EGG-LAYING REACTIONS IN POMACE FLY 329 
just visible to the naked eye. The work of others justifies the 
assumption that, on the average, the internal conditions are 
fulfilled equally well in all flies reared upon ordinary cultures 
of fermenting banana. 
The interpretation of results depends upon an understanding 
of the productivity of the female Drosophila under favorable 
conditions. According to Lutz (14), a normal female produces 
100 to 300 eggs in a lifetime, the average length of life being 30 
days. This gives an average of 6.7 eggs per day for a single 
female fly. The eggs are laid regularly rather than periodically, 
just:as in the case of the Mediterranean fruit fly (Back and 
Pemberton, ’15 b), where the average is 4.5 eggs per day. In 
Drosophila the present experiments show an average of 3.3 eggs 
per day for each female fly when allowed to oviposit upon the 
banana pulp which furnishes nourishment to the fly. In one 
case a fly laid 33 eggs in a single day. Upon the best media 
Guyénot (13, VII) obtained 20 to 25 eggs per day regularly 
from fertile female fruit flies. 
The numerical results have been correlated by averaging the 
results from similar experiments, weighting the averages accord- 
ing to the number of flies involved and the number of days that 
the tests lasted. Since the number of trials made with each 
stimulus differed, the averages are only roughly comparable. 
The more successful stimuli were used more frequently. 
I. Selective conditions. In preliminary trials the female flies 
were allowed to select situations for egg-laying from among eight 
or ten varieties, which were available at one time. This was 
done by placing a series of stimulating substances in small glass 
vials with narrow entrances (similar to those described by 
Barrows ’07) as traps within a large glass cage. The traps were 
placed parallel in such a manner that to enter them the flies 
moved away from the windows, in opposition to their positive 
phototropic impulses. The flies to be used were liberated from 
the breeding jars into an empty jar, where they were etherized. 
Females were then selected under anesthesia, usually 100, and 
transferred to the cage by means of a brush. A dish of water 
within the cage kept the atmosphere moist. 
