FERTILIZATION 



19 



After ovulation has taken place, the ovum lies in the ampulla of the uterine 

 tube. If fertilization occurs, a second polocyte is cut off, the nucleus of the 

 ovum forming no membrane between the production of the first and second polar 

 bodies (Fig. 14 A-D). The second maturation spindle and second polar cell are 



EI J 



Fig. 14. — Maturation and fertilization o£ the ovum of the mouse (after Sobotta). A, C-J, X 500; 

 B X 750. A—D, entrance of the spermatozoon and formation of the polar cells. D-E, development of 

 the pronuclei. P-J, successive stages in the first division of the fertilized ovum. 



smaller than the first. Immediately after the formation of the second polar cell, 

 the chromosomes resolve themselves into a reticulum and the female pronucleus 

 is formed (Fig. 14 D). 



FERTILIZATION 



Fertilization of the Mouse Ovum. — Normally, a single spermatozoon enters 

 the ovum six to ten hours after coitus. While the second polar cell is forming. 



