16 
Psyche 
March 
pears to be an opening through the exochorion where it 
dips into a depression (Fig. 5), but no opening through the 
endochorion was found. Other evidence suggests that there 
is none. Eggs completely immersed in tap water at 37.5° C. 
for a period of 3 or 4 days during incubation hatch into 
healthy nymphs in about the normal time. (Hatching itself 
occurs under water, but the nymphs cannot get their 
abdomens out of the shell. This is because they cannot 
get traction and also occurs in a small percentage of eggs 
hatching in an empty glass container.) If openings com- 
pletely penetrated the chorion, then water should be ex- 
pected to enter the egg by osmotic pressure and cause it 
to burst. If eggs are kept in tap water for as long as seven 
days, the incubation period is prolonged by several days 
and only about half of the eggs hatch at all. Those not 
hatching do not burst nor are they turgid. Presumably 
they die from oxygen lack, as the water was not mechanical- 
ly oxygenated. 
The follicle cells appear to become a syncytium during 
the enlargement of the oocyte. This syncytium probably 
secretes the micropylar thickening and the thin structure- 
less exochorion just before the oocyte leaves the ovariole. 
The chorionic droplets are believed to be added as the egg 
passes through the lateral oviduct, for droplets of similar 
appearance have been seen in the cells of the oviducal epi- 
thelium of females with large oocytes in the ovarioles. 
Fertilization 
After the oocyte leaves the gonopore but before it pro- 
ceeds down the ovipositor, it is undoubtedly held at the base 
of the ovipositor for a few moments while sperms are dis- 
charged onto it by the spermatheca. The sperms presum- 
ably enter the probable openings in the exochorion over the 
depressions in the micropylar thickening. They can appar- 
ently penetrate the endochorion directly. They would not 
have to penetrate the endochorion directly under the micro- 
pylar thickening, but could pass between the lamellae of the 
thickening and enter nearer the equator of the egg. 
Whether the entire sperm penetrates the egg was not deter- 
mined. Within the freshly laid egg, however, may usually 
be identified from one to six of the very long sperm heads, 
