Spatially Determined Reactions 177 



(a) They might be due to the "pull" of a force 

 upon the passive body of an animal. In the case of 

 gravity or of a current of wind or water, if one part 

 of the body were heavier or offered , more surface to 

 the force, the position assumed could be explained with- 

 out supposing any activity 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. If it acted through symmetrically placed 

 sense organs, awareness of the direction from which the 

 force operated might be present. 



(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 in- 

 volved, there is no reason to suppose the occurrence of any 

 conscious accompaniment, other than the possible un- 

 pleasantness connected with that reaction. 



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



