360 



THE ORGANS 



ovary and is known from its function as the germinal epithelium 

 (Fig. 253, he). The parenchyma or secreting portion of the ovary 

 consists of peculiar glandular elements, the Graafian follicles. 



The structure of the Graafian follicle can be best appreciated 

 by studying its development. The follicles originate from the ger- 

 minal epithelium during foetal life. At this time the germinal epithe- 

 lium is proliferating, and certain of its cells differentiate into larger 



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Fig. 252. — Semidiagrammatic Drawing of Part of Cortex and Medulla of Cat's 

 Ovary. (From Schron, in Quain's " Anatomy.") i, Germinal epithelium, beneath which 

 is 3, the tunica aljjuginea; 2, medulla, containing large blood-vessels, 4; 2,2', fibrous 

 stroma, arranged around mature Graafian follicle as its theca folliculi; 3', stroma of cor- 

 tex; 5, small (primitive) Graafian follicles near surface; 6, same deeper in cortex; 7, later 

 stage of Graafian follicle, beginning of cavity; 8 and 8', still later stages in development 

 of follicle; 9, mature foUicle; a, stratum granulosum; h, germ hill; c, ovum; d, nucleus 

 (germinal vesicle); c, nucleolus (germinal spot). 



spherical cells — primitive ova (Fig. 253, op). The primitive ova pass 

 down into the stroma accompanied by a considerable number of the 

 undifferentiated cells of the germinal epithelium. A cord-like mass 

 of cells is thus formed, extending from the surface into the stroma. 

 This is known as Pfluger's egg cord (Fig. 253). Each cord usually 

 contains several ova. In some cases the differentiation of the ova 

 cells does not occur upon the surface but in the cords after they have 

 extended down from the surface. The connection of the cord with 

 the surface epithelium is next broken so that each cord becomes 

 completely surrounded by stroma. It is now k^own. as an egg nest 

 (Fig. 253). During this process, proliferation of the epithelial cells 

 of the cords and nests has been going on, and each o^^lm surrounded 



