ORIGIN OF THE INDIVIDUAL 227 



daughter set of chromosomes along the fibers to either end 

 of the spindle. In this way each centrosome becomes asso- 

 ciated with one set of daughter chromosomes. 



The last stage, or telophase, is one of nuclear reconstruc- 

 tion and division of the cytoplasm. The chromosomes be- 

 come indistinct as they spin out to form the net-like arrange- 

 ment of the chromatin in the nucleus of each daughter cell; 

 a nuclear membrane arises; and the nucleus again assumes 

 the form of a definite spherical body characteristic of the 

 resting cell. It must be emphasized, however, that although 

 the chromosomes usually disappear from view as definitive 

 entities in the resting nucleus, nevertheless the individuality 

 of each persists and the same chromosomes emerge from the 

 nuclear complex at the next division period. 



Simultaneously with these nuclear changes, and before the 

 spindle and asters the machinery of mitosis disappear, 

 the division of the cytoplasm is initiated as indicated by an 

 indentation of the cell wall at the equator of the cell. This 

 gradually extends through the cytoplasm in the same plane 

 which the equatorial plate formerly occupied, until the cyto- 

 plasm is cut into two separate masses, each containing one 

 of the daughter nuclei and centrosomes. And one cell has 

 merged its individuality into two daughter cells by mitotic 

 division. 



A little thought will convince the reader that whereas the 

 mitotic process apparently results in merely a mass division 

 of the cytoplasm, the chromatin material is rearranged and 

 distributed in a manner which makes it possible for each cell 

 to receive a very definite share. Indeed this seems to be the 

 primary object of mitosis. For in many cases there is a very 

 great difference in the size of the resulting cells, but the num- 

 ber of chromosomes in each is the same. This, and other 

 evidence which will presently appear, has clearly established 



