476 Observations on Habits and Parasites of Common Flies 
the interior, where the bait is placed. In the lid is a circular hole over 
which a balloon trap is fitted. Except for the small amount of light 
entering by the hole just mentioned the interior is in darkness, and 
the flies which gain entrance are attracted, when they desire to leave 
the bait, to the light and pass into the balloon trap. Only species 
willing to enter dark places will be caught in these traps. For the 
sake of brevity these traps are spoken of as “tins.” 
Figs. 4 and 5. Illustrating the structure of (4) the galvanised iron trap and (5) the 
mosquito-net trap. The arrows indicate the directions taken by the flies in entering 
the traps and passing into the balloons after leaving the baits. 
Situations of the traps and baits employed. 
Traps baited with human excrement. 
I. A net trap, baited daily with fresh human excrement, was 
placed on soil in an open situation to ascertain the numbers and species 
of flies visiting this material in an exposed and sunny place (Fig 3). 
II. A net trap, baited daily with fresh human excrement, was 
placed on soil in a very shady place on the north side of a wooden 
paling running east and west, about 50 feet from trap I, to ascertain 
the species visiting excrement in shady places (Plate XXV, B). 
III. A “tin” trap, baited daily with fresh human excrement, was 
placed in an open situation protected from winds, and from the after¬ 
noon sun, to ascertain the species attracted to such material in a dark 
receptacle (Plate XXV, F). 
