SEXUAL SELECTION 399 



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 E. cribratostriatus 

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

 divided into two portions, and the female is completely desti- 

 tute 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 ex- 

 tremely fine ribs, parallel to and resembling those on the 

 abdominal rasp; whether these ridges serve as an indepen- 

 dent 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 surface of this seg- 

 ment, when held in the proper light, is seen to be clothed 

 with hairs, which are absent or are represented by exces- 

 sively fine down in the males. It should be noticed that in 

 all Ooleoptera the effective part of the rasp is destitute of 

 hairs. In 0. senegalensis the difference between the sexes 

 is more strongly marked, and this is best seen when the 

 proper abdominal segment is cleaned and viewed as a trans- 

 parent object. In the female the whole surface is covered 

 with little separate crests, bearing spines ; while in the male 

 these crests in proceeding toward the apex become more and 

 more confluent, regular, and naked; so that three-fourths 

 of the segment is covered with extremely fine parallel ribs, 

 which are quite absent in the female. In the females, how- 

 ever, of all three species of Oryctes, a slight grating or strid- 

 ulating sound is produced when the abdomen of a softened 

 specimen is pushed backward and forward. 



In the case of the Heliopathes and Oryctes there can 



