STRUCTURE AND DEVELOPMENT OP VERTEBRATE OVARY. 419 



accept his views of the relation of the stroma to the germinal 

 epithelium. 



In the very interesting paper of Foulis, the conclusion is 

 arrived at, that while the ova are derived from the germinal 

 epithelium, the cells of the follicle originate from the ordinary 

 connective tissue cells of the stroma. Foulis regards the zona 

 pellucida as a product of the ovum and not of the follicle. To 

 both of these views I shall return, and hope to be able to show 

 that Foulis has not traced back the formation of the follicle 

 through a sufficient number of the earlier stages. It thus comes 

 about that though I fully recognise the accuracy of his figures, 

 I am unable to admit his conclusions. Kolliker's statements 

 are again very different from those of Foulis. He finds certain 

 cords of cells in the hilus of the ovary, which he believes to be 

 derived from the Wolffian body, and has satisfied himself that 

 they are continuous with Pfliiger's egg-tubes, and that they 

 supply the follicular epithelium. To the general accuracy of 

 Kolliker's statements with reference to the relations of these cords 

 in the hilus of the ovary I can fully testify, but am of opinion 

 that he is entirely mistaken as to their giving rise to the follicular 

 epithehum, or having anything to do with the ova. I hope to 

 be able to give a fuller account of their origin than he or other 

 observers have done. 



My investigations on the mammalian ovary have been made 

 almost entirely on the rabbit — the type of which it is most 

 easy to procure a continuous series of successive stages ; 

 but in a general way my conclusions have been controlled and 

 confirmed by observations on the cat, the dog, and the sheep. 

 My observations commence with an embryo of eighteen days. 

 A transverse section, slightly magnified, through the ovary at 

 this stage, is represented on PI. XIX, fig. 35, and a more highly 

 magnified portion of the same in fig. 35a. The ovary is a cylin- 

 drical ridge on the inner side of the Wolffian body, composed 

 of a superficial epithelium, the germinal epithelium [g. e. ), and 

 of a tissue internal to this, which forms the main mass of 

 it. In the latter two constituents have to be distinguished — 

 (1) an epithehal-like tissue {t), coloured brown, which forms 

 the most important element, and (2) vascular and stroma 

 elements in this. 



The germinal epithelium is a layer about 0'03 — 0-04 mm. in 

 thickness. It is {vide fig. 35a, g. e.) composed of two or three 

 layers of cells, with granular nuclei, of which the outermost 

 layer is more columnar than the remainder, and has elongated 

 rather than rounded nuclei. Its cells, though they vary shghtly 

 in size, are all provided with a fair amount of protoplasm, and 

 cannot be divided (as in the case of the germinal epithelium of 



