PATTERNS OF DEVELOPMENTAL PROGRESS 711 



readily basipetally than acropetally. The axial differential in production 

 and the directional differential in transport, whether electrical, as at one 

 time suggested, or dependent on some other factor, indicate relation to 

 gradient pattern. 



Interrelations within the group of dynamic factors attain a delicacy 

 and complexity far beyond our present understanding in the functional 

 activities of the central nervous system. The variety and complexity of 

 interrelation within the chemical group, particularly in the higher verte- 

 brates, are coming to light with the progress of investigation of hormone 

 action. 



It is evident that the specificity and complexity of integrative inter- 

 relations increase during development. Transplantation experiments show 

 that, in general, tissue-specificities, individual-specificities, and even 

 species-specificities are less evident in earlier than in later stages. But 

 whatever the conditions in later stages, it is evident that an orderly or- 

 ganismic development to an integrated whole is not possible without an 

 underlying general ordering and integrating pattern of some sort — not 

 merely a structural substrate but a physiologically effective activity pat- 

 tern. 



INDEPENDENT DIFFERENTIATION 



In contrast to the ordering and integrating features of developmental 

 pattern and the dominance and subordination associated with it, experi- 

 mental isolations and transplantations of parts show that at certain de- 

 velopmental stages some parts become capable of continuing differentia- 

 tion for a time in other than the normal organismic environment or in 

 complete isolation from the rest of the organism. Such parts are said to 

 be determined and to undergo self-differentiation or independent differ- 

 entiation, as distinguished from dependent or correlative differentiation. 

 Also, removal of certain parts at certain stages results in permanent de- 

 fects, other parts being unable to reconstitute them. As far as parts show 

 this capacity for self-differentiation, development, or the stage in which 

 the capacity is present, has been regarded by many as a mosaic of inde- 

 pendent parts. Huxley and De Beer (1934) head their chapter vii: "The 

 Mosaic Stage of Differentiation," and give many examples of independent 

 differentiation, in large part from amphibian development. Many inter- 

 esting questions center about this capacity for self-differentiation. All 

 our knowledge of the progress of determination and differentiation and 

 their stability or irreversibihty results from experiments for the purpose 



