WHAT THE FISHES SEE 



possible victim which passes beside it, however near 

 it may be, if it only comes within the purview of a 

 single eye. On the other hand, if this moving prey, 

 suspended or swimming, happens to come within the 

 range of vision in front, they immediately pounce 

 upon it. Their eyes have seen. This field, in which 

 the two eyes overlap by a narrow segment of the 

 retina, has a manifest superiority over the lateral field, 

 although here the whole mechanism receives the 

 visual rays. It may be smaller, but it is more effective 

 in use because of its greater keenness. It is par- 

 ticularly in this field that the fish is capable of sight. 



The swimming species of fresh water and the 

 surface waters of the sea, whose regular abode is 

 illumined by the light of day, are mostly sensitive to 

 the light. It is possible to experiment upon them in 

 the tanks of an aquarium, and to observe that their 

 vision is affected by the power of light, and the colour 

 and movement of objects. Their eyes, which can 

 move in their orbits, turn in the direction of- bodies 

 which move a short distance away, as if these alone 

 were capable of producing a visual impression. Form 

 seems to be of no account. The same object, in 

 identical conditions, will arouse the impression if it 

 moves, if it is brilliant, if its colours are bright; but 

 it will not stimulate it, or will stimulate it less, if it 

 stays motionless, or if its hue is dark. The visual 

 world, in these fishes, is confined to a limited region, 

 and is made up of movements and flashes: shape has 

 little to do with it. It has neither consistency nor 

 permanence. It is entirely a matter of chance. 



But however inferior this sort of vision may be, 

 there is a still lower grade, that of the fishes, most 

 numerous of all, which live in the gloomy regions of 

 the sea, from four or five hundred feet down to the 

 greatest depths. I have frequently been able to examine 

 them while they were still alive, coming from the fishing- 

 boat which brought them up, and I have always been 

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