IN MAN AND OTHER MAMMATIA. 363 
these are all lined by germ epithelium. Similar tube-like structures are pro- 
duced when sections are made through the convoluted surface of a brain, and 
the grey matter might even be compared to the germ epithelium, inasmuch as 
it lines these sulci. But such structures are not tubes, nor are the similar 
appearances seen between the irregularities of the surface of a young foetal ovary. 
An examination of the young ovary, looking down on its surface from above, 
soon convinces us that there are no real tubular structures passing from the 
epithelium into the organ. On bringing the germ epithelium into view, and 
then slightly depressing the tube of the microscope, one sees large and small 
round groups of spherical corpuscles separated from each other by the connective 
tissue of the stroma, as was described by WaLpEyER. Some of these groups 
are still in communication with the germ epithelial corpuscles, as may be seen 
in vertical sections where the knife has passed through a group of corpuscles 
not yet completely included in a mesh of the upward growing stroma. 
In the germ epithelial layer which dips down into and lines the depressions 
of the surface of the ovary (fig. 22, »,p), we find the corpuscles undergoing 
changes during their development similar to the changes which the corpuscles 
of the germ epithelium in other situations undergo. At the bottom and sides 
of the sulci, among the corpuscles of the germ epithelium, we find large 
spherical nuclei with a thin investment of protoplasm, and large primordial ova, 
such as may be found in all parts of the germ epithelial layer, whether it lines 
depressions or passes over prominences of the surface of the ovary. 
Frequently large egg clusters are formed under the germ epithelium which 
lines the furrows or sulci, and it often happens that the walls of these furrows 
come in contact; pushed together, as it were, by laterally situated expanding 
ege clusters. At the bottom of the furrows, where the epithelial walls come in 
contact, connective tissue passes through among the corpuscles, and in this way 
large egg clusters become formed immediately below the germ epithelium at the 
bottom of the sulci. A vertical section passing down through such a sulcus 
and the group of corpuscles immediately below it, produces the appearance as 
if a tubular prolongation of germ epithelium was dilated at its lower part into 
a large sac, full of developing corpuscles of the germ epithelium. 
During my investigations on the structure of the ovary and development of 
the ova, I have never found any real tubular structures, neither in the human 
ovary, nor in any other mammal that I have examined, such as the cat, dog, 
calf, sheep, guinea-pig, rabbit, and in no instance have I found Graafian follicles 
formed out of such structures in the manner described by PFLiiGer, VALENTIN, 
SPIEGELBERG, WALDEYER, and others, 
(d.) Development of the Egg Clusters.—Each egg cluster is a group or collec- 
tion of germ epithelial corpuscles enclosed in a mesh or capsule of the ovarian 
stroma. 
