72 OUTLINES OF EVOLUTIONARY BIOLOGY 



time take up their positions at points corresponding to two 

 opposite poles of the original nucleus, with the spindle of fine 



FIG. 31. Diagram of the principal Stages in the mitotic Division of the 

 Nucleus in a typical Animal Cell. (From Weismann's " Evolution 

 Theory," adapted from E. B. Wilson.) 



aeq, equatorial plate ; chr, chromatin ; chrs, chromosomes ; cs, centrosome ; csph, centro- 

 sphere, containing one or two centrosomes ; kk, nucleolus ; km, nuclear mem- 

 brane; kn, nucleus; ksp, sp, nuclear spindle; p, aster; tk, daughter nucleus; 

 tz, daughter cell ; ek, cytoplasm forming the cell body. 



protoplasmic fibres stretched between them (Fig. 31, D), and the 

 chromosomes "go on the spindle," arranging themselves in a 

 so-called equatorial plate across its widest part (Fig. 31, D, aeq). 



