174 The Animal Mind 



the point stimulated. This would seem to be the most 

 primitive way of adapting response to the location of a 

 stimulus : the effect is produced just where the force 

 acts, as it might be upon a piece of inanimate matter. In 

 no animal with a nervous system, probably, is the process 

 quite so simple. The beH of the jellyfish contracts at the 

 point where a stimulus, mechanical or photic, is applied; 

 yet although these responses are made when the nervous 

 system is thrown out of function, they occur more slowly, 

 and in the normal animal the nervous tissue is probably 

 involved, while, of course, a long conduction pathway is 

 traversed when, to use a familiar illustration, the baby pulls 

 back its hand from the candle flame. 



2. Paramecium and other infusoria, planarians, the 

 earthworm, and various other animals give us illustrations 

 of movements of the entire body differing according to the 

 point affected by a single stimulus. If the front half of 

 Paramecium be touched, the animal gives the typical avoid- 

 ing reaction of darting backward and turning to one side ; 

 if the hinder end be touched, it moves forward (378, p. 59). 

 On the other hand, it makes no difference in its reactions 

 to stimuli affecting either side of the body ; the turning is 

 always to the aboral side even when the stimulus comes 

 from that direction (378, p. 52). If strong mechanical 

 stimulation be applied to the head end of a planarian, there 

 is a response which seems to belong under type (i) : the 

 head is turned away from the stimulus. If the hinder region 

 is touched, strong forward crawling movements of the body 

 are produced. The positive reaction in the planarian, 

 turning the head toward the stimulus, also suggests type (i), 

 but in reality it has been shown by Pearl to be a far more 

 complex affair than the mere flow of protoplasm at the 

 stimulated point, and to involve the contraction of several 



