248 



THE MOSAIC STAGE OF DIFFERENTIATION 



Fig. 121 



Self-differentiation of the eye and of its constituent tissues. The optic vesicle was 

 removed and grafted into the region of the ear in Rana palustris. The various 

 tissues undergo self-differentiation regardless of their morphological differentia- 

 tion, and of the proportions in which they are present. A, 19-day old graft, 

 showing absence of pigment cells; rods and cones project into the cavity of a 

 vesicle. B, 7-day old graft, showing excess of pigment cells. C, 5-day old graft, 

 showing absence of part of pigment layer; rods and cones projecting into coelom 

 of host. (From Lewis, Amer.Journ. Anat. vii, 1908, figs. 4, 5, 7.) 



