272 FRANK E. LUTZ 



The heterozygous wings are to all appearances normal but they 

 are really not relatively as long as normal. 



As is indicated in figure 1, both sexes of these flies have only 

 one dose of that part of the normal wing complex which presum- 

 abl}^ dropped out to give a wingless fly, whereas both sexes of 

 normal flies have two doses. In wingless flies, and hence in half 

 of each zygote from which these hybrids came, something has 

 been changed, at least, so that the tendency to develop the wings 

 to normal proportions has been lost. It is probable that the 

 result of this experiment, a phenomenon usually referred to as 

 'incomplete dominance,' is due to this cause. 



However that may be, the interesting point for the present 

 discussion is that the sexual dimorphism has not been changed. 

 Environmental effects are practically ruled out here since the 

 males and females of a given experiment grew up together. Nor- 

 mal females have a wing-to-femur ratio 7.42 greater than the 

 males and in these flies it is 7.86. The difference of 0.44 is less 

 than twice the probable error and certainly is not significant. 

 On the hypothesis stated above, this is what is to be expected 

 since the germinal changes are alike in the two sexes. 



Conditions are theoretically quite different in the cross between 

 normal females and miniature-winged males. It will be seen 

 from figure 1 that normal females get two doses of that part of 

 the wing complex which is connected with the sex chromosome 

 whereas the males get but one. In order that miniature wings 

 may appear, this part of the complex must be changed, either by 

 the dropping out of a factor or in some other way. In the cross 

 just mentioned the male offspring are, ^according to theory, 

 perfectly normal in their germinal make up. Theu- single X- 

 chromosome has it full share, and no more, of wing factors. The 

 female, however, has only one normal X-chromosome. The other 

 either lacks a factor or, less probably, has a new modifying fac- 

 tor. At any rate the second X-chromosome is not equipped for 

 full wing development. Hence the sexes are more nearly alike 

 in their germinal make up than are the normal. The results 

 show that they are also more nearly alike in their somatic condi- 

 tion. 



