78 THE SUB-IMAGO 



the wings, thorax, and legs, which will be used after 

 the metamorphosis of the flying condition. 



When the larvae are fully ready for this change, they 

 leave the haunts in which they have hitherto spent their 

 existence, and swim to the surface. When there the 

 mask-like membrane, under which the wings, etc., have 

 been visible (see Figs. 1 and 2, Plate XIV.), splits open, 

 and, supported on this shell as on a raft, the insect gradu- 

 ally frees every part of its body and unfolds its wings. 

 As soon as these wings are dried and the body is clear 

 of its shell, the sub-imago, as it is now called, flies to 

 the nearest bank, where it shelters itself amid the 

 grasses, leaves, etc. It is commonly known in this 

 state as a dun, and it appears at various times, when the 

 weather is favourable, in the vicinity of the water during 

 a period of from one day to two or more weeks, flying 

 with the breeze, generally down-stream. In this stage 

 of its life it can be easily recognized by its compara- 

 tively heavy, drifting flight, and its dull, semi-opaque 

 appearance. By the aid of a watchmaker's glass, cilia 

 will be seen covering the surface, and forming a fringe 

 to the posterior margin of its wings. 



The sub-imago stage of its life, which is very brief in 

 some cases, is finally forsaken when the entire mem- 

 brane of its body and wings again splits open and is 

 discarded, and the insect then assumes its perfected 

 stage as the imago or spinner. 



It is now fully matured and enters into its bridal 

 existence, which lasts but a few days. In this stage 

 it is to be seen in great numbers where the heat is not 



