SEX-CORDS AND SPERMATOGONIA IN CHICK 399 



The interstitial cells are present in greater quantity, and 

 there has been some increase in the size of the cords ; the amount 

 of cord tissue, too, as compared with the stroma, has increased 

 (fig. 4). Practically all the primordial germ-cells have been 

 changed by division, giving rise to the spermatogonia (fig. 4). 

 There is no evidence of division in the peritoneal cells but there 

 number has not decreased. In certain regions of the seminif- 

 erous cord complex, it is evident that the spermatogonia are 

 beginning to assume a position at the periphery of the cord, next 

 to the basement membrane. This is very evident in the next 

 stage. There is no evidence of a lumen beginning to appear 

 in the cords. They still are solid, although it was at this age 

 that Semon ('87), in the chick, described one as being present. 



In the next embryo, that of 20 days development, there are 

 some important changes to record. 



The seminiferous cords are very massive and seem to be grow- 

 ing at the expense of the stroma, which is considerably reduced 

 in quantity (fig. 5). The interstitial cells (fig. 5), too, are not 

 as numerous as in the two preceding stages. The greatest 

 changes, however, have taken place in the structure and orien- 

 tation of the cords. 



The spermatogonia, which hitherto have had no definite ar- 

 rangement, being scattered helter-skelter throughout the cord, 

 now begin to be arranged in a definite manner. They are 

 placed against the basement membrane of the seminiferous 

 cord in such a way that their long axes are at right angles to the 

 long axis of the cord (fig. 5). Another striking fact is to be 

 noted, that the attraction-sphere, with its mitochondrial body, 

 is next to the basement membrane, while the nucleus is turned 

 toward the axis of the cord (fig. 5). That is to say, the vege- 

 tative pole of the spermatogonium is next the basement mem- 

 brane. The nucleus is excentrically placed, and always the 

 greatest mass of cytoplasm, in which is placed the attraction- 

 sphere, is towards the basement membrane (fig. 5). 



The cords, also, are beginning to have a cavity. This cavity 

 is far from being continuous and can be seen here and there 

 only, in the central axis of the seminiferous cord (fig. 5). This 



