54 MAN AN ADAPTIVE MECHANISM 



Venus' fly-trap thus evinces just as much power 

 of perception and discrimination as is shown by the 

 amoeba; indeed, almost as much as is exhibited by 

 many highly differentiated organisms, such as the 

 frog, for example. The fly-trap catches flies, eats 

 and digests them and ejects the refuse. The frog 

 does the same, responding to the adequate stimulus 

 of the sight of a fly as the fly-trap responds to its 

 touch. Both the frog and the fly-trap catch insects 

 by comparable motor mechanisms. Each depends on 

 an adequate stimulus for the excitation of the mechan- 

 ism as a result of which stored energy is set free to be 

 manifested in the fly-catching reflex. Each then di- 

 gests and assimilates the caught insect and when hun- 

 gry catches another insect. 



If the reactions of the human organism be reduced 

 to their simplest terms, probably none will be found 

 more intricate than this food-catching reaction of 

 Venus' fly-trap and the frog. The principal difference 

 between these three living mechanisms is rather a differ- 

 ence in the range of activation by environment, resulting 

 in the frog and in man in a larger number of reactions 

 which in turn involve more complex effector mech- 

 anisms than are possessed by the fly-trap. Each reac- 

 tion of man doubtless has more component parts than 

 each reaction of Venus' fly-trap, just as a large 

 house contains more bricks than a small house. The 

 most complex machine ever invented by man looks 

 like a grotesque monster to the savage ; yet its com- 

 plex movements are compounded of the two simple 

 movements of translation and rotation. 



