ORIGIN OF THE GERM-CELLS 



147 



two-cell stage ! Moreover, from the outset the progenitor of the germ- 

 cells differs from the somatic cells not only in the greater size and rich- 

 ness of chromatin of its nuclei, but also in its mode of mitosis; for in 

 all those blastomeres destined to produce somatic cells a portion of 



ig- 73- Origin of the primordial germ-cells and casting out of chromatin in the somatic 

 cells of Ascaris. [BOVERI.] 



A. Two-cell stage dividing; j. stem-cell, from which arise the germ-cells. B. The same from 

 the side, later in the second cleavage, showing the two types of mitosis and the casting out of 

 chromatin (c) in the somatic cell. C. Resulting 4-cell stage; the eliminated Chromatin at c. 

 />. The third cleavage, repeating the foregoing process in the two upper cells. 



the chromatin is cast out into the cytoplasm, where it degenerates, and 

 only in the germ-cells is the sum-total of the chromatin retained. In 

 Ascaris megalocephala univalens the process is as follows (Fig. 73): 

 Each of the first two cells receives two elongated chromosomes. As 



