INTERSTITIAL CELLS OF THE CHICKEN TESTIS. 



37 per cent., 13 per cent., 31 per cent, and 54 per cent, of the 

 dark-staining nuclei which have the long shape of typical connec- 

 tive tissue nuclei. It seems then that staining capacity of nuclei 

 is not a satisfactory method of distinguishing interstitial cells. 

 There is one more point in the frequent descriptions of intersti- 

 tial cells to be considered. Is there any evidence that the cells 

 of the interstitial tissue are secreting fat? We have already 

 found fat present in testes of just-hatched chicks, but decided 

 that it probably was not a secretion. Fat is also present in 



FIG. 8. Same as Fig. 7, but from cf 1 2323. S = spermatozoa. X 1,000. 



the older testes, and is represented by the black dots in the 

 drawings. Comparison of Figs. 5 and 7 with Figs. 6 and 8 will 

 show that the fat is inside of the tubules as well as in the intersti- 

 tial tissue. The fat globules in the interstitial tissue are not 

 arranged like secretory granules in the cytoplasm of cells. They 

 are mostly in long rows as though packed in spaces between con- 

 nective tissue fibers. Figs. 5 and 7 show nearly as much fat 

 near typical connective tissue nuclei as near the round or dark- 

 stained nuclei of the "interstitial cells." A comparison of Figs. 

 7 and 8 shows much fat in Fig. 7 where there are only connective 

 tissue nuclei in the interstitial space, and no fat in Fig. 8, where 

 there is a small group of round dark-staining nuclei. Fig. 9 

 shows a part of a large mass of interstitial tissue where the nuclei 

 are mostly round. This is evidently a so-called interstitial gland. 



