2 EXPERIMENTS WITH DROSOPHILA AMPELOPHILA. 



of the different degrees as found during four typical months from read- 

 ings of the thermogram at 3-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 



Frequency o 



Pig. 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 

 larvae would have developed into plainly visible pupae 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 larvae 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 larvae. 

 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 larvae will have very different food from those which are 

 born later. The pupae were picked out of the "larval dish" and placed 



