384 THE EYE IN EVOLUTION 



which period their eyes lost most of the speciaHzed adaptations found 

 in Lacertihans and became degenerate ; on emerging again above 

 ground it became necessary for them to be reconstituted anew so that 

 devices of their own were invented to compensate for those lost in the 

 dark subterranean phase of their existence. That snakes developed 



Fig. 4G6. — The Head of the Gtiass Snaxk Tropiboxotus satkix 

 KATRix (Katharine Tansley). 



Fig. 467. — The Head of the }'\ ihun', Spiluteh \-Aiiit.i,ATL -. 

 ■ .' . To show the spectacle (O'Day). 



eyes quite unlike those of all other Reptiles is readily understandable 

 in terms of this hypothesis. Indeed, that they approach so nearly the 

 standard vertebrate pattern after the tremendous feat of reconstituting 

 themselves after near-extinction is more surprising than that they 

 differ so markedly from their near relations ; the fact that they did so 

 is a li'ibute to the adaptability of the vertebrate eye and the 

 biological utility of its general organization. 



