CBUSTAGEANS. 303 



statement quoted by Milne-Edwards, * the male and the 

 female live in the same burrow, and this shows that they 

 pair; the male closes the mouth of the burrow with one of 

 its chela?, which is enormously developed; so that here it 

 indirectly serves as a means of defense. Their main use, 

 however, is probably to seize and to secure the female, and 

 this in some instances, as with Gammarus, is known to be 

 the case. The male of the hermit or soldier crab {Pagurni<) 

 for weeks together, carries about the shell inhabited by the 

 female, t The sexes, however, of the common shore-crab 

 (Carcinus m(Bnas), as Mr. Bate informs me, unite directly 

 after the female has moulted her hard shell, when she is so 

 soft that she would be injured if seized by the strong 

 pincers of the male; but as she is caught and carried about 

 by the male before moulting, she could then be seized with 

 impunity. 



Fritz Miiller states that certain species of Melita are dis- 

 tinguished from all other amphipods by the females having 

 '* the coxal lamellae of the penultimate pair of feet pro- 

 duced into hook-like processes, of w hich the males lay hold 

 with the hands of the first pair." The development of 

 these hook-like processes has probably followed from those 

 females which were the most securely held during the act 

 of reproduction, having left the largest number of offspring. 

 Another Brazilian amphipod {Orchestia Darwinii, fig. 8) 

 presents a case of dimorphism, like that of Tanais; for 

 there are two male forms, which differ in the stnic- 

 ture of their chelae. J As either chela would certainly suf- 

 fice to hold the female for both are now used for this pur- 

 pose the two male forms probably originated by some 

 having varied in one manner and some in another ; 

 both forms having derived certain special, but nearly equal 

 advantages, from their differently shaped organs. 



It is not known that male crustaceans fight together for 

 the possession of the females, but it is probably the case ; 

 for with most animals when the male is larger than the 

 female, he seems to owe his greater size to his ancestors 



*" Hist. Nat. des Crust.," torn, ii, 1837, p. 50. 



f Mr. C. Spence Bate, " Brit. Assoc, Fourth Report on tlie Fauna 

 of S. Devon." 



^ Fritz Muller, "Facts and Arguments for Darwin," 1869, pp. 

 ^28, 



