CELL DIVISION 



315 



and some are attached to the chromosomes. Other fibres ex- 

 tend from the centrosomes outward into the cytoplasm, and 

 the constituents of the cytoplasm take on a radial arrangement 

 with the centrosomes as centres. The chromosomes lie regu- 

 larly arranged around the spindle in its equatorial plane. 



FIG. 181. Diagrams illustrating the metaphase and anaphases of mitosis. 

 A, Chromosomes divided; B, chromosomes approaching the centrosomes; C, 

 cytoplasm beginning to divide, the centrosomes also divided; D, cell completely 

 divided and nuclei in resting condition. (This and preceding figure from 

 McMurrich, adapted from E. B. Wilson.) 



684. The process of division begins with the splitting of each 

 chromosome lengthwise into two equal and similar parts, 

 whereby the number of chromosomes is doubled. The two 

 halves of each original chromosome separate and move in 



