WARNING COLORATION AND MIMICRY 
243 
is 
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 larvse 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 
Pieridse, 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 
(Pieridse), 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 
