OA'/CLY OF THE MITOTIC FIGURE 



55 



sphere, and that division of the sphere precedes that of the cell- 

 nucleus."^ Boveri expressed himself in similar terms in the same 

 year (^?>7, 2, p. 153), and the same general result was reached by 

 Vejdovsky nearly at the same time,^ though it was less clearly formu- 

 lated than by either Boveri or Van Beneden. 



Fig. 22. — Metaphase and anaphases of mitosis in cells (spermatocytes) of 'the salamander. 

 [DrUner.] 



E. Metaphase. The continuous central spindle-fibres pass from pole to pole of the spindle. 

 Outside them the thin layer of contractile mantle-fibres attached to the divided chromosomes, of 

 which only two are shown. Centrosomes and asters. F. Transverse section through the mitotic 

 figure showing the ring of chromosomes surrounding the central spindle, the cut fibres of the latter 

 appearing as dots. G. Anaphase ; divergence of the daughter-chromosomes, exposing the cen- 

 tral spindle as the interzonal fibres; contractile fibres (principal cones of Van Btsneden) clearly 

 shown. H. Later anaphase (dyaster of Flemming) ; the central spindle fully exposed to view; 

 mantle-fibres attached to the chromosomes. Immediately afterwards the cell divides (see Fig. 23). 



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 ofifice 



1 '87, p. 279. 



2 '88, pp. 151, etc. 



