382 SEXUAL SELECTION. Part II. 



sound bv rubbing the sliasrreened surface of the femur 

 against the granulated margin of the corresponding 

 elytron ; but I could not here detect any proper rasp ; 

 nor is it likely that I could have overlooked it in so 

 large an insect. After examining Cychrus and reading 

 what Westring has written in his two papers about this 

 beetle, it seems very doubtful whether it possesses any 

 true rasp, though it has the power of emitting a sound. 



From the analogy of the Orthoptera and Homoptera, 

 I expected to find that the stridulating organs in the 

 Coleoptera differed according to sex ; but Landois, who 

 has carefully examined several species, observed no 

 such difference ; nor did Westring ; nor did Mr. G-. R. 

 Crotch in preparing the numerous specimens which 

 he had the kindness to send me for examination. Any 

 slight sexual difference, however, would be difficult to 

 detect, on account of the great variability of these organs. 

 Thus in the first pair of the Necrojohorus humator and of 

 the Pelobius which I examined, the rasp was consider- 

 ably larger in the male than in the female ; but not so 

 with succeeding specimens. In Geotrujoes stercorarius 

 the rasp appeared to me thicker, opaquer, and more 

 prominent in three males than in the same number of 

 females ; consequently my son, Mr. F. Darwin, in order 

 to discover whether the sexes differed in their power of 

 stridulating, collected 57 liviug specimens, which he 

 separated into two lots, according as they made, when 

 held in the same manner, a greater or lesser noise. He 

 then examined their sexes, but found that the males 

 were very nearly in the same proportion to the females 

 in both lots. Mr. F. Smith has kept alive numerous 

 specimens of Mononychus pseudacori (Curculionidae), and 

 is satisfied that both sexes stridulate, and apparently in 

 an equal degree. 



Nevertheless the power of stridulating is certainly a 



