STRUCTURE, DEVELOPMENT, AND RIONOMICS OE HOUSE-FLY. 351 
are representative of the average occurrence, as I have 
observed, of the different species. 
For the proportional occurrence in similar localities we have 
interesting figures given by Howard (1900) for the United 
States. Of 23,087 Hies caught in rooms where food supplies 
ai'e exposed he found that 22,808, or 98'8 per cent, of the 
whole number, were M. domestica, and of the remaining 
J‘2 per cent. H. canicularis was the commonest species. 
Hamer (1908) found that more than nine tenths of the Hies 
caught in the kitchens and “living-rooms” of houses in the 
neighbourhood of depots for horse-refuse, manure, etc., were 
M. domestica. In a further report Hamer gives more 
details as to the different species that were found. In one 
lot of 35,000 flies caught on four fly-papers exposed in similar 
positions, 17 per cent. Avere Homalo my i a canicularis, less 
than 1 per cent. wereC. ery throcephala, and considerably 
less than 1 per cent, were Muscina stabulans, whereas of 
nearly 6000 flies caught in another situation in four fly- 
balloons 24 per cent. wereH. canicularis, 15 jrer cent, were 
C. ery throcephala, and neaily 2 percent, were M. stabu- 
lans. He gives an intei’esting diagram showing from counts 
of flies the seasonal prevalence which 1 have previously 
recorded from observation. The report shows how the pro- 
portions of the different species vary in different situations 
according to the substances and refuse that are present in 
the locality. We may therefore say with certainty that 
M. domestica is the commonest species of house-fly, aud 
next to this II. canicularis, and that in country houses 
8. calcitrans often occurs in large numbers, although 
it is not a house-fly in the strict sense of the word. 
III. Flies Occurring as Co-inhabitants of Houses with 
M. DOMESTICA OR AS ViSITANTS. 
We have seen from the preceding section that M. domes- 
tica is by far the commonest species which occurs in houses, 
and is, in fact, “domesticated” in the true sense of the word 
