OTHER THEORIES 299 



infant. If, however, this view is erroneous, the evidence is in favour 

 of delayed development of perception of blue. 



Further, if congenital colour blindness is atavistic, then such 

 evidence, again uncertain and little trustworthy, as we have of the 

 nature of the sensations experienced by gross cases of dichromatism 

 and most of these presumably belong to Edridge-Green's class of 

 dichromics is that the two colours they perceive resemble the blue 

 and yellow of normal vision. " Anomalous trichromats ' : certainly 

 perceive more than two colours, but we have adduced reasons for be- 

 lieving that this group includes different types, and it is by no means 

 certain that any of these are due to atavism. If they are, the problem 

 of discovering the nature of their colour sensations as compared with the 

 normal is even more difficult than in the case of the dichromats, and 

 certainly no dogmatic statements can be rightly made in the present 

 state of knowledge. 



