EFFECTS OF LOCALITY ON COLOUR. 



257 



orange-yellow and black. Other changes of a like 

 nature, which, it would be tedious to enumerate but 

 which are very striking when specimens are examined, 

 occur in species of the same groups inhabiting these 

 same localities, as well as Central America and the 

 Antilles. The resemblance thus produced between widely 

 different insects is sometimes general, but often so close 

 and minute that only a critical examination of structure 

 can detect the difference between them. Yet this can 

 hardly be true mimicry, because all are alike protected 

 by the nauseous secretion which renders them unpalat- 

 able to birds. 



In another series of genera (Catagramma, Callithea, 

 and Agrias) all belonging to the Nymphalidae, we have 

 the most vivid blue ground, with broad bands of orange, 

 crimson or a different tint of blue or purple, exactly 

 reproduced in corresponding, yet unrelated species, 

 occurring in the same locality ; yet, as none of these 

 groups are known to be specially protected, this can 

 hardly be true mimicry. A few species of two other 

 genera in the same country (Eunica and Siderone) also 

 reproduce the same colours, but with only a general 

 resemblance in the markings. Yet again, in tropical 

 America we have species of Apatura which, sometimes 

 in both sexes, sometimes in the female only, exactly 

 imitate the peculiar markings of another genus (Hetero- 

 chroa) confined to America : here, again, neither genus 

 is protected, and the similarity must be due to unknown 

 local causes. 



But it is among islands that we find some of the most 

 striking examples of the influence of locality on colour, 

 generally in the direction of paler, but sometimes of 



