1910-11.] Development of Germ Cells in Mammalian Ovary. 159 
central portion are lacunae filled with blood corpuscles, the walls of these 
spaces containing sparsely distributed oval stroma cells. In many places 
the blood corpuscles appear to be lying between the germ cells with a 
limiting membrane. The whole tissue is made up of small oval cells, 
granular, with a definite nuclear outline — the primitive sex-cells or oogonia. 
These cells appear to be scattered irregularly, but in places near the central 
zone they appear to be in rows of three or four cells : these rows correspond 
to the situation of the medullary cords. On the surface of the ovary the 
cells are already differentiated to form a row of protective cells or surface 
epithelium. For a clearer understanding of the description of the cells of 
the ovary this layer of cells will be referred to as the capsular epithelium 
of the ovary. The terms “ germinal epithelium,” “superficial epithelium,” 
give rise to confusion among the various writers, and I feel that this term, 
“ capsular,” is the most appropriate, as it can be made use of when referring to 
the epithelium on the surface of the adult ovary. The cells of the capsular 
epithelium at this stage show a differentiation from the other oogonia by 
their slightly larger size, deeper staining, and elongated nuclei. They lie 
somewhat obliquely to the rest of the underlying cells, or have parallel axes. 
The nuclei appear granular, and contain several small masses of chromatin, 
one of which is probably a nucleolus. Very fine chromatin threads are 
seen in irregular distribution within the nuclear membrane. These corre- 
spond to the protobroque (a) cells of v. Winiwarter. The rest of the ovary 
is composed of smaller pale cells with rounded and oval nuclei, one pole 
appearing broader than the other. The chromatin threads are coarser than 
those of the capsular cells. The chromatin masses are not so large, and lie 
closer to the nuclear membrane. The nucleolus is present, but not well 
defined. Mitotic figures are numerous. Near the central zone are small 
elongated cells, i.e. stroma cells, the nuclei of which stain deeply. The 
oogonia form all the future cells of the ovary with the exception of the 
mesenchymatous tissue. Near the hilum of the ovary are a few gland-like 
structures, the rete tubules. 
Embryo 8 cm . — Some differentiation is observed between the cortex and 
medulla ; the oogonia are increased in number. The central vascular zone 
contains more stroma cells and blood spaces. There is a slight increase in 
the transverse diameter of the organ, and its whole volume is increased. The 
capsular cells are becoming placed more at right angles to the underlying 
cells. The cells in the deeper layers are larger, more spherical, with fine 
chromatin filaments in the granular protoplasm. The nuclear membrane is 
more distinct, with chromatin granules adherent to it. A nucleolus is seen 
in some cells. In the most central portion the cells are clear, with a well- 
