CRUSTACEANS. 



301 



verted (fig. 4) into an elegant and sometimes wonderfully 

 complex prehensile organ.* It serves, as I hear from Sir 

 J. Lubbock, to hold the female, 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. 



In the higher crustaceans the a 



anterior legs are developed into 

 chelae or pincers; and these are gen- 

 erally larger in the male than in the 

 female so much so that the market 

 value of the male edible crab ( Cancer 

 paguriis), 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 ine- 

 quality 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 

 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- 



*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, 1853-1858, p. 8. With 

 respect to the zigzagged antennae mentioned below, see Fritz Milller, 

 ' I'acts and Arguments for Darwin," 1869, p. 40, foot note. 



Fig. 4. 



Labidocera Darwinii 

 (from Lubbock). 



a. Part of right anterior an- 



tenna of male, forming a 

 prehensile organ. 



b. Posterior pair of thoracio 



legs of male. 



c. Ditto of female. 



