150 The Animal Mind 



might be upon a piece of inanimate matter. In no animal 

 with a nervous system, probably, is the process quite so simple. 

 The bell of the jellyfish contracts at the point where a stim- 

 ulus, 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 is touched, the animal gives the typical avoiding 

 reaction of darting backward and turning to one side; if 

 the hinder end be touched, it moves forward (211, p. 50). 

 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 (211, p. 52). If strong mechanical stimula- 

 tion 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 

 sets of muscles (316). The earthworm creeps backward 

 if the front half of the body is affected, turns away from 

 a stimulus applied to the side of the anterior end, and creeps 



