358 Proceedings of the Royal Physical Society. 



epithelium, as well as the ovum, is derived from the outer 

 columnar epithelium of the ovary. But what is remarkable 

 is that the follicular cells, during the earliest stages of the 

 development of the ovum, are flattened and quite different in 

 appearance from what they presently become, as well as 

 different from the cells whence they are derived. The 

 columnar epithelium was frequently distinguishable by hav- 

 ing become less deep stained by Borax carmine than the 

 subjacent tissues. Beneath the columnar epithelium is the 

 ovarian stroma, which does not appear to present any great 

 difference from the same tissue in other Mammalia. The 

 outer layer of the stroma — that containing the ovarian fol- 

 licles in various stages of development — is a more compact 

 tissue, and not nearly so vascular as the central core of the 

 ovary, which, in all the sections examined by me, was filled 

 with numerous large blood-vessels, which were extremely 

 conspicuous through having in most cases retained their fluid 

 contents. In the outer part of the ovary but few blood- 

 vessels were observable, except in the immediate neighbour- 

 hood of the ova. The central tissue of the ovary is also 

 remarkable for the abundant presence of roundish cells ar- 

 ranged in groups and strings, and largely filled with a 

 yellowish matter of a fatty appearance. These are pre- 

 sumably the remnants of the Wolffian tubules. 



The immature ova are invariably, as would naturally be 

 expected, placed close to the surface of the ovary ; they are 

 surrounded by a follicular epithelium only one cell deep, 

 the cells of which, as already stated, are not columnar, but 

 appear more or less oval both in transverse section and in 

 superficial view. The vitelline membrane is no doubt pre- 

 sent, but it is so thin that I was unable to recognise it in 

 any case, and the number of sections I have studied is very 

 considerable ; on the other hand, the basement membrane of 

 the epithelium was extremely conspicuous. The stroma of 

 the ovary, which in the cortical region is more cellular, being 

 composed of a compact mass of oval to fusiform cells, be- 

 comes distinctly fibrous in the neighbourhood of the ova, 

 forming thus a special sheath for them (see PL XVII., Fig. 6). 

 The germinal vesicle is of considerable size, and separated by 



