THE FEMAU'l REPRODUCTIVE ol.MiANS 



511 



climacteric the remaining foil ides degenerate and I he process of ovulation 

 gradually ceases. 



We shall now discuss the structure of the ovum or female ;/mu cell 

 and shall then successively trace its development ;ind maturation, the 

 formation of its vesicular ((Jraafian) follicle, the rupture of the follicle, 

 and the subsequent history of the corpus luteum. 



The Ovum. The ovum is a spherical cell of large size ('300 to 

 300 p). When fully developed it is surrounded hy a thick layer of 

 exoplasm. the zona /ie/lncida, which is probahly 

 derived from the cytoplasm of the follicular epi- 

 thelium by which the ovum is closely invested. 

 The ovum itself consists of a mass of cytoplasm, 

 the ril ell ux. and a large vesicular nucleus or 

 (/mutual reside, within which is frequently a 

 single prominent nuc/eolus or aenninal x/>oL The 

 cytoplasm of the mature ovum is inclosed by a 

 very delicate cell membrane, known as the vitellinc 

 membrane, which is not demonstrable in the prim- 

 itive ova of the younger follicles. 



The CYTOPLASM of the ovum at first appears 

 finely retieular, but as its development advances 

 a fatty material is deposited within its meshes, 

 usually in the form of minute irregular spheroids, 

 by the accumulation of which the reticular cyto- 

 plasm is in great part replaced by a granulofatty 

 mass of faint yellowish color known as deuto- 

 plasm. Frequently this metamorphosis is not 



quite complete, a remnant of the original cytoplasm persists beneath the 

 vitelline membrane and in the vicinity of the nucleus. 



Numerous cytoplasmic structures have been described in these cells, 

 chief among which are the accessory nucleus (Nebenkern), and the yolk 

 nucleus (Dotterkern). The accessory nuclei, occasionally chromatinic 

 and therefore basophil, more frequently stain with cytoplasmic dyes and 

 are at times attached, at other times separate from the true nucleus. 

 They are more probably remnants of mitotic spindles. The yolk nuclei 

 of mammalian ova most frequently take the form of crescentic masses 

 of lightly staining chromatin ( Yhromidia') which partially surround the 

 nucleus, forming a so-called nuclear ca/i. They are often found in 

 various stages of disintegration, and the fragments may be transported 

 to the peripheral portions of the cytoplasm, or may be irregularly scat- 



FIG. 451 . OVUM, CON- 

 TAINING A YOLK 

 NUCLEUS (DOTTER- 

 KERN) AT THE LEFT 

 AND ABOVE THE NU- 

 CLEUS. 



The peripheral nuclei 

 are derived from the 

 adjacent stroma. Iron- 

 hematoxylin. Highly 

 magnified. (After von 

 Skrobansky.) 



