254 R. R. HUMPHREY 



of Necturus. The peripheral cytoplasm is filled with larger 

 lipoid droplets or vacuolated when these have not been pre- 

 served. Figure 22 shows a group of these cells at their maximal 

 size. 



The Sertoli cells of the emptied lobules degenerate, lipoids 

 first accumulating within them as in Necturus. Their degenera- 

 tion proceeds rapidly, so that in the late spring the lobules hre 

 practically empty. The residual spermatogonia in the lobule 

 apices, instead of beginning multiplication as soon as the lobules 

 are emptied, or even before, as in Necturus, and so bringing about 

 their prompt regeneration, remain quiescent for several months.. 

 As a result of this delay in lobule regeneration, the caudal portion 

 of the testis becomes very much reduced in size, as has been 

 previously stated. After the degeneration of the emptied lobules 

 in this shrunken region, its* interstitial cells, though persisting 

 for a time, also disappear. Finally this portion of the testis 

 (fig. 6 E) is reduced to a slender thread-like structure, made up 

 chiefly of the central collecting duct and the residual sperma- 

 togonia surrounding it — a structure similar to that shown in 

 figure 1. The primary spermatogonia do not begin multiplica- 

 tion until some time after the disappearance of the interstitial 

 cells; by their growth the lobules of the region are eventually 

 regenerated. 



Although such regeneration of the lobules in any region does 

 not occur until after the disappearance of the interstitial cells 

 therefrom, this is more probably a part of a regulated growth 

 plan than a result of any inhibitory influence the interstitial 

 cells may exert. In Necturus, in which regeneration of the 

 lobules occurs more promptly, their growth takes place while 

 interstitial cells are still present in their maximal number. Far 

 from being inhibited by the presence of the interstitial cells, the 

 growth of the lobules, on the contrary, appears instrumental in 

 hastening the disappearance of these elements from the testis. 

 The interstitial cells of Desmognathus doubtless owe their longer 

 period of existence to their freedom from such influences. 

 Though tending to disappear when the degeneration of the lobule 

 they surround is completely effected, their disappearance is not 



