150 



ALICE M. BORING. 



nuclei (Figs. 2, 5, 6). From the figures and statements in 

 Mazzetti's paper, it appears that he has made the shape of the 

 nucleus the important factor in deciding which cells are interstitial 

 cells. But his results, in entire agreement with those of the 

 present paper, show a complete series of gradations from his 

 so-called interstitial cells with round nuclei to typical connective 

 tissue cells. Also he finds a variation in the proportion of inter- 

 stitial cells in animals of widely different species. Here in the 

 chicken there is as much variation in this regard in birds of the 

 same breed, if we take the shape of the nuclei as the basis for 

 deciding which are interstitial cells, as Mazzetti describes for 

 different genera or orders. 



The only other difference evident in the cells of the interstitial 

 tissue is the staining capacity of the nuclei. This difference is 





...--., 



>- 



FIG. 7. Section of testis in c? 666, showing part of one seminal tubule (T) 

 and the adjacent interstitial tissue (/). The fat is indicated by black dots. X 

 1,000. 



not noticeable in just-hatched chicks, but very apparent in the 

 older birds. Some stain very dark, and some remain almost 

 unstained. Table I. gives the mean number and Table II. the 

 percentage of dark and light cells. In cfs 666, and 1271, there 

 are 12 per cent, and 4 per cent, dark cells, and in d* s 2323 and 147, 

 there are u per cent, and I per cent. That would be a great 

 variation in the per cent, of interstitial cells, if a dark staining 

 nucleus could be regarded as a distinctive character of an intersti- 

 tial cell. But it cannot. I made a differential count of the 

 long and round nuclei among the dark staining ones, and found 



