320 



SEXUAL SELECTION. 



[Part II. 



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

 ple tapering joints the antenna; of the female. In the male 

 the modified antenna is cither 



n 



swollen in the middle or angu- 

 larly bent, or converted (fig. 3) 

 into an elegant, and sometimes 

 ■wonderfully complex, prehensile 

 organ. '^ 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 

 chelffi on the opposite sides of the 

 body are of unequal size, the right- 

 hand one being, as I am informed 

 by Mr. D. Spence Bate, generally, 

 though not invariably, the largest. 

 This inequality is often much greater in the male than in 

 the female. The two chcloD also often diflfer in structure 

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

 male. What advantage is gained by their inequality in size 



Fig. 3.— Labirlocera Darwinii 

 (from Lubbock). 



a. Part of ric^ht-hand anterior 



nnteniia of male, forming a 

 prelionsilc organ. 



b. Postorior pair of the thoracic 



logs of male. 



c. Ditto of female. 



5 Sec Sir J. Lubbock in 'Annals, and Mas- of Nat. Hirt.' vol. xi. 1853, 

 pis. i. and x. ; and vol. xii. (18o3) pi. vii. Sec also Lubbock in ' Transact. 

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

 zagged antcnnjc mentioned below, sec Fritz Miiller, ' Facts and Argu- 

 ments for Darwin,' 1850, p. 40, foot-note. 



