500 CHARLES H. SWIFT 



The primordial germ-cells, at the stage of 31 to 33 somites, are 

 frequenty found in groups of three or four, and are typical germ- 

 cells in all respects (fig. 2) . Only two facts relating to them are 

 worthy of special attention. The yolk material found in them is 

 subject to great variation and is undergoing some change, which 

 is evidenced by the varydng reaction to the osmic acid and stain. 

 In some germ-cells the yolk is black, in others brown or yellow, 

 while in others it is stained by the dye used rather than the fixing 

 agent. In some cases all these changes are shown in a single 

 germ-cell. The yolk material is probably being used up in cell 

 metabolism, or being transported elsewhere. 



The amoeboid appearance of the primordial germ-cells at this 

 stage is also worthy of mention. This property was not evident 

 in the germ-cells of the four and one-half day chick, owing to 

 the fact that active migration had ceased. However, the germ- 

 cells at 31 to 33 somites are highly amoeboid. Nearly all pos- 

 sess an oval shape, while many are drawn out into a tapering 

 process, which extends between the somatic cells. This process 

 is single and is usually on the side of the cell opposite to the 

 attraction-sphere. 



Embryos with 29 and 26 pairs of somites may be classed to- 

 gether, since there is no difference worthy of mention as far as 

 the position of the germ-cells is concerned. In these embryos 

 of this age the primordial germ-cells are found in the splanchnic 

 mesoderm at no great distance from the point where splanchno- 

 pleure and somatopleure become continuous, that is, near the 

 coelomic angle. In the embryo possessing 29 somites 110 germ- 

 cells were counted. Of this number the vast majority (98) were 

 found to be in the splanchnic mesoderm while only 12 were 

 counted in the somatopleuric side of the angle of the coelom. 



The primordial germ-cells in both these embryos are present 

 either in the mesodermal portion of the splanchnopleure or be- 

 tween the mesoderm and entoderm. In not a single instance is 

 one to be seen in the entoderm. The germ-cells are usually 

 found singly, although, as was mentioned before, they may oc- 

 cur in groups of two to four. They are all situated behind the 

 level of the 20th mesoblastic somite. 



