THe Brotocy or EKrpHyDRA SUBOPACA LOEW 593 
mixed with water, may contaminate it to a certain extent. The writer 
observed that when some larvae reached the top layer of the water, with 
their caudal tips in contact with the floating oil, they seemed to be repelled 
by it. 
In the pools and overflowed areas the water often has greasy films 
spread here and there upon its surface, but there are enough exposed 
areas that give the larvae a chance to come up to the surface for respiration. 
Furthermore, the quantity of water underneath the films is sufficient to 
keep much oxygen in solution. 
Temperature.— Throughout the summer the average temperature of 
the water in the pools is 25° C. Taking this temperature as a mean, 
the writer subjected the larvae to various thermal conditions in order 
to find out how high and how low a temperature they could stand. In 
an aquarium provided with suitable conditions, two larvae were kept in 
a temperature of from 27° to 28° C. They lived therein perfectly well. 
Feeding, wriggling, and crawling, as usual, they did not show any 
change in habit for fourteen hours. Afterward the observations were 
interrupted. The temperature was then raised to from 35° to 37° C. and 
two larvae were introduced into the aquarium, where they were found 
alive after eleven hours; but after nine more hours they died. When the 
temperature was raised again, wavering between 38° and 49° C., the 
larvae wriggled vigorously. Continuing to live for two hours, they were 
removed to another aquarium, in which the temperature permanently 
registered 42° C. There the two larvae died within thirty minutes. This 
experiment was repeated by placing two fresh larvae in a third aquarium 
in which the temperature varied between 40° and 44° C. These larvae 
died within one hour. In addition to this it was found that two grown 
larvae did not live longer than thirty minutes under a temperature of 
from 43° to 46°C. The writer concludes that a temperature of about 
40° C. is the highest limit the larva can stand. 
The larva exhibits a remarkable ability for enduring low temperatures. 
A larva was placed on ice for periods of ten, twenty, and forty minutes, 
and one hour, and at the end of each period was removed to water of 
ordinary temperature. However paralyzed the larva was while staying 
on ice, it would soon recover and become lively again after a few seconds. 
Mature larvae were kept on ice for twelve and twenty-four hours, respec- 
tively. Though they seemed dead while on the ice, each was found to 
