REACTIONS OF WHIP-TAIL SCORPION TO LIGHT 267 



It was found impracticable to measure the reactions to light 

 of less than 0.16 candle meters. Below this intensity, hght did 

 not have kinetic effect sufficient to induce locomotion of an 

 extent justifying quantitative treatment. As far as extended 

 locomotion is involved, we may say that the threshold intensity 

 for the kinetic effect of hght is about 0.16 candle meters. The 

 fact that the responses were invariably negative to all inten- 

 sities which induced locomotion, together with the fact that a 

 reaction practically as great as the average reaction to an illu- 

 inination of 120 candle meters, was induced by illumination as 

 low as 1.18 candle meters, showed clearly that no comphcations 

 due to the comparatively small changes of intensity met with 

 under the experimental conditions need be anticipated. 



DISCUSSION 



The way in which the experimental work with normals animals 

 was planned as a basis for future investigations concerning the 

 photoreceptors of the same form has already been outlined. 

 Further consideration of the data from this point of view may 

 more profitably be taken up at a later time in connection with the 

 proposed experiments. There are, however, certain phases of 

 the reaction measurements presented above, which are of in- 

 terest in regard to methods of orientation. Without unduly 

 adding to the already lengthy discussions of this problem, atten- 

 tion may be called to some points that appear significant. 



As to the precise nature, or even the general method of opera- 

 tion of the reflex mechanisms involved in orientation, there is 

 considerable difference of opinion. The phenomena recorded 

 and the animals studied are extremely varied. 'Blanket expla- 

 nations' have so far led only to personal animosities. There is, 

 as always, helpfulness in a clearly formulated, and frankly ten- 

 tative, working hypothesis, but particularly is there need of 

 careful work on specific problems, carried out from an unpreju- 

 diced point of view, and accompanied by non-controversial 

 analysis. In the following consideration of the orientation of 

 Mastigoproctus, I have earnestly endeavored to throw aside pre- 

 conceived ideas and approach the problem with an open mind. 



