216 THE FEMALE REPRODUCTIVE SYSTEM 



cycle. Thousands of primary follicles are present in the ovaries of 

 a new-born female, but most of these undergo gradual degeneration 

 and resorption, a process known as atresia. The primary follicles 

 that are to mature undergo a complex development before the 

 ovum is ready for fertilization. 



Maturing Primary Follicles.— The rudimentary ovum, or oocyte, 

 is only slightly larger than the surrounding follicle cells. Both the 

 nucleus and cytoplasm of this cell increase in size with an accom- 

 panying increase in the number of surrounding cells which are now 

 cuboidal in appearance. Diu'ing this early period the chromosomes 

 of the o5cyte are organized for the first maturation division, after 

 which the chromatic material returns to the reticulated condition 

 characteristic of these cells. The second maturation division oc- 

 curs after the egg leaves the ovary. A highly refractive membrane, 

 the zona pellucida, forms between the cytoplasm of the ovum 

 and the surrounding polyhedral cells of the follicle which have 

 multiplied to form several layers, the stratum granulosum. 

 Ensheathing the granulosum there is a thin laj^er of connective 

 tissue, the theca folliculi, which carries a capillary network. 

 The cells of the stratum granulosum continue to divide by mitosis 

 and their multii)lication increases the size of the follicle. Spaces 

 begin to appear in the mass of cells composing the granulosum 

 region and fill with liquid, the liquor folliculi. The follicle cells 

 continue to increase in number; more spaces and more liquid 

 appear; the spaces begin to fuse and finally form one large space. 

 At one or two points a band of granulosum cells, the cumulus 

 oophorus, or germ hill, supports the ovum and its surrounding 

 radiating cells, the zona radiata. (Fig. 186.) The ovum and zona 

 radiata are thus separated from the peripheral granulosum cells by 

 the increasing amount of liquor folliculi. With this development 

 there is an accompanying development of the connective tissue 

 immediately surrounding the granulosum to form a theca folliculi 

 divisible into two regions. The inner portion, the theca interna, 

 is composed of connective tissue supporting a network of capillaries 

 and also containing peculiar polyhedral cells with lipoid material 

 in their cytoplasm. Outside the theca interna is the theca externa, 

 composed of denser connective tissue carrying small blood vessels. 

 These maturing follicles are called Graafian follicles. 



Ovulation.— The maturing follicle soon occupies the entire width 

 of the ovarian cortex, having increased many times the size of the 

 primary' follicles. The germ hill with the enclosed ovum nuiy shift 



