WHAT THE FISHES SEE 



examples of multiple ocellary composition, and especi- 

 ally to the fishes, to find eyes which, situated in the 

 most suitable place in the body, have a conformation 

 specially designed to produce a real vision of external 

 objects. The lens is sufficiently distant from the 

 retina to allow images to appear, though they are very 

 often confused. Again, the membrane of the retina 

 is sufficiently full, sufficiently rich in sensitive elements, 

 to give the visual sensations an importance and a degree 

 of co-ordination by which the individual is able to profit. 

 It better determines the behaviour, and governs it to 

 better effect. The visual faculty now exists, on a small 

 scale, limited by the physical conditions of the medium 

 in which it is exercised, but still effective. 



It is only in the world of air that vision becomes the 

 vision we ourselves know, which is known also to 

 several of the creatures by which we are surrounded. 

 The light transparent air allows the rays of light to 

 pass without retaining or absorbing them; this change 

 of physical circumstances itself brings about a con- 

 siderable improvement in the functioning. The 

 crystalline lens cut like a biconvex lens, fitted with an 

 accommodating mechanism which keeps a continual 

 focus, projects clear and detailed images upon the 

 retina. This is where vision becomes really good. 



Visual sensitivity is thus made perfect by stages. 

 It rises from a simple perception of luminosity to that 

 of intensities of lighting, then to that of colours, of 

 movements, and finally to that of forms, first diffused 

 but progressively more precise. Then consciousness 

 penetrates to the very depths of that marvellous 

 domain in which the emanations of light go forth. 

 Now everything is accessible to it, and henceforth 

 everything is its own. It makes its proudest, its most 

 splendid conquest. The many-hued realm of the 

 energy of light is fully open to it. But this is true 

 only of the worlds of air and earth. That of the 

 waters, staying at the threshold, has but its crumbs, 

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