354 HISTOLOGY 



and no active follicles may be readily identified. Usually a section of the 

 ovary may be recognized as such without magnification, owing to the pres- 

 ence of the large cysts or follicles in which the maturing ova are contained. 

 These extend from the cortex into the medulla, and are numerous even in 

 childhood (Fig. 356). 



Growth of the Follicles. It is probable that all the sexual cells which are 

 to be produced in a life-time are present in the ovaries at birth. At that 

 stage, at least, many of those previously formed have already degenerated; 

 and the ovaries contain a great excess of ova, all but a few hundred of 

 which are destined to atrophy within the limits of the genital glands. In 

 so far as the sexual cells have ceased to multiply and have entered upon 

 the growth period, they represent the last generation of oogonia, and are 

 being transformed into primary oocytes. During this transformation 



FIG. 356. CROSS SECTION OF THE OVARY OF A CHILD EIGHT YEARS OLD. X 10. 



Germinal epithelium; 2, tunica albuginea; 3, peripheral zone with primary follicles; 4, vesicular follicle; 

 5, stroma ovarii; 6, medulla; 7, 8, peripheral section of vesicular follicles; 9, hilus, containing- large 

 veins. 



they increase greatly in size, finally becoming about 0.3 mm. in diameter. 

 These egg cells have already been described in detail (p. 29). They are 

 conspicuous in sections as large, round, deeply staining cells, with round or 

 oval vesicular nuclei, each containing a prominent uucleolus. The cells 

 become so large that frequently they are cut into 'several sections, and 

 portions of protoplasm without nuclei are to be expected. The larger 

 oocytes are surrounded by the clear, radially striated zona pellucida (Fig. 

 22, p. 30); their protoplasm may contain the vitelline bodies previously 

 described. 



The follicles are composed of the cells which surround the oocytes. 

 After the groups of egg cells and indifferent cells become subdivided, each 

 oocyte is typically surrounded by a single layer of flat follicular cells, and 

 this primary follicle lies isolated in the stroma of the cortex, beneath the 

 tunica albuginea (Figs. 357 and 358). As the follicle enlarges, the follic- 



