PLATJ-: 2 



EXPLANATION OF FIGURES 



11 Photograph of section of testis of adult woodchuck practically at full 

 activity and been so for a week or more; March 21; rectal temperature 32°C.; 

 reduced body weight 1650 (about two-thirds of original weight before hiberna- 

 tion). Testes abdominal. Carnoy's fluid; 4 /x thick; iron hematoxylin. X 129. 

 Interstitial cells have greatly increased. 



12 Retouched photograph of a mass of interstial cells from preceding section 

 under higher magnification. X 527. Pigment scattered out in the abundant 

 cytoplasm which is vacuolated from having fat dissolved out. 



13 Retouched photograph of a group of interstitial cells from testis of same 

 animal as in figures 11 and 12. Modified Zenker's; 4m thick; copper hematoxylin. 

 X 527. Various stages in the expansion of the cells. 



14 Photograph of section of testis of same animal as in preceding figures in 

 this plate. Meves' fixer; 4 n thick; unstained and uncovered. X 129. Fatty 

 globules blackened with the osmic acid. Tubules contain much fat. Five 

 adipose cells are present (four in one group). Large blood vessels. Section too 

 near the surface of block to be perfect. 



15 Photograph of section of testis of adult woodchuck when interstitial cells 

 are maximal; during full activity and after feeding at least six weeks; May 10; 

 rectal temperature 37°C.; reduced body weight 2420, of which one testis consti- 

 tuted 0.111 per cent. Testes scrotal. Same technique and magnification as in 

 figures 1, -6 and 11. 



16 Retouched photograph of interstitial cells of preceding section under 

 higher magnification. X 527. Pigment nearly absent. Central cytoplasm 

 finely vacuolated (seen best in the cell marked with a +); peripheral cytoplasm 

 coarsely vacuolated. Vacuoles due to dissolving out the lipoids. To be com- 

 pared with figures 2 and 24. 



17 Retouched photograph of interstitial cells of same. animal as in figures 

 15 and 16. Modified Zenker's, etc., as in figures 7 and 13. X 527. The fine 

 vacuoles of figure 16 are here filled with granules (lipoid) stained black. Periph- 

 eral fat not stained. 



18 Photograph of section of testis with interstitial cells maximal. Meves' 

 fixer, etc., as in figure 14. X 129. Peripheral fat of interstitial cells and adi- 

 pose cells black. Two blood vessels. Insert shows three cells more highly 

 magnified. X 527. Nucleus of one cell shown as white spot. Section too near 

 the periphery of block to be perfect. The poor penetrating power of osmic 

 acid and the distortion of the testicular contents at the cut surface made perfect 

 sections illustrating relative amount of fat unavailable. 



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