WHA T ANIMALS SEE 1 2 7 



question is that of the vision of quadrupeds and 

 birds, which have * simple eyes ' constructed like our 

 own, though differing greatly from ours in positive 

 size, as well as in size compared with the animal 

 which uses them. Tradition and general consent 

 have made current a certain amount of very uncertain 

 4 data ' as to animal sight. But these are mainly 

 limited to the range or accuracy of vision possessed 

 by animals, and hardly touch the question whether 

 objects appear to them as they do to us, whether 

 their eyes readily suggest to them the ideas of solidity, 

 transparency, roundness, or squareness, how far they 

 recognise colours, or whether to many creatures of 

 considerable development the world is not all black 

 and white, or a * harmony in green and grey.' 



If they do not readily distinguish solid form and 

 colour, their ideas of things must present themselves 

 to the animal in a very different form from that in 

 which we suppose them to appear to the animal 

 brain. But though the eyes of the horse, or of the 

 dog, are adapted for presenting the image on the 

 retina coloured as we see it coloured, it does not 

 follow that the animal sees it as we do, or that by 

 seeing a mere black-and-white picture it would be 

 at any disadvantage in the life which it naturally 

 leads. The sense of colour, which is the per- 

 ception and distinction of colours and shades of 



