382 TROPICAL NATURE 



here, not only is sexual selection out of the question, but 

 the need for recognition and identification by others of the 

 same species seems equally unnecessary. We can then only 

 impute this variety to the normal production of colour in 

 organic forms when fully exposed to light and air and under- 

 going great and rapid developmental modification. Among 

 more perfect animals, where the need for recognition has been 

 added, we find intensity and variety of colour at its highest 

 pitch among the South American butterflies of the families 

 Heliconidse and Danaidse, as well as among the Nymphalidse 

 and Erycinidse, many of which obtain the necessary protection 

 in other ways. Among birds also, wherever the habits are 

 such that no special protection is needed for the females, and 

 where the species frequent the depths of tropical forests, and 

 are thus naturally protected from the swoop of birds of prey, 

 we find almost equally intense coloration, as in the trogons, 

 barbets, and gapers. 



Local Causes of Colour-development 



Another real, though as yet inexplicable cause of diversity 

 of colour is to be found in the influence of locality. It is 

 observed that species of totally distinct groups are coloured 

 alike in one district, while in another district the allied 

 species all undergo the same change of colour. Cases of this 

 kind have been adduced by Mr. Bates, by Mr. Darwin, and 

 by myself, and I will here give the more curious and important 

 examples which I have been able to collect. 1 



The Influence of Locality on Colour in Butterflies and Birds 

 Our first example is from tropical Africa, where we find 

 two unrelated groups of butterflies belonging to two very 

 distinct families (Nymphalidse and Papilionidse) characterised by 

 a prevailing blue-green colour not found in any other continent. 2 

 Again, we have a group of African Pieridse which are white 

 or pale yellow with a marginal row of bead-like black spots ; 

 and in the same country one of the Lycsenidae (Leptena 



1 These were first given in my Address to the Biological Section of the 

 British Association at Glasgow in 1876. 



2 Romaleosoma and Euryphene (Nymphalidae), Papilio zalmoxis and 

 several species of the Nireus-group (Papilionidae). 



