STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 497 
sites and its relation to man, and certain of its allies which 
frequent houses will be considered. 
Il. Breepinag Hapsits or M. pomESTICA. 
The development of M. domestica was first described by 
Carl de Geer (1776) ; but, although he stated that it developed 
in warm and humid dung, he did not give the time occupied 
by the different developmental stages. He refers to the 
enormous quantities of flies occurring from July to August. 
His statement concerning their development is especially 
interesting, as he appears to be the first investigator who 
called attention to what I consider to be one of the most 
important factors in the development of the fly, namely, the 
process of fermentation occurring in the substance in which 
development is taking place. -He says (p. 76), “ Les larves 
de cette espéce vivent donc dans le fumier, mais uniquement 
dans celui qui est bien chaud et humide, ou pour mieux 
dire qui se trouve en parfaite fermentation”? (the italics 
are mine). . Since the completion of my own investigations 
on the development, all of which indicated the importance of 
this factor fermentation, Newstead (l.c.) has come to the 
same conclusion. The work of Keller (1790), to which 
reference was made in the first part of this memoir, contains 
many interesting and careful observations on the breeding 
habits of the ‘Stubenfliege.’ He found that the eggs 
hatched from twelve to twenty-four hours after deposition. 
He reared the larve in decaying grain where, no doubt, 
fermentation was taking place; also in small portions of 
“meat, slices of melon, and in old broth. His observations 
are extremely interesting, and, excluding mistakes which 
were due to the lack of modern apparatus, his account is still 
a valuable contribution to our knowledge of the subject. 
Bouche (1834) describes the larvee as living in horse-manure 
and fowl-dung, especially when warm. He does not give the 
time occupied by the earlier developmental stages, but states 
that the pupal stage lasts from 8—14 days. Packard (1874) 
