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Chap IV

end, namely to make them appear terrible to their enemies.*(27)

It might perhaps have been thought that venomous snakes, such as the foregoing, would have being already so well defended by their poison-fangs, that they would not never been attacked by any enemies; and would consequently would have had no need to excite additional terror. But this is far from being the case, for they are largely preyed on in all quarters of the world by many animals. It is well known that pigs are employed in the United States to clear districts infested with rattle-snakes, which & this they do most effectually.*(28) In England the hedge-hog attacks and devours the viper. In India, as I hear from Dr. Jerdon, several kinds of hawks, and at least one mammal, the Herpestes, kill cobras and other venomous species:*(29) and so it is in S. Africa. Therefore it is by no means improbable that any sounds or signs by which the venomous species could instantly make themselves recognised as dangerous by to their enemies, would be of more service to them than to the innocuous species which would not be able, if attacked, to inflict any real injury.

Having said thus much about snakes, I am

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rubs its sides together, these grate against each other.*(25) Lastly, we have the familiar well-known case of the Rattle-snake. He who has merely shaken the rattle of a dead snake, can form no just idea of the sound produced by the living animal. Prof. Shaler states that the sound it is indistinguishable from that made by the male of a large Cicada (an Homopterous insect), which inhabits the same district.*(26) In the Zoological Gardens, when both the (49) rattle-snakes and thepuff-adders were greatly excited at the same time, I was much struck at the similarity of the sound produced by them; and although that made by the rattle-snake was louder and shriller than the hissing of the puff-adder, yet when standing at some yards distance I could scarcely distinguish from which animal the sound proceeded. For whatever purpose it is emitted is produced by the one species, I can hardly doubt that it is emitted produces for the same by 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 dilatation of the hood of the Cobra,—all subserve the same