244 BRADLEY M. PATTEN 



In the subsequent theoretical discussion, the data have been 

 somewhat rearranged according to the point under consideration. 

 They afford (1) the possibiUty of constructing a curve of reactive- 

 ness to differential bilateral stimulation; and (2) a means of 

 arriving at several facts of interest in connection with theories 

 of orientation, because the method of light control gave an op- 

 portunity to measure the simultaneous responses of opposite 

 sides of the same animal to equal stimuli or to stimuli of known 

 differences of intensity. 



The constancy of the angular deflection at a given intensity 

 difference (table 5) even though the absolute intensity of the 

 lights was varied from one to five glowers, strongly suggests that 

 the response follows the principle of the Weber-Fechner Law. 

 A consideration of this phase of the reactions, however, has 

 been reserved until further experiments can be made. 



DISCUSSION 

 1. The scale of reactiveness 



a. Determination. From the data already presented a scale 

 of reactiveness covering the special conditions of these experi- 

 ments may be determined for the blowfly larva. It has been 

 shown, that under equal opposed lights, there is no deflection 

 toward either side in the aggregate response, and that if the 

 intensities on opposite sides of the animal are made unequal, a 

 deflection appears which becomes progressively greater as the 

 inequality of the lights is increased. Apparently the relative 

 difference of intensity determines the amount of the deflection, 

 for it will be seen by referring to table 5 that the deflection re- 

 mains practically constant for the five different absolute intensity 

 determinations made at each of the percentage differences from 

 equality to 50 per cent. The average of the five absolute in- 

 tensity determinations at a fixed relative difference of intensity 

 would therefore represent very accurately the aggregate response 

 at the given ratio and the value of the average as determined 

 for each percentage difference between the lights may be used to 

 locate points on a curve which may be regarded as the blowfly 



