In some of the lower crustaceans, the right-hand anterior antenna of the male differs greatly in structure from the left-hand one, the latter resembling in its simple tapering joints the antennæ of the female. In the male the modified antenna is either swollen in the middle or angularly bent, or converted (fig. 3) into an elegant, and sometimes wonderfully complex, prehensile organ.[414] It serves, as I hear from Sir J. Lubbock, to hold the female, and for this same purpose 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 antennæ are “curiously zigzagged” in the males alone. [Illustration: Fig. 4. Anterior part of body of Callianassa (from Milne-Edwards), showing the unequal and differently-constructed right and left-hand chelæ of the male. N.B.—The artist by mistake has reversed the drawing, and made the left-hand chela the largest.] [Illustration: Fig. 5. Second leg of male Orchestia Tucuratinga (from Fritz Müller).] [Illustration: Fig. 6. Ditto of female.] In the higher crustaceans the anterior legs form a pair of chelæ or pincers, and these are generally larger in the male than in the female. In many species the chelæ on the opposite sides of the body are of unequal size, the right-hand one being, as I am informed by Mr. C. Spence Bate, generally, though not invariably, the largest. This inequality is often much greater in the male than in the female. The two chelæ also often differ in structure (figs. 4, 5, and 6), the smaller one resembling those 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 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. The chelæ are sometimes of such length and size that they cannot possibly be used, as I hear from Mr. Spence Bate, for carrying food to the mouth. In the males of certain freshwater prawns (Palæmon) the right leg is actually longer than the whole body.[415] It is probable that the great size of one leg with its chelæ may aid the male in fighting with his rivals; but this use will not account for their inequality in the female on the opposite sides of the body. In Gelasimus, according to a statement quoted by Milne-Edwards,[416] the male and female live in the same burrow, which is worth notice, as shewing that they pair, and the male closes the mouth of the burrow with one of its chelæ, which is enormously developed; so that here it indirectly serves as a means of defence. Their main use, however, probably is to seize and to secure the female, and this in some instances, as with Gammarus, is known to be the case. The sexes, however, of the common shore-crab (_Carcinus mænas_), as Mr. Spence Bate informs me, unite directly after the female has moulted her