316 THE NATURALIST IN NICARAGUA. [Ch. XVII. 



world was in the same favourable condition as regards 

 temperature (vegetation, according to Heer, extending to 

 the poles), and must have supported a vast number of 

 species and genera that were destroyed during the glacial 

 period, we must suppose that, in that great variety of. 

 forms, it sometimes occurred that two species belonging 

 to distinct orders somewhat resembled each other in form 

 or colouration, and that the resemblance was gradually 

 increased, when one species had special means of pro- 

 tection, by the other being benefited the more nearly it 

 approached it in appearance. 



It is to be remarked that the forms imitated have 

 always some kind of defence against insectivorous birds 

 or mammals ; they are provided with stings or unpleasant 

 odours or flavours, or are exceedingly swift in flight ; ex- 

 cepting where inanimate nature is imitated for conceal- 

 ment. Thus I had an opportunity of proving in Brazil 

 that some birds, if not all, reject the Heliconii butterflies, 

 which are closely resembled by butterflies of other families 

 and by moths. I observed a pair of birds that were bringing 

 butterflies and dragon flies to their young, and although 

 the Heliconii swarmed in the neighbourhood and are of 

 weak flight so as to be easily caught, the birds never 

 brought one to their nest. I had a still better means of 

 testing both these and other insects that are mimicked in 

 Nicaragua. The tame white-faced monkey I have 

 already mentioned was extremely fond of insects, and 

 would greedily munch up any beetle or butterfly given 

 to him, and I used to bring to him any insects that I 

 found imitated by others to see whether they were distaste- 

 ful or not. I found he would never eat the Heliconii. He 

 was too polite not to take them when they were offered to 



