286 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
colors in the spectrum. There were movements toward both lights 
in any pair, the larger percentage being always to the blue, or to the 
light nearer the blue end of the spectrum. The percentage of move- 
ments to red light in pairs with the other lights, was only slightly 
higher than the percentage of movements toward the dark, when these 
lights were used singly. 
ce. Reactions with the Skin as Receptor. 
Having demonstrated that the eyes were concerned in the reactions 
in which the whole body was exposed, it remained to test the reactions 
of toads in which only the skin was exposed to balanced pairs of 
monochromatic lights. In order to protect the eyes from the lhght, 
the hoods described on p. 269 were again used. 
The results of the tests are given in Table 9. Seven sets of twelve 
toads each were tested, and therefore a total of 1344 trials was made 
in each single pair of lights, or 8064 trials in all. For the first three 
sets, four of the lot of twelve toads which had been employed for the 
first three sets of tests where both the skin and the eyes were exposed, 
and for the first set of tests where only the eyes were exposed, were 
used. Eight of this lot of twelve had died during the course of 
former experiments, and their places were therefore supplied by eight 
other toads. Three of the present lot of twelve also died, during the 
course of these experiments, and their places were supplied by three 
other animals. For the next two sets, a new lot of twelve, and for 
the last set, another new lot of twelve toads, were again selected. 
One of each of these last two lots also died during the course of these 
experiments, and their places were supplied by two other animals. 
There were thus a total of 41 separate toads used for these tests. 
It will be seen, by referring to Table 9, that in all of the pairs there 
were some movements toward both lights, with the larger percentage 
always toward the blue, or to that light of a given pair which, in the 
spectrum, is nearer the blue. In the pairs in which red occurred, 
there were also movements to this ight, but only when paired with 
blue were these movements to red light more numerous than the 
negative responses to the lights when used singly. It was here, in 
these pairs of red with the other lights, that were most clearly brought 
out the differences in sensitiveness, when the light was received through 
the eyes, or through both the skin'and the eyes, and that when it was 
received through the skin only. If the pairs in which red occurred 
be considered, it will be seen that the percentage of movements 
