i6o Journal of Agricultural Research voi. xiii, no. 3 



ovaries in the fourth stage) all flies with ovaries past the second stage of 

 development contained spermatozoa. In 13 flies, or 22 per cent, the 

 ovaries were apparently mature, and eggs were ready for deposition. In 

 5 flies, or 8.4 per cent, the condition of the ovaries indicated clearly that 

 deposition had occurred only a short time previous to the examination. 

 The ovarioles had the appearance of figure F (PI. 7), and in 3 cases mature 

 eggs were seen lodged in the oviduct at the point where the oviducts unite 

 to form the common oviduct. 



A comparison of the foregoing findings \vith the conditions found in 

 Pollenia rndis is very instructive. There is hardly any doubt that Pol- 

 lenia hibernates in the adult state. It is found at all times throughout 

 the winter in attics, unoccupied rooms, and the like, and is often seen out- 

 doors in mild weather. Frequent collections were made during the winter 

 of 1 916-17, and the spermathecae and ovaries were studied in the same 

 way as those of the house fly. The spermathecae were found to be empty 

 in all cases examined during December, January, and February. The 

 first spermatozoa were found in a female examined on March 22. Cor- 

 related with this was the fact that, without exception, all ovaries cor- 

 responded in development to stage i (Pi. 7, A) of the house fly. Not 

 until early in March was any more advanced stage of development en- 

 countered. This agrees exactly with Kisliuk's observations (/j) on 

 Pollenia at Columbus, Ohio, where he found no development of the ova- 

 ries until early in March. Kisliuk (zj) also succeeded in obtaining eggs 

 from specimens of Pollenia captured on March 21. A specimen of Pol- 

 lenia was kept alive in a cage in the screened insectar}^ at Bethesda, Md., 

 for a period of about four months during the winter, and during this time 

 the temperature reached a minimum of— 1° F. It appears, then, that 

 those individuals of Pollenia emerging in October and November over- 

 winter as adults, being active on warm days, but clustering in comers 

 and hiding in cracks and crevices during cold periods. The ovaries re- 

 main undeveloped until spring. During warm periods in March the 

 ovaries begin to develop, copulation takes place, and eggs are soon ready 

 for deposition. 



Now, if Musca domestica did hibernate as an adult, one would expect 

 to find a similar suspension of sexual development even in warm build- 

 ings, and to find the reproductive power conserved to be exercised only 

 in the spring when outdoor activities could be resumed. M. domestica, 

 however, does not show any such retardation of ovarian development; 

 nor does it display the same ability to vvdthstand the effects of cold. 

 Another important fact is that M. domestica was never collected during 

 the winter in attics and other unused but protected places where Pollenia 

 is found in such abundance, although experiments with caged house flies 

 showed that the temperature of such locations was most favorable for 

 the prolongation of life. In other words, adults of M. domestica were 

 found during the winter only where food was available, and persisted 



