organs by which this is effected are near the muzzle, but, according to Cuvier, they are without the sinuses which exist in the heads of mammals. We have tested this sense in several species of snakes, but only pungent odors seem to specially annoy them. The tongue of the serpent is a harmless appendage, tough, horny, and double-pointed; and, like the same member in man, has a wonderful propensity to be in motion. That snakes sting with their tongues is an old but erroneous opinion. Perhaps our own species is not equally innocent in that respect. All serpents are carnivorous, and nearly all seize and swallow living food. Their teeth are bony, hard, conical in shape, and exceedingly sharp-pointed. None of the class have grinding or cutting teeth. They are formed for holding their food, not to grind, crush, or cut it. Moreover, all their teeth are recurved in form and position; that is, they point in or backward, so that an object once seized can scarcely escape, and, if the jaws be fully distended, could only with great difficulty be ejected. Instances are given where serpents have died from their inability to swallow what they could not eject from their throats, and it is obvious that life could not continue a very long time under such circumstances, for, as Prof. Owen observes, "while swallowing, the trachea may be so compressed that no air can pass, and their only resource is what is contained in the lungs."

In the non-venomous species, which includes those that constrict or crush their prey, are found four rows of teeth in the upper jaw and arch of the mouth, and two rows in the under jaw. Venomous species have usually no more than two rows above, which are on the palatal arch, and two below; but they have on the upper jaw two or more poison-fangs, as shown in Fig. 4, an account of which makes the most fearful chapters in the history of this family of reptiles.

FIG. 4.

A

A. DIAGRAMMATIC SECTION OF THE EYE
OF A VIPER.

a. Eyeball; b. Optic nerve; c. Chamber into which tears
are poured; d. Epidermic layer covering the eye.

B

B. HEAD OF VIPER, SHOWING
POISON-FANGS.

We have observed that serpents swallow their food whole. They make a meal from a mouthful, but the mouthful is sometimes a very large one, for they will swallow animals twice or thrice their own

diameter. This is permitted by the extraordinary expansibility of their body; but the enlargement of their jaws is a complicated phenomenon. In the act of swallowing, they yield at every point, sideways as well as vertically. The elastic integuments which hold the parts of their jaws in place give way, and the apparently small mouth becomes an enormous one.

Digestion proceeds slowly, and, if the meal be excessive, as it often is, the serpent remains sluggish and comparatively helpless a long time. "They have been kept four, six, and eight months, without being fed, and with very little apparent waste of substance." Bruce reports that he kept specimens of the cerastes, or horned-snake, two years in a glass vessel without food, during which time they cast their skins as usual.

FIG. 5.

-a'

CIRCULATING SYSTEM OF REPTILE.

a. Auricle receiving worn-out venous blood from the system; a'. Auricle receiving vitalized blood from the lung. Ventricle in which the two bloods are mixed, and from which it is thrown into the general circulation.

Vital activity in serpents is low. In mammals, the normal mean temperature is from 95° to 105° Fahr., and this must be maintained, or disease supervenes. With serpents, the temperature is a few degrees only above that of the surrounding atmosphere, and varies with it. Thus, it may range, in their healthy active state, from 60° to perhaps more than 80° Fahr. The temperature of a serpent was found, by Hunter and others, to be 88.46°, that of the air being 81.5°. The temperature of a frog was 48° in water at 44.4°. If the atmosphere he

continuously at 60°, some of our common snakes become sluggish and inactive. In both mammals and reptiles the source of internal heat is the same, the difference being in degree only. The low temperature of serpents (as of other reptiles) arises from the structure of their vital organs, by means of which their blood is imperfectly oxygenized. As the "worn-out or venous blood enters the heart, it is mixed with the vitalized blood from the lung (there being, in most species, only one lung and a rudiment of another), and it is this mixed blood which is thrown into the general circulation, as shown in Fig. 5. The blood of a serpent has been said for this reason to be

only half alive, and their functions are accordingly sluggish and dull. Their power of existence for long periods without food, and with little waste of tissue, is chiefly incident to their low vitality.

Hibernation is with them a period of profound torpor. In our temperate climates they gather in large numbers, in some hole, or bur

row in the ground, or in clefts of rocks, for their winter sleep. We once saw twenty-six black snakes taken from one burrow beneath the roots of a partially-fallen tree, in February. Other observers have found a much larger number. We are informed that more than 300 have been found in a single burrowing-place, and that many species, venomous and non-venomous, sometimes resort to the same rendezvous and hibernate together. In the tropics the anaconda (Fig. 6), and perhaps other species of serpents, sometimes hibernate during the dry season of summer in the hardened mud of dried-up pools. It is by the power to hibernate that serpents survive during the winters of temperate climates, but they seem unable to withstand the extreme and long-continued cold of the arctic zone. There, serpents, and in

deed reptiles of all kinds, are rare, and frequently are entirely wanting. In the Falkland Islands, Terra del Fuego, and the mountains of Southern Patagonia, no serpents have been found. The persistence of vitality in serpents is extraordinary, and continues after great mutilations. They are said to have lived several days after removal of the head and viscera. One placed in a vacuum twenty-four hours still showed signs of sensibility; and, many hours after decapitation, a rattlesnake would plunge its headless trunk as in the usual act of striking.