IO C. M. CHILD. 



more, how, unless we accept Driesch's entelechy, can we account 

 for the complex changes in orientation of the particles which 

 must occur in the development of a new polarity and radial 

 symmetry from a small area of the oral or aboral end of the piece. 

 If we turn to the process of crystallization for assistance, we 

 meet difficulties, for we should expect, if the process of organic 

 development is analogous to crystallization, that Harenactis 

 material would in general conform to a particular type of arrange- 

 ment, at least within certain limits of environmental change. 



On the other hand, if w r e regard polarity and symmetry as 

 molar phenomena resulting from the localization by any condi- 

 tions or agents of certain metabolic processes differing in degree 

 or kind, together with the physiological correlation resulting from 

 such localization, we can readily understand how new polarities 

 may arise without reference to the old, in response to local factors, 

 and how bilateral symmetry may appear in one case and radial 

 in another in the same organism. 



The greater the extent to which we interfere with or destroy 

 the old polarity and symmetry by removing or altering the locali- 

 zation of the original metabolic processes, the greater the possi- 

 bility of the origin of new polarities and symmetries in response 

 to local conditions. 



In the recent experiments of Lillie, Morgan and others on the 

 effects of centrifuging eggs, the polarity and symmetry of the 

 eggs are, at least in certain cases, apparently not altered by the 

 displacement of the visible granules. These results have led 

 various experimental embryologists to adopt the hypothesis of 

 orientation of molecules or particles as the basis of polarity and 

 symmetry. As a matter of fact, however, the visible granules 

 which are displaced in these experiments are merely the inactive 

 or relatively inactive products of metabolism and so long as they 

 are visible, have reference primarily to past activities. Their 

 localization, in so far as they are localized with respect to an 

 axis, suggests the more or less sharp localization along this axis 

 of metabolic processes differing in degree or kind. There is no 

 reason to believe that displacement of the granules by centri- 

 fuging alters essentially the localization of the processes, con- 

 sequently the polarity and symmetry of the egg may remain 



