306 



THE AMEBIC AN NATURALIST [Vol. LI 



The positive contribution of these matters to the selection 

 problem is to enable us to see the important role played by Men- 

 delism in the effectiveness of selection. Hereditary variations, 

 such as give rise to the multiple allelomorphs and multiple modi- 

 fying factors, occur in some organisms rather infrequently, as 

 measured by the time scale of human happenings. If there were 

 no interchange of factors among individuals and stocks, it would 

 take a long time to obtain in one individual all the six diluters 

 of the eosin color of the Drosophila eye; one arises in one in- 

 dividual, another in another. But by selective crossbreeding it 

 is possible to bring together into one stock q,ll the modifiers that 

 have been produced in diverse stocks. Mendelism acts as a 

 tremendous accelerator to the effectiveness of selection. 



PAPERS CITED 



Bridges, C. S. 1916. Non-Disjunction as Proof of the Chromosome Theory 



of Heredity. Genetics, 1 : 1-52, 107-163. 

 Castle, W. E., and Wright, S. 1916. Studies of Inheritance in Guinea 



Pigs and Rats. Publ. No. 241, Carnegie Institution of Washington, 



192 pp. 



Emerson, R. A. 1917. Genetical Studies of Variegated Pericarp in Maize. 

 Genetics, 2: 1-35. 



Hyde, R. R. 1916. Two New Members of a Sex-linked Multiple (sex- 

 tuple) Allelomorph System. Genetics, 1 : 535-580. 

 Safir, S. R. 1916. Buff, a New Allelomorph of White Eye Color in Dro- 



H. S. Jennings 



The Johns Hopkins University 



A WING MUTATION IN PIOPHILA CASEI 



In the early part of December, 1915, I began to breed the 

 "cheese skipper" Piophila casei, in order to see if mutations 

 were to be found in this fly. The source of my stock was a small 

 piece of Italian cheese containing a dozen or so larvae.' As these 

 were doubtless the offspring of one female, inbreeding has been 

 very close. Up to June 22, 1916, only one heritable mutation 

 had been found among the thousands of individuals bred; this 

 was the wing defect described below, which was first noted on 

 March 12, 1916. 



1 This work was carried on at the Osborn Zoological Laboratory, Yale Uni- 

 versity, New Haven, Connecticut. It was in New Haven that I obtained the 

 cheese. Contribution No. 135, Zoological Laboratory, University of Texas. 



