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THE AMERICAN NATURALIST [Vol. LI 



near Bloomington, Indiana, and had been bred in the laboratory 

 for two generations. 



The mutation chocolate eye was first observed in December, 

 1916, and here again the original mutation had probably been 

 overlooked as in the cross where the mutation was first ob- 

 served, several chocolate males and females appeared. The orig- 

 inal stock in which this mutation appeared had been bred in the 

 laboratory for three generations and was collected in the same 

 tomato patch where the original red eye stock was collected. 

 The stock in which the red eye appeared was collected on Sep- 

 tember 19, 1916, and the stock in which the chocolate eye ap- 

 peared was collected September 14 of the same year and these 

 stocks had been bred as two separate strains when the mutations 

 appeared. 



The Genetic Behavior of Red Eye 

 Some of the first observed red males were mated to virgin red 

 females and the offspring of this cross were all red flies. This 

 red stock has been kept going for several generations and has 

 ■given all typical reds. Both red males and red females were 

 crossed with normal wild flies and in of each cross nothing 

 but normal flies were found. Table I gives the results of the 

 of these crosses. 



TABLE I 

 OP Red X Wil© Cross 

 Red 9 X Wild d- 



