FORMATION OF THE EGGS. 425 



briefly notice the similar manner in which the eggs are 

 formed in the ovary. In all Mammals, the mature eggs are 

 contained in peculiar vesicles, which, after their discoverer, 

 Kegner De Graaf (1677), are called the Graafian foUicles. 

 These were formerly regarded as the actual eggs, which 

 were, however, discovered by Baer 'within the Graafian 

 foUicles (vol. i. p. 55). Each follicle (Fig. 330, 0) consists of a 

 round, fibrous capsule, which contains fluid and is coated by 

 several layers of cells. At one point this cellular layer has 

 a knob-like enlargement (C, 6), and, there, surrounds the 

 real egg (C, a). The mammalian ovary is, originally, a very 

 simple oblong little body (Fig. 320, g), formed only of 

 connective tissue and blood-vessels, and surrounded by a 

 cell-layer (the epithelium of the ovary, or the female germ- 

 epithelium). From this epithelium, cords of cells grow 

 inward, into the connective tissue or "stroma" of the 

 ovary (Fig. 330, A, 6). Single cells of these cords increase 

 in size and become egg-cells (primitive eggs, A, c) ; but the 

 greater number of the cells remain small and form an 

 enveloping and nutritive cellular layer (the follicle-epi- 

 thelium) round each egg. 



In Mammals the follicle-epithelium is at first one- 

 layered (Fig. 330, B, 1), afterwards many-layered (B, 2). In 

 all other Vertebrates, the egg-cell is, indeed, enclosed in a 

 permanent covering of small cells, an egg-follicle ; but only 

 in Mammals does fluid accumulate between the growing 

 follicle-cells, and thus extends the follicle into a round 

 bladder of considerable size, on the inner wall of which 

 the egg lies excentrically. In this point, as in his whole 

 Morphology, Man unmistakably indicates his descent from 

 Mammals. 



