. The descent of man, and selection in relation to sex. Evolution; Natural selection; Heredity; Human beings; Sexual selection in animals; Sexual dimorphism (Animals); Sex differences. rig. 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 abdomi- nal segment, each rasp* consisting of 126 to 140 fine ribs. These ribs are scraped against the posterior margins of the elytra, a s
. The descent of man, and selection in relation to sex. Evolution; Natural selection; Heredity; Human beings; Sexual selection in animals; Sexual dimorphism (Animals); Sex differences. rig. 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 abdomi- nal segment, each rasp* 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 gen- eral outline. In many Orioceridae, and in Clythra 4:-pu7Zc- tata (one of the Chrysomelidae), and in some Tenebrionidae, etc.,f 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 * Landois, ** Zeitschrift fiir wiss. * B. xvii, 1867, s. 127. f I am greatly indebted to Mr. G. R. Crotcli 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 be- lieves that the power of stridulation in the Clythra has not been pre- viously observed. I am also much indebted to Mr. E. W. Janson, for information and specimens. I may add that my son, Mr. F. Darwin, finds that Dennestes murimus stridulates, but he searched in vain for the apparatus. Scolytus has lately been described by Dr. Chapman as a stridulator, in the " Entomologist's Monthly Maga- aane," vol. vi, p. 130. I. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Darwin, Charles, 1809
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