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 with- 
out 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 
accustomed 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 out- 
going tide. 
The Purse Sponge (Grantia compressa) 
