196 



THE GERM-PLASM 



in addition to those of the endoderm, and is therefore not 

 merely a primary endoderm cell. This then divides again and 

 forms two cells, of which the one marked 3 on the left side of 

 the figure only contains primary constituents of the endoderm, 

 and is therefore an endoderm cell proper; while that marked 3' 

 represents the first rudiment of the mesoderm and of certain 

 portions of the endoderm, and contains in addition the primary 

 constituents of the primary germ-cells. This cell (3'") divides into 

 two (4' and 4"), thus separating the above-named rudiments into 

 those for the right and the left sides of the body ; and finally, the 



Fio. 16. — Diagram 0/ the germ-track of Rhabditis nigrovenosa. — The various 

 generations of cells are indicated by Arabic numbers, the cells of the germ-track 

 are connected by thick lines, and the chief kinds of cells are distinguished by vari- 

 ous markings: — the cells of the germ-track by black nuclei, those of the meso- 

 blast (Mes) by a dot in each, those of the ectoderm {Eit) are white, those of the 

 endoderm {Ent) black; in the primitive germ-cells {ur Kz) the nuclei are white. 

 The cells are only indicated up to the twelfth generation. 



complete separation of the rudiments of the mesoderm and endo- 

 derm occurs, and results in one daughter-cell (5"). containing the 

 primary constituents of the mesoderm and primary germ-cells, 

 while the other gives rise to a cell of the endoderm proper. 

 Tlie primary constituents of the primary germ-cells remain con- 



