ii ON ANIMAL LIFE 55 



moths are mottled so as to mimic the bark of 

 trees, or moss, or the surface of stones. One 

 beautiful tropical butterfly has a dark wing 

 on which are painted a series of green leaf 

 tips, so that it closely resembles the edge of 

 a pinnate leaf projecting out of shade into 

 sunshine. 



The argument is strengthened by those 

 cases in which the protection, or other advan- 

 tage, is due not merely to colour, but partly 

 also to form. Such are the insects which 

 resemble sticks or leaves. Again, there are 

 cases in which insects mimic others, which, for 

 some reason or other, are less liable to danger. 

 So also many harmless animals mimic others 

 which are poisonous or otherwise well pro- 

 tected. Some butterflies, as Mr. Bates has 

 pointed out, mimic others which are nauseous 

 in taste, and therefore not attacked by birds. 

 In these cases it is generally only the females 

 that are mimetic, and in some cases only a 

 part of them, so that there are two, or even 

 three, kinds of females, the one retaining the 

 normal colouring of the group, the other 

 mimicking another species. Some spiders 



