i86 NATURAL HISTORY OF AQUATIC INSECTS CH. 



latter part of the pupal stage, which lasts about a 

 fortnight in all, the pupa-skin becomes inflated with 

 air, which is extracted from the water, and passed 

 apparently through the spiracles of the fly into the 

 space immediately within the pupal skin. The pupal 

 skin thus becomes distended with air, and assumes 



Fig. 66. — Respiratory appendage of pupa of Simulium, consisting of four branched 

 tubes. Removed from beneath larval skin, and therefore une.\panded. 



a more rounded shape in consequence. At length it 

 splits along the back, in the way usual among Insects, 

 and there emerges a small bubble of air, which rises 

 quickly to the surface of the water and then bursts. 

 When the bubble bursts, out comes the fly. It 

 spreads its hairy legs, and runs upon the surface of 

 the water to find some solid support up which it can 



