Cell Division 



99 



The precise and orderly movements of 

 chromosomes during metakinesis and ana- 

 phase have long fascinated cytologists. Many 

 physicochemical explanations have been sug- 

 gested (for a critical discussion see Schrader, 

 '53). Unfortunately they were more often 

 based on artificial models rather than the 

 cell. Before we can attempt to understand 

 what is going on in physical and chemical 

 terms, it is necessary to know just what hap- 

 pens in cytological terms. What are the spe- 



cial cell structures concerned with the move- 

 ment of chromosomes? What is their history 

 during the mitotic cycle and how do they 

 interact to assure the orderly disjunction of 

 daughter chromosomes? Once these mitotic 

 organelles are recognized they can be investi- 

 gated with regard to their chemical compo- 

 sition, their submicroscopic structure and 

 their function in biochemical terms. 



We can recognize the following structures 

 as mitotic organelles: cell center (centro- 



mSl^S^M^Bk ''^iW^M^^f^^^^ 



Fig. 14. Mitosis during early cleavage of Drosophila, illustrating the history of the centriole (after Huettner, 



'33). 



