. 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. CRUSTACEANS. 301 verted (fig. 4) into an elegant and sometimes wonderfully complex prehensile organ.* It serves^ as I hear from Sir J. Lubbock^ to hold the female, for this same purpose one of the two posterior legs (h) on the same side of the body is converted into a forceps. In another family the inferior or posterior antennaB are ^^ curiously zigzagged ^^ in the males alone. In the higher crustaceans the ante
. 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. CRUSTACEANS. 301 verted (fig. 4) into an elegant and sometimes wonderfully complex prehensile organ.* It serves^ as I hear from Sir J. Lubbock^ to hold the female, for this same purpose one of the two posterior legs (h) on the same side of the body is converted into a forceps. In another family the inferior or posterior antennaB are ^^ curiously zigzagged ^^ in the males alone. In the higher crustaceans the anterior legs are developed into chelae or pincers; and these are gen- erally larger in the male than in the female—so much so that the market value of the male edible crab (Cancer pagurits), according to Mr. C. Spence Bate, is five times as great as that of the female. In many species the chelae are of unequal size on the opposite side of the body, the right- hand one being, as I am informed by Mr. Bate, generally though not invariably the laigest. This ine- quality is also often much greater in the male than ixx the female. The two chelae of the male often differ in structure (figs. 5, 6 and 7), the smaller one resembling that of the female. What advantage is gained by their inequality in size on the opposite sides of the body and by the inequality being much greater in the the male than in the female; and why when they are of equal size both are often much larger in the male than in the female is not known. As I hear from Mr. Bate, the chelae are sometimes of such length and size that they cannot possibly be used for carrying food to the mouth. In the males of certain fresl. Fig. 4. Labidocera DarwlnU (from Lubbock). b. Part of right anterior an- tenna of male, forming a prehensile organ. Posterior pair of thoracio legs of male. Ditto of female. * See Sir J. Lubbock in '^Annals and Mag. of Nat. Hist.," vol. xi, 1853, pi. i and x; and vol. xii, 1853, pi. vii. See also Lubb
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