ENVIRONMENTAL FACTORS OTHER THAN TEMPERA- 

 TURE AFFECTING FACET NUMBER IN THE 

 BAR-EYED MUTANT OF DROSOPHILA * 



By JOSEPH KRAFKA, Jr. 



{From the Zoological Laboratory of the University of Illinois, Urbana.) 



(Received for publication, August 5, 1920.) 



In a recent paper the author^ has undertaken to show the relation 

 between temperature and the facet number in the bar-eyed mutant 

 of Drosophila melanogaster Meig. Since it was essential to know the 

 part played by other environmental factors the experimental evalu- 

 ation of some of these was carried out. While these experiments 

 were not as critical as was desired, they give some idea as to the 

 respective value of food, humidity, and evaporation as these are com- 

 monly represented in Drosophila culture technique. The following 

 data are submitted, then, not as a final analysis, but rather as a basis 

 for further work. 



The work in all cases was carried out on the Ultra-bar mutant. For 

 a direct comparison the data on the effect of temperature are given 

 in Table I. The temperature data are for the interval 23-29°C., as 

 the experiments involving the other factors were carried out at these 

 temperatures. 



An interesting suggestion for further work appeared in the analysis 

 of the few experiments dealing with different kinds of foods. Since 

 consistent results were obtained in three successive experiments it 

 may be that they have some significance. 



It is the experience of nearly all investigators rearing Drosophila, 

 that fermented banana rapidly becomes acid at the high temperatures 

 and that oviposition is much retarded. In an attempt to eliminate 



* Contribution from the Zoological Laboratory of the University of Illinois, 

 No. 165. 



"^ Krafka, J., Jr., The effect of temperature upon facet number in the bar-eyed 

 mutant of Drosophila, J. Gen. Physiol, 1919-20, ii, 409, 433, 445. 



207 



