THE REPRODUCTIVE ORGANS. 



217 



the liquor folliculi, so that the outer layer forms the wall of a sac,, 

 while the inner layer remains as a close investment of the ovum. 

 The cells of these two layers multiply : those surrounding the 

 ovum forming the "discus proligerus," and those lining the sac the 

 " tunica granulosa " ; but they blend with each other at one point on 

 the wall of the follicle, so that the ovum retains a fixed position 

 (Fig. 195). 



Meanwhile the tissue of the stroma undergoes modifications which 



Fig. 194. 



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Graafian follicle and stroma in ovary of adult sow. (Plato.) The ovum occupies the centre 

 of the follicle, appearing as a very large cell with a large vesicular nucleus ("germinal 

 vesicle"), within which is a large nucleolus ("germinal spot"), exceeding in size the 

 whole nucleus of the surrounding epithelial cells of the follicle. The cells of the stroma 

 are arranged about the follicle as though to form the fibrous coat of the latter. In the 

 lower portion of the figure are three large cytoplasmic cells, containing globules of fat 

 and granules of pigment. These cells are analogous to those found in the interstitial 

 tissue of the testis. The epithelium of the Graafian follicle, and the ovum, also contain 

 globules of fat of various sizes, stained black by the osmic acid used in the preparation 

 of the specimen. 



contribute a clear basement-membrane and a fibrous envelope, the 

 " membrana propria," to the structure of the follicle. 



The follicle now enlarges, as the result of an increase in the 

 amount of the liquor folliculi, eventually approaches the surface of 

 the ovary at some point, and then ruptures, discharging the ovum. 



After the rupture of the Graafian follicle and the escape of 

 its contents a slight hemorrhage usually takes place into its 

 cavity, which then appears filled with remains of the liquor fol- 

 liculi mixed with coagulated blood. The cells of the tunica granu- 



