v* 1l ? 1 *?>, 106 MEANS OF EXPRESSION CHAP. IV. Another innocuous species, the Dasypeltis of South Afri- ca, blows itself out, distends its neck, hisses and darts at an intruder.24 Many other snakes hiss under similar circumstances. They also rapidly vibrate their protruded tongues; and this may aid in increasing their terrific appearance. Snakes possess other means of producing sounds besides hissing. Many years ago I observed in South America that a venomous Trigonocephalus, when dis- turbed, rapidly vibrated the end of its tail, which strik- ing against the dry grass and twigs produced a rattling noise that could be distinctly heard at the distance of six fect.2n • The deadly and fierce EcMs carinata of India produces " a curious prolonged, almost hissing sound " in a very different manner, namely by rubbing " the sides of the folds of its body against each other/-' whilst the head remains in almost the same position. The scales on the sides, and not on other parts of -the bod}', are strongly keeled, with the keels toothed like a saw; and as the coilcd-np animal rubs its sides together, these grate against each other.20 Lastly, we have the 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 %y the living animal. Professor Shaler states that it is indistinguishable from that made by the male of a large Cicada (an ITomoptcrous insect), which inhabits the same district.27 In the Zoological 21 Mr. ,T. Mansel Weale, ' Nature,' April 27, 1871, p. 50R. 35 ' .Tom-rial, of Ileson.rc.hes during' the Voyag-p. of the " Beag-le," ' 1845, p. 96. T have compared the rattling- thus produced with that of the Rattle-snake. 20 See the account by Dr. Anderson, Proc. Zool. Soc. 1871, p. 196. " The ' American Natiiralist,' Jan. 1872, p. 32. T regret that I cannot follow Prof. Shaler in believing- that the rattle has "been developed, by the aid of natural selection, for the sake of producing- sounds which deceive and at- tract birds, so that they may serve as prey to the snake.