PLATE 2 



EXPLANATION OF FIGURES 



14 Testis of Necturus April 28th; transection through the middle portion. 

 Regenerating lobules contain secondary spermatogonia. The lipoid in the 

 degenerating lobules is blackened by osmic acid. Interstitial cells with a com- 

 l)aratively small lipoid content occupy the spaces between these lobules. This 

 section is comparable to one through the caudal portion of the testis in the fall or 

 early winter. Hermann's fixation; 8;u; no stain. X 36. 



15 Testis of Necturus June 9th; caudal portion of the organ. The photo- 

 graph includes the distal ends of two regenerating lobules, between which are 

 compressed many interstitial cells, some of which will doubtless revert to the 

 original stromal-cell type. At the end of the lobule at the right is a bit of a 

 degenerating lobule, now greatly reduced in size, but containing considerable 

 lipoid. Bensley's fixation; 6/^; no stain. X 120. 



16 Same as figure 15, but with the lobules cut in cross-section through their 

 distal ends; interstitial cells are here crowded between lobules instead of being 

 arranged in distinct rings as during their developmental stages illustrated in 

 figures 10 and 12. At the left is a region into which the tips of the developing 

 lobules have not yet extended. The large fat droplets here are in a degenerating 

 lobule. X 120. 



17 Testis of Necturus July 21st. Median sagittal section. A few hyper- 

 troi)hied, fat-laden interstitial cells are scattered along the periphery of the 

 testis (right). The fat droplets in the center are in the Sertoli cells of the lobule. 

 Only very rarely are any interstitial cells found between lobules at this time. 

 Flemming's fixation; 5m ; no stain. X 120. 



18 Testis of Necturus April 3rd ; caudal portion. Shows the massing of inter- 

 stitial cells near the periphery of the organ; degenerated lobules and blood ves- 

 sels are crowded between masses and cords of these cells. A group of degener- 

 ating nuclei appears in the upper left of the photograph. Giant centrospheres, 

 now at their maximal size, are seen as lightly stained areas associated with the 

 normal nuclei. Allen's fluid; 10;u; iron hematoxylin. X 154. 



19 A portion of the same section shown in figure 18, but under higher mag- 

 nification (X 300). A blood corpuscle in the upper left corner of the photograph 

 indicates the position of a blood vessel; the interstitial cells, through crowding, 

 may become intimately associated with blood vessels at this time, although not 

 so associated in the earlier part of their cycle. 



274 



