S96 THE DESCENT OF MAN 



abdomen, on the pygidium or pro-pygidium, and is scraped 

 in the same manner 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." In certain Curculionidae and Cara- 

 bidsB" the parts are conipletely 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 segments serve as the scrapers. In Pelobius 

 Eermanni (one of DytiscidsB, 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 the extreme 

 horny margin of the abdomen being scraped against the 

 rasps. In a great number of long-horned beetles (Longi- 

 cornia) the organs are situated quite otherwise, the rasp 

 being on the meso-thorax, which is rubbed against the pro- 

 thorax; Landois counted 238 very fine ribs on the rasp 

 of Cerambyx heros. 



Many Lamellicorns have the power of stridulating, and 

 the organs diifer greatly in position. Some species stridu- 

 late very loudly, so that when Mr. P. Smith caught a Trox 

 sabulosus, a gamekeeper, who stood by, thought he had 

 caught a mouse ; but I failed to discover the proper organs 

 in this beetle. In Geotrupes and Typhceus a narrow ridge 

 runs obliquely across (r. Fig. 26) the coxa of each hind-leg 

 (having in G. stercorarius 84 ribs), which is scraped by 

 a specially projecting part of one of the abdominal seg- 

 ments. In the nearly allied Gopris lunaris, an excessively 



" Schiodte, translated in "Annals and Mag. of Nat. Hist.," vol. xx., 1867, 

 p. 37. 



" Weatring has described (Kroyer, "Naturhist. Tidskrift," B. ii., 1848-49, 

 p. 334) the stridulating organs of these two, as well as in other families. In 

 the CarabidsB I have examined Maphrns uUginosus and Blethisa multiptmctata, 

 sent to me by Mr. Crotch. In Blethisa the transverse ridges on the furrowed 

 border of the abdominal segment do not, as far as I could judge, come into play 

 in scraping the rasps on the elytra. 



