INTERSTITIAL CELLS OF URODELE TESTIS 267 



Spermatogenesis, however, is not initiated by this autumnal 

 development and regression. 



Similarly, it is not apparent that the development of the 

 interstitial cells is responsible for the checking of the spermato- 

 genetic processes toward the close of the cycle. In those urodeles 

 with a slow spermatogenetic 'wave' (Desmognathus, Diemycty- 

 lus) a 'boundary plane' is established early in the season through 

 the degeneration of the germ cells in lobules near the anterior 

 end of the testis; only the germ cells caudal to this 'boundary 

 plane' then mature as spermatozoa during the current season. 

 The 'boundary plane' is established, however, before any lobules 

 are emptied, and hence its appearance does not coincide with 

 any proliferation of interstitial cells. Neither is there any 

 marked change at this time in those interstitial cells of Desmogna- 

 thus which were formed at the close of the preceding cycle; in 

 Diemyctylus such cells have already disappeared from the testis. 



On the whole, therefore, this study of the Leydig's cells in 

 urodeles adds little or no weight to the evidence in favor of their 

 interpretation as an endocrine organ. It does, however establish 

 — and more clearly than can he determined in the anuran, sau- 

 ropsid, or mauwialian testis — the close relation of the cells to re- 

 gressive and degenerative changes in the lobules. The part, if any, 

 these cells may play in the organism, during their temporary 

 hypertrophy or transformation from stromal cells, remains more 

 or less problematic. 



i 



SUMMARY 



1. In higher vertebrates the interstitial cells of the testis have 

 been found to vary greatly in their corrrelations with the phases 

 of the spermatogenetic cycle, though as a rule their greatest 

 development appears to be correlated with the later or regressive 

 phases. 



2. Such variations as appear are believed to result from the 

 complexity of the testis in these higher forms rather than from 

 intrinsic differences in the cells themselves in the different animals 

 investigated. 



