THE EFFECT OF TEMPERATURE UPON FACET NUMBER 

 IN THE BAR-EYED MUTANT OF DROSOPHILA * 



Part I. 



By JOSEPH KRAFKA, Jr. 

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



(Received for publication, December 30, 1919.) 

 INTRODUCTION. 



Environment plays an important part in the development of 

 every organism. In a few cases, it becomes a determinative agent 

 in that particular structures are developed only under special 

 external stimuli. 



The bar-eyed mutant of Drosophila melanogaster Meig (ampelo- 

 phila) shows such a response to temperature. Primarily this germinal 

 factor produces a reduction in the number of facets in the compound 

 eyes. Under a constant environment, it produces practically a con- 

 stant effect in all individuals. Under varied temperature conditions, 

 the amount of reduction varies inversely with the temperature. 



The present study^ is an attempt to work out these relations in 

 detail. From the standpoint of the modern physiologist, the results 

 are of particular interest in demonstrating in the same living material 

 a physiological reaction whose rate is an exponential function of the 

 temperature, while another reaction has a rate which is clearly a linear 

 function of the temperature. 



From the standpoint of experimental embryology in its broadest 

 sense, this study gives an evaluation of some of the external and in- 

 ternal factors involved in the development of a particular structure, 



* Contribution from the Zoological Laboratory of the University of Illinois, No. 

 148. 



^ This investigation was developed under the direction of Dr. Charles Zeleny. 

 The study was made possible through the excellent equipment for environmental 

 control installed at the Vivarium. 



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