368 SEXUAL SELECTION. [Part II. 



is seated on the dorsal apex of the abdomen, on the py- 

 gidium or pro-pygidium, and is scraped as above by the 

 elytra. In Heterocerus, which belongs to another family, 

 the rasps are placed on the sides of the first abdominal 

 segment, and are scraped by ridges on the femora. 71 In 

 certain Curculionidse and Carabidse,™ the parts are com- 

 pletely reversed in position, 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 seg- 

 ments 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 stim- 

 ulating noise is produced by scraping the extreme horny 

 margin of the abdomen against the rasp. In a great num- 

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

 altogether 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 Ceram- 

 byx heros. 



Many Lamellicorns have the power of stridulating, 

 and the organs differ greatly in position. Some species 

 stridulate very loudly, so that when Mr. F. Smith caught 



that Dermestes murinus stridulates, but he searched in vain for the appa 

 ratus. Scolytus has lately been described by Mr. Algen as a stridulator 

 in the ' Edinburgh Monthly Magazine,' 1869, Nov., p. 130. 



71 Schiodte, translated in 'Annals and Mag. of Nat. Hist.' vol. xx. 

 1867, p. 37. 



72 Westringhas described (Kroyer, 'Naturhist. Tidskrift,' B. ii. 1848- 

 '49, p. 334) the stridulating organs in these two, as well as in other fam- 

 ilies. In the Carabidae I have examined Elaphrus uliginosus and Blethisa 

 multipunctata, sent to me by Mr. Crotch. In Blethisa the transverse 

 ridges on the furrowed border of the abdominal segment do not com« 

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



