364 DR FOULIS ON THE DEVELOPMENT OF THE OVA, ETC. 
The germ epithelial corpuscles on the surface of the ovary constantly 
produce new elements by the process of fission, and when included in a vascular 
mesh of stroma the corpuscles increase greatly in number by division, and from 
a few imbedded corpuscles a large group or cluster may be derived. It appears 
to me a most interesting and remarkable observation that these corpuscles, after 
a certain increase in number, expand or swell out into spherical bodies, and a 
careful examination of the egg clusters has convinced me that this change is 
brought about by the nucleus in each corpuscle swelling out into a spherical 
vesicular body, which afterwards becomes the germinal vesicle of the primor- 
dial ovum, and in close contact with the wall of the nucleus is gradually 
produced that protoplasm which afterwards forms the yelk of the ovum. 
In each egg cluster we find certain individuals much farther advanced in 
development than the rest, and these appear exactly like the large primordial 
ova which we described as found among the corpuscles of the germ 
epithelium on the surface of the ovary. Each corpuscle in the cluster is 
potentially a primordial ovum. At the first there is but a small quantity of 
protoplasm round the nuclei of the corpuscles in each egg cluster, but as the — 
nuclei enlarge and expand, the protoplasm round them is gradually produced in 
considerable quantity. 
This development of the germ epithelial corpuscles into primordial ova 
takes place in the egg clusters in all parts of the ovary. All the imbedded 
germ epithelial corpuscles do not reach the stage of primordial ova, many of 
them abort and disappear, and perhaps furnish a pabulum for the more vigorous 
and healthy ones. 
In the ovary of a puppy at birth, one sees, in a beautiful manner the egg — 
clusters under the germ epithelium in all stages of development. Some of the 
clusters appear to consist entirely of large primordial ova, while in others we 
can trace the growth of the germ epithelial corpuscles into ova, and — 
immediately under the germ epithelium are little groups of corpuscles in the 
act of being included in meshes of the stroma. 
In following the further development of the ovary and ova, we notice that ¥ 
around each egg cluster is a well-marked capsule or mesh of vascular connective 
tissue. This connective tissue consists almost entirely of fusiform corpuscles ,' 
and young blood-vessels. Just as at first, when delicate processes of the young 
stroma grew upwards among the ordinary germ epithelial corpuscles to include 
them in meshes, so now delicate processes of the young connective tissue with 
blood-vessels proceed from the walls of these meshes, and insinuate themselves 
in among the developing corpuscles in each egg cluster. As these processes 
thicken, the primordial ova gradually become separated from each other, and — 
at last each is included in its own mesh or capsule of the stroma. 
These single egg-containing meshes or capsules are the primordial follicles, _| 

