2 



ROUTES FROM THE SEA 



"PLANTS and animals that have left the ocean to dwell on land 

 or in fresh water have been obliged to acquire new ranges of 

 toleration to certain environmental factors. They have done this 

 chiefly where environment permitted experimental trials without 

 death. On ocean beaches, in estuaries, in marshes and swamps, in 

 temporary pools, in isolated bodies of water in which salinity 

 changes slowly, in soil where sudden changes in temperature are 

 not possible and where desiccation is inhibited, and in a few other 

 situations organisms are ever striving not only to continue to live 

 but also if possible to spread into new types of habitats in which 

 they have not lived before. Migrations from one realm to another 

 commonly take place along the borderlines of territories, where 

 there are more or less gradual or intermittent changes in environ- 

 mental factors. No pelagic marine animal has ever been trans- 

 formed into a land animal. 



Beaches 



On the beaches along the seashore the ebb and flow of the tides 

 brings about a rhythmical change in water level, temperature, and 

 other conditions of environment. Currents and waves transport 

 and beat upon plants and animals and may bring about changes in 

 salinity over a particular area. Plants and animals that live on ocean 

 beaches, attached to the bare faces of rocks, safely ensconced in 

 crevices or burrows, in rock pools, or even swimming in the littoral 



17 



