592 Cuin Pine 
to which it may be accidentally subjected. For example, the thickened, 
impermeable body wall of the mature larva, as already discussed, has 
enabled it to survive and attain pupation in water with a total absence 
of salt; the convoluted alimentary canal stores enough food for the larva 
in tiding over a period of starvation, when it happens to face scarcity of 
food in the water; and, likewise, the larva owes to its complex tracheal 
system its ability to stay at the bottom for a considerable length of time 
without obtaining air from the surface, when the conditions there are 
unfavorable and abnormal. The writer has not been able to observe 
the effect of total absence of air upon the larva, but inability to withstand 
deprivation of air has been tested in the following experiments, in each 
of which a glass relaxing jar 7 centimeters in diameter and 5 centimeters 
in depth was used as. an aquarium. 
Experiment I.— Four larvae were placed in water 40 millimeters deep, 
with a kerosene layer 5 millimeters thick. After twenty hours one larva 
was dead, and three were alive but moribund, and with air bubbles at 
the caudal tips. 
Experiment II.— Four larvae were placed in water 40 millimeters deep, 
with a kerosene layer 4 millimeters thick. After twenty-two hours two 
were dead, and two were alive but moribund. 
Experiment IJI.— Four larvae were placed in water 30 millimeters 
deep, with a thin kerosene layer. After twenty-four hours the larvae 
were all alive; after forty-six hours they were still alive but moribund, 
and some of them had air bubbles at the caudal tips. 
Experiment IV.— Four larvae were placed in water 20 millimeters 
deep with a very thin kerosene film, barely enough to cover over the water 
surface. After twenty-four hours all the larvae were alive; after forty-six 
hours one was dead, and three were alive but moribund, and with air 
bubbles at the caudal tips. 
In these experiments the larvae were deprived of a chance to come up 
to an open surface for respiration, and the air in the water underneath 
was very much limited in amount on account of the small volume of 
the aquaria. The great complexity and rich ramification of the tracheal 
branches must enable the larvae to store enough air to sustain their lives. 
The length of time through which they lived is directly proportional to 
the quantity of water from which they could gather dissolved air, and 
inversely to the thickness of the kerosene layer, which, though never 
