INSECTS AS EXAMPLES OF EVOLUTION 51 



in the number of individuals ; and finally, in the character 

 of the struggle itself, which is precisely of that highly 

 specialized kind between the keen senses and activities of 

 enemies, and the means of concealment or other modes 

 of defence of their insect prey, which leads, by action and 

 answering reaction, to a progressive raising of the standard 

 in both pursuer and pursued. This is why it is that 

 insects mean so much to the naturalist or to the philo- 

 sopher who desires to look beneath the surface for the 

 forces which have moulded existing forms of life out of 

 earlier and very different forms. The wings of butterflies, 

 it has been said, ' serve as a tablet on which Nature writes 

 the story of the modifications of species.' 1 But the careful 

 study of insects tells us even more than this ; for it gives 

 us the clearest insight we as yet possess into the forces 

 by which these changes have been brought about. Light 

 is thrown upon the causes to which organic evolution 

 is due no less than upon the course which organic evolu- 

 tion has pursued. 2 



And I think we shall find that a consideration of the 

 numerous distinct categories of forms presented by the 

 insect world is especially advantageous in an attack 

 upon the difficult question — ' What is a species ? ', while 

 properly directed observation of insects, and experiments 

 upon insects afford the most hopeful prospect of a final 

 answer. 



And here I am compelled to say a word in defence of 

 the Lepidoptera from this point of view. Undoubtedly 

 it is most unfortunate that the obvious attractions of the 

 group have led entomologists to neglect other Orders ; 

 for this can be the only explanation why naturalists have 

 so often preferred to do over again what others have 

 done already, apparently oblivious of fields comparatively 

 empty and unexplored. It must further be admitted, 

 that the greater visibility of structure, and the more 



1 H. W. Bates, quoted by A. R. Wallace in Natural Selection, London, 

 1875, p. 132. The original passage may be found in The Naturalist on 

 the Amazons (London, pp. 347, 348 of the 1879 edition). 



2 This justification for the study of insects was urged by the present 

 writer in the Hope Reports, vol. iii, 1903, preface, pp. 4, 5. 



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