S54 THE DESCENT OF MAN 



burrow with one of its che sd, which is enormously devel- 

 oped; so that here it indirectly serves as a means of de- 

 fence. 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 her- 

 mit or soldier crab {Pagurus) for weeks together carries 

 about the shell inhabited by the female." The sexes, how- 

 ever, of the common she re-crab {Carcinus mcenas), 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 Hiiller sta',es 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 produced 

 into hook -like processes, of which the males lay hold with 

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

 hook-like proce jses has probably followed from those fe- 

 males which were the most securely held during the act 

 of reproduction having left the largest number of offspring. 

 Another Brazilian amphipod {Orchestia Darwirdi^ Fig. 8) 

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

 there are two. male forms, which differ in the structure of 

 their chelae." As either chela would certainly suffice to 

 hold the female — for both are now used for this purpose — 

 the two male forms probably originated by some having 

 varied in one manner, and some in another; both forms 

 havin;; derived certain special, but nearly equal, advan- 

 tages from -their differently shaped organs. 



It is not known that male crustaceans light 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 



■' Mr. 0. Spence Bate, Brit. Assoc, "Fourth Report on the Fauna of South 

 Devon." 



" Fritz MuUer, "Facts and Arguments for Darwin," 1869, pp. 25-28. 



