3 TO SEXUAL SELECTION. [Part II. 



velopcd into regular stridulating organs. Some beetles, as 

 they move, now produce, either intentionally or uninten- 

 tionally, a shuffling noise, without possessing any proper 

 organs for the purpose. Mr. Wallace informs me that the 

 JEuchirus longimanus (a Lamellicorn, with the anterior 

 legs wonderfully elongated in the male) "makes, while 

 moving, a low hissing sound by the protrusion and con- 

 traction 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 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 Orthoj)tera 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 ac- 

 count of the great variability of these organs. Thus, in 

 the first pair of the JSTecropliorus humator and of the 

 Pelohius which I examined, the rasp was considerably 

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

 succeeding specimens. In Geotrupes stercorarius the rasp 

 appeared to me thicker, opaquer, and more prominent in 

 three males than in the same number of females ; conse- 



