EXPERIMENTS CONCERNING THE SEXUAL DIFFER- 

 ENCE IN THE WING LENGTH OF DROSOPHILA 

 .AJMPELOPHILA 



FRANK E. LUTZ 



The American Museum of Natural History, New York 



TWO FIGURES 



Two of the forms of the fruit fly, Drosophila ampelophila, 

 which have been isolated recently by Prof. T. H. JN.Iorgan are 

 distinguished from the normal by lesser wing length. One, 

 called 'wingless' in Professor Morgan's papers, really possesses 

 vestiges of wings which appear to consist largely of modified basal 

 portions of normal wings. The other, called 'miniature,' pos- 

 sesses all the veins of the normal wing in approximately normal 

 condition but the wing is only about two-thirds the normal length. 



' Winglessness' is recessive to normality according to the simple 

 Mendehan formulae. In Fi all individuals, both male and female, 

 are hybrid no matter which parent bears the abnormal character. 

 The 'miniature' wings are also recessive but are sex limited in 

 their inheritance. If the mother have miniature wings and the 

 father be normal, only the females of F] will be hj^brids while 

 all the males will be pure recessives. In the reciprocal cross the 

 females will again be hybrids but the males will be pure domi- 

 nants. The reasonable explanation which Professor Morgan has 

 advanced of these phenomena is that the factor for miniature 

 wings (using such an expression in lieu of a better) is contained 

 in, or in some way connected with, that chromosome of which 

 the female possesses two and the male but one, while the factor for 

 winglessness is connected with something which is shared equally 

 by both sexes. This idea is shown diagrammatically in figure 1 

 in which the composition of pure stock of the three forms and 

 that of two of the cross are shown, the X-chromosomes being 

 represented by squares.' 



267 



