THE FEMALE GENITAL ORGANS. 347 



stricted tubes of Pfluger. The fourth, fifth, and possibly the third 

 types are further divided by connective-tissue septa, until they 

 finally form distinct and typical follicles (Schottlander, 91, 93). 



In the adult ovary true egg tubes are no longer developed. 

 Isolated invaginations of the germinal epithelium sometimes occur, 

 but apparently lead, merely to the formation of epithelial cysts 

 (Schottlander). The theories as to when the formation of new 

 epithelial nests or follicles ceases are, however, very conflicting, 

 some authors believing that cessation takes place at birth, others 

 that it continues into childhood and even into middle age. 



The typical primitive follicle consists of a relatively large egg- 

 cell surrounded by a single layer of smaller cubical or cylindric 

 follicular cells. The growth of the follicle takes place by means 

 of mitotic division in the follicular cells and increase in size of 

 the ovum. The egg-cell is soon surrounded by several layers of 

 cells, and gradually assumes an eccentric position in the cell 

 complex. At a certain distance from the ovum and nearly in the 

 center of the follicle one or more cavities form in the follicular 

 epithelium. These become confluent, and the resulting space is 

 filled by a fluid derived, on the one hand, from a process of 

 secretion and, on the other hand, from the destruction of some 

 of the follicular cells. The cavity is called the antrum of the 

 follicle, and such a follicle has received the name of Graafian 

 follicle. Its diameter varies from 0.5 to 6 mm. The follicle in- 

 creases in size through cell-proliferation, the cavity increasing and 

 gradually inclosing the egg together with the follicular cells imme- 

 diately surrounding it, although the latter always remain connected 

 with the wall of the vesicle at some point. The egg now lies 

 imbedded in a cell-mass, the discus proligerus, which is composed 

 of follicular epithelium, and projects into the follicular cavity. 

 The follicular epithelium forming the wall of the cavity is known as 

 the stratum granulosum, the cavity as the antrum, and the fluid 

 which it contains as the liquor folliculi. Those follicular cells 

 which immediately surround and rest upon the ovum are some- 

 what higher than the rest and constitute the egg epithelium, or 

 corona radiata. 



During the growth of the follicle the connective tissue surround- 

 ing it becomes 'differentiated into a special envelope, called the theca 

 folliculi. In it two layers may be distinguished the outer, the 

 tunica externa, consisting of fibrous connective tissue, is continu- 

 ous with the inner, or tunica interna, rich in blood-vessels and 

 cellular elements. The follicle gradually extends to the surface of 

 the ovary, at which point it finally bursts (see below), allowing the 

 ovum to escape into the body cavity and thus into the oviduct. 



During the growth and development of the ovarian follicles the 

 ova undergo certain changes of size and structure which may receive 

 further consideration. These have been described for the human 

 ovary by Nagel (96), whose account will here be followed. The 



