41 



distributed between the nuclei of the two cells formed by the first division of the 

 ovum. One of the cells is almost as large as the original ovum, and is named 

 the secondary ob'cyte; the other is small, and is termed the first polar body. The 



the spindle (f.pn in VI) the female pronucleus is developed 



secondary oocyte now undergoes subdivision, during which each dyad divides and 

 contributes a single chromosome to the nucleus of each of the two resulting cells. 



"Primary oocyte 



Primary oocyte 

 (commencing 

 maturation) 



Secondary 

 oocyte 



Mature f *^ \ 

 ovum 1 ) 



First polar 

 \ J body 



Polar "bodies 





FIQ. 5. Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. 



This second division is also unequal, producing a large cell which constitutes the 

 mature ovum, and a small cell, the second polar body. The first polar body fre- 

 quently divides while the second is being formed, and as a final result four cells 



