406 A. J. NICHOLSON 
At intervals a mass of cells is cut off from the end chamber 
and consists of seven nurse cells and an oocyte surrounded by 
a follicular epithelium. This follicle increases in size till it 
reaches the resting stage (fig. 26), which is characteristic of 
the ovaries of hibernating females. When the most-developed 
follicles of the ovary are at this stage the ovary is very small 
and quite transparent. 
If the ovary of an insect which has Just had a meal of blood 
be examined in a fresh condition, it will be found that a white 
opaque cloud is visible surrounding the nucleus of the oocyte. 
This consists of fine yolk. In living ovaries at a slightly later 
period it will be found that the whole oocyte is opaque white 
and occupies about half the follicle. In sections this opaque 
inass is found to consist of both coarse and fine yolk, and the 
oocyte nucleus is no longer spherical but sends out blunt 
processes into the yolk (fig. 18). 
At a still later stage the follicles are elongated instead of 
almost spherical, and are quite opaque except for a small 
transparent cap, consisting of nurse-cells, and a thin investing 
layer of follicular epithelium. The nucleus has now become 
very much branched, branches passing throughout the yolk- 
mass and appearing to be in some connexion with the nurse- 
cells, which are evidently in a state of activity. A new structure 
has now appeared between the follicular epithelium and the 
yolk-mass. ‘This consists either of globules or of a layer of 
gelatinous material, and is the commencement of the inner wall. 
Shortly after this stage the nurse-cell nuclei are extruded 
from the yolk-mass and come to lie in the follicular epithelium, 
forming a cap over the anterior end of the egg. The oocyte 
nucleus has now reached its maximum condition of branching 
and shortly afterwards breaks down. The inner wall is 
thick but still gelatinous. The follicular epithelium becomes 
modified in two lateral areas and gives rise to the floats. The 
rest of the epithelium secretes the chorion over the whole 
surface of the egg, that portion which contains the extruded 
nurse-cell nuclei giving rise to the micropyle apparatus. 
Finally, the follicular epithelium degenerates into a mere 
