190 ADAPTATION 



and complex environment and its peculiar fauna. 

 The blind fishes of Cuba are members of a 

 family of marine fishes, but live in fresh water in 

 eaves of central and w^estern Cuba. They have 

 undoubtedly arisen with the environment in which 

 they now live. The caves are enlargements of 

 rifts in coral reefs. They can be traced from 

 the hills near Matanzas to the shore of Cuba. 

 One of the cracks is seen in the naked coral beach 

 near the Carboneria at the mouth of Matanzas 

 Bay. Another can be traced a little way inland, 

 but a few feet above sea level. The former must 

 contain salt water — the latter certainly contains 

 fresh water. In places similar to the former 

 the nearest marine relatives of the cave blind 

 fishes are found, with eyes. In the latter cave 

 blind fishes are abundant. Evidently the ances- 

 tors of the cave blind fishes have always lived in 

 the crevices in which they now live. When these 

 crevices were below the ocean's surface they con- 

 tained salt water. As the land arose the salt 

 water was gradually replaced by fresh water, to 

 which the fishes as gradually became adapted. 

 The fishes have literally grown up with the 

 country. 



Selective migration, the migration to adapted 

 locations, is the chief factor contributing to the 

 origin of adapted faunas. This factor " change 

 of location" is to the origin of adapted faunas 

 what the " change of function " is to the origin of 

 adaptive structures. 



