354 DR FOULIS ON THE DEVELOPMENT OF THE OVA, ETC. 
siderable layer of protoplasm; it is this latter substance which gives magnitude 
to the young ovum, as may be seen by the fact that though many of the nuclei 
of the larger germ epithelial corpuscles are nearly as large as the nuclei of the 
primordial ova, yet, being without the extensive investment of protoplasm, they 
do not appear markedly conspicuous among the rest like the primordial ova. 
Occasionally, two large spherical nuclei or germinal vesicles are found in a 
single large primordial ovum among the germ epithelial corpuscles on the 
surface of the ovary. 
Among the germ epithelial corpuscles in the deeper parts of the germ 
epithelial layer all round the ovary we meet with many large primordial ova, 
and in contact with their yelk or protoplasm are small fusiform bodies, 
each consisting of an oval-shaped nucleus, around which is an investment 
of protoplasm drawn out at either end in a fusiform manner. Besides these 
primordial ova, numerous germ epithelial corpuscles, in various stages of 
development into the same, are found in this situation. 
Immediately subjacent to the germ epithelial layer is the zone of egg 
clusters. In osmic acid preparations this can be seen with the naked eye as a 
well-marked thick layer. The egg clusters are large oval-shaped and spherical 
collections of round corpuscles (0, 0, 0). ‘The oval-shaped clusters lie close 
together, with their long axes directed from the centre of the ovary in a radiat- — 
ing manner towards the germ epithelium. Between the clusters, and separating 
them, are delicate bundles or strings of small fusiform corpuscles, with blood- 
vessels (7, 7,7), which may be traced growing upwards from the deeper parts of 
the ovary towards the germ epithelium. By far the greater number of the egg 
clusters are oval, but spherical-shaped groups or clusters are also met with, — 
generally deeper in the ovary. Each egg cluster consists of a collection of cor- 
puscles, most of which are spherical, and resemble very closely the larger 
corpuscles of the germ epithelium. If we direct our attention to any one egg 
cluster, it will be seen that the corpuscles vary in size, just as we described the 
corpuscles of the germ epithelium. At the lower part of each egg cluster, that 
is, farthest away from the germ epithelium, we find many large primordial ova, 
similar to those already described among the corpuscles on the surface of the 
ovary, and besides these are numerous large spherical nuclei, having round them 
protoplasm in layers of varying thickness. In each egg cluster it is possible to 
trace the corpuscles in all stages of development into primordial ova. Every 
large corpuscle in each egg cluster is potentially a primordial ovum. In con- 
tact with each primordial ovum in the egg clusters are small fusiform corpuscles, 
which may be traced as offshoots from the bundles of similar corpuscles which 
lie between and separate the egg clusters from each ocher. It is easy to 
compare the corpuscles in each egg cluster with the corpuscles of the germ 
epithelium, and to follow the steps of their development into primordial ova. 

