LAURENS: MONOCHROMATIC LIGHTS. 257 



clamata, which were positive in white hght, when exposed to different 

 colored Hghts obtained by passing white Hght through colored solu- 

 tions, turned away from red light, and moved toward blue light; that 

 they also moved toward green and yellow light, but were not oriented 

 by either. When given the choice between red and green light, which 

 were admitted at opposite ends of a receptacle, the frogs moved away 

 from the red to, or toward, the green. When given the choice between 

 red and yellow, they moved away from red to yellow; and when given 

 the choice between red and blue, they moved immediately toward the 

 blue. 



Reese ( :06) found both Nectunis and Cryptobranchus to be negative 

 to white light, the head of Necturus and the tail of Cryptobranchus 

 being the most sensitive regions. In both of these forms, blue light 

 was found to be more effective in bringing about responses than was 

 red. 



Holmes (:07, p. 349), in discussing the light reactions of frogs, said, 

 "in all animals thus far investigated it is the blue and violet rays that 

 are the most influential in evoking the phototactic response; the 

 effectiveness of the other colors of the spectrum diminishes in order 

 from blue to red. If frogs are placed in a box illuminated through 

 one end with blue light, and through the other with red, they soon 

 gather at the blue end. If they have the choice between yellow and 

 green, they go toward the green; in general it may be said that where 

 they are able to go toward one of two colors of ec^ual intensity they 

 move to the color lying nearest the violet end of the spectrum." 



Eycleshymer (:08, p. 304), while rearing larvae of Necturus, 

 placed strips of black, white, red, yellow, green, and blue paper beneath 

 the glass aquaria in which they were kept. At first, he could observe 

 no "preference" for one color over another, though later he obtained 

 evidence "that by far the highest percentage of larvae were found 

 over the green, whether this was placed on the side of greatest or least 

 diffuse daylight." Decapitated larvae "were most frequently found 

 on the colors in the half of the spectrum toward the violet end." 



Pearse (:10, p. 176) found that the toads Bufo fowleri, and B. 

 americanus were positive in white light, in the eyeless as well as in 

 the normal condition; but, when they were tested in colored lights 

 obtained b}^ passing white light through colored solutions (p. 187), 

 the reactions did not agree with those of normal frogs. When Rana 

 palustris, in the normal condition (p. 189), was tested, blue light was 

 found to be most effective in the production of positive responses, 

 and red the least, with a gradual decrease in effectiveness between 



