CH. LIX.] 



OOGONIA AND OOCYTES 



871 



around the nucleus, which is comparatively free from them. It con- 

 tains a nucleus, and usually one very well-marked nucleolus. The 

 nucleus and nucleolus are still often called by their old names, 

 germinal vesicle and germinal spot respectively. An attraction 

 sphere, not shown in the figure, is also present, and a fine mem- 

 brane, the vitelline membrane, immediately invests the protoplasm 

 within the zona pellucida. 



The oocytes are developed from the primitive germ cells which 

 in the earliest stages are interspersed amid other cells of the germinal 

 epithelium. The primitive germ cells divide and produce oogonia ; 

 and by the division of the oogonia, primary oocytes are formed 

 (fig. 559). The oogonia and primary oocytes sink into the stroma, 



FIG. 559. Diagram showing mode of development of primary oocytes from primitive germ cells iu 

 mammalian ovary. 1, Germinal epithelium; 2, primitive germ cells; 3, oogonia; 4, primary 

 oocytes. In A, two primitive germ cells are seen imbedded in the germinal epithelium. In 

 B, a primitive germ cell has descended into the stroma of the ovary accompanied by cells proliferated 

 from the germinal epithelium which will become the cells of the membrana granulosa. In C, the 

 oogonia derived from primitive germ cells, and primary oocytes produced by division of the 

 oogonia, are seen. (After Btihler.) 



surrounded by cells, produced by the proliferation of the germinal 

 epithelium, which are destined to form the membrana granulosa and 

 the discus proligerus of the Graafian follicles. 



The Fallopian Tubes or oviducts which lead to the uterus have 

 externally a serous coat from the peritoneum, then a muscular coat 

 (longitudinal fibres outside, circular inside), and most internally a 

 vascular mucous membrane thrown into longitudinal folds, and 

 covered with ciliated epithelium. 



The uterus consists of the same three layers. The muscular 



