THEORY OF EVOLUTION 11 



taken place in the wings and several of these 

 involve the size of the wings. If we arrange 

 the latter arbitrarily in the order of their size 

 there will be an almost complete series begin- 

 ning with the normal wings and ending with 

 those of apterous flies. Several of these types 

 are represented in figure 5. The order in which 

 these mutations occurred bears no relation to 



m_ , ^ 



FIG. 5. Mutants of Drosophila ampelophila arranged in 

 order of size of wings: (a) cut; (b) beaded; (c) stumpy; 

 (d) another individual of stumpy; (f) vestigial (g) apterous. 



