792 



EMBRYOLOGY 



with the vitellus. Then there forms on the surface of the vitellus what 

 is called the entrance-cone, which receives, in a little excavation at its 

 summit, the head of the male element. The spermatozoid afterward 



B 



C D 



Fig. 218. Cell-division (Wilson). 



A, Resting cell, showing A, double centrosome; N, nucleus; C, chromatin ; L, linin network; 

 B, spongioplasm. B, cell in process of division, showing A, asters; C, chromosomes split lengthwise 

 and lying in the equator of the achromatic spindle. C, later stage of karyokinesis, showing DC, 

 daughter-chromosomes moving toward the two asters, with filaments, IF, between them. D, divided 

 cell ; DN, daughter-nucleus ; A, centrosome. 



penetrates the substance of the vitellus, and as it passes inward, it 

 rotates on its short axis so that its base looks toward the centre of the 

 ovum. The head and the middle piece of the spermatozoid now form 



