. The descent of man : and selection in relation to sex. Evolution; Natural selection; Heredity; Human beings. Chap. X. Coleoptera. 303 are completely 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 Pelohius Ileriminni (one of Dytiscidje 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 uppe
. The descent of man : and selection in relation to sex. Evolution; Natural selection; Heredity; Human beings. Chap. X. Coleoptera. 303 are completely 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 Pelohius Ileriminni (one of Dytiscidje 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 Ceramhyx 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 a Trox sahidosus, 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 Typhoeus a narrow ridge runs obliquely across (r, fig. 2G) the coxa of each hind-leg (having in G. ster- corarius 84 ribs), which is scraped by a specially projecting part of one of the ab- dominal segments. In the nearly allied Copris lunaris, an excessively narrow fine rasp runs along the sutural margin of the elytra, with another short rasp near the basal outer mar- gin; but in some other Coprini the rasp is seated, according to Leconte,'^^ on the dorsal surface of the abdomen. In Oryctes it is seated on the pro-pygidium; and, according to the same entomologist, in some other Dynastini, on the under surface of the elytra. Lastly, Westring states that in Omaloplia
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