EELATIVE STIMULATING EFFICIENCY OF LIGHT 169 



It is to be noted that in the tests in continuous light (fig. 5) 

 stimulation of the butterfly had the effect of making the organism 

 move almost directly toward the weaker source of light, although 

 the illumination in the other beam was four times greater. 

 Even when the animal began a trial facing the stronger source, it 

 eventually turned toward the weaker source. This persistence 

 in turning toward the same source may possibly be due to the 

 fact that in the first five trials it faced the weaker source and in 

 the succeeding trials, although started in each trial in the other 

 direction, it turned in the same direction as that in which it had 

 turned first. This is evident if previous experience may affect 

 the reactions of this insect, as is shown below. 



When the animal started toward the weaker source the nerve 

 impulses aroused by light passed along certain nerves, and during 

 this time the pathways were probably closed to other nerve 

 impulses set up by the stronger light when the insect reached 

 that point where it was exposed to the stronger illumination. 

 If this is true, there is in this case a conflict between stimuli of 

 the same nature, and while the butterfly is reacting to the first 

 it does not react to the second, which may be stronger. This 

 phenomenon is probably similar to that property of higher 

 organisms generally known as " attention." 



A second factor which may influence the direction of the 

 course taken in light from two sources is, as stated above, the 

 previous experience of the butterfly. This is shown very beauti- 

 fully in figure 7. Butterfly 25 was given, in the method de- 

 scribed previously, 10 trials in two beams of continuous light, 

 the illumination in one being 4 times that in the other. The 

 average angle made was +9.6 degrees. Immediately after 

 this the organism was given 10 trials in two beams of equal 

 illumination, the light in one beam being continuous and that hi 

 the other intermittent of a flash-frequency of 30 per second pro- 

 duced by a disk with one-fourth removed. The average angle 

 made in these trials was +16.7 degrees. Then the insect was 

 given 10 more trials in continuous light under the same condi- 

 tions as at first. The average angle made in these trials was 

 +21.6 degrees. Why did the animal at one time make an 



P8TCHOB1OLOQY, VOL. II, NO. 2 



