720 



THE REPRODUCTIVE ORGANS 



The internal structure of the ovary consists of a peculiar soft fibrous 

 connective tissue, stroma, abundantly supplied with blood vessels. The 

 surface of the ovary is covered with cubical epithelium. Embedded in 

 the stroma in various stages of development are numerous minute follicles 

 or vesicles, the vesicular ovarian follicles, containing the ova, figure 494. 

 They are small and numerous near the surface of the ovary, either arranged 

 as a continuous layer, as in the cat or rabbit, or in groups, as in the human 

 ovary. Nearer the center are large and fully developed follicles. 



Each follicle has an external membranous envelope, or tunica externa, 

 which is lined with a layer of nucleated cells, forming a kind of epithelium 



FIG. 493. Diagrammatic Section of the Ovary, Showing its Cortical or Ovigenous 

 Layer, Formed of Ovisacs in Various Stages of Evolution. (Duval.) A, A, A, Primordial 

 ovisacs; B, B, B, ovisacs further developed; C, ovisac approaching maturity; D, ripe ovisac 

 with its proligerous disc (DP) containing the ovum; MG, membrana granulosa; H, hilum 

 of ovary. 



or internal coat and named the tunica interna. The cavity of the follicle 

 contains the ovule enclosed in a very delicate membrane. The large spher- 

 ical nucleus contains one or more nucleoli. The nucleus is known as the 

 germinal vesicle, and the nucleolus as the germinal spot. 



The human ovum measures about 0.2 mm. in diameter. Its external 

 investment, or the zona pellucida, or vitelline membrane, is a transparent 

 membrane, about lo/z in thickness, which under the microscope appears 

 as a bright ring, figure 495. The ovum itself has the characteristic structure 

 of the typical cell, with the exception that its cytoplasm is filled with nu- 

 merous yolk granules. The larger granules or globules, which have the 

 aspect of fat-globules, are in greatest number at the periphery of the yolk. 



The nucleolus, or germinal vesicle, is about o . 05 mm. in diameter. The 

 vesicle is of greatest relative size in the smallest ova. 



The Graafian follicles are formed in the following manner: The em- 

 bryonic ovary is covered with short columnar cells, or the so-called germinal 



