REGENERATION 



321 



Figure 14.6 

 Successive inductions during the regeneration of planarians. After a poster- 

 ior region is isolated (a) the first step is the formation of a gangHon (C) in the 

 blastema {b). This induces a head (T) provided with eyes' (y). The head 

 region then (d) induces a pre-pharyngeal zone (Pr), and that in turn (e f) a 

 pharyngeal zone (Ph), in which (g) a pharynx finaUy appears. (From Wolft 



I953-) 



{c) Amphibia 



Larval and adult urodele Amphibia (newts, salamanders, axolotls, etc.) 

 can regenerate legs or tails and other organs fairly readily (General Re- 

 views: J. Needham 1942, A. E. Needham 1952). The capacity of Anura 

 (frogs, toads, etc.) is much less in this respect, the power of regeneration 

 usually being lost at about the time of metamorphosis. The regenerative 

 phenomena in urodeles provide a very good example of one kind of field 

 action. It was in fact in this connection that the concept was first exten- 

 sively discussed by Weiss, one of those who introduced the notion of 



