EARLY HISTORY OF THE PLACENTALIAN EYE 689 



mammals, and that subsequent placentals evolved duplex retinae from 

 pure-rod ones just as the Boidae or their immediate ancestors had to do 

 (see Plate I). The eye of man, with its pretty-good accommodation, its 

 fovea, its miscellaneous yellow filters, and its capacity for color vision, 

 possesses in substantial degree the physiological capacities of the stand- 

 ard sauropsidan eye as we see it in the lizard or the bird. But it has 

 gained these powers through a lengthy process of re-differentiation, which 

 was carried out largely within the confines of the primate order itself. 



