HIBERNATION 85 



not take food during this period. In some females it was foumi 

 that the ovaries were very well developed, while in others they 

 were small, and mature spermatozoa were found in the males. 

 Like most animals in hibernating, M. doniestica becomes negatively 

 heliotropic and creeps away into a dark place. In houses they 

 have been found in various kinds of crevices such as occur between 

 the woodwork and the walls. They have been found behind 

 pictures, books an<l curtains. A favourite place for hibernation is 

 between wall paper which is slightly loose and the wall. A certain 

 number hibernate in stables, where, owing to the warmth, they do 

 not become so inactive, and they emerge earlier at the latter end 

 of spring. During the winter the hibernating flies are sustained 

 by means of the contents of the fat-body, which is found to be 

 extremely small in hibernating flies if dissected when they first 

 emerge in May and June. The abdominal cavity is at first con- 

 siderably decreased in size, but the fly begins to feed and soon the 

 alimentary tract regains its normal size, and together, with the 

 development of the reproductive organs, causes the abdomen to 

 regain its normal appearance. The emergence from hibernation 

 appears to be controlled by temperature, as one may frequently 

 find odd flies emerging from their winter quarters on exceptionally 

 warm days in the early months of the year. A few flies may 

 occasionally be found active throughout the winter. I have found 

 active flies frequently during the months of December to February 

 in such warm places as kitchens, restaurants and stables during 

 which time they are able to breed. Jepson (1909) caught flies 

 in the bakehouse of one of the Cambridge colleges in February 

 and used these flies in his breeding experiments. He records 

 the reported occurrence of flies in the college sculleries through- 

 out the winter months. These active and periodically active flies, 

 together with the wholly dormant flies are the progenitors of the 

 summer mill ions \ 



^ Skinner (1913) asserts on the circumstantial evidence of a single recently 

 emerged fly, found entering a window, unsupported by experimental evidence, that 

 house-flies pass the winter in the pupal stage. So far, I have been unsuccessful in 

 carrying pupae of M. doniestica over the winter months. Skinner's fly was probably 

 one bred in a. warm place during the winter. 



Copeman (1913) calls attention to the desirability of securing further evidence 

 as to where and under what circumstances surviving flies pass the winter. 



