286 



FIELDS AND GRADIENTS 



some of the more basally situated tissue, the gradient-field set 

 up by the dominant region is in relation to the reduced size of its 



U 



mi m 



mm 

 Kfe 



'Ji!'.v^^ 



Fig. 135 



Correlation between size and degree of development of a regenerated apical region 

 in Planaria, and the extent of its inductive capacity. Posterior fragments are 

 isolated as shown in a. h. Regeneration in standard conditions, c-e. Regene- 

 ration in increasing concentrations of narcotics, showing decreasing size and in- 

 creasing abnormality of the regenerated head. Correlated with this, the pharynx 

 induced in the old tissues becomes smaller and less remote from the apical 

 region. /, Regeneration at high (optimal) temperature. The head and eyes are 

 larger, the induced pharynx farther away and of greater size. (From Child, 

 Individuality in Organisms , Chicago, 19 15.) 



possible range. For instance, the reconstitution of a polyp in a 

 portion of stem of Tuhiilaria of a certain length normally results in 



