Chaf. X. Coleoptera. 305 



to the females in both the lots. Mr. F. Smith has kept alive 

 numerous specimens of Monoynchus pseudacori (Curculionidae), 

 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 discovered that 

 the males alone of two species of Heliopathes (Tenebrionida?) 

 possess stridulating organs. I examined five males of II. gibbus, 

 and in all these there was a well-developed rasp, partially 

 livided 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 

 //. 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 ; 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 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 

 nasicomis 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 segment, when 

 held in the proper light, is seen to be clothed with hairs, which 

 are absent 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 between 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- 

 fourths 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 

 etridulating 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 



