108 MEANS OF EXPKESSION CHAP. IV. no need to excite additional terror. But this is far from being the case, for they are largely preyed on in all quar- ters of the world by many animals. It is well known that pigs are employed in the United States to clear dis- tricts infested with rattle-snakes, which they do most effectually.29 In England the hedgehog attacks and de- vours 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;30 and so it is in South Africa. Therefore it is by no means improbable that any sounds or signs by which the venom- ous species could instantly make themselves recognized as dangerous, would be of more service to them than to the innocuous species which would not be able, if at- tacked, to inflict any real injury. Having said thus much about snakes, I am tempted to add a few remarks on the means by which the rattle of the rattle-snake was probably developed. Various animals, including some lizards, either curl or vibrate their tails when excited. This is the case with many kinds of snakes.31 In the Zoological Gardens, an in- 20 See the account by Dr. 11. Brown, in Proc. Zool. Soc. 1871, p. 39. He says that as soon as a pig sees a snake it rushes upon it; and a snake makes oft' immediately on the. appearance of a pig-. ao Dr. Giinther remarks ('Reptiles of British India,' p. 340) on the destruction of cobras by the ichneumon or herpestes, and whilst the cobras are young- by the jungle- fowl. It is well known that the peacock also eagerly kills snakes. 81 Prof. Cope enumerates a number of kinds in his ' Method of Creation of Organic Types,' read before the American Phil. Soc., December 15th, 1871, p. 20. Prof. Cope takes the same view as I do of the use of the ges- tures and sounds made by snakes. I briefly alluded to this subject in the last edition of my ' Origin of Species.' Since the passages in the text above have been printed, I have been pleased to find that Mr. Henderson (' The American. Naturalist,' May, 1872, p. 260) also takes a simi- lar view of the use of the rattle, namely " in preventing an attack from, being made."