190 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



enlarged in red light but contracted rapidly when it was exposed to 

 blue light of low intensity. It therefore seemed not improbable that 

 the differences in the frog's reactions to lights of different colors might 

 have been due to stimulation received through the eyes; therefore 

 another set of experiments was undertaken to ascertain if like results 

 could be obtained through the stimulation of the skin alone. 



As toads had been found to be more responsive than frogs after the 

 eyes had been excised, they were used in testing the light reactions 

 through the skin. The same apparatus (Figure 6) was used as in the 

 experiments with normal animals, except that the light was passed 

 through a square aperture, 2.7 centimeters on a side, and had an 

 intensity of 874 candle-meters for white light at the point where the 

 animals were placed. The method used for removing the eyes was the 



TABLE XV. 



Reactions of Three Eyeless Toads to Colored Lights. 



same as in previous experiments (p. 182). Three individuals were 

 tested successively with white, red, yellow, green, and blue light in the 

 order given. The next day two of the animals were tested again with 

 the same colors but in the inverse order. 



It will be seen (Table XV.) that these toads gave about seventy-five 

 per cent of positively phototropic reactions with every color. Appar- 

 ently all the colors were equally effective in inducing photic responses. 

 This fact is the more striking when we remember that the same color 

 screens were used as in the experiments with normal amphibians 

 (Table XIV.), in which case the blue was most potent. The reactions 

 to white light, in the present instance, showed an almost perfect posi- 

 tive phototropism, and it seemed possible that the lesser degree of 

 reactiveness shown in the responses to colored lights might have been 

 due to differences in intensity, as the color-screens undoubtedly cut 

 off much light. To ascertain if any difference would be manifest in 

 the responses if the intensity were lowered, a diaphragm, having a 

 circular aperture 2.8 millimeters in diameter, was interposed and 



