22 'Journal of Comparative Neurology and Psychology. 



difference limens shall have been made, the results will show that the 

 relative differences in intensity with which I worked were far in 

 excess of those needed to reverse for the animal the intensity 

 relation of any given pair of colors. 



The secoind question to be raised is concerned with the differences 

 in the energy of the different parts of the spectrum. Might not the 

 animal after all (apart from the intensity relations) be reacting to 

 secondary energy criteria of one form or another ? The writer is 

 not able at present to enter profitably into a discussion of this phase 

 of the subject. That there are problems lying here Avhich must be 

 solved, but which can be coped with in no easy manner, no one 

 acquainted M'ith the facts can doubt. 



With such questions raised (and they are not raised here for the 

 first time) is it any wonder that we find it impossible to accept the 

 uncritical results which have been obtained by the use of filters, 

 colored papers, etc., as evidence for the presence of color vision in 

 animals ? 



