WHAT THE FISHES SEE 



has its cause in another peculiarity; it is due to the 

 intimate structure of the most important parts of the 

 mechanism. At first glance these parts, the crystalline 

 lens and the retina, seem alike, but there are many 

 respects in which they are definitely unlike. The eye 



Fig. 48. — Simplified and enlarged median section of a Basilisk Blenny's 

 eye. Left, the circular section of the globular crystalline lens ; 

 right, the optic nerve spreading out over the retina, the whole 

 being surrounded by the enveloping membrane of the eye. 

 Magnification, 15 times. 



is a sensitive organ made as an optical instrument, 

 and, if we wish to understand how it works, we must, 

 so to speak, pick the mechanism to pieces, and examine 

 it both as regards its essential structure and its way of 

 acting. 



Our own eye may serve as a starting-point in this 

 investigation. We know the nature and purpose of 

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