THE CAUSE OF MIMETIC EESEMBLANCE ETC. 563 



Mr. MeLachlan suggested " the possibility that two species 

 might go on independently and yet apparently mimic each other 

 by arriving at the same results in their modifications." 



Mr. J. J. Walker and Col. Yerbury argued that birds are not 

 " eSective agents in causing mimetic resemblances." 



Mr. Blandford, replying at the close of the debate, maintained 

 that extremely close and exact resemblances are " hypertelic," — 

 going beyond the limits of the useful, and therefore inexplicable 

 by natural selection. He restated and brought further support in 

 favour of the opinion that birds rarely attack butterflies. He 

 made the fioal suggestion that possibly " sexual selection, or the 

 segregation of forms might take place as a direct act of perception 

 on the part of the insects themselves"; and quoted the observation 

 of H. W. Bates that the ItliomioG when pairing tend to select none 

 but their exact counterparts (Trans, Linn. Soc. vol. xxxiii. 1862, 

 p. 501). 



Only four speakers gave full support to the theories of Bates 

 and Pritz Miiller, as explaining the facts more satisfactorily than 

 any other theory hitherto proposed and as likely to receive 

 further confirmation in the future. These four were the President 

 Mr. E/oland Trimen, Dr. Dixey, Colonel Swinhoe, and the present 

 writer. 



(2) The various Hypotheses which have heen proposed as Sub- 

 stitutes for Natural Selection as the Explanation of 

 Mimicry and Common Warning Colours. 

 In the course of the discussion thus briefly epitomized, almost 

 every alternative theory which has been proposed to account for 

 the facts was brought forward. 

 These theories are as follows : — 



(1) The direct effect of some physical or chemical cause or 

 causes connected with locality, such as climate, food, &c. This 

 hypothesis received much support. It may be called the Theory 

 of External Causes. 



(2) The independent evolution of a similar appearance in 

 distinct species. This hypothesis was suggested by Mr. 

 McLachlan, and I have heard a similar opinion expressed by 

 Prof. Patrick Greddes. This appears to be the view sustained 

 in G. H. Elmer's just published work ' Orthogenesis der Schmet- 

 terlinge' (Leipzig, 1898). I have not yet had the opportunity 

 of studying the essay, but my friend Prof. Weldon has done so 



