20 THE HAUNTS OF LIFE 



are stormy days when the waves are literally 

 breakers. There are fresh-water floods from 

 inland, smothering masses of jetsam from the 

 sea, and clouds of wind-driven sand from the 

 beach and the dunes. In the polar regions 

 there are difficulties due to the ice ; in the 

 equatorial regions there are difficulties due to 

 the scorching sun. 



Many problems are presented by the differ- 

 ences between tide in and tide out : animals 

 that have been bathed in water for many hours 

 are left high and dry. Let us look at a few 

 of the solutions. 



All animals require oxygen to keep the vital 

 processes agoing, for there is no living without 

 combustion. Oxygen is required to keep the 

 fire of life burning. Now marine animals find 

 the indispensable oxygen mixed with the water, 

 and seashore water, where there are waves, is 

 very rich in oxygen. But an animal accus- 

 tomed to use the oxygen mixed with the water 

 cannot suddenly change and become able to 

 use the oxygen mixed with the air. This is 

 one of the problems raised by the outgoing 

 tide. 



The Purse Sponge (Grantia compressa) 



