OF THE VERTEBRATE OVARY. 551 



worth recording have taken place. By stage P a distinction is 

 observable between the right and left ovarian ridges ; the right 

 one has, in fact, grown more rapidly than the left, and the differ- 

 ence in size between the two ridges becomes more and more 

 conspicuous during the succeeding stages, till the left one ceases 

 to grow any larger, though it remains for a great part of life 

 as a small rudiment. 



The right ovarian ridge, which will henceforth alone engage 

 our attention, has grown very considerably. Its height is now 

 about O'4 mm. It has in section (vide PI. 24, fig. i) a triangular 

 form with constricted base, and is covered by a flat epithelium, 

 except for an area on the outer surface, in length co-extensive 

 with the ovarian ridge, and with a maximum breadth of about 

 O'25 mm. This area will be spoken of as the ovarian area or 

 region, since the primitive ova are confined to it. The epithelium 

 covering it has a maximum thickness of about 0^05 mm., and thins 

 off rather rapidly on both borders, to become continuous with the 

 general epithelium of the ovarian ridge. Its cells have the same 

 character as before, and are several layers deep. Scattered 

 irregularly amongst them are the primitive ova. The germinal 

 epithelium in the ovarian region is separated by a basement 

 membrane from the adjacent stroma. 



In succeeding stages, 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 different 

 embryos vary considerably. In two embryos of nearly the same 

 age, the breadth of the ovarian epithelium was 0*3 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. o'OQ mm. as compared with o - o8. In both 

 the epithelium was sharply separated from the subjacent stroma. 

 There were relatively more epithelial cells in proportion to 

 primitive ova than at the earlier date, and the individual cells 

 exhibited 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 favourable light and with high powers) 

 exhibited the spindle modification of Strasburger with great 



