352 



THE DESCENT OF MAN 



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, 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 an-, 



other family the inferior or posterior 

 antenna are "curiously zigzagged" in 

 the males alone. 



In the higher crustaceans the an- 

 terior legs are developed into chelse, 

 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 [Cancer pagurus), 

 according to Mr. C. Spence Bate, is 

 five times as great as that of the 

 female. In many species the chelee 

 are of unequal size on the opposite 

 sides of the body, the right-hand one 

 being, as I am informed by Mr. Bate, 

 generally, though not invariably, the 

 larger. This inequality is also often 



wmii ' (/roTn ^LuSbock).''^ ^uch greater in the male than in the 



Fio. 

 pinii I, 



Part of right anterior au- -fprnnlp 

 tenna o( male, forming a '■'^'^'^^'^ 



prehensile organ. .6. Poste- often differ in structurc 



nor pair of thoracic legs of ^-^"^^ ^^^^^ i^j. uuj. k^.juu.j.w 

 male. c. Ditto of female. 



that of the female. 



The two chelse of the male 

 (Figs. 5, 6, 

 and 7), the smaller one resembling 

 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. As I hear from Mr. Bate, the chelse are sometimes 

 of such length and size that they cannot possibly be used 



' See Sir J. Lulibock, in "Annals and Mag. of Nat. Hist.," vol. xi., 1853, 

 pi. i. and x. ; and vol. xii., 1853, pi. vii. See also Lubbock in "Transact. Ent. 

 See," vol. iv., new series, 1856-1858, p. 8. Witli respect to the zigzagged 

 antennae mentioned below, see Fritz Miiller, "Facts and Arguments for Darwin, " 

 1869, p. 40, footnote. 



