i2 4 THE PHYSIOLOGY OF REPRODUCTION 



plasmic processes may be seen passing from the cells of this layer 

 and projecting into radiating canals in the zona which encloses the 

 ovum, being in contact with the vitelline membrane. 



Immediately after copulation, and therefore during cpstrus, the 



FIG. 37. Human ovum examined fresh in the liquor folliculi. (From Waldeyer.) 

 The ovum shows yolk granules in the centre surrounding the nucleus (with 

 its nucleolus) and a clearer peripheral portion. It is enclosed by follicular 

 epithelial cells. 



cells of the discus proligerus (in the rabbit) 1 begin to withdraw 

 radially, and eventually remain attached to the zona radiata by the 

 extremely thin strands just referred to. At the same time the 

 ovum itself withdraws somewhat from the zona, leaving a narrow 

 circular space. These processes occupy some hours. About nine 



1 In the rabbit these processes depend on coition. (Heape, " Ovulation and 

 Degeneration of Ova in the Kabbit," Proc. Roy. Soc., B., vol. Ixxvi., 1905.) 



