SEX-CORDS AND SPERMATOGONIA IN CHICK 395 



having disappeared. The cords stain more intensely now, stand 

 out more sharply against the light connective-tissue back- 

 ground and contain peritoneal cells and i)rimordial genn-cells. 

 There has been an important change, however, for the latter 

 are much more nimierous than in any preceding age (fig. 2). 

 This increase in number of the germ-cells is evident even when 

 examining the section under the low power microscope, for 

 they are seen as clear spots thickly sprinkled throughout the 

 cords. On using the higher powers this is confirmed, and, in 

 addition, it is seen that the prmiordial genn-cells are actively 

 dividing (fig. 2). In a single section through the testis from 

 4-10 are foimd in mitosis. The increase in the size of the semi- 

 niferous cord is due to the increase in the number of the germ- 

 cells for the peritoneal cells are quiescent. 



Semon ('87) in the chick and Popoff ('09) in the chick and 

 a number of other fonns, described the 'ureier' and 'les o\ailes 

 males' (primordial germ-cells) as having a definite position near 

 the center of the seminiferous cords, while the peritoneal cells 

 occupied the periphery. I have not found that to be the case 

 (figs. 2 and 3). In all stages up to and including the 15 daj^ 

 stages examined, I find them to be scattered evenly throughout 

 the cord — some at its center and some at the periphery. Later 

 on they are all found at the periphery of the cord. 



A few words are necessary in regard to the structure of the 

 primordial germ-cells. As will be seen from all the figures illus- 

 trating this article there is little change in the primordial germ- 

 cells or their tissue. In fact, there is little change to record in 

 all their history from origin until they become oogonia or sper- 

 matogonia, unless it is a gradual loss of vitellus and a progres- 

 sive slight decrease in size (Swift, '14 and '15). However, with 

 the beginning of division in the female line of germ-cells, which 

 resulted in the oogonia, there was a change in the arrangement 

 of the mitochondria (Swift, '15). While the primordial germ- 

 cells were quiescent in the germinal epithelium of the embryonic 

 ovary, up to the 8 day stage, the mitochondria were evenly 

 scattered in the cytoplasm (Swift, '15). At 8 days the germ 

 cells began to divide, and in all the later stages the mitochon- 



