SUGGESTED CAUSES OF MIMICRY 225 



may account for certain phenomena which are usually 

 explained by the theories of Natural and Sexual Selection 

 was made by Professor D'Arcy Thompson at the Oxford 

 meeting of the British Association in 1894.^ 



The conceptions briefly set forth under this head may 

 be grouped as the Theory of Internal Causes. 



Hi. The operation of Sexual Selection. Fritz Miiller 

 proposed this idea in a letter to Darwin, who wrote not 

 unfavourably of it to Professor Meldola, on January 23, 

 1872. ' Youw^U also see in this letter a strange specula- 

 tion, which I should not dare to publish, about the 

 appreciation of certain colours being developed in those 

 species which frequently behold other forms similarly 

 ornamented. I do not feel at all sure that this view is 

 as incredible as it may at first appear. Similar ideas 

 have passed through my mind when considering the dull 

 colours of all the organisms w^ilch inhabit dull-coloured 

 regions, such as Patagonia and the Galapagos Is.' ^ 



In the present paper the attempt will be made to show 

 that many of the known facts of Mimetic Resemblance 

 do not admit of interpretation by any of the three theories 

 mentioned above, while they do receive a ready explana- 

 tion on the supposition that the resemblances are useful 

 and have been produced by Natural Selection. Certain 

 new observations upon the details of the resemblances in 

 a large group of insects, undertaken specially to test these 

 rival theories, will be found to point strongly in the same 

 direction.^ 



3. The Relation of the Resemblances under Disc7cssion to 

 other Resenibla7ices m Organic Natter e. 



To those who accept Natural Selection as the explana- 

 tion of Mimicry, the facts under discussion fall into their 

 place as part of the much wider group of Protective 



^ Only the title — On some Difficulties of Dariviiiisvi — is printed in the 

 Report of the meeting, p. 689. 



* Charles Darwin and the Theory of Natural Selection, Poulton, London, 

 1896, p. 202. 



^ See Section 12^ p. 261. 



POVLTON Q 



