60 THE FEMALE GENERATIVE ORGANS. 
Describe the parts of a Graafian follicle. 
The connective tissue of the stroma of the ovary is arranged to 
form a well-defined wall (theca folliculi), This wall is lined with 
several layers of round or irregular-shaped cells forming the membrana 
granulosa. At one side some of these cells are collected into a mass 
(cumulus proligerus) which contains the ovum. The cavity of the 
follicle is filled with a semitransparent fluid, which, by its increase, 
distends and ruptures the follicle at a menstrual period and sets free 
the ovum. 
How are the Graafian follicles formed ? 
In embryonic life the stroma of the ovum grows very fast and 
entangles in its meshes groups of the germ epithelium which covers 
the organ. These cells are at the same time increasing in number by 
cell proliferation. The stroma becomes arranged around a group of 
these irregular-shaped cells to form the theca folliculi. The cells 
begin to increase in number, one being developed more perfectly than 
the rest, to form the ovum, and is situated in the centre of the mass, 
As several layers of cells are formed the ovum is placed eccentrically. 
The cavity of the follicle now begins to appear, first as a narrow slit, 
but growing wider as fluid accumulates. 
What is the structure of the ovum ? 
It is an example of a cell of the most highly developed type. The 
cellwall, consisting of a thick hyaline membrane showing a delicate 
radial striation, is called the zona pellucida. The cell-protoplasm, 
which is granular, is called the vitellus. The cell nucleus, located in 
the protoplasm, is transparent and vesicular in appearance, and is called 
the germinal vesicle. Inside this nucleus is a dark nucleolus called 
the germinal spot. . 
What is the corpus luteum ? 
When the Graafian follicle ruptures, its cavity is filled with blood 
which coagulates, forming fibrin and serum. The cells of the mem- 
brana granulosa proliferate and form a soft mass, which soon under- 
goes fatty degeneration and shows a yellow color. So, then, the 
Graafian follicle is replaced by a mass of fibrin, degenerated bloodcells, 
with coloring matter from them and by degenerated epithelial cells. 
This mass is called the corpus Jutewm, and is succeeded by a mass of 
cicatricial tissue. 
