Facts and Factors of Development 19 



resting stage it is certain that every chromosome preserves its 

 individuality or identity, and even where this cannot be done the 

 fact that the same number of chromosomes, having the same 



ris< to a spindle (a) with astral radiations at its poles; F, Middle stage 

 of division in which the chromosomes lie in the equator of the spindle 

 forming the equatorial plate (cp) ; G, H, Stages showing the splitting of 

 each chromosome and the movement of the halves toward the poles of 

 the spindle ; ep, Equatorial plate ; if, "Interzorral filaments ; n, Nucleolus : 

 I, Complete separation of daughter chromosomes and formation of daugh- 

 ter nuclei; beginning of division of cell body; /, Complete separation of 

 daughter cells and return of nucleus and centrosome to resting condi- 

 tion. (After Wilson.) 



