64 Causes of Emigrations 



peculiar breeding conditions has been a factor in the development 

 of terrestrial animals. 



Safety 



Animals have often taken up temporary or permanent refuge in 

 fresh water or on land in order to escape dangers in the ocean. 

 Some littoral animals cannot live below certain levels, or they will 



Fig. 10. Fiddler crabs feed abo. m !, vvater at low tide. Ti 

 enemies in the ocean. 



be devoured by predaceous enemies (Huntsman, 1918a). Estuaries 

 and swamps have been looked upon by some writers (Hesse, 1920; 

 Annandale, 1922) as refuges where primitive and archaic types may 

 persist after they have been driven from the ocean. Examples of 

 animals cited as those which have thus persisted in fresh water are 

 hydras, certain crabs, and ganoid fishes. 



There are marine animals which fear the sea. For example, the 

 fiddler and macrophthalmid crabs which live in the intertidal zone 



