ANALYSIS OF BEHAVIOR IN LOWER ORGANISMS 31I 



chemical stimulation which it sends forth. The movements leading to 

 loss of the favprable stimulation are changed, the others continued, 

 till the food is found (see p. 247). 



But many animals have developed, in some way, as we have seen in 

 the account of the negative reactions, the power of localizing their reac- 

 tions precisely, so as to move in a certain definite way with relation to 

 the position of the source of stimulation. Let us suppose that such an 

 organism is reached by a favorable stimulus on one side — food, or the 

 optimum temperature. It has the power of turning directly toward this 

 favorable condition — and this, of course, is what happens in many 

 higher organisms. There is the same reason to think that this condition 

 is not primitive that we saw in the case of negative reactions. It may, 

 perhaps, be conceived as derived from behavior through selection of 

 overproduced movements in the way set forth on page 308. The precise 

 reactions shown in the actual taking of food are perhaps derivable in 

 the same way. 



In those animals whose positive reactions are precisely defined and 

 localized, there is, of course, the same evidence that the impulse to change 

 of behavior comes from within and is due to lack or hindrance of the 

 physiological processes, that we find elsewhere. If the metabolic pro- 

 cesses lack material for proper action, the medusa or sea anemone 

 changes its behavior and moves about, even though there is nothing 

 present to which it can react positively. When some object is reached, 

 whether there shall be a positive reaction or not depends again on the 

 state of the metabolic processes. If their state is bad, the animal re- 

 acts positively to almost anything; if fair, the animal reacts positively 

 to substances that will improve them ; if they are in a completely satis- 

 factory condition, the animal does not react positively even to good 

 food. 



Thus with all conditions absolutely favorable there will be no reac- 

 tion, either positive or negative. At the boundary between favorable 

 and unfavorable conditions, the animal moves in such a way as to retain 

 the favorable conditions. This is primitively due to selection from 

 varied movements — all movement leading to less favorable conditions 

 being changed. The "negative reactions" thus seem to furnish in a 

 certain sense the primitive building stones from which the derived posi- 

 tive reactions are constructed. By development of the power of precise 

 localization of reactions, the deirivation of the positive reaction in this 

 manner is in higher animals obscured. The fundamental fact for both 

 positive and negative reactions is that interference with the physiological 

 processes of the organism causes a change of behavior. 



