COLOUR PERCEPTION IN FISH '25 



In the normal human eye, only the 

 central parts of the retina are sensitive to 

 colour, the peripheral parts are practically 

 colour-blind. Anaemia of the retina, which 

 may be produced by pressure on the eye- 

 ball, will render the retina, first colour- 

 blind and then insensitive to light. To 

 me it appears that colours in relation to 

 each other assume a grey tone, and the 

 sensation of black and white disappears 

 last. 



The great difference which I have been 

 able to observe between the human retina 

 and the retina of the trout is, that while 

 the human retina contains a layer of rods 

 and cones, the retina of the trout only 

 contains cones, or if it does contain rods, 

 contains very few, as I have not found any 

 as yet. There exists also at the back of 

 the retina of the trout a " tapetum," 

 which extends over almost the whole of its 

 posterior surface. This does not exist in 

 the human eye, but is found in the eyes of 

 some of the vertebrates. It consists of a 

 layer of " guanin " crystals, and, presenting 

 as it does a metallic appearance, and having 

 great power of reflecting light, probably 



