452 THE HUMAN EMBEYO. 



manifests itself for the smaller or indifferent cells to arrange 

 themselves round the primitive ova, so as to inclose these in 

 follicles (Fig. 171, d, e,f). At first there may be in a single 

 nest several of these follicles, each containing a single ovum, but 

 the continued growth of the connective tissue stroma gradually 

 breaks up the nests, and tends to isolate the several follicles from 

 one another, forming around each of them a separate connective 

 tissue investment. 



At the time of birth of the infant, the structure of the ovary 

 is as shown in Fig. 171. The germinal epithelium, a, or super- 

 ficial layer of columnar epithelial cells, is separated from the 

 deeper layers of the ovary, at almost all parts, by a thin layer 

 of connective tissue, the tunica albuginea. A little deeper down 

 are seen large nests of epithelial cells, formed by proliferation 

 from the deeper surface of the germinal epithelium, but cut off 

 and isolated by growth of the connective tissue stroma. In 

 these nests certain of the cells, the primitive ova, are dis- 

 tinguished by their larger size, and round these the smaller cells 

 tend to arrange themselves so as to form capsules or follicles. 

 In the deeper parts of the ovary the vascular connective tissue 

 has, by its further growth, broken up the nests, and separated 

 the follicles more or less completely from one another. 



In passing from the exterior towards the deeper parts of 

 the ovary, successive stages in the development of the ova are 

 met with. In the superficial layer of columnar epithelial cells 

 the earliest stages are seen ; certain of these cells, the primi- 

 tive ova, being of rather larger size than their neighbours. 



Beneath this surface layer are large nests, composed of 

 epithelial cells, which, except in the larger size of the primitive 

 ova, differ but little from one another, and present no regularity 

 of arrangement. In the more deeply placed nests, the cells 

 immediately adjacent to the ova have arranged themselves round 

 these latter so as to form follicles ; but there are, in such nests, 

 many cells of indifferent character, whose ultimate fate is still 

 uncertain. Deeper still, the number of these indifferent cells is 

 greatly diminished; and the follicles are larger, more clearly 

 defined, and separated from one another by connective tissue 

 trabeculae. 



In such a section, therefore, as in Fig. 171, the most deeply 

 situated ova are the oldest and most mature, and have, in 



