Elementary Zoology Part 20

Where does the anterior one of these run? The main branch, or _right aortic arch_, pa.s.ses 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 pa.s.ses 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 pa.s.ses 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 pa.s.ses out from the dorsal aorta to all parts of the alimentary ca.n.a.l 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 ca.n.a.l 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 ma.s.s, the _thymus gland_. The functions of these glands are not certainly understood.

Remove the alimentary ca.n.a.l 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 _vertebrae_ placed end to end. Are there _arms_ or _legs_? Are _shoulder_ and _pelvic girdles_ present?

How many of the vertebrae bear _ribs_? The ribs connect at their lower ends with the ventral scales. Note the great number of the vertebrae and ribs as compared with those of the toad or fish. What are those vertebrae 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 s.h.i.+ft 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 l.u.s.tre. 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.

OTHER REPTILES.

The cla.s.s Reptilia includes the lizards, snakes, tortoises, turtles, crocodiles, and alligators. Although popularly a.s.sociated 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 h.o.r.n.y 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 pa.s.sing into a state of suspended animation or seasonal sleep or torpor.

[Ill.u.s.tration: FIG. 123.--A lizard in the gra.s.s. (Photograph from life by Cherry Kearton; permission of Ca.s.sell & 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 h.o.r.n.y 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 vertebrae is much smaller than in the snakes. Some turtles have only 34 vertebrae; 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.

[Ill.u.s.tration: FIG. 122.--Dissection of the garter snake, _Thamnophis_ sp.]

The tongue of many reptiles, notably the snakes, is bifid or forked, and is an extremely mobile and sensitive organ. The sophagus 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 cla.s.s. 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 papillae 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 papillae 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 nict.i.tating 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 cla.s.s 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.

=Cla.s.sification.=--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 sh.e.l.l 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 sh.e.l.l, the use of the third eyelid (nict.i.tating 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 sh.e.l.l consisting of a dorsal plate, the carapace, and ventral plate, the plastron, and the lateral uniting parts, the bridge. Note legs, and head with h.o.r.n.y 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 ca.n.a.l, the trachea and lungs, and other princ.i.p.al organs, comparing them with those of the snake.

The skeleton can be studied by dissecting and boiling and brus.h.i.+ng 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 vertebrae and ribs.

Among the common turtles and tortoises of the United States are several species of soft-sh.e.l.led turtles (Trionychidae) 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 sh.e.l.l high in front and low behind and head and tail long and not capable of being withdrawn into the sh.e.l.l; 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-sh.o.r.es; and the box-tortoise (_Cistudo carolina_), common in woods and upland pastures and readily recognizable by its ability to enclose itself completely in its sh.e.l.l by the closing down of the lids of the plastron. All of these fresh-water and land-turtles except the soft-sh.e.l.led turtles belong to one family, the Emydidae, 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 pal.u.s.tris_), used for food, is a salt-water form "inhabiting the marshes along the Atlantic coast from Ma.s.sachusetts 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."

[Ill.u.s.tration: 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 sh.e.l.l of certain species, notably the "hawk-bill" (_Eretmochelys imbricata_) the beautiful "tortoise-sh.e.l.l" 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-gra.s.s, though farther south it is called turtle-gra.s.s. 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 sh.e.l.l, withdraws the pole, and, grasping the rope, now firmly attached to the turtle's back, lifts the animal to the surface. Here, with a.s.sistance, 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 a.s.sistance 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.

[Ill.u.s.tration: FIG. 125.--The blue-tailed skink, _Eumeces skeltonia.n.u.s_. (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 gla.s.s-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.

[Ill.u.s.tration: 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 gla.s.s-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 vertebrae 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 princ.i.p.alis_). Its body is about three inches long with a slender tail of five or six inches. The normal color of the chameleon is gra.s.s-green, but it may "a.s.sume 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 (_Vara.n.u.s 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 princ.i.p.al 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."

[Ill.u.s.tration: 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 Colubridae, while all but one of the poisonous species belong to the family Crotalidae, characterized by the presence of a pair of erectile poison-fangs on the upper jaw. Among the commonest of the Colubridae 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 aestivus_), 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_), "l.u.s.trous 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 l.u.s.trous 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.

[Ill.u.s.tration: FIG. 128.--A king-snake, _Lampropeltis boylii_.

(Photograph from life by J. O. Snyder.)]

[Ill.u.s.tration: 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 h.o.r.n.y capsules or cones of shape as shown in figure 130. These h.o.r.n.y 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 ma.s.sasaugas (_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, b.i.+.c.hloride of mercury or chromic acid into the wound, and finally perhaps to take some strong stimulant as brandy or whiskey.

[Ill.u.s.tration: FIG. 130.--The rattles of the rattlesnake; the lower figure shows a longitudinal section of the rattle.]

[Ill.u.s.tration: FIG. 131.--Dissection of head of rattlesnake; _f_, poison-fangs; _p_, poison-sac.]