66 



THE CELL. 



Fig. 22 



Fig. 23. 



Fig. 24. 



Fig. 25. Fig. 26. 



Figs. 22-26. Mitotic cell-division of fertilized whitefish eggs Coregonus albus. 



Fig. 22, Cell with resting nucleus, centrosome, and centrosphere to the right of the 

 nucleus ; Fig. 23, cell with two centrospheres, with polar rays at opposite poles of 

 nucleus; Fig. 24, spirem; Fig. 25, monaster; Fig. 26, metakinesis stage. 



To give a better understanding of the process we have inserted 

 a series of figures in which several phases of mitotic division are 

 portrayed. In figures 12-21 are shown ten stages of mitotic nu- 

 clear division from the oral epithelium of the larva of a salamander, 

 in which changes undergone by the nucleus and centrosome are 

 clearly brought out. And, further, a series of figures (2229) show- 

 ing the different phases of mitotic cell-division of the fertilized eggs 

 of the whitefish {Coregonus albas} ; the changes involving the centro- 

 some, centrosphere, and cytoplasm are illustrated. Figure 30, show- 

 ing a small portion of a section through the testis of the salamander, 

 the object in which Flemming first observed this complicated series 

 of changes, presents the appearance more generally seen during 

 mitotic cell-division of the tissue cells of the higher vertebrates. 



(a) Prophases. -The changes occurring in the nucleus will 

 be considered first. At the beginning of the process of mitosis, the 

 chromatin network, consisting of chromatin granules, is transformed 

 into a twisted skein of threads, beginning at the periphery of the 



