Stridulating Organs in Colcoptcra. 449 



Elwphrxis, the elytra and abdomen are the parts concerned. 

 The structures by which it is effected have been on the 

 whole correctly described, especially by Landois in his 

 " Thierstimmen," They consist of (1) a series of very 

 short ridges on the abdomen placed in a slightly arcuate 

 row on each side of the posterior part of the penultimate 

 dorsal segment (see PI. VII, fig. 1); and (2) a series of 

 longitudinal strios lying on the posterior expanded part of 

 the epipleural ridge wdiich runs along the underside of 

 each elytron (PI. VII, fig. \ci). Darwin, in referring to the 

 stridulation of Bldliisa, says : " the transverse ridges on 

 the furrowed border of the abdominal segment do not come 

 into play, as far as I could judge, in scraping the rasps on 

 the elytra," and Landois, quoting this remark, fails to ex- 

 plain exactly how stridulation is effected. In other beetles 

 which stridulate by rubbing the abdomen against the 

 elytra, the movement of the abdomen is a backward and 

 forward one, but in the present case, judging from the 

 direction of the ridges and stria3, these parts can only come 

 into play, when the abdomen is moved from side to side, 

 and such, I conclude, is the actual way in which the stri- 

 dulation is brought about. This method of stridulating 

 would account also for the fact that the riJges on the 

 abdomen form an arc instead of being placed in a straight 

 transverse row, the actual arrangement being the one best 

 adapted in order that each ridge should act most effect- 

 ively in scraping the striae on the elytra. 



In FeloMus and Trox the stridulating file is situated on 

 the underside of each elytron close alongside its sutural 

 margin, a transverse ridge at the border of one of the 

 posterior abdominal segments acting as the scraper. Dr. 

 Sharp has given a full account (" Eut. Mo. Mag." 1897) of 

 the position and structure of the organs in the genus Trox, 

 correcting the misstatements that had previously appeared 

 in reference to them. In Ligyrus the stridulating file is 

 imperfectly developed, consisting of a number of feeble 

 ridges crossing the central part of the under surface of 

 each elytron. A similar structure is met with in a few 

 otljer genera of ScarahwidcT. 



It has long been known that certain of the weevils are 

 capable of stridulating, the sound produced being remark- 

 ably loud considering the size of the species. The position 

 of the stridulating area in these beetles was, however, never 

 accurately ascertained until Landois investigated the matter, 



