CHAPTEE II. 



COLOEATION AFFECTED BY THE ENVIRONMENT. 



There are nmnerous cases where the coloration of an animal 

 appears in part to be due directly to the influence of the 

 surroundings, and to have no possible relation to natural 

 selection. I shall reserve what is probably the most striking 

 instance of this — viz., the fauna of caves — to the last, and 

 commence with some other cases. 



The Scarlet Ibis of South America is frequently exhibited 

 alive at the Zoological Society's Gardens. It invariably 

 happens that the brilliant colour fades in captivity, and 

 becomes much duller as well as paler. Such a change does 

 not happen with all birds, and cannot therefore be set down 

 at once to insufficient food or neglect of any kind. It may 

 depend upon the nature of the food, or upon temperature ; 

 many other causes might be suggested, but the real cause is 

 not certainly known. 



Such differences of colour, due to obscure causes, are also 

 frequent in nature ; they give rise to " local varieties," which 

 are familiar enough to entomologists. 



Local Colour Varieties. 



The Isle of Man produces a small dark varietj- of the 



common Tortoiseshell butterfly. Mr. J. Jenuer "Weir has 



discovered that in the Shetland Islands the Ghost Swift 



{Hepialus humiili) has a tendency to lose the secondary 



