342 FOUNDATIONS OF BIOLOGY 



tance. Then it again swings .the anterior end around in a 

 circle till it finds a direction from which it receives no 

 more of this chemical; in this direction it swims for- 

 ward. . . . 



"In this way the daily life of the animal continues. It 

 constantly feels its way about, trying in a systematic way all 

 sorts of conditions, and retiring from those that are harmful. 

 Its behavior is in principle much like that of a blind and 

 deaf person, or one that feels his way about in the dark. 

 It is a continual process of proving all things and hold- 

 ing to that which is good." (Jennings.) 



The behavior of Paramecium leaves one with the impres- 

 sion that the animal is largely at the mercy of its surround- 

 ings that the environment rather than the organism itself 

 is the dominant factor, but this is true only to a limited 

 degree. Paramecium is not merely an automaton. Its be- 

 havior is modifiable and, in the long run, is adapted to the 

 usual changes of its surroundings. That the reactions are 

 adequate for the simple life and methods of reproduction of 

 Paramecium is attested by the fact that it is one of the most 

 common and widely distributed animals. 



In such simple beginnings, then, must be sought the largely 

 automatic responses of animals to the exigencies of external 

 conditions, known as REFLEXES and INSTINCTS. Both are the 

 result of inherited nervous structure and therefore may be 

 regarded as inherited behavior just as truly characteristics 

 of the organism as form of body or method of reproduction. 

 And increase in the complexity of life processes has involved 

 a synchronous increase in the number and complexity of in- 

 stincts. The primitive reflexes and instincts of Hydra lead 

 it to seize with its tentacles small organisms within reach 

 and pass them to its mouth: the Earthworm, to swallow 

 decaying leaves as it burrows through the soil: the Crayfish, 



