THE FACTOKS OF EVOLUTION 161 



vantage to it but a distinct disadvantage. A great white lump 

 cowering on the dark branches would be at once detected, 

 while its dark fur is but with difficulty distinguished from the 

 trunk and branches. 



Eemarkable instances of colour-adaptation are offered by 

 many animals of the temperate zones, whose covering assumes 

 an appearance which differs with the different seasons of the 

 year. We need only recall the case of the ermine, whose winter 

 fur is much sought after ; the mountain hare, and the ptarmigan. 

 Even the Arctic fox and the great white snowy owl assume in 

 summer a darker hue. Our common weasel, in the summer 

 of a simple brown colour, changes its fur in the autumn and 

 becomes gradually snow-white. It is remarkable that in the 

 southern parts of Europe, where there is little snow, the weasel 

 retains its reddish-brown summer fur throughout the winter. 



Just as in the Arctic regions and on the mountain tops the 

 white colour predominates among animals, so inhabitants of 

 deserts and jungles have chiefly a yellow or brownish-yellow 

 colour. The king of the animals is yellow, like the little desert 

 fox or its prey, the jerboa. The ground-colour of the tiger 

 is a yellow-brown, and the black stripes make it still more 

 difficult for him to be perceived in the jungle. This colour- 

 arrangement of dark stripes or spots on a yellow ground is found 

 in numerous animals of the Tropics, for instance, the zebra, 

 giraffe, okapi, leopard, panther, and gepard. In all these cases 

 we are confronted, according to the opinion of most investigators, 

 with an effective protective colouring. 



Numerous instances are found among the lower animals, 

 among others, the sand-coloured vipers, the cobras, the geckos, 

 lizards and numerous species of insects, in particular the many 

 locusts to be found in desert regions. It might be objected that 

 the locust cannot be regarded as a well chosen instance because 

 of its scarlet under-wings, as there could scarcely be anything 

 more unsuitable or unsafe than these red wings which actually 

 attract the eyes of birds afar to the welcome food. Nevertheless 

 this arrangement grants to the locust ample protection. It is 

 true that the birds are attracted by the striking colour and at once 

 give chase, but no sooner do they approach the locust than the 

 insect folds its wings and disappears as if the earth had swallowed 

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