1910-11.] Development of Germ Cells in Mammalian Ovary. 167 
membrane, are granular, and contain masses of chromatin with a nucleolus. 
In some follicles in the deeper portions of the ovary the axes of the cells are 
parallel to the oocyte membrane. The nuclei are oval and have the appear- 
ance of stroma cells, being fusiform in outline. There is a considerable 
amount of cytoplasm in the follicle cells of the puppy. In many of the 
more superficial follicles the oocyte has fallen out, or has not been included 
in the sections examined. These empty follicles have the appearance of 
tubules lined with epithelium, almost columnar in type, and give rise to 
controversy as to their follicular origin. On examination of serial sections 
the oocyte is invariably found to be present, showing their origin as a primitive 
follicle, and not glandular, as some writers suppose. (Fig. 14.) In v. Wini- 
warter and Sainmont’s work (Arch, de Biol., Avril 1909) a drawing is given 
(fig. 9, pi. xi.) of a gland-like body very similar to these found in the cortex 
of the ovary. This is the figure of a tube of the epoophoron, but the struc- 
tures in the ovary of the puppy cannot have any connection with these 
tubes as they are seen only in the periphery of the organ. For the deeper 
layers the follicle cells have the spindle-like forms. Fig. 15 shows follicles 
in the deeper layers. 
In the ovary at four months the conditions are almost the same as at 
three months. In places large follicles are seen with several rows of cells, 
some containing one oocyte, others two or three, becoming divided up by the 
stroma ingrowths and follicle cells. Fig. 16 shows a mass of oocytes becom- 
ing separated up by ingrowths of follicle cells. Some of these oocytes are 
degenerating. To one side is seen a single oocyte, with smaller cells arranged 
round it. The nuclei at this stage show double filaments (diplotenes) and 
short paired rods (dictyes). The nucleus is now the germinal vesicle, and 
the principal nucleolus the germinal spot. The deutoplasm is granular. 
The follicle cells are in close contact with the cell membrane, but there is no 
appearance of processes entering this membrane for the purpose of nutri- 
ment. To all appearance this membrane is secreted by the cell cytoplasm 
itself. An organ of Balbiani is seen in some cells, but is not evident in the 
majority. 
D. Ovary of Kitten— seventeen days after birth. 
The ovary of the kitten is chiefly remarkable for the size of the germ 
cells, which stand out very clearly from the surrounding stroma cells. There 
is a distinct differentiation between the cortical and medullary zones. The 
latter consists of fairly dense strands of stroma cells, with numerous vessels 
and masses of small cells, which are cut off into groups by the stroma cells. 
In the cortical zone are large numbers of germ cells forming columns, 
