INTRODUCTION 131 



of the lower mammal, with its less highly developed nervous system. 

 The temptation to interpret such an animal's actions in terms appropriate 

 only to the human mind has proved very great and has undoubtedly 

 given rise to error in the past. Our deductions must of necessity be 

 anthropomorphic, since such terms as visual sensation, attraction, repul- 

 sion, pleasure, pain, and so on, have no meaning for us except in so 

 far as these processes form a part of the contents of our own minds 1 . 

 Yet it should be a guarded anthropomorphism, neither exaggerating 

 the psychological elements nor flying to the impossible antithesis of 

 imagining that the anthropomorphism can be eliminated by a new 

 terminology. 



In the second place a study of the colour vision of primitive races 

 may throw some light on the evolution of visual sensations. It may be 

 that some primitive races are in a condition of arrested development- 

 of vision, as of other faculties. We have only just crossed the threshold 

 of this part of the investigation and it is to be hoped that no time will 

 be lost in carrying it forward, lest the material for the research be 

 obliterated by the march of civilisation. 



The third source of information is the development of visual sensa- 

 tions in the infant. It is generally admitted that ''' ontogeny is a 

 compressed phylogeny," that each individual passes rapidly through 

 the same stages of development which have marked the upgrowth of 

 the race. Here again, little progress has been made, and the investiga- 

 tion is arduous and full of pitfalls. 



Besides these main sources there are others of less security. We 

 are familiar with congenital defects of vision, and it may be that some 

 of them are atavistic, that development has become arrested at a stage 

 which corresponds with an earlier stage in the development of the race. 

 Some arguments too may be derived from the careful study of normal 

 colour vision, but the evidence derived from both these sources is too 

 uncertain to be of much value. 



CHAPTER II 



THE COMPARATIVE PSYCHOLOGY OF COLOUR VISION 



I shall briefly review the comparative psychology of vision in verte- 

 brates only, laying particular stress upon points of theoretical interest. 



1 Of. Washburn, The Animul Mnnl, New York, 1908. 



92 



