OVARY AND OVARIAN EGG OF ANOPHELES 418 
at which the oogonia divide to produce the oocytes, all but 
one of which become modified to form nurse-cells. 
In many end chambers, where the foregoing process has no 
doubt already taken place, the proximal nucleus is quite 
distinet from the remainder. It is clearer and contains a well- 
defined spireme, while the other cells are somewhat darker, 
and, though they often also appear to contain a spireme, 
this is never so sharply defined and usually can only be made 
out with difficulty. This proximal nucleus is the true oocyte 
nucleus, while the cells lying above it are the nurse-cells, and 
at the distal end of the chamber the remaining oogonia are found. 
The epithelial layer grows between the mass of nurse-cells 
and the oogonia, so that the former, together with the oocyte, 
are completely enclosed in a follicle. The fact that there are 
seven nurse-cells and one oocyte suggests that they are produced 
by three successive divisions of a single oogonium, seven of the 
daughter cells becoming nurse-cells and the eighth the true 
oocyte. Occasionally an aberrant number of cells are included 
inside the follicular epithelium: eight large cells, and at the 
distal end a number of smaller cells, apparently eight in number. 
In this case the epithelial layer has surrounded two masses 
of daughter cells instead of one. I have only found such 
follicles in young ovaries, so that the mass of smaller cells 
evidently does not take part in the development of the follicle 
and probably degenerates. This further supports the theory 
that the nurge-cells and oocyte are the daughter cells of a single 
oogonium. 
When the follicles are first formed the follicular epithelium 
consists of a comparatively small number of cells. These 
multiply rapidly by mitotie division (fig. 32), and at this stage 
no clear cell divisions are visible. Also there is only a small 
quantity of cytoplasm, the epithelium consisting principally 
of a large number of closely-packed nuclei. This mitotic 
division takes place throughout the first period of growth tll, 
when the resting stage is reached, the full number of epithelial 
cells is attained and also the nuclei have reached their full size. 
During the second period of growth the epithelium increases 
