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BRADLEY M. PATTEN 



tions, the theoretically perfect response of 90 degrees an animal 

 must come immediately into orientation without progression, 

 the average response of 65.8 degrees is seen to be remarkably 

 accurate and immediate. 



Table 2 shows the amount of deflection obtained by starting 

 animals directly toward the source of light. Under these con- 

 ditions the maximum response possible would be 180 degrees. 



TABLE 2 



Reactions of Mastigoproctus to anterior illumination of 120 candle meters. The 

 measurements are recorded in degrees of deflection from an initial path of loco- 

 motion. In figure 3, D the same measurements are plotted graphically 



As was the case in the experiments with lateral illumination, 

 the amount by which the experimental measurements under 

 these conditions fall below a theoretically perfect response was 

 due mostly to 'the progression of the animals while they were 

 becoming oriented. It would be po.Svsible to devise a scheme of 

 measurement based on the final orientation which would indi- 

 cate responses apparently nearer the theoretical. For our pur- 

 poses, such treatment would be disadvantageous, for it is the 

 abruptness with which orientation is attained rather than the 

 final accuracy of orientation, which shows the results of slight 

 differences in the effectiveness of the receptive mechanism. 



