Chap. IX. 



CRUSTACEANS. 



329 



their chelae ; so that of the former, those which were best 

 able to find the female, and of the latter, those which were 

 best able to hold her when found, 

 have left the greater number of 

 progeny to inherit their respec- 

 tive advantages. 4 



In some of the lower crusta- 

 ceans, the right-hand anterior 

 antenna of the male differs 

 greatly in structure from the 

 left-hand one, the latter re- 

 sembling in its simple tapering 

 joints the antennae of the fe- 

 male. In the male the modi- 

 fied antenna is either swollen 

 in the middle or angularly bent, 

 or converted (fig. 3) into an 

 elegant, and sometimes wonder- 

 fully complex, prehensile organ. 5 

 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 

 another family the inferior or 

 posterior antennae are " curiously zigzagged ' : in the 

 males alone. 



Fig. 3. 



Labidocera Darwinii (from 

 Lubbock). 



Part of right-hand anterior an- 

 tenna of male, forming a pre- 

 hensile organ. 



Posterior pair of thoracic legs of 

 male. 



Ditto of female. 



4 ' Facts and Arguments for Darwin,' English translat. 1869, p. 20. 

 See the previous discussion on the olfactory threads. Sars has de- 

 scribed a somewhat analogous case (as quoted in 'Nature,' 1870, 

 p. 455) in a Norwegian crustacean, the Pontoporeia affinis. 



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

 1853, pi. i. and x. ; and vol. xii. (185H) pi. vii. See also Lubbock in 

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

 to the zigzagged antenna? mentioned below, see Fritz Miiller, ' Facts 

 and Arguments for Darwin ' 1869, p. 40, foot-note. 



