360 DR FOULIS ON THE DEVELOPMENT OF THE OVA, ETC. 
germ epithelial corpuscles we see the nuclei undergoing fission, and by this 
process crowds of germ corpuscles are produced. The whole germ epithelial 
layer must be regarded as a thick layer of proliferating corpuscles. From the 
first appearance of the ovary as an organ until its development is completed, 
there is a constant proliferation of the germ epithelial corpuscles; and, in growth 
of the ovary, as fast as some corpuscles become imbedded in the stroma, others 
are produced to take their place. 
It is interesting to recall to recollection the statements of ScHENK%, 
WALDEYER, and others, that in the first instance the whole peritoneal cavity 
is lined by a layer of columnar corpuscles, and when the Wolffian body appears 
in connection with REemaxk’s middle plate, it likewise has an investment of 
similar corpuscles. The first appearance of the ovary is the thickening of this 
columnar epithelium on the median side of the Wolffian body (WALDEYER.) 
At the commencement of this thickening there is seen under it a small out- 
erowth of young connective tissue, continuous with and proceeding from the 
interstitial tissue of the Wolffian body. There can be little doubt that the 
thickening of the columnar epithelium is brought about by a proliferation of its 
corpuscles, and the proliferation itself is due to the influence on the corpuscles 
of the vascular young connective tissue subjacent to them. While the columnar 
corpuscles constantly proliferate to form the germ epithelial corpuscles, from — 
which all the future ova are derived, the rest of the peritoneal chamber becomes 
lined by a layer of flat epithelium, forming the peritoneal epithelium. 
From the very first appearance of the germ epithelium of the ovary as a 
distinct structure, processes of the subjacent young connective tissue grow 
upwards among the corpuscles as the first step in that process of imbedding, 
whereby the corpuscles become surrounded in meshes of vascular stroma, and 
ultimately form ova. From its earliest condition till late in the development of 
the ovary, the germ epithelium cannot be stripped off as a layer from the ovary, 
because delicate processes of the ovarian stroma are constantly growing up 
between the corpuscles as fast as they are produced. 
PFLUGER states his opinion that the ovum is simply a peritoneal epithelial 
cell. With this statement I cannot altogether agree. Both the ova and the 
peritoneal cells are undoubtedly evolved from a common ancestral source—the 
columnar layer of the great peritoneal cavity; but whilst in one limited region 
the columnar corpuscles form the germ epithelium and become converted into ova, ~ 
in the greater part of their distribution they become converted into the endo- 
thelium lining the peritoneal cavity. Hence the ovum is no more a modified 
peritoneal epithelial cell than is the peritoneal epithelial cell a modified ovum. 
From the corpuscles of the germ epithelium all the ova are derived. We 
* Beitrage Zur. Lehre von den Organ-Anlagen im motorischen Keimblatt. 

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