514 



THE EEPKODUCTIVE SYSTEM 



Certain cells in these columns, by their increased size and prominent 

 nucleus, become very early distinguishable as the primitive ova; their 

 differentiation is rapidly followed by the constriction of the columns, 

 through the activity of the surrounding tissue of the stroma, in such 

 manner that one, rarely two or more ova, and several undifferentiated 

 epithelioid cells are included in each portion whose connection with the 



FIG. 453. A PRIMARY OVARIAN FOLLICLE OF THE HUMAN OVARY. 



From within outward are seen the germinal spot, germinal vesicle, vitellus, vitel- 

 line membrane, zona pellucida, granule cell layer, membrana propria, and theca 

 folliculi. The ovarian stroma forms the border of the figure. Hematein and eosin. 

 Photo. X 575. 



layer of germinal epithelium is thus severed. In ibis way the /trintitive 

 follicles ('<'</</ nests') are formed. In the ovary of the new-born hun- 

 dreds of siicb primary follicles occur in all portions of the cortex (Fig. 

 450). They are also found persistent in large numbers in the ovary of 

 the adult. 



Many follicles never go beyond this primary stage of development, 

 but after a time undergo retrograde metamorphosis either by gradual 

 atrophy or by a process, known as atresia of the follicle, in which the 



