60 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—IQ22 
Incubation. The period of incubation normally is five or six days. 
In temperatures of 80°F. or above, five days were sufficient; with 
lower temperatures, or from 70°F. to 78°F., six days elapsed before 
the eggs hatched. One egg mass laid June 15 hatched on June 22, 
making a period of seven days for June. Since the normal color 
of the egg is black, one can not observe changes in the egg just prior 
to hatching. In one instance at least, where abnormally pale eggs were 
observed, it was possible to see changes of color in the eggs such as 
may be observed in Pentatomid eggs that are normally pale in color. 
This particular mass of 17 eggs, pale yellowish in color, was thought 
to be infertile when laid on August 5. It was observed on August 
to that certain eggs in this mass had turned dark orange red, and 
the following day these hatched in a normal manner. The egg shells 
left after hatching were pale in color, whereas the normal color of 
Perillus eggs is black before and after hatching. The nymphs from 
these particular eggs grew to maturity, and later two females from 
the lot laid eggs which were of the usual black color. 
Hatching. Vhe process of hatching requires about 10 or 12 minutes 
from the time that the nymph can be observed cutting the lid at the 
top of the egg. This is accomplished by means of the egg-burster 
or hatching spine, a T-shaped chitinous structure which rests on the 
anterior part of the head. By rotating within the egg, the emerging 
nymph gradually cuts out a lid at the top of the egg, and this hangs 
by a slender portion as if by a hinge, the hatching spine usually re- 
maining attached to the lid. This lid is almost immediately forced up 
by the head of the hatching nymph, and the act of emergence is ac- 
complished by a series of pulsating movements of the body fluids. 
The antennae and legs first appear closely appressed to the ventral 
surface, but as soon as released the legs take an active part in freeing 
the abdomen from the egg shell. Very shortly the newly emerged 
nymph moves to one side of the egg mass and remains quietly huddled 
with other newly hatched members. The gregarious habit is very 
pronounced among nymphs in the first three instars, but in the later 
stages the individuals become more or less scattered among the potato 
vines. 
Nymphal Instars 
The length of the nymphal instars varies according to the tempera- 
ture under which the bugs are reared, even when an abundance of 
food is always at hand. Table 2 gives data on three lots of eggs reared 
in glass jars under natural conditions of temperature prevailing at 
that particular time of year. The 1913 and 1914 lots were reared 
