PLATE 3 



EXPLANATION OF FIGURES 



20 Testis of Desmognathus. Longitudinal section of a single enlargement 

 to show the condition in early autumn, after some of the lobules have been 

 emptied. A, region occupied by spermatogonia; B, boundary plane; C, lobules 

 yet filled with spermatozoa; D, empty lobules surrounded by various stages 

 in the development of interstitial cells. X 16. 



21 Testis of Desmognathus. Caudal portion of the section shown in figure 20, 

 under higher magnification (X 43). Stages in the enlargement of the stromal 

 cells are readily seen; typical interstitial cells are present in the caudal region 

 first emptied. Note the condition of the interlobular tissue while spermatozoa 

 are present in the lobule as compared with that following their extrusion. 



22 Interstitial cells of Desmognathus at their maximal enlargement, during 

 the summer months. An area of dense cytoplasm containing the idiozome 

 appears at one side of the nucleus as in the interstitial cells of Necturus. The 

 smaller granules and mitochondria are largely grouped aroimd this idiozome; 

 the peripheral cytoplasm of the cell is left vacuolated through the solution of 

 larger lipoid droplets. Flemming's fixation; iron hematoxylin. X 600. 



23 Testis of Salamandra atra; lobules are yet partially filled with sperma- 

 tozoa, but the interlobular nuclei are rounding out and increasing in numbers. 

 At the lower left is a mitotic figure, bulging somewhat into the adjacent lobule. 

 Zenker's fixation; 10^; iron hematoxylin. X 120. 



24 Testis of Salamandra atra; section of a region caudal to that shown in 

 figure 23. The interstitial cells here form prominent rings around the degener- 

 ating lobules. Their osmicated lipoids make them especially prominent struc- 

 tures in this preparation. No stain. X 120. 



276 



