444 PHOTOREACTIONS OF WHIP-TAIL SCORPIONS 



The measurements given in Tables I to III are graphically summar- 

 ized in Fig. 3. The circles represent the observation circle of the 

 apparatus, and the groups of arrows the direction of, the lights. The 

 initial position of the animal is indicated by the outline in the center 

 of the circle, and the average path of an animal, based on ten trials, 

 by the radial arrows. On the same figure the average path of travel 

 followed by normal animals, under the same experimental conditions, 

 is indicated by shading. The arrows showing deflections to the right 

 and to the left indicate the courses of animals with the blackening 

 carried out on their right and on their left sides respectively. 



In every one of the ten combinations of eliminations in which the 

 photoreceptive mechanism was left functionally asymmetrical, the 

 deflection appears toward the side made less sensitive. 



Reactions to Balanced Opposed Illumination of Animals Subjected to 

 Symmetrical Interference with the Receptive Mechanism. 



As controls to the experiments in which the receptive mechanism 

 was rendered functionally asymmetrical, measurements were made 

 covering the reactions to balanced illumination of animals which had 

 been subjected to bilaterally symmetrical eliminations of their light- 

 sensitive organs. 



The measurements are summarized in Table IV and represented 

 graphically in Fig. 4. The manner of representation is the same as 

 that in Fig. 3, the shaded area representing the reaction range of nor- 

 mal animals, and the radial arrows the average paths of the experi- 

 mental animals. In none of the cases do the reactions of animals with 

 the photosensitive mechanism left functionally symmetrical vary 

 appreciably from the reactions of normal animals. This series of 

 measurements stands in striking contrast to that of Fig. 3 with which 

 it should be compared. 



Reactions to Lateral and to Anterior Illumination of Animals Subjected 

 to Symmetrical Interference with the Photoreceptive Mechanism. 



While symmetrically bhnded animals showed little or no variation 

 from the normal when subjected to balanced illumination, under lateral 

 or anterior illumination their attainment of orientation was retarded. 



