NATURAL SELECTION 



which occasionally show its blood-relationship 

 with the leopard and tiger, we more often meet 

 with colours not paralleled among the wild 

 species ; now and then we see cats which are 

 coal-black or snowy white. Cows, horses, sheep, 

 dogs, and fowl furnish parallel examples. Thus 

 too we may understand why the sable and the 

 Canadian woodchuck retain their brown fur 

 during the winter ; for the one can subsist on 

 berries, and is far more agile than any of its 

 foes, while the other lives in burrows by the 

 river-side and catches small fish that swim by in 

 the water. And thus we may understand why 

 it is that in the case of birds which build open 

 nests, the female is dull coloured like the nest ; 

 while on the other hand, the females of birds 

 which build dorhed nests are often as brightly 

 coloured as the males. 



Turning now to the insect world, we find a 

 vast abundance of corroborative proof. Among 

 the tiger-beetles examined by Mr. Wallace in 

 the Malay islands, those which lived upon wet 

 mossy stones in mountain brooks were coloured 

 velvet green ; others, found for the most part on 

 dead leaves in the forest, were brown ; others 

 again, " never seen except on the wet mud of 

 salt marshes, were of a glossy olive so exactly 

 the colour of the mud as only to be distinguished 

 when the sun shone,'' by casting a shadow. 

 "In the tropics there are thousands of species 



35 



