304 The Descent of Man. Paht IL 



stridulating organs are wonderfully diversified in position, but 

 not much in structure. Within the same family some species 

 are provided with these organs, and others are destitute of them. 

 This diversity is intelligible, if we suppose that originally various 

 beetles made a shuffling or hissing noise by the rubbing together 

 of any hard and rough parts of their bodies, which happened to 

 be in contact ; and that from the noise thus produced being in 

 some way useful, the rough surfaces were gradually developed 

 into regular stridulating organs. Some beetles as they move, 

 now produce, either intentionally or unintentionally, a shuffling 

 noise, without possessing any proper organs for the purpose. 

 Mr. Wallace informs me that the Euchirus longimanus (a 

 Lamellicorn, with the anterior legs wonderfully elongated in the 

 male) " makes, whilst moving, a low hissing sound by the pro- 

 " trusion and contraction of the abdomen ; and when seized it 

 " produces a grating sound by rubbing its hind-legs against the 

 " edges of the elytra." The hissing sound is clearly due to a 

 narrow rasp running along the sutural margin of each elytron ; 

 and I could likewise make the grating sound by rubbing the 

 shagreened 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 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 the stridulating organs in the Coleoptera 

 differing according to sex; but Landois, who has carefully 

 examined several species, observed no such difference ; nor did 

 Westring; nor did Mr. G. E. Crotch in preparing the many 

 specimens which he had the kindness to send me. Any difference 

 in these organs, if slight, would, however, be difficult to detect, 

 on account of their great variability. Thus, in the first pair of 

 specimens of Necrophorus humator and of Pelobius which I ex- 

 amined, the rasp was considerably larger in the male than in 

 the female; but not so with succeeding specimens. In Geo- 

 trvpes stercorarius the rasp appeared to me thicker, opaquer, 

 and more prominent in three males than in the same number of 

 females; in order, therefore, to discover whether the sex°s 

 differed in their power of stridulating, my son, Mr. F. Darwin, 

 collected fifty-seven living specimens, which he separated into two 

 Jots, according as they made a greater or lesser noise, when held 

 in the same manner. He then examined all these specimens, 

 and found that the males were very nearly in the same proportion 



