FIELDS AND GRADIENTS 



283 



be the most essential feature in the production of a new apical 

 region. 



The autonomy of regenerated apical regions in these forms is in 

 striking contrast to the dependence of regenerated basal (posterior) 



Fig. 133 

 The independence of the apical region. Partial regeneration in short stem- 

 fragments of Tiibularia, whether the result is uniaxial or biaxial, gives rise to 

 apical regions, together with as much of the rest of the organism as can be formed 

 from the material available. (From Child, Individuality in Organisms^ Chicago, 

 1915.) 



regions. In all Annelids and Planarians, the tail region regenerated 

 at a posterior cut surface is formed as a direct continuation of the 

 fragment, and completes the missing parts of the animal. No 

 remodelling is needed, either in the new tissues or in the original 

 fragment ; whereas after the formation of a head region of limited 



