The Problem of Orientation 79 



described are like those of such a hypothetical or- 

 ganism. 



Whatever be the part played by the indirect meth- 

 ods of orientation which have just been discussed, 

 it is evident that very many animals orient them- 

 selves by turning directly toward or away from the 

 source of the stimulus. In fact this might be said 

 to be the typical method for symmetrical organ- 

 isms, and it has been shown to apply to several that 

 are asymmetrical in structure also. Many forms 

 will accurately follow a source of light, changing 

 their direction promptly and without any preliminary 

 trial movements whenever the position of the light 

 is changed. The existence of such behavior is not 

 of course proof of any particular theory of the 

 mechanism of orientation. It is as consistent with 

 the view that light is followed through deliberate vo- 

 lition, or through curiosity as Romanes once sug- 

 gested, as it is with the reflex theory. The latter 

 interpretation has the principle of Morgan in its 

 favor which is to the effect that "In no case may 

 we interpret an action as the outcome of the exer- 

 cise of a higher psychical faculty if it can be inter- 

 preted as the outcome of one which stands lower 

 in the psychological scale." But the law of par- 

 simony in any of its forms, and the principle of rf 

 Morgan is one of them, never affords proof; it 

 only creates a certain presumption, and one, too, 

 whose strength varies greatly according to circum- 

 stances, in favor of any given conclusion. 



