396 THE FEMALE KEPKODUCTIVE OKGANS 



teric the remaining follicles degenerate and the process of ovula- 

 tion gradually ceases. 



We shall now discuss the structure of the ovum or female germ 

 cell and shall then successively trace its development and matura- 

 tion, the formation of its Graafian 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 (200 

 to 300 /x). When fully developed it is surrounded by a thick layer 

 of exoplasm, the zona pellucida, which is probably derived from 

 the cytoplasm of the follicular epithelium by which the ovum is 

 closely invested. The ovum itself consists of a mass of cytoplasm, 

 the vitellus, and a large vesicular nucleus or germinal vesicle, within 

 which is frequently a single prominent nucleolus or germinal spot. 

 The cytoplasm of the mature ovum is inclosed by a very delicate 

 cell membrane, known as the vitaline membrane, which is not 

 demonstrable in the primitive ova of the younger follicles. 



The cytoplasm of the ovum at first appears finely reticular, 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 cytoplasm is in great part 



'-. . replaced by a granulo-fatty mass of faint 



yellowish color known as deutoplasm. Fre- 



J| quently this metamorphosis is not quite 



re complete, a remnant of the original cyto- 



% * ( X-J--H A plasm persisting beneath the vitaline mem- 



yV ti brane and in the vicinity of the nucleus. 

 /p Numerous cy toplasmic structures have 



! been described in these cells, chief among 



which are the accessory nucleus (Nebenkerri), 



FIG. 321. OVUM, CONTAIN- an( j the yolk nucleus (Dotterlcern). The ac- 



(DOTOKERN) TTTHE cessory nuclei, occasionally chromatinic and 



LEFT AND ABOVE THE therefore basophile, more frequently stain 



NUCLEUS. with cytoplasmic dyes and are at times at- 



The peripheral nuclei tached at other times sep arate from the 



are derived from the adja- r . 



cent stroma. iron-herna- true nucleus. The yolk nuclei of mamma- 



toxyiin. Highly magni- ij an ova mos t frequently take the form of 



^' crescentic masses of lightly staining chroma- 



tin which partially surround the nucleus, 

 forming a so-called nuclear cap. 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 



