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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 357 



of houses, especially during wet weather, from which habit it 

 has no doubt derived the popular name of " storm-fly "; it is 

 also know as the "stable-fly." As these names may be equally 

 applicable to certain other Diptera they should be discarded. 



As I have already mentioned this species is frequently mis- 

 taken by the public for M. domestic a, which is supposed to 

 have adopted the biting habit, although the latter is unable 

 to inflict the slightest prick. Jf examined side by side the 

 sreat differences between the two will be seen readily (see 

 Part I in ' Quart. Journ. Micr. Sci., vol. 51, PL 22, fig. 4). 

 S. calcitrans has an awl-like proboscis for piercing and 

 blood-sucking ; this projects horizontally forward from 

 beneath the surface of the head (fig. 4). It is slightly 

 larger and more robust than M. domestica; the bristles of 

 the antennae bear setse on their upper sides only. The colour 

 is brownish with a greenish tinge ; the dorsal side of the 

 thorax has four dark longitudinal stripes, the outermost pair 

 being interrupted. At the anterior end of the dorsal side of 

 the thorax the medium light-coloured stripe has a golden 

 appearance, which is very distinct when the insect is seen 

 against the light. The abdomen is broad in proportion to its 

 length, and each of the large second and third segments has 

 a single median and two lateral brown spots; there is also 

 a median spot on the fourth segment. 



The life-history of S. calcitrans has been studied by 

 Newstead (1906), and I have been able to confirm his observa- 

 tions during 1907 and 1908. From fifty to seventy eggs, 

 measuring 1 mm. in length, are laid by the female. The eggs 

 are laid on warm, decaying vegetable refuse, especially in 

 heaps of fermenting grass cut from lawns ; I have frequently 

 confirmed this observation of Newstead's. The eggs are also 

 deposited on various excremental substances upon which the 

 larvje feed. Osborne (1896) reared them in horse-manure ; 

 Howard (1900) states that they live in fresh horse-manure, 

 and records their occurrence in outdoor privies in some 

 localities; Newstead reared them in moist sheep's dung; they 

 can also be reared in cow-dung. 



