386 ¥. M. BALFOUR. 



epithelium in the ovarian region is separated by a basement mem- 

 brane from the adjacent stroma. 



In succeeding stage.-s, till the embryo reaches a length of 7 

 centimetres, no very important changes take place. The ovarian 

 region grows somewhat in breadth, though in this respect diHer- 

 ent embryos vary considerably. In two embryos of nearly the same 

 age, the breadth of the ovarian epithelium was U'^i mm. in the 

 one and 0'35 mm. in the other. In the former of these em- 

 bryos, the thickness of the epithelium was slightly greater than 

 in the latter, viz. 0'09 mm. as compared with O'OS. In both 

 the epithelium was sharply separated from the subjacent stroma. 

 There were relatively more epithelial cells in proportion to primi- 

 tive ova than at the earlier date, and the individual cells exhi- 

 bited great variations in shape, some being oval, some angular, 

 others very elongated, and many of them applied to part of an 

 ovum and accommodating themselves to its shape. In some of 

 the more elongated cells very deeply stained nuclei were present, 

 which (in a favorable light and with high powers) exhibited 

 the spindle modification of Strasburger with great 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 (PI. XVII, fig. 2) the breadth 

 of the ovarian epithelium was 0"5, but its height only 006 mm. 

 It was still shar|)ly separated from the subjacent stroma, though 

 a membrane could only be demonstrated m 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. XYII, fig 3, and fig 4), shortly Wfore, 

 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. Tlie breadth of the ovarian region is 0*56 

 mm., and its greatest height close to the central border, 012 mm. 

 — a great advance on the previous s'age, mainly, however, due to 

 the larger size of the ova. 



Tlie ovarian epithelium is still in part separated from the sub- 

 jacent 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 epi- 

 thelium. The want of a clear line between the stroma and the 

 epithihum is rendered more obvious by the fact that the surface 

 of the latter is somewhat irregnhir, owing to projections formed 



