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 

 animals 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 ; 

 animals use the munitions which plants manu- 

 facture. 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 



