THE MECHANISM OF MITOSIS 



79 



reticulum, and long before the division of the centrosome (Fig. 39). 

 He therefore concludes : " With Boveri I regard the splitting as an 

 independent reproductive act of the chromatin. The reconstruction 

 of the nucleus, and in particular the breaking up of the chromosomes 

 after division into small granules and their uniform distribution 

 through the nuclear cavity, is, in the first place, for the purpose of 



B 



Fig. 39. — Formation of chromosomes and early splitting of the chromatin-granules in sperma- 

 togonia of Ascaris megalocephala, var. bivalens. [Bkauer.J 



A. Very early prophase; granules of the nuclear reticulum already divided. D. Spireme; 

 the continuous chromatin-thread split throughout. C. Later spireme. D. Sliortenmg of tlie 

 thread. E. Spireme-thread divided into two parts. F. Spireme-thread segmented into four split 

 chromosomes. 



allowing a uniform growth to take place ; and in the second place, 

 after the granules have grown to their normal size, to admit of their 

 precisely eqiial quantitative and qualitative division. I hold that all 

 the succeeding phenomena, such as the grouping of the granules 

 in threads, their union to form larger granules, the division of the 

 thread into segments and finally into chromosomes, are of secondary 

 importance ; all these are only for the purpose of bringing about in 



