THE EFFECT OF TEMPERATURE UPON FACET NUM- 

 BER IN THE BAR-EYED MUTANT 

 OF DROSOPHILA.* 



Part III. 



By JOSEPH KRAFKA, Jr. 

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



(Received for publication, December 30, 1919.) 



The Effect of Temperature upon Variability. 



Coefficient of Variability at Different Temperatures. 



This study gives some interesting data on the question of individual 

 variability at the various temperatures. The distribution of the 

 counts of Ultra-bar are given in Table XIX. Here the class size is 

 1 facet. Particular attention is called to the normal distribution in 

 all cases. 



An argument for the genetic stability of the Ultra-bar stock 

 is found in the relatively infrequent occurrence of individuals out- 

 side the bounds of normal distribution. At 27° a single 55 facet 

 male and at 16° a 72 facet male are the only two extremely wide 

 departures. 



The mean, standard deviation, and coefhcient of variability for all 

 three stocks are given in Tables XX to XXII. Two things are appar- 

 ent: (1) variability increases with the temperature when measured by 

 the coefficient of variability; and (2) the variability of the Ultra-bar 

 stock is much lower than that of the other two stocks. Both these 

 generalizations have their exceptions. Their reliability as compared 

 to statements made by other writers will be discussed later. 



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

 No. 148. 



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