580 Child, Drieseli's harmonic equipotential systems in form-regulation. 



As long as a given part of an organism remains a constituent 

 of the whole it is affected more or less by processes and conditions 

 arising from other parts, and these may induce specific localized 

 differences in it, but without necessarity altering the prospective 

 potence of the various regions. When the part is isolated the 

 effects of other parts upon it cease, but the localized differences 

 existing may determine the localization and character of following 

 processes. In other words, the past history of material which is 

 „prospektiv gleichartig" may establish a basis for the localized 

 realization of different potentialities in different parts of ma- 

 terial in a particular case. In Planaria, for example, the regu- 

 latory processes occur in visible and in part experimentally deter- 

 mined relation to visible localized differences which exist in the 

 piece, and in cases where visible differences do not exist, there is 

 no reason for assuming that they ar not present. 



Moreover, it is absolutely impossible to exclude entirely what 

 Driesch calls external conditions in the separation of a part from 

 other parts. The act of separation itself alters the complex of 

 external conditions to which the part is subjected, both in that it 

 eliminates all influence of other parts and in that it brings new 

 regions into direct relation with the surrounding medium. 



Assuming that prospective likeness is equivalent to present 

 likeness, and that external factors in the widest sense can be ex- 

 cluded, the problem of localization is simply the problem of the 

 self-production of heterogeneity from homogeneity. But Driesch 

 has never presented any real evidence to show that any case of 

 ontogenetic or regulatory development is of this kind. When we 

 look for proof we find merely assertions that it is so, but without 

 evidence, and none of his experiments constitutes proof. That such 

 assumptions must be made „damit unser Problem auftrete" I readily 

 grant, but it still remains to be proven that the problem is real 

 and not a „Scheinproblem", ,and I believe that such proof is at 

 present impossible. 



As regards Tubularia Driesch apparently does not even con- 

 sider the possibility of localized differences which are not visible. 

 He says: „1st doch die einzige am Stamm in der Längsrichtung 

 vorhandene Differenz die, dass er an einem Ende eine Wundfläche 

 hat, am anderen nicht (i. e., after the removal of the hydranth). 

 In bezug auf diese Wundfläche, aber nicht an ihr wird eben in 

 typischer Lokalisierung, die Hydrantenanlage gebildet, das ist alles, 

 was wir sagen können; mehr können wir auf Grund dessen, was 

 wir über formative Mittel wissen, eben nicht sagen, und so tritt 

 uns denn die elementare Natur des Problems der Lokalisation 

 wieder in ganzer Schärfe auch hier entgegen" (Driesch, 99a, p. 51). 

 The facts in the case are that no visible differences exist except 



