BIRDS AND BUTTERFLIES 239 



omit many facts which tend to show that their fetishes 

 are shams. They regard the discussers of the awkward 

 facts as enemies to be crushed. Hence the gulf between 

 the two classes of biologists. 



One of the fetishes of the present day is the theory 

 of protective mimicry. Butterflies and moths are the 

 organisms which exemplify best this theory. 



It often happens that two species of butterfly occur 

 in the same locality which resemble one another in 

 outward appearance. In such cases zoologists assert 

 that one species mimics the other. They maintain that 

 this mimicry has been brought about by natural selec- 

 tion, because the one species profits by aping its neigh- 

 bour. The species that is copied is said to be un- 

 palatable. The copy-cat, if I may use the expression, 

 may be either palatable or unpalatable. In either case 

 it is believed to profit by the resemblance. If it is 

 edible the birds that are supposed to prey upon butter- 

 flies are said to leave it alone, because they mistake it 

 for its unpalatable neighbour. This resemblance of an 

 edible form to an unpalatable one is called Batesian 

 mimicry. 



If the copy-cat be unpalatable it is nevertheless said 

 to profit by the likeness, because young birds are 

 supposed to feed on every kind of butterfly and only 

 to learn by experience which are unpalatable. The 

 theory is that if they attack a red-coloured butterfly 

 and find it nasty to the taste, they leave all red-coloured 

 butterflies alone henceforth. Thus, the imitating 

 species may benefit by the sacrifice of the other red- 

 coloured species. This is known as Mullerian mimicry. 



