2O4 



immature Graafian follicles present, it will be neces- 

 sary to study the way in which these structures 

 originate. They are produced from the cylindrical 

 epithelium which covers the ovary and is called 

 germ-epithelium. At an early period of life the con- 

 nective-tissue stroma of the ovary grows rapidly, and 

 partially encloses groups of the germinal epithelial 

 cells, which themselves proliferate, and dip down 

 into the stroma of the organ in the form of elon- 

 gated, solid or tubular masses. Presently these 

 groups of cells become separated from the germinal 

 epithelium at the surface, and appear then as irregu- 

 lar masses of polyhedral or spheroidal cells, enclosed 

 on all sides by connective tissue. A still further 

 growth of the stroma separates these masses of cells 

 into smaller groups, which gradually sink farther 

 from the surface of the organ and become more 

 widely separated from one another, while new 

 masses of germ-epithelium are being enclosed at the 

 surface. The cells which now lie in these separated 

 cavities may at first all look alike, but later we 

 usually find that one of them is larger than the 

 others, is spheroidal, and occupies the centre of the 

 cavity, while the rest are more or less cuboidal and 

 arranged in a single layer around the wall, closely 

 enclosing the central cell. This is -the young 

 Graafian follicle, and the central cell is the ovum 

 but it presents as yet no zona pellucida. Gradually 

 the follicular epithelium increases in quantity, form- 



