152 THE STORY OF BIRD-LIFE. 



the keyhole to serve as a guide thereto : in 

 underground railways the edge of the platform 

 is painted white to make it conspicuous, as are 

 the edges of stairs in dimly-lighted places. 



As to the coloration of the eggs and their 

 form, and the number laid by each bird, we need 

 say but little. 



In colour and coloration — for there is a great 

 difference between these two — there is an immense 

 range and variation. As we have already re- 

 marked, the ancestral bird probably laid white 

 eggs. It is also probable that the majority of 

 those that breed in holes have never at any time 

 laid eggs with coloured shells. Colour probably 

 owes its introduction to two factors : the need 

 for protection from egg-eating enemies, when the 

 general tone of coloration is for the most part of 

 a nature resembling its immediate surroundings ; 

 and the need for protection from the action of 

 the excessive light of the sun's rays. These last 

 have, as is well known, a deleterious effect upon 

 protoplasm or living matter. It is this need for 

 protection from the light that has caused the 

 black skin of the negro. 



The brilliancy and the exquisite beauty of 

 the coloration of eggs cannot be dealt with 

 here. Some eggs, such as those of our common 

 British stalling, wiid-duck, pheasant and heron, 

 are uniformly coloured. Those of the hawks 

 and eagles, the razor-bills and guillemots, the 

 terns and grouse, are beautifully blotched and 

 mottled with black or colours darker than the 

 ground-work : those of the thrushes and red- 

 shanks are spotted. In many buntings the 



