If the Boas furnish the most terrible examples of the tremendous powers of destruction possessed by a few of that division of the Serpent tribe, whose bite is unattended with the effusion of venom, the Rattlesnakes afford a no less remarkable instance of the dreadful malignity of the poison with which others of the tribe are so abundantly supplied. This poison is secreted by a gland of considerable size situated beneath the eye, the excretory duct of which terminates on each side at the base of a long and tubular fang in the upper jaw, which is concealed while the animal is at rest in a fold of the gum, but is capable of being instantaneously erected when he is irritated, and affords at the same time the means of inflicting the wound and of insinuating into it the deadly fluid with which it is charged. In the Rattlesnakes these two fangs are the only visible teeth implanted in the upper jaw; but behind each of them are several rudiments of others by which they are from time to time replaced. Their other distinguishing characters consist in the whole of the transverse plates which cover the under surface of the body and of the tail being simple, and in the singular apparatus by which the latter is terminated, and which is formed of a series, more or less numerous according to the age of the individual, of flattened rings loosely attached one within the other in such a manner as to produce a peculiar rattling sound when the tail is moved with any degree of quickness. The number of rings commonly varies from five to twelve; but in very old specimens it is said to have been found to exceed forty. All the known species are natives of America, in the vast forests of which they may be said literally to swarm; but happily, like most of the other venomous snakes, they never exert their terrible qualities upon man except in self-defence, and the warning rattle is always heard to give notice of their approach. Their bite is almost uniformly fatal even to the largest animals, and the latter frequently evince such an instinctive dread of them, that, according to M. Bosc, it is almost impossible to compel a horse or a dog to advance towards them. Their food consists principally of the smaller quadrupeds, such as squirrels and rabbits, of other reptiles, and of birds, although they rarely climb trees in pursuit of their prey. It was long believed, and the notion is still popularly current, that they possessed the power of fascinating their victims, which were thought to be so completely under the influence of their glance as to precipitate themselves of their own accord into the open throat of their enemy; but the truth appears to be that they actually inspire so great a degree of terror that the animals selected for their attacks are commonly rendered incapable of offering such resistance as might otherwise be in their power, or even of attempting to escape from their pursuit.