166 



Eventually some of these become sperruatoblasts and 

 increase greatly in size. Each spermatoblast gives rise 

 to a large number of spermatozoa. In sections through 

 a mature testis it is difficult to distinguish the follicles, 

 as the cavities of the latter become almost obliterated by 

 the growth of the spermatoblasts. When the spermatozoa 

 are ripe they break free and are carried down into the 

 vas deferens. Here they become collected together in 

 small groups, and each group becomes surrounded by a 

 capsule to form a spermatophore. 



The spermatozoa (fig. 81) are non-motile. They 

 consist of a central dark portion containing a nucleus 

 and an outer clear margin. In side view the clear margin 

 is seen to be much thinner than the central part of the 

 cell, and has the appearance shown in fig. 81. The 

 diameter of the cell is about G/x. 



The presence of the spermatophores gives rise to the 

 white appearance so characteristic of the vasa deferentia 

 of mature male crabs. In small immature crabs the vas 

 deferens is narrow and almost transparent, due to the 

 absence of spermatophores. As pointed out by 

 Williamson, " the condition of maturity in the male is 

 the presence of ripe male elements in the vas deferens." 

 It is probable that most male crabs above 4| inches in 

 width are mature, although Williamson has given 

 instances of male crabs attaining maturity at a much 

 smaller size. 



2. FEMALE (fig. 77). 



The abdomen is broad, and all the somites are freely 

 movable. There is one pair of appendages on each of the 

 second, third, fourth and fifth somites. After the ova are 

 spawned they are attached to the eudopodite setae of the 

 abdominal appendages. The external genital apertures 



