PLATE 1 



EXPLANATION OF FIGURES 



1 Longitudinal section of testis of Desmognathus fusca. May 24; fixed in 

 Hermann's fluid; iron hematoxylin stain. From the primary spermatogonia in 

 the portion at the bottom of the photograph, one passes up through a gradual 

 succession of stages to spermatids at the top of the figure. The nearly mature 

 spermatocytes i just below them may be distinguished by their larger size. The 

 boundary between the cells destined to furnish spermatozoa that season and the 

 residual cells, is not yet evident in this specimen. 



2 Longitudinal section, testis Desmognathus fusca, fixed June 7, in Hermann's 

 fluid ; iron hematoxylin stain. The interstitial cells about the degenerated lobules 

 occupy the upper portion, below them come developing spermatozoa; at the lower 

 end, spermatogonia. The boundary is becoming well marked. Enlarged photo- 

 grapli of the boundary region is shown in fig. 4. 



3 Longitudinal section, testis Desmognathus, fixed yej)tember 7 in Hermann's 

 fluid; iron hematoxylin. The body of the testis occupied by spermatozoa, the 

 lower portion by spermatogonia. The boundary is thus conspicuous. Fig. 5 

 shows an enlarged view of the boundary. An intermediate stage is shown in fig. 6. 



4 Testis Desmognathus. Photograph giving an enlarged view of the boundary 

 region of fig. 2. Spermatocytes i occupy the upper lobules, spermatogonia the 

 lower lobules, the separation being particularly clear on the right side. Three 

 lobules of spermatogonia at the boundary region show more or less extensive 

 karyolysis. 



5 Testis of Desmognathus. Photograph giving an enlarged view of the bound- 

 ary region of fig. 3. Spermatozoa occupy the lobules above the boundary, sper- 

 matogonia those below. Degenerations are .seen in one entire lobule and in 

 portions of two others. 



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