THE MECHANISM OF MITOSIS 



107 



divide without any amphiaster whatever. In Infusoria mitosis seems 

 to occur in the entire absence of asters, although the cells divide by 

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



^^^'U./^\AJ' 



" it 









\\J ;/■/// V\\ 



yir< /7lltV\ 



/ 1 \^ n' !• \\\\\ 



Fig. 52. — The later stages of mitosis in the egg of the sea-urchin Toxopneustes {A-D, X 1000; 

 E-F, X 500) . 



A. Metaphase; daughter-chromosomes 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-a.xis. In F \he centrosome appears as a single 

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

 The connection between D and F \s not definitely determined. 



In EuglypJia, 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 Q.gg a large amphiaster is formed, with 



