48 LIGHT AND TH'E BEHAVIOR OF ORGANISMS 



directly toward or away from the source of stimulation, 

 without anything in the nature of preliminary trial move- 

 ments." Reactions which show a definite relation to the 

 localization of the stimulus '' include perhaps the greater 

 number of the directed movements of the organisms." 



It is evident, judging from these quotations, that Jen- 

 nings does not hold that all organisms orient by means of 

 avoiding reactions. He does not oppose the idea of direct 

 orientation by means of differential response to localized 

 stimulation. He opposes the view that this is the only 

 method of orientation and the view that orientation is 

 caused by the direct effect of the external agent on the 

 locomotor organs. He holds that the power of differential 

 response to localized stimulation is derived from other 

 methods of reaction, as described in the following quota- 

 tions and abstracts (1906, pp. 306-308): "First we have 

 the simple phenomenon that when a portion of an organism 

 is stimulated this portion may respond by contraction, 

 extension, or other change of movement." Such local 

 reponses to local stimulation we find in Amoeba, Hydra, 

 Sagartia, flatworms and many other soft-bodied animals, 

 and even in man when the electrode of a batter}^ is applied 

 directly over a muscle. " In many cases we find that the 

 relation of the movement to the source of stimulation is 

 brought about indirectly through selection from among 

 varied movements. The organism tries moving in many 

 directions, till it finds one in which there is no stimulus to 

 further change. ... In still other cases the reaction shows 

 a definite relation to the localization of the stimulus, yet 

 it is not due to local reaction of the part stimulated, 

 nor is it brought about by trial. If an infusorian is stimu- 

 lated at the anterior end it swims backward; stimulated 

 at the posterior end it swims forward. Both these move- 

 ments are reactions of the entire organisms, all the motor 

 organs of the body concurring to produce them; they are 

 not produced by local reactions of the organs at one end 

 or the other. . . . Such behavior apparently represents 



