236 EVOLUTION OF TO-DAY. 



folded, very accurately resembles the leaves of the 

 plant on which it lives, the resemblance being 

 carried even to the veining of the leaf and its 

 petiole. In other cases the likeness may be carried 

 to even a greater extent, spots appearing on the 

 wings resembling injuries caused by fungi on the 

 leaf. Or others may resemble dry sticks, their legs 

 stretching out irregularly in various directions so as 

 to resemble branches. The object of all this is evi- 

 dent enough. It enables the animals in question to 

 avoid destruction. It is a clear case of natural 

 selection. An insectivorous bird sits on the branch 

 of a tree and watches for butterflies/ As soon as it 

 sees one flying across an open tract, if it appear to 

 be of the species which the bird knows, from 

 experience, to be pleasant to the taste, the bird 

 leaves its perch, pursues and captures the butterfly. 

 If, however, the butterfly should appear to be one 

 of the distasteful species, the bird pays no attention 

 to it. If the tasteful species have individuals bear- 

 ing slight chance resemblance to the distasteful 

 species, these individuals will be the ones to escape 

 destruction and to perpetuate their kind. Thus the 

 beginning of mimicry is easily understood. As the 

 mimicking species becomes more abundant, the 

 birds will learn to look more sharply before reject- 

 ing any individual, and it will only be those having 

 a very close mimicry that will be preserved. As the 

 bird becomes wiser and sharper in its scrutiny, the 

 mimicry must become more perfect, and eventually 

 a remarkable perfection in mimicry may be reached. 

 All this will result from the action of natural selec- 



