V 



GENERAL CONCLUSIONS 



From the evidence adduced in the foregoing sections it may fairly be claimed that the 

 two main contentions are not without substance in fact. There are dominant groups of 

 butterflies, many of them are distasteful, some possess this quality in a high degree. More- 

 over, it is evident that butterflies do form the prey of birds and other insectivorous enemies. 

 It will probably not be questioned that an animal having gustatory preferences will choose 

 the most palatable food, and hence it follows that if a palatable butterfly so closely resembles 

 another which is distasteful it will have a superior chance of escape by reason of its resem- 

 blance. It seems unreasonable to abandon a theory based on natural selection unless the 

 alternative can be shown to explain some features of the phenomenon which are otherwise 

 inexplicable.^ 



If butterflies have come to resemble each other by the operation of similar environ- 

 mental causes, then mimicry between these insects must be something apart from other 

 forms of mimetic resemblance, since environment can hardly be suggested as a cause of the 

 resemblance of an insect to a dead leaf, nor would sexual selection be of any avail. Moreover, 

 the appearance of a butterfly or other insect having a complete metamorphosis is provided 

 for in its larval and pupal stages, since the pattern of the perfect insect is complete at the 

 moment of emergence. It may be said that in the larval state there is every scope for the 

 production of similar effects by local causes. To go no further, however, than the order 

 Lepidoptera, it would be difficult indeed to imagine how any force of environment could 

 account for the case of Papilio laglazci,^ and its model, Alcidis aurora. The supposed external 

 causes which have acted on the two insects have produced a real orange-coloured body in the 

 moth and an imitation one in the butterfly. The only uniformity of result which has been 

 produced is the very deceptive one of appearance, brought about by methods widely different 

 in their nature. Turning to certain resemblances in Neotropical Lepidoptera, we have the 

 mimicry between forms of Castnia and Ithomiine butterflies, as instanced by Professor 

 Poulton. Here the larvae of the former feed inside the stems of plants, whilst those of the latter 



^ The argument in favour of natural selection 

 will be found in a paper by Professor Poulton, 

 entitled ' Natural Selection the Cause of Mimetic 

 Resemblance and Common Warning Colours ', and 

 published in the Linnaean Society's Journal (Zoology), 

 vol. xxvi, p. 558, &c., and a revised edition is included 

 in the collection of ' Essays on Evolution ' by the 

 same author. The subject has been so fully and ably 

 dealt with in these publications that I feel I can add 



nothing of importance to the convincing evidences 

 there adduced. In fact, had it not been necessary, 

 for the completeness of the present work, to make 

 use of some of these arguments I should have been 

 inclined to avoid the subject, since I can at best but 

 call attention to truths which have been expounded 

 by a far abler pen than mine. 

 2 See p. 41. 



