112 CHARLES ZELENY. 



the determinations the values are remarkably constant. The con- 

 clusion may be safely made, therefore, that a proper measure has 

 been found for the expression of the germinal value in question. 

 A homozygous ultra-bar at 15 has the same ommatidial number 

 as a heterozygote at 25 ° and a homozygote at 20 the same number 

 as a heterozygote at 30 . 



On the logarithmic scale of ommatidial number it is, therefore, 

 possible to express the relation between the germinal factor and 

 the environmental factor as a constant. The present data, there- 

 fore, strengthen the validity of the use of this scale as a measure 

 of the germinal factors as well as the environmental ones. 



LITERATURE CITED. 

 Krafka, Joseph. 



'20 The Effect of Temperature upon Facet Number in the Bar-eyed Mu- 

 tant of Drosophila. J. Gen. Physiol., 2 : 409—464. 

 Seyster, E. W. 



'19 Eye-Facet Number as Influenced by Temperature in the Bar-eyed Mu- 

 tant of Drosophila melanogaster (ampelophila). Biol. Bull., 37: 

 168-182. 

 Zeleny, Charles. 



'20 A Change in the Bar Gene of Drosophila melanogaster involving Fur- 

 ther Decrease in Facet Number and Increase in Dominance. /. Exp. 

 Zool., 30 : 293-324. 



'22 The Effect of Selection for Eye-Facet Number in the White Bar Eye 

 Race of Drosophila melanogaster. Genetics, 7: i_ 115. 



