INTERSTITIAL CELLS OF THE CHICKEN TESTIS. 145 



substance where the nuclei are mostly round is loose and retic- 

 ular, while the fibers of the sheath lie parallel and close together, 

 and look as though they were stretched tight around the testis. 

 This suggests that the difference in the shape of the nuclei may 

 be due to difference in pressure relations. 



Further, none of these cells of the interstitial substance show 

 any signs of glandular activity. The so-called "interstitial 

 cells" have been described in a recent paper by Mazzetti as 

 grouped in complexes in the intercanalicular spaces, as polyhe- 

 dral or ovoid with abundant protoplasm, large round nucleus, an 

 evident nucleolus, protoplasm in two zones, a clear peripheral 

 and an intensely-coloring central, also as containing secretory 

 granules, either crystalline or fatty in nature. There are no 

 such cells in the interstitial substance of the testis of just- 

 hatched chicks, and the connective tissue cells which make up 

 this substance show no sign of glandular activity. In sections 

 of material cleared in clove oil so as not to dissolve fat, great 

 masses of fat stained black by osmic appear in the interstitial 

 tissue, but they are not grouped about any especial cell, and 

 have no appearance of being secreted by any of these cells 

 (Fig. 2). 



This being the condition in the quiescent testes of the just- 

 hatched chick, we may next compare with it the testes of birds 

 in which active spermatogenesis is going on. 



In the older birds, there is a striking individual variation in 

 the size of the seminal tubules. This variation has no relation 

 to breed, age, time of year, or apparent stages of the germ cells, 

 but occurs in birds of the same breed, and age, killed on the same 

 day, with the germ cells in both showing all stages of spermato- 

 genesis. However, there is one constant relation, the relation 

 of the size of the seminal tubules to the amount of interstitial 

 tissue. Wherever the seminal tubules are small the inter- 

 stitial spaces are wide, and where the seminal tubes are large, 

 the interstitial spaces are narrow. Figures 3 and 4 bring out 

 this point. It is not only the width of the spaces between any 

 two tubules that varies but also the size of the triangular spaces 

 where any three or four tubules come into juxtaposition. This 

 relation can be proved by accurate measurements. 



