BRADLEY M. PATTEN 457 



The reactions of animals thus partially blinded were measured in 

 terms of angular deflection from an initial path of locomotion. Meas- 

 urements obtained under anterior, lateral, and bilaterally balanced 

 illumination were compared with measurements made on normal ani- 

 mals under the same conditions of illumination. The change from the 

 normal reaction induced by covering a photoreceptor was taken as an 

 index of the effectiveness of the receptor prevented from functioning. 



By comparing the values of the changes from normal reactions pro- 

 duced by the elimination of the several receptors, their relative effec- 

 tiveness is approximated as median eyes : lateral eyes : cutaneous 

 sensitive areas : : 1 : 1.6:2.2. 



All animals in which the receptive mechanism was rendered func- 

 tionally asymmetrical exhibited, when subjected to bilaterally bal- 

 anced illumination, deflections toward the side which had been made 

 less sensitive. In a series of measurements made on animals in ten 

 different conditions of asymmetry the amplitudes of the deflections 

 were proportional to the degree of unbalance which had been produced 

 in the photosensitive mechanism. 



Animals in which the receptive mechanism was reduced but left in a 

 symmetrical condition maintained an undisturbed balance of reac- 

 tion when subjected to equal, opposed lights. Under lateral or an- 

 terior illumination the rate of attaining a new direction of orientation 

 was reduced in proportion to the extent of the interference with the 

 receptive mechanism. 



The reactions of symmetrically and asymmetrically blinded scor- 

 pions indicate that orientation is attained and maintained by a trans- 

 mission of impulses to the muscles of locomotion which is proportional 

 bilaterally to the excitation of the symmetrically located photo- 

 receptors. 



In their effect on orientation the three pairs of receptors are com- 

 pletely coordinated. Orientation depends upon bringing the excita- 

 tion of the receptive mechanism as a whole into bilateral equilibrium, 



BIBLIOGRAPHY. 



1. Patten, B. M., /. Exp. ZooL, 1917, xxiii, 251. 



2. Borner, C, Zoologica, 1904, xvii, No. 42, 1-174. 



3. Patten, B. M., Science, 1915, xli, 141. 



