256 bulletin: museum of comparative zoology. 



ferred" to blue. He did not experiment with blinded frogs. With 

 the toad, Bufo vulgaris, he ('84, p. 124) found that, while it, too, was 

 negative in white light, it " preferred" blue to red, and green to red. 



Loeb ('90, p. 89) intimated that the frog was negatively photo- 

 tropic in white light. As to colored lights, he obtained the same 

 results, no matter through what colored medium the light was passed, 

 there being a difference only in the intensity of the stimulation, that 

 is, the difference was only cjuantitative. The stimulating effect of 

 the more refrangible rays, he found to be much stronger than that of 

 the less refrangible. This he showed by exposing a frog at the same 

 time to more and less refrangible rays whose directions were opposite. 

 Under these circumstances, only the strongly refrangible rays exerted 

 a directive influence on the animal, one end of the receptacle in which 

 the frog was placed being of blue glass, and the other of red. The 

 animals then behaved as if only the light from the blue glass were 

 falling on them, and moved quickly away from it. Loeb did not 

 mention whether he used any intermediate colors. 



Dubois ('90, p. 358) found that the blind Proteus, which has rudi- 

 mentary eyes, was strongly negatively phototropic. On exploring 

 the whole surface with a small beam of light, he found that the sensi- 

 tiveness to light was distributed over all of the body, but that the 

 tail and the head were the most sensitive regions. He then covered 

 the eyes with gelatine and lamp-black, and again obtained negative 

 responses to the light. He placed a heat screen between the light 

 and the animal, so that he was certain that heat had nothing to do 

 with the reactions. Dubois thus showed that Avhile Proteus was 

 sensitive to light through the skin, it was not as much so as through 

 the eyes. Colored glasses, transmitting lights that were non-mono- 

 chromatic, were used in testing the reactions to colored lights. Dubois 

 found that Proteus showed least sensitiveness to yellow light, and that 

 the sensitiveness to the other lights was in the following decreasing 

 series: violet, blue, red, green. When the eyes were covered, the 

 results were very inconstant. If Proteus was experimented with 

 according to Graber's method of placing animals in a chamber with 

 an opportunity to choose between two lights, as was done for the 

 blinded Triton, Dubois found that in the absence of darkness it went 

 most quickly into yellow and red light. The lights according to the 

 rapidity with which Proteus would go into them were as follows: 

 red, yellow, green, violet, blue, white. The intensities of the lights 

 ran in the following series: yellow, blue, red, green, violet. 



Torelle (:03) showed that the frogs Rana virescens virescens and R. 



