. The descent of man, and selection in relation to sex. Evolution (Biology); Sexual selection in animals; Sexual dimorphism (Animals); Sex differences; Human beings. Fig. 22.—Bledius tauras, magnified. Left-hand figure, male; right-hand figure, female. Siagonium we have a case of dimorphism, for the males can be divided into two sets, differing greatly in the size of their bodies, and in the development of their horns, without any intermediate gradations. In a species of Bledius (fig. 22), also belonging to the Staphylinidae, male specimens can be found in the same locality, as Prof. "Wes
. The descent of man, and selection in relation to sex. Evolution (Biology); Sexual selection in animals; Sexual dimorphism (Animals); Sex differences; Human beings. Fig. 22.—Bledius tauras, magnified. Left-hand figure, male; right-hand figure, female. Siagonium we have a case of dimorphism, for the males can be divided into two sets, differing greatly in the size of their bodies, and in the development of their horns, without any intermediate gradations. In a species of Bledius (fig. 22), also belonging to the Staphylinidae, male specimens can be found in the same locality, as Prof. "Westwood states, "in which the central horn of the tho- rax is very large, but the horns of the head quite rudi- mental; and others, in which the thoracic horn is much shorter, while the protuberances on the head are ; " Here, then, we apparently have an instance of compensa- tion of gi'owth, which throws light on the curious case just given of the loss of the upper horns by the males of Onitis farcifer. Law of Battle.—Some male beetles, which seem ill fitted for fighting, nevertheless engage in conflicts for the possession of the females. Mr. Wallace " saw two males of Leptorhynchus angustatus, a linear beetle with a much *• Kirby and Spence, iliid. vol. iii. p. 329. '^ 'Modern Classification of Insects,' vol. i. p. 1*72. On the same page there is an account of Siagonium. In the British Museum I noticed one male specimen of Siagonium in an intermediate condition, so that the dimorphism is not strict. «» 'The Malay Archipelago,' vol. ii. 1869, 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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