236 



THE AMKRICAX MUSEUM JOURXAL 



Fi£ 



getting mates as those which possess it, although strong evidence of 

 sexual selection with respect to other characters is being obtained. 



It is generally believed that close inbreeding is always attended by 

 decreased vitality and disuse by degeneration. This is not the case 

 with Drosophila ampelojyhila. It has been repeatedly V)red for a large 



number of generations, matins: 

 lirother and sister, without disastrous 

 results. I have, furthermore, made 

 careful measurements of the wings 

 of successive generations and found 

 that although my pedigreed stock 

 has not l)een allowed to fly for more 

 than fifty generations, there has 

 been no defeneration of the wino- 

 either as to size or as to venation. 

 On the other hand, by selective 

 breeding I have been able to get 

 specimens with greatly reduced wing 

 venation as is shown in Figure 2, 

 Figure 3 showing the normal wing. 

 Selection in the other direction, i. e., 

 for increased venation, is just as 

 effective (Fig. 4). A study of the 

 inheritance of these variations was 

 begun at the Station for Experi- 

 mental Evolution of the Carnegie 

 Institution and is being continued, 

 with other mathematical and exper- 

 imental studies of evolution, at the 

 Museum. About 200,000 pedigreed 

 individuals of this species alone have 

 already been obtained. The inter- 

 pretation of the results of this work is complicated by the fact that the 

 two sexes display the abnormalities to unequal degrees and also because 

 the mode of inheritance deviates strongly from exj^ectation on the basis 

 of the commonly accepted laws. 



F. E. LuTz. 



Fig. 3. 



Fit; 



FIG. 2. A WING OF DROSOPHILA AM- 

 PELOPHILA SHOWING REDUCTION OF 

 VENATION DUE TO SELECTION. 



FIG- 3. A NORMAL WING OF DROSOPHILA 

 AMPELOPHILA. 



FIG. 4. A WING OF DROSOPHILA AM- 

 PELOPHILA SHOWING INCREASE OF VENA- 

 TION DUE TO SELECTION. 



