1910-11.] Development of Germ Cells in Mammalian Ovary. 165 
(Fig. 9.) Groups of cells are seen in synapsis. To left of field are cells in 
reticulum stage. To left of upper cell in synapsis is a nucleus showing a 
fine spireme. The cytoplasm is granular, and the cell membranes are not 
well seen. Surrounding the group of oocytes are dense bands of stroma 
cells, and in close contact with the group are oval cells, deeply stained ; 
these are the oogonia or future follicle cells. The threads entering the 
synaptic skein are fine, those emerging are thicker. It would therefore 
appear as if a reduction of the filaments took place by means of this stage. 
On counting the filaments, the number which emerge are less numerous 
than those which enter, but no accurate conclusion can be arrived at, owing 
to the difficulty in making a count. It is most probable that two fine fila- 
ments become united by their achromatic threads to form a thick filament, 
which again separates, the union being a temporary one, and the succeeding 
longitudinal fission being only a pseudo-fission, as the filaments have never 
really united. The threads lying near one another are always fine, and 
there is no evidence of a thin and a thick filament lying side by side. 
Only a few nuclei in the thick spireme stage are seen in the ovary at birth. 
The most numerous cells are those of the first stage of the oocyte — deuto- 
broque. In the deeper layers of the cortical zones are masses of oval cells 
lying in columns and tongues, divided up by the stroma cells. These cells 
have deeply-stained nuclei, oval in outline, granular, and with fine filaments 
a nucleolus is seen, and several masses of chromatin. Some of these cells 
have a more spherical and clear nucleus, with a reticulum of chromatin 
filaments. The cell outlines are well defined, and the cytoplasm is not 
granular. These cells have the appearance of oogonia and early oocyte stage 
cells, and are the future follicle and interstitial cells of the ovary. There may 
be a retrograde process taking place in these cells, causing them to assume an 
oval outline, but I cannot find any evidence of this. (Fig. 10.) 
In the superficial layers of the cortical zone numerous cells in mitosis 
are seen in the forms of asters, diasters, and equatorial plates. These changes 
are occurring among the oocytes of the first stage as well as among the 
oogonia, being more numerous among the former. This is contrary to the 
view as expressed by v. Winiwarter. The filaments in the nucleus become 
thickened and applied against the nuclear membrane, the nucleolus in- 
creases in volume, and filaments are found in its vicinity. The filaments 
form chromosomes, which split and separate, and are scattered over the 
nucleus whose membrane is beginning to disappear. These chromosomes 
are formed into the equatorial plate, and lie on the spindle as thick rods, 
some being curved or horseshoe-shaped. In some cells the spindle threads 
are well marked; running into each attraction sphere with the row of 
