304 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



medulla, and in addition Graafian follicles in different 

 stages of development, and in older ovaries also cor- 

 pora lutea. 



Young Graafian Follicles. Early in embryonic life, 

 when the ovary is clothed with the germinal epi- 

 thelium which later becomes the epithelium of the 

 capsule, epithelial buds or strings of epithelial cells 

 push their way into the ovarian cortex. These buds 

 soon lose their connection with the germinal epithe- 

 lium and form little groups or nests of cells known as 

 young Graafian follicles. In each follicle one cell 



takes a central posi- 

 tion and is the egg 

 cell or ovum, des- 

 tined, under proper 

 conditions, to de- 

 velop into a new be- 

 ing. The ovum in- 

 creases rapidly in 

 size, receiving pro- 

 tection and possibly 



nourishment from the investing cells. The repro- 

 ductive cells, both ova and spermatozoa, can thus be 

 traced directly from the germinal epithelium, which 

 is of mesodermic origin and closely related to the 

 pavement epithelium of the peritoneum. 



The Graafian follicles occupy the cortical layer of 

 the ovary. They are all formed during embryonic 

 life, and whatever influence environment has upon 

 the offspring, that influence leaves its impression not 

 upon the origin of the reproductive cells, but upon 

 their later development. At time of birth it is esti- 



Germinal 

 epithelium. 



Young 

 Graafian 

 follicle. 



Fig. 220. Section from ovary of young 

 dog. 



