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 quantitative. 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 while 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 vy ith 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. 
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