10 



THEORY OF EVOLUTION 



ity. This conclusion is not necessarily correct. 

 Let me give some examples that have come 

 under my own observation. We have bred for 

 five years the wild fruit fly Drosophila ampelo- 

 phila (fig. 4) and we have found over a hun- 



FIG. 4. Drosophila ampelophila. a, Female and b, male. 



dred and twenty-five new types that breed true. 

 Each has arisen independently and suddenly. 

 Every part of the body has been affected by 

 one or another of these mutations. For in- 

 stance many different kinds of changes have 



