H6 THE EVOLUTIONIST AT LARGE. 



predict with certainty what line of action 

 he will pursue under any given circum- 

 stances. He is, as it were, but a piece 

 of half-conscious mechanism, answering im- 

 mediately to impulses from without, just 

 as the thermometer answers to variations of 

 temperature, and as the telegraphic indicator 

 answers to each making and breaking of the 

 electric current. 



In early life the future butterfly emerges 

 from the egg as a caterpillar. At once his 

 many legs begin to move, and the caterpillar 

 moves forward by their motion. But the 

 mechanism which set them moving was the 

 nervous system, with its ganglia working the 

 separate legs of each segment. This move- 

 ment is probably quite as automatic as the 

 act of sucking in the new-born infant. The 

 caterpillar walks, it knows not why, but 

 simply because it has to walk. When it 

 reaches a fit place for feeding, which differs 

 according to the nature of the particular 

 larva, it feeds automatically. Certain special 



