I2O C. M. CHILD. 



more affective than external, reversal of polarity is rarely or never 

 possible. 



I think it probable that there is a difference in functional con- 

 dition between the two ends of the pieces of Ceriantlnts, in con- 

 sequence of which the one end is functionally oral and the other 

 aboral. But if the aboral end be subjected to conditions which 

 typically affect only the oral end, and if these conditions continue 

 for a sufficiently long time, the response takes place and struc- 

 tures typically oral in character appear on the aboral end. 

 Whether the inherent polarity or the altered external conditions 

 will dominate in' any particular case can be determined only by 

 experiment. 



