COUES AND YARROW ON HERPETOLOGY. 263 



€titl distinction can hardly be predicated, at least upon the characters 

 as yet adduced. In any event, the specimens above enumerated are the 

 true C. confluentus of Say. Two of these are of unusual size, being both 

 over four feet in length, a dimension near the known maximum of this 

 species, though less than that of some others. The average length is 

 less than three feet, and the calibre of the body, even in the largest 

 examples, is relatively inferior to that of several Southern species. 



The number of rattles in this and other species, though of course increas- 

 ing with age, is not an infallible clue to the age of a specimen ; for, acci- 

 dental variation aside, it is far from proven that an annual increase by 

 one is regular. On the contrary, the growth of the organ must depend 

 largely, as in all parallel cases, upon the vigor of the individual, which 

 is not the same at all periods of life, granting even a continuous state 

 of perfect health. The purpose subserved in the economy of the ani- 

 mal by this singular organ has been the subject of much speculation and 

 discussion. It is difficult to perceive of what use the rattle can be, either 

 in procuring prey or avoiding enemies. We do not know that it comes 

 into play at all in the pursuit of prey, while the actual result of its use 

 as a menace in self-defence is the reverse of beneficial to the serpent, 

 since the sound serves to direct and provoke attack from all enemies 

 which the animal has occasion to fear. The theory that the rattle is a 

 part of the serpent's means of terrifying its intended victim, used as an 

 adjunct of other supposed powers of fascination, may be safely held in 

 check until it is proven that this peculiar influence is ever exerted to 

 the extent of preventing its prey from seeking safety in flight. The 

 notion that the rattle is intended to serve as a warning, and thus offset 

 the venomous nature and highly dangerous powers of the serpent, is 

 contrary to all analogy, since animals are endowed with attributes for 

 their own good, irrespective of the result upon others, and would re- 

 quire a faith in the intervention, for the benefit of the dominant species 

 of the Mammalia, of special Providences, a belief now held by few thought- 

 ful persons. It has been suggested that the rattle may be used to call 

 the sexes together, and thus serve a useful purpose in the perpetuation 

 of the species, — a hypothsis less untenable than some of the others which 

 have been advanced. Another supposition, made irrespective of "final 

 causes", is, that the rattle has resulted, in the course of time, from the 

 continual agitation of the caudal extremity of these highly nervous and 

 irritable creatures, and that it has no special function. This seems not 

 unreasonable, although, in view particularly of the fact that rattlesnakes 

 alone, of the many equally or more venomous reptiles, have such ap- 

 pendage, it is not entirely satisfactory. One thoroughly established fact 

 concerning the rattle is that its practical operation is injurious to its 

 possessor by provoking attack from those who can cope with it success- 

 fully. It may be suggested, that inasmuch as to an unpracticed ear the 

 rattle of the Crotalus cannot be distinguished from the crepitation of the 

 large Western grasshopper, it may serve the purpose of attracting 



