152 



THE WATERS OF THE EARTH 



have learned some of the chief physical properties of water, 

 and so perhaps we can understand the different effects that 

 water has had upon the development and activities of 

 living things. Some water animals move about easily to 

 get their food, but others have it brought to them in solution 

 and so obtain it without muscular effort. The air that they 

 breathe is in solution and they cannot as easily obtain a 



large quantity of it as 



can the land animals. 

 Since the energy of all 

 animals depends upon 

 the amount of oxygen 

 they use in their bodies, 

 the water animals are 

 generally less energetic 

 than the land animals. 

 Since they also have 

 such an easy time in 

 moving or floating about 



to get the things they need they have not developed as 

 high organisms as the land animals. 



Ocean Waters. The oceans which cover almost three 

 fourths of the earth's surface are the inexhaustible reser- 

 voirs from which come, directly or indirectly, the waters of 

 rivers and lakes, of wells and springs, and the moisture of 

 atmosphere and soil. 



Experiment 71. If ocean water can be obtained, boil down 

 about a pint of it in an open dish. Taste the residue. What is 

 the principal constituent of this residue ? 



There is probably no water on the surface of the earth 

 which is absolutely pure. All ordinary water has come in 

 contact with some substances which it could dissolve. 



CORALS 



Fixed animals whose food is brought to 

 them in solution by the ocean currents. 



