EYE FACET NUMBER AS INFLUENCED BY TEM- 

 PERATURE IN THE BAR-EYED MUTANT OF 

 DROSOPHILA MELANOGASTER 

 (AMPELOPHILA). 1 



E.. W. SEVSTER, 

 UNIVERSITY OF ILLINOIS. 



The effect of temperature upon facet number in the red bar- 

 eyed Drosophila was studied in connection with an extended 

 series of experiments on the effect of selection which is in progress 

 in the Zoological Laboratory at the University of Illinois. 



For the higher temperatures (27-3o) a bacteriological incu- 

 bator, varying not more than one degree centigrade was used. 

 The room temperature controlled by a Johnson regulator, re- 

 corded by means of a thermograph, and varying not more than 

 2, was used for medium temperatures. A cold plate arranged 

 by allowing tap water to flow around a dish in which the Droso- 

 phila bottles w r ere placed and varying not more than i during 

 any one experiment, was used for the low temperature. 



The parents in each experiment were taken from mass cultures 

 or stocks, no attempt being made to obtain virgin females for 

 this work. However, the average facet number of the parents 

 of any two sets in an experiment differed but little, any difference 

 occurring being much less than the difference between the aver- 

 ages of .the offspring raised at different temperatures. In experi- 

 ments 14, 15, 17, and 18 the parents were left in the bottles for 

 one day only; in all other experiments they were allowed to 

 remain for nearly the full developmental period in order that a 

 larger number of individuals might be obtained. 



That light is not an important factor for facet number was 

 determined by control experiments. 



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

 no. 141. 



The manuscript of Mr. Seyster's paper essentially in its present form was 

 completed in May, 1917, when he entered the U. S. Army Training Camp. At that 

 time it was hoped that he might eventually follow up the work but those plans 

 have not materialized and it seems best to publish the results as they stand. C. Z. 



1 68 



