392 REPORT OF NATIONAL MUSKUM, 1893. 



it for granted that tlie forms from which the Rattlesnake evolved were 

 in tlie habit of vibratin.ii' tlie ti^) of the tail at a high rate of speed. 

 This condition clearly understood, there is no difticulry in tracing the 

 origin of the rattle. 



In this connection I may again call attention to Garman's often 

 quoted article,* and to reproduce his figure of the tail and of a speci- 

 men of the Copperhead, Agkistrodon contortrix {&g;. 32). It does not 

 need long explanation to show how easily a tail cap like the one repre 

 sented might be modified into the button, the ring like swellings of 

 which would prevent the slough from being pushed oft". The develop- 

 ment once started, the increasing irritation would lead to heightened 

 nutrition and excessive accumulation of tissue, in tracing mentally 

 this evolution it must not be forgotten, as Garman on a later occasion 

 (Science, xx, 1892, p. 17) remarks, that the present 

 development of the rattle "embraces much that is a 

 consequence of its possession, much that has been 

 Fig 32. induced by its presence and use." 



TAIL END OF THE COP Garuiau expresslv protests against tlie assumi)tion 



PERHEAD I J 1 n I 



Side view. Nearly tliattherattlesnakesliavebeeii derived directly from the 

 twice uaturai size coppeiiicad, and thinks it more probable that the two 

 rattlesnake genera have had a double origin, Sistriirus 

 having been derived from a stock more nearly related to Agkistrodon; 

 the Crotah proper, with small head scales, from forms nearer to Lachesis. 

 1 can not agree to this proposition, which lays more stress on the 

 number and size of the head shields than upon the rattle and the other 

 characteristics of these snakes. The rattle is a highly specialized 

 instrument, essentially alike both in Crotalus and in iSistrwus, while 

 the nine large head shields, in the possession of which the latter genus 

 agree with Agkistrodon, is the common, generalized arrangement which 

 they share with nearly all the nonvenomous snakes, and which was 

 undoubtedly a characteristic of the ancestor from which they all — 

 including Lachesis and Crotalus — have been derived. There are, indeed, 

 numerous examples among various species of Crotalus of individuals 

 showing a tendency to a reversion to this ancestral arrangement. 



The popular belief in the power of the poisonous snake to " charm " its 

 victims into a state of helplessness is by no means exterminated. In 

 spite of all that has been argued and explained against it there are 

 people still who profess to have ocular proof of this jjower. Time and 

 again it has been related by trustworthy observers how birds or small 

 mammals have been seen to approach the coiled snake, drawn toward 

 it as by a magic spell they were unable to withstand ; how, uudcr the 

 mtuence of an excitement which made them forgetful to everything 

 around them, apparently dreading the terrible fate awaiting them yet 

 unable to avoid it, they finally ventured too near, only to be hit by the 

 lightning stroke of the hitherto almost motionless snake, whose only 



Bull. Mus. Couip. Zool., XIII, \}l. ii, tig. 14; Science, xx, 1892, p. 17, tig. 5, 



