PEAKSE. — THE HE ACTIONS OF AMPHIBIANS TO LIGHT. 171 



The illumination of a small area at the anterior or posterior end of 

 an individual produced the same reactions as in Necturus, but in 

 Cryptobranchus they took place more quickly. 



To test the sensitiveness of the skin to light, the eyes were removed 

 from one individual and it was stimulated alternately on the head and 

 tail by the same method as that used for Necturus. This animal 

 usually responded within a few seconds to such illumination. In a 

 series of fifty reactions it was found that the average time required 

 for the animal to move out of the illuminated area was more than 

 twice as great when the light fell upon the head as when the tail was 

 illuminated in the same manner. The skin of Cryptobranchus is, then, 

 a photoreceptor and the sensitiveness seems to be greater at the pos- 

 terior than at the anterior end. Reese (:06, p. 94) has stated that, 

 even with the eyes present, this species shows the greatest sensitive- 

 ness to light in the caudal region. 



This eyeless individual was strongly photokinetic. It was placed in 

 a flat porcelain dish about a meter below an ordinary gas burner, and 

 after it had been allowed to remain in the dark for about an hour, the 

 gas was suddenly lighted. There was an unfailing response to this 

 illumination within a few seconds, the animal moving restlessly about 

 in the dish. As the light was non-directive, and the animal often 

 remained quiet for hours in the dark, this uniform response to sudden 

 illumination showed this species to be strongly photokinetic. In this 

 respect it was quite different from Necturus, which often did not re- 

 spond to such stimulation for some time, even when the light intensity 

 was 220 candle-meters. 



In summarizing the results of the experiments upon Cryptobranchus, 

 it may be said that it is negatively phototropic, that it comes to rest in 

 shaded areas and is strongly photokinetic. These reactions apparently 

 take place as readily when only the skin is stimulated by light as when 

 the eyes are also affected. 



The terrestrial amphibians were found to be much more satisfactory 

 subjects for experimental work than the aquatic species. Not only 

 was it easier to arrange the apparatus for the land forms, but more 

 accurate results were obtained, as it was possible to orient the animals 

 with a perfectly uniform relation to the light before each reaction. In 

 all the experiments with terrestrial forms the apparatus shown in Fig- 

 ure 2 was used. After this apparatus had once been arranged, it was 

 a simple matter to test one species after another, and to compare the 

 reactions of normal animals with those of individuals without eyes. It 

 will be seen from the figure that the two side screens (/) were placed 



