THEORY OF EVOLUTION 107 



that is so marked a feature in the behavior of 

 D. ampelophila. As this peculiarity of the tan 

 flies is inherited like all the other sex linked 

 characters, it follows that when a tan female is 

 bred to a wild male all the sons inherit the re- 

 cessive tan color and indifference to light, while 

 the daughters show the dominant sex linked 

 character of their father, i.e., they are "gray", 

 and go to the light. Hence when such a brood 

 is disturbed the females fly to the light, but the 

 males remain behind. 



One of the first mutants that appeared in 

 D. ampelophila was called rudimentary on ac- 

 count of the condition of the wings (c). The 

 same mutation has appeared independently 

 several times. In the drawing (c) the dark 

 body color is intended to indicate "sable" and 

 the lighter color of the eyes is intended to indi- 

 cate eosin. This eye color, which is an allelo- 

 morph of white, is also interesting because in 

 the female the color is deeper than in the male. 

 In other cases of sex linked factors the char- 

 acter is the same in the two sexes. 



In the fourth figure (d) the third and fourth 

 longitudinal veins of the wing are fused into 



