THE HEREDITARY FACTORS AND DIFFERENTIATION 407 



features such as details of head-shape^ (fig. 196). In an analogous 

 experiment in which lateral halves of gastrulae of Triton taeniatiis 

 and Triton cristatiis are grafted together, it can be shown that al- 

 though the compound organism is, here again, a functional physio- 

 logical unit which can develop into a full-grown newt, the tissues 



^13- 



Fig. 196 

 Compound organisms produced by grafting together half-embryos of two species 

 of frogs in the early tail-bud stage. Above, anterior component Rana sylvatica 

 posterior component Rana palustris. Left, shortly after operation. Right, later 

 embryonic stage (note the differential growth of the anterior component). Below : 

 left, a compound frog produced in the same way, but with Rana virescens as 

 anterior component; 4^^ months after operation. Below: right, a normal Rana 

 virescens, showing pigmentation and pattern of trunk and hind legs differing 

 markedly from those of the palustris component of the compound organism 

 (After Harrison, from Wells, Huxley and Wells, The Science of Life, London 

 1929.) 



not only retain some of their specific histological characteristics, but 

 certain specific postural characteristics are retained as well, for the 

 manner in which the limbs are held is typical of the species.- 



^ Harrison, 1898. 

 ^ Spemann, 1921. 



