REACTIONS OF WHIP-TAIL SCORPION TO LIGHT 



261 



The measurements given in table 3 were made on the reac- 

 tions of animals placed heading away from the source, in a 

 horizontal beam of light of 120 candle meters intensity. They 

 show perhaps more clearly than either of the preceding sets of 

 measurements the accuracy of alignment with the rays of light, 

 which we may expect to find in this form. The individual trials 

 vary rather widely to right or left of the theoretical response. 



TABLE 3 

 Reactions of Mastigoproctus to posterior illumination of 120 candle meters. 



The 



but the character of the reaction is never in doubt, and the 

 average of a mmiber of trials conforms very closely to the 

 theoretical reaction. 



The reactions which showed least variability were those, ob- 

 tained by subjecting the animals to bilateral stimulation by 

 equal opposed rights. Table 4 gives the measurements in de- 

 tail. That the variability of these reactions is less than that 

 under any other conditions is, in all probability, due to the fact 

 that in balanced bilateral illumination the shading of the 

 photoreceptors by the animars own body is reduced to a 

 minimum. 



