Amphibians 



261 



Fig. 92. 









Fig. 93. Fig. 94. 



Fig. 92. a, Inductive effects of the "head organizer"; b, inductive effects of the "trunk-tail organizer"; 

 c. heteroplastic induction of a complete secondary embryo, oriented opposite to the main axis of the host 

 (from Hoi tfreter, '33d). 



Fig. 93. Induction of headlike structure with three balancers, by fresh mouse kidney implanted in ecto- 

 dermal vesicle of Triturus alpestris (from Chuang, '39). 



Fig. 94. Induction of neural structures and eye with lens, by fresh mouse kidney implanted in ectodermal 

 vesicle of Triturus alpestris (see Fig. 93) (from Chuang, '38). 



quired to organize this tissvie into regionally 

 specific tissue patterns, such as brain with 

 sense organs (Needham, Waddington and 

 Needham, '34; Woerdeman, '36). Evidently, 

 typical head and trunk patterns can arise 

 within the stimulated ectoderm itself, by 

 way of self-organization, and whatever the 



host influence may be, it can only modify 

 the effects of the graft. 



Using the same adult tissues as in the 

 preceding experiments, Chuang ('39, '40) 

 grafted them into the ventral region of vari- 

 ous levels of whole embryos. To simplify 

 matters we shall discuss only his results ob- 



