Chapter 5 



HOW CELLS DIVIDE- 

 INDIRECT CELL DIVISION OR MITOSIS 

 (ANIMAL AND PLANT) 



One of the most interesting and important phenomena in living cells 

 is the process of mitosis in which the cells undergo a series of very com- 

 plicated stages of division. The so-called resting stage occurs between 

 two successive periods of mitosis. The cell during this stage is resting 

 only as far as actual cell division is concerned, but metabolism and other 

 cellular activities are progressing normally. It is during this stage that 

 young cells grow to their normal, mature size. Mitosis in animal and 

 plant cells occurs in much the same general way, although, as might be 

 expected, there are certain fundamental differences. Both of these 

 methods of mitosis will be described and contrasted. 



A resting cell in animals may be characterized by the following: (1) 

 the nucleus is more or less spherical (Fig. 8) ; (2) irregular granules of 

 chromatin of various sizes and shapes are suspended in netlike fashion 

 within the nucleus; (3) a pair of granular centrioles is usually found 

 within the centrosome (central body) ; (4) the nuclear membrane and 

 the nucleolus are present; (5) the cytoplasm appears to be normal. 



I. MITOSIS IN ANIMAL CELLS (Figs. 20 and 21) 



The entire process of mitosis in animal cells is a continuous one but 

 for convenience is divided into four phases (Fig. 20): (1) prophase, 

 (2) metaphase, (3) anaphase, and (4) telophase. 



A. Prophase (Gr. pro, before or first; phasis, appearance) (Fig. 20, 

 A-D) 



In animal cells the divided centrosomes migrate away from each other 

 around the nuclear wall until finally they are at opposite sides of the 

 original nucleus. Each centrosome is surrounded by a halo of radiating, 



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