THE CELL 



either divide, to form two new cells, or they die and undergo 

 degenerative changes. The reason of this is possibly to be 

 found in the well-known physical fact that, as a sphere 

 increases in size, the mass increases more rapidly than the 

 periphery. Hence, as a cell becomes larger and larger, the 

 surface for nourishment becomes smaller and smaller in 

 relationship to the mass of material to be nourished. Pro- 

 bably the altered metabolism so produced sets up the 

 changes which lead to the division of the cell. These 

 changes have now been very carefully studied in a large 

 number of cells, and it has been shown that the nucleus 

 generally takes a most important part in division. 



(3) 



FIG. 3. Nucleus in Mitosis : (1) Convoluted stage ; (2) Monaster stage ; 

 (3) Dyaster stage ; (4) Complete division. 



Mitosis. In a cell about to divide, the first change is a 

 general enlargement of the nucleus. At the same time the 

 centrosome becomes double, and the two portions travel from 

 one another, but remain united by delicate lines to form a 

 spindle-shaped structure (Fig. 3, 1). These lines may be 



