. The descent of man, and selection in relation to sex. Evolution; Natural selection; Heredity; Human beings. 302 The Descent of Man. PartH. transition takes place by their becoming confluent and straight, and at the same time more prominent and smooth. A hard ridge on an adjoining part of the body serves as the scrape* for the rasp, but this scraper in some cases has been specially modified for the purpose. It is rapidly moved across the rasp, or conversely the rasp across the Fig. 25. Necrophorus (from Landois). r. The two rasps. Left-hand figure, part of the rasp highly magnified.
. The descent of man, and selection in relation to sex. Evolution; Natural selection; Heredity; Human beings. 302 The Descent of Man. PartH. transition takes place by their becoming confluent and straight, and at the same time more prominent and smooth. A hard ridge on an adjoining part of the body serves as the scrape* for the rasp, but this scraper in some cases has been specially modified for the purpose. It is rapidly moved across the rasp, or conversely the rasp across the Fig. 25. Necrophorus (from Landois). r. The two rasps. Left-hand figure, part of the rasp highly magnified. These organs are situated in widely different positions. In the carrion-beetles (Necrophorus) two parallel rasps (r, fig. 25) stand on the dorsal surface of the fifth abdominal segment, each rasp74 consisting of 126 to 140 fine ribs. These ribs are scraped against the posterior margins of the elytra, a small portion of which projects beyond the general outline. In many Crioceridse, and in Clyikra punctata (one of the Chrysomelidae), and in some Tenebrionidse, &c.,75 the rasp is seated on the dorsal apex of the 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 In certain Curculionidss and Carabidse,77 the parts 74 Landois, 'Zeitschrift fur wiss. Zoolog.' B. xvii. 1867, s. 127. 75 I am greatly indebted to Mr. G. R. Crotch for having sent me many prepared specimens of various beetles belonging to these three families and to others, as well as for valuable information. He believes that the power of stridulation in the Clythra has not been previously observed. I am also much indebted to Mr. E. W. Janson, for informa- tion and specimens. I may add that my son, Mr. F. Darwin, finds that Dermestes murinus stridulates, but he searched in vain for the apparatus. Scolyius has lately been
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