510 THE REPRODUCTIVE SYSTEM 



closely simulate smooth muscle on superficial examination, but are 

 readily distinguished by careful study, especially if specimens are pre- 

 pared by the various differential staining methods. 



In the vicinity of the follicles the stroma is specially rich 

 in cellular elements and is otherwise modified to form a concentric coat 

 for each of these bodies. This coat, the theca folliculi, consists of (a] 

 an outer layer, or tunica externa, composed chiefly of connective tissue 

 whose interlacing bundles are concentrically disposed, (&) an inner 

 layer, tunica interim, which is peculiarly rich in large ovoid cells, and 

 (c) an innermost membrana propria, upon which the epithelial cells of 

 the follicle directly rest. 



At the surface of the ovary the cortical stroma forms a dense layer 

 of fine connective tissue fibers whose delicate bundles interlace in a 

 close-meshed network. This layer, which immediately underlies the 

 germinal epithelium at the surface of the ovarian cortex, is known as 

 the tunica albuginea. It differs greatly in thickness in different mam- 

 malian species, in different individuals of the same species, and even 

 in different portions of the same ovary. Its deeper surface blends in- 

 sensibly with the underlying stroma of the cortex. 



The general appearance of the ovary varies according to the number, 

 size, and stage of development of its ova and their follicles. At birth 

 the cortex is packed with large numbers of newly formed ova, all of which 

 are in approximately the same stage of development. Their number 

 has been estimated at between 30,000 and 70,000. No new ova are 

 formed after birth. Since in the normal sexual cycle from puberty 

 to the menopause (from about the thirteenth to the forty-fifth year), 

 a period of about 32 years, only about 400 eggs are liberated, the vast 

 majority of potential ova must degenerate. This process of degeneration 

 is especially active after the climacteric. 



During childhood the formation of larger follicles goes forward 

 at an unequal rate, some ova rapidly approaching maturity, others ap- 

 parently remaining almost stationary, and still others undergoing retro- 

 grade development, so that at the age of puberty the ovary contains 

 germ cells and follicles in all stages of development. After puberty 

 the ripe follicles successively rupture and result in the formation of 

 many corpora lutea which promptly degenerate, and are finally replaced 

 by dense connective tissue in the form of small scar-like masses known as 

 the corpora albicantia. Hence throughout the menstrual epoch the ova- 

 rian cortex contains many corpora lutea and corpora albicantia in addition 

 to O7 r a and follicles in various earlier stages of development. After the 



