2 EXPERIMENTS WITH DROSOPHILA AMPELOPHILA. 
of the different degrees as found during four typical months from read- 
ings of the thermogram at 38-hour intervals. For the purpose of these 
experiments even this approximation to constancy does not seem neces- 
sary, as variations of temperature were found to have no influence upon 
the wing-venation. Therefore the incubator was not used in the latter 
part of the work. 
Class 18.33° 20.00° 21.66" 23.33° 25.00° 26.66° 28.33° 30.00° 31.66" 
Frequency ° 5 25 in 292 203 690 18 ie} 
Fie. 1 
Bananas were used as food. They were purchased while still quite 
green and ripened in glass-stoppered bottles. In this way accidental 
introduction of wild flies was rendered unlikely. Even had Drosophila 
eggs been laid on the green banana, they would have hatched and the 
larvee would have developed into plainly visible pupz before the banana 
was used. Frequent control-cultures were kept and in no case was a 
Drosophila found in them. The flies with their food were kept in care- 
fully washed glassware and the instruments used in handling the food 
were sterilized in an alcohol flame after every operation which could 
possibly get eggs or larvee upon them. The importance of this caution 
can not be too strongly urged upon those who carry out pedigree-work 
with this insect. 
An egg-laying female was given a fresh piece of banana every two days 
and an effort was made to have all the banana of the same degree of 
decay. Each piece was kept separate during the growth of the larve. 
This also is important, since, if one merely gives a large supply of food 
to the female at the start of oviposition, and does not change it, the 
early-born larve will have very different food from those which are 
born later. The pupe were picked out of the “‘larval dish’’ and placed 
