August, ’14] GLASER: REARING FLIES FOR EXPERIMENTAL WORK 489 
The paper collar and top are now fitted and a cork inserted into the 
opening. 
The captured wild flies are now introduced. This is effected by 
taking the corks out of the breeding jar and phials and by inserting the 
latter into the opening of the breeding jar top. By darkening or by 
shaking the phials a little, the transfers can be made quickly. Except 
when wild flies are caught early in the spring, the adults need not be 
fed. The females readily lay their eggs on the medium and development 
soon follows. During the entire life cycle the temperature and humidity 
of the rearing room must be watched. The temperature should not fall 
much below 25°C., and 30°C. seems to be very favorable. The atmos¬ 
phere- must not become dry. In the summer it is possible to ventilate 
extensively and the outside air (in New Jersey) maintains the proper 
humidity within, but when cold weather arrives and it is necessary to 
resort to artificial heat, water should be evaporated constantly, otherwise 
the breeding medium will rapidly dry out and become hard, especially 
in the upper layers. The medium must further be moistened from above 
every few days, but great care should be taken not to add too much 
water so as to avoid drowning the maggots in the lower part of the jar. 
With a little practice the necessary absorbing capacity of the medium 
for water can be readily determined. 
The first generation of reared adults will usually emerge during a 
period of several days. This is very convenient for the experimenter, 
because if the entire brood issued on one day it would be very difficult 
to utilize all the material to the best advantage. The adults are ex¬ 
tracted by the method shown on Plate I, Figure 3. The breeding jar is 
darkened with a black cotton bag having a draw string at the open end 
so that it may be closed tightly around the edges of the breeding top hole. 
The cork is now taken out of the breeding jar top and a wide-mouthed, 
six-ounce bottle is quickly placed over the opening. This type of bottle 
is large enough to hold many flies and is also flanged, so that the insects 
do not easily slide back into the jar when once extracted. By substitut¬ 
ing empty bottles every little while, by shaking the whole outfit, by 
gently tapping on the top, and by permitting either sunlight or artificial 
light to shine from above, all the flies may be extracted in a short while. 
The three species used are positively heliotrophic when they first emerge 
and are hungry, but notwithstanding this fact, they vary somewhat in 
the rapidity of their responses to light, for instance, Lyperosia and Sto- 
moxys react very quickly, on the other hand, the hopse fly responds more 
slowly and will often become negatively heliotrophic after its preliminary 
