184 THE REPRODUCTIVE SYSTEM. 



of the follicles visible for a time as corpora lutea. At any 

 one time the active ovary exhibits a number of Graafian fol- 

 licles and corpora lutea in different stages of development, 

 along with a large number of undeveloped ovisacs. 



Graafian follicles (or vesicles) : As the primitive ovisacs 

 develop they enlarge and sink deeper into the ovary. The 

 fully developed Graafian follicles are spherical or oval cysts 

 about 4 to 10 mm. in diameter. Each is surrounded by a 

 condensation of the stroma in which it is imbedded, forming 

 a vascular connective-tissue investment called the theca fol- 

 liculi; this is usually described as consisting of two layers, an 

 outer, called the tunica fibrosa, and an inner, called the tunica 

 propria. The theca, be it noted, is not really a part of the 

 Graafian follicle, but is a condensation of the ovarian stroma 

 surrounding it. 



The outer layer of the follicle proper, lying next to the 

 tunica propria, is the membrana or tunica granulosa, com- 

 posed of a few layers of small spheroidal nucleated epithelial 

 cells. This tunic encloses a large cavity which is filled with 

 an albuminous fluid, the liquor folliculi. 



At one point in its circumference the tunica granulosa is 

 thickened, having a mass projecting inward composed of cells 

 identical with those which make up the tunic elsewhere ; this 

 mass or heap of cells is called the discus proligerus, or 

 cumulus ovigerus. Within this cumulus the ovule is im- 

 bedded ; the cells in a layer immediately surrounding the 

 ovule are columnar and arranged in a radiating manner, form- 

 ing the corona radiata. 



The ovule, or ovum (Fig. 72), is a large spherical cell about 

 .2 mm. in diameter; each Graafian follicle contains one ovule, 

 rarely two or three. The wall of the ovule is a thin clear 

 hyaline membrane, showing indistinct radial markings ; it is 

 variously called the vitelline membrane, zona pellucida, zona 

 radiata, and oolemma. The cell-body of the ovule, or vitellus, 

 is a mass of protoplasm infiltrated with fat-particles. The 

 nucleus of the ovule is a spherical body, often called the 

 germinal vesicle; within it is a nucleolus, the germinal spot. 



Ovulation : The Graafian follicle, when mature, makes its 

 way to the surface of the ovary, causing a bulging at that 

 point. The tissues overlying the follicle become thinned, 



