COLOUR PERCEPTION IN FISH 27 



of most acute vision both as to colour and 

 light in the human retina. The retinae of 

 other fishes which I have examined (none 

 of them were Salmonidce) contained only 

 cones ; but these cones were some distance 

 from each other. 



The layer of pigment epithelium which 

 is present in the human eye, is present 

 also in that of the trout. It occupies the 

 same position between the layer of rods 

 and cones, or cones only, and the choroid. 

 As in the human eye, it adheres sometimes 

 to the choroid and sometimes to the retina, 

 when the retina is removed, though per- 

 haps it most often adheres to the retina. 



My space is too limited to enter into any 

 of the theories as to the possibility of the 

 pigment cells playing a part in colour 

 vision. It is quite sufficient to state that 

 they undoubtedly do play some part in our 

 sense of sight, and that they are contained 

 in the eye of the trout. 



The retina of a colour-blind person does 

 not show any organic difference from the 

 normal eye, so we cannot say to what 

 cause colour-blindness is due ; but so far as 

 our knowledge goes, there is 110 reason to 



