30 COSMIC FHILOSOPHT. [pT. n. 



so that in a fierce struggle it Yv'ill often happen that its action 

 is not prompt enough to preclude a return of conopliments 

 fatal to the snake. When a tiger tears open the jugular vein 

 of his enemy, the enemy is placed hors de combat at once ; 

 but when the rattlesnake has bitten, there is nothing to 

 prevent the foe from employing his few remaining momenta 

 in tearing the serpent to pieces. Hence the rattlesnake 

 must he peculiarly benefited by an apparatus which serves 

 as a signal to warn enemies of his presence, and to keep 

 them from attacking him. His more formidable enemies, 

 belonging chiefly to the mammalian class, are certainly 

 intelhgent enough to profit by such warning and shun the 

 danger ; and as it is plainly for the snake's advantage to 

 avoid even a conflict, it is cleai^ that he is practically helped 

 even less by his terrible bite than by his power of 

 threatening a bite. 



This explanation seems to me quite sound in principle. 

 Yet if we adopt it, there is nothing to prevent us from giving 

 due weight also to Prof. Shaler's suggestion. The success 

 with which the note of the cicada is counterfeited by the 

 rattle is a point to be more fully determined by further 

 ■)bservation. And if it turiis out that the rattle fulfiiS the 

 double purpose of alarming sundry animals that are hostile 

 and of enticing sundry others that are good for food, it will 

 not be the first case in which it has happened that a structure 

 useful in one way has also become useful in another way. 

 The question is an interesting one, and valuable if only 

 because it reminds us of the danger of reasoning too con- 

 fidently, from d priori premises, about matters the due 

 elucidation of which requires careful study of the details of 

 the every-day life of animals. It is one of the great merits 

 of the theory of natural selection that it has directed so many 

 naturalists, with eyes open, into this fruitful field of inquiry. 



It is because it so well illustrates the wealth of su^i^estive- 

 nesa in Mr. Darwin's theory, that I have ventured upon thi? 



