ARTICLES 



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differentiated first, followed by green in the mid-spectral region. 

 It is probable that many animals have not developed beyond 

 this trichromic vision, and to such a colour perception brown 

 and green are indistinguishable and would not therefore be a 

 factor for selection ; thus it would be immaterial to a species, 

 in respect to the attack of enemies, whether it be coloured green 

 or brown against either green or brown backgrounds : there is 



B 



w 



Bl 



Br 



Diagram No. 2. 

 In this diagram the occurrences are all brought to ioo. 



therefore nothing to hinder the green-brown dimorphism and 

 no reason why a butterfly should be coloured green rather 

 than brown to imitate foliage. 



The green of many larvae is derived from the chlorophyl of 

 their food, but in butterflies such a source is not available. 

 It would seem that the metabolism to form adult characters 

 is more easily able to produce brown. 



