THE MOSAIC STAGE OF DIFFERENTIATION 201 



In fish, optic cups and other organ-rudiments grafted into the 

 yolk-sac of other embryos show self-differentiation.^ 



The capacity for self-differentiation in mammalian embryos has 

 been tested in rabbits by grafting portions of the embr>'onic area 

 on to the omentum of other rabbits, where they show a degree of 

 differentiation comparable to that of normal embryos of the same 

 age." 



The self-differentiating capacity of mammalian tissues has also 

 been tested by grafting thirds of ii-day rat embryos on to the 



Fig. 96 

 ^Mosaic development and self-differentiation of the eye of the chick, grafted on to 

 the chorio-allantoic membrane. The rudiment was removed from an embryo 

 incubated for 48 hours, and grafted for 7 days. (From Hoadley, Biol. Bull. 

 XLVi, 1924.) 



chorio-allantoic membrane of the chick, where, in spite of the wide 

 taxonomic difference between donor and host (involving as it does, 

 among others, the difference between the temperatures of normal 

 uterine and incubatory development), they are able to differentiate. 

 In these conditions, different structures vary greatly as regards 

 their capacity for self-differentiation ; endoderm and nervous tissue 

 show hardly any differentiation, but epidermis with its included 

 hair-follicles, cartilage, and bone, possess it to a high degree, and 

 reach a stage comparable to that of the corresponding structures 



1 Mangold, 1931B. - Waterman, 1932. 



