THE CELL AND CELL DIVISION 



43 



part the cytoplasm, nucleus, the centrosome, and even many 

 of the plastids. So that the final result of the process is typically 

 the formation of two daughter cells similar to each other and 

 also to the parent cell in all essential respects save in size. 



The division of cells occurs in two quite dissimilar ways. The 

 simpler method, and the less frequent, is termed direct division 

 or amitosis (Flemming). Here the first step is sometimes the 

 elongation and constriction of the nucleolus, when this is 

 present, into two separate daughter nucleoli, or in other cases 

 the appearance of a new second nucleolus (Fig. 19). Next the 

 whole nucleus divides into two, sometimes by simple constric- 

 tion into two separate elements, sometimes by the ingrowth of 



FIG. 19. Amitosis in tendon cells of a new-born mouse. After Nowikoff, X 800. 



nc, nucleolus. 



a partition wall, or in still other cases, by the formation of two 

 new nuclear membranes within the original membrane, the 

 disappearance of the latter freeing the two daughter nuclei. 

 This division of a nucleus is typically followed by the division 

 of the cytoplasmic portion of the cell which is ordinarily 

 accomplished by the development of a cell wall between the 

 two daughter nuclei. Very frequently, however, division of 

 the cell body does not follow and the cell remains binucleate; or 

 this process of nuclear fission may be repeated, a multinucleate 

 cell resulting, such as a striated muscle cell. In such cases of 

 incomplete cell division the essence of the process seems to be 

 the rapid increase of nuclear surface and then volume; it is 



