3 38 LEPIDOPTERA 



believed to be specially protected by nauseous odours or taste. 

 It was, in foct, thought that the destroying enemies were 

 deceived by the resemblance into supposing that the forms that 

 were in reality edible were inedible. This subject has been 

 greatly discussed, and in the course of the discussion numerous 

 cases that could not be accounted for by Bates's hypothesis have 

 been revealed. One of these is the fiict that resemblances of the 

 kind alluded to very frequently occur amongst inedible forms. 

 This also has been thought to be accounted for l:)y a supposed 

 advantage to the Insects ; it being argued that a certain number 

 of " protected " forms are destroyed by enemies the instincts of 

 which are faulty, and which therefore always require to learn by 

 individual experience that a certain sort of colour is associated 

 with a nasty taste. The next step of the argument is that it 

 will be an advantage to a protected butterfly to form part of 

 a large association of forms having one coloration, because 

 the ignorant enemies will more easily learn the association of a 

 certain form of coloration with nastiness ; moreover such destruc- 

 tion as does occur will be distributed over a larger number of 

 species, so that each species of a large, similarly coloured, inedible 

 association will have a less number of its individuals destroyed. 

 It is scarcely a matter for surprise that many naturalists are 

 very sceptical as to these explanations ; especially as the pheno- 

 mena are supposed to have occurred in the past, so that the}' 

 cannot be directly verified or disproved. It has not, however, 

 been found, as a matter of fact, that even unprotected butterflies 

 are much destroyed in the perfect state by birds. Moreover, in 

 endeavouring to realise the steps of the process of development 

 of the resemblance, we meet with the difficulty that the amount 

 of resemblance to the model that is assumed to be efficient at 

 one step of the development, and to bring safety, is at the next 

 step supposed to be inefficient and to involve destruction. In 

 other words, while analysis of the explanation shows that it 

 postulates a peculiar and well-directed discriminative power, 

 and a persistent selection on the part of the birds, observation 

 leads to the l)e]ief that birds have been but little concerned in 

 the matter. If we add to this that there is no sufficient evidence 

 that the species now similar were ever dissimilar (as it is sup- 

 posed they were by the advocates of the hypothesis), we think 

 it is clear that the explanation from our point of view is of but 



