Spatially Determined Reactions 153 



on the animal's part. In such a case there would be no 

 reason for thinking of the reaction as conscious. 



(b) The response might be due to the effect of a force 

 acting unevenly upon the two sides of the body, and thereby 

 unevenly affecting the motor apparatus on the two sides, 

 thus causing the animal to turn until the forces acting upon 

 symmetrical points were balanced. This, although involv- 

 ing activity on the animal's part, would not, if the force 

 acted directly on the muscles, suggest any conscious ac- 

 companiment. 



(c) The orientation might take place by a negative 

 reaction on the animal's part to a definite stimulus given 

 when the animal was in any other than the final, oriented 

 position. If gravity were the force in question, the stimu- 

 lus might be the pressure exerted within the body by particles 

 of different density or by the fluid or mineral bodies in a 

 statocyst organ. If the stimulus were light, the organism 

 might be oriented by giving the negative reaction when its 

 head entered a region either brighter or darker than the 

 optimum illumination. In such cases, where the ordinary 

 negative reaction is the only one involved, there is no reason 

 to suppose the occurrence of any conscious accompaniment, 

 other than the possible unpleasantness connected with that 

 reaction. 



(d) rientation to gravity might occur through a special- 

 ized "righting" reaction, given in response either to a stimu- 

 lus within, say, a statolith organ, or, as in the planarian, to 

 the absence of accustomed contact stimulation on one sur- 

 face of the body. The reaction in these cases being a special- 

 ized one, it is possible that a peculiar sensation quality might 

 be involved. 



(e) Orientation might take place through a movement 

 occurring when the position of several stimuli perceived 



