WHAT THE FISHES SEE 



With their heads bristling with tentacles and plumes, 

 they seemed less awake, less easy to interest, more 

 indifferent to visual sensations. Their possibilities are 

 less than those of the basilisk. They settle down in 

 shelters, hollows in the rocks or fragments of shell, but 

 they change their abode ; they go and come without show- 

 ing anything which seems equivalent to the co-ordinated 

 actions of their neighbours. They are lively and agile, 

 but do not respond so quickly, or so perfectly, to the 

 optical stimulations they receive. They do not occupy 

 so high a place in the order of sensation. 



And so with most other fishes which make their abode 

 in holes, or settle down in the mud and sand of the 

 bottom. Their visual sense is stimulated only when 

 there is obvious movement and vivid colour in objects, 

 within the bounds set by the refringency and disper- 

 sive power of the surrounding water. And, further, 

 in order that this sense may attain its fullest develop- 

 ment, a simultaneous vision by both eyes is required. 



This simultaneous binocular vision is found in quite 

 a number of fishes, though it is lacking in those whose 

 eyes are placed too much on one side. The eyes, in 

 fish living in their normal environment, are not the 

 shrunken organs, drawn back into their orbits, which 

 we see when they are dead; they project like convex 

 disks, and their full cornea, jutting out, receives the 

 more readily the radiations of light. Consequently, 

 their interior parts, thus bulging, are able to gather 

 up the rays which emanate from an object, and give 

 the fish some of the advantages of binocular vision. 

 The field of this vision is undoubtedly restricted: it 

 cannot be compared with that of land creatures which 

 have stereoscopic vision, but it does exist, although 

 limited, and can offer the same possibilities, although 

 on a lesser scale. 



Fishes which pursue their prey have an advantage; 

 their vision becomes clearer when they look forward 

 and above them. A pike or trout can hardly see a 

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