ix WARNING COLORATION AND MIMICRY 243 



of the larvae or some other cause, possessed disagreeable 

 juices that caused them to be disliked by the usual enemies 

 of their kind, they were in all probability not very different 

 either in form or coloration from many other butterflies. They 

 would at that time be subject to repeated attacks by insect- 

 eaters, and, even if finally rejected, would often receive a 

 fatal injury. Hence arose the necessity for some distinguish- 

 ing mark, by which the devourers of butterflies in general 

 might learn that these particular butterflies were uneatable ; 

 and every variation leading to such distinction, whether by 

 form, colour, or mode of flight, was preserved and accumulated 

 by natural selection, till the ancestral Heliconoids became well 

 distinguished from eatable butterflies, and thenceforth com- 

 paratively free from persecution. Then they had a good 

 time of it. They acquired lazy habits, and flew about slowly. 

 They increased abundantly and spread all over the country, 

 their larvae feeding on many plants and acquiring different 

 habits ; while the butterflies themselves varied greatly, and 

 colour being useful rather than injurious to them, gradually 

 diverged into the many coloured and beautifully varied forms 

 we now behold. 



But, during the early stages of this process, some of the 

 Pieridae, inhabiting the same district, happened to be sufficiently 

 like some of the Heliconidse to be occasionally mistaken for 

 them. These, of course, survived while their companions were 

 devoured. Those among their descendants that were still more 

 like Heliconidse again survived, and at length the imitation 

 would become tolerably perfect. Thereafter, as the protected 

 group diverged into distinct species of many different colours, 

 the imitative group would occasionally be able to follow it 

 with similar variations, — a process that is going on now, for 

 Mr. Bates informs us that in each fresh district he visited he 

 found closely allied representative species or varieties of 

 Heliconidse, and along with them species of Leptalis 

 (Pieridae), which had varied in the same way so as still to be 

 exact imitations. But this process of imitation would be 

 subject to check by the increasing acuteness of birds and other 

 animals which, whenever the eatable Leptalis became numerous, 

 would surely find them out, and would then probably attack 

 both these and their friends the Heliconidse in order to devour 



