176 



EVOLUTION AND ANIMAL LIFE 



certain lizards, notably in a very primitive New Zealand lizard 

 of the genus Sphenodon (Hatteria) (Fig. 109), and that, in these 

 lizards, the pineal body ends in a more or less perfect e3^e-like 

 structure placed between the true eyes in the center of the 

 forehead. A trace of this eye is shown in the limbless lizard 

 called slow worm (Anguis), of Europe, and in several American 

 species. In the horned toad {Phrynosoma) (Fig. 110) its place 



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Fig. 110. — Head of lizard or horned toad, Phrynosom hlainvillei, showing translucent 

 pearly skin covering the pineal eye. (From specimen.) 



is covered by a translucent pearly scale. These lizards have 

 in fact three eyes, and the pineal body is the nervous gang- 

 lion from which the third eye arises. The natural conclusion 

 from this that all vertebrates originally had three eyes, is prob- 

 ably a too-hasty one. Perhaps the pineal body was an organ 

 of sense, which developed into an eye in the lizards and their 

 ancestors only, not in any of the Amphibians or fishes, and not 

 in any mammals or birds, although these are descended from 

 reptilian stock. Whatever the origin or primitive function of 

 the pineal ganglion, its existence in man as a vestigial organ 

 is due to the persistence of heredity. 



