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PROCEEDINGS OF THE AMERICAN ACADEMY. 



at the edge of the shadow made by the light that passed through the 

 heat screen (a). Thus the greatest open space was away from the 

 light, and, as far as the animal was able to see, the best chance for 

 escape lay in that direction. An individual was not, then, subjected to 

 the same conditions as one placed in a small box having a single 

 opening. It does not seem improbable that any animal with eyes, 

 after being handled and shut up in a small enclosure, would endeavor 

 to escape by the most apparent opening ; and the reactions could not 

 in that case be interpreted as being due to the influence of light alone. 

 The apparatus shown in Figure 2 is not open to such an objection. 



Figure 2. Plan of apparatus in which the reactions of terrestrial amphib- 

 ians to light were tested, a, heat screen filled with water; b, screen for 

 head of observer; c, lamp; h, screen extending to ceiling ; s, s', screen 25 cm. 

 high. 



The method of experimentation was to place an individual at a 

 distance of seventy centimeters from the light (where the intensity 

 was 225 candle-meters) and watch it through a small hole in the screen 

 b, until a definite movement had taken place. After a reaction of this 

 kind, the animal was held for a few seconds outside the screen s, where 

 it could not see the light, in order to eliminate any directive effect 

 produced by that stimulus, and it was then replaced ready for another 

 reaction. To counteract the effects of compensatory movements, the 

 animals were always turned in a clockwise direction between the re- 

 actions, and were placed with the right and left sides alternately to- 

 ward the light, the long axis of the body being at righ£ angles to the 

 direction of the rays. To avoid effects due to fatigue, no more than 



