254 
DARWINISM 
CHAP. 
merged in another much more abundant species, by similarity 
of external appearance, would be an advantage. 
The question of fact remains. Do young birds pursue and 
capture these distasteful butterflies till they have learned by 
bitter experience what species to avoid ? On this point Dr. 
Miiller has fortunately been able to obtain some direct evi¬ 
dence, by capturing several Aeneas and Heliconidae which had 
evidently been seized by birds but had afterwards escaped, as 
they had pieces torn out of the wing, sometimes symmetri¬ 
cally out of both wings, showing that the insect had been 
seized when at rest and with the two pairs of wings in contact. 
There is, however, a general impression that this knowledge is 
hereditary, and does not need to be acquired by young birds; 
in support of which view Mr. Jenner Weir states that his birds 
always disregarded inedible caterpillars. When, day by day, 
he threw into his aviary various larvae, those which were 
edible were eaten immediately, those which were inedible 
were no more noticed than if a pebble had been thrown 
before the birds. 
The cases, however, are not strictly comparable. ' The 
birds were not young birds of the first year; and, what 
is more important, edible larvae have a comparatively simple 
coloration, being always brown or green and smooth. Uneat¬ 
able larvae, on the other hand, comprise all that are of conspicu¬ 
ous colours and are hairy or spiny. But with butterflies there 
is no such simplicity of contrast. The eatable butterflies com¬ 
prise not only brown or white species, but hundreds of 
Nymphalkhe, Papilionidae, Lycaenidoe, etc., which are gaily 
coloured and of an immense variety of patterns. The colours 
and patterns of the inedible kinds are also greatly varied, 
while they are often equally gay; and it is quite impossible 
to suppose that any amount of instinct or inherited habit 
(if such a thing exists) could enable young insectivorous 
birds to distinguish all the species of one kind from all 
those of the other. There is also some evidence to show 
that animals do learn by experience what to eat and what 
to avoid. Mr. Poulton was assured by Kev. G. J. Bursch 
that very young chickens peck at insects which they after¬ 
wards avoid. Lizards, too, often seized larvae which they were 
unable to eat and ultimately rejected. 
