Invertebrates 



669 



controlling cellular differentiation is an at- 

 tractive one but beset with great difficulties 

 which should be a challenge to investigators. 

 The electrical difference in potential must 

 have its origin in concentration differences 



chemical differences and without signifi- 

 cance in regeneration? For a complete dis- 

 cussion of the problem see Lund ('47). 



2. Quite a different hypothesis is that of 

 the existence of competition among groups 



Region A 



External \ 

 Circulation 



Electrical Potential Difference 



Surface layer impermeable to I 

 ^Regeneration inhibited 



Region B 



02 



Surface layer removed, 



I diffuses out, regeneration proceeds 



ROLE OF INHIBITOR 



tSubstrates]|^^ „_ " Hydranth 



Hydranth forms in presence of [IJ|v, 

 because enzymes are at [E]|yj. 



[E]i+II^,]:^=±IEI], 



[Substrates]. 



i _^ 



Hydranth 



Hydranth fails to form in presence of [IJ^ 

 because at low concentration [E]|, 

 enzyme is removed. 



ROLE OF SUBSTRATES 



Hydranth 



[Substrates],vj t 



Hydranth forms because: 



[E]fg • [Substrates],^ = K^ which is above 



threshold for hydranth regeneration. 



[E,, 



[Substrates],^ ^ — " Hydranth 

 Hydranth fails to form because: 

 [E]i ■[Substrates]^ =Ki which is below 

 threshold for hydranth regeneration. 



EFFECT OF BLOCKING INTERNAL CIRCULATION 



Rapid utilization of substrates by high 

 concentration of [E],^ lowers concen- 

 tration to [S]m-i. However, [E]^ • [S]^-\ 

 Kfyj-i which is still well above threshold 

 ■for regeneration. 



When Region A is no longer utilizing sub- 

 strates from Region B, the concentration 

 of S rises to [SIn + i- Then [E]i- [S]n + i = K2 

 which is above threshold for regeneration. 



Fig. 230. 



arising from differences in either the kind 

 of metabolism or the rate of metabolism. 

 What is the primary difference? May not 

 the differences in metabolism themselves be 

 sufficient to account for the polarity phe- 

 nomena and control of regeneration without 

 any intervention of electrical potentials? Are 

 these potentials merely the consequence of 



of cells such that some groups more ad- 

 equately endowed or situated are able to 

 inhibit cells living under less favorable 

 conditions (Barth, '38; Spiegelman, '45). 

 The general assumption is made that differ- 

 entiating cells require energy for structural 

 changes and need materials for synthesis of 

 chemical constituents. In addition, differ- 



