194 PROCEEDINGS OF THE ACADEMY OF [Jan., 



Even in pattern there is but little difference between the most 

 nearly allied Asiatic and American species of Danaida, and if, as 

 Dr. Skinner believes, color and pattern are the expression of environ- 

 mental conditions, then they are the expression of an Old World, and 

 not of a New World environment. On Dr. Skinner's view, the 

 Old World invader, when it became exposed to the new environment, 

 should have come to resemble the New World resident. Instead 

 of this, the resident has come to resemble the invader. 



In concluding the present paper I may quote an opinion expressed 

 to me by Professor Svante Arrhenius. A few years ago I asked my 

 friend whether he thought it possible to explain by the incidence of 

 physico-chemical forces, such as those of the environment, the super- 

 ficial resemblance of one form to another when that resemblance 

 required, as in the development of a complex pattern, the co-opera- 

 tion of many different factors. He replied, as I expected, that he 

 did not consider the explanation possible; for the building up of such a 

 likeness was inconceivable except by the aid of selection. This was the 

 argument I advanced in 1898 (15), after an analysis which showed that 

 mimetic resemblance often requires the co-operation of many different 

 factors; and it was a great satisfaction to find the conclusion con- 

 firmed by an authority with Professor Arrhenius' broad outlook on 

 the sciences in their relation to one another and to mathematics. 



Bibliography. 



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