CELL-DIVISION 21 



CHAPTER IV 



CELL-DIVISION 



THE process of cell-division is one of fundamental im- 

 portance, since it is the general mode of organic growth. 

 For a certain time the cells in any organism continue 

 to grow, but the cell's increase is restricted within 



mi 



Stages in division of Amoeba. 



narrow limits, and so the cell must divide if the growth 

 of the animal is to go on. 



There are two chief types of cell-division, known as 

 the direct and indirect, or as the amitotic and mitotic 

 or karyokinetic. The former is the less complex, and is 

 usually marked by the dumb-bell-like constriction of 

 the nucleus ; and without complex preliminaries one 

 cell divides into two. In the mitotic or karyokinetic, 

 which seems to be usual, there is a whole complex series 

 of changes, the ultimate end of which is to divide every 

 part of the chromatin of the mother- cells equally between 

 the daughter-cells. 



We must content ourselves with a very brief account 

 of this karyokinesis. In a cell with a resting nucleus, 

 it will be found that the nuclear membrane is quite 



