THE MECHANISM OF MITOSIS 



107 



divide without any amphiaster whatever. In Infusoria mitosis seems 

 to occur in the entire absence of asters, althou^^h the cells divide by 

 constriction, and the analogy with Heidenhain's model entirely fails. 





^vX V 



■^> 



x 



\ 



/ 



/ 



-/ ^ 





o 



c 

 oo 



/V'-'^ 



/'^ 





X 



"lr\:\\ Z)' IW 



Mil''". '' '^ 



1 1 \^^- / \ 



E 



Fig. 52. — The later stages of mitosis in the G.gg of the sea-urchin Toxopneustcs {.4-D, X 1000; 

 £-F,X5oo). 



A. Metaphase; daughter-chronaosomes drawing apart but still united at one end. B. Daugh- 

 ter-chromosomes separating. C. Late anaphase ; daughter-chromosomes lying near the spindle- 

 poles. D. Final anaphase; daughter chromosomes converted into vesicles. E. Immediately 

 after division, the asters undivided ; the spindle has disappeared. F. Resting 2-cell stage, the 

 asters divided into tvvo in anticipation of the next division. 



In Figs. A and /? the centrosome consists of a mass of intensely staining granules, which in 

 Cand D elongates at right angles to the spindle-axis. In /-'the centrosome appears as a single 

 or double granule, which in later stages gives rise to a pluricorpuscular centrum like that in .-/. 

 The connection between D and F is not definitely determined. 



In Eiiglypha, according to Schewiakoff (Fig. 39), division of the cell- 

 body appears to take place quite independently of the mitotic figure. 

 Again, a considerable number of cases are now known in which dur- 

 ing the fertilization of the ^gg a large amphiaster is formed, with 



