AQUATIC IXSBCTS IX 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 water 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- 

 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 

 lay their eggs under water. 



