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Show 10() MEANS OF EXPRESSION CHAP. IV. t erriiie aspect. The benefit thu~ derived ought to be considerable in order to compensate for tho somewhat lessened r~pidity (though this is still ~reat) w~th which, when dilated, they can strike at the1r enemies or prey ; on the same principle that a broad, .thin piece of wood cannot be n1oved through the c1lr so quickly as a s1nall round stick. A~ inn~cuous sna~c, the Tropidonot~ts 1nacrophthalrnus, an Inhabitant of India, likewise dilates its neck when irritated ; and consequently is often mistaken for its compatriot, the deadly Cobra. 23 This resemblance perhaps serves as some protection to the rrropidonotus. An?ther inno~uous. species, the Dasypeltis of South Africa, blows Itself out, distends its neck, hisses and darts at an intruder.~4 lVIany other snakes hiss under similar circumstances. ~rhey 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 disturbed, rapidly vibrated the end of its tail, which striking 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 Echis 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 ~ 3 Dr. Gunther, 'Reptiles of British India,' p. 262. ~ ,, 1\'Ir. J. Mansel Weale, 'Nature,' April27, 1871, p. 508. ~s 'J~urnal of Researches during the Voyage of the'' Beagle,"' 1845, p. 96. I here compared the rattling thus produced with that of the Rattle-snake. CHAP. l V. L A Jl\IAL '. 107 toothed ljke a aw ; and as th coiled-up animal rnl) · it::; sides togeth '1', the , grate again t each otb r. ~u Lastly, we have the w 11-I~nown ase of the Ratti - nak . He who has 1nerely shaken the rattle of a d ad nak ', can fonn no just itlea. of tho sound produc d hy the living anin1al. Professor Shal r states that it is indisguishable from that fi t de by the male of a hugo Cicada (an Homopterous insect), which inhaLits th same district.27 In the Zoological Gardens, when tho rattle-snak and puff-adders were greatly excited at the same ti1ne, I was much struck at the imilarity of the sound produced by them; and although that made by the rattle-snake is louder and shriller than the hissing of the puff-adder, yet when standing at . orne yards distance I could scarcely distingui ·h the two. For whatever purpose the sound is produced by the onu species, I can hardly doubt that it serves for tho same purpose in the other species ; and I conclude from tho threatening gestures made at the same time by many snakes, that their hissing,-the rattling of the rattlesnake and of the tail of the Trigonocephalus,-tllo grating of the scales of the Echis,-ancl the dilatation of the hood of the Cobra,-all subserve the same end, 2 r. Sec the account by Dr. Anderson, Proc. Zool. Soc. 1871, p. 19G. 27 The 'American Naturalist,' J an. 1872, p. 32. I regret that I cannot follow Prof. Shaler in believing that the rattle has been <lev·loped, by tho aid of natural selection, for tho sake of pl'Odu ing sound~:~ which deceive and attract birds, . o that they may s rvo a prey to tho snake. I do not, however, wish to doubt that tho . ouuds may o ' Cttsionally suusm·vc this end. Dut the conclusion at which I have univ ·d, viz. that tho rattling serves as a warning to would-be devourers, ap}JCnrl:l t me much more probable, as it connects together variou1:1 cla~s s of facts. If this snake had acquired its rattle und tho habit of ruttlillg, for tho ::;akc of attracting pr y, it docs not flOcm probable that it would have invariably used its instrument when angered or disturb d. Prof. 'haler takes nearly tho samo view as I do of tho manner of dcvclopm nt of the rattle ; and I have always h ld this opinion sine obs rviug th Trigonocrphalus in South Amr rica. |
