592 RAYMOND PEARL. 



The specimen was ag-nin stirred np in the same way and 

 another series taken, with the following resnlts : 



Specimen in state of 

 excitation. 



Expt. Y. Indifferent responses (trials 



1 to 9 inclusiv^e) 

 Positive responses (trials 10 



and 11) 

 Negative responses (0) 



The positive responses in all these experiments were very 

 definite and characteristic. I have obtained the same results 

 in many other series of experiments, which need not be 

 recorded in detail. The experiments show very clearly that 

 in order for the animal to give positive responses to weak 

 stinn;li it is necessary that it be in an unexcited condition. 

 These resnlts have also an important bearing on the question 

 of the mechanism of the positive response, in that they show 

 conclusively that the reaction does not depend on the stimu- 

 lation of special sense organs located in the head regions 

 alone. 



Weak mechanical stimulation of the dorsal snrface in the 

 middle region of the body is usually without any effect other 

 than the causing of a slight local contraction at the point 

 stimulated. If any specific effect on the whole animal is 

 produced, it is merely a change from the gliding- to the 

 crawling movement^ such as results from strong stimulation 

 in the same region. 



3. Reactions to Stimuli applied to the Posterior 

 Region of the Body. — By '^posterior region of the body '^ 

 I mean that part of the body from the pharyngeal region to 

 the posterior end. This region is not sharply marked off 

 physiologically from the middle region, and it is impossible 

 to say in any given individual at just what level the demar- 

 cation will be found. The physiological distinction between 

 the two regions is founded on the fact that it is possible by 

 unilateral stimulation of the middle region of the body to 

 produce a change in the direction of the movement of 

 the animal as a whole, while in case of the posterior region. 



