REACTIONS OF NECTURUS TO STIMULI THROUGH SKIN 99 



could be suddenly thrown on different regions of the body 

 through a hole in the screen, three-eighths of an inch in diam- 

 eter. Three individuals were used for this experiment 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 following behavior 

 noted. The reactions observed agree with those of Pearse ('10, 

 p. 169) who performed similar experiments with Necturus. 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. The various regions of the body exhibit great varia- 

 tion in the time between stimulation and response. The reac- 

 tion times of the regions subjected to the ray of light are shown 

 in table XXII. 



TABLE XXII 



The Reaction Times in Seconds of Various Regions of the Body 



to Light, 144 C. M. 



As Pearse ('10, p. 170) found the head most sensitive in 

 normal Necturus while the tail was most sensitive in individuals 

 with eyes removed, the greater sensitiveness of the head is 

 due undoubtedly to stimulation received through the eye. 



When the eye only was stimulated by a ray of light (144 

 CM.) through a hole in the screen one-eighth of an inch in 

 diameter, each animal moved away from the light in about 

 thirty seconds, thus indicating the greater sensitiveness of the 

 eye over any other region of the body. 



As Pearse ('10) says: "It is evident that Necturus is nega- 

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

 Both the eyes and skin are photoreceptors, and the stimulation 

 of either brings about negative reaction." 



