INTERSTITIAL CELLS OF URODELE TESTIS 241 



€ells around each lobule. Between the cephalic and caudal 

 lobules intermediate ones present a series of intermediate types; 

 €ven in the middle of the testis interstitial cell development does 

 not reach the limits set in the most caudal region. 



It is suggested that the explanation of the above lies in the 

 modifications in this region of the conditions under which the 

 interstitial cells develop. The caudal lobules are emptied early 

 in the fall; their degeneration begins at a time when the stream 

 of nutritive material no longer used by the reproductive cells is 

 still being brought to the testis, undiminished by any decreased 

 metabolism of the animal due to the onset of colder weather. 

 Since the lobules of the next sexual cycle are as yet little devel- 

 oped, there is but slight opportunity for them to affect, either by 

 mechanical pressure or diversion of the nutritive material, the 

 modification of the stromal cells around the emptied lobules. 

 The cephalic lobules, which are emptied more slowly during the 

 winter months, undergo their degenerative changes during the 

 period of the animal's lowest metabolic activity. The developing 

 lobules of 'the anterior end of the testis are but little behind those 

 of the caudal end; and, before the spermatozoa have left all the 

 anterior lobules, these regenerated lobules are of such size that 

 they very possibly affect, both by their growth pressure and 

 demand for nutritive materials, the course of development of the 

 interstitial cells around the degenerating lobules. Though 

 factors other than those named mS^y contribute to the difference, 

 the reduced number of interstitial cells of the cephalic region 

 stands at any rate as the expression of a less favorable environ- 

 ment rather than as an indication of intrinsic differences of the 

 stromal cells of the two regions. That those of the cephalic 

 region possess the same potentialities as those in any other is 

 evidenced by the changes many of them undergo. 



d. Details of cell structure. The finer details of cell structui'e 

 in successive developmental stages require a more extended de- 

 scription than that previously accorded them. In cells around 

 recently emptied lobules (or even earlier) fuchsinophile granules 

 of a size considerably larger than the minute mitochondria 

 appear (figs. 27 and 28). Though the mitochondria are also 



