170 PKOCEEDINGS OF THE AMERICAN ACADEMY. 



In order to discover whether the skin of Necturus was sensitive to 

 light or not, the eyes were removed from two individuals and they 

 were then tested by local stimulation as described in the last para- 

 graph. Their reactions were similar to those of animals with eyes 

 except in one particular. The average time which elapsed before the 

 individuals with eyes moved out of the lighted area was shorter when 

 the head was stimulated than when the light fell upon the tail, but 

 the eyeless animals, on the contrary, reacted more quickly when the 

 tail was stimulated. The results with normal animals agree with 

 those of Reese ( : 06, p. 96) in his experiments on Necturus. He 

 ascribed the shorter reaction time for the head to greater sensitiveness 

 in that region, and he believed it to be due to stimulation received 

 through the eyes. The present experiments with eyeless animals 

 give support to his views, as the posterior end of the individuals 

 tested was apparently more sensitive to photic stimulation after the 

 eyes had been excised. The decreased sensitiveness of the head 

 region may, however, have been due to the injury incident to the 

 removal of the eyes, instead of the mere loss of the eyes themselves. 



From the experiments described it is evident that Necturus is nega- 

 tively phototropic and that it comes to rest in shaded areas. Both 

 the skin and eyes act as photoreceptors, and the stimulation of either 

 brings about negative reactions. 



(b) Cryptobranchus allegheniensis. 



The arrangement of the apparatus for the experiments with Crypto- 

 branchus was the same as for those with Necturus. The reactiveness 

 of this species to light was very marked. Seven individuals were 

 placed successively in the middle of the aquarium, the illumination 

 being from one end, whereupon they moved immediately to the end far- 

 ther from the light. When the lamp was carried to the opposite end 

 of the aquarium, they usually changed their position at once and again 

 came to rest in the end farther from the light. In these reactions they 

 were much more responsive than Necturus, though, as Reese ( : 06, 

 p. 94) has observed, they often failed to respond readily after the first 

 few reactions. 



The reactions of Cryptobranchus to conditions of light and shadow 

 were also pronounced. In testing these, half the aquarium was shaded 

 by a screen which was changed from one end to the other at five 

 minute intervals. An individual was placed in the aquarium and the 

 screen changed ten times. It never failed to move at once to the 

 shaded part of the aquarium, and furthermore it rested quietly in 

 the shadow in the intervals between the changes. 



