GROWTH AND REPRODUCTION 



757 



gradual constriction, in the same manner as the nucleolus; more 

 often in such a manner that it appears as if it has been clean cut 

 through its centre at the plane of division, leaving the two halves 

 with flat parallel surfaces where the division took place. In some 

 other cases it appears as if the nuclear membrane is the important 



FIG. 461. DIAGRAMS OF CHROMATIN CHANGES DURING THE DIVISION OF A CELL. 

 (Redrawn from Dahlgren and Kepner.) 



agent in the division. From the old nuclear membrane an extension 

 passes across the middle of the nucleus, thereby forming two new 

 nuclei with two nuclear membranes. Finally, the cell body may 

 divide; often it does not do so. In such cases, amitosis is apparently 

 a terminal process in the life activities of the cell, and is a method 

 for securing more nuclear surface for the cell's activities, especially in 

 cases of active metabolism. In the stratified epithelia of vertebrates, 



FIG. 4-62. DIAGRAM TO SHOW DISTRIBUTION OF CHROMOSOMES TO DAUGHTER CELLS 

 IN ORDINARY OR SOMATIC FORM OF DIVISION. (C. E. Walker.) 



for example, although at first the cells divide by the process of mitosis, 

 later on, towards the end of the cell's activities, the process changes 

 to amitosis, the cells remaining undivided (Fig. 460). 



Mitosis brings about an equal division of this chroinatin material 

 in the mother nucleus, and distributes it equally between the two 



