OVARY AND OVARIAN EGG OF ANOPHELES 405 
follicle to the portion of the follicular tube membrane which 
invests the lumen of the ovary, with which it fuses. 
The whole of the egg-string is invested by a thin structureless 
membrane, the tunica propria, which may also be regarded 
as the basement membrane of the follicular epithelium. I am 
here using the term ‘ tunica propria’ in the sense defined by 
J. Gross (9). The term has been used by many authors as 
synonymous with ‘peritoneal membrane’, a practice which 
has led to much confusion, The peritoneal membrane is repre- 
sented in the mosquito by the two ovarian sheaths. 
Normally the tunica propria can scarcely be observed, as 
it is very closely applied to the follicular epithelium; but it 
frequently happens that the follicles degenerate, and then the 
tunica propria can easily be seen as a somewhat wrinkled, 
structureless bag surrounding the remnants of the follicle 
(fig. 24). 
Hach follicle consists of an oocyte and seven nurse-cells 
completely surrounded by a single layer of cubical cells, the 
follicular epithelium. 
GENERAL Lines oF DEVELOPMENYT oF Ovary AND Baas. 
Before giving a detailed description of the various changes 
which take place during the oogenesis of A. mac ulipennis, 
I will first give a general outline of the development of the egg- 
follicles and of egg formation, as a comprehensive view of the 
whole subject will render it more easy to follow the detailed 
descriptions of the different processes which together produce 
the mature egg, but which, for sake of clearness, have to be 
dealt with separately. Also a description of the anatomy of 
the mature egg will be given, as with a knowledge of this it 
will be possible to understand the object of the various processes. 
The earliest stages of oogenesis are to be found in the end 
chamber. This consists of a central mass containing compara- 
tively large nuclei, which often vary considerably in appear- 
ance but are not definitely divided into nurse-cells and oocytes, 
and of a peripheral layer containing smaller nuclei which give 
rise to the follicular epithelium. 
Ee2 
