152 MODIFICATIONS OF BEHAVIOR 



but carry the process down the scale of life and it begins to 

 take on the character of other organic regulations such as we 

 find in the tissue cells of our own bodies; for even there the 

 intake and assimilation of nutriment is regulated as in free 

 organisms. In none of the animals we have described is 

 there evidence of intelligence in the selection of food. The 

 choice made is more readily explained in terms of what 

 Bohn calls differential sensibility. The organism is so con- 

 structed that it responds to certain kinds of stimuli in one 

 way and to other kinds of stimuli in a different way. But it 

 also has the faculty of responding to the same stimulus in 

 different ways at different times. Here it may be assumed 

 that the different response is the effect of changes of internal 

 conditions which alter the irritability of the animals. The 

 stimuli set up by the presence of food in the digestive tract, 

 the secretory activity of the cells, the processes of absorption 

 and assimilation going on throughout the body afford a 

 complex of influences affecting the neuro-muscular mechan- 

 ism and naturally modifying its action. 



In the sea anemones, contact tends to set in operation 

 one or the other of two mechanisms one involved in taking 

 in food, the other in its rejection. These mechanisms are 

 mutually inhibitory and often there is a struggle between 

 them resulting in a hesitation or vacillation in the response 

 of the organism. Internal conditions act as a sort of brake 

 on one or the other mechanism and thus change the nature 

 of the response to a particular external stimulus. 



This type of behavior which has often been assumed to 

 indicate consciousness if not intelligence is not anything 

 which cannot be accounted for on the basis of reflex action. 

 It is a type of behavior which is wide spread, in fact probably 

 coextensive with animal life. If it is a criterion of intelli- 

 gence we must assume that all animals are intelligent and 



