' THE FEMALE GENITAL ORGANS. 345 



its structure and thickness vary to a considerable extent. In young 

 ovaries it is irregular, but shows in its highest development three 

 layers distinguishable from each other by the different direction of 

 the fibers. In the medullary substance the connective-tissue fibers 

 are long, in the cortex short, and in the zone containing the follicles 

 (see below) are mingled with numerous connective-tissue cells. 

 Nonstriated muscle-fibers occur exclusively in the medulla. Here 

 they are gathered in bundles which accompany the blood-vessels, 

 and may even form sheaths around the latter. They are especially 

 prominent in mammalia. 



The germinal epithelium is distinguished from that of the re- 

 maining peritoneum by the greater height of its cells, which are 



Young follicle with ovum. 



Primordial ova... 



Germinal 



_ 

 thelium. 



Stroma of 

 ovary 



Ovum with fol-_ 

 licular epithe- 

 lium. 





' 



?. ,_, y? ir.-.-^: ...- 



Fig. 275. Section from ovary of adult dog. At the right the stellate figure repre- 

 sents a collapsed follicle with its contents. Below and at the right are seen the tubules 

 of the parovarium (copied from Waldeyer). 



cubic or even cylindric in shape. At an early period in the devel- 

 opment of the ovaries this epithelium pushes into the underlying 

 embryonic connective tissue in solid projections, to form the primary 

 egg tubes of Pfluger, the cells of which very soon begin to show 

 differentiation. Some retain their original characteristics and shape, 

 while others increase in size, become rounded, and develop into the 

 young ova. Those retaining their indifferent type become the fol- 

 licular cells surrounding the egg. This differentiation into ova and 

 follicular elements may even occur in the germinal epithelium itself, 

 in which case the larger round cells are known as the primitive or 

 primordial ova. In the further development of the ovarian cortex 



