20 



THE ANIMAL CELL. 



[CH. II. 



should further be noted that in all cells which are the result of 

 the sexual process the number of chromosomes is always even, 

 an equal number being contributed by each sex. 



Pole-body 



Antipodal zone 



Fig. 23. Ovum of the worm Ascaris in process of division. The attraction spheres are at 

 opposite ends of the ovum ; at the equator of the spindle which unites them, four 

 chromosomes are seen. The protoplasm of the ovum, except in the equatorial zone of 

 the cell, is arranged in lines radiating from the centre (centrosome) of the attraction 

 sphere. (Waldeyer.) 



The V-shaped chromoplasmic fibres or chromosomes sink to the 

 equator of the spindle, and arrange themselves so as to project 

 horizontally from it. 



': !._ Fine uniting 

 filaments. 



Fig. 24. Metakinesis. A. Early stage. B. Later stage, c. Latest stage formation of 

 diaster. B. and c. show how the sister threads disentangle themselves from one 

 another. (Waldeyer.) 



5. The stage of metakinesis. The sister threads separate, one 

 set going towards one pole, and the other to the other pole 

 of the spindle (fig. 24) : these form the two daughter nuclei. 

 The chromosomes are probably pulled into their new position 

 by the contraction of the spindle fibres attached to them. 



6. Each daughter nucleus goes backwards through the same 

 series of changes ; the diaster or double star is followed by 

 the dispirem or double skein, until at last two resting nuclei 



are obtained (fig. 25). 



A new membrane forms around each daughter nucleus, 

 the spindle atrophies, and the attraction sphere becomes less 



