40 NATURAL SELECTION in 



Eugby School Natural History Society, observes : " The 

 wood-dove, when perched amongst the branches of its favour- 

 ite fir, is scarcely discernible ; whereas, were it among some 

 lighter foliage, the blue and purple tints in its plumage would 

 far sooner betray it. The robin redbreast too, although it 

 might be thought that the red on its breast made it much 

 easier to be seen, is in reality not at all endangered by it, 

 since it generally contrives to get among some russet or 

 yellow fading leaves, where the red matches very well with 

 the autumn tints, and the brown of the rest of the body with 

 the bare branches." 



Reptiles offer us many similar examples. The most 

 arboreal lizards, the iguanas, are as green as the leaves they 

 feed upon, and the slender whip-snakes are rendered almost 

 invisible as they glide among the foliage by a similar color- 

 ation. How difficult it is sometimes to catch sight of the 

 little green tree-frogs sitting on the leaves of a small plant 

 enclosed in a glass case in the Zoological Gardens ; yet how 

 much better concealed must they be among the fresh green 

 damp foliage of a marshy forest. There is a North American 

 frog found on lichen -covered rocks and walls, which is so 

 coloured as exactly to resemble them, and as long as it 

 remains quiet would certainly escape detection. Some of the 

 geckos which cling motionless on the trunks of trees in the 

 tropics are of such curiously marbled colours as to match 

 exactly with the bark they rest upon. 



In every part of the tropics there are tree-snakes that 

 twist among boughs and shrubs, or lie coiled up on the dense 

 masses of foliage. These are of many distinct groups, and 

 comprise both venomous and harmless genera ; but almost all 

 of them are of a beautiful green colour, sometimes more or 

 less adorned with white or dusky bands and spots. There 

 can be little doubt that this colour is doubly useful to them, 

 since it will tend to conceal them from their enemies, and 

 will lead their prey to approach them unconscious of danger. 

 Dr. Gunther informs me that there is only one genus of true 

 arboreal snakes (Dipsas) whose colours are rarely green, but 

 are of various shades of black, brown, and olive, and these 

 are all nocturnal reptiles, and there can be little doubt 

 conceal themselves during the day in holes, so that the green 



