INTERSTITIAL CELLS OF URODELE TESTIS 239 



The wave of spermatogenesis, then, has brought into existence 

 in the testis, at one time, a complete series of stages in the 

 development of the interstitial cells; one can, by going from the 

 cephalic to the caudal lobules, see the complete history of their 

 development from stromal cells. In addition, the related changes 

 in the lobules can be seen at a glance. As some of the most 

 anterior lobules, the number varying with the individual animal, 

 may contain spermatozoa until March or early April, the testis 

 at any time between October and the succeeding spring shows 

 a similar succession of stages when examined in longisection. 

 The portion of the testis occupied by spermatozoa is of course 

 gradually reduced, with a corresponding cephalic shifting of any 

 particular stage of development of the interstitial cells. x\s 

 long as the spermatozoa remain in the lobule and the Sertoli 

 cells do not undergo degeneration, there is no development 

 around the lobule of the enlarged interstitial cells. When the 

 spermatozoa leave a lobule, however, and degeneration within 

 it begins, the surrounding cells then become modified accord- 

 ingly. The modification, then, occurs always in relation to 

 changes within the lobule — changes which can readily be seen 

 to be regressive, since the contents of the lobule undergo de- 

 generation and disappear from the testis. 



That the interstitial cells are in any way concerned with the 

 growth processes of the new spermatogenetic cycle is not evident. 

 The developing lobules of spermatogonia during the winter 

 months grow out from the hilus or region of the longitudinal 



Figs. 3, 4, and 5 Cross-sections (diagrammatic) of the testis of Necturus, to 

 illustrate the seasonal variations in its size and structure. All X 11. 



Fig. 3 The testis as it appears in August. The lobules are distended with 

 spermatids. No interstitial cells are present at this period, c, longitudinal 

 collecting duct; d, branch of the collecting duct; p, primary spermatogonia at 

 lobule apices; m, mesorchium; b, blood vessel. 



Fig. 4 The testis (caudal portion) in late December. The regenerating 

 lobules contain primary and secondary spermatogonia, while the peripheral half 

 of the testis is occupied by degenerating lobules and interstitial cells, d.l., de- 

 generating lobule; ?', interstitial cells. Other abbreviations as above. 



Fig. 5 Testis in June shortly before the final disappearance of the inter- 

 stitial cells, which at this time are seen as scattered hypertrophied cells at the 

 extreme periphery of the organ. Abbreviations as above. 



