2 AFRICAN NATURE NOTES CHAP. 



closely certain species of butterflies when resting 

 with closed wings in shady forests resemble dead 

 leaves, or moths the bark of trees. Birds too, 

 especially those which nest on the ground, often 

 harmonise with their surroundings in a most mar- 

 vellous way. 



In the open treeless regions within the Arctic 

 Circle, as well as on bare mountain ranges, nearly all 

 the resident species of animals and birds turn white 

 in winter, when their whole visible world is covered 

 with an unbroken mantle of pure white snow, and 

 become brown or grey during the short period of 

 summer. 



In treeless deserts again within the tropics, 

 where the rainfall is very scanty and the climate 

 excessively hot and dry, with intense sunlight 

 throughout the year, all resident living organisms, 

 mammals, birds, reptiles, and insects, are found to 

 be of a dull coloration which harmonises in the 

 most wonderful way with the sandy or stony soil on 

 which they live. It is also very often the case that 

 animals which live in forests where the foliage is 

 not too dense to allow the sun to penetrate are 

 spotted or striped, whilst those which live in really 

 thick jungle or amongst deep gloomy ravines are of 

 a uniform dark coloration. 



Now a most interesting question arises as to 

 the true causes which have brought about the 

 extraordinary variations of colour to be seen in 

 living organisms inhabiting different parts of the 

 world. 



It is, I believe, the general opinion of modern 

 naturalists that, putting aside cases where brilliant 

 colours may have been produced amongst birds and 

 insects by the action of the law of sexual selection, 

 the coloration of all living organisms is protective, 

 "serving," as that distinguished naturalist Mr. 

 Alfred Russel Wallace puts it, when discussing the 



