INTERSTITIAL CELLS OF URODELE TESTIS 255 



hastened by growth pressures and such other influences as may 

 be brought to bear in an organ full of rapidly developing germ 

 cells. 



b. Diemyctylus viridescens. The interstitial cell cycle in 

 Diemyctylus bears a marked resemblence to that just described 

 for Desmognathus, the two differing of course in minor details. 

 The time relations in Diemyctylus are somewhat more difficult 

 to determine, especially from examination of but a small number 

 of animals presenting more or less individual variation. 



The spermatogenetic cycle may be briefly outlined as follows: 

 The maturation divisions and the transformation of the sperma- 

 tids are accomplished during the summer months. Some of the 

 spermatozoa leave the lobules in the fall; a mating at that time 

 is known to occur frequently (Gage, '91). The testis in Novem- 

 ber or December, as in the following spring (fig. 7, showing a longi- 

 tudinal section of the testis as it appears in May), consists of a 

 cephalic region containing spermatogonia and a caudal region 

 containing mature spermatozoa. The two regions are so sepa- 

 rated by a constriction and marked by color difference as to be 

 easily recognized upon gross examination. There may appear 

 at the point of constriction numerous degenerating lobules such 

 as Kingsbury and Hirsh describe in Desmognathus ; these appear 

 to mark a 'boundary plane' cephalad of which the spermatogonia 

 hold over till the following season. 



During the winter the mature spermatozoa remain in the 

 lobules, to be extruded when mating is resumed in the spring. 

 One animal killed May 30th had practically all lobules then 

 emptied, as shown in figure 7, while another killed June 7th had 

 fully as many spermatozoa as animals killed in winter. In one 

 case mating had presumably occurred; in the other all appear- 

 ances indicated the contrary. Another animal killed June 30th 

 showed maturation divisions in progress, spermatids transforming 

 and spermatozoa yet immature, but no mature spermatozoa of 

 the previous cycle present. 



The stromal cells surrounding lobules during the progress of 

 spermatogenesis are of the ordinary flattened type, rarely con- 

 taining lipoids demonstrable with osmic acid. During the 



