THE OVA AND OVARY IN MAN AND OTHER MAMMALIA. 195 



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. The oval-shaped clusters lie close 

 together, with their long axes directed from the centre of the 

 ovary in a radiating manner towards the germ epithelium. 

 Between the clusters, and sparating them, are delicate 

 bundles or strings of small fusiform corpuscles, with blood- 

 vessels, 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 

 corpuscles, 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 contact with each pri- 

 mordial ovum in the egg clusters are small fusiform cor- 

 puscles, which may be traced as offshoots from the bundles of 

 similar corpuscles which lie between and separate the egg 

 clusters from each other. It is easy to compare the cor- 

 puscles in each egg cluster with the corpuscles of the germ 

 epithelium, and to follow the steps of their development into 

 primordial ova. In such a young kitten's ovary many of 

 the egg clusters are still in connection superiorly with the 

 corpuscles of the germ epithelium, but in most cases we find 

 the bundles of young connective tissue which lie between 

 the egg clusters have grown completely round them, separat- 

 ing them not only from each other, but also from the germ 

 epithelium above. While the corpuscles of the germ epi- 

 thelium are thus being enclosed in the meshes of young con- 

 nective tissue, the nucleus of each swells out into a spherical 

 body, around which is gradually produced that protoplasm 

 which later constitutes the yelk of the primordial ovum. 

 When we trace the bundles of young connective tissue 



