396 The Outline of Science 



between Birds and Reptiles, the one group warm-blooded, con- 

 spicuously active, and gloriously beautiful, the other cold- 

 blooded, often sluggish, but perhaps also beautiful in their way. 

 What kinship can there be between the falcon in the sky and the 

 lizard on the wall? The student of comparative anatomy answers 

 that the evidences of similarity are overwhelming : bone by bone 

 the two creatures are built up on a plan that is certainly to a very 

 great extent the same, however much the final products may 

 be modified and adapted. Without much preliminary study of 

 anatomical structure, these points might be difficult to apprehend 

 and appreciate, and we cannot discuss them here; we must ac- 

 cept the verdict of the experts, and admit that birds are the 

 descendants of a reptilian stock not necessarily of any present- 

 day group of reptiles, but rather of a common ancestor in the 

 immensely remote past. Just one simple point of similarity 

 between the two groups may be mentioned, the fact that both lay 

 eggs, and eggs which are indeed closely alike in several respects. 



The Dawn of Bird-Life 



We may imagine the ancestral forms as small lizard-like 

 animals, making the first beginnings of the kind of life which 

 we see to great perfection in the birds of to-day. Real power 

 of flight would at first be absent among these early ancestors, but 

 we may think of it as foreshadowed by a great power of leaping 

 from branch to branch in the trees of the primeval forest, where 

 these far-off ancestors of our birds had taken refuge from their 

 terrestrial enemies. We may picture them as making the most of 

 their arboreal haunt, probably using holes in the tree-trunks in 

 which to hide and to lay their eggs, and gradually developing a 

 greater and greater agility in moving about above ground in 

 search of food, and in escape from such enemies as were still able 

 to molest them. 



This mode of life would tend, generation after generation, 

 to produce strong propelling hind-limbs, together with fore-limbs, 



