612 RAYMOND PEARL. 



side stimulated quite as promptly and in the same way as 

 does a normal specimen. If now the cut edges A and B (Fig. 

 21^) are stimulated in the same way (a needle may best be 

 used for this) the specimen will always turn towards the 

 stimulus. This can best be brought out by describing a 

 typical case in which a series of fifty stimulations in the 

 regions A and B were made on a favourable individual cut in 

 this way. In thirty-nine of the reactions the animal turned 

 towards the stimulated side. That is, if the stimulus was 

 applied at A the animal turned in the direction of the arrow 

 a ; while if B was the stimulated edge the reaction was in the 

 direction of the arrow b. In eight of the remaining eleven 

 trials the reaction was indifferent. The animal stopped at 



Fig. 20. — Operation diagram. See text. 



stimulation and then started moving straight ahead again, 

 the stimulus evidently having been ineffective so far as 

 special reaction is concerned. In only three cases out of 

 fifty did the specimen turn away from the stimulus. Since 

 it required the greatest cai-e in manipulation to give the 

 stimulus to one cut edge without touching the other side, 

 especially in view of the fact that the animal was moving all 

 the time, it seems very probable that in these three cases a 

 stimulus was accidentally given to the side wliich it was not 

 intended to stimulate. The same general result of turning 



' After tills operation the two parts of the head usually take the position 

 shown in this figin-e after the first spasmodic movements following the opera- 

 tion have ceased. 



