LIGHT CF EIFFERENT WAVE-LENGTHS BY FISH 57 



is not doubted that a longer series of tests would have re- 

 established the response to blue 



Besides the percentage of correct choices in the two 

 series of training experiments, there is the incidental evi- 

 dence in delayed response and in peculiar behavior shown 

 by the fish when gray was substituted for the red to which 

 they were accustomed. But in the next section further 

 evidence of innate differential response to light of different 

 wave-length will be presented, which gains weight from the 

 results obtained by the training method. 



H. Unlearned Responses of Fish. 



a. Modified breathing rate of fish subjected to light of long 

 wave-length. — That the longer wave-lengths of light have 

 a peculiar stimulating effect on fish has been mentioned 

 on p. 2. Parker (1903) found that he could use the respira- 

 tion rate as a means of detecting effective sound stimuli 

 for fish and I have twice noted a change in breathing rate 

 following exposure to light of long wave-length. 



(1) A mud minnow, Umbra limi, had grown quite tame 

 during a year's careful feeding. The fish was somewhat 

 used to a tungsten lamp above the aquarium. One morn- 

 ing the breathing rate was counted with daylight illumina- 

 tion, before the lamp was turned on, and after the 

 lamp was turned on the rate was again counted. There 

 was no change. A piece of ruby glass was placed under 

 this lamp and it was then left for some days with the light 

 turned off so that the fish might become used to the ruby 

 glass. On the morning of the test the breathing rate was 

 normal, about 30 per minute. I turned on the red light 

 while experimenting with another fish. When I looked to 

 observe the Umbra after the red light was turned oft', the 

 fish had changed position. It had settled closer to the 

 bottom of the aquarium and was trembling and panting 

 in such a peculiar fashion that I forgot to count the breath- 

 ing. It seemed that it was more than twice as fast as 

 when counted just before the red had been thrown on it. 



(2) A black lined box with a 16 candle power incan- 

 descent carbon lamp inside it was placed with an open end 

 against an aquarium containing a number of shiners (No- 



