QUANTITATIVE DETERMINATION OF LIGHT REACTIONS 235 



TABLE 2 



Equality. Foxir-glower intensity 



conform exactly to the theoretical response. Out of the forty 

 trails, only three show no deflection whatever. But the total 

 plus and minus of each larva comes near to cancelling, and the 

 average of the four trails of a larva is close to zero degrees de- 

 flection. The average response of the whole set corresponds 

 almost exactly to the theoretical response, the average deflec- 

 tion from the perpendicular being only —0.025°. This is aston- 

 ishingly accurate when one considers that a degree on the pro- 

 tractor of 7.6 cm. radius used in measuring the trails was only 

 about 1.5 mm. 



The striking results of table 2 were confirmed by similar results 

 at various intensities of the equal beams, the details of which 

 appear later in the paper. The immediate significance of these 

 results is two-fold. The consistent closeness of the average trail 

 to the perpendicular, and the equal distribution of the trails on 

 either side of it, indicate that the method of individual measure- 

 ment has effectively eliminated asymmetry and placed the differ- 

 ent individuals on a uniform basis for comparison. The close 

 conformity of the aggregate response to the theoretical response, 

 when the lights are of equal intensity, makes a wxll grounded 

 point of departure for a whole series of experiments with opposed 



