CANADA PORCUPINE 63 



performed under natural conditions of illumination one is not 

 justified in specifying what brightness difference there was 

 between the two colors during the experimentation. More exact 

 apparatus and more constant conditions are needed. The psy- 

 chological aspect of the problem must wait its final solution on 

 the mastery of the more physical, physiological and biological 

 problems which are auxiliary to it. In the mean time it is safe 

 to say that so far as heterchromatic stimulation is concerned 

 (and that is the only kind the porcupine has ever had to develop 

 its sense organs) the porcupine discriminates a brightness differ- 

 ence of about lo shades of the Nendel series of grays. On the 

 other hand, it cannot be said that the eye of the animal is not 

 sensitive to color stimulation even though no evidence of color 

 discrimination was obtained. But one thing is sure: viz., they 

 have not reacted to color differences in determining their be- 

 havior as readily as they have to brightness differences. This 

 is as close as Miss Washburn, with her more delicate apparatus, 

 comes to a solution in her recent study of the rabbit (41). Such 

 might well be the situation with a nocturnal animal even though 

 their eyes should mechanically analyze chromatic light. The 

 phyletic history is not known as to how long and to what extent 

 the porcupine has avoided the daylight and consequently it is 

 not certain how many engraphings of earlier experience are 

 present but not now functioning. The relative pre-perception, 

 so to speak, for brightness and color stimulation might also be 

 inquired into. Is it probable that sensibility is always equiva- 

 lent to sensability, if one may adapt a word to the occasion? 

 In other words, how much is an animal's activity dominated by 

 sensory stimuli as such, and how much by the phyletic and 

 individual significance of the stimuli which are effective? These 

 problems are as yet scarcely beyond the a priori stage. It is 

 doubtful if any experimental methods now designed will throw 

 much light on the subject in its broader aspects. However, a 

 consideration of some of them may be found helpfyl in throw- 

 ing light on laboratory results. It may be found necessary for 

 the laboratory experimenter to invite the geologist as he has 

 the naturalist and biologist to aid him in interpreting his find- 

 ings. The vagueness of results in this and most other studies 

 on color vision seems to indicate that there are important fac- 

 tors not yet recognized in the problem of color vision in animals. 



