1910-11.] Development of Germ Cells in Mammalian Ovary. 171 
of the filaments is seen. These filaments are broken up into rods and loops 
in some places (dictyes). The stroma cells lie close to the follicles, but can 
be distinguished from them by their fusiform appearance. In the human 
foetal ovary the plan of development is the same as in other mammalian 
types, although the distribution of the cells is somewhat irregular. Mitosis 
has ceased long before birth, and all the oocytes are in the double-thread 
stage before or just at birth. 
Part IY. — Summary and Conclusions. 
It is seen on examination of these four types of mammaliam ovaries that 
development takes place according to a fixed rule which is constant in all 
types, although some are further advanced in embryonic life than others. 
From the early formation of the female sex organ the germ cells develop 
through a given number of stages until they reach the resting nucleus or 
final stage (of the oocytes of the first order), the chromatin filaments being 
in the form of short double threads. The medullary cords are the first 
structures to appear in the genital ridge ; these atrophy early and disappear. 
Their function is not clearly proved, although some of their cells may 
form oocytes, whether permanent or not is not clear. All the remaining 
cells in the ovary are oogonia ; these are small oval cells, with granular 
nuclei and masses of chromatin with a nucleolus faintly stained. The first 
differentiation which takes place is the formation of the capsular epithelium. 
The cells of this layer are larger in outline, and the axes of their nuclei in 
the early stages lie parallel to those of the oogonia (fig. 21). These nuclei 
afterwards become placed in a perpendicular direction, thus forming a 
cubical or columnar row of epithelium. Their function is mainly protective, 
and there is no evidence in my specimens that they form oocytes. 
The epithelial invaginations are formed from a piling up of the cells 
like rows of coins, which become pushed down among the underlying tissue, 
forming gland-like processes, but without a circular lumen. The next 
change occurring is the mutual growth of the stroma upwards and germ 
cells downwards, the former penetrating between the latter and forming 
groups or cell nests. 
In the kitten’s ovary these columns resemble tubules (Pfluger’s tubules). 
As the ovary increases in volume the stroma cells come nearer the periphery, 
until finally the capsular epithelium is isolated by a band of stroma — the 
tunica albuginea. Fig. 22 shows the surface of a rabbit’s ovary four days 
after birth, with the capsular epithelium at the surface. The stroma cells 
are fusiform in shape with deeply-staining granular nuclei ; remains of the 
