216 THE AMERICAN NATURALIST [Vol. L 



when ebony is crossed to most other stocks recombination 

 of the factors is nearly impossible. A stock has finally 

 been obtained, however, combining the following charac- 

 ters belonging to group III: sepia eye color, dichaete 

 (bristles, and wing), pink eye color, spineless body, 

 kidney eye, sooty body color, and rough eye. Data have 

 not yet been secured with this final stock, but the follow- 

 ing experiment, in which most of these factors were in- 

 volved, may be regarded as typical of crosses not involv- 

 ing factor "C," and consequently giving moderately high 

 frequencies of separation. Hybrid females from a cross 

 of sepia flies with flies containing dichsete, spineless, 

 kidney, sooty, and rough, were backcrossed to the quin- 

 tuple recessive stock— sepia, spineless, kidney, sooty, 

 rough (dichsete being a dominant). The count of off- 

 spring is shown below. The classification as regards 

 kidney has not been given, as this character can not be 

 distinguished with certainty in eyes which are also rough. 



