104 ANIMAL LIFE 



region ; and yet where oxygen has diffused, the 

 darkness is peopled by hungry strays and waifs. 

 Whether in the earth or in the waters the highest forms 

 of each order come to the surface, the lowest are 

 submerged ; and emergence or submergence corre- 

 sponds to plenty or poverty of oxygen. 



This air we breathe has only been reached by 

 epochs of struggle and new departures. The possession 

 of the earth is hardly won. Before the nimble air 

 gave strength and impetus to the conquerors they 

 had to pass the marsh and shore on their landward 

 way. Plants and animals alike have striven for the 

 face of the waters, for the beach, for the marshes, and 

 finally for the air. Man himself carries in his ears 

 an unmistakable sign of his gill-breathing, watery 

 past, and of the depths he has left behind him. Evolu- 

 tion follows the successful quest for oxygen, and there- 

 fore earth has been peopled by the highest communities. 

 The ancient stocks are scattered, some keeping to the 

 beach, some lurking in dens and caves, or, as parasites 

 and messmates, hiding away, degenerate and prolific ; 

 some, such as whales, returning to the waters, where 

 they maintain an unfair supremacy over the uneman- 

 cipated fish. Refugees from the shore and from the 

 surface of the water retire to the depths, and there, 

 at oases in the general desolation, hang out their 

 phosphorescent signal lights. 



Evolution of the respiratory methods of animals. The 

 drama needs elaboration. Its climax the possession 

 of lungs and of a good circulation comes last in the 



