PAPERS ON ZOOLOGY 313 



grown and fully-grown larvae and a few cast pupal 

 skins were found. This proves that the entire life-cycle 

 to the adult condition is not more than two months and 

 probably only six or seven weeks. At Alto Pass, in the 

 situations previously described, the larvae of Gerano- 

 myia canadensis were found li^i.ng in the irregularities 

 and crevices on the wet face of the cliff. They were 

 found lurking in delicate, silken tubes covered with a 

 deposit of silt and diatoms. They emerged from these 

 cases to feed on the exposed surface of the wet rocks 

 during twilight and even during the hours of sunlight 

 but upon being disturbed or alarmed they retreated in- 

 stantly and with great agility into their tubes. The 

 pupa occurs in a short, nearly vertical, burrow in the 

 same situations as the larvae; here they rest with only 

 the long, conspicuous breathing-horns projecting from 

 the entrance to this burrow. When transfoimed, the 

 empty pupal skin projects from the mouth of the bur- 

 row nearly to the ends of the T\-ing-sheaths. Numerous 

 larvae, three pupae and many cast pupal skins were 

 found. The ver^' scanty number of pupae as compared 

 with the abundance of larvae and pupal skins leads us 

 to believe that the pupal existence is of very short dur- 

 ation, else this stage would be found more often. 



It is probable that the flies pass the winter in the 

 larval condition, although this has not been proven. In 

 the green-houses of the Department of Floriculture of 

 the University of Illinois, the adult flies were found in 

 large numbers throughout the winter. On February 26, 

 1920, at least one himdred individuals were seen in one 

 of the buildings where the heat was maintained at ap- 

 proximately 70" in the day and 60 '^ at night. Many of 

 these flies were gravid females, a few were teneral, as 

 though newly emerged, and still others were in copula- 

 tion. However no evidences of the inmiature stages 

 could be found in spite of a diligent examination of all 

 possible situations wherein these flies might be breeding. 

 The only possibility of their breeding in these buildings 

 would appear to be in damp earth since no situations 



