434 Mr. Charles J. Galian on 



I believe, however, that Darwin's view does on the whole 

 remain true in its application to the perfect insects, 

 although I am unable to adduce any important fresh facts 

 in support of it. One objection to it was the fact that the 

 stridulating organs when present, were found to be, as a 

 rule, present alike in both sexes, showing no appreciable 

 difference in structure or position according to the sex. 

 On his own hypothesis, Darwin expected that the excep- 

 tions to this rule would prove to be very numerous, but 

 those that he could find were remarkably few. Many 

 more such exceptions have, however, since been brought 

 to light, going some way towards realising Darwin's 

 expectation, and so far lending support to his view. 



The stridulating organs of beetles are, as a rule, very 

 simple in structure, showing no great amount of variety 

 in this respect; but they are, as Darwin has remarked, 

 "wonderfully diversified in position," much more so even 

 than he supposed them to be. Wherever any part of the 

 external surface of the body is subjected to the friction 

 of an adjoining part by the movements of the insect, 

 there, in some species or another, these organs are almost 

 sure to be found. They do not remain constant in position 

 even among the different genera of the same family, yet 

 they sometimes appear unexpectedly having almost identi- 

 cally the same position and structure in one genus that 

 they have in a genus of some totally different family. 

 A Cicindelid, for example, may in this respect be exactly 

 like a Tenebrionid, while two Tenebrionids may be quite 

 unlike one another. Owing to this inconstancy in their 

 position, the stridulating organs of beetles are less important 

 for general purposes of classification than the corresponding 

 structures met with in the Orthoptera ; and for this reason 

 among others, I have thought it best to take them accord- 

 ing to their position on the body of the insect, instead of 

 in the order of the families in which they are found to 

 occur. 



1. Stridulating organs on the head. 



The presence of stridulating areas on the head, though 

 of fairly common occurrence in beetles, was evidently 

 unknown to Darwin and Landois, neither of whom has 

 mentioned any instance of the kind. It was first, I 

 believe, pointed out by Crotch, who in characterising 

 certain genera of Langurihix, noticed that there was a 



