S98 THE DESCENT OF MAN 



the grating sound by rubbing the shagreened surface of 

 the femur against the granulated margin of the correspond- 

 ing 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 

 Weslring has written about this beetle, it seems very doubt- 

 ful whether it possesses any true rasp, though it has the 

 power of emitting a sound. 



FroTQ the analogy of the Orthoptera and Homoptera, I 

 expected to find the stridulating organs in the Coleoptera 

 difEering according to sex; but Landois, who has carefully 

 examined several species, observed no such difference; nor 

 did Westring; nor did Mr. Gr. R. 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 examined, the rasp was consider- 

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

 succeeding specimens. In Oeotrupes 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 sexes differed in their 

 power of stridulating, my son, Mr. P. Darwin, collected 

 fifty-seven living specimens, which he separated into two 

 lots, 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 to the females in both the lots. 

 Mr. F. Smith has kept alive numerous specimens of 

 Monoynchus pseudacori (Curculionidse) and is convinced 

 that both sexes stridulate, and apparently in aa equal 

 degree. 



Nevertheless, the power of stridulating is certainly a 

 sexual character in some few Coleoptera. Mr. Crotch dis- 

 covered that the males alone of two species of Heliopathes 

 (Tenebrionidee) possess stridulating organs. I examined 



