CHAP. IV. IN ANIMALS. 107 Gardens, when the rattle-snakes and puff-adders were greatly excited at the same time, I was much struck at the similarity of the sound produced by them; and al- though that made by the rattle-snake is louder and shriller than the hissing of the puff-adder, yet when standing at some yards distance I could scarcely distin- guish the two. For whatever purpose the sound is pro- duced by the one species, I can hardly doubt that it serves for the same purpose in the other species; and I conclude from the threatening gestures made at the same time by many snakes, that their hissing,—the rattling of the rattle-snake and of the tail of the Trigonocephalus,— the grating of the scales of the Echis,—and the dilata- tion of the hood of the Cobra,—all subserve the same end, namely,, to make them appear terrible to their ene- mies.28 It seems at first a probable conclusion that venom- ous snakes, such as the foregoing, from being already so well defended by their poison-fangs, would never be attacked by any enemy; and consequently would have I do not, however, wish to doubt that the sounds may occasionally sxibserve this end. But the conclusion at which I have arrived, viz. that the rattling- serves as a warning1 to would-be devourers, appears to me much more probable, as it connects together various classes of facts. If this snake had acquired its rattle and the habit of rattling1, for the sake of attracting1 prey, it does not seem probable that it woiild have invariably "used its instru- ment when angered or disturbed. Prof. Shaler takes nearly the same view as I do of the manner of develop- ment of the rattle; and I have always held this opinion since observing, the Trigonocephalus in South America. 28 From the accounts lately collected, and given in the ' Journal of the Linnean Society,' by Mrs. Barber, on the habits of the snakes of South Africa; and from the accounts published by several writers, for instance by Lawson, of the rattle-snake in North America,—It does not seem improbable that the terrific appearance of snakes and the sounds produced by them, may like- wise serve in procuring prey, by paralysing, or as it is sometimes called fascinating, the smaller animals.