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 1221 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 albus}\ 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 



