580 Gideon S. Dodds. 



and flattened and their nuclei decrease in size, so that by stage 

 13 the germ-cells stand out prominently in the peritoneum 

 (fig. 33). 



During this period the cells of the coelomic mesoblast are angu- 

 lar in outline, while the germ-cells are rounded. Cell boundaries 

 between somatic cells are very indistinct and at times cannot be 

 distinguished at all, but the boundaries of germ-cells are always 

 fairly distinct. The cytoplasm of the germ-cells does not stain 

 deeply, so that they are always paler than the surrounding cells, 

 but not conspicuously so. These pale cells must not be confused 

 with other lightly staining cells scattered about in the embryo, 

 nor with the glistening white cells common in the entoblast. It 

 was also noticed that when a deep eosin stain was used the germ- 

 cells frequently took on a yellowish hue, but this was not conspic- 

 uous. 



Turning now to the nucleus we find some points of interest. 

 Figs. 29-33 show that the nucleus of germ-cells is noticeably larger 

 than that of other cells. This is already quite well marked in 

 stage 9 (fig. 29), and the difference becomes more pronounced 

 in each succeeding stage, because the nucleus of the somatic 

 cells is becoming continually smaller while that of the germ-cells 

 remains of constant size. The shape of the nucleus also is differ- 

 ent in the two kinds of cells. In somatic cells it is usually quite 

 regular, its outline being circular or elliptical, while in germ-cells 

 it is decidedly irregular, being commonly quite deeply indented 

 at one side or having a still more irregular shape. This character 

 of the cell is shown in figs. 29-33, but in some cases the nucleus 

 lies in such a position that its irregularlity of contour cannot 

 be shown in drawings. 



The chromatin is the one conspicuous feature in which the two 

 kinds of cells cannot be seen to differ. In both the greater part 

 of the chromatin-linin reticulum is next the nuclear membrane, 

 and in both it also covers the plasmosomes (nucleoli) . 



Perhaps the most striking difference between the two kinds of 

 cells is seen in the plasmosomes, and this is the feature which 

 more than any other was used in distinguishing them. In the 

 germ-cells there are tw^o small plasmosomes, usually quite widely 



