76 



CELL-DIVISION 



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 preexisting 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 {"^y, 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. [Flemming.] 



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

 ing; granules of the "mid-body" or '/Auischcnkorpcr ■M the equator of the disappearing spindle. 

 y. Connective tissue-ceil (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. 77ic cciitrosojue rep- 

 resents the dynamic cejitre of cell T "^ 



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. 153. 



