GROWTH 97 



NUCLEUS CYTOPLASM 



1. Formation of spireme. Appearance of centrosome and 



aster. 



2. Segregation of chromo- Division of centrosome and 



somes. aster. 



3. Breaking down of mem- Moving apart of centrosomes 



brane. to opposite poles; attach- 



4. Formation of equatorial ment of spindle fibers to 



plate. chromosomes. 



5. Splitting of chromosomes. 



6. Separation of daughter Contraction of spindle fibers. 



chromosomes. 



7. Re-formation of spireme. Disappearance of astral rays 



and centrosomes. 



8. Disintegration of spireme Formation of new cell-wall. 



into granules of resting 

 stage. 



Stages 1-4 are sometimes called " prophases," 

 stage 5 " metaphase," and stages 6-8 " anaphases." 



Such is the orderly series of changes undergone 

 in all cells that divide indirectly. The synchrony 

 of movements in nucleus and cytoplasm is not always 

 just the same as indicated above, but the modifications 

 are not fundamental, usually consisting in a hastening 

 or a delaying of changes on either one side or the 

 other, and the end-result is always the same. 



Abnormal Mitosis. Under certain conditions, 

 such as the division of an egg-cell fertilized by more 

 than one sperm, or in degenerative growths as in 

 cancer and tumors, often three or more centrosomes 

 and spindles appear, and as a consequence the 



