40 NATURAL SELECTION It 
Rugby 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 
