(95) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 535 



forward, and is in association with the corresponding pro- 

 thoracic and meso-thoracic ventral discs. The smaller and 

 more posterior disc (d. mt.) will develop into the remaining 

 portion of the much reduced meta-thoracic segment, including 

 the halteres. 



Reference has already been made to other imaginal rudi- 

 ments which occur in the abdominal region as circular patches 

 of embryonic cells. The abdominal segments develop from 

 numerous segmentally arranged plates of a similar nature* 

 which are found during the early pupal stage. 



During pupation the imaginal rudiments increase in size 

 and are not destroyed by the phagocytes in histolysis, as is 

 the case with most of the larval structures. The cephalic 

 discs are evaginated by the eversion of their sacs by way of 

 the anterior end of the larva, a cord of cells attached to the 

 dorsal wall of the anterior end of the pharynx marking the 

 path of eversion. A similar process takes place in the case 

 of the thoracic imaginal discs, which, by their eversion, build 

 up the whole of the skeletal case of the thorax and its dorsal 

 and ventral appendages, the wings, halteres and legs. 



VI. SUMMARY. 



1. An account of the previous work on the breeding habits 

 ofM. domesticais given, which, together with the author's 

 investigations, show that the house-fly breeds in the following 

 substances : 



Horse-manure; this is preferred by the female flies as a 

 nidus for the eggs, and forms the chief substance in which 

 they breed ; human excrement, either in the form of isolated 

 faeces or occurring in such places as latrines, privies and ash- 

 pits; cow-dung; poultry excrement ; also in substances con- 

 taminated or mixed with excremental products, such as 

 bedding from piggeries and from rabbits and guinea-pigs, 

 paper and textile fabrics which have been contaminated, as 

 cotton and woollen garments, sacking, rotten flock-beds, 

 straw-mattresses, cesspools ; decaying vegetable substances 



VOL. 52, PART 4. 41 



