320 



SEXUAL SELECTION. 



[Part II. 



a 



from the left-hand one, the latter resembling in its sim- 

 ple tapering joints the antennae of the female. In the male 



the modified antenna is either 

 swollen in the middle or angu- 

 larly bent, or converted (fig. 3) 

 into an elegant, and sometimes 

 wonderfully complex, prehensile 

 organ. 5 It serves, as I hear from 

 Sir J. Lubbock, to hold the fe- 

 male, 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 pos- 

 terior antenna? are "curiously zig- 

 zagged " in the males alone. 



In the higher crustaceans the 

 anterior legs form a pair of chelae 

 or pincers, and these are gener- 

 ally larger in the male than in 

 the female. In many species the 



Fig. 3.— Labirtocera Darwinii chelae On the Opposite sides of the 



(from Lubbock). l l . . 

 a. Part of ns?ht-band anterior body are of unequal Size, the right- 

 antenna of male, forming a l-i i • T ~~» :^-T^„*^^^ 



prehensile oro-an hand one being, as I am mlormea 



*' P £o?Se rSfthethoraciC by Mr. D. Spence Bate, generally, 

 c. Ditto of female. though not invariably, the largest. 



This inequality is often much greater in the male than in 

 the female. The two chelae also often differ in structure 

 (figs. 4, 5 and 6), the smaller one resembling those of the fe- 

 male. What advantage is gained by their inequality in size 



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

 pis. i. and x. ; and vol. xii. (1853) pi. vii. See also Lubbock in • Transact. 

 Ent, Soc' vol. iv. new series, 1856-1858, p. 8. With respect to the zig- 

 zagged antennae mentioned below, see Fritz Miiller, ' Facts and Argu- 

 ments for Darwin,' 1869, p. 40, foot-note. 



