THE COMING OF THE BIRDS 85 



Ice Age. In the colder regions no ordinary reptile 

 could live. The animal itself was cold-blooded and 

 thinly clad, and it provided no warmth for its eggs or 

 food for its young. In the stress of the struggle that 

 must have followed in the overcrowded warm regions, 

 pioneers with favourable variations were able to 

 survive in more temperate localities. We must not 

 suppose an animal suddenly changing from a three- 

 chambered to a four-chambered heart. Even here 

 gradual development is not so difficult as may be 

 imagined. Some of our reptiles to-day have hearts 

 that are not strictly either three-chambered or four- 

 chambered. There is a sort of effort to get a fourth 

 chamber. 



The feathers are less difficult to understand. They 

 are transformed scales. Look again at the next hen 

 you see, and you will notice that the scales which 

 cover its legs really bring it nearer to the reptile than 

 you had supposed. Examine a feather, and you will 

 see that it is composed of the same material. Feathers 

 are scales lengthened and "feathered," if one may 

 use the expression. The feather as we know it is the 

 outcome of millions of years of an evolution which 

 aimed at combining warmth with lightness. Even 

 the little ArchcEOpteryx, whose remains we have found, 

 does not belong to the Ice Age, but a very long time 

 afterwards. Its feathers are well formed. There 

 must have been myriads of earlier stages, with large 

 heavy scales becoming gradually more "feathery." 



