464 CHARLES H. SWIFT 



usually scattered in all parts of the cytoplasm, but which may be 

 at the margin of the cell (fig. 7) . 



The oogonia or descendants of primordial germ-cells on the 

 other hand are round or oval in all cases, have a large nucleus, 

 with rather coarse chromatin granules. The attraction sphere 

 is large and just as characteristic as at 4 days (fig. 7). The 

 mitochondria are grouped around the sphere (fig. 7). This is 

 not a new character, since there was a suggestion of it at 7 days, 

 which had become constant at 8 days. 



The only difference in the oogonia in the 9-day chick as com- 

 pared with the primordial germ-cell of the 7-day stage is the dis- 

 appearance of the vitellus, the decrease in size of the cell, and the 

 grouping of the mitochondria (compare figs. 6 and 7). The last 

 began to be evident at an earlier stage and the first two can be 

 explained by the fact of active cell division. 



To repeat, there is very little difference between the oogonium 

 at 9 days and the germ-cell in the 7-day stage. There is a vast 

 deal of difference between the oogonium and the germinal epi- 

 thelium cell at any stage (figs. 7 and 8). 



In the 9-day chick it may be of interest to compare the primor- 

 dial germ-cells found in the medullary cords and the oogonia in 

 the germinal epithelium and primordial cortical cords. In the 

 first situation the germ-cells have retained all their primitive 

 characters, but the following are to be especially noted: The 

 cell is never seen dividing, the vitellus is still present, and the 

 mitochondria are scattered in the cell. Cells of this character 

 are never seen in the germinal epithelium, except in its medial 

 portion, where a few still retain all these primitive characters. 



The oogonia, although resembling the primitive type of germ- 

 cell in many ways, are yet distinctly different in others. 



At 9 days the ovary is becoming massive, due in great measure 

 to a change in the medulla. The medullary cords in that portion 

 of the gonad next the urinary organ have lengthened, become 

 thicker and some are developing a cavity. These cavities are 

 lined by cells, which are arranged like epithelial cells around a 

 lumen, and radiate towards the germinal epithelium. The al- 

 buginea has also thickened. 



