THE TYPICAL CELL 15 



toward the opposite poles of the spindle. The two daughter 

 nuclei thus receive from the mother cell precisely equivalent por- 

 tions of chromatic substance. The cleavage of the chromatin 

 segments frequently occurs at a very early period, and may even 

 antedate the formation of the chromosomes by making its appear- 

 ance in the spireme stage. 



Anaphase. The daughter chromosomes are now drawn toward 

 the opposite poles of the achromatic spindle, about which they are 

 again arranged in a wreath-like manner to form the diaster. The 

 daughter chromosomes are apparently connected with each other 

 during their migration by the fine achromatic connecting or inter- 

 zonal fibers of the central spindle. Minute chromatic thickenings 

 in the equator of this spindle (cell plate, mid-body) indicate the 

 future plane of cytoplasmic cleavage. 



Telophase. The cytoplasm of the cell divides along the cell 

 plate or equatorial plane of the achromatic spindle. Thus each 

 daughter cell not only receives equivalent portions of chromatin 

 through the daughter chromosomes, but the achromatic structures 

 are likewise equally divided, one centrosome, with its surrounding 

 aster or attraction sphere, going to each daughter cell. Thus a 

 portion at least of the achromatic spindle persists as the attraction 

 sphere of the resting nucleus. Other portions go to form the 

 " nebenkern " which is present in many cells. 



The daughter chromosomes now become thickened, convoluted, 

 and finally crowded or fused together to form the daughter skein 

 or spireme. The nuclear wall and nucleolus reappear, though the 

 manner of their origin is not yet understood. 



As a final change, and a preparation for future division, the 

 centrosome frequently divides. In this case the double centro- 

 some (diplosomc) persists throughout the resting stage. 



