STUDIES ON PERILLUS BIOCULATUS FAB. FS 
tance of the couple from the bug. When lowering the temperature of 
the freezing chamber at the rate shown on the graph, the temperature 
of the bug showed a lag of about 1°C. This lag was more pronounced 
when the temperature of the freezing chamber was lowered more 
rapidly. 
The surprising result of freezing the bugs on April 15 and April 
17 was that not a single specimen could be undercooled to —10°C. 
without actual freezing taking place, followed by the death of the insect. 
As indicated above, it was not possible to freeze specimens at —17° 
on March 28, and one individual was reduced to —26°C. on March 29 
without actual freezing taking place. From this it is apparent that 
certain changes took place in the hibernating bugs between March 29 and 
April 15, altho the latter lot had been kept inactive at a temperature 
near 8°C. It also would appear that there must be a periodicity in that 
physiological condition which enables the bugs to withstand low tem- 
peratures. Whatever the change in the resistance of the insects to low 
temperatures, it was not due to physical activity or warming up of the 
insect. It seems more likely that this change in resistance must be 
related to time or age. 
As yet, Perillus has not been frozen at intervals during the fall 
as it goes into hibernation. Such experiments would indicate the 
rate of change and adaptation to lower temperatures. But from data 
presented above it is shown that if the bugs are to live through the 
winter they must undergo changes in the fall and adapt themselves 
to lower temperatures, something quite analogous to the well known 
hardening of plant tissue in the fall. Certainly the bugs undergo a 
drying out process, for examination of specimens during the winter 
and early spring shows that the body fluids have been practically 
eliminated. No doubt this concentration of body fluids and apparent 
elimination of free water, is largely responsible for the ability of these 
insects to withstand low temperatures during hibernation. This physical 
condition, coupled with results obtained in freezing the bugs, bears 
out the theory that the phenomenon of hibernation, which permits 
undercooling to temperatures much below the freezing point, is pos- 
sible only because of the high water-holding capacity of the body 
substance; and this in its last analysis can be explained only on a 
colloidal basis. 
In the tabulated data above, it will be observed that some of the 
bugs were frozen from three to six times, altho the bug was in each 
case killed by the first freezing. Bug No. 9 shows rather clearly that 
with successive freezing and thawing the freezing point is raised and 
