192 DARWINISM chap. 



both inconsistent with any other theory than that the white 

 colour of arctic animals has been acquired for concealment, 

 and to that theory both afford a strong support. Here we 

 have a striking example of the exception proving the rule. 



In the desert regions of the earth we find an even more 

 general accordance of colour with surroundings. The lion, 

 the camel, and all the desert antelopes have more or less the 

 colour of the sand or rock among Avhich they live. The 

 Egyptian cat and the Pampas cat are sandy or earth coloiired. 

 The Australian kangaroos are of similar tints, and the 

 original colour of the Avild horse is supposed to have been 

 sandy or clay coloured. Birds are equally Avell protected 

 by assimilative hues ; the larks, quails, goatsuckers, and 

 grouse which abound in the North African and Asiatic deserts 

 are all tinted or mottled so as closely to resemble the average 

 colour of the soil in the districts they inhabit. Canon 

 Tristram, who knows these regions and their natural history 

 so well, says, in an often quoted passage : "In the desert, 

 where neither trees, brushwood, nor even undulations of 

 the surface afford the slightest protection to its foes, a 

 modification of colour which shall be assimilated to that of 

 the surrounding country is absolutely necessary. Hence, 

 without exception, the upper plumage of every bird, whether 

 lark, chat, sylvain, or sand-grouse, and also the fur of all the 

 smaller mammals, and the skin of all the snakes and lizards, 

 is of one uniform isabelline or sand colour." 



Passing on to the tropical regions, it is among their 

 evergreen forests alone that we find Avhole groups of birds 

 whose ground colour is green. Parrots are very generally 

 green, and in the East we have an extensive group of green 

 fruit-eating pigeons ; while the barbets, bee -eaters, turacos, 

 leaf- thrushes (Phyllornis), white -eyes (Zosterops), and many 

 other groups, have so much green in their plumage as to tend 

 greatly to their concealment among the dense foliage. There 

 can be no doubt that these colours have been acquired as a 

 protection, when we see that in all the temperate regions, 

 where the leaves are deciduous, the ground colour of the 

 great majority of birds, especially on the upper surface, is a 

 rusty brown of various shades, well corresponding Avith the 

 bark, withered leaves, ferns, and bare thickets among which 



n 



