OUR FACE FROM FISH TO MAN 



the pushed-in ball, or optic cup. The space between 

 the lens and the inside of the cup becomes filled with 

 fibrillar tissue which gives rise to the transparent 

 jelly-like substance called the vitreous humor. 



The retina, derived from the inner layer of the 

 cup, comprises the following series of layers: the 

 innermost of these is a layer of nerve fibers and 

 ganglion cells which are gathered together and 

 pierce the center of the cup, issuing from it as the 

 optic nerve; next follow various layers of large and 

 smaller nerve cells, culminating in the layer of 

 cones and rods, the latter being nearest the outer 

 epithelial layer of the inner wall and directed 

 away from the source of light. The outer layer 

 of the optic cup gives rise to the pigmented layer 

 of the retina, which doubtless provides the neces- 

 sary opaque, light-proof layer, like the black inner 

 surface of a camera. Next comes the network of 

 blood vessels of the choroid, while outside of the 

 choroid is the thick sclerotic layer, which is 

 continuous in front with the cornea. 



ORIGIN OF THE HUMAN EYES 



Before attempting to trace the evolution of the 



human eye, let us recall its broader structural 



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