OUR FACE FROM FISH TO MAN 



front end of the brain tube is interpreted by 

 Plate (1924, p. 493) not as an eye at all, as it 

 lacks light cells, but as the last remnant of a 

 balancing organ. Thus the light-sensing apparatus 

 of Amphioxus is of the utmost simplicity and has 

 little obvious relation to the highly complex paired 

 eyes of vertebrates. 



In the foregoing pages we have reviewed the 

 general construction of paired eyes, we have out- 

 lined the evolution of eyes from very simple 

 beginnings, we have considered the wide contrast 

 between vertebrates and invertebrates in the 

 structure of the paired eyes and we have seen that 

 according to present evidence the vertebrate 

 paired eyes do not appear to be inherited from 

 any of the more complex invertebrate types but 

 seem to have arisen in the very ancient and still 

 undiscovered pre- vertebrates. As direct evidence 

 from successive fossil stages illustrating the origin 

 of the paired eyes of vertebrates is meager or 

 wanting and as there are apparently no surviving 

 pre- vertebrate stages except possibly Amphioxus, 

 we must rely chiefly upon the evidence afforded by 

 embryology, and such evidence is often open to 



the suspicion that we may be mistakenly inter- 



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