30 HISTOLOGY 



plasm. Other "vitelline bodies," of uncertain origin and significance, 

 have been described. Some have been considered as nuclear extrusions. 



The nucleus of the oocyte is very large and vesicular. The chromatin 

 occurs chiefly along the nuclear membrane and about the nucleolus. The 

 nucleous is also very large, and Nagel stated that in the fresh condition it 

 exhibits amoeboid movements, but this observation has not been verified. 

 The nuclei of the oocytes ordinarily show no signs of mitosis, and they 

 may remain in the resting condition for thirty years or more and then di- 

 vide. Many of them, however, will degenerate without division. 



FIG. 22. THE OVUM AS DISCHARGED FROM A VESICULAR FOLLICLE OF AN EXCISED OVARY OF A WOMAN 



THIRTY YEARS OF AGE. Examined fresh in the liquor folliculi. (Nagel.) 



c. r., Corona radiata composed of cells of the follicle; n., nucleus; p., granular protoplasm; p. s., peri vitel- 

 line space; y., yolk; z. p., zona pellucida. (From McMurrich's "Embryology.") 



The cell divisions which give rise to the secondary oocyte and the ma- 

 ture ovum respectively, have never been observed in man. Some of the 

 qells within the ovary may be secondary oocytes and the cell shown in Fig. 

 22 may be of this sort, or possibly a mature ovum, but this cannot be de- 

 termined. From what is known of other mammals, however, it may con- 

 fidently be assumed that the cell divisions take place as shown in the dia- 

 gram, Fig. 23. 



When the primary oocyte divides, the chromosomes, reduced in number, 

 also divide and are equally distributed to the daughter cells; but the great 

 mass of cytoplasm remains with one of these cells, namely, the secondary 



