. The descent of man, and selection in relation to sex. Evolution; Natural selection; Sexual selection in animals; Human beings -- Origin; Sexual dimorphism (Animals). Chap. X.] INSECTS. 333. these organs for burrowing in sand-banks and making their nests. The tarsi of the front-legs are dilated in many male beetles, or are furnished with broad cushions of hairs; and in many genera of water-beetles they are armed with a round flat sucker, so that the male may adhere to the slippery body of the female. It is a much more unusual cir- cumstance that the females of some water-beetles (Dytiscus) ha
. The descent of man, and selection in relation to sex. Evolution; Natural selection; Sexual selection in animals; Human beings -- Origin; Sexual dimorphism (Animals). Chap. X.] INSECTS. 333. these organs for burrowing in sand-banks and making their nests. The tarsi of the front-legs are dilated in many male beetles, or are furnished with broad cushions of hairs; and in many genera of water-beetles they are armed with a round flat sucker, so that the male may adhere to the slippery body of the female. It is a much more unusual cir- cumstance that the females of some water-beetles (Dytiscus) have their elytra deeply grooved, and in Acilius sul- catus thickly set with hairs, as an aid to the male. The females of some other water- beetles (Hydroporus) have their elytra punctured for the same In the male of Crabro wibrarhis (fig. 8), it is the tibia which is dilated into a broad horny plate, with mi- nute membraneous dots, giv- ing to it a singular appearance like that of a In the male of Penthe (a genus of beetles) a few of the middle joints of the antennae are dilated and furnished on the inferior surface with cushions of hair, exactly like those on the tarsi of the Carabidoe, 6 We have here a curious and inexplicable case of dimorphisrh, for some of the females of four European species of Dytiscus, and of certain species of Hydroporus, have their elytra smooth; and no intermediate gradations between sulcated or punctured and quite smooth elytra have been observed. See Dr. H. Schaum, as quoted in the ' Zoologist,' vol. 184'7-'48, p. 1896. Also Kirby and Spence, 'Introduction to En- tomology,' vol. iii. 1826, p. 305. 7 Westwood, * Modern Class.' vol. ii. p. 193. The following statement. 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, 1809-1882. New York : D.
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