XVII 



MYSTERY OF THE CELL 343 



chr- . 



cyt- 



-J3. 



-Cfffr 



Jd.. 



Jd... 



FIG. no. 

 DIAGRAM OF NUCLEAR DIVISION. 



A. Cell with nucleus () and centro- 

 somes (cs) preparatory to division. 

 Thechromatin has become thickened 

 so 35 t o fonn a spiral thread (chf). 



B. The nuclear membrane has dis- 

 appeared. Delicate threads radiate 

 from the chromosomes, and form the 

 "nuclear spindle," in the equator 

 of which eight chromosomes or 

 nuclear loops (chr=Jd) are ar- 

 ranged ; these have been formed 

 by the spiral thread of chromatin 

 in A becoming broken up. 



C. The chromosomes have each be- 

 come split longitudinally into two, 

 and are about to be drawn apart 



by means of the spindle threads. (For clearness four only of the 

 eight chromosomes are shown.) 



D. The daughter-loops pass towards the poles of the spindle. 



E. The cell has divided, each new cell containing a centrosome and 



eight nuclear loops. 

 ( From Weismann's Germ-Plasm, by permission of Walter Scott. Ltd. ) 



