270 TIIKORIKS OF MIMICRY 



seen huttcTtlics attacked hy birds. On tlu^ otIuT hand, 

 tlie Miilkrian thror)- presupposes that only j'<>/^;/;^ birds 

 test the palatcdjility of a few nienibers of each convenient 

 i^roup in their locality, and henceforward, excej^t when 

 driven by hiint^er, avoid all the members, so that the 

 recent tendenc\ to explain so many of these resemblances 

 on Mnllerian rather than on Hatesian lines is in harmony 

 with the conclusion that the members of such groups are 

 not greatl)- attacked b\- adult birds. 



As regards butterflies which do not exhil)it these 

 resemblances, 1 may point out that it is impossible to 

 exhaust the details of the struerirle 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 

 iar as I am aware, the in([uiry has never been ap- 

 proached in so thorough a manner. Even if collectors 

 wcnild pay attention to the worst specimens instead of 

 the best, some evidence of the nature and amount of 

 attack would be forthcominer. Durin^r 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 l^een asserted. Similar 

 observations were made at a much earlier date by Fritz 

 MullerJ 



The review of the whole subject during the past 

 forty-five years increases our confidence in the theories 

 of Bates and T'ritz Mliller, while it disposes of all 

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

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

 the whole field of evidence, that the exjjlanation of these 

 deejily 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. 



' See Trans. Ent. Soc. LonJ., 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. 



