348 



THE EYE IN EVOLUTION 



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Fio. 413. — The Retina of the Newt, Triturus. 

 1, optic nerve fibres ; 2, ganglion cells ; 3, inner plexiform layer ; 

 4, inner nuclear layer ; 5, outer plexiform layer ; 6, outer nuclear layer, 

 consisting of large elongated nuclei ; 7, external limiting membrane ; 

 8, visual cells ; 9, pigment ( X 253) (Katharine Tansley). 



Fig. 414. — A Double Cone in 

 THE Xewt (Azan ; X 792) 

 (Katharine Tansley). 



Fig. 41.'). — The Visu.4.l Cells of the 

 AXOLOTL, Ambystoma tigbinvm. 



A single cone, a double cone (compare 

 Fig. 414). a common rod and a green 

 (Schwalbe's) rod ( x 1,000) (Gordon Walls). 



