THE CONQUEST OF THE DRY LAND 229 



instance, is one of the strongest of all animals. 

 But it is quite different with most of the ani- 

 mals that have found their home in caves. 

 Many of them are infirm, many are weak- 

 eyed, many are nervous and delicate. While 

 we admit that some of the cave animals may 

 have degenerated because they have lived so 

 long in caves, there is much to be said for the 

 view that most of the cave animals took to 

 the caves because they were weakly. This is 

 borne out by the study of animals that have 

 recently become cave-dwellers. 



ARBOREAL LIFE 



Animals owe a great deal to plants. In the 

 long run they depend on plants for food ; ani- 

 mals use the munitions which plants manufac- 

 ture. Plants prepared the earth for animals, 

 making it friendly; they helped to secure 

 moisture and soft hiding-places. They formed 

 a subtle sieve against which animal life has 

 often beat, with the best of results. But one 

 of their crowning benefits was in providing 

 animals with trees to climb on. We some- 

 times use the phrase, "up a tree," to suggest 

 that a man is in a difficult and dangerous 



