AQUATIC INSECTS IN NEW YORK STATE 313 
water, then, when the larva transformed to a quiescent pupa, 
it would be drowned in its own coffin. Such a calamity is un- 
doubtedly averted by the larva entirely surrounding itself while 
Spinning its cocoon by a quantity of air sufficient to fill the 
vacant space in the cocoon. A small quantity of water might 
be absorbed by the body of the larva or pupa, but it does not 
seem possible that the insect could absorb the amount of water 
the cocoon would hold; while, on the other hand, the under- 
ground stems to which the cocoons are attached are always 
imbedded in a soft, clayey ooze, and, if the water were absorbed 
by the body of the insect, then the interior of the cocoon would 
‘be lined with a clay deposit which would discolor it, whereas 
in every case the interior of the cocoons were just as clean as 
if they had been spun in the open air. It would be impossible 
for the plant to absorb the waiter because the bottom of the 
cocoon would be between the water and the epidermis of the 
plant except at the paired slits and the opening near the center. 
The large excavation is always near the center of the cocoon 
and is undoubtedly made by the larva before transforming to a 
pupa. In this way the larva provides a continuous air supply 
for itself by tapping the store held in the intercellular air spaces 
of the plant. Since some individuals of Donacia live for 10 
months or more in the cocoon, need for a copious and continu- 
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ous air supply becomes apparent. That there is a bountiful 
supply can be readily proved by opening the cocoons under 
water, when it will be found that they are completely filled 
with air. 
The pupa transforms to a beetle long before it is time for it 
‘to emerge. When it is ready to emerge, the end of the cocoon is 
broken off and the beetle crawls out. The ventral surface of 
most of the species of Donacia is densely covered with fine 
silken hairs, so that, when the beetle emerges from its cocoon, 
the air contained in the cocoon at this time is held to the ven- 
tral surface of the beetle by these silken hairs and in this way 
provides an air supply for it till it reaches the surface of the 
water. This silken covering is also of use to those species that 
. their eggs under water. 
