THE CELL AND CELL DIVISION 



65 



functional period of cell life. At the time of the next division 

 much of the chromatin is usually eliminated from the nucleus, 

 is cast out into the cytoplasm and disappears along with the 

 nucleolus (Fig. 32); the chromosomes which then appear, 



FIG. 32. Early cleavages of the egg of the Nematode, Ascaris. Origin of 

 primordial germ cells and casting out of chromatin in the somatic cells. From 

 Wilson, "Cell." after Boveri. A. Two-cell stage dividing; polar view, s, stem- 

 cell, from which the germ cells are derived. B. Later stage of same division; 

 lateral view, c, chromatin in somatic cell being thrown out into the cytoplasm. 

 C. Completion of four-cell stage showing eliminated chromatin. D. Division of 

 four-cell stage showing continued chromatin elimination in the third somatic 

 cell. 



or reappear, are similar in every respect to those in the preceding 

 division (Van Beneden). The chromosomes, therefore, show 

 the same specific constancy as any other characteristic of the 

 organism. 



