320 



SEXUAL SELECTION. 



[Part II. 



a 



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

 pie tapering joints the antenna? 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. 6 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 antennae 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 

 FlG ' 3 "7from i Lu C bbock) )arwinii cnelse on tne opposite sides of the 



a. Part of right-hand anterior body are of Unequal size, the right- 



antenna of male, forming a 1 ■* •■ T . n ■* 



prehensile organ. hand one being, as I am informed 



b. Posterior pair of the thoracic -i -»«- rv o t> n 



legs of male. by Mr. L>. fepence Bate, generally, 



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 Muller, ' Facts and Argu- 

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



