History and Habits of Prtyogenes. 37 
Incusation Prrtop.— The period of incubation of the 
egg of P. hopkinsi in the laboratory is exactly seven days. 
Outdoors it varies with the temperature from five to ten 
days according to observations made this spring (1915). 
Eggs laid March 24th in the laboratory, still possessed on 
March 27th the white color and the translucent pearly 
appearance characteristic of those freshly laid. Two days 
later they were not so transparent and were slightly yellow- 
ish in color. On March 30th, on examination with a good 
hand lens (X 15), a minute brown speck was just visible. 
On studying this at a greater magnification with a binocular 
microscope, it was seen that this brown spot was caused by 
the mandibles of the embryo larva inside. That the embryo 
was still alive was shown by the movement not only of the 
mandibles but of its entire body inside the egg membranes. 
The movement of the mandibles was especially strong and 
was continuous for the ten minutes the egg was under 
observation. The larval head showed a surprisingly large 
range of motion, moving back and forth for nearly the 
length of the egg, the jaws continuing to open and close. 
The egg membranes were still entirely intact although 
slightly wrinkled. It was feared the eggs might become 
dried so after removing one to a hollow ground slide and 
placing it in a moist chamber the burrow was closed. The 
eggs, both in the ege niches and in the moist chamber, were 
examined at intervals during the day, but none had hatched 
when work ceased for the day. One of the eggs was taken 
from the burrow, the outer egg membrane removed by care- 
ful manipulation with dissecting needle and the inner mem- 
brane opened so as to allow penetration. Absolute alcohol 
was then added and later the specimen was stained with 
eosin. The shape of the embryo larva is quite similar to 
that of the larva after hatching. A, camera-lacida sketch of 
one of the mandibles is shown in Fig. 17. The biting edge 
of the mandibles is dark brown. This shades off rapidly to a 
tan brown and this in turn to white so that the entire out- 
line cannot be distinguished. 
