44 NEW ZEALAND ENTOMOLOGY. 



walls of its glass prison with numerous tubular galleries. 

 These take their rise from the mud at the bottom, and, 

 extending upwards to a distance of three or four inches, 

 afford the larva a convenient retreat from all enemies. 

 These insects are occasionally seen swimming laboriously 

 through the water with a peculiar zigzag motion. When 

 out of their burrows they have considerable difficulty in 

 keeping beneath the surface, and may be often observed 

 floating helplessly with their exposed portions quite dry ; 

 in fact the whole integment of the insect appears to have 

 a peculiar power of resisting the water. The pupa (Fig. 

 2b), is a most beautiful object, its anterior extremity being 

 obtusely thickened and the limbs of the future insect quite 

 discernible. On each side of the thorax the gills form a set 

 of graceful plumes, a much smaller group being also situated 

 at the extremity of its abdomen. In this state the insect 

 remains almost entirely concealed in the burrows previously 

 constructed by the larva, its gills imbibing sufficient air 

 from the surrounding medium, and thus rendering ascen- 

 sion to the surface unnecessary. The water is periodically 

 circulated in the tunnels by violent movements on the 

 part of the pupa. About a day before emergence the 

 insect assumes a peculiar silvery appearance, which is 

 occasioned by the presence of a large quantity of air 

 between the imago and its pupa skin. This air has been 

 first imbibed by the gills and afterwards expelled through 

 the spiracles of the enclosed gnat, thus inflating the skin of 

 the pupa, and helping to buoy it up during its last and 

 most important transformation. Leaving its tunnel the 

 insect rises to the surface, the thorax is lifted above the 

 water which retreats from it on all sides, the skin cracks 

 open at the back and the insect slowly extricates itself in 

 a similar manner to the mosquito. In about ten minutes' 

 time the wings are sufficiently hardened for use and the 

 insect then flies ashore, but we may occasionally notice, 



