874 DR FOULIS ON THE DEVELOPMENT OF THE OVA, ETC. 
between the eggs, and as these processes thicken all traces of single large egg 
clusters become obliterated, and a complete zone of eggs, passing round the 
ovary takes their place. In this egg zone a great number of eggs become 
destroyed. In some cases large vacuoles form in the yelk or protoplasm which 
surrounds the germinal vesicle, and this latter structure is often pushed aside 
or pressed against the wall of the follicle. The germinal vesicle itself does not 
seem to be involved in this process of vacuolation. The vacuoles form in the 
yelk and not in the germinal vesicle. In the human ovary at birth I have also 
seen a large number of eggs distorted or destroyed by the formation of large 
vacuoles in the yelk substance. 
I do not attempt to explain the meaning of this formation of vacuoles in 
the yelk substance of the young eggs. I have observed it in the ovaries of 
several mammals, and I have also seen it taking place in the protoplasm which 
surrounds the nuclei of large cancer cells, obtained from cancerous ovaries and 
other malignant growths. I may also mention, that I have seen vacuoles in the 
protoplasm around the nuclei of pus and renal epithelial cells. 
In the central part of this five months’ cat’s ovary large Graafian follicles are 
found in various stages of development. 
In the growth of these large Graafian follicles, many young and smaller fol- 
licles are destroyed by pressure; and it would appear that many of the imbedded 
eges simply atrophy and form a pabulum for the connective tissue corpuscles 
which surround them. 
It may be asked, What becomes of the germ epithelium after its egg-forming 
character has disappeared ? 
After birth the corpuscles of the germ epithelium gradually become smaller 
in size, losing their columnar form, till at the age of six years, in the case of the 
human ovary, they present the appearance of small flattened corpuscles (fig. 41, — 
h,). They are very small, measuring in their longest diameter not more than the - 
soooth part of an inch. The epithelial membrane composed of such corpuscles 
can be stripped off the surface of the ovary without difficulty. In the human 
ovary at twelve years of age, the epithelium has preserved an almost identical 
appearance to that above described, the epithelial corpuscles still remaining 
of very small size. In the ovary of an adult, the epithelial corpuscles do not 
measure more than the zg5pth to the s+)5th part of an inch in diameter. 
In the ovary of old rabbits, the germ epithelial corpuscles remain as a well- 
marked layer of small oval corpuscles, and in the ovary of old cats the cor- 
puscles are flattened from above downwards, and show very beautifully their | 
epithelial character (fig. 40, 2,). The corpuscles show well-marked oval nuclei, 
and the protoplasm round them is extended out and abuts against the proto- 
plasm around neighbouring nuclei; at the lines of contact there is the appear- 
ance of a cell wall. 

