Archive image from page 276 of The descent of man . The descent of man : and selection in relation to sex descentofmanseledarw Year: 1874 CRUSTACEANS. 263 resembling in its simple tapering joints the antennae of the fe- male. In the male the modified antenna is either swollen in the middle or angularly bent, or converted (fig. 4.) into an elegant, and sometimes wonderfully complex, prehensile organ.' It serves, as I hear from Sir J. Lubbock, to hold the female, and for this same pur- pose one of the two posterior legs (b) on the same side of the body is converted into a forceps. In another f
Archive image from page 276 of The descent of man . The descent of man : and selection in relation to sex descentofmanseledarw Year: 1874 CRUSTACEANS. 263 resembling in its simple tapering joints the antennae of the fe- male. In the male the modified antenna is either swollen in the middle or angularly bent, or converted (fig. 4.) into an elegant, and sometimes wonderfully complex, prehensile organ.' It serves, as I hear from Sir J. Lubbock, to hold the female, and for this same pur- pose one of the two posterior legs (b) on the same side of the body is converted into a forceps. In another family the inferior or posterior antennae are 'curi- ously zigzagged' in the males alone. In the higher crustaceans the anterior legs are developed into chelae or pincers; and these are generally larger in the male than in the female,—so much so that the market value of the male edible crab (Can- cer pagurus), 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 largest. This inequal- ity is also often much greater in the male than in 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. V/hat advantage is gained by their inequality in size on the opposite sides of the body, and by the inequality being much greater in 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 fresh-water prawns (Palaemon) the right leg is actually longer than the whole body.° The great size of the one leg with its chel® may aid the male in fighting with his Fig-. 4. Labidoce
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