REACTIONS OF WHIP-TAIL SCORPION TO LIGHT 269 



increasing the illumination above the threshold of sensitiveness 

 produces a kinetic reaction; the initial reaction may be attrib- 

 uted to change of intensity, but the persistence of the reaction 

 is due to the stimulating effect of light of constant intensity. 



The experiments made to determine the threshold of sensi- 

 tivity, brought out another point with regard to the kinetic 

 effect of light. Near the threshold intensity the locomotion 

 induced by light appeared only after a latent period, and even 

 after it began, was very slow. Increasing the intensity resulted 

 in decreasing the latent period and accelerating locomotion. 

 These results are in line with those obtained on other arthro- 

 pods by Yerkes ('00), Carpenter ('05), and Hadley ('08). We 

 may conclude that the degree of the kinetic response to light is 

 correlated with the intensity of the light. 



As a basis for considering the directive reactions of the whip- 

 tail scorpion we have, then, the facts (1) that light induces 

 locomotion; (2) that hght operates as a stimulus causing loco- 

 motion both through change of intensity and constant intensity; 

 and (3) that the degree of kinetic energy exhibited is correlated 

 with the intensity of the illumination. 



Most of the qualitative observations concerning the orientsr- 

 tion of Mastigoproctus to horizontal light are so closely in line 

 with results already familiar for many negative animals that they 

 may be dismissed with enumeration. 



1. If light of an intensity which induced undirected activity 

 when apphed from above, was allowed to act horizontally, it 

 induced orientation. 



2. The response to a horizontal light applied from behind the 

 animal was locomotion in the direction of the rays of the light. 

 Individually the reactions varied to right or left of the central 

 ray of the beam; collectively they followed the central ray 

 ccurat ely. 



3. Response to light from the side was a deflection away 

 from the light approaching 90 degrees as a maximum. 



4. Response to light from in front was a deflection approaching 

 180 degrees as a maximum. 



