PEARSE. — THE REACTIONS OF AMPHIBIANS TO LIGHT. 



189 



order was reversed, The plan followed was to test all the individuals 

 in one color and then to change the screen and test them again in the 

 same order but with the next color ; ten reactions being taken from 

 each individual in every color. Each animal was thus actually subject 

 to experiment for about one hour out of the six which were required to 

 complete the series. A second half-dozen of frogs was tested in the 

 same manner, except that the colors were used in the order red, yellow, 

 green, blue, and then the order was reversed. 



TABLE XIV. 



Reactions of Rana palustris to Colored Lights. 



The results (Table XIV.) show that blue is apparently the most 

 effective in the production of positively phototropic reactions, and that 

 there is a regular graduation from blue to red, both in the percentage 

 of positive reactions and in the rapidity with which the movements 

 took place. Other observers (p. 165) have obtained similar results in 

 experiments with other species of amphibians. It is probable that 

 these differences in the reactions are due to differences of the wave 

 lengths, but they may be due to intensity differences. 



(b) Eyeless Individuals. 



The blue end of the spectrum is known to be more potent in affect- 

 ing changes in the eyes of many animals, and in some species the 

 sensitiveness to red is apparently lacking altogether. For example, 

 Abelsdorff (:00, p. 562) observed that the pupil of the owl's eye 



