June, 1912.] AlDRICH : BlOLOGY OF WESTERN EPIIYDRA. 89 



drink in an emergency. I fonnd hiaiis in small numbers near the 

 inlet; but this was within perhaps a mile of " Mudhen Lake," a much 

 more alkaline pond close to the Truckee River just south of the Lake 

 (doubtless the one called a lagoon in the distribution, above), where I 

 was informed by an Indian that the Kootsabe was abundant— this 

 same fly. Except in these two cases, I have not found hiaus except 

 at the decidedly strong waters, but it appears to thrive well in both 

 salty waters and alkaline, while as far as known at present gracilis 

 confines itself to the former only. Neither fly seems to spread much 

 from the immediate edge of the strong waters, though near Garfield 

 I found gracilis a few hundred feet back from the main lake, at the 

 edge of nearly fresh water. Professor Voorhies told me that he 

 had not tried the experiment of rearing gracilis in pure water, and 

 I did not stop long enough in a place to undertake it myself. 



Adults of hians have the unusual habit of entering the water and 

 w^alking about on objects below the surface, enveloped in a globule 

 of air. They cannot descend unless they can have some solid object 

 to hold to, as they are quite buoyant when below the surface. I 

 repeatedly saw them walking in this way in Mono Lake, clinging to 

 stones, wood, grass, cloth, or any firm substance; when they wished 

 to come to the surface they did so by letting go and floating straight 

 up, when the enveloping bubble bursts at the surface, and the fly is 

 left standing unconcernedly on the top of the water. This is very 

 common, and in one case I found eggs that had been laid on an old 

 cloth some distance below the surface, on which I had seen numerous 

 flies. This is not the invariable mode of laying eggs, as a great many 

 of the flies are far from shore, over deep water, and have no way of 

 getting below the surface. It seems pretty certain that in such a 

 situation the eggs are simply dropped in the water while the fly 

 rests on the surface. 



The larvae are generally found near the bottom of the water. 

 They wriggle a good deal, but do not come to the surface for air, 

 having become modified in the same way as gracilis in regard to respi- 

 ration. I never saw hians about the Saltair bathing pavilion, and 

 think it likely that both larvae and adults generally remain rather close 

 to shore. The food of the larvae I did not investigate, thinking that 

 it would be a simple matter to open some of the preserved specimens 

 and identify the contents of the proventriculus ; the operation proved 



