92 HABITS 



of pigment are often found on the sucked areas when the flies 

 have previously been fed on coloured syrup. 



Flies which have access to abundant food leave numerous 

 ' spots ' (vomit and fasces). The rate of deposition seems to 

 vary with the kind of food and the temperature. 



CHAPTER VIII 



METHODS OF OBSERVING FLIES IN CAPTIVITY 



Various workers have kept flies in large, specially constructed 

 cages for some days, but very few seem to have been able to 

 keep them alive in small, easily handled cages for more than 

 a day or two. The methods adopted by the writer (Graham - 

 Smith, 1910, p. 2), which gave excellent results, are therefore 

 given in detail. 



" Flies were captured in balloon traps baited with sugar 

 moistened with stale beer or treacle and kept until required in 

 a large gauze bag, about 12 inches in diameter and two and 

 a half feet in length, suspended by a string. The sides of the 

 bag were supported by wire hoops and the bottom was composed 

 of a wooden disc. In the latter a square hole was cut the sides 

 of which were fitted with grooves so that in place of the card- 

 board panel which usually filled the space, a tray, containing 

 watch-glasses of syrup and water, could be inserted, in order to 

 supply the flies with food. A sleeve sufficiently large to admit 

 the arm and communicating with the interior of the bag was 

 attached about half way up. When it was not in use the sleeve 

 was closed by a string tied round it near its junction with the 

 bag (Plate XIX, fig. 3). The flies, when required, were captured 

 by means of a large test-tube about 12 inches long, which was 

 inserted through the sleeve. The mouth was placed over flies 

 as they walked on the inside of the bag. Once in the tube the 

 flies fell to the bottom and occasional shaking prevented them 

 from getting out. In this way a considerable number of flies could 



