FORMATION OF AN EGG 5 



in the following manner: The egg of the young Graafian 

 follicle grows until it is a large spherical cell. The fol- 

 licular cells remain small and multiply rapidly, forming 

 two layers of cells, between which at one side of the 

 follicle a cavity appears. This cavity is called the fol- 

 licular cavity. As the follicle grows larger, this cavity, 

 which is eccentric in position, is filled with -a fluid, the 

 follicular fluid. The cells composing the layer of fol- 

 licular cells, which immediately surround the egg, in- 

 crease rapidly in number until there are several layers. 

 These cells are known as the discus proligerus. The cells 

 external to the follicular cavity are the stratum granu- 

 losum. There are finally from eight to twelve layers of 

 cells in the stratum granulosum. The discus proligerus 

 is attached to the stratum granulosum. The lighter area 

 immediately outside of the vitelline membrane is the 

 area pellucida. The row of cells of the discus proligerus 

 which radiates from the ovum is the corona radiata. 



When the egg with its surrounding tissue has reached 

 this stage of development it is known as a ripe Graafian 

 follicle. 



The follicle is enclosed by a capsule composed of two 

 kinds of cells. Those cells which lie nearest the stratum 

 granulosum are more or less spherical, and the others are 

 rather elongate. This capsule is the theca folliculi. 

 Surrounding the theca folliculi and forming the sub- 

 stance of the ovary are long, fibrous cells, the stroma. 



In the section of the cat ovary, find a ripe Graafian follicle 

 and draw it. Label all the parts. 



