76 



CELL-DIVISIOX 



in rank to the nucleus itself ; and we may conclude that every central 

 corpuscle is derived from a preexisting;- corpuscle, every attraction- 

 sphere from a preexistin<!j sphere, and that division of the sphere 

 precedes that of the cell-nucleus." ^ Boveri expressed himself in 

 similar terms regarding the centrosome in the same year ('87, 2, 

 p. 153), and the same general result was reached by Vejdovsky 

 nearlv at the same time,"-^ though it was less clearly formulated than 

 bv either Boveri or Van Beneden. 



All these observers agreed, therefore, that the achromatic figure 

 arose outside the nucleus, in the cytoplasm ; that the primary impulse 

 to cell-division was given, not by the nucleus, but by the centrosome, 

 and that a new cell-organ had been discovered whose special office 



Fig. 29. — Final phases (telephases) of mitosis in salamander cells. [Fle.MMING.] 



/. Epithelial cell from the lung; chromosomes at the poles of the spindle, the cell-body divid- 

 ing; granules of the "mid-body " or Zwischenkorper at the equator of the disappearing spindle. 

 y. Connective tissue-cell (lung) immediately after division; daughter-nuclei reforming, the cen- 

 trosome just outside of each; mid-body a single granule in the middle of the remains of the 

 spindle. 



was to preside over cell-division. "The centrosome is an indepen- 

 dent permanent cell-organ, which, exactly like the chromatic elements, 

 is transmitted by division to the daughter-cells. TJie centrosome rep- 

 resents the dynamic centre of cell.'" '^ 



That the centrosome does in many cases, especially in embryonic 

 cells, behave in the manner stated by Van Beneden and Boveri seems 

 at present to admit of no doubt ; and it has been shown to occur in 



1 '87, p. 279. 



2 '88, pp. 151, etc. 



3 Boveri, '87, 2, p. 15J. 



