624 



THE AMERICAN NATURALIST 



[Vol. XL 



the undifferentiated re^rion only half as far as those of the inner 



at 5.2 /(, though the hounchiries are not so clearly defined at first 

 and some stragfrling nuclei of the inner nuclear layer are still to be 



found in it up to the beginning of the stage of differentiation. 

 At this stage the membrane of Henle is formed by the flattening 

 of the inner ends of the rod and cone cells against the cytoplasm 

 of the horizontal cells and against the entls of the fibers of Miiller 

 and of the processes from the inner nuclear layer (Fig. 13). 



The Pigment Layer 



