706 OVULATION AND MENSTRUATION. 



in hue ; and finally those which are fully developed, opaque, of a deep 

 orange color, and nearly ready to leave the ovary. 



Here, the difference between the undeveloped and the mature eggs 

 consists mainly in the size of the vitellus, which is very much larger 

 than in the quadrupeds. The ovarian follicle is distended .ind ruptured, 

 and the egg finally discharged, owing to the pressure exerted by the 

 increased 1 size of the vitellus. 



In man and mammalians, on the other hand, the microscopic egg 

 never becomes large enough to distend the Graafian follicle by its own 

 size. The rupture of the follicle and the liberation of the egg are accord- 

 ingly provided for, in these instances, by a different mechanism. 



In the earlier periods of life, in man and the mammalians, the egg is 

 contained in a Graafian follicle which closely embraces its exterior, and 

 is consequently hardly larger than the egg itself. As puberty ap- 

 proaches, the follicles situated near the free surface of the ovary become 

 enlarged by the accumulation of serous fluid in their cavity. At that 

 time, the ovary, if cut open, shows a considerable number of globular, 

 transparent vesicles, the smaller of which are deep seated, but which 

 increase in size as they approach the free surface of the organ. These 

 are the Graafian follicles, which, in consequence of the advancing matu- 

 rity of their eggs, gradually enlarge at the arrival of the period of 

 generation. 



The Graafian follicle then consists of a closed globular sac, the exter- 

 nal wall of which, though quite translucent, has a fibrous texture, and is 

 well supplied with bloodvessels. This fibrous and vascular wall is dis- 

 tinguished by the name of the " vesicular membrane." It is not very 

 firm in texture, and if roughty handled is easily ruptured. 



The vesicular membrane is lined throughout by a layer of minute 

 granular cells, which form for it a kind of epithelium. This layer is 

 termed the membrana granulosa. It adheres but slightly to the vesicu- 

 lar membrane, and may easily be detached by careless manipulation 

 before the follicle is opened, being then mingled, in the form of light 

 flakes and shreds, with the serous fluid contained in its interior. 



At the most superficial part of the Graafian follicle the membrana 

 granulosa is thicker than elsewhere. Its cells are here accumulated, in 

 a kind of mound or "heap," which has received the name of the cumu- 

 lus proligerus. It is also called the discus proligerus, because the 

 thickened mass, when viewed from above, has a nearly circular or disk- 

 like form. In the centre of this thickened portion of the membrana 

 granulosa the egg is imbedded. It is accordingly always situated at 

 the most superficial portion of the follicle, and advances in this way 

 toward the surface of the ovary. 



As the period approaches at which the egg is to be discharged, the 

 Graafian follicle becomes more vascular, and enlarges by an increased 

 exudation into its cavity. It then begins to project from the surface 

 of the ovary, still covered by the albugineous tunic and its peritoneal 



