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 feet. 25 The deadly and fierce Edits 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 body, 

 are strongly keeled, with the keels toothed like a saw; 

 and as the coiled-up animal rubs its sides together, these 

 grate against each other. 26 Lastly, we have the well- 

 known case of the Eattle-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. Professor 

 Shaler states that it is indistinguishable from that made 

 by the male of a large Cicada (an Homopterous insect), 

 which inhabits the same district. 27 In the Zoological 



24 Mr. J. Mansel Weale, ' Nature,' April 27, 1871, p. 508. 



25 ' Journal of Researches during- the Voyage of the 

 " Beagle," ' 1845, p. 96. I have compared the rattling- thus 

 produced with that of the Rattle-snake. 



28 See the account by Dr. Anderson, Proc. Zool. Soc. 

 1871, p. 196. 



27 The ' American Naturalist,' 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. 



