266 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. _ 
reaction, which I have called “ indifferent,” that is, locomotion straight 
ahead, without apparent reference to the light. 
There was some slight inconstancy in the reactions of the same and 
of different individuals. A given individual seldom showed con- 
sistently the same percentages of responses to the different lights in 
the different sets of trials. This inconstancy in the reactions was 
very noticeable in not more than two or three individuals, though 
it was very slightly present in several. The precise factors upon 
which this inconstancy depended were not ascertained, but they were 
probably functions of the physiological states of the animals, changing 
slightly from time to time, and therefore changing the nature of the 
response in any given individual. 
The results of the first series of tests are givenin Table 1. Three 
sets of twelve toads each were tested in the way described, the total 
number of trials for each light being, therefore, 288. The same 
twelve toads were used for the first two sets, and the tests for these 
followed immediately upon each other. A second lot of twelve toads 
was, however, selected for the third set of tests. The results with 
this second lot of twelve toads were so similar to those obtained with 
the first, that they are not given separately in the Table, but together 
with the other two sets. 
It will be seen, by referring to Table 1, that all the lights used 
produced more positive responses than negative. Thus, in the blue 
light, out of 288 trials, 251 were positive; in the green, 230; in the 
yellow, 194; and in the red, 167. A comparison of the effectiveness 
of the four lights can be made more easily if the percentages of positive 
responses are considered, rather than the actual numbers. This 
effectiveness was greatest for the blue light (87 %), and decreased for 
the other lights in the order of the spectrum. The green light (80 %) 
was, however, not very much less effective than the blue. The 
decrease in effectiveness between the green and yellow lights was 
greater than that between the blue and green, the number dropping 
in yellow to 67 %. The red light was again less effective than the 
yellow, the percentage of positive responses being only 58 for this 
light. This percentage of positive responses in red light, if decreased 
only 8, would make the percentage of positive and negative responses, 
under this stimulus, equal; that is, the percentage of movements 
toward the dark would be as great as that toward the light. The fact 
that there were 58 % of positive responses, and only 42 % of negative 
responses, shows clearly, however, that the red light must be regarded 
as more effective than darkness in the production of responses in toads. 
ree be or — 
4 _ 
eS ee Ss Os ee, 
