II FLIES WITH AQUATIC LARV^ 185 



of water. The respiratory filaments, which project, 

 immediately behind the future head, just as in 

 Chironomus, draw a sufficient supply of air from 

 the well-aerated \vater around. The rings of the 

 abdomen are furnished with a number of projecting 

 hooks, and as the interior of the cocoon is felted by 

 silken threads, the pupa gets a firm grip of its 

 cocoon. If it is forcibly dislodged a number of the 

 silken threads are drawn out from the felted lining. 



A serious difficulty now appears. The fly is a 

 delicate and minute Insect, with gauzy wings. How 

 does it escape from the rushing water into the air 

 above, where the remainder of its life has to be 

 passed ? This was a question upon which I spent 

 much thought, but in vain. It appeared to me for 

 many months completely insoluble. In the stream 

 at my feet I could see countless pupae. There were 

 also empty cocoons, containing, as close examination 

 showed, the cast pupal skin of Simulium, still attached 

 to the felted lining, and the last larval skin as well. 

 On the bushes which overhung the stream innumer- 

 able Simulium flies were resting. How had they 

 made their way in safety after the last transformation, 

 although their structure was to all appearance ex- 

 tremely ill adapted to such a manoeuvre, through the 

 strong current into the upper air ? I was at last 

 informed by Baron Osten Sacken of a paper written 

 by Verdat, seventy years ago, in which the emergence 

 of the fly of Simulium is described. 1 During the 



1 Gesch. d. Simulien, Natunv. anz. d. allg. Schiv. Gesellsch. 

 (1822). Translated by Osten $acken, in dwer. Ent, Vol. II, 

 p. 229. 



