78 



FERTILIZATION OF THE FROGS EGG 



egg nucleus now recedes into the egg, re-forms, and moves slightly in 

 the direction of the approaching sperm nucleus. The path of the egg 

 nucleus is not marked by any pigment as is the path of the invading 

 spermatozoon. 



Penetration and Copulation Paths of the Spermatozoon 



The sperm head generally makes a direct perpendicular contact 

 with the egg cortex, through the unswoUen jelly and the vitelline mem- 

 brane. Usually the entire spermatozoon enters the egg, taking several 



Polar body emergence: Rana pipiens. Note tension lines in the cortical layer 

 caused by the 26-micron polar body emerging through a 16-micron opening. 



