310 Dr Hindle, The Flight of the House-Fly. 
The Flight of the House-Fly. By EDWARD HINDLE, B.A, 
Ph.D., F.LS., Assistant to the Quick Professor of Biology; 
Magdalene College, Cambridge. ‘(Communicated by Mr C. Wap- 
BURTON.) ‘a 
eerie lata 
[Read 17 November 1913.] x 
During the months of July, August, and September, 1912, 
the author, in conjunction with Mr Gordon Merriman, conducted — 
an extensive series of experiments on the range of flight of Musca 
domestica Linn. in the town of Cambridge. In the course of these 
experiments upwards of 25,000 flies have been liberated under 
very variable meteorological conditions, and about 50 observation 
stations were employed for their recovery. 
In all cases the flies used in these experiments were either 
caught in balloon traps, or directly netted. The method of 
obtaining flies by breeding was abandoned, as it was almost — 
impossible to obtain them without numerous other species of © 
insects, and also on account of the possible objections to such — 
artificially bred flies. ' 
Prior to being liberated the flies were kept for about 24 hours 
in cages made of mosquito netting and were fed on brown sugar, 
the moisture being supplied by a layer of damp sand. By this — 
method it was assured that they had emerged sufficiently long to 
allow the full development of their chitinous exoskeleton, neces- 
sary in order to obtain the full power of flight. 
Preparatory to colouration the insects were transferred from 
the mosquito cages into wire balloon traps. This transference 
was effected as follows:—the loose sides of the mosquito netting 
cage were tied round the bottom of the balloon trap. The latter 
was then held towards the light and the whole of the cage sur- — 
rounded with a black cloth. Owing to the strong attraction of 
the light, the flies all made their way towards the brightly 
illuminated balloon trap and in passing through the small hole 
in the bottom of the latter, it was possible to make accurate 
counts of them, as not more than two or three were able to pass 
through at the same time. When about 1500 flies had entered 
the balloon trap it was closed, then removed and another trap 
fixed in its place. 
The most satisfactory mode of marking the flies was found to 
be that devised by Nuttall (vide Jepson, 1909), and this was 
employed in all these experiments. The balloon trap containing 
the flies was placed in a large brown paper bag containing a 
handful of powdered blackboard chalk, coloured either red, orange, 
