PDF - Wallace Online

40 NATURAL SELECTION inEugby School Natural History Society, observes " : Thewood-dove, when perched amongst the branches of its favouritefir, is scarcely discernible ; whereas, were itamong somelighter foliage, the blue and purple tints in its plumage wouldfar sooner betray The it. robin redbreast too, although itmight be thought that the red on its breast made it mucheasier to be seen, is in reality not at all endangered by it,since it generally contrives to get among some russet oryellow fading leaves, where the red matches very well withthe autumn tints, and the brown of the rest of the body withthe bare branches."Reptiles offer us many similar examples. The mostarboreal lizards, the iguanas, are as green as the leaves theyfeed upon, and the slender whip-snakes are rendered almostinvisible as they glide among the foliage by a similar coloration.How difficult it is sometimes to catch sight of thelittle green tree-frogs sitting on the leaves of a small plantenclosed in a glass case in the Zoological Gardens ; yet howmuch better concealed must they be among the fresh greendamp foliage of a marshy forest. There is a North Americanfrog found on lichen -covered rocks and walls, which is socoloured as exactly to resemble them, and as long as itremains quiet would certainly escape detection. Some of thegeckos which cling motionless on the trunks of trees in thetropics are of such curiously marbled colours as to matchexactly with the bark they rest upon.In every part of the tropics there are tree-snakes thattwist among boughs and shrubs, or lie coiled up on the densemasses of foliage. These are of many distinct groups, andcomprise both venomous and harmless genera but almost all;of them are of a beautiful green colour, sometimes more orless adorned with white or dusky bands and spots. Therecan be little doubt that this colour is doubly useful to them,since it will tend to conceal them from their enemies, andwill lead their prey to approach them unconscious of danger.Dr. Gunther informs me that there is only one genus of truearboreal snakes (Dipsas) whose colours are rarely green, butare of various shades of black, brown, and olive, and theseare all nocturnal reptiles, and there can be little doubtconceal themselves during the day in holes, so that the green