INTERSTITIAL CELLS OF URODELE TESTIS 229 



SO that to some extent successive developmental stages may be 

 obtained for study in a single longitudinal section. The wave 

 of spermatogenesis is clearly much more rapid, however, than 

 in Desmognathus, Diemyctylus, and Salamandra, tending to 

 cause the germ cells of all parts of the testis to be in more nearly 

 the same stage of development at any particular time. 



Regardless of the arrangement of the lobules in the testis and 

 the varying rapidity of the degenerative and regenerative changes 

 they undergo at the close of the spermatogenetic cycle, the testes 

 of all urodeles examined show, in common, this fundamental 

 feature: the lobule develops as a unit; its germ cells all mature 

 and leave the testis as spermatozoa, after which the lobule, 

 more or less as a unit, degenerates and disappears. And since 

 the developmental and degenerative processes of the urodele 

 testis are widely separated in this way in point of time, only one 

 spermatogenetic cycle being completed each year, or isolated 

 regionally in the organ through the cephalic movement of a 

 spermatogenetic wave, we can turn to a study of these lower 

 forms to more clearly demonstrate with which phases of sperma- 

 togenesis, if any, interstitial cell development may be most 

 closely correlated. 



Spermatogenetic cycle and mating period of Necturus 



Necturus males killed in November and the winter months 

 following show few or no spermatozoa in the testis. Those 

 present occupy a few lobules in the most cephalic portion of the 

 organ. They represent the last-matured germ cells of the 

 recently ended sexual cycle, and entirely disappear from the 

 testis before the end of the following April. During the winter 

 months primary spermatogonia occupy the apices of the lobules, 

 which are now partially filled with secondary spermatogonia. 

 Cell divisions may be seen during these winter months, sperma- 

 togenesis evidently proceeding, however, at a much reduced rate 

 in winter as compared with later spring months. In the spring 

 and early summer rapidly succeeding divisions result in the 

 secondary spermatogonia occupying the entire testis by July. 



