146 The Phenomena of Morphogenesis 



lized egg. In other instances polar behavior is subject to induction through 

 environmental factors at all stages. Many cases of polarity are like this. 

 Sometimes this polar plasticity persists indefinitely, as in Caulerpa. In 

 other cases, like the egg of Fucus, it lasts only till the polar axis is deter- 

 mined and then remains unchanged, regardless of the environment. What 

 is present in all living stuff seems to be a persistent tendency for the 

 establishment of polar behavior. This, indeed, is an essential preliminary 

 for the development of a formed and organized system. 



The study of polarity has thus far raised more problems than it has 

 solved. Most of these, however, are of a sort more amenable to analysis 

 and experimental attack than are many - others in organic development. 

 Especially through subjecting each of the various aspects of polarity 

 separately to experiment, aspects which may perhaps involve distinct 

 developmental processes, is there hope of progress. 



