THE CELL AND PROTOPLASM. Xtfl 



from its fellow, and moves to the opposite end of 

 the nucleus toward the two- cen-trosomes ('Fi-g. 

 31). Whether they are pulled apart or pushed 

 apart by the spindle fibres is not certain, although 

 it is apparently sure that these fibres from the 

 centrosomes are engaged in the matter. Certain 

 it is that some force exerted from the two centro- 

 somes acts upon the chromosomes, and forces the 

 two halves of each one to opposite ends of the 

 nucleus, where they now collect and form two new 

 nucleii, with evidently exactly the same number of 

 chromosomes as the original, and with charac- 

 ters identical to each other and to the original 

 (Fig. 32). 



The rest of the cell division now follows rap- 

 idly. A partition grows in through the cell body 

 dividing it into two parts (Fig. 32), the division 

 passing through the middle of the spindle. In 

 this division, in some cases at least, the spindle 

 fibres bear a part a fact which again points to 

 the importance of the centrosomes and the forces 

 which radiate from them. Now the chromosomes 

 in each daughter nucleus unite to form a single 

 thread, or may diffuse through the nucleus to form 

 a network, as in Fig. 32. They now become sur- 

 rounded by a membrane, so that the new nucleus 

 appears exactly like the original one. The 

 spindle fibres disappear, and the astral fibres 

 may either disappear or remain visible. The 

 centrosome may apparently in some cases disap- 

 pear, but more commonly remains beside the 

 daughter nucleii, or it may move into the nucleus. 

 Eventually it divides into two, the division com- 

 monly occurring at once (Fig. 32), but sometimes 

 not until the next cell division is about to begin. 

 Thus the final result shows two cells each with a 



