INSECTS. 345 



examined several species, observed no such difference; nor 

 did Westring; nor did Mr. G-. 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 

 liumator and of Pelobius 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 ; in order, therefore, to discover 

 whether the sexes differed in their power of stridulat- 

 ing, 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 (Cur- 

 culionidse), and is convinced that both sexes stridulate, 

 and apparently in an 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 

 (Tenebrionidse) possess stridulating organs. I examined 

 five males of H. gibbus, and in all these there was a well- 

 developed rasp, partially divided into two, on the dorsal 

 surface of the terminal abdominal segment; while in the 

 same number of females there was not even a rudiment of 

 the rasp, the membrane of this segment being transparent 

 and much thinner than in the male. In H. cribratostriatus 

 the male has a similar rasp, excepting that it is not par- 

 tially divided into two portions, and the female is com- 

 pletely destitute of this organ; the male in addition has on 

 the apical margins of the elytra, on each side of the suture, 

 three or four short longitudinal ridges, which are crossed 

 by extremely fine ribs, parallel to and resembling those on 

 the abdominal rasp; whether these ridges serve as an inde- 

 pendent rasp or as a scraper for the abdominal rasp, I could 

 not decide ; the female exhibits no trace of this latter 

 structure. 



Again, in three species of the Lamellicorn genus Oryc- 



