164 PROCEEDINGS OF THE AMERICAN ACADEMY. 



with meat extract, when he threw a strong beam of light on its back. 

 Reese (:06) found that when only the tip of the tail was illuminated in 

 Cryptobranchus or Necturus, the individuals thus stimulated moved 

 out of the lighted area. 



The reactions brought about by stimulating the eye alone agree, in 

 kind, with those brought about through the skin. Parker (:03 b ) found 

 that frogs in which the skin was covered but the eyes were exposed, were 

 positively phototropic, like individuals in which the eyes had been re- 

 moved. Torelle (:03) made an observation which bears indirectly on 

 the same point. She found that frogs which had one eye covered with 

 black cambric went toward the light at an angle or made circus move- 

 ments with the uncovered eye towards the centre. 



The positive phototropism of amphibians is apparently a reaction to- 

 ward a greater intensity of illumination; or, with the eyes, toward a 

 greater illuminated area. Plateau ('89, p. 88) observed that Rana 

 and Bufo, when placed in a box having two openings, went toward the 

 larger aperture even though it was covered with a grating. Cole (:07) 

 showed that when Acris was placed between two lights of the same 

 quality and intensity but of different areas, it went toward the larger 

 area, but when individuals in which the optic nerves had been cut 

 were placed in the same situation, they went toward either light an 

 approximately equal number of times, liana also showed the same 

 reaction toward the larger area when it was in normal condition. 

 Torelle (:03) found that the direction of the illumination made no 

 difference in photic responses, as frogs went toward the lighter end of 

 a box when the illumination was from below, and Reese (:06) has 

 made similar observations on Cryptobranchus and Necturus. Dicker- 

 son (:06, p. 32) says, " Frogs do not distinguish between a lighted 

 space and a white solid. They will turn toward a white card or 

 paper and try to jump through it, and they may struggle at the im- 

 possible task of working their way into the solid white surface made 

 by the leaf edges of a closed book." 



Torelle(:03) noted that frogs, when they were confined in a small 

 space with an opening above, pointed the head upward toward the 

 opening, and she supposed this to be evidence for the directive action 

 of the rays. Objection may be made to this view on the ground that 

 the opening offers the only opportunity for escape, and the animal, 

 seeing the opening with its eyes, points its head toward it. If she had 

 shown the same reaction with eyeless individuals, the evidence would 

 have been more conclusive. 



The rays toward the violet end of the spectrum are apparently most 

 potent in producing photic reactions, and the rays toward the opposite 



