552 THE STRUCTURE AND DEVELOPMENT 



clearness, and must therefore be regarded as undergoing division. 

 The ovarian region is at this stage bounded on each side by a 

 groove. 



In an embryo of seven centimetres (PL 24, fig. 2) the breadth 

 of the ovarian epithelium was O'5, but its height only O'o6 mm. 

 It was still sharply separated from the subjacent stroma, though 

 a membrane could only be demonstrated in certain parts. The 

 amount of stroma in the ovarian ridge varies greatly in different 

 individuals, and no reliance can be placed on its amount as 

 a test of the age of the embryo. In the base of the ovarian 

 ridge the cells were closely packed, elsewhere they were still 

 embryonic. 



My next stage (PI. 24, fig. 3, and fig. 4), shortly before the 

 time of the hatching of the embryo, exhibits in many respects 

 an advance on the previous one. It is the stage during which a 

 follicular covering derived from the germinal epithelium is first 

 distinctly formed round the ova, in a manner which will be more 

 particularly spoken of in the section devoted to the development 

 of the ovum itself. The breadth of the ovarian region is 0*56 mm., 

 and its greatest height close to the central border, O'I2 mm. a 

 great advance on the previous stage, mainly, however, due to the 

 larger size of the ova. 



The ovarian epithelium is still in part separated from the 

 subjacent stroma by a membrane close to its dorsal and ventral 

 borders, but elsewhere the separation is not so distinct, it being 

 occasionally difficult within a cell or so to be sure of the boundary 

 of the epithelium. The want of a clear line between the stroma 

 and the epithelium is rendered more obvious by the fact that 

 the surface of the latter is somewhat irregular, owing to pro- 

 jections formed by specially large ova, into the bays between which 

 are processes of the stroma. In an ovary about this stage, 

 hardened in osmic acid, the epithelium stains very differently 

 from the subjacent stroma, and the line of separation between 

 the two is quite sharp. A figure of the whole ovarian ridge, 

 shewing the relation between the two parts, is represented on 

 PI. 24, fig. 5. 



The layer of stroma in immediate contact with the epithelium 

 is very different from the remainder, and appears to be destined 

 to accompany the vascular growths into the epithelium, which 



