CHAPTER VIII 



CONFORMITY TO ENVIRONMENT 



THE most remarkable characteristic of 

 the living substance is its adaptability. 



It does a great variety of work under 

 the most varying conditions. The simplest one- 

 celled plants and animals live in fresh water and 

 salt, of all degrees of purity or foulness, of 

 varying temperature, impregnated with differ- 

 ent substances. The bacteria go almost every- 

 where. 



Similarly the complex higher animal is contin- 

 ually becoming adapted to new conditions, and 

 varies accordingly. No sooner does a form be- 

 come well established than it begins to attempt, 

 as it were, to adapt itself to live under all possi- 

 ble surroundings. The primitive reptile crept on 

 the ground. Its descendants adapted themselves 

 to live in marsh, jungle, upland, lake, river, and 

 sea. Some flew in the air. They lived on very 

 different kinds of food. This tendency toward 



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