Holmes, The Reactions of Ranaira to Light. 339 



if different areas of the compound eyes have special connection 

 with particular sets of muscles such that when a given area is 

 stimulated the muscles are set in action which bring about a 

 particular attitude of the body. 



We should bear in mind the possibility of interpreting the 

 phototaxis of Ranatra as due to the fact that the light is sought 

 because the insect derives from it an agreeable stimulus. We 

 might regard the creature as so constituted that it derives 

 pleasure from light and reacts toward it so as to get as much of 

 this stimulus as psssible. Its behavior would then come under 

 the head of what Baldwin calls the " circular reaction." The 

 movements of the head and body would be interpreted, according 

 to this conception, as efforts to place the body in such a posi- 

 tion that it can receive more of the desired stimulus. What- 

 ever the position of the light Ranatra reacts towards it so as to 

 place the upper side of the head more nearly at right angles to 

 the direction of the rays. Both the head movements and the 

 swaying movements of the body conspire to this end. And in 

 this position it is probable that more light is received by the 

 eyes than in any other. 



Whatever may be the explanation of the process in physio- 

 logical terms, it is evident that animals perform many actions 

 simply because they derive pleasure from so doing. Such 

 actions are, I am inclined to believe, not quite the same as 

 simple reflex acts, even in such a creature as Ranatra. Simple 

 reflex acts may, however, be accompanied either by pleasure or 

 by pain, although neither of these states nor their nervous 

 correlates determines the nature of the reaction. But in most 

 cases of the pleasure-pain response the character of the nervous 

 analogue of these states somehow determines whether move- 

 ments producing them shall be continued or inhibited. Move- 

 ments which bring agreeable stimulation are persisted in, while 

 those which produce painful effects are checked. If any stimu- 

 lus brings a pleasant sensation an animal is apt to make efforts to 

 get more of that stimulus. If the creature possesses any power 

 of association, movements bringing an increase of the stimulus 

 are repeated and come to be performed with ever increasing 



