LIGHT REACTIONS OF NEWT 43 



REACTIONS TO RED LIGHT 



Experiment XVI. — In this experiment the same nine animals 

 and the same arrangement of apparatus as in experiment V were 

 employed; but between the tungsten lamp, placed six inches 

 from the end of the aquarium, and the aquarium was a filter 

 composed of two glass jars each 20 mm. thick containing an 

 aqueous solution of crystal violet and of potassium monochro- 

 mate respectively, after the formula of Landholt. 



In 30 observations, taken at five-minute intervals, 225 ani- 

 mals were noted facing the red light to 46 facing away from the 

 light; and 221 animals were found in the end of the aquarium 

 nearer the light to 49 in the farther end. 



Experiment XVII. — This experiment was an exact repetition 

 of experiment XVI, made thirty days later, during which period 

 the animals had been in the darkness of the photographic dark 

 room. In 12 observations, at five-minute intervals, 86 animals 

 faced the red light to 19 that faced in the opposite direction; 

 and 82 were seen in the red end of the aquarium to 26 in the 

 other end. Comparison of experiments XVI and XVII with 

 experiment V shows that the proportion of animals attracted 

 by the light was greater with the red light than with the white. 

 This may have been due to the decrease in intensity rather than 

 to the red color. 



REACTIONS TO BLUE LIGHT 



Experiment XVIII. — This experiment was performed thirty- 

 six hours after experiment XVII ; during the interval the animals 

 were in complete darkness. The experiment differed from the 

 other only in the substitution of a blue filter for the red. This 

 filter consisted of two similar glass jars containing solutions of 

 crystal violet and copper sulphate after Landholt 's formulae. 

 The five-minute intervals between observations were somewhat 

 lengthened on four occasions by interruptions to the experiment. 



In 30 observations 197 animals were found facing the blue 

 light to 73 that faced away from it; 195 animals were found in 

 the half of the aquarium near the light to 84 in the other half. 

 It is evident that the proportion of animals attracted by the 

 blue light is less than was attracted by the red light. 



