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Chap. IX.
Crustaceans.
267

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

Fig. 5. 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.

Fig. 6. Second leg of male Orchestia Tucuratinga (from Fritz Müller).
Fig. 7. Ditto of female.

often much larger in the male than in the female, is not known. As I hear from Mr. Bate, the chelæ 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 (Palæmon) the right leg is actually longer than the whole body.[1] The great size of the one leg with its chelæ may aid the male in fighting with his rivals; but this will not account for their

  1. See a paper by Mr. C. Spence Bate, with figures, in 'Proc. Zoolog. Soc.' 1868, p. 363; and on the nomenclature of the genus, ibid., p. 585. I am greatly indebted to Mr. Spence Bate for nearly all the above statements with respect to the chelæ of the higher crustaceans.