THE CELL AND CELL DIVISION 



79 



be found, usually associated with reproductive processes, e.g., brood 

 formation. 



Regarding the real nature of the mechanism of mitosis, even less 

 can be said to be known than with respect to its causes. The arrange- 

 ment of the achromatic amphiaster and the behavior of the chromosomes 

 show that in the mitotically dividing cell the forces or tensions are 



A 



FIG. 41. Diagrams of the arrangement of the spongioplasmic network 

 (mitome) in the cell. A, B, C, from Korschelt and Heider. after Heidenhain. 

 A. Schema of the arrangement of the spongioplasm as it would appear in the 

 absence of a nucleus. Symmetrical monocentric system. B. Arrangement in 

 the presence of a nucleus. Asymmetrical monocentric system. C. Arrange- 

 ment at the beginning of mitosis. Commencement of dicentric system. D. 

 Arrangement during the process of mitosis. Symmetrical dicentric system. 

 a,b, cell axis; k, nucleus. 



arranged in a dicentric system, whereas in the vegetative cell the system 

 is monocentric (Fig. 41). As the result of the action of the forces in this 

 dicentric system the chromosome halves are separated and the cyto- 

 plasm divided. The problem here is to discover the nature of the 

 forces and the cause of the formation of the amphiaster in the form 

 which it has. In explanation of the first part of the problem, i.e., the 



