254 C. T. BRUES, 
section they always appear circular but vary considerably in shape 
in longitudinal section, usually showing a slight attenuation at one 
pole, although in rare cases this may be quite considerable, or again, 
they may be almost perfectly spherical. Eggs are present in vast 
numbers, the body of a full grown female containing on an average 
about nine hundred eggs. The number varies within wide limits 
however, as it is directly proportionate to the size of the female which 
varies considerably in length and still more in bulk. 
The peculiar environment of the egg during its formation has 
had a very decided influence upon the nature of its enveloping mem- 
branes. Not only before maturation but also during embryonic growth, 
the egg enlarges slightly, by absorption from the surrounding fat cells 
in the body cavity. This has caused the egg envelopes to assume a 
nutrient function by allowing a certain amount of fat to be absorbed 
through them. Hence they are of quite a succulent character. The 
vitelline membrane is indistinguishable and if present must be of ex- 
treme tenuity. The chorion however, which is secreted by the fol- 
licular cells of the ovarian tubules is thick and forms the principal 
egg membrane. No distinct micropyles could be seen, although they 
may possibly be present enclosed in a glutinous mass which is in- 
distinguishable from the chorion, as is sometimes the case among 
. Insects. 
Although the chorion is usually thick and fleshy, it is by no 
means of the same thickness at different stages of embryonic growth. 
Besides a series of developmental changes there is also considerable 
individual variation. Usually it is quite thin until the time when 
maturation takes place, then becomes very thick until the stage is 
reached where the blastoderm begins to draw up on the yolk. It now 
thins out again, only to become heavier again for a short period, 
during the gastrula stage. After these early stages it becomes very 
thin and delicate and remains so until the time of hatching. That 
this thicker membrane is the chorion in evident by its secretion from 
the ovarian epithelium, which disintegrates during the period of 
maturation and can be later distinguished as a number of separate 
spindle shaped cells, which remain more or less closely applied to the 
chorion (Fig. 13). 
The corpus adiposum of the female also undergoes considered 
change. While the eggs are ripening it is composed of solid cells, 
often arranged to form masses of sinuous or coiled strands. Later, when 
the eggs become evenly distributed throughout the body cavity, its cells 
