270 THEORIES OF MIMICRY 



seen butterflies attacked by birds. On the other hand, 

 the Mullerian theory presupposes that only young birds 

 test the palatability of a few members of each convergent 

 group in their locality, and henceforward, except when 

 driven by hunger, avoid all the members, so that the 

 recent tendency to explain so many of these resemblances 

 on Mullerian rather than on Batesian lines is in harmony 

 with the conclusion that the members of such groups are 

 not greatly attacked by adult birds. 



As regards butterflies which do not exhibit these 

 resemblances, I may point out that it is impossible to 

 exhaust the details of the struggle for existence, even as 

 regards a single species, in the intervals of the time 

 devoted to collecting. Such an investigation would 

 demand the whole time of a first-rate observer, and, so 

 far as I am aware, the inquiry has never been ap- 

 proached in so thorough a manner. Even if collectors 

 would pay attention to the worst specimens instead of 

 the best, some evidence of the nature and amount of 

 attack would be forthcoming. During the visit of the 

 British Association to Canada in 1897 I made a point 

 of capturing butterflies which had evidently been pecked 

 by birds. In this way, although I did not witness a 

 single attack, I obtained indirect proof that butterflies 

 are not nearly so immune as has been asserted. Similar 

 observations were made at a much earlier date by Fritz 

 Miiller. 1 



The review of the whole subject during the past 

 forty-five years increases our confidence in the theories 

 of Bates and Fritz Miiller, while it disposes of all 

 alternative hypotheses. Even more than this, — it will, 

 I believe, be claimed by all who take a broad view over 

 the whole field of evidence, that the explanation of these 

 deeply interesting facts, which form so fascinating and 

 important a department of natural history in the tropics, 

 is one of the most notable triumphs ever won by the 

 great theory of Natural Selection. 



1 See Trans. E?it. Soc. Zond., 1902, pp. 353-75, where a large body 

 of evidence, direct as well as indirect, is published. The direct evidence 

 is reprinted, p. 282, as an Appendix to the following Essay. 



