limbs into wings, and the toothless, beaked mouth are characteristic and distinguishing external features. The feathers, although covering the whole of the surface of the body, are not uniformly distributed, but are grouped in tracts called pterylæ, separated by bare or downy spaces called apteria. They are of several kinds, the short soft plumules or down-feathers, the large stiffer contour-feathers, whose ends form the outermost covering of the body, the quill-feathers of the wings and tail, and the fine bristles or vibrissæ about the eyes and nostrils called thread-feathers. The fore limbs are modified to serve as wings, which are well developed in almost all birds. However, the strange Kiwi or Apteryx of New Zealand with hair-like feathers is almost wingless, and the penguins have the wings so reduced as to be incapable of flight, but serving as flippers to aid in swimming underneath the water. The ostriches and cassowaries also have only rudimentary wings and are not able to fly. Legs are present and functional in all birds, varying in relative length, shape of feet, etc., to suit the special perching, running, wading, or swimming habits of the various kinds. Living birds are toothless, although certain extinct forms, known through fossils, had large teeth set in sockets on both jaws. The place of teeth is taken, as far as may be, by the bill or beak formed of the two jaws, projecting forward and tapering more or less abruptly to a point. In most birds the jaws or mandibles are covered by a horny sheath. In some water and shore forms the mandibular covering is soft and leathery. The range in size of birds is indicated by comparing a humming-bird with an ostrich.

Many of the bones of birds are hollow and contain air. The air-spaces in them connect with air-sacs in the body, which connect in turn with the lungs. Thus a bird's body contains a large amount of air, a condition helpful of course in flight. The breast-bone is usually provided with a marked ridge or keel for the attachment of the large and powerful muscles that move the wings, but in those birds like the ostriches, which do not fly and have only rudimentary wings, this keel is greatly reduced or wholly wanting. The fore limbs or wings are terminated by three "fingers" only; the legs have usually four, although a few birds have only three toes and the ostriches but two.

As birds have no teeth with which to masticate their food, a special region of the alimentary canal, the gizzard, is provided with strong muscles and a hard and rough inner surface by means of which the food is crushed. Seed-eating birds have the gizzard especially well developed, and some birds take small stones into the gizzard to assist in the grinding. The lungs of birds are more complex than those of batrachians and reptiles, being divided into small spaces by numerous membranous partitions. They are not lobed as in mammals, and do not lie free in the body-cavity, but are fixed to the inner dorsal region of the body. Connected with the lungs are the air-sacs already referred to, which are in turn connected with the air-spaces in the hollow bones. By this arrangement the bird can fill with air not only its lungs but all the special air-sacs and spaces and thus greatly lower its specific gravity. The vocal utterances of birds are produced by the vocal cords of the syrinx or lower larynx, situated at the lower end of the trachea just where it divides into the two bronchial tubes, the tracheal rings being here modified so as to produce a voice-box containing two vocal cords controlled by five or six pairs of muscles. The air passing through the voice-box strikes against the vocal cords, the tension of which can be varied by the muscles. In mammals the voice-organ is at the upper or throat end of the trachea.

The heart of birds is composed of four distinct chambers, the septum between the two ventricles, incomplete in the Reptilia, being in this group complete. There is thus no mixing of arterial and venous blood in the heart. The systemic blood-circulation being completely separated from the pulmonic, the circulation is said to be double. The circulation of birds is active and intense; they have the hottest blood and the quickest pulse of all animals. In them the brain is compact and large, and more highly developed than in batrachians and reptiles, but the cerebrum has no convolutions as in the mammals. Of the special senses the organs of touch and taste are apparently not keen; those of smell, hearing, and sight are well developed. The optic lobes of the brain are of great size, relatively, compared with those of other vertebrate brains, and there is no doubt that the sight of birds is keen and effective. The power of accommodation or of quickly changing the focus of the eye is highly perfected. The structure of the ear is comparatively simple, there being ordinarily no external ear, other than a simple opening. The organs of the inner ear, however, are well developed, and birds undoubtedly have excellent hearing. The nostrils open upon the beak, and the nasal chambers are not at all complex, the smelling surface being not very extensive. It is probable that the sense of smell is not, as a rule, especially keen.

Development and life-history.—All birds are hatched from eggs, which undergo a longer or shorter period of incubation outside the body of the mother, and which are, in most cases, laid in a nest and incubated by the parents. The eggs are fertilized within the body of the female, the mating time of most birds being in the spring or early summer. Some kinds, the English sparrow, for example, rear numerous broods each year, but most species have only one or at most two. The eggs vary greatly in size and color-markings, and in number from one, as with many of the Arctic ocean birds, to six or ten, as with most of the familiar song-birds, or from ten to twenty, as with some of the pheasants and grouse. The duration of incubation (outside the body) varies from ten to thirty days among the more familiar birds, to nearly fifty among the ostriches. The temperature necessary for incubation is about 40° C. (100° F.). Among polygamous birds (species in which a male mates with several or many females) the males take no part in the incubation and little or none in the care of the hatched young; among most monogamous birds, however, the male helps to build the nest, takes his turn at sitting on the eggs, and is active in bringing food for the young, and in defending them from enemies. The young, when ready to hatch, break the egg-shell with the "egg-tooth," a horny pointed projection on the upper mandible, and emerge either blind and almost naked, dependent upon the parents for food until able to fly (altricial young), or with eyes open and with body covered with down, and able in a few hours to feed themselves (precocial young).

Fig. 134.—The nest and eggs of the black phœbe, Sayornis nigricans. (Photograph by J. O. Snyder.)

More details regarding the eggs, nest, and young of birds will be given later in this chapter.

Classification.—The class Aves is usually divided into numerous orders, the number and limits of these as published in zoological manuals varying according to the opinions of various zoologists. The rank of an order in this group is far lower than in most other classes. In other words, the orders are very much alike and are recognized mainly for the convenience in breaking up the vast assemblage of species. In North America practically all the ornithologists have agreed upon a scheme of classification, which will therefore be adopted in this book. According to this classification the eight hundred (approximately) known species of North American birds represent seventeen orders. Certain recognized orders, for example, the ostriches, are not represented naturally in North America at all. As birds can usually be readily identified, the species being easily distinguished by general external appearance, and as there are many excellent book-guides to their classification, the beginning student can specially well begin with them his study of systematic zoology, which concerns the identification and classification of species. In a later paragraph are given therefore some suggestions for field and laboratory work in the determination of local bird-faunæ. In the following paragraphs each of the American orders is briefly discussed, as is also the foreign order of ostriches.

The ostriches, cassowaries, etc. (Ratitæ).—The ostriches, familiar to all from pictures and to some from live individuals in zoological gardens and menageries, or stuffed specimens in museums, together with a few other similar large species, are distinguished from all other birds by having the breast-bone flat instead of keeled. There are about a score of species of ostriches and ostrich-like birds all confined to the southern hemisphere. In them the wings are so reduced that flight is impossible, but the legs are long and strong, and they can run as swiftly as a galloping horse. They are said to have a stride of over twenty feet. They use their legs also as weapons, kicking viciously when angered. The true ostriches (Struthio camelus) (fig. [135]) live in Africa. They are the largest living birds, reaching a height of nearly seven feet and weighing as much as two hundred pounds. They are hunted for their feathers, and are now kept in captivity and bred in South Africa and California for the same purpose. About five million dollars' worth of ostrich-feathers are used each year. The eggs, which are from five to six inches long and nearly five inches thick, are laid in shallow hollows scooped out in the sand of the desert. The male undertakes most of the incubation, although when the sun is hot no brooding is necessary. The young (fig. [136]) hatch in from seven to eight weeks, and can run about immediately.

Fig. 135.—Ostriches on ostrich farm at Pasadena, California. (Photograph from life.)

The rheas, found in South America, and the cassowaries of Australia are the only other living ostrich-like birds. Their feathers are of much less value than those of the true ostrich.

Fig. 136.—Young ostriches just from egg; on ostrich farm at Pasadena, California. (Photograph from life.)

The loons, grebes, auks, etc. (Pygopodes).—The loons, grebes, and auks are aquatic birds, living in both ocean and fresh waters. Their feet are webbed or lobed, and their legs set so far back that walking is very difficult and awkward. But all the birds of this order are excellent swimmers and divers. They are distinctively the diving birds. They have short wings and almost no tail. The dab-chick or pied-billed grebe (Podilymbus podiceps) is common in ponds over all the country. Its eggs are laid in a floating nest of pond vegetation and are often covered with decaying plants. The horned grebe (Colymbus auritus) is common west of the Mississippi in lakes and ponds. The loon or great northern diver (Gavia imber), found all over the United States in winter, is the largest of this group, reaching a length (from bill to tip of tail) of three feet. It is black above with many small white spots, and with a patch of white streaks on each side of the neck and on the throat; it is white on breast and belly. The female is duller, being brownish instead of black.

Fig. 137.—Murres, Uria troile californica, on Walrus Island, (Pribilof Group) Behring's Sea. Note the eggs scattered about over the bare rocks. (Photograph from life by the Fur Seal Commission.)

The auks, guillemots, puffins, and murres (fig. [137]) are ocean birds which gather, in the breeding season, in countless numbers on the bleak rocks and inaccessible cliffs of the northern oceans. Each female lays a single egg (in some cases two or at most three) on the bare rock or in a crevice or sort of burrow. These birds mostly fly well, but are especially at home in the water, feeding exclusively on animal substances found there. A famous species is the great auk (Alca impennis), which has become extinct in historical times. The last living specimen was seen in 1844.

The gulls, terns, petrels, and albatrosses (Longipennes).—The Longipennes are water-birds, mostly maritime, with webbed feet and very long and pointed wings. They are all strong flyers, and most of them are beautiful birds. Their prevailing colors are white, slaty or lead-blue, black, and, in the young, mottled brownish. They subsist chiefly on fish, but any animal substance will be eagerly picked up from the water; some of the gulls forage inland. Occasionally great flocks may be seen following a plow near the shore and feeding on the grubs and worms exposed in the freshly-turned soil. Some of the gulls, like the great black-backed gull (Larus marinus), attain a length of two and one-half feet. The terns (Sterna) are mostly smaller than the gulls, have a bill not so heavy and not hooked, and have the tail forked.

The fulmars, shearwaters, petrels, and albatrosses are strictly maritime. The albatrosses are very large, the largest being three feet long with a spread of wing of seven feet. They are often found flying easily over the open ocean at great distances from land. Like the auks and puffins, the fulmars and shearwaters gather in extraordinary numbers on rocky ocean islets or cliffs of the coast to breed.

The cormorants, pelicans, etc. (Steganopodes).—The Steganopodes are water-birds with full-webbed feet, and prominent gular pouch, swimmers rather than flyers like the Longipennes. The cormorants (Phalacrocorax) inhabit rocky coasts and are green-eyed, large, heavy, black birds with greenish-purple and violet iridescence; they are among the most familiar of seashore birds. They feed chiefly on fish and dive and swim under water with great ability. Cormorants are rather gregarious, keeping together in small groups when fishing, migrating often in great flocks, and in the breeding season gathering in immense numbers on certain rocky cliffs or islets. They build their nests of sticks and sea-weed; the eggs are three or four, and usually bluish green with white, chalky covering substance.

The pelicans are large, long-winged, short-legged water-birds with enormous bill and large gular sac which is used as a dip-net to catch fish. There are three species in North America, the white pelican (Pelecanus erythrorhynchus) occurring over most of the United States, the brown pelican (P. fuscus) of the Gulf of Mexico, and the California brown pelican (P. californicus) of the Pacific coast.

An interesting member of this order is the famous frigate or man-of-war bird (Fregata aquila), with very long wings and tail and feet extraordinarily small. The frigates have the greatest command of wing of all the birds. They cannot dive and can scarcely swim or walk.

The ducks, geese, and swans (Anseres).—The familiar wild ducks, of which there are forty species in North American fresh and salt waters; the geese, of which there are sixteen species, and the three species of wild swans constitute the order Anseres. The bill in these birds is more or less flattened and is also lamellate, i.e. furnished along each cutting-edge with a regular series of tooth-like processes; the feet are webbed, and the body is heavy and flattened beneath. Of the fresh-water or inland ducks, the more familiar are the mallard (Anas boschas), a large duck with head (male) and upper neck rich glossy green; the blue-winged teal (Querquedula discors) and green-winged teal (Nettion carolinense); the shoveller (Spatula clypeata) with spoon-shaped bill; the beautiful crested wood-duck (Aix sponsa); the expert diver, the plump little ruddy duck (Erismatura rubida), and others. Of the coastwise ducks, the canvas-back (Aythya vallisneria) is famous because of its fine flavor, while among the strictly maritime ducks the eiders (Somateria), which live in Arctic regions, are well known for their fine down. Of the geese, the commonest is the well-known Canada goose (Branta canadensis), while the pure-white snow-goose (Chen hyperborea), with black wing-feathers and red bill, is not unfamiliar. The wild swans (Olor) are the largest birds of the order, and are less familiar than the ducks and geese.

The ibises, herons, and bitterns (Herodiones).—The tall, long-necked, long-legged, wading birds, known as herons and ibises, compose a small order, the Herodiones, of which but few representatives are at all familiar. Perhaps the most abundant species is the green heron (Ardea virescens) or "fly-up-the-creek," one of the smaller members of the order. The crown, back, and wings are green, the neck purplish cinnamon, and the throat and fore neck white-striped. This bird is commonly seen perching on an overhanging limb, or flying slowly up or down some small stream. The great blue heron (Ardea herodias) is common over the whole country. It is four feet long and grayish blue, marked with black and white. It may be seen standing alone in wet meadows or pastures, or flying heavily, with head drawn back and long legs outstretched. It breeds singly, but oftener in great heronries, in trees or bushes. Its large bulky nests contain three to six dull, greenish-blue eggs about two and one-half inches long. The white egrets of the Southern States are shot for their plumes and have been locally exterminated in some places. The night-herons (Nycticorax) differ from the other forms in having both the neck and legs short. The bittern (Botaurus lentiginosus), Indian hen, stake-driver, or thunder-pumper, as it is variously called, is a familiar member of the order, found in marshes and wet pastures, and known by its extraordinary call, sounding like the "strokes of a mallet on a stake." In color it is brownish, freckled and streaked with tawny whitish and blackish. Its nest is made on the ground; its eggs, from three to five in number, are brownish drab and about two inches long.

The cranes, rails, and coots (Paludicolæ).—The cranes, of which three species are known in North America, are large birds with long legs and neck, part of the head being naked or with hair-like feathers. The rare whooping crane (Grus americana) is pure white with black on the wings, and is fifty inches long from tip of bill to tip of tail. The sand-hill crane (G. mexicana) is slaty gray or brownish in color, never white, and although rare in the East is quite common in the South and West. Cranes build nests on the ground, and lay but two eggs, about four inches long, brownish drab in color with large irregular spots of dull chocolate-brown.

The rails are smaller than the cranes, with short wings and very short tail. They live in marshes and swamps, and in flying let the legs hang down. Their legs are strong, and for escape they trust more to speed in running than to flight. They are hunted for food. The most abundant rail is the "Carolina crake" or "sora" (Porzana carolina), small and olive-brown with numerous sharp white streaks and specks. Many of these birds are shot each year during migration in the reedy swamps of the Atlantic States. The American coot or mud-hen (Fulica americana), dark slate-color with white bill, is one of the most familiar pond-birds over all temperate North America. Its nest consists of a mass of broken reeds resting on the water; the eggs number about a dozen, and are clay-color with pin-head dots of dark brown.

The snipes, sandpipers, plover, etc. (Limicolæ).—The large order Limicolæ, the shore-birds, includes the slender-legged, slender-billed, round-headed, rather small wading birds of shores and marshes familiar to us as snipes, plovers, sandpipers, curlews, yellow-legs, sandpeeps, turnstones, etc. Most of them are game-birds, such forms as the woodcock and Wilson's or English snipe being much hunted. The food of these birds consists of worms and other small animals, which are chiefly obtained by probing with the rather flexible, sensitive, and usually long bill in the mud or sand. The killdeer (Ægialitis vocifera), familiar to all in its range by its peculiar call and handsome markings, the upland or field plover (Bartramia longicauda), with its long legs and melodious quavering whistle, the tall, yellow-shanked "telltale" or yellow-legs (Totanus melanoleucus) of the marshes and wet pastures, are among the most widespread and familiar species of the order. On the seashore the dense flocks of white-winged, whisking sandpipers and the quickly running groups of plump ring-necked plover are familiar sights. One of the largest birds of this order is the long-billed curlew (Numenius longirostris) of the upland pastures. The bill of the curlew is long and curved downwards. The nests of these shore-birds are made on the ground and are usually little more than shallow depressions in which the few spotted eggs (four is a common number) are laid. The young are precocial.

The grouse, quail, pheasants, turkeys, etc. (Gallinæ).—The Gallinæ include most of the domestic fowls, as the hen, turkey, peacock, guinea-fowls, and pheasants, and the grouse, quail, partridges, and wild turkeys. The chief game-birds of most countries belong to this order. They have the bill short, heavy, convex, and bony, adapted for picking up and crushing seeds and grains which compose their principal food. Their legs are strong and usually not long, and are often feathered very low down. The Gallinæ are mostly terrestrial in habit and are sometimes known as the Rasores or "scratchers." Among the more familiar wild gallinaceous birds are the quail or "Bob white" (Colinus virginianus), abundant in eastern and central United States, the ruffed grouse (Bonasa umbellus) of the Eastern woods, and the prairie-chicken (Tympanuchus americanus) of the Western prairies. The sage-hen (Centrocercus urophasianus), the largest of the American grouse, reaching a length of two and one-half feet, is an interesting inhabitant of the sterile sagebrush plains of the West. The ptarmigan (Lagopus) or snow-grouse, represented by several species, are found either among the rocks and snow-banks above timber line on high mountains, or in the Arctic regions. In summer their plumage is brown and white; in winter they turn pure white to harmonize with the uniform snow-covering. On the Pacific coast are several species of quail, all differing much from those of the East. These Western species have beautiful crests of a few or several long plume-feathers, the body-plumage being also unusually beautiful. The eggs of all the Gallinæ are numerous and are laid in a rude nest or simply in a depression on the ground. In many of the species polygamy is the rule. The young are precocial.

The doves and pigeons (Columbæ).—The doves and pigeons constitute a small order, the Columbæ, closely related to the Gallinæ. A distinguishing characteristic of the Columbæ lies in the bill, which is covered at the base with a soft swollen membrane or cere in which the nostrils open. The members of this order feed on fruits, seeds, and grains. Our most familiar wild species is the mourning-dove or turtle-dove (Zenaidura macroura) found abundantly all over the country. It lays two eggs in a loose slight nest in a low tree or on the ground. The beautiful wild or passenger pigeon (Ectopistes migratorius) was once extremely abundant in this country, moving about in tremendous flocks in the Eastern and Central States. But it has been so relentlessly hunted that the species is apparently becoming extinct. In the Rocky and Sierra Nevada mountains is a rather large dove, the band-tailed pigeon (Columba fasciata), which subsists chiefly on acorns. The domestic pigeon represented by numerous varieties, pouters, carriers, ruff-necks, fan-tails, etc., is the artificially selected descendant of the rock-dove (Columba livia). The young of all pigeons are altricial.

Fig. 138.—Screech-owl, Megascops asio. (Photograph by A. L. Princeton permission of Macmillan Co.)

The eagles, owls, and vultures (Raptores).—The "birds of prey" compose one of the larger orders, the members of which are readily recognizable. In all the bill is heavy, powerful, and strongly hooked at the tip. The feet are strong, with long, curved claws (small in the vultures) and are fitted for seizing and holding living prey, such as smaller birds, fish, reptiles, and mammals which constitute the principal food of the true raptorial species. The vultures feed on carrion. The turkey buzzard (Cathartes aura) is the most familiar of the three species of carrion-feeding Raptores found in the United States. The buzzard nests on the ground or in hollow stumps or logs, and lays two white eggs (sometimes only one) blotched with brown and purplish. The largest North American vulture is the California condor (Pseudogryphus californianus), which attains a length of four and one-half feet, with a spread of wing of nine and one-half feet. Of the eagles, the most widespread and commonest is the bald eagle (Haliætus leucocephalus). It is three feet long and when adult has the head and neck white. The golden eagle (Aquila chrysætos) has the neck and head tawny brown. Of the many species of hawks, the marsh harrier (Circus hudsonius), abundant all over the country and readily known by its white rump, is one of the most familiar. The name "chicken-hawk" is given to two or three different species of large broad-winged hawks of the genus Buteo. The stout little sparrow-hawk (Falco sparverius), common over the whole country, is familiar and readily recognizable by its pronounced bluish and black wings and black-and-white banded chestnut tail. Altogether fifty species of hawks and eagles are found in this country. Of the owls, the barn-owl (Strix pratincola) with its long triangular face and handsome mottled and spotted tawny coat is more or less familiar; the great horned owl (Bubo virginianus), the snowy owl (Nyctea nyctea), and the great gray owl (Scotiaptex cinerea) are the common large species, while the red screech-owl (Megascops asio) (fig. [138]), the most abundant owl in the country, and the strange burrowing owl (Speotyto cunicularia), which lives in the holes of prairie-dogs and ground-squirrels in the West, are familiar smaller ones. Thirty-two species of owls are recorded from North America.

The parrots (Psittaci).—The parrots, of which only one species is native in the United States, constitute an interesting order of birds, the Psittaci. They are abundant in tropical America. They have a very thick strongly hooked bill, with a thick and fleshy tongue. The feet have two toes pointing forward and two backward. The plumage is usually brightly and gaudily colored. The natural voice is harsh and discordant, but many of the species can imitate with surprising cleverness the speech of man. Parrots are long-lived and usually docile, and are much kept as pets. The single native species, the Carolina paroquet (Conurus carolinensis), is about a foot in length, is green, with yellow head and neck and orange-red face. Its range once extended from the Gulf of Mexico north to the Great Lakes, but it has been nearly exterminated in all the States but Florida.

The cuckoos and kingfishers (Coccyges).—The cuckoos and kingfishers are regarded as constituting an order, Coccyges, a small group whose members are without any definite bond of union. Only ten species of North American birds belong to this order. The yellow-billed and black-billed cuckoos (Coccyzus) or "rain-crows" are long-tailed, slender, lustrous drab birds, which lay their eggs in the nests of others. They are notable for their peculiar rolling call. On the plains and hills of California and the southwest lives the road-runner or chaparral cock (Geococcyx californianus), a strange bird belonging to the cuckoo family. It is nearly two feet long, of which length the tail makes half. These birds run so rapidly that a horse is little more than able to keep up with them. They feed on fruits, various reptiles, insects, etc. The one common kingfisher of this country, the belted kingfisher (Ceryle alcyon), a thick-set, heavy-billed, ashy blue-and-white bird, is familiar along streams. As it flies swiftly along it gives its rattling cry. It nests in deep holes in the stream-banks, and lays six or eight crystal-white spheroidal eggs.

The woodpeckers (Pici).—The familiar woodpeckers and sap-suckers compose a well-defined order, Pici, which is represented in North America by twenty-five species. The bill of the woodpecker is stout and strong, usually straight, fitted for driving or boring into wood; the tongue is long, sharp-pointed, and barbed, fitted for spearing insects. The feet have two toes turned forward and two backward; the tail-feathers are stiff and sharp-pointed and help support the bird as it clings to the vertical side of a tree-trunk or branch (fig. [139]). The food of most woodpeckers consists chiefly of insects, usually wood-boring larvæ (grubs). These birds do much good by destroying many noxious insect pests of trees. A few species, the true sap-suckers, probably feed on the sap of trees. Their nests are made in holes in trees, and the eggs are pure white and rounded. The harsh and shrill cries of the woodpeckers are familiar to all.

Fig. 139.—The yellow-hammer, Colaptes auratus. (Photograph by W. E. Carlin; permission of G. O. Shields.)

Fig. 140.—Nest and eggs of ruby-throat
humming-bird, Trochilus
colubris, seen from above, in apple-tree.
(Photograph by E. G. Tabor;
permission of Macmillan Co.)

The largest and one of the most interesting woodpeckers is the ivory-billed (Campephilus principalis), twenty inches long, glossy blue-black, with a high head-crest which is scarlet in the male. This bird lives in the heavily wooded swamps of the Southern States. Among the more abundant and widespread, and hence better known, woodpeckers are the yellow-hammers (fig. [139]) or flickers (Colaptes auratus in the East, C. cafer in the West), the red-headed woodpecker (Melanerpes erythrocephalus), with its crimson head and neck and pure-white "vest"; and the black-and-white downy (Dryobates pubescens) and hairy (D. villosus) woodpeckers or "sap-suckers." The California woodpecker (M. formicivorus), a near relative of the red-headed woodpecker, has the curious habit of boring small holes in the bark of oak- or pine-trees and sticking acorns into these holes. Sometimes thousands of acorns are put into the bark of one tree, to which the birds come occasionally to break open some acorns and feed on the grubs inside.

The whippoorwills, chimney-swifts and humming-birds (Macrochires).—All the birds of this order are remarkable for their power of flight. They have long and pointed wings; their feet are small and weak and used only for perching or clinging. All feed on insects, which are caught on the wing by the short-beaked, wide-mouthed swifts and whippoorwills and extracted from flower-cups by the humming-birds with their long and slender bills. The whippoorwill (Antrostomus vociferus) is common in the woods of the East and is readily known by its call. Its two brown-blotched white eggs are laid loose on the ground or on a log or stump. The night-hawk (Chordeiles virginianus), common over the whole country, is seen at twilight flying vigorously about in its search for insects. Its nesting habits are like those of the whippoorwill. The sooty-brown chimney-swifts (Chætura pelagica), popularly confused with the swallows, are the common inhabitants of old chimneys, in which they build their curious saucer-shaped open-work nests. Their eggs are pure white and number four or five. Of the humming-birds but one species, the ruby-throat (Trochilus colubris), is to be found in the Eastern States, but in the western and especially southwestern parts of the country several other species occur. In all seventeen species have been found in the United States. The nests (fig. [140]) of the hummers are very dainty little cups lined with hair or wool or plant-down. The ruby-throat lays two tiny pure-white eggs.

Fig. 141.—Horned larks, Otocoris alpestris, and snowflakes, Plectrophenax nivalis. (Photograph from life by H. W. Menke; permission of Macmillan Co.)

The perchers (Passeres).—Nearly one-half of the birds of North America belong to the great order Passeres, and of all the known birds of the world more than half are included in it. The Passeres or perching birds include the familiar song-birds and a great majority of the birds of the garden, the forest, the roadside, and the field. The feet of these birds always have four toes and are fitted for perching. The syrinx or musical apparatus is, in most, well developed. The nesting and other domestic habits are various, but the young are always hatched in a helpless condition and have to be fed and otherwise cared for by the parents for a longer or shorter time. The North American species of this order are grouped into eighteen families, as the fly-catcher family (Tyrannidæ), the crow family (Corvidæ), the sparrows and finches (Fringillidæ), the swallows (Hirundinidæ), the warblers (Mniotiltidæ), the wrens (Troglodytidæ), the thrushes, robins and bluebirds (Turdidæ), etc. In this book nothing can be said of the various species which belong to this order. However, as the passerine birds are those which most immediately surround us and which, by their familiar songs and nesting habits, most interest us, the out-door study of birds by beginning students will be devoted chiefly to the members of this order, and many species will soon be got acquainted with. The robin and bluebird will introduce us to the shyer and less familiar song-thrushes; the study of the kingbird or bee-martin will interest us in some of the other fly-catchers; from the familiar chipping sparrow and tree-sparrow we shall be led to look for their cousins the swamp-sparrows and song-sparrows, and the larger grosbeaks and cross-bills, and so on through the order.

Determining and studying the birds of a locality.—To identify the various species of birds in the locality of the school it will be necessary to have some book giving the descriptions of all or most of the species of the region, with tables and keys for tracing out the different forms. Such manuals or keys are numerous now; the study of birds is one of the most popular lines of nature study, and a host of bird books has been published in the last few years. The best general manual is Coues's "Key to the Birds of North America," which includes not only keys for tracing and descriptions of all the known species of birds on this continent, but also accounts of the distribution, of the nesting and eggs, and of the plumage of the young birds, besides a thorough introduction to the anatomy and physiology of birds, and directions for collecting and preserving them. Jordan's "Manual of Vertebrates" gives keys and short descriptions of the birds found east of the Missouri River; Chapman's "Handbook of the Birds of Eastern North America" is excellent. To be able to use these manuals it is necessary to have the bird's body in hand; and that means usually death for the bird. Recently there have been published several bird-keys which attempt to make it possible to determine species, the commoner ones at any rate, without such close examination. The birds in these books are usually grouped wholly artificially (without any reference to their natural relationships) according to such salient characteristics as color, markings, size, habit of perching, or running, or flying, etc. These characteristics are such as can presumably be made out in the living bird by aid of an opera-glass or often with the unaided eye. Such books make no pretence to be scientific manuals nor to include any but the more usual and strongly marked species. They are usually limited to the birds of a restricted region. Such books are readily obtainable. There are several popular illustrated "bird-magazines" devoted to accounts of the life and habits of birds. Of these "Bird-lore" is the organ of the Audubon Society for the Protection of Birds.

Fig. 142.—Western chipping sparrow, Spizella socialis arizonae. (Photograph from life by Eliz. and Jos. Grinnell.)

In trying to become acquainted with the birds of a locality it must be borne in mind that the bird-fauna of any region varies with the season. Some birds live in a certain region all the year through; these are called residents. Some spend only the summer or breeding season in the locality, coming up from the South in spring and flying back in autumn; these are summer residents. Some spend only the winter in the locality, coming down from the severer North at the beginning of winter and going back with the coming of spring; these are winter residents. Some are to be found in the locality only in spring and autumn as they are migrating north and south between their tropical winter quarters and their northern summer or breeding home; these are migrants. And finally an occasional representative of certain bird species whose normal habitat does not include the given locality at all will appear now and then blown aside from its regular path of migration or otherwise astray; these are visitants. As to the relative importance, numerically, of these various categories among the birds which may be found in a certain region and thus form its bird-fauna we may illustrate by reference to a definite region. Of the 351 species of birds which have been found in the State of Kansas (a region without distinct natural boundaries and fairly representative of any Mississippi valley region of similar extent), 51 are all-year residents; 125 are summer residents, 36 are winter residents, 104 are migrants, and 35 are rare visitants.

It must also be kept in mind in using bird-keys and descriptions to determine species that the descriptions and keys refer to adult birds and in ordinary plumage. Among numerous birds the young of the year, old enough to fly and as large as the adults, still differ considerably in plumage from the latter; males differ from females, and finally both males and females may change their plumage (hence color and markings) with the season. The seasonal changes of plumage accomplished by molting may be marked or hardly noticeable. "All birds get new suits at least once a year, changing in the fall. Some change in the spring also, either partially or wholly, while others have as many as three changes—perhaps, to a slight extent, a few more.... It is claimed by some that now all new colors are acquired by molt, and by others that in some instances (young hawks) an infusion or loss, as the case may be, of pigment takes place as the feather forms, and continues so long as it grows."

There is much lack and uncertainty of knowledge concerning the molting and change of plumage by birds, and careful observations by bird-students should be made on the subject.

In connection with learning the different kinds of birds in a locality, together with their names, observations should be made, and notes of them recorded, on their habits and on the relation or adaptation of structure and habit to the life of the bird. Some of the special subjects for such observation are pointed out in the following paragraphs. A suggestive book, treating of the adaptive structure and the life of birds is Baskett's "The Story of the Birds."

Bills and feet.—The interesting adaptation of structure to special use is admirably shown in the varying character of the bills and feet of birds. The various feeding habits and uses of the feet of different birds are readily observed, and the accompanying modification of bills and feet can be readily seen in birds either freshly killed or preserved as "bird-skins." Such skins may be made as directed on p. [467], or may be bought cheaply of taxidermists. A set of such skins, properly named, will be of great help in studying birds, and should be in the high-school collection. In some cases the general structure of feet and bills may be seen in the live birds by the use of an opera-glass. The characters of bills and feet are much used in the classification of birds, so that any knowledge of them gained primarily in the study of adaptations will have a secondary use in classification work.

Fig. 143.—Russet-backed thrush, Turdus ustulatus. (Photograph from life by Eliz. and Jos. Grinnell.)

Note the foot of the robin, bluebird, catbird, wrens, warblers and other passerine or perching birds. It has three unwebbed toes in front, and a long hind toe perfectly opposable to the middle front one. This is the perching foot. Note the so-called zygodactyl foot of the woodpecker, with two toes projecting in front and partly yoked together, and two similarly yoked projecting behind. Note the webbed swimming foot of the aquatic birds; note the different degrees of webbing, from the totipalmate, where all four toes are completely webbed, palmate, where the three front toes only are bound together but the web runs out to the claws, to the semi-palmate, where the web runs out only about half way. Note the lobate foot of the coots and phalaropes. Note the long slender wading legs of the sandpipers, snipe and other shore birds; the short heavy strong leg of the divers; the small weak leg of the swifts and humming-birds, almost always on the wing; the stout heavily nailed foot of the scratchers, as the hens, grouse, and turkeys; and the strong grasping talons, with their sharp long curving nails, of the hawks and owls and other birds of prey. In all these cases the fitness of the structure of the foot to the special habits of the bird is apparent.

Similarly the shape and structural character of the bill should be noted, as related to its use, this being chiefly concerned of course with the feeding habits. Note the strong hooked and dentate bill of the birds of prey; they tear their prey. Note the long slender sensitive bill of the sandpipers; they probe the wet sand for worms. Note the short weak bill and wide mouth of the night-hawk and whippoorwill and of the swifts and swallows; they catch insects in this wide mouth while on the wing. Note the flat lamellate bill of the ducks; they scoop up mud and water and strain their food from it. Note the firm chisel-like bill of the woodpeckers; they bore into hard wood for insects. Note the peculiarly crossed mandibles of the cross-bills; they tear open pine-cones for seeds. Note the long sharp slender bill of the humming-birds; they get insects from the bottom of flower-cups. Note the bill and foot of any bird you examine, and see if they are specially adapted to the habits of the bird.

The tongues and tails of birds are two other structures the modifications and special uses of which may be readily observed and studied. Note the structure and special use of the tongue and tail of the woodpeckers; note the tongue of the humming-bird; the tail of the grackles.

Flight and songs.—The most casual observation of birds reveals differences in the flight of different kinds, so characteristic and distinctive as to give much aid in determining the identity of birds in nature. Note the flight of the woodpeckers; it identifies them unmistakably in the air. Note the rapid beating of the wings of quail and grouse; also of wild ducks; the slow heavy flapping of the larger hawks and owls and of the crows; and the splendid soaring of the turkey-buzzard and of the gulls. This soaring has been the subject of much observation and study but is still imperfectly understood. The soaring bird evidently takes advantage of horizontal air-currents, and some observers maintain that upward currents also must be present. The principal hopes for the invention of a successful flying-machine rest on the power of soaring possessed by birds. The speed of flight of some birds is enormous, the passenger-pigeon having been estimated to attain a speed of one hundred miles an hour. The long distances covered in a single continuous flight by certain birds are also extraordinary, as is also the total distance covered by some of the migrants. "It is said that some plovers that nest in Labrador winter in Patagonia, their long wings easily carrying them this great distance."

Fig. 144.—Oriole's nest with skeleton of blue jay suspended from it; the blue jay probably came to the nest to eat the eggs, became entangled in the strings composing the nest, and died by hanging. (Photograph by S. J. Hunter.)

Varying even more than the manner and power of flight among different birds are the vocal utterances, the cries and calls and singing. By their calls and songs alone many birds may be identified although they remain unseen. The field-student of birds comes to know them by their songs; knows what birds they are; knows what they are doing or not doing; knows what time in their life-season it is, whether they are mating, or brooding, or preparing to migrate; knows whether they are frightened, or self-confident, whether in distress or happy. Little urging and suggestion are needed to induce the student to attend to the songs. But the naturalist should not only hear and enjoy them, but by observation and the recording of repeated observations, he should come to understand the significance of the calls and songs.

As to how these sounds are made, attention has already been called (see p. [338]) to the voice-organ or syrinx. The condition of this organ varies much in birds, as would be expected from the differing character of vocal utterances. Dissections will make these differences apparent.

Nesting and care of young.—Among the birds' most interesting instincts and habits are those domestic ones which include mating, nest-building, and care of the young. Birds' eggs and birds' nests are always attractive objects of search and collection for boys, and most boys have a considerable personal knowledge of the domestic habits of the commoner summer birds of their region. With this interest and unsystematized knowledge as a basis the teacher should be able to get from the class much excellent field-work and personal observation. The first thing to undertake in this study is the gathering of data regarding the character of the nests of different species, their situation, the time of nesting, the participation or non-participation of the male in nest-building, etc.; also the number of eggs, their size and color markings, the length of incubation, the help or lack of help of the male in brooding, etc. In connection with this gathering of data in the field by note-taking, sketching, and photographing, nests and eggs can be collected (see directions on page [469]). Let only one clutch of eggs of each species be taken for the common high-school collection, and if more than one nest is desired take used and deserted nests. When the nestlings are hatched, the bringing of food, the defence of the home, and the teaching of the young to fly should all be observed and noted.

Some attempt should be made to systematize the miscellaneous data obtained. Do all the members of a group have similar nesting habits? Note the early nesting of birds of prey; note the nests of the woodpeckers in holes in trees; note the nesting of the various swallows. Is there any significance in the colors and markings of eggs? Observe the protective coloration obvious in some (see Chap. [XXXI]). Are there differences in the condition of the newly hatched nestlings? Note the helpless altricial young of the robin; the independent precocial young of the quail.

The strong influence of the mating passion will be made plain by observations on the fighting, love-making, singing, and general behavior of the birds in the mating season. The expression of the mental and emotional traits, the psychic phenomena of birds, are most emphasized at this time, and reveal the possession among animals lower than man of many characteristics which are too commonly ascribed as the exclusive attributes of the human species.

Fig. 145.—Western robin, Merula migratoria propinqua. (Photograph from life by Eliz. and Jos. Grinnell.)

Local distribution and migration.—As explained in Chapter [XXXII], the geographical distribution of animals is a subject of much importance, and offers good opportunities in its more local features for student field-work. The field-study of the birds of a given locality will comprise much observation bearing directly on zoogeography or the distribution of animals. Certain birds will be found to be limited to certain parts of even a small region, the swimmers will be found in ponds and streams and the long-legged shore-birds on the pond- or stream-banks, or in the marshes and wet meadows, although a few like the upland plover, curlews, and godwits are common on the dry upland pastures. Distinguish the ground-birds from the birds of the shrubs and hedge-rows and these again from the strictly forest-birds. Find the special haunts of swallows and kingfishers. Which are the shy birds driven constantly deeper into the wild places or being exterminated by the advance of man; which birds do not retreat but even find an advantage in man's seizure of the land, obtaining food from his fields and gardens?

Make a map on large scale of the locality of the school, showing on it the topographic features of the region, such as streams, ponds, marshes, hills, woods, springs, wild pastures, etc., also roads and paths, and such landmarks as schoolhouses, county churches, etc. On this map indicate the local distribution of the birds, as determined by the data gradually gathered; mark favorite nesting-places of various species, roosting-places of crows and blackbirds, feeding-places, and bathing- and drinking-places of certain kinds, the exact spots of finding rare visitants, rare nests, etc., etc. The making of such a zoogeographical map will be a source of great interest and profit to the students.

As already mentioned, many of the birds of a locality are "migrants," that is, they breed farther north, but spend the winter in more southern latitudes. These migrants pass through the locality twice each year, going north in the spring and south in the autumn. They are much more likely to be observed during the spring migration than in the fall, as the flight south is usually more hurried. The observation of the migration of birds is very interesting, and much can be done by beginning students. Notes should be made recording the first time each spring a migrating species is seen, the time when it is most abundant and the last time it is seen the same spring. Similar records should be made showing the movements of the birds in the fall. A series of such records covering a few years will show which are the earliest species to appear, which the later, and which the last. Such records of appearance and disappearance should also be kept for the summer residents, those birds that come from the South in the spring, breed in the locality, and then depart for the South again in the autumn. Notes on the kinds of days, as stormy, clear, cold, warm, etc., on which the migration seems to be most active; on the greater prevalence of migratory flights by day or by night; on the height from the earth at which the migrants fly, etc., are all worth while. The Division of Biological Survey, U. S. Department of Agriculture, keeps records of notes on migration sent in by voluntary observers and furnishes blanks to be filled out by each observer. A suggestive book about migration, and one giving the records for many species at many points in the Mississippi valley is Cooke's "Bird Migration in the Mississippi Valley." Migration is discussed in most bird-books.

Feeding habits, economics, and protection of birds.—The feeding habits of birds are not only interesting, but their determination decides the economic relation of birds to man, that is, whether a particular bird species is harmful or beneficial to man. Casual observation shows that birds eat worms, grains, seeds, fruits, insects. A single species often is both fruit-eating and insect-eating. Do fruits or do insects compose the chief food-supply of the species? To determine this more than casual observation is necessary. The birds must be watched when feeding at different seasons. The most effective way of determining the kind of food which the bird takes is to examine the stomachs of many individuals taken at various times and localities. Much work of this kind has been done, especially by the investigators connected with the Division of Biological Survey of the U. S. Department of Agriculture, and pamphlets giving the results of these investigations can be had from the Division. It has been distinctly shown that a great majority of birds are chiefly beneficial to man by eating noxious insects and the seeds of weeds. Many birds commonly reputed to be harmful, and for that reason shot by farmers and fruit-growers, have been proved to do much more good than harm. Some few birds have been proved to be, on the whole, harmful. An investigation of the food habits of the crow, a bird of ill-repute among farmers, based on an examination of 909 stomachs shows that about 29 per cent of the food for the year consists of grain, of which corn constitutes something more than 21 per cent, the greatest quantity being eaten in the three winter months. All of this must be either waste grain picked up in fields and roads, or corn stolen from cribs and shocks. May, the month of sprouting corn, shows a slight increase over the other spring and summer months. On the other hand the loss of grain is offset by the destruction of insects. These constitute more than 23 per cent of the crow's yearly diet, and the larger part of them are noxious. The remainder of the crow's food consists of wild fruit, seeds and various animal substances which may on the whole be considered neutral.

Fig. 146.—Sickle-billed thrasher, Harporhynchus redevivus. (Photograph from life by Eliz. and Jos. Grinnell.)

The slaughter of birds for millinery purposes has become so fearful and apparent in recent years that a strong movement for their protection has been inaugurated. Rapacious egg-collecting, legislation against birds wrongly thought to be harmful to grains and fruit, and the selfish wholesale killing of birds by professional and amateur hunters, help in the work of destruction. Apart from the brutality of such slaughter, and the extermination of the most beautiful and enjoyable of our animal companions, this destruction[18] works strongly against our material interests. Birds are the natural enemies of insect pests, and the destroying of the birds means the rapid increase and spread, and the enhanced destructive power of the pests. It is asserted by investigators that during the past fifteen years the number of our common song-birds has been reduced to one-fourth. At the present rate, says one author, extermination of many species will occur during the lives of most of us. Already the passenger-pigeon and Carolina paroquet, only a few years ago abundant, are practically exterminated. Protect the birds!

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[CHAPTER XXVIII]

BRANCH CHORDATA (Continued). CLASS MAMMALIA: THE MAMMALS

THE MOUSE (Mus musculus)

Technical Note.—It is best to catch specimens alive in a good trap. A live trap well baited and placed in some old granary should furnish plenty for class use. White mice can often be obtained at "bird-stores." When mice are not procurable, use rats. A rat is perhaps preferable on account of its size, but all essential structures can readily be made out in the mouse. Specimens should be killed by chloroform as described for the toad, p. 5.

Structure (fig. [147]).—Compare the external characters of the mouse with those of the toad and sparrow. The mouse, unlike the other vertebrates so far studied, is thickly covered with hair all over its body except on the tip of the nose and the soles of the feet. Where are the nostrils placed? What are the large leaf-like expansions called pinnæ situated just back of the eyes? Pull open the mouth and note the large incisor teeth on the upper and lower jaws. Cut one corner of the mouth back and observe the large flat-topped molar teeth on both jaws. How does the attachment of the large fleshy tongue differ from the condition in the toad? The toad's tongue is for snapping up insects, whereas in the mouse this organ serves to move food about in the mouth. On the tongue are numerous small taste-papillæ. Notice the long hairs, "feelers," on each side of the nose. Note the similarity between the front paws and our own hands; each has four fingers with a small rudimentary thumb on the inner side of the paw. How does the hind foot of the mouse differ from the foot of man? Posteriorly the body is terminated by a long tail. At the root of the tail is a small aperture, the anus, and just below, or ventral to it, is the opening from the kidneys and reproductive organs.

Technical Note.—Place the mouse on its back in a dissecting-pan and cut through the skin from anus to the lower jaw. Extend the legs, pin down each foot and pin out the cut edges of the skin. Now carefully cut forward through the body-wall from the anal region and on through the breast-bones and ribs. Pin each side out.

Fig. 147.—Dissection of the Mouse, Mus musculus.

Near the hindmost pair of ribs note a sheet of muscles, the diaphragm, which extends across the body-cavity, dividing it into an anterior portion, the thoracic cavity, and a posterior, the abdominal cavity. What are the most conspicuous organs in the thoracic cavity? Leading anteriorly to the mouth-cavity is a long tube, the trachea, composed of a series of cartilaginous parts of rings placed end to end. Note at its anterior end the glottis and epiglottis. Insert a blowpipe into the glottis and inflate the lungs, which will fill all the otherwise unfilled space in the thoracic cavity. The abdominal cavity contains the viscera suspended in a fold of the lining membrane, as in the other vertebrates studied. Note lying against the diaphragm a large, red, glandular structure, the liver. Separate the two large lobes of the liver and expose the opalescent gall-bladder. By passing a canula into this and ligaturing, the cystic duct may be injected. Beneath the liver is a large loop-shaped expansion of the alimentary canal, the stomach. Arising from the right end of the stomach is the narrow duodenum, which gradually merges into the very much convoluted small intestine, or ileum, which is followed by the large intestine, or colon, the last part of which is a straight tube, the rectum. The small intestine occupies most of the space in the peritoneal cavity. Within the loop of the pylorus will be found an irregular pinkish mass of tissue, the pancreas. Beneath the stomach on the left side of the body lies a very dark glandular mass not much unlike the liver but altogether detached from it. This structure is the spleen, a ductless gland.

Note dorsally of the trachea a long tube passing through the diaphragm and connecting the mouth with the stomach. What is this tube? Note the Eustachian tubes extending from the mouth to the ears. The median part of the roof of the mouth is the palate, hard in front, soft behind. A pair of small bodies at the sides of the soft palate near its hinder end are the tonsils. At the posterior angle of the lower jaw are glandular bodies, the sub-maxillary glands, which lead by a short duct anteriorly to open on the floor of the mouth. On the sides of the neck just below the ears are pink or yellowish bodies, the parotid glands, opening anteriorly in the sides of the mouth-cavity. These two sets of glands are collectively known as the salivary glands, the function of which is to secrete the saliva. Push apart the sub-maxillary glands and note below them overlying the trachea on either side two dark-red lobes connected by a band of tissue. These constitute the thyroid gland, another of the so-called ductless glands. Within the thoracic cavity anterior to the heart note a mass of pinkish tissue, the thymus gland. Observe the large masseter muscles, which cover the jaws. What is their function? On either side of the neck lies a large blood-vessel, the external jugular vein, which collects blood from the head and carries it down to the heart. Note the large pectoral muscles which cover the breast and extend out into the arms, and which are so strong and highly developed in the sparrow. The head is supported by large muscles which run down the back of the neck to the ribs. Others are attached to the ribs, which they raise and lower. These movements, together with the contraction of the diaphragm, cause the expansion and contraction of the thoracic cavity whereby the lungs are regularly filled and emptied. Note that the abdomen is covered by a double layer of muscular tissue, the outer part made up of the external oblique muscles, the inner by the internal oblique muscles.

Fig. 148.—Diagram of
the circulation of the
blood in a mammal; a,
auricles; l, lung; lv,
liver; p, portal vein
bringing blood from the
intestine; v, ventricles;
the arrows show the direction
of the current;
the shaded vessels
carry venous blood, the
others arterial blood.
(From Kingsley.)

Examine the heart. How many auricles has it? The ventricles in the mouse, as in the bird, are entirely separated, forming two complete compartments, a right and a left ventricle. The blood flowing from the veins of the body is collected in the right auricle, thence it passes into the right ventricle, whence it is conveyed to the lungs; returning it flows through the left auricle into the left ventricle, whence it is forced through the arteries of the body. For a study of the circulatory system in mammals (fig. [148]), a rat or a rabbit should be injected by the teacher and an advanced text-book, as Parker's "Zootomy" or Marshall and Hurst's "Practical Zoology," used as a guide. A sheep's heart is very good to cut open for a class demonstration.

Make a drawing of the organs observed thus far in the dissection.

The kidneys in the mouse are situated in the dorsal region next to the backbone. They consist of two bean-shaped smooth glands. From them a pair of ducts, the ureters, can be traced down to a median thin-walled muscular sac, the bladder. The bladder opens to the exterior of the body by means of a short tube, the urethra. Cut open a kidney longitudinally and examine the cut surfaces.

The two egg-glands of the female mouse lie in the median portion of the abdominal cavity, somewhat below the kidneys, and from the vicinity of each runs an egg-tube. These tubes meet below the bladder, and open to the exterior of the body through the aperture noted below the anus. In the posterior parts of these tubes lie until birth the developing embryos.

Technical Note.—For a study of the nervous system place the specimen ventral side down and cut through the skull with the bone-cutters or heavy scissors, exposing the brain and spinal cord.

Note the large brain (fig. [149]), composed of small optic lobes, large cerebrum, cerebellum, and medulla oblongata, followed by the long spinal cord. Note the nerves arising from the brain and spinal cord.

Fig. 149.—Diagram of brains of vertebrates; Olf. L., olfactory lobes; Cbr., cerebrum; Md. Br., midbrain (optic lobes); Cbl., cerebellum; Med. Ob., medulla oblongata; Sp. Cd., spinal cord. (From specimens.)

For a careful dissection of the mammalian nervous system a larger mammal, such as a cat or dog or rabbit, should be used. For guide use a text-book such as, for the dog, Howell's "Dissection of the Dog"; for the cat, Reighard and Jennings' "Anatomy of the Cat"; and for the rabbit, Parker's "Zootomy" or Marshall and Hurst's "Practical Zoology." Make a good preparation of the brain and preserve it for future use in some fluid like Fischer's fluid (see page [453]).

Technical Note.—Prepare a well-cleaned skeleton by boiling a specimen in a soap solution and thoroughly cleansing it (see p. [452]).

Note the very compact skeleton of the mouse. Note the closely sutured skull. How many cervical or neck vertebræ are there? The ribs are attached to the thoracic vertebræ. How many pairs of ribs? The bony thorax supports the shoulder-girdle and bones of the fore legs. The thorax is followed by a series of ribless vertebræ, the lumbar vertebræ, which in the posterior region of the body fuse with the pelvic girdle supporting the hind limbs. The body vertebræ are succeeded by the very much smaller caudal vertebræ. Compare the skeleton of the mouse with that of the bird; also with that of the toad. For directions for a detailed study of the skeleton see in Parker's "Zootomy" an account of the skeleton of the rabbit, pp. 263-286.

Fig. 150.—Diagram of vertebrate
eye; c, choroid; i, iris; l, lens; n,
optic nerve; r, retina; s, sclerotic.
(From Kingsley.)

Technical Note.—For the study of the eye (fig. [150]) the teacher should obtain the eye of some large mammal, as the ox or sheep, with which to make a class demonstration. The eye of a rabbit or cat can of course be used. For an account of the vertebrate eye see Parker and Haswell's "Text-book of Zoology," Vol. II. pp. 103-107. For a study of the ear use a bird or mammal, and see pp. 107-110 of the same book.

Life-history and habits.—The house-mouse is not a native of North America, but was introduced into this country from Europe, to which, in turn, it came from Asia, its original habitat. The mouse came to this country in the vessels of early explorers. Similarly the brown and black rats, now so abundant all over North America, and members of the same genus as the mouse, were introduced from Europe. Accompanying man in his travels the mouse has spread from Asia until it is now to be found over the whole world.

The habits of mice are well known; their fondness for living in our homes and outbuildings makes them familiar acquaintances. Their food is varied; they seem to thrive best, however, on a vegetable diet. Grains and nuts are favorite foods. The house-cat is their greatest enemy, but man takes advantage of their instinct to go into holes by constructing traps with funnel or tunnel entrances which, baited with cheese or other favorite food, are fatally attractive. In climbing, mice are aided by the tail. Their strong hind legs enable them to stand erect, and even to take several steps in this posture. They can swim readily, although naturally they rarely take to water. Their special senses are keen, the senses of hearing and taste being unusually well developed. Their "singing," which has been the subject of much discussion, seems to be actually a voluntary and normal performance which, however, hardly deserves to be called singing, but rather a slightly varied peeping or whistling.

The mouse is a prolific mammal, producing from four to six times a year broods of from four to eight young. The mouse makes a cosy nest of straw, bits of paper, feathers, wool or other soft materials, and in this the young are born. The newly born mice are very small and are blind and helpless. They are odd little creatures, being naked and almost transparent. They grow rapidly, being covered with hair in a week, although not opening their eyes for about two weeks. A day or two after their eyes are open they begin to leave the nest, and hunt for food for themselves.

OTHER MAMMALS

The mammals constitute the highest group of animals, including man, the monkeys and apes, the quadrupeds, the bird-like bats and fish-like seals and whales; in all about 2500 species. They are found everywhere except on a few small South Sea islands. Only a few species, however, have a world-wide distribution. The name Mammalia is derived from the mammary or milk glands with which the females are provided and by the secretion of which the young of this class, born free in all but a few of the lowest forms, are nourished for some time after birth. In size mammals range from the tiny pigmy-shrew and harvest mouse, which can climb a stem of wheat, to the great sulphur-bottom whale of the Pacific Ocean, which attains a length of a hundred feet and a weight of many tons. Mammals differ from fishes and batrachians and agree with reptiles and birds in never having external gills; they differ from reptiles and agree with birds in being warm-blooded and in having a heart with two distinct ventricles and a complete double circulation; finally, they differ from both reptiles and birds in having the skin more or less clothed with hair, the lungs freely suspended in a thoracic cavity separated from the abdominal by a muscular partition, the diaphragm, and in the possession by the females of mammary glands. In economic uses to man mammals are the most important of all animals. They furnish the greater portion of the animal food of many human races, likewise a large amount of their clothing. Horses, asses, oxen, camels, reindeer, elephants, and llamas are beasts of burden and draught; swine, sheep, cattle, and goats furnish flesh, and the two latter milk for food; the wool of sheep, the furs of the carnivores, and the leather of cattle, horses, and others are used for clothing, while the bones and horns of various mammals serve various purposes.

Body form and structure.—The mammalian body varies greatly. Its variety of form and general organization is explained by the facts that, although most of the species live on the surface of the earth, some are burrowers in the ground, some flyers in the air, and some swimmers in the water. Mammals never have more than two pairs of limbs; in most cases both pairs are well developed and adapted for terrestrial progression. In the aerial bats the fore limbs are modified into organs of flight; among the aquatic seals, sea-lions, walruses, and whales both sets are modified to be swimming flippers or paddles. In many of these aquatic forms the hind limbs are greatly reduced or even completely wanting.

Most mammals are externally clothed with hair, which is a peculiarly modified epidermal process. Each hair, usually cylindrical, is composed of two parts, a central pith containing air, and an outer more solid cortex; each hair rises from a short papilla sunk at the bottom of a follicle lying in the true skin. In some mammals the hairs assume the form of spines or "quills," as in the porcupine. The hairy coat is virtually wanting in whales and is very sparse in certain other forms, the elephant, for example, which has its skin greatly thickened. The claws of beasts of prey, the hooves of the hoofed mammals, and the outer horny sheaths of the hollow-horned ruminants are all epidermal structures.

The bones of mammals are firmer than those of other vertebrates, containing a larger proportion of salts of lime. Among the different forms the spinal column varies largely in the number of vertebræ, this variation being chiefly due to differences in length of tail. Apart from the caudal vertebræ their usual number is about thirty. The mammalian skull is very firm and rigid, all the bones composing it, excepting the lower jaw, the tiny auditory ossicles, and the slender bones of the hyoid arch, being immovably articulated together. The correspondence between the bones of the two sets of limbs is very apparent. The number of digits varies in different mammals, and also in the fore and hind limbs of a single species. Among the Ungulates the reduction in the number of digits is especially noticeable; the forefoot of a pig has four digits, that of the cow two, and that of the horse one. The two short "splint" bones in the horse are remnants of lost digits. The teeth are important structures in mammals, being used not only for tearing and masticating food, but as weapons of offence and defence. A tooth consists of an inner soft pulp (in old teeth the pulp may become converted into bone-like material) surrounded by hard white dentine or ivory, which is covered by a thin layer of enamel, the hardest tissue known in the animal body. A hard cement sometimes covers as a thin layer the outer surface of the root, and may also cover the enamel of the crown. The teeth in most forms are of three groups: (a) the incisors, with sharp cutting edges and simple roots, situated in the centre of the jaw; (b) the canines, often conical and sharp-pointed, next to the incisors; (c) next the molars, broad and flat-topped for grinding, and divided into premolars and true molars. There is great variety in the character and arrangement of these structures in mammals, their variations being much used in classification. The number and arrangement of the teeth is expressed by a dental formula, as, for example, in the case of man

2—2 1—1 2—2 3—3
i ——, c ——, p ——, m —— = 32.
2—2 1—1 2—2 3—3

The mouth is bounded by fleshy lips. On the floor of the mouth is the tongue, which bears the taste-buds or papillæ, the organs of taste. The œsophagus is always a simple straight tube, but the stomach varies greatly, being usually simple, but sometimes, as in the ruminants and whales, divided into several distinct chambers. The intestine in vegetarian mammals is very long, being in a cow twenty times the length of the body. In the carnivores it is comparatively short—in a tiger, for example, but two or three times the length of the body.

Fig. 151.—A group of Rocky Mountain sheep, or "big horns," Ovis canadensis, including males, females and young. (Photograph by E. Willis from specimens mounted by Prof. L. L. Dyche, University of Kansas.)

The blood of mammals is warm, having a temperature of from 35° C. to 40° C. (95° F. to 104° F.). It is red in color, owing to the reddish-yellow, circular, non-nucleated blood-corpuscles. The circulation is double, the heart being composed of two distinct auricles and two distinct ventricles. Air is taken in through the nostrils or mouth and carried through the windpipe (trachea) and a pair of bronchi to the lungs, where it gives up its oxygen to the blood, from which it takes up carbonic-acid gas in turn. At the upper end of the trachea is the larynx or voice-box, consisting of several cartilages attaching by one end to the vocal cords and by the other to muscles. By the alteration of the relative position of these cartilages the cords can be tightened or relaxed, brought together or moved apart, as required to modulate the tone and volume of the voice.

The kidneys of mammals are more compact and definite in form than those of other vertebrates. In all mammals except the Monotremes they discharge their product through the paired ureters into a bladder, whence the urine passes from the body by a single median urethra. Mammary glands, secreting the milk by which the young are nourished during the first period of their existence after birth, are present in both sexes in all mammals, though usually functional in the female only.

Fig. 152.—A group of moose, Alce americana, showing male, female, and young. (Photograph by E. Willis from specimens mounted by Prof. L. L. Dyche, University of Kansas.)

The nervous system and the organs of special sense reach their highest development in the mammals. In them the brain is distinguished by its large size, and by the special preponderance of the forebrain or cerebral hemispheres over the mid- and hind-brain. Man's brain is many times larger than that of all other known mammals of equal bulk of body, and three times as large as that of the largest-brained ape. In man and the higher mammals the surface of the forebrain is thrown into many convolutions; among the lowest the surface is smooth. Of the organs of special sense, those of touch consist of free nerve-endings or minute tactile corpuscles in the skin. The tactile sense is especially acute in certain regions, as the lips and end of the snout in animals like hogs, the fingers in man, and the under surface of the tail in certain monkeys. All the other sense-organs are situated on the head. The organs of taste are certain so-called taste-buds located in the mucous membrane covering certain papillæ on the surface of the tongue. The organ of smell, absent only in certain whales, consists of a ramification of the olfactory nerves over a moist mucous membrane in the nose. The ears of mammals are more highly developed than those of other vertebrates both in respect to the greater complexity of the inner part and the size of the outer part. A large outer ear for collecting the sound-waves is present in all but a few mammals. A tympanic membrane separates it from the middle ear in which is a chain of three tiny bones leading from the tympanum to the inner ear, composed of the three semicircular canals and the spiral cochlea. The eyes (fig. [150]) have the structure characteristic of the vertebrate eye, consisting of a movable eyeball composed of parts through which the rays of light are admitted, regulated, and concentrated upon the sensitive expansion, retina, of the optic nerve lining the posterior part of the ball. The eye is protected by two movable lids. In almost all mammals below the Primates there is a third lid, the nictitating membrane. In some burrowing rodents and others the eye is quite vestigial and even concealed beneath the skin.

Development and life-history.—All mammals except the Monotremes give birth to free young. The two genera of Monotremes produce their young from eggs hatched outside the body; Tachyglossus lays one egg which it carries in an external pouch, while Ornithorhynchus deposits two eggs in its burrow. The embryo of other mammals develops in the lower portion of the egg-tube, to the walls of which it is intimately connected by a membrane called the placenta. (In the kangaroos and opossums, Marsupialia, there is no placenta.) Through this placenta blood-vessels extend from the body of the mother to the embryo, the young developing mammal thus deriving its nourishment directly from the parent.

The duration of gestation (embryonic or prenatal development in the mother's body) varies from three weeks with the mouse, eight weeks with the cat, nine months with the stag, to twenty months with the elephant. Like the birds, the young of some mammals, the carnivores for example, are helpless at birth, while those of others, as the hoofed mammals, are very soon able to run about. But all are nourished for a longer or shorter time by the milk secreted by the mammary gland of the mother.

Habits, instinct, and reason.—Despite the wonderful examples of instinct and intelligence shown by many insects and by the other vertebrates, especially the birds, it is among mammals that we find the highest development of these qualities and of reason. In the wary and patient hunting for prey by the carnivora, in the gregarious and altruistic habits of the herding hoofed mammals, in the highly developed and affectionate care of the young shown by most mammals, and in the loyal friendship and self-sacrifice of dogs and horses in their relations to man, we see the culmination among animals of the development of the functions of the nervous system. In the characteristics of intelligence and reason man of course stands immensely superior to all other animals, but both intelligence and reason are too often shown by many of the other mammals not to make us aware that man's mental powers differ only in degree, not in kind, from those of other animals.

Pure instinct is hereditary, and purely instinctive actions are common to all the individuals of a species. Those actions which the individual could not learn by teaching, imitation, or experience are instinctive. The accurate pecking at food by chicks just hatched from an incubator is purely instinctive. Purely instinctive also is the laying of eggs by a butterfly on a certain species of plant which may have to be sought for over wide acres, so that the caterpillars when hatched shall find themselves on their own special food-plant. Yet the butterfly never ate of this plant and will never see its young. Such elaborate instincts as these have been developed from the simplest manifestations of sensation and nervous function, just as the complex structures of the body have been developed from simple structures (see Chapter [XXIX]).

The feeding and domestic habits and the whole general behavior of animals are extremely interesting subjects of observation and study. And such observation intelligently pursued will be of much value. The point to be kept ever in mind is that all animal habits are connected with certain conditions of life; that in every case there is an answer to the question "why." This answer may not be found; in many cases it is extremely difficult to get at, but often it is simple and obvious and can be found by the veriest beginner.

Classification.—The mammals of North America represent eight orders. Three additional mammalian orders, namely, the Monotremata, including the extraordinary duck-bills (Ornithorhynchus) and a species of Tachyglossus in Australia and Tasmania; the Edentata, including the sloths, armadillos, and ant-eaters found in tropical regions; and the Sirenia, including the marine manatees and dugongs, are not represented (except by a single manatee) in North America. In the following paragraphs some of the more familiar mammals representing each of the eight orders represented in North America are referred to.

The opossums (Marsupialia).—The opossum (Didelphys virginiana) is the only North American representative of the order Marsupialia, the other members of which are limited exclusively to Australia and certain neighboring islands. The kangaroos are the best known of the foreign marsupials. After birth the young are transferred to an external pouch, the marsupium, on the ventral surface of the mother, in which they are carried about and fed. The opossum lives in trees, is about the size of a common cat, and has a dirty-yellowish woolly fur. Its tail is long and scaly, like a rat's. Its food consists chiefly of insects, although small reptiles, birds, and bird's eggs are eaten. When ready to bear young the opossum makes a nest of dried grass in the hollow of a tree, and produces about thirteen very small (half an inch long) helpless creatures. These are then placed by the mother in her pouch. Here they remain until two months or more after birth. Probably all the North American opossums found from New York to California and especially common in the Southern States belong to a single species, but there is much variety among the individuals.

The rodents or gnawers (Glires).—The rabbits, porcupines, gophers, chipmunks, beavers, squirrels, and rats and mice compose the largest order among the mammals. They are called the rodents or gnawers (Glires) because of their well-known gnawing powers and proclivities. The special arrangement and character of the teeth are characteristic of this order. There are no canines, a toothless space being left between the incisors and molars on each side. There are only two incisor teeth in each jaw (rarely four in the upper jaw), and these teeth grow continuously and are kept sharp and of uniform length by the gnawing on hard substances and the constant rubbing on each other. The food of rodents is chiefly vegetable.

Of the hares and rabbits the cottontail (Lepus nuttalii) and the common jack-rabbit (L. campestris) are the best known. The cottontail is found all over the United States, but shows some variation in the different regions. There are several species of jack-rabbits, all limited to the plains and mountain regions west of the Mississippi River. The food of rabbits is strictly vegetable, consisting of succulent roots, branches, or leaves. Rabbits are very prolific and yearly rear from three to six broods of from three to six young each. There are two North American species of porcupines, an Eastern one, Erethizon dorsatus, and a Western one, E. epixanthus. The quills in both these species are short, being only an inch or two in length, and are barbed. In some foreign porcupines they are a foot long. They are loosely attached in the skin and may be readily pulled out, but they cannot be shot out by the porcupine, as is popularly told. The little guinea-pigs (Cavia), kept as pets, are South American animals related to the porcupines.

The pocket gophers, of which there are several species mostly inhabiting the central plains, are rodents found only in North America. They all live underground, making extensive galleries and feeding chiefly on bulbous roots. The mice and rats constitute a large family of which the house-mice and rats, the various field-mice, the wood-rat (Neotoma pennsylvanica) and the muskrat (Fiber zibethicus) are familiar representatives. The common brown rat (Mus decumanus) was introduced into this country from Europe about 1775, and has now nearly wholly supplanted the black rat (M. rattus), also a European species, introduced about 1544. The beaver (Castor canadensis) is the largest rodent. It seems to be doomed to extermination through the relentless hunting of it for its fur. The woodchuck or ground-hog (Arctomys monax) is another familiar rodent larger than most members of the order. The chipmunks and ground-squirrels are commonly known rodents found all over the country. They are the terrestrial members of the squirrel family, the best known arboreal members of which are the red squirrel (Sciurus hudsonicus), the fox-squirrel (S. ludovicianus), and the gray or black squirrel (S. carolinensis). The little flying squirrel (Sciuropterus volans) is abundant in the Eastern States.

The shrews and moles (Insectivora).—The shrews and moles are all small carnivorous animals, which, because of their size, confine their attacks chiefly to insects. The shrews are small and mouse-like; certain kinds of them lead a semi-aquatic life. There are nearly a score of species in North America. Of the moles, of which there are but few species, the common mole (Scalops aquaticus) is well known, while the star-nosed mole (Condylura cristata) is recognizable by the peculiar rosette of about twenty cartilaginous rays at the tip of its snout. Moles live underground and have the fore feet wide and shovel-like for digging. The European hedgehogs are members of this order.

The bats (Chiroptera).—The bats (fig. [153]), order Chiroptera, differ from all other mammals in having the fore limbs modified for flight by the elongation of the forearms and especially of four of the fingers, all of which are connected by a thin leathery membrane which includes also the hind feet and usually the tail. Bats are chiefly nocturnal, hanging head downward by their hind claws in caves, hollow trees, or dark rooms through the day. They feed chiefly on insects, although some foreign kinds live on fruits. There are a dozen or more species of bats in North America, the most abundant kinds in the Eastern States being the little brown bat (Myotis subulatus), about three inches long with small fox-like face, high slender ears, and a uniform dull olive-brown color, and the red bat (Lasiurus borealis), nearly four inches long, covered with long, silky, reddish-brown fur, mostly white at tips of the hairs.

Fig. 153.—The hoary bat, Lasiurus cinereus. (Photograph from life by J. O. Snyder.)

The dolphins, porpoises, and whales (Cete).—The dolphins, porpoises, and whales (Cete) compose an order of more or less fish-like aquatic mammals, among which are the largest of living animals. In all the posterior limbs are wanting, and the fore limbs are developed as broad flattened paddles without distinct fingers or nails. The tail ends in a broad horizontal fin or paddle. The Cete are all predaceous, fish, pelagic crustaceans, and especially squids and cuttlefishes forming their principal food. Most of the species are gregarious, the individuals swimming together in "schools." The dolphins and porpoises compose a family (Delphinidæ) including the smaller and many of the most active and voracious of the Cete. The whales compose two families, the sperm-whales (Physeteridæ) with numerous teeth (in the lower jaw only) and the whalebone whales (Balænidæ) without teeth, their place being taken in the upper jaw by an array of parallel plates with fringed edges known as "whalebone." The great sperm-whales or cachalots (Physeter macrocephalus) found in southern oceans reach a length (males) of eighty feet, of which the head forms nearly one-third. Of the whalebone whales, the sulphur-bottom (Balænoptera sulfurea) of the Pacific Ocean, reaching a length of nearly one hundred feet, is the largest, and hence the largest of all living animals. The common large whale of the Eastern coast and North Atlantic is the right whale (Balæna glacialis); a near relative is the great bowhead (B. mysticetus) of the Arctic seas, the most valuable of all whales to man. Whales are hunted for their whalebone and the oil yielded by their fat or blubber. The story of whale-fishing is an extremely interesting one, the great size and strength of the "game" making the "fishing" a hazardous business.

Fig. 154.—Male elk or wapiti, Cervus canadensis. (Photograph by E. Willis from specimen mounted by Prof. L. L. Dyche, University of Kansas.)]

Fig. 155.—Antelope, male, female, and young, Antilocapra americana. (Photograph by E. Willis from specimens mounted by Prof. L. L. Dyche, University of Kansas.)

The hoofed mammals (Ungulata).—The order Ungulata includes some of the most familiar mammal forms. Most of the domestic animals, as the horse, cow, hog, sheep, and goat, belong to this order, as well as the familiar deer, antelope, and buffalo of our own land and the elephant, rhinoceros, hippopotamus, giraffe, camel, zebra, etc., familiar in zoological gardens and menageries. The order is a large one, its members being characterized by the presence of from one to four hooves, which are the enlarged and thickened claws of the toes. The Ungulates are all herbivorous, and have their molar teeth fitted for grinding, the canines being absent or small. The order is divided into the Perissodactyla or odd-toed forms, like the horse, zebra, tapir, and rhinocerus, and the Artiodactyla or even-toed forms, like the oxen, sheep, deer, camels, pigs, and hippopotami. The Artiodactyls comprise two groups, the Ruminants and Non-ruminants. All of the native Ungulata of our Northern States belong to the Ruminants, so called because of their habit of chewing a cud. A ruminant first presses its food into a ball, swallows it into a particular one of the divisions of its four-chambered stomach, and later regurgitates it into the mouth, thoroughly masticates it, and swallows it again, but into another stomach-chamber. From this it passes through the other two into the intestine.

The deer family (Cervidæ) comprises the familiar Virginia or red deer (Odocoileus americanus) of the Eastern and Central States and the white-tailed, black-tailed, and mule deers of the West, the great-antlered elk or wapiti (Cervus canadensis) (fig. [154]), the great moose (Alce americana) (fig. [152]), largest of the deer family, and the American reindeer or caribou (Rangifer caribou). All species of the Cervidæ have solid horns, more or less branched, which are shed annually. Only the males (except with the reindeer) have horns. The antelope (Antilocapra americana) (fig. [155]) common on the Western plains also sheds its horns, which, however, are not solid and do not break off at the base as in the deer, but are composed of an inner bony core and an outer horny sheath, the outer sheath only being shed. The family Bovidæ includes the once abundant buffalo or bison (Bison bison) (frontispiece), the big-horn or Rocky Mountain sheep (Ovis canadensis) (fig. [151]), and the strange pure-white Rocky Mountain goat (Oreamnos montanus). The buffalo was once abundant on the Western plains, travelling in enormous herds. But so relentlessly has this fine animal been hunted for its skin and flesh that it is now practically exterminated (fig. [156]). A small herd is still to be found in Yellowstone Park, and a few individuals live in parks and zoological gardens. In all of the Bovidæ the horns are simple, hollow, and permanent, each enclosing a bony core.

The carnivorous mammals (Feræ).—The order Feræ includes all those mammals usually called the carnivora, such as the lions, tigers, cats, wolves, dogs, bears, panthers, foxes, weasels, seals, etc. All of them feed chiefly on animal substance and are predatory, pursuing and killing their prey. They are mostly fur-covered and many are hunted for their skin. They have never less than four toes, which are provided with strong claws that are frequently more or less retractile. The canine teeth are usually large, curved, and pointed.

Fig. 156.—A buffalo, Bison bison, killed for its skin and tongue, on the plains of Western Kansas thirty years ago. (Photograph by J. Lee Knight.)

While most of the Feræ live on land, some are strictly aquatic. The true seals, fur-seals, sea-lions, and walruses comprise the aquatic forms, all being inhabitants of the ocean. The true seals, of which the common harbor seal (Phoca vitulina) is our most familiar representative, have the limbs so thoroughly modified for swimming that they are useless on land. The fur-seals, sea-lions, and walruses use the hind legs to scramble about on the rocks or beaches of the shore. The fur-seals (fig. [157]) live gregariously in great rookeries on the Pribilof or Fur Seal Islands, and the Commander Islands in Bering Sea.

The bears are represented in our country by the widespread brown, black, or cinnamon bear (Ursus americanus) and the huge grizzly bear (U. horribilis) of the West. The great polar bear (Thalarctos maritimus) lives in arctic regions. The otters, skunks, badgers, wolverines, sables, minks, and weasels compose the family Mustelidæ, which includes most of the valuable fur-bearing animals. Some of the members of this family lead a semi-aquatic or even strictly aquatic life and have webbed feet. The wolves, foxes, and dogs belong to the family Canidæ. The coyote (Canis latrans), the gray wolf (C. nubilus), and the red fox (Vulpes pennsylvanicus) are the most familiar representatives of this family, in addition to the dog (C. familiaris), which is closely allied to the wolf. "Most carnivorous of the carnivora, formed to devour, with every offensive weapon specialized to its utmost, the Felidæ, whether large or small, are, relatively to their size, the fiercest, strongest, and most terrible of beasts." The Felidæ or cat family includes the lions, tigers, hyenas, leopards, jaguars, panthers, wildcats, and lynxes. In this country the most formidable of the Felidæ is the American panther or puma (Felis concolor). It reaches a length from nose to root of tail of over four feet. Its tail is long. The wildcat (Lynx rufus) is much smaller and has a short tail.

Fig. 157.—The Lukanin rookery of fur seals, Callorhinus alascanus, on St. Paul Island, Pribilof Group, Bering Sea. (Photograph from life by the Fur Seal Commission.)

The man-like mammals (Primates).—The Primates, the highest order of mammals, includes the lemurs, monkeys, baboons, apes, and men. Man (Homo sapiens) is the only native representative of this order in our country. All the races and kinds of men known, although really showing much variety in appearance and body structure, are commonly included in one species. The chief structural characteristics which distinguish man from the other members of this order are the great development of his brain and the non-opposability of his great toe. Despite the similarity in general structure between him and the anthropoid apes of the Old World, in particular the chimpanzee and orang-outang, the disparity in size of brain is enormous.

Fig. 158.—"Bob Jordan," a monkey of the genus Cercopithecus. (Photograph from life by D. S. Jordan.)

The lowest Primates are the lemurs found in Madagascar, in which island they include about one-half of all the mammalian species found there. The brain is much less developed in the lemurs than in any of the other monkeys. The monkeys and apes may be divided into two groups, the lower, platyrrhine monkeys, found in the New World, and the higher, catarrhine forms, limited to the Old World. The platyrrhine monkeys have wide noses in which the nostrils are separated by a broad septum and with the openings directed laterally. These monkeys are mostly smaller and weaker than the Old World forms and are always long-tailed, the tail being frequently prehensile. They include the howling, squirrel, spider, and capuchin monkeys common in the forests of tropical South America. The catarrhine monkeys have the nose-septum narrow and the openings of the nostrils directed forwards, and the tail is wanting in numerous members of the group. They include the baboons, gorillas, orang-outangs, and chimpanzees. These apes have a dentition approaching that of man, and in all ways are the animals which most nearly resemble man in physical character.

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[PART III]

ANIMAL ECOLOGY

[CHAPTER XXIX]