300 MAN --AN ADAPTIVE MECHANISM 



pattern. In my laboratory, Miss Menten identified the 

 conducting path over which the stimulus apparently 

 travels to the effector mechanism of Venus' fly-trap. 

 (Fig. 77.) Here a response takes place by means of 

 one continuous path of conduction without any break in 

 its entire length. Without a brain or a nervous system, 

 but with the equivalent of nerve fiber in the form of a 

 tissue which contains lecithin-like compounds and salts 

 similar to those in nerve tissue, the plant organism 

 makes a response to an adequate stimulus as specific 

 as are any of the responses made by man. When a 

 fly alights upon the skin of man, it causes a tickling 

 sensation and is immediately brushed off; when it 

 lights upon the hairlike appendages of Venus' fly-trap, 

 it is caught by the motor mechanism of the plant, 

 bathed with digestive fluid and consumed. By an 

 analogous process the same stimulus has caused two 

 similar reactions in vastly dissimilar beings one 

 without a brain, the other with a brain. In one case 

 the stimulus traveled to a central organ where energy 

 was released which in turn activated a specific set 

 of muscles to perform a specific act. In the second 

 case the stimulus traveled directly to the effector 

 mechanism, probably releasing energy along the way. 

 In Venus' fly-trap but one receptor and one effector 

 mechanism has been evolved for but one adaptive re- 

 action. In man many receptor and effector mechanisms 

 have been evolved for numerous reactions in response 

 to numberless stimuli. 



If it were necessary for Venus' fly-trap to catch 

 its food by running instead of by passive attraction, 

 the plant would doubtless have evolved a mecha- 



