254 DARWINISM 



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. 

 Midler has fortunately been able to obtain some direct evi- 

 dence, by capturing several Acraeas 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 

 Nymphalidae, Papilionidae, Lycaenidae, 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 Rev. 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. 



