ZooL.— Vol. III.] KELLOGG— NET-WINGED MIDGES. 213 



along, makes this fixed diatom supply about the only food 

 resource. In the Colorado and California larvag of the 

 Bibiocephala species and of Blepharocera jordani, the 

 dorsal covering of diatoms is rather uncommon, though 

 not infrequently to be seen. 



Frequently the attempt has been made to bring living 

 larvse into the laboratory, but only when the collecting 

 ground is very near the laboratory is this possible, and even 

 then it is not worth while. The larvae cannot live in stagnant 

 or even in quiet or slow-running water. Indeed if, in the 

 falling of the stream, larvse get stranded in a suddenly made 

 pool or still, quiet-water part of the stream they soon die. 

 They must have the highly aerated, swift water of the 

 stream's center; they like the lip of a fall, the rocks of 

 cascades, and the sides of a pot-hole in which the water is 

 ever whirling and boiling. 



Pufce. — The pupae are found in the same places as the 

 larvse; that is, the larvae when ready to pupate do little more 

 than arrange themselves, almost always in small or large 

 groups, with heads pointing down stream, and there make 

 the last larval moult. Each pupa is fastened to the rocks 

 by six pads, three on each lateral margin of the ventral 

 aspect of the abdomen; these pads are not like the suckers 

 of the larva whose hold can be voluntarily loosened, but 

 they permanently attach the pupa to one spot. The pupa is, 

 strongly convex above, with a dark brown or black, heavily 

 chitinized body-wall, and is perfectly flat on its ventral 

 aspect, which lies smoothly against the rock. The wings 

 and legs lie folded on this ventral aspect, which is covered 

 only by a thin, colorless, pupal cuticula. From the prothorax 

 projects dorsally a pair of respiratory organs, each composed 

 of four thin, double-walled plates, the outer plates of each 

 set being strongly chitinized and acting as protecting covers 

 for the two delicate membranous inner ones (the whole 

 arrangement like a two-leaved book with board covers). 



Of absorbing interest to the observer is the course of 

 emergence of the adult from its submerged, fixed pupal 

 case. Professor Comstock seems to have been the first to 



