Chap. X.] COLEOPTERA. 371 



quently my son, Mr. F. Darwin, in order to discover 

 whether the sexes differed in their power of stridulating, 

 collected fifty-seven living 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 

 sexual character in some few Coleoptera. Mr. Crotch has 

 discovered that the males alone of two species of Helio- 

 pathes (Tenebrionidae) possess stridulating organs. I ex- 

 amined five males of II. gibbus, and in all these there way 

 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 rudi- 

 ment of the rasp, the membrane of this segment being 

 transparent and much thinner than in the male. In II. 

 cribratostriatus the male has a similar rasp, excepting 

 that it is not partially divided into two portions, and the 

 female is completely destitute of this organ ; but in addi- 

 tion the male 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 independent 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 

 Oryctes, we have a nearly parallel case. In the females 

 of 0. gryphus and nasicornis the ribs on the rasp of the 

 pro-pygidium are less continuous and less distinct than in 

 the males ; but the chief difference is that the whole upper 



