380 



SEXUAL SELECTION. 



Part II. 



for the rasps are seated "on the inferior surface of the 

 elytra, near their apices, or along their outer margins, 

 and the edges of the abdominal segments serve as the 

 scrapers. In Pelobius hermanni (one of Dytiscidse or 

 water-beetles) a strong ridge runs parallel and near to 

 the sutural margin of the elytra, and is crossed by ribs, 

 coarse in the middle part, but becoming gradually finer 

 at both ends, especially at the upper end ; when this 

 insect is held under water or in the air, a stridulating 

 noise is produced by scraping the extreme horny margin 

 of the abdomen against the rasp. In a great number 

 of long-horned beetles (Longicornia) the organs are alto- 

 gether differently situated, the rasp being on the meso- 

 thorax, which is rubbed against the pro-thorax ; Landois 

 counted 238 very fine ribs on the rasp of Ceramlyx 

 hews. 



Many Lamellicorns have the power of stridulating, 

 and the organs differ greatly in position. Some species 

 r stridulate very loudly, so that when 



Mr. F. Smith caught a Trox sabu- 

 losus, a gamekeeper who stood by 

 thought that he had caught a 

 mouse ; but I failed to discover the 

 proper organs in this beetle. In 

 Geotrupes and Typhaeus a narrow 

 ridge runs obliquely across (r, fig. 

 25) the coxa of each hind-leg, 

 having in Gr. stercorarius 84 ribs, 

 which are scraped by a specially- 

 projecting part of one of the abdo- 



Fig. 25. Hind-leg of Geotrupes . , T , , 



stercorarius (from Landois). niinal segments. In the nearly 



allied Copris lunar is, an excessively 

 narrow fine rasp runs along the 

 sutural margin of the elytra, with another short rasp 

 near the basal outer margin ; but in some other Coprini 



8 



Easp. c Coxa, /. Femur. 

 t. Tibia, tr. Tarsi. 



