272 bulletin: museum of comparative zoology. 



blue, and yellow than green, the decrease in effectiveness for the two 

 pairs of lights being the same. The lights thus formed a decreasing 

 series with blue as the most effective stimulus, and red as the least, this 

 light being not much more effective than darkness. 



D. Reactions of Nonial Toads, compared with those of Toads from 

 ivhich the Eyes had been removed. 



In describing the method of experimentation used in exposing only 

 the eye to the light (p. 268), it was stated that the eye and a very small 

 area of skin around it were illuminated. It therefore seemed desirable 

 to ascertain whether this small area of skin had any influence upon the 

 reactions of the toads. To test this, it was decided to make use of 

 only the blue light, since this had proved more effective than the other 

 lights, and if no results were obtained with it to show that this small 

 area of skin around the eye had any influence, it was reasonable to 

 suppose that with the other lights none would be obtained. 



For these tests three toads that had not previously been experi- 

 mented with were selected, and their reactions tested both in the 

 normal condition, and after the eyes had been removed. Each toad 

 was tested, first with the whole body, then with only the eye, and 

 finally with only the skin exposed. The eyes were then removed and 

 the same tests repeated. The methods and procedure were the same 

 as have been previously described for each condition of exposure, 

 except that a period of fifteen minutes, instead of five, was given each 

 toad in which to react. No toad was experimented with for three 

 days after the operation' of removing the eyes. A toad from which 

 the eyes had been excised very seldom hopped after turning, but 

 usually crawled toward, or away from, the light. 



The results of the tests are given in Table 4. Each toad was given 

 a total of sixty-four trials, but not more than eight consecutively, an 

 interval of at least an hour intervening before it was again tested. 

 The total number of trials for each of the three conditions of exposure 

 was, therefore, 192. It will be seen, by referring to Table 4, that the 

 reactions of the toads in normal condition agreed closely with those 

 shown in a later Table (6), also for blue light, though there were 2 % 

 more positive responses when only the eye was exposed, than when the 

 whole body was exposed. This, however, is not an important de- 

 parture, and would probably not be present if a larger number of 

 toads had been used. The eyeless toads, when the whole body, or 

 onlv the skin, was exposed, also showed a close agreement with the 



