PREFACE 5 



Nature writes the story of the modifications of species.' 

 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 those modifications have been 

 brought about. Light is thrown upon the causes to which 

 organic evolution is due no less than upon the course 

 which organic evolution has pursued. 



In issuing the third volume of Hope Reports it may be 

 claimed not unjustly that these insistent ' larger problems ' 

 have received during the past ten years that special atten- 

 tion which Huxley advocated. The subject which more 

 than any other has claimed the attention of the Hope 



other group of animals or plants, to furnish facts in illustration of the 

 modifications which all species undergo in nature under changed local 

 conditions. This accidental superiority is owing partly to the simplicity 

 and distinctness of the specific characters of the insects, and partly to the 

 facility with which very copious series of specimens can be collected and 

 placed side by side for comparison. The distinctness of the specific 

 characters is due probably to the fact that all the superficial signs of change 

 in the organization are exaggerated and made unusually plain by affecting 

 the framework, shape, and colour of the wings, which, as many anatomists 

 believe, are magnified extensions of the skin around the breathing orifices 

 of the thorax of the insects. These expansions are clothed with minute 

 feathers or scales, coloured in regular patterns, which vary in accordance 

 with the slightest change in the conditions to which the species are exposed. 

 It may be said, therefore, that on these expanded membranes nature writes, 

 as on a tablet, the story of the modifications of species, so truly do all 

 changes of the organization register themselves thereon. Moreover, the 

 same colour-patterns of the wings generally show, with great regularity, the 

 degrees of blood-relationship of the species. As the laws of nature must 

 be the same for all beings, the conclusions furnished by this group of 

 insects must be applicable to the whole organic world; therefore the study 

 of butterflies — creatures selected as the type of airiness and frivolity — 

 instead of being despised, will some day be valued as one of the most 

 important branches of biological science.' In this case the seer may be 

 said to have brought about the fulfilment of his own prophecy by the 

 inspiration given in his epoch-making theory of mimicry. 



