But the most remarkable peculiarity in this snake is that no other way _is_ in its power: _a rattlesnake never hisses_. Throughout the numerous arguments, theories, explanations, and suggestions, there is such an absence of allusion to this fact that we must suppose it to be very little known. Says Dumeril in describing _les petits étuis cornés, comparé à celui que feraient plusieurs grelots peu sonorés: ‘Les Crotales diffèrent de tous les autres serpents connus par la faculté qu’ils ont de produire des sons sourds et rapides, cu plutôt des bruits continus et prolongés à l’aide d’un organe spécial, qui supléerait—pour ainsi dire—à la voix, dont ces serpents sont toujours privés.’_[89] But the sibilations of the rattle are often so like hissing that they have been compared to the whistling of wind among the leaves, to the escape of water through a pipe, to the whizzing of insects, the rattling of seed pods, and many similar sounds, showing at the same time the character of the noise and its variability. Concisely recapitulating what this rattle does, we understand that in the first place it is a substitute for the voice—so far as hissing can be called voice; and that what would cause other excessively nervous, timid, terrified snakes to hiss, causes the rattle to vibrate. It may attract insectivorous birds; it may alarm other timid creatures; it may summon its mate; and, as is well known, it has sympathy with its mate; for a second rattle is almost sure to be sounded, and they have been observed to sound in pairs or numbers responsively—it may be to express anger, fear, and for aught we know _pleasure_, in a state of liberty and enjoyment, feelings expressed by the tail of other creatures. Why it is formed as it is, so wholly different from all other tails; from what it has been evolved; and how long in evolving,—all these are problems to be solved by future Darwins and future Evolutionists. This chapter, therefore, closes with only feeble speculations after feeble attempts to explain an inexplicable phenomenon. The simplest and truest solution seems to be found in those few words, ‘_qui supléerait à la voix, dont ces serpents sont toujours privés_.’ Again, we wonder whether in the non-hissing serpents any peculiarity of trachea may be observed. [Illustration] [Illustration] CHAPTER XVIII. _THE INTEGUMENT—‘HORNS,’ AND OTHER EPIDERMAL APPENDAGES._ HAVING decided that in animal organization nothing exists without its especial use; assuming also that the peculiar development of cuticle forming the rattle is to supply the deficiency of voice, we are next induced to examine those other appendages in serpents which are also modifications of the integument, such as the ‘horns’ of the Cerastes, the tentacles, snout-protuberances, and developments occasionally seen about the head of snakes, and which have all, no doubt, their uses.