. The descent of man, and selection in relation to sex. Evolution (Biology); Sexual selection in animals; Sexual dimorphism (Animals); Sex differences; Human beings. 10 SEXUAL SELECTION [Part EC strictly compared with those which are so frequent with gallinaceous Pio. 29.— Xiptaophorus Hellerii. Upper figure, male; lower figure, female. In a siluroid fish, inhabiting the fresh waters of South America, namely the Pltcostomus barbatus " (Fig. 30), the male has its mouth and interoperculum fringed with a beard of stiff hairs, of which the female shows hardly a trace. These hairs ar
. The descent of man, and selection in relation to sex. Evolution (Biology); Sexual selection in animals; Sexual dimorphism (Animals); Sex differences; Human beings. 10 SEXUAL SELECTION [Part EC strictly compared with those which are so frequent with gallinaceous Pio. 29.— Xiptaophorus Hellerii. Upper figure, male; lower figure, female. In a siluroid fish, inhabiting the fresh waters of South America, namely the Pltcostomus barbatus " (Fig. 30), the male has its mouth and interoperculum fringed with a beard of stiff hairs, of which the female shows hardly a trace. These hairs are of the nature of scales. In another species of the same genus, soft flexible tentacles project from the front part of the head of the male, which are absent in the female. These tentacles are prolongations of the true skin, and therefore are not homologous with the stiff hairs of the former species; but it can hardly be doubted that both serve the same purpose. What this purpose may be it is difficult to conjecture; ornament does not here seem probable, but we can hardly suppose 15 Dr. Gunther makes this remark: ' Catalogue of Fishes in the Brit- ish Museum,' vol. iii. 1861, p. 141. M See Dr. Gunther on this genus, in 'Proc. Zoolog. Soc.' 1868, p. 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. Appleton and Company
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