28O NATHAN FASTEN. 



divisions. Also, many of the tubules show spermatids trans- 

 forming into spermatozoa, although the mature spermatozoa are 

 mainly confined to the tubules located near the inner or median 

 portion of the testicular lobe as well as in the spermatophores 

 of the vasa deferentia. 



When sections of the tubules are examined, many of them are 

 observed to be constructed on the same plan as those of Menippe 

 mercenaria which were described and pictured by Binford ('13). 

 Two or three well-defined zones may oftentimes be distinguished 

 in one tubule. For instance, at one pole in the sectioned tubule 

 there might be a thin layer of spermatogonia and the rest of the 

 tubule might contain either transforming spermatids, or mature 

 spermatozoa, or primary spermatocyte divisions, or those of the 

 secondary spermatocyte stage, or even growth stages. When 

 there are three zones in the tubule these are often made up of (i) 

 a thin region of spermatogonia at one end, (2) a middle portion 

 filled with transforming spermatids, and (3) a region of mature 

 spermatozoa filling in the opposite pole. 



The mature spermatozoa, when they enter the vasa deferentia, 

 are surrounded by pouches known as spermatophores (Fig. 67). 

 These spermatophores are formed by the secretions of the inner 

 layer of epithelium which lines the vas deferent tube. For a more 

 detailed description of these structures see Fasten, '17. During 

 copulation the spermatophores are discharged from the vasa 

 deferentia of the male and are deposited within the seminal 

 receptacle of the female, where they remain dormant until the 

 ova are mature for fertilization. 



4. SPERMATOGENESIS. 

 A. Spermatogonial Stages. 



The Spermatogonial cells generally line one end of the tubule. 

 They are fairly large cells, with distinct cytoplasmic outlines and 

 prominent nuclei. In Cancer magister, primary and secondary 

 Spermatogonial stages can be distinguished (Figs. I 8). Of the 

 two, the primary spermatogonium (Fig. i) is somewhat larger in 

 size, and from it by division (Figs. 2-7), is derived the secondary 

 spermatogonium (Fig. 8). 



The resting primary spermatogonium (Fig. i) contains numer- 



