CRUSTACEANS. 



263 



resembling in its simple tapering joints the antennae of the fe- 

 male. In the male the modified antenna is either swollen in the 

 middle or angularly bent, or converted 

 (fig. 4.) into an elegant, and sometimes 

 wonderfully complex, prehensile organ." 

 It serves, as I hear from Sir J. LubboclJ, 

 to hold the female, and for this same pur- 

 pose 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 "curi- 

 ously zigzagged" in the males alone. 



In the higher crustaceans the anterior 

 legs are developed into chelae 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 (Can- 

 cer pagurus), according to Mr. C. Spence 

 Bate, is five times as great as that of the 

 female. In many species the chelae are of 

 unequal size on the opposite side of the 

 body, the right-hand one being, as I am 

 informed by Mr. Bate, generally, though 

 not invariably, the largest. This inequal- 

 ity is also often much greater in the male 

 than in the female. The two chelae of the 

 male often differ in structure (figs. 5, 6, 

 and 7), the smaller one resembling that of 

 the female. 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 

 chelae are sometimes of such length and size that they 

 cannot possibly be used for carrying food to the mouth. 

 In the males of certain fresh-water prawns (Palaemon) the right 

 leg is actually longer than the whole body." The great size of 

 the one leg with its chelaB may aid the male in fighting with his 



Fig. 4. Labidocera Dar- 

 winil (from Lubbock). 



a. Part of right anterior 

 antenna of male, form- 

 ing a prehensile organ. 



b. Posterior pair of thor- 

 acic legs of male. 



c. Ditto of female. 



" See Sir J. Lubbock 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. Soc," vol. iv. new series, 1856-1858, p. 8. With respect 

 to the zig-zagged antennae mentioned below, see Fritz MuUer, 'Facts 

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



"" See a paper by Mr. C. Spence Bate, with flgures, in 'Proc. Zoolog. 



