PLATE 1 



EXPLANATION OF FIGURES 



1 Photogiapli of section of testis of adult woodchuck in early stage of 

 hibernation; Dec. 1; rectal temperature 19°C. ; reduced body weight 2525 grams, 

 of which one testis constituted 0.034 per cent. Carnoy's fluid; 4 ^ thick; iron 

 hematoxylin. X 129. Testes abdominal. Shows the relative amount of in- 

 terstitial tissue. Tubules filled with spermatocytes. 



2 Retouched photograph of characteristic interstitial space of above section 

 under higher magnification. X 527. Many small ordinary interstitial cells 

 with pigment granules stained black. Three large interstitial cells so filled with 

 large pigment granules that nucleus is obscured. 



3 Retouched photograph of section of testis of above animal showing a 

 characteristic group of large and especially pigmented interstitial cells. Car- 

 noy's fixer; 4 ^t thick; hematoxylin and eosin. X 527. Nucleus is irregular and 

 frequently displaced. A few ordinary interstitial cells, containing a few pigment 

 granules, are present. 



4, 5 Retouched photographs of newly foruLcd 'pigment cells' from same ani- 

 mal as in figure 23, under higher magnification. X 1053. In figure 5 the pig- 

 ment granules appear to have a peripheral distribution, occupying the position 

 of the fat globules froin which they were evidently formed. 



6 Photograph of a section of the testis of adult woodchuck in last stage of 

 hibernation; March 6; rectal temperature 12°C. ; reduced body weight 1S49 grams, 

 about two-thirds of the weight before hibernation. Same technique and mag- 

 nification as in figure 1. Testes abdominal. Animal beginning to wake up. 



7 Retouched photograph of section of testis of same animal as in figure 6. 

 Modified Zenker's fluid; 4/i thick; copper hematoxylin (Weigert). X 527. Many 

 granules (lipoid?) in addition to pigment. One large h^avily pigmented cell 

 present. 



8 Camera luoida drawing of cell pictures not infrequently met with during 

 the enlarging period in the interstitial cell cycle. Carnoy's fluid; 4 ^i thick; 

 iron hematoxylin. X 527. A suggestion that there has been nuclear division. 



9 Retouched photograph of interstitial cell at maximal stages of develop- 

 ment containing two nuclei. Carnoy's fluid; 4 n thick; iron hematoxylin. 

 X 1053. 



10 Photograph of section of testis of adult woodchuck with interstitial cells 

 maximal; May 8. Carnoy's fixer; 6 n thick; iron hematoxylin. X 200. Illus- 

 trates how the interstitial cells tend to be arranged in 'nests' in about half of 

 the animals in which the interstitial cells were greatly developed. 



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