302 THE DESCENT OF MAN. 



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 ap- 

 parently in an equal degree. 



Nevertheless, the power of stridulating is certainly a sexual char- 

 acter in some few Coleoptera. Mr. Crotch discovered that the 

 males alone of two species of Heliopathes (Tenebrionidae) 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; whilst 

 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 partially divided into 

 two portions, and the female Is completely destitute of this or- 

 gan; 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 resem- 

 bling 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 struc- 

 ture. 



Again, in three species of the Lamellicorn genus Oryctes, we 

 have a nearly parallel case. In the females of O. gryphus and 

 nasicornis the ribs on the rasp of the pro-pygidium are less con- 

 tinuous and less distinct than in the males; but the chief differ- 

 ence is that the whole upper surface of this segment, when held 

 in the proper light, is seen to be clothed with hairs, which are ab- 

 sent or are represented by excessively fine down in the males. It 

 should be noticed that in all Coleoptera the effective part of the 

 rasp is destitute of hairs. In 0. senegalensis the difference be- 

 tween the sexes is more strongly marked, and this is best seen 

 when the proper abdominal segment is cleaned and viewed as a 

 transparent object. In the female the whole surface is covered 

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

 these crests in proceeding towards the apex, become more 

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

 of the segment is covered with extremely fine parallel ribs, which 

 are quite absent in the female. In the females, however, of all 

 three species of Oryctes, a slight grating or stridulating sound is 

 produced, when the abdomen of a softened specimen is pushed 

 backwards and forwards. 



In the case of the Heliopathes and Oryctes there can hardly be a 

 doubt that the males stridulate in order to call or to excite the 

 females; but with most beetles the stridulation apparently serves 

 both sexes as a mutual call. Beetles stridulate under various emo- 



