PEARSE. — THE REACTIONS OF AMPHIBIANS TO LIGHT. 169 



ininated from one end in such a way that the light had an intensity 

 of about 220 candle-meters at its centre. Under these conditions an 

 individual usually went at once to the end of the aquarium farther 

 from the light. It then wandered about from one end to the other for 

 some time, but finally came to rest as far as possible from the light. 

 If the lamp was then changed to the opposite end of the aquarium, the 

 animal again moved to the end which was farther from the light and 

 came to rest. 



In order to test the reactions of Necturus to light and shadow, the 

 lamp was moved to the side of the aquarium and a movable screen 

 interposed in such a way that one half of the aquarium was in shadow 

 and the other half in light (220 candle-meters at the centre of the 

 aquarium). Two animals were successively introduced. One of 

 these, after wandering back and forth from one end to the other, 

 came to rest in the shaded end of the aquarium. When the screen 

 was changed to the opposite half, the animal moved again into the 

 shaded area, and this action was repeated for five successive trials on 

 two different occasions. The other individual remained at the side 

 of the aquarium nearer the light, and in two experiments it kept going 

 back and forth from light to shadow for more than one hour. It ap- 

 parently did not avoid the light, but, by comparing the time it spent 

 in the light with that spent in shadow during half an hour, it was 

 found that three-fifths of that period had been passed in the shaded 

 part of the aquarium. The first individual, then, invariably came to 

 rest in the shadow, and the second one, while it continued to move 

 actively, spent somewhat less time in the light than in the shadow. 



The most decisive reactions shown by Necturus were brought about 

 by illuminating a small area at its anterior or posterior end. The 

 apparatus was in the same position as for the experiments just de- 

 scribed, except that a screen was arranged in such a manner that a 

 vertical band of light about five centimeters wide could be suddenly 

 thrown on different regions of the body. Four individuals were used 

 for these experiments and all of them behaved in essentially the same 

 manner. After an animal had remained quiet in the dark for five 

 minutes, it was suddenly illuminated, and a reaction usually took 

 place within a few seconds. When the light fell on the tail, the 

 animal moved forward, but when it was allowed to fall on the head, 

 the movement was usually backward. Since the animals were never 

 tested with the light until they had been quiet in the dark for five 

 minutes, these reactions were without doubt due to the illumination, 

 for they took place within a few seconds of the time when the light 

 was thrown on the animals. 



