272 BRADLEY M. PATTEN 



ing of movements out of alignment by the operation again of 

 change of intensity. Certain data obtained in other experi- 

 ments than those under balanced illumination bear on these 

 points. The fact that when animals are moving under the 

 stimulation of light from above the locomotion is aimless, and 

 characterized by frequent changes of direction, would seem to 

 indicate that the tendency to continue locomotion in a given 

 direction is a factor which is so easily overcome that it is not 

 sufficient to account for extended locomotion in a given direc- 

 tion. The same conclusion is strengthened by the haphazard, 

 and non-persistent locomotion exhibited by totally blinded 

 scorpions when induced to move by mechanical stimulation. 

 While the tendency to continue locomotion in a definite direction 

 is not sufficient of itself to account for an accurately main- 

 tained orientation, it might be contended that any radical change 

 in the direction of crawling would produce changes of intensity 

 which would throw the animal back into orientation. In the 

 reactions of Mastigoproctus under balanced illumination no 

 wide or sudden variations of direction occurred which would 

 produce the necessary changes of intensity. Inasmuch as the 

 frequent changes in direction characteristic of the animals' 

 locomotion under non-directive stimulation do not appear under 

 bilaterally balanced illumination, it is only reasonable to con- 

 clude that there is a factor present which over-rides any 'spon- 

 taneous' tendency to change direction, or any minor stimuli 

 encountered in locomotion. The very fact that variations in 

 direction do not occur, precludes the operation of changes of 

 intensity as the factor effective in the maintenance of orientation. 

 On the other ha;nd it is quite logical to attribute the absence of 

 variations from the established direction of locomotion to the 

 directive effect of light of constant intensity. 



The unbalanced reactions induced by blackening one eye are 

 also difficult to explain if we deny the effectiveness of con- 

 stant intensity as a stimulus. Neither right nor left photo- 

 rective systems are subjected to a series of intensity changes 

 when asymmetrically blinded animals are subjected to balanced 

 illumination. It is hardly possible to explain the curved path 



